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"Hyper-elastic material may become unstable" message for Mooney-Rivlin model

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  • "Hyper-elastic material may become unstable" message for Mooney-Rivlin model

    Hi All,

    I am trying to use my experimental data for vulcanized natural rubber for some finite element simulation in ANSYS, and noticed that the closest fit is given by Mooney-Rivlin. But unfortunately, this material model gives the warning mentioned in the subject prior to solving, and the process terminates with "error in element formulation".

    Other material models like Neo-Hookean and Ogden don't seem to be providing a good fit with the experimental stress-strain curve, but there's no such warning or element formulation error for those.

    I'm simply using a rectangular area with Plane Stress w/Thk element real constant specified, plus the aforementioned curve fitting of my experimental curve.

    Please advise.


  • #2
    Can you show figures with the experimental stress-strain curve(s) that you have?

    Jorgen Bergstrom, Ph.D. PolymerFEM Administrator


    • #3
      Hi Jorgen,

      I was able to curve-fit by unchecking the "Use Normalized Error" checkbox in the curve-ftting dialog in ANSYS. I'm not exactly sure what purpose it serves, but the fits are good now.

      Currently I don't have access to the images. I will share as soon as availble.

      Many thanks!