It was recalled that a cause of intergranular wedge crack nucleation in polycrystalline materials was the piling-up of extrinsic grain boundary dislocations around triple lines. An approximate theoretical analysis was carried out here in order to compare nucleation at I-, U- and amorphized triple lines; due to edge dislocations which had Burgers vectors that were tangential to the grain-boundary planes. The analysis was based upon an energy approach to fracture mechanics. Numerical results for Al showed that the overall equilibrium pile-up configurations of the dislocations were not significantly affected by the type of triple line. Two types of crack: sub-microscopic (smaller than 0.05 and microscopic (10 to 20 were predicted, depending upon the strength of the disclination defects at the triple line. It was noted that the pile-up populations, and the Burgers vectors of the dislocations, could significantly affect the nucleation behavior.

M.S.Wu: Mechanics of Materials, 1997, 25[2], 215-34