Analysis of wave propagation in anisotropic materials and application to NDE

各向异性介质中弹性波的动力学行为与各向同性介质中的弹性波有很大不同，因为弹性波的速度取决于波的传播方向。因此，有必要发展弹性波的散射和传播分析，以便对各向异性材料进行定量的超声无损评价。本文采用数值和实验相结合的方法，研究了各向异性对弹性波特性的影响，并将其应用于各向异性厚板缺陷的超声定量检测。主要结果如下：1.编制了分析无限大各向异性固体中体积缺陷引起的弹性波的动力学行为的程序代码。该方法基于时间域边界积分方程法和配点法。给出了不同入射波和材料常数条件下缺陷周围的散射和传播的数值结果。2.给出了各向异性固体中裂纹散射问题的边界积分方程法，其中超奇异积分用Galerkin方法正则化。3.利用倾斜波束换能器对含有人工圆柱缺陷的厚钢板进行了超声实验。结果表明，随着入射波角的增大，各向异性的影响增大，这意味着除非采取适当的补救措施，否则无损检测的精度可能会降低。4.对超声实验的入射、散射和辐射全过程进行了数值模拟。理论与实验结果吻合较好，为各向异性材料的超声定量评价提供了有用的信息。

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.