Modelling the constitutive behaviour of poly(ethylene terephthalate) for the stretch blow moulding process

Understanding and modelling the behaviour of amorphous PET (aPET) is critical for design the optimum product and process.<br><br>However due to its nonlinear viscoelastic behaviour, the behaviour of aPET is highly sensitive to its thermomechanical history making the task of modelling its constitutive behaviour very complex.

This means that the constitutive model will be useful only if it is known to be valid under the actual conditions of the SBM process of interest. The aim of this work was to develop a material model capable of capturing the deformation behaviour of aPET subject to an arbitrary strain history, and to develop a new material characterization method providing new data for the deformation behaviour of aPET relevant to the SBM process.<br><br>In order to achieve this goal, a reliable, robust and non-touch characterization method was developed based on the data acquisition system and digital image correlation system to determine the stress-strain relationship of material in deforming preforms during free stretch-blow tests.<br><br>Considerable experimental work, including conventional biaxial stretching tests and free stretch-blow tests, was carried out to characterize the mechanical properties of the material.