Dual-scale micromechanics-based analysis of stiffness and thermal expansion coefficients in montmorillonite nanoclay-reinforced graphite fiber-polymer composites

In this study, a hierarchical micromechanics-finite element modeling framework is developed to predict the effective elastic constants and thermal expansion coefficients (TECs) of epoxy-based ternary composites reinforced with graphite fibers and montmorillonite (MMT) clay nanofillers. At the nanoscale, representative volume elements (RVEs) are constructed by randomly dispersing MMT platelets within the epoxy matrix to capture their thermomechanical response. The homogenized properties obtained from the nanoscale RVEs are subsequently employed as the matrix phase in microscale RVEs, where continuous graphite fibers are embedded in the MMT nanoclay-filled epoxy matrix. The present modeling approach is validated through comparison with established analytical models and data reported in the literature. Parametric investigations are conducted to evaluate the effects of nanoclay volume fraction and aspect ratio, interphase region properties, and graphite fiber content on the elastic moduli, Poisson’s ratios, and TECs of the composite system. Results reveal that the incorporation of MMT nanoclay improves the thermo-elastic properties of the fibrous epoxy composites specifically in the transverse direction. In general, the engineering constants of the graphite fiber-reinforced epoxy composites containing MMT nanoclay fillers can be tuned by the microstructural features.