Modeling Thermo-viscoelastic Mechanical Behavior of Amorphous Polymers

What are the considerations for modeling thermo-viscoelastic mechanical behavior of amorphous polymers?

Amorphous polymers are known to behave hard and brittle below the glass transition temperature, and this behavior changes to compliant and rubbery beyond the glass transition temperature. Due to this, it is generally recommended to use the thermo-viscoelasitc models in temperature ranges that do not include the glass transition temperature. However, there is no mathematical limitations in the WLF or the TN shift functions.

A better way to go about this is to obtain the data and develop the viscoelastic master curve, then plot the shift function over the range of interest and see if you can fit the WLF or TN function to the experimental shift function. If you can't fit the shift function with a built-in model, a user shift function or user material will be required.