Thermal and Mechanical Responses of BCC Metals to the Fast-Transient Process in Small Volumes

Abstract

Plasticity in heterogeneous metallic materials with small volumes is governed by the interactions of dislocations within the bulk. Energy (heat) transfer, on the other hand, is micromechanically related to the interaction within phonons, electrons, or photons. To address the experimentally observed characteristics of small-volume metallic components such as thin films, these microstructural interactions need to be included in modeling. This gives rise to a large variety of generalized multiscale models that are developed on the continuum level and used to bridge the gap between the micromechanical and classical continuum models by means of certain characteristic time and length scales. A higher-order strain gradient model accounting for the size effect is combined in this paper with the generalized heat equation to identify the coupling effect of thermal and mechanical behavior of body-centered cubic (BCC) materials with small volumes and in transient time. A fully thermodynamically consistent framework is provided in this study based on the decomposition of mechanical state variables into energetic and dissipative counterparts to address the strengthening and hardening mechanisms exhibited in micro-/nanostructured materials. As an application, the size and rate effect of shear loading of a film-substrate system is presented. The effect of time and length scales on thermal and mechanical behavior, such as the formation of a boundary layer, energetic hardening and dissipative strengthening, and the size and rate effect of the system, is investigated.