Pergamon

Abstract-Shock-wave deformation of tantalum to a pressure of 45 GPa and duration of 1.8 ps generates profuse twinning. The post-shock mechanical response is significantly affected, with shock hardening exceeding the expected hardening due to the transient shock strain t, = (4/3) ln ( V / V,,); this enhanced hardening, and other alterations in response, are attributed to the barriers presented to plastic deformation by the deformation twins. A constitutive mode1 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 mode1 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 0 1996 Acta Metallurgica Inc. 1