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-FeSuzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito; Mori, Hideki*
Journal of Applied Physics, 135(7), p.075102_1 - 075102_7, 2024/02
Times Cited Count：0 Percentile：0.00Fracture of body centred cubic (bcc) metals and alloys below the ductile-to-brittle transition temperature is brittle. This is theoretically explained by the notion that the critical stress intensity factor of a given crack front for brittle fracture is smaller than that for plasticdeformation; hence, brittle fracture is chosen over plastic deformation. Although this view is true from a macroscopic point of view, such brittle fracture is always accompanied by small-scale plastic deformation in the vicinity of the crack tip, i.e. crack tip plasticity. This short paper investigates the origin of this plasticity using atomistic modeling with a recently developed machine-learning interatomic potential of -Fe. The computational results identified the precursor of crack tip plasticity, i.e. the group of activated atoms dynamically nucleated by fast crack propagation.
Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Keikinzoku, 73(11), p.530 - 536, 2023/11
In Al-Zn-Mg alloys, suppression of hydrogen embrittlement is necessary to improve their strength. In this study, the distribution of stress, strain, and hydrogen concentration in the actual fracture region was investigated using the crystal plasticity finite element method and hydrogen diffusion analysis based on a model derived from three-dimensional polycrystalline microstructural data obtained by X-ray CT. In addition, the distributions of stress, strain, and hydrogen concentration were compared with the actual crack initiation behavior by combining in-situ observation of tensile tests using X-ray CT and simulation. The results show that stress loading perpendicular to the grain boundary due to crystal plasticity dominates grain boundary crack initiation. It was also found that internal hydrogen accumulation due to crystal plasticity has little effect on crack initiation.
Ao, N.*; Zhang, H.*; Xu, H. H.*; Wu, S. C.*; Liu, D.*; Xu, P. G.; Su, Y. H.; Kang, Q. H.*; Kang, G. Z.*
Engineering Fracture Mechanics, 281, p.109166_1 - 109166_14, 2023/03
Times Cited Count：5 Percentile：89.51(Mechanics)Nara, Yoshitaka*; Kato, Masaji*; Sato, Tsutomu*; Kono, Masanori*; Sato, Toshinori
Journal of MMIJ, 138(4), p.44 - 50, 2022/04
It is important to understand the long-term migration of radionuclides when considering rock engineering projects such as the geological disposal of radioactive waste. The network of fractures and pores in a rock mass plays a major role in fluid migration as it provides a pathway for fluid flow. The geometry of a network can change due to fracture sealing by some fine-grained materials over long-term periods. In the present study, we use a macro-fractured granite sample to investigate the change of permeability that occurs under the flow of water that includes two different amounts of clay. Findings showed that clay accumulated in a fracture and that the permeability (hydraulic conductivity) of the granite sample decreased over time, which was greater in for the higher clay content. We concluded that the accumulation of clay minerals in the fracture decreased the permeability of the rock. Furthermore, we consider that the filling and closure of fractures in rock is possible under the flow of groundwater that includes clay minerals.
Machida, Hideo*; Arakawa, Manabu*; Wakai, Takashi
Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05
This paper describes the effect of local plastic component on J-integral and crack opening displacement (COD) evaluation of a circumferential penetrated crack, applicable to the leak before break (LBB) assessment for sodium cooled fast reactor (SFR) components. J-integral COD evaluation methods are generally formulated as a summation of elastic and plastic components, and so far many evaluation formulae based on these two components have been proposed. However, strictly, the plastic component consists of local plastic and fully plastic components. Many of the conventional evaluation methods often consider only the fully plastic component as the plastic component. The reason for this is that the effect of the local plastic component is much smaller than that of the fully plastic component excluding materials with extremely small work hardening. In contrast, for materials with high yield stress and small work hardening, such as modified 9Cr-1Mo steel which is one of the candidate materials for SFR piping, the effect of the local plastic component on J-integral and COD cannot be ignored. Therefore, the authors propose formulae taking the effect of local plastic component on J-integral and COD into account, based on finite element analysis (FEA) results, so that it is easy to apply to crack evaluation. The formulae will be employed in the guidelines on LBB assessment for SFR components published from Japan Society of Mechanical Engineers (JSME).
Xiong, Z.*; Naoe, Takashi; Futakawa, Masatoshi
Metals, 9(4), p.412_1 - 412_11, 2019/04
Times Cited Count：8 Percentile：41.69(Materials Science, Multidisciplinary)The effect of surface defects on the very high cycle fatigue (VHCF) behavior were investigated on the solution annealed (SA) and cold-rolled (CW) 316L. Surface defects were artificially created using indentation. VHCF test was conducted using an ultrasonic fatigue method. The results showed that the fatigue crack initiation was independent of the indent with the applied range of depth in this research. Furthermore, the critical depth of the indent was evaluated based on an empirical formula. In the case of SA, the VHCF strength was not affected when the indent depth was less than 40 
m, which is consistent with the value obtained from the empirical formula. In the case of 20% CW, VHCF strength was not affected when the indent depth was less than 80 m. The results were much larger than the results obtained from the empirical formula and might have been caused by the plastic deformation, residual stress and probable deformation induced martensite transition around the indent.
