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W Zeng - One of the best experts on this subject based on the ideXlab platform.

  • A smoothing technique based beta finite element method (βFEM) for crystal Plasticity modeling
    Computers and Structures, 2016
    Co-Authors: W Zeng, G. R. Liu, Di Li, X.w. Dong
    Abstract:

    This paper presents a novel class of smoothing techniques based beta finite element method (βFEM) for modeling of crystalline materials. The method is first examined by a simple standard patch test and applied in elastic problems. It is then implemented to model the anisotropic Plastic deformation of rate-independent single crystals and bi-crystal. Several representative examples are studied to demonstrate the capability of proposed method with the integration algorithm for capturing the strain localization and dealing with Plastic Incompressibility. It is also performed to simulate the mechanical behavior of polycrystalline aggregates through modeling the synthetic microstructure constructed by Voronoi tessellation technique.

  • A smoothing technique based beta finite element method (βFEM) for crystal Plasticity modeling
    Computers & Structures, 2015
    Co-Authors: W Zeng, Di Li, Xiaohu Dong
    Abstract:

    A novel smoothing technique based beta finite element method (βFEM) is proposed.The method can produce super-accurate solution and treat volumetric locking issue.A framework for large strain rate-independent crystal Plasticity model is introduced.Plastic Incompressibility and large mesh distortion during strain localization are tackled.The approach is further developed for modeling bi-crystal and polycrystalline Plasticity. This paper presents a novel class of smoothing techniques based beta finite element method (βFEM) for modeling of crystalline materials. The method is first examined by a simple standard patch test and applied in elastic problems. It is then implemented to model the anisotropic Plastic deformation of rate-independent single crystals and bi-crystal. Several representative examples are studied to demonstrate the capability of proposed method with the integration algorithm for capturing the strain localization and dealing with Plastic Incompressibility. It is also performed to simulate the mechanical behavior of polycrystalline aggregates through modeling the synthetic microstructure constructed by Voronoi tessellation technique.

  • Smoothing technique based crystal Plasticity finite element modeling of crystalline materials
    International Journal of Plasticity, 2015
    Co-Authors: W Zeng, J. M. Larsen, G. R. Liu
    Abstract:

    The smoothed finite element method (S-FEM) is known for its outstanding performance for solid mechanics problems, and working effectively with triangular or tetrahedral mesh that can be generated automatically for complicated geometries. In this work, a framework of S-FEM for modeling anisotropic crystalline Plasticity is presented to simulate the mechanical behavior with rate-independence. The strain smoothing technique is extended to deal with finite strains in a nonlinear incremental integration procedure based on the Newton–Raphson scheme. The constitutive model utilizes a hyperelastic-based multiplicative Plasticity method, which involves a local multiplicative decomposition of the deformation gradient into an elastic and a Plastic part. The stress updates for a planar double-slip model exploit the return-mapping method with exponential map algorithm. The capability of the simulations to capture the strain localization and to handle Plastic Incompressibility of single crystal are demonstrated in representative examples. The proposed formulations and algorithms are also implemented to explore the mesoscopic and macroscopic elasto-Plastic behavior of polycrystalline aggregates through modeling the synthetic microstructure constructed by Voronoi tessellation technique.

G. R. Liu - One of the best experts on this subject based on the ideXlab platform.

  • A smoothing technique based beta finite element method (βFEM) for crystal Plasticity modeling
    Computers and Structures, 2016
    Co-Authors: W Zeng, G. R. Liu, Di Li, X.w. Dong
    Abstract:

    This paper presents a novel class of smoothing techniques based beta finite element method (βFEM) for modeling of crystalline materials. The method is first examined by a simple standard patch test and applied in elastic problems. It is then implemented to model the anisotropic Plastic deformation of rate-independent single crystals and bi-crystal. Several representative examples are studied to demonstrate the capability of proposed method with the integration algorithm for capturing the strain localization and dealing with Plastic Incompressibility. It is also performed to simulate the mechanical behavior of polycrystalline aggregates through modeling the synthetic microstructure constructed by Voronoi tessellation technique.

