Cheung, Hoi Cheung = Fe₈₁C₁₄Si₅旋節合金的變形 / 張凱翔. / "December 2010" / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Cheung, Hoi Cheung = Fe₈₁C₁₄Si₅ xuan jie he jin de bian xing / Zhang Kaixiang. / Abstract --- p.i / Acknowledgements --- p.iii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Spinodal Decomposition --- p.1 / Chapter 1.3 --- Theory of Elasticity --- p.5 / Chapter 1.4 --- Deformation of Metals --- p.9 / Chapter 1.5 --- Fracture Mechanics --- p.10 / Chapter 1.6 --- Contact Mechanics --- p.12 / Chapter 1.7 --- Indentation Fracture --- p.16 / Chapter 1.8 --- Deformation and Failure of Tungsten Carbide --- p.20 / References --- p.22 / Figures --- p.25 / Chapter Chapter 2 --- Experiment / Chapter 2.1 --- Sample Preparation --- p.40 / Chapter 2.2 --- Indentation --- p.42 / Chapter 2.3 --- Analysis Method --- p.43 / References --- p.46 / Figures --- p.47 / Chapter Chapter 3 --- Result and Discussion / Chapter 3.1 --- Introduction --- p.50 / Chapter 3.2 --- Deformation on the Top Surfaces --- p.50 / Chapter 3.3 --- Deformation on the Side Surfaces --- p.52 / Chapter 3.4 --- A comparison with Tungsten Carbide (WC/Co) --- p.59 / Chapter 3.5 --- Discussion --- p.60 / Chapter 3.6 --- Conclusion --- p.63 / References --- p.64 / Figures --- p.67

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Rice hull ash (RHA) is a by-product of the rice industry. RHA is produced when rice hulls are incinerated, for example, when they are used to power steam engines in rice milling plants. Typically, this ash is disposed of in landfill sites, which may cause environmental problems. RHA has a naturally occurring silica content that is very high, ranging from 95 to 98%. This high silica content makes RHA a potential filler for polymer products. The aim of this project was to investigate the application of RHA as a filler in polypropylene. The study used a systematic approach to characterising the RHA physiochemical properties and comparing these to another commercially available grade of silica filler. The processing conditions for mixing RHA with Polypropylene (PP) were optimised to obtain the maximum tensile modulus value. Attempts were made to improve the interaction of RHA and PP by treating the RHA surface with silane coupling agents and adding functionalised polymers to the composite. Mechanical, rheological and morphological properties of the non-silanated, silanated and coupled composites were characterised and compared to determine their structure -property relationships. Rice hull ash (RHA) has a similar chemical structure to other silicas. Like any metals and metalloids, the surface of RHA contains -OH functional groups but these are very limited in quantity. RHA and PP composites have a wide processing window and the optimised processing conditions in a small batch mixer are 12 minutes, 60 rpm and 180°C. Addition of RHA into PP increases the modulus but decreases the tensile strength of the composites, attributed to poor compatibility between RHA and PP, as RHA is hydrophilic and PP is hydrophobic. The optimum loading of RHA is 20wt%. To improve the RHA and PP composites, 2 grades of silane and maleic anhydride grafted PP (MAPP) is used. Silane treated RHA composites have improved mechanical properties, especially tensile strength, attributed to enhanced interfacial interaction. The optimum is 1.5wt% for APS and 2.wt% for MPS in this system. The optimum MAPP concentration in this system is 3wt%. Properties of the RHA / PP composites show modest improvements compared to PP. The properties are not sufficient to make RHA a commercially attractive reinforcing filler for PP for high performance composite. It has potential for a cost reduction filler for low end application composites.

Mechanical behavior of Nb-Ti superconducting composites with copper matrices have been studied experimentally and theoretically. Experimental work includes extensive measurements of Cu/Nb-Ti composite system. Techniques for fine fiber testing and composite wire measurement have been developed. Experimental parameters examined in this research include geometry, hardness, Young's modulus, Poisson's ratio, yield strength and ultimate strength. Three theoretical models have been developed to study the mechanics of the Cu/Nb-Ti composite system. The influence of several design parameters on the mechanics of the Nb-Ti composites was studied and provides some insight on superconducting composite design for improvements in processing and performance. The mechanical behavior of the Cu/Nb-Ti composite system are found to be functions of geometry, composition and processing. Geometry of Nb-Ti superconducting composites is different from most engineering composites and there are two factors affecting sample geometry: the variability of fiber geometry and the placement of fibers within the composite. The strength distribution of Nb-Ti fibers is closely related to the distribution of fiber geometry and the composite strength increases as the scatter of fiber strength decreases. Heat treatment reduces the hardness of the bulk copper dramatically. The first heat treatment increases the strength and hardness of the Nb-Ti fibers, further heat treatments reduce the strength and hardness while increasing Young's modulus of the fibers. As the extent of cold work increases, the strength of Nb-Ti fibers and that of the composite wires increases. Cold work effects on the Young's modulus of the composites and the Nb-Ti fibers are not significant. For a constant global Cu/SC ratio, the lower the local Cu/SC ratio, the lower the micro-in-plane stresses. From this point of view, the fibers should be packed as close as possible to one another. For a constant local Cu/SC ratio, when the inner radius of the Nb-Ti assembly increases (the fibers are packed further from center), the macro-in-plane stresses increase. From this point of view, the fibers should be packed as close to the center of the wire as possible. For a constant geometry, the higher the difference between E[subscript f] and E[subscript m], the lower the in-plane stresses, and the higher the difference of the Poisson's ratio between the components, the higher the in-plane stresses. / Graduation date: 1995

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 119-121). Also available in electronic version.

