DISLOCATION MECHANICS BASED ANALYSIS OF MATERIAL DYNAMICS BEHAVIOR - ENHANCED DUCTILITY, DEFORMATION TWINNING, SHOCK DEFORMATION, SHEAR INSTABILITY, DYNAMIC RECOVERY

Further developments are described for the dislocation mechanics based constitutive equation analysis previously used to describe the separa te dynamic stress-strain behavior of fee and bcc metal polycrystals. A n enhanced hardening and ductility in copper and certain tantalum mate rials at higher strain rates in split Hopkinson pressure bar tests and in shock loading are attributed to enhanced dislocation generation ra ther than to dislocation drag. Added material strengthening is account ed for also by deformation twinning in ARMCO iron and titanium and in shocked copper and tantalum. The separate equations are applied to cal culate the critical strain for shear banding in copper, iron, and the titanium alloy, Ti-6Al-4V. In the two latter cases, the results are ve ry sensitive to the details of the strain-hardening behavior and the n eed is demonstrated for a dynamic recovery factor to account for the o nset of shear banding. Consideration is given also to the possibility that shear band behavior requires explanation on a more fundamental Ha ll-Fetch dislocation pile-up basis.