Author: Pan, Dongyue
Title: Additive manufacturing-driven design and fabrication of nanocomposite sensing units for ultrasonics-based structural health monitoring
Advisors: Su, Zhongqing (ME)
Degree: M.Sc.
Year: 2019
Subject: Hong Kong Polytechnic University -- Dissertations
Structural health monitoring
Structural analysis (Engineering)
Department: Faculty of Engineering
Pages: xii, 107 pages : color illustrations
Language: English
Abstract: In engineering structures, the defects that are initiated from imperceptible fatigue cracks would not give obvious warning until they deteriorate to an irretrievable level. With recognition of this concern, structural health monitoring (SHM) methods have recently emerged to fulfill the damage detection in its preliminary stage and hence provide real-time assessment of the health status of the structure. To implement existing SHM methods, a sensor capable of obtaining signals with high accuracy and fidelity is a prerequisite, so a sensor with better performance is continuously pursued in the field. The sensor inspired by the principle of tunneling effect has opened up a novel avenue for the measurement of ultrasonic waves which feature strain of low amplitude and serve as cornerstone for the ultrasonic guided waves-based SHM methods. To start with, a new breeze of nanocomposite-inspired, lightweight, flexible, broadband ultrasonic sensor is developed in this study. With carbon black (CB) nanoparticles as the filler and polyvinylpyrrolidone (PVP) polymers as the matrix, the sensors are fabricated using two kinds of high-efficiency, rapid prototyping techniques: spraying and inkjet printing. Experimental examination of the spray-coated sensor has demonstrated its sensitivity to guided ultrasonic waves, and its high fidelity which is compatible with conventional lead zirconium titanate ceramics wafers. The nanocomposite sensor is also fabricated using the inkjet printing technique, in which sensor is directly printed on the polyimide film with high resolution. With the high precision of digital printing, the thickness of the sensor can be controlled. Utilizing the scanning electron microscope, it is observed that the conductive networks in the sensor are evenly distributed. With the tunneling effect triggered in the conductive network, the inkjet-printed sensor is able to capture the ultrasonic waves up to 500 kHz accurately. To fabricate a sensing unit that is capable of capturing ultrasonic waves and transmitting signals, the electrodes and connecting circuits are also inkjet-printed through a drop-on-demand process, forming an all-printed sensing unit with the sensor. The inkjet printing method proposed in this study enables the manufacture of customized sensing unit, which is able to adapt complex engineering structures, benefiting for in-situ active ultrasonic-based structural health monitoring.
Rights: All rights reserved
Access: restricted access

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