Kinematics of plasticity-induced rotation during shock or ramp compression to extreme pressures*

When a metallic specimen is rapidly compressed via laser-plasma ablation, its underlying crystal structure must often rotate as it plastically deforms. There is growing interest in the dynamic compression community in exploiting x-ray diffraction measurements of lattice rotation to infer which combinations of plasticity mechanisms are operative in uniaxially shocked crystals, and thus inform materials science at extreme pressures and strain rates [see for example Wehrenberg et. al., Nature 550, 496-499 (2017)]. However, it is not widely appreciated that many existing models linking rotation to slip activity are fundamentally inapplicable to a planar shock-loading scenario. We have conducted molecular dynamics simulations of single crystals suffering true uniaxial strain, and have found that the Schmid and Taylor analyses frequently used in traditional materials science fail to predict the ensuing texture evolution. We propose a simple alternative framework that successfully recovers the observed rotation, and can further be used to correctly identify the active slip systems in the idealised cases of single and conjugate slip [Heighway and Wark, J. Appl. Phys. 129, 085109 (2021)].