Microvoid growth mechanism in FCC polycrystals and a statistical damage model

Abstract

In polycrystalline materials, microvoid size is usually of the same order of magnitude as grain size. However, in most previous studies, matrix around microvoid is generally assumed to be isotropic and homogeneous, ignoring local heterogeneous polycrystalline microstructure. In this paper, microvoid growth under finite deformation in a face centered cubic (FCC) polycrystal is studied, focusing on the effect of local heterogeneous polycrystalline microstructure. Crystal plasticity finite element simulation (CPFEM) of polycrystalline representative volume element (RVE) is performed, with special attention to three important factors influencing the microvoid growth, i.e., external macroscopic stress triaxiality, internal crystallographic orientation of grains and ratio of microvoid size to grain size. The results indicate that the crystallographic orientation of grains has significant influences on the microvoid growth, especially when the stress triaxiality is not high. The local heterogeneous polycrystalline microstructure in polycrystals is found to retard the microvoid growth, suggesting that the traditional microvoid growth models based on the assumption of homogeneous isotropic matrix can significantly overestimate the microvoid growth. Besides, the size ratio of microvoid to the voided grain can heavily influence the microvoid growth, showing a strong size effect due to the first order heterogeneous deformation effect around the microvoid in heterogeneous polycrystals. Due to random grain-orientation distributions in polycrystals, the microvoid growth rate exhibits randomness and dispersion. To assess this dispersion under different stress triaxialities, a statistical microvoid growth model is proposed, which well envelops all the dispersed CPFEM results.