Development of Stress Intensity Factors for Surface Cracks With Large Aspect Ratio in Plates

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Genshichiro Katsumata ◽  
Kazuya Osakabe ◽  
Hiroshi Okada
Keyword(s):  
Stress Intensity ◽  
Aspect Ratio ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Crack Depth ◽  
Surface Cracks ◽  
Large Aspect Ratio ◽  
Element Analysis ◽  
Integrity Assessment

A number of surface cracks with large aspect ratio have been detected in components of nuclear power plants (NPPs) in recent years. The depths of these cracks are even larger than the half of crack lengths. When a crack is detected during in-service inspections, methods provided in ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on fitness-for-service for NPPs can be used to assess the structural integrity of cracked components. The solution of the stress intensity factor (SIF) is very important in the structural integrity assessment. However, in the current codes, the solutions of the SIF are provided for semi-elliptical surface cracks with a limitation of a/ℓ ≤ 0.5, where a is the crack depth, and ℓ is the crack length. In this study, the solutions of the SIF were calculated using finite element analysis (FEA) with quadratic hexahedron elements for semi-elliptical surface cracks with large aspect ratio in plates. The crack dimensions were focused on the range of a/ℓ = 0.5–4.0 and a/t = 0.0–0.8, where t is the wall thickness. Solutions were provided at both the deepest and the surface points of the surface cracks. Furthermore, some of solutions were compared with the available existing results as well as with solutions obtained using FEA with quadratic tetrahedral elements and the virtual crack closure-integral method (VCCM). Finally, it was concluded that the solutions proposed in this paper are applicable in engineering applications.

Stress Intensity Factors for Cracks With Large Aspect Ratio in Cylinder

2013 ◽  
Author(s):  
Yinsheng Li ◽  
Hiroaki Doi ◽  
Kunio Hasegawa ◽  
Kazuya Osakabe ◽  
Hiroshi Okada
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Surface Cracks ◽  
Large Aspect Ratio ◽  
Intensity Factors

A number of surface cracks with large aspect ratio have been detected in components of nuclear power plants in recent years. The depths of these cracks are even larger than the half-lengths. The solution of the stress intensity factor is very important for the structural integrity assessment of such cracked components. However, in the current codes, such as ASME Boiler and Pressure Vessel Code Section XI and the JSME Rules on Fitness-for-Service for Nuclear Power Plants, solutions of the stress intensity factors are provided for semi-elliptical surface cracks with a limitation of a/l ≤ 0.5, where a is the crack depth and l is the crack length. In order to assess structural integrity in a more rational way, the authors previously developed solutions of the stress intensity factor for semi-elliptical surface cracks in flat plates with a/l = 0.5 to 4 and a/t = 0.0 to 0.8, where t is the wall thickness. In this study, the solutions of the stress intensity factors were calculated for circumferential and axial surface semi-elliptical cracks with large aspect ratios in cylinders. The geometrical dimensions focused on were in the ranges of a/l = 0.5 to 4, a/t = 0.0 to 0.8 and t/Ri = 0 to 1/2, where t is the wall thickness and Ri is the inner radius of the cylinder. Some solutions were compared with the available existing solutions in order to confirm their applicability.

Development of Stress Intensity Factors for Deep Surface Cracks in Plates and Cylinders

2012 ◽  
Author(s):  
Yinsheng Li ◽  
Hiroto Itoh ◽  
Kunio Hasegawa ◽  
Kazuya Osakabe ◽  
Hiroshi Okada
Keyword(s):  
Finite Element Analysis ◽  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Surface Cracks ◽  
Element Analysis

A number of deep surface cracks have been detected in components of nuclear power plants in recent years. The depths of these cracks are even greater than the half of crack lengths. When a crack is detected during in-service inspections, methods provided in the ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be used to assess the structural integrity of cracked components. The solution of the stress intensity factor is very important in the assessment of structural integrity. However, in the current codes, the solutions of the stress intensity factor are provided for semi-elliptical surface cracks with a limitation of a/l ≤ 0.5, where a is the crack depth, and l is the crack length. In this study, in order to assess the structural integrity in a more rational manner, the solutions of the stress intensity factor were calculated using finite element analysis with quadratic hexahedron elements for deep semi-elliptical surface cracks in plates, and for axial and circumferential semi-elliptical surface cracks in cylinders. The crack dimensions were focused on the range of a/l = 0.5 to 4.0. Solutions were provided at both the deepest and the surface points of the cracks. Furthermore, some of solutions were compared with the available existing studies and with solutions obtained using finite element analysis with quadratic tetrahedral elements and the virtual crack closure-integral method. As the conclusion, it is concluded that the solutions proposed in this paper are applicable in engineering applications.

