基于兰姆波技术的搭接焊缝抗拉强度的无损评价研究

Lap joints are common in engineering components, and its tensile strength (Rm) affects the quality safety of the components. So non-destructive evaluating the R m of lap joints has great potential application values. The purposes of this project are to extract the acoustic parameters from the scattering waves of Lamb wave at the lap joints and establish the relationship between acoustic parameters and Rm. Then, the Rm of lap joints can be non-destructive evaluated quickly. We try to make efforts in the following three aspects. Firstly, the scattering fields of Lamb wave at lap joints are solved by modal decomposition method and multiple reflecting theory, and then the expression between acoustic parameters and shape parameters is established. At the same time, the propagation of Lamb wave at the lap joints is simulated by numerical method, and the effects of shape parameters on the scattering of Lamb waves are studied. Secondly, the relationship between Rm and the shape parameters is established by tensile test. Finally, the multivariable nonlinear relationship between acoustic parameters and Rm can be found by neural network method, and the effectiveness of the neural network prediction model will be verified by experiments. The Lamb wave technology for non-destructive evaluating Rm of the lap joints will be formed from these studies.

工程构件中存在着大量的搭接焊缝，其抗拉强度（Rm）影响着构件的质量安全。对搭接焊缝Rm进行快速地无损评价，具有巨大的潜在应用价值。本项目的研究目的在于从兰姆波在搭接焊缝上的散射场中，提取出能反映搭接焊缝Rm的声参量，并建立其与Rm的关系，进而实现快速无损评价搭接焊缝Rm。拟从以下三个方面开展研究：首先，采用模式展开法和多次反射理论求解兰姆波在搭接焊缝上的散射场，建立声参量与搭接焊缝形状参数的解析表达式；并数值模拟兰姆波在搭接焊缝上的传播过程，分析形状参数对兰姆波散射的影响。其次，通过拉伸试验测得搭接焊缝Rm与形状参数的关系；最后，通过人工神经网络法建立声参量与Rm的多变量非线性关系，并实验验证神经网络预测模型的有效性。拟通过以上研究，形成适用于工程应用的快速无损评价搭接焊缝Rm的兰姆波技术方案。

工程构件中存在着大量的搭接焊缝，其抗拉强度影响着构件的质量安全。因此对搭接焊缝抗拉强度进行快速地无损评价，具有巨大的工程应用价值。本项目研究了低频兰姆波S0和A0模态在典型的搭接焊缝结构上的反射和透射，揭示了兰姆波在搭接焊缝上的传播特性。结果显示500kHz的兰姆波S0模态在搭接焊缝上的反射率和焊缝宽度呈线性关系。基于上述线性关系，采用入射角32°斜探头在2mm厚的304不锈钢中激励出500kHz的兰姆波S0模态，实验验证了有限元模拟的有效性；利用上述测试原理搭建了一套兰姆波检测装置，该装置已应用于列车车体上的激光搭接焊缝检测。同时，研究发现兰姆波在搭接焊缝上产生了干涉现象，通过构建搭接焊缝左模型解释了低频兰姆波在搭接焊缝上的干涉现象。该现象说明兰姆波反射回波的频谱偏移可用于搭接焊缝的宽度检测。以上研究基于传统的压电超声传感器，需要通过耦合剂将能量导入被检工件。为了消除耦合影响，本研究搭建了一套激光超声非接触测量系统，检测了搭接焊缝结构的简化模型——加强筋的宽度。通过激光超声C扫描对加强筋的成像和进一步的小波降噪、均值处理等图像处理后，激光超声C扫描的检测精度可达0.05 mm。该激光超声方法可用于搭接焊缝的宽度检测。