An arrayed uniform eddy current probe design for crack monitoring and sizing of surface breaking cracks with the aid of a computational inversion technique

• Applicability of eddy current testing to crack monitoring was discussed.
• An arrayed uniform eddy current probe was designed.
• A numerical inversion algorithm was developed.
• Validations were conducted using fatigue cracks with different depths.
• The depths and the lengths of the cracks were evaluated well.

This study demonstrates that eddy current testing can be an effective method for monitoring the growth of surface breaking cracks with the aid of computational inversion techniques. A uniform eddy current probe with 23 arrayed detectors was designed, and pseudo monitoring tests were carried out to measure signals due to six mechanical fatigue cracks introduced into type 316L austenitic stainless steel plates. In the test the position of the probe was fixed to simulate monitoring. The depths of the cracks were evaluated using a computational inversion method developed on the basis of k-nearest neighbor algorithm. The depths of the mechanical fatigue cracks whose actual depths were 1.1, 2.1, 3.1, 5.5, 6.7, and 8.5 mm were evaluated to be 0.9, 1.9, 3.8, 4.3, 7.0, and 5.7 mm, respectively. Additional simulations were conducted to demonstrate the stability of the method.