Homogeneous nucleation of dislocation loops under stress in perfect crystals

We present an analysis and results on the homogeneous nucleation of a dislo cation loop under stress in a perfect crystal. By using a variational bound ary integral method in the Peierls-Nabarro framework, we have determined th e saddle-point configurations of embryonic dislocation loops and their asso ciated activation energies under stress levels up to the ideal shear streng th. The high-energy barriers under the usual levels of applied shear stress es, differing markedly from the ideal shear strength, confirm the widely he ld view that thermal motion should play no role in such nucleation. The res ult provides means for more definitive solutions elf fundamental problems i nvolving homogeneous nucleation of dislocation loops and has significant im plications for models based on the mechanism of nucleation of dislocations from a perfect crystal.