A variational boundary integral method was used as the basis for studying dislocation nucleation from atomically sharp cracks under combined mode-I and mode-II loading. The tension-shear potential was extended so as to allow for skewness in the shear resistance curve and to take account of the surface production resistance which accompanied ledge formation. The calculated unstable equilibrium configurations of the incipient dislocations and the dependence of the associated activation energies upon crack tip energy release rate were found to differ from the Rice-Beltz perturbation solution and the more approximate Schöck-Püschl solution. Simulations of dislocation nucleation on inclined slip planes revealed that, whereas tension softening facilitated nucleation, surface production resistance impeded it. The extent to which these 2 effects affected the critical conditions for dislocation nucleation was quantified. The results suggested that homogeneous dislocation nucleation on inclined planes was not favored for materials with any but the lowest unstable stacking-energy to surface-energy ratios. This emphasized the importance of heterogeneous dislocation nucleation, and nucleation on oblique slip planes; where free surface production should play a much less important role.

G.Xu, A.S.Argon, M.Ortiz: Philosophical Magazine A, 1995, 72[2], 415-51