A constitutive model for predicting the large deformation thermomechanical behavior of fluoropolymers

This paper presents a newly developed constitutive model for predicting the time and temperature-dependent mechanical behavior of fluoropolymers, including PTFE, PFA and FEP. The mathematical details of the theory and its connection with the underlying microstructure are presented together with aspects of its numerical implementation into large-strain finite element simulations. A set of uniaxial tension, uniaxial compression, hydrostatic compression, multi-cycle thermomechanical, and small sample punch (disk bend) tests were performed on glass fiber filled PTFE to evaluate the predictive capabilities of the model. The tests were performed using monotonic and cyclic load histories, at different deformation rates and temperatures. A direct comparison between the experimental data and the model predictions show that the constitutive theory accurately captures the material response. The model is also capable of predicting the influence of hydrostatic stress on both the deviatoric and volumetric flow rates, enabling accurate predictions of fluoropolymers with small amounts of porosity.