Ductility of sheet metal in the negative minor strain region of forming limit diagrams

Path-dependent forming limits have been computed for sheet metals undergoing various combinations of plane stress loading conditions. This paper presents a theoretical model for prediction of stress-based forming limit curves (SFLC) based on the Marciniak and Kuczynski (MK) model. Acceptable agreement was observed between calculated forming limit curves (FLC) and experimental data for AISI-1012 steel (Molaei 1999) and AA-2008-T4 alloys (Graf and Hosford Metallurgical Trans 24A:2503-2512, 1993. In this paper, the path dependency of SFLCs predicted for different non-proportional loading histories has been investigated. For a range of prestrain values in different bilinear loading paths, the SFLC remains practically unchanged. However, some strain path dependency is observed for large values of prestrain (e ! 0:35 for AISI-1012 steel) and for abrupt changes in strain path. Nevertheless, the SFLC remains a good failure criterion for virtual forming simulations because the path dependency of SFLCs is much less significant than that of strain-based FLCs.

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“…The associated flow rule in the principal axes of orthotropic anisotropy is expressed in the form [28]:…”

Section: Strain-based Forming Limit Curvesmentioning

confidence: 99%

Investigation on the strain-path dependency of stress-based forming limit curves

Nurcheshmeh

Green

2010

Int J Mater Form

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“…Nevertheless, formability can be described in different ways, being the forming limit diagram (FLD), one of the most employed. These diagrams are defined in the principal strain space (e 1 -e 2 ) where safe strain combinations are separated from the fracture or necking condition (Ravishankar & Venkadesan, 1996). For characterizing a wide area of the principal strain space, different strain combinations can be obtained by changing the shape of the tested samples, which allow covering from the uniaxial tension to equi-biaxial tension states range.…”

Section: Introductionmentioning

confidence: 99%

Study on the Formability and Texture evolution of AA6061 Alloy Processed by Repetitive Corrugation and Straightening.

Elizalde

Ezequiel

Cabrera

et al. 2021

JART

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The enhanced mechanical properties obtained by refining the grain size down to the ultrafine-grained (UFG) regime have attracted considerable attention in recent years. The severe plastic deformation (SPD) techniques allow obtaining ultrafine-grained materials. Different SPD techniques permit processing sheet shape materials such as repetitive corrugation and straightening (RCS) and accumulative roll bonding (ARB). In this study, the formability of an AA 6061-T6 processed by RCS was evaluated. The forming limit diagrams (FLD) were obtained by Nakazima tests of samples in initial condition (T6 state) and after one and two RCS cycles. The FLD curves showed that the forming capacity decreased from the first RCS cycle. Likewise, uniaxial tensile tests at different temperatures and strain rates were conducted to analyze the effect of the RCS process on the strain rate sensitivity. They showed a relatively high strain rate sensitivity coefficient in the samples after one and two RCS cycles, which indicates an improvement of i) the capacity of the material to delay the onset of the necking and ii) the formability at increasing temperatures. Finally, texture analysis was carried out employing X-ray diffraction, calculating the orientation distribution functions (ODFs). The initial texture showed a predominant cube texture component, whereas, for further RCS cycles, a weakening of the cube texture and an increment of the S texture component were observed.

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The Influence of Material Properties on the Shape and Level of the Forming Limit Diagram

Assempour

Nurcheshmeh

2003

SAE Technical Paper Series

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Ductility of sheet metal in the negative minor strain region of forming limit diagrams

Cited by 3 publications

References 6 publications

Investigation on the strain-path dependency of stress-based forming limit curves

Investigation on the strain-path dependency of stress-based forming limit curves

Study on the Formability and Texture evolution of AA6061 Alloy Processed by Repetitive Corrugation and Straightening.

The Influence of Material Properties on the Shape and Level of the Forming Limit Diagram

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