M.S. Thesis Presentation by Antoine Béchet
Tuesday, June 3, 2003
(Dr. Yves Berthelot, advisor)
"Ultrasonic detection of debonding within a Gradient Enhanced Piezoelectric Actuator (GEPAC)"
The purpose of this study is the ultrasonic characterization of debonding defects that may occur in gradient-enhanced piezoelectric actuator composites (GEPACs). GEPACs are unimorph based curved actuators with enhanced performance derived from the presence of a stress gradient in the piezoelectric material. These transducers are primarily used as low-frequency actuators that are imbedded within an aircraft skin. However, they can also be used at ultrasonic frequencies to monitor continuously the integrity of the actuator/skin assembly, or that of the skin itself.
This study will focus on the detection of debonding defects at the interface between the piezoelectric layer and the outer layers. Actuators have been manufactured with segmented electrodes so that the actuator can perform integral ultrasonic damage detection. Part of the actuator performs as an ultrasonic transmitter and part of it as a receiver. The design allows the actuator to detect damage to itself as well as delaminations in the material between an array of actuators. The originality of the present work is that the medium itself is piezoelectric, and that no outside transducers are required to interrogate the interface. The key contribution of this research includes: (a) the computation of slowness curves; (b) Finite Element Method (ABAQUS) to simulate the propagating ultrasonic guided wave in the embedded actuators; and (c) an experimental validation using an actuator sandwiched between two steel plates.