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Jeong Whan Yoon - One of the best experts on this subject based on the ideXlab platform.

  • analytical description of an asymmetric yield Function yoon2014 by considering anisotropic hardening under non associated flow rule
    International Journal of Plasticity, 2021
    Co-Authors: Jeong Whan Yoon
    Abstract:

    Abstract A simple analytical form for yield surface distortion under non-associated flow rule is developed from the expression of the transformed second and third deviatoric stress invariants in Yoon et al. (2014). The developed analytical yield criterion has the same ability as the original yield criterion to describe material's strength differential (SD) effect. Compared with Yoon et al. (2014) criterion, the material parameters in the analytical form presented in this study can be directly calculated from the tension and compression stresses along 0°, 45°, 90° and equi-biaxial directions, which doesn't need any optimization process and interpolation to describe the evolution of asymmetric yield surface under the proportional loadings. The proposed yield criterion can accurately predict the anisotropic hardening along 0°, 45°, 90° and equi-biaxial directions under tension and compression, which will make the significant improvements in the stress predictions including 15°, 30°, 60° and 75°. To guarantee the convexity of yield surface during loading history, the minimum order of principal minor determinant is checked. The proposed yield criterion has been successfully applied for HCP materials to validate its general applicability for describing anisotropy/asymmetry-induced distorted yield surface during deformation. In addition, an analytical asymmetric Plastic Potential Function is developed based on Poly4 yield Function. The accuracy of the proposed Plastic Potential Function for r-value evolution under tension and compression has been verified by applying it to different materials.

  • the roles of yield Function and Plastic Potential under non associated flow rule for formability prediction with perturbation approach
    IDDRG 2020 : Proceedings of the 39th International Deep-Drawing Research Group Annual Conference 2020, 2020
    Co-Authors: Jeong Whan Yoon
    Abstract:

    In this study, the perturbation approach for predicting material's forming limit strains under non-associated flow rule (non-AFR) is proposed. The influence of yield Function and Plastic Potential Function on the forming limit curve (FLC) evaluated by the perturbation approach are discussed through analyzing the normalized growth rate of a perturbation. In the framework of non-AFR, Hill'48 and Yld2000-2d are chosen for AA5754-O. The results show that the left side of FLCs predicted with the different forms of yield Function and Plastic Potential nearly overlap. Hence, it is concluded that the yield Function and Plastic Potential have a negligible influence on the forming limit strain under a negative strain path. However, the FLC under a positive strain path is principally dependent on the relationship between strain ratio β and stress ratio α, which can be determined by the Plastic Potential. Additionally, in comparison to the FLC under AFR, an increase in the forming limits strain is observed near the plain strain region, when the derivative of the normalized yield Function concerning α is positive and vice versa.

  • a non associated Plasticity model with anisotropic and nonlinear kinematic hardening for simulation of sheet metal forming
    International Journal of Solids and Structures, 2015
    Co-Authors: Aboozar Taherizadeh, Daniel E Green, Jeong Whan Yoon
    Abstract:

    Abstract A material model for more thorough analysis of Plastic deformation of sheet materials is presented in this paper. This model considers the following aspects of Plastic deformation behavior of sheet materials: (1) the anisotropy in yield stresses and in work hardening by using Hill’s 1948 quadratic yield Function and non-constant stress ratios which leads to different flow stress hardening in different directions, (2) the anisotropy in Plastic strains by using a quadratic Plastic Potential Function and non-associated flow rule, also based on Hill’s 1948 model and r -values, and (3) the cyclic hardening phenomena such as the Bauschinger effect, permanent softening and transient behavior for reverse loading by using a coupled nonlinear kinematic hardening model. Plasticity fundamentals of the model were derived in a general framework and the model calibration procedure was presented for the Plasticity formulations. Also, a generic numerical stress integration procedure was developed based on backward-Euler method, so-called multi-stage return mapping algorithm. The model was implemented in the framework of the finite element method to evaluate the simulation results of sheet metal forming processes. Different aspects of the model were verified for two sheet metals, namely DP600 steel and AA6022 aluminum alloy. Results show that the new model is able to accurately predict the sheet material behavior for both anisotropic hardening and cyclic hardening conditions. The drawing of channel sections and the subsequent springback were also simulated with this model for different drawbead configurations. Simulation results show that the current non-associated anisotropic hardening model is able to accurately predict the sidewall curl in the drawn channel sections.

