Processing, characterization, and modeling of nanoparticle reinforced fiber composites

Continuous fiber/epoxy composites have been widely used for structural applications due to their excellent mechanical properties, but the benefits of using these composites is limited by their lower than desired matrix-dominated properties. In this study, epoxy matrix in carbon fiber/epoxy composites was modified with graphite nanoplatelets to improve their mechanical properties. Two processing methods, prepreg-autoclave process and vacuum assisted wet lay-up, were adopted to prepare the nanoparticle-reinforced fiber composites. It was found that both the in-plane shear modulus and the compressive strength obtained by the prepreg-autoclave method were improved more prominently than those obtained by the vacuum assisted wet lay-up process. This can be attributed to the higher mechanical enhancement in the matrix phase by the prepreg-autoclave process than by the vacuum assisted wet lay-up process. In the prepreg-autoclave process, the compressive strength of the composites was increased by 44% with 3 wt% nanoparticle loading, and the in-plane shear modulus was improved by 15% and 24% with 3 wt% and 5 wt% of nanoparticle loadings, respectively. Prepregs normalized to a consistent partial cure (B-stage) with or without graphite nanoparticles were obtained as a byproduct, thus making the proposed prepreg-autoclave method valuable for fabricating prepregs of nanoparticle reinforced composite materials. The effect of the crimping of the transverse glass fiber yarns holding the carbon fibers, was analyzed. The crimps are viewed as local fiber misalignment and taken into account in simulation models for prediction of compressive strength. Numerical simulation models, based on the fiber geometry observed in the composites, showed good agreement with the experimental results. It is shown that the compressive strength of the composite can be enhanced by increasing modulus of the matrix. Reducing the fiber misalignment in the composite will further increase the compressive strength.