Tangent modulus

In solid mechanics, the tangent modulus is the slope of the stress-strain curve at any specified stress or strain. Below the proportional limit the tangent modulus is equivalent to Young's modulus. Above the proportional limit the tangent modulus varies with strain and is most accurately found from test data. The Ramberg-Osgood equation relates Young's modulus to the tangent modulus and is another method for obtaining the tangent modulus.