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Plasticity correction on stress intensity factor evaluation for underclad cracks in reactor pressure vessels

Lu, K.; 勝山 仁哉; Li, Y.

Journal of Pressure Vessel Technology, 142(5), p.051501_1 - 051501_10, 2020/10

 被引用回数:2 パーセンタイル:21.37(Engineering, Mechanical)

Structural integrity assessment of reactor pressure vessels (RPVs) is essential for the safe operation of nuclear power plants. For RPVs in pressurized water reactors (PWRs), the assessment should be performed by considering neutron irradiation embrittlement and pressurized thermal shock (PTS) events. To assess the structural integrity of an RPV, a traditional method is usually employed by comparing fracture toughness of the RPV material with the stress intensity factor ($$K_{rm I}$$) of a crack postulated near the RPV inner surface. When an underclad crack (i.e., a crack beneath the cladding of an RPV) is postulated, $$K_{rm I}$$ of this crack can be increased owing to the plasticity effect of cladding. This is because the yield stress of cladding is lower than that of base metal and the cladding may yield earlier than base metal. In this paper, detailed three-dimensional (3D) finite element analyses (FEAs) were performed in consideration of the plasticity effect of cladding for underclad cracks postulated in Japanese RPVs. Based on the 3D FEA results, a plasticity correction method was proposed on $$K_{rm I}$$ calculations of underclad cracks. In addition, the effects of RPV geometries and loading conditions were investigated using the proposed plasticity correction method. Moreover, the applicability of the proposed method to the case which considers the hardening effect of materials after neutron irradiation was also investigated. All of these results indicate that the proposed plasticity correction method can be used for $$K_{rm I}$$ calculations of underclad cracks and is applicable to structural integrity assessment of Japanese RPVs containing underclad cracks.


Development of stress intensity factors for subsurface flaws in plates subjected to polynomial stress distributions

Lu, K.; 真野 晃宏; 勝山 仁哉; Li, Y.; 岩松 史則*

Journal of Pressure Vessel Technology, 140(3), p.031201_1 - 031201_11, 2018/06

 被引用回数:9 パーセンタイル:51.3(Engineering, Mechanical)

The stress intensity factor (SIF) solutions for subsurface flaws near the free surfaces of components, which are known to be important in engineering applications, have not been provided yet. Thus, in this paper, SIF solutions for subsurface flaws near the free surfaces in flat plates were numerically investigated based on finite element analyses. The flaws with aspect ratios a/l = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5, the normalized ratios a/d = 0.0, 0.1, 0.2, 0.4, 0.6 and 0.8, and d/t = 0.01 and 0.10 were taken into account, where a is the half flaw depth, l is the flaw length, d is the distance from the center of the subsurface flaw to the nearest free surface and t is the wall thickness. Fourth-order polynomial stress distribution in the thickness direction was considered. In addition, the developed SIF solutions were incorporated into a Japanese probabilistic fracture mechanics (PFM) code, and PFM analyses were performed for a Japanese reactor pressure vessel containing a subsurface flaw near the inner surface. The PFM analysis results indicate that the obtained SIF solutions are effective in engineering applications.


Plasticity correction on the stress intensity factor evaluation for underclad cracks under pressurized thermal shock events

Lu, K.; 勝山 仁哉; Li, Y.

Proceedings of 2016 ASME Pressure Vessels and Piping Conference (PVP 2016) (Internet), 8 Pages, 2016/07

When conducting structural integrity assessments for reactor pressure vessels (RPVs) under pressurized thermal shock (PTS) events, the stress intensity factor (SIF) is evaluated for an underclad crack which is postulated near the inner surface of RPVs. It is known that cladding made of the stainless steel is a ductile material which is overlay-welded on the inner surface of RPVs for corrosion protection. Therefore, the plasticity of cladding should be considered in the SIF evaluation for a postulated underclad crack. In our previous study, we performed three-dimensional (3D) elastic and elastic-plastic finite element analyses (FEAs) for underclad cracks during PTS transients and discussed the conservatism of a plasticity correction method prescribed in the French code. In this study, additional FEAs were performed to further investigate the plasticity correction on SIF evaluation for underclad cracks. Based on the 3D FEA results, a new plasticity correction method was proposed for Japanese RPVs subjected to PTS events. In addition, the applicability of the new method was verified by studying the effects of the RPV geometry, cladding thickness and several loading conditions. Finally, it is concluded that the newly proposed plasticity correction method can provide a conservative and more rational evaluation on SIFs of underclad cracks in Japanese RPVs.


