Reference-Free Crack Diagnosis Based on Polarization Characteristics of Smart Materials

该项目将开发一种新的无损检测(NDT)的概念和理论框架，其中损伤可以在不使用过去的基线数据的情况下进行检测。特别是，将制定一种无损检测方法来检测民用应用中常用的金属结构的裂缝。将开发一种新的无损检测方法，其前提是可以即时检测到某些类型的损害，而无需与以前获得的基线数据进行直接比较。首先，基于锆钛酸铅(PZT)晶片换能器的极化特性，建立了无参考诊断的理论框架。然后，通过比较两个瞬时采集的信号来提取对损伤敏感但对现场桥梁结构的环境变化不敏感的特征，而不参考过去的基线数据。在这里，有源传感装置，如锆钛酸铅，将被用来产生和测量金属结构中的导波。一旦确定了损伤敏感特征，将开发统计分类器，以在不使用先前参考数据的情况下建立决策边界，并将损伤的错误指示降至最低。最后，将通过宾夕法尼亚州布法罗克里克大桥的现场测试明确考虑在役桥梁所受的现实环境和运营条件。这一策略通过集成主动传感、智能材料、统计模式识别技术以及迄今尚未尝试的损伤诊断的新理论发展，为SHM/NDT实践提供了重大突破。这种现场可部署的无损检测技术将是独一无二的，因为(1)可以在不依赖先前参考数据的情况下完成损伤诊断，(3)监测系统将具有自己的智能，可以自主地将实时传感器数据转换为损伤诊断信息，而不需要最终用户进行数据解释，(4)无损检测范例可以应用于经常出现裂缝的复杂几何形状，例如焊接/螺栓连接，以及(5)在役结构经历的环境和操作变化不会影响损伤诊断，将损坏的错误迹象降至最低。这将是钢筋混凝土结构无损检测的重大进步。无损检测方法为民用和国防基础设施提供的技术进步程度和随之而来的质量改进，以及广泛的潜在应用，使这项研究具有重要价值。无损检测方法将降低与目测、数据收集、数据解释和昂贵的损害错误警报相关的复杂性和成本。决策过程的自主性使得这种无损检测方法对于桥梁结构的连续长期监测具有吸引力。瞬时无参照物无损检测方法的成功开发对民用基础设施、机械系统、飞机和许多其他设备的状态评估和监测具有巨大的积极影响。此外，在这项研究中获得的大量知识将为商业实体将这项技术应用于自己的市场铺平道路。最后，所有领域的安全关键系统的所有者将是最大的受益者，因为无损检测将转化为更少的检查、更好的性能和总拥有成本的降低。

This project will develop a new concept and theoretical framework of nondestructive testing (NDT), in which damage can be detected without using past baseline data. In particular, a NDT methodology will be formulated for detecting cracks in metallic structures commonly used in civil applications. A new NDT methodology will be developed based on the premise that certain types of damage can be instantaneously detected without direct comparison with previously obtained baseline data. First, the theoretical framework for the reference-free diagnosis will be developed based on the polarization characteristics of lead zirconate titanate (PZT) wafer transducers. Then, features that are sensitive to damage but insensitive to ambient variations of the bridge structures in the field will be extracted by comparing two instantaneous collected signals without referencing to past baseline data. Here, active sensing devices such as lead zirconate titanate will be used to generate and measure guided waves in metallic structures. Once damage-sensitive features are identified, statistical classifiers will be developed to establish decision boundaries without using prior reference data and to minimize false indications of damage. Finally, realistic environmental and operational conditions that in-service bridges are subject to will be explicitly considered through a field test of the Buffalo Creek Bridge in Pennsylvania. This strategy offers a potential for a significant breakthrough in SHM/NDT practice via the integration of active sensing, smart materials, statistical pattern recognition techniques and new theoretical development for damage diagnosis that has not been attempted to date. This field deployable NDT technique will be unique because (1) damage diagnosis can be accomplished without relying on prior reference data, (3) the monitoring system will have its own intelligence that autonomously converts real-time sensor data to damage diagnosis information without requiring data interpretation by the end users, (4) the NDT paradigm can be applied to complex geometries such as welded/bolted connections where cracks often occur, and (5) environmental and operational variations that in-service structures experience will not affect damage diagnosis, minimizing false indications of damage. This will be a significant advancement to non-destructive testing of RC structures.The degree of technical advancement and attendant quality improvement for both civilian and defense infrastructure provided by the NDT methodology, combined with a broad range of potential applications, render this research of significant value. The NDT methodology will reduce complexity and costs related to visual inspection, data collection, data interpretation and expensive false alarms of damage. The autonomous decision making procedure render this NDT methodology attractive for continuous long-term monitoring of bridge structures. Successful development of the instantaneous reference-free NDT methodology has the potential for an enormous positive impact in condition assessment and monitoring for civil infrastructure, mechanical systems, aircraft, and many others. Furthermore, the body of knowledge obtained in this research will pave the way for commercial entities to adapt this technology to their own market places. Finally, owners of safety critical systems in all fields will be the biggest beneficiaries as the NDT translates into fewer inspections, better performance and a decrease in the total cost of ownership.