A finite deformation theory of dislocation thermomechanics

TL;DR

This paper introduces a nonlinear, measurable-variable-based theory of dislocation thermomechanics that captures the effects of temperature fields on dislocation evolution and predicts dispersive thermal waves.

Contribution

It develops a novel additive decomposition of the velocity gradient and derives governing equations from fundamental conservation laws, incorporating measurable state variables.

Findings

Captures transient temperature effects on dislocation density evolution

Allows computation of the material and strain rate dependent Taylor-Quinney factor

Predicts dispersive thermal waves with finite propagation speed

Abstract

A geometrically nonlinear theory for field dislocation thermomechanics based entirely on measurable state variables is proposed. Instead of starting from an ordering-dependent multiplicative decomposition of the total deformation gradient tensor, the additive decomposition of the velocity gradient into elastic, plastic and thermal distortion rates is obtained as a natural consequence of the conservation of the Burgers vector. Based on this equation, the theory consistently captures the contribution of transient heterogeneous temperature fields on the evolution of the (polar) dislocation density. The governing equations of the model are obtained from the conservation of Burgers vector, mass, linear and angular momenta, and the First Law. The Second Law is used to deduce the thermodynamical driving forces for dislocation velocity. An evolution equation for temperature is obtained from the First Law and the Helmholtz free energy density, which is taken as a function of the following measurable quantities: elastic distortion, temperature and the dislocation density (the theory allows prescribing additional measurable quantities as internal state variables if needed). Furthermore, the theory allows one to compute the Taylor-Quinney factor, which is material and strain rate dependent. Accounting for the polar dislocation density as a state variable in the Helmholtz free energy of the system allows for temperature solutions in the form of dispersive waves with finite propagation speed, despite using Fourier's law of heat conduction as the constitutive assumption for the heat flux vector.