Ultrasonic NDE testing of a gradient enhanced piezoelectric actuator (GEPAC) undergoing low frequency bending excitation
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Gradient Enhanced Piezoelectric Actuators (GEPAC) are thin piezoelectric plates embedded between two composites layers having different thermal properties. Compared to standard unimorph bending actuators, GEPACs offer superior performances for operations at low frequencies. Potential applications are in the area of multifunctional aircraft skins. In practice, delaminations or debonding within the actuator itself can occur, and it is highly desirable to develop an ultrasonic nondestructive method to monitor the integrity of the actuator in real time. For this study, the composite material is unidirectional Kevlar-epoxy, with fibers oriented at 90 and 0 for the upper and lower layers to achieve different coefficient of thermal expansion. A thin PZT plate is inserted between the two layers, and extended copper foil is used for electrodes on the PZT. The first objective of the research is to demonstrate that, by using segmented electrodes, one can simultaneously launch an ultrasonic pulse (1 MHz) for NDE testing while the actuator is undergoing low frequency actuation (less than 100 Hz). The second objective is to show that the ultrasonic signal can be used to detect damage induced during fatigue testing of the actuator. The third objective is to use the technique to monitor the integrity of a composite plate containing several embedded GEPACs.