Products

M a rkets/Prod u ets

Overview Throughout this book, different subjects are reviewed that pertain to reinforced plastic (RP) products. This chapter provides additional information on RP products and marketing aspects effecting RP products. The gradual growth of the total USA plastic [RP and URP (unreinforced plastic)] industry for over a century has been spectacular evolving into today's routine to sophisticated high performance products (parts). Examples of these products are in building and construction (34 wt%), transportation (33%), sports and appliances (14%), electrical and electronic (10%), and others (9%). Use is made of thermoplastic (TP) and thermoset (TS) plastic matrixes. Plastics data source, such as the Society of Plastics Industry's (SPI's) suite of economic studies and statistics, provide current, comprehensive data, and analysis of the domestic and international trade markets for USA plastic materials, processing, machinery, and moldmaking industries that follows the ups and downs of the overall local and worldwide economy (www.plasticsdatasource.org or tel. 800.541.0736). During the most recent economy downturn SPI reported plastics total USA industry shipments for year 2000 was $420.9 billion and 2002 was $393.2 billion. The year 2002 included 37% plastic products, 21% upstream impact products, 20% captive plastic products (products from activities such as auto assembly and milk bottling are not classified by the government or most economists as being part of the plastic industry), 11% plastic materials, 10% captive plastic products, and 1% molds for plastics fabrication. SPI also reports that the top ten plastics processing states for year 2002 were in billions of sales dollars: $13.8

4 8 4 Reinforced Plastics Handbook

California, $11.2 Ohio, $10.1 Texas, $9.8 Illinois, $9.4 Michigan, $8.3 Pennsylvania, $7.3 Indiana, $5.5 Wisconsin, $4.9 North Carolina, and $4.9 New Jersey. These totaled for 2002 at $143.9 compared to $151.6 during year 2000. During the latest economy downturn that started during 2001, unlike its usual behavior home building and new construction remained steady. USA industry suffers from a competitive disadvantage because USA manufacturers have relatively high tax rates and pay more for health care, according to a new study by the National Association of Manufacturers (NAM) and the Manufacturers Alliance (MA). The study determined that the USA industry generally is competitive against other developed countries, but it calls for changes to help combat a 22% premium that USA industry shoulders for things like benefits and litigation. Efforts by other industrialized nations to cut their corporate tax rates in the past five years have left the USA and its 40% rate the second highest, trailing only Japan. This report is the first comprehensive look at how USA manufacturing costs stack up with other countries in USA dollars per hour (year 2002): $29.77 Germany, 25.77 France, 24.30 USA, 23.14 UK, 22.67 South Korea, 22.46 Canada, 16.64 Japan, 12.85 Taiwan, 6.19 Mexico, and 3.50 China. Plastic products (includes RPs) is ranked as the 4th largest USA manufacturing industry with motor vehicles in 1st place, petroleum refining in 2ed place, and automotive parts in 3ed place. Plastic is followed by computers and their peripherals, meat products, drugs, aircraft and parts, industrial organic chemicals, blast furnace and basic steel products, beverages, communications equipment, commercial printing, fabricated structural metal products, grain mill products, and dairy products (in 16th place). At the end of the industry listings are plastic materials and synthetics in 24th place and ending in the 25th ranldng is the paper mills. Total plastics consumption yearly worldwide is estimated at 399.5 billion lb (200 million ton). In USA about 106.9 billion lb is consumed with about 90% are thermoplastics (TPs) and 10% thermoset (TS) plastics. USA and Europe consumption's are each about 27% of the world total with Japan, China, Australia, and the Pacific RIM countries accounting for 20%, central and South America 10%, India and Southwest Asia 8%, and Africa, Middle East, and rest of the world (ROW) 8% (Chapter 3). Of the total plastic industry, RPs consuming about 18 wt% or 19.2 billion lb. Of the RPs 18%, at least 82% (15.7 billion lb) represents injection molded products using different type fiber, powder (includes

6-Markets/Products 485 fibers with one end/milled fibers), and flake reinforcements. Fibers include glass, cotton, cellulosic sisal, flax, jute, polypropylene, polyethylene, and nylon with by far most being milled, short, and/or long glass fibers (Chapters 3 and 5). Remaining 3.5 billion lb represents products other than those IM. RP products have gone worldwide into the deep ocean waters, on land, and into the air including landing on the moon and in spacecraft. Major markets are aerospace, appliances/business machines, building/ construction, consumer, corrosion, electrical/electronic, marine, and transportation. Practically all markets worldwide use RPs. Examples of the thousands of products or parts include electrical and electronic devices, pipes/tubes, furniture, automobiles, boats, toys and games, recreations, sports, appliances, water filters, corrosion resistant containers, windmill blades, gas filters, liners, papers, missiles and rockets, farm equipment, USA postal service handling equipment, toilet and water conservation devices, bearings, gears, and so on with new developments always on the horizon. Very high performance RPs for over a half century has been required in specialty applications. As an example the first Delta IV Heavy Launch Vehicle was successfully rolled out and erected in preparation for its summer 2004 launch. The Delta IV is the newest and largest of Boeing's Delta family of expendable launch vehicles. The Delta IV's carbon fiber/epoxy sandwich structure, including interstages, heat shield, nose cone, and payload fairings is produced by Alliant Techsystems Inc., Edina, Minn., USA.

Buildings and Constructions This industry consumes at least 20 wt% of all plastics (includes RPs) produced. It is the second-largest consumer of plastics following packaging. This amount of plastics only represents about 5% of all materials that industry consumes. URPs and RPs will eventually significantly expand in this market. Its real growth will occur when plastic performance is understood by the building industry (meeting their specifications, etc.) and more important when the price is fight in order to compete with other materials. There are many applications of structural and nonstructural plastics being used in the building and construction industry worldwide. Plastic use continues to expand in homes. One application that has not received much consideration yet in USA is the Homeland Security Act's requirement for strengthened, blast-hardened critical structures, for which carbon fiber is, so far, the only qualified material, according to GHL Inc., USA (Figures 6.1-6.3).

O0 03 t'i} n,,

,,m, Ijl

,-r

O" 0 0~ - -

Figure 6.1

Schematic of different plastics in a house

6. Markets/Products 487

Figure 6,2 All-plastic GE house in Pittsfield, MA (courtesy of GE)

Figure 6.3 Carbon fiber reinforced plastic bridge (Herning, Denmark) components resulted in significant savings in maintenance costs

Engineering RP ideas using unconventional approaches to building houses have evolved since at least the 1940s from commercial and military groups. As an example during 1957 one of the first all RP house was the Monsanto House of the Future erected in Disneyland, CA, USA (Figures 6.4 and 6.5). The key structural components were four 16 ft (4.9 m) U-shaped cantilever (monocoque box girders) RP designs by MIT. Different plastics were used throughout the house including

488 Reinforced Plastics Handbook

different plastic sandwich panels. When this house was to be removed in 1977 to provide a different scene (a main attraction for two decades), it had suffered almost no change in deflection. It was estimated to have been subjected to winds, earthquakes, subjected to families using it to the equivalent of centuries based on all the people that passed through it, etc. Destruction by conventional techniques (wrecking ball, etc.) was impossible without first cutting sections, etc.

Figure 6.4 Monsanto house in Disneyland,CA, USA

The present and growing large market for plastics in building and construction is principally due to its suitability in different internal and external environments. The versatility of different plastics to exist in different environments permits the ability for plastics to be maintenance-free when compared to the more conventional and older materials such as wood. As the saying goes if wood did not have its excellent record of performances and costs for many centuries, based on present laws and regulations they could not be used. They burn, rot, etc. Regardless it would be ridiculous not to use wood. The different plastics inherently have superior properties such as high strength and stiffness, durability, insulation, cosmetics, etc. so eventually their use in building and construction will expand particularly as they become more economical.

6-Markets/Products 489

Figure 6,5 Schematic of Monsanto's cantilever type structure of House of the future

490 Reinforced Plastics Handbook Bathtubs The USA Commerce Department report on the tub-shower business. In 2001, the U.S. construction industry made wholesale shipments of approximately 4.5 million conventional bathtubs, 700,000 whirlpooltype bathtubs, one million shower stalls, and 250,000 hot tubs. RPs account for about two-thirds of the bathtubs and 80-90% of the other tub-shower components. The government does not identify whether units are consumed in new housing or remodeling but, knowing that 56% of new homes in 2001 had 2.5 or more bathrooms, leads one to some rough estimating that perhaps 20-30% of all tub-showers are used for aftermarket replacement and remodeling projects. RP predominantly used was glass fiber/TS polyester.

Walkways/Bridges/Fences Since the 1940s, RP simple to complex suspended and or partially to fully supported walkways, bridges, fences, and other construction products have been built. They have performed as required for many decades. Early work by the USA army engineers using these different products were built and put to use permitting moving soldiers to heavy military tanks. Included were RP sprayed on the ground as walkways to aircraft landing strips. As an example, a large RP truss structure has been designed and installed to support one end of an 850 m long floating walkway on a river in Brisbane, Australia. The truss was developed by the University of Southern Queensland's Fibre Composites Design and Development (FCDD) Centre of Excellence. It measures 18 m long and 2.5 m deep with a 1 m cutout in the middle to accommodate another part of the walkway. A number of horizontal, vertical, and diagonal glass fiber reinforced isophthalic pultruded profiles are held together with stainless steel pins to create the structure. At the joints, the pultruded members are reinforced locally using solid glass fiber RP inserts. A 0.5 mm thick epoxy coating painted on the entire structure provides extra protection against corrosion. The truss is partially submerged in salt water and is expected to be used by up to 20,000 pedestrians and cyclists per day. RPs was chosen over traditional materials to provide the necessary durability and corrosion resistance. The structure is said to cost about a third of an equivalent steel truss, with its low weight (5 tonnes) making construction and installation much easier than if metal had been used. Assembly took place at FCDD's facility in Toowoomba before the completed truss was transported by truck to the site 150 km away.

6 9 Markets/Products 4 9 1

Once in position, the truss sits between 12 concrete pontoons, with the structures tied together with a number of 20 mm and 30 mm diameter stainless steel through-rods. (website: www.fcdd.com.au). Hardcore Composites' fabrication of wind fairings for the New York City Metropolitan Bridge and Tunnel Authority's Bronx-Whitestone Bridge earned The Dow Chemical Co's 2003 Americas Fabricator Excellence Awards (FEA). The RP wind fairings replaced 7400 ft (2.2 km) of heavy steel trusses. Hardcore used vacuum assisted resin transfer molding (VARTM) and Dow's Derakane 8084 epoxy vinyl ester resin to fabricate the fairings. The Derakane was chosen because it has the chemical resistance required to withstand the harsh conditions on top of the bridge, but it is also lightweight and two to three times as strong as other resins. This means that the wind fairings are very durable, offering a longer service life and, reducing long-term maintenance costs. Dow reports that to date this project represents the largest use of structural RPs in the world, requiring 890,000 lb (400 tonnes) of FRP to complete the project. RP fencing is considered better than metal. Prestige TM Series ornamental RP fencing is said to look like wrought iron fencing but is more durable and virtually maintenance-free. Prestige fence posts, rails, and pickets are manufactured from Saint-Gobain Vetrotex's Twintex | a 75 wt% glass fiber, 25% chemically coupled, heat- and light-stabilized polypropylene based concentrate. Prestige fencing is 60% stronger than aluminum, and at lower load stress levels it is slightly more flexible than aluminum, absorbing impacts better. At higher stress loads it becomes more rigid than aluminum, which means it can better withstand heavier impacts such as fallen tree limbs and the occasional climber. The RP also gives Prestige fencing a fade-resistant, matte finish. Roofs

The following example provides information on designing of plastic structural products to take static loads. It will be a structural problem common to a number of different structures to show how the different structural requirements will affect the choice designers have to make. The design problem will be a roof section that may be used for anything from a work shed, to a house, to a vehicle, or even to a simple weather shelter. The analysis begins with a definition of the function that a roof performs. A roof is the overhead product of a structure intended to

492 Reinforced Plastics Handbook

protect the occupants a n d / o r contents of the structure from the outside environment. It involves rain, snow, wind, sun, falling objects, hurricanes, and the other elements that make up the outside or surrounding environment. In order to perform this function the roof must be capable of supporting its own weight and the weight of snow or any other possible accumulations on the roof. It must be resistant to wind loads that are quite severe in some regions. The roof must also support loads imposed by people walking on it, usually for maintenance. In some instances the roof may double as a deck and the traffic may be constant. The roof must be able to shed water that falls on it, although it need not be waterproof in the sense of being a waterproof membrane structure. The roof surface is exposed to sun, wind and driven debris and must be resistant to erosion by the action of sunlight and the abrasive action of wind driven debris. In most cases the roof is insulated thermally to prevent heat loss in cold weather and heat input during warm weather. Obviously, not all roof requirements apply to all roof situations, but most of them do so you can set up your own requirements. The major load applied to a roof is the static load of the roof structure itself. Since roofs come in a wide variety of types, the self-load will depend on the basic roof design. The simplest is the corrugated RP panel structure. This type of structural element is widely used for roofs on industrial buildings to admit daylight, porch and patio roofs, shelter roofs such as those used at bus stops, and a variety of similar applications. Variations of this simple roof are used for roof sections on transportation vehicles such as buses and trains. Since this section is one of the easier ones on which to describe loading conditions, it will be used to illustrate the design procedure. Other roof sections such as the domes, arches, geodesics, and paraboloids involve complicated stress analysis and the results would not be particularly useful in a general analysis of a static structure. The corrugated materials are available in sheets which vary from 4 ft x 8 ft to as large as 10 ft x 20 ft. A typical material is 0.100 in. thick with 2 in. corrugations, and a corrugation depth of 1 in. The RP material from which they are made is glass fiber mat as the reinforcement and weather-resistant TS polyester plastic. In general, the sheet material is nailed or screwed to wooden supports (could be pultruded RP supports if the price was fight) at proper intervals. In some cases the roof section is made in one piece with spars of TS polyester-glass material molded into the product to provide the stiffening support needed. In this case the only requirement for installation involves anchoring the edge of the section to the structure.

6. Markets/Products 493 This type of design problem is somewhat different from others in that the unit is made from standardized sections that have specific physical properties and are available in only a limited number of thicknesses and configurations. The design problem now consists of trying the available materials in the structure with the supports that can be used and then determining if the material will perform. The self load is easily determined from the weight of the materials. The snow load is a design value available from experience obtained in the area where the structure is to be used. Similarly, the maximum wind load and people load can be determined from experience factors that are generally known. The problem is worked out using several different sheet types and different support spacings in an environment that would be typical of a city in the Midwestern part of the USA. The indicated solution is that the material selected will take the required loads without severe sagging for a 15 year period with no danger that the structure will collapse due to excessive stress on the material. If a standard material had not been suitable, it would have been possible to use one specifically molded for the application, or by the use of several layers of the material. One typical way in which excessive loading for a single section is handled is to bond two layers of the corrugated panel together with the corrugations crossed. This results in a very stiff section capable of substantially greater weight bearing than a single sheet and it will meet the necessary requirements. The double sheet material also provides significant thermal insulation because of the trapped air space between the sheets particularly if they are edged sealed. The roof section was designed to meet the static load requirements. However, it is necessary to consider transient loads such as people walking on the roof and fluctuating wind loads. The localized loads represented by people walldng on the roof can be solved by assuming concentrated loads at various locations and by doing a short time solution to the bending problem and the extreme fiber stress condition. The local bearing loads and the localized shear should also be examined since they may cause possible local damage to the structure. Stresses from varying winds are general alternating stress loads and occur over wide areas of the structure. When the wind changes direction, the stress frequently changes direction, and the tendency is for the roof to lift away from the structure. The main point of stress caused by the wind is at the anchorage points of the roof to the rest of the structure. They should be designed to take lifting forces as well as bearing forces; the lower the angle of roof, the less wind lifting force. Proper anchorage of the support structure to the ground is also essential. Local fire and building codes impose additional restrictions.

494 Reinforced Plastics Handbook

A large area of plastics, such as described here, has a substantial change in dimension with temperature. Surprisingly, very few of the traditional building materials, including wood, have significant expansion under normal temperature shifts. The RP materials generally are not a problem since they have low thermal coefficients of expansion and the corrugated shape tends to flex and accommodate the changes caused by heating and cooling. In the case of materials such as vinyl siding, the expansion factor becomes significant and is an important consideration in the fastening system. The effects of the environment on the performance of the material must be considered. Using the initial physical properties of the materials, the structure is sound. Exposure to weather, which includes water and sunlight, has a significant effect on the physical properties of the materials and this must be taken into account in the design. This type data is available from the reliable panel producers. Let us assume that there is a 50% or more drop in the physical properties in 5 years; actually far less. This can be due to surface damage and to changes in the bulk of the material. In general, this type of loss of physical properties levels off to a low rate of deterioration in suitable materials so that any potential failure can be anticipated. This loss of properties can be compensated for by increasing the strength requirements by a suitable factor of safety, probably about three in this case, and by using a protective coating on the sheet material to minimize the effects of weathering. The preferred type of coating would be a fluorocarbon material that has the best resistance to sunlight and other weathering factors of all of the plastics. If this type of surfacing is used, the material will retain its surface integrity for at least 20 years. The example of the roof structure represents the simplest type of problem in static loading in that the loads are clearly long term and well defined. Creep effects can be easily predicted and the structure can be designed with a sufficiently large safety factor to avoid the probability of failure (Chapter 7). Infrastructures

RPs continue their use during the past half century in civil infrastructure such as in highway structures within the USA and worldwide primarily due to their high strength and stiffness to weight ratios and their design flexibility for specific structural characteristics. In addition, the serviceability and functional service life of an RP structure such as a bridge may be greater than those built using conventional structural materials. Investigators continue to develop its environmental durability data. Freeze-thaw durability is one such environmental condition.

6. Markets/Products 495 A work targeted specifically to civil infrastructure application has reported mechanical data on freeze-thaw tests conducted on isophthalic polyester and vinyl ester pultruded/glass fiber RPs (Chapter 3). Specimens were aged in accordance with ASTM C666 (namely, 40F to OF followed by a hold at OF and a ramp up to 40F followed by a hold) while submerged in 2% sodium chloride and water. Specimens were removed after every 50 cycles and tested in ASTM 3-point flexure mode. The results clearly indicated a reduction in flexure strength and modulus after 300 cycles. One of the first reports highlighted the importance of cracks in the matrix and fiber-matrix interface as being the cause of the damage in RP materials. When these cracks form beyond a certain critical size and density, they coalesce to form macroscopic matrix cracks which tends to increase the diffusion of water into the system. Water can then condense within these cracks resulting in crack propagation as well the formation of micro and macro level ply delamination during the expansion of water undergoing a liquid-solid phase transition. In Kevlar fabric laminates subjected to two-hour temperature cycles f r o m - 2 0 F to 125F, ultimate tensile strength of the laminate was found to decrease by 23% after 360 cycles and by 63% after 1170 cycles. When differential scanning calorimetry (DSC) was used to identify the nature and presence of freezable water for each constituent material within an E-glass/vinyl ester RP, i.e., matrix, and interphase (via an assembled RP). Thawing heat flow measurements taken for a single cycle (-150C to +50C, 5 C / m i n ) on saturated, NEAT (Chapter 1), unreinforced vinyl ester resin samples indicated no thawing endotherm and thus the absence of freezable water. This was attributed to the fact that water would reside in the free volume of the resin. Since this free volume size is on the order of about 6 to 20 A., it indicates that these voids will be thermodynamically too small for water to freeze. Heat flow measurements taken for an E-glass/vinyl ester RP with the same cycle parameters clearly indicated a melt endotherm a t - 6 . 8 C thus indicating the presence of small voids at the interphase region within the RP and potential susceptibility t o freeze-thaw degradation. Cyclic DSC cycling (-18C to +4C, 5C/rain) of an E-glass/vinyl ester RP displayed a shift up in the thaw endotherm as cycling progressed, indicative of freeze-thaw damage via increased void size. It seems unlikely that water can freeze in limited void system of a NEAT plastic (Chapter 3), but the crack dimensions in an RP system appear are large enough to facilitate the freezability of water. The following review concerns both saturated and dry fiber RP samples that will be placed in an accelerated freeze-thaw environment and

496 Reinforced Plastics Handbook

tested for mechanical property degradation, changes in crack density, and moisture uptake at specified intervals to assess damage. A group of saturated controls will be held at a constant temperature above freezing and will be tested in the same manner as the freeze-thaw samples. All samples are pultruded glass reinforced cross-ply ( 0 / 9 0 ) laminates with plastic matrix materials.

Pultruded Materials All materials were pultruded using an open resin impregnation bath (Chapter 5). During pultrusion both pull force and die temperature were monitored at all times and allowed to reach steady state before any material was considered usable. Three different matrix resins were used in this study: a toughened vinyl ester, an untoughened vinyl ester, and an epoxy. Two different fiber layups were used designated by the letters "L" and "P". The vinyl ester laminates were pultruded with the "L" lay-up while the epoxy laminate employed the "P" lay-up in order to prevent scaling problems in the epoxy resin system. From the batch of pultruded material, 510 samples were cut to 25.4 mm by 177.8 mm (1 in. by 7 in.) from the larger as-received panels using an abrasive wet saw. Special care was taken to align all saw cuts with the principal material directions with the long direction corresponding to pull direction. All laminates were nominally 4 mm (0.160 in.) thick. After the cutting operation, the edges of each sample were wet sanded smooth with 400-grit abrasive paper and blown dry with compressed air. All samples destined for saturation were edge coated with an oven cured two-part epoxy to prevent moisture infusion through cut edges.

Tests and Analyses Ultimate tensile strength, stiffness, and strain-to-failure were determined quasi-statically for each class of as-received material in accordance with ASTM D 3039 Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials using a deflection rate of 2.5 ram/rain (0.10 in./min). A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. A total of 324 samples were fully saturated in a 65C (149F) water bath with moisture uptake measured throughout the saturation process. Weight measurements were taken hourly on the first day the samples were placed in the saturation tank, every three hours on the second day, every four hours the third day, every six hours the fourth day, and once everyday thereafter. The samples reached saturation within 45 days.

6 9 Markets/Products

The freeze-thaw conditioning parameters chosen for this study were based on ASTM C 666 Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing. This test protocol calls for a ramp down from 4.4C (40F) t o - 1 7 . 8 C (OF) followed by a hold at -17.8C (OF), a ramp up to 4.4C (40F) and a hold a t - 1 7 . 8 C (OF). There may be a minimum of 4.8 and a maximum of 12 conditioning cycles per day with 75% of the cycle time set aside for freezing and 25% for thawing. Two high performance cascading refrigeration freeze-thaw conditioning chambers were used to achieve a ten cycle per day rate. A series of trays were fabricated to hold each sample in accordance with ASTM C 666, namely to surround the samples with between 0.8 mm ( 1 / 3 2 in.) to 3.2 mm ( 1 / 8 in.) of water. Additional design goals for the trays were to minimize the volume of water and maximize convective heat transfer with the air inside chamber. Each tray can hold eight samples and every other slot were machined all the way through to allow airflow vertically through the trays. A second type of tray were also fabricated to allow the application of four point bending loads to each sample capable of causing 0.55% strain at the centerline on the surface of the tension face. This strain level was chosen because it is beyond the knee in the stress-strain curve for each material in this study and it likely opens up cracks that might be large enough to allow additional freezing to take place. This tray can also hold up to eight samples. Three levels of freeze-thaw exposure were included in this study: 100, 300, and 500 cycles. A set of control samples were also placed in a constant 4.4C (40F) bath for the duration of each freeze-thaw exposure level. Similar to the as-received testing regime, ultimate tensile strength, stiffness, and strain-to-failure were determined quasi-statically in accordance with ASTM D 3039 for each class of material after saturation. A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. Similar mechanical testing and crack density analyses were performed at each of the three specified freeze-thaw conditioning levels for both unloaded and loaded samples in each of the general conditioning categories, i.e., saturated freeze-thaw (144 samples), saturated constant temperature (144 samples), and dry freeze-thaw (144 samples).

Crack Density Analyses Crack density was assessed using non-destructive acousto-ultrasonic (AU) techniques with confirmation by optical microscopy. AU is an

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ultrasonic NDT technique useful for quantifying small, distributed changes not easily detected with traditional ultrasonic techniques. It returns results related to the ability of the interrogated material to transfer mechanical energy. In this setup, the transducers are spaced in a manner (typically, far apart) so that there is no direct or minimally reflected energy transmission between them and the primary transmission is by plate wave propagation. AU results are calculated from the energy spectral distribution of the AU signal by moment analysis. The most useful AU parameters tend to be the area under the stress-strain curve and the centroidal frequency (ratio of the first and zero moments). The area is directly related to the amount of energy transfer along the specimen. Shifts in the centroidal frequency also indicate changes in the materials ability to propagate particular modes. Typically, the spectral content of the AU signal has several relatively discrete frequency peaks with a few dominant ones. Each peak corresponds to a different mode or order of plate wave propagation. The modes were typically categorized as symmetric (extensional) and anti-symmetric (flexural). The order of a particular mode indicated the complexity of that type of deformation. Since each peak represents energy propagating with a different type of deformation, it possibly can be sensitive to different types of degradation. AU samples were taken from the general sample population and have already been base-lined for as-received and post-saturation conditions. For optical microscopy, representative sections of material were cut, potted, and polished for each post-conditioning group and examined using an inverted optical microscope. Though this initial study some data was reported. Strength for the toughened vinyl ester was 389 MPa in the as-received condition vs. 237 MPa for the post-saturation condition. Likewise, for the untoughened vinyl ester, strengths were 432 MPa vs. 240 MPa. For the epoxy, strengths were 424 MPa versus 237 MPa. Stiffness for the toughened vinyl ester was 19.9 GPa in the as-received state v. 22.1GPa for the post-saturation condition. Stiffness for the untoughened vinyl ester was 23.9 GPa for both conditions. For the epoxy, stiffness was 26.2 GPa versus 25.6 GPa. Strain-to-failure for the toughened vinyl ester was 2.49% in the asreceived condition versus 1.26% for the post-saturation condition. For the untoughened vinyl ester, strain-to-failure was 2.58% vs. 1.36% and for the epoxy, 2.29% vs. 1.20%. Strength and strain-to-failure were approximately 50% lower after saturation for all three materials. Stiffness effectively remained unchanged.

6. Markets/Products 499 The moisture content at saturation was 0.70% for the toughened vinyl ester samples, 0.74% for the untoughened vinyl ester samples, and 0.84% for the epoxy samples. Because of this, the moisture aging experiment had to be terminated after 45 days at which point the heaters were turned off and the tank was allowed to equilibrate to room temperature. Conclusions It is virtually impossible to freeze water in a highly crosslinked amorphous plastic. This is in part due to geometric space constraints in addition to hydrogen bonding that further impedes the process. In the RP system however, the crack dimensions are large enough to facilitate the freezability of water. It is believe that this is the mechanism of freezing and the associated volume increase during the transition leads to the propagation of cracks and the accumulation of damage.

Plastics Lumber Plastic lumber is recycled plastics processed such as commingled plastic, polyethylene plastic, and polypropylene plastic. To improve their performances different developments have been used such as specialty additives (lubricants, deoxidizers, etc.). An example is by adding as low as 10 wt% of short glass fiber to these recycled plastics can double their strength. Other fibers used include hemp, flax, and sisal. They are principally extruded; other processes are used such as injection and compression molding, to produce products competitive to wood lumber on land and in the water. Compression molding allows for a deep-molded grain and a much more dense board. The density also helps the product resist moisture absorption and improves weatherability. Mixed recycled plastic lumber bridge decks, boat docks, doors, floors, furniture, windows, fences, pallets, etc. are product examples in service. Plastic lumber would be maintenance-free for at least half a century, as opposed to 15 years for treated wood and 5 years for untreated wood. Extensive use is made in applying plastics in wood to improve their structural and decorative properties. Different forms/profiles of plastic/wood are used. Extruded profiles can contain at least 70 wt%, some up to 90%, wood content and produce wood-like appearance. Proper drying of the wood is required since it is hygroscopic otherwise burning can occur and properties are reduced. These products compete in different markets particularly the building and construction market and where water is located like a boating dock. It is entering the $8 billion USA residential siding market that is now at least half vinyl.