Overview of Recent NUGENIA Activities Particularly in Relation to Structural Integrity

2015 ◽  
Author(s):  
John Sharples ◽  
Elisabeth Keim
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Nuclear Research ◽  
Joint Research ◽  
Non Profit ◽  
Integrity Assessment ◽  
Industry Research ◽  
Implementation And Dissemination ◽  
Technical Area

NUGENIA, an international non-profit association founded under Belgian legislation and launched in March 2012, is dedicated to nuclear research and development (R&D) with a focus on Generation II and III power plants. NUGENIA is the integrated framework between industry, research and safety organisations for safe, reliable and competitive nuclear power production, and is aimed at running an open innovation marketplace, to promote the emergence of joint research and to facilitate the implementation and dissemination of R&D results. The technical scope of NUGENIA consists of eight technical areas. One of these areas, Technical Area 4, is associated with the structural integrity assessment of systems, structures and components. A brief overview of recent NUGENIA activities in general is provided in this paper and a specific focus is given on developments in relation to Technical Area 4.

Stress Intensity Factors for Semi-Elliptical Surface Cracks With Flaw Aspect Ratio Beyond the ASME XI Limit

2009 ◽  
Author(s):  
Christian Malekian ◽  
Eric Wyart ◽  
Michael Savelsberg ◽  
Anne Teughels ◽  
Pierre-Eric Fouquet ◽  
...  
Keyword(s):  
Stress Intensity ◽  
Finite Elements ◽  
Aspect Ratio ◽  
Stress Intensity Factors ◽  
Large Range ◽  
Crack Depth ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Flat Plates ◽  
Circular Shape

Most of the literature about fracture mechanics considers cracks having an elliptical shape with a flaw aspect ratio a/l lower or equal to 0.5 where ‘a’ is the crack depth and ‘l’ the total length of the crack. This is also case in the ASME XI Appendix A where Stress Intensity Factors KI formulations are given for a large range of crack depths and for a flaw aspect ratio a/l between 0 and 0.5. The limitation to 0.5 corresponds to a semi-circular shape for surface cracks and to a circular shape for subsurface cracks. This limitation does not seem to be inspired by a theoretical limitation nor by a computational limit. Moreover, it appears that limiting the ratio a/l to 0.5 may generate in some cases some unnecessary conservatism in flaw analysis. The present article specifically deals with the more unusual narrow cracks having a/l >0.5, in the case of surface cracks in infinite flat plates. Several Finite-Elements calculations are performed to compute KI for a large range of crack depths and for 4 typical load cases (uniform, linear, quadratic and cubic). The results can be presented with the same formalism as in the ASME XI Appendix A, such that the work can provide an extension of the ASME coefficients in table A-3320-1&2. By doing the study, one had the opportunity to compare the results obtained by two different Finite-Elements softwares (Systus and Ansys), each one with a different cracked mesh. In addition, a comparison has been made for some cases with results obtained by a XFEM approach (eXtended Finite-Element Method), where the crack does not need to be meshed in the same way as in classical Finite-Elements. The results indicate how the KI can be reduced when considering the real flaw aspect ratio instead of the conventional semi-circular flaw shape. They also show that, for specific theoretical stress distributions, it is not always possible to reduce the analysis of KI to only 2 points, namely the crack surface point and the crack deepest point. The crack growth evaluation of such unusual crack shape should still be investigated to verify whether simple rules can be established to estimate the evolution of the crack front.

Mode III Stress Intensity Factors of Surface Crack in Round Bars

2011 ◽  
Vol 214 ◽  
pp. 192-196 ◽  
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
Ruslizam Daud
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Crack Depth ◽  
Crack Tip ◽  
Bending Moment ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Mode Iii ◽  
Element Analysis ◽  
Proposed Model

This study presents a numerical investigation on the stress intensity factors (SIF), K of surface cracks in round bars that were obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node ¼-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed this proposed model validated for analyzing mode III problems. It was found that, the mode II SIF, FII and mode III SIF, FIII were dependent on the crack geometries and the sites of crack growth were also dependent on a/b and a/D.

Nuclear Reactor Pressure Vessel Integrity Assessment: Enhancement Provided by 3D Modeling Flaw Stability Calculations

2013 ◽  
Author(s):  
Adolfo Arrieta-Ruiz ◽  
Eric Meister ◽  
Henriette Churier
Keyword(s):  
Pressure Vessel ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Reactor ◽  
Structural Integrity ◽  
Reactor Pressure Vessel ◽  
Integrity Assessment ◽  
Potential Damage ◽  
Vessel Integrity ◽  
Reactor Pressure

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main considerations regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Brittle fracture risk associated with the embrittlement of RPV steel in irradiated areas is the main potential damage. In France, deterministic integrity assessment for RPV is based on the crack initiation stage. The stability of an under-clad postulated flaw in the core area is currently evaluated under a Pressurized Thermal Shock (PTS) through a fracture mechanics simplified method. One of the axes of EDF’s implemented strategy for NPP lifetime extension is the improvement of the deterministic approach with regards to the input data and methods so as to reduce conservatisms. In this context, 3D finite element elastic-plastic calculations with flaw modelling have been carried out recently in order to quantify the enhancement provided by a more realistic approach in the most severe events. The aim of this paper is to present both simplified and 3D modelling flaw stability evaluation methods and the results obtained by running a small break LOCA event.

