Fatigue crack growth in cast austenitic steel in thermo-mechanical fatigue regime

This study aims to assess the thermo-mechanical fatigue (TMF) crack growth mechanisms and associated fatigue crack growth rate (FCGR) for loadings implying large-scale yielding conditions. The target component is made of a cast alloy with a coarse microstructure with grain sized to millimeter range. However, despite the complex crack path associated with this heterogeneous microstructure, it was observed that the FCGR was independent of the microstructure. In situ image analysis was the basis of experimental measurement of the crack closure effect, demonstrating a master curve for FCGR as a function of crack mouth opening displacement for both isothermal and anisothermal loadings. On this basis, to obtain a FCGR model independent of the tested geometry, a model based on macroscopic strain energy partitioning into elastic and inelastic contributions succeeded in evaluating both isothermal and TMF FCGR. This was possible by integrating the measured force at crack opening into this model.