Material, relationship between "E" and yield strength

[EngForm78]

I am working on a plastics problem where there are a variety of formulations with a varitety of strength properties. I can see that when the material Modulus of Elasticity, E increases the yield strength does as well, and vice versa. Is there a real realationship here? If I get a range of E values and a range of yield values is it correct to assume that there is a linear relationship between the max and min values of each.

Thanks

EngForm78

 

[meshparts]

Hi,

do you mean the yield stress?
If yes, as far as I know, there is no such relationship.

Alex

 

[feadude]

There is no linear relationship . This is why plastic analysis in non-linear.In FEA for plastic analysis stress strain data is input in preprocessor and strain is calculated in solve. Then stress is calculated/charted from calculated strain values. So your stress/strain input data is very important because if input stress values are not correct, then postprocessor stresses will be wrong.

good57morning@netzero.com

 

[rb1957]

feadude,

i think engform78 was asking is the a relationship between yield stress and E; rather than stress = E*strain.

as mihaiupb notes, there isn't. different "flavours" of Al (2024, 7075) have the same E, but different yields.

 

[gwolf]

Engforum78,

It is just a coincidence and there is no linear relationship. For a lot of metals, the stronger they are, the stiffer they are.

A simple exception is Titanium which is not very stiff compared to steel but is stronger than many steels. Titanium is not, however stronger than the strongest steels.

 

[JStephen]

Most steels have similar E's, although yield varies widely.

I'm sure if you narrow the material down sufficiently, you can get some sort of relationship. For example, I think ACI has a formula for E vs. fc' for concrete. If you were just varying one component of the plastic, you could probably do something similar.

I seem to recall from long ago that E with plastics was also time dependent, which would further complicate matters.