Nondestructive Material Characterization with Laser Ultrasound

Abstract

Laser ultrasonic techniques are attractive for in line characterization of material, because they can transmit and recieve ultrasound with fully non-contact condition to the target. Especially, the system, using Fabry-Perot interferometer, is widely studied because of its apllicability to the evaluation of the rough surface material and its wide-band detectability.
In this paper, the detectability of the vibration and the characteristics of laser generated ultrasound are investigated with constructed laser ultrasonic system, using Fabry-Perot interferometer. And grain size of thin steel plates are evaluated from the frequency spectra of the attenuation constant of laser ultrasound.
It is proved that the vibration on the rough surface can be detected with this system, and the grain size of thin steel plates can be measured with faily good accuracy, but pre-processing of the signal is needed, such as the selection of the orders of the deformation free multiple echos and low-cut filtering.