Identification of polymer behavior from nonequibiaxial elongation test with temperature and strain rate conditions close to blow molding process

An anisotropic visco-hyperelastic (VHE) model for polyethylene terephthalate (PET) is used to simulate the stretch blow molding process. The biaxiality needs to be taken into account for an accurate identification of the model parameters related to the induced anisotropy. Thanks to the use of a biaxial elongation apparatus developed at MSME, nonequibiaxial tension tests on PET have been managed on optimized specimen in order to provide data complementary to the equibiaxial (EB) tension test. This last enables the correct identification of the temperature and strain rate influence, because both viscous and elastic parts of the model need to test the material in nonequibiaxial (NEB) conditions. The procedure already used for EB tension test is extended to constant width and an intermediate case, NEB cases. The VHE model developed to simulate the PET behavior in the stretch blow molding conditions is identified from these three different biaxial tests: differences and dispersions are discussed. The origin of this dispersion is found out and solved by a modification of the model. This leads to a reduction of the number of parameters in the proposed VHE model.