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Composites news
news Still selling w e l l With an estimated 910 000 tonnes of reinforced plastics being used during its course, 1978 was another record year for the US rp industry, and the prospect for this year is a growth of 6.7% to just over 970 000 tonnes. These were the encouraging statistics presented by T. Richard Evans, General Chairman of the SPI Reinforced Plastics/Composites Institute at the opening of the Institute's 34th annual conference in New Orleans in February. Perhaps not surprisingly land transportation was the industry's biggest market in 1978, with some 241 000 tonnes being consumed. However, all nine of the market areas surveyed by the Insitute showed gains - see Table 1. Reinforced thermosets continue to dominate the overall market in the USA, although there are signs that reinforced thermoplastics are being increasingly used. Of the new developments reported in Evan's report, perhaps one ofthe most interesting was that of the HIMAT
Table 1.
Cutting cutter costs An extensive cost evaluation exercise by a manufacturer of grp components has indicated "a convincing a d v a n t a g e " of p o l y c r y s t a l l i n e diamond tools over those employing carbide tips. The basis of the cornparisonwastheturningof2rnmthick discs consisting of glass fibrereinforced epoxy resin with a glass content of 60% by weight. The discs, which had previously been cut from rod by a bandsaw, were reduced in diameter from 262 mm to 256 mm in
Shipments of reinforced plastics by markets in the USA*
Market Aircraft/aerospace Appliance and equipment Construction Consumer products Corrosion-resistant products Electrical rods, tubes, parts Marine and marine accessories Land transportation Other
Totals
research aircraft manufactured by Rockwell, in which some 29% of the structural weight is attributable to composites, a major proportion of which is graphite-reinforced plastics, On a more commercial level, Boeing is now specifying glass reinforced epoxy/honeycomb core panels for the flooring in its 727, 737 and 747 models in place of the balsa wood/aluminium previously used. Significant weight savings and increased service life have resulted,
Shipments (tonnes x 103) 1977" 1978'* 1979"** 9.53 50.8 130 48.6 87.1 66.7 181 216 31.8 821.53
9.98 55.8 147 52.6 98.0 77.1 195 241 33.6 910.08
10.4 59.0 155 56.7 106 81.7 205 263 34.9 971.9
* Source: SPI Reinforced Plastics/Compositeslnstitute-figures have been converted by Composites ** Estimate *** Forecast
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stacks of 15 giving a total turning length of 32 ram, including an approach and overrun of I mm each. The tests were carried out in Germany using a lathe fitted first with a fine grade, 180° Syndite polycrystalline diamond tool and then with a conventionally used KO5 carbide tool, both tools having identical tip geometry. In each case machining was carried out dry using an appropriate dust extraction system. Using the Syndite tool with a chuck speed of 530 rev/min, a cutting rate of 426 m/min, a feed of 0.12 mm/rev and a cutting depthofapproximately3mm, the stack of15 discs was machined to the final size in 16 seconds. Since, under these conditions the carbide tool became dull after a turning distance of only 5 mm and exhibited a wear band 0.5 mm wide after 15mm, chuckspeedhadtobereducedto47.5 rev/min giving a cutting speed of 38 m/ram. Feed rate, however, was increased to 0.22 mm/revand cutting depth maintained at approximately3 mm. As a result, the machining time in the case of the carbide tool was found to be 98 seconds, giving a time saving of more than 80% for the Syndite tool. Since it was found that the Syndite tool could machine 8 000 discs (ie 533 stacks) before resharpening became necessary, a total saving of 725 minutes could be achieved between tool changes. It was calculated that on the basis of the manufacturer's production costs of, say, 1l p per minute in this particular operation, the time saving of 725 minutes per 8 000 batch realised a saving of around £80, which, coupled with the tool cost saving of more than £3 per batch netted a total in excess of £83 saved per 8 000 parts.
De Beers Industrial Diamond Division (Pty) Ltd, Charters, Sunninghill, Ascot, Berks SL5 9PX, England.
COMPOSITES. JULY 1979
lnews Safe a n d s o u n d Designed for use
in
chemically
aggressive atmospheres or soil conditions, a new range of grp conduit systems has been launched by Ciba-Geigy Plastics Division (Fig. 1). The new conduit, which is sold in sizes upto 152 mm diameter, is manufactured by the company in the USA using the filament winding process. An Araldite thermosetting epoxy resin is used, and the conduit is said to have high flexural and compressive strengths with good electrical properties. Of particular interest is the material's resistance to environmental attack such as salts, acid soils and corrosive atmospheres. It is thought that this good resitance to
i i !
I
I
Fig. 1 Underground installation of a power cableusing Ciba-Geigy's new lightweight grp conduit
predominantly saline.
Formed in 1975 to serve the growing glass-reinforced cement industry, the Glass Reinforced Cement Association (GRCA) now has over 80 members throughout the world, representing manufacturers, material and equipment suppliers and research establishments. However, aware of
V i s c o u s resins no problem
New developments in mouldability, handling and rapid air release have been incorporated in Deltamat, a new csm from Fibreglass Limited. A fastdissolving binder is used, with a new size system, to enable an extended rate of wet-out to be used; strand integrity isretained during impregnation and consolidation, when more than one layer is being consolidated. Deltamat is designed to ensure that airwill not betrapped in the laminate: this open construction also allows high viscosity resins such as epoxy and some fire-retardant grades of polyester to be used without significant problems of void formation,
Fibreglass Limited, StHelens, Merseyside, WAlO3TR, England.
COMPOSITES. JULY 1979
laminate. They are said to be suitable for use in all road and marine transport applications, in fact.
BP Chemicals Limited, Devonshire House, Mayfair Place, Piccadilly, London WlX6AY, England. Check the levels
I
aggressive environmental conditions will make the pipes particularly suitable in the Persian G u l f - an increasingly important market area for such products-whereothe ground water is
Ciba-Geigy, Plastics Division, Duxford, Cambridge, CB2 4QA, England.
