Piezoresistive response of carbon nanotube yarns under tension: Parametric effects and phenomenology (original) (raw)
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Investigation of electro-mechanical behavior of carbon nanotube yarns during tensile loading
Carbon nanotube (CNT) yarns were evaluated for sensor applications by measuring electrical properties during uniaxial tension loading. Mechanical properties (tenacity and failure strain) and electrical properties (resistivity and gauge factor) were investigated and statistical distributions for these properties were obtained. Cyclic loading test results showed that permanent strain after unloading exists and that the resistance at zero load increases linearly with permanent strain. Furthermore, the relative resistance change during loading was found to be linear with strain. Although mechanical properties of CNT yarns exhibited a significant statistical variation, the resistance was found to have much less statistical variation making them good candidates as sensors for structural health monitoring in composites.
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Multifunctional Nanocomposites, 2006
By forming composite structures with Carbon Nanotube (CNT) yarns we achieve materials capable of measuring strain and composite structures with increased mechanical strength. The CNT yarns used are of the 2ply and 4-ply variety with the yarns having diameters of about 15-30 μm. The strain sensing characteristics of the yarns are investigated on test beams with the yarns arranged in a bridge configuration. Additionally, the strain sensing properties are also investigated on yarns embedded on the surface of a flexible membrane. Initial mechanical strength tests also show an increase in the modulus of elasticity of the composite materials while incurring a weight penalty of less than one-percent. Also presented are initial temperature characterizations of the yarns.
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Carbon nanotube yarns are micron-scale fibers comprised by tens of thousands of carbon nanotubes in their cross section and exhibiting piezoresistive characteristics that can be tapped to sense strain. This paper presents the details of novel foil strain gauge sensor configurations comprising carbon nanotube yarn as the piezoresistive sensing element. The foil strain gauge sensors are designed using the results of parametric studies that maximize the sensitivity of the sensors to mechanical loading. The fabrication details of the strain gauge sensors that exhibit the highest sensitivity, based on the modeling results, are described including the materials and procedures used in the first prototypes. Details of the calibration of the foil strain gauge sensors are also provided and discussed in the context of their electromechanical characterization when bonded to metallic specimens. This characterization included studying their response under monotonic and cyclic mechanical loading. ...
Strain and Temperature Sensing Properties of Multiwalled Carbon Nanotube Yarn Composites
2008
Strain and temperature response of Multiwalled Carbon Nanotube (MWCNT/CNT) yarns on a stainless steel test beam has been studied. The carbon nanotube yarns are spun from a multiwalled carbon nanotube forest grown on a silicon substrate to a 4-ply yarn with a diameter of about 15-20 microns. Four of the 4-ply CNT yarns are arranged in a Wheatstone bridge configuration on the stainless steel test beam using a thin layer of polyurethane resin that insulates and protects the yarns from the test beam. Strain sensitivities of the CNT yarn sensors range from 1.39 to 1.75 mV/V/1000 microstrain at room temperature, and temperature sensitivity of the CNT yarn bridge is 91 microA/degC. Resistance of the yarns range from 215 to 270 ohms for CNT yarn length of approximately 5 mm. Processes used in attaching the CNT yarns on the test beam and experimental procedures used for the measurements are described. Conventional metallic foil strain gages are attached to the test beam to compare with the C...
Effect of twist on the electromechanical properties of carbon nanotube yarns
Carbon, 2019
Twist is used in dry-spinning of carbon nanotube (CNT) yarn mostly to establish a high degree of association between the loosely bound CNT bundles. By doing so, the CNT yarn undergoes mechanical densification, which increases its strength and changes its electrical properties. The effect of twist on the elastic modulus, tensile strength, strain-to-failure, toughness and piezoresistivity was studied and discussed for CNT yarns subjected to uniaxial tension. Due to the interplay of inter-tube slippage and structural reformation with twist, there is an optimal twist level to achieve desired properties. Low-twist CNT yarns exhibited a lower breaking strength and elongation at rupture but higher elastic modulus compared to medium-and high-twist CNT yarns. The piezoresistive response of the CNT yarns was highest at medium twist followed by high twist levels. Twist-induced compaction in the CNT yarn increases contacts between CNT bundles, improving the mobility of charge carriers. Consequently, porosity is reduced while toughness and conductivity increase with increasing twist. It was observed that specific conductivity of the CNT yarn is not constant but increases with twist angle. The understanding of the piezoresistivity of CNT yarns with respect to twist levels could be useful in optimizing their properties as sensors and actuators.
