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 vici nity of cracks, disbonds, or delaminations, are imaged as a function of tim e 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 similar to 2 degrees C above the def ect. As an example, sonic infrared images are presented for two fatigue cra cks in Al and of interply delamination impact damage in a graphite-fiber-re inforced polymer composite. The shorter of the two fatigue cracks is simila r to 0.7 mm in length, and is tightly closed. Thus, this new technique is s ensitive, and capable of rapid imaging of defects under wide surface areas of an object. (C) 2000 American Institute of Physics. [S0034-6748(00)05006- 1].