Bulk Waves for the Nondestructive Inspection of Immersed Structures

Abstract

Laser-generated ultrasonic guided and bulk waves are increasingly considered for the nondestructive testing (NDT) and structural health monitoring of engineering systems. Methods based on the use of pulsed laser or continuum laser are ideal when a non-contact approach for the generation and detection of stress waves is desired. This paper presents the initial progresses of an ongoing study where pulsed laser is used to generate stress waves in underwater structures. In particular, in this paper we show the results of few experiments where stress ultrasonic waves are generated in an aluminum block. Owing to the geometry of the specimen, ultrasonic bulk waves are generated and detected by means of either a dry or an immersion transducer. The study presented here aims at investigating the effect of certain water parameters on the ultrasonic energy propagating through the specimen. The results of three experiments are presented. In the first experiment the effect of water level on the signal-to-noise ratio of laser generated bulk waves was evaluated. Then, the effect of laser energy was studied. Finally, the effect of water temperature on the amplitude of the bulk waves was investigated. With the exception of the latter experiment, we used laser pulses at 1064 nm and 532 nm wavelengths.KeywordsWater LevelStress WaveStructural Health MonitoringBulk WaveAluminum BlockThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.