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http://en.wikipedia.org/wiki/Formability

FormabilityFrom Wikipedia, the free encyclopedia

Formabilityis the ability of a given metal workpiece to undergo plastic deformation without being damaged. The

plastic deformation capacity of metallic materials, however, is limited to a certain extent, at which point, the materi

could experience tearing or fracture (breakage).

Processes affected by the formability of a material include: rolling, extrusion, forging, rollforming, stamping, andhydroforming.

Contents

1 Fracture strain

2 Forming limits for sheet forming

3 Deep drawability

4 Ductility5 Use of formability parameters

6 IDDRG

7 References

Fracture strain

A generalparameter that indicates theformability and ductility of a material is the fracture strain which is determine

by a uniaxial tensile test (see also fracture toughness). The strain identified by this test is defined by elongation withrespect to a reference length. For example, a length of 80 mm (3.1 in) is used for the standardized uniaxial test of

flat specimens, pursuant to EN 10002. It is important to note that deformation is homogeneous up to uniform

elongation. Strain subsequently localizes until fracture occurs. Fracture strain is not an engineering strain since

distribution of the deformation is inhomogeneous within the reference length. Fracture strain is nevertheless a rough

indicator of the formability of a material. Typical values ofthe fracture strain are: 7% for ultra-high-strength materia

and over 50% for mild-strength steel.

Forming limits for sheet forming

One main failure mode is caused by tearing of the material. This is typical for sheet-forming applications.[1][2][3]A

neck may appear at a certain forming stage. This is an indication of localized plastic deformation. Whereas more o

less homogeneous deformation takes place in and around the subsequent neck location in the early stable

deformation stage, almost all deformation is concentrated in the neck zone during the quasi-stable and instable

deformation phase. This leads to material failure manifested by tearing. Forming-limit curves depict the extreme, bu

still possible, deformation which a sheet material may undergo during any stage of the stamping process. These

limits depend on the deformation mode and the ratio of the surface strains. The major surface strain has a minimum

value when plane strain deformation occurs, which means that the corresponding minor surface strain is zero.

Forming limits are a specific material property. Typical plane strain values range from 10% for high-strength grade

and 50% or above for mild-strength materials and those with very good formability. Forming limit diagrams are
http://en.wikipedia.org/wiki/Plastic_deformationhttp://en.wikipedia.org/w/index.php?title=EN_10002&action=edit&redlink=1http://en.wikipedia.org/wiki/Rollinghttp://en.wikipedia.org/wiki/Extrusionhttp://en.wikipedia.org/wiki/Forginghttp://en.wikipedia.org/wiki/Rollforminghttp://en.wikipedia.org/wiki/Stamping_(metalworking)http://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Forming_limit_diagramhttp://en.wikipedia.org/wiki/Plastic_deformationhttp://en.wikipedia.org/w/index.php?title=EN_10002&action=edit&redlink=1http://en.wikipedia.org/wiki/Fracture_toughnesshttp://en.wikipedia.org/wiki/Tensile_testhttp://en.wikipedia.org/wiki/Fracturehttp://en.wikipedia.org/wiki/Ductilityhttp://en.wikipedia.org/wiki/Hydroforminghttp://en.wikipedia.org/wiki/Stamping_(metalworking)http://en.wikipedia.org/wiki/Rollforminghttp://en.wikipedia.org/wiki/Forginghttp://en.wikipedia.org/wiki/Extrusionhttp://en.wikipedia.org/wiki/Rollinghttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Plastic_deformationhttp://en.wikipedia.org/wiki/Metal


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often usedto graphically or mathematically represent formability. It is recognized by many authors that the nature o

fracture and therefore the Forming limit diagrams are intrinsically non-deterministic, since large variations might be

observed even within a single experimental campaign.[4]

eep drawability

A classic form of sheetforming is deep drawing, which is done by drawing a sheet by means of a punch tool

pressing onthe inner region of the sheet, whereas the side material held by a blankholder can be drawn toward thecenter. It has been observed that materials with outstanding deep drawability behave anisotropically (see:

anisotropy). Plastic deformation in the surface is much more pronounced than in the thickness. The lankford

coefficient(r) is a specific material property indicating the ratio between width deformation and thickness

deformation in the uniaxial tensile test. Materials with very good deep drawability have an rvalue of 2 or above.

