Application of Composites in Rail Vehicles

Application of Composites in Rail Vehicles

Application of Composites in Rail Vehicles$ M Robinson, Newcastle University, Newcastle Upon Tyne, UK r 2016 Elsevier Inc. All rights reserved. 1 2 2...

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Application of Composites in Rail Vehicles$ M Robinson, Newcastle University, Newcastle Upon Tyne, UK r 2016 Elsevier Inc. All rights reserved.

1 2 2.1 2.2 2.3 3 4 4.1 4.2 4.3 5 5.1 5.2 5.3 5.4 5.5 5.6 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 7 7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 7.4 7.5 7.5.1 7.6 7.6.1 7.6.2 7.6.3 7.6.4 7.6.5 7.6.6 7.6.7 7.6.8 7.7 7.8 7.8.1 7.8.2 7.8.3 7.8.4

Introduction Materials for Railway Applications Reinforcements Resins Cores Process Selection for Railway Applications Composites in Today's Railways Cab Ends Internal Fittings Lightweight Panels Composites in Tomorrow's Railways Bodyshells Bogies Wheelsets Pantographs Crashworthy Vehicles Freight Case Study 1 – The Use of Composite Materials for Crashworthy Rail Vehicle Bodyshells Introduction Technical Challenges in the Development of Crashworthy Composite Bodyshells The HYCOTRANS Project Material and Structural Design Crush Testing of Small-Scale Structures Summary HYCOPROD: The Way Forward for Crashworthy Rail Vehicle Bodyshells Case Study 2 – Design of Composite Vehicle End Structures in Railway Rolling Stock Abstract Introduction Benefits of Composite End Structures Strength and weight Aerodynamics and styling Integration of interior and exterior systems Use of Composites in Crashworthy Structures Existing Designs of Composite Vehicle End Structures Inter City 125 high speed train composite cab structure Modern Applications of Composite Structural Ends Sandwich structure construction Assembly of the cab Manufacture Impact testing of the sandwich construction Collision testing of the sandwich construction Suitability of findings for crashworthy cab Structural driving cab of C20 Stockholm Metro car Comments on findings of C20 with respect to UK heavy rail Challenges for Use of Composite Materials For End Structures Technical Requirements of Designing Composite End Structures Structural requirements Environmental requirements Production requirements Operational requirements

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Change History: July 2015. M. Robinson updated article title and author contact information, added Abstract and introduced edits in text, including citations and updated reference section. Figures 2, 3, and 17 were added. Section 6.20.5.7 was removed.

Reference Module in Materials Science and Materials Engineering

doi:10.1016/B978-0-12-803581-8.03965-5

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Application of Composites in Rail Vehicles

7.9 Conclusions 8 Conclusions References Further Reading

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32 32 33 34

Introduction

This chapter reviews components of rail vehicles in which composite materials have been employed successfully to date and those in which they are most likely to be exploited in the near future (Robinson et al., 2005). Specific references are made to some of today's rail vehicles in which composites are employed routinely for the fabrication of complex three-dimensional molded profiles and high stiffness-to-weight ratio paneling for cab ends and vehicle interiors. Specific materials are considered as are the processing routes employed to manufacture the various rail structures. The chapter goes on to consider research conducted by railway organizations around the world into more advanced composite structures such as bodyshells, bogies, and wheelsets, as well as the use of composites in infrastructure applications such as overhead cable gantries and track. Design case studies demonstrate the considerations for use of composites in rail cab structures and the use of composites for improved rail vehicle bodyshell crashworthiness. In comparison with the aerospace, marine, and automotive industries, the railways are generally perceived to have been slow in their adoption of composite materials. While this is true to a certain extent, composites (or more specifically fiber-reinforced plastics, FRPs) have been employed routinely for certain applications within the railway industry for many years now. In the UK, the suburban electric stock of the Southern Region was running with doors which incorporated glass fiber-reinforced plastic (GRP) from as early as the 1950s (Batchelor, 1981). These were found to have at least twice the fatigue life of the traditional metal-clad wooden doors they replaced. As a result of this early success, the use of FRPs was gradually extended to other applications in which their particular properties made them a superior and viable alternative to more traditional materials such as steel and aluminum. In today's rail vehicles, composites are often the first choice material for components with complicated three-dimensional profiles (such as cab ends, seats, and other internal fittings) and panels which require a high stiffness-to-weight ratio. Section 6.20.4 presents some examples of the use of composites in such instances. Furthermore, with the railway industry increasingly recognizing the importance of issues such as lightweighting (Robinson et al., 2006), life-cycle costing, and crashworthiness, it seems almost certain that the use of composites is set to rise substantially in the years to come. Section 6.20.5 highlights some of the areas in which more advanced prototype composite assemblies have been developed successfully by railway organizations around the world.

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Materials for Railway Applications

Since the 1960s there has been a rapid expansion in the growth of the FRP industry. Although this rate of growth has somewhat declined over recent years, all indications suggest that demand will continue into the twenty-first century. The unique advantages of FRPs derive from their superior strength and stiffness when compared on a weight-for-weight basis with the more traditional structural materials. This is a factor of particular importance in the design of moving components, especially in all forms of transport where reductions in weight translate into greater efficiency and cost effectiveness. In 1997 land transport was projected to account for up to one-third of all Western European sales of composites by the year 2000 (Fernyhough and Yasunao, 1997; Figure 1). This prediction proved to be correct (Holmes, 2013, 2014; Weaver, 1994; Starr, 1999; Reinforced Plastics, Nov/Dec 2012, Nov 2008, Nov/Dec 2009; Starr, 1992). These references, when reviewed, also show that the proportion of composite application is remarkably constant. This fact is surprising based on the fluctuating GRP production in Europe, Figure 3. Figure 2 shows that distribution of GRP production in different application areas was reasonably constant. Transport and construction fields dominated, but individual shares were constant.

2.1

Reinforcements

Figure 4 illustrates a breakdown of reinforcement fibers used in the manufacture of composites for rail vehicle applications according to fiber type (Kettle et al., 1997). Despite inroads over recent years in this sector by both aramid fibers and carbon fibers, particularly in the design of load-bearing components, the principal choice of reinforcement remains glass fibers. Although in

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Figure 1 Projected Western European sales of composites in the year 2000 (source Fernyhough and Yasunao, 1997).

Transport Construction Electro/Electronic Sports & Leisure

2013

2012

2009

2007

2005

2004

2003

2001

2002

2000

1999

1997

1998

Others 1994

40% 36% 32% 28% 24% 20% 16% 12% 8% 4% 0%

Figure 2 Percentage of GRP application areas in Europe.

GRP Production in Europe (x1000 tonnes)

GRP Prod…

1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013

1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0

Figure 3 GRP production tonnage in Europe (x1000 tonnes).

general this predominance may be attributed to the relatively low cost of glass fibers, there are a number of other factors which have contributed to its continued application. The processing characteristics of particular types of glass fiber have been modified and optimized over many years to achieve the required performance, such as choppability, low static build up, conformance to complex shapes, etc., and resin compatibility requirements such as fast wet out and good fiber/matrix adhesion. Of course, in addition to material type, reinforcements are also available in a variety of formats to suit the processes and design requirements most likely to be encountered. An indication of the relative usage of available formats within the rail sector is given in Figure 5. For the majority of nonstructural components, chopped strand mat (CSM) and continuous filament mat (CFM) provide the most economic choice of reinforcement design (Kettle et al., 1997). For more demanding applications, woven fabrics and noncrimp fabrics have found more widespread suitability.

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Application of Composites in Rail Vehicles

Figure 4 Breakdown of reinforcement fibers used in the manufacture of composites for rail vehicle applications according to fiber type (Kettle et al., 1997).

Figure 5 Breakdown of reinforcement fibers used in the manufacture of composites for rail vehicle applications according to fiber format (Kettle et al., 1997).

2.2

Resins

Thermosetting resins invariably are used in the manufacture of composites for rail vehicle applications, dominating the present and foreseeable market. An indication of the relative usage of the more popular systems within the rail sector is given in Figure 6. The principal choice remains polyester, with the rest of the market generally divided between vinyl esters, epoxies, phenolics, and modified acrylics (Kettle et al., 1997). Essential to the success of polyesters is the fact that their rheological properties can, by the addition of a selected filler such as hydrated silica, be further modified into gelcoats. However, their more widespread application in railway passenger rolling stock is limited by their general lack of fire retardance (Elmughrabi et al., 2008). In the unmodified form unsaturated polyesters burn readily, evolving large quantities of smoke and toxic fumes. This problem has been addressed to some extent by the range of inorganic fillers that are currently available. Perhaps the most well known and commonly employed are antimony trioxide and aluminum trihydrate, whose percentage additions impart differing degrees of flame retardancy, a property also afforded by the introduction of bromine or chlorendic acid into the original chemical structure. Other common additives, such as thermoplastics, can impart a low-shrink, low-profile nature to the resin, or by other chemical manipulation be employed to improve the optical stability or the resin's resistance to ultraviolet degradation. The use of such additives is common with other resin systems, especially where fire retardance is required. However, the drawback of using mineral fillers, such as those described above, is that improvements in matrix performance are often achieved at

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Figure 6 Breakdown of matrix resins used in the manufacture of composites for rail vehicle applications according to resin type (Kettle et al., 1997).

the expense of component weight. Furthermore, at high filler contents the resin becomes increasingly viscous and difficult to process. Where good fire performance is required phenolics are increasingly becoming the first choice of resin system and have attracted considerable attention from the rail sector. Phenolics are inherently fire safe, offering excellent low smoke, low toxicity properties. Current applications include the 38 ‘Le Shuttle’ motive power cars running through the Channel Tunnel. With each primary cab molding weighing-in at 240 kg, the ‘Le Shuttle’ front ends represent some of the largest hand-laid phenolic moldings produced to date. Phenolics are capable of achieving very exacting fire standards for composite materials (Chapman, 1995) such as BS EN 5545-Z: 2013, Railway applications – Fire Protection on railway vehicles. If extreme fire performance is necessary, there are a number of possible solution such as paints and coatings. It has been stated (Woodward and Brown, 1997) that with advances in material technologies of low viscosity highly reactive modified acrylic resins systems, improvements in the aluminum trihydroxids, rheology, and with highly efficient surface active additives, that fire safe composite parts can be produced that exceed the standards set by phenolic laminates (Feih et al., 2008).

