Investigation on the effect of curvature and sheet thickness on forming limit prediction for aluminium sheet metal alloys

This paper presents an overview of published test methods for determination of formability of a sheet metal cut-edge. The presented test methods were developed to evaluate formability of a sheet metal edge that was produced by shear cutting. Due to high local strains, hardening, or even microcracks, the cut-edge might have less formability than the base material. The presentation of the tests is structured according to the three steps each test can be divided into: cutting, forming and evaluation. Similarities and differences concerning these steps were worked out. Additionally, a classification of the tests is made regarding their strain gradients in the vicinity of the cut-edge. For this, finite element models of exemplary tests were built up using LS-DYNA explicit and analyzed accordingly. Evaluation approaches that go beyond the common hole expansion ratio (HER) from the hole expansion test (HET) standardized in the ISO 16630 are also described. The tests can be used not only for a quantitative comparison of materials and cutting processes with regard to the cut-edge formability but to determine input data for the finite element analysis (FEA) of forming processes to allow a simulation based cut-edge failure prediction. The paper also presents appropriate procedures on the transfer of the test results into the FEA of forming of a workpiece with a cut-edge.

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“…The specimens for the Hemmability-And-Bendability-Test (HAB ® -Test) were punched or milled on a straight edge with a length of 20 mm [42,43].…”

Section: Cut-edge Bending Out Of the Sheet Planementioning

confidence: 99%

Overview and comparison of various test methods to determine formability of a sheet metal cut‐edge and approaches to the test results application in forming analysis

Schneider

Geffert

Peshekhodov

et al. 2015

Materialwissenschaft Werkst

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“…Thus, a further investigation of combined failure modes between homogeneous stretching and bending is reasonable. Applying the optical forming analysis according to Schleich et al [5] on the uniaxial tensile test, the Nakajima test and on bending test for several inner radii an increase of formability of sheet metal can be observed. Hence, a vertical shift of the major strain component at planar drawing by using a correlation function M is proposed.…”

Section: Determination Of Forming Limits Under Combined Deep Drawing mentioning

confidence: 99%

“…Figure 1 shows the experimentally determined major strain values of an AA6016 alloy with a thickness of 1.1mm and 2.0mm. Due to [5] the maximal achievable strain value significantly depends on the respective membrane strain value. It can also be seen in Figure 1 that an increase of sheet thickness from 1.1mm to 2.0mm leads to an increase of major strain value of 0.2.…”

Section: Effect Of Sheet Thickness On Material's Formabilitymentioning

confidence: 99%

“…The so called Forming Limit Curve (FLC) describes material failure for arbitrary in-plane load conditions [1]. For consideration of additionally superposed bending loads several approaches concerning the so-called Concave Side Rule (CSR) [4] or the cFLC [5] as an enhancement of the Bending Limit Curve [2] have been developed during recent years.…”

Section: Introductionmentioning

confidence: 99%

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Development of an Anisotropic Failure Criterion for Characterising the Influence of Curvature on Forming Limits of Aluminium Sheet Metal Alloys

Liewald

Schleich²

2010

Int J Mater Form

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For characterising formability of sheet metal materials the so called Forming Limit Curve (FLC) due to the ISO 12004-2 standard to predict material potential, subjected to static multi-axial in-plane load conditions has been developed during recent years [1]. Experimental results have shown that forming limits under bending loads cannot be described by the conventional FLC at all. This is due to the fact that the FLC describes first occurrence of membrane instability and no material failure in consequence of an inter-crystalline fracture at bending. However, first experimental and simulative approaches concerning the Bending Limit Curve (BLC) describe the material formability under pure bending conditions, such as hemming [2]. Thus, the investigation of bendability of sheet metal alloys is of great importance for the evaluation of process robustness for the production of mechanically joined sheet metal assemblies. Furthermore, material cracks due to a dominant bending load can also occur during deep drawing. The so called combined load FLC (cFLC) enables the failure prediction for such load cases under the assumption of an isotropic damage evolution at drawing [3]. This contribution focuses on the development of an improved failure criterion based on the cFLC concept to take the influence of curvature and anisotropic damage evolution on failure prediction at deep drawing into account.

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“…Die Proben werden in Hutlage umgeformt und die Blechhaltekraft von der Unterseite mittels Gasdruckfedern aufgebracht. Auf diese Weise ist die Umformzone für die Formän-derungsanalyse frei einsehbar gestaltet [10].…”

Section: Introductionunclassified

Semi‐empirische Berechnungsmethode zur Bestimmung des Grenzformänderungsdiagramms auf Basis mechanischer Kennwerte

Held¹,

Dadrich²,

Denninger³

et al. 2009

Materialwissenschaft Werkst

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For characterisation purposes of sheet metal forming processes concerning feasibility of material mainly the Forming Limit Curve (FLC) is commonly used. This failure model can either be measured experimentally or can be predicted by using semi-empirical approaches. These mathematical approaches mainly are validated for Mild Steels. However, prediction of FLCs for modern High Strength Steels or Aluminium sheet alloys is not possible with acceptable accuracy today. This is why this contribution deals with a new semi-empirical approach for FLC prediction, which is valid for all sheet metal materials used in car body production. This approach uses a correlation of mechanical properties of uniaxial tensile test an experimentally determined limit strains.

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Investigation on the effect of curvature and sheet thickness on forming limit prediction for aluminium sheet metal alloys

Cited by 18 publications

References 4 publications

Overview and comparison of various test methods to determine formability of a sheet metal cut‐edge and approaches to the test results application in forming analysis

Overview and comparison of various test methods to determine formability of a sheet metal cut‐edge and approaches to the test results application in forming analysis

Development of an Anisotropic Failure Criterion for Characterising the Influence of Curvature on Forming Limits of Aluminium Sheet Metal Alloys

Semi‐empirische Berechnungsmethode zur Bestimmung des Grenzformänderungsdiagramms auf Basis mechanischer Kennwerte

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