Elongation - PowerPoint Presentation

Elongation
Elongation

Elongation - Description


Requirements for Stainless Steel Rebar Presented by Suresh Gupta ASTM Committee Meeting A0105 May 8 2012 Purpose of Elongation Elongation is a measure of ductility which provides confidence that metals can be ID: 273554 Download Presentation

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astm elongation length gage elongation astm gage length grade stainless rebar requires diameter steels grades sizes duplex ductility fixed

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Presentation on theme: "Elongation"— Presentation transcript


Slide1

Elongation

Requirements

for

Stainless Steel

Rebar

Presented by:

Suresh Gupta

ASTM Committee Meeting A01.05 May 8, 2012Slide2

Purpose of Elongation

Elongation

is a measure of ductility, which provides confidence that metals can be

formed,

without cracking or fracturing

.

In

rebar,

it defines ductility so that bars can be bent without cracking.

I

f bars do not crack during fabrication, any excess elongation is irrelevant

.Slide3

Alloy Characteristics

With

all other variables remaining same

,

Austenitic Alloys have highest elongation.

Duplex Alloys have elongation in mid range

Ferritic Alloys have lowest elongationSlide4

Measurement Methods and Facts

% Elongation, when measured

in

a fixed gage length, e.g. 8 inches,

is lower than when measured in a gage length, as a multiple of

diameter,

e.g.

4 X diameter (4d

).

(when

4d is less than

fixed gage length)

.

Elongation is generally lower as diameter goes smaller

.

This fact is clearly described in ASTM E8, Appendix XISlide5

ASTM E8

Standard Test Method for Tension Testing of Metallic

Materials

Appendix

XI – Factors Affecting Tensile Test Results

Comparison of elongation values determined using different specimens requires that the following ratio be controlled:

L

o

/(A

o

)

1/2

(XI.1)

Where:

L

o

= original gage length of specimen, and

A

o

= original cross-sectional area of specimen.

XI.4.4.1 Specimens with smaller L

o

/(A

o

)

1/2

ratios generally give greater elongation.

Note:

(A

o

)

1/2

is proportional to diameter (d).

Therefore, for same ductility, larger diameter samples result in greater elongation values, when measured in fixed gage length.Slide6
Slide7
Slide8
Slide9

ASTM A955-9a

Until revision 10a, elongation was not required for

sizes #

3-5

Grade 75, probably

because it was known that it is unrealistic or not necessary.

Grade 40 for sizes 7 and larger because, in any condition it will meet the requirement, anyway.Slide10

% Elongation Requirements

for Rebar

Carbon

and Alloy steels

ASTM A615 requires 6 to 7

%

for Grade 75

ASTM A706 requires 10 to 14% for all Grades.

Stainless

Steels

BS 6744 requires 14% minimum in

5d gage length

for Grade 500 (72.5 ksi

).

ASTM A955 requires 20% minimum in

8 inch gage length

for all grades, all sizes.Slide11

Manufacturing

&

Process Control

Even with precise chemistry and process control,

duplex stainless steels

meet the elongation requirement very marginally.

If rebar is supplied in coils, machine straightening will cause work hardening and elongation will go down even further.

This may cause unnecessary dispute.Slide12

Rationale

If 6% elongation in carbon steel is sufficient

If

14

% in

5d

is sufficient for stainless steel rebar per BS6744 in Europe,

It should be sufficient for us as well.

FYI

ASTM Specifications for plain smooth bars require elongation in 4dSlide13

Proposal

It is therefore recommended that,

Using a foot note to Table 3, elongation requirements be lowered to 14% for Grade 75,

for all sizes of duplex grades and,

all grades of stainless steels under 1.00 inch.

Shom More....
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