On temperature-related shift factors and master curves in viscoelastic constitutive models for thermoset polymers

Reliable accelerated testing routines involving tests at enhanced temperatures are of paramount importance in developing viscoelastic models for polymers. The theoretical basis, the time-temperature superposition (TTS) principle, is used to construct master curves and temperature-dependent shift factor, which is the necessary information to simulate the material response in arbitrary temperature and strain regimes. The Dynamic Mechanical and Thermal Analysis (DMTA) TTS mode, being one of the most promising approaches in terms of time efficiency and maturity of the software, is compared in this paper with macrotests at enhanced temperatures in their ability to give reliable master curves. It is shown, comparing simulations with test data for a chosen epoxy polymer, that none of the three DMTA TTS mode-based attempts used (at different temperature steps during frequency scanning) was successful in predicting the epoxy behavior in tests. On the contrary, using one-hour macrotests at enhanced temperatures gives a viscoelastic model with a very good predicting accuracy. Simulations were performed using an incremental formulation of the previously published VisCoR model for linear viscoelastic materials