Effects of Local and Nonlocal Substructure Spin on Localization in Tantalum Top-Hat Specimen

Abstract

Effects of local and nonlocal substructure spin on the localization behavior of tantalum top-hat specimens subjected to high-rate compression are investigated. The orientation of a quadratic yield surface within the space of the intermediate configuration second Piola Kirchhoff stress is defined by a triad of substructure unit director vectors. Local evolution kinetics for the substructure directors are based on a plastic constitutive spin proportional to the non-coaxiality between stress and plastic rate of deformation within the spinless intermediate configuration. An extension of the local plastic constitutive spin to reflect nonlocal kinetics is made by attenuating or amplifying the spin rate depending on the misorientation of the substructure directors at a material point with those at adjacent material points within some neighborhood. Increased local spin rates tend to accentuate localization of plastic deformation and acts as a constitutive softening mechanism. On the other hand, the constraint imposed by nonlocal evolution of substructure orientation affects the plastic deformation field by reducing the propensity for flow, thus delaying localization and increasing the spatial coherence of the director vector field.