ABSTRACT In rolling contact fatigue of rails, cracks form at a shallow angle, and grow primarily in the direction of travel underneath the rail surface. Once nucleated, cracks may branch to a Mode I direction, whereas shallow cracks grow when the crack is filled with fluid. This paper attempts to model the response of shallow-angle cracks through fracture mechanics analysis, using finite element stress analysis and multiaxial fatigue tests to simulate the rolling contact history. The evolution of the history of mixed- Mode I and II stress intensity factors is derived from a 2D finite element model. Biaxial fatigue crack propagation experiments have been conducted on BS11 rail steel to investigate the effect of sequential mixed-mode loading on angled cracks. The effects of fluid in the crack, residual stress in the rail head and braking are considered to demonstrate that “squat” rolling contact fatigue cracks can only develop under prescribed loading conditions.
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