USISG ULTFASOL.iD kill TINE-VARY ING TEMPERATURE GKADIENTS

nate as . Since the temperature within the bar is a function of both position (x) and time (t), the velocity within the bar is also dependent The dependence of ultrasonic velocity in metals upon temperature and stress includes a term which on those quantities. We let u(x,t) represent the varies as the product of these two factors. As a temperature, and so we can write result, the rate of chanEe of velocity with re(1) spect to temperature is a linear function of the stress. This suggests that by monitoring the ultrasonic velocity while inducing time-varying temperature gradients in a metal we might be able to deduce the presence, location and magnitude of subsurface stress. In this paper we report the results of a theoretical and experimental investigation that confirms this possibility.