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Wakai, Takashi; Kobayashi, Sumio; Kato, Shoichi; Ando, Masanori; Takasho, Hideki*
Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 7 Pages, 2017/07
This paper describes a thermal fatigue test on a structural model with a dissimilar welded joint. In the present design of JSFR, there may be dissimilar welded joints between ferritic and austenitic steels especially in IHX and SG. Creep-fatigue is one of the most important failure modes in JSFR components. However, the creep-fatigue damage evaluation method has not been established for dissimilar welded joint. To investigate the evaluation method, structural test will be needed for verification. Therefore, a thermal fatigue test on a thick-wall cylinder with a circumferential dissimilar welded joint between Mod.9Cr-1Mo steel and 304SS was performed. Since the coefficients of thermal expansion of these steels were significantly different, buttering layer of Ni base alloy was installed between them. After the completion of the test, deep cracks were observed at the HAZ in 304SS, as well as at HAZ in Mod.9Cr-1Mo steel. There were many tiny surface cracks in BM of 304SS. According to the fatigue damage evaluation based on the finite element analysis results, the largest fatigue damage was calculated at HAZ in 304SS. Large fatigue damage was also estimated at BM of 304SS. Fatigue cracks were observed at HAZ and BM of 304SS in the test, so that analytical results are in a good agreement with the observations. However, though relatively small fatigue damage was estimated at HAZ in Mod.9Cr-1Mo steel, deep fatigue cracks were observed in the test. To identify the cause of such a discrepancy between the test and calculations, we performed a series of finite element analyses. Some metallurgical investigations were also performed.
Ando, Masanori; Takasho, Hideki*; Kawasaki, Nobuchika; Kasahara, Naoto*
Journal of Pressure Vessel Technology, 135(6), p.061207_1 - 061207_10, 2013/12
Times Cited Count：5 Percentile：27(Engineering, Mechanical)The stress generation mechanism of a tubesheet was revealed through finite element analysis. Semi-spherical tubesheet models were investigated for the first survey of the thermal stress mechanism. The calculated results of the semi-spherical tubesheet model indicated an extensive peak stress around the outermost hole. The recognized thermal stress mechanism of a semi-spherical tubesheet is summarized, and on the basis of the stress generation mechanism, we proposed a stress-mitigated tubesheet, a center-flattened spherical tubesheet (CFST), as an improved configuration. The stress generation mechanism of the CFST was also desicibed.
Kasahara, Naoto*; Takasho, Hideki*; Kawasaki, Nobuchika; Ando, Masanori
Proceedings of International Symposium on Plasticity 2010 (CD-ROM), p.34 - 36, 2010/01
The method to determine equivalent solid materials of perforated plates was proposed. One of difficulties of plastic analysis is dependency of their solutions on constitutive equations. To overcome this problem, plastic behaviors of perforated plate were systematically investigated on various kinds of constitutive equations. These studies have found existence of the effective stress ratio (ESR) which is defined as the stress ratio between average stress of perforated plates and solid plates of base materials. The ESR is a function of geometrical parameters and is independent from constitutive equations. Therefore, the ESR can determine plastic solid materials of perforated plates from any kind of constitutive equations of base materials.
Asayama, Tai; Takasho, Hideki*; Kato, Takehiko*
Journal of Pressure Vessel Technology, 131(1), p.011402_1 - 011402_9, 2009/02
Times Cited Count：9 Percentile：42.76(Engineering, Mechanical)The application of risk-based technologies is the way to be pursued for the improvement of design of new reactors such as fast breeder reactors. When doing so it is necessary to develop an analytical method that is capable of estimating failure probabilities without a large failure database that requires operational experiences. The prediction method should estimate failure probabilities based on actual mechanisms that cause failure. For this purpose, this study developed a probabilistic structural reliability evaluation method for fatigue. This method is capable of modeling crack initiation, crack propagation, as well as crack depth density distribution at a given cycle. To verify the methodology, crack depth distribution observed in thermal fatigue test specimens were evaluated, and it was shown that the method could reproduce the observed crack depth distributions fairly well. Further improvement will allow this methodology to be applied to the procedure of optimization of inservice inspection planning, as well as to the optimization of safety factors in component design of nuclear plants.