panels, which are used in the construction of commercial vehicle bodies and 150 shipping containers, are made with BP Chemicals' CelIobond polyester resins in a sandwich
Grc - j o i n in
the need to operate from as broad a base as possible the Association is currently mounting a recruiting campaign; interested prospective members are asked to contact the Secretarial office for further details,
GRCA, Farthings End, Dukes Ride, Gerrards Cross, Bucks, SL9 7LD, England. Well d o n e Recognizing the success of Glasonit grp panels, BP Chemicals has awarded a Certificate of Excellence to the manufacturers, Technical Panel Industries Limited. The Glasonit
Advice on the protection of workers against the risks of carbon dust was published in January, for the first time in a new Guidance note* from the Health and Safety Executive. The note underlines the employer's responsibility to protect workers against dust and points out that dust emissions should be prevented by the enclosure of processes or, when emissions cannot be prevented, exhaust appliances should be installed and protective equipment used. Carbon is used in various forms in a wide range of industrial applications, including of course carbon fibre for reinforcement. According to the Note, there does not appear as yet to have been an adequate study of workers exposed to carbon fibre to enable any possible hazards to be evaluated. However, it doesstatethat mild skin irritation has occurred, especially amongst those working with the fibre for the first time. Irritation to the upper respiratory tract "is possible" says the Note, although it is suggested that only a small proportion might be expected to penetrate deep into the lungs, given the narrow range of diameter of most fibres used (a mean o f a b o u t 8 - 9 / J m ) . T h e s e *'Carbon dust: health and safety precautions'. GuidanceNote EH 21, (HMSO) price 30p plus postage
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newsl factors mean that the recommended nuisance dust Threshold Limit Value (TLV) of 10 mg/m a continues to be recommended for carbon fibre. An additional problem with carbon is its electrical conductivity, and the Note makes the point that electrical equipment should preferably not be located where carbon particles, fibres, dusts, etc, may be present. Where this is not reasonably practicable, electrical equipment should, it suggests, be suitably constructed in view of the possible exposure to contamination. Full details of the safety precautions and recommended TLV's for the other various forms of carbon - mineral or natural graphite, synthetic graphite, carbon black and activated carbon - are all covered in the Note, including a summary and statutory requirements. S a n d w i c h keeps it cool Insulation values better than those required by new Building Regulations in the UK are the main features
Resin injection moulding is used to manufacture the two halves of a grp lifeboat at the Ljungbyfactory of Bofors Plastics in Sweden. The resin injection equipment and moulds were supplied by J. Coudenhove who believe that this is one of the first such large components in the boat-building industry being produced by the resin injection technique. Polyester resin is used, with a combination of mat and cloth glass reinforcement; overall weight of the finished boat is 32 kg. J. Coudenhove GmbH, Probst-Peitlstrasse 60, A-2103 Langenzersdorf, Austria.
Fig. 2 TheseUniahield metal/foam sandwich profile panelsall havegood thermal insulation properties
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of a new range of metal/foam/metal sandwich panels from Cape Universal Claddings. Marketed under the brand name Unishield, the panels are available in three profile shapes (see Fig. 2), each profile being marketed as a complete system including flashings, fittings and translucent lights, Cape Universal Claddings has invested some £500 000 in a new plant, to enable it to increase the metal rolling capacity and provide the
thickness of 33 mm. It isthisthickness of foam that gives the panels a thermal transmittance value of better than 0.6 W/m = °C. Already successfully used, during developmenttrials, in a number of food processing factories, bottling plants, cold-stores and air-conditioning plant rooms, the Unishield panels are expected to find uses in the construction of factories, schools, etc, aswellasrefurbishment of existing buildings.
means for rapid production of the metal/foam sandwich. Polyisocyanurate foam is used, to a minimum
Cape Universal Claddings Limited, PO Box 165, Tolpits, Wafford, Herts WDI 8QZ, England.
COMPOSITES. JU LY 1979
Ie=mcm
lnews the following headings: research and development; design or creative innovation; manufacturing achievement; general contribution. Full details are available from: The Secretary, GRCA, Farthings End, Dukes Ride, Gerrards Cross, Bucks, SL9 7LD, England. Spring cleaning Glass-reinforced Maranyl - ICl's nylon- is used to make a new tool for removing valve springs from overhead valve engines (Fig. 4). Using the reinforced plastic has provided many advantages over conventional, metal 'G-clamp' devices, not the least of which is the elimination of the risk of injured knuckles. Other benefits
Fig. 3
Pultruded sections and profiles in grp and cfrp are now available in an increased range of
shapesand sizesfrom Fothergill &Harvey More choice Additional equipment to produce a wider variety of puItruded sections
ing cycle. This in turn gives a highstrength product with good d/mens/anal and structural consistency.
and profiles for applications in the electrical, chemical, building, sports goods and other industries has recently been installed by the Composites Division of Fothergill and Harvey at their Littleborough plant. This means that designers can now specify glass- or carbon-reinforced sections and profiles in lengths up to 6 m with profile cross sections up to 150 mm x 100 mm. Solid sections can be round, half-round, square or rectangular: profiles can be strips, angles, round channel, square channel, round tube or square tube (see Fig. 3).
Fothergi//&HarveyLimited, Summi¢ Litt/eborough, Lancs OL 15 9QP, Eng/and. The International grc congress in October of this year has been chosen by the Glassfibre Reinforced Cement Association as the time at which its GRCAAwardwill be presentedforthe first time. The Award, which will be produced for the GRCA by Pilkington Brothers Limited, will be given to one individual, chosen by a panel of judges appointed by the GRCA Council.
The new manufacturing equipment has been specially designed by Fothergill and Harvey engineers and incorporates features to ensure that the reinforcing fibres are correctly positioned and maintained at a specified tension throughout the cur-
Nominations have been requested forpersonsfromanypartoftheworld - not necessarily members of the GRCA - who are considered to have made "an outstanding contribution" to the grc industry since the farinat/on of the Association in 1975, under
COMPOSITES. JULY 1979
Award-winning possibilities
include light weight, ease of handling and storage and the fact that its design means that little effort is needed to operate the tool. Designed by GKL Special Tools Limited in conjunction with the moulders, Wragby Plastics Limited, the new tool is expected to find a ready market world-wide. Some 50 000 have already been delivered for distribution over the next 12 months.
/C/P/astics Division, We/wyn Garden City, Hens. AL7 1HD, Eng/and.
Fig. 4 Injured knuckles may be s thing o f the
pest if this n e w tool from GKL Special Toolsis u=~dtoremovethe valve=pHngsfrom y o u r c a r engine
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news Grp going up Although the use of grp for cladding panels - - and other applications in the building industry ~ is no longer a, novelty, it is interesting to note the variety of designs and finishes that are used. Four recent uses of grp are highlighted on these two pages,///ustrating the way in which the mater/a/ can be made to blend in with "traditiona/" building materials such as brick and concrete.
The buildings shown on this page both use Parkstone grp cladding panels, manufactured by Parkstone Plastics in Poole, Dorset. That on the right is one of several new extensions at Fisons' Agrochemical Division Research Station near Saffron Walden. The grp panels are supplied in three basic shapes (for the general exterior elevation, as wholly radiused corner sections and as coping sections on the roof). The general clad-
....... ...... .....
/ fi f}
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!!iiiiii~'
ding panels are attached to battens themselves fixed to concrete wall panels: installation of the grp was thus rapid and achieved with the minimum of site involvement. The building, illustrated left, is a recent extension to Hardye's School in Dorchester; it links the original stone mullion school building to three other new extensions. In this case Parkstone grp panels with an aggregate finish were used, between the red brick structure, to create an overall effect similar to that of the original building. The panels were delivered to the site ready for face fixing to stud work around the windows and along the brick facings. As with Fisons' building, site involvement was minimized, allowing similarly rapid installation of the panels.
