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Use of fibre reinforced composites in modern railway vehicles
Use of Fibre Reinforced Composites in Modern Railway Vehicles
J. B A T C H E L O R
British Rail Research, Railway Technical Centre, London Road, Derby DE2 8UP, U.K. The use of glass reinforced plastics (GRP) within British Railways for rolling stock is well established. A number of examples are discussed which illustrate how the applications have developed to satisfy the specific requirements of the Railway Industry. The cab for the High Speed Train is a particularly good illustration of a structural use of composites where a GRP sandwich structure was designed to protect the driver from high speed missile impact. Passenger doors and seat shells are other examples where the structural capabilities of GRP have been used to good effect. In general, the quantities required for a particular item are relatively low and thus production technology is an important consideration in the development of composites. British Railways have developed a vacuum assisted mouMing process which is currently being used to produce a wide variety of components. The future potential for high performance composites, particularly those based on carbon and aramid fibres, is discussed and a number of possible applications are identified. However, the high costs of carbon and aramid fibres will preclude widespread use of these materials in the immediate future.
1. Introduction
British Railways have a long involvement in the use of glass fibre reinforced plastics (GRP) and may almost claim to be one of the pioneers in this area in the UK. GRP doors were designed, produced and introduced to suburban electric stock in the 1950's. They were introduced initially because of their increased fatigue life when compared with cast aluminium and steel panels clad on a timber frame. Since those early days GRP has been introduced more and more into rolling stock for semi-structural and decorative purposes. The requirements for relatively small runs of complex shapes, good fire resistance, design flexibility, low maintenance, self colouring and general toughness have provided the spur for increasing the use of these materials. As a consequence GRP has become established in the UK railway environment and is accepted by the design engineers. At present components are almost solely concerned with the use of short fibre glass in a polyester matrix at relatively low volume fractions. However, engineers are becoming increasingly aware of the potential of composites based on continuous fibres of glass, carbon and aramid at much higher volume fractions because of the
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
opportunity to produce a structural material with high strength and high stiffness to weight ratios. Thus there is a continuing development programme of work in the area of high performance composites. British Rail Engineering Ltd., which is a fully owned subsidiary of British Railways, is the manufacturing arm who undertake the manufacture and repair of locomotives and rolling stock for both internal use and for export. It has a large GRP production facility with a current annual turnover of about 260 tonnes. Most of the items are manufactured by hand lay, cold press moulding or spray up, however, new methods are being developed to meet specific requirements. British Railways also buy in approximately 200 tonnes of GRP items per annum, the bulk of which are hot press moulded seat shells. On modern rolling stock the range of GRP items is very considerable. For example, in a modern Inter-City Mk 3 coach there are over 80 GRP items and the total weight of material used is about 1.6 tonnes per vehicle. Similarly, in the High Speed Train (HST) power car there are over 60 items with a total weight of 1.3 tonnes per vehicle. These items range in size from small handles and panels weighing less
172
than 1 kg to the outer shell of the cab which weighs 250 kg. Although the range of items is vast there are only a relatively small number produced for each vehicle and there is only a limited build of new stock every year. For example, only 5 Mk 3 coaches are manufactured per week and the number of HST power cars required will be correspondingly lower. Thus, suitable manufacturing techniques must be developed to meet the relatively small numbers produced of each item.
The shape of the cab must be aerodynamically designed to reduce drag and minimise the effects of shockwaves, particularly when passing through stations, passing other trains, or entering tunnels. The complex curved shape required could be easily achieved using GRP. (iv) Manufacture. The method of manufacture must be suitable for the relatively short production runs envisaged. (v) Aesthetic considerations. Industrial designers are becoming It would be inappropriate to discuss more involved in the aesthetics the development of anything but a of engineering components and small number of the components in they made a minor but significant this paper. Instead, we will highlight contribution to the final design. the more important items which we GRP offers a very wide scope for hope will indicate something of the aesthetic features to be incorporphilosophy of the use of composites ated. in the railway environment and this A double skin GRP/sandwich strucwill include the development of manuture was proposed with a rigid polyfacturing technology to meet the rather specialised requirements. In urethane foam core. An additional addition we will attempt to indicate advantage of a sandwich structure is areas where composites will be con- that service ducting for air conditionsidered for future applications with ing, electrical wiring etc. could be particular reference to the high per- incorporated at the production stage resulting in a comfortable environment formance materials. for the driver which is relatively easy to clean and maintain. 2. Locomotive Cab Fronts Resistance to impact damage was The introduction of high speed trains on British Railways has brought the most serious problem to be overabout a number of significant changes come and the objective was to design in the design and appearance of modern a structure which could resist penerolling stock. For example, the drivers tration into the cab of a sharp corncab of the HST, which came into ered hollow steel cube 70 to 75 mm regular service in 1977 with a maximum side having a mass of 0.9 kg travelspeed of 200 km/h, is a GRP/sandwich ling at 350 km/h. This requirement is structure and is the most ambitious based on the windscreen specification 1 , use of composite materials on British which all forward facing components Railways to date. The requirements on locomotives and power cars must which led to the choice of a GRP meet. There are several classifications depending on the maximum service structure were as follows: speed of the train in question. Experi(i) Impact resistance. It is essential that the driver is ments were carried out on a variety of protected from missiles which sandwich panels to determine the most strike the front of the cab. Thus suitable construction. Test panels the structure must be capable measuring 914 x 914 x 50 mm were of withstanding local high speed produced by the hand-lay up process impacts and this was the main and a foam core injected into the problem to overcome in the cavity formed by the two skins. For the impact tests an air gun was used design of the cab. and the panels bolted to a rigid frame (ii) Lightweight. The cab must be light to reduce at right angles to the direction in which energy and track maintenance the missile travelled. The steel cube costs. Preliminary design studies was then fired corner on at the panel. indicated that a composite struc- Typical results are shown in Fig. 1. ture would weigh about 30 to Details of the final cab construction 35% less than a conventional chosen as a result of these tests have been reported 2 . steel structure. (~) Streamlined shape. The cabs were manufactured by
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Fig. 1. Section through HST test panel showing impact damage at 330 km/hpanel not penetrated. conventional contact moulding techniques by British Raft Engineering Ltd (BREL). The outer face is laminated as a single moulding and the inner face made in 3 separate parts. Subsequently the two faces are assembled to form the cavity for the foam core. Before this operation is carried out the cavity is divided into a number of compartments using GRP laminated over flexible foam strips laid into the outer skin. Flexible hose is also incorporated to allow the foam core to be injected into the various compartments. When the moulding has cured the cavities are then injected with foam. The hoses are left in situ in the inaccessible compartments at the end of the operation, and provision is made between the skins for the various ducting which is required. Finally the inner mould is removed and a GRP floor and bulkhead are bonded in position and the whole structure is completed as one component. To complete the furnishings, switch panels, cupboards and a drivers desk inside the cab are manufactured in GRP. The completed cab front is shown in Fig. 2. The mass of the sheU including the floor and rear bulkhead is about 1 tonne and up to the end of 1979 160 cabs have been manufactured. We are confident that this type of construction will provide the drivers of the HST with adequate protection from high speed missiles and similar constructions are being incorporated as part of the Advanced Passenger Train (APT) cab and on the access door for the front of the Class 212 and 313 Electric Multiple Units. The drivers' reaction to the cab has been
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
design to produce an item which would be lighter by removing the steel frame and using the composite more as a structural material. In addition it was proposed to consider alternative methods of manufacture to the rather labour intensive hand-lay technique. The net result would be a lighter door which could be produced more economically with a significant improvement in the quality. It was not possible to alter the basic shape of the door since it must conform to the vehicle profile, but this was not a serious design constraint. There were a number of loading conditions specified to simulate, for example, a passenger leaning on the door, air pressure due to trains passing in tunnels, effect of wind on open doors etc. However, probably the most stringent requirement is that the door when closed must withstand a uniformly distributed load o f ' 44 kPa over the inside. This condition represents a crash loading with the coach on its side and a load of 10 passengers in the vestibule. The proposed door consisted essentially of a box section surrounding the central recess and hole for the droplight Fig. 5). Finite element analysis of the structure using NEWPAC s , indicated that such a structure is too flexible in torsion (Fig. 6) which gives rise to excessive distortion at the corners when under load. The section was therefore stiffened by providing a closed box section. In practice this can be achieved by incorporating blocks of rigid polyurethane foam in the corners. It was still necessary to incorporate steel inserts in certain critical areas
Fig. 2. HST power car showing GRP cab front. very favourable and it is encouraging to see design engineers ready to accept fibre reinforced plastics in such a stringent structural application. The large-scale ballistic impact tests, which must be carried out on these structures before final approval, are time consuming and expensive. An airpowered laboratory gun has, therefore, been developed for preliminary assessment of materials and to obtain a more fundamental understanding of the behaviour of composites a . The effects of missile mass, shape and size can also be evaluated. Initial results (Figs. 3, 4) show that GRP laminates can give better all-round ballistic impact resistance than aluminium or steel of equivalent mass a . This investigation is part of a continuing research programme to develop fibre reinforced plastics (FRP) structures for ballistic impact applications, which minimise mass.
