Molecular dynamics simulations of thermally activated edge dislocation unpinning from voids inα-Fe

Abstract

In this study, thermal unpinning of edge dislocations from voids in α-Fe is investigated by means of molecular dynamics simulations. The activation energy as a function of shear stress and temperature is systematically determined. Simulations with a constant applied stress are compared with dynamic simulations with a constant strain rate. We found that a constant applied stress results in a temperature dependent activation energy. The temperature dependence is attributed to the elastic softening of iron. If the stress is normalized with the softening of the specific shear modulus, the activation energy is shown to be temperature independent. From the dynamic simulations, the activation energy as a function of critical shear stress was determined using previously developed methods. The results from the dynamic simulations are in good agreement with the constant stress simulations, after the normalization. This indicates that the computationally more efficient dynamic method can be used to obtain the activation energy as a function of stress and temperature. The obtained relation between stress, temperature, and activation energy can be used to introduce a stochastic unpinning event in larger scale simulation methods, such as discrete dislocation dynamics.

Multiscale modeling of crystal plasticity in Reactor Pressure Vessel steels: Prediction of irradiation hardening

“…One may even question the relevance of this concept in the case of any defect of finite size. In our model, we use alternatively the concept of obstacle shear resistance, that has been used to describe interactions with voids [39,40] and other precipitates [38]. It has been shown that implementing this resistance as a local rule in DD simulations is straightforward.…”