Role of twinning and slip during compressive deformation of beryllium as a function of strain rate

An experimental and theoretical investigation was carried out to study the strain rate dependent plastic response of beryllium over a wide range of applied compression strain rates, 10(-4)-10(4)/s. At each rate, the evolution of flow stress and the final texture with deformation was obtained from a non-textured hot-pressed (HP) sample and a textured rolled sheet. The rolled sheet material was compressed in both the in-plane (IP) and through-thickness (TT) direction for comparison. The twin volume fraction was determined from the change in texture. The activity of twinning was strongly dependent on strain rate in the IP and HP samples. We applied a multi-scale constitutive model for hexagonal close packed polycrystals that accounts for crystallographic slip and twinning on individual systems in each crystal, as well as twin reorientation. Rate effects enter the calculations only through thermally activated dislocation glide on the active slip modes. The importance of this study is that it points to the necessity of using a crystallographic model based on microstructure evolution to understand the role played by plastic anisotropy, slip-slip competition, and slip-twin competition, in the mechanical response of HCP aggregates. The model reproduces the observed flow curves and texture evolution for all tests with a unique single crystal set of parameters. (C) 2011 Elsevier Ltd. All rights reserved.