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Yun-jae Kim - One of the best experts on this subject based on the ideXlab platform.
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Reference Stress based J estimation equations applicable to cracked cylinders with a Wide range of radius-to thickness ratios: Part I- axial surface cracks
International Journal of Pressure Vessels and Piping, 2020Co-Authors: Jae Min Gim, Ji Su Shin, Yun-jae KimAbstract:Abstract This paper compares systematic finite element results with Reference Stress based J estimation equations for pressurised axial surface and through-wall cracked cylinders with the radius-to-thickness ratio ranging from five up to seventy. It is found that, for the Reference Stress, the use of the Tresca limit pressure given in R6 provides satisfactory results for all cases considered; for both inner and external axial surface cracks; for both semi-elliptical and constant-depth axial surface cracks. These results are obtained for high strain hardening materials such as Type 304 stainless steel.
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Reference Stress based J estimation formula for cracked cylinders with a wide range of radius-to thickness ratios: Part II- circumferential surface cracks
International Journal of Pressure Vessels and Piping, 2020Co-Authors: Jae Min Gim, Ji Su Shin, Yun-jae KimAbstract:Abstract In this paper, Reference Stress based J estimation equations are presented for circumferential constant-depth surface and through-wall cracked cylinders with the radius to thickness ratio ranging from three up to seventy. The equations are developed based on extensive finite element (FE) analysis results. Firstly it is shown that application of existing J estimation equations is limited to thick-walled cylinder problems and can give non-conservative J estimates for a cylinder with a large radius-thickness ratio. To accommodate the effects of the crack depth, length and the radius-to-thickness ratio, correction factors for the Reference Stress are proposed based on FE results. By comparing with FE results, it shows that the proposed solutions can be applied to both an external and internal crack; and to combined axial tension and global bending.
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Engineering Approach Based on Reference Stress Concept for Calculating J and Crack Opening Displacement of Complex-Cracked Pipes
Journal of Pressure Vessel Technology, 2017Co-Authors: Jae Uk Jeong, Nam Su Huh, Do-jun Shim, Jae-boong Choi, Yun-jae KimAbstract:In this study, an engineering approach for estimations of fracture mechanics parameters, i.e., J-integral and crack opening displacement (COD), for complex-cracked pipes was suggested based on Reference Stress concept, where Stress-strain data of the material was used to assess structural integrity of complex-cracked pipes. In the present study, new Reference loads that can reduce the dependency on strain hardening of the material have been suggested for complex-cracked pipes under each loading mode. By using the proposed optimized Reference load for complex-cracked pipes, J-integral and COD estimation procedures have been proposed based on the Reference Stress concept together with the elastic solutions for complex-cracked pipes. The predicted J-integrals and CODs based on the proposed method have been validated against published experimental data and FE results using actual Stress–strain data. Moreover, the predictions using the proposed methods are also compared with those using the existing solutions for simple through-wall cracks (TWCs) based on reduced thickness analogy concept.
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Reference Stress based J and COD estimation of circumferential through-wall cracked elbows under in-plane bending
Engineering Fracture Mechanics, 2015Co-Authors: Chul Goo Kim, Yun-jae Kim, Kyung Dong Bae, Peter J. BuddenAbstract:Abstract This paper proposes J-integral and crack opening displacement (COD) estimation equations based on the Reference Stress method for circumferential through-wall cracked elbows under in-plane bending. For best estimates of J and COD, an optimized Reference load, used to define the Reference Stress, is given. The proposed equations are compared with detailed finite element results. They are further validated against eight published full-scale pipe test data. Comparison of crack initiation and maximum loads shows good agreement.