  • Smoothing technique based crystal Plasticity finite element modeling of crystalline materials
    International Journal of Plasticity, 2015
    Co-Authors: W Zeng, J. M. Larsen, G. R. Liu
    Abstract:

    The smoothed finite element method (S-FEM) is known for its outstanding performance for solid mechanics problems, and working effectively with triangular or tetrahedral mesh that can be generated automatically for complicated geometries. In this work, a framework of S-FEM for modeling anisotropic crystalline Plasticity is presented to simulate the mechanical behavior with rate-independence. The strain smoothing technique is extended to deal with finite strains in a nonlinear incremental integration procedure based on the Newton–Raphson scheme. The constitutive model utilizes a hyperelastic-based multiplicative Plasticity method, which involves a local multiplicative decomposition of the deformation gradient into an elastic and a Plastic part. The stress updates for a planar double-slip model exploit the return-mapping method with exponential map algorithm. The capability of the simulations to capture the strain localization and to handle Plastic Incompressibility of single crystal are demonstrated in representative examples. The proposed formulations and algorithms are also implemented to explore the mesoscopic and macroscopic elasto-Plastic behavior of polycrystalline aggregates through modeling the synthetic microstructure constructed by Voronoi tessellation technique.

X.w. Dong - One of the best experts on this subject based on the ideXlab platform.

  • A smoothing technique based beta finite element method (βFEM) for crystal Plasticity modeling
    Computers and Structures, 2016
    Co-Authors: W Zeng, G. R. Liu, Di Li, X.w. Dong
    Abstract:

    This paper presents a novel class of smoothing techniques based beta finite element method (βFEM) for modeling of crystalline materials. The method is first examined by a simple standard patch test and applied in elastic problems. It is then implemented to model the anisotropic Plastic deformation of rate-independent single crystals and bi-crystal. Several representative examples are studied to demonstrate the capability of proposed method with the integration algorithm for capturing the strain localization and dealing with Plastic Incompressibility. It is also performed to simulate the mechanical behavior of polycrystalline aggregates through modeling the synthetic microstructure constructed by Voronoi tessellation technique.

Stefanie Reese - One of the best experts on this subject based on the ideXlab platform.

  • Efficient Finite Element and Contact Procedures for the Simulation of High Speed Sheet Metal Forming Processes
    2020
    Co-Authors: A. Brosius, Stefanie Reese, M. Kleiner, Marco Schwarze
    Abstract:

    A large variety of forming processes is used in industrial manufacturing processes. The numerical simulation of such processes puts high demands on the finite element technology. Usually first order isoparametric elements are preferred because of their robustness and numerical efficiency. Unfortunately, these elements tend to undesired numerical effects like ”locking”, predominant in situations characterized by Plastic Incompressibility or pure bending. To overcome this problem, several authors [1, 2, 4] propose finite element formulations based on the concept of reduced integration with hourglass stabilization by applying the ”enhanced strain method”. The main advantage of the proposed new isoparametric solid-shell formulation with linear ansatz functions is the fact that the undesirable effects of locking are eliminated. The previously described element technique can be applied to analyze specific problems of high speed forming into a cavity: Working with contact surfaces discretized by first order finite elements leads to discontinuities of the normal patch vector and, subsequently, to non-smooth sliding [5]. In quasi-static forming processes these discontinuities will not influence the contact forces noticeably. However, in dynamic investigations the sudden change of contact forces due to the rough surface description leads to a very high acceleration of the contact nodes. To avoid this effect, a smoothing algorithm will be described.

  • A finite strain constitutive model for non-quadratic yield criteria and nonlinear kinematic/isotropic hardening: application to sheet metal forming
    Archive of Applied Mechanics, 2016
    Co-Authors: Tiago Jordão Grilo, Ivaylo N. Vladimirov, Robertt A. F. Valente, Stefanie Reese
    Abstract:

    In this paper, a finite strain material model for complex Plastic anisotropy with nonlinear isotropic and kinematic hardening is consistently derived. The model is based on the classical multiplicative decomposition of the deformation gradient and derived in a thermodynamically consistent way. An important new aspect of the work is the straightforward implementation of general and anisotropic yield criteria into a constitutive model, which is entirely formulated in the reference configuration. Nevertheless, and for the sake of illustrating the potential of the model, in this work a Barlat-type ( Yld2004-18p ) yield criterion is employed. The kinematic hardening formulation follows the continuum mechanical extension of the classical rheological model of Armstrong–Frederick hardening. The numerical integration of the evolution equations is carried out using the exponential map approach, which is able to preserve Plastic Incompressibility. For numerical efficiency purposes, the exponential tensor functions are evaluated in a closed form using the spectral decomposition, and special attention is given to the preservation of the internal variables’ symmetry. The model is assessed by means of several numerical simulations for anisotropic materials at finite strains, including sheet metal forming processes with comparison to experimental data.

