Automatic Detection of Defects in Riveted Lap-joints using Eddy Current
7th European Conference on Non-destructive Testing, Copenhagen, Denmark, 26-29 May, 1998
A method for detection and classification of defects originating from rivet holes in a riveted
lap-joint using eddy current (EC) inspection is presented in this paper. The EC-signals were
acquired from a number of lap-joints using a tailor-made deep penetrating probe, and a digital single frequency EC-instrument.
A number of rivets in the lap-joints had defects located in the second layer of the lap-joint.
The problem consisted in detecting and classifying defect signals in presence
of strong interference due to rivet responses. The preprocessing before detection consisted of
median filtering, rotation and de-biasing of the eddy current pattern.
The rotation was performed so that the signal energy from the rivet responses was maximized
along the quadrature direction, and the defect response energy was maximized in the in-phase
direction of the EC-signal. Feature extraction was then performed using wavelets, PCA and
block-mean values of the defect signal. The classification was performed using a standard
multi-layer perceptron neural network.
Postscript, 562K ;