Non-destructive Evaluation using Laser-generated Ultrasonic Waves

摘要

Laser generated ultrasonic technique is shown to be advantage in detecting the flaws of high temperature materials or complicated structures which are difficult to investigated by using conventional ultrasonic testing method. In the present study, a Nd;YAG Laser (pulse type) was used to generate ultrasonic waves in a test material. In addition, a total ultrasonic investigation system was designed by adopting a Fabry-Perot interferometer, which receives ultrasonic signals without any contact. For non-destructive test SM45C, which contains some flaws was used as a test material. Because it is easy to align light beam in receiver, and the length of the light beam does not change much even if convex mirror leans towards one side, confocal Fabry-Perot interferometer, which has stable frequency, and PI(Proportional Integral) control are used to correct interfered and unstable signals from temperature, fluctuation and time shift of laser frequency. Stable signals are always obtained by the feedback of PI circuit signals in the confocal Fabry-Perot interferometer. The type, size and position of flaws inside the test material were examined by achieving the stabilization of an interferometer. This study presented a useful method, which could quantitatively investigate the fault of objects by using a Fabry-Perot interferometer.