time. When the larger wrap-round corner door was introduced for Mk II InterCity coaching stock, it was decided to construct the item around a jig welded steel frame which is clad with GRP. In theory, the steel frame would accommodate the loads and the GRP would effectively provide a weatherproof cladding. This approach was later adopted for the current Mark III coaches. Doors constructed by this technique have an excellent record of reliability but tend to be heavy and expensive to produce. It seemed likely that the same standards of safety and reliability could be achieved by simplifying the 120
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3. Carriage Doors The earliest application of GRP on British Railways was in the Southern Region for suburban stock doors, which were introduced in the 1950's. Fatigue experiments demonstrated that the composite would be expected to have at least double the life of the standard metal doors based on cast aluminium or steel panels clad on a timber frame. As a result of this early success for GRP it has been widely used for this application since that
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MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
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This exercise illustrated that the use of the composites must undergo a continual scrutiny to ensure that they are being used in a most effective and economical manner.
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16 mm diameter. such as the lock, hinge, etc. but the massive jig welded steel frame (Fig. 7) has been removed. A fully cored structure was also considered at the design stage but rejected because it produced too heavy a door. Mechanical tests carried out on prototype items showed that the new design would meet the requirements specified.
moulding process indicated that a cost saving of £100 per door could be achieved with additional benefits accruing from the lighter structure.
The potential of GRP in the manufacture of seat shells in passenger rolling stock was appreciated initially in the late 1960's. The complex curved shaped shell could be produced as one moulding which would be self coloured, light, easy to install, robust and aesthetically pleasing. Such a design would eliminate the need for extensive fabrication and finishing (e.g. painting) inherent in a more conventional metal/timber structure. Preliminary design studies demonstrated that GRP seat shells could be economic. Since there would be relatively large numbers of each item required, typically about 15,000 per
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Fig. 5. Sketch of Mk Ill corner door.
Various processes were considered for production but it was decided that cold press moulding s was the most economical and appropriate. The two skins of GRP were moulded separately, the inserts bonded in position and the two skins then bonded together using a gap f'filing adhesive. The redesigned door weighs 38 kg compared with the original design of 58 kg (Fig. 7). Economic analysis of the cold press
175
DIAPHRAGM D I A G R A M B - SHOWS D I A P H R A G M M A I N T A I N I N G T H E S E C T I O N A L SHAPE AND RESISTING DEFLECTION
Fig. 6. Deflection of open and closed box sections.
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
annum, it becomes a viable proposition to use hot press moulding techniques to produce the component using sheet moulding compound 6 . This is one of the few railway applications where the high tool costs essential for the process can be justified. Consequently, GRP seat shells have been produced by this technique and supplied to British Railways since 1969 for both Inter-City and commuter rolling stock.
stress from one shell to its neighbour through ribs at the back of the seat. The final thickness of the component chosen was 5 mm which produces a single shell mass of about 5 kg and total mass of a complete double seat assembly (including frame and cushions) of 26.5 kg. Static load tests have been carried out on the finished item, which have confirmed that the design requirements have been achieved. The finished item (Fig. 10) is attractive, lightweight, easily assembled and a good example of a structural application of GRP in rolling stock.
toilet compartments (Fig. 11) to produce an attractive yet functional unit which is easy to clean and maintain. 6. GRP Production
As composite components were being developed and introduced into rolling stock it was necessary to set up an in-house facility through BREL, to produce many of the items required in new designs. Thus within British Railways development of appropriate production technology has proceeded in parallel with component development. At present much of the manufacture within BREL is by hand lay-up and cold press moulding with a limited amount of spray-up s . We have seen that the requirements for the railway industry in this country are relatively modest, thus in general it is not appropriate to consider capital intensive processes such as hot press moulding for in-house manufacture since few components could justify the expenditure required. Items such as seat shells for which the numbers required will
5. Coach Interiors It was indicated earlier that GRP is used extensively for decorative and semi-structural Finishes inside modern railway passenger coaches. The facility to mould complex shapes combined with excellent appearance and good mechanical properties of the material has been used by designers to good advantage in, for example, the saloon and vestibule areas where much of the cladding is GRP. Similarly, these advantages have been exploited in
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Fig. 7. Mk III corner doors - showing original jig welded steel frame in foreground. The most recent example of this application is for the Advanced Passenger Train (APT) which comes into service during 1981. The shells are moulded individually, bolted together at the back of the seat and fixed in pairs to an aluminium tube. Each pair of seats is supported on an aluminium pedestal in the centre and one seat is fixed to the side of the coach body (Fig. 8). The various loading factors considered in the design are shown diagrammatically in Fig. 9 where a safety factor of 1.5 is assumed. Stress analysis was carried out using NEWPAC s, to determine the minimum thickness of the item commensurate with the loading specifications and practicalities of production. A material tensile strength of 70 MPa was assumed in the stress analysis, which represents the minimum value specified for GRP requirements on British Railways. It is interesting to note that the ashtray housing between seats was included in the analysis since it contributes to the overall structure by transferring tensile
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
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Fig. 10. Completed APT second class seat showing GRP shell. build of new coaches (approximately 5/week) and the numbers required of any particular item are relatively small. Thus the potential for capital intensive processes such as hot press moulding is very limited. The objectives of our production development studies are to improve the consistency and quality of the final item, increase output capacity and improve the working environment. Furthermore, it is essential to keep tooling costs low and concurrent with process development alternative techniques for producing tools are being investigated. The selection of any particular process depends on design complexity and total numbers
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Fig. 9. Design loads for APT second class seat. justify the use of such techniques are produced outside the railway industry by the Plastics Industry. In common with the UK reinforced plastics business in general hand-lay techniques have been the mainstay of GRP production within BREL. This process is very labour intensive, operative sensitive and can result in a very variable product and thus quality control procedures must be vigilant. Furthermore, there is a major problem with styrene emission from the polyester resin used in the hand laminating process and thus adequate extraction must be provided to produce a satisfactory working environment for the
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operators. Health & Safety legislation is, quite rightly in our opinion, becoming much stricter and this must be a major factor to consider when setting up manufacturing facilities. It is likely that standards will become more rigorous and legislation is likely to follow Scandinavian practice which is considerably stricter than current UK regulations. Thus we have a continuing development programme evaluating and developing suitable production processes for the manufacture of composite items. British Railways have a specific problem in that there is a limited
Fig. 11. APT toilet compartment with GRP vanity unit, wall and ceiling panels.
