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Long Term Stability of Guided Wave Structural Health Monitoring Using Distributed Adhesively Bonded Piezoelectric Transducers



Guided wave SHM is a potential technique for structural health monitoring of plate like industrial structures. Previous studies have shown that it allows detection of small defects (1.5% reflection changes) in the presence of environmental changes. Most guided wave SHM systems use bonded piezoelectric sensors to excite and receive wave propagation in the structure a temperature and advanced subtraction algorithms that subtract signals and baselines from the “healthy” structure are used to robustly discriminate damage from benign changes. This works well in laboratory environments for short periods of time. The long term stability of SHM using these techniques was investigated in this paper. Instrumented aluminium plates were exposed to thermal cycling in an environmental chamber while S0 mode signals were acquired. Analysis of the SHM data revealed drifts in baseline subtraction results corresponding to progressive reduction in defect sensitivity levels of the experimental setup. These drifts were correlated with increases in coherent variability and suspected to be due to variations in the adhesive properties of the bonds between the sensors and the structure. Finite element analysis and further experimental results confirmed that changes in adhesive properties were a likely cause of the degradation in monitoring capability with time.

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