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Wakui, Takashi; Takagishi, Yoichi*; Futakawa, Masatoshi
Zairyo, 73(6), p.520 - 526, 2024/06
Cavitation damage is one of crucial issues to predict the structural endurability of the mercury targets for highly intensive pulsed neutron sources. Based on the comparison with numerical simulation on the pit shape and results of the basic test, the cavitation bubble collapsing was assumed to be resulted in the micro jet with the impact velocity of 160-200 m/s, imposing then impact pressure of 3-4 GPa at the input power simulating the operation condition in the mercury targets. It was statistically understandable that cavitation damage evolution was proportional to 4th power of the input power approximately, as taking the aggressivity of cavitation bubbles, the distribution of the maximum diameter of grown bubbles and the space of distribution of bubbles in the mercury into account.
Wakui, Takashi; Takagishi, Yoichi*; Futakawa, Masatoshi; Tanabe, Makoto*
Jikken Rikigaku, 23(2), p.168 - 174, 2023/06
Cavitation damage on the inner surface of the mercury target for the spallation neutron source occurs by proton bombarding in mercury. The prediction method of the cavitation damage using Monte Carlo simulations was suggested taking variability of the bubble core position and impact pressure distribution into account. The impact pressure distribution was estimated using the inverse analysis with Bayesian optimization was conducted with comparison between cavitation damage distribution obtained from experiment and the cumulative plastic strain distribution obtained from simulation. The average value and spread of maximum impact pressure estimated assuming the Gaussian distribution were 3.1 GPa and 1.2 
m, respectively. Simulation results reproduced experimental results and it can be said that this evaluation method is useful.
Futakawa, Masatoshi; Naoe, Takashi*; Kogawa, Hiroyuki; Date, Hidefumi*; Ikeda, Yujiro
JSME International Journal, Series A, 48(4), p.234 - 239, 2005/10
Mercury target will be installed at the material science and life facility in J-PARC, which will promote innovative science. The mercury target will be subjected to the pressure wave caused by proton bombarding in the mercury. The pressure wave propagation induces the cavitation in mercury that imposes localized impact damage on the target vessel. The impact erosion is a critical issue to decide the lifetime of target. An electromagnetic impact testing machine, MIMTM, was developed to reproduce the localized impact erosion damage and evaluate the damage formation. Additionally, droplet impact analyses were carried out to investigate the correlation between isolate pit profile and micro-jet velocity. We confirmed that the value of depth/radius was applicable to estimate micro-jet velocity, and the velocity at 560 W in MIMTM equivalent to 1MW proton beam injection was 300 m/s approximately.
Soyama, Hitoshi*; Futakawa, Masatoshi; Homma, Kana*
Journal of Nuclear Materials, 343(1-3), p.116 - 122, 2005/08
Times Cited Count：10 Percentile：55.66(Materials Science, Multidisciplinary)In order to estimate life time of the mercury target vessel of spallation neutron source which will be subjected to cavitation impacts, prediction methods of pitting damage induced by the cavitation impact were proposed. It is very important to estimate incubation time, in which plastic deformation occurs without mass loss, because the thickness of vessel is very thin. In the present paper, two estimation methods were proposed. One of them is estimatiion from erosion test of severely damaged specimen by plotting the mass loss as a function of exposure time to cavitation on the logarithmic scales. Another method is the observation method of plastic deformation pits on damaged surface at very early period in incubation stage.
Futakawa, Masatoshi; Naoe, Takashi; Kogawa, Hiroyuki; Tsai, C.-C.*; Ikeda, Yujiro
Journal of Nuclear Science and Technology, 40(11), p.895 - 904, 2003/11
Times Cited Count：52 Percentile：93.89(Nuclear Science & Technology)A liquid-mercury target system for the MW-scale target is being developed in the world. The pitting damage induced by pressure wave propagation gets to be one of critical issues to estimate the life of the target structure with mercury and to evaluate its structural integrity. The off-line test on the pitting damage at high cycles over 10 millions was carried out using a novel device, the MIMTM which drives electromagnetically to impose pulse pressure into the mercury. It was found that from the pitting damage data obtained by the MIMTM that the pitting damage can be characterized in two steps, an incubation period that can extend to more than 106 cycles in 316SS and 107 cycles in surface hardening treated one and steady state erosion where mass loss scales with the number of cycles to approximately the 1.27 power for mercury. The length of the incubation period is primarily a function of the material and the intensity of the pressure. This observation provides a simple model for estimating lifetime for different materials and beam power.
Futakawa, Masatoshi; Kogawa, Hiroyuki; Tsai, C.-C.*; Ishikura, Shuichi*; Ikeda, Yujiro
JAERI-Research 2003-005, 70 Pages, 2003/03
JAERI-Research-2003-005.pdf:12.08MB
A liquid-mercury target system for the MW-scale target is being developed in the world. The moment the proton beams bombard the target, stress waves will be imposed on the beam window and pressure waves will be generated in the mercury by the thermally shocked heat deposition. Provided that the negative pressure generates through its propagation in the mercury target and causes cavitation in the mercury, there is the possibility for the cavitation bubbles collapse to form pits on the interface between the mercury and the target vessel wall. In order to estimate the cavitation erosion damage due to pitting, two types of off-line tests were performed: Split Hopkinson Pressure Bar (SHPB), and Magnetic IMpact Testing Machine (MIMTM). The data on the pitting damage at the high cycle impacts up to 10 million were given by the MIMTM. As a result, it is confirmed that the mean depth erosion is predictable using a homologous line in the steady state with mass loss independently of testing machines and the incubation period is very dependent on materials and imposed pressures.