  • study on the definition of equivalent Plastic strain under non associated flow rule for finite element formulation
    International Journal of Plasticity, 2014
    Co-Authors: Mohsen Safaei, Jeong Whan Yoon, Wim De Waele
    Abstract:

    Abstract As opposed to associated flow rule (AFR) in which yield Function and Plastic Potential are equal, the different definitions for them is an inherent characteristic of non-associated flow rule (non-AFR). This imposes a specific relation (but not equality) between equivalent Plastic strain and Plastic compliance factor. Unavoidably, this leads to a laborious effort for FE implementation of non-associated constitutive model specifically when several internal variables (such as kinematic hardening or damage parameters) are involved. This paper is mainly devoted to studying the conditions at which the non-AFR approach can be simplified so that the numerical implementation scheme is more convenient without loss of accuracy. It will be shown that by scaling the Plastic Potential Function, the equality of equivalent Plastic strain and compliance factor can be reserved. The effect of scaling of the non-AFR based on Barlat et al.’s (2003) anisotropic model (called Yld2000-2d) is comprehensively studied with FE simulation of tensile loading under uniaxial tensions along the different orientations as well as balanced biaxial stress condition. A fully implicit return-mapping scheme was introduced for stress integration of the constitutive model in a User-defined MATerial subroutine (UMAT). Cup drawing simulations of a highly textured aluminum alloy 2090-T3 were performed using simplified and original approaches. The results prove that the proposed simplified technique is a reliable alternative for the full expression.

  • anisotropic hardening model based on non associated flow rule and combined nonlinear kinematic hardening for sheet materials
    Numisheet 2014: The 9th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes: Part a Benchmark Problems a, 2013
    Co-Authors: Aboozar Taherizadeh, Daniel E Green, Jeong Whan Yoon
    Abstract:

    A material model for more effective analysis of Plastic deformation of sheet materials is presented in this paper. The model is capable of considering the following aspects of Plastic deformation behavior of sheet materials: the anisotropy in yielding stresses in different directions by using a quadratic yield Function (based on Hill’s 1948 model and stress ratios), the anisotropy in work hardening by introducing non-constant flow stress hardening in different directions, the anisotropy in Plastic strains in different directions by using a quadratic Plastic Potential Function and non-associated flow rule (based on Hill’s 1948 model and Plastic strain ratios, r-values), and finally some of the cyclic hardening phenomena such as Bauschinger’s effect and transient behavior for reverse loading by using a coupled nonlinear kinematic hardening (so-called Armstrong-Frederick-Chaboche model). Basic fundamentals of the Plasticity of the model are presented in a general framework. Then, the model adjustment procedure is derived for the Plasticity formulations. Also, a generic numerical stress integration procedure is developed based on backward-Euler method (so-called multi-stage return mapping algorithm). Different aspects of the model are verified for DP600 steel sheet. Results show that the new model is able to predict the sheet material behavior in both anisotropic hardening and cyclic hardening regimes more accurately. By featuring the above-mentioned facts in the presented constitutive model, it is expected that more accurate results can be obtained by implementing this model in computational simulations of sheet material forming processes. For instance, more precise results of springback prediction of the parts formed from highly anisotropic hardened materials or that of determining the forming limit diagrams is highly expected by using the developed material model.

Hyunyong Jeong - One of the best experts on this subject based on the ideXlab platform.

