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Chang-yu Zhou - One of the best experts on this subject based on the ideXlab platform.

  • effect of bend angle on Plastic Limit loads of pipe bends under different load conditions
    International Journal of Mechanical Sciences, 2017
    Co-Authors: Chang-yu Zhou, Xiangming Pan
    Abstract:

    Abstract The effect of bend angle on Plastic Limit loads of pipe bends under different load conditions is presented using three-dimensional non-linear finite element analyses. Based on finite element analysis, the characteristics of deformation, stress and strain were studied and effect of bend angle on the Limit load was discussed. The results show that the effect of bend angle on Limit load is great both at 0°∼120° range under internal pressure, torsion moment and in-plane bending moment and at 0°∼90° under out-of-plane moment. Then existing expressions of Limit load and the finite element results were compared, and the solutions of Limit load under single load condition were made. The proposed unified load solutions were obtained by fitting the finite element data under internal pressure, in-plane bending moment, out-of-plane bending moment and torsion moment. The results show that the proposed unified load solutions are consistent and in good agreement with the current finite element results.

  • Plastic Limit load of Grade 91 steel pipe containing local wall thinning defect at high temperature
    Engineering Failure Analysis, 2015
    Co-Authors: Chang-yu Zhou, Xiaofeng Lu, Xiaochun Yu
    Abstract:

    Abstract This paper aims to predict the Plastic Limit load of Grade 91 pipe at high temperature by experimental and numerical analysis methods. The elastic–Plastic constitutive relation of P91 considering creep damage at high temperature is proposed and the effectiveness is verified by high-temperature instantaneous tensile test after creep of P91 sample. Then, using the elastic–Plastic constitutive relation considering creep damage, the Plastic Limit loads of P91 pipe containing local wall thinning (LWT) defect at high temperature have been calculated by finite element (FE) method and the accuracy is checked by high-temperature burst experiment after creep of T91 pipe containing LWT. Finally, the fracture analysis and metallographic analysis of Grade 91 sample and pipe containing LWT defect are performed. The results show that the elastic–Plastic constitutive relation of P91 considering creep damage proposed by this paper can well describe the elastic–Plastic behavior of P91 under creep condition and is useful to calculate the Plastic Limit load of P91 pipe containing LWT. The failures of P91 tensile samples and T91 pipes containing LWT defect are both Plastic fracture. This research would provide an optional method for structure integrity analysis of the pipe containing LWT defect at high temperature.

  • Plastic Limit loads for pipe bends with circumferential through wall crack under torsion moment
    International Journal of Mechanical Sciences, 2015
    Co-Authors: Chang-yu Zhou, Xinting Miao, Le Chang
    Abstract:

    Abstract In this work, finite element (FE) method is used to determine Plastic Limit load solutions for pipe bends with circumferential through-wall crack under torsion moment. Both extrados and intrados crack are considered regarding of crack location. Based on FE results estimated solutions are proposed for application, and are also compared with corresponding solutions in previous literatures showing that existing solutions are unfit for prediction of torsion load. The weakening factor W decreases with crack length increasing, and the decreasing rate exhibits three typical stages which performs a similar trend to that with bending moment. Finally a detailed analysis for the mechanical behavior of pipe bends has been conducted which provides some evidence to explain the weaken effect caused by the presence of crack. In torsion mode results show that the non-uniform distributed shear stress is performing symmetric to the profile plane and may have a crucial influence on the weakening factor, while in bending mode the distribution in axial stress and circumferential stress is symmetric to the profile plane and has a decisive influence. Therefore crack is pulled open by in-plane bending load while torn open by torsion load. Some evidence also can be obtained from the Mises stress distribution, where similar variation rule will provide another argument to support such description.

  • Plastic Limit loads for pipe bends under combined bending and torsion moment
    International Journal of Mechanical Sciences, 2015
    Co-Authors: Chang-yu Zhou, Peng Cui
    Abstract:

    Abstract In present paper, 3D finite element (FE) method is used to determine Plastic Limit load solutions for pipe bends under combined bending and torsion moment. With a detailed analysis and comparison, a common awareness for loading effect is showing which will raise researchers concern. By the way, past solutions are not appropriate to estimate FE results. In this respect of finite element analysis, overall yielding considering the spread process of yield region from crown to the straight pipe shows these promising finite element results. A wide range of non-dimensional parameters for pipe bends are considered and Plastic Limit load solutions are suggested. The results show that r/t is the main factor affecting the Limit loads. Plastic Limit load is independent on the loading path and material constants by normalizing. Results show that the circular interaction rule is a great approximation for pipe bends under combined bending and torsion moment. A series of approaches are confirmed in order to validate our finite element method on Plastic Limit analysis. Based on the finite element results, approximate Plastic Limit load solutions are proposed. Present work will further improve the Limit load solution for pipe bends under complex loading conditions.

Yutaka Miyamoto - One of the best experts on this subject based on the ideXlab platform.

