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Journal Articles

Formulation of plastic strain distribution derived from long-distance travel of temperature distribution based on residual stress required for elastic shakedown behavior

Okajima, Satoshi

Mechanical Engineering Journal (Internet), 8(4), p.21-00080_1 - 21-00080_15, 2021/08

It was reported that the long distance travel of temperature distribution causes a new type of thermal ratcheting, even in the absence of primary stress. When the distance of temperature travel is moderate, the accumulation of the plastic strain due to this mechanism is finally saturated. We have found the strong relationship between hoop-membrane distributions of accumulated plastic strain and residual stress in this saturated case. Focusing on this relationship, we have aimed to predict the saturated distribution of the plastic strain based on the residual stress distribution that is required for the elastic shakedown behavior. In this paper, based on classical shell theory, we formulated the plastic strain distribution that brings uniform hoop-membrane stress in the given region. The formulated strain distribution was validated by the comparison with the accumulated plastic strain distribution obtained by finite element analyses using an elastic-perfectly plastic material.

Journal Articles

Development of the external pressure charts of 2 $$^{1}/_{4}$$Cr-1Mo and Mod.9Cr-1Mo steel at elevated temperature design

Ando, Masanori; Okajima, Satoshi; Imo, Kazumichi*

Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 7 Pages, 2019/07

For the required thickness estimation against buckling in the elevated temperature design, the external pressure chart for two kinds of ferritic steel, 2 $$^{1}/_{4}$$Cr-1Mo and Mod.9Cr-1Mo steel, was developed. On the basis of the guideline described in the ASME BPVC Section II, Part D, Mandatory Appendix 3 with mechanical and physical properties provided in the JSME fast reactor code, the external pressure charts for each material were constructed. As the result, three external pressure charts with digital values were proposed for elevated temperature design. And the rationalization effect from the current alternative using was evaluated by the sample problem. This proposal resolves the two issues. One is alternative use of inferior material strength chart over the 150$$^{circ}$$C. The other is the external pressure chart above 480$$^{circ}$$C for these ferritic steels are not available.

Journal Articles

Journal Articles

Study on path independency on shape of plastic strain distribution accumulated due to long distance travel of temperature distribution

Okajima, Satoshi

Dai-23-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (USB Flash Drive), 5 Pages, 2018/06

no abstracts in English

Journal Articles

Study on a unified criterion for preventing plastic strain accumulation due to long distance travel of temperature distribution

Okajima, Satoshi; Wakai, Takashi; Kawasaki, Nobuchika

Mechanical Engineering Journal (Internet), 4(5), p.16-00641_1 - 16-00641_11, 2017/10

Journal Articles

Study of the calculation method for the elastic follow-up coefficient by inelastic analysis

Watanabe, Sota*; Kubo, Koji*; Okajima, Satoshi; Wakai, Takashi

Nihon Kikai Gakkai M&M 2017 Zairyo Rikigaku Kanfarensu Koen Rombunshu (Internet), p.581 - 585, 2017/10

no abstracts in English

Journal Articles

Saturation behavior of thermal ratcheting strain due to long range travel of temperature distribution

Okajima, Satoshi; Wakai, Takashi

Nihon Kikai Gakkai 2017-Nendo Nenji Taikai Koen Rombunshu (DVD-ROM), 5 Pages, 2017/09

It was reported that the long distance travel of temperature distribution causes a new type of thermal ratcheting, even in the absence of primary stress. In this paper, based on the results of inelastic finite element analyses, we investigated saturation behavior of thermal ratcheting strain due to long range travel of temperature distribution. As a result, we revealed that the long distance travel of temperature distribution generates plastic strain distribution made maximum at the central part. Because of the shape of the generated strain distribution, the residual stress accumulates even at the central part of the region passed through the temperature distribution. In the case with excessive long traveling of temperature distribution, the region with plastic deformation extended to the surrounding region. Otherwise, sufficient magnitude of residual stress to cause shakedown behavior accumulated on entire region, and the accumulation of the plastic strain saturated.

Journal Articles

Introduction and development of reliability evaluation in the field of mechanical engineering; Introduction of partial safety factor method into metal loss assessment for pressure equipment

Okajima, Satoshi

Nihon Kikai Gakkai 2017-Nendo Nenji Taikai Koen Rombunshu (DVD-ROM), 3 Pages, 2017/09

Fitness-For-Service (FFS) assessment for the component with metal-loss is desired to reflect the effect of usual maintenance. Introduction of evaluation method based on reliability is one of the effective measures to achieve this. High Pressure Institute of Japan published HPIS Z 109TR:2016 "Metal loss assessment for pressure equipment based on reliability", which provides methods and technical backgrounds of metal loss assessment for pressure equipment based on reliability. This technical report provides evaluation method for simply evaluating reliability of the pressure equipment with metal loss based on the partial safety factor method. We present outline of the evaluation method based on the partial safety factor method.

