Unified viscoplastic constitutive model for creep–fatigue behavior of austenitic stainless steel 304 under axial–torsional loading

Based on the Abdel-Karim and Ohno model framework, a unified viscoplastic constitutive model (UVCM) is developed in order to simulate the mechanical behavior of austenitic steel under low-cycle fatigue (LCF) loading at room temperature and 600 °C and creep–fatigue (CF) loading at 600 °C, respectively. The effects of viscoplastic static recovery, mean stress evolution and strain range-dependent cyclic softening are incorporated into the UVCM. Moreover, the material parameters are categorized and each type of parameter is subjected to a sensitivity analysis in order to explore its effect on the simulation results. For LCF loading at room temperature and 600 °C, the influence of axial loading, cyclic torsional angle, and loading rate on LCF response are, respectively, studied, and different viscous behavior and cyclic softening characteristics are found. For CF loading at 600 °C, the influence of hold time on CF response is investigated, with shear stress relaxation occurring during the hold time and becoming more pronounced the longer the hold time is. The predicted results are in good agreement with the experimental results, which indicates that the model has good accuracy.