Finite-element method and micromechanical formulations have been used to predict mechanical properties of epoxy-based nanocomposites in recent years. The results of these investigations, however, show large scatters and do not agree well with experimental measurements. The differences in the results may be due to the fact that these approaches do not take some important material parameters into account, such as resin crosslinking ratio, nanotube/matrix interface, and nanotube agglomeration. The main objective of this article is to investigate the effects of resin crosslinking ratio on mechanical properties of epoxy-based nanocomposites using molecular dynamics (MD). First, models of partially cured epoxy resin were created in Materials Studio software to determine resin properties at different crosslinking ratios. Next, one sample of neat epoxy and four samples of nanocomposite with different resin crosslinking ratios were modeled using MD. These models were analyzed using constant strain method to determine mechanical properties of the five samples. Also, the effects of crosslinking ratio on nanocomposite density were investigated. The simulation results show that nanocomposite Young's modulus increases with resin crosslinking ratio. Resin crosslinking ratio, however, did not have a significant effect on nanocomposite density. Further, molecular simulation results were compared with rule of mixtures and Mori-Tanaka predictions. In addition, the results were compared with those found in the literature and good agreement was observed between the results. POLYM. COMPOS., 38:E433-E442, 2017.

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Multiscale modeling has been developed to calculate the Young's modulus of carbon nanotube (CNT) reinforced epoxy-based nanocomposites. Molecular dynamics was used to construct nanocomposite models consisting of crosslinked network structure of epoxy resin as the matrix material and CNT as the reinforcement at nanoscale. Transversely, isotropic stiffness matrices were calculated using constant strain method on four cases with different CNT chiralities. Effective fiber method was employed to scale bridging from nanoscale to microscale. In multiscale calculations, various types of micromechanical methods were investigated and Halpin-Tsai formulation was selected due to its more realistic predictions. The results showed that increasing CNT aspect ratio from 1 to 1,000 results in an increase in nanocomposite Young's modulus by about three times for nanocomposite reinforced with CNT(20,0). Comparing CNT(5,0) with CNT(20,0) reinforced polymer results, suggested that increasing the CNT radius resulted in a decrease in nanocomposite moduli to about one half. Multiscale results indicated that CNT agglomeration can decrease nanocomposite Young's modulus to one-third compared to the dispersed CNT case. Predicted results were compared with numerical and experimental results found in the literature and good agreement was observed. POLYM. COMPOS., 00:000-000,

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