Development of stress intensity factors for surface cracks with large aspect ratio in plates

Li, Y.; 長谷川 邦夫; 勝又 源七郎; 小坂部 和也*; 岡田 裕*

Journal of Pressure Vessel Technology, 137(5), p.051207_1 - 051207_8, 2015/10

 被引用回数:8 パーセンタイル:39.83(Engineering, Mechanical)



Fracture mechanics analysis including the butt joint geometry for the superconducting conductor conduit of the national centralized tokamak

高橋 弘行*; 工藤 祐介; 土屋 勝彦; 木津 要; 安藤 俊就*; 松川 誠; 玉井 広史; 三浦 幸俊

Fusion Engineering and Design, 81(8-14), p.1005 - 1011, 2006/02

 被引用回数:2 パーセンタイル:17.58(Nuclear Science & Technology)




柴田 勝之*; 鬼沢 邦雄; 鈴木 雅秀; Li, Y.*

日本機械学会M&M2005材料力学カンファレンス講演論文集, p.299 - 300, 2005/11



Development of Stress intensity factor coefficients database for a surface crack of an RPV considering the stress discontinuity between cladding and base metal

鬼沢 邦雄; 柴田 勝之*; 鈴木 雅秀

Proceedings of 2005 ASME/JSME Pressure Vessels and Piping Division Conference (PVP 2005), 12 Pages, 2005/07



Improvements to a probabilistic fracture mechanics code for evaluating the integrity of a RPV under transient loading

Li, Y.*; 加藤 大輔*; 柴田 勝之; 鬼沢 邦雄

International Journal of Pressure Vessels and Piping, 78(4), p.271 - 282, 2001/04

 被引用回数:5 パーセンタイル:41.71(Engineering, Multidisciplinary)

原研では、破壊評価モデルや数値解析法に新規モデルに導入したPFMコードPASCAL(PFM Analysis of Structural Components in Aging LWR)の開発を進め、これまでに、ほぼコード開発を終えている。本コードには、半楕円亀裂進展評価,破壊基準,焼鈍効果等に新規モデル導入しているが、その他、モンテカルロ解析法やクラッド部の応力拡大係数解析法にも新規の解析技法を開発し導入している。本論文は、解析の信頼性向上と効率化のため、数値解析法における新規モデルや改良点等をまとめたものである。本論文では、以下の項目について紹介している。(1)無限長亀裂の新規応力拡大係数式の作成と導入。(2)クラッド部熱応力による不連続部の応力拡大解析モデルの作成と導入。(3)層別モンテカルロ法における最適層分割及びサンプリング法の開発と導入。(4)その他: 乱数発生法,偏差再計算法等。


Fracture toughness of a fine-grained nuclear graphite by means of various methods

衛藤 基邦; 石山 新太郎; 西山 裕孝; 奥 達雄*; T.D.Burchell*

Int. Symp. on Carbon New Processing and New Applications; Extended Abstracts,Vol. 1, p.170 - 173, 1990/11



Effect of stress ratio on crack extension rate of fine-grained isotropic nuclear graphite

石山 新太郎; 衛藤 基邦; 奥 達雄

Journal of Nuclear Science and Technology, 24(9), p.719 - 723, 1987/09

 被引用回数:5 パーセンタイル:51(Nuclear Science & Technology)

微粒等方性黒鉛IG-11のき裂進展速度da/dNに及ぼす荷重負荷モードの効果(応力比効果)を調べた。試験片の形状をダブルカニチレバービーム(DCB)型とし、繰り返し荷重は251N/secの荷重速度で荷重容量1500Nのサーボ式疲労試験機を用いて負荷した。荷重負荷モードは応力拡大係数範囲の最小値Kminと最大値Kmaxの比R(=Kmin/Kmax)を0から0.8の範囲の5段階で変化させた。実験結果から、き裂進展速度と応力拡大係数範囲の間に次式が得られた。da/dN=C(?K-?Kth)$$^{n}$$ ここでC,nは定数、応力拡大係数範囲?K=Kmax-Kminで、?Kthはしきい値である。?KthはR値に依存し、R=0の応力拡大係数範囲を?Kthoとすると?Kth/?Ktho=(1-R)$$^{A}$$ となる。ここでAは定数でIG-11黒鉛では0.89となった。


Stress Intensity Factor Analyses of Surface Cracks in Three-Dimensional Structures

宮崎 則幸*; 柴田 勝之; 渡辺 隆之*; 田形 一則*

JAERI-M 83-189, 44 Pages, 1983/11





近藤 達男; 中島 甫; 新藤 雅美; 鈴木 富男; 木内 清; 菊地 正彦; 辻 宏和; 塚田 隆; 鈴木 正彦*; 高橋 秀明*; et al.

JAERI-M 82-062, 23 Pages, 1982/06




Fatigue behavior of pipes containing multiple flaws in inner surface

柴田 勝之; 横山 憲夫; 大場 敏弘; 川村 隆一; 宮園 昭八郎

Nucl.Eng.Des., 74(2), p.199 - 213, 1982/00

 被引用回数:1 パーセンタイル:22.65(Nuclear Science & Technology)


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