• Title, Summary, Keyword: Anisotropic Yield Function

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An advanced criterion based on non-AFR for anisotropic sheet metals

  • Moayyedian, Farzad;Kadkhodayan, Mehran
    • Structural Engineering and Mechanics
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    • v.57 no.6
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    • pp.1015-1038
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    • 2016
  • In the current research an advanced criterion with non-associated flow rule (non-AFR) for depicting the behavior of anisotropic sheet metals is presented to consider the strength differential effects (SDEs) for these materials. Owing to the fact that Lou et al. (2013) yield function is dependent on structure of an anisotropic material (BCC, FCC and HCP), an advanced yield function with inspiring of Yoon et al. (2014) yield function is proposed which is dependent upon anisotropic structures. Furthermore, to compute Lankford coefficients, a new pressure sensitive plastic potential function which would be dependent to anisotropic structure is presented and coupled with the proposed yield function with employing a non-AFR in a novel criterion which is called here 'dvanced criterion'. Totally eighteen experimental data are required to calibrate the criterion contained of directional tensile and compressive yield stresses for the yield function and directional Lankford coefficients for the plastic potential function. To verify the criterion, three anisotropic sheet metals with different structures are taken as case studies such as Al 2008-T4 (a BCC material), Al 2090-T3 (a FCC material) and AZ31 (a HCP material).

Approximate Yield Criterion for Voided Anisotropic Ductile Materials

  • Kim, Youngsuk;Sungyeun Won;Kim, Dogsoo;Hyunsung Son
    • Journal of Mechanical Science and Technology
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    • v.15 no.10
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    • pp.1349-1355
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    • 2001
  • As most fractures of ductile materials in metal forming processes occurred due to the results of evolution of internal damage - void nucleation, growth and coalescence. In this paper, an approximate yield criterion for voided (porous) anisotropic ductile materials is developed. The proposed approximate yield function is based on Gurson's yield function in conjunction with the Hosford's non-quadratic anisotropic yield criterion in order to consider the characteristic of anisotropic properties of matrix material. The associated flow rules are presented and the laws governing void growth with strain are derided. Using the proposed model void growth of an anisotropic sheet under biaxial tensile loading and its effect on sheet metal formability are investigated. The yield surface of voided anisotropic sheet and void growth with strain are predicted and compared with the experimental results.

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Effect of Strain Rate on the Anisotropic Deformation Behavior of Advanced High Strength Steel Sheets (변형률속도에 따른 고강도 강판의 이방성 변화에 관한 연구)

  • Huh, J.;Huh, H.;Lee, C.S.
    • Transactions of Materials Processing
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    • v.20 no.8
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    • pp.595-600
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    • 2011
  • This paper investigates the effect of strain rate on the anisotropic deformation behavior of advanced high strength steel sheets. Uniaxial tensile tests were carried out on TRIP590 and DP780 steel sheets at strain rates ranging from 0.001/sec to 100/sec to determine yield stresses and r-values at various loading angles from the reference rolling direction. R-values were determined by the digital image correlation technique. Hill48 and Yld2000-2d yield functions were tested for their capability to describe the plastic deformation anisotropy of the materials. Initial yield loci were constructed using the Yld2000-2d yield function, which adequately described the anisotropic behavior of the materials. The shape of the initial yield loci was found to change with different strain rate, and the anisotropic behavior decreased with increasing strain rate.

A New Yield Function for Voided Materials (보이드 재료에 대한 새로운 항복함수의 제안)

  • 김성태
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.13-16
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    • 2000
  • In this paper the authors proposed a new anisotropic yield criterion for porous ductile materials. By using the proposed yield criterion and its flow rules a damage evolution of anisotropic sheet under biaxial tensile loading is investigated. A comparison of yield locus and damage evolution between the proposed yield criterion and experiments are carried out. the results are in good agreement.

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Time-Dependent Spring-back Prediction of Aluminum Alloy 6022-T4 Sheets Using Time-Dependent Constitutive law (시간 의존성 구성방정식을 이용한 AA6022-T4 판재의 탄성 복원 예측)

  • Park, T.;Ryou, R.;Lee, M.G.;Chung, K.H.;Wagoner, R.H.;Chung, K.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.330-333
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    • 2009
  • The time-dependent constitutive law was developed based on viscoelastic-plasticity to describe the time-dependent spring-back behavior of aluminum alloy 6022-T4 sheets. Besides nonlinear viscoelasticity, non-quadratic anisotropic yield function, Yld2000-2d, was used to account for the anisotropic yield behavior, while the combined isotropic-kinematic hardening law was used to represent the Bauschinger effect and transient hardening. For verification purposes, finite element simulations were performed for the draw-bending and the results were compared with experimental results.

