The nucleation of a loop under an applied simple shear stress in a perfect crystal was analyzed by using a variational boundary integral method, together with an interlayer potential, in the Peierls-Nabarro framework. The saddle-point configurations of embryonic dislocation loops, and their associated activation energies under stress levels of up to the ideal shear strength, were determined. The results for typical materials (Au, Cu, Al, Si) indicated that the energy barriers were far too high for thermal motion to play a role in the nucleation of a dislocation loop in a perfect crystal under normal stress levels; which were markedly below the ideal shear strength. The new results extended the existing understanding of homogeneous dislocation nucleation in crystalline materials, and had significant implications for models that were based upon the dislocation nucleation mechanism in deformation and fracture.

Energetics of Homogeneous Nucleation of Dislocation Loops under a Simple Shear Stress in Perfect Crystals. G.Xu, A.S.Argon: Materials Science and Engineering A, 2001, 319-321, 144-7