Young's Modulus / Steel / Abnormal values

Young's modulus of polycrystalline materials depends on crystallographic texture. 207 GPa is just a typical value for bcc iron.

Michael Dahms

f'up2 sci.materials

If you go here and look at the slide near the very end.... titled anisotropy....

you will find listed the claim that the elastic modulus for Iron in the face edge 100 directions is about 135 Gpa and the modulus for Iron in the cell diagonal 111 direction is about 273 Gpa.

Very nice presentation.

Thanks Jim, it is just what I was looking for unfortunately he link is broken.

Email the author......

snipped-for-privacy@polyu.edu.hk

Ask if he will give you the link to his excellent materials notes.

I fully agree that E depends on orientation. Nevertheless, our steels are mainly Quenched and Tempered types, and I don't expect them to be textured. But maybe I'm wrong... What's your opinion ?

Michel

"jbuch" a écrit dans le message de news: snipped-for-privacy@enews4.newsguy.com...

Sheets are usually rolled, and do generally have texture from the planar nature of the cold work.

You can partly eliminate texture by examining tensile specimens cut parallel to the rolling direction and 90 degrees to it, parallel to the axis of the rolls used to produce the sheet.

Tough to take specimens in the thickness direction, but if you were to be careful, you might be able to get a compressive Young's modulus from the through thickness direction.

You could perhaps even investigate ultrasonic modulus measurements to dig into the question of texture....... and some metallography would always be informative.

If it isn't texture, then your measuring techniques are called into question as otherwise potentially a waste of time and money.

You don't want to be in that position.

Jim

try this, you can get all chapter listed there. I think link was missing .pdf

independently

obtained is

Mike,

Check out "Fundametals of Cyclic Stress and Stain" by Bela I Sandor

What you are experiencing is cyclic softening (low cycle fatigue), sometimes this is addressed as the "Bauschinger effect"for large strains (see Mechanical Metallurgy by G. Dieter).

As for the root cause of you poor Young modulus slope do a sensitivity analysis (uncertainty analysis - if your A2LA accedited you should know of this) on the modulus slope itself I think you will find the major errors are involved with measurement and determination of area (stress=F/A= F/(thickness*width) and strain e=dl/L (change in length/orginal: plud into error differential form of "Youngs modulus equation": E=F*dl/(A*L)

dE/E = [ (dF/F)^2+(ddl/dl)^2+(dA/A)^2+(dL/L)^2)^(1/2) where d = partial differential NOTE dA/A = [(dw/w)^2+(dt/t)^2]^(1/2) for flats

You would think the manufactures of the stress frame would know...HA HA they got rid of the ol' timers and saved money...make you and us pay the cost.

Ed

Two years ago I did some tensile tests of aluminium and copper foils and found that the moduli were significantly smaller than quoted values. It is quite difficult to test foils though, so my colleague took the foils to another place and performed some sensitive three point bend instead. The values he got were similar to the quoted values. So perhaps you could perform a three point bend test (apparently you can design it to be very sensitive) to check.

At the same time, we were also interested in the yield values, and it was surprising to me that it was such a difficult measurement. Further depending on how the stress-strain curve is fitted, e.g. power law/bilinear, the yield value varies significantly. Now, I am more of a soft matter person and was not so experienced with stiff, plastically deforming materials, so I was generally surprised to find that those whom I was working with (whom I presumed were more well verse with the problem) were scratching their heads over this matter. Does anyone have similar experience on measuring yield stress/strain?