2.3

Cores

Materials such as polymer foams, balsa, and honeycomb are used for the production of lightweight, stiff paneling which has for many years found widespread application in the rail industry (Kettle et al., 1997). The more common systems, and an indication of their relative use, is illustrated in Figure 7. Expanded polymer foams have for a long time been a popular option. These are often thermoset to achieve reasonably high temperature tolerance, though thermoplastic foams are used as well. Almost any polymer may be expanded, but the most common ones in sandwich applications are probably polyurethanes (PUR) and poly(vinyl chloride)s. PUR may be foamed in situ between the faces and thus do not need to be preformed into blocks. The most economic option for the majority of applications is balsa. Applications include the driver's cab of the new C20 Stockholm metro car supplied by Adtranz commenced service in December 1997. Balsa is used as the core material in all sections other than around the headlight box where it is replaced by polyurethane to simplify manufacturing. Other recent applications include flooring (Hudson et al., 2009, 2010) for the Kuala Lumpur Monorail manufactured by Flexadux Plastics in the UK. In this case, end-grain balsa clad in a phenolic laminate was used to fabricate large 3 m  3.2 m panels. Materials consisting of cellular arrays, such as honeycombs, have a number of unique properties which have led to their specification in rail vehicles. They are most commonly employed as cores in lightweight, high stiffness, high strength sandwich panels, such as in the Italian ETR 460 and ETR 500. The uniform compressive properties of honeycombs have also led to their use as energy absorbing components in crashworthiness applications. A more recent development are the three-dimensional woven glass fabrics which offer improved shear properties compared to foam cores at competitive prices (see, e.g., Alba and Miravete, 1995). Also known as distance or space fabrics, they are constructed with thin skins separated by a vertical pile (illustrated schematically in Figure 8). The gaps between the vertical piles may be foam filled, thereby enhancing the mechanical performance of the sandwich structure as well as significantly improving the thermal and acoustic insulative properties. Tradenames under which such products are marketed include Parabeam and Vorwerk Cloth.

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Application of Composites in Rail Vehicles

Figure 7 Breakdown of core materials used in the manufacture of sandwich panels for rail vehicle applications according to material type (Kettle et al., 1997).

Figure 8 Schematic representation of a three-dimensionally woven fabric.

The former was used for flooring on the Glasgow Metro. The panels, manufactured by Flexadux, were constructed using the Parabeam fabric and phenolic resin. The completed panels were then filled with a phenolic foam.

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Process Selection for Railway Applications

While composites are used in an impressive variety of applications, the techniques employed to manufacture components tend to be few and usually involve a large degree of manual labor. The more common variants are illustrated in Figure 9. Despite the trend toward automated and semiautomated processes, hand lay-up and spray lay-up remain the most popular methods for the manufacture of components used in rail vehicle applications (Kettle et al., 1997). These techniques are very flexible yet labor intensive, and thus best suited for a short production series of especially large structures, such as in the case of the ‘Le Shuttle’ motive power cars discussed above. In this example, despite their size, the cabs were manufactured to a high degree of accuracy, with the molding dimensions held within a tolerance of 72 mm. One advantage of hand-lay technique is that the tool costs are relatively low. Any inserts can be incorporated very easily but there must be adequate extraction facilities if manufacturers are to conform to current legislation.

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Figure 9 Breakdown of manufacturing processes used in the production of composites for rail vehicle applications (Kettle et al., 1997).

Cold press molding offers advantages for many components and has been used for many years in the manufacture of window surrounds, toilet modules, and vestibule panels. This semiautomatic process achieves better quality control than hand-lay and styrene levels in the working environment are considerably reduced. Where the large production runs justify the high tooling costs involved, hot pressing of sheet molding compound (SMC) has been used to fabricate passenger seat shells. Improved decorative surfaces can be achieved by painting and lacquering SMC parts. Resin transfer molding (RTM) has also found increasing application in this sector. Product examples include the Strasbourg light rail vehicles which feature both seat components and sliding doors manufactured in the UK by Astec using RTM. RTM is a viable production method for the mass transport market (Brown and Woodward, 1995). As the RTM process develops and materials technology improves, there are improved prospects for the production of cost-effective parts for the rail industry. Fire safety is of paramount importance to designers and RTM products such should not compromise this feature in the drive to replace metals. The French railways fire standard is NFF 16–101 which provides M/F ratings where M is the reaction to fire and F is a combined smoke and toxicity index. The Ml/F0 combination indicates a very low fire risk indeed and lower than could be achieved using state-of-the-art RTM composite materials until recently. The limitation on achieving this standard for the modified acrylic resins was the high viscosity processing limitations. Recently, a development which combines modified acrylic resin, aluminum hydroxide (ATH – for fire retardant properties) and a viscosity modifier has achieved Ml/F0. Processing additives are widely used in the plastics industry to lower process viscosities in the case of modified acrylic and ATH, the processing aid supplied by BYKChemie (W-996) was a solution of copolymerics with acidic groups. The monofunctional molecules have both resin compatible and filler seeking groups, the latter adsorbing on to the ATH particle surfaces, thereby reducing interactive forces and consequently resulting in lower filled resin viscosity. The following injectable Ml/F0 formulation was developed: (i) modified acrylic – Modar 835 S, 100 parts by weight; (ii) processing aid – BYK-W 996, 3 parts by weight; and (iii) aluminum hydroxide (ATH) – Martinal ON-904, 150 parts by weight. The viscosity of the formulation at 20 1C is about 700 MPa. which is a dispersion viscosity comfortably below the 1000 MPa accepted to be the maximum acceptable for satisfactory injectability. A variation on this RTM process, Network Injection Molding (NIM), was used by Fiberlite Composites, based in the UK, in the development of seating for the Networker 465. (NIM is basically a resin injection process that allows very high rates of resin to be injected to produce complex structures.) Composed of glass fiber, Modar resin, aluminum trihydrate filler, and polyurethane foam, the complete seat shell weighs less than 6 kg. SCRIMP (Seemann Composite Resin Infusion Manufacturing Process) has been used for the production of a number of rail products (Marsh, 1997). This has come about due to the need to reduce and contain emissions of organic volatiles, usually styrene, during manufacture. Until this development, during vacuum molding, the main obstacle was achieving rapid long-range flow of resin into all areas of the dry fiber pack before cure takes place. SCRIMP addresses this problem by using a medium which rapidly distributes resin across the entire surface area of the pack, leaving the liquid to infuse across the part's thickness only with vacuum assistance. An example of the distribution medium essential for SCRIMP is a knitted mesh fabric incorporating a criss-crossing network of resin distribution channels, being placed on the fiber pack so that thorough wetting is achieved. A resin permeable ply should be placed between the distribution layer and the part being molded. This allows the mesh and the excess resin to be removed and disposed of afterwards. Generally the SCRIMP process becomes more economically attractive the larger the molded items are which explains why it has been used for the manufacture of rail cabs.

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Application of Composites in Rail Vehicles

Composites in Today's Railways

The use of composites in rail vehicle applications has increased quite substantially in recent years as designers have come to appreciate the benefits afforded by such material systems. At the moment, the utilization of composites in rail vehicles is restricted largely to components with complicated three-dimensional profiles such as cab-ends, seats, and other internal fittings and panels which require a high stiffness-to-weight ratio. The cab fronts of trains, lightweight fittings for passenger vehicle internals, and panels are considered in turn below.

4.1

Cab Ends

Composites have been used extensively in rail vehicle cab ends because the complex three-dimensional profiles demanded by the aerodynamics and esthetics of modern trains can be both difficult and expensive to manufacture from metal. With benefits also arising in terms of lightweighting and impact resistance, increased confidence in the use of composite self-supporting structures has led to the extensive application of FRPs in this area. One of the earliest such structures was the front end of the UK's high-speed InterCity 125 power car which came into regular service in 1977. This was fabricated from a sandwich structure consisting of laminated GRP facings around a polyurethane foam core (Batchelor, 1981). The outer facing was fabricated as a single molding and the inner facing from three separate parts. These two facings were then brought together and assembled so as to form a cavity into which the polyurethane foam was injected. Additionally, provision was made within the sandwich structure for the incorporation of service ducting for air conditioning and electrical wiring, thus making a very tidy overall arrangement. The resulting structure was estimated to be some 30–35% lighter than a conventional steel cab, and had sufficient impact resistance to prevent penetration by a 0.9 kg steel cube traveling at 350 km h1. A different materials system was employed for the nose of the more recent Italian ETR 500 high speed train. The 300 km h1 running speed required the extra rigidity and resistance to impact afforded by the combination of aramid fibers and an epoxy resin. These materials were molded into an aerodynamic profile which has good dimensional stability at high speeds. The ETR 460 aerodynamic front cab manufactured by Sistemi Compositi (Jacob, 1997) is manufactured using RTM and uses an aramid fabric, S-glass, fire retardant polyester resin, and polyurethane foam. The aramid fabric ensures that the impact resistance requirements are met. This nose however is not structural, requiring that it is produced to close tolerances in order that it can be attached to the aluminum frame. The composite nose costs more than the metal equivalent, but the shape is much improved and the final assembly is quicker with the composite making the composite solution more competitive. The 38 ‘Le Shuttle’ motive power cars running through the Channel Tunnel have a cab fabricated from yet another type of composite material system. Due to the fact that the vehicles spend the majority of their operating life underground, they are required to meet very stringent fire regulations. Consequently, a fire retardant phenolic resin was specified for use in the vehicle's GRP cabs. With each primary cab molding weighing in at 240 kg, the ‘Le Shuttle’ front ends represent some of the largest hand-laid phenolic moldings produced to date. However, despite their size, the cabs were manufactured to a high degree of accuracy, with the molding dimensions held to within a tolerance of 2 mm. Phenolic resins have been used for new build and refurbishment of the London Underground rolling stock since 1985. The cab ends produced for GEC Alstrom and running on the Northern and Jubilee Lines were fabricated using phenolic resins. The necessary missile resistance was achieved using a single phenolic laminate of 6 mm thickness. Thirty two phenolic airport express fronts with ploughs were produced for Adtranz Norway in conjunction with ABB Offshore Technology. These vehicles run between Oslo and the new Gardemoen Airport. Phenolic resins were selected due to the 30% tunnel running time of vehicles. Initially the train fronts were prepared by hand-lay but as the project developed the SCRIMP process was used. An example that composites are now the only sensible choice for cab front ends is provided by the decision made for the C20 Stockholm metro car supplied by Adtranz (Von Werne, 1997). The complex shape of the driver's cab left the manufacturer with no other possibility than to use composite materials. In order to make a virtue out of a necessity it was decided for the first time in an Adtranz Sweden vehicle to make the composite cab load-bearing. The cab was designed to contribute to the overall stiffness while still fulfilling the fire safety requirements for tunnel operations. The drivers cab is a large molding of approximately 15 m2 which was hand laminated in one piece. Hand lamination was selected due to the very cost competitive nature of this manufacturing method for relatively low volume components. The skins were constructed using knitted multiaxial glass fabrics in a polyester resin. The fire safety requirements resulted in the addition of alumina trihydrate (ATH) to the polyester resin to achieve low flammability and low toxic gas emission. The core material used was balsa apart from in the area around the headlight box where polyurethane was used. The cab structure created is subsequently bolted to the steel carbody.

