A carbon nanotube strain sensor for structural health monitoring

Abstract

A carbon nanotube polymer material was used to form a piezoresistive strain sensor for structural health monitoring applications. The polymer improves the interfacial bonding between the nanotubes. Previous single walled carbon nanotube buckypaper sensors produced distorted strain measurements because the van der Waals attraction force allowed axial slipping of the smooth surfaces of the nanotubes. The polymer sensor uses larger multi-walled carbon nanotubes which improve the strain transfer, repeatability and linearity of the sensor. An electrical model of the nanotube strain sensor was derived based on electrochemical impedance spectroscopy and strain testing. The model is useful for designing nanotube sensor systems. A biomimetic artificial neuron was developed by extending the length of the sensor. The neuron is a long continuous strain sensor that has a low cost, is simple to install and is lightweight. The neuron has a low bandwidth and adequate strain sensitivity. The neuron sensor is particularly useful for detecting large strains and cracking, and can reduce the number of channels of data acquisition needed for the health monitoring of large structures.

A Flexible Multifunctional Sensor Based on Carbon Nanotube/Polyurethane Composite

“…The published data show that the electrical response to strain or stress is sufficient and the sensing can be performed in real time [2,3,[10][11][12][13].…”

“…The copper has a GF of about 2.5, the metal sheet strain gauges have values of GF 2-5, GF of the pure MWCNT network (buckypaper) was experimentally determined as 0.34 [1], or 7 [2] at small strain about 0.1 % due to the weak van der Waals attraction between nanotubes. GF of stretchable composite consisting of multi-walled carbon nanotubes network/polyurethane (MWCNT/PU) stretched up to 400 % and GF was found to be nearly 69 at this strain [3].…”

Resistive–conductive transitions in the time-dependent piezoresponse of PVDF-MWCNT nanocomposites

“…Many researchers are applying this phenomenon using various materials systems with a range of electrically conductive fillers. The materials systems, which are being investigated in this study, are thermoplastics, [1][2][3][4][5][6][7][8][9][10][11][12] thermoset resins, 13,14 and cement. 15 Of the various types of nanofillers, carbon nanotubes (CNTs) are the dominant choice when conductivity is necessary, because they provide high strength and modulus at low concentration.…”

“…The main reason for piezoresistance is differences in the compressibility of matrix and filler constituents, material composition, load content and filler content. 11 When the concentration of the filler content is increased, the resistance of the material slowly decreases to the percolation threshold and then decreases rapidly until the conducting particles come in close contact with each other. Once the conducting particles come in close contact, the resistance remains constant at very high filler concentration.…”

“…Previous research on PVDF/MWCNT composites showed various outstanding properties such as a low percolation threshold for electrical conductivity, 26 improved piezoresitivity, 27 improved strain-sensing ability, 28 good interfacial adhesion between nanotubes and PVDF 29 and improved crystallinity. 11 There are very few reports on the timedependent piezoresistive behavior of conducting composites. For HDPE/short carbon fiber conductive composites, Zheng et al 30 suggested that the molecular motion of the matrix due to creep causes local rearrangement of the percolation network, which leads to resistance creep and resistance relaxation.…”