周向SH导波的激励机理、压电换能器设计及其用于管道健康监测的研究

Ultrasonic guided-wave-based inspection method is widely used in structural health monitoring (SHM) of pipe-like structures. As conventional inspection is based on axisymmetric wave modes propagating in axial direction of a pipe, it has the difficulty of detecting the circumferential location of a defect. The circumferential guided waves can be used to identify the circumferential location of a defect and quantitatively evaluate it. Among them, the circumferential fundamental shear horizontal wave(CSH0) is of practical importance in SHM due to its virtually non-dispersive characteristics. Currently, unidirectional pure CSH0 wave can only be generated by electromagnetic acoustic transducers(EMAT), which are not suitable for SHM due to their poor energy conversion efficiency and relative large size. In this project, considering that the CSH0 wave in a thin pipe is essentially equivalent to the SH0 wave in a plate, we are planning to develop a unidirectional CSH0 wave piezoelectric transducer based on our previously developed face-shear piezoelectric ceramics which can generate SH0 wave along four main directions (0°, 90°, 180° and 270°). A theoretical model will be firstly developed to analyze the radiation patterns generated by the face-shear deformation. Then, based on the analysis by the theoretical model and finite element simulation, the excitation mechanism of unidirectional CSH0 wave will be revealed. After that, a piezoelectric transducer which can generate pure CSH0 wave and focus the wave beam in one direction around the circumference of a pipe will be developed. Furthermore, experiments will be conducted to evaluate the typical defect detection capability of the beam-focused CSH0 wave. Based on above results, a SHM plan will be proposed to monitor large diameter pipes using CSH0 wave. If the project can be conducted smoothly, the applications of CSH0 wave in SHM of pipe-like structures will be greatly promoted.

超声导波是管道健康监测常用的手段。传统管道监测技术使用的是轴向传播的轴对称导波，难以确定缺陷的周向位置。管道中沿周向传播的0阶SH波（SH0波）由于其近似非频散特性，是发展识别缺陷周向位置和大小的监测技术的理想模态。目前单向传播的单模态周向SH0波仅能由电磁超声换能器激励，该换能器的功耗高，体积质量大，不适用于健康监测。本项目拟在申请人先前研发的可在平板中沿四个主方向（0°，90°，180°和270°）激励SH0波的面内剪切压电陶瓷的基础上，利用管道周向SH0波和平板SH0波的相似性，建立解析的力学模型描述面内剪切变形诱导的SH0波的声场，找到可控激励周向SH0波的荷载条件。在此基础上设计和制备出能够激励单向传播的单模态周向SH0波的压电换能器，并实验研究周向SH0波检测典型缺陷的能力。最后，设计一套基于周向SH0波的管道缺陷在线监测方案。本项目将推动周向SH0波在管道健康监测中的应用。

管道中沿周向传播的0阶SH波（SH0波）由于其近似非频散特性，是发展大口径管状类结构在线监测技术的理想导波模态。本项目针对管道周向SH波的激励机理、换能器设计及其用于缺陷识别的方法展开研究，取得的主要成果如下：1. 厘清了SH0波的激励机理，从理论上证明了施加切应力和诱导波导产生面内剪切变形对于激励SH0波具有等价性，建立了面内剪切变形诱导SH0波声场的解析力学模型，给出了宽频范围激励双向传播的周向SH0波的荷载条件；2. 研制了宽频双指向型周向SH0波压电换能器，在此基础上提出了全新的激励单向传播的SH0波的方法，并以此设计制备了两类单指向型SH0波压电换能器；3. 提出了计算导波接触声非线性效应的双势谱方法，并以此开发了可高效计算弹性波与缺陷相互作用规律的软件；4. 搭建了基于周向SH0波的大口径管道在线监测系统，在实验室条件下实现了对缺陷的准确识别；5. 基于周向SH波在管道中传播特性的研究成果，提出了拱形超表面用于调控SH0波的波前，并以此实现了平面SH0波的激励、SH0波的定向折射及能量在曲线上聚焦。本项目的研究成果将为诸如空间站密封舱这类大口径管状结构的早期缺陷监测提供一个可行的途径，并奠定重要的理论及技术基础。