Application of Self Nulling Eddy Current Probe Technique to the Detection

With the recent development of a smaller self-nulling probe it is now possible to characterize the early stage of fatigue crack initiation in compact tension specimens and to trace the movement of the tips as the crack propagates. Unlike the conventional eddy current probes, the self-nulling probe provides a well defined local maximum in the probe''s response near the crack tip which makes the probe ideal for monitoring the crack propagation process. For the present study the tracing of cracks tips was performed during the actual fatigue, demonstrating that the technique is capable of fully automating the test procedure. To gain a deeper insight into the eddy current distribution near the crack tip and the probe''s response a 3-D FEM simulation was performed both for the crack initiation and propagation stage.