Development of an innovative nano-engineered sensor network coating and a case study of structural health monitoring of Mass Transit Railway's rails

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Development of an innovative nano-engineered sensor network coating and a case study of structural health monitoring of Mass Transit Railway's rails


Author: Liao, Yaozhong
Title: Development of an innovative nano-engineered sensor network coating and a case study of structural health monitoring of Mass Transit Railway's rails
Degree: M.Sc.
Year: 2016
Subject: Detectors.
Railroads -- Maintenance and repair.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Engineering
Pages: xiv, 157 pages : color illustrations
Language: English
InnoPac Record:
Abstract: In order to overcome the shortcomings of conventional nanocomposite hybrid sensors in sensing high-frequency dynamic strains in micro scale, a novel nanocomposite-based sensor was developed in this M.Sc dissertation. A light weight carbon black (CB)/ polyvinylidenefluoride (PVDF) sensor, which can be used to sense low-frequency vibrations, medium-frequency impact and high-frequency ultrasonic guided waves (GUWs), was fabricated to meet the requirements of in-situ structural health monitoring (SHM). The working principle of CB/PVDF hybrid sensors is related to the tunneling effect. Distances between neighbouring CB particles will change when the sensor senses dynamic elastic disturbances, leading to resistance alteration. It is expected that CB particles can disperse uniformly to form up a perfect conductive network with proper conductivity, avoiding agglomeration of CB particles which may eliminate tunneling effect. Electrical analysis, morphological characterization, and static/dynamic electro-mechanical response interrogation were implemented to explore the microscopic mechanism and meanwhile to help determine an optimal percolation threshold. According to the percolation threshold (~6.5%), 8 wt% CB, which is near the percolation threshold and can form up a proper conductive network in internal structure, was selected to fabricate the novel sensor, which exhibits high-fidelity, fast-response, and high-sensitivity to ultrafast elastic disturbance (in an ultrasonic regime up to 400 kHz) yet with an ultralow magnitude (of the order of micrometer).
The performance of the CB/PVDF hybrid sensor was evaluated. In comparison with traditional piezoelectric transducer and strain gauge, the sensor showed larger gauge factor and frequency-independent piezoresistive behaviours. Moreover, thanks to the excellent mechanical and chemical properties of the nanocomposite hybrid materials used, this novel sensor can be tailored into different geometries and later coated permanently onto structural surfaces to form up a dense sensing network. This nanocomposite sensor, with its light weight and chemical stability, will lead the trend for in-situ structural health monitoring in aviation and aerospace engineering. With the development of fabrication technologies, some improvements will be carried out subsequently to make this composite better (e.g., mixing CB and CNTs together to increase tunneling resistance and using chemical modification technology to reform the surface of nanofillers). An application of SHM system of mass transit railway's (MTR) Rails was carried out in two steps: (1) active examination; (2) passive examination. In the first step, a laboratory experiment was conducted to confirm the propagation velocity of Ultrasonic Guided Waves (GUWs) when they transmited inside a railway track with an artificial damage or a crack. The velocity of the first arrived wave was affirmed by analysing time of flight of GUWs. Later, an actual field test will be conducted to monitor the running status of the operation railway track in Tsuen Wan Line.

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