COMPOSITES. JULY 1979
news
I
Nil,,., , C O M P O S I T E S . JU L Y 1979
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news, Safety overhead Following fatigue and electrical tracking t e s t s w h i c h i n d i c a t e d a maintenance-free life of at least 20 years, more than 7000 grp insulators for the 1500 V DC overhead-line equipment (for the Tyne and Wear Metro) have been delivered to the Tyne and Wear Passenger Transport Executive in the north of England by manufacturers R.P. Mouldings. It is believed that this is the first largescale use of the new glass-reinforced epoxy insulators in the UK. Several times lighter than conventional ceramic types, the grp insulators have proved particularly easy to handle and install, having a high tolerance to damage. An inner glass/epoxy rod (see Fig. 5) provides the mechanical strength of the insulator system; a shrunk-on sleeve and skirts of HV (high voltage) polymer (a highly modified silicone rubber) provide long term resistance to surface tracking. The new insulators are suitable for any overhead system of railway electrification, including 50 kV AC. Other versions are available for overhead power transmission lines energised at up to 145 kV; these are under evaluation in the UK at present, R.P. Mouldings, NEI Electronics Ltd, Queensway, Team Valley Trading Estate, Gateshead, Tyne and Wear, N E l l OQU, England.
All-round improvements Refinement and redesign of the BP13s-D electric motor has enabled GEC Machines to make good use of Kelanex glass-reinforced polyester in the insulation system. The new version, called the BP13K, has greatly improvedinsulationbymeansofthe in situ moulded system that has obviated the need for PET film slot liners,
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Fig. 5 Pultrudedglan/epoxy rodsprovidethe mechanicalstrengthfor a newwetem of insuletors for overhead power lines; end fitrnen~ are metal
The new form slot insulation (ie the barrier insulating the windings from the iron core) is insert-moulded in Kelanex 330, a 30% glass-reinforced grade of the thermoplastic polyester from Amcel. Eliminating the separate PET film liners has enabled GEC Machines to reduce overall assembly costs for the new motor; other cost reductions have been possible with the use of less copper wire for winding around the pole pieces, AmcelLimited, 78/80StAIbansRoad, Watford, Herts, England.
Taking over Terms for offers made by BP Capitala subsidiary of BP Company Ltd - for the whole of the issued share capital of Bristol Composite Materials were agreedatthebegirmingofthisyear between the Boards of the two companies. In taking over BCM, BP Capi-
tal will be in a position to providethe support necessary for BCM to continue with its work on the development of composite materials technology and the use of high performance composites in areas such as the aircraft and automobile industries. Feeling fresh Already established in a number of industries where dust and fumes are a problem, the Airstream anti-dust helmet from Racal Safety is now in use in the finishing shop at Lotus Cars. It has been found that the Airstream helmet provides adequate and comfortable- relief from the fine dust produced as the grp body shells and mouldings are cut and trimmed to shape.
Racal Safety Limited, 21 Market Place, Wokingham, Berkshire, RG 11 1AJ, England.
COMPOSITES. JU LY 1978
lnewsl Preview The following is a preview of some forthcoming events, arranged in chronological order. Further details can be obtained from the address given at the end of each item. A comprehensive list of future meetings relating to composite matedals can be found in the Calendar.
...........
The use of plastics in household appliances is the title of a one-day conference being organised by the Processing and Engineering Group of the Plastics and Rubber Institute. The meeting will be held in London on 15 November; and will be specifically aimed at industrial designers, materials suppliers and engineers in the household appliances industry. Speakers will represent designers, materials specifiers, consumer and standards organisations, and manufacturers, Full details are available from: Trish Durston, PRI, 11 Hobart Place, London, SWIW OHL, England. New Orleans will again be the venue for the SPI Reinforced Plastics/Composites Institute's annual conference the 35th in the series - in 1980: dates for the meeting are 4-8 February. The organisers are challenging potential speakers to broaden the scope of the meeting to include specific details on how reinforced plastics are helping to solve problems such as energy conservation, materials management, environmental improvement, waste reduction, inflation control and meeting new statutory regulations. In addition to papers on n e w p r o d u c t s and developments in the reinforced plastics industry's major markets (ie automotive, marine, construction, corrosion-resistant products, appliances and business equipment,
oo ,
1 ~
Passengers in the Arabian Gulf will find themselves travelling in this Leyland Vehicles double-decker bus as it undergoes performance trials in Kuwait for three months. The bus is in fact a specially adapted left-hand drive version of the type already familiar to British travellers. A particular feature of its construction is the use of BP Chemicals" Cellobond Polyester resin, reinforced with glass fibre, for the roof and body corner panels. ~ii~
-
COMPOSITES . JULY 1979
One of 19 tanks fabricated by Kenneth Forbes (Plastics) Limited being loaded for delivery to the Marchon Division of Albright and Wilson Limited. The vesselsareall4m in diameter, a n d f r o m 6 - - 9 m h i g h , andwillbeusedtostore concentrated phosphoric acid in organic solution at temperatures of up to 100°C.British Celanese Celmar polypropylene /glass fabric laminate was used throughout to build the tanks. British Celanese Limited, 22 Hanover Square, London, WIA 1 BS, England.
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news, electrical, consumer and aerospace), contributions demonstrating the benefits of composites in the areas outlined above will be particularly welcomed. RP/C Conference Management, SPI Inc, 355 Lexington Avenue, New York, NY 10017, USA.
Plastics in the automobile industry is the overall theme of a two-day conference being planned by the Processing and Engineering Group of the Plastics and Rubber Institute for mid-1980: finaldatesandvenuetobe confirmed. The following main areas will be covered in the meeting; Moti-
Concrete International 1980 (CI "80) is the title of a major international conference being organised by the Concrete Society. The meeting will be held in London on 13-18 April 1980
vation and restraints (eg market pressures, new legislation, safety regulations); design (including design data and stress analysis); materials (including smc, RIM, pp and variations and composites); components; and finishing,
and will cover four main topics: lightweight concrete; admixtures; sprayed concrete; and fibrous concretes. The programme has been arranged to incorporate two 2-day congresses on lightweight concrete and admixtures, and two 1-day symposia on sprayed concrete and fibrous concretes. An exhibition of related plant, materials and equipment will be held in conjunction with the conference sessions. Technical visits to sites and factories in Southern England have also been planned, Fulldetailsareavailablefrom:Gerald Young, CI 80, The Concrete Society, TerminalHouse, GrosvenorGardens, London, SWlW OAJ, England.
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Full details can be obtained from: Trish Durston, Plastics and Rubber Institute, 11 Hobart Place, London, SWlWOHL, England.
