Trans-Iso Mooney Rivlin Incorrect Material Input?

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  • orsialex
    Member
    • Sep 2010
    • 45

    Trans-Iso Mooney Rivlin Incorrect Material Input?

    Hello All,

    so I had created ligament structures, and applied trans-iso mooney rivlin properties to them. My initial model was in meters, and when I applied the parameters in Pascals, the simulations did not run. However, when I entered the parameters in Megapascals, they ran just fine. So, I thought all I would need to do is to switch my model to millimeters. So I reconstructed my model in millimeters, brought everything back in to FEBio, and applied the trans-iso mooney rivlin properties to my model using MPa. When I run these simulations now, there seems to be some sort of negative poissons effect. I am applying a simple extension to the ligament structures. As I extend the structures, there is some sort of mid-substance bloating effect rather than hourglassing, which is what one would expect to happen.

    I am thinking that there is some incorrect input that I am applying. Because when I use a iso-elastic material prop as a test, I am seeing the hourglassing. So maybe I am incorrectly applying the material fiber orientation or something like that? not sure

    I have all the files, but I seem to have trouble uploading them. Any help debugging would be greatly appreciated.

    Thanks,

    -Alex
  • maas
    Lead Code Developer
    • Nov 2007
    • 3400

    #2
    Hi Alex,

    In my experience, these negative Poisson's effects are caused by a bulk-modulus that is too low. Try increasing that parameter and see if it has any effect.

    Cheers,

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

    Comment

    • orsialex
      Member
      • Sep 2010
      • 45

      #3
      Thanks for the reply

      thanks for the reply.

      I should have posted that I had already solved this issue. I believe it was both an incorrect bulk modulus (just as you said) as well as an incorrect density.

      thanks again

      -Alex

      Comment

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