This work is aimed at studying the effect of different morphological features on the stiffness of discontinuous fiber reinforced composites and nanocomposites by means of FEM analysis. The morphological features include not only volume fraction and aspect ratio of reinforcement, but also its orientation. The FEM approach, based on continuum mechanics, required the definition of a proper representative volume element, in which reinforcement is randomly dispersed in the simulation domain. The developed model has been used in order to calculate the stiffness matrix of unidirectional discontinuous glass fiber reinforced composite (DGFRC) as well as carbon nanotubes reinforced nanocomposites (CNTRNC). Comparison with closed form analytical models showed that the Halpin-Tsai (HT) model is able to predict the evolution of the elastic constants over a wide range of volume fractions and aspect ratio. The Tandon-Weng (TW) model, in contrast, shows a poor agreement with the simulation results. On the other hand, the developed FEM model also allowed accounting for reinforcement orientation. The calculated elastic properties are in excellent good agreement with the corresponding values calculated according to the classical lamination theory, indicating the accuracy of the developed FEM model for estimation of stiffness of composites and nanocomposites, also accounting for reinforcement orientation.
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