Stress/strain distribution under mechanical fatigue loading in advanced steels for machinery application : simulation and experiment

Abstract

This master’s thesis investigates the microstructure, fatigue behaviour, fracture characteristics and stress distribution of Hadfield manganese steels under mechanical fatigue loading, with the aim of understanding fatigue crack initiation and failure mechanisms in machinery applications. The study combines hardness testing, optical microscopy, SEM/EDS, XRD, fatigue testing, ARAMIS strain-field measurement and finite element analysis to correlate material characteristics with mechanical response. The results show that the investigated steels were mainly austenitic after solution treatment and water quenching, but their hardness, local heterogeneity and fatigue behaviour differed. Fatigue failure in sample A and B was associated with localized strain accumulation, surface-related crack initiation, progressive crack propagation and final overload fracture. Finite element analysis identified stress concentration near the gauge-to-grip transition, supporting the interpretation that fatigue failure was controlled by the interaction between microstructural heterogeneity, local strain localization and geometrical stress concentration rather than by nominal stress alone.