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There are compregs. They are compressed plastic impregnated wood usually referring to wood assembly veneer layers and other wood-plastic impregnated combinations. There is also compressed wood that is also called densified wood or laminated wood. It is wood that has been subjected to high compression pressure to increase its density with plastics. Laminated wood is a high-pressure bonded wood product composed of layers of wood with plastic such as phenolic as the laminating agent. Compreg or impregnated wood-plastic was produced in the early part of the 20th century after phenolic was developed (1909). Plastic loaded wood (impregnated) resulted in significant increased performance for the wood such as higher mechanical properties, hardness, etc. In addition, gains with longer life, rot resistance, etc. Originally most of the plastics used were phenolics. By the 1950s other plastics were used that includes acrylic and vinyls. For certain applications vinyl polymerization was an improvement over phenolic condensation polymerization that would leave by-products such as water that had to be removed. Dry wood is used with the impregnating of the plastics after the wood is evacuated of air using a vacuum. The wood is put into a bath of plastic solution. The soaking period, like the evacuation period, depends on the type and structure of wood. Curing of plastics is usually by a radiation rather than regular polymerization reactions. Compressed wood is also called densified wood or laminated wood. It is wood that has been subjected to high compression pressure to increase its density with or without plastics. It is usually supplied in the form of a laminate in which plastics have been incorporated by drying the wood and using a vacuum. Laminated wood is a high-pressure bonded wood product composed of layers of wood with plastic such as phenolic as the laminating agent. There are wood composition boards that refer to a product that is usually made by reducing wood to small particles and re-forming into a rigid board. Bonding is by adhesion developed from the natural adhesive action of the wood substance and/or through addition of various binders such as different plastics (phenolic, etc.) to meet different structural and environment performance requirements. Plastic lumber scored a major commercial breakthrough during 1999 with Home Depot Inc. to stock products from USA Plastic Lumber Co., Boca Raton, F1 (USA's largest maker of recycled plastic lumber made mostly from HDPE milk jugs and shampoo bottles). Home Depot is the world's largest home-improvement retail chain. Also aboard in USA stocking Boca's lumber were the nation's second (Loewes) and third (Menard) largest home-improvement retailers

6 9 Markets/Products 501

Rising consumer awareness of alternative decking materials is translating into manufacturing expansions as highlighted at the halls of the Las Vegas Convention Center were decked out with boards made of 100% plastic or RP composites during the International Builders' Show, held January 2004. Product acceptance is being pushed along by factors including the Environmental Protection Agency's phase-out of arsenic-treated lumber, and the desire of consumers to make the most of outdoor living space. This action of using plastic lumber all started decades ago with vinyl fencing, taking business away from wood fencing. Following this action, decking came aboard. The Freedonia Group Inc., Cleveland, OH, reported that in USA during year 2002 plastic composite decking represented 9% with 91% wood of a total 4,873 million board feet. They expect that during year 2007 plastic composite decking will represent 17% with 83% wood of a total 5,460 million board feet. Pallets

In the industrialized countries there are almost more pallets then people. USA has about 1.6 billion with Europe at least 0.5 billion. Virtually all are wood. Since at least the 1950s various organizations have fabricated URP and RP pallets. Major problem has been to produces pallets meeting performances at costs competitive to wood. Gradually slight market penetration has occurred particularly where special requirements exist in favor of plastics with its superior performances and cost advantages. Underwriter's Laboratories (UL) during 2001 developed a standard for pallets. The new UL 2335 was created to classify plastic pallets to meet requirements of the recently revised National Fire Protection Assoc. standard NFPA 13. That change allows plastic pallets to be treated like wood pallets if test data indicate that the burning characteristics of the plastic pallets are equal or better than wood (UL telephone 847-6641508). Heat Resistant Column

RL Industries won a Dow FEA (Fabricator Excellence Awards) award, for the fabrication of a high temperature, dual-laminate FRP chemical absorber column for Rubicon Inc in Geismar, Louisiana, USA. The column needed to work in temperatures greater than 250F (120C). RL Industries fabricated the column using a combination of hand lay-up and filament winding with Dow's Derakane 470HT-400 epoxy vinyl

502 Reinforced Plastics Handbook

ester resin, which combines maximum chemical resistance with high temperature performance.

Transportation URP and RP play a very important role in the vital areas of transportation technology by providing special design considerations, process freedom, novel opportunities, economy, aesthetics, durability, corrosion resistance, lightweight, fuel savings, recyclability, safety, and so on. As an example designs include lightweight and low cost principally injection molded TP car body to totally eliminate metal structure to support the body panels including combining component parts (Figure 6.6). There is the recently designed Human Transporter by Segway LLC, Manchester, NH with its exterior PC/PBT film fimsh, 20 wt% glass fiber/PPE/PA RP molded wheels, PC/ABS RP molded control shaft, etc. Skydivers with their RP glass or carbon fiber helmets now use non-circular high strength nylon fiber parachutes that include harness and hardware.

Figure 6.6 Graphite fiber RP automobile (courtesy of Ford Co.) Practically all types of plastics are used (literally from seats to the outside shells), and in many cases required in all methods of transportation; such as, automotive, railroad, buses, trucks, trailers, boats, submarines,

6. Markets/Products 503 aircraft and space vehicles. A major reason for its use is resistance to corrosion. Other reasons pertain to many different inherent characteristics that range from attractiveness to durability, mechanical strength or toughness to quick mass production techniques, light-weight, etc. In USA RP consumption in automobiles represents the largest market. It accounts for 32 wt% of the total demand.

Design Concepts URPs and RPs are extensively used in all types of transportation vehicles providing aesthetics to structural performances. To assure the structural integrity/durability and cost effectiveness of RP structural components for vehicles requires careful consideration of numerous factors during the design. These factors generally include: 1 service load environment (loads, temperatures, moisture time); 2 types of RPs (conventional, advanced, hybrid); 3 constituent materials (glass fibers, graphite fibers, aramid fibers, epoxies, polyesters, etc.); 4 environment effects on material properties (temperature, moisture. fatigue, creep, strain rate); 5 fabrication process; 6 quality control; 7 attachments; 8 structural analysis methods to validate the design concept with respect to previously established design criteria; 9 unique test methods to characterize the RP selected; 10 simulated and full component testing to verify that the component has been fabricated as designed; and 11 attendant costs of ad these factors. RPs takes advantage of the fibers directional properties. They have evolved as a logical sequel to conventional RPs particular since at least the 1940s and to intraply hybrids, lntraply hybrid RPs have unique features that can be used to meet diverse and competing design requirements in a more cost-effective way than either advanced or conventional RPs. Some of the specific advantages of intraply hybrids over others are balanced strength and stiffness, balanced bending and membrane mechanical properties, balanced thermal distortion stability, reduced weight a n d / or cost, improved fatigue resistance, reduced notch sensitivity, improved fracture toughness a n d / o r crack-arresting properties, and improved impact resistance. By using intraply hybrids, it is possible to obtain a

504 Reinforced Plastics Handbook

viable compromise between mechanical properties and cost to meet specified design requirements. Structural mechanics analyses arc used to determined design variables such as displacements, forces, vibrations, buckling loads, and dynamic responses, including application of corresponding special areas of structural mechanics for simple structural elements. General purpose finite element programs such as NASTRAN arc used for the structural analysis of complex structural shapes, large structures made from simple structural elements, And structural parts made from combinations of simple elements such as bars, rods and plates. Plastic composite mechanics in conjunction with structural mechanics can be used to derive explicit equations for the structural response of simple structural elements. These explicit expressions can then be used to perform parametric studies (sensitivity analyses) to assess the influence of the hybridization ratio on structural response. For example the structural response (behavior variables) equations for maximum deflection, buckling load and frequency of a simply supported beam made from intraply hybrids are summarized in Figure 6.7 Flexural modulus is used to dcterminc the maximum deflection, buckling load, and frequency of a simple supported beam made from intraply hybrids.

P

L_

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-I

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-1

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Un'lmr)2~. 2~112 +V ~SC ~] 112 + VSC(P~c Figure 6.7 Loadsrelatedto flexuralmodulus The notation in these and further equations are as follows: a~, a2

B'cl,k B'c2, k

Correlation coefficients for longitudinal compressive stength. Buckling limit (buckling behaviour constraint) due to loading condition k. Strength limit (strength behaviour constraint) due to loading condition k.

6-Markets/Products 505 Interply delamination limit (delamination constraint) due to loading condition k. Flexural modulus. EF Ef11, Ef22 Longitudinal and transverse fiber moduli Emil, Era22 In situ matrix longitudinal and transverse moduli. Modulus primary composite. Epc Modulus secondary composite. Esc Fiber shear modulus. Gf12 Matrix shear modulus. em12 Hj Matrix interply layer effect. / Moment of inertia. Correlation coefficients in the combined-stress failure criterion; Ke12~13 cz, [3 = Tor C denoting stress direction. Fibre volume ratio. Void volume ratio. K-- I, 2, 3, denotes loading condition index. k Length. f Number of plies. N Inplane loads - x and y directions corresponding to k. NxkNyk P Load. Buckling load. Per Buckling load of reference composite. Pcro Fiber tensile strength. 5# Strength primary composite. Strength secondary composite. Volume fraction secondary composite. W Panel cost units per unit area. ,&#" Correlation coefficients in composite micromechanics to predict ply elastic behaviour. Interply delamination factor. ~del Displacement. 6 Displacement of reference composite. 60 ~moc, S, T In situ allowable matrix strain for compression, shear and tension. Ply angle measured from x-axis. 0 Fiber Poisson's ratio, numerical subscripts denote direction. 13f Matrix Poisson's ratio, numerical subscripts denote direction. I)m CO~] Frequency of the nth vibration mode. Frequency of the nth vibration mode of the reference composite. COqo

B'c3, k

The equations are first expressed in terms of Ef, the equivalent flexural modulus, and then in terms of the moduli of the constituent composites (Epc and Esc) and the secondary composite volume ratio (Vsc). These equations were used to generate the parametric nondimensional plots shown in Figures 6.8-6.10. The nondimensionalized structural response is plotted versus the hybridizing ratio Vsc for four different intraply hybrid systems. These

506 Reinforced Plastics Handbook INTRAPLY HYBRID

4 --

p

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Effects of hybridizing ratio and constituent composites on center deflection of intraply hybrid composite beams

1.00 INTRAPLY HYBRID ASIKEV

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Effects of hybridizing ratio and constituent composites on buckling load of intraply hybrid composite beams

INTRAPLY HYBRID ASIKEV

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Figure 6. I0

Effects of hybridizing ratio and constituent composites on frequencies of intraply hybrid composite beams

6-Markets/Products 507 figures show that small amounts of secondary composite (V~c<0.2) have negligible effect on the structural response. However, small amounts of primary composite (Vsc >0.8) have a substantial effect on the structural response. A parametric plot of Izod-type, impact energy density is illustrated in Figure 6.11. This parametric plot shows also negligible effects for small hybridizing ratios (V~c <0.2) and substantial effects for hybridizing ratios (Vsc >0.2).

f

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Figure 6.11

'~-~2

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Effects of hybridizing ratio and constituent composites on Izod-type impact energy density of intraply hybrids

The parametric curves in Figures 6.8 to 6.11 can be used individually to select hybridization ratios to satisfy a particular design requirement or they may be used jointly to satisfy two or more design requirements simultaneously, for example, frequency and impact resistance. Comparable plots can be generated for other structural components, such as plates or shells. Also plots can be developed for other behavior variables (local deformation, stress concentration, and stress intensity factors) and/or other design variables, (different composite systems).This procedure can be formalized and embedded within a structural synthesis capability to permit optimum designs of intraply hybrid composites based on constituent fibers and matrices. Low-cost, stiff, lightweight structural panels can be made by embedding strips of advanced unidirectional composite (UDC) in selected locations in inexpensive random composites. For example, advanced composite strips from high modulus graphite/resin, intermediate graphite modulus/resin, and Keviar-49 DuPont resin can be embedded in planar random E-glass/resin composite. Schematics showing two possible locations of advanced UDC strips in a random composite are shown in Figure 6.12 to illustrate the concept. It is important to note that the embedded

508 Reinforced Plastics Handbook

strips do not increase either the thickness or the weight of the composite. However, the strips increase the cost.

RANDOM UNIDIRECTIONAL "OMPOSITE,., STRIP

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Figure 8.12 Schematicof strip hybrids

It is important that the amount, type and location of the strip reinforcement be used judiciously. The determination of all of these is part of the design and analysis procedures. These procedures would require RP mechanics and advanced analyses methods such as finite element. The reason is that these components are designed to meet several adverse design requirements simultaneously. Henceforth, planar random RP with advanced composite strips will be called strip hybrids. Here, the discussion is limited to some design guidelines inferred from several structural responses obtained by using finite clement structural analysis. Structural responses of panel's structural components can be used to provide design guidelines for sizing and designing strip hybrids for aircraft engine nacelle, windmill blades and auto body applications. Several examples are described below to illustrate the procedure. The displacement and base material stress of the strip hybrids for the concentrated load, the buckling load, and the lowest natural frequency are plotted versus reinforcing strip modulus in Figure 6.13. As can be seen the displacement and stress and the lowest natural frequency vary nonlinearly with reinforcing strip modulus while the buckling load varies linearly. These figures can be used to select reinforcing strip moduli for sizing strip hybrids to meet several specific design requirements. These figures are restricted to square fixed-end panels with 20% strip reinforcement by volume. For designing more general panels, suitable graphical data has to be generated. The maximum vibratory stress in the base material of the strip hybrids due to periodic excitations with three different frequencies is plotted versus reinforcing strip modulus in Figure 6.14. The maximum vibratory stress in the base material varies nonlinearly and decreases

6.

Markets/Products

20'/,, BY VOL, 20 BY 20 BY 0. 05 in.

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Figure Go13 Structural responsesof strip hybrid plates with fixed edges

rapidly with reinforcing strip modulus to about 103 GPa (15 x 106 psi). It decreases mildly beyond this modulus. The significant point here is that the modulus of the reinforcing strips should be about 103 GPa (18 x 1 0 6 psi) to minimize vibratory stresses (since they may cause fatigue failures) for the strip hybrids considered. For more general strip hybrids, graphical data with different percentage reinforcement and different boundary conditions are required.

5O 40 STRESS, 30 ksi

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Figure 6,14 Maximum stress in base material due to periodic vibrations

! 35

509

510 Reinforced Plastics Handbook

The maximum dynamic stress in the base material of the strip hybrids due to an impulsive load is plotted in Figure 6.15 vs. reinforcing strip modulus for two cases: (1) undamped and (2) with 0.009% of critical damping. The points to be noted from this figure arc: (a) the dynamic displacement varies nonlincarly with reinforcing strip modulus and (b) the damping is much more effective in strip hybrids with reinforcing strip moduli less than 103 GPa (15 x 106 psi). Corresponding displacements arc shown in Figure 6.16. The behavior of the dynamic displacements is similar to that of the stress as would be expected.

~'- 100

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Maximum impulse stress at center

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I 15

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6 9 Markets/Products

The previous discussion and the conclusions derived there from were based on panels of equal thickness. Structural responses for panels with different thicknesses can be obtained from the corresponding responses in Figure 6.15 as follows (let t = panel thickness): The displacement due to a concentrated static load varies inversely with t 3 and the stress varies inversely with t 2. 2

The buckling load varies directly with t 3.

3

The natural vibration frequencies vary directly with t.

No simple relationships exist for scaling the displacement and stress due to periodic excitation or impulsive loading. Also, all of the above responses vary inversely with the square of the panel edge dimension. Responses for square panels with different edge dimensions but with all edges fixed can be scaled from the corresponding curve in Figure 6.13. The significance of the scaling discussed above is that the curves in Figure 6.13 can be used directly to size square strip hybrids for preliminary design purposes. The effects of a multitude of parameters, inherent in composites, on the structural response a n d / o r performance of composite structures, a n d / or structural components are difficult to assess in general. These parameters include several fiber properties (transverse and shear moduli), in situ matrix properties, empirical or correlation factors used in the micromechanical, equations, stress allowables (strengths), processing variables, and perturbations of applied loading conditions. The difficulty in assessing the effects of these parameters on composite structural response arises from the fact that each parameter cannot be isolated and its effects measured independently of the others. Of course, the effects of single loading conditions can be measured independently. However, small perturbations of several sets of combined design loading conditions are not easily assessed by measurement. An alternate approach to assess the effects of this multitude of parameters is the use of optimum design (structural synthesis) concepts and procedures. In this approach the design of a composite structure is cast as a mathematical programming problem. The weight or cost of the structure is the objective (merit) function that is minimized subject to a given set of conditions. These conditions may include loading conditions, design variables that are allowed to vary during the design (such as fiber type, ply angle and number of plies), constraints on response (behavior) variables (such as allowable stress, displacements, buckling loads, frequencies, etc.) and variables that are assumed to remain constant (preassigned parameters) during the design.

51 1

512 Reinforced Plastics Handbook

The preassigned parameters may include fiber volume ratio, void ratio, transverse and shear fiber properties, in situ matrix properties, empirical or correlation factors, structure size and design loads. Once the optimum design for a given structural component has been obtained, the effects of the various preassigned design parameters on the optimum design are determined using sensitivity analyses. Each parameter is perturbed about its preassigned value and the structural component is re-optimized. Any changes in the optimum design are a direct measure of the effects of the parameter being perturbed. This provides a formal approach to quantitatively assess the effects of the numerous parameters mentioned previously on the optimum design of a structural component and to identify which of the parameters studied have significant effects on the optimum design of the structural component of interest. The sensitivity analysis results to be described subsequently were obtained using the angle plied composite panel and loading conditions as shown in Figure 6.17. ,/ I_ / /

~1"

J

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-I

16"

NYk

LOAOr LOAOS i..l~~ k-Z. k-]l I~k (litlln.I -1200 .100 !~ (llllln.I -I10 ~llm

Figure 6,17 Schematicof composite panel used in structural synthesis

Sensitivity analyses are carried out to answer, for example, the following questions: What is the influence of the preassigned filament elastic properties on the composite optimum design? What is the influence of the various empirical factors/correlation coefficients on the composite optimum design? Which of the preassigned parameters should be treated with care or as design variables for the multilayered-filamentary composite? What is the influence of applied load perturbations on the composite optimum design?

6 9 Markets/Products 5 1 3

The load system for the standard case consisted of three distinct load conditions as specified in Figure 6.17. The panel used is 20 in. x 16 in. made from an [(+0)n]s. angle plied laminate. The influence of the various preassigned parameters and the applied loads on optimum designs are assessed by sensitivity analyses. The sensitivity analyses consist of perturbing the preassigned parameters individually by some fixed percentage of that value which was used in a reference (standard) case. The results obtained were compared to the standard case for comparison and assessment of their effects. Introductory approaches have been described to formally evaluate design concepts for select structural components made from composites including intraply hybrid composites and strip hybrids. These approaches consist of structural analysis methods coupled with composite micromechanics, finite element analysis in conjunction with composite mechanics, and sensitivity analyses using structural optimization. Specific cases described include: Hybridizing ratio effects on the structural response (displacement, buckling, periodic excitation and impact) of a simply supported beam made from intraply hybrid composite. Strip modulus effects on the structural response of a panel made from strip hybrid composite and subjected to static and dynamic loading conditions. Various constituent material properties, fabrication processes and loading conditions effects on the optimum design of a panel subject to three different sets of biaxial in-plane loading conditions. Automobiles

RPs continue to make impressive inroads in automobiles. General Motors Corp., Detroit, MI via Plastics News (Feb. 23, 2004) compared the materials used per vehicle in North America during 1977 and 2003. Weight percentage was ferrous at 71.4 (1977) and 52.6 (2003), h i g h / medium-strength steel at 3.4 and 16.3, aluminum at 2.6 and 8.3, plastics and reinforced plastics at 4.6 and 7.6, and others at 18 and 20.2. The pounds per vehicle was high/medium-strength steel at about 130 (1977) and 375 (2003), aluminum at 175 and 250, plastics and reinforced plastics at 100 and 275. Intake manifolds, camshafts, and engine blocks are just a few such parts under development for tomorrow's cars. The plastic auto engine has been a reality since the debut of the Polimotor in 1980, with its subsequent success as a power plant in racing cars.

514 Reinforced Plastics Handbook

Both RP strength and appearance qualities continue to be new designs in the latest models. The Smart Roadster roof module has a glossy, pigmented surfacing film backed up with long fiber polyurethane RP in an innovative example of in-mold film decorating. In a BMW underbody closure compression molded glass mat thermoplastic (GMT) material made from a blend of chopped glass and polypropylene fibers was used. A VW Golf front-end carrier demonstrated the commercial viability of in-line compounding long glass polypropylene in a twinscrew extruder piggybacked on an injection machine. Glass filled/phenolic RPs, namely SMCs and BMCs was used in the Powertrain category. Also aboard were a carbon-fiber Corvette hood and Nissan driveshaft. There are body interior parts that did nothing to improve appearance, strength, or weight. Rather, it was the fulfillment of an engineer's dream. A material substitution cut costs 43% without any changes to product design, tooling, or assembly methods. RP components continue to find more use in the OEM and replacement field. They include such items as primary structural supports, fenders, hoods, etc. Most of the RP used is SMC (Chapter 4). The continued development of improved primer surfacing for the RPs will undoubtedly increase the use of RPs in bodies and components. Large components and entire auto bodies have been designed and built indicating what may lie in the future for RPs. In areas where volume is limited and the number of models is increased, the tooling advantages of plastics become evident. There was a new design approach for the use of plastics in the auto construction was used on the DeLorean DMC-12 car that was designed and built (1967). Process used was principally the elastic recovery molding (ERM); also called foamed reservoir molding (FRM) that included glass fiber reinforcements. It consisted of fabricating a sandwich of plastic-impregnated in opencelled flexible P U R foam between the face layers of fibrous reinforcements. When heated in a mold and squeezed, the foam is compressed, forcing the plastic and air outward and into the reinforcement contacting the mold cavity. Unfortunately the car never took off into the market. At present, there is an increasing number of special, medium volume cars in production and others under consideration extending the use of RPs. Over the last few years, the injection-molded bulk molding compound (BMC/Chapter 4) hatchback program of Citroen has developed to a two-part design using an outer skin for class A surface and an inner panel providing mechanical properties, injected from a single port on the parting line (which produces fewer weld lines, no need for a cold

6 9 Markets/Products

channel in the mold and easier mold machining). Both moldings are adhesively bonded together and coated with a conductive primer. The flow length, however, measures about 2 m (6.56 ft) which produced its own problems. The latest version, for the Xantia, is a three-part design. Chrysler specified a modified polymethyl methacrylate (PMMA) laminating resin for the body panels of the high-performance sports car, the 400 bhp 10 cylinder Dodge Viper, which went on sale in January 1992. The transition from styling to production took only three years. The decision to use glass fiber reinforced PMMA resin, molded by resin transfer, was a fundamental departure from established Chrysler practice, where previously all main exterior bodywork had been in sheet metal. However, at expected sales of 3000 a year and a unit price of about $50,000, sheet metal would not have been viable and the annual volume was too low to justify injection or compression molded plastics. Chrysler used glass-reinforced polyethylene terephthalate (PET) fenders for its main 1990s family saloons, the LH range, from 1993 model year, saving around 3.17 kg (7 lb) per car and up to 80% tooling costs. They are painted on-car and are claimed to be the first plastics parts to go through the E-coat (with temperatures up to 200~ meeting the requirement for electrophoretic coating of the whole car body and allowing the plastics components to withstand the temperature necessary for the steel parts. However, Chrysler proposed to injection-mold bodywork panels for its planned Composite Compact Vehicle, which weighs 544 kg and register a fuel economy of 4.7 liters/100 km. Mming to design a vehicle which is as easy to assemble as a toy, the body is envisaged as four large moldings, in glass reinforced PET, bonded with adhesive, produced on a gas-assisted 8200 ton clamp molding machine. The target cost of the composite was $3.3/kg, which the company compared with carbon fiber ($22/kg), polyester SMC, and polyurethane structural (with glass mat) reaction injection molding (SKIM) ( $ 1 1 - 1 3 / k g ) and steel (less than $0.90/kg). Carbon fiber RPs are showing up (2004) on a spectrum of concept cars and prototypes at auto shows, both on predictable vehicles, high-end super sports cars, and the unexpected, including a roadster concept aimed at selling for less than $20,000. Whether any of the dream cars actually make it into production with the RP still on board is hard to predict, but the number of vehicles rolling out show an increasing interest in the material. Many people continue to examine these vehicles. Resin and fiber suppliers, RP experts, universities and automakers themselves are researching ways to make carbon fiber a more

51 5

51 6 Reinforced Plastics Handbook

economical alternative. The attraction is easy to understand since it relates to high strength and low weight of the material make it possible to fine-tune structural systems. There is some prestige that goes along so certain people are willing to pay for performance and prestige. Prestige comes into play on two major concept cars that debuted at the 2004 Detroit show. The Chrysler division of DaimlerChrysler AG stormed onto the stage with the ME Four-Twelve sports car, that would sell for well in excess of $100,000 if produced. The car goes from zero to 60 mph in 2.9 seconds. Designers wanted this car to be as rigid and as light as possible. Carbon fiber and aluminum make up the Four-Twelve's body, while carbon fiber is used as the frame for the seat structure. Chrysler was looking at a cheaper prospect with the Dodge Slingshot concept. Based on DaimlerChrysler's European-made Smart roadster, which uses thermoplastic and standard RP for its body. The Slingshot also would have a plastic exterior, but the dream is to take it to carbon fiber. In the case of the Slingshot, carbon fiber would lend its light weight to a vehicle measuring in at 1,800 pounds that develops 45 miles per gal in fuel usage. Any possible future vehicle probably would not keep with the high-cost, high technology RP, since the automaker wants to sell it for less than $20,000. Price remains a problem for carbon fiber's wide acceptance. The Ford Motor Co. may have found a place for carbon fiber in the seat structures of the high-end Shelby Cobra concept vehicle, and while it is being used in limited editions of GM's Corvette and the Chrysler Dodge Viper, it is expected that it will take time for the material to go into other vehicles. What is occurring is a continual, gradual increase in carbon-fiber use. What was thought to be the world's largest yet surface-finished molded sandwich panel is being produced in Germany: an 8 m 2 (86 ft 2) polyester roof for the camper version of the Volkswagen T4 van. A push-up California design, it was molded in tools based on epoxy resin. Following trial molds with epoxy tools, Westfalia opted for twin counter-molds faced with nickel alloy on an epoxy/silica sand backing mix (which offered superior compression strength at temperatures in the 60-70C range). In production, the twin counter-molds are mounted on a sliding table and operated alternately with the mold, allowing one roof panel to cure while materials for the next are laid up on the other. Nissan reduced the weight of the front panel of its low-production Fairlady Z model by 30% by replacing a standard class A SMC with a lightweight grade: density of 1.3, against 1.85 g / c m 3, with no increase

6 9 Markets/Products

in material costs. A high-pressure in-mold coating gives a class A surface with good paintability. SMC also offers a cost-saving potential against steel in two-part closures, such as tailgates and bonnets. Studies by USA car manufacturers suggest that it is cost competitive on high-volume cars, at up to 200,000 a year. Other studies indicate that SMC has a clear advantage up to 150,000 cars a year and is competitive with steel up to 350,000 units. There are additional benefits such as weight reduction, freedom of styling and improved acoustic behavior. Production and marketing requirements in North America have tended to favor the use of glass-reinforced. A design for a high-back automobile safety seat, molded in carbon fiber and engineering TPs, won the UK's 1990 Plastics on the Road design competition. The winners were a team of industrial design students from the Istituto Europeo di Design, Milan, Italy. Incorporating an integral safety harness, it used pneumatics to cushion bumps and shocks. Driver and passenger seat shells for the BMW 3-Series arc in production in polypropylene GMT, following two years' use of this material for seat shells and rests for the BMW 8-Series. Computer-aided design and computer aided engineering techniques were employed. As well as good structural properties, the GMT parts are suitable for recycling (by re-pressing or by grinding and re-formulating as molding granules) and can also be incinerated with energy recovery at the end of the recycling chain. Corvettes

The facility of hand lay-up of TS polyester/glass fiber laminates led to early use in construction of bodywork for special car models requiring only limited production, such as sports and racing cars, leading to development of the all fiber glass reinforced plastic (FRP) monocoque body. The first car in the world to have an aI1-FRP body was the 1953 Chevrolet Corvette (fabricated by Morrision Fiber Glass Co., Ohio, USA); just over a half century ago General Motors Corp.'s Corvette sports car made its debut. Over 40 years later, the Corvette illustrated the development of technology, with nearly 100 kg (220 lb) of RPs, the main changes being the introduction of SMC and the use of recycled material in low-density inner panels. The original 1953 production run was 300 hand-built cars: the 1992 Corvette production was 24,000. Its makers continue to make improvements on how best to produce it that includes doing more with the tooling and finishes. For the sixthgeneration Chevrolet Corvette, this is debuting at the 2004 North American International Auto Show in Detroit that means tweaking the

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molding process to create better fit to the RP body panels. Launch of the 2005 model is an important milestone for the Detroit automaker since Corvette is a consistent icon as well as one of the most desired American-made vehicles on the road. Its introduction was a highlight of the auto show. The vehicle has been a hallmark for the plastics industry throughout its history, made of glass fiber/TS polyester RP from its first models. The new version retains a sheet molding compound outer body as well as an RP flooring. The carmaker and its suppliers also are using techniques developed for the 2003 launch of Corvette's sister sports car, the Cadillac XLR. To create a fighter fit and crisper lines, workers on the XLR carefully shifted freshly molded panels onto a special fixture to prevent warping or distortions. Result was to obtain a higher level of surface perfection than in the past. Higher-technology materials may not be part of the new standard Corvette, but plans are under way for special-edition vehicles. Carbon fiber RPs is being used on 2004 Z06 Commemorative Edition Corvettes. GM's two concept cars at the 2004 auto show also shared a body heritage with the Corvette, with both the Saturn Curve and Chevrolet Nomad using glass fiber/TS polyester RPs for their sports car bodies. The concept models were built on a new rear-wheel-drive sports car platform, called the Kappa architecture. The automaker built that platform for the future Pontiac Solstice, that began as a concept car in 2001 and will hit the roads within 2005.

