Longitudinal Wave Scattering From Rough Crack-Like Defects
Longitudinal Wave Scattering From Rough Crack-Like Defects
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DOI：
10.1109/tuffc.2011.2066
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发表时间：
2011-10-01
影响因子：
3.6
通讯作者：
Wilcox, Paul D.
中科院分区：
文献类型：
--
作者：
Zhang, Jie;Drinkwater, Bruce W.;Wilcox, Paul D.
裂纹类缺陷的粗糙度影响超声波散射，这反过来又影响缺陷检测和表征。本文的第一部分是关于粗糙裂纹散射的有效数值模拟，即，有限元局部散射（FELS）模型。散射场以散射矩阵的形式呈现，该散射矩阵描述了入射和散射方向的所有可能组合的远场散射系数。粗糙裂纹的许多不同实现的散射矩阵进行了模拟，使用FELS模型和基于基尔霍夫近似的模型。结果表明，对于标准差小于0.3个波长、相关长度大于0.5个波长的粗糙裂纹，当入射角和散射角与平均表面法线方向成-80 ° ~ 80 °时，从Kirchhoff模型和FELS模型提取的散射矩阵之间的差异小于8%.由于基尔霍夫模型比FELS模型更有效，因此它被用于随后的模拟，其中研究了许多粗糙裂纹的实现，以深入了解散射过程的统计性质。在与以前的工作，区分的相干和扩散的贡献的整体散射场，其中前者代表的合奏平均在多个表面实现。模拟了各种粗糙裂纹散射场的相干和漫射贡献。结果表明，表面粗糙度直接影响的相干散射行为的贡献，而扩散的贡献是由表面粗糙度和相关长度的影响，特别是粗糙的裂纹。
The roughness of crack-like defects affects ultrasonic wave scattering and this, in turn, affects defect detection and characterization. The first part of this paper is concerned with the efficient numerical modeling of scattering from rough cracks, i.e., a finite element local scattering (FELS) model. The scattered field is presented in the form of a scattering matrix, which describes the far-field scattering coefficient for all possible combinations of incident and scattering directions. The scattering matrices for many different realizations of rough cracks are simulated using both a FELS model and a model based on the Kirchhoff approximation. It is shown that the difference between scattering matrices extracted from the Kirchhoff model and the FELS model is less than 8%, for rough cracks with a standard deviation less than 0.3 wavelengths and a correlation length longer than 0.5 wavelengths, at incident and scattering angles ranging from -80 degrees to 80 degrees relative to the normal direction of the mean surface. Because the Kirchhoff model is significantly more efficient than the FELS model, it is used for subsequent simulations in which many realizations of rough cracks are studied to gain insight into the statistical nature of the scattering process. In line with previous work, a distinction is made between the coherent and diffuse contributions to the overall scattered field, in which the former represents the ensemble average over multiple surface realizations. The coherent and diffuse contributions of scattered field from various types of rough cracks are simulated. It is shown that surface roughness directly affects the coherent contribution to scattering behavior, whereas the diffuse contribution is affected by both surface roughness and correlation length, especially for rougher cracks.