Naoe, Takashi; Xiong, Z.*; Futakawa, Masatoshi
Journal of Nuclear Materials, 506, p.12 - 18, 2018/08
Times Cited Count：7 Percentile：57.22(Materials Science, Multidisciplinary)A mercury target for neutron source (made of 316L SS) suffers not only proton and neutron radiation damage, but also cyclic impact stress caused by pressure waves. In the previous study, we carried out an ultrasonic fatigue test to investigate the gigacycle fatigue strength of 316L SS, concluding that specimen surface temperature rose abruptly more than 300
C just before failure. In this study, to clarify the mechanism of the temperature rise, we measured temperature distribution with a thermography during the fatigue test. The experimental results showed that the temperature rose locally only at the crack tip and the peak position moved with the crack propagation. We also carried out a nonlinear structural analysis by LS-DYNA to estimate the temperature rise with strain energy of elements. The analytical result showed that the heat due to plastic deformation at the crack tip is dominant for the temperature rise rather than the friction between crack surface.
Yamaguchi, Yoshihito; Hasegawa, Kunio; Li, Y.
Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 6 Pages, 2018/07
Crack closure during fatigue crack growth is an important phenomenon for predicting fatigue crack growth amount. Much experimental data shows that fatigue cracks close at not only negative loads but also positive loads during a constant amplitude loading cycle. The Appendix A-4300 in the ASME Code Section XI provides two equations of fatigue crack growth rates expressed by stress intensity factor range for ferritic steels under negative stress ratio. One is the equation taking into account crack closure and the other does not consider the crack closure. The boundary of crack closure is classified by the magnitude of applied stress intensity factor range. The objective of this paper is to investigate the influence of the magnitude of stress intensity factor range on crack closure. Fatigue tests have been performed on ferritic steel in air environment at room and high temperatures. Crack closures were obtained as a parameter of stress ratio. It was found that crack closure occurs more small applied stress intensity factor range than the definition given by the Appendix A-4300.
Yamaguchi, Yoshihito; Katsuyama, Jinya; Li, Y.
Yosetsu Kozo Shimpojiumu 2017 Koen Rombunshu, p.21 - 27, 2017/12
no abstracts in English
Pokor, C.*; Herbelin, A.*; Couvant, T.*; Kaji, Yoshiyuki
NEA/NSC/R(2016)5 (Internet), p.317 - 360, 2017/05
In aged BWR plants, certain locations in the mid-plane of the core shroud experience fluence levels at which the materials become susceptible to irradiation assisted stress corrosion cracking (IASCC). BWRVIP (Boiling Water Reactor Vessel Internals Program) has developed crack growth disposition methodologies for evaluating intergranular stress corrosion cracking (IGSCC) in the internal components of BWRs and the Japan Nuclear Energy Safety organization (JNES) has been conducting a project related to IASCC crack growth rate data as a part of safety research and development study for the aging management and maintenance of the nuclear power plants. Although many investigators proposed prediction models for SCC and IASCC growth rates for austenitic stainless steels and Ni alloys, even more improvements of models are necessary as compared with the detailed experimental results, because these models are still preliminary models.
Ebihara, Kenichi; Kaburaki, Hideo; Itakura, Mitsuhiro
"Hagane No Kikaiteki Tokusei Ni Oyobosu Suiso No Koka To Sono Hyoka" Shimpojium Yokoshu (USB Flash Drive), 6 Pages, 2014/09
Since hydrogen(H) embrittlement is one factor causing degradation and/or fracture of steel, understanding its mechanism is required. The grain-boundary(GB) decohesion due to segregation of H is considered to cause the delayed fracture of high strength steels and the cold cracking in welding. In the model based on GB decohesion, information of strength of GBs estimated in the atomic scale is used for the estimation of strength or crack propagation in the macroscopic scale. However the modeling between the atomic and the macroscopic scales is not clear. In particular, the validity of the model using the elastic continuum around nano-cracks for stress concentration at the crack tip is not clear. Thus, we examined the difference of the stress distribution around the nano-crack which was estimated by molecular dynamics and by a continuum calculation. As a result, the discrepancy became remarkable at high strain. The stress concentration was not simulated by the elastic continuum model.
Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi
Nihon Kikai Gakkai M&M 2005 Zairyo Rikigaku Kanfarensu Koen Rombunshu, p.175 - 176, 2005/12
From results of analysis of plastic deformation behavior at SCC crack tip by EBSP method, the conclusions was obtained as follows: (1)Regarding to basic data for quantitative evaluation of plastic deformation behavior at SCC crack tip, we obtained relationship between plastic deformation and misorientation of grain using SSRT result for SUS316L stainless steel in high temperature water and local plastic strain was able to estimate using this relationship. (2)From experimental results of plastic strain at SCC crack and ductile crack tips using relationship between misorientation and plastic deformation, plastic strain near ductile crack tip was larger than that at SCC crack tip. Plastic deformation region was, however, corresponded to region of about one grain at crack tip for both SCC and ductile cracks.
Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Hayakawa, Masao*; Nagashima, Nobuo*; Matsuoka, Saburo*
JAERI-Research 2005-029, 156 Pages, 2005/09
JAERI-Research-2005-029.pdf:57.24MB
This report describes a result of the research conducted under contract with JNES that was concerned with a multi-scale analysis of plastic deformation behavior at the crack tip of SCC. The research was carried out to evaluate the validity of the SCC growth data acquired in the IGSCC project based on a mechanistic understanding of SCC. For the purpose, in this research, analyses of the plastic deformation behavior and microstructure around the crack tip were performed in a nano-order scale. The hardness measured in nano, meso and macro scales was employed as a common index of the strength, and the essential data necessary to understand the SCC propagation behavior were acquired and analyzed that are mainly a size of plastic deformation region and a microstructural information in the region, e.g. data of crystallografy, microscopic deformation and dislocations at the inside of grains and grain boundaries.
Kurihara, Ryoichi
JAERI-Tech 2004-052, 39 Pages, 2004/07
The problems in the thermal structural design of the plasma facing component such as the blanket first wall and the divertor plate which receives very high heat flux were examined in the design of the fusion power reactors. Compact high fusion power reactor must give high heat flux and high-speed neutron flux from the plasma to the first wall and the divertor plate. In this environmental situation, the micro cracks should be generated in material of the first wall. Structural integrity of the first wall would be very low during the operation of the reactor, if those micro-cracks grow in a crack having significant size by the fatigue or the creep. The crack penetration in the first wall can be a factor which threatens the safety of the fusion power reactor. This paper summarizes the problems on the structural integrity in the first wall made of the SiC/SiC composite material or the ferritic steel.
Onizawa, Kunio; Tsutsumi, Hideaki*; Suzuki, Masahide; Shibata, Katsuyuki; Ueno, Fumiyoshi; Kaji, Yoshiyuki; Tsukada, Takashi; Nakajima, Hajime*
JAERI-Tech 2003-073, 125 Pages, 2003/08
JAERI-Tech-2003-073.pdf:11.62MB
Concerning the cracks due to stress corrosion cracking (SCC) observed on the core shrouds of BWRs, a study was conducted on structural integrity evaluation based on crack growth analysis. The cracks investigated were those observed on the regions of lower ring and support ring of the core shroud at Kashiwazaki-Kariwa Nuclear Power Station (NPS) Unit-3, and that on the middle shell region of the core shroud at Fukushima Daiichi NPS Unit-4 of Tokyo Electric Power Company. It was confirmed through data analysis of past SCC growth rate experiments applicable to the condition of the ring regions that the SCC growth rate prescribed in the JSME rule was conservative. The analysis on the core shroud rigidity with a crack indicated that the rigidity reduction was small enough not to affect the dynamic seismic response for the regions studied. Through the comparison of the required area in a cracked section or the allowable crack length, and crack growth analysis results, it was confirmed that the integrity of the core shrouds would be maintained even 4 effective full power years later.
Li, Y.*; Kato, Daisuke*; Shibata, Katsuyuki; Onizawa, Kunio
Nihon Kikai Gakkai Rombunshu, A, 69(678), p.239 - 245, 2003/02
no abstracts in English
Nishi, Hiroshi; Eto, Motokuni; Tachibana, Katsumi; Koizumi, Koichi; Nakahira, Masataka; Takahashi, Hiroyuki*
Fusion Engineering and Design, 58-59, p.869 - 873, 2001/11
Times Cited Count：2 Percentile：19.60(Nuclear Science & Technology)no abstracts in English
Nishi, Hiroshi; Eto, Motokuni; Tachibana, Katsumi; Nakahira, Masataka
Transactions of 16th International Conference on Structural Mechanics in Reactor Technology (SMiRT-16) (CD-ROM), 8 Pages, 2001/08
Fatigue test of the weldments was performed to investigate their fatigue behavior and the effect of the incomplete penetrations on the fatigue strength. Fatigue crack propagation test of their weld metals was also carried out using CT specimen. By calculating stress intensity factors of the weldments contained the incomplete penetrations and cracks using FEM analysis, the fatigue crack propagation rates of weldments were evaluated and compared those of their weld metals. Fatigue life of the weldments was evaluated based on fracture mechanics to discuss the effect of incomplete penetrations on the fatigue strength. As the results, the incomplete penetration behaved as a crack and most of total fatigue life for the weldment was crack propagation life. The crack propagation rates of weldment were in accordance with those of the weld metals. The fatigue strength of the weldment was considerably lower than that of smoothed specimen. The incomplete penetrations affected greatly the fatigue strength of the weldments even if the depth of incomplete penetrations was small.
Kato, Daisuke*; Li, Y.*; Shibata, Katsuyuki; Onizawa, Kunio
Nihon Kikai Gakkai 2001-Nendo Nenji Taikai Koen Rombunshu, p.391 - 392, 2001/00
no abstracts in English
Shibata, Katsuyuki; Onizawa, Kunio; Kato, Daisuke*; Li, Y.*
Nihon Kikai Gakkai 2001-Nendo Nenji Taikai Koen Rombunshu, p.389 - 390, 2001/00
no abstracts in English