  • Limit angular velocity of rotating disc with unified yield criterion
    International Journal of Mechanical Sciences, 2001
    Co-Authors: Hong Hao, Yutaka Miyamoto
    Abstract:

    Plastic Limit analysis of a rotating solid or annular disc with variable thickness is presented in terms of a unified yield criterion (UYC). Stress distributions of the discs in Plastic Limit state corresponding to different yield curves are deduced. Upper and lower bounds of the Plastic Limit solutions are derived by selecting a weighting coefficient in the unified yield criterion. Stress redistribution is solved when the stress field violates yield criterion locally. Limit angular velocity as well as the stress distributions with respect to three special criteria, namely the Tresca criterion, the Mises criterion (close form solution) and the Yu criterion are illustrated and compared. The influences of yield criterion as well as the thickness on Plastic Limit solution of a rotating disc are demonstrated and discussed.

  • Plastic Limit analyses of circular plates with respect to unified yield criterion
    International Journal of Mechanical Sciences, 1998
    Co-Authors: Ma Guowei, Yutaka Miyamoto, Shoji Iwasaki, Hideaki Deto
    Abstract:

    Plastic Limit analysis of a circular plate under uniform transverse loading is presented in terms of an unified yield criterion (UYC). Exact and unified solutions of load-carrying capacities, moment fields and velocity fields for simply supported circular plate, clamped circular plate and annular plate in Plastic Limit state are derived. Moment fields of the three typical circular plates correspond to different distribution fields on the yield curves. Maximum and minimum Plastic Limit solutions are deduced for the three types of circular plates by selecting the weighted coefficients with upper and lower bound values in the unified yield criterion. Moment fields and velocity fields with respect to the three special criteria, namely the Tresca criterion, the Mises criterion (close-form solution) and the twin shear stress criterion are illustrated and compared. The paper presents an effective analytical method to compute the exact Plastic Limit solution for circular plates in terms of a piecewise linear yield criterion.

Do-jun Shim - One of the best experts on this subject based on the ideXlab platform.

  • Plastic Limit loads for slanted through wall cracks in cylinder and plate based on finite element Limit analyses
    Journal of Pressure Vessel Technology-transactions of The Asme, 2014
    Co-Authors: Dooho Cho, Do-jun Shim, Young Hwan Choi, Namsu Huh, Jaeboong Choi
    Abstract:

    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.)

  • Relevance of Plastic Limit loads to reference stress approach for surface cracked cylinder problems
    International Journal of Pressure Vessels and Piping, 2005
    Co-Authors: Do-jun Shim
    Abstract:

    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.

  • finite element based Plastic Limit loads for cylinders with part through surface cracks under combined loading
    International Journal of Pressure Vessels and Piping, 2003
    Co-Authors: Yun Jae Kim, Do-jun Shim, Youngjin Kim, Kamran Nikbin, Seong Sik Hwang, Joung Soo Kim
    Abstract:

    This paper provides detailed Plastic Limit load solutions for cylinders containing part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3D) finite element (FE) Limit analyses using elastic-perfectly-Plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both circumferential and axial cracks, and for each case, both external and internal cracks are considered. Furthermore, in terms of the crack shape, calculations are presented for both semi-elliptical and constant-depth surface cracks. The resulting Limit load solutions are given in a closed form, and thus can be simply used in practical situations and defect assessment documents. In general, differences between analytical solutions based on equilibrium stress fields and the proposed solutions are more significant for axial cracks than for circumferential cracks. Since the calculations are based on detailed 3D FE Limit analysis no assumption is needed concerning the state of stress. The present solutions, therefore, are an accurate estimate of the Limit loads of the geometries that have been considered and are thus very useful information for assessing the integrity of pressurised piping.

  • Plastic Limit pressure solutions for cracked pipes using 3 d finite element method
    Transactions of The Korean Society of Mechanical Engineers A, 2003
    Co-Authors: Do-jun Shim, Yun Jae Kim, Namsu Huh, Youngjin Kim
    Abstract:

    Based on detailed FE Limit analyses, the present paper provides tractable approximations fer Plastic Limit pressure solutions fur axially through-wall-cracked pipe; axially (inner) surface-cracked pipe; circumferentially through-wall-cracked pipe; and circumferentially (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 pressurised piping but also for estimating non-linear fracture mechanics parameters based on the reference stress approach.

  • Plastic Limit pressures for cracked pipes using finite element Limit analyses
    International Journal of Pressure Vessels and Piping, 2002
    Co-Authors: Do-jun Shim
    Abstract:

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

Hideaki Deto - One of the best experts on this subject based on the ideXlab platform.

