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; Aoto, Kazumi; ;
JNC TN9400 2000-022, 46 Pages, 2000/03
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.
JNC TN9400 2000-021, 104 Pages, 2000/03
ln this report, research works performed in the Structura1 Safety Engineering Group of OEC/JNC are summarized as the final report of the doctoral fellowship. The main objective of this study is for the enhancement of the nondestructive evaluation techniques for structural components of both magnetic and nonmagnetic material. Studies in three topics have been carried out aiming at the quantitative evaluation of crack with the eddy current testing and the validation of a natural magnetic field based NDE method for detecting mechanical damages in a paramagnetic material. ln the first part of the study, an approach to the reconstruction of the natural crack was proposed and implemented with an idealized crack model for its validation. ln the second part, the correlation of the natural magnetization and the mechanical damages in the SUS304 stainless steel was investigated by using an experimental approach. ln part 3, an inverse method of the measured magnetic fields is proposed for the reconstruction of magnetic charges in the inspected material by using an optimization method and wavalet. As the first work, an approach to the reconstruction of an idealized natural crack of non-vanishing conductivity is proposed with use of signals of eddy current testing. Two numerical models are introduced at first for modeling the natural crack in order to represented it with a set of crack parameters. A method for the rapid prediction of the eddy current testing signals coming from these idealized cracks is given then by extending a knowledge based fast forward solver to the case of a non-vanishing conductivity. Based on this fast forward solver, the inverse algorithm of conjugate gradient method is updated to identify the crack parameters. Several examples are presented finally as a validation of the proposed strategy. The results show that both the two numerical models can give reasonable reconstruction results for signal of low noise. The model concerning the touch of ...
Kawasaki, Hirotsugu; *
JNC TN9400 2000-018, 37 Pages, 2000/03
The damage evaluation for the vessel model on the cyclic thermal transient loading in sodium were performed by the ultrasonic detection method. The wavelet analysis that was an analysis method of the waveform was applied to detect the micro damage before a sign of the crack initiation. The time-frequency analysis by the wavelet transform was performed to evaluate the ultrasonic parameter for the micro damage. As the results, the ultrasonic echo was analyzed by some mother wavelet, and Gabor wavelet was reasonable. The analysis of ultrasonic echo by Gabor wavelet showed drop of the sound velocity at higher frequency than the peak frequency because of attenuation in the high frequency component. The difference of the peak frequency △fp between B1 and B2 echoes increased with the amount of damage, and △ fp was available as a parameter for the micro damage detection. The correlation between the sound velocity and the micro hardness for the amount of damage was also found, and each method suggested to available alternately. ln this study, it was indicated that an ultrasonic wave characteristic value that can detect damaged state before crack initiation was obtained from the wavelet analysis.
; Ueno, Fumiyoshi
JNC TN9400 2000-017, 10 Pages, 2000/03
lt is difficult to get hold the behave of growth of cavity which nucleates in grain boudaly in experimental observation. lt is considerd that numerical simulation is effective for the grasp of behave of cavity growth, because it is able to grasp the microscopic behavior of internal material whici is hardly observation. We examine the factor that the diffusive ratio and the stress etc., affected growth of cavity on grain boundary with numerical simulation using diffusive equation. As the result, a following knowledge was obtained. (1)With dominant of grain boundary diffusion, the shape of cavity transitions from quasi-equilibrium to crac-like. ln other hand, with dominant of surface diffusion, cavity grows up with initial shape. (2)With dominate of grain boundary diffusion, it accelerates the growth rate of the cavity near the tip by grain boundaly diffusion induced stressing perpendicular to gain boundary (3)With dominant of surface diffusion, the distribution of chemical potential is uniformity on cavity surface. ln other hand, with dominant of grain boundary diffusion compare to that of surface diffusion, the gradient of chemical potential is increased at the tip of cavity.
Yoshida, Eiichi; Aoto, Kazumi; Hirakawa, Yasushi;
JNC TN9400 2000-024, 42 Pages, 1999/10
For the purpose of improving the reliability of evaluation, the corrosion rate equation of the carbon steel SM400B (JIS G3106) in the high-temperature sodium compounds (NaOH-Na0 system) was revised. ln this revision, the data acquired after 1997 was used. Based on the experimental results, the evaluation was made to be an approach to the following; (1)Metal loss of carbon steel in NaOH-Na0 system was evaluated as increases in exposure to the time, which is linear rate law. (2)There were no significant effects of the experiment atmosphere and mixing speed of the reagent on corrosion rate. (3)The concentration of Na0 in sodium compound is considered for the evaluation. The concentration under experiment is made to be the over concentration necessary for maintaining the dominant reaction between Fe and Na20. As a result of the evaluation, the additional data are 67 points. The data for the revision of the evaluation equation became the total of 105 points, when existing data of 38 points were added. The statistical evaluation of 105 points was carried out, and following recommended equation was obtained. C = C exp(-Q/RT) Where; C : Corrosion rate, mm/h C : Material constant Q : Apparent activation energy, cal/mol R : Gas constant, 1.986 cal/mol K T ; Absolute temperature, K Q = 9.61 kcal/mol C = 148.29 (average), 262.11 (99% UCL), 83.90 (99% LCL)
; *; Yoshida, Eiichi; Aoto, Kazumi
JNC TN9400 2000-011, 33 Pages, 1999/03
The damage was observed in rupture disk for the A-loop superheater of sodium-water reaction products releasing system for MONJU on March 3, 1998. Low temperature creep and stress corrosion cracking tests were carried out as the causes investigation of the damage. As the result, the followings are clarified. (1)The possibility that low temperature creep is the principal damage is small. (2)The stress corrosion cracking under NaOH environment due to the reaction of Na vapor and moisture condensed on the surface of glass beads as remains is the most probable cause on the damage. (3)Comparatively many glass beads remained in damaged surface. The gap between rupture disk and vacuum support was narrower than other parts, and they were not directly exposed to the Na vapor for a long time. The above factors caused the perfect intergranular cracking by stress corrosion. Since NaOH was chemically changed into the harmless NaO on the location except for damaged zone by full Na vapor, the stress corrosion cracking was not generated.