A damage detection capability of the flexible ultrasonic transducer (FUT) array bonded onto a planar and a curved surface are presented. The piezoelectric lead zirconate titanate composite (PZT-c) film FUT arrays are fabricated on the 75 \ub5m titanium membrane substrate using a sol-gel spray technique. The test article was a complex aluminum component that is representative of aircraft structural complexity. Room temperature curable adhesive is used as the bonding material and ultrasonic couplant between the FUT and the test article. The glue has been successfully tested in the temperature range of -80\ub0C to 100\ub0C, which covers the sensor operating temperatures commonly required for aircraft structure. For a planar surface the selected FUT arrays were able to detect the fasteners and the 2.54 mm long electrical discharge machining (EDM) notch up to the distance of 176 mm with sufficient signal to noise ration. The pulse-echo measurements obtained by the FUT array were compared with the ones using a commercial 10 MHz ultrasonic transducer (UT). The results showed that the performance of the FUT array was as good as the commercial UT. Another FUT array was bonded onto a curved surface of the test article using the same adhesive. No measurement using commercial UTs was taken on the curved surface because restricted access around this area did not allow such measrement. The pulse-echo measurements confirmed the detection of EDM notches of 2.54 mm long and 1.27 mm long. The experimental results demonstrated the potential of FUT arrays for aircraft structural health monitoring.
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