Structural Health Monitoring of Immersed Structures by Means of Guided Ultrasonic Waves

Abstract

Guided ultrasonic waves (GUWs) are increasingly considered in the nondestructive evaluation and structural health monitoring of engineering systems that benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. Sometimes, owing to the kind of system being inspected, a non-contact approach for the generation and detection of GUWs is desired. This article presents an initial study of the feasibility of using a hybrid laser/immersion transducer system for the detection of damage in submerged structures. A pulsed laser was used for the generation of stress waves in an aluminum plate immersed in water, which were detected by a pair of conventional immersion transducers. The detected time waveforms were processed using the joint time-frequency analysis of the Gabor wavelet transform to extract information about the velocity and the attenuation of the propagating modes. Damage was simulated by devising a rectangular notch and a small circle on the face of the plate exposed to the probing system. The study shows promising results and may pave the road toward an innovative approach to the non-contact inspection/monitoring of underwater structures.