• Title, Summary, Keyword: Plastic Bending

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Closed-Form Plastic Collapse Loads of Pipe Bends Under Combined Pressure and In-Plane Bending (압력과 모멘트의 복합하중을 받는 곡관의 소성 붕괴하중 예측식 개발)

  • Oh Chang-Sik;Kim Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.8
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    • pp.1008-1015
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    • 2006
  • Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit, collapse and instability load solutions for pipe bends under combined pressure and in-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide plastic collapse loads (using the twice-elastic-slope method) and instability loads. For the bending mode, both closing bending and opening bending are considered, and a wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and collapse load solutions for pipe bends under combined pressure and bending are proposed.

Estimation of Plastic Bending Moment of Offshore Pipelines (해저관로의 대변형 굽힘에 의한 소성 모멘트 추정)

  • 이종현;최한석;이승건
    • Journal of Ocean Engineering and Technology
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    • v.17 no.2
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    • pp.21-26
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    • 2003
  • The reel-lay method of submarine pipelines a continuous string of pipe coiled onto a reel. Assembly of this pipe that is string is accomplished onshore by welding, and nondestructive testing is carried out prior to coiling the pipe. The total length of pipes on the reel depends on the reel and pipe diameters. Pipeline installation is accomplished by uncoiling, straightening the pipe, and laying out the pipe string onto the seabed as the barge moves forward. Installation associated with coiling and uncoiling is related to the bending moment and strain relationship of the pipeline, A highgrade pipe material is required when the reel-lay method is used. This paper is concerned with the highly plastic bending moment of the pipeline, including the effect of ovality. Moment calculation in the pipe is accomplished by the numerical method, including the variable ovalities during the plastic bending of the pipe string. The new calculation method of the high plastic bending moment was applied to the reel-lay method.

Spring Back on the Compound Bending of the Plastic Fuel Tube for Automobile (자동차용 플라스틱 연료튜브의 복합 벤딩에 대한 스프링백)

  • Moon, C.Y.;Park, J.S.;Jeong, Y.D.
    • Journal of the Korea Society For Power System Engineering
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    • v.7 no.2
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    • pp.51-55
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    • 2003
  • Recently the requirements for light weight and high performance of the automobile have increased. Especially, the plastic fuel tube makers have made their efforts to dove]op the various plastic fuel tube module with not only dimensional accuracy but also cost competitiveness. The experiment is performed to investigate spring backs for PA12 plastic fuel tubes in case of compound bending. In the experiment, steam bending process is adopted as bending method. In this study, the results we obtained are used to design the bending fixtures and the compound bending system.

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Finite element modeling of rolled steel shapes subjected to weak axis bending

  • Saliba, Najib G.;Tawk, Issam;Gergess, Antoine N.
    • Steel and Composite Structures
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    • v.29 no.2
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    • pp.161-173
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    • 2018
  • Point bending is often used for cambering and curving structural steel girders. An analytical solution, applicable in the elasto-plastic range only, that relates applied loads to the desired curve was recently developed for inducing horizontal curves using four-point bending. This solution does not account for initial residual stresses and geometric imperfections built-in hot-rolled sections. This paper presents results from a full-scale test on a hot-rolled steel section curved using four-point bending. In parallel, a numerical analysis, accounting for both initial geometric imperfections and initial residual stresses, was carried out. The models were validated against the experimental results and a good agreement for lateral offset and for strain in the elasto-plastic and post-plastic ranges was achieved. The results show that the effect of initial residual stresses on deformation and strain is minimal. Finally, residual stresses due to cold bending calculated from the numerical analysis were assessed and a revised stress value for the service load design of the curved girder is proposed.

EVALUATION MODEL FOR RESTRAINT EFFECT OF PRESSURE INDUCED BENDING ON THE PLASTIC CRACK OPENING OF A CIRCUMFERENTIAL THROUGH-WALL CRACK

  • Kim, Jin-Weon
    • Nuclear Engineering and Technology
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    • v.39 no.1
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    • pp.75-84
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    • 2007
  • This paper presents a closed-form model for evaluating the restraint effect of pressure induced bending on the opening of a circumferential through-wall crack, which is considered plastic deformation behavior. Three-dimensional finite element analyses with different crack lengths, restraint conditions, pipe geometries, magnitudes of internal pressure, and tensile properties were used to investigate the influence of each parameter on the pressure-induced bending restraint on the crack opening displacement. From these investigations, an analytical model based on elastic-perfectly plastic material was developed in terms of the crack length, symmetric restraint length, mean radius to thickness ratio, axial stress corresponding to the internal pressure, and normalized crack opening displacement evaluated from a linear-elastic crack opening condition. Finite element analyses results demonstrate that the proposed analytical model reliably estimated the restraint effect of pressure-induced bending on the plastic crack opening of a circumferential through-wall crack and properly reflected the dependence on each parameter within the range over which the analytical expression was derived.