  • A new yield Function and a hydrostatic stress-controlled void nucleation model for porous solids with pressure-sensitive matrices
    International Journal of Solids and Structures, 2002
    Co-Authors: Hyunyong Jeong
    Abstract:

    Abstract A macroscopic yield Function for porous solids with pressure-sensitive matrices modeled by Coulomb's yield Function was obtained by generalizing Gurson's yield Function with consideration of the hydrostatic yield stress of a spherical thick-walled shell and by fitting the finite element results of the yield stresses of a voided cube. The macroscopic yield Function is valid for the negative hydrostatic stress as well as for the positive hydrostatic stress. From the yield Function, a Plastic Potential Function for the porous solids was derived either for Plastic normality flow or for Plastic non-normality flow of the pressure-sensitive matrices. In addition, void nucleation was modeled by a normal distribution Function with the macroscopic hydrostatic stress regarded as a controlling stress. This set of constitutive relations was implemented into a finite element code abaqus as a user material subroutine to analyze the cavitation and the deformation behavior of a rubber-modified epoxy around a crack tip under the Mode I plane strain conditions. By comparing the cavitation zone and the Plastic zone obtained in the analysis with those observed in an experiment, the mean stress and the standard deviation for the void nucleation model could be determined. The cavitation and the deformation behavior of the rubber-modified epoxy were also analyzed around notches under four-point bending. The size and shape of the cavitation zone and the Plastic zone were shown to be in good agreement with those observed in an experiment.

  • a macroscopic constitutive law for porous solids with pressure sensitive matrices and its implications to Plastic flow localization
    International Journal of Solids and Structures, 1995
    Co-Authors: Hyunyong Jeong
    Abstract:

    A macroscopic yield criterion for porous solids with pressure-sensitive matrices modeled by Coulomb's yield criterion is obtained by generalizing Gurson's yield criterion with consideration of the hydrostatic yield stress for a spherical thick-walled shell and by fitting the finite element results of a voided cube. From the macroscopic yield criterion, a Plastic Potential Function for porous solids is derived for either Plastic normality or non-normality flow for pressure-sensitive matrices. In addition, the elastic relation, an evolution rule for the Plastic behavior of the matrices, the consistency equation and the void volume evolution equation are presented to complete a set of constitutive relations for porous solids with rate-dependent pressure-sensitive matrices. Based on the constitutive relations, Plastic flow localization is analysed for porous solids with various pressure-sensitive dilatant matrices with power-law strain hardening or with intrinsic strain softening under plane strain tension, axisymmetric tension and plane stress biaxial loading. Our numerical results indicate that the non-normality of the pressure-sensitive matrices promotes localization under plane strain tension. Under axisymmetric tension the critical strain at localization decreases significantly as the pressure sensitivity of the matrices increases. Under plane stress biaxial loading conditions, the pressure sensitivity of the matrices with normality retards localization significantly. However, the pressure sensitivity of the matrices with non-normality retards localization slightly for positive strain ratios and promotes localization slightly for negative strain ratios. Under all three deformation modes, the strain softening coupled with a moderate amount of void volume inhomogeneity is shown to have a dominant role in Plastic flow localization.

Jun Yanagimoto - One of the best experts on this subject based on the ideXlab platform.

  • analysis of rectangular cup drawing considering anisotropic hardening and cyclic effect for orthogonal anisotropic materials
    Mechanics of Materials, 2021
    Co-Authors: Honghao Wang, Akira Yoshimura, Tom Taylor, Nan Liu, Jun Yanagimoto
    Abstract:

    Abstract An anisotropic Plasticity model is developed based on the non-associated flow rule with anisotropic hardening. The model combines non-quadratic yield Function and quadratic Plastic Potential Function for orthogonal anisotropic sheet metals. The model is also expanded to properly reproduce the cyclic effect during forming processes. The simple formulations can contribute to cost saving in the parameter acquisition process and implementation. The developed model was implemented into the finite element code ABAQUS as a user material subroutine under a general three-dimensional condition. To evaluate the capability of the Plasticity model, different loading conditions and prediction of the yield surface were considered. A multi-step rectangular cup drawing process with the AA5182-O and DP600 sheets including draw/re-draw effects was applied to evaluate the performance of capturing complex Plastic behavior by finite element simulation. The results show that the anisotropic Plasticity model is capable of describing the anisotropic behaviors including anisotropic hardening and cyclic hardening with high accuracy and efficiency.

