J. Kendall, V. Giurgiutiu, B. Xu, J. Laskis, University of S. Carolina, Columbia, SC; J. Chung, Global Contour Ltd., Rockwall, TX
Structural health monitoring (SHM) research using piezoelectric wafer active sensors (PWAS) has made considerable progress in recent years. By using guided waves and electro-mechanical standing waves, PWAS have demonstrated successful detection of delaminations, cracks, disbonds, and corrosion. Of considerable interest is the extension of this technology to high temperature applications such as space reentry vehicle thermal protection systems (TPS), jet engine turbine blades and engine exhaust washed structures (EEWS), etc. This paper presents the conceptual architecture of high-temperature piezoelectric wafer active sensors (HT-PWAS). In this initial effort, several essential aspects have been investigated: (a) identification of piezoelectric materials that can survive in harsh and aggressive environment; (b) development of active SHM (i.e., pitch-catch, pulse-echo, phased-array, electromechanical impedance) that can be applied to TPS tiles and engine parts monitoring; and (c) development of self-powered low-power consumption electronics with wireless capability for implementing the active SHM principles, and transmiting the diagnostic results. In initial tests conducted, we created HT-PWAS from x-cut Gallium orthophosphate (GaPO4) single crystal discs with sputtered platinum (Pt) 100 nm electrodes. A HT-PWAS of 7mm diameter and 0.2mm thickness successfully maintained piezo-functionality at 700°C (1300°F). The small HT-PWAS was also capable of transceiving (transmit and receive) ultrasonic waves in ultralight TPS tiles during the test. The test results provided the potential application to SHM of the TPS tile and jet engine parts operating in harsh and aggressive environments. In the TPS SHM study, a technique to detect the disbond between the TPS tile and the airframe structure was researched. In the engine SHM study, we developed a coupled field finite element method (FEM) modeling technique that allows the prediction of the SHM reading for different levels of damage. Our planned future research includes in-depth piezoelectric material formulation research and HT-PWAS installation/wiring technique development.
Summary: This presentation will introduce the investigation of Gallium Ortho-Phosphate single crystal material and its application as a piezoelectric wafer active sensor (PWAS). This material and sensor system have properties which make it a candidate solution to address monitoring requirements in harsh environments such as turbine engine and thermal protection system applications.
