Transient dislocation emission from a crack tip under dynamic mode III loading

Transient dislocation emission from a crack tip under dynamic mode III load ing is analyzed. By taking into account the dynamic interaction between the crack and dislocation, the governing equation for the dislocation motion i s derived under the quasi-steady assumption. The behavior of dislocation em ission is explored in detail by solving this equation numerically. A critic al initial speed can be determined, which must be exceeded by dislocations to escape from the crack tip. The dislocation emission process is found to be completed in such a short time period that the applied load may be appro ximately treated as constant during dislocation emission. Based on this fac t, an asymptotic criterion for transient dislocation emission is developed, from which the critical initial speed can be evaluated. In the case that t he dislocation is emitted from rest, we recover the quasi-static criterion of dislocation emission.