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contact between an irregular cylinder and 2 plates PLEASE!!!

contact between an irregular cylinder and 2 plates PLEASE!!!

contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
Dear all,

I'm trying to model contact in the following case:
an irregular cylinder, 2 parallel plates, one on top and one below the cylinder; the one below has 0 displacements prescribed and the one on top is subject to a traction force; the edge of the cylinder is encastred (to the wall perpendicular to the plates).

Following suggestions in this forum I have "nudged" the plates to the highest and lowest nodes in the cylinder respectively.


The crazy thing is CSTATUS shows all the nodes in the surface of the cylinder are closed, CPRESS is 0 everywhere and COPEN shows very small values in the bottom and 10 orders or magnitude higher in the top of the cylinder surf. Besides the dat file does not say there are 3 or 2 unconnected regions.


A bit more about the model:

I've set two surface-to-surface contact interactions, one between the surface of the cylinder and the top plate and the other with the bottom plate.
For some reason i can use clearance=0 and adjustment to the top interaction while, if i use clearance=0 and adjustment to the bottom interaction, in the analysis all the nodes try to move to the top plate and I get 0 volumes.


Im not an Abaqus expert (you know that already, right?) but it seems all the nodes are trying to contact/move towards the bottom plate.

When i made the preliminary tests the model worked even to 70% of the displacement and now i cant make it work any more, not even one increment and IM DESPERATE!

Any ideas on how to fix this and make Abaqus set contact of nodes on the top with the top plate and the ones in the bottom to the top plate? Please, please, please?


Thank you so much in advance,

Carolina

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

Please attach the model.
 

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
Do you mean a screen capture of the CAE or the .inp fule?
Thanks!

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

The model .cae file.

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
hi Mechfeeney,
I guess the file is too big for ENGINEERING.com coz i get an error message.
i could put it in dropbox but id need an email address...
Let me know what youd prefer!
Carolina

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

I think that's against site policy. Is there a personal message option on this site?

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
im trying to find an alternative!

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

just take a wild guess..... at gmail.com

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
Sorry, rstupplebeen, ive just seen your message.

There are orphan meshes in my model that come from previous analysis. And I cannot upload even split zip files of the .inp here.
I see youre in the Yahoo group. I can send it to you there if thats ok with you. Please let me know.

Thank you!

 

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

Sure you can post it there.  Please be sure to provides links between the forums.  Alternatively you could place your file in filehippo, dropbox...

Rob Stupplebeen
https://sites.google.com/site/robertkstupplebeen/

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
hi rstupplebeen!

here it is:
http://www.mediafire.com/?o6u16jw6og0nt11

Its massive but as i said these are orphan meshes and i did not want to delete any part.

Thank you so much for your help!
Carolina

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

Here is a running list:
1. Try using 2 analytical surfaces as the compression plates.
2. My guess is that you want to use a hyperelastic material model i have used this link in the past assuming you do not have material test data
http://polymerfem.com/faq.php?faq=polymerfem_faq
3. Try using a displacement on the top plate instead of surface traction
I hope this helps.
 

Rob Stupplebeen
https://sites.google.com/site/robertkstupplebeen/

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

Hi Carolina,
Sorry it has taken so long to get back to you (things have been really busy at work). Upon investigation of your model, I have arrived to similar conclusions as Rob.
1. The 3d scan imported cylinder is not refined enough. It contains several abrupt edges (almost like discontinuities; and the elements come to very sharp inverted spikes). The geometry is thus incredibly complex, but moreover, not realistic. Geometry like you have in the 3D scan is nearly impossible to work with, too many sharp edges and areas that resemble discontinuities.
2. For the purpose of your work, a better solution would be to drastically simplify the cylinder and work out a good material model.
3. Analyzing it with linearly elastic material is indeed a good starting point, but will not yield realistic results (for your application).
4. I noticed that you had several suppressed features here and there throughout the model and redundant material / section definitions. It is really important to keep a model clear, concise, and as simple as possible. Clutter makes things confusing. (This is just advice for the future : ] and I mean no disrespect).

For a first cut analysis, I would model a linearly elastic cylinder between a fixed plate and a plate that has a displacement (not a force). The cylinder should initially be very close, almost tangent to the plates. Do not apply a fixed boundary condition to the backside of the cylinder, as this would add unrealistic stresses and moments. Instead allow the cylinder freedom to move along the same axis of the displacement. Once you have the basic contact model setup and working, you can start to introduce the complexities like a hyperE material config. You can then start modifying the geometry of the cylinder to be a bit more realistic. It is highly impractical and inaccurate to try and model the 3d scan you have. As I said, the geometry is too complex and the scan is not smooth enough. One of the key FEA principles is to simplify as much as possible while maintaining accuracy. Your situation is that you have something so complicated that even if you get a working model, the results will not be trustworthy. For my own interest I will be working on an approach I think best suited for this problem. Good luck in the mean time.

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
Dear rstupplebeen and mechfeeney,
Thank you for taking the time.
Ive considered smoothing but i dont have access to cad software that is compatible with Abaqus right here right now.
"Clutter" is mainly related to things i still have to add to the model. And, of course, i already have the hyperelastic version, but if i cant deal with elastic...

I will try using 2 analytical surfaces as the compression plates and displacements instead of tractions.

Thank you again,
Carolina

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

Any CAD software should be able to create this geometry.  Then simply save as a SAT, STEP, IGS in that order of preference.

You can also create a simplified shape with Abaqus's sketcher.  I made some measurements on your mesh and believe that a revolved ellipse with a height of 0.120mm and a diameter at the base of 0.135mm would be a good approximation.


I hope this helps.

Rob Stupplebeen
https://sites.google.com/site/robertkstupplebeen/

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

Nice Rob. That's a great starter model. Very kind of you.

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

(OP)
Dear friends,
This is very kind of you, but i need to model real breasts.
I need to find the way with the real thing.
Cheers,
Carolina

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

I would break the problem into 2 parts.
1. figure out how to get a similar representative model to solve efficiently.  Modeling 1 quarter of 1 cylinder will greatly increase turnover time.
2. figure out how to get a nicer mesh from your scan data.
Once you have both of these solved apply the methods from 1 on 2.
I hope this helps.

Rob Stupplebeen
https://sites.google.com/site/robertkstupplebeen/

RE: contact between an irregular cylinder and 2 plates PLEASE!!!

If you are trying to simulate the real thing, Rob's model is probably more accurate than your scan.  

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