Finite Element Analysis of Polyethylene Pipe Butt Fusion Joints with Circumferential Surface Cracks

2013 ◽  
Vol 785-786 ◽  
pp. 1151-1158
Author(s):  
Zhi Bin Zhu ◽  
Xiao Xiang Yang ◽  
Li Jing Chen ◽  
Nai Chang Lin ◽  
Zhi Tuo Wang ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Viscoelastic Material ◽  
Surface Crack ◽  
Crack Depth ◽  
Surface Cracks ◽  
Element Analysis ◽  
Polyethylene Pipe

Based on the viscoelastic material property of polyethylene pipe, software ANSYS was used to simulate and analyze the mechanical property of polyethylene pipe butt fusion joints with circumferential surface crack defects. The viscoelastic material creep parameters were characterized as Prony series and 1/4 node singular element was selected for meshing along the boundaries of the crack, then the stress intensity factor of polyethylene pipe butt fusion joints with circumferential surface crack was calculated under the uniform internal pressure. Through the finite element simulation, the result showed that polyethylene pipe were most likely to fracture failure when crack initiated. Thus the viscoelasticity of materials can be ignored when analyzing the stress intensity factor of circumferential surface cracks of polyethylene pipe. the main influencing factor of the circumferential crack defects was the ratio of the crack depth to the thickness of polyethylene pipe.

Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs Affected by Hydrogen Flakes: Refined X-FEM Analyses

2016 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Extended Finite Element Method ◽  
Structural Integrity ◽  
Pressure Vessels ◽  
Extended Finite Element ◽  
Integrity Assessment ◽  
Safety Case ◽  
Component Manufacturing ◽  
Reactor Pressure

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, specific ultrasonic in-service inspections revealed a large number of quasi-laminar indications in the base metal of the reactor pressure vessels, mainly in the lower and upper core shells. The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, a Flaw Acceptability Assessment had to be performed as a part of the Safety Case demonstrating the fitness-for-service of these units. In that framework, detailed analyses using eXtended Finite Element Method were conducted to model the specific character of hydrogen flakes. Their quasi-laminar orientation as well as their high density required setting up 3D multi-flaws model accounting for flaw interaction. These calculations highlighted that even the most penalizing flaw configurations are harmless in terms of structural integrity despite the consideration of higher degradation of irradiated material toughness.

Effects of Local Wall Thinning With Crack on Stress Intensity Factor for Pipes Subject to Combined Pressure and Bending

2019 ◽  
Author(s):  
Joy (Xiaoya) Tao ◽  
Lei Zhu
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Nuclear Power ◽  
Power Plants ◽  
Limit Load ◽  
Minimum Thickness ◽  
Element Analysis ◽  
Accelerated Corrosion

Abstract At ageing power plants, local thinning of pipework or vessel is unavoidable due to erosion/corrosion or other reasons such as flow accelerated corrosion (FAC) — one of the common degradation mechanisms in pipework of nuclear power plant. Local thinning reduces the structure strength, resulting in crack initiation from the corrosion pit or welding defect when subject to cyclic loading. General practice is to use the minimum thickness of the thinned area to calculate both limit load and stress intensity factor (SIF) in performing Engineering Critical Assessment (ECA) using Failure Assessment Diagram (FAD). Using the minimum thickness is normally overly conservative as it assumes that thinning occurs grossly instead of locally, leading to unnecessary early repair/replacement and cost. Performing cracked body finite element analysis (FEA) can provide accurate values of limit load and SIF, but it is time consuming and impractical for daily maintenance and emergent support. To minimise the conservatisms and provide a guidance for the assessment of locally thinned pipework or vessel using existing handbook solutions, a study was carried out by the authors on the effect of local thinning on limit loads. The study demonstrates that local thinning has significant effect on limit load if the thinning ratio of thinning depth to original thickness is larger than 25%. It concluded that the limit load solutions given in handbooks (such as R6 or the net section method) are overly conservative if using the minimum local thickness and non-conservative if using the nominal thickness. This paper discusses the effect of local thinning on SIFs of internal/external defects using cracked body finite element method (FEM). The results are compared with R6 weight function SIF solutions for a cylinder. A modified R6 SIF solution is proposed to count for the effect of local thinning profile. Along with the previous published paper on limit load it provides comprehensive understanding and guidance for fracture assessment of the local thinned pipework and vessel.

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