Development of computational inversion techniques to size cracks from eddy current signals

This paper reviews the recent advance in computational inversion techniques to size defects using eddy current signals. Studies reporting the sizing of artificial slits with the aid of computational inversion techniques are briefly overviewed and then several recent studies dealing with the sizing of fatigue and stress corrosion cracks are introduced. The results of the studies confirm computational techniques for sizing slits are sufficiently mature, and even though the measured signals are polluted with high noise, the boundary profile of slits can be evaluated from the signals. Furthermore, the studies demonstrate fatigue cracks can be dealt with almost identically to artificial slits from the viewpoint of eddy current testing; fatigue cracks introduced inside weld with a rough surface are well sized using eddy current testing with the aid of computational inversion techniques. In contrast, there is a large discrepancy between artificial slits and stress corrosion cracks, and thus conventional approaches are not always applicable to the sizing of stress corrosion cracks. This paper introduces several recent activities in the author's group to overcome this problem.