SHOCK-INDUCED DEFORMATION TWINNING IN TANTALUM

hock-wave deformation of tantalum to a pressure of 45 GPa and duration of 1.8 mu s generates profuse twinning. The post-shock mechanical res ponse is significantly affected, with shock hardening exceeding the ex pected hardening due to the transient shock strain epsilon(s)=(4/3)ln( V/V-o); this enhanced hardening, and other alterations in response, ar e attributed to the barriers presented to plastic deformation by the d eformation twins. A constitutive model is proposed that predicts the t hreshold shock stress for mechanical twinning; it is based on the appl ication of the Swegle-Grady relationship between shock stress and stra in rate to constitutive equations describing the critical stress for s lip and twinning. This constitutive model incorporates grain-size effe cts and predicts a threshold twinning stress that is a function of tem perature and grain size; predictions of the model are in qualitative a greement with experimental results. Copyright (C) 1996 Acta Metallurgi ca Inc.