Statistical analysis of the effect of micro-defect size on the low cyclic fatigue and creep fatigue response of 316FR stainless steel using crystal plasticity finite element method

Abstract

The main purpose of this study is to explore and discuss the effect of micro-defects of different sizes on the low cyclic fatigue (LCF) and creep fatigue (CF) behavior in 316FR stainless steel. From the crystal plasticity finite element (CPFE) perspective, representative volume element (RVE) models including different micro-defect sizes are systematically developed, and an extended Armstrong-Frederick (A-F) nonlinear kinematic hardening rule is used to capture the LCF and CF behavior of the 316FR stainless steel. Statistical probability analysis shows that the relative errors between the macroscopic stress–strain simulation results and the experimental data ranged from 0.24% to 16.52%, indicating that the model has high accuracy. Three fatigue index parameters (FIPs) are used to characterize the degree of fatigue of the material: the standard deviation of strain increases with increasing micro-defect size, and the standard deviation of the maximum strain at CF loads exceeds that at LCF loads by 0.0173; the larger the size of the micro-defects are, the coarser the persistent slip band (PSB) around the defects is; the strain distribution under CF loading is wider than that of LCF, and the strain at 99% of the strain accumulation frequency at CF loading exceeds that at LCF loading by 0.078. These results indicate that the larger the defect sizes are, the higher the degree of fatigue accumulation in 316FR stainless steel is, and that the deformation behavior of the material is more complex under CF loading.