Abstract: Pulsed eddy-current detection and characterization of wall- thinning in aircraft lap-splices due to corrosion is studied theoretically. The relevant lap-splices consist of two one mm thick sheets of aluminum bonded together by bolts and separated a small distance by a insulating sealant. Corrosion changes the thickness of both plates and the size of the gap between them. The problem is to determine nondestructively the thickness of both the 'top' and 'bottom' plates as well as the intervening gap. We calculate the time-domain current-voltage response function of a small cylindrically symmetric coil of wire that is placed next to a lap-joint and excited by a step-function current. The result for air-core coils is obtained as a simple quadrature, while coils that contain ferrite-cores are modeled with a finite element code. The characteristic features of the transient response are shown to depend sensitively on the thickness of the top plate, the gap and the bottom plate. !9
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