Continuum metrics for in-situ analysis of crystal plasticity and twinning at the atomic scale

The definition of multiscale constitutive laws for metals under extreme conditions requires a detailed understanding of irreversible deformation mechanisms, such as dislocation mobility and interaction, twinning, etc. In order to overcome the lack of experimental data at the atomic scale on these mechanisms, we use classical molecular dynamics simulations with in-situ Lagrangian measures to extract the signature of crystal plasticity and twinning. Thanks to the calculation of the eigenvectors of the deformation gradient tensor, we are able to distinguish, for example, the directions of sliding/twinning as well as the corresponding habitat planes.

The tools developed in this work allow the extraction of crucial information if one wants to identify mechanical field statistics from MD simulations and to build constitutive laws at the mesoscopic scale in a bottom-up approach. The effectiveness of the presented method is first demonstrated for the analysis of deformation mechanisms caused by dynamic uniaxial compression of Copper and Tantalum single crystals containing a cavity. In a second study, we examine the strain rate sensitivity of the competition between crystal plasticity and twinning for a Tantalum single crystal under dynamic shear.