Étude et modélisation mécanique de la cristallisation induite par la déformation des polymères : caoutchouc naturel réticulé et PET

Abstract : The present PhD thesis aims at a better understanding and modeling of strain-induced-crystallization. The phenomenon is characterized for two polymers: PET and crosslinked natural rubber. Strain conditions leading to strain-induced-crystallization are determined by thermal and dynamic mechanical analysis. The developing microstructure is observed by X-ray scattering.The PET is stretched in uni- and biaxial tension. A part of samples is rapidly quenched after stretching and another is submitted to a stress relaxation after stretching. The studies demonstrate that the stretching of PET does not enable the formation of a complete PET crystal with all its own families of planes.The crosslinked natural rubber is stretched in uniaxial tension and in shear preceded by uniaxial stretching. In shear, the crystalline phase, appeared during the pre-stretching or during the shear rotates and has a tendency to orient as the directions of the principal strains. The principal elongation is used to compare the crystallization under the different stresses.A constitutive modeling for visco-hyperelastic behaviors, in a complete thermodynamics framework of irreversible processes, is extended in order to reproduce le mechanical hardening related to the development of an organized/crystalline phase. The modeling successes in reproducing the experimental behaviors in uploading/unloading for various strain conditions.
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Grégoire Quandalle. Étude et modélisation mécanique de la cristallisation induite par la déformation des polymères : caoutchouc naturel réticulé et PET. Matériaux. PSL Research University, 2017. Français. ⟨NNT : 2017PSLEM033⟩. ⟨tel-01774634⟩

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