Application of an Extended Stress-Based Forming Limit Curve to Predict Necking in Stretch Flange Forming

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
C. Hari Manoj Simha ◽  
Rassin Grantab ◽  
Michael J. Worswick
Keyword(s):  
Aluminum Alloy ◽  
Metal Forming ◽  
Shell Element ◽  
Forming Limit ◽  
Limit Curve ◽  
Forming Limit Curve ◽  
Circumferential Crack ◽  
Flange Forming ◽  
Failure Location ◽  
Forming Limit Curves

An extension of the stress-based forming limit curve (FLC) advanced by Stoughton (2000, “A General Forming Limit Criterion for Sheet Metal Forming,” Int. J. Mech. Sci., 42, pp. 1–27) is presented in this work. With the as-received strain-based FLCs and stress-strain curves for 1.6-mm-thick AA5754 and 1-mm-thick AA5182 aluminum alloy, stress-based FLCs are obtained. These curves are then transformed into extended stress-based forming limit curves (XSFLCs), which consist of the invariants, effective stress, and mean stress. By way of application, stretch flange forming of these aluminum alloy sheets is considered. The AA5754 stretch flange displays a circumferential crack during failure, whereas the AA5182 stretch flange fails through a radial crack at the edge of the cutout. It is shown that the necking predictions obtained using the strain- and stress-based FLCs in conjunction with shell element computations are inconsistent when compared with the experimental results. By comparing the results of the shell element computations with those in which the mesh comprises eight-noded solid elements, it is demonstrated that the plane stress approximation is not valid. The XSFLC is then used with results from the solid-element computations to predict the punch depths at the onset of necking. Furthermore, it is shown that the predictions of failure location and failure mode obtained using the XSFLC are in accord with the differences observed between the two alloys/gauges.

scholarly journals Aluminum Alloy Sheet-Forming Limit Curve Prediction Based on Original Measured Stress–Strain Data and Its Application in Stretch-Forming Process

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1129 ◽  
Author(s):  
Lirong Sun ◽  
Zhongyi Cai ◽  
Dongye He ◽  
Li Li
Keyword(s):  
Aluminum Alloy ◽  
Alloy Sheet ◽  
Forming Limit ◽  
Aluminum Alloy Sheet ◽  
Limit Curve ◽  
Forming Process ◽  
Forming Limit Curve ◽  
Stress Strain ◽  
Strain Relation ◽  
Stress Strain Relation

A new method, by directly utilizing original measured data (OMD) of the stress–strain relation in the Marciniak–Kuczynski (M–K) model, was proposed to predict the forming limit curve (FLC) of an aluminum alloy sheet. In the groove zone of the M–K model, by establishing the relations of the equivalent strain increment, the ratio of shear stress to the first principle stress and the ratio of the second principle stress to the first principle stress, the iterative formula was established and solved. The equations of theoretical forming limits were derived in detail by using the OMD of the stress–strain relation. The stretching specimens of aluminum alloy 6016-T4 were tested and the true stress–strain curve of the material was obtained. Based on the numerical simulations of punch-stretch tests, the optimized specimens’ shape and test scheme were determined, and the tests for FLC were carried out. The FLC predicted by the proposed method was more consistent with the experimental results of FLC by comparing the theoretical FLCs based on OMD of the stress–strain relation and of that based on traditional power function. In addition, the influences of anisotropic parameter and groove angle on FLCs were analyzed. Finally, the FLC calculated by the proposed method was applied to analyze sheet formability in the stretch-forming process, and the predicted results of FLC were verified by numerical simulations and experiments. The fracture tendency of the formed parts can be visualized in the forming limit diagram (FLD), which has certain guiding significance for fracture judgment in the sheet-forming process.

