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 response is significantly affected, with shock hardening exceeding the expected hardening due to the transient shock strain epsilon(s)=(4/3)ln(V/V-o); this enhanced hardening, and other alterations in response, are attributed to the barriers presented to plastic deformation by the deformation twins. A constitutive model is proposed that predicts the threshold shock stress for mechanical twinning; it is based on the application of the Swegle-Grady relationship between shock stress and strain rate to constitutive equations describing the critical stress for slip and twinning. This constitutive model incorporates grain-size effects and predicts a threshold twinning stress that is a function of temperature and grain size; predictions of the model are in qualitative agreement with experimental results. Copyright (C) 1996 Acta Metallurgica Inc.