超声Lamb波在缺陷处的二维散射特性研究

利用散射系数周向分布图研究了超声Lamb波在缺陷处的二维散射特性。建立了超声Lamb波与缺陷交互作用的有限元仿真模型，采用双元激励法产生单一S0模态入射信号，利用吸收边界消除边界回波的影响，采集缺陷所有方向上的散射信号并产生散射系数周向分布图。此模型的计算结果与实验结果一致，证明了模型的正确性。研究了S0模态与通孔和通透裂纹两种缺陷的交互作用，并测量了S0模态以零度角入射缺陷时的周向散射系数分布图，利用其图形特征可以进行缺陷种类识别。分析了散射场中多模态信号的能量分布，指出检测中若激励单一模态，而接收多模态信号，可以防止漏检，更有效地检测缺陷。

2D SCATTERING CHARACTERISTICS OF LAMB WAVE AT DEFECTS

A scattering parameter circumferential distribution chart was employed to present the 2D scattering characteristics of defects. The FE model of a Lamb wave interaction with defects was investigated. A dual-element exciting method was used to produce a pure S0 mode as incident wave. An absorbing boundary was used to eliminate the wave reflection of a border. Scattering signals in all the directions were acquired and post-processed so that a scattering parameter circumferential distribution chart could be plotted. This FE model was validated experimentally and a good agreement was obtained between FE and experimental results. The interaction of an S0 mode with a trough-thickness hole and a crack was studied and scattering parameter distribution charts with 0 degree incident were measured. The charts could be used to characterizing the kinds of defects. The energy distribution of multi scattering modes also was studied. The results show that the single mode exciting and multi-modes receiving could avoid undetected defects.