Further details have been made available of ICCM-3, being held in Paris on26-29August 1980. Particular emphasisistobeplacedonthetransfer of composite technology from the high performance aerospace industry '¢o more general engineering fields. The conference will consist of presentations of plenary and contributed research and technical papers, and workshops to encourage the exchange of information between
research workers and industry. The call for papers is still open (see Composites, April 1979, p 58) and authorsare now asked to submit abstracts to: Dr A.R. Bunsell, Ecole des Mines de Paris, Centre des Mat~riaux, BP 87, 91003 Evry Cedex, France; or, for US authors, to: Mr Bryan Noton, Structure and Mechnics Department, Battelle ~ Columbus Laboratories,
Columbus, Ohio 43201, USA. Adhesion and adhesives: science, technologyandapplicationsisthetitle of a 3-day conference being planned by the Polymer Properties Group of thePRI, tobeheldattheUniversityof Durham on 3-5 September1980. The following main subject areas have been chosen: Surface chemistry; Durability and fatigue; Stress analysis and joint design; Fracture; Non-destructivetesting; Elastomeric adhesion; Interfaces in composites; and New adhesive materials. A call for papers within any of the above areas has been issued, and prospective authors are asked to submit short abstracts (100-200 words) by 30th September (1979) to: Mrs Sheila Serjeant, PRI, 11 Hobart Place,London, SW1W OHL, England.
COMPOSITES • JULY 1979
news In t e u c h w i t h T e c h A l e r t
ing procedures, mechanical and
Over 50 000 reports of publically-funded research projects are received annually by the Technology Reports Centre in the UK; the majority come from the USA, although the network is worldwide. These reports generally remain unpublished, or are difficult to obtain from source. Summaries of reports likely to be of interest to readers of Composites are now regularly prepared by the CentreandwillbeincludedintheNewsSectionineachissue. Fullcopiesofthe original reports are available from: TechAlert, Technology Reports Centre, Orpington, Kent, SR5 3RF. The title and reference number given at the end of each item should be quoted with all orders,
UV-curable resins Some resin systems now used in the
face preparation material,
US for field repairs to composites in aircraft suffer from the disadvantages of high cure temperature and long cure times. Resin systems that can be cured by ultraviolet radiation thus offer particular advantages for this application, and a report from the US Naval Air Development Center describes tests indicating that repairs to damaged composites can be made safely, quickly and easily using
Further information is contained in the 15-page report "The application of ultraviolet cure resins for repair of composites" by H.D. Gillman and J.L. Eichelberger. reference AD-A055 731, available as microfiche (£1.19) (inc VAT) or reproduced paper-copy (£1.50).
selected resins of this type. Sixteen commercially available UV-curable resin systems were tested: they were used to repair a graphite/epoxy composite cornmonly used in US naval aircraft, Damage in the composite was simulated by machining a 'V' groove to a depth of about one third of the laminate thickness. Different repair methods and five types of ultraviolet light source were investigated, Although the best repair achieved gave only 76 per cent of the flexural strength of the undamaged laminate, stronger repairs are thought to be possible: however, no attempt was made to optimize repair procedures to maximize repaired strength. It is thought likelythatimprovedstrength could be secured with, for example, changes in the resin system, cure time, light intensity, wavelength, sur-
Although several adhesives for bonding high temperature composites have been available for some time, either commercially or experimentally, most of these suffer from deficiencies such as long and involved processing cycles, brittleness and poor crack resistance, or severely reduced bond strength after prolongedexposuretohightemperatures. However, under a recent NASA c o n t r a c t , an a l u m i n i u m - f i l l e d polyimide resin adhesive has been developed which has the potential to eliminate many of these problems, It is easier to process than other aromatic polyimide adhesives, and should have applications for bonding both metal and composite components exposed to harsh environments for prolonged periods at temperatures of at least 300°C. Details of the curing process, bond-
COMPOSITES . JULY 1979
and
reinforcing
Bondinghigh temperature cornposites
environmental tests, and the characteristics of the new adhesive that requires further investigation, are contained in a report from NASA.
The adhesive consists of a 1:~:¼ mole ratio of 2,2 bis (3', 4', dicarboxyphenyl) hexafluoropropane; parahenylenediamine; oxydianiline, 48 percent by weight cured resin solids in diglyme, containing 65 percent aluminium powder based on total cured solids. The adhesive is said to have excellent resistance to the following environments: 500 hours in air at 316°C; 35 days in 95 percent RH at 49°C; 34 days immersed in jet fuel at room temperature; and 34 days immersed in methyl ethyl ketone at room temperature. Its excellent toughness and stability were demonstrated by performing a wedge-type crack propagation test at 316°C on 3.175 mm thick unidirectional graphite fibre-reinforced polyimide samples. A bond strength of 23.44 MN/m =was recorded for lap shear samples prepared from graphite fibre/polyimide matrix adherends at room temperature, with a value of 15.51 MN/m 2at 360°C. Both values arehigherthanNASA'soriginal targets. The adhesive is also capable of producing wide area bonds having acceptable strengths. However, these were achieved by using abnormally long cure cycles in order to allow diffusion of the volatiles out of the bond line; and the bond lines were not free from voids. Areas for further investigation recommended by the report include: methods for improving the adhesive prepreg toughness; the application ofathinner, more highly cured primer by spraying to achieve a more uniform coating; reduction of bond-
139
lnews ing temperatures which may result in an adhesive more suitable for bonding wide areas; the evaluation of bonds under cyclical stress tests at various temperatures, comparison of their performance with other adhesive systems; and the use of other fillers, eg glass grit, mica, alumina, as well as other metals and metal oxide powders, Further information is contained in
the125-pagereport'NR-150B2adhesive development" by P.S. Blatz, reference N78-27273, available as microfiche (£1.19, inc VAT) or reproduced paper-copy (£6.70).
Ceramic matrix composites By using either particulate or fibrous reinforcement, the advantages of ceramics (such as excellent high temperature properties, corrosion resistance and hardness) can be combined with significantly reduced brittleness- their single largest disadvantage. With this in mind, an investigation into the potential usefulness of ceramic matrix composites (CMC) in structural applications, where components must be able to withstand tensile stresses with a high reliability, was carried out in the USA
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on behalf of the US Department of Defense. Details of the study group's findings and recommendations, based on a survey of the opinions of the entire US technical ceramics community, and a workshop of scientists actively involved in CMC technology, as well as a literature survey, are contained in a report now available. In addition, areas of beneficial application are outlined, the scientific and engineering state of the art reviewed, and areas for further study noted. Almost all potential applications for (CMC: examples of which are graphite reinforced with carbides, SiC-C/Si, and non metal fibrereinforced glass) involve hightemperature and a corrosive environment, and often temperature cycling, which may have a deleterious effect on the performance of the component. Short-term applications considered by the group include: reinforced concrete structures; gas turbines where increases in inlet temperatures up to 1200°C may be feasible using silicon carbide/fibre silicon composites, thereby offering promise of increased fuel savings; and the use of ceramic fibres in
refractory linings. Potential applications in the longer term include: reinforced glass composites able to withstand temperatures above 650°C; the use of alI-CMC hot moving parts in diesel engines, thustaking advantage of the high cermic strength to weight ratios; and a ceramic heat exchanger, for a marine engine, to operate for up to 10 000 h at 1370°C, allowing the weight of the power plant to be reduced by a factor of ten. Other possible applications for CMC reviewed by the study group include ceramic gun tube inserts, nozzles for chemical laser systems, high-speed rolling and sliding bearings, seals, magnetohydrodynamic generator components, dental and orthopaedic implants, and roads and runways. The report also briefly reviews the technology of ceramic materials for the non-specialist reader. Further information is contained in the 175-page report "Assessment of
ceramic-matrix composite technology and potential DoD application by J.E. Hove and H.M. Davis, reference AD-A054017, available as microfiche (£1.19, inc VAT) or reproduced paper-copy (£9.30).
