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論文

Closed-form stress intensity factor solutions for circumferential and axial surface cracks with large aspect ratios in pipes

東 喜三郎*; Li, Y.

Journal of Pressure Vessel Technology, 144(6), p.061303_1 - 061303_13, 2022/12

 被引用回数:0 パーセンタイル:0(Engineering, Mechanical)

In this paper, we investigate the influence of the stress intensity factor at the maximum point for a circumferential crack and an axial crack with a large aspect ratio in a cylinder. First, we obtained the influence coefficients Gi for the stress intensity factor at the surface point, the deepest point, and the maximum point by finite element analysis, and developed a series of closed-form Gi solutions. Then, we proposed methods for evaluating the stress intensity factor for a crack with a large aspect ratio in a manner that characterizes the influence of the solutions at the maximum point.

論文

Pilot study on seismic fragility evaluation for degraded austenitic stainless steel piping using the probabilistic fracture mechanics code PASCAL-SP

東 喜三郎*; 山口 義仁; Li, Y.

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 7 Pages, 2021/07

Seismic probabilistic risk assessment is a standard methodology to quantify the risk of earthquakes including beyond-design-basis levels. The quality of fragility analysis is one of the major factors that affect the results of seismic probabilistic risk assessments. A previous study revealed that component degradation could affect seismic fragility. In practice, inspection and maintenance programs are implemented to control an undesirable effect of the degradation such as stress corrosion cracking. However, the relation between seismic fragility of degraded component and inspection, maintenance, and mitigation models has not been thoroughly discussed so far. This study discussed the effect of inspection and maintenance on seismic fragility of austenitic stainless steel piping susceptible to stress corrosion cracking. Failure probability was calculated by using a probabilistic fracture mechanics code. The results indicated that the adverse effects of stress corrosion cracking on failure probability could be controlled at a relatively low level if inspection, maintenance, and mitigation measures were implemented properly.

論文

Closed-form stress intensity factor solutions for surface cracks with large aspect ratios in plates

東 喜三郎*; Li, Y.; Xu, S.*

Journal of Pressure Vessel Technology, 142(2), p.021207_1 - 021207_10, 2020/04

 被引用回数:1 パーセンタイル:8.25(Engineering, Mechanical)

Alloy 82/182/600, which is used in light-water reactors, is known to be susceptible to stress-corrosion cracking. The depth of some of these cracks may exceed the value of half-length on the surface. Although the stress intensity factor (SIF) for cracks plays an important role in predicting crack propagation and failure, Section XI of the ASME Boiler and Pressure Vessel Code does not provide SIF solutions for such deep cracks. In this study, closed-form SIF solutions for deep surface cracks in plates are discussed using an influence coefficient approach. The stress distribution at the crack location is represented by a fourth-degree-polynomial equation. Tables for influence coefficients obtained by finite element analysis in the previous studies are used for curve fitting. The closed-form solutions for the influence coefficients were developed at the surface point, the deepest point, and the maximum point of a crack with an aspect ratio a/c ranging from 1.0 to 8.0, where a is the crack depth and c is one-half of the crack length. The maximum point of a crack refers to the location on the crack front where the SIF reaches a maximum value.

論文

Failure bending moment of pipes containing multiple circumferential flaws with complex shape

Li, Y.; 東 喜三郎*; 長谷川 邦夫

International Journal of Pressure Vessels and Piping, 171, p.305 - 310, 2019/03

 被引用回数:3 パーセンタイル:29.95(Engineering, Multidisciplinary)

Flaws due to stress corrosion cracking have been detected in piping systems in nuclear power plants. Failure bending moment of a ductile pipe containing a circumferential flaw is predicted using the net-section stress approach according to ASME Code Section XI as a limit load criterion. However, in the current code, the failure bending moment can only be adopted for a pipe containing a single circumferential flaw with constant depth. In this study, a failure estimation method for pipes containing multiple circumferential flaws with complicated shapes was proposed. Furthermore, failure experiments were performed for stainless steel pipes containing two circular circumferential flaws. The failure bending moments obtained from the experiments were compared with the estimated results. Based on the experimental results, it was concluded that the proposed failure estimation method satisfactorily represents the failure behavior of the pipes and can be applied in engineering application.

