Complete Evaluation of Residual Stress States Using Acoustoelasticity Introduction

The acoustoelastic technique for the nondestructive evaluation of stress is based on the stress-induced changes in the speed of wave propagation. In the application of acoustoelasticity. three different approaches have been adopted. For the sake of discussion. we will consider the case of a plane state of stress in an initially isotropic material. The most common technique uses shear waves propagating normal to the plane of stress [1.2]. This technique takes advantage of the stress-induced birefringence of the shear waves which. in the case considered. is proportional to the difference in the principal stresses. Another technique which is currently receiving considerable attention involves two shear-horizontal (SH) waves propagating in the principal stress directions. with their polarizations in the other principal direction [3-5]. In this approach. the difference in the speeds of the two SH waves can be related to the difference in principal stresses directly. Knowledge of the material's elastic or acoustoelastic constants is not required. The final approach uses a single longitudinal wave propagating perpendicular to the plane of stress. with the change in the speed of this wave being proportional to the sum of the principal stresses [6.7].