Damage Inspection of Shell Structures Using a Technology of Ultrasonic Propagation Visualization Based on Laser Scanning Excitation

Abstract

In this work, a small pit on the internal surface of an aluminum thin-walled shell was inspected by using a technology of ultrasonic propagation visualization. This technology employs laser scanning within an inspection area to excite ultrasonic Lamb waves, and three cheap lead zirconate titanate (PZT) sensors to receive the wave signals. The laser scanning area and the three PZT sensors were located on the outside surface of the shell. Betti's reciprocal theorem was further incorporated into the present technology to visualize the wave propagation in the time-domain. The occurrence of notable scattering around the pit identified from the wave propagation snapshots at different time points can be used to detect the pit damage easily. We further adopted a method based on wave energy flow (WEF) map concept proposed by us to evaluate the size and shape of the pit. It was found that, even using a fast laser scanning of a step size of 8 mm, the present technology can still detect the damage quickly, and evaluate the damage accurately.