Influence of representative volume element size on predicted elastic properties of polymer materials

Molecular dynamics (MD) simulations and micromechanical modeling are used to predict the bulk-level Young’s modulus of polycarbonate and polyimide polymer systems as a function of representative volume element (RVE) size and force field type. The bulk-level moduli are determined using the predicted moduli of individual finite-sized RVEs (microstates) using a simple averaging scheme and an energy-biased micromechanics approach. The predictions are compared to experimental results. The results indicate that larger RVE sizes result in predicted bulk-level properties that are in closer to the experiment than the smaller RVE sizes. Also, the energy-biased micromechanics approach predicts values of bulk-level moduli that are in better agreement with experiment than those predicted with simple microstate averages. Finally, the results indicate that negatively-valued microstate Young’s moduli are expected due to nanometer-scale material instabilities, as observed previously in the literature.