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Reference Stress-Based J Estimation of Circumferential Through-Wall Cracked Elbow With Unequal Thickness Under Bending
Volume 6A: Materials and Fabrication, 2014Co-Authors: Kyung Dong Bae, Chul Goo Kim, Zalikha Murni, Seung Jae Kim, Yun-jae KimAbstract:In large plant facilities, elbow and straight pipe have large potion in whole piping system. When the cracks are initiated in pipe, the cracks have to be evaluated using fracture mechanics parameter such as J-integral. Unlike calculating J-integral of straight pipes, estimation J-integral of elbow using finite element analysis is not easy. Because the effect of geometries for crack behavior of elbow are more complex than straight pipes. Also, there is another difference between elbow and straight pipe. That is unequal thickness in intrados and extrados. Unequal thickness of elbow pipes generally occurs by the manufacturing process. Thickness in intrados is getting thicker than nominal thickness but thickness in extrados is getting thinner than nominal thickness. So first, this paper provides a Reference Stress-based J-integral estimation of circumferential through-wall cracked elbow with equal thickness. And this paper provides also a Reference Stress-based J-integral estimation of circumferential through-wall cracked elbow with unequal thickness. To find the Reference Stress-based approximate J-integral, various ratio of thickness (t), pipe radius (r), pipe bend radius (R) and crack length (θ) are considered. And three-dimensional finite element analyses using elastic property for elastic crack behavior and elastic–perfectly plastic property for limit load are performed. Finally Results in this research are presented in the failure assessment diagram (FAD) space.Copyright © 2014 by ASME
Young-jin Kim - One of the best experts on this subject based on the ideXlab platform.
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Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Combined Loading
Journal of Pressure Vessel Technology, 2005Co-Authors: Do-jun Shim, Young-jin Kim, Yun-jae KimAbstract:In the previous work carried out by the authors, a new method to estimate failure strength of a pipe with local wall thinning subject to either internal pressure or global bending has been proposed. The proposed method was based on the equivalent Stress averaged over the minimum ligament in the locally wall thinned region, and the simple scheme to estimate the equivalent Stress in the minimum ligament was proposed, based on the Reference Stress concept for creep Stress analysis. This paper extends the new method to combined internal pressure and global bending. The proposed method is validated against FE results for various geometries of local wall thinning under combined loading. The effect of internal pressure is also investigated in the present study. Comparison of maximum moments, predicted according to the proposed method, with published full-scale pipe test data for locally wall thinned pipes under combined internal pressure and global bending, shows good agreement.
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Reference Stress Approach for Failure Strength Estimates of a Pipe With Local Wall Thinning
Volume 6: Materials and Fabrication, 2005Co-Authors: Yun-jae Kim, Young-jin KimAbstract:This paper proposes a method based on the Reference Stress a approach to estimate residual strength of a pipe with local wall thinning. The method is based on the equivalent Stress averaged over the minimum ligament in the locally wall thinned region. Inspired by the Reference Stress method for approximate creep Stress analysis, approximate estimation equations for the equivalent Stress in the minimum ligament are proposed, which are then calibrated using detailed elastic-plastic 3-D FE analysis. The resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement.Copyright © 2005 by ASME
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Reference Stress Based J-Integral Estimates Along the Semi-Elliptical Surface Crack Front
Transactions of the Korean Society of Mechanical Engineers A, 2004Co-Authors: Jin-su Kim, Yun-jae Kim, Do-jun Shim, Young-jin KimAbstract:This paper discusses applicability of the enhanced Reference Stress method to estimate J-integral along the semi-elliptical surface crack front. It is found that angular variations of normalized Jintegral are strongly dependent on the geometry, loading mode and loading magnitude. As application of the Reference Stress approach to semi-elliptical surface cracks implies proportional increases in the normalized J-integral, the present results pose a question in applicability of the Reference Stress approach. However, investigation of the error in the estimated J-integral in the present work suggests that the enhanced Reference Stress approach, recently proposed by authors, provides an effective engineering tool fur estimating crack driving force along the semi-elliptical surface crack front.
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Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Single Loading
Journal of Pressure Vessel Technology, 2004Co-Authors: Yun-jae Kim, Do-jun Shim, Hwan Lim, Young-jin KimAbstract:This paper proposes a new method to estimate failure strength of a pipe with local wall thinning. The method is based on the equivalent Stress averaged over the minimum ligament in the locally wall thinned region. The highlight of the proposed method is to propose a simple scheme to estimate the equivalent Stress in the minimum ligament. Inspired by the Reference Stress method for approximate creep Stress analysis, approximate estimation equations are proposed for the equivalent Stress in the minimum ligament, which are then calibrated using detailed elastic-plastic three-dimensional FE analysis. Remarkably the resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement, which provides confidence in the use of the proposed method to assess local wall thinning in pipes. Furthermore, the proposed method is conceptually simple and thus easy to be extended to more complex situations.
