Infrared imaging of defects heated by a sonic pulse

High-frequency pulsed sonic excitation is combined with an infrared camera to image surface and subsurface defects. Irreversible temperature increases on the surface of the object, resulting from localized heating in the vicinity of cracks, disbonds, or delaminations, are imaged as a function of time prior to, during, and following the application of a short pulse of sound. Pulse durations of 50 ms are sufficient to image such defects, and result in surface temperatures variations of ;2 °C above the defect. As an example, sonic infrared images are presented for two fatigue cracks in Al and of interply delamination impact damage in a graphite–fiber-reinforced polymer composite. The shorter of the two fatigue cracks is ;0.7 mm in length, and is tightly closed. Thus, this new technique is sensitive, and capable of rapid imaging of defects under wide surface areas of an object. © 2000 American Institute of Physics. @S0034-6748~00!05006-1#