COMPOSITES. JULY 1979
Table 1.
Cutting cutter costs An extensive cost evaluation exercise by a manufacturer of grp components has indicated "a convincing a d v a n t a g e " of p o l y c r y s t a l l i n e diamond tools over those employing carbide tips. The basis of the cornparisonwastheturningof2rnmthick discs consisting of glass fibrereinforced epoxy resin with a glass content of 60% by weight. The discs, which had previously been cut from rod by a bandsaw, were reduced in diameter from 262 mm to 256 mm in
Shipments of reinforced plastics by markets in the USA*
Market Aircraft/aerospace Appliance and equipment Construction Consumer products Corrosion-resistant products Electrical rods, tubes, parts Marine and marine accessories Land transportation Other
Totals
research aircraft manufactured by Rockwell, in which some 29% of the structural weight is attributable to composites, a major proportion of which is graphite-reinforced plastics, On a more commercial level, Boeing is now specifying glass reinforced epoxy/honeycomb core panels for the flooring in its 727, 737 and 747 models in place of the balsa wood/aluminium previously used. Significant weight savings and increased service life have resulted,
Shipments (tonnes x 103) 1977" 1978'* 1979"** 9.53 50.8 130 48.6 87.1 66.7 181 216 31.8 821.53
9.98 55.8 147 52.6 98.0 77.1 195 241 33.6 910.08
10.4 59.0 155 56.7 106 81.7 205 263 34.9 971.9
* Source: SPI Reinforced Plastics/Compositeslnstitute-figures have been converted by Composites ** Estimate *** Forecast
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stacks of 15 giving a total turning length of 32 ram, including an approach and overrun of I mm each. The tests were carried out in Germany using a lathe fitted first with a fine grade, 180° Syndite polycrystalline diamond tool and then with a conventionally used KO5 carbide tool, both tools having identical tip geometry. In each case machining was carried out dry using an appropriate dust extraction system. Using the Syndite tool with a chuck speed of 530 rev/min, a cutting rate of 426 m/min, a feed of 0.12 mm/rev and a cutting depthofapproximately3mm, the stack of15 discs was machined to the final size in 16 seconds. Since, under these conditions the carbide tool became dull after a turning distance of only 5 mm and exhibited a wear band 0.5 mm wide after 15mm, chuckspeedhadtobereducedto47.5 rev/min giving a cutting speed of 38 m/ram. Feed rate, however, was increased to 0.22 mm/revand cutting depth maintained at approximately3 mm. As a result, the machining time in the case of the carbide tool was found to be 98 seconds, giving a time saving of more than 80% for the Syndite tool. Since it was found that the Syndite tool could machine 8 000 discs (ie 533 stacks) before resharpening became necessary, a total saving of 725 minutes could be achieved between tool changes. It was calculated that on the basis of the manufacturer's production costs of, say, 1l p per minute in this particular operation, the time saving of 725 minutes per 8 000 batch realised a saving of around £80, which, coupled with the tool cost saving of more than £3 per batch netted a total in excess of £83 saved per 8 000 parts.
De Beers Industrial Diamond Division (Pty) Ltd, Charters, Sunninghill, Ascot, Berks SL5 9PX, England.
COMPOSITES. JULY 1979
lnews Safe a n d s o u n d Designed for use
in
chemically
aggressive atmospheres or soil conditions, a new range of grp conduit systems has been launched by Ciba-Geigy Plastics Division (Fig. 1). The new conduit, which is sold in sizes upto 152 mm diameter, is manufactured by the company in the USA using the filament winding process. An Araldite thermosetting epoxy resin is used, and the conduit is said to have high flexural and compressive strengths with good electrical properties. Of particular interest is the material's resistance to environmental attack such as salts, acid soils and corrosive atmospheres. It is thought that this good resitance to
i i !
I
I
Fig. 1 Underground installation of a power cableusing Ciba-Geigy's new lightweight grp conduit
predominantly saline.
Formed in 1975 to serve the growing glass-reinforced cement industry, the Glass Reinforced Cement Association (GRCA) now has over 80 members throughout the world, representing manufacturers, material and equipment suppliers and research establishments. However, aware of
V i s c o u s resins no problem
New developments in mouldability, handling and rapid air release have been incorporated in Deltamat, a new csm from Fibreglass Limited. A fastdissolving binder is used, with a new size system, to enable an extended rate of wet-out to be used; strand integrity isretained during impregnation and consolidation, when more than one layer is being consolidated. Deltamat is designed to ensure that airwill not betrapped in the laminate: this open construction also allows high viscosity resins such as epoxy and some fire-retardant grades of polyester to be used without significant problems of void formation,
Fibreglass Limited, StHelens, Merseyside, WAlO3TR, England.
COMPOSITES. JULY 1979
laminate. They are said to be suitable for use in all road and marine transport applications, in fact.
BP Chemicals Limited, Devonshire House, Mayfair Place, Piccadilly, London WlX6AY, England. Check the levels
I
aggressive environmental conditions will make the pipes particularly suitable in the Persian G u l f - an increasingly important market area for such products-whereothe ground water is
Ciba-Geigy, Plastics Division, Duxford, Cambridge, CB2 4QA, England.
panels, which are used in the construction of commercial vehicle bodies and 150 shipping containers, are made with BP Chemicals' CelIobond polyester resins in a sandwich
Grc - j o i n in
the need to operate from as broad a base as possible the Association is currently mounting a recruiting campaign; interested prospective members are asked to contact the Secretarial office for further details,
GRCA, Farthings End, Dukes Ride, Gerrards Cross, Bucks, SL9 7LD, England. Well d o n e Recognizing the success of Glasonit grp panels, BP Chemicals has awarded a Certificate of Excellence to the manufacturers, Technical Panel Industries Limited. The Glasonit
Advice on the protection of workers against the risks of carbon dust was published in January, for the first time in a new Guidance note* from the Health and Safety Executive. The note underlines the employer's responsibility to protect workers against dust and points out that dust emissions should be prevented by the enclosure of processes or, when emissions cannot be prevented, exhaust appliances should be installed and protective equipment used. Carbon is used in various forms in a wide range of industrial applications, including of course carbon fibre for reinforcement. According to the Note, there does not appear as yet to have been an adequate study of workers exposed to carbon fibre to enable any possible hazards to be evaluated. However, it doesstatethat mild skin irritation has occurred, especially amongst those working with the fibre for the first time. Irritation to the upper respiratory tract "is possible" says the Note, although it is suggested that only a small proportion might be expected to penetrate deep into the lungs, given the narrow range of diameter of most fibres used (a mean o f a b o u t 8 - 9 / J m ) . T h e s e *'Carbon dust: health and safety precautions'. GuidanceNote EH 21, (HMSO) price 30p plus postage
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newsl factors mean that the recommended nuisance dust Threshold Limit Value (TLV) of 10 mg/m a continues to be recommended for carbon fibre. An additional problem with carbon is its electrical conductivity, and the Note makes the point that electrical equipment should preferably not be located where carbon particles, fibres, dusts, etc, may be present. Where this is not reasonably practicable, electrical equipment should, it suggests, be suitably constructed in view of the possible exposure to contamination. Full details of the safety precautions and recommended TLV's for the other various forms of carbon - mineral or natural graphite, synthetic graphite, carbon black and activated carbon - are all covered in the Note, including a summary and statutory requirements. S a n d w i c h keeps it cool Insulation values better than those required by new Building Regulations in the UK are the main features
Resin injection moulding is used to manufacture the two halves of a grp lifeboat at the Ljungbyfactory of Bofors Plastics in Sweden. The resin injection equipment and moulds were supplied by J. Coudenhove who believe that this is one of the first such large components in the boat-building industry being produced by the resin injection technique. Polyester resin is used, with a combination of mat and cloth glass reinforcement; overall weight of the finished boat is 32 kg. J. Coudenhove GmbH, Probst-Peitlstrasse 60, A-2103 Langenzersdorf, Austria.
