Discontinuous Dynamics of Mode-I Crack Propagation in Single Crystals

Abstract

Discontinuous propagation of a crack tip in heterogeneous media is characterized by a power-law distribution, but discontinuity of crack propagation in homogeneous media is still unclear. In this study, we investigate the discontinuous features of the mode-I crack propagation in single crystals by performing molecular dynamics simulations of uniaxial tensile deformation for a two-dimensional single crystal model with an open cleavage. Temporal dynamics of the crack propagation is extracted by locating the position of the crack tip in the model. In the simulations, discontinuous crack propagation, go-stop motions of crack propagation, has been observed. The displacement of the crack seems to follow an exponential distribution depending on the temperature rather than power-law distributions. The observation indicates that the discontinuous behavior is due to dislocation emissions; a crack propagation started by increasing of local stress due to external loading stops by decreasing of the stress due to dislocation emission from the crack tip. This picture directly provides an exponential distribution consistent with the observed statistical feature.