Measurement on the Acoustoelastic Effect of Lamb Waves Using Laser Ultrasound Technique

• Main Authors: TSENG YI HSUAH, 曾義軒
• Other Authors: C. H. Yang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/15983024825799497172

碩士 === 長庚大學 === 機械工程研究所 === 91 === In this research a laser ultrasonic technique (LUT) is used to investigate the acoustoelastic effect on the dispersion relation of Lamb waves propagating in three kinds of plates. Acoustoelastic effect is the stress or strain induced change in the wave propagation speed in an elastic body. Lamb waves are guided acoustic waves propagating in flat plates. The LUT technique uses a Q-switched Nd:YAG Pulse laser for thermoelastic generation of acoustic waves. While laser propagation along the plate, the acoustic modes are detected with another set of laser system. With the generation laser focused along the propagation direction of the Lamb modes, a narrow plate technique date can be obtained. Using one-dimensional fast-Fourier transform signal-processing scheme, the dispersion relations of Lamb waves propagating in the plates are determined. A loading frame with load-cell is used to apply axial tensile stress on stainless, Brass, Phosphor Bronze, Aluminum plates of 0.2 and 0.5 mm.. For this method, very small reduction of Lamb wave speeds is observed due to the acoustoelastic effect. Finally, the acoustoelastic effect are measured with the LUT.