Modelling the three-dimensional behaviour of shallow rolling contact fatigue cracks in rails

A model of the fatigue behaviour of three-dimensional (3D) semi-elliptical shallow-angle rolling contact fatigue (RCF) cracks was developed by combining numerically obtained (3D FEM) linear elastic fracture mechanics (LEFM) crack front loading histories with mixed-mode fatigue crack growth rate data. The model was applied for the “squat” type of crack—typical of rail RCF failure, to predict (i) shape development, (ii) co-planar extension, (iii) spalling, and (iv) branching to transverse defects. The model demonstrated that propagation of “squats” under the rail surface is feasible when a fluid entrapment mechanism is introduced, encouraging a mixed-mode shear dominated growth. However, cracks may branch to a Mode I direction when the residual stress, crack inclination and braking force create favourable conditions.