On Induced Properties and Self Heating during Free Blowing of PET Preform

The great influence of temperature on polymer's behavior is well known and a 10 degrees C increase can lead to a 10-time reduction of the viscosity near the glass transition temperature. To manage accurate simulation of thermoforming processes, and particularly the stretch blow molding process that is managed in the vicinity of T-g, it is necessary to take into account the self heating phenomena that may have impact on induced properties. In the particular case of polyethylene terephthalate (PET), injected preforms have been blown with different initial temperature and followed using a thermal camera. For an identical final volume of the blown preform, the influence of initial temperature on self-heating is discussed. Back to room temperature, induced mechanical properties are measured using digital image correlation: bottles are blown under different pressures and the strain fields are measured. Using the virtual field method on a region of interest of the bottle, these results allow the identification of the induced mechanical properties. Comparison between the self-heating and the induced modulus is managed and the effect of the self heating on the free blown shapes and induced properties is discussed.