How can I enforce a sticky contact in FEBio?

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  • shima
    Junior Member
    • Dec 2016
    • 16

    How can I enforce a sticky contact in FEBio?

    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?
  • maas
    Lead Code Developer
    • Nov 2007
    • 3400

    #2
    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,

    Steve
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

    Comment

    • shima
      Junior Member
      • Dec 2016
      • 16

      #3
      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.

      Comment

      • maas
        Lead Code Developer
        • Nov 2007
        • 3400

        #4
        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,

        Steve
        Department of Bioengineering, University of Utah
        Scientific Computing and Imaging institute, University of Utah

        Comment

        • shima
          Junior Member
          • Dec 2016
          • 16

          #5
          Hi
          I've just sent you the model. Thanks a lot for your time

          Comment

          • maas
            Lead Code Developer
            • Nov 2007
            • 3400

            #6
            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,

            Steve
            Department of Bioengineering, University of Utah
            Scientific Computing and Imaging institute, University of Utah

            Comment

            • shima
              Junior Member
              • Dec 2016
              • 16

              #7
              I did as you said, I also updated my FEBio but the problem still persists. It either gives an error termination or the amniotic sac passes through the uterus.
              what should I do?

              Comment

              • shima
                Junior Member
                • Dec 2016
                • 16

                #8
                Originally posted by maas View Post
                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,

                Steve
                sorry for the late reply, but I had to check everything to see if they were ok and my FEBio couldn't run my model, it took me a while till I could update it and make it work, I do still have the problem, could you help me plz?

                Comment

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