Bumpers RPs for bumpers are used in USA, whereas in Europe the mass market to date is primarily in unreinforced injection molded TPs, with RPs used mainly for larger structures and bumper support systems, especially on export models. Front and rear bumper impact beams of some General Motors models are made of 60 wt% glass vinyl ester sheet molding compound, reinforced with a chopped and continuous strand glass fiber giving strength in all directions, replacing steel and withstanding 8 k m / h pendulum and impact testing on the 1700-1800 kg cars. The beams have been designed to aid reduction in number of parts, cutting assembly time from 33.7 to 14.5 min. They weigh 6.4 kg (14 lb) with 4-8 mm wall thickness and are molded on a standard compression molding machine. In Europe, the 5 kg recyclable front bumper beam for the Mercedes S range is produced in series quantifies in a special grade of polypropylene GMT. To withstand impact up to 4 k m / h without damage to itself or the car chassis a Mercedes internal requirement, approximating to USA

6 9 Markets/Products

standards, the GMT has directional glass fiber reinforcement. One part of the fiber is laid unidirectionally, lengthwise across the bumper and random fibers give consistent distribution of the TP matrix in the flow regions. The front and back layers are GMT with horizontally laid fibers about 1800 mm (70 in) long. The part is molded in a fully automatic plant, heating the blanks to over 200C, placing them in the press by robot and molding at about 1700 ton of pressure. The beam gains further absorption strength from four polyurethane core units, with three items behind and one in front. Finally, the structure is clad with a shell of reinforced reaction injection molding (RRIM), using a glass fiber reinforced paintable polyurethane (PUR) system. Integrated front ends in polypropylene GMT stampings of SMC were adopted by many automobile manufacturers. Replacing a conventional metal stamping comprising 15-20 pieces and weighing more than 6 kg, they integrate functions such as attachment for cooling fans, radiator, headlamps, bonnet locking device and a metal crossbeam, making the part lighter and more cost effective. The unit is preassembled with all these components, including the front grille and bumper fascia and the complete sub-assembly is finally assembled to the car after the engine has been installed. The approach has been proved in the USA, by Ford (in SMC) and in Europe, by VW (in GMT). Glass manufacturer Vetrotex estimated that some 25% of European vehicles have some form of integrated front-end concept, of which about 30% are produced in RPs. French manufacturers have been particularly to the forefront, including Renault (RI9, Laguna and Safrane), Peugeot (205, 306 and 605), and Citroen (AX and Xantia). By the year 2000 50% of European cars were integrated front-end systems and 63% of these were in RPs. SMC/BMC have a good chance in such applications, in which up to 20 other components can be brought together on one molded supporting framework which can also play a structural role in the car bodywork. The need is for good engineering properties and heat resistance, with moldability and lightness. Steel is a competitor, as also are glass-reinforced polypropylene (PP) or nylon and PP glass mat thermoplastics (GMT) but, the more work the part is required to do, the more likely it is to be made in SMC/BMC. German automotive suppliers of front-end modules Hella KG Hueck and Co. (Lippstadt, Germany) and Behr GmbH (Stuttgart, Germany) already are major players through their joint venture with Hella-Behr Fahrzeugsysteme GmbH. France's Plastic Ommum SA (Levallois, France) is joining this business arrangement as of year 2004. This threeway joint venture will launch a 350 million euros ($440.4 million) in annual sales, strengthen Hella and Behr's existing capabilities and

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provides for more expansion in the modules. The new company would be based in Lippstadt with a dedicated research and development center at Plastic Omnium's office in Lyon, France. It would launch with 550 employees in eight production sites in Germany, Czech Republic, Slovakia, Spain, Mexico and South Korea, making an estimated 1.25 million modules in 2004 and a predicted output climbing to 2 million/year during 2005 and 2006. Different module designs are manufactured having different definitions. Some North American suppliers use it to refer to bumper systems completed with painted fascia, energy absorption, and lighting. A full module produced in Europe is different, reflecting a change in manufacturing at the auto assembly plant. A typical module Hella-Behr now produces for Volkswagen AG and other auto makers includes the entire front vehicle structure and multiple parts from the radiator forward, including cooling, lighting, hoses and connectors, hood latch assemblies and wiring. North American automakers do not use the complete systems as widely as their European counterparts do because they would have to change their assembly architecture Vehicles made with the modules are open on the front end through manufacturing, with the module carrying the tie bars that unite the frame. The typical USA-based auto plant is designed to build the car around a complete frame from the start of the line. Future proposals to expand the systems in Europe would add the bumper beam and painted fascia to those parts, increasing the value of the overall system. Each company is a leader in its respective businesses. Plastic Omnium brings talent into the venture, while also strengthening Hella-Behr's capabilities in existing modules through its expertise in the structural plastics used in the carrier that holds all of the individual components. Hella-Behr has a lot of experience on how to design and develop the carrier. With Plastic Omnium, the German companies will have access to proprietary technology, since the French firm already has expertise with long glass fiber RPs in both thermoplastics and thermoset materials.

Window Regulators Innovative design by North American Body and Glass Division of Dura Automotive Systems Inc., Rochester Hills, MI during 2003 launched production during 2004 of a new plastic window regulator system. The basic window regulator, which is used to raise and lower the glass in an auto door, was developed in the 1920s as two pieces of steel, liberally coated in grease and operated with a hand crank to work like a pair of scissors.

6 9 Markets/Products

A drum and cable system has become more popular with wider use of powered window systems, but still require heavy steel components, grease, and expensive and fragile cable systems. The old designs with grease solves the problems with lubrication, however it catches a lot of sand, grit, and dust and makes it a mess. When temperatures drop, the greasy mess does not permit ease of the window operation. The new basic design uses interlocking gears directly driving along a thermoplastic rack, outperformed the existing standard. This RP glass-filled nylon track and gears have integrated lubrication, eliminating the need for grease. It is 2 lb lighter than a drum and cable system, capable of saving 8-12 lb per vehicle. It is more efficient, requiring fewer volts, which can make a difference for automakers looking to package more electrical options with the same battery. It performs better in all weather conditions and requires less space in the door. Very important, it is easier and less expensive to manufacture, requiring only three to five assembly steps and 20-30% less in up-front investments. Dura featured this new design system at the Society of Automotive Engineers 2004 World Congress March 8-11 in Detroit. Batteries

The combination gasoline and electric motor systems making up the new hybrid range of vehicles hitting the roads are drawing increased interest from drivers, carmakers, and the plastic (including RPs for fuel cells as reviewed in Chapter 10) industry. They must package several cubic feet of batteries. Early on, carmakers were packaging them in metal, but that is moving forward into plastics now; they could be all plastic. The first commercial consumer hybrid systems introduced by Japanese automakers Toyota Motor Corp, and Honda Motor Co. in 2000 relied on in-house battery and electric motor developments. Ford Motor Co. took its first hybrid to the market during the summer of 2004, a gas-electric version of the Escape SUV. With North American automakers joining the interest in the vehicles, suppliers of existing standard batteries, like JCI, with an auto unit based in Plymouth, MI, are moving toward production of battery modules for hybrids that may occur by 2006 or 2007 in autos. JCI's automotive unit is in talks with a cross-section of automakers for future products. Its European battery unit, under the Varta name, already makes systems for hybrid buses. Hybrids fuel up on standard gasoline used in an internal combustion vehicle, but also have a supplemental electric motor that taps into batteries that store energy created during vehicle use, such as when brakes are applied. Those batteries, currently nickel hydride, arc

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expected to shift to lithium ion eventually, hold about 4 volts of electricity per cell. Hybrids need between 144 volts and 350 volts, so the battery modules can be sizable, measuring 2 to 4 ft in width and length and a few inches in depth. The second generation of Toyota's power system in the Prius won notice from car buyers and industry watchers in 2003. Honda has hybrid power available with its Insight and a version of the Civic. Following on their heels arc new offerings from a cross-range of vehicles. Toyota's Lexus brand will introduce a hybrid sport utility vehicle later 2004, the RX:400H, and will focus on hybrid technology in advertising. In March, 2001 BP announced that it had joined a project with DaimlerChrysler, First Bus, Transport for London, UK, and the Energy Saving Trust to introduce three hydrogen fuel cell buses to England in year 2003. BP built and managed the infrastructure to supply hydrogen to the vehicles. The fuel cell engines work by producing electricity when hydrogen (H2) reacts with oxygen (02) to form water, a process more efficient than the internal combustion engine. This energy drives an electric motor that generates no local emissions. The H2 can be produced from a number of sources, including natural gas and oil, but in the case of the fuel cell buses 40% of it will be produced from renewable energies. Each bus will have a range of 400 km (250 mile). As well as London, nine other European cities are set to join the twoyear program. This 2001 project was one of at least five different potential technologies that may emerge this decade. As well as fuel cells, where hydrogen is only one of the potential fuel sources, other possibilities exist. They include liquefied petroleum gas and compressed natural gas for internal combustion engines; advanced direct-injection gasoline and diesel engines; hybrids that comprise an electric battery motor and a gasoline or diesel engine; and for limited range, purely electrically motored cars. An update as of 2004 of buses in the UK has this radical transport project supported by B P that could be a vital breath of fresh air for inner city travel in London. Commuters taking the number 25 from Ilford to Oxford Street can say goodbye to the noisy rattle and choking fumes that are usually associated with London's roads if they are fortunate enough to catch one of the three hydrogen-powered buses that have been trialed on the route since 14 January. The buses have none of the vibration and noise of traditional diesel because they are powered by electricity, produced when hydrogen is combined in a fuel

6. Markets/Products 523 cell with oxygen to become water that is the buses' only emission. The $1 million buses are now specially-built versions of the single-decker Mercedes Benz Citaro, used in most European cities. They are part of Clean Urban Transport for Europe, a Europe-wide two-year pilot project to test hydrogen as a viable alternative fuel. BP is acting as fuel provider in five of the nine cities taking part. Recognize that what might look commercial by 2005 may not be competitive during 2010. The winning emergent technologies have to be market-developed activities. As reported, it goes through three phases namely: 1

making it possible;

2

integrating it back into the vehicle; and

3

then creating a commercial infrastructure that makes the vehicle a commercial option to buy.

With fuel cells, for instance, they are currently between phases two and three. Other Parts Leaf springs for some passenger cars and trucks have been developed in RPs, using unidirectional glass fibers and special resins. These were also be used in a major German research project on a Mercedes Benz transporter and, on customer request, MAN installed two of the springs in heavy loading trucks, thus achieving a weight-saving of some 150 kg on each truck.

One of the most significant applications for RPs in automobiles in recent years has been the development of air intake manifolds. These are injection molded in 30-35% glass fiber-reinforced nylon 6 or 6 / 6 , either in one part, using fusible metal cores to produce the complex internal air channels, or as two mirror halves that are then welded together. The parts are up to 50% lighter than their metal counterparts and contribute to improved engine efficiency and better emissions, by providing a way to optimizing the flow and mixture of air. Latest developments are moving to integrating other components, with positive cost savings. It is estimated that about 40-45% of all new models are using plastic manifolds, with more in the future. The original development was by Porsche, in 1972, but the massproduction breakthrough was by Ford Europe, molded with fusible core technology by Dunlop Automotive in the UK (subsequently taken over by Siemens). Ford's interest dates back to the 1970s, when it developed a manifold compression molded in TS polyester BMC, but

524 Reinforced Plastics Handbook

this was overtaken by the development of TPs. In particular, USA manufacturers have actively taken up the technology and Japanese companies have also taken up plastics manifolds. The market will probably split evenly between fusible core and two-part welding, depending on the complexity of the part and the required production numbers. Fusible core molding is costly and requires dedicated investment in a production cell that includes not only the injection molding machine but also a complete loop for molding, inserting, melting out, and recycling the low melting point metal alloy. This makes it economical for long production runs of the more complex designs. For more flexible production, where the design is relatively simple, the economic solution is to mold in two parts that are then welded together. Nylon type 6 / 6 tends to be used for fusible core moldings and type 6 gives better properties for welding, but manufacturers have developed special grades that cross over this distinction. A variation, developed by Bayer and Mercedes, brings together more than two parts that are vibration welded at 120-240 Hz frequency, in multi shell technology. Other molding techniques have been studied, particularly molding with sliding cores and a variation of blow molding. Fiber-RP s, both TS and TP, are also used for the oil sump and rocker covers of automobile engines, both in the USA and Europe. Dimensional stability is a major problem, however. In a recent development, Rover UK specified mineral-reinforced nylon for cam valve covers for its K8 1.1 and 1.4 engines, in the Metro and 200 Series, specifying good mechanical properties at 120C, acceptable creep at 140C, excellent resistance to hot engine oil and low distortion/low tolerance moldings. The same, larger, parts on trucks in the USA are specified in vinyl ester. Pedal clusters are also injection molded in glass-reinforced nylon, replacing steel, with weight-saving and simplified manufacture. Clutch and accelerator pedals are in plastics but there is more caution about the brake pedal. Ford is typical in replacing steel with 33% glassreinforced nylon 6 (Allied Signal Capron 8233) for a C-channel floor pedal, molded by Comcord Technologies. The pedal completed two million cycles at 18 kg loading without incident, passing 113 kg loading requirements a t - 20 to + 70C. Assembly weight and number of parts are both reduced by 50%, with 10% cost saving. Special applications for RPs include lightweight armor for police cars are being investigated as a potential application for Dyneema, DSM's high-strength polyethylene (PE) fiber. A special ballistic yarn SK66, thought to be suitable on grounds of high energy absorption and low weight, is being tested for door and seat armoring on 50 Volvo 440

6. Markets/Products 525 police cars in major cities in the Netherlands. A key advantage is that, unlike steel armor, the lightweight PE armor does not require any structural changes to the car. The system used by the Dutch police is to the German class 1 standard, meaning that it is an effective shield against 90% of all ballistic threats against police forces in Europe. Typical arm our weighs only 1.7 kg (door) and 2.3 kg (seat), amounting to only about 8 kg additional weight. It can be mounted virtually invisibly. The shields are made by pressing binder-impregnated fabrics of Dyneema SK66 into the required form. Special requirement for Class A finish on preimpregnated material such as SMC is to being used on some of DaimierChysler's 2004 coupe models. It is in response to the reliance by today's vehicles on electronic systems that communicate via satellite and electromagnetic waves. Modern cars need several antennae, and for styling and design reasons these are, where possible, hidden beneath a body panel section. However, an all-metal body needs external antennae since electromagnetic waves cannot penetrate sheet metal. Designs exists of all-in-one metal/plastic antennae modules. An upper class car is now equipped with an average of ten antennae, and the figure will rise as car makers introduce systems for monitoring and automatically regulating the distance from the vehicle in front, and install warning sensors to avoid collisions when reversing. The antennae have generally been spread over the entire body shell, a challenge for designers because the area near the antenna has to be suitably designed to guarantee optimum rcccption. The antenna modulc in Volvo's XC90 SUV, developed by Johnson Controls and Volvo, demonstrates a way round the problem. The module accommodates all the antennae and relevant receivers (radio, TV, GPS) in one unit. It is made of steel and Durethan| BM 130 H2.0 polyamide supplied by Bayer MaterialScience AG, Leverkusen, Germany, manufactured using the plastic/metal hybrid technology already established for the series production of vehicle front-ends. RPs is also used in this type design. The antenna module weighs 1.8 kg and is located under a plastic cover on the rear of the roof of the off road vehicle. The antennae are integrated into a film that forms part of the plastic cover so as not to impair their performance. The backing for the film, which extends almost across the entire width of the vehicle, and various fixing elements are also made of polyamide. The receivers, such as the F M / A M , Digital Audio Broadcasting (DAB) and TV tuners, are screwed to the metal support of the hybrid construction. This compact module design with its high level of integration obviates the need for a large number of cables.

526 Reinforced Plastics Handbook

SMC is transparent to electromagnetic waves and is said to offer additional benefits such as lower systems costs compared with metal over the same production volumes. SMC also offers dimensional stability, stiffness, low weight, and high temperature resistance to enable online painting. To ensure a consistent product quality, DaimlerChrysler teamed up with molder Peguform, SMC manufacturer, molder MenzolitFibron, and resin supplier DSM Composite Resins in a quality improvement and consistency program called CCC (compound, characterization, consistency). The goal is guaranteed product consistency across all levels of the supply chain from raw material to the Class A painted part. The European Alliance for SMC reports that since the introduction of the CCC project during 2001, scrap and rework rates have been substantially reduced and many process improvements have been implemented. The changes introduced range from raw material analysis and tightening of tolerances to improvements in mold heating and materials handling practices. A Cadillac hood assembly includes a complex-shaped SMC inner panel that is bonded to an SMC outer panel. The outer panel has a Class A finish. The hood surface has a four-sided, tapered design and includes steel hinges, brackets and the hood latch. Here is an example where SMC has the ability to create high style, lower vehicle weight, reduce tooling costs and resist corrosion and denting. The new Cadillac ZLR attracted sports car enthusiasts. The vehicle's hood is compression molded from SMC by ThyssenKrupp Budd Company, of Troy, Michigan, USA. The SMCs used are based on AOC resins. HiPer Technology Inc., Armada, MI. has new carbon fiber/nylon RP wheels that came during 2004. The company has an exclusive use agreement with DuPont Co. of Wilmington, DE. for DuPont's patented carbon fiber material. HiPer's goal is to provide products designed to replace those currently made in aluminum. They are offering a new ATV wheel for professional circuit racers, a micro-sprint car wheel, a junior dragster motorcycle wheel, and a motocross wheel. The ATV production is now 30,000 wheels a year. Products expected 2005 include baseball and softball bats, a 15 inch automotive spare tire, and wheels for golf cart, marine trailers, and mountain bikes. The RP is lighter than aluminum, 2.7 times stronger than aluminum, and five times tougher than aluminum. You can beat it with a sledge hammer with no damage. Thomas A. Darnell, 33, the president and founder of HiPer, worked as project manager for Ford Light Truck Development for Automotive

6. Markets/Products 527 Molding Co. of Warren, MI, and later for Plastech Engineered Products Inc., Dearborn, MI. Darnell worked with DuPont to develop the material used in the energy-absorbing, impact-resistant wheels, and shared the patents with DuPont. DuPont has assigned the patents to HiPer. North America's first high-volume thermoplastic (RP) valve cover made its debut on the 2004 Chrysler Town and Country, Dodge Caravan and Grand Caravan with 3.3 and 3.8 liter V6 engines. The valve cover, manufactured by Bruss Sealing Systems (Bruss North America, 4405 Baldwin Rd., Orion, MI48359) from DuPont Minion mineral reinforced nylon, reduces weight by more than 65% and cuts cost significantly compared to metal. The innovative thermoplastic valve cover also delivers benefits through integrated functionality: an integrated air/oil separator significantly reduces the amount of oil pulled into the engine to reduce environmental impact; an integrated Positive Crankcase Ventilation (PCV) valve housing helps reduce evaporative emissions and ensures the PCV system stays secure. A global team from Chrysler Group, Bruss, and DuPont Engineering Polymers ensured this program went from CAD drawing to commercial launch in just under 22 weeks. The rapid development ensured the benefits of thermoplastics were delivered in the current vehicle model year. The valve cover is made of a specially formulated grade of glass/ mineral reinforced Minion that delivers a balance of stiffness, strength, dimensional stability, and warpage resistance to meet stringent requirements for the application. Switching to thermoplastics made it possible to eliminate the cosily e-coating process along with several secondary machining steps. The Minion runners and scrap from the injection molding manufacturing process are melt recycled. The USA plastic industry is looking to expand its plastic under the car hood, trying to convince North American automakers to use reinforced thermoplastics (RTPs) in valve covers in place of the existing metal components. Just over 50% of the autos made in Western Europe use RTPs for the covers, but in North America metal is the material of choice with 37wt% being thermoset. About 15wt% of global Market use glass and mineral filled nylon. The switch may not be easy or sudden, but the change is beginning to occur. It is expected to take the same route the intake manifold did in that the RTPs was a longtime coming but now it is accepted everywhere. The North American RTPs usage number is expected to climb to 4% by 2006. DaimlerChrysler AG is backing the first high-volume use of RTPs for valve covers with its decision to use DuPont's Minion

528 Reinforced Plastics Handbook

reinforced nylon on sixcylinder versions of its 2004 Chrysler Town and Country, Caravan and Grand Caravan minivans.

Buses

Buses and public transport in general, offer wide opportunities for the use of RPs. Unreinforced plastics (URPS) and reinforced plastics (RPs) have been used in different types of buses. In the world of buses during year 2000 Brunswick Technologies (Brunswick, ME) fabricated the socalled CompoBus. Its design incorporates oriented glass fiber satin woven tri-axial fabrics with TS polyester plastics in its chassis and body. Delphi Automotive Systems, Woodridge, IL and Hendrickson Innovations International developed and manufactured a plastic composite (glass/ carbon fiber hybrid reinforcement) for use in the medium and heavy duty truck and bus markets. When compared to metals they are lighter and more impact resistant, require less mounting hardware, and designed to conduct 50% less vibration. The facility of small volume production in RPs by hand lay-up led quickly to the use of these materials for van and truck bodies. Today, however, numbers have built up to justify press-molding many panels in SMC. Lighter weight and improved aerodynamics (reducing fuel costs), with lower maintenance, reduction in noise and overall improvement in comfort have been the reasons. While it is difficult for RPs to match the economics and flexibility of metal sheet for flat bodywork panels, they become interesting as soon as curvature, contouring or any additional function is introduced. RPs also lend themselves to production of special vehicle bodies, including sandwich-structure insulated bodies for refrigerated transport and very high performance filament wound tanks for oil, gasoline and chemicals tankers. Insulated containers are also a strong candidate for the SCRIMP resin infusion molding process. This Seeman Composites Resin Infusion Process (SCRIMP) has been used to manufacture corrosion resistance bus shells (Chapter 5). North America Bus Industries (NABI) of Anniston, AL uses glass fiberpolyester plastic material from TPI Composites of Warren, RI. These new buses weigh about 10,000 kg (22,000 lb) that is 3200 kg (7000 lb) lighter than steel units. Lighter weight results in reduced axial loads, brake wear, etc. and improved fuel efficiency. Schindler Waggon, Switzerland, is studying using its large-scale filament winding technology for bus bodies, insulated and double-shell

6. Markets/Products 529 containers and passenger bridges for airports and shelters. Internacional de Composites SA, Toledo, Spain is also investigating composite bus and coach bodies, based on a series of filament wound rings joined elements that are also filament wound. Different cross-sections can be used, both open and closed, and it is possible to wind and element which does not contain external concave geometry. The majority of frames are rectangular box beams or square frames. TS polyester resin and E-glass are used, with local use of carbon fiber to improve the structure. Mechanical properties are reported to be excellent.

Trucks Use of P,_Ps in trucks goes back to the early days when plastics were produced and throughout past years. Here is a brief introduction to RP applications. During 1946 to 1950 DVR designed and fabricated for Strick Trailers, Philadelphia, PA. 32 to 40 ft. long RP floors, side panels, translucent roofs, aeronautical over-the-cabin structures, etc. Practically all products were made of RPs (glass fiber-TS polyester plastic) providing lighter weight trucks, streamlining frontal area, insulator for refrigerator trucks, and lower product costs. The lighter weight products permitted trailers to carry heavier loads, conserve fuel, refrigerated trucks traveled longer distance (due to improved heat insulation), etc. Different plastics continued to be used in the different truck applications to meet a static and dynamic load that includes high vibration loads. Continued use is in the 4x4 pickup truck 100 lb boxes using thermoformed thermoplastic PEs and for the tougher requirements resin transfer molded SMC. A series of trucks using sheet molding compounds (SMC/Chapter 4) for at least part of the bed, began with the introduction of the 2005 Tacoma X-Runner by Toyota Motor Corp. They were introduced during the February 2004 Chicago Auto Show. Production on the 2005 Tacomas began late 2004. ThyssenI~upp Automotive AG's plastics division, formerly called Budd Co. has built a plant in Tijuana, Mexico, to make these inner truck beds for Toyota from SMCs. Toyota's adoption of SMC marked an expansion of RPs in pickup beds. Ford Motor Co. of Dearborn, Mich., uses SMC for the bed of its Explorer Sport Trac. General Motors Corp. uses mostly reinforced reaction injection molding (RIM/Chapter 5) for the beds of its Chevrolet Avalanche and Escalade EXT trucks.

530 Reinforced Plastics Handbook

Tanks Extensive use is made in using commercial and engineering plastics to fabricate all tank sizes and shapes used in the transportation industry as well as many other industries (agriculture, chemical storage, filtration, etc.). The processes in other chapters review fabricating tanks and containers using different types of URPs and RPS (Chapter 5).

Hopper Rail Car Tanks In the past (1973) a severe shortage of railroad covered hopper cars for the transportation of grain developed. Cargill, Inc. provided a contract to Structural Composites, Inc. for determine feasibility studies on the potential of using RP in the design and fabrication of these cars. Test results showed structural deficient existed. By 1978 an acceptable design resulted fabricating the Glasshopper (registered name). It was used in rail service March 1981. Cargill Inc., Southern Pacific Transportation Co., and ACF Industries, Inc. (Figure 6.18). It was larger and lighter in weight than the conventional steel covered hopper car resulting in being able to deliver more commodities per fuel dollar. Other advantages included corrosion resistance, and lower maintenance costs.

