The use of fibre reinforced composite materials is one method by which the lightweighting of rail vehicles can be achieved. However, the issue of impact damage, amongst other challenges, limits their safety certification. This issue is accentuated by the high levels of loading a rail vehicle may be subjected to during service. This paper addresses the significance of pre-tension on large composite structures, specifically for a composite redesign of a pressure vessel for a freight tank wagon. Preloading was determined to be detrimental to the overall impact resistance of a large composite vessel. At 15.71 J of impact energy, there was a 22% increase in mean absorbed energy for a uniaxially loaded panel over an unloaded panel. However, there was only a 4% difference in penetration depth between uniaxial and biaxial loading. A novel finding from these results is that the effects of preloading are more profound if the loading does not act parallel to a principal fibre direction. Matrix cracking and delaminations are the most common failure modes observed for specimens under low-velocity impact and are intensified by preload.

The current performance requirements for the global rail industry demand that trains are more reliable, efficient and can accommodate an increased capacity for more passengers. Lightweight construction of rail vehicles is thus required to meet these requirements. This paper has identified the key components for lightweighting of rail vehicles using fibre reinforced polymer composite materials. A methodology used to select and rank those metallic components suitable for redesign in composite, developed as part of the ACIS (Advanced Composite Integrated Structures) UK project is described. From the audit, five demonstrator components – a cantilevered seat bracket, luggage rack module, intermediate end structure, body side structure and roof structure – were identified by the consortium using the methodology. These are components that the consortium believes to be the most suitable to demonstrate the benefit of a composite replacement in terms of integration potential, lightweighting benefits and commercial viability. Furthermore, rail car body structural components, forming the primary structure of a rail vehicle, were determined to be the most optimal components to replace in composites for maximum lightweighting of the sprung mass. It was estimated that a composite redesign of these components would result in a mass savings of 57% for intermediate end structures, 47% for body side structures and 51% for roof structures.

The potential for lightweighting of railway axles was investigated to primarily reduce the unsprung mass of rail vehicles. The reduction of unsprung mass equates to an overall lighter train, which will help to reduce track damage, energy consumption and total operating costs. Two approaches were considered for the lightweighting of railway axles, which include a hollow axle design and material substitution using advanced composite materials, to offer a more track-friendly design. The first approach showed that if the outer diameter of a hollow axle is increased by 30% over that of the solid axle diameter, a mass reduction of 56% is achievable for a hollow steel axle design. The second approach explored further mass savings that could be achieved through material substitution of a hollow axle. A systematic approach to material selection for the design requirements and constraints of a railway axle was considered to identify the candidate materials for the application. The optimum material identified was a ‘bismaleimide matrix + carbon fibre composite.’ A hollow axle manufactured from this composite material offered 64% savings in mass when compared to a hollow steel axle, and 84% savings in mass when compared to a solid steel axle. Estimates for the cost savings of lightweighting of an axle were quantified by utilising Network Rail’s variable usage charge calculator, to assess the track access charge savings that can be achieved. For the scenario described in this paper, a potential £5.58 million per year could be saved for an intercity 220/M Voyager train, in terms of variable usage charges, over the entire fleet of 34 trains (four carriages per train) by implementing hollow composite axles. This is an example of a costing approach to support the decision making of lightweighting of rail vehicles.

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