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Elastic–plastic fracture mechanics assessment of test data for circumferential cracked pipes
Engineering Fracture Mechanics, 2004Co-Authors: Yun-jae Kim, Do-jun Shim, Nam Su Huh, Young-jin KimAbstract:This paper presents experimental validation of two Reference Stress based methods for circumferential cracked pipes. One is the R6 method where the Reference Stress is defined by the plastic limit load. The other is the enhanced Reference Stress method, recently proposed by the authors, where the Reference Stress is defined by the optimised Reference load. Using 38 published pipe test data, the predicted maximum instability loads according to both methods are compared with the experimental ones for pipes with circumferential through-thickness cracks and with part circumferential surface cracks. It is found that the R6 method gives conservative estimates of the maximum loads for all cases. Ratios of the experimental maximum load to the predicted load range from 0.54 to 0.98. On the other hand, the proposed method gives overall closer maximum loads than R6, compared to the experimental data. However, for part through-thickness surface cracks, the estimated loads were slightly non-conservative for four cases, and possible reasons are fully discussed.
Do-jun Shim - One of the best experts on this subject based on the ideXlab platform.
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Engineering Approach Based on Reference Stress Concept for Calculating J and Crack Opening Displacement of Complex-Cracked Pipes
Journal of Pressure Vessel Technology, 2017Co-Authors: Jae Uk Jeong, Nam Su Huh, Do-jun Shim, Jae-boong Choi, Yun-jae KimAbstract:In this study, an engineering approach for estimations of fracture mechanics parameters, i.e., J-integral and crack opening displacement (COD), for complex-cracked pipes was suggested based on Reference Stress concept, where Stress-strain data of the material was used to assess structural integrity of complex-cracked pipes. In the present study, new Reference loads that can reduce the dependency on strain hardening of the material have been suggested for complex-cracked pipes under each loading mode. By using the proposed optimized Reference load for complex-cracked pipes, J-integral and COD estimation procedures have been proposed based on the Reference Stress concept together with the elastic solutions for complex-cracked pipes. The predicted J-integrals and CODs based on the proposed method have been validated against published experimental data and FE results using actual Stress–strain data. Moreover, the predictions using the proposed methods are also compared with those using the existing solutions for simple through-wall cracks (TWCs) based on reduced thickness analogy concept.
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Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Combined Loading
Journal of Pressure Vessel Technology, 2005Co-Authors: Do-jun Shim, Young-jin Kim, Yun-jae KimAbstract:In the previous work carried out by the authors, a new method to estimate failure strength of a pipe with local wall thinning subject to either internal pressure or global bending has been proposed. The proposed method was based on the equivalent Stress averaged over the minimum ligament in the locally wall thinned region, and the simple scheme to estimate the equivalent Stress in the minimum ligament was proposed, based on the Reference Stress concept for creep Stress analysis. This paper extends the new method to combined internal pressure and global bending. The proposed method is validated against FE results for various geometries of local wall thinning under combined loading. The effect of internal pressure is also investigated in the present study. Comparison of maximum moments, predicted according to the proposed method, with published full-scale pipe test data for locally wall thinned pipes under combined internal pressure and global bending, shows good agreement.
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Relevance of plastic limit loads to Reference Stress approach for surface cracked cylinder problems
International Journal of Pressure Vessels and Piping, 2005Co-Authors: Yun-jae Kim, Do-jun ShimAbstract:To investigate the relevance of the definition of the Reference Stress to estimate J and C* for surface crack problems, this paper compares finite element (FE) J and C* results for surface cracked pipes with those estimated according to the Reference Stress approach using various definitions of the Reference Stress. Pipes with part circumferential inner surface cracks and finite internal axial cracks are considered, subject to internal pressure and global bending. The crack depth and aspect ratio are systematically varied. The Reference Stress is defined in four different ways using (i) a local limit load, (ii) a global limit load, (iii) a global limit load determined from the FE limit analysis, and (iv) the optimised Reference load. It is found that the Reference Stress based on a local limit load gives overall excessively conservative estimates of J and C*. Use of a global limit load clearly reduces the conservatism, compared to that of a local limit load, although it can sometimes provide non-conservative estimates of J and C*. The use of the FE global limit load gives overall non-conservative estimates of J and C*. The Reference Stress based on the optimised Reference load gives overall accurate estimates of J and C*, compared to other definitions of the Reference Stress. Based on the present findings, general guidance on the choice of the Reference Stress for surface crack problems is given.