Journal Articles

Development of simple estimation method for the influence of parameter uncertainty of probability distributions against evaluation result of probabilistic fracture mechanics

Okajima, Satoshi; Takaya, Shigeru; Asayama, Tai

Nihon Kikai Gakkai Rombunshu (Internet), 83(845), p.16-00434_1 - 16-00434_13, 2017/01

no abstracts in English

Journal Articles

A Screening method for prevention of ratcheting strain derived from movement of temperature distribution

Okajima, Satoshi; Wakai, Takashi; Ando, Masanori; Inoue, Yasuhiro*; Watanabe, Sota*

Journal of Pressure Vessel Technology, 138(5), p.051204_1 - 051204_6, 2016/10

 Times Cited Count:2 Percentile:18.02(Engineering, Mechanical)

Journal Articles

Study on unified criteria for preventing plastic strain accumulation due to thermal stress with long range travel

Okajima, Satoshi; Wakai, Takashi; Kawasaki, Nobuchika

Proceedings of International Conference on Asia-Pacific Conference on Fracture and Strength 2016 (APCFS 2016) (USB Flash Drive), p.269 - 270, 2016/09

Journal Articles

A Study on plastic strain accumulation caused by traveling of temperature distribution synchronizing with temperature rise

Okajima, Satoshi

Mechanical Engineering Journal (Internet), 3(3), p.15-00574_1 - 15-00574_10, 2016/06

Journal Articles

A Study on plastic strain accumulation caused by traveling of temperature distribution synchronizing with temperature rise

Okajima, Satoshi

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

Journal Articles

Void reactivity evaluation by modified conversion ratio measurements in LWR critical experiments

Yoshioka, Kenichi*; Kikuchi, Tsukasa*; Gunji, Satoshi*; Kumanomido, Hironori*; Mitsuhashi, Ishi*; Umano, Takuya*; Yamaoka, Mitsuaki*; Okajima, Shigeaki; Fukushima, Masahiro; Nagaya, Yasunobu; et al.

Journal of Nuclear Science and Technology, 52(2), p.282 - 293, 2015/02

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

We have developed a void reactivity evaluation method by using modified conversion ratio measurements in a light water reactor (LWR) critical lattice. Assembly-wise void reactivity is evaluated from the "finite neutron multiplication factor", $$k^ast$$, deduced from the modified conversion ratio of each fuel rod. The distributions of modified conversion ratio and $$k^ast$$ on a reduced-moderation LWR lattice, for which the improvement of negative void reactivity is a serious issue, were measured. Measured values were analyzed with a continuous-energy Monte Carlo method. The measurements and analyses agreed within the measurement uncertainty. The developed method is useful for validating the nuclear design methodology concerning void reactivity.

Journal Articles

Proposal of the screening method for prevention of the accumulation of the ratcheting strain derived from the movement of the temperature distribution

Okajima, Satoshi; Wakai, Takashi; Ando, Masanori; Inoue, Yasuhiro*; Watanabe, Sota*

Proceedings of 2014 ASME Pressure Vessels and Piping Conference (PVP 2014) (DVD-ROM), 8 Pages, 2014/07

Journal Articles

Development of structural codes for JSFR based on the system based code concept

Asayama, Tai; Wakai, Takashi; Ando, Masanori; Okajima, Satoshi; Nagae, Yuji; Takaya, Shigeru; Onizawa, Takashi; Tsukimori, Kazuyuki; Morishita, Masaki

Proceedings of 2014 ASME Pressure Vessels and Piping Conference (PVP 2014) (DVD-ROM), 6 Pages, 2014/07

This paper overviews the ongoing research and development as well as activities for codification of structural codes for the Japan Sodium Cooled Fast Reactor (JSFR). Not only the design and construction code which has been published and updated on a regular basis, codes on welding, fitness-for-service, leak-before-break evaluation as well as the guidelines for structural reliability evaluation are being developed. The basic strategy for the development is to fully take advantage of the favorable technical characteristics associated with sodium-cooled fast reactors; the codes will be developed based on the System Based Code concept. The above mentioned set of codes are planned to be published from the Japan Society of Mechanical Engineers in 2016.

