X-ray diffraction pattern of a strained rock-salt crystal

Laue photographs were taken with a rock-salt crystal under compressing force applied to one of the natural cleavage surfaces and in the direction perpendicular to the incident X-ray beam. As the compressing load was increased step by step up to a certain value the spots on the photograph were lengthened into nearly concentric arcs which had not been observed in previous experiments. When the load reached a higher value broadening of the spots in the radial direction also occurred. These phenomena are interpreted as due to two stages of deformation of the crystal. The first stage is considered as a simple bending of the crystal about a fixed axis, which is found to be nearly perpendicular to the largest surface of the crystal. The second stage of deformation is complicated and has not been explained in detail; it may consist in bendings about axes parallel to the largest surface or inclined at small angles to it. The deformation was found to be of a plastic nature.