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In-situ NDE of Composite Repair Patch and Thick Panel with Substructures using Mobile Pulse-Echo Ultrasonic Propagation Imager



Composites are widely used as structural materials due to its advantage for weight to strength ratio compared to metallic structures in aircrafts. Thus, their usage is increasing in aircraft industry and the technique of composite manufacturing has been rapidly developing. However, detection of defects in composite structure is challenging compared to that in metallic structure. Based on this, various structural health monitoring and nondestructive inspection techniques have been researched to detect the defect in composite structure. Among the techniques, in-situ nondestructive evaluation (NDE) is increasingly used to avoid time-consuming work such as aircraft disassembly for inspection. Recently, laser ultrasonic generator is widely used because it generates broadband ultrasound of diverse modes by thermoelastic mechanism and it works as non-contact excitation. In addition, non-contact sensing laser for measuring ultrasound is drawing attention because it has a benefit of non-contact sensing in inaccessible area. In this study, fully non-contact mobile pulse-echo ultrasonic propagation imager (PE UPI) based on laser ultrasound is introduced as an in-situ NDE tool. The mobile PE UPI is configured with scanning laser head, two-axis translation scanner and UPI controller. The scanning laser head including generation and sensing lasers scans with two-axis translation stage to generate and sense pulse-echo through-the-thickness ultrasounds as bulk wave. After completing the scan, the defects are visualized by fullfield pulse-echo ultrasonic wave propagation imaging (FF PE UWPI) technique and variable time window amplitude map (VTWAM). For nondestructive evaluation, the mobile PE UPI inspected composite repair patch and composite thick panel with substructures. As a result, the defects in the composite repair patch and composite panel with substructures were visualized by FF PE UWPI video and VTWAM


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