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Time-Dependent Spring-back Prediction of Aluminum Alloy 6022-T4 Sheets Using Time-Dependent Constitutive law (시간 의존성 구성방정식을 이용한 AA6022-T4 판재의 탄성 복원 예측)

  • Park, T.;Ryou, H.;Lee, M.G.;Chung, K.H.;Wagoners, R.H.;Chung, K.
    • Transactions of Materials Processing
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    • v.18 no.6
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    • pp.494-499
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    • 2009
  • The time-dependent constitutive law was utilized based on viscoelastic-plasticity to predict the time-dependent spring-back behavior of aluminum alloy 6022-T4 sheets. Besides nonlinear viscoelasticity, non-quadratic anisotropic yield function, Yld2000-2d, was used to account for the anisotropic yield behavior, while the combined isotropic-kinematic hardening law was used to represent the Bauschinger effect and transient hardening. For verification purposes, finite element simulations were performed for the draw-bending and the results were compared with experimental results.

Numerical Implementation of Modified Coulomb-Mohr Yield Criterion for Anisotropic and Asymmetric Materials

  • Lee Myoung-Gyu;Kim Ji-Hoon;Ryou Han-Sun;Chung Kwan-Soo;Youn Jae-Ryoun;Kang Tae-Jin
    • Fibers and Polymers
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    • v.7 no.3
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    • pp.276-285
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    • 2006
  • Development and numerical implementation for an elastoplastic constitutive model for anisotropic and asymmetric materials are presented in this paper. The Coulomb-Mohr yield criterion was modified to consider both the anisotropic and asymmetric properties. The modified yield criterion is an isotropic function of the principal values of a symmetric matrix which is linearly transformed from the Cauchy stress space. In addition to the constitutive equation, the numerical treatment for the singularity in the vertex region of yield surface and stress integration algorithm based on elastoplasticity were presented. In order to assess the accuracy of numerical algorithm, isoerror maps were considered. Also, extension of a strip with a circular hole was simulated and results compared with those obtained using the (smooth) Mises yield criterion to validate stress output for a complex stress state.

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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    • 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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Springback Prediction of Friction Stir Welded DP590 Steel Sheet Considering Permanent Softening Behavior (영구연화거동을 고려한 마찰교반용접(FSW)된 DP590 강판의 탄성복원 예측)

  • Kim, J.;Lee, W.;Chung, K.H.;Park, T.;Kim, D.G.;Kim, Chong-Min;Kim, D.
    • Transactions of Materials Processing
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    • v.18 no.4
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    • pp.329-335
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    • 2009
  • In order to better predict the springback for friction stir welded DP590 steel sheet, the combined isotropic-kinematic hardening was formulated with considering the permanent softening behavior during reverse loading. As for yield function, the non-quadratic anisotropic yield function, Yld2000-2d, was used under plane stress condition. For the verification purposes, comparisons of simulation and experiments were performed here for the unconstrained cylindrical bending, the 2-D draw bending tests. For two applications, simulations showed good agreements with experiments.

3-D FEM Analysis of Forming Processes of Planar Anisotropic Sheet Metal (평면이방성 박판성형공정의 3차원 유한요소해석)

  • 이승열;금영탁;박진무
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.8
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    • pp.2113-2122
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    • 1994
  • The 3-D FEM analysis for simulating the stamping operation of planar anisotropic sheet metals with arbitrarily-shaped tools is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The consistent full set of governing relations, comprising equilibrium equation and mesh-normal geometric constraints, is appropriately linearized. The linear triangular elements are used for depicting the formed sheet, based on membrane approximation. Barlat's non-quadratic anisotropic yield criterion(strain-rate potential) is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and non-quadratic function parameter. The planar anisotropic finite element formulation is tested with the numerical simulations of the stamping of an automotive hood inner panel and the drawing of a hemispherical punch. The in-plane anisotropic effects on the formability of both mild steel and aluminum alloy sheet metals are examined.