Piezoresistive Response of Integrated CNT Yarns under Compression and Tension: The Effect of Lateral Constraint

Abstract

Carbon nanotube (CNT) yarns are fiber-like materials that exhibit excellent mechanical, electrical and thermal properties. More importantly, they exhibit a piezoresistive response that 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 polymeric medium while subjected to either tension or compression, and compare it with that of the free or unconstrained CNT yarns. The rationale is the need to know the piezoresistive response of the CNT yarn while in a medium, which provides a lateral constraint to the CNT yarn, thus mimicking the response of integrated CNT yarn sensors. The experimental program includes the fabrication of samples and their electromechanical characterization. The CNT yarns are integrated in polymeric beams and subjected to four-point bending, allowing the determination of their response under tension and compression. The electromechanical data from a combined Inductance-Capacitance-Resistance (LCR) device and a mechanical testing system were used to determine the piezoresistive response of the CNT yarns. At a strain rate of 0.006 min −1 , the gauge factor obtained under tension for a maximum strain of 0.1% is 29.3 which is higher than~21.2 obtained under compression. The CNT yarn sensor exhibited strain rate dependence with a gauge factor of approximately 23.0 at 0.006 min −1 , in comparison to 19.0 and 1.3, which were obtained at 0.0005 min −1 and 0.003 min −1 , respectively. There is a difference of up to two orders of magnitude in the sensitivity of the constrained CNT yarn under bending with respect to that of the free CNT yarn under uniaxial tension. However, the difference becomes smaller when the constrained CNT yarn was tested under uniaxial tension. This data and information will be used for future modeling efforts and to study the phenomena that occur when CNT yarns are integrated in polymeric and composite materials and structures.

Electrical Resistance Sensing of Epoxy Curing Using an Embedded Carbon Nanotube Yarn

“…The electrical and thermal conductivity of CNTYs may be similar to that of carbon fibers [4] and their porosity makes them even more attractive for the polymer composites community. The excellent electrical properties of CNTYs make them attractive candidates in various applications such as strain sensing [5][6][7][8][9][10][11][12], supercapacitors, antennas, and other electrical devices [12][13][14]. CNTYs can be integrated into thermosetting polymer composites and used as in situ sensing elements for stress build-up and damage monitoring [3,8,15].…”

“…The excellent electrical properties of CNTYs make them attractive candidates in various applications such as strain sensing [5][6][7][8][9][10][11][12], supercapacitors, antennas, and other electrical devices [12][13][14]. CNTYs can be integrated into thermosetting polymer composites and used as in situ sensing elements for stress build-up and damage monitoring [3,8,15]. An important concern in thermosetting polymer composites is the development of residual stresses during resin polymerization (curing) [16][17][18][19].…”

Monitoring of Curing and Cyclic Thermoresistive Response Using Monofilament Carbon Nanotube Yarn Silicone Composites

“…The CNTY used in this study was fabricated from a vertically aligned CNT array at Nanoworld Laboratories (Cincinnati, OH, USA). The diameter, density, angle of twist, and average electrical resistivity of the densified CNTYs are~30 µm,~0.65 g/cm 3 ,~30 • and 1.7 × 10 −3 Ω cm, respectively [1,2]. Figure 1 shows images of the twisted yarn obtained by Scanning Electron Microscopy (SEM).…”

“…Carbon nanotube yarns (CNTYs), continuous fiber-like materials comprised of carbon nanotube (CNT) bundles, may become candidates for in situ sensors in structural health monitoring (SHM) because of their significant sensitivity to temperature and strain, small size, light weight, high surface area, high electrical and thermal conductivity, and multifunctionality [1][2][3][4][5]. The coupling between the electrical resistance (R) of the yarn and temperature (T) makes them candidates for the development of self-sensing smart materials for thermal analysis inside structures [4][5][6].…”

Effect of Curing Temperature of Epoxy Matrix on the Electrical Response of Carbon Nanotube Yarn Monofilament Composites

“…CNTYs show lower physical properties than their individual CNTs [9,11]. Potential applications of CNTYs include damage monitoring in composite materials [12,13], electronics devices [14], energy storage [15], artificial muscles [16], and strain sensing [17]. A considerably less investigated potential application for CNTYs is as temperature sensors, using their intrinsic thermoresistivity while integrated in polymeric materials [9,18].…”