Sano, Tomokazu*; Eimura, Takayuki*; Hirose, Akio*; Kawahito, Yosuke*; Katayama, Seiji*; Arakawa, Kazuto*; Masaki, Kiyotaka*; Shiro, Ayumi*; Shobu, Takahisa; Sano, Yuji*
Metals, 9(11), p.1192_1 - 1192_13, 2019/11
The purpose of the present study was to verify the effectiveness of dry laser peening (DryLP), which is the peening technique without a sacrificial overlay under atmospheric conditions using femtosecond laser pulses on the mechanical properties such as hardness, residual stress, and fatigue performance. After DryLP treatment of the laser-welded 2024 aluminum alloy, the softened weld metal recovered to the original hardness of base metal, while residual tensile stress in the weld metal and heat-affected zone changed to compressive stresses. The fatigue life almost doubled at a stress amplitude of 180 MPa and increased by a factor of more than 50 at 120 MPa. As a result, DryLP was found to be more effective for improving the fatigue performance of laser-welded aluminum specimens with welding defects at lower stress amplitudes.
Ishikura, Shuichi*; Shiga, Akio*; Futakawa, Masatoshi; Kogawa, Hiroyuki; Sato, Hiroshi; Haga, Katsuhiro; Ikeda, Yujiro
JAERI-Tech 2005-026, 65 Pages, 2005/03
Failure probability analysis was carried out to estimate the lifetime of the mercury target which will be installed into the JSNS (Japan spallation neutron source) in J-PARC (Japan Proton Accelerator Research Complex). The lifetime was estimated as taking loading condition and materials degradation into account. Considered loads imposed on the target vessel were the static stresses due to thermal expansion and static pre-pressure on He-gas and mercury and the dynamic stresses due to the thermally shocked pressure waves generated repeatedly at 25 Hz. Materials used in target vessel will be degraded by the fatigue, neutron and proton irradiation, mercury immersion and pitting damages, etc. The imposed stresses were evaluated through static and dynamic structural analyses. The material-degradations were deduced based on published experimental data. As results, it was quantitatively confirmed that the failure probability for the lifetime expected in the design is very much lower, 10 in the safety hull, meaning that it will be hardly failed during the design lifetime. On the other hand, the beam window of mercury vessel suffered with high-pressure waves exhibits the failure probability of 12%. It was concluded, therefore, that the leaked mercury from the failed area at the beam window is adequately kept in the space between the safety hull and the mercury vessel to detect mercury-leakage sensors.
Ishikura, Shuichi*; Kogawa, Hiroyuki; Futakawa, Masatoshi; Kaminaga, Masanori; Hino, Ryutaro; Saito, Masakatsu*
Nippon Genshiryoku Gakkai Wabun Rombunshi, 3(1), p.59 - 66, 2004/03
The development of a MW-class spallation neutron source facility is being carried out under the Japan Proton Accelerator Research Complex (J-PARC) Project promoted by JAERI and KEK. A mercury target working as the spallation neutron source will be subjected to pressure waves generated by rapid thermal expansion of mercury due to a pulsed proton beam injection. The pressure wave will impose dynamic stress on the vessel and deform the vessel, which would cause cavitation in mercury. To evaluate the effect of mercury micro jets, driven by cavitation bubble collapse, on the micro-pit formation, analyses on mercury sphere collision were carried out: single bubble dynamics and collision behavior on interface between liquid and solid, which take the nonlinearity due to shock wave in mercury and the strain rate dependency of yield stress in solid metal into account. Analytical results give a good explanation to understand relationship between the micro-pit formation and material properties: the pit size could decrease with increasing the yield strength of materials.
Nakagawa, Tatsuo*; Mihara, Yorichika*; Komurasaki, Kimiya*; Takahashi, Koji; Sakamoto, Keishi; Imai, Tsuyoshi
Journal of Spacecraft and Rockets, 41(1), p.151 - 153, 2004/02
A launching experiment of a microwave-boosted vehicle model was carried out using the 110GHz, 1MW gyrotoron and a propulsive inpulse to lift up the vehicle was measured. The rf power and pulse was 1MW and 0.175 0.8msec. The launching mechanism is as follows. Plasma is produced in the nozzle of the vehicle model when the rf beam is injected toward it. The plasma heated by the rf beam can produce a shock wave that gives a propulsive impulse to the vehicle. Maximum momentum coupling coefficient from the impulse to the vehicle is 395N/MW which is comparable to that of a laser boosted vehicle. The rf pulse was 0.175msec. The coupling coefficient is limitted by the gyrtron operation in pulse length and can increase if the pulse length is shorter than 0.175msec.