4.2

Internal Fittings

The combined requirements of lightweighting and ease of manufacture have also led to the extensive use of composite components in rail vehicle interiors. Indeed, FRPs now account for approximately 8% (around 3 t) of the overall weight of an InterCity

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passenger coach (Sawley, 1989). In general, the most commonly employed composite material system for internal fittings has been glass fibers in a fire retardant polyester resin. Window trim surrounds, toilet module and vestibule panels, and end of roof canopies have all been manufactured successfully using cold-pressed, sprayed, or hand-laid random or semicontinuous glass mat. Where the large production runs justify the high tooling costs involved, hot pressing of SMC has been used to fabricate passenger seat shells. Similarly, RTM has found increasing application; the Strasbourg light rail vehicles feature seat components and sliding doors (Roberts, 1994) manufactured by this process. As well as the molded components described above, composites have also being incorporated into high stiffness-to-weight ratio sandwich paneling for vehicle interiors. Such panels, which typically consist of a foam or honeycomb core between two FRP skins, have been employed in the aerospace industry for many years. However, as designers increasingly attempt to realize the benefits of lighter rail vehicles, their application in railway coaches is becoming more widespread. The Italian ETR 500 again provides a good example of the use of such composites in a modern high-speed train, with interior side walls, ceilings, and luggage compartments all fabricated from sandwich panels. The sandwich consists of a honeycomb core between glass-phenolic laminated skins with a surface finish of polyvinyl fluoride film. This lightweight combination of materials was chosen for its versatility and high mechanical resistance. Similarly, Eurotunnel's tourist shuttle wagons employ phenolic honeycomb panels for their interior bodysides. To date the mass transit market has proved to be the most significant for phenolic composites. In 1994 there was a problem with the existing internal thermoplastic fittings which had environmentally stress-cracked. The replacements were made from a phenolic composite; the rationale behind this was to combine fire performance weight saving and environmental resistance. Sets of panel moldings for end, side, door, window masks, and luggage racks were manufactured using hand lay-up. The roofs were manufactured by spraying fibers and resin onto a phenolic core to produce a lightweight sandwich structure.

4.3

Lightweight Panels

Light but stiff composite panels (Hudson et al., 2011), typically consisting of a foam or honeycomb core sandwiched between two fiber-reinforced skins, have been employed successfully in the aircraft industry since the early 1970s. However, as designers increasingly attempt to realize the benefits of lighter rail vehicles, their application in railway carriages is becoming more widespread. The ETR 500 again provides a good example of the use of composites in a modern high-speed train with all interior furnishings (side walls, ceilings, and luggage compartments) fabricated from sandwich panels. The sandwich consists of a NOMEX honeycomb core between two glass-phenolic laminated skins with a surface finish of the PVC film Tedlar. This structure was chosen for its high mechanical resistance, lightness, and structural flexibility. In Germany, all exterior panels for the Regio Shuttle produced by Adtranz were based on phenolic skins surrounding a polyvinyl chloride (PVC) foam core (Chapman, 1995). The panels were attached to a welded aluminum frame using an elastomeric adhesive. The composite panels were not load bearing and therefore the foam selected was selected on the basis of low weight. The phenolic resin was the preferred choice to comply with the German fire standard DIN 5510 part 2. The surface finish was achieved by applying a filler surface paste prior to painting. The Danish firm LM Glasfiber produces roofs for Talent trains which use a composite sandwich structure. A composite roof resulted from the requirement of the Talent to be production friendly and lightweight. The low weight train is preferred to reduce environmental impact through reduced energy consumption. The roof is a self-supporting sandwich structure produced in glass-reinforced polyester with a PVC foam core. The roof is manufactured using a vacuum injection technique which gives a fiber volume. The core is placed in a large mold with a polyester gel coat which provides the external appearance and color of the roof. The product is then covered with a vacuum bag and the polyester is drawn under vacuum into the mold to provide thorough wetting. The roofs are molded in two parts 1.75 m wide and 7.5 m long; these are assembled along with the attachment to the body using adhesive. This construction meets the fire requirements of DIN 5510. Talbot's Talent train was the first one to use pultruded side walls (Jacob, 1998).

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Composites in Tomorrow's Railways

The previous section has reviewed some of the areas within the rail industry in which composite materials have found proven application and are, as such, employed routinely. This section describes some of the more recent research and development which has attempted to extend the use of FRPs into other aspects of railway engineering in which metals have a traditional stronghold. The use of composites in the rail industry is becoming widespread (Goedel, 1998; Robinson, 1998; Robinson et al., 1999) and their use for stressed structures is becoming usual as the advantages of composite structures become enhanced. Following the high profile use of composites in the filament wound passenger coach body shells by Schindler Waggon, the rail industry has become aware of the possibilities offered by composite materials. Europe and Japan are leading the world in the application of composites to passenger trains; in America the principal applications are freight vehicles and track components, particularly sleepers. The driving force for much of the current research is the need for lightweight yet energy absorbent composite materials to replace traditional metal structures fabricated from steel or aluminum. Generally, metals are costly and employ labor intensive

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Application of Composites in Rail Vehicles

procedures such as welding and cleaning during fabrication. Metals also contribute to higher life cycle costings due to their low energy efficiency, whereas composites can offer weight savings of up to 50%. Additionally, composites offer noncorrosive properties that promote extended service life. Composite materials offer a versatility that can form complex shapes demanded by aerodynamic and ergonomic considerations. Not only do composites need to absorb energy, but also they need to be affordable and therefore research has shown that standard glass fiber composites can be designed innovatively to absorb large energy levels in a predictable manner. The traditional antiquated view that lightweight constructions offer lightweight protection is being severely challenged by composite designers in all transport sectors.

5.1

Bodyshells

The bodyshell of a rail vehicle accounts for a significant proportion of both its mass and production costs. With manufacturing methods for traditional materials such as steel and aluminum now well developed, attention is being directed increasingly toward the use of composites in an attempt to achieve further savings in these areas. One of the most exciting recent developments in the field of bodyshell construction was unveiled by the Swiss company Schindler Waggon in May 1995 (Brooks, 1995). Their prototype three-car tilting train features a bodyshell fabricated entirely from composites using a pioneering automated production process. A mold representing the rail vehicle's interior is first attached to a rotating mandrel and this is then sprayed with a colored material which will eventually provide the finished internal surface. An initial layer of either glass or carbon fiber saturated with resin is then fed on to the rotating mold, with the rate at which the feeder traverses the mold varied to give the appropriate fiber orientation. An insulating layer of hard foam panels is then added, together with ducts for cable and ventilation systems. This is then followed by another fiber–resin layer, a further layer of insulation and a final exterior fiber–resin layer which gives a higher class of surface finish than either steel or aluminum. Door and window openings are incorporated by simply cutting out appropriate sections. Schindler Waggon cite the benefits of this new composite bodyshell as being the virtually fully automated production process, the greatly reduced number of parts, the integrated cable and ventilation ducting, the excellent resistance to corrosion, and the savings in life cycle costs due to lower weight and better thermal insulation. With their existing facilities Schindler Waggon can complete an entire bodyshell in 8 days, although once the technology has been accepted and proven in service, they have plans for a future capacity of 200 shells per year. Interior modules for refurbished vehicles have also been manufactured using this technique. Railway engineers in Japan have also looked at ways of reducing bodyshell weight through the application of FRPs. However, rather than adopting the entirely composite approach of Schindler Waggon, the Tokyo Car Corporation, and the East Japan Railway Company have investigated the incorporation of carbon fiber-reinforced plastic (CFRP) roof shells into an otherwise aluminum structure using a novel transition welded joint (Matsuoka and Nakamura, 1993). Tests have shown that car bodies with such roof shells are able to sustain higher fluctuations in pressure, have a lower center of gravity, and are around 300–500 kg lighter per vehicle. Similarly, the Japanese Railway Technical Research Institute has developed and tested hybrid aluminum-CFRP structures (Suzuki and Satoh, 1993). In order to keep production costs down, an automated pultrusion process was used to produce the CFRP panels. These were then riveted onto an aluminum frame to complete the bodyshell structure. As an extension of this work, two 1 m long, integrally stiffened, curved half-sections were produced from CFRP using an autoclave process. The two halves were then riveted together to form a complete bodyshell section which was nearly 30% lighter than an equivalent aluminum structure. The use of FRPs in structural foam sandwiches has been a subject of bodyshell research interest in France. SNCF are investigating the use of lightweight structures consisting of carbon and glass-reinforced epoxy around a foam or honeycomb core (Cléon, 1995). These are being developed specifically for use in their double decker high-speed train in which axle load margins are extremely tight. The research undertaken by Cléeon is essential for the evolution of the TG V train designs which require the development of lighter vehicles in the future. The metallic bodyshells currently used in the bilevel stock are just (with the use of optimized aluminum structures) achieving an axle load of 17 t. This leaves very little weight tolerance on the vehicle and if additional axle load cuts are required the use of composite materials is essential. The approach of Cléeon and his team was to create the bodyshell from two half-tubes requiring only one vacuum bag mold due to the symmetrical nature of the parts. The intermediate floor is produced separately and then the whole is glued together. The positioning of the joints ensures that a feature can be created thereby reducing the finishing required on this relatively low-cost system. Similarly, ANF Industrie (a division of Bombardier Eurorail) in conjunction with the Universite de Technologie de Compiegne have produced a fifth scale model of a metro car bodyshell fabricated from glass/epoxy skins around a polyurethane foam core (Barre et al., 1994). Although the design was very much in its infancy, static analyses using both experimental and finite element techniques yielded promising results. While the bodyshells described above are still relatively unproven in regular service, the monorail cars at the Walt Disney World complex in Florida have been running with composite bodies since the early 1990s (Humphries, 1991). In order to increase the passenger carrying capacity of the system, the car bodies were redesigned using a variety of materials which included honeycomb, carbon and glass fibers, and epoxy and phenolic resins. Weight savings in excess of 40% were achieved over a conventional

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aluminum construction and it has been estimated that the composite car bodies are actually 9% less expensive than the competing aluminum design due to reduced labor and scrappage.

5.2

Bogies

Rail vehicle bogies make an important contribution to the overall performance of a train. They must meet demanding requirements concerning safety, ride comfort, wear, and maintenance, and are a substantial component of a vehicle's overall mass. FRPs, with their low weight, high specific strength, high fatigue strength, low crack propagation rate, good structural damping, and resistance to corrosion would appear to have much potential as structural materials for bogie frames. As such, their use has been considered in a number of countries around the world. As a result of research and development by AEG Westinghouse Transport-Systeme and Messerschmitt-Bolkow-Blohm (MBB), a German intercity coach with FRP bogie frames ran successfully in service for the first time in January 1988 (Leo, 1991). The composite bogie was 1 t lighter than a conventional bogie, had a reduced number of parts, had excellent strength and fatigue properties, and attained running behavior results that were equal to, if not better than, those of a standard bogie. Since its introduction, the coach fitted with the FRP bogie frames has clocked up well over a million kilometers. The Japanese Railway Technical Research Institute has also been conducting research into FRP bogie frames. Using CFRP, weight savings of as much as 70% over conventional steel-fabricated frames have been achieved. Furthermore, it has been reported that a technical breakthrough for practical application is imminent. Similarly, the French SNCF and ‘École Supérieure des Arts et Metiers’ have recently developed a half-scale prototype bogie featuring a monobloc chassis fabricated from laminated glass fiber/epoxy layers. The prototype is two-thirds lighter than a conventional metal chassis, has improved fatigue resistance, and a substantially reduced number of parts.