Fig. 2 TheseUniahield metal/foam sandwich profile panelsall havegood thermal insulation properties
132
of a new range of metal/foam/metal sandwich panels from Cape Universal Claddings. Marketed under the brand name Unishield, the panels are available in three profile shapes (see Fig. 2), each profile being marketed as a complete system including flashings, fittings and translucent lights, Cape Universal Claddings has invested some £500 000 in a new plant, to enable it to increase the metal rolling capacity and provide the
thickness of 33 mm. It isthisthickness of foam that gives the panels a thermal transmittance value of better than 0.6 W/m = °C. Already successfully used, during developmenttrials, in a number of food processing factories, bottling plants, cold-stores and air-conditioning plant rooms, the Unishield panels are expected to find uses in the construction of factories, schools, etc, aswellasrefurbishment of existing buildings.
means for rapid production of the metal/foam sandwich. Polyisocyanurate foam is used, to a minimum
Cape Universal Claddings Limited, PO Box 165, Tolpits, Wafford, Herts WDI 8QZ, England.
COMPOSITES. JU LY 1979
Ie=mcm
lnews the following headings: research and development; design or creative innovation; manufacturing achievement; general contribution. Full details are available from: The Secretary, GRCA, Farthings End, Dukes Ride, Gerrards Cross, Bucks, SL9 7LD, England. Spring cleaning Glass-reinforced Maranyl - ICl's nylon- is used to make a new tool for removing valve springs from overhead valve engines (Fig. 4). Using the reinforced plastic has provided many advantages over conventional, metal 'G-clamp' devices, not the least of which is the elimination of the risk of injured knuckles. Other benefits
Fig. 3
Pultruded sections and profiles in grp and cfrp are now available in an increased range of
shapesand sizesfrom Fothergill &Harvey More choice Additional equipment to produce a wider variety of puItruded sections
ing cycle. This in turn gives a highstrength product with good d/mens/anal and structural consistency.
and profiles for applications in the electrical, chemical, building, sports goods and other industries has recently been installed by the Composites Division of Fothergill and Harvey at their Littleborough plant. This means that designers can now specify glass- or carbon-reinforced sections and profiles in lengths up to 6 m with profile cross sections up to 150 mm x 100 mm. Solid sections can be round, half-round, square or rectangular: profiles can be strips, angles, round channel, square channel, round tube or square tube (see Fig. 3).
Fothergi//&HarveyLimited, Summi¢ Litt/eborough, Lancs OL 15 9QP, Eng/and. The International grc congress in October of this year has been chosen by the Glassfibre Reinforced Cement Association as the time at which its GRCAAwardwill be presentedforthe first time. The Award, which will be produced for the GRCA by Pilkington Brothers Limited, will be given to one individual, chosen by a panel of judges appointed by the GRCA Council.
The new manufacturing equipment has been specially designed by Fothergill and Harvey engineers and incorporates features to ensure that the reinforcing fibres are correctly positioned and maintained at a specified tension throughout the cur-
Nominations have been requested forpersonsfromanypartoftheworld - not necessarily members of the GRCA - who are considered to have made "an outstanding contribution" to the grc industry since the farinat/on of the Association in 1975, under
COMPOSITES. JULY 1979
Award-winning possibilities
include light weight, ease of handling and storage and the fact that its design means that little effort is needed to operate the tool. Designed by GKL Special Tools Limited in conjunction with the moulders, Wragby Plastics Limited, the new tool is expected to find a ready market world-wide. Some 50 000 have already been delivered for distribution over the next 12 months.
/C/P/astics Division, We/wyn Garden City, Hens. AL7 1HD, Eng/and.
Fig. 4 Injured knuckles may be s thing o f the
pest if this n e w tool from GKL Special Toolsis u=~dtoremovethe valve=pHngsfrom y o u r c a r engine
133
news Grp going up Although the use of grp for cladding panels - - and other applications in the building industry ~ is no longer a, novelty, it is interesting to note the variety of designs and finishes that are used. Four recent uses of grp are highlighted on these two pages,///ustrating the way in which the mater/a/ can be made to blend in with "traditiona/" building materials such as brick and concrete.
The buildings shown on this page both use Parkstone grp cladding panels, manufactured by Parkstone Plastics in Poole, Dorset. That on the right is one of several new extensions at Fisons' Agrochemical Division Research Station near Saffron Walden. The grp panels are supplied in three basic shapes (for the general exterior elevation, as wholly radiused corner sections and as coping sections on the roof). The general clad-
....... ...... .....
/ fi f}
134
!!iiiiii~'
ding panels are attached to battens themselves fixed to concrete wall panels: installation of the grp was thus rapid and achieved with the minimum of site involvement. The building, illustrated left, is a recent extension to Hardye's School in Dorchester; it links the original stone mullion school building to three other new extensions. In this case Parkstone grp panels with an aggregate finish were used, between the red brick structure, to create an overall effect similar to that of the original building. The panels were delivered to the site ready for face fixing to stud work around the windows and along the brick facings. As with Fisons' building, site involvement was minimized, allowing similarly rapid installation of the panels.
