Strategies for small-footprint devices in structural health monitoring

结构健康监测（SHM）已被提出，以允许航空航天工业从基于计划的维护，使用无损检测（NDT）技术进行，以基于状态的维护过渡。最有前途的方法是使用安装在金属或复合材料结构上的原位压电陶瓷（PZT）换能器来产生和接收超声导波传播并与缺陷相互作用。尽管已经提出了许多SHM技术，尽管有可能降低飞机维护成本并提高飞机可用性，但民用航空航天工业尚未实施该方法。该计划旨在实现一个重大突破的要求仍然有待解决：损伤量化（分辨率低于1毫米），更小的足迹，并证明了SHM技术的耐用性，通过开发战略的PZT换能器（在1平方厘米的顺序）在损伤量化在高频率的小足迹阵列。损伤量化将来自高频下较小的波长，以及具有紧凑阵列的更好分辨的产生和测量位置。这项研究计划将沿着沿着三个不同的研究方向进行。1)导波传播模式的判别是损伤定量的关键。因此，高频模式选择换能器将被设计成在PZT和主机结构之间的界面处产生目标应力分布，该目标应力分布从模态功率流的系统优化获得。通过创新的3D配置，将利用剪切应力和法向应力的组合，以克服由于换能器尺寸减小而在结构中产生的波功率降低，从而可能导致对损坏的敏感性降低。2)由于高分辨率损伤成像需要从检测和定位过渡到量化，超分辨率工具将被集成到基于相关性的损伤成像算法已经验证了较大的阵列。PZT的动态模型以及它们在阵列内的机械和电相互作用将被集成到用于相关性的分析原子中，以获得更高的分辨率。3)PZT阵列的3D微制造将结合联合收割机使用激光微加工技术从PZT的大块进行烧蚀以获得高功率密度、利用光刻技术进行溶胶-凝胶沉积以获得贯穿厚度和多层特征、以及组装诸如惯性质量的部件。利用三维激光多普勒测振仪和损伤成像测量速度场，以验证制作的PZT阵列。PZT的小足迹阵列的策略将允许通过更高的分辨率进行损伤量化，并且这种系统预计将通过较少的侵入性和对环境的较低敏感性来实现所需的耐久性。

Structural Health Monitoring (SHM) has been proposed to allow the aerospace industry transitioning from scheduled-based maintenance, conducted using Non-Destructive Testing (NDT) techniques, to condition-based maintenance. The most promising approach uses in situ piezoceramic (PZT) transducers mounted on metallic or composite structures to generate and receive ultrasonic guided waves propagating and interacting with defects. Although a number of SHM technologies have been proposed, and despite the potential reduction of aircraft maintenance costs and increased aircraft availability, the civil aerospace industry has not implemented the approach yet. This program intends to achieve a major breakthrough on the requirements still to be addressed: damage quantification (resolution below 1 mm), smaller footprint, and demonstrated durability of SHM technologies, by developing strategies for small-footprint arrays of PZT transducers (in the order of 1 cm2) in damage quantification at high frequency. Damage quantification will come from smaller wavelengths at high frequency, and better resolved generation and measurement locations with a compact array. This research program will be conducted along three distinct research thrusts. 1) The discrimination of the guided wave mode propagating is critical in damage quantification. Thus, high-frequency mode-selective transducers will be designed to generate target stress profile at the interface between the PZT and the host structure, obtained from systematic optimization of modal power flow. Combined shear and normal stresses will be exploited through innovative 3D configurations to overcome the reduced wave power generated in the structure because of the transducer size reduction, potentially leading to reduced sensitivity to damage. 2) As high resolution damage imaging is required to transition from detection and localization to quantification, super-resolution tools will be integrated into the correlation-based damage imaging algorithms already validated for larger arrays. The dynamic model of the PZTs, as well as their mechanical and electrical interactions within the array will be integrated in the analysis atoms used in the correlation for higher resolution. 3) 3D microfabrication of the PZT arrays will combine ablation from a bulk piece of PZT for high power density, using laser micro-machining techniques, sol-gel deposition with photolithography techniques for through-the-thickness and multi-layer features, and assembly of components such as inertial masses. Velocity field measured with a 3D Laser Doppler Vibrometer and damage imaging will be used to validate the fabricated PZT arrays. Strategies for small-footprint arrays of PZT will allow damage quantification through higher resolution and such systems are expected to achieve the required durability by being less intrusive and less sensitive to environment.