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Furukawa, Tomohiro; ; Yoshida, Hidekazu;
PNC TN9410 93-042, 56 Pages, 1993/02
Mod.9Cr-1Mo steel is a candidate material of once-through type steam generators for the Fast Breeder Reactors, and it is required to clarify low-cycle fatigue properties in air at high temperature on this material for structural design. So the tests were carried out for three heats (12mmt plate, 25mmt plate and 250mmt forged) on conditions that temperature is 450
650
C and strain range is 0.41.2%. Results obtained are su㎜araized as follows. (1)For cyclic stress-strain behavior of Mod.9Cr-1Mo steel cyclic hardening was. observed in the early stage, and after that changed to softening to failure. The behavior was similar to normalized and tempered 2.25Cr-1Mo steel. (2)Low-cycle fatigue strength of Mod.9Cr-1Mo steel in air was remarkably higher than that of 2.25Cr-1Mo steel, and almost same as much as that of SUS304 steel. Moreover, fatigue life of Mod.9Cr-1Mo steel was longer than that of 9Cr-2Mo or Low C-9Cr-1Mo-Nb-V steel under low strain conditions. (3)In the case of Mod.9Cr-1Mo forged steel, the influence of the sampling position and direction of specimens was not effective. These results were reflected to prepare of tentative material strength standard in 1992.
; Kawasaki, Hirotsugu; Aoto, Kazumi; Yoshida, Eiichi; ;
PNC TN9410 92-089, 61 Pages, 1992/03
The allowable strain range 
of Mod.9Cr-1Mo (NT) steel has been substituted by that for 2-1/4Cr-1Mo (NT) steel in last version of material strength standard in 1989. Because of the a small amount of fatigue test data on Mod.9Cr-1Mo (NT) steel, it is difficult to determine the best fit curve and allowable strain range of Mod.9Cr-1Mo (NT) steel can be evaluated conservatively by the values of 2-1/4Cr-1Mo (NT) steel. Low-cycle fatigue tests by various strain rates and the high-cycle fatigue tests were carried out to determine the new best fit fatigue life equation of this material. In this report, the fatigue life equation of Mod.9Cr-1Mo (NT) steel is and the interim new version of allowable strain range is proposed. The obtained results are as follows, (1)In the best fit fatigue life equation of Mod.9Cr-1Mo (NT) steel the effects by both of the temperature and low strain rate should be considerd. As the analytical methods to consider these dependency in the fatigue life equation, the correlation to the fatigue properties of 2-1/4Cr-1Mo (NT) steel is examined. Some data fitting methods based on the fatigue equation for 2-1/4Cr-1Mo (NT) steel are tried and compared. One of these methods could give a good prediction for the fatigue properties of the Mod.9Cr-1Mo (NT) steel up to high cycle range. (2)The interim standard of allowable strain ranges A , B and C (for strain rate of 10
, 10
and 10
s 
) for Mod.9Cr-1Mo (NT) steel could be proposed by the new best fit fatigue life equation. (3)The proposed allowable strain range at 375C was compared to the present design fatiuge curve of low alloy steel of MITI Notice No501, and it was clarified that the fatigue strength of Mod.9Cr-1Mo steel was too higher. The design fatigue curve for Mod.9Cr-1Mo (NT) steel will be revised to higher design value (twice for starin range at l0
cycles) than the present design fatigue curve of low alloy steel.
*
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.
*; *; Koakutsu, Toru; *; *
PNC TN9410 89-148, 158 Pages, 1989/10
For the purpose of the verification of the evaluation method on the sodium environmental effect on the mechanical properties of the structural materials used for the prototype LMFBR "MONJU" and the rationalization of the evaluation method for large scale LMFBRs, SUS 304 and 316 austenitic stainless steels and 2.25Cr-1Mo steel (NT) were carried out. Test specimens were exposed to a sodium loop for 10,000 hours at 400 600C simulating the primary and secondary coolant systems of the prototype LMFBR "MONJU". After the exposure, fatigue tests were performed in sodium environment. Fatigue tests were also performed on the thermal aged material for 10.000 hours in inert gas. The results obtaind were as follows. (1)The difference between the fatigue lives of sodium exposed materials and thermal aged materials was very small for both kinds of steels and these lives were almost the same as these of as - received materials. (2)Caburization was recognized on the surface of SUS 304 and SUS 316 austenitic stainless steels in the cage tested in sodium after sodium exposed. In the case of 2.25Cr-1Mo steel (NT), some decarburization was observed at 500 C. (3)The fatigue lives didnot depend on the exposure history such as sodium exposed materials and thermal aged materials for 10,000 hours. The carburization and decarburization effects were very small on fatigue life. The fatigue lives were affected by the environment in which fatigue tests are conducted.
*; *; Tsukimori, Kazuyuki*
PNC TN9410 87-073, 206 Pages, 1987/03
The development of piping bellows as one of the cost reduction measures for Large FBR plants has been conducted in the Power Reactor and Nuclear Fuel Development Corporation since 1984. Fatigue and creep-fatigue strength evaluation is an important issue in practical application of bellows to the primary piping systems of FBR. This is the first report of a series of the fatigue and creep-fatigue tests for 42 inches diameter bellows. Fatigue tests described in this report were conducted on type 316 Stainless steel U-shaped bellows with seven convolutions at room temperature and 600 C. Through the present tests and analytical studies, the following conclusions were obtained. (1)Many of fatigue cracks distribute on the root surfaces near the both sides of bellows and they are almost intergranular fracture. (2)Fundamental characteristics of bellows in elastic region such as spring and strain response can be properly estimated by EJMA standards and FEM analysis. (3)Fatigue life of bellows can be properly estimated by material based fatigue life prediction using measured strains of bellows. (4)Maximum actual strain ranges can be reasonably estimated by using the elastic nominal strain range multiplied by the inelastic amplification factor per convolution (f
f
) and the factor (f
) caused by stiffness fluctuation between convolutions. The effectiveness of the practical evaluation of strain range and fatigue life of bellows has been validated through this study.
*; Tsukimori, Kazuyuki*; Iwata, Koji
PNC TN9410 87-053, 74 Pages, 1987/03
PNC is promoting the feasibility study of piping bellows expansion joints as one of the measures that rationalize large scale FBR plants, and the fatigue and creep fatigue test of bellows is one of the R&D tests. This report describes the fatigue test and analysis result of the bellows fundamental unit model (corrugated plates) at room temperature. The following is the main result. (1) The fatigue life data of the corrugated plates favorably coincide with the material fatigue curve. (2) The strain response of the corrugated plates can be satisfactorily analized by both theoretical and numerical method. (3) The relationship between the corrugated plate and the bellows (42 inches in diameter) was examined by using the shallow beam theory, the standards of EJMA and unmerical analyses (FEM). As the result there was no remarkable difference between them. (4) The degree of the strain concentration by plasticity in 1 convolution is estimated conservatively due to the factor Ke' (q = 2.0) which is bounded by test and analysis results.
