Stress-Strain Relation 1

[pronur]

Hello I am a Nastran beginner. I am modeling wind blades using PCOMPG entry. I am using linear static solver (SOL 101). I request stress and strain outputs. However when I check the ply stresses and strains I have a problem with the stress strain relation. Normally Stress / Strain must give the Young's Modulus (E). But when I divide the computed ply stresses by computed ply strains I don't obtain E value of the material. The value I get is way different from E. Is this reasonable what might be the reason of that?

Thanks a lot in advance.

 

[rob768]

stress divided by E = strain?

 

[pronur]

That's what I expect. However, there is a difference between the one I calculate and the nastran strain output.

 

[rob768]

may be due to Multi-axial stress conditions. What you see in the stress is the sum of all stress, where strain may be in one

 

[Kwan]

I think you have to take into account poisson's ratio.

Strain-x * E = Fx - uFy - uFz

That's for isotropic materials. For orthotropic it get more complicated because you have Ex, Ey, and Ez. And we haven't talked about shear.
Look up hooke's law for orthotropic composites

http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_orthotropic.cfm

Hope this helps.

 

[pronur]

Thanks a lot for the answers. The link was pretty helpful.

 

[stressebookllc]

If you are talking about a solid lamiate, the strain is the same, but the stress will vary based on many factors such as individual ply properties, ply orientation etc. Like Kwan said, E1 (warp) and E2 (weft) are typically different for a UDP ply, and may be the same or close for a cloth depending on the weave type.

I think you could use this link:

http://www.stressebook.com/engineering-resources/

http://www.stressebook.com

Stressing Stresslessly!