Modeling of Thermal Fatigue Crack for Enhancement of Electromagnetic Nondestructive Evaluation of Nuclear Power Plant

The present study investigates modeling of thermal fatigue crack by the finite element method from the view point of eddy current testing. Three artificially produced thermal fatigue cracks introduced into Inconel 600 specimens are prepared. Eddy current signals are gathered by a differential type plus point probe with 25 kHz and 100 kHz. Subsequent destructive tests show the profile of these cracks. In the numerical simulation thermal fatigue crack is modeled as a region with constant width, uniform conductivity and real profile. Results of the study combining the previous study on modeling of thermal fatigue crack in type 304 stainless steel specimen reveal that thermal fatigue crack, unlike stress corrosion crack, generally should be modeled as an almost nonconductive region regardless of frequencies. Furthermore the resistance of thermal fatigue crack defined as width divided by conductivity is almost unchanged, even though the appropriate conductivity and width are changing with the frequency.