Lawrence Berkeley National Laboratory

The carbon fiber/polymer matrix interphase region plays an important role in failure initiation and accurate modeling techniques are integral to study the effects of this complex region on the composite response. In composites infused with nanoparticles such as carbon nanotubes (CNT), the interphase region is more complex due to the presence of multiple constituents and their interactions with each other. An atomistic methodology to simulate the constituent interphases in carbon fiber reinforced CNT/epoxy nanocomposites is presented in this paper. The interphase model consisting of voids in multiple graphene layers enable the simulation of physical entanglement between the polymer matrix and the irregular carbon fiber surface. The voids in graphene layers are generated by removing carbon atoms and hydrogenating the end carbon atoms, which better represent the roughness of the carbon fiber surface. The epoxy curing studies and the response of fiber/matrix interphase under mechanical loading are investigated through molecular dynamic (MD) simulations with appropriate classical/harmonic and bond order-based force fields. Furthermore, the atomistic force-displacement behavior is also extracted to formulate a traction-separation law for interface cohesive zone models. The cohesive behavior determined from molecular models is parameterized in equations that can be integrated with an atomistically informed multiscale modeling framework.