Tension-compression asymmetry modelling: strategies for anisotropy parameters identification

This work presents details concerning the strategies and algorithms adopted in the fully implicit FE solver DD3IMP to model the orthotropic behavior of metallic sheets and the procedure for anisotropy parameters identification. The work is focused on the yield criterion developed by Cazacu, Plunkett and Barlat, 2006 [ 1], which accounts for both tension-compression asymmetry and orthotropic plastic behavior. The anisotropy parameters for a 2090-T3 aluminum alloy are identified accounting, or not, for the tension-compression asymmetry. The numerical simulation of a cup drawing is performed for this material, highlighting the importance of considering tension-compression asymmetry in the prediction of the earing profile, for materials with cubic structure, even if this phenomenon is relatively small.- The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under projects with reference PTDC/EMS-TEC/0702/2014 and PTDC/EMS-TEC/6400/2014. The first author is also grateful to the FCT for the PhD grant SFRH/BD/98545/2013.info:eu-repo/semantics/publishedVersio

Sheet forming simulations of automotive parts using different yield functions

In this work, the influence of the yield function on finite element (FE) forming simulation results for two auto-body panels, hood inner and door outer, was investigated. Simulations were conducted with different yield functions, Hill's1948. Yld91 and Yld2000-2d, which are available in the PAM-STAMP and LS-DYNA commercial codes. Although moderate, some differences in the results were observed.open111Nsciescopu

Advanced constitutive modeling for application to sheet forming

Continuum constitutive descriptions of plasticity suitable for finite element simulations of sheet forming processes are succinctly discussed. Although multi-scale approaches allow for a more explicit representation of the physical deformation mechanisms occurring at microscopic scales, they are usually not suitable for industrial applications because of the quick turnaround time needed for process design simulations. Therefore, advances in classical concepts such as plastic anisotropy and strain hardening are still very much in demand. This article describes possible ways to make use of multi-scale results for application to sheet metal forming simulations.11Ysciescopu

Modeling of plastic anisotropy with reduced polycrystalline models. Application to aluminum alloys

From the issue entitled "Proceedings of the 11th ESAFORM Conference on Material Forming, Lyon (France), 23-25 April 2008, edited by P. Boisse, F. Morestin, E. Vidal-Sallé, LaMCoS, INSA de Lyon)"International audienceThe modeling of deviations from isotropic hardening still is a difficult task for macroscopic models, in particular for non-proportional loading paths. The alternative polycrystalline models suffer from large CPU time in FE analyses and do not always give simultaneously a good description of flow stresses and transverse strain rates. Due to a specific parameter calibration procedure, a “reduced” polycrystalline model with 8 orientations only is in excellent agreement with all experimental curves for a 2090-T3 aluminum sheet. FE calculations of a punch test with contact and friction give CPU times only 15% larger than with a macroscopic model

Evaluation of constitutive models for springback prediction in U-draw/bending of DP and TRIP steel sheets

U-draw/bending experiments and simulations were performed to investigate the characteristics of springback in sheet metals. The finite element method is frequently used for the simulation of springback, but the predictions are strongly influenced by the constitutive models such as yield criteria and hardening laws. In the present study, springback of DP and TRIP steel sheets after U-draw/bending was predicted with a finite element analysis. Various yield functions were considered, namely, the isotropic von Mises and anisotropic Hill models. For strain hardening, isotropic, non-linear kinematic and combined isotropic-kinematic hardening models were considered. In order to characterize the isotropic hardening behavior, both uniaxial and balanced biaxial (hydraulic bulge) tension tests were carried out. For the characterization of the combined isotropic-kinematic hardening model, forward-reverse simple shear tests were conducted. The springback predictions were greatly influenced by the choice of the hardening model but slightly affected by the choice of the yield criterion. The kinematic hardening and combined isotropic-kinematic hardening models provided satisfactory predictions for DP590 and TRIP590 sheets, respectively. Due to an extended measurable strain range, the use of the flow curves from the hydraulic bulge test led to more reliable results than those of uniaxial tension.ope

Plastic instability in complex strain paths predicted by advanced constitutive equations

The present paper aims at predicting plastic instabilities under complex loading histories using an advanced sheet metal forming limit model. The onset of localized necking is computed using the Marciniak-Kuczinslcy (MK) analysis [I] with a physically-based hardening model and the phenomenological anisotropic yield criterion Yld2000-2d [2]. The hardening model accounts for anisotropic work-hardening induced by the microstructural evolution at large strains, which was proposed by Teodosiu and Hu [3]. Simulations are carried out for linear and complex strain paths. Experimentally, two deep-drawing quality sheet metals are selected: a bake-hardening steel (BH) and a DC06 steel sheet. The validity of the model is assessed by comparing the predicted and experimental forming limits. The remarkable accuracy of the developed software to predict the forming limits under linear and non-linear strain path is obviously due to the performance of the advanced constitutive equations to describe with great detail the material behavior. The effect of strain-induced anisotropy on formability evolution under strain path changes, as predicted by the microstructural hardening model, is particularly well captured by the model.open1134Nsciescopu

