Effects of Temperature and Strain Rate on the Forming Limit Curves of AA5086 Sheet (original) (raw)
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Materials & Design, 2015
This paper proposes a method to investigate the effects of temperature and strain rate on the forming limit curves (FLCs) by combining a modified Voce constitutive model (Lin-Voce model) with the numerical simulation of Marciniak test. The tensile tests are firstly carried out at different forming temperatures (20, 230 and 290℃) and strain rates (2.5, 120 and 150s-1) for AA5086 sheet. A modified Voce constitutive model (named Lin-Voce model) is proposed to describe the deformation behavior of AA5086 and its material parameters are identified by inverse analysis technique. Then, the proposed constitutive model is verified by comparing numerical and experimental results obtained by tensile tests and Marciniak test, respectively. Finally, the numerical simulation of Marciniak test is carried out at different temperatures (100, 200 and 300℃) and strain rates (2.5, 120 and 150s-1), and the effects of temperature and strain rate on the FLCs of AA5086 are investigated and discussed.
International Journal of Mechanical Sciences, 2014
Due to the high-strength to weigh ratio, corrosion resistance, good workability and weldability characteristics, aluminium alloys are increasingly used in many sectors. Researches on formability of aluminium alloy sheets have always been a hot topic these last years while very few works taking into both temperature and strain rate effects on formability limits can be found in the literature. In this study, the formability of sheet metal AA5086 is investigated at different temperatures (20, 150 and 200°C) and strain rates (0.02, 0.2 and 2 s −1 ) through a Marciniak test setup. Experimental results show that the formability of AA5086 increases with temperature and decreases with forming speed. Based on the analytical M-K theory, a Finite Element (FE) M-K model is proposed to predict the Forming Limit Curves (FLCs). A modified Ludwick hardening law with temperature and strain rate functions is proposed to describe the thermo-elasto-viscoplastic behavior of the material. The influence of the initial imperfection (f 0 ) sensitivity in the FE M-K model is discussed and a strategy to calibrate f 0 is proposed. The agreement between experimental and numerical FLCs indicates that the FE M-K model can be an effective model for predicting sheet metal formability under different operating conditions if the initial imperfection value is calibrated for each forming condition.
Journal of Materials Engineering and Performance, 2015
A solution to improve the formability of aluminium alloy sheets can consist in investigating warm forming processes. The optimization of forming process parameters needs a precise evaluation of material properties and sheet metal formability for actual operating environment. Based on the analytical M-K theory, a Finite Element (FE) M-K model was proposed to predict Forming Limit Curves (FLCs) at different temperatures and strain rates. The influences of initial imperfection value (f 0 ) and material thermos-viscoplastic model on the FLCs are discussed in this work. The flow stresses of AA5086 were characterized by uniaxial tensile tests at different temperatures (20, 150 and 200°C) and equivalent strain rates (0.0125, 0.125 and 1.25 s −1 ). Three types of hardening models (power law model, saturation model and mixed model) were proposed and adapted to correlate the experimental flow stresses. The three hardening models were implemented into the FE M-K model in order to predict FLCs for different forming conditions. The predicted limit strains are very sensitive to the thermo-viscoplastic modeling of AA5086 and to the calibration of the initial geometrical imperfection which controls the onset of necking.
The use of sheet metal forming processes can be limited by the formability of materials, especially in the case of aluminium alloys. To improve the formability, warm forming processes can be considered. In this work, the effects of temperature and strain rate on the formability of a given aluminium alloy (AA5086) have been studied by means of both experimental and predictive approaches. Experimental tests have been carried out with a Marciniak stamping experimental device. Forming limit curves (FLCs) have been established on a temperature range going from ambient temperature to 200°C and on a strain rate range going from quasi-static up to 2s -1 . In order to predict the experimental temperature and strain rate sensitivities, a predictive model based on the finite element simulation of the classical Marciniak and Kuczynski (M-K) geometrical model is proposed. The limit strains obtained with this model are very sensitive to the thermo-viscoplastic behaviour modeling and to the calibration of the initial geometrical imperfection controlling the onset of necking.
Experimental and numerical study on effect of forming rate on AA5086 sheet formability
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
With increasing application of aluminum alloys in automotive or aeronautic industries, it is necessary to characterize their deformation behaviors at large strains, high strain rates and elevated temperatures, which is relatively lacking today. The aim of this paper is to experimentally and numerically investigate the influence of forming rate and temperature on formability of an AA5086 sheet. Firstly, tensile tests are carried out at different temperatures (20, 230, 290 and 350°C) and at different forming rates (10, 750 and 1000 mm/s). A technique of digital image correlation (DIC) associated with a high-speed camera is applied to evaluate the surface strains and a complete procedure is built to detect the onset of localized necking during the experiments. The influences of initial testing temperature and forming rate on the sheet formability are analyzed. Then in order to numerically determine the formability of this sheet, a form of Voce's constitutive law taking A c c e p t e d M a n u s c r i p t into account the temperature and strain rate is proposed. An inverse analysis is carried out to identify the material parameters of the law for the tested aluminum alloy. Finally, with the above identified law, tensile tests are simulated. The experimental and numerical results show that the testing temperature and forming rate have a great influence on sheet formability.