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
contribution to make to the manufacture of GRP and is currently used by BREL for the production of window surrounds, doors etc. Recently British Railways have developed a novel vacuum impregnation process which is suitable for production runs between hand4ay and cold press moulding and is thus eminently attractive for the production requirements within BREL. The process has been described in detail elsewhere 6 7 but basically it relies on the injection of resin using a vacuum into a closed mould containing a glass pack. The capital investment required for this process is relatively low and inserts can be incorporated in the moulding cycle. The process is much more flexible than cold press moulding and very complex sections can be produced. Since the process is a closed mould technique styrene emission is low and additional extraction facilities would not normally be required (Table 1). Production rates and tooling costs lie between that of cold press moulding and hand-lay (Table 1) but material wastage is very low (less than 5?;) and quality and consistency of the product very high. For complex items it is essential to use a low yiscosity resin to ensure mould filling and special resins have been developed for this process. A major advantage of this process is that items which contain undercuts can be produced and for components where only one moulded surface is required a simple flexible bag can be used. The process is very attractive for BREL's production requirements and is being used for a wide variety of components at present, e.g. transponders, vestibule end doors. A more recent development is looking at the
required. One advantage of hand-lay techniques is that the tool costs are relatively low and the process is ideal for short production runs, prototype development and design approval. Any inserts can be incorporated very easily but there must be adequate extraction facilities if manufacturers are to conform to current legislation (Table 1). For large items such as the HST cab fronts it is likely that for the forseeable future the only economic method for producing these items will be by the hand-lay process and thus it will always have some part to play in our manufacturing capability. For higher production rates cold press moulding offers advantages for many components s. This process is a semi-automatic process where pressure is applied between matched moulds to distribute the resin throughout a prepared glass blank laid in the mould. This process gives much higher production rates than hand-lay, better quality control is achieved, and styrene levels in the working environment are considerably reduced (Table 1). Tool design is very critical and costs are correspondingly higher (Table 1). One disadvantage of the cold press moulding technique is that metal inserts cannot be included and must be located in position subsequently. These can be bonded by the use of structural adhesives and the use of such techniques can increase the potential of this particular process. The waste of material is very high (greater than 20%) and it cannot accommodate components with large thickness variations and is therefore restricted to items which are relatively simple in shape. In spite of these disadvantages cold press moulding does have a significant
TABLE 1: Comparison of Various GRP Processes
Process
Hand-lay
Styrene concentration (ppm) Tool Costs Without With (arbitrary Materials Wastage Extraction Extraction units) % 60-160
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160-30~ (deep draw items)
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60
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25
Production Rate (items/8 hour shift)
25-80
1
5
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3.5
25-47
6-8
2.5 to 3
5
2-3
Not measurable
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
possibility of incorporating foam cores into the component to produce a structural item. This development is still at a very early stage but preliminary results look very promising. It is clear that the actual production process will depend on a number of factors but we have illustrated that mechanised processes can be used for relatively short runs required and these can be economic without the need for expensive capital investment. Clearly further work is needed to develop the processes further but the potential looks promising. At present the processes are restricted to conventional low glass/resin ratios but we see no difficulty in deveioping the process to produce higher fibre concentrations with other types of reinforcement and resins. Work along these lines is already being undertaken and the early results look encouraging. 7. Fire and Flammability
It is essential that high fire resistance standards are maintained for components used in passenger coaches. British Railways' basic approach is to use materials which are difficult to ignite, self extinguishing with a low surface spread of flame. GRP used for coach interiors must conform to Class 1 of BS. 476 for day stock and Class 0, according to the Building Regulations 1976, for sleeping cars. Furthermore, before any new design is approved in the future, large scale tests will be carried out to simulate realistic fire situations using facilities similar to those described by Woolley et al 8. Polyester resins have been developed in co-operation with the raw material suppliers which meet these requirements and can also be processed by the techniques discussed earlier. The specifications take no account of smoke generation at present, but it is fully appreciated that future developments must consider this problem, particularly as air conditioning in passenger coaches is likely to be standard. Future materials and process technology must change to meet future demands for increased safety. Smoke generation in GRP can be reduced either by modifying polyester resins or by using alternative polymers. The latter approach looks more promising and phenolic resins are becoming available for use with glass fibre reinforcement which greatly
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TABLE 2: Smoke Density of GRP
BS. 476 Classification
*Maximum Optical Density (Arbitrary Units)
0
1.6
Polyester
1
0.6
Phenolic
0
0.35
Matrix
Polyester
* Measured using similar technique to Woolley et als . reduces the smoke generation (Table 2). However, further studies are needed to establish the long term mechanical properties of phenolic based composites and to develop suitable manufacturing methods. 8. Future Potential for Composite Materials Previous discussion has shown that GRP is well established on BR particularly for semi-structural and decorative items. In these applications the glass fibre is in short lengths ( < 100 mm) at relatively low volume fractions (10-15%), which does not make full use of the mechanical properties of the reinforcement. The introduction of high modulus high strength carbon fibre in the early 1960's created a great deal of interest in the potential use of fibre reinforced plastic composites for high performance applications. The initial enthusiasm, however, has not been sustained because of the continuing high price of the fibre. More recently aramid fibres have been introduced with properties and price intermediate between glass and carbon and these are finding applications in some areas. Composites based on carbon and aramid fibres are of interest as structural materials as they combine stiffness and strength with light weight (Table 3). However, it should be noted that GRP even with high volume fractions and a continuous fibre does not offer any significant advantage over aluminium. GRP will therefore be selected primarily where its other advantages can be exploited to the full, e.g. corrosion resistance, impact resistance, ease of manufacture into complex shapes. Applications on the railways for carbon and aramid fibre based composites have been limited up to the present time. Clearly high material costs, particularly for carbon fibre,
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have been the main reason but other contributory factors are the poor impact performance of carbon fibre reinforced plastics (CFRP) and low compressive strength of aramid reinforced plastics (ARP) and the fact that a new design approach is necessary if the full potential of these anisotropic materials is to be realised. It is appropriate to review the future potential of high performance composites as lightweight structural materials for railway rolling stock applications. There are two main advantages of lightweight construction: (i)
(ii)
Reduction of fuel consumption and associated benefits, e.g. reduced power unit size for given power/weight ratio, lower brake capacity etc. Reduction of track damage and hence maintenance costs caused by high unsprung mass. We have carried out theoretical
studies on selected journeys and showed that the cost benefits of reducing mass are about £0.40 to £3/kg. These figures are very modest when compared with the aircraft industry 9 and are unlikely to rise much above £5/kg (at 1980 figures) even if there was a substantial increase in passenger or goods traffic. It has not been possible to calculate the benefits which arise from reduced unsprung mass. Thus it is difficult to assess the economics of composite c o m p o n e n t s designed primarily to reduce unsprung mass. Lightweight construction in the railway industry at present is synonymous with the use of aluminium for nearly all practical purposes 1°. Thus it is pertinent to compare composites with aluminium. For the sake of this exercise we will assume that the materials are simple beams subjected to plane bending. The only geometrical variable is the depth of the beams which is adjusted so that all beams have the same stiffness. This is a very simplistic approach to the problem but it does give us some realistic basis for comparison of materials. The results are shown in Table 4 and we see that there are substantial mass reductions obtainable with CFRP and to a lesser extent for ARP. The saving for GRP is not significant and furthermore it produces a deeper beam for the same stiffness. Space is often at a premium in railway applications and clearly this increased depth could be a serious disadvantage with GRP.
TABLE 3: Mechanical Properties of Various Materials
Material
**CFRP - Type 1 Carbon **CFRP - Type 2 Carbon **CFRP - Type 3 Carbon **GRP **ARP Aluminium HE15WP Steel BS4360 Grade 55 *Pure Titanium 130 *Titanium Alloy 679
Specific Gravity
Tensile Modulus (GPa)
1.62 1.53 1.56 2.1 1.35 2.8 7.8 4.54 4.4
186 128 108 39 74 69 207 116 110
Tensile Strength (MPa)
1,330 1,560 1,500 850 1,270 450 625 540 1,030
Specific Tensile Modulus (GPa)
115 84 69 19 55 25 27 26 25
Specific Tensile Strength (MPa)
820 1,020 960 405 940 160 80 118 234
* ICI Designations ** Unidirectional laminate, volume fraction 0.60
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
TABLE 4: Comparison of Beams of Equivalent Stiffness
Composite *
Weight of Aluminium Beam Weight of FRP Beam
Thickness of Aluminium Beam Thickness of FRP Beam
CFRP - Type 1 - Type 2 ARP
2.17 1.91 1.81
1.39 1.15 1.02
GRP
1.08
0.83
* Unidirectional laminate, volume fraction 0.60
and ensure continuous contact between carbon collector strips and overhead wire 13, particularly at high speeds. The use of composite materials offers some potential and initial work has concentrated in reducing the mass of the pantograph head, that is the area closest to the overhead wire, which is the most critical area and offers the greatest benefit. Preliminary work was focused on CFRP but field experiments indicated that the material became badly eroded and was not suitable for application in this electrical environment. Subsequent work has concentrated on ARP which has proved satisfactory in these preliminary environmental tests. A straightforward replacement of the aluminium component is not desirable and a full composite head was developed from the outset. The bow shaped head was produced as a single moulding thus eliminating the bolted joint present in the conventional design which could cause load transfer problems An "U" cross section was chosen from aerodynamic considerations and the prototype items were produced by vacuum bag technique using pre-impregnated aramid cloth and fibre. The total weight saved is about 37% and a number of experimental heads la are being evaluated in service trials at present (Fig. 13). The main objectives have been to reduce carbon wear and increase the life of the component. Initial results are encouraging and it has helped to gain acceptance of these materials by
Although there are significant satisfactory in both static and fatigue advantages technically in using CFRP tests. Unfortunately, the impact and ARP as a direct replacement for behaviour of the tubes was very poor aluminium for lightweight structures and since they contain a hydrokinetic the economic argument is not so braking system this is a serious disstrong. We have calculated the costs advantage for this application. Neverwhich the fibres would have to come theless, it seems possible that the down to before they become econo- impact performance could be improved mical and concluded that carbon and by the use of hybrid composites or by aramid fibres would have to fall below using a protective shield connected to £10/kg and £7/kg respectively before the sprung mass of the structure. It they become feasible. These are does appear that substantial benefits considerably lower than the current might accrue by incorporating comselling price of the fibres and thus posites in the wheelset area but this we must seek additional technical concept is at a very early stage of reasons for selecting high performance development. Nevertheless, this study composites in any particular appli- has made engineers aware of the potential of the material which is a ation. There are a number of applications very important criteria for any new for composites, possibly in hybrid materials development. form with glass or other materials, where their technical advantages may (ii) Pantograph On electrified lines, there is a outweigh the initial high fibre cost. Ease of manufacture into complex requirement for a lightweight pantoshape is an added advantage in many graph to improve dynamic performance cases. Development work has been undertaken in a number of these critical areas. ( i ) Wheelsets This area is critical and significant reductions in track damage could be achieved if wheelset mass could be reduced. Hegenbarth 11 described an experimental composite wheelset evaluated by Deutsche Bundesbahn in the laboratory which looked promising. More recently British Railways ~2 have completed tests on two experimental CFRP axle tubes for the experimental AFr (Fig. 12). These tubes were made by resin injection and Fdament winding and an anisotropic f'mite element routine was employed to carry out the stress analysis 4 . The mass of the composite tubes was about 30% of the equivalent Fig. 12. CFRP axle tube for experimental APT under test. steel item and their behaviour was
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Fig. 13. Pantograph composite head showing ARP support for the carbon current collectors.
