Triple Functional UPI (Ultrasonic Wave Propagation Imager) and Applications to Aircraft

Abstract

As a fast nondestructive inspection (NDI) system, triple functional ultrasonic wave propagation imager (UPI) was developed. It features three modes: Q-switched laser scan guided UPI (QL-scan G-UPI), angular pulse-echo UPI (A PE UPI), and laser Doppler vibrometer scan guided UPI (LDV-scan G-UPI). QL-scan G-UPI utilizes Lamb waves created by the Q-switched laser, with a PZT sensor receiving waves distorted by structural damage. A PE UPI employs bulk waves induced by the same laser, and the LDV captures bulk waves reflected from the back face or internal defects in the thickness direction. LDV-scan G-UPI uses standing waves generated by a PZT exciter, which are captured by the same LDV used in the A PE UPI. By employing acoustic wavenumber spectroscopy (AWS), the thickness changes in structures due to damage can be identified through the calculated wavenumber of the standing waves. A significant advantage of this equipment is its inspection speed. The maximum scanning speeds of each mode are 32.11 m2/h for A PE UPI, 23.21 m2/h for QL-scan G-UPI, and 28.35 m2/h for LDV-scan G-UPI, respectively. The scanning speed can be adjusted based on the required precision of the damage detection, as smaller scan intervals are required to detect minute internal damage. The post processing algorithms for diagnosing structures in this equipment are variable time window amplitude mapping (VTWAM), ultrasonic energy mapping (UEM) and AWS. It takes less than one minute to visualize the results for a 1 x 1 m2 plate. The current equipment was evaluated by detecting various types of damage in aircraft structures. The detected damage includes cracks and corrosions in aluminum structures, as well as film inserts, debonding and delamination in composite structures. In particular, damage growth in a composite plate during fatigue tests, and debonding between rivets in an aircraft were successfully detected using A PE UPI without any disassembly or interference.