基于电磁声激励Lamb波的裂纹深度检测

本文采用电磁声传感器接收单一S₀模态激励，测量Lamb波在板中不同深度的槽形裂纹处的反射与透射，用于对已知扩展长度的表面裂纹进行深度测量。然后分析了Lamb波模态的频散与波动特性，由超声Lamb波的波结构，近似计算了S₀模态入射到裂纹时的反射系数。计算结果与实验结果一致。结果表明，Lamb波在有限长裂纹处的反射系数可采用二维模型中的反射系数求解公式近似求解。采用电磁超声传感器接收单一S₀模态激励，重复测量稳定性高，适用于Lamb波反射系数的测量。Lamb波的反射系数与裂纹深度有很好的对应关系，可用于板表面已知长度裂纹的深度测量。

On the Crack Depth Measurement Based on Lamb Wave Electromagnetic Acoustic Excitation

Electromagnitic acoustic tranducers (EMAT) were adopted to receive single S₀ mode exitation. The reflection and transmission of Lamb wave in a plate were measured at slotted cracks with different depths, which was used for depth measurement of surface crack with known extended length. The modal dispersion characteristics and fluctuation properties of Lamb wave was analyzed. The reflection coefficient of incident S₀ mode on the crack was approximately calculated, based on the structure of ultrasonic Lamb wave. The calculated results are consistent with experimental ones. Results show that the reflection coefficient of Lamb wave at carck with finite length can be approximately solved by using two-dimensioanal model reflection coefficient solving formula. EMAT provides high stability in repeated measurements and is suitable for measurement of Lamb wave reflection coefficient There is a good corresponding relation between the crack depth and Lamb wave reflection coefficient, which can be used for depth measurement for plate surface crack with known length.