Determination of Forming Limit Curves of Steel Pipes for Hydroformability Evaluation

2012 ◽  
Vol 622-623 ◽  
pp. 484-488
Author(s):  
Ramil Kesvarakul ◽  
Suwat Jiratheranat ◽  
Bhadpiroon Sresomroeng
Keyword(s):  
Forming Limit ◽  
Tool Geometry ◽  
Test Machine ◽  
Low Carbon ◽  
Limit Curve ◽  
Forming Process ◽  
Forming Limit Curve ◽  
Axial Feeding ◽  
Loading Paths ◽  
Forming Limit Curves

The aims of this research are to establish the forming limit curve (FLC) of tubular material low carbon steels commonly used in Thai industry, verify these FLCs with real part forming experiments and compare these experimentally obtained FLCs against analytical ones available in FEA software database. A self-designed bulge forming apparatus of fixed bulge length and a hydraulic test machine with axial feeding are used to carry out the bulge tests. Loading paths resulting to linear strain paths at the apex of the bulging tube are determined by FE simulations in conjunction with a self-compiled subroutine. These loading paths are used to control the internal pressure and axial feeding punch of the test machine. In this work a common low carbon steel tubing grade STKM 11A, with 28.6 mm outer diameter and 1.2 mm thick is studied. Circular grids are electro chemically etched onto the surface of tube samples. Subsequently, the tube samples are bulge-formed. The forming process is stopped when a burst is observed on the forming sample. After conducting the bulge tests, major and minor strains of the grids located beside the bursting line on the tube surface are measured to construct the forming limit curve (FLC) of the tubes. The forming limit curves determined for these tubular materials are put to test in formability evaluations of test parts forming in real experiment. It was found that the tool geometry can keep the strain ratio constant is not dependent on the thickness but only on OD of the tube, as in equations L=OD and rd=(15xOD)/25.4. The experimen-tal FLDs have predicted failures in forming process consistently with the real experiments. The ex-perimentally obtained forming limit curves (determined following STKM 11A) differ from empiri-cal one (from FEA software) and analytical one by about 0.02339 and 0.15736 true strain respec-tively at FLD0, the corresponding plane strain values.

Prediction of Necking in Tubular Hydroforming Using an Extended Stress-Based Forming Limit Curve

2006 ◽  
Vol 129 (1) ◽  
pp. 36-47 ◽  
Author(s):  
C. Hari Manoj Simha ◽  
Javad Gholipour ◽  
Alexander Bardelcik ◽  
Michael J. Worswick
Keyword(s):  
Finite Element ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
Forming Limit ◽  
Limit Curve ◽  
Forming Limit Curve ◽  
Load Paths ◽  
Final Failure ◽  
Stress States ◽  
Failure Location

This paper presents an extended stress-based forming limit curve (XSFLC) that can be used to predict the onset of necking in sheet metal loaded under non-proportional load paths, as well as under three-dimensional stress states. The conventional strain-based ϵFLC is transformed into the stress-based FLC advanced by Stoughton (1999, Int. J. Mech. Sci., 42, pp. 1–27). This, in turn, is converted into the XSFLC, which is characterized by the two invariants, mean stress and equivalent stress. Assuming that the stress states at the onset of necking under plane stress loading are equivalent to those under three-dimensional loading, the XSFLC is used in conjunction with finite element computations to predict the onset of necking during tubular hydroforming. Hydroforming of straight and pre-bent tubes of EN-AW 5018 aluminum alloy and DP 600 steel are considered. Experiments carried out with these geometries and alloys are described and modeled using finite element computations. These computations, in conjunction with the XSFLC, allow quantitative predictions of necking pressures; and these predictions are found to agree to within 10% of the experimentally obtained necking pressures. The computations also provide a prediction of final failure location with remarkable accuracy. In some cases, the predictions using the XSFLC show some discrepancies when compared with the experimental results, and this paper addresses potential causes for these discrepancies. Potential improvements to the framework of the XSFLC are also discussed.

scholarly journals Forming limit curve determination of AA6061-T6 aluminum alloy sheet

2017 ◽  
Vol 20 (K2) ◽  
pp. 51-60
Author(s):  
Hao Huu Nguyen ◽  
Trung Ngoc Nguyen ◽  
Trung Ngoc Nguyen ◽  
Hoa Cong Vu
Keyword(s):  
Aluminum Alloy ◽  
Constitutive Model ◽  
Sheet Metal ◽  
Damage Model ◽  
Alloy Sheet ◽  
Analytical Models ◽  
Forming Limit ◽  
Aluminum Alloy Sheet ◽  
Limit Curve ◽  
Forming Limit Curve

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 Swift analytical models.