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Reference Stress Based J-Integral Estimates Along the Semi-Elliptical Surface Crack Front
Transactions of the Korean Society of Mechanical Engineers A, 2004Co-Authors: Jin-su Kim, Yun-jae Kim, Do-jun Shim, Young-jin KimAbstract:This paper discusses applicability of the enhanced Reference Stress method to estimate J-integral along the semi-elliptical surface crack front. It is found that angular variations of normalized Jintegral are strongly dependent on the geometry, loading mode and loading magnitude. As application of the Reference Stress approach to semi-elliptical surface cracks implies proportional increases in the normalized J-integral, the present results pose a question in applicability of the Reference Stress approach. However, investigation of the error in the estimated J-integral in the present work suggests that the enhanced Reference Stress approach, recently proposed by authors, provides an effective engineering tool fur estimating crack driving force along the semi-elliptical surface crack front.
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Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Single Loading
Journal of Pressure Vessel Technology, 2004Co-Authors: Yun-jae Kim, Do-jun Shim, Hwan Lim, Young-jin KimAbstract:This paper proposes a new method to estimate failure strength of a pipe with local wall thinning. The method is based on the equivalent Stress averaged over the minimum ligament in the locally wall thinned region. The highlight of the proposed method is to propose a simple scheme to estimate the equivalent Stress in the minimum ligament. Inspired by the Reference Stress method for approximate creep Stress analysis, approximate estimation equations are proposed for the equivalent Stress in the minimum ligament, which are then calibrated using detailed elastic-plastic three-dimensional FE analysis. Remarkably the resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement, which provides confidence in the use of the proposed method to assess local wall thinning in pipes. Furthermore, the proposed method is conceptually simple and thus easy to be extended to more complex situations.
T. Shirakashi - One of the best experts on this subject based on the ideXlab platform.
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Flow Stress equation with effect of strain-rate and temperature histories under processing
Journal De Physique Iv, 2000Co-Authors: T. Shirakashi, M. YoshinoAbstract:The effects of strain, strain-rate, temperature on the flow Stress variation of some metals are experimentally discussed by using the modified Hopkinson bar type impact testing machine. It is found through the test that flow Stress is greatly affected by both histories of temperature and strain rate. In order to obtain a flow Stress including the both effects under deformation, a Reference Stress is proposed. The Reference Stress is defined as the yield Stress under the Reference condition. The Reference Stress is defined by only generalized deformation energy, which is accumulated by plastic deformation and annihilated by annealing. The new practically useful flow-Stress equation is proposed, in which the Reference Stress, strain-rate and temperature but total strain are included. The proposed flow-Stress equation is applied to deformation process with varying condition and compared with experimental results.
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Flow-Stress equation including effects of strain-rate and temperature history
International Journal of Mechanical Sciences, 1997Co-Authors: M. Yoshino, T. ShirakashiAbstract:Abstract This paper addresses effects of deformation history, temperature history and heat treatment history on the flow-Stress variation in terms of the mathematical theory of plasticity. On the basis of this discussion, a new flow-Stress equation taking account of effects of such histories is proposed. The equation consists of the strain rate; temperature, and the Reference Stress which is determined by the plastic deformation energy. The Reference Stress, the yield Stress under the Reference condition, is proposed as a measure of the history, and flow-Stress is shown to depend on the Reference Stress but not on total plastic strain. The Reference Stress is shown to depend only on the generalized deformation energy, which is believed to be related to the stored energy of lattice defects introduced by plastic deformation. Plastic deformation accumulates the generalized deformation energy, and the recovery annihilates the energy. This study proposes a new flow-Stress equation consisting of the Reference Stress, strain rate and temperature. The new flow-Stress equation is applied to a forming process With varying conditions, and is consistent with experimental data. Finally, this paper provides mathematical account of the new flow-Stress equation. It is shown that the deformation energy is the only parameter that can connect structural change in a lattice and the mathematical theory of plasticity. While any other parameters are possible, the deformation energy is the simplest and a justifiable parameter to evaluate the history.
Y Lei - One of the best experts on this subject based on the ideXlab platform.
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Reference Stress solutions for plates with embedded off-set elliptical cracks under combined biaxial forces and cross-thickness bending
International Journal of Pressure Vessels and Piping, 2018Co-Authors: Y Lei, Zengliang GaoAbstract:Abstract The Reference Stress solutions for plates with embedded off-set elliptical cracks under combined biaxial forces and cross-thickness bending are derived based on the Mises yield criterion and net-section collapse principle. The newly developed Reference Stress solutions are compared with the Reference Stresses of plates with embedded rectangular cracks evaluated using the available limit load solutions. The developed Reference Stress solutions have been used to predict J via the Reference Stress J scheme. Elastic-plastic 3-D finite element (FE) analyses are used to calculate J values along the crack front and the results are compared with the Reference Stress predictions. The results show that the estimated J values based on the Reference Stress method with the Reference Stress solutions developed in this paper are very close to the FE J values, but the predictions may be non-conservative. However, the non-conservatism could be removed by simply applying a constant factor less than 1 to the Reference Stress solutions when they are used in the Reference Stress J scheme.
