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Hexa mesh inflates itself after deformation

Good evening!

I'm trying to fix an issue that occurs simulation the deformation of a "deformation tube".

After the deformation process is already complete, the deformed structure starts to "inflate", resulting in a giant energy error. Any ideas where this Problem could originate from?

It's Hex-Mesh and I already tried using a finer mesh as well as different Isolid: 14 (HA8), 18, 24 in PROP/SOLID.

unfortunately I can't share the model and didn't find the time to reproduce this issue in another dummy project so I hope this issue sounds familiar to someone.

I'm thankful for all suggestions!

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English

Radioss

v2022

Accepted answers

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PaulAltair

Not something I've seen, what material law? 36? Are your stress/strain curves ok (monotonically increasing)? How is self contact defined? Any clue in timestep?

Simon_21768

Not something I've seen, what material law? 36? Are your stress/strain curves ok (monotonically increasing)? How is self contact defined? Any clue in timestep?

Thank you for the quick response!

I'm using MAT/LAW2_PLAS_JOHNS and as far as I know the stress/strain - courves should be fine. Is there a way to check?

The time step doesn't change dramatically, it only fluctuates by less than 1%.

What might be of interest as well: I receive plenty of these messages right before I get the aforementioned energy error:

MESSAGE ID : 260

** WARNING ZERO OR NEGATIVE SUB-VOLUME: 3D-ELEMENT ID: 690582

ELEMENT IS SWITCHED TO SMALL STRAIN OPTION

Would it be an option if I send you the file anyhow? I can't upload it here publicly...

PaulAltair

Thank you for the quick response!

I'm using MAT/LAW2_PLAS_JOHNS and as far as I know the stress/strain - courves should be fine. Is there a way to check?

The time step doesn't change dramatically, it only fluctuates by less than 1%.

What might be of interest as well: I receive plenty of these messages right before I get the aforementioned energy error:

MESSAGE ID : 260

** WARNING ZERO OR NEGATIVE SUB-VOLUME: 3D-ELEMENT ID: 690582

ELEMENT IS SWITCHED TO SMALL STRAIN OPTION

Would it be an option if I send you the file anyhow? I can't upload it here publicly...

Yeah, really need to take a look, LAW2 should be fine, If you are a commercial customer and you need formal support, (it is included in your license agreement), you can contact Altair technical support and get it to me that way, mention me in the email and it will make its way back to me if they can't resolve it themselves.

your local office should have a direct support email alias:

listed here: Altair Technical Support