A New Workability Criterion for Ductile Metals

1986 ◽  
Vol 108 (3) ◽  
pp. 245-249 ◽  
Author(s):  
V. Vujovic ◽  
A. H. Shabaik
Keyword(s):  
Effective Stress ◽  
Forming Limit ◽  
Limit Curve ◽  
Forming Process ◽  
Forming Limit Curve ◽  
Ductile Metals ◽  
State Of Stress ◽  
Forming Limit Curves ◽  
Hydrostatic Component

The forming limit curves are important aids in determining the extent of deformation a material can be subjected to during a forming process. In this paper a forming limit criterion for bulk metalworking processes, based on the magnitude of the hydrostatic component and the effective stress of the state of stress, is proposed. The determination of the forming limit curve by means of three simple tests, namely, tension, compression, and torsion tests, is presented.

scholarly journals A Modified M-K Method for Accurate Prediction of FLC of Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 394
Author(s):  
Xiaoxing Li ◽  
Yangkai Chen ◽  
Lihui Lang ◽  
Rui Xiao
Keyword(s):  
Empirical Formula ◽  
Metal Forming ◽  
New Method ◽  
Forming Limit ◽  
Limit Curve ◽  
Initial Thickness ◽  
Forming Limit Curve ◽  
Theoretical Derivation ◽  
The Relationship ◽  
Imperfection Factor

Forming limit curve (FLC) is an important failure criterion for sheet metals in sheet metal forming, while the M-K model is widely used for the prediction of the FLC. In the M-K model, such prediction is greatly influenced by the initial thickness imperfection factor and material properties, from which the original M-K model’s theoretical derivation is proposed as a solution to the above mentioned issue in this paper. Then the relationship between the M-K model and Keeler’s empirical formula is then studied, from which a new method to predict FLC is proposed that combines the M-K model with Keeler’s empirical formula according to the previous analyses. It turns out that this new method can simplify the calculation procedure. Finally, the experimental results of two kinds of aluminum alloys, AA6016 and AA5182, have verified the effectiveness of the proposed method.

A New Calibration Method for FLCs in the M-K Frame-Work

2011 ◽  
Vol 341-342 ◽  
pp. 426-431
Author(s):  
Amir Ghazanfari ◽  
Ahmad Assempour
Keyword(s):  
Metal Forming ◽  
Calibration Method ◽  
Forming Limit ◽  
Experimental Point ◽  
Trial And Error ◽  
Limit Curve ◽  
Forming Limit Curve ◽  
Frame Work ◽  
Inhomogeneity Factor ◽  
Good Agreement

The main drawback of the method proposed by Marciniak and Kuczynski for prediction of the limit strains in sheet metal forming processes is requirement of an experimental point of the forming limit curve (FLC) in order to calibrate the curve. The purpose of this work is to introduce a new method to calibrate the FLC using the M-K model in which no experimental data is needed. To achieve this goal, many experimental FLCs were collected from the literature and the values of the initial inhomogeneity factors were determined for them with trial and error aproach. Using these data, an empirical law was developed to predict the value of inhomogeneity factor. The resultant curves show good agreement with the experiments.

Failure Prediction in Hydroforming of Pre-Bent HSLA Tube Using an Extended Stress-Based Forming Limit Curve

2006 ◽  
Author(s):  
M. Sorine ◽  
C. H. M. Simha ◽  
I. van Riemsdijk ◽  
M. J. Worswick
Keyword(s):  
Tube Hydroforming ◽  
Forming Limit ◽  
Limit Curve ◽  
Expansion Tube ◽  
Forming Limit Curve ◽  
Free Expansion ◽  
Explicit Finite Element ◽  
User Subroutine ◽  
Failure Location ◽  
Good Agreement

This paper examines the prediction of failure during the hydroforming of pre-bent HSLA350 tubes using the Extended Stress-Based Forming Limit Curve (XSFLC) [1]. The process of obtaining a strain-based forming limit curve (ε-FLC) for the tube and its application to the prediction of failure in tube hydroforming, utilizing the XSFLC, is presented in detail. The XSFLC was obtained from ε-FLC that was calibrated using the results of free expansion tube burst tests. Tube bending and hydroforming experiments were carried out and modeled using the dynamic explicit finite element code, LS-DYNA. An LS-DYNA user subroutine that utilizes the XSFLC to predict the onset of necking was used to model the tube material. The predicted failure location and pressure at the onset of necking were found to be in a good agreement with the experimental results.

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