論文

Closed-form stress intensity factor solutions for deep surface cracks in cylinders subjected to global bending

東 喜三郎*; Li, Y.; 長谷川 邦夫; Shim, D. J.*

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 7 Pages, 2017/07

Materials made of alloy 82/182/600 used in pressurized water reactors are known to be susceptible to primary water stress corrosion cracking. The depth, ${it a}$, of flaws due to primary water stress corrosion cracking can be larger than the half of crack length ${it c}$, which is referred to as cracks with large aspect ratios. The stress intensity factor solution for cracks plays an important role to predict crack propagation and failure. However, Section XI of the ASME Boiler and Pressure Vessel Code does not provide the solutions for cracks with large aspect ratios. This paper presents the stress intensity factor solutions for circumferential surface cracks with large aspect ratios in cylinders under global bending loads. Finite element solutions were used to fit closed-form equations with influence coefficients ${it G}$gb. The closed-form solutions for coefficient ${it G}$gb were developed at the deepest points and the surface points of the cracks with aspect ratios ranged from 1.0 to 8.0.

論文

Study on the relationship between interaction factors and stress intensity factor for elliptical flaws

東 喜三郎*; Li, Y.; 長谷川 邦夫

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 6 Pages, 2017/07

The interaction of multiple flaws in close proximity to one another may increase the stress intensity factor of the flaw in structures and components. This interaction effect is not distributed uniformly along the crack front. For instance, the strongest interaction is generally observed at the point closest to a neighboring flaw. For this reason, the closest point shows a higher value of the stress intensity factor than all other points in some cases, even if the original value at the point of the single flaw is relatively low. To clarify the condition when the closest point shows the maximum stress intensity factor, we investigated the interaction of two equal elliptical flaws in an infinite model subjected to remote tension loading. The stress intensity factor of the elliptical flaws was obtained be performing finite element analysis of a linear elastic solid. The results indicated that the interaction factors along the crack front can be expressed by a simple empirical formula. Finally, we show the relationship between geometrical features of the flaw and the stress intensity factor at the closest point.

論文

Closed-form stress intensity factor solutions for deep surface cracks in plates

東 喜三郎*; Li, Y.; 長谷川 邦夫; Xu, S.*

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 9 Pages, 2017/07

Materials made of alloy 82/182/600 used in light-water reactors are known to be susceptible to stress corrosion cracking. It is known that the depth ${it a}$ of some cracks due to primary water stress corrosion cracking is larger than the half of crack length ${it c}$. The stress intensity factor solution for cracks plays an important role to predict crack propagation and failure. However, Section XI of the ASME Boiler and Pressure Vessel Code does not provide the solutions for cracks with large aspect ratios. In this study, closed-form stress intensity factor influence coefficients for deep surface cracks in plates are discussed. The crack tip stress distribution was represented by a fourth degree polynomial equation. Influence coefficient tables obtained by using finite element analysis in previous studies were used for curve fitting. The closed-form solutions for the coefficient were developed at the surface points, the deepest points, and the maximum points of the cracks with aspect ratios ranged from 1.0 to 8.0.

論文

Interaction factors for two elliptical embedded cracks with a wide range of aspect ratios

東 喜三郎*; Li, Y.

AIMS Materials Science, 4(2), p.328 - 339, 2017/02

The value of stress intensity factor may be increased through the interaction of multiple cracks that are in close proximity to one another. We investigated the interaction factors of two equal elliptical cracks with a wide range of aspect ratios. Finite element analysis for a linear elastic solid was used to obtain the interaction factor for embedded cracks in an infinite model subjected to remote tension loading. Relationships between interaction factors and dimensionless distances between the cracks were discussed. The results demonstrated that the interaction factors depend on the crack aspect ratio, whose effect is related to the dimensionless distance. Thus, it is suggested that interaction factors can be reasonably characterized using different dimensionless distances depending on the aspect ratio. Finally, we provide a simple empirical formula for obtaining the interaction factors for embedded cracks.