  • Influence of Explicit and Implicit Integration of Hyperelastic-Plastic Combined Hardening Models on the Springback in Sheet Forming
    Volume 1: Applied Mechanics; Automotive Systems; Biomedical Biotechnology Engineering; Computational Mechanics; Design; Digital Manufacturing; Educati, 2014
    Co-Authors: Michael P. Pietryga, Ivaylo N. Vladimirov, Stefanie Reese
    Abstract:

    In this paper, we investigate the computational efficiency of explicit and implicit integration schemes for hyperelastic-Plastic combined hardening Plasticity and examine the influence on the simulated springback in sheet metal forming. Due to the deviatoric character of the evolution equations, the finite strain combined hardening model discussed here is integrated by means of the exponential map algorithm in order to fulfil Plastic Incompressibility. We focus here on different possibilities of evaluating the exponential tensor functions of the material model. One option is to use the spectral decomposition to evaluate the exponential tensor functions in closed form. Alternatively, the latter functions can be evaluated by Taylor series expansion. Furthermore, we examine the potential of an explicit formulation of elasto-Plasticity with combined hardening regarding accuracy and efficiency. The material model equations have been implemented as user material subroutines UMAT and VUMAT for use in the commercial solvers ABAQUS/Standard and ABAQUS/Explicit, respectively. The numerical models are applied to the finite element simulation of draw bending, where the forming step is simulated both in implicit and explicit manner, whereas the ensuing springback step is carried out only implicitly.Copyright © 2014 by ASME

  • Modelling Non-Quadratic Anisotropic Yield Criteria and Mixed Isotropic-Nonlinear Kinematic Hardening at Finite Strains
    Key Engineering Materials, 2014
    Co-Authors: Tiago Jordão Grilo, Ivaylo N. Vladimirov, Robertt A. F. Valente, Stefanie Reese
    Abstract:

    A constitutive model that accounts for mixed isotropic-nonlinear kinematic hardening, suitable for any non-quadratic yield criteria, is proposed. The finite strain model is derived from a thermodynamically consistent framework and relies on the multiplicative split of the deformation gradient in the context of hyperelasticity. The nonlinear kinematic hardening approach is introduced in the constitutive model by means of the multiplicative split of the Plastic deformation gradient. The constitutive equations are consistently derived by exploiting the dissipation inequality, and expressed by symmetric tensor-valued internal variables only. The exponential map algorithm was employed in the integration of the evolution equations. This algorithmic strategy has the advantage of preserving both the Plastic Incompressibility and the symmetry of the internal variables. The model was implemented into a material user-subroutine of a commercial finite element code (ABAQUS), and some numerical results are presented to assess the performance of the present model.

  • On the influence of kinematic hardening on Plastic anisotropy in the context of finite strain Plasticity
    International Journal of Material Forming, 2011
    Co-Authors: Ivaylo N. Vladimirov, Michael P. Pietryga, Stefanie Reese
    Abstract:

    The paper discusses the application of a newly developed material model for finite anisotropic Plasticity to the simulation of earing formation in cylindrical cup drawing. The model incorporates Hill-type Plastic anisotropy, nonlinear kinematic and nonlinear isotropic hardening. The constitutive framework is derived in the context of continuum thermodynamics and represents a multiplicative formulation of anisotropic elastoPlasticity in the finite strain regime. Plastic anisotropy is described by means of second-order structure tensors which are used as additional tensor-valued arguments in the representation of the yield criterion and the Plastic flow rule. The evolution equations are integrated by a form of the exponential map that fullfils Plastic Incompressibility and preserves the symmetry of the internal variables. The numerical examples investigate the influence of the hardening behaviour on an initially anisotropic yield criterion. In particular, the influence of using the kinematic hardening component of the model in addition to isotropic hardening in the earing simulations is examined. Comparisons with test data for aluminium and steel sheets display a good agreement between the finite element results and the experimental data.

H. Baaser - One of the best experts on this subject based on the ideXlab platform.