• Title/Summary/Keyword: Isotropic hardening.

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A Study on Thermal Ratcheting Structure Test of 316L Test Cylinder (316L 시험원통의 열라체팅 구조시험에 관한 연구)

  • Lee, H.Y.;Kim, J.B.;Koo, G.H.
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.243-249
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    • 2001
  • In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The inelastic deformation of the reactor baffle cylinder can occur due to the moving temperature distribution along the axial direction as the hot free surface moves up and down under the cyclic heat-up and cool-down of reactor operations. The ratchet deformations were measured with the laser displacement sensor and LVDTs after cooling the structural specimen which experiences thermal load up to $550^{\circ}$ and the temperature differences of about $500^{\circ}C$. During structural thermal ratchet test, the temperature distribution of the test cylinder along the axial direction was measured from 28 channels of thermocouples and the temperatures were used for the ratchet analysis. The thermal ratchet deformation analysis was performed with the NONSTA code whose constitutive model is nonlinear combined kinematic and isotropic hardening model and the test results were compared with those of the analysis. Thermal ratchet test was carried out with respect to 9 cycles of thermal loading and the maximum residual displacements were measured to be 1.8mm. It was shown that thermal ratchet load can cause a progressive deformation to the reactor structure. The analysis results with the combined hardening model were in reasonable agreement with those of the tests.

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Analysis of Springback and Die Material Suitability in the UHSS Sheet Forming Process (초고강도 강판 성형 시의 스프링백 해석 및 금형 소재 적합성 검토)

  • Oh, I.S.;Yun, D.Y.;Cho, J.H.;Lee, M.G.;Kim, H.Y.;Kim, H.J.
    • Transactions of Materials Processing
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    • v.29 no.4
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    • pp.203-210
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    • 2020
  • In this study, formability and springback behavior of 1.5 GPa grade ultra-high strength steel (UHSS) sheet were predicted through the finite element simulation, and structural stability of the forming dies was verified by the coupled forming-structural analysis. Uniaxial tension and uniaxial tension-compression tests were performed to obtain experimental data for modeling the springback properties of the sheet material. The springback values predicted by simulation were compared with those from actual measurements. The results calculated from the kinematic hardening model were found to be much more accurate than those from the isotropic hardening model. Deformation of the forming die and springback of the product were calculated by the coupled forming-structural analysis. The higher the strength of the die material, the smaller the surface displacement of the die and the springback of the product. The internal stresses of the dies made of three materials, FC300, FCD550 and STD11 were compared with the yield stress of each material. The results provided a basis for determining the most suitable material for each part of the die set. As a result, simulation techniques have been established for predicting formability and springback in the UHSS sheet forming process.

Plastic Buckling Analysis of Rectangular Plates Considering Plastic Compressibility (소성 압축성을 고려한 평판의 소성 좌굴해석)

  • Chan-Ho Shin;Young-Bok Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.32 no.1
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    • pp.141-146
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    • 1995
  • In this study the plastic buckling analysis of a simply supported plate under biaxial compression/tension loading is carried out considering the plastic compressibility. Plastic buckling of a biaxially loaded rectangular plate is governed by two kinds of mechanism, the tension strengthening and plastic weakening under which the optimal combination of tension and compression is obtained for the buckling strength. To consider the plastic compressibility, the Drucker-Prayer plastic potential is employed. General eigenvalue equations are derived for a rectangular plate within the framework of small strain plasticity and isotropic hardening.

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Constitutive equations for polymer mole and rubbers: Lessons from the $20^{th}$ century

  • Wagner, Manfred H.
    • Korea-Australia Rheology Journal
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    • v.11 no.4
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    • pp.293-304
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    • 1999
  • Refinements of classical theories for entangled or crosslinked polymeric systems have led to incommensurable models for rubber networks and polymer melts, contrary to experimental evidence, which suggests a great deal of similarity. Uniaxial elongation and compression data of linear and branched polymer melts as well as of crosslinked rubbers were analyzed with respect to their nonlinear strain measure. This was found to be the result of two contributions: (1) affine orientation of network strands, and (2) isotropic strand extension. Network strand extension is caused by an increasing restriction of lateral movement of polymer chains due to deformation, and is modelled by a molecular stress function which in the tube concept of Doi and Edwards is the inverse of the relative tube diameter. Up to moderate strains, $f^2$ is found to be linear in the average stretch for melts as well as for rubbers, which corresponds to a constant tube volume. At large strains, rubbers show maximum extensibility, while melts show maximum molecular tension. This maximum value of the molecular stress function governs the ultimate magnitude of the strain-hardening effect of linear and long-chain branched polymer melts in extensional flows.

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Numerical simulations of localization of deformation in quasi-brittle materials within non-local softening plasticity

  • Bobinski, J.;Tejchman, J.
    • Computers and Concrete
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    • v.1 no.4
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    • pp.433-455
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    • 2004
  • The paper presents results of FE-calculations on shear localizations in quasi-brittle materials during both an uniaxial plane strain compression and uniaxial plane strain extension. An elasto-plastic model with a linear Drucker-Prager type criterion using isotropic hardening and softening and non-associated flow rule was used. A non-local extension was applied in a softening regime to capture realistically shear localization and to obtain a well-posed boundary value problem. A characteristic length was incorporated via a weighting function. Attention was focused on the effect of mesh size, mesh alignment, non-local parameter and imperfections on the thickness and inclination of shear localization. Different methods to calculate plastic strain rates were carefully discussed.

