Driving forces on dislocations due to strain gradients and higher order gradients

TL;DR

This paper investigates how strain gradients and higher order gradients influence dislocation dynamics, confirming the existence of a core force through atomistic simulations and exploring its implications for dislocation behavior.

Contribution

It introduces a direct observation of strain gradient-driven forces on dislocations and examines the role of higher order gradients, advancing understanding beyond classical elasticity.

Findings

Confirmed the existence of a core force driven by strain gradients.

Demonstrated that higher order strain gradients can act as relevant forces on dislocations.

Provided a method to estimate core energy using scale-invariant systems.

Abstract

Dislocations are topological defects known to be crucial in the onset of plasticity and in many properties of crystals. Classical Elasticity still fails to fully explain their dynamics under extreme conditions of high strain gradients and small scales, which can nowadays be scrutinized. In such conditions, corrections to the Volterra dislocation fields and to the Peach-Koehler force, for example, become relevant. One way to go beyond the Volterra solution is to consider other terms in the total Laurent series solution. This is the so called core field. One of its consequences is to predict a driving force on the dislocation due to background strain/stress gradients, which has also been suggested by other core energy calculations. Here we confirm its existence by presenting a direct observation of strain gradients driving edge dislocations in 2D atomistic simulations. We show that, in systems with scale invariance, the results for such core force can be used to obtain the total core energy, allowing a standard value for this energy to be compared with other classical methods of obtaining it. The force measured in our system differs from the prediction obtained by a direct core field analysis. Moreover, we found that higher order gradients of strains can also act as relevant forces.