Micromechanics of Ductile Damage during High Triaxiality Loading of a Refractory Metal*

Accurately representing the process of porosity-based ductile damage in polycrystalline metallic materials via computational simulations remains a significant challenge. The heterogeneity of deformation in this class of materials creates the conditions for the formation of a damage field. A technique of soft-coupled linkage between a macro-scale damage model and micro-mechanical calculations of a suite of polycrystal realizations of a representative BCC tantalum with non-Schmid effects is presented. The macro-scale model, which accounts for rate-dependence and micro-inertial effects, was used to model two plate impact experiments and predict the point in the loading profile when porosity is initiated. A single-crystal model is used for polycrystal calculations of statistically representative microstructures of the tantalum material subjected to the extreme loading conditions informed from the macro-scale calculations. This provides local-scale stress conditions for porosity initiation within the polycrystalline network. The results suggest that the non-Schmid effects significantly influence the local stress conditions across grain boundaries and triple junctions and stress at grain boundaries depend upon orientation of each boundary with respect to the shock direction. Results also suggest that the von Mises stress and triaxiality at the grain boundaries and the grain boundary triple lines are highly variable but the variability is diminished with distance to the grain center.