Quasi-static dislocation model around a crack tip with moving dislocations and the analysis of its stress concentration

With regard to fracture under dynamic load, an interaction model in the form of a fracture model of a crack and an inverse pile-up of dynamic dislocation groups at the tip of a dislocation-free zone was proposed. It was analyzed based on a coexisting model of static equilibrium and dynamic distribution of dislocation arrays. From these analyses, the following results were obtained. The stress concentration at a crack tip is reduced by the shielding effect of dislocation groups emitted from a stressed source near the crack tip. On the other hand, the stress concentration at the tip of the dislocation-free zone, due to the inverse pile-up of dislocation groups ahead of the crack tip, is induced by the effective stress distribution in a dislocation array which is a result of the dynamic dislocation distribution. Therefore, at the tip of the dislocation-free zone which exists ahead of the crack, stress singularity can be found, and the stress intensity factor can be defined. This result shows a theoretical foundation for the experimental result of the existence of a fracture trigger point under dynamic load.