MODELING STRAIN HARDENING OF GLASSY POLYMERS BASED ON HYPERELASTIC MODELS

Classic hyperelastic models have been widely adopted to describe the mechanical response of rubbers. In early studies, the strain hardening of glassy polymers is also modeled by using a hyperelastic model, such as the Neo-Hookean model and the eight-chain model. To verify whether other hyperelastic models can better simulate the strain hardening behavior of glassy polymers, in this work, we develop a viscoplastic model to describe the mechanical behavior of the glassy polymers. The model consists of three components to characterize the mechanical response of glassy polymers and a Langevin statistical model is adopted for the entropic elastic free energy. The model incorporates a back stress for strain hardening behaviors based on different hyperelastic models, including the three-chain model, the eight-chain model, the full-chain model and the p-root model. The models are then applied to simulate the stress responses of PC and PMMA under uniaxial compression and plane strain compression conditions, as well as the mechanical behavior of PETG at different strain rates in the literature, in order to obtain a comprehensive assessment. The results of the simulations and experiments show that the models based on the p-root model and the eight-chain model can better simulate the deformation behaviors of the glass polymers in uniaxial loading and plane strain conditions. The p-root model performs slightly better than the eight-chain model. In addition, the relative error of these two models are significantly smaller than that of the three-chain model and the full-chain model. This work may shed light on developing constitutive models for glassy polymers.