Nonlinear elasticity of prestressed single crystals at high pressure and various elastic moduli

TL;DR

This paper develops a comprehensive nonlinear elasticity theory for pre-stressed single crystals, defining various elastic moduli, analyzing their relationships, and applying the theory to complex problems like superdislocations and polycrystalline aggregates.

Contribution

It introduces a unified framework for nonlinear elastic moduli in pre-stressed crystals, including B moduli, and clarifies their roles and limitations in elasticity modeling.

Findings

B moduli relate to the Gibbs energy and stress derivatives.

Elastic energy expressions are derived for small distortions.

Inconsistencies in previous works are identified and analyzed.

Abstract

A general nonlinear theory for the elasticity of pre-stressed single crystals is presented. Various types of elastic moduli are defined, their importance is determined, and relationships between them are presented. In particular, B moduli are present in the relationship between the Jaumann objective time derivative of the Cauchy stress and deformation rate and are broadly used in computational algorithms in various finite-element codes. Possible applications to simplified linear solutions for complex nonlinear elasticity problems are outlined and illustrated for a superdislocation. The effect of finite rotations is fully taken into account and analyzed. Different types of the bulk and shear moduli under different constraints are defined and connected to the effective properties of polycrystalline aggregates. Expressions for elastic energy and stress-strain relationships for small distortions with respect to a pre-stressed configuration are derived in detail. Under initial hydrostatic load, general consistency conditions for elastic moduli and compliances are derived that follow from the existence of the generalized tensorial equation of state under hydrostatic loading obtained from single crystal or polycrystal. It is shown that B moduli can be found from the expression for the Gibbs energy. However, higher-order elastic moduli defined from the Gibbs energy do not have any meaning since they do not directly participate in any known equations, like stress-strain relationships and wave propagation equation. The deviatoric projection of B can also be found from the expression for the elastic energy for isochoric small strain increments, and the missing components of B can be found from the consistency conditions. Numerous inconsistencies and errors in the known works are analyzed.