Stress-strain curve API 579 FFS-Level III

[usecheijk]

Hi everyone!

I have doubt about Tangent Modulus (Etan) calculation for FEM elasto-plastic anaysis using equation F.22 (Annex F, MPC model) in API 579. In the Bilinear elasto-plastic with isotropic hardening model a constant Etan is needed, but Etan calculation from F-22 depends on the level of strain (it is not constant), which value must be taked?

Thanks!

Jack

 

[TGS4]

What is the purpose of using a bilinear material? In F.2.3.1 you are provided with a continuous curve, which can be approximated with a multi-linear curve. The only bilinear curve permitted in Annex B is the elastic-perfectly-plastic curve, where the tangent modulus is identically zero.

The tangent modulus calculation in equation F.22 is just calculating the first derivative of the stress-strain curve.

 

[usecheijk]

You are right TGS4. I will use a multilinear plasticity model instead of bi-linear one.

Thanks a lot!

Jack