Analysis of wave propagation in anisotropic materials and application to NDE

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Dynamic behaviors of elastic waves in anisotropic media are much different from those in isotropic media since elastic wave speeds depend on the directions of wave propagation. It is, therefore, necessary to develop the analysis for scattering and propagation of elastic waves for quantitative ultrasonic nondestructive evaluation for anisotropic materials. In this paper, numerical and experimental approaches are pursued to investigate the effect of anisotropy on the characteristics of elastic waves and are applied to the ultrasonic testing to detect quantitatively a defect in a thick anisotropic plate. The main results are obtained as follows: 1. The program code is developed to analyze the dynamic behaviors of elastic waves by a volumetric defect in an anisotropic solid of infinite extent. The method is based on a time domain boundary integral equation in conjunction with a collocation point method. Numerical results are visualized for scattering and propagation around defects subjected to various conditions of incident waves and material constants. 2. A boundary integral equation method is also developed for the scattering problem by a crack in an anisotropic solid, where the hypersingular integrals are regularized using the Galerkin method. 3. Ultrasonic experiments with angled beam transducers are carried out for a thick steel plate with artificial cylindrical defects. It is shown that as the incident wave angle increases, the effect of anisotropy increases, which implies that the accuracy of the nondestructive testing may decrease unless appropriate remedy is given. 4. All processes of ultrasonic experiments including incidence, scattering and radiation are numerically simulated. Good agreement is obtained between theory and experiment, which will give useful information for quantitative ultrasonic evaluation for anisotropic materials.