The influence of wheel flats formed from different braking conditions on rolling contact fatigue of railway wheel

The objective of this study is to explore the rolling contact fatigue (RCF) behaviors of wheel materials with a flat under different braking conditions using a JD-1 wheel/rail simulation apparatus. The results indicates that the microstructure of wheel flat zone is composed of white etching layer (WEL), transition layer (TL), plastic deformation layer (PDL). The martensite caused by thermal effect is clarified in the WEL of wheel flat zone. There are three kinds of damage forms including the material accumulation, plowing and peeling in the front, the middle and the back of wheel flat zone, respectively. Fatigue cracks caused by impact only initiate and propagate in the back of wheel flat zone. Meanwhile, with the braking speed or braking time increasing, the fatigue damage of wheel flat zone worsen and the thickness of WEL increases, which brings an increase of fatigue crack length and propagation angle.