Effects of Thermally Induced Distress on Adhesively Bonded Piezoelectric Wafer Active Sensors and Implications on Damage Detection and Localization

Abstract

Structural Health Monitoring (SHM) systems enable informing on structural health on a continuous time basis, resulting in optimized maintenance and reduced risk of failure. However, airborne equipment is commonly subjected to harsh environments including extremely high and low temperatures, transient loads, humidity, or radiation. As a result, the sensing function gradually degrades, ultimately impairing the performance of the SHM system to detect and localize damage. In this study, we analyze through two numerical experiments the effects that degrading bonding PWAS interface may produce on electromechanical impedance measurements and guided wave propagation testing. The first experiment investigates the effects of degraded adhesive bonding on electromechanical impedance and guided wave emission using a Finite Element Model (FEM). The results demonstrate that PWAS debonding modifies the electromechanical response, producing considerable distortion on the generated and received wave fields. The alteration of the bonding layer affects the wave tuning curve, resulting in non-uniform wave amplitudes across the plate. The second experiment focuses on the impact of PZT bonding degradation on damage localization. A circular sensor layout with multiple PWAS was considered. The FEM is solved for both intact and damaged plates, as well as for partially bonded PWAS. Tomographic imaging algorithms, including RAPID and Delay-and-Sum (DAS) were used. In summary, this study emphasizes the significance of understanding the effects of degraded bonding in PWAS for a more accurate assessment of aeronautical structures.