Fundamentals of Mode III Fracture: A Discrete Dislocation Simulation Approach

摘要

The mode III fracture is studied based on the discrete dislocation simulation. Under a remote mode III stress, when the stress intensity factor at the crack tip K is greater than that for dislocation emission K_D, dislocations would be emitted from the crack tip. The quantity of K_D depends not only on the dislocation core radius, frictional stress and shear modulus, but also on the number of the characteristics of the type of dislocations emitted in the vicinity of crack tip. The velocity of dislocations is assumed to be proportional to the third power of effective stress. The dislocations dynamically and quasi-statically emitted from a static sharp surface crack tip during loading and upon unloading are investigated. The mechanical behavior of dislocations for the dynamic emission has an opposite trend to that for the quasi-static emission. The dislocations dynamically emitted from a propagating sharp surface crack tip are also studied. The propagation rate of the crack tip is porportional to the third power f the stress intensity factor. When the dislocations emitted and the propagating crack tip have the same velocity, the system is at steady state. Dislocations emitted in the radial directions from the radial crack tips emanating from a circular hole are considered. The effects of crack length, crack geometry and frictional stress on fracture are also analyzed.