超声兰姆波斜入射裂纹时的散射特性

Scattering Characteristic of Lamb Wave at Crack with Oblique Incident

裂纹是导致众多结构失效的主要原因之一,采用超声兰姆波可有效地对板类结构中的裂纹等缺陷实现定位,但目前的技术尚无法实现对缺陷精细特征的测量。研究超声兰姆波与缺陷的交互作用,可为实现缺陷高精度检测奠定理论基础。采用散射系数矩阵表征弹性波与缺陷的交互作用,对兰姆波斜入射到裂纹时的散射特性进行仿真和试验研究,结果表明其散射场在周向上的分布并不均匀,有明显的波束指向性。随着入射角从0°变化到90°,波束指向角呈非单调性变化,且散射波能量迅速减小。当入射角为0°和90°时,S矩阵有明显的对称性,据此可测量裂纹的扩展方向。利用斜入射时裂纹散射场的特征可以设计合理的成像算法及传感器布置方案,以更有效地实现超声兰姆波对板类结构中裂纹的精细检测。

Crack is one of the main reasons for structure failure, and using ultrasonic Lamb wave can efficiently locate it in plate-like structures. Currently this technology can＇t achieve specific characteristics of defects. Research on the interaction of Lamb waves with defects provides principle bases for high resolution inspection. Scattering parameter matrix（S-matrix） is employed to present the interaction of elastic wave with defects. FE and experiment research on Lamb wave oblique incident to crack is studied. Results illustrated that scattering field is non-uniform and show significant beam form phenomenon. With incident angle changing from 0° to 90°, the angle of the beam non-monotonic changes and energy of scattering wave rapidly decreases. When incident angle equal 0° and 90°, S-matrix is symmetric so that can be used to evaluate the expanding direction of crack. Using the characteristic of Lamb wave scattering in crack with oblique incident, more reasonable imaging algorithms and transducer distribution methods can be designed, which will provide an efficient way to inspect the crack with high resolution.