Lamb波频域逆散射全聚焦成像方法研究

Lamb波因其传播距离远、衰减小常被用于板状结构的无损检测中,在基于Lamb波损伤检测的诸多成像技术中,全聚焦方法(Total Focus Method,TFM)方法因其成像分辨率高、信噪比高而受青睐。然而Lamb波的频散效应导致时域延时量不能被准确计算,进而影响传统TFM方法对损伤定位及成像的精度;此外,既有的TFM方法仅以回波幅值作为成像指标,忽略了Lamb波与损伤的相互作用,故而不能通过损伤表面的物理参数增强成像质量。针对这两个问题,本文首先在时域TFM基础上发展了频域TFM,在计算中纳入频散关系以规避频散的影响;其次以包含明确的损伤特征参数--反射率为成像指标,结合频域TFM方法建立损伤逆散射模型,以实现对损伤的准确成像。仿真和实验结果表明:频域逆散射TFM成像方法能够实现对铝板结构中的损伤检测,在工程实践中具有应用价值。

Research on frequency-domain inverse scattering total focus method based on Lamb wave

Lamb wave is often used in nondestructive testing of plate structure due to its long propagation distance and small attenuation.Among many imaging technologies based on Lamb wave,Total Focus Method(TFM)is favored for its high imaging resolution and high signal-to-noise ratio.However,due to the Lamb wave dispersion effect,the time-domain delay is unable to be accurately calculated,which affects the accuracy of the traditional TFM method for damage positioning and imaging.In addition,the current TFM method only takes the echo amplitude as the imaging index,ignores the interaction between the incident wave and the damage,and fails to use the physical parameters of the damage surface to enhance the quality of imaging.To solve these two problems,this paper develops the frequency-domain TFM imaging method,in which the dispersion relation is considered in the calculation to avoid the dispersion,and the reflectance containing damage characteristic parameter is used as the imaging index.Then,the damage inverse scattering model is established combining the frequency-domain TFM method to achieve a relatively accurate damage assessment.The simulation and experimental results show that the damage of aluminum plate structure can be detected using the inverse scattering TFM imaging method,which plays an important role in engineering practice.