Ultrasonic Wave Velocities in Stressed Nickel Steel

Abstract

EXISTING methods for detection of residual stresses in metals are limited to surface or near-surface examination, and will not reveal stresses within the material. A possible method of detection is the use of ultrasonic waves in a manner analogous to the use of light waves in photoelasticity. An ultrasonic shear (transverse) wave entering a stressed solid body splits up into two components travelling at different velocities depending on the relevant elastic ‘constants’ which are slightly different along the two principal stress axes normal to the wave propagation direction. This action is analogous to photoelasticity, where the two components of a polarized light wave are due to electrical anisotropy (variation of permittivity with direction) caused by the stress within a transparent body. Internal stress, including residual stress in metallic bodies, might therefore be detected by observation of the phase shift between the two ultrasonic waves occurring in what has been called ‘sono-elasticity’.