In situ neutron diffraction analysis of microstructural evolution-dependent stress response in austenitic stainless steel under cyclic plastic deformation

Kumagai, Masayoshi*; Kuroda, Masatoshi*; Matsuno, Takashi*; Harjo, S.; Akita, Koichi*

Materials & Design, 221, p.110965_1 - 110965_8, 2022/09

https://doi.org/10.1016/j.matdes.2022.110965

A Trajectory generation method for mobile robot based on iterative extension-like process

Kawabata, Kuniaki

Artificial Life and Robotics, 21(4), p.500 - 509, 2016/12

https://doi.org/10.1007/s10015-016-0305-6

In this paper, we propose a trajectory generation method for mobile robot based on iterative extension-like process. Due to use mobile robots in the real world, trajectory generation must be done depending on the faced situation on each occasion. Proposed method enables online iterative trajectory extension process based on a low-order polynomial curve named as trajectory segment. The waypoints on the existing trajectory segment and a waypoint designated every fixed interval are the constraints to trigger the trajectory extension. For maintaining the smooth continuity of the trajectory, the velocity state must be sustained at the connecting point. Resultantly, the trajectory segments are organized into a single smooth trajectory.

Finite element analysis on the application of Mini-C(T) test specimens for fracture toughness evaluation

Takamizawa, Hisashi; Tobita, Toru; Otsu, Takuyo; Katsuyama, Jinya; Nishiyama, Yutaka; Onizawa, Kunio

Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07

http://doi.org/10.1115/PVP2015-45412

Fracture toughness evaluation by the Master Curve method using miniature compact tension (Mini-C(T)) specimens taken from the broken halves of surveillance Charpy specimens has been proposed. We performed finite element analysis (FEA) to examine the difference in constraint effect of the crack tip for the different size C(T) and precracked Charpy v-notch specimens. The constraint effect for Mini-C(T) specimens in terms of the T-stress and Q-parameter was similar to the larger C(T) specimens. To optimize the fatigue precracking conditions for the Mini-C(T) specimen fabrication, plastic zone distribution analysis was performed. We confirmed the fatigue precrack length and the availability of the mitigated crack shape for Mini-C(T). We also obtained the fracture toughness data for different sizes specimen. It was shown that To obtained from the Mini-C(T) specimens is in reasonably good agreement with that from others. We compared the fracture toughness data with T41J based fracture toughness curves proposed in recent study. All of the data were well enveloped by the proposed lower bound curve.

Development of vortex model with realistic axial velocity distribution

Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki

Nihon Kikai Gakkai Rombunshu (Internet), 80(818), p.FE0299_1 - FE0299_9, 2014/10

https://doi.org/10.1299/transjsme.2014fe0299

A vortex is considered as one of significant phenomena which may cause gas entrainment (GE) and/or vortex cavitation in sodium-cooled fast reactors. In this study, a new vortex model with realistic axial velocity distribution is proposed. As the verification, the new vortex model is applied to the evaluation of a simple vortex experiment, and shows good agreements with the experimental data in terms of the circumferential velocity distribution and the free surface shape. In addition, it is confirmed that the Burgers vortex model fails to calculate accurate velocity distribution with the assumption of uniform axial velocity. However, the calculation accuracy of the Burgers vortex model can be enhanced close to that of the new vortex model in consideration of the effective axial velocity which is calculated as the average value only in the vicinity of the vortex center.

Structural safety assessment of a tokamak-type fusion facility for a through crack to cause cooling water leakage and plasma disruption

Nakahira, Masataka

Journal of Nuclear Science and Technology, 41(2), p.226 - 234, 2004/02

https://doi.org/10.3327/jnst.41.226

A tokamak-type fusion machine is said to have inherent safety associated with plasma shutdown. A small leak of water can terminate the plasma safely and can cause a plasma disruption which will induce electromagnetic(EM) forces in the vacuum vessel (VV). From a radiological safety view point, the VV forms the physical barrier that encloses tritium and activated dust. If the VV can sustain an unstable fracture by EM forces from a through crack to cause the leak, the structural safety will be assured and the inherent safety will be demonstrated. Therefore, a systematic approach to assure the structural safety is developed. A new analytical model to evaluate the through crack and leak is proposed, with verification by experiment. Based on the analyses, the critical crack length to terminate plasma is evaluated as about 2 mm, and the critical crack length for unstable fracture is obtained as about 400 mm. It is therefore concluded that EM forces induced by small leak to terminate plasma will not cause the unstable fracture of VV, and then the inherent safety is demonstrated.

Impact behavior of mercury droplet

Date, Hidefumi*; Futakawa, Masatoshi; Ishikura, Shuichi*

Jikken Rikigaku, 2(2), p.103 - 108, 2002/06

https://doi.org/10.11395/jjsem2001.2.103

In order to examine the impact behavior of mercury, which is one of important key-issues in a facility for high intensity neutron sources, the falling and colliding profiles of mercury droplets were recorded by high-speed video recorder. The impact force was also measured using the strain gage glued on an elastic bar. The falling mercury droplet oscillated between a prolate spheroid and an oblate one, repeatedly. The regathering and jumping of mercury at the collision point on the impact face of the target were observed after impact because of the strong surface tension of mercury. The impact force of mercury droplet was in proportion to the impact velocities and the square root of the potential energy. Scince the non-dimensional duration time K that obtained experimentally is independent of the impact velocity and the size of the droplet, the mean applied stress due to the mercury droplet against the target is easily predictable by the equatiion using K value and the impact velocity is known.

Free surface shear layer instabilities on a high-speed liquid jet

Ito, Kazuhiro*; Tsuji, Yoshiyuki*; Nakamura, Hideo; Kukita, Yutaka*

Fusion Technology, 37(1), p.74 - 88, 2000/01

no abstracts in English

JAERI negative ion injectors

; Hanashima, Susumu

Nuclear Instruments and Methods in Physics Research A, 268, p.461 - 464, 1988/00

https://doi.org/10.1016/0168-9002(88)90556-6

no abstracts in English

Recent algorithms and computer programs for interpolation

;

Joho Shori, 17(5), p.417 - 425, 1976/05

http://ci.nii.ac.jp/naid/110002753299

no abstracts in English

Development of the surface tension model for the evaluation of vortex cavitation

Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki; Kawamura, Takumi*; Nakamine, Yoshiaki*

no journal, , 

The prevention of vortex cavitation is one of key factors in the safety design criteria for sodium-cooled fast reactors. Therefore, the authors have developed a CFD-based evaluation method to determine the occurrence of the vortex cavitation. In this paper, the accuracy of the evaluation method is enhanced by developing a surface tension model by which the cavity radius is calculated in consideration of radial pressure distribution, saturated vapor pressure and the pressure jump condition at an interface. As a basic validation of the developed surface tension model, numerical analyses of a simple experiment under various velocity and pressure conditions are performed. The evaluation results give qualitatively appropriate cavity radius which becomes larger with the higher liquid velocity and/or lower reference pressure. Therefore, the developed surface tension model is considered to be physically-appropriate.