In-Situ Imaging of Crack Growth with Piezoelectric Wafer Active Sensors

Piezoelectric-wafer active sensors are small, inexpensive, noninvasive, elastic wave transmitters/receivers that can be easily affixed to a structure. As wide-band nonresonant devices, piezoelectric-wafer active sensors can selectively tune in various Lamb-wave modes traveling in a thin-wall structure. This paper presents results obtained using a linear piezoelectric-wafer phased array to in situ image crack growth during a simulated structural health monitoring test on a large 2024-T3 aluminum plate. During the test, in situ readings of the piezoelectric-wafer phased array were taken in a round-robin fashion while the testing machine was running. Additional hardware was incorporated to prefilter the received signals before digitization to obtain usable readings. The received signals were postprocessed with the embedded ultrasonic structural radar phased-array algorithm and a direct imaging of the crack in the test plate was obtained. The imaging results were compared with physical measurements of the crack size using a digital camera. Good consistency was observed. The results of this investigation could be used to predict the gradual growth of a crack during structural health monitoring