Strain dependence of electrical resistance in carbon nanotube yarns

Abstract Carbon nanotube forests or arrays can be drawn into a web and further twisted into threads. These carbon nanotube threads contain thousands of carbon nanotubes in their cross-sections and can be further composed into yarns that consist of one or more threads. The superior mechanical, thermal and electrical properties of carbon nanotubes are not translated into the carbon nanotube yarns. However, carbon nanotube yarns still exhibit relatively high mechanical stiffness and strength, and low electrical resistivity. More importantly, carbon nanotube yarns exhibit piezoimpedance that could be used for sensing purposes. In order to use carbon nanotube yarns as piezoimpedance-based sensors for structural health monitoring, it is necessary to determine the change in impedance of the yarn as a function of its mechanical strain or stress. This paper presents the results of an experimental study on the coupled mechanical response and electrical response in the direct current mode of the carbon nanotube yarn. A behavior consisting of a negative piezoresistive response was encountered during most of the deformation range of the yarn. This response was shown to exhibit a parabolic response and it was followed by a linear positive piezoresistive response that preceded the failure of the yarn.