Non-linear viscoelasticity of epoxy resins: Molecular simulation-based prediction and experimental validation
The precise knowledge of the temperature-dependent non-linear viscoelastic material behaviour of polymers is of great importance for engineering applications. The present work is a contribution to meet the challenge of bridging the inherently different time scales of molecular dynamics (MD) and experiments by providing a consistent comparison and assessment of viscoelastic theories. For this reason, the physically motivated theories for viscoelasticity of Eyring and Argon as well as the Cooperative model are evaluated with regard to their predictive capability for the characterisation of the viscous behaviour over a broad range of temperatures and strain rates. MD simulations of tensile tests are performed and the effect of strain rate and temperature on the yield stress is examined. The distinctive feature of this study is to demonstrate that viscoelastic theories can be successfully calibrated using only MD results. For a comparison to experimental data, we conduct tensile tests at three different strain rates and at three temperatures in the glassy regime. Experimental validation confirms the predictive capability of the Argon model, which can provide an accurate formulation of epoxy viscoelasticity for physically motivated constitutive models. The present study not only underlines the ability of MD simulations for identifying and characterising physical phenomena on the molecular level, but also shows that molecular simulations can substitute experimental tests for the characterisation of the viscoelastic material behaviour of polymers.