CONTINUUM THEORY OF THE VOLUME EFFECT CAUSED BY POINT-DEFECTS IN HEXAGONAL MEDIA

The volume change caused by a point defect in the center of a spherica l reference volume which is embedded into the infinite medium is calcu lated analytically for hexagonal crystal symmetry, Two new dimensionle ss coefficients which we call generalized Eshelby coefficients are int roduced to describe the correction of volume change which appears if t hat reference volume has a free, unforced surface. These coefficients play a similar role for hexagonal crystals as the Eshelby factor in th e isotropic medium does. It is shown that the influence of elastic ani sotropy on the Eshelby coefficients is essentially determined by the c losest elastic instabilities. In the limit of an isotropic medium thes e coefficients reduce to the well-known Eshelby factor.