# Bilinear Model

Hi,

I am modeling a nonlinear material using bilinear.

It is a plastic material where stress is dropping after yield point and modulus given in the specification is secant modulus NOT tangent modulus (initial best straight line).

I wanted to know for the ANSYS bilinear input below:

Modulus: Should I use tangent modulus or secant modulus (usually use this for linear properties)

Yield Strength: Should I use the stress point at the end of best straight line or yield point (usually use it for linear properties)

Tangent modulus: Should the tangent modulus be calculated based on engineering stress/strain or true stress/strain?

## Answers

It would help if you paste an image of the curve you have available into a reply so we can see what you are looking at.

The Modulus ANSYS needs is the initial steep slope of the curve that goes from zero to the point where the slope changes.

The Tangent Modulus is the shallow slope of the curve after the change. The slope should be true stress/strain.