Effect of vacancy diffusion on crack initiation and propagation in the Lennard-Jones crystal subjected to tension

The effect of vacancy diffusion on crack initiation and propagation in 2D LJ crystals is investigated numerically using a molecular statics approach. A crystal is represented by a basal plane of a hexagonal closed-packed lattice and the seed vacancy is created by removing one atom. The crystal is subjected to tension by displacing one of its boundaries. The vacancy is allowed to diffuse within some rectangle so that its migration to the crystal surface is prevented. It is assumed that the event of an exchange between the vacancy and the neighboring atom will take place between two sequential loading steps and that there is no preferred direction for a jump, which leads to the vacancy’s random walk. It is shown that the migrating vacancy not only results in dislocation formation but also leads to formation of nanovoids and nanocracks. Since the vacancy migration is random, the patterns of structural changes leading to nanovoids, nanocracks and to the fracture are different for each numerical test.