Finite Element Simulation Technique for Evaluation of Opening Stresses Under High Plasticity

The crack closure phenomenon is important to study as it estimates the fatigue life of the components. It becomes even more complex under low-cycle fatigue (LCF) since under LCF high amount of plasticity is induced within the material near notches or defects. As a result, the assumptions used by the linear elastic fracture mechanics (LEFM) approach become invalid. However, several experimental techniques are reported on the topic, the utilization of numerical tools can provide substantial cost and time-saving. In this study, the authors present a finite element simulation technique to evaluate the opening stress levels for two structural steels (25CrMo4 and 30NiCrMoV12) under low-cycle fatigue conditions. The LCF experimental results were used to obtain kinematic hardening parameters through the Chaboche model. The finite element analysis (FEA) model was designed and validated, following the fatigue crack propagation simulation under high plasticity conditions using abaqus. Crack opening displacement versus stress data were exported from abaqus, and 1.5% offset method was employed to define opening stress levels. Numerical simulation results were compared with the experimental results obtained earlier through the digital image correlation (DIC) technique. To conclude, FEA could be a valuable tool to predict crack closure phenomena and, ultimately, the fatigue life of components. However, analysis of opening stresses using crystal plasticity models or extended finite element method (XFEM) tools should be explored for a better approximation in future studies.