Cryogenic composites find critical application in the manufacture of fuel tanks for reusable launch vehicles due to significant reduction in overall structural weight of the tank. These fuel tanks contain pressurized cryogen such as hydrogen at cryogenic temperatures. Exposure to varying temperatures and mechanical loads resulting from flight cycle, containment of pressurized cryogen causes thermo-mechanical loading of the composite. The thermo-mechanical loading cycles combined with anisotropy of the composite and mismatch in the thermal and mechanical properties of fibers and matrix lead to transverse matrix cracks (TMC) in each ply. TMC in adjacent plies intersect in localized regions at ply interfaces called crack junctions, which open up due to delamination on application of thermo-mechanical load. TMC and crack junctions usually form a network of leakage paths that assists leakage of cryogen through the composite. In this study, the volumetric flow rate of cryogen leaking through a damaged cross-ply composite with five plies is determined by estimating the effective conductance of the leakage paths. For a given damage state and applied load, crack junction and TMC openings are obtained by finite element analysis. A computational fluid dynamics model is first used to estimate the effective conductance of a leakage path to hydrogen leakage and then a simplified analytical model is used to compute the effective conductance from individual conductances of each crack junction and TMC through a series-parallel combination. A single phase flow model is considered for the numerical analysis of hydrogen flow through TMC and crack junctions. The simulations are carried out using a commercial computational fluid dynamics software, FLUENT. Parametric studies are carried out to investigate the dependence of leak rate of hydrogen on the irregularities of the TMC geometry and TMC, crack junction openings. The simplified model predictions of the effective conductance for the five ply composite show good comparison with numerical simulations.

Abstract The Nylon and liquid crystal polymer(LCP) filled with conductive carbon fiber applied to 155Mbps and 1.25Gbps transceiver modules for electromagnetic(EM) shielding were studied. The measured results showed that the shielding effectiveness(SE) of 155Mbps and 1.25Gbps transceiver module were 13dB and 20dB to conform to FCC class B standard, respectively. This indicates that the plastic housing filled with conductive carbon fiber is suitable for EM shielding in plastic laser transceiver module applications.

Cryogenic composites find critical application in the manufacture of fuel tanks for reusable launch vehicles due to significant reduction in overall structural weight of the tank. These fuel tanks contain pressurized cryogen such as hydrogen at cryogenic temperatures. Exposure to varying temperatures and mechanical loads resulting from flight cycle, containment of pressurized cryogen causes thermo-mechanical loading of the composite. The thermo-mechanical loading cycles combined with anisotropy of the composite and mismatch in the thermal and mechanical properties of fibers and matrix lead to transverse matrix cracks (TMC) in each ply. TMC in adjacent plies intersect in localized regions at ply interfaces called crack junctions, which open up due to delamination on application of thermo-mechanical load. TMC and crack junctions usually form a network of leakage paths that assists leakage of cryogen through the composite. In this study, the volumetric flow rate of cryogen leaking through a damaged cross-ply composite with five plies is determined by estimating the effective conductance of the leakage paths. For a given damage state and applied load, crack junction and TMC openings are obtained by finite element analysis. A computational fluid dynamics model is first used to estimate the effective conductance of a leakage path to hydrogen leakage and then a simplified analytical model is used to compute the effective conductance from individual conductances of each crack junction and TMC through a series-parallel combination. A single phase flow model is considered for the numerical analysis of hydrogen flow through TMC and crack junctions. The simulations are carried out using a commercial computational fluid dynamics software, FLUENT. Parametric studies are carried out to investigate the dependence of leak rate of hydrogen on the irregularities of the TMC geometry and TMC, crack junction openings. The simplified model predictions of the effective conductance for the five ply composite show good comparison with numerical simulations.

This thesis focused on making composites consisting of a polymethylmethacrylate matrix, with various carbon fillers. The fillers that were examined were 3 different carbon blacks: N-550, N-772 and pureblack, and short multi-wall carbon nano-tubes. The carbon fillers were coated onto the polymethylmethacrylate, and compression molded in order to form a segregated microstructure. The goal of this thesis is to compare the electrical and optical properties of the composites consisting of a segregated microstructure, containing various carbon fillers. Scanning electron microscopy was used to investigate the fracture surface of the composites. Impedance Spectroscopy measured the electrical response of the material, and was used to determine the conductivity and dielectric properties of the composites and estimate the percolation threshold. The multi-wall carbon nano-tubes were found to have the lowest percolation threshold, due to their rod like structure. All of the carbon black fillers displayed similar characteristics in their conductivity and dielectric properties. As the filler content increased, the conductivity and the dielectric constant of the composites increased. Optical absorption measurements determined the amount of light that travel through the specimen. These measurements, showed that the absorbance for the carbon black sample N-550 were lower than the multi-wall carbon nano-tubes at filler contents below a phr of 0.1 The absorption of the carbon black samples was then higher than multi-wall carbon nano-tubes at phrs higher than 0.1. This was found to be related to the nano-tubes starting to form a segregated microstructure at lower filler contents than the sphere-like carbon black nano-particles.

Reproduction de : Thèse de doctorat : Génie des procédés et de l'environnement : Toulouse, INPT : 2005. / Titre provenant de l'écran-titre. Bibliogr. 88 réf.