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

  1. #1

    "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.

    Farhan

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

    -Jorgen
    Jorgen Bergstrom, Ph.D.
    PolymerFEM Administrator

  3. #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!

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