Stability of the compression axis in bcc tantalum and fcc copper under shock-loading conditions *

When dynamically compressed via laser-plasma ablation, a metallic specimen will generally undergo changes to its crystallographic texture due to plasticity-induced rotation. The axis and the extent of the local rotation can provide hints about the combination of plasticity mechanisms activated by the rapid uniaxial compression, thus providing valuable information about the underlying dislocation kinetics that are operative under extreme loading conditions. We present molecular dynamics simulations of shock-induced lattice rotation in three model crystals whose behaviour has previously been characterised in dynamic-compression experiments:  tantalum shocked along its [101] direction, and copper shocked along either [001] or [111]. Our simulations indicate that while tantalum loaded along [101] and copper loaded along [001] both show pronounced rotation due to asymmetric multiple slip, the orientation of copper shocked along [111] is stabilised by opposing rotations arising from competing, symmetrically equivalent slip systems. In all three cases, the sense of the reorientation predicted by the simulations is consistent with that measured experimentally using in situ x-ray diffraction.