Modeling and crystal plasticity simulations of lath martensitic steel under fatigue loading

Abstract

A computational study for the modeling of lath martensitic steels, considering morphological and crystallographic features, is presented. A two-dimensional multi-scale tessellation is proposed to generate idealized microstructures with several scales of heterogeneities. The proposed approach is applied to lath martensite where prior austenite grain, packet and block boundaries are explicitly considered as well as their crystallographic relationships. The role of the different sources of heterogeneity on fatigue crack initiation is then investigated by finite element simulations including a single-crystal plasticity model. A fatigue criterion based on the Tanaka-Mura model is evaluated. The results indicate that block morphology and their orientation relationship significantly affects the strain distribution and the predicted location of crack initiation. In this regard, the effective critical size for crack initiation in low-carbon steels appears to be the block size as the Tanaka-Mura model mainly predicts cracks initiation along the block direction.