Significance of - Reduction of area in a Tensile testing.doc

8/10/2019 Significance of - Reduction of area in a Tensile testing.doc

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Signifcance o - Reduction o area in a tensile test.

Ductility

An important behaviour observed during a tension test is ductility

- The extent of plastic deformation that the material undergoes before fracture.

1. Elongation

2. Reduction of area

The second measure of ductility - the reduction of area. ! r "

#here $A%&and $Af&are' respectively' the original and final (fracture) cross-sectionalareas of the test specimen.

Reduction of area and elongation are generally interrelated ' as sho*n in +ig. 2., for some

typical metals.

Tensile reduction of area has been sho*n - to predict the bend-ability (sec 1.) and

spinnability (sec 1.11) of metals.

The bend-ability

Sec 16.5 .There is an inverse relationship bet*een bend ability and the tensile reduction

of the area of the material (+ig. 1.1/). The minimum bend radius' R' is' approximately'

#here ! r " is the tensile reduction of area of the sheet metal.

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Thus' for r 0' the minimum bend radius is ero that is' the sheet can be folded over

itself (see hemming' +ig. 1.23) in much the same *ay as a piece of paper is folded.

To increase the bend ability of metals' *e may increase their tensile reduction of area

either by heating or by bending in a high-pressure environment (*hich improves theductility of the material see hydrostatic stress' 4ection 2.2./).

5end ability also depends on the edge condition of the sheet. 4ince rough edges are points

of stress concentration' bend ability decreases as edge roughness increases.

4pinnability

Sec 16.11

The spinnability of a metal in this process generally is defined as the maximum

reduction in thic6ness to *hich a part can be sub7ected by spinning *ithout fracture.

4pinnability is found to be related to the tensile reduction of area of the material' 7ust as is

bend-ability (see +ig. 1.1/). Thus' if a metal has a tensile reduction of area of 08 or

higher' its thic6ness can be reduced by as much as /08 in 7ust one spinning pass.

+or metals *ith lo* ductility' the operation is carried out at elevated temperatures by

heating the blan6 in a furnace and transferring it rapidly to the mandrel.

Reference:

1.9rof. 4erope :alpa67ian and Dr. 4teven .R 4chmid.' ;anufacturing Engineering and

technology ,thEdition'

2.Dats6o


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Significance of - Reduction of area in a Tensile testing.doc

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