railway engineers. More recently a completely new pantograph design has been developed which requires a pair of lightweight aerofoils to improve the aerodynamics of the head 14. The aerofoils were required to conform to a standard profile (NACA6721) and these have been produced in ARP with a balsa wood core. These heads are currently under extensive experimental evaluation. The potential use for composites in the pantograph area has been readily accepted and there are numerous other areas in the main frame where the use of composites based on ARP or CFRP where it is away from the overhead wire could be attractive. This whole area is promising and is currently under detailed study. (iii) Drive Shafts The automotive industry1 s is considering the use of composites for main drive shafts to reduce mass and noise and they could offer a number of benefits in the railway area, e.g. - lightweight - enhanced damping - less balancing required - higher whirling speeds possible - excellent fatigue properties CFRP was considered for the APT cardan shaft and a 50% weight reduction could be achieved, but it was not considered an economic proposition in the present state of the art. In order to gain experience of this area of
181
application for composites two fan drive shafts have been installed in Diesel Multiple Units. Although this is not a critical application, these components have been in service since 1975 and covered over 300,000 miles without any mishap. Rotating shafts do look a feasible application for composites which is likely to become real within the next decade. (iv) Leaf Springs The Use of composites based on glass and carbon fibre reinforced materials is currently being evaluated for leaf springs in the heavy goods vehicle area. The advantages are that it will reduce mass and increase the fatigue life. A subsidiary benefit is that it would make maintenance much easier. This is an area of great potential application for the railway industry and feasibility studies are currently being undertaken. The initial results look promising. (v) Freight Applications The use of fibre reinforced plastics for freight applications on British Railways is minimal at present although railway industries in Japan and France 16 are considering the use of Filament wound GRP tankers for the transport of wine and milk. The potential for composites in this area is large and a number of development projects are currently being carried out. One area of current interest is in
the use of composites for the floors of conventional covered wagons. At present these are 6 mm steel sandwich structures with 25 mm plywood. The loading requirements are given in BS. 3951 and in particular they must be able to withstand the load of a fork lift truck. A number of sandwich structures have been considered based on both GRP and aluminium skins with foam, balsa or plywood cores. All these combinations meet the stiffness criteria but impact tests have demonstrated the need for a high density core and hence the reccommendation that plywood is used for this particular use. There is little to choose between the performance of aluminium or GRP as skin materials but the material costs of GRP are 50% less. The mass of a plywood/ GRP structure is 65% of the original steel floor which corresponds to a reduction of the tare weight by about 1 tonne. Clearly this is a very attractive economic proposition and is an interesting example of how traditional materials, in this case timber, can be combined with modern fibre reinforced plastic materials to produce lightweight structures which are cost effective. This study is being extended to look at the feasibility of using composites on other parts of covered wagons, e.g. roofs, end panels, etc. The use of GRP for the construction of rail tanker wagons could offer advantages in several areas and the properties of the material that are being considered for exploitation are: (a)
(b)
corrosion resistance in tanks that carry corrosive or edible materials. These tanks are at present constructed of stainless steel or have some corrosive resistant lining. low coefficient of thermal conductivity of GRP has some very significant advantages in this area. In a fire engulfment situation the Ministry of Defence have already demonstrated the advantage of using GRP over steel and aluminium 17. Furthermore, in tanks carrying materials at above ambient temperature the use of composites could eliminate the necessity to use lagging on steel or aluminium tanks.
Although railway designs are unlikely to involve significant amounts of CFRP as a structural material in
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
the forseeable future because of high fibre costs, they may find application in some specialist applications where there are added technical advantages of using lightweight construction. Further it may be possible to use these advanced composite materials in hybrid composites with glass or in combination with aluminium and there is possibly further scope for evaluating the potential of these materials in sandwich structures with foam or plywood cores. Clearly further development work is required in this area to realise the full potential of the materials.
10.
Concluding Remarks
Glass reinforced plastics are used extensively in the passenger environment and it is unlikely that this will increase significantly. Future designs of rolling stock are likely to use the glass reinforcement more effectively and there will be a need to offer passengers greater protection from fire and smoke, particularly as legislation becomes stricter. Thus, the use of phenolic resins is likely to increase substantially at the expense of polyester resins as the matrix material. It will be necessary to develop or modify existing production methods to process phenolic based composites and further development work must be carried out to establish the mechanical properties of these materials so that items can be designed with the same degree of confidence that is currently accepted for glass reinforced polyesters. The problems are not intractable and are being investigated as a continuous part of British Rail's development work on composite technology. High fibre costs will preclude the use of carbon and aramid fibre composites in the immediate future as a lightweight structural material per se,
but there are a number of potential applications for these materials where their advantages may justify the high material costs. The future in these areas is promising provided that the anisotropic nature of the materials is appreciated and a multi-disciplinary approach is adopted involving engineers, polymer technologists and materials scientists.
7.
8.
9.
Acknowledgements
I would like to thank British Railways Board and Director of Research for permission to publish this paper. Thanks are also due to my colleagues in the Plastics Development Unit of British Rail Research for their assistance.
10.
11.
References 1.
2.
3.
4.
5.
6.
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
"High Impact Resistance Windscreens", BR Specification 556: 1978, British Railways Board, London, UK. Batchelor, J., "GRP Driver's Cab for High Speed Train", Birmingham, UK, September 1977. Batchelor, J. & Garrington, P.J., "Impact Considerations and Performance for FRP on British Rail", Paper presented at BPF Reinforced Plastics Congress, Brighton, UK, November 1980. Dodd, R.J.M., "Application of the British Railways Finite Element Program NEWPAC to Railway Vehicles". Proc. conf. 'Application of Finite Elements in Mechanical Engineering - A Survey of current practice'. I. Mech E. 1972. Gotch, T.M. & Plowman, P.E.R., "Improved Production Process for Manufacture of GRP on British Rail", Paper presented at BPF Reinforced Plastics Congress, Brighton, UK, November 1978. Mohr, J.G., Oleesky, S.S., Spook, G.D. & Mayer, L.S., "SPI Handbook of Technology and Engineering of Reinforced Plastics Corn-
12.
13.
14.
15.
16.
17.
posites", Van Nostrand Reinhold Company, New York, 1973. Gotch, T.M., "Vacuum Impregnation Techniques for GRP on British Rail", Reinforced Plastics April 1979. Woolley, W.D., Raftery, M.A., Ames, S.A., & Murrell, J.V., "Smoke Release from Wall Linings in Full-Scale Compartment Fires", Fire Safety Journal, 2, 1979, 61-72. Locke, H.B., "Some Economic Aspects of Composite Materials", Plastics & Polymers 41, 1973, 136-140. Kato, M., "How the Weight of Passenger Cars has been Trimmed", Railway Gazette International 132, 1976, 334-338. Hegenbarth, F., "Some thoughts on Wheelset Manufacturing Techniques", The Wheelset of the Future at the I.V.A., Munich 1965, Leichtb.B.Verk, 11, 1967, 217-222. Garrington, P.J., "Reinforced Plastics in Rail Transportation", Paper presented at N.E.L. Reinforced Plastics:Design and Technology Conference, Glasgow, U.K., November 1975. Beadle, A.R., Betts, A.I., & Smith, W.R., "Pantograph Development for High Speeds". Paper presented to the Railway Division of l.Mech. E., London, UK, December 1975. Coxon, D.J., Gostling, R.J., & Whitfield, K.M., "Evolution of a Simple High-performance Pantograph", Railway Gazette International, 136, 1980, 44. Simanaitis, D.J., "High Performance Composites: An Automotive Revolution", Auto-Engrg, 85(3), 1977, 40-47. Anon, "Going beyond Glass for Reinforcement", Modern Plastics International, October 1975, 22-25. Taylor, A.J. & Hards, D.J., "Engulfment Fire Tests on Road Tanker Sections", Ministry of Defence, U.K., RARDE Technical Report 7/75, July 1975.
