Per Cent elongation for 304L tube? 4

[MrAnxious]

Hi all, I have trawled the web looking for data on 304L stainless steel tube. I can find plenty of websites giving % elongation to tensile failure but I cannot find a figure for % elongation to the materials elastic limit. Is this data not published at all? Thanks very much.

 

[TVP]

The % elongation to reach the elastic limit will be ~ 0.1 to 0.2% elongation, or a strain of 0.001 to 0.002. It is essentially the same for all ductile metals, which is why the yield strength is usually measured as the stress produced by 0.2% elongation.

 

[redpicker]

I have to disagree with TVP, at least in theory. Yes, the 0.2% elongation is often used to measure the yield stress, but that is typically offset by the elastic constant.

In general, you can calcualte the extension (strain) at yield by dividing the yield stress by the elastic constant. So for Grade 304L with a yield stress of 25,000 PSI and assuming a elastic constant of 29 E+6 PSI, you would get an extension at yield of .0009 or 0.09%. Of course, the elastic limit is less than the 0.2% offset yield stress, so, for annealed material, the extension at the elastic limit would be much less.

For cold worked material, the yield stress would be higher and the difference between the yield stress and the elastic limit would be less, but the end result is that TVP was correct in that it would be unlikely for the elastic extension to be over 0.2% (this would require a yeild stress over 50000 PSI).

rp

 

[MrAnxious]

Thank you both. I have a figure of ~40% elongation for 304L. I have assumed this to be at tensile failure. I can't figure out what the % elongation at elastic limit will be (or even better, what the % elongation to limit of proportionality would be). Thank you for being patient with a dumb chemical engineer working outside her discipline!

 

[EdStainless]

Just remember that while the elastic limit is a real property it has nothing to do with yield strength. Yield is a construct of convenience that is meant to be a handy approximation. The actual elastic limit for 304 will be well below the yield strength, probably near a strain of 0.005.
But what makes these useful alloys is that with their high ductility you can go to loads that result is some yielding and all that you get is some general stretching and the load is distributed.
With 304L tubes is the tensile testing was done on tubular samples you should have elongations over 55%. Flat plate or cut samples will be around 40%.

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Plymouth Tube

 

[Compositepro]

The total elastic strain is the yield stress divided by the elastic modulus. As the others have pointed out, the yield stress is defined as the stress that produces 0.2% plastic strain. If you had the stress-strain curve you could read the elongation directly, but usually the data that is published is elastic modulus, yield stress, and ultimate elongation. This data summarizes most of the useful information in the curve.

 

[MrAnxious]

Thank you all.