Screw dislocations near to a semi-infinite crack, parallel to a free surface, were analyzed. The present problem was mapped into the case of a screw dislocation near to a free surface by using the Schwarz-Christoffel transformation. It was found that the magnitude of the x-component of the image force, stress intensity factor and strain energy increased with increasing distance between the free surface and the crack surface. The stress intensity factor at the crack tip was zero when the dislocation was situated at the free surface or crack surface. The effect of a sub-surface layer upon the x-component of the image force was marked when the dislocation was on the crack coplanar surface. The y-component force was significantly affected by the distance between the free surface and the crack surface when the dislocation was located between the free surface and the crack tip. The critical angles between the positive x-axis and the line which connected the dislocation and the crack tip changed from -64.8º (maximum strain energy), -38.7º (stress intensity factor and x-component image force) to zero as the distance between the free surface and the crack surface was increased from 50b to infinity.

Screw Dislocations near a Subsurface Crack S.D.Wang, S.Lee: Journal of Physics D, 1998, 31[6], 602-8