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Temperature and shore hardness dependence of BB model parameters

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  • Temperature and shore hardness dependence of BB model parameters

    Hi all,

    I have calibrated the Ansys implementation of the Bergstroem Boyce model by use of MCalibration. It is an polyurethane elastomer used at strains between -40%/+40% at strain rates between 0.1-10%/s. I used uniaxial tension, compression and shear tests (stress-relaxation) for calibration and ball indentation tests for verification. All works fine. A great model.

    Now I would like to establish separate models for different temperatures and different shore hardnesses of the same material just by adjusting certain parameters of the BB model. I will perform the above mentioned tests. I am not sure whether the compression or shear test is better to determine the temperature/hardness influence?

    Jorgen, in a post, you recommended to make the hyperelastic shear modulus and the flow resistance tau_base linearly temperature dependent. Can you recommend the same for the shore hardness?

    A general question: Jorgen, how do you cope with shore hardness variation of the test specimen? In my experiments the influence of shore hardness variation was greater than different strain rates.

    Thanks!

  • #2
    Hi all, hi Jorgen,

    do you have any recommendation for my above problem?

    An additional question: If I have uniaxial compression, tension and shear tests, not all test data can be fitted to an optimum by the BB model. So I am going to weight the test data dependent on my application. For example if I know that my application implies a lot of shearing, I would weight the shear test data more.

    But in general how do I know which test data to weight more in the material model fitting? Should I use weighting factors dependent on the application OR should I use weighting factors dependent on the estimated error in the different material test data?

    Thanks for any ideas

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    • #3
      I recommend using weight factors based on the estimated error in the experimental tests, and if necessary also consider weight factors based on your application.

      In your orig post you mentioned that the Shore hardness may vary in a single specimen, is that right?

      -Jorgen
      Jorgen Bergstrom, Ph.D. PolymerFEM Administrator

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      • #4
        Thanks for your recommendation, Jorgen. Would you recommend a paper for error estimation of material tests? Do I therefore have to use the continuum mechanics description of the BB model?

        Yes, the shore hardness may vary within a specimen and between different specimen. I try to have a set of specimen of same shore hardness for testing.

        To include weight factors based on my application, I need to know the predominant state of strain. I have long been thinking about how to get such an information. I thought about writing the principal strains and max shear in the Gauss points to a file and building average values for the model, e.g. in 80% of the elements shear strains are dominant. A good approach?

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        • #5
          I don't have a paper that I can recommend for error estimation of test data.
          Your approach to use Gauss points seems fine.

          -Jorgen
          Jorgen Bergstrom, Ph.D. PolymerFEM Administrator

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