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Elongation Requirementsfor

Presented by:

Suresh Gupta

ASTM Committee Meeting A01.05 May 8, 2012

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Purpose of Elongation

Elongation is a measure of ductility, which

provides confidence that metals can beformed, without cracking or fracturing.

In rebar, it defines ductility so that bars can bebent without cracking.

If bars do not crack during fabrication, any excesselongation is irrelevant.

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Alloy Characteristics

With all other variables remaining same,

Austenitic Alloys have highest elongation.

erritic Alloys have lowest elongation

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Measurement Methods and Facts ! Elongation, when measured in a fixed gage

length, e.g. " inches, is lower than whenmeasured in a gage length, as a multiple of diameter, e.g. # $ diameter %#d&.

when #d is less than fixed a e len th .

Elongation is generally lower as diameter goessmaller.

'his fact is clearly described in A(') E",Appendix $I

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ASTM E8

Standard Test Method for Tension Testing of Metallic MaterialsAppendix $I * actors Affecting 'ensile 'est +esults

omparison of elongation values determined using differentspecimens re-uires that the following ratio be controlled

/o0%Ao&102 %$I.1&

Where

/ 3 ori inal a e len th of s ecimen and

Ao3 original cross4sectional area of specimen.

$I.#.#.1 (pecimens with smaller /o0%Ao&102 ratios generally give

greater elongation.

Note: %Ao&102 is proportional to diameter %d&.

'herefore, for same ductility, larger diameter samples result ingreater elongation values, when measured in fixed gage length.

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ASTM A955-9a

5ntil revision 16a, elongation was not re-uired for

si7es 8 94: ;rade

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% Elongation Requirements for

Rebar

Carbon and Alloy steels

A(') A=1: re-uires = to

A(') A( =

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Manufacturing & Process Control

Even with precise chemistry and process

control, duplex stainless steels meet theelongation re-uirement very marginally.

,

will cause work hardening and elongation will go

down even further.

'his may cause unnecessary dispute.

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Rationale If =! elongation in carbon steel is sufficient

If 1#! in :d is sufficient for stainless steelrebar per >(=

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Proposal It is therefore recommended that,

5sing a foot note to 'able 9, elongation

,

for all si7es of duplex grades and,

all grades of stainless steels under 1.66 inch.