Atomistic modeling of the dislocation dynamics and evaluation of static yield stress

A.V Karavaev,V.V Dremov,G.V Ionov,E Cadoni

doi:10.1051/epjconf/20159404007

Abstract

Static strength characteristics of structural materials are of great importance for the analysis of the materials behaviour under mechanical loadings. Mechanical characteristics of structural materials such as elastic limit, strength limit, ultimate tensile strength, plasticity are, unlike elastic moduli, very sensitive to the presence of impurities and defects of crystal structure. Direct atomistic modeling of the static mechanical strength characteristics of real materials is an extremely difficult task since the typical time scales available for the direct modeling in the frames of classical molecular dynamics do not exceed a hundred of nanoseconds. This means that the direct atomistic modeling of the material deformation can be done for the regimes with rather high strain rates at which the yield stress and other mechanical strength characteristics are controlled by microscopic mechanisms different from those at low (quasi-static) strain rates. In essence, the plastic properties of structural materials are determined by the dynamics of the extended defects of crystal structure (edge and screw dislocations) and by interactions between them and with the other defects in the crystal. In the present work we propose a method that is capable to model the dynamics of edge dislocations in the fcc and hcp materials at dynamic deformations and to estimate the material static yield stress in the states of interest in the frames of the atomistic approach. The method is based on the numerical characterization of the stress relaxation processes in specially generated samples containing solitary edge dislocations.

Highlights

Detailed description of the initial sample generation procedure for the proposed method is given in the caption of Fig. 2 by example simulations of copper with the Embedded Atom Model (EAM) interatomic potential [8]
In the present work we introduce a novel approach to the simulations of the dislocation dynamics in closepacked materials
The method is based on the numerical characterization of the shear stress relaxation processes in specially generated samples containing solitary edge dislocations of particular orientations

Summary

Traditional methods of edge dislocation dynamics simulations

The dynamics of edge dislocations in close-packed materials under dynamic loading has been studied earlier in the frames of classical molecular dynamics (CMD) by other researchers [1,2,3,4,5,6,7] as following. In order to reproduce in the frames of CMD the processes related to the plastic deformations of fcc crystals one needs to be sure that the model of the interatomic interactions used is capable to describe basic properties of the edge dislocations. We propose instead of the fixed deformation rate or fixed shear stress calculations to perform CMD simulations of the dislocation motion during the relaxation of shear stress. In such approach one can obtain in a single simulation an entire dependence of the dislocation velocity on the actual shear stress and get Peierls-Nabarro stress as the limit when the dislocation stops

Stress relaxation approach

Conclusion