Piezoresistive Strain Sensors Based on Carbon Nanotube Networks
june 2015 | IEEE nanotEchnology magazInE | 11 S zhEng h. zhu Piezoresistive Strain Sensors Based on Carbon Nanotube Networks Treated CNT/SPU [84] Pristine CNT/PP [85] Pristine CNT/PA12 [86] Pristine CNT/TPU [87] Pristine CNT/IPPAM [88] Pristine CNT/PP12 [89] Pristine CNT/PBT [89] Pristine CNT/PC [89] Pristine CNT/PEEk [89] Pristine CNT/LDPE [89]
A Review: Carbon Nanotube-Based Piezoresistive Strain
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The use of carbon nanotubes for piezoresistive strain sensors has acquired significant attention due to its unique electromechanical properties. In this comprehensive review paper, we discussed some important aspects of carbon nanotubes for strain sensing at both the nanoscale and macroscale. Carbon nanotubes undergo changes in their band structures when subjected to mechanical deformations. This phenomenon makes them applicable for strain sensing applications. This paper signifies the type of carbon nanotubes best suitable for piezoresistive strain sensors. The electrical resistivities of carbon nanotube thin film increase linearly with strain, making it an ideal material for a piezoresistive strain sensor. Carbon nanotube composite films, which are usually fabricated by mixing small amounts of single-walled or multiwalled carbon nanotubes with selected polymers, have shown promising characteristics of piezoresistive strain sensors. Studies also show that carbon nanotubes display a stable and predictable voltage response as a function of temperature.
Sensors (Basel, Switzerland), 2015
This paper describes the development of an innovative carbon nanotube-based non-woven composite sensor that can be tailored for strain sensing properties and potentially offers a reliable and cost-effective sensing option for structural health monitoring (SHM). This novel strain sensor is fabricated using a readily scalable process of coating Carbon nanotubes (CNT) onto a nonwoven carrier fabric to form an electrically-isotropic conductive network. Epoxy is then infused into the CNT-modified fabric to form a free-standing nanocomposite strain sensor. By measuring the changes in the electrical properties of the sensing composite the deformation can be measured in real-time. The sensors are repeatable and linear up to 0.4% strain. Highest elastic strain gage factors of 1.9 and 4.0 have been achieved in the longitudinal and transverse direction, respectively. Although the longitudinal gage factor of the newly formed nanocomposite sensor is close to some metallic foil strain gages, the ...
Carbon nanotube yarns: sensors, actuators, and current carriers
Proceedings of SPIE, 2008
Carbon nanotubes (CNTs) have attracted extensive attention in the past few years because of their appealing mechanical and electronic properties. Yarns made through spinning multi-walled carbon nanotubes (MWNTs) have been reported. Here we report the application of these yarns as electrochemical actuators, force sensors and microwires. When extra charge is stored in the yarns, change in length. This actuation is thought to be because of electrostatic as well as quantum chemical effects in the nanotube backbones. We report strains up to 0.7 %. At the same time, the charged yarns can respond to a change in the applied tension by generating a current or a potential difference that is related to the applied tension force. As current carriers, the yarns offer a conductivity of ~300 S/cm, which increases linearly with temperature. We report a current capacity of more than 10 8 A/m 2 , which is comparable to those of macroscopic metal wires. However, these nanotube yarns have a density (0.8 g/cm 3) that is an order of magnitude lower than metallic wires. The MWNT yarns are mechanically strong with tensile strengths reaching 700 MPa. These properties together make them a candidate material for use in many applications including sensors, actuators and lightweight current carriers
Fused Filament Fabrication of Piezoresistive Carbon Nanotubes Nanocomposites for Strain Monitoring
Frontiers in Materials
Conductive carbon nanotubes (CNT)/acrylonitrile butadiene styrene (ABS) nanocomposites parts were easily and successfully manufactured by fused filament fabrication (FFF) starting from composite filaments properly extruded at a laboratory scale. Specific specimens for strain monitoring application were properly evaluated in both short term and long term mechanical testing. In particular, samples of ABS filled with 6 wt.% of CNT were additively manufactured in two different infill patterns: HC (0 • /0 •) and H45 (−45 • /+45 •). The piezoresistivity behavior was investigated under various loading conditions such as ramp tensile tests at different rate and extension, and also creep and cyclic loading at room temperature. Experimental work revealed that the resistance changes in the conductive samples were properly detectable during stress or strain modification, as consequence of damage and/or reassembling of the percolation network. The measurement of the gauge factor in various testing conditions evidenced an initial higher sensitivity of the 3D-built parts within H45 pattern in comparison to the correspondent HC counterparts. The CNT conductive network path in the investigated samples seems to be reformed during creep and cycling experiments, showing a progressive reduction of gauge factor that seems to stabilize at about 2.5 for both HC and H45 samples after long term testing. These findings suggest that conductive CNT/ABS nanocomposites at 6 wt.% of loading can be successfully processed by FFF to produce stable strain sensors in the range −25 • and +60 • C, as confirmed by the constancy of resistivity in these temperatures.