5.3

Wheelsets

Researchers in Germany at the Institute for Machine Tools and Product Engineering (IWF) have been investigating the use of composites for rail vehicle wheels. The wheels consist of CFRP over a molded foam core and weight savings of as much as 50% have been achieved while retaining the strength required to support in-service loads. In the UK, British Rail investigated the use of CFRP for rail vehicle axle tubes during its development of the ill-fated Advanced Passenger Train (APT) (Batchelor, 1981). The tubes were made by resin injection and filament winding and gave a weight saving of about 70% over an equivalent steel item. However, although their static and fatigue performances were satisfactory, their impact behavior was very poor and they were subsequently dropped. However, it was suggested that this problem could be overcome by the use of hybrid composites or by using protective shields.

5.4

Pantographs

For electric trains which draw their power from overhead lines, composite materials have been considered for the fabrication of the pantograph (the jointed, self-adjusting framework on top of the vehicle which conveys the current from the overhead lines). Early work by British Rail (Batchelor, 1981) focused on the use of CFRP for the pantograph head, but it was soon found that this material did not perform well in an electrical environment and became badly eroded. Aramid fiber-reinforced plastic was therefore selected as an alternative and was found to perform satisfactorily. Prototype components were manufactured using a vacuum bag technique and yielded weight savings of 37%.

5.5

Crashworthy Vehicles

In recent years, crashworthiness has become recognized as an important issue in virtually every transportation sector. Considerable research interest has been shown in the use of FRPs for crashworthy structures (Pitarresi et al., 2007) because it has been found that they can be designed to provide collision energy absorption capabilities which are superior to those of metals when compared on a weight-for-weight basis (Hull, 1985). The bulk of the research in this area has been of an experimental nature and has focused on the axial compression of tubular specimens. British Rail has conducted vehicle crash simulations with cab ends that have included GRP tubes mounted in the buffer positions (Scholes and Lewis, 1993). It was anticipated that large amounts of kinetic energy would be absorbed in a controlled manner through brittle fracturing of the composite material. However, difficulties were experienced in the accurate prediction of the collapse force and in the reliable reproduction of the desired failure mode. A general difficulty in the use of composites for crashworthiness applications has been the reproduction of the high energy absorptions demonstrated by simple geometries such as tubes in actual vehicle structures. In other words, the question remains of how best to harness the energy absorption potential of FRPs such that they can be employed realistically in structural applications. The transportation industry has for a long time been engaged in the application of new lightweight materials for primary structural design in an effort to develop more energy efficient structures to meet low emissions targets without compromising public safety.

12

Application of Composites in Rail Vehicles

This is also true for the rail industry, but the implementation of new lightweight materials has been slow mainly due to the lack of suitable certification procedures addressing the specific operational requirements of a railway vehicle. Such procedures are necessary so that rail vehicle manufacturers and operators can be confident that rolling stock made of a new material will perform as intended and will be at least as safe in terms of crashworthiness as a vehicle made out of the material it replaces. A current European project (REFRESCO) project aims to achieve this goal by creating the regulatory framework for the use of composite and other new materials in rail car bodies. The existing certification procedures are being analyzed, gaps identified and test and assessment methodologies for both isotropic and orthotropic materials are being developed. It is expected that the output from REFRESCO will accelerate the implementation of new materials and composites in transport applications improve the competitiveness of transport industries, ensure sustainable, efficient and affordable transport services will be available and will create new skills and job opportunities through research and development in new material technologies. REFRESCO has identified that the crashworthiness standard EN15227 is independent from the materials used. However the following remarks apply to the use of composites:

• • •

Even though EN15227 is independent from the (exact) material used, it currently presumes the use of materials having ductile behavior. It can be used except where criteria in terms of maximum plastic deformation percentages are required. The way the energy is dissipated by the carbody structure depends on the material. It also has an effect on the acceleration levels achieved.

A driver’s cab was designed and produced by the De-Light project (Carruthers et al., 2012; Ingleton et al., 1999), a ‘reaction zone’ was conceived which would form the driver’s survival space and designed not to fail under the loads imparted to it by the crash scenarios of EN 15227. Consisting of a composite sandwich structure the design underwent physical testing to prove the capability of the structure, which exceeded the design requirements by a factor of 2.5. The monocoque design merges the outer skin of the cab with the internal reaction zone elements, allowing loads to be reacted over the entire cab structure, further increasing the factor of safety in the design.

5.6

Freight

In general, composite materials have not been employed extensively in freight applications although there is thought to be considerable potential in this area. A notable exception has been the development of composite car carriers by the Union Pacific Railroad in the USA (Ashley, 1990). Excessive damage to new cars on their way from the factory to the showroom led Union Pacific to re-examine the design of their freight wagons. Problems with corrosion and a desire to reduce fuel consumption led to the specification of pultruded glass/polyester composite sections for the freight wagons’ housings. With each module 10 m long, 2.5 m wide, and weighing over 3 t, they are believed to be some of the largest single units ever assembled from pultruded structural stock. Furthermore, weight savings in the region of 5–10% were achieved over conventional equipment. Other areas in which composite materials have potential for freight applications include corrosion resistant containers for the transport of corrosive or edible materials and for situations in which the low thermal conductivity of GRP can be exploited. Thermally insulated freight wagons manufactured by Hardcore-Du-Pont for the brewing company Coors exploit all these benefits (Perrella, 1996). The impetus to develop a composite insulated refrigerated freight rail car came from the fact that the vast majority of the 39 000 fleet in North America were over 25 years old. This provided a market opportunity for the manufacturer that developed an affordable, lightweight, corrosion resistant, and thermally insulated composite alternative, as the vehicles need replacing within 5–15 years. After a program to develop the replacement freight vehicle resulted in a collaboration between Trinity Industries, a US freight railcar builder, and Hardcore DuPont Composites with their SCRIMP process technology. Using this process the entire carbody was manufactured in one piece; this had a number of advantages such as: (i) minimized assembly costs; (ii) elimination of thermal leaks; and (iii) improved structural durability and reliability. Subsequently, the roof, doors, and load dividers were manufactured and assembled prior to fitting to the underframe. Employing glass fibers, vinyl ester resin, and urethane foam the finished bodies have a mass around 7 t which is approximately half of the equivalent steel design. The completed railcar is then painted with a urethane paint prior to being placed into service.

6 6.1

Case Study 1 – The Use of Composite Materials for Crashworthy Rail Vehicle Bodyshells Introduction

The objective of any crashworthy vehicle design is to ensure that, in the event of a collision, the kinetic energy of the impacting masses is dissipated safely so as to minimize the risk of injury to the vehicle's occupants. Research into the use of composite

Application of Composites in Rail Vehicles

13

Figure 10 Comparison of material mass specific energy absorptions (tubular specimens) (data taken from Parley, 1983; Thornton, 1979; Thornton and Magee, 1977).

materials for crashworthy structures has demonstrated that they can be designed to provide collision energy absorption capabilities which are superior to those of metals when compared on a weight-for-weight basis. However, there are still a number of technical challenges which must be resolved before composite materials can be employed routinely for crashworthy rail vehicle bodyshells. This section reviews these challenges, and describes how one project in particular, HYCOTRANS, is addressing them. It has become increasingly accepted that structural design philosophies based principally on strength and stiffness are far from optimal when it comes to the protection of passengers or cargo in the event of an accident. Rather, it is preferable to design a vehicle to collapse in a controlled manner which safely dissipates the kinetic energy and limits the accelerations transmitted to the occupants. In the automotive and aerospace industries, considerable research interest has been shown in the use of composite materials for crash-worthiness applications. This is because it has been demonstrated that they can be designed to provide collision energy absorption capabilities which are superior to those of metals when compared on a weight-for-weight basis (Figure 10). It has been found that, in general, FRPs do not exhibit the ductile failure processes associated with metals. Instead, the brittle nature of most fibers and thermosetting polymers tends to generate a brittle mode of failure. Provided that the crushing mechanisms can be controlled so that the FRP fails in a stable, progressive manner, very high levels of energy can be absorbed. However, despite some promising laboratory demonstrations, there are still a number of issues relating to the practicalities of implementation which are yet to be resolved. Furthermore, little attention has been paid to the role of energy absorbing composites in rail vehicle applications. With the advent of all-composite train bodyshells, such as Schindler Waggon's filament wound construction (Brooks, 1995), it is important that the crash-worthiness properties of such structures are understood in order that they can be suitably optimized.

6.2

Technical Challenges in the Development of Crashworthy Composite Bodyshells

Although our understanding of the energy absorption properties of composite materials has advanced significantly over the last 30 years, there would still appear to be a number of concerns which are imposing limitations upon their widespread adoption in crashworthy structures. Not least of these is the development of high energy absorbing composite systems which are affordable across the broad range of transportation industries; much of the pioneering work has been done with expensive high-grade aerospace materials. Similarly, design methodologies and manufacturing techniques need to be developed which will enable the viable production of real crashworthy components for specific applications. This is especially important if composites are to be competitive with their metallic counterparts. On a more fundamental level, there is a lack of clear understanding about the behavior of FRPs under dynamic loading, with some researchers reporting increases in energy absorption over quasistatic results, and others decreases. Furthermore, little work has been done with geometries other than simple tubes. Although tubular specimens can be considered structurally representative to a first approximation, the question still largely remains of how best to reproduce the high energy absorptions demonstrated in the laboratory within real applications. In addition to the above, there are a number of important issues relating to the energy absorption of composites which, to date, have received relatively little attention. These include the crashworthiness properties of joints and joining methods (failure is often triggered by degraded material properties at joints and/or stress concentration effects), and the implications of scaling the results obtained from laboratory specimens to full-sized vehicle structures. The development of accurate and reliable methods for predicting the energy absorption behavior of composite structures will also be essential for efficient design.

14 6.3

Application of Composites in Rail Vehicles The HYCOTRANS Project

Many of the challenges described in Section 6.2 are being addressed by the 3-year Brite Euram project HYCOTRANS (Hybrid Composite Structures for Crashworthy Body-shells and Safe Transportation Structures). The project includes representatives from the rail, coach, and composite manufacturing industries, as well as technical experts in the fields of energy absorbing FRPs, collision modeling, composites processing, materials testing, and computer-aided design. The principal objectives of HYCOTRANS were threefold: (1) to develop an energy absorbing composite structural system applicable to a wide range of materials, (2) to produce standard procedures for determining the properties of a structure by scaling without the need for expensive full-scale testing, and (3) to develop a predictive tool for designing energy absorbing composite structures. Furthermore, a full-size prototype crash-worthy bodyshell was constructed and tested to demonstrate the results of the project.

