Question

Initial tangent modulus, E0, is often reported from tensile stress-strain tests. If true stress is used rather than engineering stress, will this modulus be bigger, smaller or the same?

Answer 1

The initial tangent modulus will be same for both engineering and true stress strain curves.

In a stress strain curve, below the proportionality limit, both tangent modulus and Young's modulus are equal and same.

Below the proportionality limit, the engineering stress strain curve and true stress strain curve looks perfectly same. Only after the yield point, these two curve varies according to the change in cross section.

Therefore, the initial tangent modulus will be same for both engineering and true stress strain curves.