Evaluations and enhancements of fatigue crack initiation criteria for steels subjected to large shear deformations

While large accumulated plastic deformations occur in the rail surface layer where rolling contact fatigue cracks initiate, many available Low Cycle Fatigue (LCF) crack initiation criteria focus on small plastic strains. Accordingly, this paper evaluates available fatigue crack initiation criteria for highly shear-deformed R260 steels, reflecting the conditions in the surface layer of rails. Furthermore, modified crack initiation criteria are suggested. The evaluation is based on three different experiments: Large shear strain increments under varying axial loading (predeformation), strain-controlled LCF tests after some predeformation, and axial High Cycle Fatigue (HCF) experiments. For the predeformation, Finite Element (FE) simulations, with a large-strain plasticity model for cyclic and distortional hardening, provide predictions of the local stress and strain histories. A cross-validation procedure is used to assess the accuracy and reliability of both established and modified fatigue crack initiation criteria. The proposed modifications to one of the criteria show an improved fit to the experimental data. However, there is a tendency to overfitting, which can be improved by including more experimental data. • Three crack initiation criteria in rolling contacts of rail steel are evaluated. • Large strain cyclic axial-torsion experiments are used. • Finite element simulations are done using a large strain plasticity model accounting for anisotropy. • A cross-validation approach is used to assess the criteria. • Improved crack initiation criteria are proposed, leading to enhancements in fitting without worsening the prediction.