Molecular dynamics simulation of mechanical behaviour

A molecular dynamics (MD) simulation of strain and failure of a crystal, the effect of environment on these processes, the interaction between the adsorption-active atoms and the environment walls, the effect of stress on mobility of interstitial admixtures, the formation and the failure of a contact between two crystals has been performed using a two-dimensional system consisting of Lennard-Jones atoms. The basic features of strain observed by means of MD included generation and motion of dislocations, various mechanisms of shear and brittle-to-ductile transition at low temperature. Environmentsensitive mechanical behaviour has been studied for the first time on an atomic scale. It is shown that rapid local processes whose unit act takes about 10^–10 sec and involves several tens or a few hundred atoms may provide for environment-induced embrittlement. The features common to these microscopic processes are (1) pronounced interaction between the foreign atoms and the atoms of the solid, i.e. a sharp decrease in the surface energy of the solid in contact with the environment, and (2) direct participation of thermal fluctuations in the failure and rearrangement of interatomic bonds. By interacting with the crack walls, the environment atoms create a force compatible with the interatomic bond strength, which promotes crack propagation. Tensile stress causes appreciable acceleration of diffusion of interstitial admixtures in the direction normal to the strain axis and hinders diffusion along the axis. Under constant load the failure of interatomic bonds and sintering involve a thermal fluctuation mechanism.