Processing‐induced properties in glassy polymers: Application of structural relaxation to yield stress development

A method is presented to predict the yield stress distribution throughout an injection‐molded product of an amorphous polymer as it results from processing conditions. The method employs the concept of structural relaxation combined with a fictive temperature, following the Tool–Narayanaswamy–Moynihan formalism. The thermal history, as it is experienced by the material during processing, is obtained by means of numerical simulation of the injection molding process. The resulting predictions of yield stress distributions are shown to be in excellent agreement with experimental findings, both for different mold temperatures and for different part thicknesses.