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9 Parameter Mooney-Rivlin Model

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  • 9 Parameter Mooney-Rivlin Model

    Hello All!

    I'm trying to use MCalibration to fit the 9 parameter mooney rivlin model for my data (attached). However, the algorithm doesn't converge well and I need it to match especially at that starting part where strain is below 0.3. Can somebody please get me the calibrated constants for Mooney Rivlin 9 parameters?
    I tried ANSYS but those values are seriously different and larger than Mcal values and did not give good results in LS Dyna.
    Please help

    Data
    https://drive.google.com/file/d/1Les...ew?usp=sharing


  • #2
    Hi dakshita92,

    I've performed an optimization on your data with particular attention on the first part of your curve ...

    Regards, Bernhard
    Attached Files

    Comment


    • #3
      Originally posted by Bernhard Kager View Post
      Hi dakshita92,

      I've performed an optimization on your data with particular attention on the first part of your curve ...

      Regards, Bernhard
      Dear Dr. Kager!

      Many thanks for your response and your time.

      I have a few questions though. I just plugged in the values you sent me to this MCalibration software by Dr. Bergstrom. The match was as attached below. And I plotted the data points against the experimental F-t curve of a tensile test using this model, and the result is also attached.

      If you don't mind me asking, can you please tell me how you managed to find these coefficients? Did you write your own program for this?

      Many thanks in advance.

      Dakshitha

      Comment


      • #4
        Hi Dakshitha,

        I've messed up strain measures in my previous optimization ... I assumed your data to be of engineering stress/strain type.

        So I tried with true stress and strain once again but unfortunately I couldn't get better results than the ones you provided in your initial post.
        Good news: I've found a material model that could capture your uniaxial data quite well - a quite new model proposed by Oskar Lopez-Pamies.

        Find attached the results of the optimization ... this time with true stress/strain ;-)

        Bad news: You have to implement the new model to your code - have you done that before?
        If you need any help in programming a user routine for that material model let me know ...

        Regards, Bernhard
        Attached Files

        Comment


        • #5
          Dear Dr. Kager,

          Many thanks for your time on this matter. I really appreciate it.

          Thank you for introducing me to a new constitutive model. It looks easy to programme than Mooney Rivin even. However, the problem is I'm continuing some previous research work before my time (I'm a first year PhD student) by my research group.
          https://www.sciencedirect.com/scienc...61306913006444
          It is based on the above publication.

          Therefore, my options are petty much confined. That is the problem, sir. The paper deals with coefficients obtained from ANSYS. You will notice that some coefficients are extremely high (55 GPa, -28 GPa etc). And as soon as I input these coefficients to my LS Dyna code, elements go unstable and into negative volumes. In that case, MCalibration values run the simulation very smoothly, however, the material behaviour at the beginning of the test is not well-captured. This is my problem.

          However, there is also another strand of research I'm trying to pursue, on modelling the behaviour of shear thickening fluids at high strain rates. In fact, I have an idea to propose a modified constitutive model for this. We could discuss more if you have some time for me. Please do let me know. My email is dakshitha.weerasinghe@sydney.edu.au

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