Extraction of slip systems and twinning variants from a Lagrangian analysis of molecular dynamics simulations

The definition of multiscale constitutive laws for metals under extreme conditions requires a detailed understanding of the irreversible deformation mechanisms, e.g., dislocation motion and their interaction with obstacles: other dislocations, twin boundaries, etc. We propose to study the signature of dislocation-mediated plasticity and twinning deformation in large-scale molecular dynamics simulations with Lagrangian deformation measures. Through the computation of the deformation gradient tensor, we are able to discriminate, e.g., the slip/twinning directions and slip/twinning planes. The effectiveness of the developed method is demonstrated on two applications. We first study the identification of activated slip systems during the dynamic uniaxial deformation of a single-crystal copper containing voids, operating as dislocation nucleation sources. An application on a single crystal tantalum under high strain-rate loading demonstrates the accuracy of the presented method to extract statistics related to the activation of twinning variants and the details of their interaction with slip systems. The developed tool is entitled S2TXA for Slip System and Twinning eXtraction Algorithm and will be made available publicly. • Lagrangian measures in molecular dynamics help extract atomic scale defects. • Slip direction and habitat plane are extracted from the deformation gradient tensor. • New atomic-scale information about crystal plasticity and twinning can be extracted. • Demonstration cases involve crystal plasticity in copper and twinning in tantalum.