Constitutive model for HIPS in the thermoforming range

Within their thermoforming range amorphous polymers are deformed while they are in their rubbery state (i.e., above glass transition temperature). In this range their mechanical behavior results of a combination of hyperplasic, viscous and anelastic components. Roughly speaking constitutive model should account for very specific and coupled temperature and strain rate effects and for the combination of some anelastic strain and heperelasticity. Based on experimental data obtained in monotonic and non monotonic tension over a wide range of strain rates and temperatures a revisited network model is presented that allow modeling strain rate and temperature dependence and loading unloading loops. This “visco hyperlestic” models allows 3D modeling a thermodynamical frame and should allow easier numerical modeling though some physical aspects should be assessed now. Paper also stress on the necessary quality of experimental measurements.