Explicit Simulation of Forming Processes Using a Novel Solid-Shell Concept Based on Reduced Integration

2012 ◽  
Vol 504-506 ◽  
pp. 425-430 ◽  
Author(s):  
Mara Pagani ◽  
Stefanie Reese ◽  
Umberto Perego
Keyword(s):  
Kinematic Hardening ◽  
Plastic Anisotropy ◽  
Material Model ◽  
Isotropic Hardening ◽  
Element Formulation ◽  
Solid Shell ◽  
Explicit Integration ◽  
Assumed Strain ◽  
Shell Finite Element ◽  
Assumed Natural Strain

The contribution deals with the simulation of sheet metal forming processes by means of a recently developed hexahedral solid-shell finite element. In contrast to this earlier work, we pursue here explicit integration. The element formulation has the following features. In order to avoid undesired effects of locking an enhanced assumed strain (EAS) concept using only one EAS degree-of-freedom has been implemented. In addition, by means of the assumed natural strain (ANS) method an excellent performance in bending situations is obtained. A key point of the element formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This procedure leads to the important advantage that the sensitivity of the results with respect to mesh distortion is noticeably reduced. Further the hourglass stabilization is in this way designed that locking is eliminated and numerical stability guaranteed. The finite strain material model for plastic anisotropy and non-linear kinematic and isotropic hardening is motivated by a rheological model including Armstrong-Frederick kinematic hardening. The element formulation has been implemented into the academic code FEAP. Some standard benchmark examples are computed.

Constitutive Modelling of Anisotropy, Hardening and Failure of Sheet Metals

2011 ◽  
Vol 473 ◽  
pp. 631-636 ◽  
Author(s):  
Ivaylo N. Vladimirov ◽  
Yalin Kiliclar ◽  
Vivian Tini ◽  
Stefanie Reese
Keyword(s):  
Kinematic Hardening ◽  
Plastic Anisotropy ◽  
Forming Limit Diagram ◽  
Material Model ◽  
Constitutive Modelling ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Continuum Damage ◽  
Aluminium Sheets ◽  
Good Agreement

The paper discusses the application of a newly developed coupled material model of finite anisotropic multiplicative plasticity and continuum damage to the numerical prediction of the forming limit diagram at fracture (FLDF). The model incorporates Hill-type plastic anisotropy, nonlinear Armstrong-Frederick kinematic hardening and nonlinear isotropic hardening. The numerical examples investigate the simulation of forming limit diagrams at fracture by means of the so-called Nakajima stretching test. Comparisons with test data for aluminium sheets display a good agreement between the finite element results and the experimental data.

An improved assumed strain solid shell element formulation with bubble function displacements

1997 ◽  
Author(s):  
Chahngmin Cho ◽  
Brian Kemp ◽  
Sung Lee ◽  
Chahngmin Cho ◽  
Brian Kemp ◽  
...  
Keyword(s):  
Shell Element ◽  
Element Formulation ◽  
Solid Shell ◽  
Assumed Strain ◽  
Bubble Function

On the Modeling of Evolving Elastic and Plastic Anisotropy in the Finite Strain Regime – Application to Deep Drawing Processes

2012 ◽  
Vol 504-506 ◽  
pp. 679-684 ◽  
Author(s):  
Ivaylo N. Vladimirov ◽  
Michael P. Pietryga ◽  
Vivian Tini ◽  
Stefanie Reese
Keyword(s):  
Deep Drawing ◽  
Evolution Equations ◽  
Finite Strain ◽  
Kinematic Hardening ◽  
Plastic Anisotropy ◽  
Material Model ◽  
Internal Variables ◽  
Time Step ◽  
Finite Element Software ◽  
Structure Tensors

In this work, we discuss a finite strain material model for evolving elastic and plastic anisotropy combining nonlinear isotropic and kinematic hardening. The evolution of elastic anisotropy is described by representing the Helmholtz free energy as a function of a family of evolving structure tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the same family of structure tensors. Exploiting the dissipation inequality leads to the interesting result that all tensor-valued internal variables are symmetric. Thus, the integration of the evolution equations can be efficiently performed by means of an algorithm that automatically retains the symmetry of the internal variables in every time step. The material model has been implemented as a user material subroutine UMAT into the commercial finite element software ABAQUS/Standard and has been used for the simulation of the phenomenon of earing during cylindrical deep drawing.

Advanced High Strength Steel Sheet Forming and Springback Simulation

2010 ◽  
Vol 97-101 ◽  
pp. 200-203 ◽  
Author(s):  
Ke Chen ◽  
Jian Ping Lin ◽  
Mao Kang Lv ◽  
Li Ying Wang
Keyword(s):  
High Strength Steel ◽  
Yield Criterion ◽  
Kinematic Hardening ◽  
Sheet Material ◽  
High Strength ◽  
Material Model ◽  
Sheet Forming ◽  
Isotropic Hardening ◽  
Advanced High Strength Steel ◽  
Springback Prediction

With the increasing use of finite element analysis method in sheet forming simulations, springback predictions of advanced high strength steel (AHSS) sheet are still far from satisfactory precision. The main purpose of this paper was to provide a method for accurate springback prediction of AHSS sheet. Material model with Hill’48 anisotropic yield criterion and nonlinear isotropic/kinematic hardening rule were applied to take account the anisotropic yield behavior and the Bauschinger effect during forming processes. U-channel forming and springback simulation was performed using ABAQUS software. High strength DP600 sheet was investigated in this work. The simulation results obtained with the proposed material model agree well with the experimental results, which show a remarkable improvement of springback prediction compared with the commonly used isotropic hardening model.

