Orientation and Path Dependence of Formability in the Stress- and the Extended Stress-Based Forming Limit Curves

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
C. Hari Manoj Simha ◽  
Kaan Inal ◽  
Michael J. Worswick
Keyword(s):  
Strain Path ◽  
Path Dependence ◽  
Forming Limit ◽  
Stress Space ◽  
Forming Limit Diagrams ◽  
Metall Trans ◽  
Strain Paths ◽  
Strain Path Changes ◽  
Path Dependent ◽  
Forming Limit Curves

This article analyzes the formability data sets for aluminum killed steel (Laukonis, J. V., and Ghosh, A. K., 1978, “Effects of Strain Path Changes on the Formability of Sheet Metals,” Metall. Trans. A., 9, pp. 1849–1856), for Al 2008-T4 (Graf, A., and Hosford, W., 1993, “Effect of Changing Strain Paths on Forming Limit Diagrams of Al 2008-T4,” Metall. Trans. A, 24A, pp. 2503–2512) and for Al 6111-T4 (Graf, A., and Hosford, W., 1994, “The Influence of Strain-Path Changes on Forming Limit Diagrams of Al 6111 T4,” Int. J. Mech. Sci., 36, pp. 897–910). These articles present strain-based forming limit curves (ϵFLCs) for both as-received and prestrained sheets. Using phenomenological yield functions, and assuming isotropic hardening, the ϵFLCs are transformed into principal stress space to obtain stress-based forming limit curves (σFLCs) and the principal stresses are transformed into effective stress and mean stress space to obtain the extended stress-based forming limit curves (XSFLCs). A definition of path dependence for the σFLC and XSFLC is proposed and used to classify the obtained limit curves as path dependent or independent. The path dependence of forming limit stresses is observed for some of the prestrain paths. Based on the results, a novel criterion that, with a knowledge of the forming limit stresses of the as-received material, can be used to predict whether the limit stresses are path dependent or independent for a given prestrain path is proposed. The results also suggest that kinematic hardening and transient hardening effects may explain the path dependence observed in some of the prestrain paths.

Effects of Processing, Texture and Temperature on the Formability of AZ31 and ZE10 Sheets

2011 ◽  
Vol 690 ◽  
pp. 298-301 ◽  
Author(s):  
Dietmar Letzig ◽  
Lennart Stutz ◽  
Jan Bohlen ◽  
Karl Ulrich Kainer
Keyword(s):  
Metal Forming ◽  
Alloy Composition ◽  
Deformation Mechanisms ◽  
Forming Limit ◽  
Forming Limit Diagrams ◽  
Sheet Formability ◽  
Strain Paths ◽  
Twin Roll Cast ◽  
Twin Roll ◽  
Forming Limit Curves

Sheet metal forming experiments have been carried out on AZ31 and ZE10 sheets produced by rolling conventionally DC cast slabs as well as twin roll cast (TRC) strips. Nakajima tests were performed on the various sheet materials over the temperature range from RT to 200 °C using Hasek type samples of specified geometries to generate various strain paths. The strain path data were used to derive the forming limit curves as plotted in forming limit diagrams for the two alloys. The temperature dependence of the sheet formability is discussed in terms of the operating deformation mechanisms and the roles of alloy composition, initial texture and processing history.

A comparative study on determination of forming limit diagrams for industrial aluminium sheet alloys considering combined effect of strain path, anisotropy and yield locus

2012 ◽  
Vol 47 (6) ◽  
pp. 350-361 ◽  
Author(s):  
Milad Janbakhsh ◽  
Faramarz Djavanroodi ◽  
Mohammad Riahi
Keyword(s):  
Finite Element ◽  
Strain Path ◽  
Small Deviation ◽  
Axial Strain ◽  
Simulation Software ◽  
Forming Limit ◽  
Plastic Strain Ratio ◽  
Forming Limit Diagrams ◽  
Aluminium Sheet ◽  
Strain Paths

Suitability of AA2024-T3 and AA5083-H111 aluminium sheet alloys for forming operations in room temperature were examined by using forming limit diagrams with different strain paths. In the experimental part, circular bulge, non-grooved tensile as well as grooved tensile specimens were used. This was done to simulate the following: (a) biaxial stretching region (positive range of minor strain), (b) uni-axial strain path and (c) strain path from uni-axial tension to plane strain region of the forming limit diagram, respectively. The effects of combined strain paths coupled with material anisotropy were taken into account in each stage. Tensile properties as well as formability parameters were correlated in accordance with the attained forming limit diagrams. Average plastic strain ratio and planar anisotropy, in addition to work hardening exponents of the samples, were calculated from the test data and the effects on the forming limit diagrams were discussed. Moreover, comparisons were made between experimental and theoretical forming limit diagrams. It is shown that experimental forming limit diagrams are in very good agreement with the theoretical predictions, particularly when BBC2000 yield criteria are used for the M–K model. In addition, theoretical prediction by using the Hill93–Swift model showed small deviation with the experimental forming limit diagrams. Finally, finite element simulations were carried out to investigate the numerical forming limit diagrams through an industrial sheet metal forming simulation software. It was consequently shown that, due to frictional effects resulting from hemispherical-shaped punch, the finite element results depicted small deviation compared to the experimental data.