Figure 6.18

RP railroad covered hopper car

6 9 Markets/Products

The first to be built was Glasshopper I. It successfully passed all of the required American Association of Railroads (AAR) tests including the 454,000 kg (1,000,000 lb) static end compression test and the 568,000 kg (1,250,000 lb) coupler force impact test in the laboratory, and then successfully completed a round trip between St. Louis, MO and Oakland, CA [9700 km (6000 mile)]. From outward appearance, the RP designs were very similar to the standard ACF steel-covered hopper car. The first RP prototype, Glasshopper 1 that was in grain service, had four compartments. The car had a total capacity of 142 m 3 (5000 ft 3) and an overall length of about 16 m (53 ft). Its basic specifications are shown in Table 6.1. Table 6.1 Glasshopper 1 basic specifications Length inside Length over end sills Length over strikers Length over coupler pulling face Length over running boards Length between truck centres Extreme width Height, rail to top of running boards Height, rail to bottom of outlet Extreme height, rail to top of hatch bumper Number of discharge outlets Roof hatch opening, continuous Curve negotiability, uncoupled Cubic capacity Tare weight Gross rail load AAR clearance diagram

50 ft 31/2 in 51 ft 55/8 in 52 ft 11 in 55 ft 61/2 in 53 ft 7/8 in 42 ft 3 in 10 ft 8 in 15 ft 1 27/32 in 12 in 15 f t 6 i n 4 20 in x 44 ft 73/4 in 150 ft 500 ft 3 59,000 Ib 263,000 Ib Plate 'C'

The second prototype car Glasshopper 11 that was latter put into service had three compartments. The tare weight of the second car was 24,600 kg (54,200 lb), which was 4000 kg (8800 lb) lighter than a standard steel car weight of 28,600 kg (63,000 lb). Construction details for Glasshopper I consist of a filament wound (FW) RP car body, RP/balsawood core sandwich panel bulkheads and slope sheets, steel side sills and shear plates, steel bolster webs, and RP hatch covers. Standard running gear and safety appliances were utilized, as were standard gravity outlets. Several changes in construction details

531

532

R e i n f o r c e d Plastics H a n d b o o k

such as the use of single laminate slope sheets were made in the design of Glasshopper 11 to reduce weight and manufacturing costs. Table 6.2 shows the weight percentages of steel or RP materials. A significant amount (30 wt%) of the RP car structure is fabricated using RP materials. By subtracting the trucks steel weight, the remaining structure is RP. This construction allows the significant weight reduction to be possible. Finite element analysis (FEA) modeling was used throughout the design stages of the program to aid the structural analysis effort. The structural response in both static and dynamic loading conditions was characterized prior to initiation of the car construction. Table 6.2 Glasshopper 1 component weight summary

Component

Moteriol

Weight Ibs

Car body Sandwich panels Wide flange beams Stiffeners Top sill Roof/side angles Adhesive/bonding strip Hatches Outlets End arrangement Side sills Running boards/safety appln. Brake system Misc. hardware Trucks

R)

R~

RD R~ R~ R~ R~ R~

Steel Steel Steel Steel Steel Steel Steel Total weight

6800 4410 640 2910 46O 510 1070 860 1800 9640 4420 1650 1570 1060 21200 59000

Componentweight x 100 Totol weight 11.5 7.5 1.1 4.9 0.8 0.9 1.8 1.5 3.0 16.3 7.5 2.8 2.7 1.8 35.9 100.0

2 RPcomponentpercentages= 30 Steel componentpercentages= 70

FW process was used to fabricate both Glasshopper car bodies. It was determined that this process afforded the best mechanical properties for the lowest cost. Fabricating processes exist that can be highly automated which would help towards having RP-covered hopper cars compete economically with conventional steel-covered hopper cars in the marketplace.

6. Markets/Products 533 Resin matrix material system chosen for fabrication of the car bodies was a proprietary (TS) isophthalic polyester resin system developed by Cargill specifically for the Glasshopper project. PPG, Certain Teed, and OCF supplied the reinforcement of E-glass rovings. Both OCF 450 and 675 yield glass was used successfully in conjunction with the Cargill resin during FW operation. To provide adequate mechanical properties in the directions required to withstand the externally applied service loads, the FW apparatus was programmed to provide the multi-axial filament directional orientation capability. Secondary bonding operations involving the attachment of stiffeners, etc., for the first RP car, used Hysol's epoxy adhesive (EA 919). This same adhesive was used in joints where both bonding and bolting with mechanical fasteners were employed. Lord Corp.'s acrylic adhesive system (TS 3929-70) was used successfully for Glasshopper 11. Hat section stiffeners and wide flange beams were fabricated using the hand lay-up and pultrusion processes, respectively. The material used in the construction of the hat stiffeners included 1/2 oz mat, 24 oz woven rovings, 221/2 oz unidirectional fabric, and the isophthalic polyester resin. Pultrusions were purchased finished, and were fabricated using standard pultrusion processes. In order to demonstrate structural adequacy, Glasshopper 1 was tested in the ACF test laboratory located in St. Charles, MO. The test program was designed to show that the car meets and exceeds all requirements as specified by the AAR. Both static and dynamic tests were included in the testing. To determine the car's structural response under various applied loading conditions, Glasshopper 1 was instrumented with a total of 224 strain gauges, located at various areas determined through structural analysis to be of greatest importance and to provide maximum information. Glasshopper 11, instrumented with 310 strain gauges, successfully completed the test program in 1983. A series of six different static tests were successfully passed by Glasshopper 1, including end compression, draft, vertical coupler-up, vertical coupler-down, coupler shank, and torsional jacking. The end compression test consisted of "squeezing" the car, while empty, with a hydraulic ram until a coupler force of 1,000,000 lb was measured. The draft test was conducted on the loaded car (105.9 tons) and consisted of pulling on the coupler until a force of 630,000 lb was experimentally observed. The remaining static tests were all conducted on the loaded car and involved using calibrated hydraulic rams to: Jack the car upward with a vertical force of 22,700 kg (50,000 lb) applied at the coupler pulling face.

534 Reinforced Plastics Handbook

Jack the car downward with a vertical force of 22,700 kg (50,000 Ib) applied at the coupler pulling face. Lift the car free of the truck bolster by jacking at the coupler shank, a vertical force of 50,400 kg (111,000 lb) was required. Lift the car free of the truck bolster by jacking at the lifting lug/jacking pad assembly to verify torsional rigidity and stability, a vertical force of 31,780 kg (70,000 Ib) was required. An analysis of test results show the experimentally observed strains to be very close to those predicted using FEA techniques and "hand" calculations. This fact made it possible to use these techniques to further optimize the Glasshopper 11 design. After successfully passing all required static tests, Glasshopper 1 was subjected to a series of impact tests. For these tests, the car that was fully loaded, was pulled by cable up an inclined ramp and released to impact another fully loaded standing car that had its brakes released. Velocity of the car at impact was controlled by its height on the ramp at the time of release. Car's velocity was incrementally increased until an experimentally measured coupler force of 113,500 kg (250,000 lb) was developed during the impact. Velocity of 14.9 k m / h (9.24 m / h ) was required to obtain the AAR specified load. It is noted that this velocity is significantly higher than the velocity required to reach the specified force with conventional steel covered hopper cars, which is about 12.1 k m / h (7.5 m/h). Glasshopper 1, with modified bulkhead joints, successfully passed the AAR impact test required and was subsequently prepared for the extended road test. Following completion of laboratory testing, Glasshopper 1 was tested over a 9700 km (6000 m) route on the Southern Pacific system. Fully loaded car with 9,600 kg (211,000 lb) made the trip from St. Charles, MO to Oakland, CA and back to Houston, TX. The car was unloaded at the Cargill export grain terminal in the Houston area and then returned empty to the facility in St. Charles, MO. The car was accompanied on the trip by the fully instrumented ACF test car used for data acquisition that monitored key strain gauges and load cells throughout the trip. All test results and visual observations showed the car performed well, and as predicted. During certain segments of the testing, speeds of 113 k m / h (70 m / h ) were reached with no dynamic problems (flutter, hunting, etc.) being observed. It was determined that two major advantages of the RP covered hopper rail car are its tare weight and its corrosion resistance. As a result of its significantly lower weight and large size, the car is capable of carrying

6. Markets/Products 535 more payload per fuel dollar. This fact is extremely important in today's conditions of escalating and high-fuelled prices. Glasshopper is able to carry many highly corrosive commodities (salts, potash, fertilizer, ore, etc.) without the need for expensive linings and with significantly reduced car maintenance costs. Also, the car's service lifetime would be greatly extended in these severe service environments. Other advantages include the potential to eliminate painting requirements, reduced labor costs in manufacturing, lower center of gravity in the unloaded condition, ability to easily adapt to internal pressure designs, and rapid production changeover to alternate capacity cars.

Highway Tanks RP tanks on firm/above ground have been holding corrosive materials safely since the 1940s. The same technology, with some enhancements material wise and design wise, has been applied to over-the-road highway tankers. As an example tankers fabricated by Comptank Corp., Bothwell, Ontario, Canada are on the road in the USA and Canada since 1998 carrying a wide range of corrosive and hazardous liquids (Figure 6.19). These RP tank trailers are coded 312 for hauling corrosive and hazardous materials; special designed models haul acids or other corrosive chemicals; they unload by pressure, vacuum, or gravity.

Figure 6.19

Plastic tank trailer safely transports corrosive and hazardous materials on the highway

536 Reinforced Plastics Handbook

The tankers are filament wound using E-glass rovings with TS polyester resin (Reichhold Atlac 4010 AC) and surfacing veil. RP moldings are integrated parts of the shell that is usually 15.88 mm (0.625 in.) thick. These parts include external rings/ribs, covers for steel rollover guards, spill dam, catwalk, hose trays, etc. Corrosion-Resistant Tanks

As reviewed throughout this book part of the wide acceptance of plastics is from their relative compatibility to chemicals, particularly to moisture, as compared to that of other materials. Because plastics are largely immune to the electrochemical corrosion to which metals are susceptible, they can frequently be used in transportation and other markets successfully to contain water and corrosive chemicals that would attack metals. RP fabricators also have a major market for tanks as well as pipes, grating, and a variety of other structures used to withstand corrosive working environments that serve industrial customers. Plastics are often used in corrosive environments for chemical tanks, water treatment plants, and piping to handle drainage, sewage, and water supply. Structural shapes for use under corrosive conditions often take advantage of the design capability and properties of RPs. Glass fiber TS polyester RP water filtration tank is shown in Figure 6.20. It is 20 ft diameter, 32 ft high structure made in sections by a low-pressure RP fabricating method. This bonded, assembled tank was shipped on a water barge to its destination. Structural shapes such as this tank for use under corrosive conditions often takes advantage of the properties of RPs and other plastics.

Figure 6.20 Large water filtration tank with 6 ft opening

6 9 Markets/Products 537

However, certain plastics are subject to attack by aggressive fluids and chemicals, although the same media attacks not all plastics. It is thus most practical to select a plastic to meet a particular design performance condition. For example, some plastics like H D P E are immune to almost all commonly found solvents. Polytetrafluoroethylene (PTFE) in particular is noted principally for its resistance to practically all-chemical substances. It includes what has been generally identified as the most inert material known worldwide. It is important to recognize that all materials will have problems in certain environments, whether they are plastics, metals, aluminum, or something else. For example, the corrosion of metal surfaces has a damaging effect on both the static and dynamic strength properties of metals because it ultimately creates a reduced cross-section that can lead to eventual failure. The combined effect of corrosion and stress on strength characteristics is called stress corrosion. When the load is variable, the combination of corrosion and the varying stress is called corrosion fatigue. This problem can be controlled in several ways. One is to select the best material, such as stainless steel, a copper alloy, or titanium. Another is to use a nonmetallic protective coating of plastic. Certain systems like plating can reduce fatigue strength. Shot peening rather then plating seems to produce much greater improvement, but shot peening, plating, and then baldng can bring the fatigue limit to a point lower even than that of the base metal. The point in this review is that all materials have their limitations and must be critically analyzed if no prior experience exists upon which to draw. Underground Storage Tanks

Glass fiber-TS polyester RP (GFRP) underground tanks for storing gasoline and other materials used in transportation have been in use worldwide since the 1950s (Figure 6.21). Experience with them initiated many tank standards. RPs provided much longer life than their steel counterparts. In fact, steel tanks previously had no "real life" or no requirement standards until the RPs entered the market. It has been estimated that more than 200,000 GFRP tanks were installed in the USA from 1960-1990. A previous study by the Steel Tank Institute (Lake Zurich, IL) reported 61% were of steel and 39% of GFRP. At present, at least 50% of all tanks are GFRP. This RP vs. steel debate escalated when the EPA gave service stations and fleet refueling areas 10 years to remove steel tanks that leaked. Historically a Chicago service station documented the long life of RPs. A May 1963 installations remained leak tight and structurally sound

538 Reinforced Plastics Handbook

Figure 6.21 Underground glass fiber/TS polyester filament wound RP gasoline storage tank

when unearthed in May 1988. After testing the vessel, engineers buried it at another gas station. This tank was one of sixty developed by Amoco Chemical Co. It was fabricated in two semi-cylinder sections of glass fiber woven roving and chopped strand mat impregnated by an unsaturated isophthalic TS-polyester resin selected for its superior resistance to acids, alkalis, aromatics, solvents, and hydrocarbons. Two sections were bonded to each other and to end caps with RP lap joints. Today, the tanks are fabricated by using chopped glass fiber mixed with the isophthalic resin. This mixture is dropped from above onto a rotating steel mandrel. The glass-resin mix is sprayed to make the end caps. Demand for this type of petroleum storage tank has grown rapidly as environmental regulations have become more stringent. Marina installation has taken advantage of these RP tanks. They permit for boat owners to purchase gasoline at the pier. Before they were installed,

6-Markets/Products 539 gasoline either had to be carried to the marina or purchased elsewhere, because of corrosive conditions underground for metal or other tanks, particularly ones next to salt water. Standards require that today's underground tanks must last thirty or more years without undue maintenance. To meet these criteria, they must be able to maintain structural integrity and resist the corrosive effects of soil and gasoline, including gasoline that has been contaminated by moisture and soil. The tank just mentioned that was removed in 1991 met these requirements, but two steel tanks unearthed from the same site at that time failed to meet them. One was dusted with white metal oxide and the other showed signs of corrosion at the weld line. Rust had weakened this joint so much that it could be scraped away with a pocketlmife. Tests and evaluations were conducted on the RP tank that had been in the ground for 25 years; tests were also conducted on similarly constructed tanks unearthed at 51 and 71 years that showed the RP tanks could more than meet the service requirements. Table 6.3 provides factual, useful data from these tests. Table 6.3 Unearthed underground gasoline storage tank data Test results Age at testing Property

5.5 years

Z5 years

25.0 years

Buried-excavated Flexural strength:

1/7/65-8/21/70 19,500 134

4/4/64-10/24/71 24,200 167

5/15/63-5/11/88 22,400 154

Flexural modulus: Tensile strength: Tensile modulus: Tensile elongation: Notched Izod impact strength:

Psi MPa Psi

MPa Psi MPa Psi MPa O/o

ft.-lb./in Jim

725 x 103

795 x 103

4,992 10,700 74 1,160 x 103 7,260 1.11

5,482 13,600 94 1,053 x 103 8,000 1.25

9.7 518

11.0 587

635 x 103

4,378 10,500 72 1,107 x 103

7,630 1.13 14.1 753

Prior to the development of the GFRP tanks, no standards were required for buried tanks such as loads or loading conditions, minimum depths of earth cover, or structural safety factors were available. At that

540 Reinforced Plastics Handbook

time, sizes were 22,704 to 45,408 liter (6,000 to 12,000 gal), with a nominal width and height of 2.44 m (8 ft) for truck shipments to local gasoline stations. Standards have developed listing requirements for stored fluid type, environmental resistance, minimum earth cover, ground water submerged limits, and surface wheel load over tank. Increasing acceptance of buried GFRP tanks has widened the size range from 2,081 to 181,632 liter (550 to at least 48,000 gal) and the range in typical diameters from about 1.22 to 3.35 m (4 ft to at least 11 ft). The tank configuration is cylindrical, in order to provide the required design volumes within the established envelope of heights and widths. Length ranges are from 5.5 to 11 m (18 to 36 ft); they are well within practical truck shipment limits. A circular shape is required to support the substantial internal and external fluid and earth pressures with good structural efficiency. Other considerations in selection of an efficient configuration are used. With a vertical axis, tank underlay requires that much less land area than with axis horizontal, but very deep excavation is required where expensive ledge or ground water conditions will frequently be encountered. Both internal and external pressures are large, requiring a substantial increase in wall thickness and rib stiffness, compared with a horizontally-placed tank. With axis horizontal, maximum external and internal pressures do not vary with size (length), and can be resisted with economically feasible wall thickness and rib proportions. Tanks underlay a larger ground area. Uniform bedding is more difficult to attain. Hemispherical shells, low-rise dished-shaped heads and flat plate closures were all considered. Hemispherical shells were found structurally very efficient because of good buckling resistances under external fluid and earth pressure, good strength under internal pressure, no requirement for edge ring, and low discontinuity stresses at the junction with the cylinder. Flat end closures result in excessive deflections and large edge bending moments on the cylinder. Sandwich construction could be used to improve structural efficiency of flat ends. Sandwich wall construction was also investigated for attaining necessary buckling resistance of spherical shell end closures and found to be feasible but less cost effective. Use of rib stiffening was required. It was found necessary to stiffen the cylindrical shell against buckling under external pressure from ground water and dimpling from local earth pressure due to surface wheel loads. Sandwich wall construction was investigated as an alternative to use of stiffening ribs and found to be feasible but less cost effective. Shape-wise, a hollow trapezoid provides efficient bending strength and stiffness, a wide base for proper spacing of cylinder shell support against

6 9 Markets/Products

local buckling, and a narrower top to resist local buckling with high circumferential flange forces. Figure 6.22 provides a design concept for a tank with hollow trapezoidal ribbing.

0.28" SO0.3

Shop 9.,--- Splice (Overwr I:) f.Typical Rib a/l/Detail A

F h o l d down straps with guides

W[_. _ . . . , . _ .

~ "'"w'7, , ' " "1~U _

. =

-;,-

77

_

i "

i

I

!

,,L.,, 1'-3"

,,.o. 2"_,

. ].

21 '-8" L.2V=" ,~_2"_,

Detail A

4'-0"

(3FRP Laminates Tank Wall: .28" Spray-up 9125" Mat Woven Roving Rib: Top: .12" Filament Winding 9125" Mat Woven Roving

Sides: .25" Mat Woven Roving Feet: .125" Mat Woven Roving .060" Filament Winding 9125" Mat Woven Roving Bottom: .125" Mat Woven Roving

added over entire rib for 3'-6" length centered on invert9

Figure 6.22 Example of a design for 10,000 gal gasoline RP storage tank

Base width and clear spacing between ribs are established to minimize the number of ribs while providing adequate local buckling resistance for a cylinder wall of approximately the minimum practical shell thickness. Clear spacing must also be sufficient to permit installation of sleeves or nozzles for fill pipes and vents between ribs. The RPs selected for detailed consideration is designed to provide both structural and liquid-sealing qualifies. For example, a smooth liquid tight inner surface is obtained with a resin rich surface layer reinforced with glass filament surfacing veil. It is backed up by a 3.2 mm (1/8 in.) thick liquid seal layer of chopped glass/polyester spray-up. Discontinuous fibers are provided to avoid a continuous path for liquid migration into and along the reinforcement. Additional thickness for structural purposes is provided, either by adding more chopped fiber

541

542 Reinforced Plastics Handbook

reinforced spray-up, or by filament winding. An outer resin rich surface layer is reinforced with a surfacing veil. A silica sand filler may be used of bulk, improved compressive stiffness and economy. Minimum practical total RP thickness is established as 4.8 m m (3/16 in.) for the combined spray-up liquid seal and filament wound structural layers and 6.4 mm (1/4 in.) for an all-chopped fiber spray-up laminate with sand filler. The choice for any construction is made on the basis of comparative design thickness, weight, and fabrication costs. The allchopped fiber reinforced construction using somewhat greater wall thickness than the composite filament wound-chopped fiber wall is determined to provide the lowest tank cost; filament winding provides lower weight. The National Petroleum News Survey, as of the first quarter of 2002 reported that the USA had 170,678 retail gasoline underground storage tank outlets, down from 187,892 at year-end 1987. Total sales of gasoline have grown modestly resulting in average sales volume per outlet increasing. Size and ownership of many stations have changed over the last decade and new, larger-scale facilities are replacing the traditional owner-operated service stations. The wholesale tank replacement business of the 1990's is over and was replaced by more modest growth paralleling the growth rate of GDP and vehicle miles. Adding some new approaches to this segment have been new hyper-market entrants in the gasoline retailing business like Wal-Mart and Lowe's. Another important corrosion segment is the chemical processing industry (CPI), a mature and cyclical, industry that produces 70,000 chemical substances, many of which need protection or require protection for employees handling them. Industrial production of chemicals was expected to grow 4.5% in 2003, according to most recent forecast. Capital spending in 2000 (latest available year) was $31.2 billion, according to the American Chemistry Council. While this total number appears large, chemical producers suffer from the same restrictions on spending as most USA businesses in this economic down cycle. Oilfield activity has benefited from relatively high prices of crude oil in 2001 to 2003 but that has not translated into more exploration nor any more production of plastics such as RP down-hole pipe, line pipe, or sucker rods for the oil patch. Crude prices peaked in 2000 and drilling rig activity declined along with pricing since then. Industrial production indices for this business have been flat through 2002, and 2003 show more of the same. New investments declined about 8% in 2003 and expect the same decline in 2004. The price for West Texas Intermediate was $26 per barrel late in 2002 and ranged from $25-26 per barrel in 2003.

6. Markets/Products 543 Rocket Motor Tanks Very small to large filament wound cases have been fabricated for use on rockets and missiles. As an example, a racetrack filament winding RP fabricating technique was used to fabricate a very large tank (rocket motor case) for NASA. See Chapter 5 Filament Windings, Racetrack and Other Winders.

Cryogenic Fuel Tanks NASA's $5.3 million contract (year 2003) to Northrop Grumman, USA provides continued developing and refining manufacturing processes for constructing large-scale reinforced plastic (RP) cryogenic fuel tanks. One half of a 3.2 m diameter, reusable fuel tank will be fabricated. The manufacturing process will involve a cost saving process that eliminates the need for autoclave curing. Current launch vehicles use single-use, aluminium tanks for storing cryogenic fuels. The RP multiple use tank will weigh 20-30% less than an aluminium tank of the same size. For a given payload. Weight reductions will result in about an 8% decrease in vehicle acquisition costs and a 6% decrease in operational costs.

Marine From boats (ships) to submarines to mining the sea floor, certain URPs and RPs can survive the sea environment. The sea can bc considered more hostile than that on earth or in space. For water surface vehicles, many different plastics have been used in designs in successful products in both fresh and more hostile seawater. Plastic boats have been designed and fabricated since at least the 1940s. Anyone can now observe that practically all boats, at least up to 9 m (30 ft) are made from RPs that are usually hand lay-up moldings from glass rovings, chopper glass spray-ups, a n d / o r glass fiber mats with TS polyester resin matrices. Because of the excellent performance of many plastics in flesh and seawater, they have been used in practically all-structural and nonstructural applications from ropes to tanks to all kinds of instrument containers. Statistics on full year 2002 wholesale shipments of new boats activity was down about 5% compared to the prior year. Industry spokespeople report that consumer confidence and discretionary spending was affected by the events of September 11, 2001 Twin Tower disaster that carried over into 2002 boat sales. The weak state of the economy also compelled many buyers to defer buying-decisions. As expected, various categories of boats fared differently. Outboard boats seemed to be

544 Reinforced Plastics Handbook

holding their own quite well while personal watercraft and jet drive boats continued their declines and were down about 15%. Inboard cruisers recorded their first decline since 1996 (estimated at 11%) and sterndrives were expected to be down 5%. The 2003 boat sales ranging from flat to +5% following the economy situation. Consumer confidence, job creation, and growth in disposable income are relevant indicators of boat buying sentiment. Boats

By far the most important application of RP in marine structures, particularly with respect to volume consumed, has been in boat construction (Table 6.4). This has occurred in both civilian and military markets. Growth continues where it already dominates the small boats with the larger boat market growing. Materials of construction are reviewed in Tables 6.5-6.7. The Mirabella V, to date the largest RP vessel and largest single-masted sailing yacht yet built, was launched in late November 2003 by VT Shipbuilding (formerly Vosper Thornycroft of Portchester, U.K.). The 75m (244 ft) long super-yacht was designed by Ron Holland from Kinsale, County Cork, Ireland and engineered by High Modulus Europe Ltd. Of Hamble, Hampshire, U.K. VT's sister company VT Halmatic built the ship's 90m (292 ft) high carbon fiber mast, the world's tallest RP mast. Its sandwich construction hull and deck were hand laid up and vacuum bagged in disposable open female molds made with wood (medium density fiberboard) with steel backup structures. Duratec mold surfacing material, supplied by Hawkeye Industries Inc., Marietta, Ga., USA, was used to prepare the mold surface, which was treated with an inexpensive wipe-on wax mold release. A vinyl ester primer gel formed the gel coat. Use was made of non-styrenated vinyl ester to avoid pinholes. Stitched multiaxial E-glass materials, supplied by SaintGobain BTI of Andover, Rants, U.K., reinforced with several plies of aramid fiber were wet out with vinyl ester resin from Reichhold of Research Triangle Park, N.C., USA to form the hull skins. Core material was Airex closed-cell foam from Alcan Airex of Sins, Switzerland, with a higher density used below the water line. The 50 mm (2 in.) thick foam was too thick to thermoform, so VT created tongue-in-groove foam planks that were fitted together to form the sandwich core. In order to provide sufficient stiffness to support working and entertainment areas as well as to resist the high longitudinal bending

6. Markets/Products 545 Table 6.4 Material choice/design considerationsfor boat hulls Resin

Phenolic Epoxy Vinyl ester Polyester

Fiber

Carbon: Unidirectionals Cloths Aramid: Unidirectionals Cloths Glass: Unidirectionals Biaxals Multiaxials CSM/combination mats

Core material

Dynamic loading: high strain rate foam Hot climate/dark color hull: crosslinked foam Balsawood/cedar Flame retardant: honeycomb

Flame-retardant properties/available in prepreg format/requires temperature cure Good mechanical properties/available in prepreg format/requires temperature cure/use with any fiber CSM possible required at bond lines/osmosis problems reduced compared with polyester Most inexpensive resin/CSM required between layers/osmosis concern/avoid high performance fibers Used for shells of high performance race craft and stiffening of internal structure Used on all weight critical components not directly exposed to impacts Used mainly on racing sailboats Used to increase penetration resistance and toughness Avoid female mould construction with unidirectionals

Reduce the number of layers and hence the construction time Avoid high modulus thin skins with low densities/care with high processing temperatures Avoid high processing temperatures

High compressive strength/temperature stable/poor shear elongation properties Excellent shear strength/density. Can be expensive

Source: RoyalInstitutionof NavalArchitects,UK.

forces of the very long hull, the upper deck has carbon/vinyl ester skins over a foam core. The deck is built up at rigging attachment points and reinforced with additional unidirectional carbon fiber to carry stress around openings. All internal decks, tanks, and interior bulkheads were vacuum-infused as large, flat glass/vinyl ester, foam cored sandwich panels, then cut to shape by hand and installed. The disposable mold

546 Reinforced Plastics Handbook Table 6.5 Mechanical properties of various laminate constructions

Unit

Single skin CSM/WR polyester

Single skin aramid/ glass epoxy

SandwichSandwich oramid/ carbon/ Strip Fromed glass aramid wood/ aluminum Framed epoxy epoxy epoxy alloy steel

Density

kg/m 3 1900

1300

1400

2010

1800

1350

1450

Fiber weight

%

52

46

47

60

58

50

58

0~ strength

MPa

352

360

424

1050

1090

1000

1133

0 ~Tensile modulus

GPa

13.46

21.97

31.38

55.0

67.0

70.0

100.0

Ultimate

O/o

2.7

1.7

1.4

3.3

2.3

1.8

1.28

MPa

242

75

122

350

360

200

380

GPa

12.99

16.27

19.07

47.0

57.0

50.0

80.0

900 Tensile strength

MPa

283

310

389

39

39

37

42

900 Tensile modulus

GPa

11.70

18.57

32.98

6.0

6.0

5.7

5.9

900

MPa

242

75

122

100

95

90

95

GPa

12.99

14.05

19.07

9.0

10.0

9.0

11.0

Shear strength

MPa

55

38

50

55

55

40

58

Shear

MPa

5.0

5.0

5.0

4.7

4.75

2.57

4.8

fraction %

strain 0o Compressive strength 0o Compressive modulus

Compressive strength 900 Compressive modulus

modulus

Source:SPSystems

6 . Markets/Products T a b l e 6 . 6 Effect of thickness of laminate on strength

7/8-3/16 in (psi)

7/4 in (psi)

9,000

Minimum ultimate tensile strength

5/76 in (psi)

12,000

3/8 in and over (psi)

13,500

15,000

Minimum flexural strength

16,000

19,000

20,000

22,000

Minimum flexural modulus

700,000

800,000

900,000

1,000,000

T a b l e 6 . 7 Possible construction for a 20 m powerboat hull, giving equivalent strength

Single Skin CSM/WR Polyester

Single skin Sandwich aramid/ aramid/ glass glass epoxy epoxy

Sandwich carbon/ Strip Framed aramid wood aluminum Framed e p o x y epoxy alloy steel

Weight

***

**

.

.

.

.

