Microstructural modeling of fatigue crack initiation in austenitic steel 304L

A methodology for modeling realistic microstructures of metallic polycrystalline material is presented. This approach is applied to the prediction of cyclic behavior of austenitic steel 304L in order to study the role of microstructural effects on fatigue crack initiation. The microscope observations show crack initiation and microcrack propagation are dependent on crystallographic orientations, indicating the need for such modeling approach. A representative volume of the material corresponding to a realistic microstructure, containing about 200 grains, has been numerically modeled with the crystal plasticity approach. This model takes account of dislocation densities on the 12 slip systems, isotropic and kinematic hardening, grain sizes, crystal orientations and elastic anisotropy. The material parameters used in this model were obtained through experimental measurements and the literature or identified through an inverse procedure, which give good predictions of stress- strain response at the macroscale. The field results of local strain, stress, slip-based and energy-based initiation metrics are simulated at grain scale. The results show that some of these metrics are in good agreements with experiments and can be used in fatigue crack initiation criteria.