Abstract
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A finite element study has been made of subsurface rail/wheel contact stresses in a heavy-haul railway rail, and the near-threshold fatigue behaviour investigated for both standard carbon and head-hardened rail steels under Mode II and Mode III shear loading conditions. Small, semi-elliptical regions of shear mode growth were found in the Mode III tests and are though to be equivalent to shell cracks. Mode I branch cracks arising from these are similarly believed to correspond to the generation of a transverse defect. Gauge corner shear stresses from the finite element analysis are used together with threshold stress intensity factor ranges from the fatigue tests on standard carbon rail in a fracture mechanics model of the transition from a shell to a transverse defect. When the effects of crack face friction and residual stress in the rail head are incorporated into the model, excellent agreement is obtained between the predicted size of a shell and that found from fractographic examinations of failed rail samples.