Stiffness

*

**

.

.

.

.

Abrasion/indent

*

**

****

**

** .

**

** .

. .

.

.

.

.

.

.

.

.

.

. .

. .

.

.

. .

.

.

resistance Low-velocity

.

.

.

.

.

.

.

.

impact: ult. safety from puncture High-velocity

.

.

.

.

.

.

i m p a c t ballistic projectiles Ease of repair

****

***

.

Ease of

***

****

****

.

.

.

. ***

.

.

. *

.

.

. **

. *

maintenance

Key: *Poor, **fair,***good,****excellent, *****outstanding. Source: SP Systems.

was disassembled once fabrication was complete, leaving the hull in position for launching. The huge, hollow mast was fabricated in five internally heated female molds. Stitched unidirectional carbon/epoxy prepreg from Cytec Engineered Materials Inc. of Wrexham Clwyd, U.K. was hand laid up to form the two back sections and the three front sections. Cure was controlled by a computer that monitored the mold heating system to prevent excessive exotherm heat. The five cured sections were bonded

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together with an epoxy adhesive. Maximum mast laminate thickness is 40 mm (1.5 in.), to support the 3,400 m 2 (35,912 ft 2) (about an acre) of sail. In 1972, the British launched the world's largest (at that time) RP ship. The H.M.S. Wilton was 46.7 m (153 ft). It became the forerunner of a new class of minehunters that involved other countries (Netherlands, Belgium, Germany, France, Italy, USA, and others). The British program followed with 45.8 to 61 m (100-200 ft) RP minesweepers. The U.S. Navy pioneered in glass-TS polyester RP (hand lay-up) large boat construction with the production of an 8.5 m (28 ft) hull in 1947. RP Navy boats (in the USA and other countries) range from 3.7 m (12 ft) to over 30.5 m (100 ft). Small boat construction was initiated during 1944 at the Philadelphia Navy Yard, Materials Laboratory (D. V. Rosado involved; unfortunately the first vacuum bag molded 15 ft boat gradually sank due to unsatisfactory cure cycle but thereafter none sunk). Untraditional hull design by the U.S. Navy upgraded its minehunter fleet (1991) with a successful ship design based on using glass fiber glass/TS polyester resin. The glass-to-plastic ratio was 1:1. This "Osprey" class minehunter was designed and built by Interimarine S.P.A. of Sarzana, Italy (Figures 6.23 and 6.24). Unlike traditional ships, the new minehunter class does not have longitudinal or transverse framing inside the hull. It has a one piece RP super structure. The design and material combine to provide enough strength and resiliency to withstand underwater explosions. The hull that is not stiffened is engineered to deform elastically as it absorbs the shock waves of a detonated mine. Judicious design simplifies inspection and maintenance from within the structure. The hand lay-up molding process was used, with 98wt% of the structure via a semiautomated lay-up process. Each mat layer was unrolled and sent through an impregnation liquid plastic bath. Up to six layers were laid-up, wet-on-wet, as a package. A crane laid the wet lay-up along a path in the ship's huge female stainless steel mold. Decks, similarly fabricated, were form-fitted to the hull and bolted in place. Not all the RPs was hand lay-ups. Storage tanks for fuel and water used the filament winding process, etc. The ship's RP hull was up to 17.8 cm (7 in) thick in the thickest sections. No core materials were used. Final outfitting with gear and equipment resulted in a 55 m (188 ft) long warship that holds a crew of 44 people. In addition to their use in boat hull construction, RPs has been used in a variety of shipboard structures (internal and external). RPs was used generally to save weight a n d / o r to eliminate corrosion problems

6. Markets/Products 549

Figure 6.23 us Navy's all RP minehunter" view of hull

Figure 6~

us Navy's all RP minehunter; view of deck

550 Reinforced Plastics Handbook

inherent in the use of aluminum and steel or other metallic constructions. Applications included masts, booms, spinnaker poles, deckhouses, bridge housings, radio rooms, storage tanks (potable water, fuel, etc.), ventilation ducts, piping systems, reefer boxes, hatch covers, sonar domes, radomes, floats, buoys, small safety boats, and more. Much more history exists on RP boats/ships in the literature. Aramid, though trailing glass and carbon as a choice for marine composite reinforcement, is favored where resilience is required. Kevlar (DuPont) canoes, for example, are a popular alternative to rotarymolded plastic types and aramid has stood up well to tough, round-theworld duty on Volvo Ocean 60 sailboats. Barracuda Technologies in Brazil chose aramid in designing the hulls for a Hobie 21 beach catamaran intended to sail from Cape Horn to Antarctica. With possible encounters with ice in mind, engineers specified skins of 220 g / m 2 woven aramid cloth sandwiching a core of 10 mm DLAB Divinycell polyvinyl chloride (PVC) structural foam. A 900 g / m 2 glass/aramid stitched fabric (Saint-Gobain BTI) provides extra ice protection below the waterline. Unidirectional aramid/E-glass tape (SP) further reinforces the forward 1 m portion of each hull. A low-viscosity epoxy resin formulated by Barracuda was used in infusing the hulls by vacuumassisted resin transfer molding (VARTM). This aramid-based hybrid construction shaved 70 kg from the weight of standard Hobie cat hulls. Low weight was a particular requirement for a high-speed dash across one of the world's stormiest ocean tracts, between weather windows. Cross beams are of DivinyceH core inside carbon composite skins. Hull-beam attachment points are carbon reinforced. US company Hylas Offshore Yachts uses Twaron aramid, combined with glass, in the hulls and decks of luxury yachts, particularly its latest 54 and 66 ft models. The aramid adds resilience, helping to secure a light structure that can, nevertheless, withstand the rigors of ocean going. In Europe, French builder Catana had resistance to collision damage in mind in selecting Twaron for its latest Catana 52 catamarans. A composite sandwich structure on these yachts incorporates aramid in the outer hull laminates, as well as triaxial glass fiber. Various cores, including PVC foam and balsa, used in the sandwich are 20-40 mm thick, according to purpose and location. Shaped foam core is used below the waterline, though where the hull bottoms could take the ground, the laminate is solid. Weight saving carbon/honeycomb bulkheads are bonded into the hulls while they are still in the mold. Plastic use in boat construction is in both civilian and military boats [28 to 247 ft. (8.5 to 75 m)]. Hulls with non-traditional structural shapes

6 9 Markets/Products

do not have longitudinal or transverse flaming inside the hull. Growth continues where it has been dominating in the small boats and continues with the longer boats. Big boats in the past were up to 188 ft long have been designed and built in different countries (USA, UK, Russia, etc.). Figure 6.25 shows a 247 ft being built. In practically all of these boats low-pressure RP molding fabrication techniques were used.

Figure 6.25 The 247 ft long Mirabella Vunder under construction (courtesy of RP magazine and Julian Hickman)

Material Trends GRPs has been used to build boats in production since the 1940s and now dominate the boatbuilding world. Preliminary work occurred during the 1940s. They provided monocoque structures that are smooth and hydro/aerodynamic as welt as aesthetically pleasing. GRPs are being challenged by other materials that include light, corrosionresistant steels and marine-grade aluminum as well as more advanced fiber FRPs, and by environmentally-driven legislative pressures. Additionally, its maritime reputation has suffered with the awareness that, like any other boatbuilding material, it is subject to degenerative attack by water.

What makes RPs desirable is that plastics can be modified chemically to meet different property requirements. Unfortunately, these requirements are not always compatible. For example, modifications used to cut

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552 Reinforced Plastics Handbook

emissions of hazardous air pollutants (HAPS) can reduce resistance to hydrolysis, the mechanism behind that insidious enemy of marine GRP, osmotic blistering. At a time when failure to meet Maximum Achievable Control Technology (MACT) limits in the USA and similar limits elsewhere could put companies out of business, the drive for low styrene emissions (LSE) and other pollutants may take precedence over properties like blister resistance, weatherability, and processability (Chapter 3). Glass reinforcement has also moved on since the standard alumina borosilicate E-glass first used in the 1950s. Improved thermal, electrical and mechanical characteristics available with S/R/T, E-CR, S-, R-, T-, and other grades have been combined with sizings and surface modifications designed to produce a stronger fiber/resin interface (Chapter 2). Chopped strand mats (CSMs) and rovings for spray-up have been joined by continuous fiber forms such as knitted, woven or braided fabrics, enabling fibers to be oriented in particular directions. This has led to glass technical textiles moving alongside, and in some cases displacing, textiles of higher-specification fibers such as aramid. Companies with a strong glass focus like Owens Coming, PPG Industries, Ahlstrom and Saint Gobain Vetrotex have between them significantly improved the glass performance. Aromatic polyamide or aramid is an extremely tough fiber that has become most familiar to boaters in characteristic yellow sails, but is also used in boat hulls and rigging. Though not as strong as carbon (specific strength about two thirds), it is (unlike glass or carbon) extremely resilient with good impact resistance. In a collision, sport rigid inflatable boats (RIBs), personal watercraft, canoes, and other small vessels made from Kevlar or Twaron (DuPont and Akzo Nobel trade names) are as likely to bounce as break. With its low weight, aramid competes with rotary-molded plastic in performance canoes, used either alone or in glass or carbon hybrids. In larger craft, although the material is often specified for outer skins to confer damage tolerance, there is perhaps greater merit in utilizing its high tensile strength for inner skins especially in sandwich construction. Inner skins see greater tension loadings due to the pressure of water outside the hull or on external impact. Carbon has attracted a dedicated following among owners willing to pay a premium for performance. An advantage is its specific strength (strength per weight) in tension that is up to 1.5 times that of constructional steel and specific stiffness (Young's modulus per weight). It is about three times that of most metals. It was first used as black RPs by aerospace engineers followed by the marine community. Extremely

6. Markets/Products 553 thin, light, and rigid hulls were a hallmark of the America's Cup yachts that performed in New Zealand (2002 year), while carbon has for some time been a material of choice for performance masts. Other structures made possible by carbon RPs include radical figs, such as the AeroRig (an entire m a s t / b o o m and sails assembly that rotates as one around a pivot point on deck) and unstayed masts. Such innovations avoid the major disadvantage of conventional rigs that masts are strongly loaded in compression by tensioning wires that are, in effect, trying to push the mast through the bottom of the boat. Analogies can be made with a bow and arrow. Carbon's strength and stiffness also make innovative winged and canting keels practical (the latter can be rotated round a pivot to vary their angle to the hull). Racing and cruising powerboat design has similarly benefited from the material's possibilities. Brodrene Aa, based in Hyen, western Norway, has made a breakthrough in the use of carbon fabrics in commercial ferries. The company is experienced in the construction of high speed boats made from carbon fiber such as the Moonraker, the world's fastest luxury yacht with a top speed of 67.6 knots. Recently it has turned its attention to the producing a cost effective carbon composite vessel. Using multiaxial fabrics produced by Devoid AMT AS, Langevag, Norway, over a core material, Brodrene has produced the Rygerkatt. This boat is designed for use as a passenger ferry and will make an average of 200 stops a day, carrying up to 62 passengers. Industrial design company Harreide Designmill has given the boat its distinctive look. Carbon fiber was used to reduce the weight of the boat so that it will use less fuel. This makes the use of carbon fiber (previously the exclusive territory of luxury yachts, racing boats, and military ships) economical by greatly reducing operating costs over the life of the vessel. At 18.5 m (60 ft) long, 7.5 m (24 It, 6 inches) wide, the boat weighs just 27 tonnes. The use of carbon fibers has resulted in a structural weight reduction of 40% over traditional materials. With the increased strength and reduced weight achieved by using multiaxial fabrics the boat has a top speed of 29 knots and an operational speed of 24.9 knots. At normal operating speeds the ferry requires 5.90 liters of fuel per nautical mile. The commercial series was launched with the Ryger Doktoren an ambulance boat with a top speed of 44 l~ots. This model combines great maneuverability with high speeds. The successes of this vessel led to the construction of the Rygerkatt ferry. A representative of the high-tech marine market, Sydney's (Australia) leading yacht manufacturer, McConaghy's, reported that changes in

554 Reinforced Plastics Handbook

processing along with changes in design tools arc driving the highperformance yacht market. Once described as "standing under the shower tearing up $100 bills," today ocean racing enthusiasts ride on hulls virtually designed and built in an environment of increasing sophistication. In the past three years (2002-2004) each major project at McConaghy's has involved improvements in materials, processing, and design, such as specialized vacuum infusion processing. The company recently built the 90 ft long, 135 ft high all-carbon-fiber Alfa Romeo and others, like the new 98 ft Wild Thing out of Hart Marine (Mornington, Melbourne). These boats are definitely large, elite applications of advanced composites. Though high specifications and, perversely, high prices have fed the fashionable desire for carbon in premium markets, continued fails in carbon prices could extend the material's market base. Producers (notably Zoltek) that have developed production routes based on alternative cheaply sourced acrylic precursors believe that breaching the psychological $5/lb barrier would transform carbon's prospects. So far price levels of some $7/lb are about the best that can be obtained. Underwater Hulls

Information on underwater hulls is reviewed in Chapter 7 Filament Windings, Pressure Hull Structures.

Windmills Overview

Use of RP energy rotor blades continues to expand worldwide. During 2001 worldwide it was estimated billion dollars worth of wind energy rotor blades were in use. These blades, up to 45 m (148 ft) long in the case of some of the new offshore installations, used about 55,000 ton of materials, most of which are glass fiber reinforced plastic (GFRP). It was determined that only RPs could deliver the combination of strength, stiffness, low weight, damage resistance, durability and low maintenance that today's larger blades must exhibit. Producing RP blades, which account for about a fifth of the total cost of a turbine installation, is becoming a considerable industry in its own fight. This industry has expressed a great willingness to invest and undertake R&D projects. During 2000 saw a dip in the growth rate for the global wind market to 26%, from 37% in 1999. This was largely because of a hiatus in the

6-Markets/Products 555 USA, where just 53 megawatts (MW) of new capacity were added of a world 3500 MW. Fortunately, this was partly compensated by European growth rates of up to 40% and investment that broadly held up in other regions. With its limited land area, Denmark is leading moves towards offshore wind exploitation, a sector in which the economics favor very large turbines and blades. Small facilities erected at Vindeby in the Baltic and near Jutland in the early 1990s were the world's first offshore wind farms of any sort. The first large offshore wind farm in Europe was at Middelgrunden, near Copenhagen, where twenty 2 MW turbines provide the power. Turbines of up to 5 MW are offshore, with Denmark and Germany being lead adopters. Such turbines required large advanced blades in which carbon RP is needed to confer the required stiffness. In the Netherlands, providing all 400,000 kWh of electrical power for a conference center at the Hague from wind and solar sources during recent climate change negotiations constituted a symbolic statement supporting this important international event. One of the world's largest wind plants was recently completed near Naples in southern Italy. Under a $260 million contract, the Italian Vento Power Corp and the Tomen Corp of Japan erected 282 Vestas 600 kW turbines, power from which is sold to Italian state utility ENEL. Finance has been arranged, with 23 participating banks, for new wind farms totaling 283 MW planned for southern Italy and Sardinia. Shell could be on the brink of a massive windfall in Nigeria in which the oil giant triples its production from the West African country. In a move that kicks off Shell Wind Energy's European commercial wind operations, the company will purchase a 40% stake of the La Muela Wind Park in northeast Spain from TXU Europe Energy Trading B.V. Muela comprises 132 N E G - M I C O N 750-kilowatt wind turbines, split into two 49.5 megawatt wind parks located 15 kilometers southwest of the city of Zaragoza. To determine potential wind sources for wind farms in New Mexico and South Dakota, USA, two 82 m carbon fiber RP meteorological measurement towers are to be used. These guyed towers, built by IsoTruss Structures of Brigham City, Utah, USA, will measure wind resources at the hub height of a number of large, megawatt-size wind turbines. Compared with the steel towers often used, the carbon fiber structure is easier to transport and can be delivered and assembled at a significantly lower cost. Global Energy Concepts of Dayton, OH, USA is using carbon fiber prepreg for large wind blades for the Vestas' 90 m long blade. This

556 Reinforced Plastics Handbook

company has an order for ten 65 ft long production drilling riser joints for the Magnolia Platform in the Gulf of Mexico. Different parts of the USA are gradually evaluating the potential of developing RP energy rotor blades such as off the shores of Cape Cod, Massachusetts. About 25% of the USA has enough wind power to generate electricity at the cost of natural gas or coal-fired plants. Wind power accounts for less than 1% of the nation's energy supply, while coal and natural gas generate about two-thirds of the electricity. A study by Stanford University, California, USA, researchers measured wind speeds that hit turbines perched at the equivalent of a 20-storey building. Because wind is, intermittent wind power farms in locations with high wind speeds could be linked into energy networks that may provide a reliable and abundant source of electric power. The mill, Mohawk Paper Mills in Cohoes, NY located near the banks of the Hudson River, began purchasing nonpolluting wind power, malting it one of the first paper mills in the USA to use wind power for manufacturing operations. There interest was due to wind turbines being cost-effective renewable energy technology, produced electricity with zero fuel and zero pollution. Mohawk purchases wind energy from Community Energy, Inc., a marketer of emission-free wind energy in the Eastern USA. The wind energy for the Cohoes facility comes from New York State's largest wind farm near Syracuse. The project uses state-of-the-art 1.5megawatt (MW) wind turbines. The wind turbine power Mohawk is using translates into 4-million kilowatt hours of power, enough for 12,000 tons of paper production. Community Energy officials said this move would help remove more than 6.1 million pounds of carbon dioxide from the air; the equivalent of taldng more than 300 cars off the road each year. These wind plants use many wind turbines, often assembled on a large singe wind site called a wind farm, to produce electricity. In Germany the wind is overtake water as the most important sustainable source of electricity. Just around one hundred twenty years ago, Germany commissioned the first hydroelectric plants, and water was the most important green source of electricity in Germany. However, 2002, wind blew away water as the most important sustainable source of electricity. At the end of September 2002 year, there were 14,467 wind turbines with a capacity of 13,404 MW installed in Germany. The 2002 wind-based electricity generation in Germany was about 25 billion kilowatt hours or for the first time more than the hydroelectric plants can achieve.

6. Markets/Products 557 The use of RP materials in turbine blades used to generate electricity from wind is one of the more exciting, new developments in the USA RP industry. The USA pioneered much of the early development and first installations in the 1970s, but commercial efforts languished in subsequent years. Wind turbine designs continued to make efficiency gains in the 1990s and Denmark, Germany, Spain and other European countries accelerated their adoption of wind energy encouraged by government support of renewable energy. According to estimates from early 2002, Germany is now the world leader in installed wind energy with approximately 8,000 MW of capacity. Spain has 3,000 MW, Denmark has 2,500 MW, and the United. States is around 4,000 MW India, Brazil and China have progressive wind energy programs, as do other countries. Driving demand is the fact that the cost to produce electricity using wind turbines dropped from 34-38 cents per kwh in the 1970s to around 4 cents per kwh today. That compares well with natural gasgenerated electricity at 3-5 cents and coal at 2-4 cents. Plus wind energy produces no environmental side effects. Globally, the business has been growing more than 30%/yr during the past five years. This worldwide growth rate will slow down but is likely to remain in the double-digit growth range for several more years.

Underwater Blades A prototype power station featuring RP blades is running in a northern Norway strait. Hammerfest Strom's 120 tonne submerged turbine uses similar principles to a wind turbine, with 10 m long glass reinforced plastic (GRP) blades capturing the energy of tidal currents. The installation is located in a narrow strait where the current speed is both fast and uniform. Unlike wind energy, tidal currents are highly predictable, repeating themselves in known cycles. This simplifies plant design as the loads subjected to the components are known to a high level of accuracy. Currents generally flow in only two directions, unless the strait is very wide. This means the nacelle of the turbine can remain in a fixed position, with only the blades rotating with the reversing current (pitch control) to capture the maximum energy. Access is much more of a challenge than for wind turbines, and therefore the turbines are built with a modular design allowing critical components to be lifted out of the water for maintenance or repair. The plant generates 700,000 kWh of power per year, which is enough electricity for 35 homes. (Website: www.e-tidevannsenergi.com).

558 Reinforced Plastics Handbook Fabrication

Wind turbine blades represent one of the success stories for the RP industry with increasing market demand for longer blades. This has caused designers to incorporate carbon fibers adding stiffness, while blade manufacturers are moving away from wet lay-up processes to ensure that the several tonnes of materials that make up a blade can be processed safely and quickly. As a result the raw materials have changed from wet-lay up systems to prepregs and both wet and dry infusion materials (Chapters 4 and 5). Within this rapidly altering environment, there is the need to continually reduce costs and increase output. As final refinements are made to the process and materials, the focus switches to the mold as a means to deliver further improvements. At present blade molds incorporate several common features as follows: 1

two or three robust blade mold shells fabricated from RP materials, often formed over a male plug of the blade shape

2

structural steel framework to support each mold shell during blade processing

3

mechanical closing mechanism to bring the blade mold shells together to form the blade shape

4 5

heating system to cure the blade; and several ancillary systems and features specific to the blade manufacturing process, including vacuum and a resin delivery system.

Because of their size, these molds are often stand-alone equipment packages and as such need to be sufficiently robust to permit repeated daily process cycles with the minimum of maintenance downtime. They must offer the blade manufacturer the means to reliably produce blades with the minimum number of operators in the shortest possible time. Benefits gained with proper designed blades include: reduced mold height to eliminate cumbersome platforms around the molds; improved speed and safety of mold closing mechanisms; accurate blade shape and blade edge tolerances; and all electrical, vacuum, and other services within the structural framework. All of these elements contribute to minimize the blade manufacturing and finishing time permitting the blade manufacturer to reduce costs while meeting targets for blade output. The high quality and robust design of these blade molds ensures minimum downtime and maximum output both of which serve to reduce costs. As blades become longer, the molds themselves obviously will become larger and heavier. The molds will be required to process a larger

6. Markets/Products 559 quantity of materials in an increasingly rapid cycle time. Such molds will need to permit a variety of blades to be produced with the minimum downtime. The molds will need to process a larger quantity of materials in an increasingly rapid cycle time. To achieve this target the mold maker will offer improvements such as: 1 2

automation for safe materials handling, improved processing and fast demolding delivery of one-shot manufacturing processes to increase output and eliminate finishing

3

modular design permitting blade alternatives by only changing parts of the mold

4

smart molds that are self monitoring both for blade processing and for maintenance purposes; and elevated temperature performance for more rapid cure of the blade.

5

Appliances, Electrical/Electronic Both TS and TP compounds have many applications in electrical appliances and electronics products, both as internal components and as external housings (Figure 6.26). The choice between the two groups of materials depends largely on size and service temperature. Processes used are primarily injection molding and compression molding.

Figure 6.2G An iron includes the use of RPs

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Polyester bulk molding compounds (BMCs) are widely used for large electrical switchgear moldings, and the latest types of low-shrink high impact BMCs are used for the housings of power tools and small kitchen appliances that must meet severe impact standards and may also have to resist heat. A long-established application of TSs is for printed circuit boards (PCBs), and the trend towards 3-D molded PCBs; also are TPs. High performance PCBs use glass fiber constructions where the others use paper, wood fibers, etc. Pultruded profiles are ideal for electrical trunking, conduit, and high voltage line insulators where outdoor environmental conditions are likely to be harsh (for impact, chemicals, moisture, and heat). Using a special grade of polyester molding compound, a Belgian lighting manufacturer has replaced metal components for an emergency lighting unit for hospitals, offices and public places. It now uses two injection moldings in TS polyester molding compound, one of which has a special white coating and acts as a reflector, withstanding a working temperature of 100C. The compound has UL flammability approval to V-0 at 1.5 mm thickness. A special low-smoke sheet molding compound (SMC) is used for highperformance electrical housings used in the channel tunnel and in the Eurostar train. Combining good electrical properties with exceptionally high fire retardancy and low smoke without use of halogens, the molding forms part of a larger module, the common block that converts power flow to the train motors. Filament-wound RPs are increasingly replacing ceramics for insulators for transformers and high-voltage switchgear, insulating and supporting tubes in high-voltage test equipment and switch rods in power switchgear. They do not shatter in the event of an internal explosion and offer more reliable performance in earthquake-risk areas. Typical are epoxy resin/glass tubes with silicone rubber shielding, as produced by Isola, Germany, using CNC winding machines. Production to close tolerances reduced the need for subsequent machining. Low mass and high stiffness are other advantages in dynamic switchgear applications, using aramid fiber where it was necessary to achieve the stiffness. Tensile breaking load of a switch rod of 36 mm inner diameter and 3 mm wall thickness is more than 100 kN and density of aramid-RPs is only 65% of that of glass. GEC Alsthom is using a void-free filament winding process to produce insulating linings for end-bells of large two-pole 1000 MW generators. This replaces phenolic/asbestos-lined woven glass fiber molded by

6 9 Markets/Products

vacuum bag, giving a more resilient medium to counter the greater forces of very large generators. The technique is based on vacuum treatment of the glass and resin before wet filament winding. The wound element is gelled and step cured on the mandrel. By careful attention to processing conditions, the final product is transparent, confirming voidfreedom. Interlaminar shear strength can be increased by up to 35% over conventional GRP and increase in glass content from 55% to 75% by weight gives a much higher compressive modulus. A new plastic pulley, a cost effective replacement of a cast aluminum counterpart, is now used in all Hotpoint washing machines. The injection molded pulley, made of DuPont glass fiber reinforced Zytel nylon resin offers lower part cost vs. casting, without compromise in mechanical properties. The pulley was designed and manufactured by Rolinx Plastics Co. Ltd., UK, in conjunction with appliance maker Merloni UK. Most domestic washing machines use a pulley to transmit torque from the motor to spin the washing machine inner drum. Rolinx saw an opportunity to replace the cast aluminum pulley with a reinforced nylon resin, a mechanically stiff plastic used to make reliable, highperformance and cost-effective components and systems. Dimensions of the Zytel replacement part needed to remain identical to the aluminum one, while the center boss section had to withstand a compressive force of 105 Newton (N). At the same time the pulley was required to withstand a belt tension of over 300 N and operating temperatures of 70C and above, with noise levels not permitted to be greater than the aluminum variant. Finite element and mold flow injection analyses confirmed that the Zytel part offered the most mechanically sound option. Additional physical testing, involving the continuous running of the washing machine for the duration of the machine's 'lifetime' confirmed the analytical data (Rolinx Plastics Co. Ltd., Ledson Rd., Wythenshawe, Manchester, UK; telephone: +44161-610-6400; fax: +44-161-610-6474; e-mail: enquires@rolinx, co.uk).

