Modeling of mechanical damping and electrical properties of carbon nanotube reinforced composites.

摘要

Carbon nanotubes (CNTs) possess unique and superior properties that can effectively enhance the mechanical damping and electrical performances of polymers. This thesis presents the micromechanical modeling of damping characteristics and numerical simulation of electrical properties of CNT reinforced composites. Influences of a variety of material and application factors on composites performances have been discussed.;First, we review the existing micromechanical models that predict effective modulus of short fiber composites. Influences of nanotube waviness, modeling CNT as solid isotropic cylinder, and nanotube bundling effect have been investigated based on Mori-Tanaka model.;Based on the understanding of static mechanical reinforcement induced by CNTs, we further study energy dissipation in nanocomposites under dynamic loading. To quantify the main source of energy dissipation, a micromechanical model based on the quasi-static stick-slip analysis has been developed to predict both loss and storage moduli of polymer composites containing CNTs ( 2 vol. %) as a function of external strain in elastic region ( 1.2%). Influence of nanotube bundling, nanotube alignment, and test frequency on damping property of composites was studied using this micromechanical model.;To better understand nanotube waviness influence on percolation threshold of CNT reinforced polymer composites, a 3D Monte Carlo model has been proposed to represent curved nanotube as a chain of three straight segments. Simulation results show that the value of percolation threshold increases with nanotube waviness.;The calculation of electrical conductivity of nanocomposites can be a challenging task because of the complexity of nanotube networks and the difficulty in quantifying electronic tunneling through junctions. Numerical simulation has been widely utilized, but due to computation capacity restraints most studies are limited to solve 2D problems or low filler aspect ratios. In our approach, the simulation is effectively simplified based on the fact that tunneling resistance plays a determinant role in composites electrical resistance and contributions from intrinsic filler resistance can be neglected. As a result, the number of effective resistors in the complex resistor network can be reduced more than half and 3D simulation on nanotubes with high aspect ratios up to 1000 and volume fraction up to 1 vol. % becomes possible.