中文摘要：

超声兰姆（Lamb）波在结构缺陷检测方面愈来愈受到重视，但目前Lamb波的应用局限于单信号源激励，单通道接收的方法，容易受到噪声干扰，其后续的信号分析处理也比较复杂。本文旨在采用多通道Lamb波对板状结构中的裂纹进行定量分析与诊断。在铝板的表面凿刻出不同深度的凹槽作为裂纹，通过线阵换能器采集在一定传播距离内的多通道Lamb波信号，并采用二维傅里叶变换分析在不同深度的裂纹下，Lamb波模式能量的变化规律。结果表明，相对于完好铝板中的Lamb波信号，裂纹的存在会使Lamb波发生模式转换现象，并且转换模式能量百分比随裂纹深度的增加而线性增加。其结果为Lamb波评价板状结构中的裂纹状况提供了一种可能的方法。

英文摘要：

Utilizing ultrasonic Lamb waves to detect cracks in plate structures has been an important technique in non-destructive testing （NDT） area. However, up to now, most practical applications just use one source to excite and one receiver to obtain Lamb wave signals, which is susceptible to noise. Besides, the one channel signal processing method is usually complex because of the multi-mode and dispersion characteristics of Lamb waves. The object of this study is using multi-channel ultrasonic Lamb waves to quantitatively evaluate cracks in aluminum plates. Notches with various depths were curved out from the aluminum plate to regard as cracks. The multi-channel Lamb waves were collected in a certain propagation distance range through linear array transducer. The relationship between energy of different Lamb wave modes and the depth of crack was analyzed using two dimensions Fourier transform （2DFT）. Results show that comparing to the intact aluminum plate, new Lamb wave modes would occur due to exist of cracks. And, the energy percentage of converted modes increases linearly with the depth of crack. This study may provide a rapid and reliable method to evaluate the crack condition in plate structures.