Stress estimation in weak anisotropic materials by using acoustoelastic effect of Rayleigh waves

Abstract

Acoustoelasticity is the property of a material in which the ultrasound velocity changes as a function of stress. This acoustoelastic effect can be used to estimate the stress in a material. The acoustoelastic effect of Rayleigh waves is widely used to estimate the stresses present on a material surface because of the energy concentration there. Furthermore, compared to bulk waves, Rayleigh waves have the advantage of velocity measurement accessibility, because there is no need to know the precise thickness. Moreover, it is also possible to set the propagation distance easily and accurately. However, most of the research has been limited to isotropic materials, which cannot be applied to a real environment. This study proposed a simple method to estimate the stress in weak anisotropic materials by modifying the equation for isotropic materials. In this method, the ratio of the Rayleigh wave velocity in a stressed material to that in the unstressed material in three directions was used, which enabled the simultaneous estimation of the principal stresses and their directions. The proposed method was verified first by conducting numerical simulations. The estimated stresses in the simulations agreed well with the given stresses when using the proposed method. For the experimental verification, the proposed method was applied to two types of specimens having a different anisotropies. The Rayleigh wave velocities in three directions were measured while applying tensile stresses to the specimen. The proposed method could estimate the stress even when the measurement direction did not coincide with the principal stress direction. The results showed that the stress was estimated with a small error, even for an anisotropic material. The principal stress axis was also in good agreement with the given axis.