焊缝能陷导波形成机理与检测应用研究

In the proposed project we will study a new kind of guided waves, the weld-guided waves, which can propagate along a weld and concentrate the energy in and around the weld, thus very attractive to weld inspection. The research will be carried out to reveal the generation mechanism of the trapped modes and to exploit their application techniques for some regular weld inspections. In research the trapped modes are recognized as local resonances in the vertical plane of a weld while traveling along the weld, which as eigenvalue problems of the scattering feature, can be solved when the scattering fields of obliquely incident plane guided waves at the weld are theoretically modeled by modal decomposition. The dispersion relation of the trapped mode can be obtained by relating the resonant frequency to the component wave numbers in the weld direction, of the refracted Lamb or SH modes,which after multiple reflections in the weld region,resonant in vertical direction of the weld. Then the mechanism is used to exploit a technique after numerical optimization to generate weld-guided waves by angle beam SV or SH probes, which could either be put on the weld cap to generate the mode directly or put at the side(s) of the weld to generate the obliquely incident Lamb waves or SH waves, transferred to the trapped mode after refraction. This technique is supposed to experimentally generate high-order trapped modes in some regular welds at high frequency. The optimal modes for a particular kind of weld inspection will be investigated corresponding to different defects and cap qualities, to eventually reach a feasible technique solution for industrial application.

本项目研究一种新导波形式- - 焊缝能陷导波。这种导波能量主要集中在焊缝区域，沿焊缝作一维传播，对于工程构件中的焊缝结构检测具有极大的潜在应用价值。本项目研究的目的在于完成对其机理研究的探索，对一些常见焊缝结构形成实用的焊缝能陷导波检测技术方案。研究中首先采用模式展开法建立斜入射板波在焊缝区域的谐响应散射场求解模型，在此基础上进行散射区特征值即局部谐振频率求解，结合斜入射板波在焊缝区的波数分解关系建立沿焊缝延伸方向波数分量与谐振频率的关系即焊缝能陷导波频散曲线。其次，结合理论与数值方法研究焊缝能陷导波的声场特征与激励效率，建立并优化采用SV波、SH波斜探头通过板波模式转换或者跨焊缝盖面直接产生焊缝能陷导波的激励方案。最后，将其应用于高频高阶能陷导波对常见焊缝的检测实验，分析焊缝、缺陷类型与盖面状况对于焊缝能陷导波传播与散射的影响进而确立优选模式，形成适用于工程应用的焊缝能陷导波检测技术方案。

本项目《焊缝能陷导波形成机理与检测应用研究》以工业领域焊缝的无损检测需求为研究背景，以国际学术界对于能陷导波的最新研究成果为依据，主要从焊缝导波形成机理与检测应用要求两方面进行理论与实验研究。依据“散射——谐振——导波”的理论研究思路，项目扩展了模式展开法在散射场计算中的应用，使其应用对象不限于垂直入射的板波，也可以用于斜入射板波；不限于断面规则的散射体，也可以用于不规则断面的条形缺陷；不限于散射场计算，也可用于散射场特征值问题的研究；不限于板上条形缺陷的研究，也可以用于管、柱中环形缺陷的的研究。通过这一研究方法，全面研究了板波在在焊缝结构处的散射特征，建立了能陷导波频散曲线的分波场理论模型。在此基础上对于棱波、矩形肋条（焊缝模型）中能陷导波进行了研究，发现采用该研究方法不但可以获得的低频、低阶、低泄漏模式的频散曲线，并为现有研究方法所验证，而且可以研究它们的高频、高阶、高泄漏模式；同时，斜入射导波“散射——谐振——传播”的导波机理研究也明确了通过板波模式转换激励能陷导波的方法。这两个方面的研究结果可以扩展能陷导波检测的技术手段，提高检测的灵敏度。本项目实验研究结果初步验证了以上理论成果。