6.4

Material and Structural Design

HYCOTRANS’ approach to the development of structural Crashworthy composites is based on the use of foam-cored sandwich panels with integral energy absorbing FRP elements. Sandwich panel designs were chosen as the basis for the project because their mechanical properties are somewhat analogous to those of I-beams; they therefore have the necessary strength and stiffness for use in structural applications. The function of the FRP inserts is to control the failure loads and hence the energy absorption capability of the panels. In designing such systems, the intention is to harness the high energy absorption capability of FRPs within a single structurally-useful hybrid composite. In order to produce a component as complex as a rail vehicle bodyshell, the composite material system must offer a high degree of flexibility. It should be possible to manufacture curved profiles of variable wall thickness, and it should be possible to locally tailor the fiber reinforcement according to anticipated loading conditions. With these points in mind, HYCOTRANS is investigating the suitability of three different types of sandwich panels for bodyshell construction. These are shown in Figure 11. Each consists of a polymer foam core, incorporating some form of internal FRP structure, surrounded by FRP facings. The design shown

Figure 11 General structural designs of the energy absorbing composite sandwich panels under development as part of HYCOTRANS.

Application of Composites in Rail Vehicles

15

in Figure 11(a) is based on the use of integrally molded tubular or conical braided FRP inserts (Carruthers et al., 1997; Found et al., 1997), that in Figure 11(b) on the use of an internal corrugated FRP structure (Carruthers, 1997), and that in Figure 11(c) on the use of pre-produced bidirectional tubular and conical FRP elements. Although the three designs are quite different in terms of their geometry and method of manufacture, they all share the common feature of using an internal FRP structure to tie opposing facings together. Richardson et al. (1994) have previously shown that such an arrangement greatly enhances the mechanical properties of a sandwich panel, particularly with respect to shear stiffness and strength. Furthermore, it prevents separation of the face plates, even after core debonding, thus improving the structural integrity of the panel under edgewise loading.

6.5

Crush Testing of Small-Scale Structures

Although the development of fundamental material systems such as those described in Section 4 is an important aspect of HYCOTRANS, there is obviously a need to extend promising designs to include their use within more generally applicable threedimensional fabrications. Only by doing this will it be possible to study the effects of features such as macroscopic geometry and joining methods, both of which can significantly effect the crash-worthiness properties of a structure. Investigations have therefore commenced into the energy absorption characteristics of hollow rectangular structures (external dimensions 200 mm  200 mm  450 mm) fabricated from the various material systems. In particular, the performance of different joining techniques under axial compressive loading is being examined. Not surprisingly, preliminary tests on specimens fabricated from the corrugated FRP sandwich concept (Figure 11(b)) have shown that joint design is of critical importance in determining the collapse behavior of a structure. Structures joined using a mechanical fastening system have generally performed poorly in tests (Figure 12). This is because the fasteners tend to fail prematurely, rather than transferring the load to the energy absorbing composite sandwich panels. Furthermore, the fact that the fasteners fail in a catastrophic manner precludes the onset of any stable progressive crushing. Energy absorption is therefore very low. Slightly better performances have been obtained from structures in which flat sandwich panel sections are joined with laminated miter joints (Figures 13 and 14). A limited amount of high energy progressive crushing can occur, although ultimate failure is still due to the separation of the corner laminates and the subsequent global collapse of the structure. The best performances have been obtained from wholly integral structures produced as single-piece moldings (Figure 15). In the absence of any inherent structural weaknesses (such as joints), the specimens collapse in a stable progressive manner, at remarkably constant crush loads. Observed failure mechanisms include both conventional brittle fracture, and a progressive folding type response (somewhat analogous to more ductile materials) resulting from regularly spaced local lines of fracture. It is also encouraging to note that the sandwich structures retain their structural integrity outside the immediate crush zone. Therefore, in terms of their ability to prevent face plate separation, the internal FRP corrugations are a significant success. Furthermore, the desired collapse behavior has been observed with a number of different FRP material systems (glassepoxy, jute-epoxy). This implies that the generic structural concept is largely materials independent, thus allowing considerable design flexibility.

Figure 12 A mechanically fastened specimen before and after quasistatic axial compression.

16

Application of Composites in Rail Vehicles

Figure 13 Cross-section of a laminated mi tre joint.

Figure 16 compares the compressive responses of structures with the different types of joint. It can be seen that the distinction between the limited low energy failure of the jointed structures and the extensive high energy crushing of the integral single piece moldings is clearly marked. Table 1 presents a comparison of mean mass specific energy absorptions for specimens with the different types of joint. It can be seen that there is a direct correlation between the amount of progressive crushing exhibited by the specimens and the level of energy absorbed. With respect to repeatability, specific energy absorptions between specimens of the same type were typically to within 71 kJ kg1 or less.

6.6

Summary

This case study has provided a brief overview of the technical challenges which must be addressed in the development of crashworthy composite bodyshells for rail vehicles. Furthermore, the manner in which the HYCOTRANS project is addressing these challenges has been described. In doing so, it is hoped that HYCOTRANS will provide the impetus that is required to translate energy absorbing composite technologies, from being predominantly a topic of laboratory research, to a practical proposition for real vehicle structures. Compared to aluminum and steel carriages, bodyshells based on composite sandwich panel technology offer numerous advantages. Composite structures lend themselves to higher production, while their noncorrosive properties offer extended service life. The flexibility of composites also means that the complex shapes required for aerodynamic design can be achieved at a significantly lower cost. More fundamentally, significant reductions in vehicle weight can be achieved. These are factors of particular importance to train builders. Additionally the use of the corrugated system allows for changing cross-section of the wall structure and three-dimensional profiles; importantly other composites systems such as Parabeam cannot permit this level of flexibility. Composite structures can be designed to achieve the necessary strength and stiffness for use in load-bearing applications. However, their use in safety critical areas has been severely restricted due to the fact that composites are generally brittle in nature, failing in an unpredictable and often catastrophic manner. HYCOTRANS has overcome this limitation by way of an innovative design approach based on the corrugated ‘tied’ core sandwich concept shown in Figure 11(b). The corrugation represents an integral part of the construction, forming a continuous channel between the upper and lower faces. In the event of a collision, the corrugation is designed to fail at a predetermined stress level, selected in order to protect passengers from experiencing severe impact forces. Tests conducted on small scale tubular structures have shown that the resultant collapse mode is one of progressive failure, absorbing large amounts of energy in a stable and reproducible manner. The side impact strength of panels is also suitably high, as demonstrated by ball impact tests (Torre et al., 1999). This research has clearly shown that the development of an innovative process to manufacture large composite sandwich structures using the ‘corrugated system’ would have led to products with enormous competitive advantages over similar products manufactured using steel, aluminum, or conventional composites systems. The structural response of a composite material is influenced strongly by the way it is formed. If the material is to offer optimum performance, the processing technology must be utilized correctly and understood. However, while the sandwich concept is used in an impressive variety of applications, the techniques employed to fabricate components tend to be few and

Application of Composites in Rail Vehicles

17

Figure 14 Specimen with laminated mitre joints (upper) before and (lower) after quasistatic axial compression.

usually involve a large degree of manual labor (Bridge and Robinson, 1999). This inability to manufacture these corrugated structures in a controllable manner is a major drawback of HYCOTRANS. The European Commission are partly supported a project to address the development of manufacturing technologies which lend themselves to the economic, semiautomated production of crash-worthy sandwich structures. This project is called HYCOPROD – HYbrid Composite PRODuction.

6.7

HYCOPROD: The Way Forward for Crashworthy Rail Vehicle Bodyshells

There is a major problem in the composite manufacturing industry that at present there is no feasible method for manufacturing very large monocoque composite sandwich structures. HYCOPROD addressed this problem. It was the major objective of

18

Application of Composites in Rail Vehicles

Figure 15 An integral single-piece molding (left) before and (right) after quasistatic axial compression.

Figure 16 Comparison of representative compressive stress–displacement characteristics.

Table 1

Mean normalized energy absorption data for the different types of test specimen

Specimen type

Mean energy absorbed per unit mass (kJ kg  1)

Mechanical fastened Laminated mitre joints Integral single piece molding

1.7 11.5 24.4

Application of Composites in Rail Vehicles

19

HYCOPROD to design an advanced composite production process for the systematic manufacture of very large monocoque hybrid composite sandwich structures for the transportation sector. HYCOTRANS (BRPR CT96 0257) has demonstrated that monocoque composite sandwich structures can be designed to absorb energy and perform in a predictable and stable manner. The exploitation of this novel technology, however, depended on the invention of a new production process that can cope with very large structures such as buses, trains, trams, refrigerated containers, and trailers. For all transport sectors the need for advanced composite sandwich monocoques is driven by the need to: (i) have a sustainable and improving product to maintain and improve market share; (ii) react to the societal need for efficiency and quality of transport systems and services; and (iii) improve the safety and security of people and goods in nonpersonal transport and more environmentally friendly modes. The manufacture of transportation structures using HYCOPROD provided the enabling technology to assist the European Union in implementing the objectives of the Common Transport Policy and the transport policies of national governments. Providing a lightweight economic and crashworthy transportation structure which resuledt in the following advantages: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii)

improved competitiveness, reduce the time to market and development costs for new vehicle concepts, lower emissions due to lower power requirements, improved performance and energy savings, more attractive public transport, improved modal shift from road to rail for goods transport, innovative and safe vehicles, and reduction in vehicle whole life-cycle costs.

With metallic vehicle structures, such an approach is employed with a reasonable level of confidence. The crashworthiness properties of a vehicle can be optimized ‘virtually’ using computer simulation and then verified with a minimum of experimental testing. With composites, the confidence in employing finite element techniques to simulate crash performance is much lower. It is doubtful as to whether the representation of composite failure within existing commercially available finite element codes is sufficiently comprehensive. Other concerns include the availability of reliable material property data for input to the analyses (particularly relating to elevated strain rates), and the solution times that are required for fully-featured models that attempt to capture the wide range of composite damage mechanisms. Consequently, it is currently quite common for composite rail vehicle cabs (which might weigh upwards of 500 kg) to be deliberately neglected in rail vehicle crashworthiness analyses simply because of the difficulties in accurately modeling them. Instead, only the metallic components of the body structure are considered. In summary, the lack of reliable methods for cost-effectively predicting the crashworthiness properties of composites is inhibiting the exploitation of their considerable potential as materials with inherently high energy absorptions. However, it is clear that these two potential benefits of composites, which are widely known even to noncomposite specialists, have not been sufficiently strong drivers for the more widespread adoption of composites for structural rail applications. Procurement in the rail industry is currently dominated by initial costs. Furthermore, the operating cost benefits of lightweighting are perceived to be much lower (probably closer to €10 kg1). In this framework, it becomes much more difficult to justify a switch to composites. Prototype composite rail vehicle structures (Figure 17) have been shown to offer weight savings of around 20% over equivalent aluminum designs. However, unless the rail industry embraces the principles of life-cycle costing more extensively than at present, the initial cost of composite structures must be equivalent to, or even cheaper than, metallic alternatives if they are to be considered a viable option. The wider issues and uncertainties surrounding composites, exacerbate this situation.