Consumer and Other Products In this chapter and throughout this book different RP products have been presented that only provide an introduction to the many produced during the past half century. New products tend to always be on the horizon. Zoltek Companies Inc. (St. Louis, Mo., U.S.A.) receive a 1 million lb order for its commercial grade fiber tow, the largest single order the

561

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company has received for that fiber type (2003). Two additional orders also were announced totaling 800,000 lb. The customers are sporting goods manufacturers in China and Taiwan. The large-scale orders are expected to generate up to $10 million in revenue through the end of calendar year 2004. RP high technology has been in the sports and leisure markets, in the shape of advanced materials that were originally developed for aerospace applications. Carbon fiber-RPs is used for fishing rods, pole vault pools, golf clubs, tennis racquets, kayaks, and others. In these products, justification was based on their ability to provide considerable improvement in operational efficiency (Table 6.8). Table 6.8 Examplesof reinforced plastic leisure and sport products Industry

Process

Reinforcement

Resin

Fishing rods Golf club shafts Snowmobile hoods golf carts Snow skis water skis RV bodies

Pultrusion

Roving

Pultrusion Spray-up

Roving Gun roving

Polyester Vinyl ester Polyester Vinyl ester Polyester

Low pressure compression Woven roving roving Spray-up Gun roving Continuous lamination Panel roving

Polyester

The global market for sports and recreation products has been stagnant during the last few years. This fact has been blamed on a number of causes however, the Sporting' Goods Manufacturers Association International (SGMAI) reports that the electronics and entertainment industries are providing the chief competition for leisure dollars. For example, the movie and home electronics industries in the USA each grew 21% in sales, while wholesale sporting goods and accessories dropped 2% in 2001. The increased popularity of these indoor, sedentary activities may continue to cause a decline in the number of people who only occasionally participate in sport or exercise activities. According to SGMAI, a large portion of sporting goods production has moved to Asian countries to take advantage of lower manufacturing costs. USA exports of sports and recreation equipment decreased substantially during 2002. Exports of golf clubs, fishing rods, tennis and other racquets, water skis, and arrows all declined in both sales value and volume, some losing up to 52% compared to 2001. However, there are opportunities for smaller volume applications for RPs such as

6-Markets/Products 563 hockey sticks and baseball bats continue to grow within the sports in terms of participation and consumption of RPs, making up for losses experienced in other applications. Developed during 1960s was a form of composite armor that uses glass ceramic files bonded to an aramid fiber reinforced multi-ply laminate. A projectile rapidly dissipates its kinetic energy in destroying the ceramic layer and any remaining energy is absorbed as the laminate is deformed to contain the broken fragments of the projectile completely. It can deflect high-velocity rifle rounds at about half the weight of conventional steel armor. The system has been developed for the C-130 Hercules aircraft, where it is fitted to the cockpit floor and sides and the crew seats, giving protection against high-velocity small arms fire. A liquid oxygen (LOX) converter situated in the nose wheel bay is also protected. The overall thickness of the composite armor is 14.5 mm (0.57 in.); the typical weight is 26.4 k g / m 2 (5.4 Ib/ft2). The Hercules armor comprises 83 panels coveting 14.8 m 2 (160 ft 2) of the flight deck and LOX unit, with a total weight of 392 kg (864 lb). Panels can be quickly applied or replaced by ground support staff. Fire-resistant storage boxes and crates, to meet the requirements of the German VdS (Association of Indemnity Assurance Companies) are molded in an especially developed TS polyester sheet molding compound (by DSM-BASF Structural Resins, in association with BYK Chemic, Martinswerke, Mitras Kunststoffe and Wientjes). They have been classified by VdS as class VI (nonflammable packaging), according to the guidelines for sprinkler systems- a classification previously held only by sheet metal containers. The crates measure 500 x 390 x 280 mm and are compatible with all commonly used transport systems and existing crates with regard to dimensions and stackability. The surface resistance of the sheet-molded compound (SMC) can be adapted to meet requirements for storage of parts sensitive to electrostatic charges, and the crates can easily be cleaned with common agents and processes. A unique system for restoring wooden poles, used throughout the USA for supporting utilities such as telegraph wires, is to wrap deteriorating or mechanically damaged poles with alternating layers of glass fiber fabric and phenolic resin. This gives them outstanding strength and fire resistance, with a significant extension of service life. Poles are usually treated with creosote and pentachlorophenol for preservation. Once treated, they are considered hazardous waste in some states, so costly disposal methods must be used. M1 told, it can cost up to $10,000 for each pole replacement. Glass-fiber reinforced has been solving the problem of many agricultural corrosive environmental parts. As examples are mudguards

564 Reinforced Plastics Handbook

on machinery carrying mud from fields on to roads, for crop-sprayer, and chemical sprayers. Different RPs is used in furniture. An example is SMC used in the office furniture sector. One of the world's largest suppliers of office furniture continues to mold nearly 50% of its output of office chairs in SMC instead of conventional wood or steel. Use is also made for chair backs and seat shells, where it finds the material sufficiently stiff and dimensionally accurate. The SMC used is A graded, giving class 2 fire retardancy, meeting British Standard 5459 level S for continuous loading service. Production of SMC chairs is about 2000 units a week: cost-savings arise from reduced costs of tooling and assembly, as well as the elimination of the need for painting. Paper industry producers are generating additional demand for corrosion products due to environmental projects required by the socalled "Cluster Rule" published by EPA in 1998. MACT regulations have been very slow in coming but phases for compliance fall due by 2006. Due to the massive scale of some of these facilities, potential sales of plastics such as RP materials could be on the up swing.

Aerospace Plastics use is rather extensive in primary and secondary aeronautical structures that include aircraft, helicopters, balloons, to missiles space structures. Lightweight durable plastics and high performance RPs save on fuel while resisting all kinds of static and dynamic loads (creep, fatigue, impact, etc.) in different and extreme environments. The chief challenge to the plastics industry is not in pounds of plastics needed but rather in the translation of plastic development technology into production line expertise. The aerospace industry is geared to pay high prices for plastics with exceptional properties; as high as hundreds of dollars per pound with up to ten-fold cost increases for fabricated products plus additional dollars to conduct continual testing and evaluation to insure safety of aircraft operation. Aircraft

Starting in the past, RPs continue to expand their use in aircraft. These RP materials have been used in primary and secondary components. Table 5.5 (p. 284) includes some of the applications. Figures 6.276.29 and Table 6.9 provide information on the growth of primary structural use of RPs.

6 . Markets/Products Figure 6.27 Historical trend with plastic composites (RPs)

Figure 6.28 RP composites implementations

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Figure 6.29 USA RP composites aerospace airframe primary and secondary structure production

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565

566 Reinforced Plastics Handbook

Table 6.9 Examplesof RP in aerospace

Material

Application

Molded secondary components, substitution for metal castings, electrical housings, and parts. Complex electrical components, leading and Chopped E-glass/epoxy trailing edges, and highly loaded complex shapes. Primary and secondary structure for subsonic E-glass fabric/epoxy aircraft, ducts, housings, bulkheads, intake manifolds, helicopter blades, radomes, etc. (Probably the most versatile material) High temperature resistant applications; high E-glass fabric/polyimide energy radomes, engine fairings. Higher strength application; rotor blades, wing E-glass - unidirectional/epoxy tapes components for smaller aircraft. Stiffer and stronger than E-glass for more critical S-glass- unidirectional tape/epoxy applications. E- and S-glass, filament wound/epoxy Radomes, high pressure tanks. Same as above for higher temperature use. E- and S-glass, filament wound/ polyimide Structural application for higher stiffness and Graphite/epoxy fatigue resistance; suitable for most higher loaded structural parts. Boron/epoxy Same as above, but limited to shapes with simple curvature. Used for high speed aircraft for high temperature Graphite/polyimide resistance. Aramid (Kelvar)/epoxy Higher efficiency radomes, high impact resistance, lower weight. Excellent for helicopters and ITL-aircraft. Many Glasslgraphitelaramidlboronlepoxy combinations of fibers may produce a better part hybrids than individual fibers alone. Chopped glass/polyester

Figure 6.30 provides a comparison between advanced RPs and metallic specific tensile strengths. Here, the strengths of the RPs used are realistic working stress levels for multidimensional laminates as they would be used for wing or stabilizer covers. It also shows that RPs can be very hole-sensitive relative to metals that can be corrected or compensated for with proper RP designs. However, this problem is offset by far less sensitivity to tension fatigue. Their effectiveness in compression applications is shown in Figure 6.31 where the low density significantly reduces panel weight but, in contrast to metals,

6. Markets/Products 567 2.0

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compression fatigue and low ener~Ampact damage become design considerations. In the past, RP components were commonly designed with a safety factor of 5 times the ultimate strength, such as the 1944 all plastic airplane. In the meantime, significant improvements in materials of construction and quality control during processing with sophisticated design analysis via computers have been developed. Safety factors have

568 Reinforced Plastics Handbook

been reduced for certain structural parts having values such as 1.2 or less. The result has been to reduce the weight and cost of components. Although the general parameters for optimizing airplanes arc well known, their relative importance is permanently changing, and diverging cost development redefines design criteria and "cost-efficiency". In the field of structural design the cost of fuel, and consequently the demand of the operators for the best fuel-efficient aircraft, has pushed the development activities and their components in the direction of advanced RPs. Where even if the RP component may cost more than that of aluminum or other material, its weight savings can significantly reduce fuel consumption; thus, cost-efficiency results. Fuel efficiency is a function of the aircraft's power plant, aerodynamics, and structural efficiency. With military aircraft, flight distance is gained is an important gain. Producing airplanes at lower costs is another aspect of advanced RP structural applications. In many cases, the carbon and aramid fiber RP components compare favorably with the cost of conventional component structures, in spite of the rather high material costs. An important aspect here is the possible simplification of the design. For example, the complicated leg fairing of the Airbus was replaced by a simple all-RP sandwich (honeycomb core) panel reinforced by two RP beams. Besides a weight savings of about 30%, the production hours were reduced by 27%. The technology of RPs reached a level of maturity which led to its use on stabilizers for practically all USA fighter aircraft since 1970 (F-14, F-15, F-16, YF-17, F-18, etc.), and these parts are generally giving long-fife, trouble-free service. Fighter wing covers (F-18 is an example) and the covers and substructures of a V/STOL attack aircraft (A V-8B) are made from graphite/epoxy advanced composite material (Figure 6.32). The unconventional and revolutionary LearAvia Lear Fan 2100 twin turboprop set a trend for business aircraft with the use of graphite and aramid/epoxy for all primary and secondary structures with the exception of the landing gear (Figure 6.33). The single engine Smith Prop-Jet also used graphite/epoxy for its wing, fuselage, and tail. The latest generation of large commercial aircraft [Boeing 757, 767, 757, and 777 (Figure 6.34)] uses advanced RPs extensively for such secondary structural parts as ailerons, rudders, and spoilers. The RP technology's current level of maturity and experience makes it a strong candidate for a large proportion of the airframes of future commercial and military aircraft. Extensive usage of advanced composites has been committed to production on the Boeing aircraft family of the 757, 767, and 737. The history of Boeing's use of RPs is well documented. Applications include secondary exterior structure with functional and decorative internal

6. Markets/Products 569

Figure 6.32 RP applications in the AV-8B airplane

Figure 6,33 RP applications in the LearAvia Lear Fan 2100 twin turboprop airplane

components. The application of RP materials to Boeing is not new. An RP fabrication facility existed in the 1920s using cellulose fibers from spruce lumber in a lignin binder matrix and linen fabric coated with dope. As these early composite materials were replaced by aluminum, the industry has now gone through a full-scale materials and process evolution. Now the advanced fiber RPs has been replacing aluminum in a number of aircraft applications. The first of the fiber-RP materials to be used on Boeing commercial airplanes was the glass fiber/epoxy composition. Boeing has an extensive

570 Reinforced Plastics Handbook 9 GRAPHITE/KEVLAR EPOXY 9 1900 LB TOTAL WEIGHT

BOEING 757

9 COMPOSITE COMPONENTS NOSE LANDING GEAR DOORS MAIN LANDING GEAR DOORS RUDDER ELEVATORS SPOI LE RS AILERONS WING TO BODY FAIRINGS ENGINE STRUT FAIRINGS FLAP TRACK FAIRINGS NACELLE COMPONENTS (TOTAL WEIGHT OF SIMILAR PARTS ON BOEING 767 IS 2860 LB)

Figure 6.34 RPapplications in the Boeing 757 airplane

and very successful experience base with this material. The first Boeing commercial jet transport, the 707, used glass fiber RP components, and usage increased with each succeeding model through the 747. Most of these applications were lightly loaded components such as fairings and interior components. Even with the extensive exterior surface area involved, the 747 has only approximately 1% structural weight of glass/ epoxy RPs, aluminum at 81%, steel at 13%, titanium at 4%, and other materials at 1%. Boeing is now developing their twin-aisle 7E7 commercial passenger jetliner, a plane designed to lower operating costs sharply. It is targeted to cost less than $8 billion. It is targeted to compete with the low cost successful Airbus jets. Airbus undercuts Boeing by as much as 15%. Boeing expects that the 7E7 will be attractively priced and still generate a 10% profit margin. With the performance to weight advantages of carbon fiber the 200 to 250 passenger Boeing 7E7 high speed jet (mach 0.85) light weight commercial airplane will have the majority of its primary structure (wings, fuselage, etc.) made of carbon RPs. Result will be that more than 50% of the aircraft's structural weight will be RPs. This program alone will consume about 25 ton (55,000 lb) of carbon fiber RPs on each aircraft, translating to about 1,450 ton (4 million lb) per year, based on production of five aircraft per month.

6. Markets/Products 571

It will use 15 to 20% less fuel when compared to other wide-body airplanes. Production will begin 2005. First flight is expected in 2007 with certification, delivery, and entry into service 2008. To get there, Boeing is rewriting the way it does business. While they devise the 7E7s basic outlines, an unprecedented amount of detail work is being farmed out, especially to Japanese companies. For the first time, Mitsubishi, Kawasaki, and Fuji, which helped build the 777, have been invited to design and produce the fuselage and wings. Boeing is taking this step in part to get Japan Airlines and All Nippon Airways to launch the 7E7. But Boeing also expects the Japanese government to provide money to local suppliers to help fund the development. In the mid-1960s, design studies started at Boeing for the structural application of advanced RPs. At that time, boron filament was considered the most promising reinforcing material. As studies, component fabrication, and testing continued, it became increasingly clear that graphite or carbon fiber would be the predominant high strength, high modulus material used because of economic and other practical considerations. Up to 50% of all home built airplanes today are made with RPs. Commercial airplanes have at least 5wt% (some projections have been at 10 wt%) unreinforced and RPs. Certain past to future military airplanes, contain up to 60 wt% plastics used in primary and secondary structures). Other airplanes take advantage of plastics performances such as the McDonald-Douglas AV-8B Harrier with over 26 % of this aircraft's weight using carbon fiber-epoxy RPs; other plastics also used (Figure 6.35). Examples of plastic used in other aircraft are shown in Figures 6.36-6.38. The use of RPs in successful secondary structures occurred during the early 1940s. A major product designed and fabricated (E-glass fiber/TS polyester resin) were radomes that have continued to be used (Figure 6.39). Figure 6.40 radome configurations show effects on radar waves emanating from the radar reflector or antenna through the RP material (meeting fight thickness requirements of the glass fiber/TS polyester laminated structure) so that the waves are properly focused in the required direction. This is basically the same setup as when optical waves are transmitted through a transparent medium so as not to cause visual distortion (Figure 6.40). Small to large ground radomes using RP spherical and other shapes are used. Figure 6.42 shows the use of RPs in the more modem Boeing 767 airplane that has been in service for a long time. In this commercial airplane use is made of RP and URP. In this view G = graphite, K =

572 Reinforced Plastics Handbook

Figure 6.35 View of the McDonald-DouglasAV-88 Harrier combat aircraft using carbon-epoxy RPs

Figure 6.36 AirbusA-320 componentsof RPs

6 9 Markets/Products

Figure 6,37 Examplesof RPs in the de Havilland Dash-8 only on exterior

Figure 6~

Large RP rotating radome on top of the Grumman Hawkeye airplane; airplane also contains RP components

573

574 Reinforced Plastics Handbook

Figure 6 . 3 9 Exampleof an RP radome with a rain erosion coated surface that is located on the front of the airplane

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6 9 Markets/Products

Figure 6.41 Ground antenna protected by a 150 ft diameter RP radome

Kevlar (DuPont's aramid), and F-fiber glass. During the past half century, other airplanes have included RPs, including all RP airplanes. Figure 6.43 highlights RP parts on the Boeing 777 that include improved damage resistance and damage tolerance; parts that have been redesigned for simple, bolted, or bonded repairs; weight savings; and corrosion and fatigue resistance.

Figure 6 . 4 2 Examplesof RP on commercial aircraft such as the Boeing 767 in use for many decades

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576 Reinforced Plastics Handbook

Figure 6,43 Examplesof reinforced plastic parts on Boeing 777 The first 14 m (46 ft) tall vertical tail fin, for the Boeing 777 airliner was one of the first major uses of RPs for primary structures in a USA commercial aircraft, and saves about 450 kg (992 lb) compared with a comparable metal fin. RPs will represent about 9% of the structural weight of the 7 7 7 - more than ten times the use of RPs in thc 757 and 767 jets. Other structural composite parts include horizontal tail stabilizers, control surfaces, engine cowlings, landing gear and nose radome. Non-structural applications include the interior and systems ducting. The trend is to expand the use of plastics, particularly RPs. The past, present, and what arc ahead innovations in aircraft target for faster, smoother flights. They have given rise to more new plastic developments and have kept the plastics industry profits at a higher level than any other major market principally since they can meet different structural-to-weight to environmental conditions. Virtually all plastics have received the benefit of the aircraft industry's uplifting influence. The use of optically transparent plastics in windshield canopies and other glazing areas is another example of their functional use. Low K-

6 9 Markets/Products

factor of urethane foam, silicone and polyimide require them in the different thermal environments. Adhesives have made it possible to make lighter metal structures without the use of rivets that give nonhomogeneous stresses and interfere with surface smoothness. Innovations range from individual parts to the complete plane. There is the armored flight deck door to help secure flight decks. The one-inch thick door includes an RP sandwich structure using a phenolic honeycomb core between phenolic-glass fiber laminated facing sheets. New on the drawing board is the preliminary Lockheed Martin's F-35, the Joint Strike Fighter (JSF), plane with extensive use of RPs. This $19 billion system-development and demonstration phase extends to year 2012 with initial flights in 2005. Included are thick composite wings to help carry the physical load in this multifunction aircraft, which is targeted for a broad international market. On its outside it uses low observable of the stealth plane. The program uses more primary structural composites and less titanium than recent designed and built fighter airplanes. Composites account for about 36wt% of the proposed structural weight. Of the total, graphite fiber-epoxy RPs represents about 32% with glass fiber- and graphite fiber-bismaleimide make up 2% each. By comparison, composites make up about 30% of the structural weight of the Air Force's B-2 bomber, 26% of the Air Force's nextgeneration F-22 fighter, and 18% of the Navy's upgraded F / A - 1 8 E / F . The RPs will be fabricated to close-tolerance composite components. When these parts are assembled to the aluminum substructure, they will be a perfect fit. In the monocoque construction, thick, heavy composite skins carry more of the total load than in other fighters by unitizing the skins. This approach minimizes the number of seams on the aircraft. With this design the interior frame uses one-half as much substructure as exists on the F-22. What has been happening is the development in use of RP in aerospace, with the breakthrough to major structural components. In multi-role combat aircraft there is widespread use of RPs, including wings, tail, and most of the fuselage, almost all of the visible airframe structure of which is RPs. Carbon fiber RPs arc used for the front fuselage, wings, fin, control surfaces, doors, engine covers, and much of the landing gear; aramid RPs for wing fillets, tail fairing and nose radome. The European fighter aircraft (EF A) will have substantial use of RP, and would have been some 30% heavier with a conventional metal structure. Necessarily, the culture of commercial aviation is driven by safety-first philosophy, which has to ensure that nothing can go on an aircraft until it is fully characterized RPs, with their inherent high variability, have

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578 Reinforced Plastics Handbook

not always fitted well into that culture. The pioneering use of glass and carbon fiber for fin and wing box structures in the European A TR series regional turboprops remains pioneering: few airframe manufacturers have to date followed this example for larger aircraft. The largest manufacturers, Boeing, McDonnell-Douglas and Airbus Industrie are gradually adopting RPS for primary airframes. The European Airbus has been more progressive, but much of the growing content remains in secondary and tertiary structures such as appendages, doors/hatches, floors and control surfaces. Airbus, will need greater RP capacity, based on their two new programs. The A380 double-deck passenger jet is using RPs in many new applications, such as the flap track beams, floor beams, the resin film infusion (RFI) rear bulkhead, and much of the center wing box. For much of its fuselage and for the leading edge on the vertical stabilizer, the aircraft will feature GLARE (GLAss fiber-REinforced aluminum) panels, multilayered laminates built up with glass fiber/epoxy and aluminum sheet. GLARE is in the vanguard of advanced composites, using three different materials to achieve a unique set of properties. No simple RP can match GLARE's impact resistance (or enable airlines to continue to have shiny fuselages) The future of RPs will certainly lie with optimizing different combinations of fibers, plastics, ceramic, and metallic materials in ways that will only be limited by imaginations. Although the A380 will use a lower proportion of RPs than the 7E7 and fewer will be built, it will still require more than 1,000 ton (2.2 million lb) of RP per year. Another program at Airbus is the A400M military transport aircraft. The aircraft will be able to carry a greater proportion of its weight due to the extensive use of RPs, which will make up 35 to 40% of the latter's structural weight. RP components will include not only the usual RP stabilizers and moveable wing components, but the main wing box as well as the first application of RPs on a wing of this size. These three Boeing and Airbus programs alone will use more than 3,000 ton (6.6 million lb) of RPs per year. This compares with current RP structures capacity in civil aircraft, which has been estimated at just over 2,000 ton (4.4 million lb) a year, most of which will still be required, as the aircraft that the new programs will replace use very small amounts of RPs. Airbus has targeted to match Boeing's 7E7 materials technology leap, launching a new aircraft of its own with an RP wing and fuselage. There are many indications from the program's research into RPs for fuselage, center wing box, and wing that Airbus is preparing to do just that. Question is whether Airbus will build an RP mid-sized, twin aisle to

6 9 Markets/Products

rival Boeing's new aircraft or go for a smaller, high-tech single aisle aircraft. For the RP industry, it makes little difference. The total quantity of material used is a function of the number of aircraft and the weight of RPs on each plane. The quantities required will be similar. For the main use of RPs in structures, one has to turn to the defense industry. There are major RP structures in the US Stealth bomber, including wings, aft body and other components, produced at Boeing's 22,000 m 2 Composites Center of Excellence at Seattle, Washington. Mso made there are the wings, aft body and other components of the F-22 air superiority fighter; advanced new folding wings for the US Navy's cartier-borne A-6 Intruder strike jet; lightweight primary and secondary tail structure for advanced technology Boeing 777 widebody twin-jet; and most of the structure of the Condor high-altitude long-endurance HALE aircraft. The B-2 represents the world's largest application of RPs in aerospace engineering to date; the upper and lower skin panels of the wing are thought to be the largest single-piece aircraft RP structure yet made. The outboard wing sections are effectively flying fuel tanks, each of 20 m length, with a total wingspan of 52 m (170.5 ft). The aft center section includes a weapons delivery system for nearly 20 tonnes of munitions, twice the capacity of the B-52. Boeing has a raked wing design for the stretched B767-400, with carbon fiber skins over metal spars, saving 1000 kg over previous metal winglets, and is considering composite spars as the next stage. Boeing is also pursuing RP fuselage and wing structures, which were being separately studied by it and McDonnell-Douglas prior to their merger, under a $130 million NASA-funded Advanced Composites and Technology (ACT) program, aiming at 25% weight-saving and 20% cost-saving compared with conventional aluminum structures. A sewing technology for RPs, developed by NASA and Boeing (and based on traditional methods) could make aircraft wings based on aluminum a thing of the past. The airframe manufacturer has invested $6 million in the development by Ingersoll Milling Machine, Illinois, of a 28 m long advanced stitching machine (ASM), which can produce 12.3 x 2.5 m wing panels by stitching together up to 20 layers of carbon fiber/resin RPs, to a total thickness of over 30 mm. The process replaces riveting with metals. In practical terms this can eliminate the need for some 80,000 mechanical metal fasteners in the panel sizes under study. The result is that a full-scale aircraft wing could be manufactured, not only 25% lighter in weight but also 20% less expensive.

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580 Reinforced Plastics Handbook

The ASM is controlled by an overhead gantry, with computers and lasers to position stitches along 38 axes of motion. Four heads stitch 36 mm thick fabric at 3200 stitches/min and braided stiffeners are then sewn on to give greater strength. Finally, the panels are treated with an epoxy film adhesive and autoclaved. High-performance RTPs have moved out of prototypes into commercialscale production and are out-performing RTSs for certain aircraft applications. Glass/polyether imide (PE1) stamp-formed components are used in commercial helicopter interiors, where they give mechanical performance equal to RTSs, particularly phenolics, but offer significantly lower heat release. Airworthiness Notice 61 specifies that, using the modified Ohio State University test rig, figures of 6 5 / 6 5 should be achieved (total positive heat release over the first two minutes of exposure for each of three or more samples must not exceed 65 kW mins/m2). Phenolic systems usually average about 5 4 / 5 5 , which is dangerously close to the limit when painted. A decorated monolithic glass/PE1 panel, however, has given results of 13/17, offering a valuable safety margin. Techniques such as stamp forming, a method similar to stamping of sheet metal, have been developed. The Bell/Boeing V22 Osprey flit-rotor aircraft uses carbon fiberreinforced polyether etherketone (PEEK) for doors and housings of the engine air particle separator and for fuel vent tanks (Figure 6.44). TP polyimide (TPI) forms the basis for an injection-molded spline adapter in the drive train which tilts the rotors. Costs were reduced some 22%. The parts were developed by RTP Company with Bell Helicopter and molder RAM Inc., Texas. The tanks are molded by the lost core process. Business aircraft made from RPs include the mainly glass fiber Chichester Miles Leopard (UK) and the Raytheon Permier 1 six-seater, notable for a largely filament-wound carbon-epoxy/honeycomb/ carbon-epoxy fuselage. A hybrid light jet aircraft was developed in the

Figure 6.44 A range of RPs is used for components of the Osprey tiltrotor aircraft

6 9 Markets/Products

USA by Raytheon, following the success of its all composite turboprop, Starship. Called Premier 1, the business jet has an all RP fuselage with metal alloy wing. The carbon fiber/epoxy honeycomb fuselage is produced by computer-controlled automated machines, which are quicker than the hand lay-up used for the Starship. The cabin is reported to be 178 mm higher and 203 mm wider than competitors. The construction saves weight and is stronger than aluminum. Westland, the UK helicopter manufacturer, which is also a leading molder of RP aerospace structures, is molding main wing flaps for the MD-11 civil airliner. Measuring some 5 m and 10 m (16.4 ft and 32.8 ft) long, the flaps are made of advanced technology RPs, incorporating carbon fiber-reinforced epoxy top and bottom skins bonded to a methacrylic foam core, the only metallic components being goose-neck attachments to the flap track mechanism of the aircraft. The design and construction was selected to be significantly lighter than conventional metal vanes, improving damage tolerance and giving better interchangeability, validated by experience in service. Phenolic RPs is used. In the cargo hold of the Jetstream 41, the lining material is a self-extinguishing glass fiber/phenolic laminate, giving also durability and lightweight with low smoke and toxic emissions. Fiber RPs is used for the interior surfaces of the 4.8 m 3 size (170 ft 3) baggage area. Contract awards for military RPs continued to proliferate. GKN Aerospace Services of Farnam, Surrey, UK recently was awarded an approximately $4 million contract to supply the control surfaces and edges package, including tool design and production, for the 14 flying and 8 ground test aircraft being built during the F-35 Joint Strike Fighter's System Development and Demonstration (SDD) phase. The carbon/bismaleimide RP details require very close manufacturing tolerances, due to the stealthy nature of the aircraft. Other F-35 work was awarded recently to GKN's subsidiary in Australia, which will support Northrop Grumman in the design, analysis and manufacture of F-35 center fuselage parts. GKN Australia is one of 19 Australian firms that will be involved in the F-35 program. GKN Aerospace also has received a contract from Sikorsky Aircraft Co., USA to develop and manufacture side skin panels for the RAH-66 Comanche military helicopter. The contract initially calls for 42 cored RP test panels for material qualification and three actual 3-ft by 4-ft forward side panels. Sikorsky has the option to extend the contract to include 73 actual production panel sets, for a total value of $1.5 million.

