Pages 245-246
A new nondestructive testing technique was developed based on the lock-in measurement of the surface temperature under the application of periodical xenon light heating. Experimental study was made on the applicability to the detection of flat bottom hole defects and delamination defects. Xenon light beam was periodically chopped by the electric shutter to generate thermal wave in the objective body. In-phase and out-of-phase temperature amplitude images were taken by the lock-in thermography, synchronized to the reference signal of the electric shutter operation. It was found that the location and size of the defects can be identified by the localized contrast change in the out-of-phase image. Further, the depths of the defects can be identified from the heat penetration depth, which was changed by the frequency of thermal wave stimulation.
