Comparative Study of the Piezoresistivity of Free and Medium-constrained Carbon Nanotube Yarns: Effect of Slippage

Abstract

Carbon Nanotube (CNT) yarns have gained increased attention in structural health monitoring due to their multifunctional properties. They exhibit a unique change in their resistivity when subjected to mechanical strain. This piezoresistive response can be tapped for sensing purposes. The objective of this study is to determine experimentally the piezoresistive response of CNT yarns that are embedded in a medium while subjected to tension, and compare it with that of the free or unconstrained CNT yarns. The constraint is achieved by embedding the CNT yarns in epoxy to produce coated CNT yarns and fiber monocomposite beams. Tensile tests were performed on the coated yarn while the monocomposites were subjected to both uniaxial and bending tests. The curves of the constrained CNT yarns are fairly linear and produce higher gauge factors than that of the free CNT yarn. Consequently, the piezoresistivity of the constrained CNT yarns is higher than that of the unconstrained CNT yarns. This difference between them may be explained by the lack of the effective slippage, fiber unraveling and subsequently, Poisson’s effect of the CNT yarn when integrated in the polymer. The composite samples tested under bending showed a higher gauge factor than under uniaxial tension. CNT yarns that were dipcoated in the polymer showed high fiber impregnation due to the yarns porous structure. However, they also showed improved strength, more linearity and higher piezoresistive response but lower strain to failure when compared to the uncoated CNT yarn.