What stress-strain definition should be used in Plastic material csv file.

Engineering stress or true stress?

Engineering strain or true strain or true plastic strain?

# Plastic material stress-strain definition

**Thorbjorn**#1

**jousefm**#2

Hi @Thorbjorn and thanks for your question!

I would say true stresses (cauchy-stresses) because the FEM also describes the real geometry which is the current cross-section.

\sigma_{true} = \sigma_{eng}*(1+ \epsilon_{eng})

\epsilon_{true} = ln (1+ \epsilon_{eng})

Maybe my colleagues @ahmedhussain18 & @rszoeke as well as the @PowerUsers_FEA can give you some additional information or correct me if I am mistaken here.

All the best!

Jousef

**rszoeke**#3

Hi @Thorbjorn @jousefm, sorre for the late replay.

Jousef is right, the stress-strain data has to be given in “true” stresses and strains.

Also not that the first point in the curve should not be (0, 0), but the yield point (\epsilon_{yield}, \sigma_{yield}) and that the Young’s Modulus should be consistent with that:

E = \sigma_{yield} / \epsilon_{yield}

Best,

Richard