7 7.1

Case Study 2 – Design of Composite Vehicle End Structures in Railway Rolling Stock Abstract

This section discusses the use of and design of composite vehicle end structures in railway rolling stock (Ingleton et al., 1999). It describes the research being undertaken at ARRC to design and develop such structures for application in the UK heavy rail markets and examines the potential benefits of using such materials. Research into the existing applications of composite end structures are presented and the suitability of the applications of these findings for future developments examined. Key challenges that designers will face in producing composite end structures capable of satisfying current industry criteria are discussed along with the major technical requirements that these composite end structures will have to meet if they are to feature in such applications in the future.

20

Application of Composites in Rail Vehicles

Figure 17 A prototype composite double-deck coach section, providing a 20% weight saving over aluminum (courtesy of Fibrocom).

7.2

Introduction

During recent years the UK rail industry has been subjected to a number of major changes both in its organizational structure through privatization and also with the introduction of new technological developments. One of the most significant technological developments which has taken place within the rail industry has been the improvement of vehicle safety and, in particular, protection to vehicle occupants during collisions. Until recent new rolling stock introduction, passenger carrying trains running on the Rail-track network were not designed for structural collapse in collision situations, i.e., the trains were not ‘Crashworthy’. As a result of work undertaken by British Rail Research new standards GM/RT2100 (Railtrack, 1997) were introduced which were to specify not only strength and fatigue requirements of rail vehicle bodies but also their performance regarding controlled structural collapse where peak force levels, deformation, and minimum energy levels are stipulated. The introduction of these standards provided engineers with a new set of challenges which would require fundamental novel design concepts to be employed in order that bodyshell structures would be able to provide structural integrity and yet collapse in a predictable manner. In meeting the challenges of the new standards, engineers have recently developed and tested successfully vehicle end structures providing high energy absorption capability in traditional materials such as carbon steels and aluminum. The use of composite materials in the design of energy absorbing vehicle end structures has, however, until recently received little attention or investigation despite widespread use of composite materials in many related applications throughout the world. The aims of the research being undertaken at the ARRC are to design and develop a crashworthy composite vehicle end structure principally to satisfy the standards required in the UK rail environment but also focusing on the engineering and development of techniques suitable for wider use. The end structures of vehicles are without doubt one of the most complex elements in modern train design and as such in order to incorporate composites safely into these structures the research will explore a number of key areas namely: (i) (ii) (iii) (iv) (v) (vi)

design methodology; approach to analysis; joint configuration and failure modes; energy absorption mechanisms; material selection criteria, and integration of the end structures into the overall bodyshell concept.

Application of Composites in Rail Vehicles

21

Vehicle end structures are a vital element in the operation of all new rolling stock and are required to perform a variety of functions ranging from providing structural integrity as part of the overall vehicle body to protection of occupants in collisions and derailments. The end structures are also required to provide many aspects of train operation including provision of safe passage between vehicles, access/egress, and aerodynamic styling to name but a few and the research will also require the incorporation of these requirements if effective design solutions are to be produced. Although composites structures are used widely in many industries, such as the aircraft and automotive, it is only recently that use of composites for structural applications in the rail industry has started to receive the attention it deserves. Traditionally in the UK rail industry, composites have been limited to use for vehicle interiors where these materials have been used extensively for a number of years in applications such as floor, ceiling panels, and partitions. In contrast to this, the use of composites for the main bodyshell structural applications where a high degree of structural integrity is required has remained relatively unexplored, but if this is the case why should the rail industry be interested in composite end structures?

7.3

Benefits of Composite End Structures

There are a number of reasons why the use of composite end structures can be of particular benefit to the industry which can be summarized into three main categories: (i) strength and weight, (ii) aerodynamics and styling, and (iii) integration of interior systems.

7.3.1

Strength and weight

The high strength to weight ratio of composites coupled with the capability to optimize strength where required provides engineers with an opportunity to produce efficient lightweight end structures, particularly as these structures are subject to both severe and varied load cases which often result in current structures being excessively heavy. Weight, as with most transport-related products, is a key criterion and the rail industry is no exception. As rolling stock manufacturers respond to the new private markets with the emphasis on providing operators with vehicles with a much greater operational flexibility, new rolling stock is becoming heavier. As a consequence of heavier vehicles, energy consumption increases with the heavier axle loads reducing both track life and quality and as such weight savings provided by composite end structures provide a whole range of benefits.

7.3.2

Aerodynamics and styling

Currently the majority of vehicles in the UK provide aerodynamics and styling by superficially cladding the main load bearing structures which, due to the severity of the applied loading, are less irregular and of simple shape to aid production. Composite structures can combine these two requirements, eliminating the need to produce and match two rather large and complex shapes and also provide an opportunity to generate a more distinctive and artistic approach to end structures. Certainly with high speed train developments the styling of the end structures is becoming increasingly important not just aerodynamically but also visually as can be seen with the end styling of the trains shown in Figures 18 and 19. Using composites provides designers with the

Figure 18 Shinkansen high speed train (Japan).

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Application of Composites in Rail Vehicles

Figure 19 Artist's impression of a new high speed train for operation in the UK.

Figure 20 Integration of system functions into composite end structures.

opportunity to produce vehicle end structures which match the visual inspiration of the industrial designer, something currently rarely achieved but which with composites becomes more feasible.

7.3.3

Integration of interior and exterior systems

The ability to integrate a number of systems into one single composite element is one of the main areas where composites provide a significant opportunity to remove cost compared to current practice. Currently designs of vehicle end structures are developed and built on an individual system basis, i.e., structures, interiors, electrical installation, ventilation ducts, etc. Composite structures provide an opportunity with their flexibility to accommodate the manufacturing costs from several of these functions into one element combining the various functions as illustrated in Figure 20. An example of the integration of these system functions is to combine the structural strength, aerodynamic, acoustic, and thermal insulation requirements into one composite component, eliminating several separate design and manufacturing operations. This principle is illustrated in Figures 19 and 20 which show a cross-section through a conventional design for a cab corner pillar and an comparable design of the same section in composite materials. As can be seen by comparing the two types of section, the composite design has a number of advantages over current practice in that it offers a reduction in the number of components, provides inherent acoustic and thermal insulation, and the inner and outer laminates of the composite as well as providing structural strength also perform the function of the outer cosmetic covering and interior panel (Figures 21 and 22). When evaluating the cost of producing composite end structures against current practice, the cost of the composite structure should not be simply compared against the cost of an existing replacement in steel or aluminum but should be measured against the total cost of producing a vehicle end.

Application of Composites in Rail Vehicles

23

Figure 21 Section through cab corner pillar using conventional design.

This comparison should also include integration of the other systems such as the outer cosmetic covering, insulation, and interior paneling to provide a true comparison of the existing cost of producing end structures against those in composites. If integration of systems into the composite structures is to fulfill its potential then coordinating the design of several systems to produce an overall effective solution with optimum manufacture will be an essential requirement and a new design methodology may need to be developed to incorporate these aspects effectively.

7.4

Use of Composites in Crashworthy Structures

At the moment in the UK rail industry no rolling stock incorporates composite structures which are designed specifically to be crashworthy. An attempt to use the energy absorption capabilities of composite structures was however investigated by Scholes and Lewis (1993) as part of collision tests commissioned by the Office for Research and Experiments (ORE), the research arm of the International Union of Railways (UIC). The tests examined the feasibility of a proposed structural design philosophy to examine the crashworthiness of the structure and provide verification of recommended progressive collapse and energy absorption characteristics. As part of the testing of the crashworthy structures, two GRP energy absorption devices were used, one mounted at each buffer position and were designed to collapse at 800 KN (400 KN each). The rear of the tubes were mounted on to the vehicle structure and the front of the tubes fitted with a ribbed anti-climb buffer or plate, the purpose of which was to provide resistance to the vertical forces also generated on impact, the ribbed device ensuring that the absorption devices remain in contact during collapse and do not separate. The GRP energy device used in the test can be seen in Figure 23 along with the basic structural design adopted. The energy absorbing GRP tubes started to collapse in the test at 5% above their combined collapse load of 800 KN, which in itself is not significant, but the manner of failure was as the expected energy absorption characteristics of the tubes were some 50% less than predicted. Scholes and Lewis (1993) reported that the failure mechanisms of the tubes were due to gross shear failure of the resin matrix causing large fragments to break away rather than delaminate and as a result much of the inherent energy capacity of the elements were lost. Upon summary of the tests it was recognized by Scholes and Lewis that further work was required in the area of inexpensive easily replaceable energy absorption devices and that the GRP tubes provided poor results for the designs used in this particular test.

24

Application of Composites in Rail Vehicles

Figure 22 Section through cab corner pillar using composite design.

Figure 23 Cab structure used for laboratory crush test incorporating GRP energy absorbing tubes (from Scholes and Lewis, 1993).

Application of Composites in Rail Vehicles 7.5 7.5.1

25

Existing Designs of Composite Vehicle End Structures Inter City 125 high speed train composite cab structure

Nearly all rolling stock cabs designed and built in the UK to date have been based on the construction of a load bearing metallic structure, usually steel, surrounded by an outer cosmetic covering of GRP, and even today this is still the traditional method employed by rolling stock manufacturers. Use of composite structures has, however, been introduced successfully into rolling stock cabs in the UK as early as 1977 in the Inter City 125 High Speed Train cabs as shown in Figure 24. The cab front of the high speed train was produced from a 50 mm sandwich construction with the outer and inner skins being made of glass-reinforced polyester between which existed a foam core of polyurethane as described by Nock (1980). The power car of the HST was the leading vehicle and as with all trains protecting the driver from the noise emanating from the diesel engines and wheel/rail interface was an essential requirement. In order to determine the noise performance of the cab environment, a prototype train including the composite cab was produced and running trials were performed to assess among other aspects of the train the cab environment. The tests revealed that at higher speeds noise levels were unacceptable in the cab as result of which several changes were made to the train generally and more specifically related to the cab the entire floor structure was completely redesigned from the prototype. The new floor construction consisted of several acoustical and structurally decoupled layers as well as acoustically absorbent materials. The construction of the floor of the cab can be seen in Figure 25. It should also be noted that the production vehicle had air conditioning ducts incorporated in the floor as climatic control of the cab was also seen as an essential requirement for producing a suitable cab environment for the driver, particularly at speeds of 125 mph where it was not possible to open windows for natural ventilation.

