Energy storage under high-rate compression of single crystal tantalum

TL;DR

This study uses molecular dynamics simulations to analyze energy dissipation and storage during high-rate compression of single-crystal tantalum, proposing models for energy conversion and defect contributions.

Contribution

It introduces a phenomenological and a detailed model for energy storage during high-rate deformation, emphasizing defect contributions and energy convergence behavior.

Findings

TQC approaches 1.0 with increasing strain

Energy stored is mainly due to dislocation networks and point defects

Point defect debris significantly contributes to energy storage

Abstract

When a material is plastically deformed the majority of mechanical work is dissipated as heat, and the fraction of plastic work converted into heat is known as the Taylor-Quinney coefficient (TQC). Large-scale molecular dynamics simulations were performed of high strain rate compression of single-crystal tantalum, and the resulting integral and differential TQC values are reported up to true strains of 1.0. A phenomenological model is proposed for the energy stored in the material as a function of time with an asymptotic limit for this energy defined by the deformation conditions. The model reasonably describes the convergence of TQC values to 1.0 with increasing plastic strain, but does not directly address the physical nature of thermo-mechanical conversion. This is instead developed in a second more detailed model that accurately accounts for energy storage in two distinct contributions, one being the growing dislocation network and the other the point defect debris left behind by the moving dislocations. The contribution of the point defect debris is found to lag behind that of the dislocation network but to be substantial under the high-rate straining conditions considered here.