The effects of non-perfect bonding in carbon nanotube reinforced composites are studied in the context of continuum mechanics through the use of micromechanics and finite element approaches. Constitutive properties describing the nanotubes themselves are derived from computational efforts at lower length scales involving ab initio and molecular dynamics simulations. Similar simulations as well as experimental data obtained from composite samples using Raman spectroscopy are employed to ascertain the bonding and load transfer properties between the nanotubes and a polymer matrix. Effective composite properties for ideally bonded nanotube-polymer composites are then obtained using two-step (composite cylinders coupled with both the generalized self-consistent technique or the Mori-Tanaka technique) and single-step (n-phase composite cylinders) micromechanics approaches, and are compared to the effective properties obtained for composites wherein the ideal bonding assumption has been relaxed to varying degrees. Relaxation of the ideal bonding assumption is accomplished via the homogenization of material properties obtained from finite element simulation results of individual nanotubes in the polymer matrix involving cohesive zones. This homogenized system is then used with the Mori-Tanaka method to obtain effective composite properties. Full composite finite element simulations using periodic boundary conditions are used to validate the effective properties obtained as is the available experimental data.
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