Effect of Frequency on Texture-induced Ultrasonic Wave Birefringence in Metals

Abstract

AN ultrasonic shear (transverse) wave entering a stressed solid body splits into two components travelling at slightly different velocities depending on the relevant elastic ‘constants’ which are slightly different along the two principal stress axes normal to the wave propagation direction. Thus the velocity difference between the two orthogonally polarized shear waves propagated normal to, and polarized parallel and perpendicular to, a principal stress axis should be stress dependent because of this effect of ‘acousto-elasticity’ or ‘sonoelasticity’. This shear wave birefringence has been used in recent years to detect internal stresses in polycrystalline metallic specimens^1,2, but the interpretation of the results was difficult because the preferred grain orientation (texture) had identical effects to the internal stress. In the work described here, attempts were made with some success to separate the effects of stress and grain orientation on the ultrasonic shear wave birefringence.