Strain gradient crystal plasticity with evolving length scale: Application to voided irradiated materials

Abstract

A micromorphic crystal plasticity model is used to simulate slip band localization in single crystals under simple shear at finite deformations. Closed form analytical solutions are derived for single slip in the case of positive, zero and negative strain hardening. Linear negative strain hardening, i.e. linear softening, leads to a constant localization slip bandwidth, while non linear softening and saturating behaviour results in an increasing bandwidth. An enhanced model is therefore proposed in order to maintain a bounded localization slip bandwidth when considering an exponential softening behaviour. Analytical solutions are used to validate finite element computation of the same boundary value problems. The enhanced micromorphic crystal plasticity model is then applied to predict the interaction between localized slip bands and voids encountered in porous irradiated materials. For that purpose, periodic porous unit cells are loaded in simple shear with a strain gradient crystal plasticity matrix material. The finite element simulation results show that, for a given void volume fraction, the larger the voids, the wider the localization band. However, for a given void size, the larger the void volume fraction, the narrower the localization band. In addition a satisfactory qualitative agreement of the rotation and elongation of the voids with the experimental observations made in irradiated materials is observed, where small voids are shown to remain ellipsoidal for larger shear strains. Large voids deform into peanut-like shapes.