Microstructures changes in Poly(ethylene terephthalate) under complex biaxial loading
Yann MARCO, Luc CHEVALIER, Mohend CHAOUCHE
LMT-Cachan
FRANCE

Keywords: Biaxial, Microstructure, Fast cooling

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This study presents an experimental investigation into the strain-induced crystalline
microstructure, under biaxial elongation in poly(ethylene terephthalate) (PET).
We examined how the microstructure of a polymer subjected to a complex strain field
evolves in terms of its crystalline ratio, its molecular orientation and the size of its crystallite.
PET injection-molded specimens have been subjected to biaxial elongation tests, both
equibiaxial and sequential, at different drawing speeds, draw ratios and temperatures above and close to Tg.
A home-developed image correlation technique allowed us to determine all the strain
components at each point of the specimen, even with a non-homogeneous strain field.
At the end of the deformation process performed with new biaxial set-up, the specimens were either quenched to room temperature
or cooled downed very quickly in order to dissociate the stretching and relaxation
contribution to microstructural changes.Their microstructures were finally investigated,
using both differential densimetry and WAXD using a synchrotron beam. The results
are then correlated with ex- and in-situ uniaxial WAXD measurements.