Analysis on the Mechanism of Fluting in the Bending of Low Carbon Steels (저탄소강판을 이용한 굽힘 가공에서 발생하는 꺾임 현상에 대한 발생기구 해석)

  • Park, K.C.;Yoon, J.B.
    • Transactions of Materials Processing
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    • v.16 no.4
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    • pp.317-322
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    • 2007
  • In order to investigate the cause and condition of fluting in tangential bending of low carbon steel sheet, an analytic analysis, an experiment and a series of finite element analysis for bending process were done. The fluting in bended sheet was related with the yield point elongation of material. Due to the yield point elongation, unstable plastic hinge was occurred in course of bending of elastic perfectly plastic sheet. According to the analysis and computational results, lower yield point elongation than 5% was required to prevent fluting in 0.5-0.6t sheet in $15{\sim}25mm$ radius bending. The tendency of fluting occurrence was reduced as decreasing the radius of bending, increasing thickness of bended sheet, and removing irregularity in sheet and bending processes.

Analysis on the Mechanism of Fluting in the Bending of Low Carbon Steel Sheets (저탄소강판을 이용한 굽힘 가공에서 발생하는 꺽임현상에 대한 발생 기구 해석)

  • Park, K.C.;Yoon, J.B.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.336-339
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    • 2007
  • In order to investigate the cause of fluting in tangential bending of low carbon steel sheet, an analytic analysis, an experiment and a series of finite element analysis for bending process were done. The fluting in bended sheet was due to the yield point elongation of material. Due to the yield point elongation, unstable plastic hinge was occurred in course of bending of elastic perfectly plastic sheet. According to the analysis and computational results, lower yield point elongation than 5% was required to prevent fluting in $0.5{\sim}0.6t$ sheet in $15{\sim}20mm$ radius bending.

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Effect of Internal Pressure on Plastic Limit Loads for Elbows with Circumferential Through-wall Crack under Closing Bending Incorporating Large Geometry Change Effects (대변형 효과를 고려한 원주방향 관통균열 엘보우의 닫힘굽힘 한계하중에 미치는 내압 영향 평가)

  • Hong, Seok-Pyo;Kim, Yun-Jae
    • Proceedings of the KSME Conference
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    • pp.1778-1782
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    • 2007
  • Based on three-dimensional (3-D) FE limit analyses, this paper estimates effect of internal pressure on plastic limit loads for elbows with circumferential through-wall crack under in-plane bending incorporating large geometry change effects. Circumferential through-wall crack in extrados is considered. The FE limit analyses using the large geometry change option provide plastic collapse loads (using the twice-elastic-slope method). For the bending mode, closing bending is considered. Other relevant variables affecting plastic limit loads are systematically varied, related to pipe bend geometry (the mean radius, thickness and bend curvature) and defect geometry (the length of circumferential through-wall crack).

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Plastic loads of pipe bends under combined pressure and out-of-plane bending (면외 굽힘하중과 내압의 복합하중을 받는 곡관의 소성하중)

  • Lee, Kuk-Hee;Kim, Yun-Jae;Park, Chi-Yong;Lee, Sung-Ho;Kim, Tae-Ryong
    • Proceedings of the KSME Conference
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    • pp.1836-1841
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    • 2007
  • Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit and TES(Twice-Elastic-Slope) loads for pipe bends under combined pressure and out-of-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly-plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide TES plastic loads. A wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and TES plastic load solutions for pipe bends under out-of-plane bending are proposed.

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An Investigation about Dynamic Behavior of Three Point Bending Specimen

  • Cho, Jae-Ung;Han, Moon-Sik
    • Transactions of the Korean Society of Automotive Engineers
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    • v.8 no.4
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    • pp.149-157
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    • 2000
  • Computer simulations of the mechanical behavior of a three point bend specimen with a quarter notch under impact load are performed. The case with a load application point at the side is considered. An elastic-plastic von Mises material model is chosen. Three phases such as impact bouncing and bending phases are found to be identified during the period from the moment of impact to the estimated time for crack initiation. It is clearly shown that no plastic deformation near the crack tip is appeared at the impact phase. However it is confirmed that the plastic zone near the crack tip emerges in the second phase and the plastic hinge has been formed in the third phase. Gap opening displacement crack tip opening displacement and strain rate are compared with rate dependent material(visco-plastic material). The stability during various dynamic load can be seen by using the simulation of this study.

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