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Nakata, Toshiya; Tanigawa, Hiroyasu
Fusion Engineering and Design, 87(5-6), p.589 - 593, 2012/08
Times Cited Count：19 Percentile：79.52(Nuclear Science & Technology)In tensile and fatigue testing, the deformation behavior of local domains of tungsten inert gas (TIG) and electron beam (EB) welded joint specimens of F82H steel was evaluated by using digital image correlation. For the tensile test specimens, tensile strength declined in the TIG welded joint material and ductility declined in both the EB and TIG welded joint materials. Because axial strain increased in the tempered heat-affected zone (HAZ) and led to fracture of the TIG welded joint material, strength was considered to deteriorate. In fatigue testing, the number of cycles to fracture for the welded joint material decreased to less than 40-50% that for the base metal. For both fracture metals, shear strain exhibited the largest value approximately between the fine-grained HAZ and the tempered HAZ, leading to fracture. Cavities and macrocracks formed in the fine-grained HAZ and tempered HAZ in the fracture metal cross section, and geometrical damage possibly resulted in deterioration of fatigue lifetime.
Nakata, Toshiya; Komazaki, Shinichi*; Kono, Yutaka*; Tanigawa, Hiroyasu
Metallurgical Journal, LXIII(Sp.), p.146 - 150, 2010/08
The small punch (SP) test is one method of small specimen test technology. We constructed a model for finite element analysis (FEA) using the Ramberg-Osgood equation to try to estimate tensile properties from the SP test. The results showed that the SP curve obtained from previous experiments could be reproduced by FEA to the point where the necking behavior of SP specimens became prominent. It was found that the relationship between the Mises equivalent stress at the point giving the largest equivalent plastic strain, and the total strain based on the Ramberg-Osgood equation, in the SP specimens, agreed well with the true stress-true strain curve plotted from tensile test measurements, and could thus be used to evaluate the 0.2% proof stress, tensile strength and uniform elongation.
Nakata, Toshiya; Tanigawa, Hiroyasu; Shiba, Kiyoyuki; Komazaki, Shinichi*; Fujiwara, Mikio*; Kono, Yutaka*; Koyama, Akira*
Nihon Kinzoku Gakkai-Shi, 71(2), p.239 - 243, 2007/02
Times Cited Count：4 Percentile：33.26(Metallurgy & Metallurgical Engineering)no abstracts in English
Nakata, Toshiya; Komazaki, Shinichi*; Nakajima, Motoki*; Kono, Yutaka*; Tanigawa, Hiroyasu; Shiba, Kiyoyuki; Koyama, Akira*
Nihon Kinzoku Gakkai-Shi, 70(8), p.642 - 645, 2006/08
Times Cited Count：4 Percentile：34.16(Metallurgy & Metallurgical Engineering)no abstracts in English
Nakata, Toshiya; Tanigawa, Hiroyasu; Komazaki, Shinichi*; Kono, Yutaka*
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Nakata, Toshiya; Tanigawa, Hiroyasu; Ando, Masami; Komazaki, Shinichi*; Kono, Yutaka*
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Ando, Masami; Tanigawa, Hiroyasu; Li, M.*; Nakata, Toshiya; Stoller, R.*; Kono, Yutaka*
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Irradiation creep of RAF/M steels has been recognized as one of the most important properties for engineering data due to the ITER test blanket structural design. The objective of this work is to examine an irradiation creep mechanism by using a microstructural observation in pressurized tubes of irradiated F82H and JLF-1. Irradiation was performed in the HFIR up to 5 dpa at 573 and 773 K. A small piece was cut from the center of each irradiated tube after diametral measurement. The microstructural examination with FIBed samples and replica films was carried out using a TEM. The creep strain for all steels at 573 and 773 K shows linear dependence on the applied hoop stress up to 
250 MPa and 100 MPa, respectively. As results of extraction replica samples irradiated at 573 K, finer spherical precipitations were observed in highest hoop stress level. The detailed discussion will be presented along with the results of microstructure observation for irradiated specimens.
Nakata, Toshiya; Tanigawa, Hiroyasu; Shiba, Kiyoyuki; Komazaki, Shinichi*; Kono, Yutaka*; Koyama, Akira*
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no abstracts in English
Nakata, Toshiya; Tanigawa, Hiroyasu; Ando, Masami; Komazaki, Shinichi*; Kono, Yutaka*
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Reduced activation ferritic/martensitic steels are the first candidate material for fusion reactor, and will be used as the structural materials of ITER test blanket modules (TBM). TBM will be assembled by welding various parts, it is important to be clearly mechanical properties of weldments to qualify TBM structure. In this paper, unirradiated mechanical properties of weldments, which is consisted of weld metal, heat affected zone (HAZ) and base metal region, obtained from TIG and EB welded F82H IEA-heat were evaluated by charpy impact and creep test. The creep tests were carried out at temperatures of 773-873 K and at stress levels of 150-260 MPa, with the specimens which include weld metal and HAZ region in the gage section. In these conditions, rupture time of weldments yield to about 100-1000 hours. The mechanism of these properties deterioration will be discussed based on the detailed analyses on microstructure changes.
