A boundary element method for the analysis of CNT/polymer composites with a cohesive interface model based on molecular dynamics

In this paper, a new cohesive interface model is applied to characterize carbon nanotube (CNT) composites using the boundary element method (BEM). In the previous BEM models of CNT composites, a rigid-inclusion model was employed to represent the CNTs in a polymer matrix due to their extremely high stiffness as compared with the polymer. Perfect bonding interface conditions between the CNT fibers and matrix were used in these earlier models. Very good BEM results for the effective moduli were obtained as compared with other multi-scale models based on molecular dynamics (MD) and continuum mechanics. However, these simulation results yield much higher estimates of the effective Young's moduli of CNT/polymer composites than those observed in experiments of such composites. This discrepancy is largely due to the interfaces in CNT composites which have been found to be weakly, rather than strongly bonded. In this work, a new cohesive interface model has been developed by using MD simulations and employed in the BEM models to replace the perfect bonding interface models. The parameters in the cohesive interface model are obtained by conducting CNT pull-out simulations with MD and these parameters are subsequently used in the BEM models of the CNT/polymer composites. Marked decreases of the estimated effective Young's moduli are observed using the new BEM models with the cohesive interface conditions. The developed BEM models combined with the MD can be a very useful tool for studying the interface effects in CNT composites and for large-scale characterizations of such nanocomposites.