Identification of the anisotropic behavior of an aluminum alloy subjected to simple and cyclic shear tests

2018 ◽  
Vol 233 (3) ◽  
pp. 911-927 ◽  
Author(s):  
Daghfas Olfa ◽  
Znaidi Amna ◽  
Gahbiche Amen ◽  
Nasri Rachid
Keyword(s):  
Aluminum Alloy ◽  
Kinematic Hardening ◽  
Plastic Anisotropy ◽  
Mechanical Tests ◽  
Material Behavior ◽  
Isotropic Hardening ◽  
Cyclic Tests ◽  
Shear Tests ◽  
2024 Aluminum Alloy ◽  
Cyclic Shear

The main purpose of this paper is to study the behavior of the 2000 aluminum alloy series used particularly in the design of Airbus fuselage. The characterization of the mechanical behavior of sheet metal on 2024 aluminum alloy and its response to various loading directions under monotonic and cyclic tests are extremely considered. To solve this problem, first, an experimental platform which essentially revolves around mechanical tests and then a series of optical and transmission electronic visualizations have been carried out. These mechanical tests are monotonic and cyclic shear tests applied under the same conditions on the test specimens of 2024 aluminum alloy. Cyclic shear tests have been carried out in order to show the Bauschinger effect and then the kinematic hardening phenomenon. The hardening curves of the simple shear test showed the Portevin-Le Chatelier effect for all loading directions. Next, the experimental results obtained (Portevin-Le Chatelier and Bauschinger effects) are discussed and analyzed in relation to the microstructure of the studied alloy using an optical microscope and a transmission electron microscope. Thereafter, the plastic anisotropy is modeled using an identification strategy that depends on a plastic criterion, an isotropic hardening law, a kinematic hardening (linear and nonlinear) law, and an evolution law. More precisely, particular attention is paid to the isotropic power Hollomon law, the saturation Voce law, and the saturation Bron law. In the case of the cyclic tests, linear kinematic hardening described by the Prager law and nonlinear kinematic hardening expressed by the Armstrong–Frederick law are introduced. Finally, by smoothing the experimental hardening curves for the various simple and cyclic shear tests, a selection is made in order to choose the most appropriate law for the identification of the material behavior.

The Simulation of Robot Based Incremental Sheet Metal Forming by Means of a New Solid-Shell Finite Element Technology and a Finite Elastoplastic Model with Combined Hardening

2011 ◽  
Vol 473 ◽  
pp. 875-880 ◽  
Author(s):  
Yalin Kiliclar ◽  
Roman Laurischkat ◽  
Stefanie Reese ◽  
Horst Meier
Keyword(s):  
Finite Element ◽  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Kinematic Hardening ◽  
Industrial Robots ◽  
Solid Shell ◽  
Forming Process ◽  
Incremental Sheet Metal Forming ◽  
Shell Finite Element

The principle of robot based incremental sheet metal forming is based on flexible shaping by means of a freely programmable path-synchronous movement of two tools, which are operated by two industrial robots. The final shape is produced by the incremental infeed of the forming tool in depth direction and its movement along the geometry’s contour in lateral direction. The main problem during the forming process is the influence on the dimensional accuracy resulting from the compliance of the involved machine structures and the springback effects of the workpiece. The project aims to predict these deviations caused by resiliences and to carry out a compensative path planning based on this prediction. Therefore a planning tool is implemented which compensates the robot’s compliance and the springback effects of the sheet metal. Finite element analysis using a material model developed at the Institute of Applied Mechanics (IFAM) [1] has been used for the simulation of the forming process. The finite strain constitutive model combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamical setting. It is based on the multiplicative split of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening which is widely adopted as capable of representing the above metal hardening effects. The major problem of low-order finite elements used to simulate thin sheet structures, such as used for the experiments, is locking, a non-physical stiffening effect. Recent research focuses on the large deformation version of a new eight-node solid-shell finite element based on reduced integration with hourglass stabilization. In the solid-shell formulation developed at IFAM ([2], [3]) the enhanced assumed strain (EAS) concept as well as the assumed natural strain (ANS) concept are implemented to circumvent locking. These tools are very important to obtain a good correlation between experiment and simulation.

A Solid Shell Finite Element Formulation for Dielectric Elastomers

2013 ◽  
Vol 80 (2) ◽  
Author(s):  
Sven Klinkel ◽  
Sandro Zwecker ◽  
Ralf Müller
Keyword(s):  
Finite Element ◽  
Electric Potential ◽  
Electromechanical Coupling ◽  
Coupling Effect ◽  
Finite Element Formulation ◽  
Dielectric Elastomers ◽  
Element Formulation ◽  
Elastic Model ◽  
Solid Shell ◽  
Shell Finite Element

This paper is concerned with a solid shell finite element formulation to simulate the behavior of thin dielectric elastomer structures. Dielectric elastomers belong to the group of electroactive polymers. Due to efficient electromechanical coupling and the huge actuation strain, they are very interesting for actuator applications. The coupling effect in the material is mainly caused by polarization. In the present work, a simple constitutive relation, which is based on an elastic model involving one additional material constant to describe the polarization state, is incorporated in a solid shell formulation. It is based on a mixed variational principle of Hu-Washizu type. Thus, for quasi-stationary fields, the balance of linear momentum and Gauss' law are fulfilled in a weak sense. As independent fields, the displacements, electric potential, strains, electric field, mechanical stresses, and dielectric displacements are employed. The element has eight nodes with four nodal degrees of freedom, three mechanical displacements, and the electric potential. The surface oriented shell element models the bottom and the top surfaces of a thin structure. This allows for a simple modeling of layered structures by stacking the elements through the thickness. Some examples are presented to demonstrate the ability of the proposed formulation.

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