182
J. B A T C H E L O R
British Rail Research, Railway Technical Centre, London Road, Derby DE2 8UP, U.K. The use of glass reinforced plastics (GRP) within British Railways for rolling stock is well established. A number of examples are discussed which illustrate how the applications have developed to satisfy the specific requirements of the Railway Industry. The cab for the High Speed Train is a particularly good illustration of a structural use of composites where a GRP sandwich structure was designed to protect the driver from high speed missile impact. Passenger doors and seat shells are other examples where the structural capabilities of GRP have been used to good effect. In general, the quantities required for a particular item are relatively low and thus production technology is an important consideration in the development of composites. British Railways have developed a vacuum assisted mouMing process which is currently being used to produce a wide variety of components. The future potential for high performance composites, particularly those based on carbon and aramid fibres, is discussed and a number of possible applications are identified. However, the high costs of carbon and aramid fibres will preclude widespread use of these materials in the immediate future.
1. Introduction
British Railways have a long involvement in the use of glass fibre reinforced plastics (GRP) and may almost claim to be one of the pioneers in this area in the UK. GRP doors were designed, produced and introduced to suburban electric stock in the 1950's. They were introduced initially because of their increased fatigue life when compared with cast aluminium and steel panels clad on a timber frame. Since those early days GRP has been introduced more and more into rolling stock for semi-structural and decorative purposes. The requirements for relatively small runs of complex shapes, good fire resistance, design flexibility, low maintenance, self colouring and general toughness have provided the spur for increasing the use of these materials. As a consequence GRP has become established in the UK railway environment and is accepted by the design engineers. At present components are almost solely concerned with the use of short fibre glass in a polyester matrix at relatively low volume fractions. However, engineers are becoming increasingly aware of the potential of composites based on continuous fibres of glass, carbon and aramid at much higher volume fractions because of the
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
opportunity to produce a structural material with high strength and high stiffness to weight ratios. Thus there is a continuing development programme of work in the area of high performance composites. British Rail Engineering Ltd., which is a fully owned subsidiary of British Railways, is the manufacturing arm who undertake the manufacture and repair of locomotives and rolling stock for both internal use and for export. It has a large GRP production facility with a current annual turnover of about 260 tonnes. Most of the items are manufactured by hand lay, cold press moulding or spray up, however, new methods are being developed to meet specific requirements. British Railways also buy in approximately 200 tonnes of GRP items per annum, the bulk of which are hot press moulded seat shells. On modern rolling stock the range of GRP items is very considerable. For example, in a modern Inter-City Mk 3 coach there are over 80 GRP items and the total weight of material used is about 1.6 tonnes per vehicle. Similarly, in the High Speed Train (HST) power car there are over 60 items with a total weight of 1.3 tonnes per vehicle. These items range in size from small handles and panels weighing less
172
than 1 kg to the outer shell of the cab which weighs 250 kg. Although the range of items is vast there are only a relatively small number produced for each vehicle and there is only a limited build of new stock every year. For example, only 5 Mk 3 coaches are manufactured per week and the number of HST power cars required will be correspondingly lower. Thus, suitable manufacturing techniques must be developed to meet the relatively small numbers produced of each item.
The shape of the cab must be aerodynamically designed to reduce drag and minimise the effects of shockwaves, particularly when passing through stations, passing other trains, or entering tunnels. The complex curved shape required could be easily achieved using GRP. (iv) Manufacture. The method of manufacture must be suitable for the relatively short production runs envisaged. (v) Aesthetic considerations. Industrial designers are becoming It would be inappropriate to discuss more involved in the aesthetics the development of anything but a of engineering components and small number of the components in they made a minor but significant this paper. Instead, we will highlight contribution to the final design. the more important items which we GRP offers a very wide scope for hope will indicate something of the aesthetic features to be incorporphilosophy of the use of composites ated. in the railway environment and this A double skin GRP/sandwich strucwill include the development of manuture was proposed with a rigid polyfacturing technology to meet the rather specialised requirements. In urethane foam core. An additional addition we will attempt to indicate advantage of a sandwich structure is areas where composites will be con- that service ducting for air conditionsidered for future applications with ing, electrical wiring etc. could be particular reference to the high per- incorporated at the production stage resulting in a comfortable environment formance materials. for the driver which is relatively easy to clean and maintain. 2. Locomotive Cab Fronts Resistance to impact damage was The introduction of high speed trains on British Railways has brought the most serious problem to be overabout a number of significant changes come and the objective was to design in the design and appearance of modern a structure which could resist penerolling stock. For example, the drivers tration into the cab of a sharp corncab of the HST, which came into ered hollow steel cube 70 to 75 mm regular service in 1977 with a maximum side having a mass of 0.9 kg travelspeed of 200 km/h, is a GRP/sandwich ling at 350 km/h. This requirement is structure and is the most ambitious based on the windscreen specification 1 , use of composite materials on British which all forward facing components Railways to date. The requirements on locomotives and power cars must which led to the choice of a GRP meet. There are several classifications depending on the maximum service structure were as follows: speed of the train in question. Experi(i) Impact resistance. It is essential that the driver is ments were carried out on a variety of protected from missiles which sandwich panels to determine the most strike the front of the cab. Thus suitable construction. Test panels the structure must be capable measuring 914 x 914 x 50 mm were of withstanding local high speed produced by the hand-lay up process impacts and this was the main and a foam core injected into the problem to overcome in the cavity formed by the two skins. For the impact tests an air gun was used design of the cab. and the panels bolted to a rigid frame (ii) Lightweight. The cab must be light to reduce at right angles to the direction in which energy and track maintenance the missile travelled. The steel cube costs. Preliminary design studies was then fired corner on at the panel. indicated that a composite struc- Typical results are shown in Fig. 1. ture would weigh about 30 to Details of the final cab construction 35% less than a conventional chosen as a result of these tests have been reported 2 . steel structure. (~) Streamlined shape. The cabs were manufactured by
173
Fig. 1. Section through HST test panel showing impact damage at 330 km/hpanel not penetrated. conventional contact moulding techniques by British Raft Engineering Ltd (BREL). The outer face is laminated as a single moulding and the inner face made in 3 separate parts. Subsequently the two faces are assembled to form the cavity for the foam core. Before this operation is carried out the cavity is divided into a number of compartments using GRP laminated over flexible foam strips laid into the outer skin. Flexible hose is also incorporated to allow the foam core to be injected into the various compartments. When the moulding has cured the cavities are then injected with foam. The hoses are left in situ in the inaccessible compartments at the end of the operation, and provision is made between the skins for the various ducting which is required. Finally the inner mould is removed and a GRP floor and bulkhead are bonded in position and the whole structure is completed as one component. To complete the furnishings, switch panels, cupboards and a drivers desk inside the cab are manufactured in GRP. The completed cab front is shown in Fig. 2. The mass of the sheU including the floor and rear bulkhead is about 1 tonne and up to the end of 1979 160 cabs have been manufactured. We are confident that this type of construction will provide the drivers of the HST with adequate protection from high speed missiles and similar constructions are being incorporated as part of the Advanced Passenger Train (APT) cab and on the access door for the front of the Class 212 and 313 Electric Multiple Units. The drivers' reaction to the cab has been
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
design to produce an item which would be lighter by removing the steel frame and using the composite more as a structural material. In addition it was proposed to consider alternative methods of manufacture to the rather labour intensive hand-lay technique. The net result would be a lighter door which could be produced more economically with a significant improvement in the quality. It was not possible to alter the basic shape of the door since it must conform to the vehicle profile, but this was not a serious design constraint. There were a number of loading conditions specified to simulate, for example, a passenger leaning on the door, air pressure due to trains passing in tunnels, effect of wind on open doors etc. However, probably the most stringent requirement is that the door when closed must withstand a uniformly distributed load o f ' 44 kPa over the inside. This condition represents a crash loading with the coach on its side and a load of 10 passengers in the vestibule. The proposed door consisted essentially of a box section surrounding the central recess and hole for the droplight Fig. 5). Finite element analysis of the structure using NEWPAC s , indicated that such a structure is too flexible in torsion (Fig. 6) which gives rise to excessive distortion at the corners when under load. The section was therefore stiffened by providing a closed box section. In practice this can be achieved by incorporating blocks of rigid polyurethane foam in the corners. It was still necessary to incorporate steel inserts in certain critical areas
Fig. 2. HST power car showing GRP cab front. very favourable and it is encouraging to see design engineers ready to accept fibre reinforced plastics in such a stringent structural application. The large-scale ballistic impact tests, which must be carried out on these structures before final approval, are time consuming and expensive. An airpowered laboratory gun has, therefore, been developed for preliminary assessment of materials and to obtain a more fundamental understanding of the behaviour of composites a . The effects of missile mass, shape and size can also be evaluated. Initial results (Figs. 3, 4) show that GRP laminates can give better all-round ballistic impact resistance than aluminium or steel of equivalent mass a . This investigation is part of a continuing research programme to develop fibre reinforced plastics (FRP) structures for ballistic impact applications, which minimise mass.
