Design, fabrication and validation of a carbon nanotube-based sensor for in-situ acquisition of impact and guided waves

Pao Yue-kong Library Electronic Theses Database

Design, fabrication and validation of a carbon nanotube-based sensor for in-situ acquisition of impact and guided waves

 

Author: Liu, Weijian
Title: Design, fabrication and validation of a carbon nanotube-based sensor for in-situ acquisition of impact and guided waves
Degree: M.Sc.
Year: 2015
Subject: Detectors -- Design.
Detectors -- Testing.
Nanotubes -- Impact testing.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: x, 109 leaves : illustrations ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2817962
URI: http://theses.lib.polyu.edu.hk/handle/200/8049
Abstract: For the purpose of enhancing the efficiency and robustness of existing structural health monitoring (SHM) techniques based on the examination of structural dynamic signals, i.e., vibration, impact and guided wave signals. A novel sensor network was developed in this MSc project. The elements of the sensor network were made of carbon nanotube (CNT)/polymer composite, the sensitivity and stability of which can be conveniently adjusted experimentally. Moreover, it is expected that the sensing elements can be easily coated onto structural surfaces with arbitrarily designed distributions in accordance with the material and geometric properties of tested structures. It is anticipated that the developed sensor network is capable of capturing dynamic signals with much improved accuracy and efficiency compared with traditional sensors, e.g., strain gauges and lead zirconate titanate (PZT) sensor,. In this study, the elements of the sensor network were fabricated experimentally by using multi-wall carbon nanotube (MWNT) and resin epoxy, which were mixed with the assistance of equipment such as three mill roller. As an example, the sensor elements were incorporated into a one-dimensional network, showing potential of measuring dynamic signals in both beam and plate structures. The electromechanical behaviors of the CNT/polymer sensor elements were sophisticatedly investigated. The dispersion of MWNTs in the polymer matrix was examined relying on the assistances of scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM), respectively. The percolation thresholds and resistances of the sensor elements were obtained under different weight fractions of the MWNTs. A measurement system, including an external power supply, a Wheatstone bridge and a voltage amplifier, was then designed referring to the resistance values of the sensor elements. Subject to dynamic tensile and compressive strains, the piezoresistivities of the sensors can be exactly reflected and characterized according to voltage signals obtained using the measurement system. The MWNT/polymer sensors were then utilized to capture dynamic strain signals in beam and plate structures with different material properties (e.g., metal and glass fiber-epoxy composite). Signals subject to impact and guided wave were measured, respectively, and were compared with signals captured using traditional PZT sensors. Some conclusions were made based on the experimental results, and recommendations were proposed to facilitate the further improvement of the sensitivity and stability of the current MWNT/polymer sensors.

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