COMPOSITES. JULY 1979
news
I
Nil,,., , C O M P O S I T E S . JU L Y 1979
135
news, Safety overhead Following fatigue and electrical tracking t e s t s w h i c h i n d i c a t e d a maintenance-free life of at least 20 years, more than 7000 grp insulators for the 1500 V DC overhead-line equipment (for the Tyne and Wear Metro) have been delivered to the Tyne and Wear Passenger Transport Executive in the north of England by manufacturers R.P. Mouldings. It is believed that this is the first largescale use of the new glass-reinforced epoxy insulators in the UK. Several times lighter than conventional ceramic types, the grp insulators have proved particularly easy to handle and install, having a high tolerance to damage. An inner glass/epoxy rod (see Fig. 5) provides the mechanical strength of the insulator system; a shrunk-on sleeve and skirts of HV (high voltage) polymer (a highly modified silicone rubber) provide long term resistance to surface tracking. The new insulators are suitable for any overhead system of railway electrification, including 50 kV AC. Other versions are available for overhead power transmission lines energised at up to 145 kV; these are under evaluation in the UK at present, R.P. Mouldings, NEI Electronics Ltd, Queensway, Team Valley Trading Estate, Gateshead, Tyne and Wear, N E l l OQU, England.
All-round improvements Refinement and redesign of the BP13s-D electric motor has enabled GEC Machines to make good use of Kelanex glass-reinforced polyester in the insulation system. The new version, called the BP13K, has greatly improvedinsulationbymeansofthe in situ moulded system that has obviated the need for PET film slot liners,
136
Fig. 5 Pultrudedglan/epoxy rodsprovidethe mechanicalstrengthfor a newwetem of insuletors for overhead power lines; end fitrnen~ are metal
The new form slot insulation (ie the barrier insulating the windings from the iron core) is insert-moulded in Kelanex 330, a 30% glass-reinforced grade of the thermoplastic polyester from Amcel. Eliminating the separate PET film liners has enabled GEC Machines to reduce overall assembly costs for the new motor; other cost reductions have been possible with the use of less copper wire for winding around the pole pieces, AmcelLimited, 78/80StAIbansRoad, Watford, Herts, England.
Taking over Terms for offers made by BP Capitala subsidiary of BP Company Ltd - for the whole of the issued share capital of Bristol Composite Materials were agreedatthebegirmingofthisyear between the Boards of the two companies. In taking over BCM, BP Capi-
tal will be in a position to providethe support necessary for BCM to continue with its work on the development of composite materials technology and the use of high performance composites in areas such as the aircraft and automobile industries. Feeling fresh Already established in a number of industries where dust and fumes are a problem, the Airstream anti-dust helmet from Racal Safety is now in use in the finishing shop at Lotus Cars. It has been found that the Airstream helmet provides adequate and comfortable- relief from the fine dust produced as the grp body shells and mouldings are cut and trimmed to shape.
Racal Safety Limited, 21 Market Place, Wokingham, Berkshire, RG 11 1AJ, England.
COMPOSITES. JU LY 1978
lnewsl Preview The following is a preview of some forthcoming events, arranged in chronological order. Further details can be obtained from the address given at the end of each item. A comprehensive list of future meetings relating to composite matedals can be found in the Calendar.
...........
The use of plastics in household appliances is the title of a one-day conference being organised by the Processing and Engineering Group of the Plastics and Rubber Institute. The meeting will be held in London on 15 November; and will be specifically aimed at industrial designers, materials suppliers and engineers in the household appliances industry. Speakers will represent designers, materials specifiers, consumer and standards organisations, and manufacturers, Full details are available from: Trish Durston, PRI, 11 Hobart Place, London, SWIW OHL, England. New Orleans will again be the venue for the SPI Reinforced Plastics/Composites Institute's annual conference the 35th in the series - in 1980: dates for the meeting are 4-8 February. The organisers are challenging potential speakers to broaden the scope of the meeting to include specific details on how reinforced plastics are helping to solve problems such as energy conservation, materials management, environmental improvement, waste reduction, inflation control and meeting new statutory regulations. In addition to papers on n e w p r o d u c t s and developments in the reinforced plastics industry's major markets (ie automotive, marine, construction, corrosion-resistant products, appliances and business equipment,
oo ,
1 ~
Passengers in the Arabian Gulf will find themselves travelling in this Leyland Vehicles double-decker bus as it undergoes performance trials in Kuwait for three months. The bus is in fact a specially adapted left-hand drive version of the type already familiar to British travellers. A particular feature of its construction is the use of BP Chemicals" Cellobond Polyester resin, reinforced with glass fibre, for the roof and body corner panels. ~ii~
-
COMPOSITES . JULY 1979
One of 19 tanks fabricated by Kenneth Forbes (Plastics) Limited being loaded for delivery to the Marchon Division of Albright and Wilson Limited. The vesselsareall4m in diameter, a n d f r o m 6 - - 9 m h i g h , andwillbeusedtostore concentrated phosphoric acid in organic solution at temperatures of up to 100°C.British Celanese Celmar polypropylene /glass fabric laminate was used throughout to build the tanks. British Celanese Limited, 22 Hanover Square, London, WIA 1 BS, England.
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news, electrical, consumer and aerospace), contributions demonstrating the benefits of composites in the areas outlined above will be particularly welcomed. RP/C Conference Management, SPI Inc, 355 Lexington Avenue, New York, NY 10017, USA.
Plastics in the automobile industry is the overall theme of a two-day conference being planned by the Processing and Engineering Group of the Plastics and Rubber Institute for mid-1980: finaldatesandvenuetobe confirmed. The following main areas will be covered in the meeting; Moti-
Concrete International 1980 (CI "80) is the title of a major international conference being organised by the Concrete Society. The meeting will be held in London on 13-18 April 1980
vation and restraints (eg market pressures, new legislation, safety regulations); design (including design data and stress analysis); materials (including smc, RIM, pp and variations and composites); components; and finishing,
and will cover four main topics: lightweight concrete; admixtures; sprayed concrete; and fibrous concretes. The programme has been arranged to incorporate two 2-day congresses on lightweight concrete and admixtures, and two 1-day symposia on sprayed concrete and fibrous concretes. An exhibition of related plant, materials and equipment will be held in conjunction with the conference sessions. Technical visits to sites and factories in Southern England have also been planned, Fulldetailsareavailablefrom:Gerald Young, CI 80, The Concrete Society, TerminalHouse, GrosvenorGardens, London, SWlW OAJ, England.
138
Full details can be obtained from: Trish Durston, Plastics and Rubber Institute, 11 Hobart Place, London, SWlWOHL, England.
Further details have been made available of ICCM-3, being held in Paris on26-29August 1980. Particular emphasisistobeplacedonthetransfer of composite technology from the high performance aerospace industry '¢o more general engineering fields. The conference will consist of presentations of plenary and contributed research and technical papers, and workshops to encourage the exchange of information between
research workers and industry. The call for papers is still open (see Composites, April 1979, p 58) and authorsare now asked to submit abstracts to: Dr A.R. Bunsell, Ecole des Mines de Paris, Centre des Mat~riaux, BP 87, 91003 Evry Cedex, France; or, for US authors, to: Mr Bryan Noton, Structure and Mechnics Department, Battelle ~ Columbus Laboratories,
Columbus, Ohio 43201, USA. Adhesion and adhesives: science, technologyandapplicationsisthetitle of a 3-day conference being planned by the Polymer Properties Group of thePRI, tobeheldattheUniversityof Durham on 3-5 September1980. The following main subject areas have been chosen: Surface chemistry; Durability and fatigue; Stress analysis and joint design; Fracture; Non-destructivetesting; Elastomeric adhesion; Interfaces in composites; and New adhesive materials. A call for papers within any of the above areas has been issued, and prospective authors are asked to submit short abstracts (100-200 words) by 30th September (1979) to: Mrs Sheila Serjeant, PRI, 11 Hobart Place,London, SW1W OHL, England.
