Study on wear and rolling contact fatigue behaviours of defective rail under different slip ratio and contact stress conditions

Surface defects play a vital role in wheel/rail rolling contact fatigue (RCF) damage, and materials around the defects act different under various working conditions. This study aims to investigate the effect of slip ratio and contact stress on the evolution of RCF behaviour of material around the surface defect on the rail. A wheel/rail twin disc machine was used to realise the experimental study and the defects were prepared by conical impacts. Optical microscope, scanning electron microscope and electron backscattered diffraction were used to analyse the microstructure. Results indicate that the evolution of material around the defect mainly include three parts: material flowing into and covering the defect, crack initiation and propagation, defect being worn off after the test stop and leaving a remaining crack. With the slip ratio increased, the cycling number when the defect being removed was decreased except the sudden change in the slip ratio of 12%. The slip ratio was regarded as the main factor of the change in the remaining crack angle. The cycling number when defect being removed was also decreased when the contact stress increased. Meanwhile, the change of the remaining crack depth was basically due to the contact stress. Furthermore, the most severe working condition is referred to the slip ratio of 12% with the contact stress of 1800 MPa.