Figure 24 InterCity 125 high speed train composite cab (after Robinson and Carruthers 1995).

Figure 25 InterCity 125 high speed train composite cab floor construction of production vehicle (from Nock, 1980).

26

Application of Composites in Rail Vehicles

The HST was designed and built prior to the crashworthy standards being introduced, which came in after the Clapham rail accident in 1988 and were not required to meet the severe proof and collapse criteria required in modern rolling stock designed to Railtrack Group Standards (Railtrack, 1997). While the acoustic, thermal, and impact properties of the construction were well established, the crash performance was not a key function of the design and as such little or no material exists on the structures collision behavior. The HST cab was the first composite structure designed to withstand missile resistance on the BR network and the specification imposed for the forward facing surfaces of the cab are the same as those required on modern rolling stock today as described by Brown (1997). Modern rolling stock must withstand penetration into the vehicle of a hollow section steel cube weighing 0.9 kg traveling at twice the velocity of the vehicle's maximum operating speed: in the case of the High Speed Train operating at 125 mph requiring resistance to impact penetration of the steel cube at 110 ms1. For the HST the impact resistance testing was carried out by impacting the center of a panel 1 m2, the sandwich panels being produced from laminates using unidirectional roving plies laid alternatively at 901 to each other with an injected foam core as described by Brown (1997). Figure 26 depicts a picture of an HST cab involved in a collision and which remarkably resulted in no fatality but as result of the extensive damage to the cab it was replaced rather than repaired with a new cab as shown in Figure 27. The collision of the HST composite cab highlights some of the difficulties in designing composite structures for collision purposes where conventionally a certain degree of structural integrity is still required when subject to large-scale deformation. As can be seen by the illustration, the top area of the structure has been completely separated from the lower portion below the window area, with the high level shearing action causing gross failure of the rear main cab section exposing the foam cores.

Figure 26 Intercity 125 high speed train composite cab with collision damage.

Figure 27 InterCity 125 high speed train composite cab (courtesy of Interfleet Technology).

Application of Composites in Rail Vehicles 7.6

27

Modern Applications of Composite Structural Ends

Cortesi et al. (1991) describe the development of the drivers cab of the new locomotive 2000 series for the Swiss Federal Railways specifically designed to reduce the weight of the locomotive and to introduce FRP into the design. The use of FRP was important in designing the vehicle cab providing opportunities to engineer styled, smooth, and attractive shapes for the locomotive using the full three-dimensional manufacturing capabilities of the material, provide opportunities to optimize aerodynamic requirements, and replace components previously produced in steel with FRP. For the design two types of construction were initially considered: one with a very lightweight steel structure with a superimposed lightweight glass fiber-reinforced laminate, and the second a self-supporting sandwich structure. The findings of the study are significant in that they revealed a number of key reasons why the superimposed version could not be used when compared to the sandwich structure, namely: (i) (ii) (iii) (iv) (v)

Little or no weight saving; Concern over integrating windows and other items where a flush finish is required; Lack of rigidity and subsequent capability to withstand pressure pulses generated by passing trains; Poor resistance to missile penetration of small objects; and Requirement for internal sound and thermal insulation still required.

Based on the above findings it is not surprising that the self-supporting sandwich construction was selected and produced subsequent weight savings of 1000 kg per locomotive (500 kg per cab).

7.6.1

Sandwich structure construction

The type of sandwich construction used by Cortesi et al. (1991) in the locomotive 2000 consisted of glass fiber-reinforcedmodified polyester resin encapsulating a PVC foam. The sandwich construction is shown in Figure 28 and consists of three layers of glass fiber all of a different thickness and two layers of PVC foam core material. The central trapping layer considerably increased the resistance to missile penetration. This type of sandwich replaces the 2 mm of steel skin attached to a conventional steel frame and also the steel frame itself. When selecting the material for the composite cab Cortesi et al. (1991) selected a rigid, damage tolerant core material of PVC foam to allow expansion due to temperature effects to take place, as the range of temperatures from the inside of an air conditioned cab to the outside skin temperature could be considerable. This temperature differential is an important aspect for the design of the composite structure for material selection.

7.6.2

Assembly of the cab

Due to the size of the cab of the locomotive, Cortesi et al. (1991) split the design of the sandwich construction into four major parts to aid manufacture, handling, and storage, with the final components brought together as shown in Figure 29 with the four individual parts bonded together using a structural adhesive with a special joint arrangement as shown in Figure 30. The part used for the roof section appears to be about two-thirds the thickness of the front section described earlier in Figure 28, with the joint configuration connecting the two components providing a large surface area for the adhesive to provide an effective joint between the two components.

7.6.3

Manufacture

Vacuum injection was selected by Cortesi et al. (1991) as the manufacturing process as opposed to a hand-lay method mainly due to the large quantity of cabs required but also due to several other factors, namely: (i) improved dimensional control of components;

Figure 28 Section of self-supporting FRP sandwich construction (from Cortesi et al., 1991).

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Application of Composites in Rail Vehicles

Figure 29 Assembly of cab locomotive (from Cortesi et al., 1991).

Figure 30 Structural bonded joint design of cab front and roof (from Cortesi et al., 1991).

(ii) (iii) (iv) (v)

smooth surfaces on both sides; repeatability of the components; economic production; and Improved health and safety to production staff.

The sandwich panels were produced in a mold with the precut dry glass fabrics, foam cores, and inserts placed between a male and female tool arrangement. Resin was subsequently pumped into the joint and dispersed throughout the mold by means of the vacuum process.

7.6.4

Impact testing of the sandwich construction

Impact tests on the sandwich panels of 80 cm  80 cm with a 1 kg impact mass to UIC standards with the sandwich section are shown in Figure 31 withstanding an impact of 280 km h1. The UK Railtrack Group Standard GM/RT2100 (Railtrack, 1997) states

Application of Composites in Rail Vehicles

29

Figure 31 Steel and sandwich panel crush (from Cortesi et al., 1991).

that similar forward facing structures must withstand an impact of twice the maximum speed of the vehicle. Currently for the UK, the maximum speed of operation is 200 km h1 soon to be increased for the West Coast mainline upgrade to 225 km h1, requiring composite structures to withstand an impact resistance of a 0.9 kg mass of 400 and 450 km h1, respectively. Impact resistance is an important aspect of the cab design as this provides protection to the driver from projectiles such as track ballast disturbed by the slip stream of passing trains and, more seriously, stones and bricks deliberately thrown at trains by vandals. The results of the tests on the tests performed by Cortesi et al. (1991) revealed that at 280 km h1 the damage remained localized and penetration of the object was only partial. Interestingly when a rigid core material was used a larger area of the sandwich panel was destroyed.

7.6.5

Collision testing of the sandwich construction

Cortesi et al. (1991) performed tests on the sandwich construction to compare the collision performance of the sandwich construction with that of a steel construction. Two test pieces were constructed, one in each material, and the energy absorption capacity of the materials measured when crushed. The testing of the samples and the resultant energy absorption are shown in Figures 31 and 32. The samples were compressed under load to 38% of their original height with the sandwich construction absorbing 25% more energy than the steel counterpart. The tests performed by Cortesi et al. (1991) did not discuss the failure mechanisms of the sandwich panel or the force displacement characteristics but from the results of the test there are several aspects which provide useful criteria for the behavior under collision of composite structures. The sandwich structure peak collapse force shown in Figure 32 was almost twice that of the steel structure and exhibited a decreasing force level as deflection increased compared to the steel sample which increased gradually. This suggests that the sandwich structure started to delaminate or fracture when compared to the steel sample which increased its resistance to the applied load. Peak loads are an important aspect of the crashworthiness philosophy in the UK and are specified in the Railtrack Group Standard GM/ RT2100 (Railtrack, 1997) as they are related directly to passenger safety as a function of acceleration during train collisions. The control of peak forces for the design of the crashworthy composite structure is an area where methods must be explored to control such behavior.

30

Application of Composites in Rail Vehicles

Figure 32 Energy absorption characteristics of the steel and sandwich test panels (from Cortesi et al., 1991).

Figure 33 Cab end nosing of locomotive 2000 in passenger service (courtesy of Alusuisse).

The sandwich construction force dropped to almost zero where for the corresponding deflection the steel sample retained a load approaching its average collapse force. The composite cab of the locomotive 2000 in passenger service can be seen in Figure 33.

7.6.6

Suitability of findings for crashworthy cab

The sandwich construction cab produced for the locomotive 2000 produced very interesting information about the collision behavior of composite structures and a number of aspects for consideration. There are, however, several elements not covered or inherent in the design of the cab which have a significant effect on the production of crashworthy structures. The cab was not designed specifically to be crashworthy and the results of the collision test and the manner in which the load was applied bear no resemblance to the crashworthy standards adopted for the UK by Railtrack. The design of the cab does not explore the controlled collapse of the entire cab structure but merely provides by way of a test piece a benchmark from which the performance can be compared to that of a steel test piece. Controlling peak forces are not discussed or set as a design parameter, aspects which along with the very high proof load required for the UK are dictated in GM/RT2100 (Railtrack, 1997). Collapse mechanisms and the behavior of joints are not specifically discussed in the work of Alberto et al., but overall provide a clear indication into areas where some of the major issues lie with producing these type of structures.

7.6.7

Structural driving cab of C20 Stockholm Metro car

For the design of the C20 Stockholm Metro Car, great emphasis was placed on the styling of the driver's cab and, in order to deliver a design which satisfied the aspirations of the customer, the decision was made to produce the driving structures in composite

Application of Composites in Rail Vehicles

31

materials. Use of composites to produce stylish shapes is not new even to the rail industry as traditionally composites have been used to provide esthetic front end shapes as superficial cladding to a substantial but hidden metallic load bearing structure for many years. The main difference of the C20 against the ‘traditional method’ of manufacture was that the composite structure was to provide not only appearance characteristics but would also be capable of withstanding a wide range of structural loads applied locally to the vehicle end and contribute to the overall stiffness performance of the vehicle structure as described by Werne (1997). Werne describes the design of the structure employed for the C20 cab which consisted of a GRP/balsa sandwich construction with the skins being produced from knitted multiaxial fabrics in a polyester matrix. The cab was 2 m long and 3 m high and produced as a one-piece hand laminate which in turn was bolted to the main vehicle structure as a modular unit, i.e., ‘bolt on cab’. From the resulting design of the cab, Werne concluded that there was much to be gained by varying the laminate lay-up over the structure to satisfy particular requirements with the more heavily loaded forward facing structural areas using thicker laminates reinforced predominantly in one direction with a 50 mm core as opposed to the roof and side structures which employed thinner laminates with quasi-isotropic reinforcement and a 25 mm core. The cab design included due to its construction in-built thermal insulation, thus removing the requirement from the interior trimming and made use of ‘Bighead’ fasteners laminated into the inner sandwich skin to mount major pieces of interior equipment such as air conditioning units and drivers door actuating mechanisms.

