ASA 124th Meeting New Orleans 1992 October

1aPA2. Laser generation of Rayleigh and Lamb waves for ultrasonic testing.

R. Daniel Costley, Jr.

Yves H. Berthelot

School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332

The thermoelastic generation of surface waves by a Q-switched ruby laser is investigated both experimentally and analytically. The motivation is to improve the amplitude and to control the frequency content of the ultrasonic signal by taking advantage of the tremendous flexibility that one has in controlling the size and the shape of the thermoelastic source. Waveforms have been recorded for several source geometries at the surface of an aluminum block: spot source, line source, periodic array of spot sources, and periodic array of line sources. Also, focusing effects have been measured with a periodic array of curved line sources obtained with a Fresnel lens. In all cases, the waveforms are reasonably well predicted by a simple and efficient convolution technique. Waveforms have also been generated in a 1-mm-thick aluminum plate and recorded over a distance of 50 mm at increments of 0.5 mm. Processing of these waveforms in the frequency--wave-number domain allows for the extraction of the dispersion curve and the various modes propagating in the plate. [Work supported by NSF.]