A multiscale damage initiation model for CNT-enhanced epoxy polymers

A multiscale methodology that accurately simulates the inelastic behavior of epoxy polymers initiating at the molecular level due to bond elongation and subsequent bond dissociation is presented in this paper. The system investigated in this study comprises a combination of crystalline carbon nanotubes (CNTs) dispersed in amorphous epoxy polymer molecules. Molecular dynamics (MD) simulations are performed with an appropriate bond order based force field to capture deformation-induced bond dissociation between atoms within the simulation volume. In order to overcome the influence of thermal vibrations of bonds on bond dissociation energy (BDE), a quasi-continuum (QC) approach, excluding the effects of temperature, is explored. Results indicate that a QC approach can simulate bond breakage leading to brittle behavior in amorphous epoxy polymer. The novel combination of MD deformation tests with high strain rates at near-zero temperatures, however, is seen to provide a more computationally efficient alternative for the study of bond dissociation phenomenon in amorphous epoxy polymer. The corresponding BDE extracted from the simulation volume is used as input to the continuum damage mechanics (CDM) model to study matrix failure at the microscale. The material parameters for the CDM model are directly obtained from physics-based atomistic simulations, thus, significantly reducing the propagation of errors in the multiscale framework.