Kasahara, Naoto*; Takasho, Hideki*; Kawasaki, Nobuchika; Ando, Masanori
Nihon Kikai Gakkai M&M 2008 Zairyo Rikigaku Kanfarensu Koen Rombunshu (CD-ROM), p.OS0623_1 - OS0623_2, 2008/09
For design analysis of perforated plates, axi-symmetric models with equivalent solid plates are conventionally adopted to simplify perforated geometries. ASME Sec.III Appendix A-8000 provides elastic constants for equivalent solid plates. To extend applicable area of equivalent solid plates to inelastic analysis, the general determination method of non-linear equivalent material properties for perforated plates was proposed based on the effective stress ratio (ESR). This study examined applicability of effective stress concept to structural design of plat and spherical tubesheet structures.
Kawasaki, Nobuchika; Takasho, Hideki*; Kobayashi, Sumio; Hasebe, Shinichi; Kasahara, Naoto
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 9 Pages, 2008/07
To clarify frequency-dependent attenuation effects of fluid temperature fluctuation on fatigue strength, thermal fatigue strength tests subjected to superposed sinusoidal temperature fluctuations were performed by the SPECTRA test facility. After these fatigue tests, cylindrical test pieces were cut away from the test loop, and cracks were observed on the inner surface of the test pieces. Fatigue lives at crack initiation positions were evaluated based on the test conditions. Adopting power spectrum density functions and frequency transfer functions, fatigue lives were predicted within a factor 3.
Ando, Masanori; Takasho, Hideki*; Kawasaki, Nobuchika; Kasahara, Naoto
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 10 Pages, 2008/07
Adoption of double-wall-straight tube steam generators made of Mod.9Cr-1Mo steel is planned for next generation fast breeder reactors in Japan. One of the major concerns relevant to the SG is structural integrity of tubesheets. In the reactor transient operation, thermal stress is induced by the temperature distribution in tubesheet and the magnitude of it depends on configurations of tubesheet. Stress generation mechanism of tubesheets was revealed through Finite Element analysis. Semi-spherical tubesheet models were investigated for the first survey of the thermal stress mechanism. As calculated results, semi-spherical tubesheet model gave the extensive peak stress around the outermost hole. Based on the those stress generation mechanism, authors proposed a stress mitigated tubesheet. It is center flatted spherical tubesheet as improved configuration.
Kasahara, Naoto; Takasho, Hideki*
Nihon Kikai Gakkai M&M 2007 Zairyo Rikigaku Kanfarensu Koen Rombunshu (CD-ROM), p.421 - 422, 2007/10
For design analysis of perforated plates, axi-symmetric models with equivalent solid plates are conventionally adopted to simplify perforated geometries. ASME Sec.III Appendix A-8000 provides elastic constants for equivalent solid plates. However, no design codes give inelastic material properties of equivalent plates. This study reveals that perforated plates have their own effective stress ratio (ESR), which is a function of geometry and is independent from their materials. ESR enables the general determination method of non-linear equivalent material properties for perforated plates.
Kasahara, Naoto; Takasho, Hideki*; Ando, Masanori
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.1, p.683 - 684, 2007/09
Tubesheet structures utilized in heat exchangers have complex perforated portions. For design analysis of these structures, axi-symmetric models with equivalent materials of perforated plate are conventionally adopted to simplify perforated portions. Double wall steam generators expected for commercial FBRs require new type of tubesheets, where conventional design methods are not applicable. Therefore, JAEA started research programs to develop a design by analysis method of these structures. This paper reports on the mechanism of thermal stress developments in new tubesheets with an associated paper.
Kasahara, Naoto; Kawasaki, Nobuchika; Wakai, Takashi; Takasho, Hideki*
Transactions of the 19th International Conference on Structural Mechanics in Reactor Technology (SMiRT-19) (CD-ROM), 8 Pages, 2007/08
Tubesheet structures utilized in heat exchangers have complex perforated portions. For design analysis, axi-symmetric models with equivalent materials of perforated plate are conventionally adopted to simplify perforated portions. ASME Sec.III Appendix A-8000 provides elastic constants for equivalent materials of perforated plate. In the case of elevated temperature reactors, elastic-plastic-creep deformation occurs in tubesheets. Therefore, design of these structures requires simplified models with non-linear equivalent materials for perforated plate. This study proposes a general determination method of non-linear equivalent material properties for perforated plates. Perforated plates have their own effective stress ratio (ESR). ESR is a function of geometry only and is independent from constitutive equations. ESR can determine non-linear equivalent material properties of perforated plates for any kind of constitutive equations of base metals.