Journal Articles

Probabilistic properties of measurement for thickness of pipe with metal loss

Kaida, Takuyo*; Ishizaki, Yoichi*; Okajima, Satoshi

Atsuryoku Gijutsu, 52(2), p.53 - 63, 2014/04

Probabilistic approach for Fitness-For-Service (FFS) assessment of pressure equipment in petroleum and petrochemical plant helps to quantify the safety margin and rationalize the assessment. As for local metal loss assessment, several studies have been made on reliability analysis of the damaged equipment by use of limit state function, denoted by deterministic FFS model in published standard. Stochastic properties of random variables are needed in the reliability analysis. Remaining thickness of the pressure equipment is one of the important variables in limit state function for metal loss assessment. The thickness readings on a prescribed grid, which characterize the remaining thickness and size of the region of metal loss, might be varied by each inspector. There has been, however, no studies on stochastic properties of thickness readings for the local metal loss assessment. In this study, the stochastic properties of thickness readings were investigated by analyzing of the results of Round-Robin test. The cause of variation of thickness readings was clarified for the purpose of either protection of failure by pressure or that of leakage. The results of investigation indicated that standard deviation of thickness readings in the region of metal loss was more than that of thickness away from metal loss. Finally, the reliability of pressure equipment with local metal loss was analyzed using stochastic properties.

Journal Articles

Investigation of probability characteristic about thinning speed in actual plants and application for reliability analysis

Kurihara, Tomoyuki*; Kaida, Takuyo*; Okajima, Satoshi

Atsuryoku Gijutsu, 52(2), p.64 - 71, 2014/04

In Fitness-For-Service (FFS) assessment of pressure equipment, high reliability is needed in petroleum and petrochemical plant. Future Corrosion Allowance (FCA) is one of the most important factors in the metal loss assessment of FFS because it decides predicted value of the thickness during service periods. For the evaluation of FCA, the accurate corrosion rate from actual thinning data is needed and it is necessary to make a consideration of their variability of the thinning phenomena. In this study, the measured thickness data of the oil piping in the actual plant are collected and statistically analyzed as corrosion rate data which are classified by the operation condition. By the analysis, the probabilistic properties of corrosion rate are clarified in this piping system. Especially it is cleared that the corrosion rate of the air injection part is higher than that of the no air injection part. And the reliabilities of the protection of the failure by pressure and their change are quantitatively evaluated from the probabilistic properties of corrosion rate. From this case study, the procedure of FCA evaluation of FFS assessment was established and it's clear that the statistical analysis by the feature of thinning phenomena is important for accurate evaluation of corrosion data.

Journal Articles

Development of constitutive models for fast reactor design

Tsukimori, Kazuyuki; Iwata, Koji*; Kawasaki, Nobuchika*; Okajima, Satoshi; Yada, Hiroki; Kasahara, Naoto*

Nuclear Engineering and Design, 269, p.23 - 32, 2014/04

 Times Cited Count:1 Percentile:10.7(Nuclear Science & Technology)

R&D to enable a practical fast breeder reactor plant is proceeding in Japan, which is called "FaCT" (Fast reactor Cycle Technology development). One of the key issues of R&D is to realize a reasonably compact reactor vessel by eliminating the wall protection equipment which is installed inside the vessel in order to reduce thermal loading in the conventional design. Most important concern is the amount of the inelastic strain of the vessel accumulated around the liquid sodium surface which moves upward and downward cyclically with start-up and shut-down. The aim of this study is to develop rational constitutive models that enable prediction of this kind of complex inelastic behaviors precisely and to prepare the design guide based on inelastic analysis. We developed a high accuracy plasticity model and a simplified plasticity model and valuated them by organized experiments.

Journal Articles

Intra-pellet neutron flux distribution measurements in LWR critical lattices

Yoshioka, Kenichi*; Kikuchi, Tsukasa*; Gunji, Satoshi*; Kumanomido, Hironori*; Mitsuhashi, Ishi*; Umano, Takuya*; Yamaoka, Mitsuaki*; Okajima, Shigeaki; Fukushima, Masahiro; Nagaya, Yasunobu; et al.

Journal of Nuclear Science and Technology, 50(6), p.606 - 614, 2013/06

 Times Cited Count:1 Percentile:12.53(Nuclear Science & Technology)

We have developed an intra-pellet neutron flux and conversion ratio distribution measurement method. A foil activation method with special foils was used for the neutron flux distribution measurement. A $$gamma$$-ray spectrum analysis method with special collimators was used for the conversion ratio distribution measurement. Using the developed methods, intra-pellet neutron flux distributions and conversion ratio distributions were measured in critical experiments on a reduced-moderation LWR. Measured values were analyzed with a deterministic method and a Monte Carlo method. The neutron flux distribution measurements and analyses agreed within the range of 1% to 2%. The conversion ratio distribution measurements and analyses were consistent with each other. We found that the measurement methods are useful for the validation of neutron behavior in a fuel pellet, which is known as micro reactor physics.

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