Testing and analysis of solid polymers under large monotonic and long-term cyclic deformation

The deformation behavior of solid polymers under isothermal, quasi-static loadings is investigated. A comprehensive test program consisting of tension, torsion, and combinations thereof was conducted on a polycarbonate polymer under both monotonic and long-term cyclic loadings. The effects of different loading modes, creep load conditions, mean stress, stress amplitude, and loading rate are addressed. The possibility of simulating costly tests with existing models is also demonstrated. A viscoelastic-viscoplastic constitutive model proposed by Barriere et al. 2019 is applied for this purpose. Compared to state-of-the-art models, this model requires a reduced set of material parameters to be defined. The validation experiments demonstrate the model robustly predicts various loading scenarios. In light of both the experimental and model results, the material shows an apparent hardening with increasing loading rates, and the ratcheting strain increases with the stress amplitude and mean stress. When applying the same stress ratio, stress rate, and maximum axial and torsional stresses relative to the strengths, the superimposed tension increased the torsional ratcheting for all load combinations. The ratcheting-fatigue failure interaction is also investigated. The experimental data show the interaction at least 90% of the fatigue life, which the important observation is used for the development of a fatigue model.