Composites are widely used as structural materials in aircrafts made recently and its usage is increasing rapidly. However, it is easy to occur structural damages and defects such as disbond, delamination, impact damage and so on in composite structures unlike those of common aircraft made of metallic materials. In this research, to detect this kinds of damage or defect of composite structures in aircraft, we suggest concept of the Smart Hangar which is a full-scale structural inspection technique for aircraft based on the built-in ultrasonic propagation imaging (UPI) system, mobile UPI systems for built-in PZT sensors and for external noncontact/contact sensors and full-field pulse-echo UPI system. The high-performance mobile ultrasonic propagation imaging is a non-destructive inspection technique to visualize damage or defect in structures by combination of high-accuracy rapid laser scanning excitation and highspeed DAQ and signal processing based on the field programmable gate arrays. The UPI technique is able to scan rapidly at a pulse repetition rate of 20 kHz. After acquiring the generated ultrasonic wave signal induced by laser excitation, ultrasonic wave propagation imaging movies for the in-plate guide wave or through-transmission wave are displayed. The built-in UPI system is based on long-range scanning and is integrated in the Smart Hangar. The built-in UPI system is also extended to multi-area simultaneous inspection by adding a beam expander, a laser mirror scanner and a beam splitter. In case of the full-field pulse-echo UPI system, the two laser beams scan real structures along raster scanning pattern based on two-axis linear translation stage. The sensing laser can capture pulse-echo through-the-thickness ultrasound by impinging the sensing laser beam at the same point as the generation laser beam. In this work, we present a few real world applications, a large military UAV with 10 m long composite wing, a military transport airplane with composite fairing. In the application results using the mobile UPI system, the developed mobile UPI system and built-in UPI system provided the damage visualization results showing disbond area between the skin and spar and disbond damage in the fairing. In the application results using the full-field pulse-echo UPI system, barely visible impact damages in a carbon fiber reinforced plastic (CFRP) wing skin panel and artificial defects which are two drilled holes in a glass fiber reinforced plastic (GFRP) aircraft encoder case.
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