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582 Reinforced Plastics Handbook

Boeing has announced that itsAH-64 Apache Longbow helicopter will receive a new RP main rotor blade, manufactured by the company's Mesa, Ariz. facility. The blade, with a more efficient airfoil shape and higher overall twist rate, provides improved hover and forward flight performance. Made with S-2 glass fiber and carbon fiber with epoxy resin, the new blade has a much simpler design than the original and costs less to manufacture. The original blade had four spars and was difficult to fabricate. The new blade, although it is hand laid up, has a single spar and a simpler design, still meets ballistic requirements and lasts longer. The new blade fits all existing AH-64s and will be part of the 269 new aircraft to be manufactured and delivered through the year 2006. Boeing will award this work to a outside contract manufacturer. Hitco Carbon Composites Inc. of Gardena, CA., USA has won a fouryear contract to build vapor barrier assemblies for 60 Boeing C-17 aircraft. The autoclaved, foam-cored glass fiber/epoxy panel assemblies measure 6.5 m long by 5.5 m wide (21 ft by 18 ft) with compound curvature, designed to prevent fuel and fuel vapors from the main fuel tanks from penetrating the plane's cargo area. The Boeing 7E7 and Airbus A380 as well as the growing military applications, such as unmanned aerial vehicles, are using more carbon fiber. Designs are targeted for low-cost ways to incorporate carbon fiber into parts, using puhrusion, carbon fiber sheet molding compound (SMC), and automated manufacturing methods. One application that has not received much consideration yet in USA is the Homeland Security Act's requirement for strengthened, blast-hardened critical structures, for which carbon fiber is, so far, the only qualified material, according to GHL Inc. Interestingly enough, the prognosticators believe that aside from the traditional aerospace and recreational arenas, the biggest growth area will be industrial applications. Boeing Co. announced an end-of-year blockbuster award from the U.S. Navy for the production of an additional 210 F / A - 1 8 ElF Super Hornet aircraft. The multi-year contract is valued at $8.6 billion. An additional $1 billion is earmarked for design and development of an upgraded F / A 1 8 - G version that will carry more weaponry and electronics. Forty-two planes will be purchased each year from 2005 through 2009. Boeing's Super Hornet program in St. Louis has already produced 170 of the tactical aircraft, which are roughly 20% RPs. Boeing builds the forward fuselage and wings and performs final assembly while parmer Northrop Grumman supplies the center and aft fuselage. Commercial small airplane business jet segment appears to be booming. Honda Motor Co. entered the market with its new experimental

6. Markets/Products 583

compact jet, featuring an all-carbon fiber RP fuselage and fuel-efficient Honda-developed HFl18 jet engine. The plane recently completed a successful flight test. Meanwhile work continues at Adam Aircraft, Englewood, CO., on the A700 small business jet, with first deliveries expected in late 2004. The A700's airframe is a carbon fiber/epoxy and honeycomb sandwich construction, powered by two Williams International FJ33 fanjet engines. FAA certification is expected. Carbon fiber RPs have played a key role in commercial and military aircraft for the Antonov Aeronautical Scientific/Technical Complex located in Kiev, Ukraine. RPs have been used in aircraft designs since the early 1970s. Over the company's history, a large number of its aircraft designs have been manufactured, including the AN-225 sixengine jet transport, the largest aircraft on record. A team of Antonov engineers initially began designing and manufacturing RP components to replace noncritical metallic parts such as doors, trim tabs, and panels, but in the few years that followed, comparative performance tests convinced the company that RPs could meet design specifications, so they were put into production. In 1975, the AN-72 model carried approximately 980 kg/2,156 lb of glass fiber RP in the belly fairing, engine nacelles, radome, and other areas. The AN-124 super heavyweight model, the world's largest series production aircraft, incorporated RP parts throughout the airframe for a total of 5,500 kg/12,100 lb. The experience accumulated during their first stage opened the way for the transfer from low-stressed and medium stressed RP structural components to highly loaded structures. In the late 1980s, design work began on the AN-70 transport model. They made the decision to develop RP torsion boxes for the tail structure. An analysis of RP designs used by other aircraft OEMs for highly loaded structures demonstrated that all showed, to some degree, the influence of more traditional metallic designs. Antonov designers wanted a completely new design concept to fully exploit the unique properties of RPs, while eliminating stress concentrators, minimizing the potential for impact damage and making production as straightforward and automated as possible. Their concept was a torsion box structure for the vertical and horizontal stabilizers. They reduced the number of parts to be joined, and rejected, to the extent possible, the use of mechanical fasteners to eliminate stress concentrator sources of RPs. The design for the 10m/32.5 ft high vertical stabilizer and the two 7m/22.75 ft long horizontal stabilizer torsion boxes essentially involved tape-wound, hollow rectangular spar

584 Reinforced Plastics Handbook

sections with spar caps (five in the vertical stabilizer and four in the horizontal stabilizer), molded with each other and covered with a core and outer skins to form a sandwich structure. The walls of the hollow spars and the outer sandwich skins, loaded primarily in shear, are designed with a high percentage of 45 ~ fibers. The unconventional sandwich core consists not of honeycomb, but 15 m m / 0 . 6 inch square continuous carbon fiber prepreg tubing wound with 45 ~ prepreg tape bonded to the spars and oriented chord-wise (parallel to the airflow, or front to back). Spar caps were made mainly with unidirectional prepreg tape. Root and tip ends of the spar caps were reinforced and the parts are attached to the fuselage with metallic fittings at a flange joint. Structural strength analysis showed that the deformation of the integral structure under load differed considerably from the deformation of a traditional ribbed and riveted structure, which required a new approach for stress and strain analysis. Analytical tools and an in-house software program were developed to allow accurate strain analysis and optimum use of the RP material for this unusual design. A major challenge for developing the RP torsion boxes was manufacture. Automation was obviously preferred, given the parts as well as their critical structural function. Tape winder, by PROGRESS Production Assoc. (Savelovo, Russia), was winding parts as large as 2.5 m / 8 . 1 ft in diameter and up 39 ft in length.

design for size of the developed capable of to 12 m /

A matched set of tapered rectangular winding mandrels for the spars was designed from glass fiber, based on the similarity of its linear coefficient of thermal expansion (GTE) characteristics with the GTE characteristics of carbon. One kit of five mandrels was fabricated for the vertical stabilizer, and a second kit of four mandrels was made for the horizontal stabilizer. For the small, square tubing used as core, a cable braider was used to wind prepreg tape over long, hollow mandrels made with extruded PVG and silicon rubber. Selected materials included unidirectional carbon fiber/epoxy prepreg tape, 0.08 mm/0.003-inch thick and 10mm/0.4inch or 2 0 m m / 0 . 8 inch wide, used for the skins, spar webs and the tubular cores. Thicker 0.24 mm/0.009-inch (240 to 265 g m / m 2) carbon/epoxy tapes were used for the spar caps. The 130C (265F) cure epoxy was selected for its long out-time (three to four months). The ARGON facility (Balakovo, Russia) was the material supplier. All materials were certified by the AllRussian Aviation Materials Research Institute (VIAM, Moscow, Russia).

6. Markets/Products 585 Turbine Engine Fan Blades Developments of aircraft RP turbine intake engine blades that started during the early 1940s may now reach an important stage in its development. Major problem that caused destruction of engines in the past has been to control the expansion of the blades that become heated during engine operation. The next generation of turbine fan blades should significantly improve safety and reliability, reduce noise, and lower maintenance and fuel costs for commercial and military planes because engineers will probably craft them from carbon fiber RP composites. Initial feasibility tests by University of California at San Diego (UCSD) structural engineers, NASA, and the U.S. Air Force show these carbon composite fan blades are superior to the metallic, titanium blades currently used. Turbine fan blades play a critical role in overall functionality of an airplane. They connect to the turbine engine located in the nacelle, a large chamber that contains wind flow to generate more power. These usually 6 ft long blades create high wind velocity and 80% of the plane's thrust. It is reported that the leading cause of engine failure is damaged fan blades. Failure may occur from the ingestion of external objects, such as birds, or it may be related to material defects. If it is a metallic blade and it breaks, it can tear through the nacelle as well as the fuselage and damage fuel lines and control systems. When this happens, the safety of the aircraft and its passengers is threatened, and the likelihood of a plane crash increases. In contrast, if an RP blade breaks, it simply crumbles to bits and does not pose a threat to the structure of the plane. However, breakage is less likely because composite materials arc tougher and lighter than metallic blades and exhibit better fatigue characteristics. A multiengine plane can shut down an engine and continue to fly if a blade is lost and no other damage has occurred. A composite blade disintegrates into many small pieces because it is really just brittle graphite fibers held together in a plastic. A titanium blade, however, will fail at the blade root, causing large, 4- to 6-foot blades to fly through the air. As designed, the RP blades are essentially hollow with an internal rib structure. These rib like vents direct, mix, and control airflow more effectively which reduces the amount of energy needed to turn the blades and cuts back on noise. Most engine noise actually comes from wind turbulence that collides with the nacelle. By directing air out the back of the fan blades, the noise can be reduced by a factor of two. And by drawing more air into the blades, engine efficiency is improved by 20%.

586 Reinforced Plastics Handbook There also exists an embedded elastic dampening material in the blades, which minimizes vibrations to improve resiliency. Because the blade is lighter and experiences lower centrifugal force further enhanced the blade's durability occurs. Small-scale wind tunnel tests show they last 10 to 15 times longer than any existing blade. The No. 1 maintenance task is the constant process of taking engines apart to check the blades. These new blades should lend themselves to more efficient production techniques. If you use titanium, you need to buy a big block of it and machine it down to size, wasting a lot of material. As reported, this is very time consuming, and one has to worry about thermal warping. The RP allows for mass production. It is fabricated into a mold, making the process more precise and ensuring the blades are identical. NASA will test the new blades in large-scale wind tunnels at the NASA Glenn Research Center in Cleveland. If successful, they could see installation by year 2004.

All Plastic Airplanes A historical event occurred during 1944 at U. S. Air Force, WrightPatterson AF Base, Dayton, O H with a successful all-plastic airplane (primary and secondary structures) during its first flight. The BT-19 aircraft was designed, fabricated, and flight-tested in the laboratories of WPAFB using RPs (glass fiber/TS polyester surface skins hand lay-up that included the use of the lost-wax process (Chapter 5) sandwich constructions (Chapter 7) for the fabrication of monocoque fuselage, wings, vertical stabilizer, etc. The sandwich (cellular acetate foamed core) constructions provide meeting the static and dynamic loads that the aircraft encountered in flight and on the ground. (D. V. Rosato worked on the development and fabrication of this airplane.) This project was conducted in case the aluminum that was used to build airplanes became unavailable (plants destroyed) or capacity limited. The wooden airplane, the Spruce Goose built by Howard Hughes was also a contender for replacing aircraft aluminum. Extensive material testing was conducted to obtain new engineering data applicable to the loads the sandwich structures would encounter; data was extrapolated for long time periods). Short term creep and fatigue tests conducted proved to be exceptionally satisfactory. Latter 50 of this type aircraft were built by Grumman Aircraft that also resulted in more than satisfactory technically performance going through different maneuvers. Figure 6.45 shows the first flight of the all plastic airplane. In order to develop and maximize load performances required in the aircraft structures, glass fabric reinforcement/TS polyester resin sandwich

6-Markets/Products 587

Figure 6.45

Flight test of the first all reinforced plastic airplane

laminated construction (with varying thickness) was oriented in the required patterns (Chapter 7). Figure 6.46 shows is an example of the fabric layout pattern for the wing structure. Figure 6.47 is a view of a section of the wing after fabrication and ready far attachments, etc. The fabricated monocoque sandwich fuselage structure is shown in Figure 6.48.

Figure 6.46

Layout of fabric reinforcement designed to meet structural requirements

In addition to this all RP airplane being built and flown, their have been other planes built and flown with parts or complete structures that used RPs and URPs. Examples follow:

588 Reinforced Plastics Handbook

Figure 6.47

View of RP fabricated monocoque sandwich aircraft wing

Figure 6.48 View of RP fabricated monocoque sandwich fuselage structure

1934 Fibrous sheet material, such as paper, is used together with a heat-hardened phenolic condensation product and a layer of vulcanized rubber bonded to the material to minimize sound transmission. It gives desired flexibility for airplane cabin construction. Developed by H. Swan and S. Higgins USA. 1937 In Germany, airplane builders use polyester to bond wooden subassemblies. 1939 Germany builds ME-109 airplane wings with polyester resin developed from Ellis's patent.

6. Markets/Products 589

1942 J. F. Dryer, USA, develops a luminous material suitable for use in instrument boards of automobiles, airplanes, etc., made by adding fluorescent dye to a urea-formaldehyde varnish and impregnating the fabric body sheet with it. 1943 Prepreg wood (plastic-impregnated reinforced wood) used to construct airplane propellers. 1944 Army Air Force (latter the Air Force), Dayton, OH, USA issues Technical Reports on the BT-15 airplane that was made of RP. An example is the report entitled Molded Glass Fiber Sandwich Fuselage for BT-15 Airplane issued 8 November. 1944 Helicopters are being designed using glass fiber-TS polyester primary and secondary structures, including rotor blades. 1950 A. Dreyling and C. W. Johnson, Du Pont, USA, patent an airplane fabric which is pre-doped with an aqueous emulsion of a cellulose derivative, dried, and then mounted on the airframe and doped again. 1955 Taylor Craft Model 20 airplane uses RP wings, engine cowlings, doors, seats, fuel tanks, instrument panels, and fuselage skins from nose to fin trailing edges. 1960 Leo Windecker (dentist) builds the Windecker Eagle airplane. The Windecker aI1-RP airplane, after seven years (1967) of development, is successfully flight tested. It is the first plastic composite to receive USA FAA certification. This glass fiber-epoxy (Dow plastic and construction) plane has a monocoque fuselage. 1974 Upper aft carbon/epoxy rudder program begins on the DC-10 airplane by McDonald Douglas Aircraft Co., CA, USA, 1981 The Solar Challenger aircraft on 7 July flew. It was a lightweight sun-powered airplane that made aviation history by flying from France to England [370 km (230 miles in 5 h and 23 min.). Its 16,128 wing-mounted solar cells powered an all plastic lightweight plane 98 kg (217 lb)]. It used DuPont's Kevlar aramid fiber reinforced plastic structures, Mylar shrunk polyester film outboard skins, Delrin acetal control pulleys, Zytel ST supertough nylon landing gear wheel, etc. 1984 Beech's (USA) Starship, an all plastic RP composite, lightweight business turboprop airplane, successfully completes its proof-ofconcept flight. 1984 The twin-turboprop Aviek 400 aircraft promotes the use of advanced plastic composites. 1984 Five sets of plastic composite horizontal stabilizers are installed on the Boeing aircraft 737.

590 Reinforced Plastics Handbook

1986 Burt Rutan and Jeanna Yeager, USA, designed and built the Voyager. This twin-boomed airplane using advanced RP composites is the first to fly around the world without refueling. 2003 The small airplane business jet segment appears to be booming. Honda Motor Co. entered the market with its new experimental compact jet, featuring an all-carbon fiber RP fuselage and fuelefficient Honda-developed HFl18 jet engine. The plane recently completed a successful flight test. Meanwhile work continues at Adam Aircraft, Englewood, CO., on the A700 small business jet, with first deliveries expected in late 2004. The A700's airframe is a carbon fiber/epoxy and honeycomb sandwich construction, powered by two Williams International FJ33 fanjet engines. FAA certification is expected. 2003 With the performance to weight advantages of carbon fiber the 200 to 250 passenger Boeing 7e7 high speed jet (mach 0.85) light weight commercial airplane will have the majority of its primary structure (wings, fuselage, etc.) made of carbon RPs. It will use 15 to 20% less fuel when compared to other wide-body airplanes. Production will begin 2005. First flight is expected in 2007 with certification, delivery, and entry into service 2008. The crash of American Airlines Flight 587 in November 2001 briefly threatened growing public acceptance of RP structures, when newspaper accounts suggested that faulty carbon fiber/epoxy laminates in its vertical tail fin might have caused the Airbus A300 to go down. The ongoing investigation exonerated RPs with the aircraft industry moving ahead with new designs, featuring more composites than ever before. Observers look for an upturned in late 2004 or 2005 of carbon reinforced composites. Boeing and Airbus are using more carbon fiber on their new models, and older models take on more carbon as they get updated. Innovative aerospace fabricators push the carbon-fiber envelope with new, low-cost advanced RPs such as pultruded key parts on the Airbus A380. The huge Airbus A380 will carry 30 metric tons/66,000 lb of structural composites; 16% of its airframe weight. 2003 Many subcontractors supply Boeing and Airbus Industrie. An example is Mitsubishi Rayon Co. Ltd.. Tokyo, Japan. They were selected as an Airbus A380 supplier of unidirectional and woven carbon fiber prepregs, incorporating two types of carbon fiber (medium-elasticity and high-strength fiber). Materials will be produced both in Japan and by the company's affiliate Structit SA, Vert le Petit, France. Airbus expects to complete materials certification by the end of 2004.

6 9 Markets/Products

2003 FACC AG (Ried, Austria) fabricated a demonstration RP replacement part for a highly stressed aluminum spoiler center fitting on the Airbus A340-600. It used a low-viscosity epoxy resin in the resin transfer molding (RTM) process because the part's complex shape would be difficult to produce consistently and costeffectively with hand lay-up. 2003 Contract awards for military RPs continued to proliferate. GKN Aerospace Services of Farnam, Surrey, UK recently was awarded an approximately $4 million contract to supply the control surfaces and edges package, including tool design and production, for the 14 flying and 8 ground test aircraft being built during the F-35 Joint Strike Fighter's System Development and Demonstration (SDD) phase. The carbon/bismaleimide RP details require very close manufacturing tolerances, due to the stealthy nature of the aircraft. Other F-35 work was awarded recently to GKN's subsidiary in Australia, which will support Northrop Grumman in the design, analysis and manufacture of F-35 center fuselage parts. GKN Australia is one of 19 Australian firms that will be involved in the F-35 program. GKN Aerospace also has received a contract from Sikorsky Aircraft Co., USA to develop and manufacture side skin panels for the RAH-66 Comanche military helicopter. The contract initially calls for 42 cored RP test panels for material qualification and three actual 3 ft by 4 ft forward side panels. Sikorsky has the option to extend the contract to include 73 actual production panel sets, for a total value of $1.5 million. Boeing has announced that its A H - 6 4 Apache Longbow helicopter will receive a new RP main rotor blade, manufactured by the company's Mesa, Ariz. facility. The blade, with a more efficient airfoil shape and higher overall twist rate, provides improved hover and forward flight performance. Made with S-2 glass fiber and carbon fiber with epoxy resin, the new blade has a much simpler design than the original and costs less to manufacture. The original blade had four spars and was difficult to fabricate. The new blade, although it is hand laid up, has a single spar and a simpler design, still meets ballistic requirements and lasts longer. The new blade fits all existing AH-64s and will be part of the 269 new aircraft to be manufactured and delivered through the year 2006. Boeing will award this work to a outside contract manufacturer. Hitco Carbon Composites Inc. of Gardena, CA., USA has won a four-year contract to build vapor barrier assemblies for 60 Boeing C-17 aircraft. The autoclaved, foam-cored glass fiber/epoxy panel

591

592 Reinforced Plastics Handbook assemblies measure 6.5 m long by 5.5 rn wide (21 ft by 18 ft) with compound curvature, designed to prevent fuel and fuel vapors from the main fuel tanks from penetrating the plane's cargo area. 2003 The latest version of the A H - 6 4 Apache helicopter has improved structurally to carry more weaponry and payload. RP structures makes the rotor blades with a filament-wound fiberglass spar that is combined with aramid core material and titanium forgings in a metal-bonding process. 2003 Utah State University, Logan, Utah, U.S.A. was one of several groups who took on the challenge of creating a replica of the original Wright Brothers' flying machine, which first took to the air 100 years ago, on Dec. 17, 1903. The Utah State creation, while a replica of the historic aircraft, was constructed with a number of RP materials, which the Utah group claims would have been the basics available to the Wright Brothers had they conceived their design today.

Wright Brothers Flying Machine Replica Utah State University, Logan, Utah, U.S.A. was one of several groups who took on the challenge of creating a replica of the original Wright Brothers' flying machine, which first took to the air 100 years ago, on Dec. 17, 1903. The Utah State creation, while a replica of the historic aircraft, was constructed with a number of RP materials, which the Utah group claims would have been the basics available to the Wright Brothers had they conceived their design today. The USU Wright Flyer replica made its maiden flight in March 2003, in Utah, and then traveled in September to Dayton, Ohio where it was displayed at the SAMPE Technical Conference (Figure 6.49). The aircraft and the USU team were featured in a December History Channel special commemorating the flight anniversary. The tubular spars that support the two 40 ft long wings were filament wound by ATK Thiokol Propulsion (Brigham City, Utah, U.S.A.) using T C R Composites (Ogden, Utah, U.S.A.) c a r b o n / e p o x y tow prepreg material. Fitted over the spars were evenly spaced 0.5 in. (12.5 ram) thick ribs made of Rohacell polymethacrylimide (PMI) foam (supplied by Degussa Performance Plastics, Darmstadt, Germany) with aramid/epoxy face skins. The aramid was needed to give the foam some additional strength for torsional loads. Other RP components included the struts that connect the two wings and the wings' leading and trailing edges. All RP materials were donated

6. Markets/Products 593

Figure 6.49

Wright Brothers flying machine replica with Donald V. Rosato (right) and Dominick V. Rosato at the controls

by suppliers, including Patterned Fiber Composites Inc., Lindon, Utah, U.S.A. and Hexcel Composites, Dublin, Calif., U.S.A., in addition to those mentioned above. Majority of the fabrication and assembly was accomplished by USU flight technology students.

Atmospheric Flights During the past decades, progress in aeronautics and astronautics has been remarkable because people have learned to master the difficult feat of hypervelocity flight. A variety of manned and unmanned aircraft have been developed for faster transportation from one point on earth to another. Similarly, aerospace vehicles have been constructed for further exploration of the vast depths of space and the neighboring planets in the solar system. RPs has found numerous uses in specialty areas (ablation, insulation, etc.) such as hypersonic atmospheric flight and chemical propulsion exhaust systems. The particular RP employed in these applications is based on the inherent properties of the material or the ability to combine it with another component material to obtain a balance of properties uncommon to either component. Plastics have been development for uses in very high temperature environments. It has been demonstrated that RPs are suitable for

594 Reinforced Plastics Handbook

thermally protecting structures during intense rocket and missile propulsion heating. This discovery became one of the greatest achievements of modern times, because it essentially initially eliminated the thermal barrier to hypersonic atmospheric flight as well as many of the internal heating problems associated with chemical propulsion systems. Modern supersonic aircraft experience appreciable heating. This incident flux is accommodated by the use of an insulated metallic structure, which provides a near balance between the incident thermal pulse and the heat dissipated by surface radiation. The result is that only a small amount of heat has to be absorbed by mechanisms other than radiation. With speeds increasing (8,000 fps), heating increases to a point where some added form of thermal protection is necessary to prevent thermo structural failure. Hypervelocity vehicles transcending through a planetary atmosphere also encounter gas-dynamic heating. The magnitude of heating is very large, however, and the heating period is much shorter. This latter type of thermal problem is frequently referred to as the reentry heating problem, and it posed one of the most difficult engineering problems of the twentieth century. A vehicle entering the earth's atmosphere at 25,000 fps has a kinetic energy equivalent to 12,500 Btu/lb of vehicle mass. Assuming the vehicle weighs a ton, it possesses a thermal energy equivalent to 25,000,000 Btu. This magnitude of energy greatly exceeds that required too completely vaporize the entire vehicle. Fortunately, only a very small fraction of the kinetic energy converted to heat reaches the body while the remainder is dissipated in the gas surrounding the vehicle. Materials performance during hypersonic atmospheric flight depends upon certain environmental parameters. These thermal, mechanical, and chemical variables differ greatly in magnitude and with body position. In general, they are concerned with temperatures from about 2,000 to over 20,000F (1,100 to 11,000C), gas enthalpies up to 40,000 Btu/lb, convective/radiative heating from 10 to over 10,000 Btu/ft2/see. The stagnation pressures is less than 1 to over 100 arm., surface shear stresses up to about 900 psf, heating times from a few to several thousand seconds, and gaseous vapor compositions involving molecular, dissociated, and ionized species. To operate in these extreme conditions ablative materials can be used (Table 6.10). Mechanical Parameters Structures traveling at very high velocities are adversely influenced by many mechanical aspects of the environment, which may include external and internal pressure forces, gasdynamic shear, solid and liquid

6-Markets/Products 595 Table 6.10 RPs and other high temperature performance materials (courtesy of Plastics FALLO)

Ablative Plastics

Elastomer

Ceramic

Metal

Polytetrafluoroethylene

Silicone rubber filled with microspheres and reinforced with a plastic honeycomb

Porous oxide (silica) matrix infiltrated with phenolic resin

Porous refractory (tungsten infiltrated with a low melting point metal {silver)

Epoxy-polyamide resin with a powdered oxide filler

Polybutadiene-acrylonitrile elastomer modified phenolic resin with a subliming powder

Porous filament wound composite of oxide fibers and an inorganic adhesive, impregnated with an organic resin

Hot-pressed refractory metal containing an oxide filler

Hot pressed oxide, carbide, or nitride in a metal honeycomb

Phenolic resin with an organic (nylon), inorganic (silica), or refractory (carbon) reinforcement Precharred epoxy impregnated with a noncharring resin

Major property Of interest

Type of plastics

Ablative

Phenol-formaldehyde

Charring resin for rocket nozzle

Chemical resistance

Fluorosilicone

Seals, gaskets, hose linings for liquid fuels

Cryogenic

Polyurethane

Insulative foam for cryogenic tankage

Adhesion

Epoxy

Bonding reinforcements on external surface of combustion chamber

Dielectric

Silicone

Wire and cable electrical insulation

Elastomeric

Polyb utad ie ne-a cryl o n it ri le

Soil propellant binder

Propulsion system application

Power transmission

Diesters

Hydraulic fluid

Specific strength

epoxy-novolac

Resin matrix for filament wound motor case

Thermally nonconductive

Polyamide

Resin modifier for plastic thrust chamber

Absorptivity :emissivity ratio

Alkyd silicone

Thermal control coating

Gelling agent

Polyvinyl chloride

Thixotrophic liquid propellant

596 Reinforced Plastics Handbook

impact, mechanical and acoustical vibration, and inertial and dynamic forces. The general effect is to cause destruction of a material or premature failure before it has accomplished its intended purpose. Chemical Parameters At subsonic velocity flight, the environment is essentially composed of rigid, rotating diatomic molecules. The energy of these molecules is distributed among five degrees of freedom (equipartition of energy theorem), and a kinetic energy corresponding to its microscopic relative velocity. In the supersonic regime, however, air is in vibration excitation as a result of the energy imparted to it. At even higher speeds of the hypervelocity regime, the molecules are heated to a level at which they dissociate and ionize. These processes occur first for oxygen and then for nitrogen. Thermal Protection Systems The design of vehicles for hypersonic atmospheric flight represents a compromise between the intended mission, the thermo structural aspects of the environment, the rate and magnitude of vehicle deceleration permitted, and the amount of lift necessary for flight control and landing at a predetermined point on some planet. The heating problem associated with high performance vehicles has been solved by a variety of design techniques. These include radiative cooling, heat sinks, transpiration cooling, ablation, and combinations thereof. Each thermal protective scheme is applicable to a particular portion of the flight regime, with reduced efficiency or no utility at other flight conditions. Ablation Materials The ablation technique can be used to handle the intense heating and extremely high temperatures encountered. Surface material is physically removed or a temperature-sensitive component of a composite is preferentially removed. The injected vapors alter the chemical composition, transport properties, and temperature profile of the boundary layer, thus reducing the heat transfer to the material surface. At high ablation rates, the heat transfer to the surface may be only 15% of the thermal flux to a non-ablating surface. This approach can absorb up to tens of thousands of Btu's of heat. The ablation action dissipates material through chemical reactions, phase changes, surface radiation and boundary layer cooling of the ablator (Figure 6.50). The heating rate temperature of an ablative system is no limit. The total heat load limits it. Even with this limit the versatility of ablation has permitted it to be used on hypervelocity atmospheric vehicles.

6. Markets/Products 597 Glass Droplets

CONVECTION RADIATION GAS-PHASE COMBUSTION SURFACE COMBUSTION RERADIATION TRANSPIRATION < COOLING CHEMICAL REACTIONS-" BOUNDARY LAYER COOLING

Figure 6~50 Schematic shows ablation energy exchange action of an RP material No single, universally acceptable ablative material has been developed. Nevertheless, the interdisciplinary efforts of materials scientists and engineers have resulted in obtaining a wide variety of ablative compositions and constructions. These thermally protective materials have been arbitrarily categorized by their matrix composition. During ablation its surface material is physically removed. The injected vapors alter the chemical composition, transport properties, and temperature profile of the boundary layer, thus reducing the beat transfer to the material surface. At high ablation rates, the heat transfer to the surface may be only 15% of the thermal flux to a non-ablating surface. Up to tens of thousands of Btu's of heat can be absorbed, dissipated and blocked per pound of ablative material through the sensible heat capacity, chemical reactions, phase changes, surface radiation and boundary layer cooling of the ablator. R P Plastics Plastic-base RPs, which employ an organic matrix, are a

widely used class of ablative heat protective materials. They respond to a hyper-thermal environment in a variety of ways, such as depolymerization-vaporization (polytetrafluoroethylene), pyrolysisvaporization (phenolic, epoxy), and decomposition-melting-vaporization (nylon fiber RP). The principal advantages of plastic-base ablators are their high heat shielding capability and low thermal conductivity. The major limitations are high erosion rates during exposure to very high gas-dynamic shear forces and, limited capability to accommodate very

598 Reinforced Plastics Handbook

high heat loads. Most TS plastics and highly crosslinked plastics (especially those with aromatic ring structures) form a hard surface residue of porous carbon. Elastomers Another major class of plastic ablators is elastomeric-base materials and particularly silicones. During ablation, they thermally decompose by such processes as depolymerization, pyrolysis, and vaporization. The silicone elastomers provide low thermal conductivity, high thermal efficiency at low to moderate heat fluxes, low temperature properties, elongation of several hundred percent at failure, oxidative resistance, low density, and compatibility with other structural substrate materials. Elastomeric materials are generally limited by the amount or structural quality of the char formed during ablation, which restricts their use to hyperthermal environments of relatively low mechanical forces. Ceramics Ceramic-base ablators constitute another class of heat shielding materials. They generally have high thermal efficiency, but this capability is difficult to realize because of their susceptibility to thermal stress failure. During thermal shock, the material may crack extensively and fail catastrophically. Placing the ceramic in a metal honeycomb tends to alleviate this problem by restricting any cracks to the outer walls of the cell structure.

