Zhang Jie, Drinkwater Bruce W, Wilcox Paul D
Department of Mechanical Engineering, University Walk, University of Bristol, Bristol, UK.
IEEE Trans Ultrason Ferroelectr Freq Control. 2008 Oct;55(10):2254-65. doi: 10.1109/TUFFC.924.
Ultrasonic nondestructive evaluation is used for detection, characterization, and sizing of defects. The accurate sizing of defects that are of similar or less size than the ultrasonic wavelength is of particular importance in assessing structural integrity. In this paper, we demonstrate how measurement of the scattering coefficient matrix of a cracklike defect can be used to obtain its size, shape, and orientation. The scattering coefficient matrix describes the far field amplitude of scattered signals from a scatterer as a function of incident and scattering angles. A finite element (FE) modeling procedure is described that predicts the scattering coefficient matrix of various cracklike defects. Experimental results are presented using a commercial 64-element, 5 MHz array on 2 aluminum test samples that contain several machined slots and through thickness circular holes. To minimize the interference from the reflections of neighboring defects, a subarray approach is used to focus ultrasound on each target defect in turn and extract its scattering coefficient matrices. A circular hole and a fine slot can be clearly distinguished by their different scattering coefficient matrices over a specific range of incident angles and scattering angles. The orientation angles of slots directly below the array are deduced from the measured scattering coefficient matrix to an accuracy of a few degrees, and their lengths are determined with an error of 10%.
超声无损评估用于检测、表征和测量缺陷尺寸。对于尺寸与超声波长相近或更小的缺陷，准确测量其尺寸在评估结构完整性方面尤为重要。在本文中，我们展示了如何通过测量类裂纹缺陷的散射系数矩阵来获取其尺寸、形状和取向。散射系数矩阵描述了散射体散射信号的远场幅度随入射角和散射角的变化。文中描述了一种有限元（FE）建模程序，用于预测各种类裂纹缺陷的散射系数矩阵。使用商用64阵元、5MHz阵列对2个铝制测试样品进行了实验，样品中包含多个加工槽和贯穿厚度的圆孔。为了最小化相邻缺陷反射的干扰，采用子阵列方法依次将超声聚焦在每个目标缺陷上，并提取其散射系数矩阵。在特定的入射角和散射角范围内，圆孔和细槽可以通过它们不同的散射系数矩阵清晰区分。从测量的散射系数矩阵推导出阵列正下方槽的取向角，精度可达几度，其长度测量误差为10%。