time. When the larger wrap-round corner door was introduced for Mk II InterCity coaching stock, it was decided to construct the item around a jig welded steel frame which is clad with GRP. In theory, the steel frame would accommodate the loads and the GRP would effectively provide a weatherproof cladding. This approach was later adopted for the current Mark III coaches. Doors constructed by this technique have an excellent record of reliability but tend to be heavy and expensive to produce. It seemed likely that the same standards of safety and reliability could be achieved by simplifying the 120
~-~
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3. Carriage Doors The earliest application of GRP on British Railways was in the Southern Region for suburban stock doors, which were introduced in the 1950's. Fatigue experiments demonstrated that the composite would be expected to have at least double the life of the standard metal doors based on cast aluminium or steel panels clad on a timber frame. As a result of this early success for GRP it has been widely used for this application since that
loo
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MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
20
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6 Mass/Area
Aluminium I
8
,
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(kg/m z)
Fig. 3. Penetration speed of various materials - 64 g pointed missile, 16mm diameter.
174
This exercise illustrated that the use of the composites must undergo a continual scrutiny to ensure that they are being used in a most effective and economical manner.
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16 mm diameter. such as the lock, hinge, etc. but the massive jig welded steel frame (Fig. 7) has been removed. A fully cored structure was also considered at the design stage but rejected because it produced too heavy a door. Mechanical tests carried out on prototype items showed that the new design would meet the requirements specified.
moulding process indicated that a cost saving of £100 per door could be achieved with additional benefits accruing from the lighter structure.
The potential of GRP in the manufacture of seat shells in passenger rolling stock was appreciated initially in the late 1960's. The complex curved shaped shell could be produced as one moulding which would be self coloured, light, easy to install, robust and aesthetically pleasing. Such a design would eliminate the need for extensive fabrication and finishing (e.g. painting) inherent in a more conventional metal/timber structure. Preliminary design studies demonstrated that GRP seat shells could be economic. Since there would be relatively large numbers of each item required, typically about 15,000 per
D I A G R A M A - SHOWS D I S T O R T I O N IN A N OPEN B O X S E C T I O N
i INTERIOR TRIM
PANELS
\
I
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J J
Fig. 5. Sketch of Mk Ill corner door.
Various processes were considered for production but it was decided that cold press moulding s was the most economical and appropriate. The two skins of GRP were moulded separately, the inserts bonded in position and the two skins then bonded together using a gap f'filing adhesive. The redesigned door weighs 38 kg compared with the original design of 58 kg (Fig. 7). Economic analysis of the cold press
175
DIAPHRAGM D I A G R A M B - SHOWS D I A P H R A G M M A I N T A I N I N G T H E S E C T I O N A L SHAPE AND RESISTING DEFLECTION
Fig. 6. Deflection of open and closed box sections.
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
annum, it becomes a viable proposition to use hot press moulding techniques to produce the component using sheet moulding compound 6 . This is one of the few railway applications where the high tool costs essential for the process can be justified. Consequently, GRP seat shells have been produced by this technique and supplied to British Railways since 1969 for both Inter-City and commuter rolling stock.
stress from one shell to its neighbour through ribs at the back of the seat. The final thickness of the component chosen was 5 mm which produces a single shell mass of about 5 kg and total mass of a complete double seat assembly (including frame and cushions) of 26.5 kg. Static load tests have been carried out on the finished item, which have confirmed that the design requirements have been achieved. The finished item (Fig. 10) is attractive, lightweight, easily assembled and a good example of a structural application of GRP in rolling stock.
toilet compartments (Fig. 11) to produce an attractive yet functional unit which is easy to clean and maintain. 6. GRP Production
As composite components were being developed and introduced into rolling stock it was necessary to set up an in-house facility through BREL, to produce many of the items required in new designs. Thus within British Railways development of appropriate production technology has proceeded in parallel with component development. At present much of the manufacture within BREL is by hand lay-up and cold press moulding with a limited amount of spray-up s . We have seen that the requirements for the railway industry in this country are relatively modest, thus in general it is not appropriate to consider capital intensive processes such as hot press moulding for in-house manufacture since few components could justify the expenditure required. Items such as seat shells for which the numbers required will
5. Coach Interiors It was indicated earlier that GRP is used extensively for decorative and semi-structural Finishes inside modern railway passenger coaches. The facility to mould complex shapes combined with excellent appearance and good mechanical properties of the material has been used by designers to good advantage in, for example, the saloon and vestibule areas where much of the cladding is GRP. Similarly, these advantages have been exploited in
/
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Fig. 7. Mk III corner doors - showing original jig welded steel frame in foreground. The most recent example of this application is for the Advanced Passenger Train (APT) which comes into service during 1981. The shells are moulded individually, bolted together at the back of the seat and fixed in pairs to an aluminium tube. Each pair of seats is supported on an aluminium pedestal in the centre and one seat is fixed to the side of the coach body (Fig. 8). The various loading factors considered in the design are shown diagrammatically in Fig. 9 where a safety factor of 1.5 is assumed. Stress analysis was carried out using NEWPAC s, to determine the minimum thickness of the item commensurate with the loading specifications and practicalities of production. A material tensile strength of 70 MPa was assumed in the stress analysis, which represents the minimum value specified for GRP requirements on British Railways. It is interesting to note that the ashtray housing between seats was included in the analysis since it contributes to the overall structure by transferring tensile
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
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Fig. 8. Sketch of APT second class seat unit.
176
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Fig. 10. Completed APT second class seat showing GRP shell. build of new coaches (approximately 5/week) and the numbers required of any particular item are relatively small. Thus the potential for capital intensive processes such as hot press moulding is very limited. The objectives of our production development studies are to improve the consistency and quality of the final item, increase output capacity and improve the working environment. Furthermore, it is essential to keep tooling costs low and concurrent with process development alternative techniques for producing tools are being investigated. The selection of any particular process depends on design complexity and total numbers
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Fig. 9. Design loads for APT second class seat. justify the use of such techniques are produced outside the railway industry by the Plastics Industry. In common with the UK reinforced plastics business in general hand-lay techniques have been the mainstay of GRP production within BREL. This process is very labour intensive, operative sensitive and can result in a very variable product and thus quality control procedures must be vigilant. Furthermore, there is a major problem with styrene emission from the polyester resin used in the hand laminating process and thus adequate extraction must be provided to produce a satisfactory working environment for the
177
operators. Health & Safety legislation is, quite rightly in our opinion, becoming much stricter and this must be a major factor to consider when setting up manufacturing facilities. It is likely that standards will become more rigorous and legislation is likely to follow Scandinavian practice which is considerably stricter than current UK regulations. Thus we have a continuing development programme evaluating and developing suitable production processes for the manufacture of composite items. British Railways have a specific problem in that there is a limited
Fig. 11. APT toilet compartment with GRP vanity unit, wall and ceiling panels.
