Mild steel yield stress

[ManDV]

Hello,

i have some mild steel test sample and they are tested with tensile stress. I have obtained the Young's modulus is in the range of 290 to 320 GPa,poisson ratio is 0.27-0.29. However, those stress and strain curve of tho mild steel do not have upper and lower yield strength. So what may be the reason of this problem?thanks

[zeroUSA]

Did you get any elongation before rupture?Was the machine properly calibrated?Perhaps your specimen had a crack in it.

Mild steel should be ductile, but unless you have good source documentation you might have been sold a pig in a poke.

What temperature was your test done at? Steel pressure vessels are not supposed to be hydrotested below 70 deg F due to concerns about brittle fracture. It's questionable if this rrestirction is really necessary with properly documented steels.

Edited December 15, 2013 by zeroUSA

[Enthalpy]

The measured Young is wrong. It's 210GPa for any ferritic steel, unless heavily alloyed -and no alloying element would bring steel to 290GPa.

 

There is no lower limit to the yield strength of mild steel. As steel gets purer iron and is well annealed, the yield strength drops and drops. For instance Armco steel (it bears a different name in their catalogue) is extremely soft; it's a cheap iron core for electromagnets, relays, and is horrible to machine. So you may experience difficulty measuring an elastic behaviour while your steel is essentially plastic.

 

By the way, mild steel is one example of a centered cubic crystal that is very ductile.