Fatigue crack initiation in the presence of stratified surface layers on rail wheels

Abstract

This work presents a study on the fatigue crack initiation in the presence of stratified surface layers (SSL) – a combination of white and brown etching layer – on rail wheels. Reproducible SSLs comparable to field samples are created by a defined mechanical load and two consecutive laser surface treatments on discs made from two wheel materials (ER7, ER9). Fatigue testing is done by a twin disc tribometer, where the wheel discs with SSLs are driven against discs made from R260 rail material. The results show significant fatigue crack initiation and propagation in the presence of the SSLs, exclusively on the leading edge of the SSL, more pronounced for the wheel grade ER9. Based on topographical, light optical and scanning electron microscopy analysis an explanatory model is presented, describing fatigue crack morphologies and outpointing the relevance of SSLs on rail wheels to fatigue crack initiation.