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Pre-Tension in Foam and Spring elements

Hi,

I have the following questions running over my mind. I would appreciate if any one can brief out their knowledge

1. My model has a foam over which there is a firm seat cover. Since the foam is in compression because the seat cover holds it tight, I would like to define a post-tension to the foam. I used - /MAT/LAW70 for this, and I could not find this in ver 12. Can anyone suggest will I be able to do this?

2. A more similar question related to Pre-tension, but this time it is for a spring element. I use PROP/TYPE13 for these elements so that I could give rupture criteria. I have seen pre tension option in TYPE/32, but unfortunately I can't use this type. Can anyone help me out is there a way to define with existing type?

3. Might be funny, but sorry. I have been running simulation since a couple of months and all seem well till today. Strangely the runs I did today have generated a couple of .rst files, though I used the same engine file I did for previous runs. Is it a sign of any modeling error?

I have defined the same interval for all of my runs

/RFILE
200000 0 0

I appreciate for any of your suggestions. Thanks in advance

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Altair Forum User

Hi Ushay,

1. You can try with /REFSTA, which will describe the reference state for elements belonging to a part, using given nodal coordinates. The nodal coordinates has to created in a txt file which has to be included in the new model file thereby providing the reference state of elements.

2. You can apply pre tesnion in Type 13 spring. Create a function accordingly and assign the same, that is you can load it from time 0 so that the spring will be under pre tension. I'm attaching a sample model file for your reference, In the functions please check the curve defined.

3. Please recheck if you have mentioned number of restart files to be written. That is, if the keyword is /RFILE/2.

Also check the total number of cycles in the engine out file.

Unable to find an attachment - read this blog

Ushay

Hi George, thank you very much for making a cleared explanation and the model was very helpful. Concerns related to points 2 and 3 are resolved, thanks for that. I still have a question with point 1. Do I need to create a reference geometry which is similar to the actual geometry? should I define the reference state with a geometry in undeformed state? I have seen the document of creation of reference state for airbag folding, I have understood the concept, but could you please give reference to any examples or documents which guide how to do it.

Altair Forum User

Hi,

Yes, you need a geometry in an undeformed state. May be a slightly scaled foam model and these nodal coordinates has to be used in the /REFSTA file.

Unfortunately no tutorials or examples or documents are available with me. I'll just search internally for some documents and if I get some useful documents I'll share the same with you very soon.

Ushay

Okay George. Thank you