Free energy function of dislocation densities by large scale atomistic simulation

TL;DR

This study uses large-scale atomistic simulations to directly measure the free energy of dislocation microstructures, revealing a linear relationship with dislocation density that aligns with classical models.

Contribution

It provides the first ab-initio measurements of dislocation free energy and density, clarifying their relationship through direct simulation rather than theoretical assumptions.

Findings

Dislocation free energy is linearly related to dislocation density.

Simulation results agree with classical models of dislocation energy.

Nanoindentation effectively induces complex dislocation microstructures.

Abstract

This paper discusses the free energy of complex dislocation microstructures, which is a fundamental property of continuum plasticity. In the past, multiple models of the self energy of dislocations have been proposed in the literature that partially contradict each other. In order to gain insight into the relationship between dislocation microstructures and the free energy associated with them, instead of deriving a model based on theoretical or phenomenological arguments, here, these quantities are directly measured using large scale molecular dynamics simulations. Plasticity is induced using nanoindentation that creates an inhomogeneous distribution of dislocations as the result of dislocation nucleation and multiplication caused by the local deformation. Using this approach, the measurements of dislocation densities and free energies are ab-initio, because only the interatomic potential is defining the reaction of the system to the applied deformation. The simulation results support strongly a linear relation between the scalar dislocation density and the free energy, which can be related very well to the classical model of mechanical energy of straight dislocations, even for the complex dislocation networks considered here.