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How to use stress relaxation curve data in modeling viscoelastic material in Ansys v.

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  • How to use stress relaxation curve data in modeling viscoelastic material in Ansys v.

    Hi every one

    I have the tensile test stress -relaxation data from literature and the function of curve fitting on them .
    But I dont know how to use them in modeling viscoleastic material
    in Ansys v.10
    beacause the predefined viscoelastic models in Ansys needs the shear and Bulk module vs time or shift function ,volumetric response coefficients .

    Thanks a lot

  • #2
    I don't know what material you are working with, but the assumption that most people make is that the material is almost incompressible and hence the shear relaxation modulus can be approximated from the uniaxial relaxation modulus divided by 3.

    -Jorgen
    Jorgen Bergstrom, Ph.D. PolymerFEM Administrator

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    • #3
      thanks for your advise
      so how can I use the stress relaxation data to obtain bulk module or shear
      module vs time?
      would you mind help me more
      thanks

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      • #4
        I don't know what polymer that you are working with, but you can probably assume that the bulk modulus is 50 times the Young's modulus, and that the shear modulus is equal to the Young's modulus divided by 3.

        -Jorgen
        Jorgen Bergstrom, Ph.D. PolymerFEM Administrator

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        • #5
          Ansys

          hi
          once you used the curve fitting technique in ANSYS for different model with experimental data, one of the model will closely matches with experimental data, that material model can be used for further analysis.
          Regards-
          Nandish R.V
          Sr. Lecturer
          Dept. of Mechanical Engineering,
          The Oxford College of Engineering,
          Bengaluru - 068

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          • #6
            For using the fitting data option in Ansys I need to have the shear module and
            bulk module data vs. time

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            • #7
              curve fitting

              no. only strain vs. stress data (experimental data) is required for curve fitting. later for further analysis you may need youngs' modulus and poisons ratio.
              Regards-
              Nandish R.V
              Sr. Lecturer
              Dept. of Mechanical Engineering,
              The Oxford College of Engineering,
              Bengaluru - 068

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              • #8
                Viscoelastic Ansys

                Hi nandish.rv

                So wat is the procedure for converting the stress strain curve into bulk modulus VS TIME or shear modulus Vs TIME. so that we can input using the curve fitting tab in ANSYS.

                Plz can you explain the procedure clearly.

                Thanks

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                • #9
                  stress relaxation

                  dear all,

                  I am new user to this family and ABAQUS as well. I tried to model my viscoelastic materials during the uniaxial compression. The stress relaxation data was used to get prony parameters in ABAQUS.

                  To check if the model is ok, I ran a stress relaxation simulation. However, no stress decay at all ! The shape of force vs. time (displacement) during loading looks reasonable. BUT I really do not understand why the force did not decay during holding in my simulation. I checked the time scale, they are correct.

                  It is greatly appreciated if you could please gvie me some advice.

                  Great thanks,

                  Vicky

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                  • #10
                    shear modulus and bulk modulus versus Young's modulus

                    . . . what jorgen said concerning shear and bulk modulus in relation to Young’s modulus is right. But in case of rubbery materials there may be an additional complication, because for very small time intervalls (. . . at the beginning of the relaxation proccess) the material may be in the glassy state and therefore exhibit a smaller Poisson Ratio (smaller that 0.5). How this can be incorporated is for example shown in the attached report.

                    regards
                    Manfred
                    Last edited by manfred; 2009-10-14, 13:18.

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                    • #11
                      I need to model viscoelastic behavior of polymer. I have storage modulus and loss modulus data in tensile mode as a function of temperature. I have found, to determine the Prony series coefficients using Ansys I need shear and bulk modulus as a function of time-temperature. I can calculate shear and bulk modulus from tensile modulus using poisson ratio. But does it mean complex modulus which can be calculated from storage and loss modulus. I have seen the document posted by Dr. Jorgen to calculate Prony series from storage modulus and loss modulus data writing a code. But I want to use Ansys to calculate the Prony coefficients. Can anyone advise me how I can use my data to calculate Prony series coefficients using Ansys?

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