The carbon fiber/polymer matrix interphase region plays an important role in the behavior and failure initiation of polymer matrix composites and accurate modeling techniques are needed to study the effects of this complex region on the composite response. This paper presents a high fidelity multiscale modeling framework integrating a novel molecular interphase model for the analysis of polymer matrix composites. The interphase model, consisting of voids in multiple graphene layers, enables the physical entanglement between the polymer matrix and the carbon fiber surface. The voids in the graphene layers are generated by intentionally removing carbon atoms, which better represents the irregularity of the carbon fiber surface. The molecular dynamics method calculates the interphase mechanical properties at the nanoscale, which are integrated within a high fidelity micromechanics theory. Additionally, progressive damage and failure theories are used at different scales in the modeling framework to capture scale-dependent failure of the composite. Comparisons between the current molecular interphase model and existing interphase models and experiments demonstrate that the current model captures larger stress gradients across the material interphase. These large stress gradients increase the viscoplasticity and damage effects at the interphase which are necessary for improved prediction of the nonlinear response and multiscale damage in composite materials.

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This paper presents the development of a novel methodology for modeling the interphase between carbon fiber and polymer matrix using atomistic scale simulations. The model is integrated within a multiscale framework for the analysis of polymer matrix composites. The interphase region that exists between carbon fiber and polymer matrix plays an important role in damage initiation and it is critical for modeling damage propagation across length scales. The developed interphase model in this work consists of multiple pseudo-damaged graphene layers, and is capable of capturing the physical entanglement between the polymer matrix and the carbon fiber through the use of molecular dynamics simulations. The pseudo-damage model simulates voids in the graphene layer by removing carbon atoms, while multiple pseudo-damaged graphene layers represent the amorphous structure of the carbon fiber surface. In order to accurately model the chemical structure of the polymer, a numerical curing process is employed that captures the stochastic interactions between resin and hardener molecules for crosslinking (carbon-nitrogen covalent bond generation). The molecular dynamics model also enables extraction of the material properties of the interphase at the nanoscale which is then integrated within a high fidelity generalized method of cells micromechanics theory. A modified Bodner-Partom viscoplastic theory is applied to the polymer matrix subcells. Additionally, progressive damage and failure theories are used at different scales in the modeling framework to accurately capture scale-dependent failure of the composite material. Comparative studies are performed by applying different interphase properties that are obtained from the literature to the interphase subcells. The results indicate that the responses for each type of interphase model are similar, but the transverse tensile strength, obtained using the MD simulated interphase properties, is approximately 7% lower than the other interphase types and also has a maximum difference of 10% in failure strain.@en