In this case, v p is related to the average strain rate and t* is the pulse holding duration. To generate the stress wave a velocity-controlled boundary condition ( v p) with finite rise time ( t rise) is applied on the upper surface over a short period of time ( t*). In order to achieve the uniaxial strain involved in shock loading, the four sides are confined so that they can only move in the loading direction. 1, the simulation setup consists of a block with dimensions 2.5 µm X 2.5 µm X25 µm. The simulations are designed to mimic uniaxial strain loading at extreme conditions of high strain rates > 10 6/ s, and short pulse durations of few nanoseconds (Loveridge et al. MDDP simulations are performed to investigate the deformation process at high pressure and high strain rates in copper and aluminum single crystals. Following the original concept of Nabarro, Bardeen and Herring, Weertman, and Balluffi and Granato, this contribution can enter the equation of motion through an expression of the form
The force that results from the tendency of the system to return to thermal equilibrium is quantified in terms of an osmotic force F osm. This leads to an under- or oversaturation of such defects, that is, to a deviation from chemical equilibrium.
However, nonconservative motion of edge dislocation segments generally occurs by the generation of intrinsic point defects. In contrast to 2D simulations, which are confined to one slip plane, the extension of discrete dislocation simulations to three dimensions implies the occurrence of climb. While in the latter approach one deals with a conservative system and can thus describe the local force as a negative gradient of the potential, dislocation motion is highly dissipative and reveals a strong anisotropy in its kinetic modes, that is, the existence of glide and climb. Dislocation dynamics shows a fundamental difference from molecular dynamics.