Forming limit curve determination of AA6061-T6 aluminum alloy sheet
Science and Technology Development Journal, 2017
The forming limit curve (FLC) is used in sheet metal forming analysis to determine the critical strain or stress values at which the sheet metal is failing when it is under the plastic deformation process, e.g. deep drawing process. In this paper, the FLC of the AA6061-T6 aluminum alloy sheet is predicted by using a micro-mechanistic constitutive model. The proposed constitutive model is implemented via a vectorized user-defined material subroutine (VUMAT) and integrated with finite element code in ABAQUS/Explicit software. The mechanical behavior of AA6061-T6 sheet is determined by the tensile tests. The material parameters of damage model are identified based on semi-experience method. To archive the various strain states, the numerical simulation is conducted for the Nakajima test and then the inverse parabolic fit technique that based on ISO 124004-2:2008 standrad is used to extracted the limit strain values. The numerical results are compared with the those of MK, Hill and Swif...
Prediction of Forming Limit Curves for 2021 Aluminum Alloy
Procedia Engineering, 2017
The forming limit curve (FLC) is a line that is consisted of the major and minor strain pairs for variety kinds of strain paths. It has been widely adopted as a practical criterion in evaluating the formability of different sheet metals. Predicting FLC numerically could avoid the drawbacks of time-consuming and hard-sledding effectively which is shared by the corresponding experimental approach. In this paper, the formability of 2021 aluminum alloy was investigated by conducting forming experiments and corresponding simulations. Firstly, uniaxial tensile tests were conducted to acquire the material properties, as well as to calibrate the hardening model for the 2021 aluminum alloy. Secondly, the numerical model for Nakazima test was established with commercial FE software ABAQUS, and a finite element based criterion was then proposed for predicting the FLC. To verify the validity of predicted FLC, nine sets of tests have been performed, leading to the conclusion that the result of simulation has a better agreement with experimentally determined FLC. Finally, the influence of friction on the strain path was discussed.
Journal of Strain Analysis for Engineering Design, 2017
Formability of AA5182-O aluminum alloy sheets in the warm working temperature range has been studied. Forming limit strains of sheets of two different thicknesses have been determined experimentally in different modes of deformation (biaxial tension, plane strain and tension-compression) by varying temperature and punch speed. A correlation has been established for plane strain intercept of the forming limit diagram (FLD 0) with temperature, punch speed and thickness from the experimental results. This correlation has been used to plot the forming limit diagrams for failure prediction in the finite element analysis of warm deep drawing of cylindrical cups. The effect of strain and strain rate on material flow behavior has been incorporated using a strain rate-sensitive power hardening law in which the strain hardening exponent and strain rate sensitivity index have been experimentally determined. The predictions from simulations have been validated by warm deep drawing experiments. Large improvement in accuracy of failure prediction has been observed using the FLDs plotted based on the developed correlation when compared to the existing method of calculating FLD 0 using only strain hardening coefficient and thickness. The results clearly indicate the importance of incorporating temperature and punch speed in failure prediction of Al alloys using FLDs in the warm working temperature range.
International Journal of Plasticity, 2011
Finite deformation anisotropic responses of AA5182-O, over a wide range of strain-rates (10 À4 to 10 0 s À1) and temperatures (293-473 K) are presented. The plastic anisotropy parameters were experimentally determined from tensile experiments using specimens from sheet material. Using the experimental results under plane stress conditions, the anisotropy coefficients for Barlat's yield function (YLD96) were calculated at different strain-rates and temperatures. The correlations obtained from YLD96 are in good agreement with the observed experimental results. The strain-rate sensitivity of AA5182-O alloy changed from negative at 293 K to positive at 473 K. Khan-Huang-Liang (KHL) constitutive model is shown to correlate the observed strain-rate and temperature dependent responses reasonably well. The material parameters were obtained from the experimental responses along the rolling direction (RD) of the sheet. Marciniak and Kuckzinsky (M-K) theory was used to obtain the theoretical strain and stress-based forming limit curves (FLCs) at different strain-rates and temperatures. The experimental result from the published literature is compared with the FLCs from the current study.
Experimental and Numerical Analysis on the Formability of a Heat-Treated AA1100 Aluminum Alloy Sheet
Journal of Materials Engineering and Performance, 2015
The objective of this work is to experimentally and numerically determine the influence of plastic anisotropy on the forming limit curve (FLC) for a heat-treated (300°C-1 h) AA1100 aluminum alloy sheet. The FLCs were obtained by the Nakajima test, where the anisotropy effect on the FLC was evaluated using hourglass-type samples taken at 0°, 45°, and 90°with respect to the sheet rolling direction. The effect of crystal orientations on the FLC is investigated using three micro-macro averaging schemes coupled to a Marciniak and Kuczynski (MK) analysis: the tangent viscoplastic self-consistent (VPSC), the tuned strength aVPSC, and the full-constraint Taylor model. The predicted limit strains in the left-hand side of the FLC agree well with experimental measurements along the three testing directions, while differences are found under biaxial stretching modes. Particularly, MK-VPSC predicts an unexpected limit strain profile in the right-hand side of the FLC for samples tested along the transverse direction. Only MK-aVPSC, with a tuning factor of 0.2, predicts satisfactorily the set of FLC measurements. Finally, the correlation of the predicted limit strains with the predicted yield surface by each model was also discussed.