Ductility limit prediction for polycrystalline aggregates using a CPFEM-based multiscale framework

The ductility of polycrystalline aggregates is usually limited by two main phenomena: plastic strain localization and void coalescence. The goal of this contribution is to develop a new multiscale framework, based on the crystal plasticity finite element method (CPFEM), for the prediction of ductility limits set by these two phenomena for porous and non-porous polycrystalline aggregates. This numerical framework is based on the combination of crystal plasticity constitutive modeling with the periodic homogenization scheme. Within this strategy, the single crystal constitutive modeling follows a finite strain rate-independent approach, where the plastic flow is governed by the classical Schmid law. Thereby, the competition between the two aforementioned phenomena, which limit ductility, is thoroughly analyzed using the bifurcation theory and a strain-based coalescence criterion. To cover a wide range of mechanical states in this analysis, two types of loadings are applied to the studied aggregates: proportional triaxial stress paths and proportional in-plane strain paths. The developed CPFEM-based framework is well suited to account for essential microstructural features: pre-existence of spherical voids, crystallographic and morphological anisotropy, matrix polycrystallinity and interactions between grains and their surrounding medium. Extensive sensitivity studies are performed to analyze the impact of these microstructural features on the ductility limit predictions. The main trends obtained by classical phenomenological frameworks are extended here within the framework of crystal plasticity constitutive modeling.