Photoelastic study of dislocation arrangements in crystals

Abstract

The plastic deformation of single crystal bars of silver chloride in tension and bending has been studied by using the photoelastic effect. It is found that in tension the plastic deformation is not uniform over a given cross section but is greatest near the surfaces. In bending the plastic deformation is found to propagate longitudinally along the bars rather than transversely. The distribution of birefringence, and hence that of stress, has been measured and the result interpreted by means of a simple dislocation model. It is concluded that, in silver chloride, the ratio of the stress necessary to propagate dislocations to the stress necessary to generate them is less than about 0–6. The shear stress on the glide plane necessary to propagate dislocations is approximately 5–2 × 10⁶ dynes/cm².