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

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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.