Strain localization analysis using a large deformation anisotropic elastic–plastic model coupled with damage (original) (raw)
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2007
The aim of this work is to study the strain localization during the plastic deformation of sheets metals. This phenomenon is precursor for the fracture of drawing parts, thus its prediction using advanced behavior models, such as in [2], is important in order to obtain safe final parts. Most often, an accurate prediction of localization during forming process requires damage to be included in the simulation. For this purpose, an advanced, anisotropic elastoplastic model, combining isotropic and kinematic hardening, has been coupled with an isotropic damage model [1]. The coupling with the damage model is carried out within the framework of continuum damage mechanics [3]. The resulting model is then able to reproduce both strain path change phenomena and damage evolution. In order to detect the strain localization during sheet forming process, Rice’s localization criterion is combined with this model [4]. The coupled elastoplastic-damage model is implemented in the Abaqus/Implicit so...
AIP Conference Proceedings, 2007
In this work, an advanced anisotropic elastic-plasticity model is combined with a damage model and a strain localization criterion in the aim to describe accurately the mechanical behavior of sheet metals. Large strain, fully threedimensional, implicit time integration algorithms are developed for this model and implemented in the finite element code Abaqus. The resulting code is used to predict the strain localization limits as well as the springback after forming of sheet steels. The impact of strain-path dependent hardening models on the limit strains and on the amount of springback is addressed.
Journal of Materials Processing Technology, 2009
Formability of sheet metal is usually assessed by the useful concept of forming limit diagrams (FLD) and forming limit curves (FLC) represent a first safety criterion for deep drawing operations. The level of FLC is strongly strain path dependent as observed by experimental and numerical results and therefore nonproportional strain paths need to be incorporated when analyzing formability of sheet metal components. Simulations using finite element method allow accurate predictions of stress and strain distributions in complex stamped parts. However, the prediction of localized necking is a difficult task and the combination of forming limit diagram analysis with finite element simulations often fail to give the right answer, if complex strain paths are not included in these predictions.
Mathematics
The present paper proposes a mathematical development of the plasticity and damage approaches to simulate sheet metal forming processes. It focuses on the numerical prediction of the deformation of the sheet metal during the deep drawing process when a crack appears. Anisotropic plasticity constitutive equations are proposed. A fully implicit integration of the coupling constitutive equations is used and leads to two nonlinear local scalar equations that are solved by Newton’s method. The developed model allows predicting the onset of cracks in sheet metals during cold forming operations. The numerical model is implemented in ABAQUS software using user-defined subroutines, which are VUMAT and UMAT. The accuracy of the anisotropic elastoplastic model fully coupled with ductile damage is evaluated using numerical examples.
2016
In this work, ductility limits of metallic materials, associated with the occurrence of strain localization, are predicted using the GTN damage model coupled with bifurcation theory. The resulting approach is implemented into the finite element code ABAQUS within the framework of large plastic strains and a fully three-dimensional formulation. A parametric study with respect to damage and hardening parameters is conducted in order to identify the most influential material parameters on strain localization. The analysis shows that the damage parameters have a significant impact on the predicted ductility limits, while the effect of hardening parameters on strain localization depends on the choice of void nucleation mechanism.
Investigation of advanced strain-path dependent material models for sheet metal forming simulations
International Journal of Plasticity, 2007
Sheet metal forming processes often involve complex loading sequences. To improve the prediction of some undesirable phenomena, such as springback, physical behavior models should be considered. This paper investigates springback behavior predicted by advanced elastoplastic hardening models which combine isotropic and kinematic hardening and take strain-path changes into account. A dislocation-based microstructural hardening model formulated from physical observations and the more classical cyclic model of Chaboche have been considered in this work. Numerical implementation was carried out in the ABAQUS software using a return mapping algorithm with a combined backward Euler and semi-analytical integration scheme of the constitutive equations. The capability of each model to reproduce transient hardening phenomena at abrupt strain-path changes has been shown via simulations of sequential rheological tests. A springback analysis of strip drawing tests was performed in order to emphasize the impact of several influential parameters, namely: process, numerical and behavior parameters. The effect of the two hardening models with respect to the process parameters has been specifically highlighted.
Fracture in sheet metal forming: Effect of ductile damage evolution
Computers & Structures, 2007
This work deals with the virtual simulation of the sheet metal stamping process. The main objective is to predict when and where the cracks can appear in the workpiece during the forming operation. A local approach based on the strong coupling between anisotropic elastoplasticity with mixed nonlinear work hardening (isotropic and kinematic) and an isotropic ductile damage is proposed. The theoretical and numerical aspects of the constitutive equations are, first, presented. The resolution of the resulting system of equations is carried out via a Vumat user material, using ABAQUS/Explicit finite element code. The results obtained, in the context of Swift's benchmark deep-drawing test show the efficiency and the potential interest of the proposed damage model.
2011
The strain localization phenomenon that may occur during sheet metal forming represents a major cause of defective parts produced in the industry. Several instability criteria have been developed in the literature to predict the occurrence of these instabilities. The proposed work aims to couple a Gurson-type model to the Rice’s localization criterion. The implementation of the modeling is achieved via a user subroutine (Umat) in Abaqus/std using a Runge-Kutta explicit integration scheme. Finally, we show the effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets.