I am currently modeling uterus cervix and amniotic sac in FEBio and I have this problem with enforcing sticky contact. I'm applying force as the pressure inside the amniotic sac, there's a sticky contact between amniotic sac and the uterus. The problem is that amniotic sac won't stick to the uterus, it expands and passes right through it. what can I do about it?
How can I enforce a sticky contact in FEBio?
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Hi,
The most common cause for contact surfaces passing through each other is a penalty value that is too low. Try increasing the penalty property in your contact definition and see if that helps. You may also want to turn augmentation on, laugon = 1. Please give that a try and let us know what you find.
Cheers,
SteveDepartment of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
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thanks for your prompt reply, I've put penalty value on 100 and also enabled augmentation, now I get negative Jacobins and amniotic sac still penetrates the uterus. My material and boundary conditions are same as the article "A Parameterized Ultrasound-Based Finite Element Analysis of the Mechanical Environment of Pregnancy" but my geometry is gained from MRI.
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Hi,
Can you send the model? I assume it's too big to upload here, so you may email it to me at steve dot maas at Utah dot edu. Or you can use drop box service of course if that's more convenient.
Cheers,
SteveDepartment of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
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Hi,
I've received the model and I would like to suggest a few changes:
1. Replace the isotropic-elastic with neo-Hookean, since the latter has proven to be more stable than the former.
2. Replace the "tied" contact, with "tied-facet-on-facet", which also often results in better behavior. You can also try "tied-elastic", but you'll have to set the symmetric_stiffness flag to 0 in the Control section.
3. But I think the biggest problem is the "continuous fiber distribution" materials. You are using these materials as stand-alone, but these materials only contribute in tension, and most of your loading is compressive. I suggest that you insert these fiber distributions in a solid mixture material. See for example, section 4.2.1 of the FEBio User's manual.
I hope these suggestions prove helpful. If not, let us know.
Cheers,
SteveDepartment of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
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Originally posted by maas View PostHi,
I've received the model and I would like to suggest a few changes:
1. Replace the isotropic-elastic with neo-Hookean, since the latter has proven to be more stable than the former.
2. Replace the "tied" contact, with "tied-facet-on-facet", which also often results in better behavior. You can also try "tied-elastic", but you'll have to set the symmetric_stiffness flag to 0 in the Control section.
3. But I think the biggest problem is the "continuous fiber distribution" materials. You are using these materials as stand-alone, but these materials only contribute in tension, and most of your loading is compressive. I suggest that you insert these fiber distributions in a solid mixture material. See for example, section 4.2.1 of the FEBio User's manual.
I hope these suggestions prove helpful. If not, let us know.
Cheers,
Steve
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