4. Conclusion
This study probabilistically evaluated the size of fatigue cracks
in type 304 stainless steel plates using eddy current signals. The
fatigue cracks were artificially introduced using a cyclic four-
point bending test, and eddy current tests to gather the signals
were performed using a differential-type plus point probe
driven at 200 kHz. The fatigue crack was modeled as a rectan-
gular domain with a constant width of 0.5 mm and uniform
electromagnetic properties.
Because fatigue damage changes the austenitic phase of
type 304 stainless steel into the martensitic phase, both the
electrical conductivity and magnetic properties of the discon-
tinuity were explicitly considered. The depth and length of
the crack, together with their predicted uncertainty, were esti-
mated using a Bayesian-based inverse algorithm.
The size evaluated by assuming the crack was equivalent
to air differed from the actual crack size, even though the algo-
rithm indicated the results were reliable. In contrast, assuming
the electromagnetic properties to be unknown produced better
evaluations with quantified uncertainty.
ACKNOWLEDGMENTS
This work was supported in part by a Grant-in-Aid for Japan Society for
the Promotion of Science (JSPS) Fellows (grant number 22KJ0223).
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cracks were modeled as an air domain (no conductivity or magnetic
property): (a) TP1 (b) TP2 (c) TP3.
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