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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.
; kasahara, Naoto; ; ; Kamide, Hideki
JNC TN9400 2000-010, 168 Pages, 2000/02
JNC-TN9400-2000-010.pdf:8.78MB
Thermal striping is significant issue of the structural integrity, where the hot and cold fluids give high cycle fatigue to the structure through the thermal stress resulted from the time change of temperatur distibution in the structure. In the sodium cooled fast reactor, temperature change in fluid easily transfers to the structure because of the high thermal conductivity of the sodium. It means that we have to take care of thermal striping, The thermal striping is complex phenomena between the fluid and structure engineering fields. The investigations of thermal striping are not enough to evaluate the integrity directly. That is the fluctuation intensity at the structure surface is assumed to be temperature difference between source fluids (upstream to the mixing region) as the maximum value in the design. 0therwise, the design conditions are defined by using a mockup experiment and large margin of temperature fluctuation intensity. Furthermore, such evaluation manners have not yet been considered as a design rule. Transfer mechanism of temperature fluctuation from fluid to structure has been investigated by the authors on the view points of the fluid and structure. Attenuation of temperature fluctuation was recognized as a dominant factor of thermal fatigue. We have devdoped a numerical analysis system which can evaluate thermal fatigue and crack growth with consideration of the attenuation of temperature fluctuation in fluid, heat transfer, and structure. This system was applied to a real reactor and the applicability was confirmed. Further verification is planned to generalize the system. For the higher cost performance of the fast reactor, an evaluation rule is needed, which can estimate thermal loading with attenuation and can be applied to the design. An idea of the rule is proposed here. Two methods should be prepared; one is a precise evaluation method where mechanism of attenuation is modeled, and the other is simple evaluation method where ...
; Aoto, Kazumi;
JNC TN9400 99-061, 32 Pages, 1999/07
In this report, reconstruction of magnetic charges induced by mechanical damages in a test piece of SUS304 stainless steel is performed as a part of eforts to establish a passive nondestructive testing method on the basis of the inspection of leakage magnetic field. The approach for solving this typical ill-posed inverse problem is selected as a way in the least square method category. Concerning the ill-poseness of the system of equations, an iteration algorithm is adopted to its solving in which the designations of initial profile, the weight coefficients and the total number of iterations are taken as means of reqularization. From examples using simulated input data, it is verified that the approach gives good reconstruction results in case of signals with a relative high S/N ratio. For improving the robustness of the proposed method, a Galerkin procedure with base functions chosen as the Daubechies' wavelet is also introduced for discretizing the governing equation. By comparing the reconstruction results of the least square method and those using wavelet discretization, it is found that the wavelet used approach is more feasible in the inversion of noise polluted signals. Reconstruction of 1-D and 2-D magnetic charges with the least square strategy and reconstruction of an 1-D problem with the wavelet used method are carried out from both simulated and measured magnetic field signals which are used as the validation of the proposed inversion strategy.
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PNC TJ9601 96-003, 38 Pages, 1996/03
In this study, for the purpose of development of a nondestructive detection technique of creep-fatigue damage in Type 316FR stainless steel for fast reactors, application study of electrochemical methods and the Induced Current Potential Drop(ICFPD) was done. Applicability of electrochemical methods to evaluation of grain boundary precipitates which, provide preferred site for cavities was investigated. Anodic polarization curves were measured both in 1N KOH solution and in 1N H
SO
+KSCN solution. An anodic current peak that, corresponds to preferential dissolution of the grain boundary precipitates was observed in the measurements using in the KOH solutlon. It was suggested that evolution of the grain boundary precipitates which should be associated with creep-fatigue damage can be evaluated by the electrochemical method using KOH solution. The results of reactivation ratio of the material in 1N HSO+KSCN solution, which is recognized as the sensitive indicator of Cr-depletion, suggested a correlation between the reactivation ratio and creep-fatigue damage. Clear differences between the as-received material and the creep-fatigue damaged sample were found in ICFPD results. Although more detailed investigation is required to make a conclusion, it was expected that potential drop can reflect creep-fatigue damage in the microstructure, e.g. precipitates cavities, surface cracks. Based on the preliminaly result, the ICFPD technique may be expected to provide a quantitative monitoring capability of creep-fatigue damage.
Furuhashi, Ichiro*; *
PNC TN9410 94-201, 301 Pages, 1994/04
Development and revisions of simplified crack analysis code CANIS-system were done for fracture mechanics evaluation of FBR structures. CANIS-system is composed of CANIS-G, K and -I. Following revisions were done on CANIS-G that evaluate creep fatigue crack growth history. (1.1)0uter crack of cylinder can be treated, addition to inner crack. (1.2)Axial bending load on cylinder can be treated. (1.3)Displacement controlled load such as thermal stresses can be easily treated. (1.4)Libraly of shape functions for net section stress and libraly of stress intensity factor solutions were expanded to support above subjects. (1.5)Material properties such as elasto-plastic stress-strain relation, creep strain relation, creep rupture time and fatigue failure life of 7 kinds of materials those have been gotten in PNC were added on libralies. (1.6)Backward analysis can be done to estimate past time crack shapes. And now CANIS-K that evaluate fracture mechanics parameters and CANIS-I that evaluate crack initiation probability have been developped. CANIS-K can be used in the following subjects. (2.1)Calculate and print details of fracture mechanics parameters such as stress intensity factor K, J-integral and creep J-integral for given crack shapes, and maximum and minimum values and time histories of those parameters. (2.2)Calculate and print crack growth rates, crack opening area and leak rates. CANIS-I can be used in the following subjects. (3.1)Evaluate time dependant fatigue damage and creep damage. (3.2)Evaluate time dependant crack initiation probability with reference of statistical crack initiation data that caused by fatigue damage or by creep damage. Input data format and subroutine programs of these CANIS-G, -K and -I are commonly, so future expansions and revisions will be done easily and commonly. CANIS is very powerful computational tool in the following regions and can be employed in many practical applications. (4.1)Remaining life predictions of cracked ...
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PNC TN9410 90-053, 56 Pages, 1990/02
A series or multiaxial creep-fatigue tests (uniaxial fatigue, pure torsional fatigue, pure torsional creep-fatigue, proportional fatigue, proportional creep-fatigue) was conducted by Toshiba Corporation as a part of a joint study with PNC. The results of the tests were evaluated by the multi-axial creep-fatigue evaluation method which was developed by the authors in the previous report. The following observation were obtained. (1)Results of multiaxial creep-fatigue tests obtained by Toshiba Corporation coincide well with those obtained by PNC, except those of pure torsional fatigue/creep-fatigue tests. In the case of pure torsional fatigue/creep-fatigue, Toshiba data showed slightly longer lives, (2)Pure torsional creep-fatigue lives reduced as the peak strain hold time increased from 3 minites to 60 minites. A longer hold time would have redeced the creep-fatigue lives even more. (3)In pure torsional creep-fatigue tests with a peak strain hold of 15 minuites, recovery of life was not observed with an additional strain hold time (from 3 minites to 15 minuites) at the other strain peak. (4)It was shown that the multiaxial creep-fatigue evaluation method proposed by the authors could cvaluate the Toshiba data conservatively. Life predictionswere conservative for a factor of 5 and nonconservative for a factor of 2.