  • Plastic anisotropic constitutive equation based on stress rate dependency related with non associated flow rule for bifurcation analysis
    Journal of Physics: Conference Series, 2017
    Co-Authors: Tetsuo Oya, Jun Yanagimoto, Koichi Ito, Gen Uemura, Naomichi Mori
    Abstract:

    In metal forming, progress in material models is required to construct a general and reliable fracture prediction framework because of the increased use of advanced materials and growing demand for higher prediction accuracy. In this study, a fracture prediction framework based on bifurcation theory is constructed. A novel material model based on the stress-rate dependence related to a non-associated flow rule is presented. This model is based on a non-associated flow rule with an arbitrary higher-order yield Function and a Plastic Potential Function for any anisotropic material. This formulation is combined with the stress-rate-dependent Plastic constitutive equation, which is known as the Ito–Goya rule, to construct a generalized Plastic constitutive model in which non-normality and non-associativity are reasonably included. Then, by adopting three-dimensional bifurcation theory, which is referred to the 3D theory, a new theoretical framework for fracture prediction based on the initiation of a shear band is constructed. Using virtual material data, a numerical simulation is carried out to produce a fracture limit diagram, which is used to investigate the characteristics of the proposed methodology.

  • Material Model based on Stress-rate Dependency Related with Non-associated Flow Rule for Fracture Prediction in Metal Forming
    Procedia Engineering, 2017
    Co-Authors: Jun Yanagimoto, Uemura, Naomichi Mori
    Abstract:

    Abstract Fracture prediction in metal forming has captured attention because of its practical importance. Recently, demand for fracture prediction has grown to conduct an effective forming process design using numerical simulation; however, the increasing use of high-strength steels and anisotropic materials prevents accurate simulation in large strains in which fracture tend to occur. In this study, a fracture prediction framework based on the bifurcation theory is constructed. The core is a material model based on stress-rate dependency related with non-associate flow rule. This model is based on non-associated flow rule with arbitrary higher order yield Function and Plastic Potential Function for any anisotropic materials. And this formulation is combined with the stress-rate-dependency Plastic constitutive equation, which is known as the Ito-Goya Plastic constitutive equation, to construct a generalized Plastic constitutive model in which non-normality and non-associativity are reasonably included. Then, by adopting the three-dimensional bifurcation theory, more accurate prediction of the initiation of shear band is realized, leading to general and reliable construction of forming limit diagram.

  • material model based on non associated flow rule with higher order yield Function for anisotropic metals
    Procedia Engineering, 2014
    Co-Authors: Tetsuo Oya, Jun Yanagimoto, Koichi Ito, Gen Uemura, Naomichi Mori
    Abstract:

    Abstract A new expression for the Plastic constitutive model for materials with initial anisotropy is proposed. A Plastic strain rate tensor should be permitted to follow, to a certain extent, the rotation of the stress rate tensor, which rotates instantly from the direction of the current stress tensor as in the case of Plastic instability. For this purpose, a non-associated normality model, in which the Plastic Potential Function is defined independently of the yield Function, has been adopted in the proposed model. An explicit expression for the equivalent Plastic strain rate, which is Plastic-work-conjugated with the defined equivalent stress corresponding to the proposed yield Function, is also presented. This is important for expressing a generalized work-hardening rule for materials with Plastic flow stress anisotropy. The proposed theory is expected to overcome the serious problems in the associated Plastic flow theory.

Michael Brünig - One of the best experts on this subject based on the ideXlab platform.