Effect of Plastic Anisotropy on Forming Limit Prediction

2005 ◽  
Vol 495-497 ◽  
pp. 1573-1578 ◽  
Author(s):  
S. He ◽  
Albert Van Bael ◽  
Paul van Houtte
Keyword(s):  
Strain Path ◽  
Plastic Anisotropy ◽  
Yield Locus ◽  
Material Behavior ◽  
Forming Limit ◽  
Sheet Metals ◽  
Forming Process ◽  
Forming Limit Diagrams ◽  
Strain Path Changes ◽  
Complex Strain

A model based on Marciniak-Kuczynski (M-K) theory [1] for the prediction of forming limit diagrams (FLDs) for anisotropic sheet metals is presented. The plastic anisotropy is taken into account by the shape of the yield locus generated on the basis of measured crystallographic texture. As a result, not only the material behavior during the monotonic loading can be well described and predicted, but also the complex strain-path changes during the forming process can be taken into account. Examples of predicted FLDs for two aluminum alloys are given. Comparisons with experimental results are presented.

Forming Limit Curves for Complex Strain Paths

2013 ◽  
Vol 58 (2) ◽  
pp. 587-593 ◽  
Author(s):  
J. Rojek ◽  
D. Lumelskyy ◽  
R. Pęcherski ◽  
F. Grosman ◽  
M. Tkocz ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Strain Path ◽  
Experimental Studies ◽  
Polar Coordinates ◽  
Forming Limit ◽  
Effective Plastic Strain ◽  
Steel Blank ◽  
Strain Paths ◽  
Complex Strain ◽  
Forming Limit Curves

This paper presents results of experimental studies of forming limit curves (FLC) for sheet forming under complex strain paths. The Nakazima-type formability tests have been performed for the as-received steel blank and for the blank pre-strained by13%. Prestraining leads to abrupt change of strain path in the blank deformation influencing the forming limit curve. The experimental FLC of the pre-strained blank has been compared with the FLC constructed by transformation of the as-received FLC. Quite a good agreement has been found out. The concept of strain-path independent FLCs in polar coordinates has been verified. Two types of the polar diagrams have been considered, the first one with the strain-path angle and effective plastic strain as the polar coordinates, and the second one originally proposed in this work in which the thickness strain has been used instead of the effective plastic strain as one of the polar coordinates. The second transformation based on our own concept has given a better agreement between the transformed FLCs, which allows us to propose this type of polar diagrams as a new strain-path in dependent criterion to predict sheet failure in forming processes.

Investigation of Critical Stress Concentration Factor in Analytical Stress Based Forming Limit Criterion

2009 ◽  
Author(s):  
Kyle R. McLaughlin ◽  
Tugce Kasikci ◽  
Igor Tsukrov ◽  
Brad L. Kinsey
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Failure Criterion ◽  
Concentration Factor ◽  
Critical Stress ◽  
Strain Path ◽  
Path Dependence ◽  
Forming Limit ◽  
Concentration Factors ◽  
Stress Concentration Factors

Tearing concerns in sheet metal forming have traditionally been predicted by comparing the strain state imposed on a material to its associated strain based Forming Limit Diagram. A shortcoming of this strain based failure criterion is that the Forming Limit Curves exhibit strain path dependence. Alternatively, a stress based failure criterion was introduced and shown analytically and numerically to exhibit less strain path dependence. In our past research, an analytical model was created to predict the stress based Forming Limit Curve. Inputs into the model include a material constitutive relationship, anisotropic yield criterion and a critical stress concentration factor, defined as the ratio of the effective stress in the base material to the effective stress in the necking region. This stress concentration factor is thought to be a material parameter, which characterizes a material’s ability to work harden and prevent the concentration of stress which produces the necking condition. In this paper, the critical stress concentration factors for steel and aluminum alloys were determined by comparing analytical model predictions and experimental data and found to be significantly different. A setup is then proposed to experimentally measure the critical stress concentration factors and initial results are presented.

scholarly journals Effect of continuous strain path changes on forming limit strains of DP600

Strain ◽  
2019 ◽  
Vol 55 (6) ◽  
Author(s):  
Xiao Song ◽  
Lionel Leotoing ◽  
Dominique Guines ◽  
Eric Ragneau
Keyword(s):  
Strain Path ◽  
Forming Limit ◽  
Strain Path Changes
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