Characterization of Viscoelastic Properties of EPDM Molding Compound for Door Grommet Component Using Molecular Dynamics and Phenomenological Modeling

The automotive industry is evolving by incorporating innovative tools to improve production processes. A proper manufacturing process influences the behavior of the door grommet during its lifetime. In this paper, molecular dynamics simulations are conducted to evaluate the chemical and physical crosslinking of the EPDM rubber over a range of temperatures using a COMPASS force field. Then, once the ethylene propylene diene monomer (EPDM) model was equilibrated and all possible crosslinks were formed, additional simulations were performed on the model to explore its mechanical behavior. Subsequently, using the superposition principle, viscosity and curing kinetics were evaluated using phenomenological models. To validate the results of the simulations, three injection tests of the door grommet were performed at different temperature conditions. The results indicate that the viscosity and elastic properties increase with increasing levels of crosslink density and that the critical gel point decreases with temperature. Molecular dynamics superposition results in phenomenological models are in reasonable agreement with the kinetic and viscoelastic behavior of EPDM during and after the injection process. The results presented in this paper provide novel molecular-level findings on the crosslinking mechanisms of amorphous polymers and their influence on viscoelastic behavior, which could facilitate the design of the injection process for door grommet applications.