Thermosonics: Detecting Cracks and Adhesion Defects Using Ultrasonic Excitation and Infrared Imaging

We describe a new nondestructive evaluation technique which makes cracks and adhesion defects visible to infrared cameras. This is accomplished by infusing the sample with a short pulse of low frequency ultrasound. The sound causes the faying surfaces of defects to heat up by friction or clapping, and thus makes them visible in the infrared. Surface or near-surface defects appear to the camera within milliseconds of the initiation of the ultrasonic pulse, while the appearance of subsurface defects is delayed by the thermal propagation time from the defect to the surface being observed.