Tanigawa, Hiroyasu; Nakata, Toshiya*; Kim, D.-H.*; Ando, Masami; Shiba, Kiyoyuki; Hirose, Takanori; Komazaki, Shinichi*; Kono, Yutaka*; Koyama, Akira*
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Reduced activation ferritic/martensitic steels (RAFMs) are recognized as the primary candidate structural materials for fusion blanket systems, as they have been developed based on massive industrial experience of ferritic/martensitic steel replacing Mo and Nb of high chromium heat resistant martensitic steels (such as modified 9Cr-1Mo) with W and Ta, respectively. F82H (Fe-8Cr-2W-V, Ta) is the RAFM which is designed with emphasis on high temperature property and weldablility. Fusion blanket system will be suffer from high temperature/high pressure of its coolant, heat flux of fusion plasma etc., which cause creep and fatigue load on blanket system. On the other hand, the current blanket system design have complicated structure to achieve its function, and require long weld to fabricate its structure. In this paper, unirradiated creep and fatigue properties of base metal and weldments of F82H will be reviewed, and critical issues for design will be discussed.
Nakata, Toshiya; Komazaki, Shinichi*; Kono, Yutaka*; Tanigawa, Hiroyasu
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The small punch (SP) test method has many. However, because of the complex deformation process, it is difficult to evaluate the stress and strain distributions in the SP test specimen. The ability to evaluate material's tensile properties using the SP test would be of great engineering significance. In this research, in order to establish a new procedure for evaluating tensile properties by the SP test, we attempted the stress and strain analyses of the SP test specimen using the finite element method. As the result, the relationship between the maximum von-Mises equivalent stress in the SP specimen and the strain calculated based on the Ramberg-Osgood's law was in good agreement with the true stress-true strain curve obtained from the actual tensile test within uniform elongation. These results indicate that the tensile properties such as yield strength, tensile strength and uniform elongation can be estimated by the SP test and the subsequent finite element analysis.
Nakata, Toshiya; Tanigawa, Hiroyasu
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Komazaki, Shinichi*; Chida, Shinji*; Nakata, Toshiya; Kono, Yutaka*; Tanigawa, Hiroyasu
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Nakata, Toshiya; Tanigawa, Hiroyasu
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Reduced activation ferritic/martenstic steel (RAMs) is expected to be used for structural material for the DEMO blanket module in Japan. It is essential to join members by welding for blanket module fabrication. In welding steel material, however, strength properties degrade greatly depending on the effects of heat during welding. Therefore, it is necessary to fully evaluate the strength properties of welds, to clarify their strength deterioration mechanism. But as the widths of welds are extremely narrow, it is hard to evaluate deformation behavior quantitatively by a conventional evaluation method. In this research we attempted to evaluate local deformation behavior accompanying fatigue damage using digital image correlation method about electron beam welding material made of RAMs. We clarified in this research that the strain distributions that arise during fatigue tests clearly differ by realizing the evaluation of deformation behavior in each local area of welds.
Nakata, Toshiya; Tanigawa, Hiroyasu; Kimura, Kazuhiro*
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Nakata, Toshiya; Tanigawa, Hiroyasu
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Kawamura, Seiko; Yokoo, Tetsuya*; Kambara, Wataru; Munakata, Koji*; Kajimoto, Ryoichi*; Nakatani, Takeshi; Kaneko, Koji; Kawakita, Yukinobu; Takata, Shinichi; Nakajima, Kenji; et al.
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In large user facilities such as neutron experimental facilities, sample environment (SE) is one of the most important factors to yield high-quality output. In the Materials and Life Science Experimental Facility (MLF) in J-PARC, various neutron experiments have been performed in wide range of scientific researches and industrial applications, and the number and variety of proposals will further increase after resuming operation of J-PARC. At the beginning stage, the SE team in MLF has discussed SE standardization, to save the cost and manpower, to make compatibility among instruments, and to increase the experimental efficiency by sharing the SE devices and techniques for operation. Recently we started preparation of "SE area" in the experimental hall, where we can do maintenance of equipments, pre-cooling of cryostats and so on. The SE team is now discussing future plan including user support system.
Nakata, Toshiya; Tanigawa, Hiroyasu
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Nozawa, Takashi; Nakata, Toshiya; Ozawa, Kazumi; Tanigawa, Hiroyasu
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Tanigawa, Hiroyasu*; Nakajima, Motoki*; Sakasegawa, Hideo; Ando, Masami*; Watanabe, Yoshiyuki*; Nozawa, Takashi*; Kato, Yutai*; Nakata, Toshiya*
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