Ultrasonic evaluation of stresses in orthotropic materials using Rayleigh waves

The characterization of stress states in materials is often necessary in mechanical construction. The realization of aeronautical structures increasingly needs knowledge concerning the initial states of the internal stresses, because they induce bending or twisting deformations on the pieces during the tooling. Several non-destructive methods for the determination of stresses have been developed. As the material being characterized here is an aluminum alloy in which the size of grains is very important (order of 150 mu m) and, moreover, that the control must be performed on-line, the ultrasonic techniques seem to be more convenient. In this paper, we present a method based on the measurement of ultrasonic Rayleigh wave velocity variations versus the stress state in the thickness of sheets. We show some residual stress profiles obtained by this method. These are then compared with other profiles determined using a destructive technique that makes it possible to check our results. Finally, we discuss various factors that could affect the acoustic measurement of stress profiles in sheets with our method. (C) 1999 Elsevier Science Ltd. All rights reserved.