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Stress Strain Curve

Altair Forum User

hello,

I want to make the stress strain curve going down after reach the ultimate.

But if I add descending value for stress it say

TABLES1 bulk data ID=8 has a segment that corresponds to zero or negative hardening. This may lead to poor convergence and excessive plastic flow.

Any body know how to decrease it without getting error?

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Benjamin Joemann_20337

Hello,

My guess would be that it shows this message because the stres/strain curve in a TABLES1 entry is only for describing the plasticity of a material, not its failure model. I know from solvers like RADIOSS that the ultimate stress (or other failure criterias) are defined seperately there.

Maybe this is a starting point:

Best regards,

Benjamin

Altair Forum User

hello Mr Joemann,

It means I cant do it in optistruct?

Benjamin Joemann_20337

To be honest, I don't know. I haven't worked woth MATF cards yet, so I dont know how they behave.

You could set up a quick model of, for example, a beam under a over critical bending load and check what happens when using the MATF card. Maybe post your findings here to let others know who wonder as well.

Other than that, the stress simulation departement in the company I write my thesis in advised me to use RADIOSS for any non-linear analysis I have.

Adriano_Koga

For failure where you need stiffness to decrease, only Radioss or use some usermaterial law in OS, such as with multiscale designer coupling.

With regular elasto plastic material in OS, only perfect plasticity limit is possible so far.