Characterization of RCF crack growth in different grain microstructures of railway U75V rail under high coefficient of friction conditions

The grain topology, grain size, grain orientation of rail have significant influences on the crack growth of early rolling contact fatigue (RCF). In this study, a microstructural RCF crack growth model was established and the growth characteristics of RCF cracks in different grain microstructures were investigated. Firstly, based on the crystal plasticity theory, the microstructure deformation behavior of U75V rail material was simulated. Then, based on the Voronoi principle, the grain model was established with Electron Back Scatter Diffraction (EBSD) observation results. Finally, the damage accumulation law was introduced into the cohesion elements and the material damage evolution was simulated by the introduction of cohesive elements at grains and grain boundaries. In the simulation results, the emergence of plastic deformation layer on the surface of U75V rail increased the initiation risk of RCF cracks, inhibited the growth rate of RCF cracks, and changed the crack growth form. In addition to oblique cracks (α-cracks) which formed an angle with the conventional rolling direction, new cracks (β-cracks) which were initiated on the subsurface and grew in parallel along grain boundaries. The two kinds of cracks existed on the contact surface, as confirmed by the crack morphology observed in the twin-disc test.