Rolling contact fatigue of rails—finite element modelling of residual stresses, strains and crack initiation

Abstract

Numerical models that can be used to evaluate crack initiation in rails owing to rolling contact loads are of great value. Very few models on rail fatigue assessments exist in the literature that consider the non-linear stress and strain response in the rail caused by both global dynamic track response and local wheel-rail contact loads. In the present investigation, such a tool has been developed using finite element (FE) models. The tool can be used to calculate governing fatigue conditions such as residual stresses, plastic strains and orientation of crack planes for crack initiation. The ability to perform parameter studies of, for example, track properties, different materials and load cases is inherent in the tool. The tool was used in a case study of commuter train traffic at a Swedish test site. In the FE simulations, a material model with non-linear isotropic and kinematic hardening, which was able to consider ratchetting behaviour, was used. Ratchetting material response near the railhead surface was found. A criterion for fatigue crack initiation caused by ratchetting and a criterion for fatigue crack initiation caused by low-cycle fatigue (LCF) were compared. The LCF criterion showed the lowest number of cycles to crack initiation, which, given the models used, indicates that cracks will initiate owing to LCF rather than ratchetting. Good agreement for the direction of surface cracks between the rail track at the test site and the results from the simulations was achieved.