COMPOSITES • JULY 1979
news In t e u c h w i t h T e c h A l e r t
ing procedures, mechanical and
Over 50 000 reports of publically-funded research projects are received annually by the Technology Reports Centre in the UK; the majority come from the USA, although the network is worldwide. These reports generally remain unpublished, or are difficult to obtain from source. Summaries of reports likely to be of interest to readers of Composites are now regularly prepared by the CentreandwillbeincludedintheNewsSectionineachissue. Fullcopiesofthe original reports are available from: TechAlert, Technology Reports Centre, Orpington, Kent, SR5 3RF. The title and reference number given at the end of each item should be quoted with all orders,
UV-curable resins Some resin systems now used in the
face preparation material,
US for field repairs to composites in aircraft suffer from the disadvantages of high cure temperature and long cure times. Resin systems that can be cured by ultraviolet radiation thus offer particular advantages for this application, and a report from the US Naval Air Development Center describes tests indicating that repairs to damaged composites can be made safely, quickly and easily using
Further information is contained in the 15-page report "The application of ultraviolet cure resins for repair of composites" by H.D. Gillman and J.L. Eichelberger. reference AD-A055 731, available as microfiche (£1.19) (inc VAT) or reproduced paper-copy (£1.50).
selected resins of this type. Sixteen commercially available UV-curable resin systems were tested: they were used to repair a graphite/epoxy composite cornmonly used in US naval aircraft, Damage in the composite was simulated by machining a 'V' groove to a depth of about one third of the laminate thickness. Different repair methods and five types of ultraviolet light source were investigated, Although the best repair achieved gave only 76 per cent of the flexural strength of the undamaged laminate, stronger repairs are thought to be possible: however, no attempt was made to optimize repair procedures to maximize repaired strength. It is thought likelythatimprovedstrength could be secured with, for example, changes in the resin system, cure time, light intensity, wavelength, sur-
Although several adhesives for bonding high temperature composites have been available for some time, either commercially or experimentally, most of these suffer from deficiencies such as long and involved processing cycles, brittleness and poor crack resistance, or severely reduced bond strength after prolongedexposuretohightemperatures. However, under a recent NASA c o n t r a c t , an a l u m i n i u m - f i l l e d polyimide resin adhesive has been developed which has the potential to eliminate many of these problems, It is easier to process than other aromatic polyimide adhesives, and should have applications for bonding both metal and composite components exposed to harsh environments for prolonged periods at temperatures of at least 300°C. Details of the curing process, bond-
COMPOSITES . JULY 1979
and
reinforcing
Bondinghigh temperature cornposites
environmental tests, and the characteristics of the new adhesive that requires further investigation, are contained in a report from NASA.
The adhesive consists of a 1:~:¼ mole ratio of 2,2 bis (3', 4', dicarboxyphenyl) hexafluoropropane; parahenylenediamine; oxydianiline, 48 percent by weight cured resin solids in diglyme, containing 65 percent aluminium powder based on total cured solids. The adhesive is said to have excellent resistance to the following environments: 500 hours in air at 316°C; 35 days in 95 percent RH at 49°C; 34 days immersed in jet fuel at room temperature; and 34 days immersed in methyl ethyl ketone at room temperature. Its excellent toughness and stability were demonstrated by performing a wedge-type crack propagation test at 316°C on 3.175 mm thick unidirectional graphite fibre-reinforced polyimide samples. A bond strength of 23.44 MN/m =was recorded for lap shear samples prepared from graphite fibre/polyimide matrix adherends at room temperature, with a value of 15.51 MN/m 2at 360°C. Both values arehigherthanNASA'soriginal targets. The adhesive is also capable of producing wide area bonds having acceptable strengths. However, these were achieved by using abnormally long cure cycles in order to allow diffusion of the volatiles out of the bond line; and the bond lines were not free from voids. Areas for further investigation recommended by the report include: methods for improving the adhesive prepreg toughness; the application ofathinner, more highly cured primer by spraying to achieve a more uniform coating; reduction of bond-
139
lnews ing temperatures which may result in an adhesive more suitable for bonding wide areas; the evaluation of bonds under cyclical stress tests at various temperatures, comparison of their performance with other adhesive systems; and the use of other fillers, eg glass grit, mica, alumina, as well as other metals and metal oxide powders, Further information is contained in
the125-pagereport'NR-150B2adhesive development" by P.S. Blatz, reference N78-27273, available as microfiche (£1.19, inc VAT) or reproduced paper-copy (£6.70).
Ceramic matrix composites By using either particulate or fibrous reinforcement, the advantages of ceramics (such as excellent high temperature properties, corrosion resistance and hardness) can be combined with significantly reduced brittleness- their single largest disadvantage. With this in mind, an investigation into the potential usefulness of ceramic matrix composites (CMC) in structural applications, where components must be able to withstand tensile stresses with a high reliability, was carried out in the USA
140
on behalf of the US Department of Defense. Details of the study group's findings and recommendations, based on a survey of the opinions of the entire US technical ceramics community, and a workshop of scientists actively involved in CMC technology, as well as a literature survey, are contained in a report now available. In addition, areas of beneficial application are outlined, the scientific and engineering state of the art reviewed, and areas for further study noted. Almost all potential applications for (CMC: examples of which are graphite reinforced with carbides, SiC-C/Si, and non metal fibrereinforced glass) involve hightemperature and a corrosive environment, and often temperature cycling, which may have a deleterious effect on the performance of the component. Short-term applications considered by the group include: reinforced concrete structures; gas turbines where increases in inlet temperatures up to 1200°C may be feasible using silicon carbide/fibre silicon composites, thereby offering promise of increased fuel savings; and the use of ceramic fibres in
refractory linings. Potential applications in the longer term include: reinforced glass composites able to withstand temperatures above 650°C; the use of alI-CMC hot moving parts in diesel engines, thustaking advantage of the high cermic strength to weight ratios; and a ceramic heat exchanger, for a marine engine, to operate for up to 10 000 h at 1370°C, allowing the weight of the power plant to be reduced by a factor of ten. Other possible applications for CMC reviewed by the study group include ceramic gun tube inserts, nozzles for chemical laser systems, high-speed rolling and sliding bearings, seals, magnetohydrodynamic generator components, dental and orthopaedic implants, and roads and runways. The report also briefly reviews the technology of ceramic materials for the non-specialist reader. Further information is contained in the 175-page report "Assessment of
ceramic-matrix composite technology and potential DoD application by J.E. Hove and H.M. Davis, reference AD-A054017, available as microfiche (£1.19, inc VAT) or reproduced paper-copy (£9.30).
COMPOSITES. JULY 1979