Orientation dependent spall strength of tantalum single crystals
EN Hahn and SJ Fensin and TC Germann and GT Gray, ACTA MATERIALIA, 159, 241-248 (2018).
It is generally recognized that single crystals exhibit orientation- dependent elastic and plastic responses. However, it is less known how the dynamic tensile, or spall, strength depends on crystalline orientation, especially for BCC materials. It has been previously shown that the dynamic tensile strength of FCC materials is highly dependent on their plastic response under compression, with a direct correlation between plastic deformation and spall strength. In BCC materials like Ta, where the primary deformation mechanism at high strain rates is a combination of slip and twinning, the quantitative dependence of spall strength on these deformation mechanisms is less understood. To fill this gap in our knowledge, a series of non-equilibrium molecular dynamics simulations are completed for six tantalum single crystal orientations: <001>, <011>, <111>, <013>, <112>, <149>, to explore the role of directional anisotropy on ductile spallation. Our results show that due to the role of non-Schmid and release effects in BCC Ta, the evolution of plasticity follows a complex trajectory through shock compression, release, and tension. Orientations that contain residual twinning deformation have a reduced spall strength proportional to the amount of twinning present. Twins and their intersections function as regions of increased stress localization within the system due to compatibility requirements and their interactions with dislocations. (C) 2018 Published by Elsevier Ltd on behalf of Acta Materialia Inc.
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