Experimental study on the effect of bending stress on rail RCF crack initiation and propagation behavior: Based on a newly designed rail specimen

Rolling contact fatigue (RCF) is one of the main rail damage forms. Severe RCF damage can cause rail fracture and seriously endanger the safety of train operation. In this study, the influence mechanism of bending stress on RCF propagation of rail was studied. Firstly, a twin-disc rolling rail specimen considering bending stress was designed by finite element (FE) simulation, and the bending stress was introduced into the twin-disc rolling test. Secondly, the evolution behavior of RCF crack propagation of rail under bending stress and the comparative study of RCF crack propagation behavior of rail under different crack propagation driving forces were carried out by using the twin-disc rolling rail specimen considering bending stress and traditional twin-disc rolling wheel-rail specimen. Results indicate that the bending stress had a significant effect on the initiation and propagation of the RCF crack of the rail. Compared with the non-bending stress affected zone (NBSA zone), the bending stress promoted the initiation of cracks and drove them to propagate rapidly along the plastic deformation layer. When the crack propagation depth was greater than the thickness of the plastic deformation layer, the crack had an obvious tendency to propagate inside the material, which was manifested as the crack propagating almost perpendicular to the rail surface. Compared with the crack behavior only under contact stress, the angle and depth of crack propagation increased significantly under bending stress, indicating that the bending stress promoted the crack propagation. Compared with the crack propagation behavior under water medium, the crack propagation under bending stress was directional, and the crack propagation behavior was highly consistent with the crack propagation of field rail.