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Journal Articles

Pulsed pressure induced cavitation erosion in mercury narrow channel under flowing conditions

Naoe, Takashi; Kogawa, Hiroyuki; Tanaka, Nobuatsu*; Futakawa, Masatoshi

Advanced Experimental Mechanics, 4, p.17 - 21, 2019/08

We have introduced the following two techniques to mitigate the pressure wave-induced cavitation damage in the mercury target. One is the gas microbubble injection into the flowing mercury, and the other is the double-walled structure with a narrow gap channel at the proton beam entrance portion of the mercury vessel. The latter is expected to mitigate the cavitation damage due to the high-speed liquid flow ($$sim$$ 4 m/s) and the narrow gap boundary (2 mm). To quantitatively investigate the effect of double-walled structure on cavitation damage, cavitation damage tests were conducted by parametrically changing mercury flow velocity and gap width of the channel wall. The results showed that the damage evaluated as a surface roughness was reduced by increasing the flow velocity. By contrast, the effect of gap width on cavitation damage was hardly observed under flowing conditions.

Journal Articles

Evaluation growing and collapsing behaviors of cavitation bubbles under flowing condition

Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa*; Tanaka, Nobuatsu*; Futakawa, Masatoshi

Advanced Experimental Mechanics, 4, p.33 - 37, 2019/08

A mercury enclosure vessel made of stainless steel is used as a spallation target in the pulsed spallation neutron source at J-PARC. It is severely damaged by the cavitation induced with pressure waves in association with the pulsed proton beam injection. A double-walled structure with a narrow mercury channel was adopted in the front end of the target vessel to reduce the cavitation damage. It has been experimentally demonstrated that the cavitation damage could be mitigated in the narrow channel but its mechanism has been unclarified yet. In this study, we investigated the cavitation from growing to collapsing through visualizing the spark-induced cavitation bubbles under flow field using a high-speed video camera. Furthermore, we measured the wall vibration due to the cavitation bubble collapse with changing flow velocity parametrically. It was found that the microjet collided perpendicular to the wall in the stagnant flow condition while it collided with an inclined angle from the perpendicular direction, suggesting that the collision pressure on the wall was reduced by flowing.

Journal Articles

Development on high-power spallation neutron sources with liquid metals

Futakawa, Masatoshi

Proceedings of 13th International Symposium on Advanced Science and Technology in Experimental Mechanics (13th ISEM'18) (USB Flash Drive), 6 Pages, 2018/10

Issues on the engineering technologies relating to high-power spallation neutron sources with liquid metals are introduced. The present status on research activities and results was reviewed.

Journal Articles

Effect of welding on gigacycle fatigue strength of austenitic stainless steels

Naoe, Takashi; Wakui, Takashi; Kogawa, Hiroyuki; Wakai, Eiichi; Haga, Katsuhiro; Takada, Hiroshi

Advanced Experimental Mechanics, 3, p.123 - 128, 2018/08

A mercury target vessel, composed of SUS316L, is used for the pulsed neutron source and is assembled via TIG welding. While in operation, the target vessel suffers ca. 10$$^9$$ loading cycles with a high strain rate of ca. 50 s$$^{-1}$$ because of the proton-beam-induced pressure waves in mercury. The gigacycle fatigue strength for solution annealed SUS316L stainless steels and its welded specimens were investigated through ultrasonic fatigue tests. The experimental results showed that an obvious fatigue limit was not observed at fewer than 10$$^9$$ cycles for the base metal. In the case of no weld defects observed via penetration tests, the fatigue strength of the removed-weld-bead specimen, in which the weld lines were arranged at the center of the specimen, appeared to be slightly higher than that of the base metal. By contrast, as-welded specimens with the weld bead intact showed apparent degradation of the fatigue strength owing to the stress concentration around the weld toe.

