Yield stress distribution in injection-moulded glassy polymers

A methodology for structural analysis simulations is presented that incorporates the distribution of mechanical propertiesalong the geometrical dimensions of injection-moulded amorphous polymer products. It is based on a previously developedmodelling approach, where the thermomechanical history experienced during processing was used to determine the yield stressat the end of an injection-moulding cycle. Comparison between experimental data and simulation results showed an excellentquantitative agreement, both for short-term tensile tests as well as long-term creep experiments over a range of strain rates,applied stresses, and testing temperatures. Changes in mould temperature and component wall thickness, which directly affectthe cooling profiles and, hence, the mechanical properties, were well captured by the methodology presented. Furthermore, itturns out that the distribution of the yield stress along a tensile bar is one of the triggers for the onset of the (strong) localizationgenerally observed in experiments.