Relevance of plastic limit loads to reference stress approach for surface cracked cylinder problems

The plastic limit load solutions for cylinder and plate with slanted through-wall cracks (TWCs) are developed based on the systematic three-dimensional (3D) finite element (FE) limit analyses. As for loading conditions, axial tension, global bending, and internal pressure are considered for a cylinder with slanted circumferential TWC, whereas, axial tension and internal pressure are considered for a plate and a cylinder with slanted axial TWC. Then, the verification of FE model and analysis procedure employed in the present numerical work was confirmed by employing the existing solutions for both cylinder and plate with idealized TWC. Also, the geometric variables of slanted TWC which can affect plastic limit loads were considered. Based on the systematic FE limit analysis results, the slant correction factors which represent the effect of slanted TWC on plastic limit load were provided as tabulated solutions. By adopting these slant correction factors, the plastic limit loads of slanted TWC can be directly estimated from existing solutions for idealized TWC. Furthermore, the modified engineering estimations of plastic limit loads for slanted TWC are proposed based on equilibrium equation and von Mises yield criterion. The present results can be applied either to diverse structural integrity assessments or for accurate estimation of fracture mechanics parameters such as J-integral, plastic crack opening displacement (COD) and C*-integral for slanted TWC based on the reference stress concept (Kim, et al., 2002, “Plastic Limit Pressure for Cracked Pipes Using Finite Element Limit Analyse,” Int. J. Pressure Vessels Piping, 79, pp. 321–330; Kim, et al., 2001, “Enhanced Reference Stress-Based J and Crack Opening Displacement Estimation Method for Leak-Before-Break Analysis and Comparison With GE/EPRI Method,” Fatigue Fract. Eng. Mater. Struct., 24, pp. 243–254; Kim, et al., 2002, “Non-Linear Fracture Mechanics Analyses of Part Circumferential Surface Cracked Pipes,” Int. J. Fract., 116, pp. 347–375.)

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Estimates of Plastic Limit Loads of Thick-Walled Cylinders With Non-Idealzied Through-Wall Cracks

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2013-97610 ◽

2013 ◽

Author(s):

Tae-Song Han ◽

Nam-Su Huh ◽

Do-Jun Shim

Keyword(s):

Fracture Mechanics ◽

Structural Integrity ◽

Limit Load ◽

Ductile Material ◽

J Integral ◽

Plastic Limit ◽

Limit Loads ◽

Elastic Plastic ◽

Reference Stress ◽

Plastic Limit Load

In order to assess a structural integrity of cracked components made of highly ductile material based on fully plastic fracture mechanics concept, an accurate plastic limit load of components of interest is crucial element. Such a plastic limit load can also be applied to estimate elastic-plastic J-integral based on the reference stress concept. In this context, during last several decades, many efforts have been made to suggest plastic limit load solutions of cracked cylinder. Recent works for evaluating rupture probabilities of nuclear piping indicate that the only use of idealized circumferential through-wall crack leads to very conservative results which in turn gives higher rupture probabilities of nuclear piping, thus the considerations of more realistic crack shape during crack growth due to primary water stress corrosion cracking (PWSCC) and fatigue and axial through-wall crack were recommended to come up with more realistic rupture probabilities of nuclear piping. Then, the needs of fracture mechanics parameters of non-idealized through-wall cracks both in axial and circumferential directions have been raised. In the present work, the plastic limit loads of thick-walled cylinder with non-idealized axial and circumferential through-wall cracks are proposed based on detailed 3-dimensional finite element analyses. The present results can be applied either to assess structural integrity of thick-walled nuclear piping with non-idealized through-wall cracks or to calculate elastic-plastic J-integral using the reference stress concept.

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Elastic-Plastic J and COD Estimates for Circumferential Through-Wall Cracks Between Elbows and Straight Pipes Under Bending

Volume 5: High-Pressure Technology; Non-Destructive Evaluation; Student Paper Competition ◽

10.1115/pvp2007-26223 ◽

2007 ◽

Author(s):

Tae-Kwang Song ◽

Yun-Jae Kim

Keyword(s):

Crack Opening ◽

Small Strain ◽

Opening Displacement ◽

Limit Loads ◽

Elastic Plastic ◽

Perfectly Plastic ◽

Reference Stress ◽

Plastic Materials ◽

Elastic Perfectly Plastic ◽

Reference Stress Approach

A method for elastic-plastic fracture mechanics analyses is presented for the circumferential through-wall crack in weldment joining elbows and attached straight pipes, subject to in-plane bending, based on the reference stress approach. Based on small strain finite element limit analyses using elastic-perfectly plastic materials, closed-form limit loads for circumferential through-wall cracks in between elbows and straight pipes under bending are given. Then applicability of the reference stress based method to approximately estimate J and crack opening displacement (COD) is proposed.

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Plastic Limit Solutions for Cracked Pipes Based on 3-D Finite Element Limit Analyses

Piping and Component Analysis and Diagnosis ◽

10.1115/pvp2002-1523 ◽

2002 ◽

Author(s):

D. J. Shim ◽

Y. J. Kim

Keyword(s):

Surface Cracks ◽

Plastic Limit ◽

Reference Stress ◽

Limit Pressure ◽

Crack Problems ◽

Collapse Analysis ◽

Inner Surface ◽

Plastic Limit Pressure ◽

Limit Solutions ◽

Reference Stress Approach

Based on detailed 3-D FE limit analyses, the present paper provides tractable approximations for plastic limit pressure solutions for axial through-wall cracked pipe; axial (inner) surface cracked pipe; circumferential through-wall cracked pipe; and circumferential (inner) surface cracked pipe. In particular, for surface crack problems, the effect of the crack shape, the semi-elliptical shape or the rectangular shape, on the limit pressure is quantified. Comparisons with existing analytical and empirical solutions show a large discrepancy in circumferential short through-wall cracks and in surface cracks (both axial and circumferential). Being based on detailed 3-D FE limit analysis, the present solutions are believed to be the most accurate, and thus to be valuable information not only for plastic collapse analysis of pressurized piping but also for estimating non-linear fracture mechanics parameters based on the reference stress approach.

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