Passive electromagnetic NDE for mechanical damage inspection by detecting leakage magnetic flux; II An experimental study on the correlation of natural magnetization and mechanical damages in the SUS304 stainless steel

; Aoto, Kazumi; ;

JNC TN9400 2000-022, 46 Pages, 2000/03

JNC-TN9400-2000-022.pdf:3.2MB

ln this report, a study on the behaviors of the magnetization induced by mechanical damages is carried out. By introducing mechanical damages to a test-piece with a tension or/and a zero, tension fatigue testing and measuring the corresponding leakage flux signal, natural magnetization change is proved and found increasing with the mechanical damages (viz. plastic deformation or fatigue damages) though a saturation occurs when damage gets too large. From the experimental results of fatigue testing utilizing test-pieces with a central slit, it was verified that observing the natural leakage flux density (leakage flux without applying external magnetic field) is a reasonable way to identify fatigue cracks. A feature parameter (area of the B hysteresis curve) of the in-situ magnetic field signal measured during the fatigue testing is proposed for predicting the fatigue damages, which is found depending on the cyclic number of the applied loading. At last, residual magnetic fields of a magnetized test-piece are also measured and found depending on the applied plastic deformation in case that the plastic strain is not too small. From these experimental results, it is found that the approach detecting natural magnetization is applicable for monitoring the damage status though it may be not efficient for a scanning inspection concerning its small signal magnitude. On the other hand, the method employing permanent magnet is robust against the environment noise but possibly not valid for the ISl of a structural component with a relative low damage level. For practical application, efforts to evaluate the feasibility of the proposed method are necessary for more testing conditions especially its suitability in a practical environment.