How to calculate Tangent modulus?

i'd've thought that Ramberg-Osgood parameters should get you there

@ rb1957 Many thanks for reply

I got yield stress, youngs modulus in linear region, ultimate tensile strength.
In order to use Ramberg-Osgood equation I will need K & n value which I dont have.

If you know the elongation to fracture, you can calculate the tangent modulus (under the assumption of a bilinear model).

Beyond that, there is no such thing as "calculating" a material property. It is a measured property (test data).

Brian

do you want an equation for tangent modulus with respect to stress (or strain) ? or a single value ?

if you're doing crash analysis i guess you're trying to capture plasticity effects. a cheap and dirty answer would be (ult. stress- yield stress)/(ult strain-yield strain)

The tangent Modulus is just that - the tangent of the stress-strain curve at any particular point. If you have a stress-strain curve, then you can calculate the tangent modulus either symbolically, if you have a formula (derivatives, calculus-type stuff), or numerically (delta stress / delta strain).

Don't over-think this. Draw the stress-strain curve out. draw your tangent modulus lines. Should be easy...