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In this paper, the effects of additives of a single-walled carbon nanotube (SWCNT) on the nonlinear free vibration of neat resin and carbon fiber reinforced polymer composites (CFRPs) are investigated experimentally. To establish this purpose a sensitive noncontact setup is designed and prepared. In order to obtain a proper SWCNT dispersion pattern, a simple multistage method is presented to fabricate and test nanocomposite beams. First, the increase in the Young's modulus of the nanocomposites by adding carbon nanotube is investigated using the mechanical bending test and validated with available test results. Next, the nonlinear free vibration behavior of cantilever beams under small to large-deflection is investigated. The results of the vibration tests indicate that the nonlinear vibration behavior of all models is close to homogenous materials with increasing SWCNT. The results also show that transverse initial excitation (displacement) imposed an axial load on the slender beams, which thus leads to an increase in the nonlinear frequency of oscillation. In addition, the increase in frequency bears a relation to the initial displacement. Also, large initial displacements, especially on models without carbon fiber (reinforced epoxy), cause that the convergence of frequencies under different initial excitation did not occur. The results of this study show that adding SWCNT can lead to convergences of frequencies’ hybrid composites and reinforced epoxy during final cycles.

In this paper, the mechanical behavior of epoxy polymer nanocomposite with continuous single-walled carbon nanotubes (SWCNT) with and without vacancy defects has been investigated based on two approaches of deformation, molecular mechanics (static) and molecular dynamics. In this regard, molecular simulation has been performed on the basis of the compass force field. In order to validate the research steps, the results obtained for pure epoxy polymer were compared with similar molecular dynamic simulations, which confirmed the simulation process. The research process proposed a method for controlling the symmetry of the system during equilibration with an asymmetric barostat. The Souza-Martins barostat was also used to apply loading and deformation control over a constant strain rate range. The results showed that in both deformation approaches (with and without calculating the contribution of kinetic energy), the presence of defects improved the transverse tensile and shear moduli, while the longitudinal tensile modulus decreased. Also, the improvement and decrease of the longitudinal tensile modulus and longitudinal shear modulus of the nanocomposite in comparison with the net polymer have been observed in both approaches, respectively. As a general result, it was observed that the contribution of kinetic energy has a major effect on the mechanical properties of pristine and defective nanocomposites.