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Elongation Requirementsfor

Presented by:

Suresh Gupta

ASTM Committee Meeting A01.05 May 8, 2012



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.



Alloy Characteristics

With all other variables remaining same,

• Austenitic Alloys have highest elongation.

•

• erritic Alloys have lowest elongation



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



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 givegreater 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.









ASTM A955-9a

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

– si7es 8 94: ;rade <:, probably because it was known that it is

unrealistic or not necessary.

– ;rade #6 for si7es < and larger because, in any condition it will meetthe re-uirement, anyway.



% Elongation Requirements for

Rebar

Carbon and Alloy steels

• A(') A=1: re-uires = to <! for ;rade <:

• A(') A<6= re-uires 16 to 1#! for all ;rades.

• >( =<## re-uires 1#! minimum in :d gage

length for ;rade :66 %<2.: ksi&.

• A(') A?:: re-uires 26! minimum in " inchgage length for all grades, all si7es.



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.



Rationale• If =! elongation in carbon steel is sufficient

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

– .

FYI

• A(') (pecifications for plain smooth barsre-uire elongation in #d



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.