7.6.8

Comments on findings of C20 with respect to UK heavy rail

One of the key areas of the C20 cab is its capability to withstand the structural loads placed upon the end structures as well as provide styling. In the UK the load cases applied to the vehicle end structures for the heavy rail vehicles are very severe and are classified in terms of proof, fatigue, and collapse requirements. The C20 load cases by comparison are relatively small, few in number and no collapse requirements in case of collision are specified. The work provided on the C20 does provide an indication that the proof load design within structures can be met with careful design but provides no evidence of collapse characteristics of composites when loaded beyond these levels.

7.7

Challenges for Use of Composite Materials For End Structures

Using composite materials for crashworthy vehicle end structures provides a tremendous challenge for the future, but what are the real challengers that lie ahead? In general, FRPs do not exhibit a ductile failure mode when compared to their steel counterparts but tend to exhibit a brittle mode of failure with high peak forces and catastrophic degradation of the laminates. For UK rolling stock the design requirements for proof loading and collision are some of the most stringent in the world and as result to date the preferred material for such application is low carbon steels. Although composites used in rolling stock cabs provide many advantages and evidence suggests they are capable of meeting the high proof load requirements, meeting the collision performance is quite different. Designing a composite structure to absorb 1 or 2 MJ of energy with peak forces below 3000 KN requires composite structures to absorb energy over areas of large deformation. This is the real challenge with the composite structure designs as the brittle failure modes typically exhibited by fiber-reinforced plastics combined with inherent strength requires these failures under collisions to be controlled by limiting peak force while retaining a high degree of structural integrity to protect occupants as gross failure is occurring.

7.8

Technical Requirements of Designing Composite End Structures

In order to design composite structures for the UK rail network there are a number of technical requirements which the end structures must meet if they are to be allowed to be used in passenger carrying services; some of these requirements are mandatory regulation and some inherent requirements due to the nature of the operating environment. The requirements can be broadly categorized into four main groups, namely: structural, environmental, production, and operation.

7.8.1

Structural requirements

There are a number of structural requirements which the end structures must satisfy and these are well defined in Railtrack Group Standard GM/RT2100 (Railtrack, 1997) and cover aspects ranging from proof and collision loads to fatigue and missile protection. The structural requirements are a dominating feature in the design of the vehicle ends where the severity and variety of loads applied test the structure, particularly in terms of proof and collapse requirements. Typical proof loads vary from 1500 KN at the underframe coupler position to 300 KN at the upper cantrail areas at the front of the structure. Although fatigue is not normally of significance in the design of the structure at the vehicle ends due to the dominance of proof and collapse loads, it is of greater significance with the use of composites particularly as the front of trains often receive minor superficial damage which may result in crack propagation being undetected and this aspect will require assessment, possibly by a risk-based approach. Missile protection is required in the structure to protect the driver from injury caused by missile penetration into the driver's cab and evidence suggests that composites provide this feature inherently where laminates and foam cores are used.

32

Application of Composites in Rail Vehicles

7.8.2

Environmental requirements

Fire performance is a key requirement for trains, the details of which are contained within British Standard BS6853 (British Standard Institution (BSI), 1987a,b). The requirements of this standard are particularly onerous and the standard describes the requirements for spread of flame and toxicity and specific testing which is required in order to demonstrate compliance. This aspect will be of major significance when selecting suitable composite materials. The composite cab must be able to cope with the demands of climatic change ranging typically from subzero temperatures of  15 1C to elevated temperatures of þ 30 1C. The composite selected for the construction will be operating in a harsh environment where it will be subject to an operational routine of daily cleaning and the chemical agents used in this cleaning process coupled with use of oils and greases found in maintenance depots can be particularly aggressive. Ingress of moisture into the composite structure must also be guarded against particularly where foam cores are used to prevent frost damage. The composite structures will also be required to be painted to suit operator livery and withstand removal of graffiti and any chemical agents required to facilitate this removal. If the material selected can offer recycling capabilities then this would also be a desirable objective even if not a mandatory requirement as disposal will eventually be required.

7.8.3

Production requirements

Although there are no specific Railtrack Group Standards relating to the production of the end structure there are several considerations which need to be reflected in the design if composite end structures are to succeed. The design will need to be modular to reflect market changes by providing an adaptable base product with an inbuilt degree of flexibility to suit a range of vehicle applications. The component itself must be cost effective. The composite material will require a production process capable of being self-supporting, providing repeatability, and produced to tolerances which complement those required for interfacing the component to the main bodyshell structure. There are significant amounts of production work to be undertaken in vehicle end structures and the methodology for producing these ends and the build sequence will require considerable planning at the conceptual design level in order to capitalize on this aspect to minimize labor costs.

7.8.4

Operational requirements

As the market for rail vehicles enters a new era with trains being potentially owned by several operators over the life of a vehicle, the operational characteristics become increasingly important. The end structure of a rail vehicle will be typically designed for 30 years and the cost of the component over this period should therefore also be a consideration of the product, not just the ‘first cost’. Vehicle structures suffer damage in service ranging from small abrasion to minor and major impacts. In order to reduce the amount of time a vehicle is out of service the vehicle conceptual design should address the issue of vehicle damage by repair or replacement. Potential repair scenarios of damaged end structures needs to be evaluated as an inherent feature from the start of the design process, not as an afterthought when the product has its first incident. The composite end structures are also driven by the key requirements of geometry and the need to produce effective aerodynamic and stylish end shapes as described in Chapter 6.02. Also a factor is that the external shapes are tapered in plan elevation to avoid contact with tunnels, bridges, and platforms as the vehicle overthrows on negotiating track curvature. Finally, a key factor in the design of the end structures will be the ergonomic relationship of the train driver within the boundaries of the end structure itself and the need to cater for the requirements of providing driver visibility of track and signals ahead.

7.9

Conclusions

The research work undertaken shows clearly that it is possible to design composite end structures for rolling stock and there are a number of vehicles across Europe in passenger service which adequately demonstrate this for a range of operating applications. The requirements to introduce collision performance into the composite designs represents a step change in technical complexity and requires a new approach to provide designs which are capable of meeting this and the stringent technical requirements for heavy rail passenger service in the UK.

8

Conclusions

This chapter has shown that composite materials are well established in the railways for semistructural and decorative items. Applications for carbon and aramid fiber based composites have been limited up to the present time. Clearly high material costs, particularly for carbon fiber, have been the main reason but other contributory factors are the poor impact performance of carbon fiber-reinforced plastics and the low compressive strength of aramid-reinforced plastics. This problem is compounded by the fact that a new design approach must be adopted if the full potential of composite materials is to be realized. Nevertheless, the benefits

Application of Composites in Rail Vehicles

33

that are to be gained, in terms of design flexibility, lightweighting, life-cycle costs, etc., are enormous. This fact is reflected by the impressive breadth of applications for which composites are currently considered. Within the rail and composite industries there is a general level of optimism concerning the future of composites in rail vehicle applications. Composites can be engineered to perform competitively with metals and, therefore, opportunities remain for the direct replacement of metal components by composite ones. However, there a number of hurdles which must first be overcome before composites receive widespread acceptance. Generally, the composites industry recognizes that there is a widespread inflexibility, a form of mental inertia, on the part of rail operators to foster new designs, allow sufficient trial times, and provide feedback. One example of the problem of introducing composite materials into the rail industry is that in order into achieve approval for this composite flooring it is required that it be tested in-service and yet to qualify for in-service testing necessitated prior approval! Nevertheless, it is clear that the rail industry will be an important market for composites in the twenty-first century, even if at present the rail industry does not fully appreciate it. In 1992 the Suppliers of Advanced Composites Materials Association (SACMA) voted the high speed rail industry as the primary target for future market development focus, ahead of the chemical processing, petroleum offshore drilling and pumping, and marine industries (Burg and Loud, 1992). This chapter has demonstrated that composite materials are already routinely employed in a range of applications within the rail industry, and that with several promising initiatives currently underway, this use is set to rise in the near future.

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Railtrack,, M.O.W., 1997. Structural Requirements For Railway Vehicles. Railway Group Standard GM/RT2100. London: Institute of Mechanical Engineers. Reinforced Plastics, Nov 2008. Composites in Europe. Reinforced Plastics 0034−3617/08. Reinforced Plastics, (Nov/Dec 2009). European Composites Industry Set for slow Recovery. Reinforced Plastics 0034−3617/09. Reinforced Plastics, Nov/Dec 2012. The European Composite Market. Reinforced Plastics 0034−3617/12. Richardson, M.O.W., Robinson, A.M., Eichler, K., Moura Branco, C., 1994. Cellular Polymers 13, 305–317. Roberts, S., 1994. Plastics and Rubber Weekly 1521, 6. Robinson, M., 1998. Composites: Growing use in rail vehicles. European Railway Review, 4 (4), 75–78. Robinson, M., Carruthers, J.J., 1995. Reinforced Plastics 39 (11), 20–26. Railways, 1998, May, 296−298.. Robinson, M., Carruthers, J., Gibson, G., 2005. The future use of composite materials in the rail industry. Railway Strategies, Issue 30 (May−June), pp. 81−83. Robinson, M., Hiroshi., N., 2006. Strategic thinking can reduce the mass of commuter EMUs. Railway Gazette International 162 (5), 267–270. Robinson, M., Ingleton, S., Found, M.S., 1999. Wider applications for composites. European Railway Review 5 (4), 43–46. Sawley, K., 1989. Metals and Materials 5 (4), 210–214. Scholes, A., Lewis, J.H., 1993. Proceedings of the Institution of Mechanical Engineers. Part F. Journal of Rail and Rapid Transit. 1–16. Starr, T., 1999. Profile of the Worldwide Reinforced Plastics Industry, Markets and Suppliers, third ed. Elsevier Science. Starr, T. Reinforced Plastics 0034−3617/92. Suzuki, Y., Satoh, K., 1993. Proceedings of the Third Japanese International SAMPE Symposium. Covina, CA: SAMPE. Thornton, P.H., 1979. J. Comp. Mat. 13, 247–262. Thornton, P.H., Magee, C.L., 1977. J. Engng. Mater. Tech. 99, 114–120. Torre, L., Kenny, J.M., Mamalis, A.G., 1999. Proceedings of the 20th International SAMPE Europe Conference of the Society for the Advancement of Material and Process Engineering. Covina, CA: Paris SAMPE. pp. 457−468. Weaver, A., Reinforced Plastics 0034−3617/1994. Werne, D.V., 1997. Composites in the Rail Industry Conference. Derbyshire, UK: Railview Ltd. Woodward, M.G., Brown, N., 1997. Proceedings of Review − Composites in the Rail Industry Conference, Sheffield, UK.

Further Reading Ingleton, S., Found, M., Robinson, M., 1999. Design of composite rail vehicle cabs. Composites, 32 (March/April), 42–44. Richardson, M.O.W., Robinson, A.M., 1994. Composites 25 (6), 438–442.