Calculate Tangent Modulus

[Rolfman]

Is there any way of calculating the tangent modulus of a material if I have Youngs Modulus, the 0.2% yield and ultimate strengths?

I want to use it for a bi-linear manual calculation.

 

[corus]

For a bi-linear material you would have to assume something for the tangent modulus. If you look at a similar material and the slope of the stress-strain curve above yield, then that would be a good aprroximation to apply to your material. If you have no information then it is always best to assume the worst, which in your case may be to assume ideally plastic material.

 

[EnglishMuffin]

The definition of Tangent Modulus is the slope of the Stress v Total Strain curve at any point. It is usually used in the plastic region. So in order to calculate it for some point in the plastic region, you would obviously need to know stresses and strains at two points, and the curve would need to be approximately linear between them. Since you have given only two stresses (yield and ultimate) and no strains, it is obviously impossible to calculate from the given data alone, except for the trivial case of the elastic region where the Tangent Modulus is equivalent to the Youngs Modulus.

 

[EnglishMuffin]

Actually - I should modify my answer somewhat. You have actually given one stress (the yield) and the approximate strain at that point can be deduced by dividing it by E, which you have also given. And that's about all you have, because the ultimate strength, being based on the original area (ie before necking) is not really a true stress, which strictly speaking I think you should be using for the tangent modulus.