論文

Stress intensity factor solutions for circumferential surface cracks with large aspect ratios in pipes subjected to global bending

東 喜三郎*; Li, Y.; 長谷川 邦夫; Shim, D. J.*

Proceedings of 2016 ASME Pressure Vessels and Piping Conference (PVP 2016) (Internet), 7 Pages, 2016/07

In some cracks attributed to primary water stress corrosion cracking, the crack depth a was greater than half-length of the crack 0.5$$ell$$, namely, cracks with large aspect ratio a/$$ell$$. This paper presents details of stress intensity factor solutions for circumferential surface cracks with large aspect ratios in piping system subjected to global bending. The stress intensity factor solutions for semi-elliptical surface cracks were obtained by finite element analyses with quadratic hexahedron elements. Solutions at the deepest and the surface points of the cracks with various aspect ratio (0.5 $$leq$$ a/$$ell$$ $$leq$$ 4.0), crack depth ratio (0.0 $$leq$$ a/t $$leq$$ 0.8) and pipe sizes (1/80 $$leq$$ t/R$$_{i}$$ $$leq$$ 1/2) were investigated, where t and R$$_{i}$$ are wall thickness and inner radius of pipe, respectively. Proposed stress intensity factor solutions for cracks with a/$$ell$$ = 0.5 are consistent with the values reported in the previous study. The solutions developed in this study are widely applicable to various engineering problems related to crack evaluation in piping systems.

論文

Characterization of interaction between elliptical subsurface flaws

東 喜三郎*; Li, Y.; 長谷川 邦夫

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

Multiple flaws are often observed in engineering structures and components. Since interaction between multiple flaws may lead to increase of the stress intensity factors, fitness-for-service codes provide combination rules to consider the effect. However, the criteria for flaw combination are not unified among the codes. In order to establish a reasonable combination rule, it is necessary to clarify what parameter is dominant to interaction. The interactions of stress intensity factors for two coplanar subsurface flaws in a plate were investigated. The plate was subjected to a remote tension acting normal to the flaw surface. The stress intensity factor solutions for the elliptical subsurface flaws with various shapes and distances were obtained from finite element analyses. It was concluded that distance and flaw area are important parameter to characterize interaction factor between two subsurface flaws.

論文

Evaluation of stress intensity factor interactions between adjacent flaws with large aspect ratios

東 喜三郎*; Li, Y.; 長谷川 邦夫

Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 5 Pages, 2015/07

供用期間中検査で検出された複数欠陥は、維持規格に規定されている合体基準に基づいて合体評価が行われる。この合体基準は欠陥深さを基にしたものである。しかし、最近その存在が明らかにされた高アスペクト比欠陥(長さの半分よりも深さが大きい欠陥)に対しては、この基準の適用性は明らかにされていない。本研究では、有限要素法を用いた数値解析により、膜応力に対する複数欠陥の応力拡大係数の相互作用を考察した。その結果、欠陥深さではなく、欠陥長さを基にした評価は、高アスペクト比欠陥を含めた欠陥に対する合体基準として適切であることが分かった。

口頭

Application of probabilistic fracture mechanics to seismic fragility analysis of piping systems

東 喜三郎*; 山口 義仁; 勝山 仁哉; Li, Y.

no journal, , 

本研究では、確率論的破壊力学解析コードPASCAL-SPを用いて、SCCや疲労等の経年事象を考慮して、長期に供用される炭素鋼及びオーステナイトステンレス鋼配管のフラジリティ評価手法を示し、代表的な解析条件及び代表的事例を検討した。

口頭

Failure bending moment for pipes containing multiple circumferential flaws with complicated shape

Li, Y.; 東 喜三郎*; 長谷川 邦夫

no journal, , 

Flaws due to stress corrosion cracking have been detected in stainless steel or nickel-based alloy dissimilar metal weld joints of piping systems in nuclear power plants. Generally, stainless steel and nickel-based alloy are ductile materials with high toughness, and the failure mode of flawed pipes made of ductile materials is expected to be net-section plastic collapse. Failure bending moment of a ductile pipe containing a circumferential flaw is predicted using the net-section stress approach according to ASME Code Section XI as a limit load criterion. However, in the current code, the failure bending moment can only be adopted for a pipe containing a single circumferential flaw with constant depth, although many flaws detected actually are multiple flaws, and the flaw shapes are generally complicated. In this study, a failure estimation method for pipes containing multiple circumferential flaws with complicated shapes was proposed. Furthermore, failure experiments were performed for 8-inch diameter Schedule 80 stainless steel pipes containing two circular circumferential flaws. The failure bending moments obtained from the experiments were compared with the estimated results. Based on the experimental results, it was concluded that the proposed failure estimation method satisfactorily represents the failure behavior of the pipes and can be applied in engineering application.

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