The behavior of an extended dislocation near to a semi-infinite crack was investigated. Criteria were developed for the determination of the equilibrium separation between Shockley partials and for the formation of extended dislocations via dissociation. It was found that the equilibrium separation increased as the extended dislocation approached the crack. If the stacking fault energy was comparable to the critical energy for dissociation in a perfect medium, complete dislocations could dissociate to form extended dislocations near to the crack. An extended edge (or screw) dislocation near to a crack produced not only a primary shielding/anti-shielding effect upon modes I and II (or mode III) of fracture but also a secondary effect upon mode-III (or modes I and II) of fracture. The shielding/anti-shielding effect upon fracture was closely related to the stacking fault energy. With decreasing stacking fault energy, the primary effect decreased but the opposite was true of the secondary effect. If the extended dislocation slipped on a plane which contained the crack tip and was inclined to the crack plane, the maximum shielding effect occurred when that angle was about 70º (mode-I fracture) or 0º (modes II and III) while the dislocation remained a constant distance from the crack tip.

Extended Dislocations around a Semi-Infinite Crack. K.M.Lin, H.C.Lin, K.C.Chen: Engineering Fracture Mechanics, 1996, 54[3], 395-403