DEFORMATION TWINNING DURING IMPACT - NUMERICAL-CALCULATIONS USING A CONSTITUTIVE THEORY-BASED ON MULTIPLE NATURAL CONFIGURATIONS

When materials such as Armco iron, titanium etc., are subject to impac t it can be observed that two basic inelastic processes take place - s lip and deformation twinning. Of these processes, inelasticity associa ted with the slip mechanism has received considerable attention. For e xample, Zerilli and Armstrong (1988) modeled the Taylor impact test fo r a variety of materials using traditional plasticity theories. They f ound that there was a significant discrepancy between the theoretical and experimental results for some materials. They attributed this to t he fact that they had neglected deformation twinning in their models. Subsequent metallurgical studies have indicated that twinning had inde ed taken place in these materials. In this study, we focus on the inel astic processes solely due to deformation twinning (i.e., neglecting s lip). We model these processes using The approach of Rajagopal and Sri nivasa (1995, 1997) and Srinivasa et al., (1997), the results of which are briefly summarized in section 2.1. In order to better understand the twinning; process, we study the Taylor impact test for a 2-D slab under the assumption that only deformation twinning takes place and so lve the governing dynamical equations by using the finite element meth od. The results show that the twinned zone is concentrated near the po int of impact and indeed it contributes significantly to the overall p ermanent shape change due to the impact.