A numerical approach for modeling carbon nanotube (CNT) percolating network towards development of a CNT-based sensor

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A numerical approach for modeling carbon nanotube (CNT) percolating network towards development of a CNT-based sensor

 

Author: Lu, Bo
Title: A numerical approach for modeling carbon nanotube (CNT) percolating network towards development of a CNT-based sensor
Degree: M.Sc.
Year: 2015
Subject: Carbon nanotubes
Detectors
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xv, 187 leaves : illustrations ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2817853
URI: http://theses.lib.polyu.edu.hk/handle/200/8047
Abstract: To circumvent the drawback of traditional carbon nanotube (CNT) composite sensors in capturing high-frequency dynamic strains in micro level, which largely hampers the application of the sensors in guided-wave-based structural health monitoring (SHM), a multi-scale numerical approach was developed in this M.Sc. dissertation project to facilitate the improvement of the electromechanical behavior of existing CNT composite sensors. A Finite Element (FE) model of CNT/polymer composite, including a pair of adjacent CNTs and polymer matrix, was established to study the local strain-resistance relationship of CNT composite subject to tunneling effects. And the resistance response of the model subject to dynamic strains was also examined with and without the influence from the viscoelastic property of the polymer matrix. A numerical model comprising of a significant number of CNTs was then built to study the statistical behavior of CNT resistor network. The overcall electrical conductivity of the model was calculated based on Kirchhoff Current Law (KCL) and matrix representation method. By adjusting the weight fraction of the CNTs, the percolation threshold of the model was estimated, showing great similarity with existing experimental results. More importantly, the piezoresistivity of the CNT network was comprehensively studied, subject to both tensile and compressive strains. Exponential and linear distributions of resistance change ratio were observed under large and small strain levels, respectively. Moreover, the characteristic of the model{174}s piezoresistivity under harmonic excitation was simulated and discussed. As a proof-of-concept investigation, some experiments were conducted to validate the observations obtained from the proposed multi-scale numerical approach. The fabrication of CNT/polymer composite sensors was introduced. And the percolation thresholds of the sensors were measured and compared with numerical results. Moreover, signals of lamb wave, which were widely adopted in practical SHM, were captured and analyzed using the fabricated sensors. Finally, some important conclusions were made depending on the proposed numerical approaches, revealing the limitations of existing experimental configurations. And some suggestions were given subsequently (e.g., increasing the percentage of tunneling resistances by conducting surface treatment of the CNTs), relying on which the sensitivity and stability of the composite sensors were expected to be largely improved.

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