AIR-COUPLED ULTRASONIC NDE OF BONDED ALUMINUM LAP JOINTS

This paper describes an investigation into the feasibility of using wi deband air-coupled ultrasonic transducers for evaluating the integrity of bonded aluminum lap joints. Micromachined capacitance transducers are used to generate and detect ultrasonic Lamb waves in aluminum lap- joints through an intervening air layer. The transmission of Lamb wave s through the bond is affected by the bond's local state, such that sc anning a pair of air-transducers allows images to be produced either w ith the transducers on opposite sides of the plate, or on the same sid e. It is shown that defects in the bond-line can be detected and image d by such a non-contract system. Confirmation of defect positions are obtained by comparing the results of the air-coupled scans to a conven tional immersion ultrasonic C-scan.