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
contribution to make to the manufacture of GRP and is currently used by BREL for the production of window surrounds, doors etc. Recently British Railways have developed a novel vacuum impregnation process which is suitable for production runs between hand4ay and cold press moulding and is thus eminently attractive for the production requirements within BREL. The process has been described in detail elsewhere 6 7 but basically it relies on the injection of resin using a vacuum into a closed mould containing a glass pack. The capital investment required for this process is relatively low and inserts can be incorporated in the moulding cycle. The process is much more flexible than cold press moulding and very complex sections can be produced. Since the process is a closed mould technique styrene emission is low and additional extraction facilities would not normally be required (Table 1). Production rates and tooling costs lie between that of cold press moulding and hand-lay (Table 1) but material wastage is very low (less than 5?;) and quality and consistency of the product very high. For complex items it is essential to use a low yiscosity resin to ensure mould filling and special resins have been developed for this process. A major advantage of this process is that items which contain undercuts can be produced and for components where only one moulded surface is required a simple flexible bag can be used. The process is very attractive for BREL's production requirements and is being used for a wide variety of components at present, e.g. transponders, vestibule end doors. A more recent development is looking at the
required. One advantage of hand-lay techniques is that the tool costs are relatively low and the process is ideal for short production runs, prototype development and design approval. Any inserts can be incorporated very easily but there must be adequate extraction facilities if manufacturers are to conform to current legislation (Table 1). For large items such as the HST cab fronts it is likely that for the forseeable future the only economic method for producing these items will be by the hand-lay process and thus it will always have some part to play in our manufacturing capability. For higher production rates cold press moulding offers advantages for many components s. This process is a semi-automatic process where pressure is applied between matched moulds to distribute the resin throughout a prepared glass blank laid in the mould. This process gives much higher production rates than hand-lay, better quality control is achieved, and styrene levels in the working environment are considerably reduced (Table 1). Tool design is very critical and costs are correspondingly higher (Table 1). One disadvantage of the cold press moulding technique is that metal inserts cannot be included and must be located in position subsequently. These can be bonded by the use of structural adhesives and the use of such techniques can increase the potential of this particular process. The waste of material is very high (greater than 20%) and it cannot accommodate components with large thickness variations and is therefore restricted to items which are relatively simple in shape. In spite of these disadvantages cold press moulding does have a significant
TABLE 1: Comparison of Various GRP Processes
Process
Hand-lay
Styrene concentration (ppm) Tool Costs Without With (arbitrary Materials Wastage Extraction Extraction units) % 60-160
)
160-30~ (deep draw items)
) )
Cold press Moulding
60
Vacuum Impregnation
25
Production Rate (items/8 hour shift)
25-80
1
5
1
25
3.5
25-47
6-8
2.5 to 3
5
2-3
Not measurable
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
possibility of incorporating foam cores into the component to produce a structural item. This development is still at a very early stage but preliminary results look very promising. It is clear that the actual production process will depend on a number of factors but we have illustrated that mechanised processes can be used for relatively short runs required and these can be economic without the need for expensive capital investment. Clearly further work is needed to develop the processes further but the potential looks promising. At present the processes are restricted to conventional low glass/resin ratios but we see no difficulty in deveioping the process to produce higher fibre concentrations with other types of reinforcement and resins. Work along these lines is already being undertaken and the early results look encouraging. 7. Fire and Flammability
It is essential that high fire resistance standards are maintained for components used in passenger coaches. British Railways' basic approach is to use materials which are difficult to ignite, self extinguishing with a low surface spread of flame. GRP used for coach interiors must conform to Class 1 of BS. 476 for day stock and Class 0, according to the Building Regulations 1976, for sleeping cars. Furthermore, before any new design is approved in the future, large scale tests will be carried out to simulate realistic fire situations using facilities similar to those described by Woolley et al 8. Polyester resins have been developed in co-operation with the raw material suppliers which meet these requirements and can also be processed by the techniques discussed earlier. The specifications take no account of smoke generation at present, but it is fully appreciated that future developments must consider this problem, particularly as air conditioning in passenger coaches is likely to be standard. Future materials and process technology must change to meet future demands for increased safety. Smoke generation in GRP can be reduced either by modifying polyester resins or by using alternative polymers. The latter approach looks more promising and phenolic resins are becoming available for use with glass fibre reinforcement which greatly
178
TABLE 2: Smoke Density of GRP
BS. 476 Classification
*Maximum Optical Density (Arbitrary Units)
0
1.6
Polyester
1
0.6
Phenolic
0
0.35
Matrix
Polyester
* Measured using similar technique to Woolley et als . reduces the smoke generation (Table 2). However, further studies are needed to establish the long term mechanical properties of phenolic based composites and to develop suitable manufacturing methods. 8. Future Potential for Composite Materials Previous discussion has shown that GRP is well established on BR particularly for semi-structural and decorative items. In these applications the glass fibre is in short lengths ( < 100 mm) at relatively low volume fractions (10-15%), which does not make full use of the mechanical properties of the reinforcement. The introduction of high modulus high strength carbon fibre in the early 1960's created a great deal of interest in the potential use of fibre reinforced plastic composites for high performance applications. The initial enthusiasm, however, has not been sustained because of the continuing high price of the fibre. More recently aramid fibres have been introduced with properties and price intermediate between glass and carbon and these are finding applications in some areas. Composites based on carbon and aramid fibres are of interest as structural materials as they combine stiffness and strength with light weight (Table 3). However, it should be noted that GRP even with high volume fractions and a continuous fibre does not offer any significant advantage over aluminium. GRP will therefore be selected primarily where its other advantages can be exploited to the full, e.g. corrosion resistance, impact resistance, ease of manufacture into complex shapes. Applications on the railways for carbon and aramid fibre based composites have been limited up to the present time. Clearly high material costs, particularly for carbon fibre,
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have been the main reason but other contributory factors are the poor impact performance of carbon fibre reinforced plastics (CFRP) and low compressive strength of aramid reinforced plastics (ARP) and the fact that a new design approach is necessary if the full potential of these anisotropic materials is to be realised. It is appropriate to review the future potential of high performance composites as lightweight structural materials for railway rolling stock applications. There are two main advantages of lightweight construction: (i)
(ii)
Reduction of fuel consumption and associated benefits, e.g. reduced power unit size for given power/weight ratio, lower brake capacity etc. Reduction of track damage and hence maintenance costs caused by high unsprung mass. We have carried out theoretical
studies on selected journeys and showed that the cost benefits of reducing mass are about £0.40 to £3/kg. These figures are very modest when compared with the aircraft industry 9 and are unlikely to rise much above £5/kg (at 1980 figures) even if there was a substantial increase in passenger or goods traffic. It has not been possible to calculate the benefits which arise from reduced unsprung mass. Thus it is difficult to assess the economics of composite c o m p o n e n t s designed primarily to reduce unsprung mass. Lightweight construction in the railway industry at present is synonymous with the use of aluminium for nearly all practical purposes 1°. Thus it is pertinent to compare composites with aluminium. For the sake of this exercise we will assume that the materials are simple beams subjected to plane bending. The only geometrical variable is the depth of the beams which is adjusted so that all beams have the same stiffness. This is a very simplistic approach to the problem but it does give us some realistic basis for comparison of materials. The results are shown in Table 4 and we see that there are substantial mass reductions obtainable with CFRP and to a lesser extent for ARP. The saving for GRP is not significant and furthermore it produces a deeper beam for the same stiffness. Space is often at a premium in railway applications and clearly this increased depth could be a serious disadvantage with GRP.
