Motion parallel to, and perpendicular to, the crack surface were considered. It was found that, due to the free surface, the nett Burgers vector inside the crack was zero. After deducing the dislocation distribution in the crack, the stress field in the medium was calculated. It was shown that, relative to a static screw dislocation, the magnitude of the ‘y-z’ stress that was due to the moving screw dislocation decreased with increasing velocity. Here, y was perpendicular to the surface, and z was parallel to the surface. It was noted that the effect of dislocation shielding upon fracture decreased as the velocity increased. The magnitude of the image force on the dislocation also decreased with increasing velocity. The effect of velocity along the y-direction, upon the stress intensity factor and image force, had an opposite effect to that of motion in the x-direction. In the limit, these results reduced to the cases of a moving dislocation near to a semi-infinite crack and a static dislocation near to a surface crack.

Y.Z.Tsai, C.T.Hu, S.Lee: Journal of Materials Research, 1995, 10[10], 2668-75