Stres 1

[Staszkinson]

Hello,
According to Abaqus, it is well-known that he needs true stress - true strain input data in the material module.
In this case user have to convert engineering values for true stress - true strain values manually.

What type of data should I use in Ansys Workbench - engineering stress-strain or true stress-strain? I want to define steel with bilinear isotropic hardening.
I can set only yield strength and tangent modulus. As can I see bilinear isotropic hardening is calculated according to young modulus from "isotropic elasticity" module.

Thank You.

 

[rickfischer51]

Ideally you need true stress/true strain, but if your strains are small, typically below 5%, there is little difference. The correction is e(true) = ln (1 + e(eng) and sigma(true)= sigma(eng) * (1 = e(eng)). Note this is accurate only below the onset of necking.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[Staszkinson]

Hello, Sorry for incorrect topic of this thread.

I agree with you. Let's talk about technical problems in Ansys WB.

Correct me if I'm wrong. In WB I can define isotopic hardening in two ways:
1/ by "Bilinear Isotropic Hardening" option. In this case I use tangent modulus instead of strain values. Tanget modulus can be 0 (no strain hardening - first plastic stresses in model as failure criteria) or tangent modulus is not equal to 0, but it should represent part of true stress - true strain curve after yield strength point.

2/ by "Multilinear Isotropic Hardening". In this case I simply use true stress - true strain values like:
true plastic strain / true stress
0.0 / 275e06
0.12 / 300e6

 

[rickfischer51]

Correction:
sigma(true)= sigma(eng) * (1 - e(eng))

You are not wrong. With MISO, make sure all your slopes are positive. Also, it sticks in my mind that the slopes may not increase in value. Each slope must be less than the previous slope. Not sure if this is true or not, but I think I remember a posting on another bulletin board. Increasing slopes occurs with elastomers and some thermoplastics. If you are working with metals, it shouldn't be a problem.


Rick Fischer
Principal Engineer
Argonne National Laboratory