TABLE 3: Mechanical Properties of Various Materials
Material
**CFRP - Type 1 Carbon **CFRP - Type 2 Carbon **CFRP - Type 3 Carbon **GRP **ARP Aluminium HE15WP Steel BS4360 Grade 55 *Pure Titanium 130 *Titanium Alloy 679
Specific Gravity
Tensile Modulus (GPa)
1.62 1.53 1.56 2.1 1.35 2.8 7.8 4.54 4.4
186 128 108 39 74 69 207 116 110
Tensile Strength (MPa)
1,330 1,560 1,500 850 1,270 450 625 540 1,030
Specific Tensile Modulus (GPa)
115 84 69 19 55 25 27 26 25
Specific Tensile Strength (MPa)
820 1,020 960 405 940 160 80 118 234
* ICI Designations ** Unidirectional laminate, volume fraction 0.60
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
TABLE 4: Comparison of Beams of Equivalent Stiffness
Composite *
Weight of Aluminium Beam Weight of FRP Beam
Thickness of Aluminium Beam Thickness of FRP Beam
CFRP - Type 1 - Type 2 ARP
2.17 1.91 1.81
1.39 1.15 1.02
GRP
1.08
0.83
* Unidirectional laminate, volume fraction 0.60
and ensure continuous contact between carbon collector strips and overhead wire 13, particularly at high speeds. The use of composite materials offers some potential and initial work has concentrated in reducing the mass of the pantograph head, that is the area closest to the overhead wire, which is the most critical area and offers the greatest benefit. Preliminary work was focused on CFRP but field experiments indicated that the material became badly eroded and was not suitable for application in this electrical environment. Subsequent work has concentrated on ARP which has proved satisfactory in these preliminary environmental tests. A straightforward replacement of the aluminium component is not desirable and a full composite head was developed from the outset. The bow shaped head was produced as a single moulding thus eliminating the bolted joint present in the conventional design which could cause load transfer problems An "U" cross section was chosen from aerodynamic considerations and the prototype items were produced by vacuum bag technique using pre-impregnated aramid cloth and fibre. The total weight saved is about 37% and a number of experimental heads la are being evaluated in service trials at present (Fig. 13). The main objectives have been to reduce carbon wear and increase the life of the component. Initial results are encouraging and it has helped to gain acceptance of these materials by
Although there are significant satisfactory in both static and fatigue advantages technically in using CFRP tests. Unfortunately, the impact and ARP as a direct replacement for behaviour of the tubes was very poor aluminium for lightweight structures and since they contain a hydrokinetic the economic argument is not so braking system this is a serious disstrong. We have calculated the costs advantage for this application. Neverwhich the fibres would have to come theless, it seems possible that the down to before they become econo- impact performance could be improved mical and concluded that carbon and by the use of hybrid composites or by aramid fibres would have to fall below using a protective shield connected to £10/kg and £7/kg respectively before the sprung mass of the structure. It they become feasible. These are does appear that substantial benefits considerably lower than the current might accrue by incorporating comselling price of the fibres and thus posites in the wheelset area but this we must seek additional technical concept is at a very early stage of reasons for selecting high performance development. Nevertheless, this study composites in any particular appli- has made engineers aware of the potential of the material which is a ation. There are a number of applications very important criteria for any new for composites, possibly in hybrid materials development. form with glass or other materials, where their technical advantages may (ii) Pantograph On electrified lines, there is a outweigh the initial high fibre cost. Ease of manufacture into complex requirement for a lightweight pantoshape is an added advantage in many graph to improve dynamic performance cases. Development work has been undertaken in a number of these critical areas. ( i ) Wheelsets This area is critical and significant reductions in track damage could be achieved if wheelset mass could be reduced. Hegenbarth 11 described an experimental composite wheelset evaluated by Deutsche Bundesbahn in the laboratory which looked promising. More recently British Railways ~2 have completed tests on two experimental CFRP axle tubes for the experimental AFr (Fig. 12). These tubes were made by resin injection and Fdament winding and an anisotropic f'mite element routine was employed to carry out the stress analysis 4 . The mass of the composite tubes was about 30% of the equivalent Fig. 12. CFRP axle tube for experimental APT under test. steel item and their behaviour was
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
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Fig. 13. Pantograph composite head showing ARP support for the carbon current collectors.
railway engineers. More recently a completely new pantograph design has been developed which requires a pair of lightweight aerofoils to improve the aerodynamics of the head 14. The aerofoils were required to conform to a standard profile (NACA6721) and these have been produced in ARP with a balsa wood core. These heads are currently under extensive experimental evaluation. The potential use for composites in the pantograph area has been readily accepted and there are numerous other areas in the main frame where the use of composites based on ARP or CFRP where it is away from the overhead wire could be attractive. This whole area is promising and is currently under detailed study. (iii) Drive Shafts The automotive industry1 s is considering the use of composites for main drive shafts to reduce mass and noise and they could offer a number of benefits in the railway area, e.g. - lightweight - enhanced damping - less balancing required - higher whirling speeds possible - excellent fatigue properties CFRP was considered for the APT cardan shaft and a 50% weight reduction could be achieved, but it was not considered an economic proposition in the present state of the art. In order to gain experience of this area of
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application for composites two fan drive shafts have been installed in Diesel Multiple Units. Although this is not a critical application, these components have been in service since 1975 and covered over 300,000 miles without any mishap. Rotating shafts do look a feasible application for composites which is likely to become real within the next decade. (iv) Leaf Springs The Use of composites based on glass and carbon fibre reinforced materials is currently being evaluated for leaf springs in the heavy goods vehicle area. The advantages are that it will reduce mass and increase the fatigue life. A subsidiary benefit is that it would make maintenance much easier. This is an area of great potential application for the railway industry and feasibility studies are currently being undertaken. The initial results look promising. (v) Freight Applications The use of fibre reinforced plastics for freight applications on British Railways is minimal at present although railway industries in Japan and France 16 are considering the use of Filament wound GRP tankers for the transport of wine and milk. The potential for composites in this area is large and a number of development projects are currently being carried out. One area of current interest is in
the use of composites for the floors of conventional covered wagons. At present these are 6 mm steel sandwich structures with 25 mm plywood. The loading requirements are given in BS. 3951 and in particular they must be able to withstand the load of a fork lift truck. A number of sandwich structures have been considered based on both GRP and aluminium skins with foam, balsa or plywood cores. All these combinations meet the stiffness criteria but impact tests have demonstrated the need for a high density core and hence the reccommendation that plywood is used for this particular use. There is little to choose between the performance of aluminium or GRP as skin materials but the material costs of GRP are 50% less. The mass of a plywood/ GRP structure is 65% of the original steel floor which corresponds to a reduction of the tare weight by about 1 tonne. Clearly this is a very attractive economic proposition and is an interesting example of how traditional materials, in this case timber, can be combined with modern fibre reinforced plastic materials to produce lightweight structures which are cost effective. This study is being extended to look at the feasibility of using composites on other parts of covered wagons, e.g. roofs, end panels, etc. The use of GRP for the construction of rail tanker wagons could offer advantages in several areas and the properties of the material that are being considered for exploitation are: (a)
(b)
corrosion resistance in tanks that carry corrosive or edible materials. These tanks are at present constructed of stainless steel or have some corrosive resistant lining. low coefficient of thermal conductivity of GRP has some very significant advantages in this area. In a fire engulfment situation the Ministry of Defence have already demonstrated the advantage of using GRP over steel and aluminium 17. Furthermore, in tanks carrying materials at above ambient temperature the use of composites could eliminate the necessity to use lagging on steel or aluminium tanks.
Although railway designs are unlikely to involve significant amounts of CFRP as a structural material in
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
the forseeable future because of high fibre costs, they may find application in some specialist applications where there are added technical advantages of using lightweight construction. Further it may be possible to use these advanced composite materials in hybrid composites with glass or in combination with aluminium and there is possibly further scope for evaluating the potential of these materials in sandwich structures with foam or plywood cores. Clearly further development work is required in this area to realise the full potential of the materials.
10.
Concluding Remarks
Glass reinforced plastics are used extensively in the passenger environment and it is unlikely that this will increase significantly. Future designs of rolling stock are likely to use the glass reinforcement more effectively and there will be a need to offer passengers greater protection from fire and smoke, particularly as legislation becomes stricter. Thus, the use of phenolic resins is likely to increase substantially at the expense of polyester resins as the matrix material. It will be necessary to develop or modify existing production methods to process phenolic based composites and further development work must be carried out to establish the mechanical properties of these materials so that items can be designed with the same degree of confidence that is currently accepted for glass reinforced polyesters. The problems are not intractable and are being investigated as a continuous part of British Rail's development work on composite technology. High fibre costs will preclude the use of carbon and aramid fibre composites in the immediate future as a lightweight structural material per se,
but there are a number of potential applications for these materials where their advantages may justify the high material costs. The future in these areas is promising provided that the anisotropic nature of the materials is appreciated and a multi-disciplinary approach is adopted involving engineers, polymer technologists and materials scientists.
7.
8.
9.
Acknowledgements
I would like to thank British Railways Board and Director of Research for permission to publish this paper. Thanks are also due to my colleagues in the Plastics Development Unit of British Rail Research for their assistance.
10.
11.
References 1.
2.
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4.
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6.
MATERIALS IN ENGINEERING, Vol. 2, JUNE 1981
"High Impact Resistance Windscreens", BR Specification 556: 1978, British Railways Board, London, UK. Batchelor, J., "GRP Driver's Cab for High Speed Train", Birmingham, UK, September 1977. Batchelor, J. & Garrington, P.J., "Impact Considerations and Performance for FRP on British Rail", Paper presented at BPF Reinforced Plastics Congress, Brighton, UK, November 1980. Dodd, R.J.M., "Application of the British Railways Finite Element Program NEWPAC to Railway Vehicles". Proc. conf. 'Application of Finite Elements in Mechanical Engineering - A Survey of current practice'. I. Mech E. 1972. Gotch, T.M. & Plowman, P.E.R., "Improved Production Process for Manufacture of GRP on British Rail", Paper presented at BPF Reinforced Plastics Congress, Brighton, UK, November 1978. Mohr, J.G., Oleesky, S.S., Spook, G.D. & Mayer, L.S., "SPI Handbook of Technology and Engineering of Reinforced Plastics Corn-
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