Fracture mechanics-based evaluation method for Mode II crack propagation rates under rolling contact fatigue in railway wheel steels

This study aims to evaluate shear-mode crack propagation rates under rolling contact fatigue (RCF) in railway wheel steels. Presently, no standardized evaluation method has been established for shear-mode crack propagation under RCF. In this study, twin-disc-type RCF tests were conducted on railway wheel steels with artificial defects, alongside finite element analyses (FEA) simulating these tests. The RCF test results indicated that the cracks initiated from the leading side of the defects propagated inward, while those initiated from the trailing side propagated toward the surface. The stress intensity factor (SIF) calculations revealed that cracks initiated from the leading side of the defects propagated through a mixed modes I and II, whereas cracks initiated from the trailing side propagated exclusively in Mode II. Additionally, crack propagation rates on the trailing side of the defects were higher than those on the leading side, attributed to a larger Mode II equivalent SIF range on the trailing side compared to the leading side. These results suggest that the FEA results corresponded to those of the RCF tests. Therefore, the relationship between the RCF crack propagation rate and shear mode SIF range could be evaluated by combining twin-disc-type RCF tests using test specimens with artificial defects and FEA.