Depth-Selective Squid Eddy Current Techniques for Second Layer Flaw Detection
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Begun in 1973, the Review of Progress in Quantitative Nondestructive Evaluation (QNDE) is the premier international NDE meeting designed to provide an interface between research and early engineering through the presentation of current ideas and results focused on facilitating a rapid transfer to engineering development.
This site provides free, public access to papers presented at the annual QNDE conference between 1983 and 1999, and abstracts for papers presented at the conference since 2001.
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Abstract
Detecting hidden damage at the second layer of lap joint structures in aircraft by using eddy current techniques is difficult because the cracks are usually located beneath the head of the rivets, which cause large signals that mask the relatively smaller signals from the second layer cracks. In addition, using lower frequency excitation for deeper penetration of the eddy currents reduces the signal-to-noise ratio. Several new techniques have been tried, such as using a sheet inducer to increase the penetration depth or using sensors that have a frequency independent response, to improve the signal to noise ratio [1, 2]. To better extract the information due to the cracks beneath the rivet at the second layer, we have developed a phase analysis of the magnetic field produced from the eddy currents induced by the sheet inducer.