Experimental Evaluation of Carbon Nanotubes for High-Stiffness Damping Augmentation in Carbon/Epoxy Composites

Carbon nanotubes (CNTs) are promising materials for increasing the damping of fiber reinforced composites on account of a hypothesized stick-slip dissipation mechanism. The current investigation aims to increase the damping of a carbon/epoxy composites by adding different types and amounts of CNTs to the interlayer regions. [90] , [0] and [0/±45] carbon/epoxy laminates were manufactured using various types and concentrations of CNTs and surfactant. Dynamic behavior was characterized in terms of the storage and loss moduli and loss factor under tensile cyclic loading. For [0] and [0/±45] laminates, the maximum increases in loss factor and loss modulus of roughly 400-600% were obtained with 10 volume percent CNT yarns aligned in the 0-deg. loading direction. The storage modulus of these laminates was not appreciably affected by the CNT yarns. Aligned CNT yarns provided higher damping than equivalent amounts of unaligned CNT buckypapers. In a series of tests on 0-deg. laminates with and without aligned CNT yarns, damping increased with strain amplitude but not with mean strain, while damping in the baseline laminate was nearly invariant with strain. This series of tests also detected no lower threshold of strain for the onset of slip by CNT and a 10x reduction in the rate of increase of damping with strain amplitude when the amplitude exceeded 190 μ.