Material modelling and springback analysis for multi-stage rotary draw bending of thin-walled tube using homogeneous anisotropic hardening model

The aim of this paper is to compare several hardening models and to show their relevance for the prediction of springback and deformation of an asymmetric aluminium alloy tube in multi-stage rotary draw bending process. A three-dimensional finite-element model of the process is developed using the ABAQUS code. For material modelling, the newly developed homogeneous anisotropic hardening model is adopted to capture the Bauschinger effect and transient hardening behaviour of the aluminium alloy tube subjected to non-proportional loading. The material parameters of the hardening model are obtained from uniaxial tension and forward-reverse shear test results of tube specimens. This work shows that this approach reproduces the transient Bauschinger behaviour of the material reasonably well. However, a curve-crossing phenomenon observed for this material cannot be captured by the homogeneous anisotropic hardening model. For comparison purpose, the isotropic and combined isotropic-kinematic hardening models are also adopted for the analysis of the same problem. The predictions of springback and cross-section deformation based on these models are discussed. (C) 2014 The Authors. Published by Elsevier Ltd.open1134Nsciescopu

On the determination of flow stress using bulge test and mechanical measurement

The standard uniaxial tensile test is a widely accepted method to obtain relevant properties of sheet metal materials. These fundamental parameters can be used in numerical modeling of sheet forming operations to predict and assess formability and failure analysis. However the range of strain obtained from tensile test is limited and therefore if one will need further information on material behavior, extrapolation of tensile data is performed. The bulge test is an alternative to obtain ranges of deformation higher than tensile test, thus being possible to obtain non-extrapolated data for material behavior. Several methods may be used to obtain stress-strain data from bulge test, but a common concept is behind them, which needs the measurement of bulge pressure, curvature of bulge specimen, its thickness at the pole and the application of membrane theory. Concerning such measurements, optical methods are being used recently but classical mechanical methods are still an alternative with its own strengths. This paper presents the use and development of a mechanical measuring system to be incorporated in a hydraulic bulge test for flow curve determination, which permits real-time data acquisition under controlled strain rates up to high levels of plastic deformation. Numerical simulations of bulge test using FEM are performed and a sensitivity analysis is done for some influencing variables used in measurements, thus giving some directions in the design and use of the experimental mechanical system. Also, first experimental results are presented, showing an efficient testing procedure method for real time data acquisition with a stable evaluation of the flow curve.open11617Nsciescopu

Numerical simulation of the mechanical response during strain path change: application to Zn alloys.

The microstructure-based hardening model (Beyerlein and Tome, 2007), that accounts for the dislocation reversal-related mechanisms and the cut-through effect, is extended to HCP metals. This model, which is embedded in the visco-plastic self-consistent framework, is applied in this work to predict the mechanical response of Zn alloy during strain path change. The predicted mechanical behavior and texture evolution during pre-loading and reloading is in good agreement with experimental observations. The change in hardening behavior after reloading is well reproduced by this model. The contributions of the different mechanisms are also analyzed. (C) 2014 Published by Elsevier Ltd.open1111Nsciescopu

Influence of the characteristics of the experimental data set used to identify anisotropy parameters

This work presents an investigation into the effect of the number and type of experimental input data used in parameter identification of Hill’48, Barlat’91 (Yld91) and Cazacu and Barlat’2001 (CB2001) yield criteria on the accuracy of the finite element simulation results. Different sets of experimental data are used to identify the anisotropy parameters of two metal sheets, exhibiting different anisotropic behaviour and hardening characteristics: a mild steel (DC06) and an aluminium alloy (AA6016-T4). Although it has been shown that the CB2001 yield criterion can lead to an accurate description of anisotropic behaviour of metallic sheets, its calibration requires a large set of experimental input data. A calibration procedure is proposed for CB2001 based on a reduced set of experimental data, i.e. where the results are limited to three uniaxial tensile tests, combined with artificial data obtained using the Barlat’91 yield criterion. Evaluation of the predictive capacity of the studied yield criteria, calibrated using different sets of experimental data, is made by comparing finite element simulation results with experimental results for the deep drawing of a crossshaped part. A satisfying agreement is observed between experimental and numerical thickness distributions, with a negligible effect of the number and type of experimental data for the Hill’48 and Yld91 yield criteria. On the contrary, CB2001 calibration is quite sensitive to the experimental data available, particularly biaxial values. Nevertheless, CB2001 calibration based on the combination of effective and artificial experimental data achieves satisfying results, which in the worst case are similar to the ones obtained with the Yld91.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) via the projects PTDC/EMS-TEC/1805/2012 and PEst-C/EME/UI0285/2013 and by FEDER funds through the program COMPETE – Programa Operacional Factores de Competitividade, under the project CENTRO-07-0224-FEDER-002001 (MT4MOBI). The first author is also grateful for the Post-Doc grant.info:eu-repo/semantics/publishedVersio