面内剪切压电陶瓷的设计制备、表征及其用于SH波激励的研究

Ultrasonic testing is the most widely used method in nondestructive testing (NDT) and structural health monitoring (SHM). The fundamental shear-horizontal (SH0) wave in plates and fundamental torsional wave in pipes are non-dispersive and very convenient for signal processing, thus have received wide attentions in academics and industries. Currently, the SH wave is usually generated by electromagnetic acoustic transducers (EMAT), which require high-energy excitation, but has a low signal-to-noise ratio (SNR) and can only be applied to conductive materials. The EMAT actually generates SH waves by inducing face-shear deformation in plates. Conventional piezoelectric ceramics is transversally isotropic around the poling axis and thus cannot appear the face-shear deformation mode. In this project, we are planning to design and fabricate two types of face-shear piezoelectric ceramics via ferroelastic domain switching and periodic poling, respectively. The piezoelectric and mechanical properties of these two types of ceramics will be systematically characterized. Then, finite element method (FEM) will be used to simulate SH wave generation using these two types of ceramics, followed by experimental verifications. Based on above results, a NDT plan will be proposed to detect the defects in plates using SH waves. The plan will be improved by using FEM simulations and finally validated by testing. If the project can be conducted smoothly, the applications of SH waves in NDT and SHM of engineering structures will be greatly promoted.

弹性波是结构无损检测和健康监测中最常用的手段，平板中的0阶SH波(或圆管中的0阶扭转波)由于非频散的特点，给信号处理带来了很大方便，从而引起了学术界和工业界的广泛关注。目前SH波主要采用电磁超声换能器（EMAT）激励，该方法需要的能量很高，检测信噪比低，而且只能用于导电材料。EMAT 激励SH波的本质是诱导平板发生面内剪切变形。传统的压电陶瓷由于横观各向同性的特点，无法产生面内剪切的变形模式。本项目拟分别采用铁弹畴变和周期性极化的手段，设计和制备能产生面内剪切变形的两类压电陶瓷，对这两类压电陶瓷的压电性能和力学性能进行系统的表征。然后采用有限元方法设计利用这两类压电陶瓷在平板中激发并检测SH波的实验方案并进行验证。在此基础上设计一套基于SH波的平板内缺陷检测方案，对该方案进行有限元模拟并改进，最后进行实验验证。本项目如能顺利实施，将有力地推动基于SH波的检测和监测方法应用于工程结构。

结构健康监测日益成为工程结构安全保障的有效手段，然而目前广泛研究的基于Lamb波的结构健康监测方法，由于Lamb波的频散、多模态等问题，限制了其在实际中的应用。零阶SH波是平板中唯一非频散的导波，它具有模态转换少、信号处理简单等优势，在结构健康监测领域具有很好的应用前景。本项目原定的目标是研究面内剪切压电陶瓷来激励SH波，该目标已经提前实现。我们主要研制了面内剪切d24型压电换能器，成功在平板中激励出单模态的SH波，并基于d24压电模式研制了全向型和双向聚焦型SH波换能器，在此基础上构件了基于SH波换能器稀疏阵和相控阵的结构健康监测系统。结果表明，基于双向聚焦型SH波换能器的相控阵系统，其监测能力比当前的Lamb波系统高10倍。同时,研制了基于混合变形模式的管道T(0,1)扭转导波换能器，实现了沥青涂层埋地管道监测距离20米以上，明显好于此前的国际最好水平5-8米。这些研究成果为基于SH波的结构健康监测方法的广泛应用提供了技术基础。项目执行期间共发表SCI论文23篇，其它论文2篇，授权发明专利4项。培养已毕业博士生3人，在读博士生2名。