Porous ceramics per se are potential ablative-insulative materials, but by plastic impregnation, their ablative characteristics are greatly improved. Specifically, the resin component increases the composite strength and thermal shock resistance, decreases the thermal conductivity, and permits higher environmental temperatures to be tolerated without exceeding the melting or decomposition temperature of the ceramic. Typical compositions of porous ceramics include silica, zirconium, alumina, magnesia, carbides, borides, and suicides. They are prepared by such processes as hot pressing, isostatic pressing, slip casting, pyrolysis of organic inclusions, and chemical bonding. Suitable plastic infiltrants include the phenolics, epoxies, acrylics, polystyrenes, and others. Of the numerous combinations available, phenolic resin impregnated porous silica composite has found the greatest use. The principal limitations of this material (like other internally ablating composites) are a reduced thermal efficiency with exposure time, or loss of molten surface material by the shearing action of the high temperature aerodynamic stream. Metals Metal-base ablators are a fourth major class of thermal protection materials. The most common type of ablator is a porous refractory skeleton containing a lower melting point metallic infiltrant.

6. Markets/Products 599

Tungsten matrices with up to 80% porosity are generally employed. Fiber felting or cold pressing powder followed by sintering prepares them. The porous matrix is then infiltrated with such metals as copper or silver using high pressures, high vacuum, or a combination of both. The resultant composite has high strength, good thermal shock resistance, and can be easily machined. Its low thermal efficiency (about 1,500 Btu/lb), high density, and high thermal conductivity tend to restrict its use to intensely heated areas where the original configuration of the matrix must be maintained.

Material Properties The properties and characteristics of ablative composites are greatly influenced by the presence of a plastic component. The inherently wide range of material properties available in these plastic containing composites has led to broad use in a variety of entry thermal protection systems.

Comparative Performances The capability of various types of ablative materials for insulating entry vehicles has been reviewed. The more refractory materials like graphite and infiltrated tungsten dissipate a considerable amount of heat by radiation, but their inherently high thermal conductivities introduce severe insulation problems. The charring plastics are also capable of reaching very high surface temperatures, but their ability to restrict the internal transfer of heat is significantly better. Ceramic-base ablators operate at intermediate surface temperatures. The plastic impregnated porous ceramics provide better insulation than the bulk ceramics, until the organic material is expended. The subliming plastics operate at relatively low ablative surface temperatures, and hence are inefficient in disposing of heat by surface radiative cooling. The low density elastomeric and plastic composites combine the desirable charring attribute of the aromatic polymers with the insulative characteristic of the subliming plastics. They are thus very effective in environments comprising low to moderate heating rates and long heating times.

Entry Simulations Tests There are different entry simulation testing equipment to evaluate plastic materials. The utility of polymeric materials for hypersonic atmospheric flight applications is determined by a series of sequential evaluations. Initial screening of candidate materials is carried out in the laboratory, using the high temperature apparatuses. The performance data obtained is then analyzed collectively to determine both the mechanism and magnitude of thermo-chemical degradation at high temperatures. Plastics exhibiting promising properties

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and characteristics are subsequently screened in small, subsonic air are jets to identify their unique ablative characteristics and limitations, type of entry environment in which the material will most likely best perform, need for additional specialized testing, and other factors which could influence the nature and rate of subsequent developmental efforts. Plastic materials receiving the highest overall rating are then evaluated in other ground simulation facilities. The wind tunnel is most frequently employed for this purpose. Perfect simulation is impossible, however, and thus the choice of facility is dictated by the importance of closely simulating either the thermal, chemical, or mechanical aspects of the entry environment. Subsequent specialized testing is then carried out to determine the importance of environmental parameters not closely simulated in the previous evaluation work. Finally, the plastic material is flown in the actual service environment to prove its heat shielding effectiveness, confirm previous theoretical prediction of material behavior, and to provide a sound basis for the selection and design of heat shields for operational flight vehicles. The selection of an appropriate ground test facility for ablative characterization of plastic and composite materials requires consideration of a large number of factors. These include: the environmental conditions desired and ability to generate them simultaneously, degree of control over the environmental parameters and ability to vary them individually, uniformity and reproducibility of the test medium, ability to accurately calibrate the test medium, and the available testing time and area. Numerous ground base facilities have been developed for materials characterization. The more widely used facilities have been reviewed, together with their capability to simulate various flight velocity-altitude (enthalpy-pressure equivalent) conditions. Each facility is characterized by its capability to generate a high temperature fluid stream, differing in static and impact pressure, temperature and enthalpy, velocity, species concentration., energy states, and heat and mass transfer.

Entry Environmental Affects The mechanism and magnitude of ablation of plastics is a strong function of the individual thermal, mechanical and chemical parameters of the entry environment. While it is difficult and often impossible to independently study the particular influence of each parameter, some of the more important material-environment interactions have been identified.

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Gas Enthalpies The ablative efficiency of all plastics increases with gas enthalpy. This is due to the transpiration cooling effect of the newly formed pyrolytic species and to increase surface emission caused by higher surface temperatures. Gaseous products formed by material ablation are injected into the hot boundary layer. In diffusing through this high temperature region, they absorb heat by sensible temperature rise. The boundary layer is thus increased in thickness, and its original enthalpy or temperature is lowered. Consequently, less heat is transferred from the environment to the ablating surface.

Intense Convective Heatings The subsonic air arc heater is widely employed to ablatively screen plastic materials for potential entry heat shielding applications. The chemical composition and structure of the polymer exerted the greatest influence on the ability of the composite to accommodate intense heating and to impede the flow of heat into the specimen. Cold wall heats of ablation values ranged between 7700 and 13,800 Btu/lb. The best performance was obtained with the heterocyclic polyimide and polybenzimidazole and the aromatic polyphenylene resins, all of which exceed the heat of ablation for the widely used phenol formaldehyde (phenolic) resin. The superior charring characteristics of these polymers contributed greatly to their high heats of ablation. The various plastic materials, with their inherently low thermal conductivities, greatly restricted the flow of heat from the surface region into the specimen substrate. The stable char forming polymers and those capable of producing an appreciable amount of pyrolytic gaseous species provided the best insulative characteristics. Both polyphenylene and phosphonitrilic chloride polymers exhibited significantly lower back wall temperatures during ablation, as compared to the phenolic resin composites. Surface temperatures of the composite materials were within a 4290 to 5350F range, and apparently controlled by the ratio of vaporized: retained molten surface on the specimen. Surface emittance values varied appreciably, i.e., between 0.19 and 0.62. The higher emittance values were either due to a thin surface layer of silica (high emission from the subsurface char, or an appreciable amount of polymer carbon particles in the molten silica layer). The ablative characteristics of the carbon fabric RP composites were significantly different from that containing silica reinforcement. The carbon reinforced composites had higher heats of ablation, poorer

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insulative characteristics, higher surface temperatures, higher surface emittance values, and higher surface re-radiation. Plastics that yielded a structurally sound char of high surface emittance possessed the highest heats of ablation. These included many of the heterocyclic and aromatic polymers, like the polyirnides and modified phenolics. The poorer char forming polymers, like epoxy novolacs, had a higher ablation rate, and consequently, lower heat of ablation. Poor dimensional stability during ablation was obtained with the semiorganic phosphonitrilic chloride polymer. With respect to the insulative characteristics, the high char yielding polymers performed the best. Polyphenylene, polybenzimidazole, and polyimide-containing composites provided about 50% more insulation than the conventional phenolic resin. The poor insulative characteristic of the phosphonitrilic chloride composite was apparently due to its high rate of ablation during exposure. With respect to surface temperature and emittance, the type of polymer in the composite had little effect.

Summary The outstanding performance of plastics in providing thermal protection for hypersonic atmospheric vehicles, and the broad base of knowledge concerning ablative technology could mistakenly give the impression that the reentry problem has been solved. Moreover, one may have the false impression that only minor improvements will be made in future ablative materials. Nothing could be further from the truth. New types of ablative plastics are required to accommodate the ever increasing severity of the entry environments, to keep pace with new and improved vehicle missions and designs, and to provide satisfactory performance in new service environments. Chemical Propulsion Exhausts

Plastics with their wide range of properties and characteristics have found numerous uses in chemical propulsion systems. The particular plastic employed in these applications is based on the inherent properties of the plastic or the ability to combine it with another component material to obtain a balance of properties uncommon to either component. Various propulsion systems have been developed over the years, which are dependent upon chemical, mechanical, electrical, nuclear, and solar means for accelerating the working fluid by high temperatures. Only chemical propulsion will be further discussed, and in particular, that associated with liquid, solid, and hybrid motors and engines. These motors and engines are uniquely different from other chemical

6. Markets/Products 603 propulsion systems in that they carry on board the necessary propellants, as contrasted to jet engines that rely on atmospheric oxygen for combustion of the fuel. The basic purpose of a propulsion system is to convert the thermal energy of a chemical reaction into useful kinetic energy by directing the flow of the resultant products. In other words, the propulsion system is to provide thrust for the movement of a vehicle. Expulsion of material is the essence of thrust production and without material to expel no thrust can be produced, regardless of how much energy is available. The amount of thrust generated is equal to the rate of propellant consumption multiplied by the exhaust gas velocity. In order to maximize the exhaust velocity, it is necessary to have the combustion process take place at the highest possible temperature and pressure. Energy is released in the process, with a major fraction appearing as thermal (heat) energy. The amount of heat released is the difference value in bond energies of the newly formed reaction products and those of the precursory reactants. The reaction products are usually energetic, and characterized as being thermally reactive, chemically corrosive, and mechanically erosive. Yet, they must be contained and controlled in order to achieve the desired magnitude and direction of thrust. The development of engineering materials, which can accommodate the hyper-environmental conditions of chemical propulsion thus, constitutes a very difficult problem. The combustion process is carried out in a thrust chamber or a motor case, and the reaction products are momentarily contained therein. The newly formed species are heterogeneous in composition and involve a wide variety of low molecular weight products. The temperature of these products is generally high, and it ranges from about 2000F in gas generators to well over 8000F in advanced liquid propellant engines. The combustion products leave the chamber and are directed and expanded in a nozzle to obtain velocities from about 5,000 to 14,000 R/see. The mass rate of flow through the nozzle will generally vary from less than 1 lb/see-in, 2 in small liquid space engines to more than 6 lb/see-in. 2 in solid and liquid propellant engines. The firing period may last from a few seconds as in tactical missiles, and range upwards to over 20 min as in spacecraft engines. Since the flow is highly turbulent and the temperature level of the reaction products and the local pressure are numerically great, heat may be transferred at a high rate to the walls of the combustion chamber, nozzle, and adjacent parts. With an increase in firing time, heat protection becomes more important and ultimately approaches the critical stage. It then becomes necessary to thermally protect or cool the

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exposed parts. High-performance materials and cooling techniques are thus necessary to accommodate the hyper-environmental conditions associated with rocket engines and motors. Ablation Processes

Since 1950, plastics have been seriously considered and under development for used in very high temperature environments. By 1954, it was demonstrated that plastic materials were suitable for thermally protecting structures during intense propulsion heating. This discovery became one of the greatest achievements of modern times, because it essentially initially eliminated the "thermal barrier" to hypersonic atmospheric flight as well as many of the internal heating problems associated with chemical propulsion systems. Plastics in the form of rigid TSs, flexible elastomers and TPs, and semi rigid elastomer-modified TS materials have thus acquired a new function in the engineering world, namely, that of providing thermal protection. As reviewed this mode of heat protection is now known as the "ablation" or "ablative" process, and the functional materials employed are commonly referred to as "ablators." While significant progress has been made in understanding the complex nature of materials ablation, many of the subtle aspects continue to elude the researcher. Nevertheless, the ablation process for a fiber RP or elastomeric RP will be described for the purpose of illustration. At the onset of heating, energy is absorbed at the exposed surface and then conducted internally. The rate of heat penetration is dependent upon the surface temperature (driving force), and it is diffusion limited by the inherent properties of organic materials. The containment of heat in the surface region causes its surface temperature to rise rapidly. The net heat flux to the material surface is thus decreased continuously as the surface temperature value moves toward the radiation equilibrium temperature. Eventually the material is heated sufficiently to generate volatiles, which have varying compositions such as water, residual diluents, or low molecular weight polymers. At higher temperatures, the plastic begins to soften and it may physically slump. Thermal agitation eventually becomes severe enough to split side groups off the polymer backbone, and finally the chemical bonds in the backbone structure arc ruptured. The polymer is thus undergoing pyrolysis, which continues over a broad temperature range. The organic component of the composite is degraded into numerous gaseous products of varying molecular weights, such as water vapor, carbon monoxide, carbon dioxide, hydrogen, methane, ethylene, acetylene, and other unsaturated and saturated hydrocarbon fragments.

6. Markets/Products 605 These pyrolytic species are injected into the adjacent hot boundary layer, and they effectively lower the enthalpy (heat content) of the environment. In this manner, less heat is convected to the ablating surface. TP and elastomeric plastics tend to thermally degrade into simple monomeric units with the formation of considerable liquid and a lesser amount of gaseous species. Little or no solid residue generally remains on the ablating surface. On the contrary, most TS and highly crosslinked polymers (especially those with aromatic ring structures) form a hard surface residue of porous carbon. The amount of char formed depends upon such factors as the carbon-hydrogen ratio present in the original polymer structure, degree of crosslinldng and tendency to further crosslink during heating, presence of foreign elements like the halogens, asymmetry and aromaticity of the polymer structure, degree of vapor pyrolysis of the ablative hydrocarbon species percolating through the char layer, and type of elemental bonding. With the formation of a carbonaceous layer, the primary region of pyrolysis gradually shifts from the surface to a substrate zone beneath the char layer. The newly formed char structure is attached to the virgin substrate material and remains thereon for at least a short period of time. Meanwhile, its refractory nature serves to protect the temperaturesensitive substrate from the environment. Gaseous products formed in the substrate pass through the porous char layer, undergo partial vapor phase cracking, and deposit pyrolytic carbon (or graphite) onto the walls of the pores. As the organic polymer or its residual char are removed by the ablative aspects of the hypcr-environment, the reinforcing fibers or particle fillers are left exposed and unsupported. If vitreous in composition, they undergo melting. The resultant molten material covers the surface as liquid droplets, irregular globules, or a thin film. Continued addition of heat to the surface causes the melt to be vaporized. A fraction of the melt may be splattered by internal pressure forces, or sloughed away when acted upon by external pressure and shear forces of the dynamic environment. These reactions and products are favored at given temperature levels. For example, silicone carbide is formed at temperatures up to about 2800F. At higher temperatures, equilibrium mixtures of metallic silicon and silicon monoxide gas are favored. The summation of all of these reactions is a tremendous potential for absorbing heat. Naturally, only a fraction of these endothermic reactions actually take place in any given ablation situation. The objective, then, is to control the materials

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variables so as to maximize the heat absorbed and dissipated by any given material. From a thermo-physical point of view, ablation may be defined as an orderly heat and mass transfer process in which a large amount of thermal energy is expended by sacrificial loss of surface region material. The heat input from the environment is absorbed, dissipated, blocked, and generated by numerous mechanisms. These are:

(a) heat conduction into the material substrate and storage by its effective heat capacity, (b) material phase changes, heat absorption by gases in the substrate as they percolate to the surface, (d) convection of heat in a surface liquid layer, if one exists, (e) transpiration of gases from the ablating surface into the boundary layer with attendant heat absorption, (t) surface and bulk radiation, and (g) endothermic and exothermic chemical reactions. These energy absorption processes take place automatically and simultaneously. It is apparent, then, that the performance of an ablative plastic is achieved in a manner quite unlike that for heat-resistant plastics. Ablators depend upon various degradative reactions to absorb, dissipate, and block a copious amount of heat. On the contrary, heat-resistant plastics must essentially remain intact during high temperature exposure to retain a significant fraction of their room-temperature properties.

Liquid Propulsions Liquid propellant engines have been used for many years to propel aircraft, guided missiles, rockets, research devices, and other types of vehicles. They have provided thrust levels ranging from a few ounces for altitude control to several hundred thousand pounds for the earth launching of vehicles. Liquid propulsion is characterized by its high state of development, relatively complicated systems design, capability for repeated operation, long firing times, and of course the propellants employed. Their use has been based on a number of selection criteria, such as the operational mission, performance required, reliability, minimum weight, logistics, economics, availability, maintainability, mobility, and others. Ablative cooling has been used in a number of liquid propellant engines. The materials employed are generally of an oriented fiber reinforced resin,

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and they are used in direct contact with the exhaust products. A thin layer of elastomeric material may also be used to insulate the outer structure from the inner ablating plastic. Fibrous oxides and in particular silica and quartz have consistently shown superior performance in oxidizing environments. This desirable performance has been attributed to their inherently high heat absorbing capability. By realizing a significant fraction of the theoretical heat absorption, high ablative cooling is insured. Another reason for the desirable performance of silica fibers is their ability to reinforce the char layer, and form a viscous melt during intense heating. This molten layer covers the thermally degrading resin surface, and acts as an oxidative barrier for the charred residue. In fluorine environments, however, oxide reinforcement experience increased vaporization. Carbon and graphite reinforcements exhibit greater chemical inertness in fluorine-containing products of combustion, and thus have been used exclusively. With respect to resins, only the high char yielding phenolics and epoxy novolacs have been employed. Ablative plastics have certain limitations in the liquid propellant exhaust environments. Their service life is time dependent, and varies with the firing time to about the one-half power. Firing times in excess of 310 s have been obtained, however, with a low thrust (150 lb) and low chamber pressure (130 psia) engine. At lower chamber pressures, engine operations up to about 1980 s have been achieved. Ablative plastic composites are generally not used in the throat region of liquid propellant engines, unless the total erosion can be maintained at 5% or less at the end of the firing period. Very high mass-flow rates of exhaust products, extremely long firing times, and small diameter nozzle throat regions tend to decrease the attractiveness of ablative plastic cooling. Ablators are somewhat sensitive to the propellant injector performance. Poorly designed injectors have been noted to cause recirculation hot spots at the chamber wall, which resulted in a nonpredictable, nonuniform, and excessive localized erosion. Some residual thrust may also be encountered in liquid propellant engines that utilize ablative cooling. During engine cool down, gaseous products may be formed by continued resin vaporization in the hot char layer. With respect to the high thrust engines of launch vehicles, ablative materials have only been used sparingly. The frequent need for proof testing, availability of cryogenic propellants for cooling, and the previously mentioned long firing durations and high mass-flow rates of exhaust products tend to favor other forms of cooling. Ablative plastic chambers have been built and successfully used on liquid engines having small to moderately high thrust levels.

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Solid Propellants The evolution of propulsion for ordnance purposes, weapon delivery systems, ballistic and space vehicles, and scientific exploration suggests an ever-increasing role for solid propellant motors. Unlike the previously discussed liquid propellants, the solid rocket fuels are characterized by their obvious solid phase propellants, lower specific impulse (about 8 to 20% less), higher densities, fixed fuel oxidizer ratios, and higher costs. Motors employing the solid propellants exhibit certain performance traits, which include simplicity, compactness, safety, instant firing readiness, short developmental times, reduced developmental costs, greater reliability, shorter firing times, .storability, ease of maintenance, and a passive thermal protection system. Other motor characteristics that were once exclusive to liquid propellant engines, such as throttling and restarting, have been achieved in certain rocket engines. A solid propellant is a mixture of an oxidizing and a reducing material that can coexist in the solid state at ordinary temperatures. It is generally composed of three elements, the oxidizer, fuel or binder, and various additives.

Materials of Construction Rocket motors are constructed of composite materials with each component material performing a specific function depending on its location. This type of construction is optimum, since the environmental conditions and hence the materials requirements vary greatly with motor position. The forward bulkhead of the motor case is exposed to stagnant but hot gases, and thus must be lined with an insulative material. The modulus of this insulator is sufficiently low so as to transmit the chamber pressure into the external structural member. Insulators that are brittle tend to crack during the initial pressurization, with possible catastrophic burn-through of the motor case wall. Insulators are composed of an elastomer-modified charring resin (like a copolymer of butadieneacrylonitrile and phenolic) with various reinforcements a n d / o r low conductivity fillers. The bulkhead insulator is generally premolded in segments and then adhesively (plastic) bonded in place. In the cylindrical portion of the motor, a liner material is required to prevent corrosion of the structural case during storage and overheating during motor firing. Since the liner must transmit the chamber pressure forces into the structural case, it must posse flexibility, an elongation greater than the propellant, and high tensile strength. Optimum performance also requires that it have a low thermal conductivity, some

6. Markets/Products 609 erosion resistance, low density consistent with ablative and mechanical properties, low gas permeability, good bonding characteristics, compatibility with the propellant and the case, and a resistance to longtime aging effects. This demanding combination of requirements along with a need for ease of fabrication and low cost are difficult (if not impossible) to achieve in a single material. By far, the plastic elastomers have been found to be most suitable. They are flexible and have elongations up to several hundred percent. As a result, they will follow (without cracking or bond separation) the shrinkage of a solid propellant during curing as well as the compressive loading during motor firing. The liner material is frequently very similar to that employed as the propellant binder, and is generally composed of a nitrile, urethane, butyl, or polysulfide rubber. To these elastomeric polymers are added various particulate and fibrous matter, such as powders of boric oxide, potassium oxalate, silica, alumina, carbon, or phenolic, and long fibers of asbestos, silica, or possibly carbon. These liners are applied to the motor case by conventional spray or centrifugal sling methods, or by hand rolling solid sheets to the interior of the case. In the aft end of the motor case, sidewall insulation is necessary in those areas exposed throughout the motor firing and those locations left exposed by recession of the propellant grain front. The materials used in these areas must have performance capabilities similar to the insulator in the forward bulkhead, except improved erosion resistance is required because of the moving gas stream. In general, the sidewall insulator is composed of an clastomer-resin copolymer or charring rubber reinforced with various fibrous compositions. The external case of the rocket motor supports the mechanically and thermally induced stresses, which are due to internal gas pressure, vibration, acceleration, thrust vector control, and differential thermal expansion of component materials. To accommodate these factors, the structural material should have high strength, adequate modulus, and resistance to buckling. Either a continuous glass filament wound epoxy plastic or a high temperature metal (steel, titanium, or aluminum) case serves as the exterior structural member. Material requirements become more demanding as the gases move into the aft bulkhead section of the nozzle. Increased material rigidity, resistance to erosion and thermal insulations is required. Some degree of surface recession is permitted, since its influence on thrust is small. The aft bulkhead insulator is usually composed of a material similar to that employed in the case sidewall. Both elastomer-modificd TS resins and heavily loaded rubber compositors have been employed with success.

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The divergent entrance cone of the nozzle must exhibit even greater erosion resistance because it is redirecting the propellant gases at a relatively steep angle. Refractories like metals, ceramics, and graphites are unsuitable for use in this section because of certain property limitations, and the configuration and size of the part. Instead, ablative plastic composites, which form a surface char and possibly a viscous melt during heating , appear to be optimum. They are composed of either phenolic or epoxy resins reinforced with fibers or fibrous constructions of asbestos, glass, silica, quartz, carbon, or graphite. The latter material in the form of a woven fabric or tape impregnated with phenolic resin has shown exceptionally good performance. Undoubtedly, the most critical materials requirements are those of the nozzle throat. Its configuration and dimensions must remain essentially unchanged throughout motor firing to insure constant chamber pressure and thrust conditions. Small diameter (5 in. or less) throats generally require the use of steel, molybdenum, tungsten, a high density graphite wit or without an oxide coating, a metal carbide, a highly crystalline pyrolytic graphite, or a metal infiltrated porous refractory. Nozzle throat inserts of molybdenum and steel are most frequently used for short duration firings, while bulk graphite is much better for longer duration operations. When it is critical to maintain throat dimensions, a metal (like silver) infiltrated porous refractory (such as tungsten) is employed. M1 of these materials are heavy, however, and they possess certain other limitations. Molybdenum and tungsten are inherently brittle below their ductile-to-brittle transition temperatures. Graphites and carbides are brittle because their crystallographic structures preclude plastic flow at low temperatures. Moreover, the carbides are sensitive to thermal shock. The use of thermally conductive throat materials necessitates the addition of an insulative backup material. An example of this type of construction is a phenolic-asbestos fiber (PSI 150 type; R-M) insulator molded around a graphite throat insert. The insulator should have a high thermal stability, little or no gasification at temperature, high strength, medium to low density, high heat capacity, and moderate thermal conductivity. Asbestos and silica fiber reinforced phenolics have many of these attributes, and thus have been used in virtually every application. Resin gasification at high temperatures presents a potential problem, and when encountered, a thin layer of fibrous oxide insulation is placed between the throat and the backup material. Ablative plastics are also used in the throat region of solid propellant motors when the firing duration is short, the chamber pressure is relatively low, or the throat diameter is quite large.

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Ablative plastics are also employed in the divergent exit cone region. The material adjacent to the throat insert must have a high erosion resistance. It is therefore composed of graphite or carbon fabric reinforced phenolic resin backed up with an insulative phenolic-silica fabric laminate. The exit cone is usually prepared by a tape wrapping operation. Reinforcing fibers are oriented normal to the nozzle centerline or canted downstream (shingle lay-up). In the smaller nozzles, compression molded parts are generally adequate. Diced fabric (one-half inch impregnated fabric squares) or chopped fibers are compacted by means of match metal molding, autoclaving, or hydroclaving. Since the thermal severity of the exhaust stream decreases with distance from the nozzle throat, ablative materials having a good balance of insulative and erosion characteristics are employed. These materials are of a phenolic resin composition with silica, glass, or asbestos fibrous reinforcements. The fabrication process used is identical to that previously noted for the forward exit cone section, but in some cases, may involve, a filament wound plastic (Chapter 5). Jet vanes and tabs are sometimes employed in solid rocketry for thrust vector control. They are normally located behind the nozzle and protrude into the exhaust stream. Their basic purpose is to provide directional control at low missile speeds following launch, and at very high altitudes where air vanes become less effective. They offer the advantages of being reliable, simple in design, low in cost, and produce less than 1% thrust loss. Since the jet vanes and tabs are subjected to highly erosive environmental conditions, their service lives are generally short. Nevertheless, RPs have been found suitable for use in certain solid propellant motors. For other designs, alloys of tungsten and molybdenum are more promising. Structural parts and control accessories in the aft region of a solid propellant motor may be overheated by thermal radiation from the exhaust gases and nozzle, recirculation of the combustion products, and after burning of the fuel rich gases. This basic heating problem was solved by the use of heat barriers in the aft end of the motor. They are generally constructed of a rigid plastic sandwich material overcoated with a metallic reflective film or an elastomeric coating. Heat barriers in the region of movable or gimballed nozzles require both flexibility and thermal protection, and for these areas, asbestos blankets coated with an elastomeric material have proven to be adequate. In addition to the ablative materials employed in the primary propulsion systems, specialty purpose ablators are also required in the launching area of rocket motors. During ignition and takeoff of the solid propelled vehicle, the launch equipment may be immersed in the

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exhaust plume for up to 5 s. Severe damage by heat and blast may result unless suitable thermal protection is afforded to the exposed areas. A number of ablative elastomeric coatings have been developed which exhibit a high degree of transient thermal protection, good adhesive properties, permanence characteristics, and case of application. Millions of dollars of cables, hoses, umbilical cords, piping, electronic equipment, etc., have been saved from destruction by use of these coatings.