Non-Destructive Evaluation of Fatigue Damage in Type 316 Stainless Steel by Using β<SUP>+</SUP>-γ Coincidence Positron Lifetime Spectrometer

Newly developed β+-γ coincidence positron lifetime spectroscopy was applied to analysis of fatigue damage aiming at non-destructive evaluation of fatigue stored in type 316 stainless steel which is mostly used in primary water line of pressurized water reactor. Stress-controlled fatigue specimens and strain-controlled fatigue specimens were prepared and relations between fatigue life and positron lifetime were investigated. Mean positron lifetime increases with the fatigue life monotonically in both fatigue test modes. In the strain-controlled mode, mean positron lifetime increases faster at early stage than that in the stress-controlled mode; however, it converges to the same value at the end of the fatigue life in both conditions. Component analysis of positron lifetime spectra revealed that main defects are dislocations and their density increases with fatigue life to a critical value. With this non-destructive evaluation method, the fatigue damage can be analyzed precisely without destruction of the sample.