Dislocation interaction with a cohesive crack was of increasing importance to computational modelling of crack nucleation/growth and related toughening mechanisms in confined structures and under cyclic fatigue conditions. Here, dislocation shielding of a Dugdale cohesive crack described by a rectangular traction-separation law was studied. The shielding was completely characterized by three non-dimensional parameters representing the effective fracture toughness, the cohesive strength, and the distance between the dislocations and the crack tip. A closed form analytical solution showed that, while the classical singular crack model predicts that a dislocation could shield or anti-shield a crack depending on the sign of its Burgers vector, at low cohesive strengths a dislocation always shields the cohesive crack irrespective of the Burgers vector. A numerical study showed the transition in shielding from the classical solution of Lin and Thomson (1986) in the high strength limit to the solution in the low strength limit. An asymptotic analysis yields an approximate analytical model for the shielding over the full range of cohesive strengths. A discrete dislocation simulation of a large (>103) number of edge dislocations interacting with a cohesive crack described by a trapezoidal traction-separation law confirmed the transition in shielding, showing that the cohesive crack does behave like a singular crack at very high cohesive strengths (~7GPa), but that significant deviations in shielding between singular and cohesive crack predictions arise at cohesive strengths around 1GPa, consistent with the analytic models. Both analytical and numerical studies indicate that an appropriate crack tip model was essential for accurately quantifying dislocation shielding for cohesive strengths in the GPa range.

Dislocation Shielding of a Cohesive Crack. T.K.Bhandakkar, A.C.Chng, W.A.Curtin, H.Gao: Journal of the Mechanics and Physics of Solids, 2010, 58[4], 530-41