Plastic Flow in Two-Dimensional Solids

TL;DR

This paper introduces a time-dependent Ginzburg-Landau model for plastic deformation in 2D solids, highlighting slip formation, dislocation behavior, and metastable disordered states under large strains.

Contribution

It presents a novel dynamic model incorporating elastic energy and slip formation, advancing understanding of plastic flow in two-dimensional materials.

Findings

Dislocation slips form at specific orientations during shear and stretching.

High-density dislocations persist after flow stops, leading to metastable states.

Plastic deformation involves a nearly constant defect energy component.

Abstract

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field $\bi u$ and the lattice velocity ${\bi v}=\p {\bi u}/\p t$. Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers vectors. The formation energy of a slip is minimized if its orientation is parallel or perpendicular to the flow in simple shear deformation and if it makes angles of $\pm \pi/4$ with respect to the stretched direction in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow is stopped. Thus large applied strains give rise to metastable, structurally disordered states. We divide the elastic energy into an elastic part due to affine deformation and a defect part. The latter represents degree of disorder and is nearly constant in plastic flow under cyclic straining.