Sonic IR Imaging of delaminations and disbonds in composites

Sonic IR is a nondestructive evaluation (NDE) technique that makes images of defects in objects using an infrared camera with an ultrasonic transducer as an active stimulation source. The advantages of the method are its speed, taking only seconds, or, more usually, only a fraction of a second to make a dark-field image that shows the location and size of the defect, and its ability to cover a wide area, typically a square meter, or a significant fraction of a square meter, in a single image. This NDE method has principally been used for finding cracks in metals, but its application to polymeric composites has been lagging, in part because of artefacts that mask the indications of defects. In this paper we discuss the application of sonic IR to disbonds and delaminations in composites, and describe the use of broadband chaotic sound to eliminate artefacts resulting from acoustic interference. An additional benefit arises from the simultaneous stimulation of defects with different resonant frequencies.