Thermal damage of rails can occur through brake lock-up, or traction control system failure to prevent wheel spin. In most cases the damage produced is shallow and takes the form of a Òwhite etching layerÓ, usually thought to have a martensitic structure, formed as the steel is heated above its eutectoid temperature and then rapidly cooled as the wheel moves away. In many cases such layers are benign, but there is evidence of crack initiation at their interface with the sub-surface layers of the rail in ÒstudÓ defects. The metallurgical transformation during the formation of white etching layers leads to a volume change for the steel, leaving not only a transformed microstructure, but also locked-in stress. The influence of this additional locked-in stress on development of an initiated crack is studied in this paper, and the work extended to consider how alternative materials which react differently to the thermal input may offer a means to suppress crack development through locking in beneficial rather than problematic stresses.

Abstract. Manufacturing defects such as porosity that formed in the rail could result in catastrophic failure if it remain in service. In this study, a crack that initiated from a large void was modelled using boundary element model to investigate the effect of white etching layer patches on larger defects in rail. The configuration studied represents a large defect in the rail that was observed from a rail removed from service. These investigation has provided a better understanding of how a crack initiated from a larger defect grows under the effect of white etching layer. The results highlight that a continuous white etching layer region will dominates the growth of the crack compared to a patches white etching layer region for a smaller crack size while patches of white etching layer will accelerates the crack growth for a larger crack size. The crack growth predicted in this study for a small crack size is at least 6 times higher than the wear rate mentioned in the literature and will increase further if the expansion of a transformed layer is considered making it impossible to be removed by natural wear.

Biomaterials with a porous structure are beneficial for a wide range of medical engineering applications such as filtration, bone replacement and implant development. Stainless Steel 316L (SS316L) foam has been fabricated by foam replication method at different SS316L powder composition which is 60 wt%, 65 wt%, and 70 wt%. The binders used were Polyethylene Glycol (PEG), Carboxymethyl Cellulose (CMC) and Polyvinyl Alcohol (PVA), while distilled water was used as a solvent. The effects of using different composition of SS36L powd er, binders and sintering time to the SS316L foam properties was studied. The materials were mixed by usin g a mechanical stirrer at 250 rpm for 1 hour. Polyurethane foam (PU) which was used as a sacrificial template was dipped into the SS316L slurry until fully coated. The coated samples were then dried in a drying oven within 24 hours before being sintered in an argon gas environment at 1200C. The samples were characterized to observe the microstructure of the SS316L foam produced. As expected, the viscosity of the SS316L slurry was increased as the SS316L composition increases. The viscosity of SS316L slurry prepared by using PVA as a binder is higher than the SS316L slurry prepared with CMC and PEG as binder. The SS316L foam produced consisted of a larg e volume of open and interconnected pores especially at higher SS316L composition.