Modeling the morphology evolution of PET during equi-biaxial elongation: from SAXS measurement to viscoelastic behavior prediction

The microstructure induced by the biaxial stretching of PET under conditions representative of the stretch blow-molding process enhances the material’s mechanical performance. Using equi-biaxial tensile tests combined with small-angle synchrotron scattering, the evolution of the deformation-induced microstructure can be monitored in situ. This approach enables the characterization of the size and morphology of the crystalline phase, as well as the evolution of the degree of crystallinity during stretching. A constitutive model accounting for this microstructural evolution, based on a double homogenization of the viscoelastic behavior of the amorphous phase and the quasi-elastic response of the crystalline phase, successfully reproduces the macroscopic mechanical behavior of PET, including its characteristic strain-hardening during elongation. This modeling framework represents a significant advancement and provides a basis for extending the approach to other biaxiality ratios encountered in industrial stretch blow-molding processes. • In situ SAXS characterization of PET morphological evolution under biaxial stretching • Mesoscale modeling of PET morphology evolution during biaxial deformation • Development of an analytical viscoelastic micromechanical homogenization framework • Incremental multiscale modeling of the mechanical response under biaxial stretching (micro/meso–macro) • Quantification of strain-rate and temperature effects on mechanical behavior and final morphology