聚焦超声Lamb波法环焊缝检测机理及缺陷定位研究

Because of the coupling needs, before the defect testing using the conventional ultrasonic technique, the coating and painting layer of the girth weld structure should be cleaned according to the probe scanning path. It is time consuming and costly, and seriously hinders the application of the ultrasonic testing methods. In order to tackle the common engineering problems, the project put forward a new testing idea "using a focusing ultrasonic Lamb wave probe, realize all girth weld static detection only by several points testing", which breaks the concept of dynamic scanning detection mode employs by conventional ultrasonic methods. According to this idea, the numerical analysis will be applied to analysis the excitation and formation of focusing Lamb wave field, Lamb wave propagations in the structure with complex geometric which composed by curved surface, weld crown and bottom surface and weld toe, as well as the process of ultrasound act with the defect. Under the guidance of simulation, modern digital signal processing technique is employed to suppress the clutter components in multi-mode Lamb echoes, and to identify the defect signal effectively. Finally, the defect is hopeful to be located at the circumferential position in the girth weld. This project aims to elucidate the acoustic mechanism for defect detection in complex structural using ultrasonic Lamb wave method, to reveal the relationship between characteristics of the signal and the defect location. The results of the research have important potential application value for the rapid identification and localization of weld defects.

由于声耦合的需求，在实施常规超声波法缺陷检测前，需根据探头扫查范围对环缝结构进行包覆层去除或漆面清理。这一技术环节既费时费力又耗财，严重阻碍了超声波法的推广应用。针对这一普遍存在的工程问题，本项目突破常规超声波法动态扫查检测的理念，提出“采用聚焦超声Lamb波法实现有限点处激发、环缝全缝静态检测”的思路。针对这一构思，拟采用数值模拟方法分析聚焦Lamb波场的激发形成、Lamb波在由环缝曲面、焊缝上下表面及焊趾组成的复杂边界结构中的传播、Lamb波与缺陷的作用过程；在仿真研究的指导下，采用数字化信号处理技术对多模态回波中的杂波成分进行抑制并提取缺陷信息，最终实现静态检测方式下缺陷在环缝周向的定位。本项目旨在阐明基于超声Lamb波法复杂结构缺陷的声学检测机理，揭示多模态Lamb波信号特征与缺陷位置之间的内在联系规律。相关研究成果对焊缝缺陷快速识别及定位有着重要的潜在应用价值。

针对大型焊接结构缺陷现有声学检测方法存在的动态扫查、需要去除包覆层、防寒层、对被测体表面光洁度要求高等技术弊端，项目突破常规超声波法动态接触扫查的检测理念，提出了“焊缝导波一点激发、长距离静态检测”的解决思路。围绕这一思路，开展了相关研究并取得如下主要进展及成果：研究发现了导波在焊缝中传播时具有声能量汇聚的通道效应，将其命名为“焊缝导波”；采用试验和仿真相结合的研究方法，阐明了焊缝导波的传播规律及与缺陷体的作用机制。以理论研究为指导，试验研究获得了有效的焊缝导波激励策略及优化模态选择方法。在此基础上，提出了一种基于RLS滤波的杂波抑制方法，有效识别距离测点10mm以内的缺陷信号，从而减小了检测盲区，扩大了有效检测范围；提出了基于相邻测点信号相关的改进小波包噪声抑制方法，克服了粗晶材料噪声难以抑制的技术问题，有效识别了奥氏体焊缝中直径1.5mm的人工孔；提出一种基于双测点信号渡越时差的焊缝导波缺陷定位方法，焊接缺陷（气孔）定位精度最大绝对误差不超过6mm，平均绝对误差为3.6mm；焊缝导波技术的检测灵敏度达到：采用1.5MHz超声探头，有效识别距离测点500mm、直径2mm、深4mm的人工孔，人工孔回波信号幅值达屏高34%；研发了便携式焊缝导波检测系统及自动爬壁焊缝缺陷检测行走机构。相关研究成果对大型焊缝缺陷快速识别及定位有着重要的潜在应用价值。

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