Theoretical results suggested that an observed cleavage was related to the effect of a high density of dislocations in the tip region. Simulation results could be rationalized in terms of the added stress from emitted dislocations. The latter added an effective mode-I stress intensity which was opposite in sign to that applied. The emitted dislocations were also expected to add an effective mode-II stress intensity, which prevented the emission of more dislocations and increased the total K-value at the tip. The mode-II stress intensity was usually small, and caused an embrittling effect only when the dislocations were unable to move away from the crack tip. The tip region therefore represented a high density of dislocations. The results supported models that took account of the effects of dislocation mobility after they had been emitted from the crack tip.

Fracture Toughness from Atomistic Simulations: Brittleness Induced by Emission of Sessile Dislocations D.Farkas: Scripta Materialia, 1998, 39[4-5], 533-6