Influence of yield functions and initial back stress on the earing prediction of drawn cups for planar anisotropic aluminum alloys (평면이방성 알루미늄 재료의 귀발생 예측에 있어서 항복함수와 초기 Back-Stress의 영향)

  • ;F. Barlat
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1998.03a
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    • pp.58-61
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    • 1998
  • Anisotropy is closely related to the formability of sheet metal and should be considered carefully for more realistic analysis of actual sheet metal forming operations. In order to better describe anisotropic plastic properties of aluminum alloy sheets, a planar anisotropic yield function which accounts for the anisotropy of uniaxial yield stresses and strain rate ratios simultaneously was proposed recently[1]. This yield function was used in the finite element simulations of cup drawing tests for an aluminum alloy 2008-T4. Isotropic hardening with a fixed initial back stress based on experimental tensile and compressive test results was assumed in the simulation. The computation results were in very good agreement with the experimental results. It was shown that the initial back stress as well as the yield surface shape have a large influence on the prediction of the cup height profile.

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Finite Element Analysis of Axisymmetric Sheet Hydroforming Processes (축대칭 박판 액압성형 공정의 유한요소 해석)

  • Jeong, Y. H.;Lee, S. H.;Keum, Y. T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.03b
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    • pp.26-29
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    • 1999
  • The sectional forming analysis program for analyzing the hydroforming processes of axisymmetric sheet parts was tleveloped. The rigid-viscoplastic FEM formulation based on membrane theory was derived, wh~cta simi~ltaneously solve force equilibrium as well as non-penetration condition. Hill's non-quadratic normal anisotropic yield theory(1979) was used for material behaviour. For describing the liquid pressure iaction, the flexible tool concept was introduced. Isotropic hardening law was also assumed. To verify the \,alidity of the formulation, the stepped cup forming process as well as the hydrostatic bulging test were \imnlated. Simulation results agreed well with Finckenstein and experimental ones.

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Sectonal Forming Analysis of Stamping Processes of Aluminum Alloy Sheet Metals (알루미늄 합금 박판 스탬핑 공정의 단면 성형 해석)

  • 이광병;이승열;금영탁
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1996.10a
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    • pp.38-47
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    • 1996
  • Sectional analysis program for plane strain or axisymmetric geometry of aluminum alloy sheet metals was developed. For modeling the anomalous behavior of aluminum alloy, Barlat's strain rate potential and Hill's 1990 non-quadratic yield theory arranged under the plane stress assumption were employed. 2-D rigid-viscoplastic FEM formulation based on the bending-augmented membrane theory was derived, solving simultaneously force equilibrium as well as non-penetration condition. Isotropic hardening law was also assumed for yielding behavior. To verify the validity and availability of the developed program, 2-D stretch/draw forming process for plane strain geometry and cylindrical cup deep drawing process for axisymmetric geometry were simulated.

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Sectional Forming Analysis of Stamping Processes for Luminum Alloy Sheet metals (알루미늄 합금 박판 스탬핑 공정의 단면 성형 해석)

  • 이광병;이승열;금영탁
    • Transactions of Materials Processing
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    • v.6 no.4
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    • pp.279-290
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    • 1997
  • The sectional forming analysis of stamping pocesses for aluminum alloy sheet metals was investigated. For the modeling of the anomalous behavior of aluminum alloy sheet. the Barlat's strain rate potential and Hill's 1990 non-quadratic yield theory with an isotropic hardening rule were employed. The rigid-viscoplastic FEM formulation which solves equilibrium equation for plane-strain stage with mesh-normal geometric constraints was derived. A new method to determine the Barlat's anisotropic coefficients was also suggested. To verify the validity of the formulation, the stretch and draw forming processes of a square cup were simulated.

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A controlled destruction and progressive collapse of 2D reinforced concrete frames

  • El houcine, Mourid;Said, Mamouri;Adnan, Ibrahimbegovic
    • Coupled systems mechanics
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    • v.7 no.2
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    • pp.111-139
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    • 2018
  • A successful methodology for modelling controlled destruction and progressive collapse of 2D reinforced concrete frames is presented in this paper. The strategy is subdivided into several aspects including the failure mechanism creation, and dynamic motion in failure represented with multibody system (MBS) simulation that are used to jointly capture controlled demolition. First phase employs linear elasto-plastic analysis with isotropic hardening along with softening plastic hinge concept to investigate the complete failure of structure, leading to creation of final failure mechanism that behaves like MBS. Second phase deals with simulation and control of the progressive collapse of the structure up to total demolition, using the nonlinear dynamic analysis, with conserving/decaying energy scheme which is performed on MBS. The contact between structure and ground is also considered in simulation of collapse process. The efficiency of the proposed methodology is proved with several numerical examples including six story reinforced concrete frame structures.