| Carbon nanotube reinforced polymer nanocomposites have been extensively researched for their strength and stiffness properties. Unless the interface is carefully engineered, poor load transfer between individual nanotubes (in bundles) and between nanotubes and surrounding polymer chains may result in interfacial slippage and consequently reduced performance. Interfacial shear, while detrimental to high stiffness and strength, could result in very high mechanical damping, which is a hugely important attribute in many commercial applications. Our objective in this thesis is to quantify the energy dissipation that takes place as a result of interfacial sliding in nanotube polymer composites and to explore the mechanisms by which this energy dissipation could be harnessed to efficiently inject mechanical damping into heterogeneous/composite systems.; We identify two basic energy dissipation mechanisms in this thesis, namely; (1) interfacial tube-polymer sliding and (2) interfacial tube-tube sliding. In both mechanisms, the nanoscale dimensions of the tubes not only results in large interfacial contact area, thereby generating high damping efficiency, but also enables seamless integration of the nanoscale fillers into the polymer matrix. Carefully designed uniaxial and shear loading experiments are conducted over a range of strain amplitudes and test frequencies to quantify the energy dissipation responses. The tests indicate that nanotube fillers can provide very significant damping enhancement (>1000%) compared to the baseline polymer. However the tube-polymer slip mechanism was shown to be far more effective at increasing damping than one based on tube-tube sliding. The latter mechanism requires a large number of tube-tube contacts necessitating a very high packing density of nanotubes, restricting practical applications to thin films. In contrast, the tube-polymer sliding mechanism allows the efficient introduction of damping into bulk polymer structures.; This work shows that minimally-intrusive and high aspect ratio nanoscale filler materials show potential to "efficiently" and "reliably" inject damping into composite systems. These nanocomposite damping materials could significantly advance the state-of-art in the field of polymeric damping, helping to ensure stability and low vibratory loads in a wide variety of structural components and systems. |
