Simulation of nucleation and emission of dislocations by molecular-dynamics method

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Abstract
The nucleation and emission of dislocations from the crack tip under mode II loading are analyzed by the molecular-dynamics method in which the Finnis–Sinclair potential has been used. A suitable atom lattice configuration is employed to allow one to fully analyze the nucleation, emission, dissociation, and pileup of the dislocations. The calculated results show that although the pure mode II loading is applied, the crack tip generally exhibits a combined mode. The stress distributions before the dislocation emission are in agreement with the elasticity solution, but are not after the emission. The critical stress intensity factor corresponding to the dislocation nucleation KIIe is dependent on the loading rate K̇II. The separations of a pair of partial dislocations and the full dislocations are also dependent on the loading rate. When the first partial dislocation is blocked, a pileup of dislocations can be set up. It is also found that the dislocation can move at subsonic wave speed (less than the shear wave speed) or at transonic speed (greater than the shear wave speed but less than the longitudinal wave speed) depending on the loading rate, but at the longitudinal wave speed which just corresponds to K̇II=1.15 MPa √m/ps for copper, the atom lattice breaks down.