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Best way to include complex temperature dependence with the TNM

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  • Best way to include complex temperature dependence with the TNM

    I am new to polyumod, but I am attempting a pretty tough analysis of PTFE. I modeling a part that is highly deformed when 250F and under pressure, but is then later cooled significantly and further loaded. Mechanically I can get a very good fit to tension and compression data at various rates from ambient to the hot temperature with the TNM. I have also fit a PNM. There is a significant difference between tensile and compression yield in this range of temperature. However, the model does very poorly for cooler temperatures. Steeper stiffness and yield temperature dependence is required, a significantly smaller limiting chain stretch is needed, and the the difference between tensile and compression yield greatly decreases with decreasing temperature below ambient. The stress exponents could also potentially need to change. The cte is also quite complex, and is not well approximated by the constant value that can be used with the TNM. My current idea is to have theta0, n, lambaL,a, alpha, and potentially ma, mb, and beta have a changing temperature dependence below ambient temperature, as cryogenic temperatures are approached.

    I am using polyumod with ANSYS. Can polyumod work with the tbtemp definition in ansys to define the tnm or pnm parameters as functions of temperature, or must the material model number 99 in polyumod be used? Also, if either of these options is used, will the theta0 and the n parameters still be used to adjust the stiffness and flow resistance in the TNM?

    I would greatly appreciate any assistance.