Material modeling of ferritic steel on microscopic length scale under cyclic loading

Abstract

A material model for the polycrystalline microstructure of formable steels is developed to determine the residual stress state resulting from incompatible plastic deformation of individual grains under non-monotonic loading. The glide of mobile dislocations on a specific slip system mainly governs the shear rates. During the movement, dislocations experience several types of resistance. The existing immobile dislocation structures on non-parallel slip planes reduce the slip activities. This is reflected in a nonlinear isotropic hardening criterion. Furthermore, piled up dislocations on parallel slip planes also create hindrance to mobile dislocations. This effect creates residual stresses within the material which are taken into account by an additional kinematic hardening law. Residual stresses play a crucial role as well, especially during cyclic loading. Both, nonlinear isotropic and kinematic hardening criteria can define the plastic character of ferritic steel under non-monotonic loadings.