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model of material for high strains: Engineering or True ? SOL 601/106

Hello all,

 

I just were asked about one important thing when performing non linear analysis for 'hihg' strains in SOL 601/106. The question is related to the material model of the steels and aluminium alloys.

 

When the strain of the material is in the plastic region but still strain is recognized as 'not so high' we can use an engineering model of the stress-strain curve, but for larger strains there is a significant difference between thosce curves and now my question is which model we shall use for such analysis?

My first thought is that true stress-strain curve shall be used, because the geometry of the elements is constantly changed throuh the steps in advanced non linear solutions. Am I right ?

I mainly work with steels and aluminium so I usually define the ISOTROPIC material, but is there any entry that specifies which stress-strain curve are we defining ?

 

 

Additionally is there any option in NX Nastran that allows conversion of the material input data form one model to another ?

 

300px-Stress_v_strain_A36_2.svg.png

 

Thanks for help Smiley Happy

4 REPLIES

Re: model of material for high strains: Engineering or True ? SOL 601/106

@TomekZeWschodu,

 

See section 3.1.1 of the Advanced Nonlinear Theory and Modeling Guide for stress/strain input requirements. In general, SOL 601 requires multilinear plastic stress-strain data to be input as true stress-true strain.

 

The CVSSVAL parameter on NXSTRAT can be used to convert engineering stress-strain data to true stress-strain.

Betreff: model of material for high strains: Engineering or True ? SOL 601/106

Hello TomekZeWschodu,

 

I've got the impression that you deal also with non linear problems and I have problems with nonlinear material and solution 601, too. Therefore I'm interested in your range of non linear stress/strains occuring in your simulations. My questions:

- What are the strain values which you reached in maximum, 20 % or even more 30 %?

- Do you think this is case sensitve (tension, compression, bending or torsion)?

- Can you see any differences in solution results for ATS or TLA-S or the others in your cases?

I'm still not sure if and where the calculation limits exists - may be in deforming elements until having a negative jacobian determiant at the integration points.

 

Do you have more experiences here and would you be so kind to share it with me?

Best wishes, Michael

Betreff: model of material for high strains: Engineering or True ? SOL 601/106

For fist, thanks @JimB for an answer Smiley Happy

 

Dear Michael, I do not have very big experience with non-linear solutions and especially with solutions with large strains. Sometimes at work we do the non-linear solutions but with use of SOL106. Few months ago I started my 'adventure' with this type of simulations and in the free time I try to perform some excersises, however it hard to find spare time to do so due to high work load.

 

With reference to your questions, I would rather do not try to answer for them. First I need to digg deeper into the subject. It's like the: "the more you know about the subject, the more you realize that you know not so much". I would suggest to perform some comparison solutions and try to find out the answers based on your private investigation Smiley Happy At least, that's the way I follow apart of reading about the subject.

 

Thanks again Smiley Happy

 

Betreff: model of material for high strains: Engineering or True ? SOL 601/106

Hello Tomek, thank you for your honesty. Then I have to fight for myself furthermore. Michael