Mean strain in crystals containing dislocation loops

摘要

For a crystal containing prismatic dislocation loops there are, even within linear elastic theory, two conceivable definitions for the mean strain. The strains defined are distinguished as the mean ’’elastic’’ strain and the mean’’total’’ strain. It is emphasized that every component of the mean elastic strain is zero, while the mean total strain has components which are nonzero and correspond precisely to those changes in the macroscopic dimensions of the crystal which result when loops are introduced. The fact that two definitions of mean strain are possible may account in part for a current controversy concerning the x‐ray lattice parameter. However, as the details of the x‐ray diffraction from a crystal containing loops are undoubtedly complex, it seems unlikely that the lattice parameter would in general be simply related to the mean strain of either definition.