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Material Tests best suited for MCalibration

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  • Material Tests best suited for MCalibration

    Hi,

    I am trying to model the behaviour of urethane rubber in Abaqus, with a material model that capture hyperelasticity, viscoelasticity and the Mullin's effect. To do so, I was planning to do these tests: tensile test; stress relaxation test; and compression test; and calibrate the results in MCalibration. However, for the compression test I have read about two different approaches:

    1) Sandpaper between the rubber surface and the test machine platens
    ASTM D575 (Standard Test Methods for Rubber Properties in Compression) says that you should place sheets of sandpaper between the rubber surface and the test machine platens, to resist lateral slippage of the rubber at the contact surfaces.

    2) Use a friction reducer to get a homogenous deformation
    A basic assumption in material testing is the existence of a uniform stress state, where the loading surfaces are usually the principal planes. During compressive loading, however, this condition becomes untenable because a frictional constraint develops at the interface between the material and loading system. A cylindrical geometry, for example, takes on a barrel shape and a nonuniform stress state develops throughout the cylinder so that the observed response may be due to unknown boundary conditions.

    Which of these tests are preferred for material calibration in MCalibration, and why? Do you recommend doing any other material tests?

    Rubber Properties in Compression

  • #2
    MCalibration can analyze the results from both of those tests.

    If you use sand paper then the stress state will not be homogeneous, and you will need to use the "Compression with Friction" load case. If you use a friction reducer then you can use a simple "Experimental Data" load case.

    Your selection of tests seem fine. Most of the time I try to minimize the friction when I do testing.

    Also, I wrote a long section on this topic in my Polymer Mechanics book.

    -Jorgen
    Jorgen Bergstrom, Ph.D. PolymerFEM Administrator

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