Oil STUDY OF ULTRASONIC METHODS FOR NONDESTRUCTIVE MEASUREMENT OF RESIDUAL STRESS

The study of streas-induced birefringence has been continued in both polycrystalline and single crystal experiments. The effect is explained on the basis of nonlinear elasticity theory. Experiments indicate that dislocation activity does not strongly affect results in polycrystalline specimens, however, a pronounced influence may be observed in single crystals. Nonlinear elasticity theory has been used to investigate the interaction of two intersecting, plane, elastic waves in a homogeneous, isotropic medium. A criterion for the occurrence of a strong scattered wave has been derived. The criterion is formulated as a relationship between the second order elastic constants of the material, the angle between the intersecting wave vectors, and the ratio of primary wave frequencies. The amplitude of the scattered wave is found to be proportional to the volume of interaction and dependent on the third order elastic constants of the material. Preliminary efforts to experimentally verify the theoretical predictions are described. This report has been reviewed and is approved. W. J. TRAPP Chief, Strength and Dynamics Branch '4etals and Ceramics Laboratory Directorate of Materials and Processes