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

Schleich, Ralf; Sindel, M.; Liewald, Mathias

doi:10.1007/s12289-009-0394-z

Cited by 27 publications

(8 citation statements)

References 1 publication

(1 reference statement)

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“…This device provides five hydraulic clamps on each side which can be moved separately. In order to pre-stretch the samples (with the dimensions 240 mm x 1,000 mm x 1.04 mm) in uniaxial direction only two of the five available hydraulic clamps were used to avoid wrinkling [2]. To sufficiently cover the interval of uniaxial pre-stretching up to a major true strain of about 0.17 the stretching levels in uniaxial direction up to major strains (φ 1 ) of 0.05, 0.1, 0.14 and 0.17 were imposed (see Fig.…”

Section: Methodsmentioning

confidence: 99%

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

Werber

Liewald

Nester

et al. 2012

KEM

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In order to evaluate the formability of sheet materials forming limit diagrams (FLD) are recorded which represent the values of major and minor strain when necking occurs. FLDs are recorded based on the assumption that exclusively linear strain paths occur. In real forming parts, however, particularly in those with complex shapes, predominantly non-linear strain paths occur which reduce the accuracy of the failure prediction according to a conventional FLD. For this reason forming limits after loading with non-linear strain paths have to be investigated. In this contribution a systematic analysis of the forming limits of a conventional AA6014 alloy after loading with non-linear strain paths is presented. This material is pre-stretched in uniaxial, plane strain and biaxial direction up to several levels before performing Nakajima experiments in order to determine FLDs. During the pre-stretching process as well as during the Nakajima experiment the strain distribution can be measured online very precisely with the optical deformation measurement systems GOM Aramis or VIALUX. The gained curves are compared to the FLD of the as-received material. The results prove a significant influence of the pre-stretching condition on the forming limits of the used aluminum alloy. For a low pre-stretching in uniaxial as well as in biaxial direction the FLDs show a slightly reduced formability while after higher pre-stretching levels the forming limit can be improved such as for biaxial loading after uniaxial pre-stretching. The formability after pre-stretching in plane strain direction was changed. Also, a shift of the FLD depending on the direction of pre-stretching can be observed.

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Section: Methodsmentioning

confidence: 99%

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

Werber

Liewald

Nester

et al. 2012

KEM

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“…The influence of strain hardening was taken into account by strain dependent definition of  b in Equation 3.…”

Section: Enhancement Of Cflc Approach By Taking Arbitrary Biaxial Strmentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

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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“…The dominant load on these edges during hemming or bending is plane strain. As many researchers, Denninger [1], Schleich [2], Liewald [3] have described in their work, the conventional FLC is not suitable to predict the formability in bending or hemming operations. This is due to a different failure mechanism under bending loads compared to stretch-dominated forming processes.…”

Section: Introductionmentioning

confidence: 99%

Bending Limit Curves in Sheet Metal Bending Evaluation

Panich

2017

KEM

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Bending and hemming process are used in automotive industries for assembling the car body panel.The main failure mechanism under bending loads is the intercrystalline fracture. This is due to the fact that the Forming Limit Curve (FLC) describes first occurrence of membrane instability and no material failure in consequence of an intercrystalline fracture at bending.The FLC fails to predict the formability in hemming processes since difference in failure mechanism. A new failure criterion, the so-called Bending Limit Curve (BLC) has been developed. In this work, the left hand side BLCs are experimentally determined for Advanced High Strength Steel grade DP1000, Stainless Steel grade SUS430 and Deep Drawing Steel grade SPCC having a thickness of 1.0 mm. The influence of various bending radii and level of pre-strain on the bending strains are investigated and discussed by using the Three Point Bending Test. Bendability of investigated materials are evaluated by using optical strain measurement system GOM-Aramis to determine maximal achievable bending strain on the specimens. The developed left hand side BLCs were found to be higher level than conventional FLCs. The bigger bending radius established lower bending limit strain. The higher bending strain was obtained from the higher pre strain level.

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

Cited by 27 publications

References 1 publication

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

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

Bending Limit Curves in Sheet Metal Bending Evaluation

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