Abstract and subjects
The subsonic motion of a fast-moving, extended screw dislocation in an fcc metal under constant stress is studied using continuum linear elastic dislocation theory and molecular dynamics (MD) simulation. In this regime, many phenomena predicted by the theory are shown to prevail in simulation, in particular, relativistic effects and stress orientation effects. Due to the former, the fault width is found to contract as it moves faster until approximate to 80% of the shear wave speed, beyond which a turning point occurs preventing it from constricting to a perfect one as speed increases further. The stress orientation effect, which is first introduced by Nabarro [Philos. Mag. 14, 861 (1966)], is demonstrated here to manifest when the shear stress resolved in the direction of motion and glide plane becomes high. A simple analytical expression for the steady-state fault width accounting for both stress orientation and relativistic effects is presented. In MD simulation under arbitrary stress states, both the dislocation velocity and separation width achieve a quasisteady state, about which they oscillate with an amplitude and frequency that reduces with speed. The separation width oscillates about a value close-to that predicted by the new analytical expression. The drag coefficient is found to linearly increase with speed for speeds greater than 20% of the shear wave speed.