The non-local stresses on a screw dislocation near to a free surface in such a medium were investigated by using a surface dislocation model. The non-local image force on the screw dislocation, due to the existing free surface, was also obtained. All of the classical singularities in the stress and image forces were eliminated, and the maxima in the stress and image forces were evaluated. A zero point of the stress was found. This predicted that different states of the shear stress existed simultaneously near to the dislocation. The appearance of a zero value at the free surface, and a maximum in the dislocation image force, were used to explain the existence of the dislocation-free zone.

Screw Dislocation in a Semi-Infinite Non-Local Hexagonal Medium. K.L.Pan: Radiation Effects and Defects in Solids, 1995, 133[2], 167-78