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A local limit load model for J prediction via the Reference Stress method
Procedia Structural Integrity, 2018Co-Authors: Y LeiAbstract:Abstract A local limit load model is developed for shell/plate type components with surface cracks for determining the local limit load or local Reference Stress used in J prediction via the Reference Stress J scheme for defective components. The model is a plate which contains a rectangular surface crack circumscribing the real surface defect and has the same thickness as the component at the crack location. The model is remotely loaded by the primary Stresses of the component at the crack location obtained from elastic uncracked-body Stress analysis. The global limit load of this model is used as the local limit load of the defective component. The model is validated using 273 cases of 3-D finite element (FE) J results for semi-elliptical surface cracks in plates, cylinders and elbows. The results show that when this local limit load is used in the Reference Stress J prediction scheme, the predicted J values are reasonably accurate but conservative, compared with the FE J values.
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The Effect of Biaxial Loading on the Limit Load and J Estimate for Plates with Extended Surface Cracks
Procedia Materials Science, 2014Co-Authors: Y Lei, Peter J. Budden, Chris AirdAbstract:A plate with an extended surface crack under combined biaxial force and in-plane bending moment is considered. The limit load solution is first derived based on the Mises yield criterion to take account of the effect of Stress parallel to the crack plane. The J values are then evaluated using elastic-plastic FE analyses and compared with the predictions of the Reference Stress method using the developed limit load solution. The results show that the biaxial loading effect on J estimation may be taken into account in the Reference Stress method if the limit load value considering the biaxial loading effect is used.
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j integral and limit load analysis of semi elliptical surface cracks in plates under combined tension and bending
International Journal of Pressure Vessels and Piping, 2004Co-Authors: Y LeiAbstract:Abstract Systematic detailed finite element (FE) analyses are performed for semi-elliptical surface cracks in plates under combined tension and bending. The Newman and Raju Stress intensity factor solution is confirmed and non-linear J solutions are generated and expressed as the EPRI type h 1 function for a wide range of geometry factors and ratios of bending to tensile load. Limit load solutions are obtained from the FE J results through the Reference Stress method. The results show that relationship between J and the limit load depends on a / t , a / c and the load ratio λ . Here a and c are the depth and half-length of the crack and t is the plate thickness. When both tension and bending are effective (e.g. λ =0.5), for a / t ≤0.5 and a / c =0.2, J for any position along a crack front can be predicted by the Reference Stress method using a single limit load value except for the points very close to the plate surface. For all other cases analysed, it can only be approximately estimated by the Reference Stress method because a limit load value that can satisfy all the FE J solutions along the crack front cannot be found. However, for all the cases, the maximum J along the crack front can be well predicted by the Reference Stress method when a proper global limit load is used. The FE limit load data can be well predicted by the extended Goodall and Webster solution.
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j integral and limit load analysis of semi elliptical surface cracks in plates under tension
International Journal of Pressure Vessels and Piping, 2004Co-Authors: Y LeiAbstract:Systematic detailed linear and non-linear finite element (FE) analyses are performed for semi-elliptical surface cracks in plates under bending. Limit load (moment) solutions are obtained from the FE J results via the Reference Stress method. The FE results show that the Newman and Raju Stress intensity factor equation is reasonably accurate and the Yagawa et al. J solution may significantly under estimate J for bending load. The relationship between J and the limit load is found to be dependent on the ratio a/t and a/c, where a and c are the depth and the half-length of the crack and t is the plate thickness. For a/t≤0.5 with a/c=0.2, J for any position along a crack front can be predicted by the Reference Stress method using a single limit load value except for the points very close to the plate surface. For all other cases, it can only be approximately estimated by the Reference Stress method because a limit load value that can satisfy all the FE J solutions along the crack front cannot be found. However, for all the cases examined, the maximum J along the crack front can be well predicted by the Reference Stress method when a proper global limit load is used. The Goodall and Webster global limit load equation is extended to any crack depth. The limit load data obtained in this paper can be well reproduced by the extended equation.
