Nanomechanics of Plasticity

Ting Zhu
Woodruff School of Mechanical Engineering
Georgia Institute of Technology

Abstract

Recent nanoscale experiments have revealed a host of plastic flow phenomena controlled by the nucleation and reaction of dislocations. We have developed the multiscale and atomistic modeling methods to quantitatively understand the dislocation processes in these experiments. We first develop a multiscale modeling approach of interatomic potential finite element method for simulating nanoindentation. This facilitates the modeling at the length scales of laboratory experiments, while remaining faithful to the nonlinear interatomic interactions. Our results demonstrate that the hyperelasticity and crystallography control critically the onset of plasticity during the nanoscale contact. We further bridge the timescale gap between atomistic simulations and laboratory experiments by integrating the transition state theory and the exploration of atomistic energy landscape. We show that the interfacial dislocation reaction is the rate-controlling mechanism in nano-twinned copper, giving rise to an unusual combination of ultrahigh strength and high ductility. Our results also reveal a small activation volume associated with surface dislocation nucleation. This leads to the sensitive temperature and strain-rate dependence of the nucleation stress, providing an upper bound to the size-strength relation in nanopillar compression experiments.