  • Plastic Limit analyses of circular plates with respect to unified yield criterion
    International Journal of Mechanical Sciences, 1998
    Co-Authors: Ma Guowei, Yutaka Miyamoto, Shoji Iwasaki, Hideaki Deto
    Abstract:

    Plastic Limit analysis of a circular plate under uniform transverse loading is presented in terms of an unified yield criterion (UYC). Exact and unified solutions of load-carrying capacities, moment fields and velocity fields for simply supported circular plate, clamped circular plate and annular plate in Plastic Limit state are derived. Moment fields of the three typical circular plates correspond to different distribution fields on the yield curves. Maximum and minimum Plastic Limit solutions are deduced for the three types of circular plates by selecting the weighted coefficients with upper and lower bound values in the unified yield criterion. Moment fields and velocity fields with respect to the three special criteria, namely the Tresca criterion, the Mises criterion (close-form solution) and the twin shear stress criterion are illustrated and compared. The paper presents an effective analytical method to compute the exact Plastic Limit solution for circular plates in terms of a piecewise linear yield criterion.

Yun Jae Kim - One of the best experts on this subject based on the ideXlab platform.

  • Plastic Limit loads for piping branch junctions under out-of-plane bending
    The Journal of Strain Analysis for Engineering Design, 2011
    Co-Authors: Kuk Hee Lee, Yun Jae Kim, Jun Young Jeon, Peter J. Budden
    Abstract:

    This paper presents approximate closed-form Plastic Limit load solutions for branch junctions under out-of-plane bending and under combined pressure and out-of-plane bending, based on three-dimensi...

  • Plastic Limit loads for thick walled branch junctions
    Journal of Strain Analysis for Engineering Design, 2009
    Co-Authors: Kuk Hee Lee, Yun Jae Kim, Peter J. Budden, Kamran M Nikbin
    Abstract:

    This technical note extends the validity of Limit load solutions for thin-walled branch junctions, previously proposed by the current author, to thick-walled cases. It is achieved simply by re-normalizing the thin-wall expressions by the Limit loads of thick-walled tubes instead of those of thin-walled tubes. Comparison with finite element results shows overall good agreement.

  • effects of local wall thinning on net section Limit loads for pipes under combined pressure and bending
    Nuclear Engineering and Design, 2009
    Co-Authors: Yun Jae Kim, Chi Yong Park
    Abstract:

    This paper provides Plastic Limit loads of pipes with local wall thinning under combined pressure and bending, by quantifying effects of the axial extent and the shape of local wall thinning. The effect of the axial extent on Plastic Limit loads is not so significant for bending but could be more significant for internal pressure. It is also found that the effect of the shape of local wall thinning on Limit loads could be significant. Thus idealization of local wall thinning as a rectangular shape rather than a circular one could lead to significantly conservative estimates of maximum loads, which is also supported by comparison with published full-scale pipe test data.

  • effects of local wall thinning on Plastic Limit loads of elbows using geometrically linear fe Limit analyses
    Engineering Fracture Mechanics, 2008
    Co-Authors: Yun Jae Kim, Jonghyun Kim, Joonghyuk Ahn, Seok Pyo Hong, Chi Yong Park
    Abstract:

    This paper provides closed-form Plastic Limit load solutions for elbows under in-plane bending and internal pressure, via three-dimensional (3D), geometrically linear FE Limit analyses using elastic-perfectly Plastic materials. Wide ranges of elbow and thinning geometries are considered. To investigate the effect of the axial thinning length on Limit loads systematically, two Limiting cases are considered; a sufficiently long thinning, and the circumferential part-through surface crack. Closed-form Plastic Limit load solutions for wall thinning with intermediate longitudinal extents are then obtained from these two Limiting cases. The effect of the axial extent of wall thinning on Plastic Limit loads for elbows is highlighted by comparing that for straight pipes. Although the proposed solutions are developed for the case when wall thinning exists in the center of elbows, it is also shown that they can be applied to the case when thinning exists anywhere within the elbow.

  • finite element based Plastic Limit loads for cylinders with part through surface cracks under combined loading
    International Journal of Pressure Vessels and Piping, 2003
    Co-Authors: Yun Jae Kim, Do-jun Shim, Youngjin Kim, Kamran Nikbin, Seong Sik Hwang, Joung Soo Kim
    Abstract:

    This paper provides detailed Plastic Limit load solutions for cylinders containing part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3D) finite element (FE) Limit analyses using elastic-perfectly-Plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both circumferential and axial cracks, and for each case, both external and internal cracks are considered. Furthermore, in terms of the crack shape, calculations are presented for both semi-elliptical and constant-depth surface cracks. The resulting Limit load solutions are given in a closed form, and thus can be simply used in practical situations and defect assessment documents. In general, differences between analytical solutions based on equilibrium stress fields and the proposed solutions are more significant for axial cracks than for circumferential cracks. Since the calculations are based on detailed 3D FE Limit analysis no assumption is needed concerning the state of stress. The present solutions, therefore, are an accurate estimate of the Limit loads of the geometries that have been considered and are thus very useful information for assessing the integrity of pressurised piping.