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.

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.

New Methodologies for the Determination of Precise Forming Limit Curve in Single Point Incremental Forming Process

2010 ◽  
Vol 97-101 ◽  
pp. 126-129 ◽  
Author(s):  
Ghulam Hussain ◽  
Gao Lin ◽  
Nasir Hayat ◽  
Nameem Ullah Dar ◽  
Asif Iqbal
Keyword(s):  
Incremental Forming ◽  
Single Point ◽  
Forming Limit ◽  
Single Point Incremental Forming ◽  
Limit Curve ◽  
Forming Process ◽  
Forming Limit Curve ◽  
Groove Test ◽  
New Methodologies

Straight groove test is a widely-used formability test in Single Point Incremental Forming (SPIF). This test does not cover all the forming aspects of SPIF process, however. In order to ascertain its legitimacy, two new tests covering necessary SPIF aspects are devised. The FLC of an aluminum sheet is determined using the newly proposed and straight groove tests. It is found that the straight groove test shows much lower formability than the new tests. Therefore, the employment of newly devised test(s) is proposed for the determination of precise formability limits.

Thermal Influences on Deep Drawing Process of Ferritic and Metastable Austenitic Stainless Steels

2013 ◽  
Vol 769 ◽  
pp. 221-228 ◽  
Author(s):  
Philipp Schmid
Keyword(s):  
Stainless Steels ◽  
Deep Drawing ◽  
Austenitic Stainless Steels ◽  
Forming Limit ◽  
Martensite Formation ◽  
Forming Process ◽  
High Dependency ◽  
Forming Tools ◽  
Forming Limit Curves

Sheet metal forming processes, in particular deep drawing processes, are highly influenced by occurrence of latent and friction heat. Especially when forming metastable austenitic stainless steels, strain-induced martensite formation is suppressed by higher temperatures and therefore influences the material behavior and so called TRIP-effect. This study gives an overview about thermal influences on the deep drawing forming process of metastable austenitic CrNi-steel 1.4301 in comparison with ferritic stainless steels such as 1.4016. Measurements on serial and evaluation tools were carried out to determine occurring temperatures within forming tools. Attention is paid to effects on tribological aspects such as behavior of lubricants at higher temperatures, influence of temperature development on the martensite formation, mechanical properties, forming limit curves as well as heat flow within the forming tools. Lubricants with different temperature stability were compared to each other with determination of friction coefficient in strip drawing tests. Martensite and temperature development during forming of material was measured in non-isothermal tensile tests approving a high dependency of martensite formation on temperature. Forming limit curves for temperatures determined from RT to 140°C for EN 1.4301 are showing high dependency of necking behavior especially under plain strain conditions. Determination of thermal contact conductance coefficients for process and tool relevant material combinations allows interpreting heat flow mechanisms in forming tools and improving forming process to higher robustness. Results of this paper can be used to individually set boundary conditions for thermo-mechanical coupled forming simulation of austenitic stainless steel and process layout of tool temperature control systems.

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.

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.

A methodology for determination of extended strain-based forming limit curve considering the effects of strain path and normal stress

2014 ◽  
Vol 229 (9) ◽  
pp. 1537-1547 ◽  
Author(s):  
R Hashemi ◽  
K Abrinia ◽  
G Faraji
Keyword(s):  
Strain Path ◽  
Flow Direction ◽  
Plane Stress State ◽  
Forming Limit ◽  
Limit Curve ◽  
Forming Limit Curve ◽  
Path Dependent ◽  
New Criterion ◽  
State Assumption

In this paper, an approach based on the modified Marciniak-Kuczynski (M-K) method for computation of an extended strain-based forming limit curve (FLC) is presented. An extended strain-based FLC is built based on equivalent plastic strains and material flow direction at the end of forming. This curve has some advantages in comparison with other necking criteria such as the traditional FLC and also the stress-based FLC. This new criterion is much less strain path dependent than the conventional FLC. Furthermore, the use and interpretation of this new curve is easier than the stress-based FLC. The effect of strain path on the predicted extended strain-based FLC is reexamined. For this purpose, two types of pre-straining on the sheet metal have been imposed. Moreover, the plane stress state assumption is not adopted in the current study. The verifications of the theoretical FLCs are performed by using some available published experimental data.

scholarly journals Determination of forming limit curve by finite element method simulations

2019 ◽  
Vol 27 ◽  
pp. 78-82 ◽  
Author(s):  
D. Lumelskyj ◽  
J. Rojek ◽  
L. Lazarescu ◽  
D. Banabic
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Forming Limit ◽  
Limit Curve ◽  
Forming Limit Curve ◽  
Element Method
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