Prediction of quasistatic constitutive equations of moisture-absorbed epoxy polymers using atomistic simulations

Abstract

The quasistatic constitutive equations of moisture-absorbed epoxy polymers were predicted from molecular dynamics (MD) simulations based on the Argon theory and cooperative model to overcome the timescale limitation of classical MD simulations. A nonlinear degradation of the elasto-plastic mechanical behavior corresponding to moisture uptake, which arose from the involvement of water molecules on the accommodation of deformation, was identified and reflected in the proposed method to derive the quasistatic deformation behaviors. The influence of the moisture uptake on the glass transition temperature (Tg) was also evaluated by the Kelly–Bueche equation to determine the uncertainty of the Tg predicted by typical MD cooling-down simulations. It was revealed that the one-dimensional constitutive equations constructed by contemporary methods exhibited a severe stress reduction in stress–strain relations after the 8 wt% moisture content. The proposed method can provide a means to construct a multiscale model while considering changes in the mechanical properties according to the microstructural variation from polymer–solvent interactions.