Thermosonic imaging of cracks and delaminations

摘要

We describe a new hybrid ultrasonic/infrared technology in which a single short (50 to 200 ms) pulse of ultrasound is used to cause cracks in a variety of materials to heat up and become visible in the infrared. A low frequency (10's of kHz) ultrasonic transducer infuses the sample with sound. If the sample contains cracks or other defects that have surfaces which are free to move, the sound pulse causes the defects to heat locally. The resulting temperature field is imaged by an infrared video camera. The technique is applicable to large and irregularly shaped objects. We present a variety of images to show the capability for this technique to image cracks and other defects in metals as well as in other materials. Both surface-interrupting and subsurface cracks are shown. The technique takes only milliseconds, so can utilize hand-held ultrasonic sources. It is insensitive to the position of the source on the sample, and yields wide-area images, with the defects showing as bright (higher temperature) regions against a dark (lower temperature) background.