Micromechanical modeling of the effects of crystal content on the visco-hyperelastic-viscoplastic behavior and fracture of semi-crystalline polymers

In this work, we present a novel physically based visco-hyperelastic-viscoplastic micromechanical constitutive model, which establishes a link between the evolution of the macromolecular network properties to the me-chanical and fracture behavior of variable-crystallinity semi-crystalline polymers. Unlike previous micro-mechanical constitutive models that were only time independent, we propose a time-dependent scheme. It employs the computational effective eight-chain model for micro-macro transition while assuming a composite structure for the polymer. Thus, an innovative approach that couples the deformation and damage of individual polymer chains is developed. The proposed constitutive framework assumes that the stress developed through the deformation of semi-crystalline polymers is the sum of a macromolecular network and an intermolecular part. The macromolecular part accounts for the conformational change associated with Kuhn segments reor-ientation and the bond potential associated with the deformation of the bonds between Kuhn segments. Meanwhile, the intermolecular part accounts for the deformation of the crystalline and the amorphous phases. The constitutive equations are integrated using a mixed explicit/implicit integration algorithm. To validate and calibrate our model, we utilize uniaxial tensile experimental data obtained from three different polyethylene materials with varying crystallinity levels and different strain rates. We propose a robust calibration procedure, ensuring the identification of a single set of parameters that remain independent of crystal content and strain rate. Finally, we assess the model's predictive capabilities in predicting the mechanical behavior and fracture at different strain rates for variable-crystallinity polyethylene is evaluated. This comprehensive approach enhances our understanding and predictive capacity in modeling the intricate mechanical response up to fracture of semi-crystalline polymers under diverse conditions.