Abstract
A previously developed variational boundary integral method in the Peierls-Nabarro framework is extended to analyse nucleation of half dislocation loops at a semicircular surface crack of near-atomic dimensions. The saddle-point configurations of embryonic dislocations and their associated thermal activation energies are determined. The influence of the crack on the energetics of dislocation nucleation is ascertained by calculating these activation energies for cracks of various radii. As the radius of the crack approaches zero, the result naturally converges to that for homogeneous nucleation of a half dislocation loop from the perfect surface. Compared with previous studies of this problem based on continuum elastic dislocation theory, the model presented in this paper provides a more definitive solution because it eliminates the uncertain core cutoff parameter and presumption that the dislocation loop is of semicircular shape.