The atomistic structure and energy of nascent dislocation loops

An harmonic lattice theory is used, in conjunction with Mura's theory of ei gendistorsions, to study the structure and energetics of nascent dislocatio n loops in face-centred-cubic (FCC) crystals. An analytical expression for the activation energies of such loops is derived. The results obtained here in indicate that thermal activation of small dislocation loops is possible at high stress levels such as those found in the vicinity of a crack tip. T he implications of these results in understanding phenomena such as the bri ttle-ductile transition are discussed.