Ishikura, Shuichi*; Kogawa, Hiroyuki; Futakawa, Masatoshi; Kikuchi, Kenji; Haga, Katsuhiro; Kaminaga, Masanori; Hino, Ryutaro
JAERI-Tech 2003-093, 55 Pages, 2004/01
To estimate the structural integrity of the heavy liquid-metal (Hg) target used in a MW-class neutron scattering facility, static and dynamic stress behaviors due to the incident of a 1MW-pulsed proton beam were analyzed. In the analyses, two-type target containers with semi-cylindrical type and flat type window were used as analytical models of the structural analysis codes LS-DYNA. As a result, it is confirmed that the stress generated by dynamic thermal shock becomes the largest at the center of window, and the flat type window is more advantageous from the structural viewpoint than the semi-cylindrical type window. It was confirmed to erosion damage the target container by mercury's becoming negative pressure in the window and generating the cavitation by the experiment. Therefore, it has been understood that the point top of the window was in the compression stress field by the steady state thermal stress because of the evaluation from destroying the dynamic viewpoint for the crack in the generated pit and the pit point, and the crack did not progress.
Physical Review Letters, 92(1), p.015503_1 - 015503_4, 2004/01
Molecular dynamics simulations on a three dimensional defective Lennard-Jones solid containing a void are performed in order to investigate detailed properties of hot spot generation. In addition to the temperature, I monitor the number of energetically colliding particles per unit volume which characterizes the intensity of shock-enhanced chemistry. The quantity is found to saturate for nanoscale voids and to be maximized after voids have completely collapsed. It makes an apparent comparison to the temperature which requires much larger void for the enhancement and becomes maximum during the early stage of the collapse. It is also found that the average velocity and the temperature of ejected molecules inside a cubic void are enhanced during the collapse because of the focusing of momentum and energy towards the center line of a void.
Ishikura, Shuichi*; Kogawa, Hiroyuki; Futakawa, Masatoshi; Hino, Ryutaro; Date, Hidefumi*
Koon Gakkai-Shi, 28(6), p.329 - 335, 2002/11
The developments of the neutron scattering facilities are carried out under the high-intensity proton accelerator project promoted by JAERI and KEK. To estimate the structural integrity of the heavy liquid-metal (Hg) target used as a spallation neutron source in a MW-class neutron scattering facility, dynamic stress behavior due to the incident of a 1MW-pulsed proton beam were analyzed by using FEM code. Two-type target containers with semi-cylindrical type and flat-plate type window were used as models for analyses. As a result, it is confirmed that the stress (pressure wave) generated by dynamic thermal shock becomes the largest at the center of window, and the flat-plate type window is more advantageous from the structural viewpoint than the semi-cylindrical type window. It has been understood that the stress generated in the window by the pressure wave can be treated as the secondary stress.
Kogawa, Hiroyuki; Futakawa, Masatoshi; Ishikura, Shuichi*; Kikuchi, Kenji; Hino, Ryutaro; Eto, Motokuni
International Journal of Impact Engineering, 25(1), p.17 - 28, 2001/01
no abstracts in English
Kikuchi, Kenji; Futakawa, Masatoshi; Ishikura, Shuichi*; Kogawa, Hiroyuki
Nippon Kikai Gakkai Zairyo Rikigaku Bumon Koenkai (M&M'99) Koen Rombunshu, p.467 - 468, 1999/10
no abstracts in English
*; Kunugi, Tomoaki
Journal of Nuclear Materials, 258-263, p.618 - 621, 1998/00
no abstracts in English
*; Abe, Yutaka*; *; Yamano, N.; Sugimoto, Jun
JAERI-Research 94-041, 64 Pages, 1994/12
no abstracts in English