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Thread: Negative Jacobian Error When Running FEBio2

  1. #1
    Join Date
    Sep 2019
    Posts
    4

    Unhappy Negative Jacobian Error When Running FEBio2

    Hi,

    I am a graduate student and currently working on a class project.
    My professor provided us video tutorials. I followed the steps, and the previous knee model worked perfectly.
    However, she recently gave us a new, similar model with more parts in it.
    Again, I used the exact same material properties, contacts, boundary conditions, steps, curve editor settings etc, but this time I get the Negative Jacobian error.

    Can anyone please help me troubleshoot this?
    Below is the link to the .prv file. Let me know if you can't access the file.

    https://drive.google.com/file/d/1e-M...LGhEFdSJQ/view

  2. #2
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,064

    Default

    Hi,

    I took a quick look at your model and it seems that the negative jacobian is caused by the sliding contact interfaces. This might be caused by the large difference in material parameters between the two contacting parts. FemCart has a Young's modulus of 2e7, but TibCart's value is only 20. Was that your intention?

    I also want to point out that in general we do not recommend using the "isotropic elastic" material, since this material does not produce realistic results for large deformations. Instead, we recommend using the "neo-Hookean" material, which has the same small-strain behavior, but remains valid under large deformations.

    Cheers,

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

  3. #3
    Join Date
    Sep 2019
    Posts
    4

    Default

    Hello,

    Thank you for the reply.
    For your question, yes, they are the values that my professor used, and her model worked.
    Actually, my model works now, too. I just tried re-making the contact between the two cartilages that you mentioned.

    Plus, thank you for your recommendation.

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