Modeling and simulation of strain-induced phase transformations under compression and torsion in a rotational diamond anvil cell

Strain-induced phase transformations (PTs) under compression and torsion in rotational diamond anvils are simulated using a finite-element approach. Results are obtained for three ratios of yield strengths of low-pressure and high-pressure phases and are compared with those for the compression without torsion from Levitas and Zarechnyy [Phys. Rev. B 82, 174123 (2010)]. Various experimental effects are reproduced, including a pressure self-multiplication effect, plateau at pressure distribution at the diffuse interface, simultaneous occurrence of direct and reverse PTs, and irregular stress distribution for PT to a weaker phase. The obtained results change the fundamental understanding of strain-induced PT in terms of interpretation of experimental measurements and the extracting of information on material processes from sample behavior. Intense radial plastic flow moves the high-pressure phase to the low-pressure region, which may lead to misinterpretation of measurements. Various interpretations based on a simplified equilibrium equation (for example, about zero yield strength of phase mixture and hydrostatic conditions during PT) appears to be wrong because of inapplicability of this equation for cases with large gradients of phase concentration and yield strength. The approach developed represents a tool for designing experiments for different purposes and for controlling PTs, and it opens unexpected ways to extract material information by combining simulation and experiment.