The elastic energies of elliptical dislocation loops

Abstract

The elastic energy of an elliptical dislocation loop rotating on a glide cylinder of circular cross section is computed. It is found that the loop has minimum energy in the pure edge orientation, a result which is at variance with those obtained previously for loops on glide prisms with polygonal cross sections. The variation of elastic energy with axial ratio for an elliptical loop with the Burgers vector lying either normal to the loop plane or parallel to the major, or minor, axis of the ellipse is also determined. The results provide evidence for the formation mechanism of loops in irradiated b.c.c. metals proposed by Eyre and Bullough (1965). The predictions of the present study are compared with the observed orientations and shapes of non-polygonal dislocation loops, and conclusions are drawn regarding the validity of the assumption that loops which produce elliptical images in the electron microscope are circular on planes inclined to the foil surface.