Local Stress and Damage Response of Polycrystal Materials to Light Shock Loading Conditions via Soft Scale-Coupling

Accurately representing the process of porosity-based ductile damage in polycrystalline metallic materials via computational simulation remains a significant challenge. The heterogeneity of deformation in this class of materials due to the anisotropy of deformation of individual single crystals creates the conditions for the formation of a damage field. The work reported upon here is interested in the formation of porosity in the body-centered cubic metal tantalum. This chapter reports on the soft-coupled linkage between a macroscale damage model and mesoscale calculations of a suite of polycrystal realizations of tantalum. The macroscale model is used to represent a tantalum on tantalum plate impact experiment and predict the point in time in the loading profile when porosity is likely to initiate. The 3D loading history from the macroscale calculation is then used to define the probable loading history profile experienced within the experimental sample. Tantalum displays non-Schmid behavior in the motion of the dominant screw dislocations during deformation. This introduces directionality in the magnitude of stress required to propagate glide of these screw dislocations. A model is presented which provides representation of non-Schmid effects in tantalum. This model is employed in performing of meso-scale calculations of statistically equivalent microstructures of the tantalum material to provide local-scale stress condition at the time of the loading profile where initiation of porosity is anticipated. The results of these simulations suggest that non-Schmid effects significantly impact the local stress conditions within the microstructure and are very important to represent. The results also suggest that vonMises stress conditions at grain boundaries and grain boundary triple lines are highly variable close to those features but the variability is reduced with distance to the grain center. The computational results also suggest that the stress traction conditions at the grain boundary are a strong function of the orientation of each boundary with respect to the shock direction. Grain boundaries whose surface normal is parallel to the shock direction have a significantly higher normal tensile traction than other grain boundaries. Grain boundaries whose normal is at 45 or 135 degrees to the shock direction have relatively higher magnitudes of shear stress.