Experimental molecular dynamics for individual atomic-scale plastic events in nanoscale crystals

Abstract

The experimental determination of critical stresses for yielding and plastic flow is of upmost importance for the understanding of the atomic-scale mechanical behaviors of nanoscale metals, which is limited in computational molecular dynamics due to their inherent high strain rates and empirical interatomic potentials. Here, we propose an in situ atomic-scale experimental mechanics, the so-called experimental molecular dynamics, which is capable of studying the stress-strain relations with respect to the individual atomic-scale plastic events, including full dislocation slip, deformation twinning and shear band in nanoscale metals with different crystal structures. The local stress, strain and their relationships were obtained based on the analyses of the change in lattice strain gauge, interplanar spacing and gauge length. Using this method, drastic stress drops and strain bursts, the characteristics of individual plastic events, are investigated. The critical stresses for activating the nucleation and growth of atomic-scale defects are obtained. The newly developed experimental molecular dynamics with in situ mechanics approach has the advantage of quasi-static strain rate and no requirement of interatomic potentials over the computational one, which may provide new clues to establish the stress-based criteria for atomic-scale yielding and plastic flow.