Journal Articles

Changes of dislocation density and dislocation arrangement during tensile deformation in lath martensitic steels

Harjo, S.; Kawasaki, Takuro; Morooka, Satoshi

Advanced Experimental Mechanics, 2, p.112 - 117, 2017/10

Journal Articles

Comparison of residual stress distributions of similar and dissimilar thick butt-weld plates

Suzuki, Hiroshi; Katsuyama, Jinya; Morii, Yukio*

Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM '11) (CD-ROM), 9 Pages, 2011/09

Residual stress distributions of 35 mm thick dissimilar butt-weld between A533B ferritic steel and Type 304 austenitic stainless steel (304SS) with Ni alloy welds and similar metal butt-weld of 304SS were measured using neutron diffraction. Effects of differences in thermal expansion coefficients and material strengths on the weld residual stress distributions are discussed by comparison of the residual stress distributions between the similar and dissimilar metal butt-welds. Residual stresses in the similar metal butt-weld exhibited typical distributions of a thick butt-weld and they were distributed symmetrically on either side of the weld line. Meanwhile, asymmetric residual stress distributions were observed near the root region of the dissimilar metal butt-weld, which was caused by differences in thermal expansion coefficients (CTEs) and yield strengths between parent and weld metals. Transverse residual stress distribution of the dissimilar metal butt-weld was similar to that of the similar butt-weld, since effects of differences in CTEs are negligible. Magnitude of the transverse residual stress near the root region depended on the yield strengths of each metal. The normal and longitudinal residual stresses in the dissimilar metal butt-weld distributed asymmetrically on either side of weld line due to the effects of differences in CTEs.

Journal Articles

Study of residual stress for c/c composite by neutron scattering

Baba, Shinichi; Ishihara, Masahiro; Minakawa, Nobuaki; Suzuki, Junichi

Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2003 (ATEM '03) (CD-ROM), 4 Pages, 2003/09

The aim of the present paper is to clarify the residual stress occuring in the c/c composite to improve the manufacturing process. The residual stress was measured by a neutron diffraction method using the RESA in the JRR-3M of JAERI in this study. As a results of the residual stress measurment, it was found that the residual stress of the ring type c/c composite is the comporessive stress, and the macroscopic residual strain/stress is absorbed mainly microstructural change such as pore shape change.

Journal Articles

Mechanical property evaluation method for graphite materials by ultrasonic wave propagation in porous body

Shibata, Taiju; Ishihara, Masahiro

Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2003 (ATEM '03) (CD-ROM), 5 Pages, 2003/09

no abstracts in English

Journal Articles

Effects of superplastic deformation on dynamic hardness and young's modulus of 3Y-TZP

Shibata, Taiju; Ishihara, Masahiro; Takahashi, Tsuneo*; Motohashi, Yoshinobu*

Proceedings of Asian Pacific Conference on Fracture and Strength '01(APCFS '01) and International Conference on Advanced Technology in Experimental Mechanics '01 (ATEM '01), p.894 - 898, 2001/00

no abstracts in English

Journal Articles

Probabilistic distribution of tensile strength of nuclear grade graphite on the basis of mesoscopic microstructure

Ishihara, Masahiro; Takahashi, Tsuneo*; Hanawa, Satoshi

Proceedings of Asian Pacific Conference on Fracture and Strength '01(APCFS '01) and International Conference on Advanced Technology in Experimental Mechanics '01 (ATEM '01), p.152 - 156, 2001/00

no abstracts in English

Journal Articles

Correlation between cleavage fracture toughness and charpy impact properties in the transition range of reactor pressure vessel steels

Onizawa, Kunio; Suzuki, Masahide

Proceedings of Asian Pacific Conference on Fracture and Strength '01(APCFS '01) and International Conference on Advanced Technology in Experimental Mechanics '01 (ATEM '01), p.140 - 145, 2001/00

In the structural integrity assessment of reactor pressure vessel, fracture toughness values are estimated by assuming that the radiation effect on fracture toughness is equivalent to that on Charpy properties. Therefore, it is necessary to establish the correlation between both properties especially on irradiation embrittlement. In this paper, we present the fracture toughness data obtained by applying the master curve approach that was adopted recently in the ASTM test method. Materials used in this study are five ASTM A533B class 1 steels and one weld metal. Neutron irradiation for Charpy-size specimens as well as standard Charpy-v specimens was carried out at the Japan Materials Testing Reactor. The shifts of the reference temperature on fracture toughness due to neutron irradiation are evaluated. Correlation between the fracture toughness reference temperature and Charpy transition temperature is established. Based on the correlation, the optimum test temperature for fracture toughness testing and the method to determine a lower bound fracture toughness curve are discussed.

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