| Summary: | 碩士 === 國立中山大學 === 機械工程研究所 === 83 ===
The Objective of this research is to develop a laserultrasound system in nondestructive applications. The surface waves were launched thermoelastically in the adhesive jointed sample using a Q-switched Nd: YAG pulsed laser to measure the bonding condition of the lap joint. In addition, the samples were also tested using surface wave launched by a PZT (piezoelectric) transducer. The experimental data from both tests were then compared to evaluate the benefits or drawbacks of using laser ultrasound. It was found that the laser induced ultrasound inspection is free of couplant, has good reproducibility, and has no transmission loss. However, the ultrasound generated by laser has low propagating energy and signal to noise ratio that increase the difficulty of measurement. In this thesis, several solutions have been proposed to overcome the above-mentioned drawbacks in this paper. Digital signal processing techniques are first used to improve the resolution of the ultrasound signal. Furthermore, the rise time of the signal is shorten by reducing the radiated area of the laser beam. Both methods are proved to be useful.
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