  • Numerical simulation of the localization behavior of hydrostatic-stress-sensitive metals
    International Journal of Mechanical Sciences, 2000
    Co-Authors: Michael Brünig, Simone Berger, Hans Obrecht
    Abstract:

    Abstract The present paper deals with the numerical simulation of the elastic–Plastic deformation and localization behavior of solids which are Plastically dilatant and sensitive to hydrostatic stresses. The model is based on a generalized macroscopic theory taking into account macroscopic as well as microscopic experimental data obtained from tests with iron-based metals. It shows that hydrostatic components may have a significant effect on the onset of localization and the associated deformation modes, and that they generally lead to a notable decrease in ductility. The continuum formulation relies on a generalized I1–J2–J3 yield criterion to describe the effect of the hydrostatic stress on the Plastic flow properties of metals. In contrast to classical theories of metal Plasticity, the evolution of the Plastic part of the strain rate tensor is determined by a non-associated flow rule based on a Plastic Potential Function which is expressed in terms of stress invariants and kinematic parameters. Numerical simulations of the elastic–Plastic deformation behavior of hydrostatic-stress-sensitive metals show the physical effects of the model parameters and also demonstrate the efficiency of the formulation. Their results are in excellent agreement with available experimental data. A variety of large-strain elastic–Plastic problems involving pronounced localizations is presented, and the influence of various model parameters on the deformation and localization behavior of hydrostatic-stress-sensitive metals is discussed.

  • numerical simulation of the large elastic Plastic deformation behavior of hydrostatic stress sensitive solids
    International Journal of Plasticity, 1999
    Co-Authors: Michael Brünig
    Abstract:

    Abstract The present paper deals with the numerical simulation of the large elastic–Plastic deformation and localization behavior of metals which are Plastically dilatant and sensitive to hydrostatic stresses. The model is based on a generalized macroscopic theory taking into account macroscopic as well as microscopic experimental data obtained from tests with iron based metals. It shows that hydrostatic components may have a significant effect on the onset of localization and the associated deformation modes, and that they generally lead to a notable decrease in ductility. The continuum formulation relies on the mixed-variant metric transformation tensor which leads to the definition of an appropriate logarithmic strain measure. Its rate is additively decomposed into elastic and Plastic as well as isochoric and volumetric strain rate tensors. Particular attention is focused on the formulation of a generalized I 1 – J 2 yield criterion to describe the effect of the hydrostatic stress on the Plastic flow properties in metals. In contrast to classical theories of metal Plasticity, the evolution of the Plastic part of the strain rate tensor is determined by a non-associated flow rule based on a Plastic Potential Function which is expressed in terms of stress invariants and kinematic parameters. Numerical analyses of the elastic–Plastic deformation and localization behavior of hydrostatic stress-sensitive metals will demonstrate the influence of the constitutive description on critical strains as well as on localization behavior.

Jerzy Gawad - One of the best experts on this subject based on the ideXlab platform.

  • hierarchical multi scale modeling of texture induced Plastic anisotropy in sheet forming
    Computational Materials Science, 2013
    Co-Authors: Albert Van Bael, Paul Van Houtte, Philip Eyckens, Jerzy Gawad, Giovanni Samaey, Dirk Roose
    Abstract:

    Abstract In this paper we present a Hierarchical Multi-Scale (HMS) model of coupled evolutions of crystallographic texture and Plastic anisotropy in Plastic forming of polycrystalline metallic alloys. The model exploits the Finite Element formulation to describe the macroscopic deformation of the material. Anisotropy of the Plastic properties is derived from a physics-based polycrystalline Plasticity micro-scale model by means of virtual experiments. The homogenized micro-scale stress response given by the micro-scale model is approximated by an analytical Plastic Potential Function. The methods to reconstruct the Plastic Potential upon a sufficient change of the crystallographic texture are discussed. A dedicated stress integration scheme is elaborated to utilize the hierarchy of the models. Cup drawing from circular blanks is considered as an example of sheet forming process. The results from the HMS simulations with updating of texture and anisotropy are compared to the outcomes of the FE model assuming constant anisotropy. Experimental verification of the HMS model is provided for two steel grades and one aluminum alloy. An assessment of the texture evolution calculated by the HMS model reveals very high reliability of the predictions. Macroscopic cup profiles obtained by the HMS model show good agreement with the experiment. A substantial improvement of the predicted cup profile is found for one of the investigated steels. The origin of this enhancement is discussed in the context of evolving Plastic anisotropy.