Development of a stress gradient enhanced piezoelectric actuator composite (GEPAC) with integrated ultrasonic NDE capablity

Abstract

Stress gradient enhanced piezoelectric composites (GEPACs) are unimorph based curved actuators that can be primarily used as low-frequency actuators embedded within an aircraft skin. The actuator is made of a thin PZT ceramic bonded between two composite layers with different coefficients of thermal expansion. Actuators have been manufactured with segmented upper electrodes so that they can also be used at ultrasonic frequencies to monitor continuously the integrity of the actuator itself (cracks), or of the actuator/skin assembly (debonding). This study will focus on the detection of debonding at the interface between the piezoelectric layer and the outer layers. The input signal is a one cycle burst at 1 MHz. The time domain signals recorded experimentally are compared with predictions from a finite element model (ABAQUS explicit). It is shown that the presence of a debonding defect can convert a symmetric pulse into a primarily antisymmetric wave. A simple correlation technique is used to estimate the size of the debonding defect. The ultrasonic NDE operation superposed to the low frequency actuation is demonstrated. [Work supported by the AFOSR.]