• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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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.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.574-580
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• 2006

Anisotropy has an important effect on the strain distribution in aluminum alloy sheet forming, and it is closely related to the thinning and formability of sheet metals. Thus, the anisotropy of the material should be properly considered for the realistic analyses of aluminum sheet forming processes. For this, anisotropy can be approached in two different scales: phenomenological and microstructural (polycrystal) models. Recent anisotropic models (Yld2000-2d; Barlat et al.[1] 2003, Cuitino et al.[2] 1992) were employed in this work. For the simulation using shell element, the method which can impose plane stress condition in the polycrystal model is developed. Lankford values and yield stress ratios are calculated along various directions. As planar anisotropic behavior, a circular cup deep drawing simulation was carried out to compare the phenomenological and microstructure models in terms of earing profile.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.332-335
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• 2005

A model is developed to quantitatively analyze the dilatometry curve of carbon steel for the evaluation of phase fraction during transformation. The effect of anisotropic volume change due to transformation mismatch plasticity as well as carbon enrichment in austenite during the transformation is considered in the developed model. The developed model is applied for the analysis of dilatometry curves of carbon steels. The result shows that considering the anisotropic dilatation is very essential to quantitatively evaluate the phase fraction from the dilatation curve.

• Korean Journal of Computational Design and Engineering
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• v.2 no.2
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• pp.71-76
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• 1997

The deformations of polycrystalline materials are modelled by linking a constitutive equation for the crystallographic slip of a single crystal to the macroscopic behavior of the aggregate. In this study, anisotropic elasticity (lattice stretching) of a cubic crystal is incoporated into the anisotropic plasticity from crystallographic slip. The constitutive description for the aggregate, derived from a crystal plasticity theory, is used to formulate a Consistent Penalty Finite Element Method for the anisotropic elasto-viscoplastic deformation of polycrystalline materials. As an application, a plane-strain forging process is simulated and the effects of the initial textures on the deformation behavior of the workpiece are examined.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.10a
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• pp.44-54
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• 1994

A variational formulation and the associated finite elemet equations have been derived for general three-dimensional deformation of a planar anisotropic rigid-plastic sheet metal which obeys the strain-rate potential proposed by BARLAT et al [13]. By using the natural convected coordinate system, the effect of geometric change and the rotation of planar anisotropic axes are considered efficiently. In order to check the validity of present formulation, a cylindrical cup and a square cup deep drawing test was modeled. good agreement was found between the FE simulation and the experiment. The results have shown that the present formulation for planar anisotropic deformation can be efficiently applied to the analysis of sheet metal working processes for planar anisotropic nonferrous metals.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.118-128
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• 1994

The planar anisotropic FEM analysis for predicting the earing profiles and draw-in amounts in the deep-drawing processes is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-based unit vectors and the normal contact pressure. the consistent full set of governing relations, comprising equilibrium and geometric constraint equations, is appropriately linearized. Barlat's strain-rate potential is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and potential parameter. The linear triangular membrane elements are used for depicting the formed sheet. with the numerical simulations of deep drawing processes of flat-top cylindrical cup for the 2090-T3 aluminum effects on the earing behavior are examined. Earing predictions made for the 2090-T3 aluminum alloy sheet show good agreement with experiments, although some discrepancies were observed in the directional trend of cup height and thickness strains.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.153.1-156
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• 1999

Based upon the experimental data from multi-stage tensile loading at angles to the rolling direction of steel sheets, anisotropic hardening rules are proposed. Experiments show that orthotropic anisotropy is maintained and the orientations of orthotropy axes are changed during tensile loading. A phenomenological model is proposed which includes the rotations of orthotropy axes, work hardening and kinematic hardening. Using the model, uniaxial tensile stress, R-value and tensile necking strain are predicted and compared with the experimental data.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.304-307
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• 2008

In order to evaluate the effect of permanent softening behavior on springback prediction, 2D-draw bending simulations were compared with experiments for friction stir welded DP590 steel sheets. To account fur the nonlinear hardening behavior, the combined isotropic-kinematic hardening law was utilized with and without considering the permanent softening behavior during reverse loading. Also, the non-quadratic orthotropic yield function, Yld2000-2d, was used to describe the anisotropic initial-yielding behavior of the base sheet while anisotropic properties of the weld zone were ignored for simplicity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.144-147
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• 2003

In order to evaluate spring-back behavior in automotive sheet forming processes, a panel shape idealized as a SS-rail has been investigated. After spring-back kas been predicted fer SS-rails using the finite element analysis, results has been compared with experimental measurements for three automotive sheets. To account for hardening behavior such as the Bauschinger and transient effects in addition to anisotropic behavior, the combined isotropic-kinematic hardening law based on the Chaboche type single-surface model and a recently developed non-quadratic anisotropic yield function have been utilized, respectively.