Damping Behavior of Dry and Epoxy-Impregnated Carbon Nanotube Yarn

Multiwalled carbon nanotubes (CNTs) are believed to add beneficial damping to fiber reinforced polymer composites on account of their weak, reversible inter-wall bonding and CNT/polymer bonding. An effective way to add a large volume fraction of CNTs to a fiber composite is to form the CNTs into condensed yarns and add the yarns to the interlayer regions of composites with the CNTs oriented along the primary loading direction. To address the ongoing need for additional data on the damping provided to fiber composites by CNT yarns, the current investigation focuses on the tensile damping behavior of a commercially available yarn with and without epoxy impregnation. Based on quasi-static tensile tests using cross-sectional areas measured by ethanol immersion testing, dry yarn was observed to have an elastic modulus of 109 GPa and an ultimate tensile strength of 1.30 GPa, while impregnated yarn had a modulus of 62 GPa and a strength of 0.813 GPa. Dry and impregnated yarns exhibited a ratcheting mechanism, where permanent strain is accumulated with repeated load cycling. Through dynamic mechanical analysis, it was shown that both dry and impregnated yarns exhibited high damping, with average initial loss factors of 0.110 and 0.0953, respectively. With continued cycling and increased strain, the storage modulus of impregnated yarns increased by 450%, while the loss modulus increased by 256% and the loss factor decreased by 35%. Dry and impregnated yarns exhibited quasi-static and dynamic properties that were highly sensitive to loading history, although impregnated yarns showed greater degrees of change over larger numbers of loading cycles. It is shown that an established micromechanical model can predict to within 6% the loss factor of a [90]6 hybrid carbon/epoxy laminate containing 10 vol% CNT yarns aligned in the 0° orientation, based on known dynamic properties of the impregnated yarn and the baseline laminate without CNTs.