Anti-shielding of a crack tip by a dislocation was examined at the atomistic level for a simple geometry to test classical singular-crack and recent cohesive-crack models of crack/dislocation interactions. The atomistic model showed that, as an anti-shielding dislocation approaches the crack tip, it causes less anti-shielding than predicted by the singular-crack model. The trend was qualitatively consistent with predictions of a cohesive-crack model, but the atomistic effect was even larger. The cohesive-crack model was consistent with the atomistic results if a reduced cohesive strength of about 3.5GPa was used instead of the actual value of 13GPa. The difference was shown to be due to the non-linear deformation of material around the crack tip, which cannot be fully represented by a cohesive zone law along the fracture surface. It was then shown that, at the point of fracture, there was a unique traction–displacement cohesive law acting behind the crack tip, independent of the position of the anti-shielding dislocation. The maximum traction of 12.8GPa and fracture energy of 1.9J/m2 were both in excellent agreement with the values obtained from independent atomistic calculations on this material. Both the shielding and cohesive results have implications for the accurate modeling of fracture processes in metallic materials.

Dislocation Shielding and Crack Tip Decohesion at the Atomic Scale. J.Song, W.A.Curtin, T.K.Bhandakkar, H.J.Gao: Acta Materialia, 2010, 58[18], 5933-40