Energetics of homogeneous nucleation of dislocation loops under a simple shear stress in perfect crystals

We present an analysis of homogeneous nucleation of a dislocation loop under an applied simple shear stress in a perfect crystal. By using a variational boundary integral method together with an interlayer potential in the Peierls-Nabarro (P-N) framework, we have determined the saddle-point configurations of embryonic dislocation loops and their associated activation energies under stress levels up to the ideal shear strength. The results, for typical materials such as Au, Cu, Al, and Si, indicate that energy barriers are far too high to suggest that thermal motion could play a role in nucleation of a dislocation loop in perfect crystals under usual stress levels, markedly below the ideal shear strength. These new findings broaden the earlier understanding of homogeneous nucleation of dislocations in crystalline materials and have significant implications on a number of existing models based on the mechanism of dislocation nucleation in deformation and fracture.