The positive aspect of formability with respect to the forming limit curve (forming limit diagram) is seen in the

deformation paths of the material that are concentrated in the extreme left of the diagram, where the forming limits

become very large.

uctilityAnother failure mode that may occur without any tearing is ductile fracture after plastic deformation (ductility). Thi

may occuras a result of bending or shear deformation (inplane or through the thickness). The failure mechanism

may be dueto void nucleation and expansion on a microscopic level. Microcracks and subsequent macrocracks

may appear when deformation of the material between the voids has exceeded the limit. Extensive research has

focused inrecent years on understanding and modeling ductile fracture. The approach has been to identify ductile

forming limits using various small-scale tests that show different strain ratios or stress triaxialities. [5][6]An effective

measure ofthis type of forming limit is the minimum radius in roll-forming applications (half the sheet thickness for

materials with good and three times the sheet thickness for materials with low formability).

Use offormability parameters

Knowledgeof the material formability is very important to the layout and design of any industrial forming process.

Simulationsusing the finite-element method and use of formability criteria such as the forming limit curve (forming

limit diagram) enhance and, in some cases, are indispensable to certain tool design processes (also see: Sheet met

forming analysis).

IDDRG

One major objective of the International Deep Drawing Research Group (IDDRG, from 1957) is the investigation

exchange and dissemination of knowledge and experience about the formability of sheet materials.

References

1. ^Pearce, R.: Sheet Metal Forming, Adam Hilger, 1991, ISBN 0-7503-0101-5.

2. ^Koistinen, D. P.; Wang, N.-M. edts.: Mechanics of Sheet Metal Forming Material Behavior and Deformation

analysis, Plenum Press, 1978, ISBN 0-306-40068-5.

3. ^Marciniak, Z.; Duncan, J.: The Mechanics of Sheet Metal Forming, Edward Arnold, 1992, ISBN 0-340-5640
http://en.wikipedia.org/wiki/Special:BookSources/0340564059http://en.wikipedia.org/wiki/Special:BookSources/0340564059http://en.wikipedia.org/wiki/Special:BookSources/0306400685http://en.wikipedia.org/wiki/Special:BookSources/0750301015http://en.wikipedia.org/wiki/IDDRGhttp://en.wikipedia.org/wiki/Sheet_metal_forming_analysishttp://en.wikipedia.org/wiki/Forming_limit_diagramhttp://en.wikipedia.org/wiki/Finite-element_methodhttp://en.wikipedia.org/wiki/Ductilehttp://en.wikipedia.org/wiki/Ductilehttp://en.wikipedia.org/w/index.php?title=Macrocrack&action=edit&redlink=1http://en.wikipedia.org/wiki/Nucleationhttp://en.wikipedia.org/wiki/Ductilityhttp://en.wikipedia.org/wiki/Ductilehttp://en.wikipedia.org/wiki/Forming_limit_diagramhttp://en.wikipedia.org/wiki/Lankford_coefficienthttp://en.wikipedia.org/wiki/Anisotropyhttp://en.wikipedia.org/w/index.php?title=Punch_tool&action=edit&redlink=1http://en.wikipedia.org/wiki/Deep_drawinghttp://en.wikipedia.org/wiki/Forming_limit_diagram


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9.

4. ^Strano, M.; Colosimo, B.M. (30 April 2006). "Logistic regression analysis for experimental determination of

forming limit diagrams".International Journal of Machine Tools and Manufacture46(6): 673682.

doi:10.1016/j.ijmachtools.2005.07.005 (http://dx.doi.org/10.1016%2Fj.ijmachtools.2005.07.005).

5. ^Hooputra, H.; Gese, H.; Dell, H.; Werner, H.: "A comprehensive failure model for crashworthiness simulation o

aluminium extrusions", IJ Crash 2004 Vol 9, No. 5, pp. 449-463.

6. ^Wierzbicki, T.; Bao, Y.; Lee, Y.-W.; Bai, Y.: Calibration and Evaluation of Seven Fracture Models, Int. J.

Mech. Sci., Vol. 47, 719 743, 2005.

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