kasahara, Naoto; Takasho, Hideki*
Nihon Kikai Gakkai Dai-18-Kai Keisan Rikigaku Koenkai Koen Rombunshu, p.831 - 832, 2005/11
Kawasaki, Nobuchika; Takasho, Hideki*; kasahara, Naoto
5.1
5.20, 0 Pages, 2004/10
None
Takasho, Hideki*; Kasahara, Naoto; Kazuteru Garatani/CRC Solution*
JNC TN9400 2003-096, 76 Pages, 2003/12
JNC-TN9400-2003-096.pdf:4.05MB
Commercialized fast reactors, intend to adopt large scale heat exchangers, since they aim at capacity enlargement and reduction of the cooling loops from a demand of the economical efficiency. And, they have planned the adoption of the double-wall heat transfer tubes for reliable design against sodium coolant, which become straight type without tube welding. As the result, steam generators change to large double straight pipe types and the large-scale dished tubesheets are required from a balance with the pressure proof design. The establishment of method of structural analysis for the complicated and three-dimensional shape is required in order to realize the large-scale dished tubesheets. Conventional analysis models for tubesheets are equivalent solid plates with stress multipliers, which are difficult to be applied to dished tubesheets since their un-homogeneity. A large-scale three-dimensional analysis model is desirable to consider precious configurations around holes.. The iterative solver for efficiently calculating, when the large-scale analysis is carried out, was developed, and it was mounted to FINAS code. A dished tubesheet model for commercialized fast reactors was made in three-dimensional element which exceeded 1 million degrees of freedom. FINAS code with the iterative solver analyzed thermal transient stress under the manual trip condition. 20 step calculation was carried out within 72 hours on PC. As the result, it was confirmed that applicability of three dimensional analysis methods to dished tubesheets.
kasahara, Naoto; Ando, Masanori; *; Furuhashi, Ichiro*; Takasho, Hideki*
Proceedings of 2003 ASME Pressure Vessels and Piping Conference, 461, 119 Pages, 2003/00
None
Kasahara, Naoto; Takasho, Hideki*; Yacumpai, A.*
Nuclear Engineering and Design, 212(1-3), p.281 - 292, 2002/00
Times Cited Count：55 Percentile：94.44(Nuclear Science & Technology)None
Kasahara, Naoto; Yacumpai, A.*; Takasho, Hideki*
JNC TN9400 99-019, 34 Pages, 1999/02
At incomplete mixing area of high temperature and low temperature fluids near the surface of structures, temperature fluctuation of fluid gives thermal fatigue damage to wall structures. This thermohydraulic and thermomechanical coupled phenomenon is called thermal striping, which has so complex mechanism and sometimes causes crack initiation on the structural surfaces that rational evaluation methods are required for screening rules in design codes. In this study, frequency response characteristics of structures and its mechanism were investigated by both numerical and theoretical methods. Based on above investigation, a structural response diagram was derived, which can predict stress amplitude of structures from temperature amplitude and frequency of fluids. Furthermore, this diagram was generalized to be the Non-dimensional structural response diagram by introducing non-dimensional parameters such as Biot number, non-dimensional frequency, and non-dimensional stress. The use of the Non-dimensional structural response diagram appears to evaluate thermal stress caused by thermal striping, rapidly without structural analysis, and rationally with considering attenuation by non-stationary heat transfer and thermal unloading. This diagram can also give such useful information as sensitive frequency range to adjust coupled thermohydraulic and thermomechanical analysis models taking account of four kinds of attenuation factors: turbulent mixing, molecular diffusion, non-stationaly heat transfer, and thermal unloading.
Kasahara, Naoto; Takasho, Hideki*
Transactions of 15th International Conference on Structural Mechanics in Reactor Technology (SMiRT-15), 0 Pages, 1999/00
None
Ando, Masanori; Takasho, Hideki*; Kawasaki, Nobuchika; Kasahara, Naoto
no journal, ,
no abstracts in English
Ando, Masanori; Kanasaki, Hiroshi*; Date, Shingo*; Kikuchi, Koichi*; Sato, Kenichiro*; Takasho, Hideki*; Tsukimori, Kazuyuki
no journal, ,
To assess the failure estimation methods, cyclic thermal loading tests of cylindrical models with thick part were performed. In the tests, crack initiation and propagation processes at stress concentration area were observed by replica method. Besides those, finite element analysis (FEA) was carried out to estimate the number of cycles to failure. The crack initiation life was in a good agreement with the FEA result by considering the short term compressive holding. Through these test and FEA results, fatigue and creep-fatigue life assessment methods of Mod.9Cr-1Mo steel including evaluation of cyclic thermal loading, short term compressive holding and failure criterion, were discussed.
