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Ku, Sin Yee = 添加鎳對網絡結構Fe₈₀C₂₀合金機械性能的影響 / 古倩儀. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Ku, Sin Yee = Tian jia nie dui wang luo jie gou Fe₈₀C₂₀ he jin ji xie xing neng de ying xiang / Gu Qianyi. / Abstract --- p.i / Acknowledgements --- p.v / List of Tables --- p.viii / List of Figures --- p.ix / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Composite Materials --- p.1 / Chapter 1.1.1 --- Parti culate-reinforced Composites --- p.2 / Chapter 1.1.2 --- Fibre-reinforced Composites --- p.2 / Chapter 1.1.3 --- Structural Composites --- p.3 / Chapter 1.1.4 --- Metal Matrix Composites --- p.3 / Chapter 1.2 --- Phase Transformations --- p.4 / Chapter 1.2.1 --- Introduction --- p.4 / Chapter 1.2.2 --- Stability and Equilibrium --- p.4 / Chapter 1.2.3 --- Undercooling --- p.6 / Chapter 1.2.4 --- Solidification of Undercooled Melts --- p.7 / Chapter 1.2.4.1 --- Nucleation --- p.8 / Chapter 1.2.4.1.1 --- Homogeneous Nucleation --- p.8 / Chapter 1.2.4.1.2 --- Heterogeneous Nucleation --- p.9 / Chapter 1.2.4.2 --- Growth --- p.11 / Chapter 1.2.5 --- Binary Systems with a Solid Miscibility Gap --- p.12 / Chapter 1.2.6 --- Phase Separation Mechanisms in a Solid Miscibility Gap --- p.14 / Chapter 1.2.6.1 --- Nucleation and Growth --- p.14 / Chapter 1.2.6.2 --- Spinodal Decomposition --- p.15 / Chapter 1.2.6.2.1 --- Uphill Diffusion --- p.16 / Chapter 1.2.6.2.2 --- Diffusion Equation of Spinodal Decomposition --- p.17 / Chapter 1.2.6.2.3 --- Solution to the Diffusion Equation --- p.19 / Chapter 1.2.7 --- Metastable Liquid Miscibility Gap --- p.21 / Chapter 1.3 --- Mechanical Properties --- p.22 / Chapter 1.3.1 --- Hardness --- p.22 / Chapter 1.3.2 --- Strength --- p.23 / Chapter 1.3.3 --- Ductility --- p.23 / Chapter 1.3.4 --- Strengthening Mechanisms --- p.25 / Chapter 1.3.4.1 --- Grain Boundary Strengthening --- p.25 / Chapter 1.3.4.2 --- Solid Solution Strengthening --- p.26 / Chapter 1.4 --- Objectives of This Project --- p.27 / Figures --- p.29 / References --- p.42 / Chapter Chapter 2: --- Experimental --- p.43 / Chapter 2.1 --- Formation of Bulk Network Nanostructured Alloys --- p.43 / Chapter 2.1.1 --- Preparation of Fused Silica Tubes --- p.43 / Chapter 2.1.2 --- Weighing and Alloying --- p.44 / Chapter 2.1.3 --- Fluxing and Quenching --- p.45 / Chapter 2.2 --- Sample Preparation --- p.46 / Chapter 2.2.1 --- "Cutting, Grinding and Polishing" --- p.46 / Chapter 2.2.2 --- Etching --- p.47 / Chapter 2.2.3 --- Sample Preparation for Transmission Electron Microscopy Analysis --- p.48 / Chapter 2.3 --- Mechanical Tests --- p.49 / Chapter 2.3.1 --- Microhardness Test --- p.49 / Chapter 2.3.2 --- Compression Test --- p.50 / Chapter 2.4 --- Microstructural Analysis --- p.51 / Chapter 2.4.1 --- Scanning Electron Microscopy Analysis --- p.51 / Chapter 2.4.2 --- Transmission Electron Microscopy Analysis --- p.52 / Chapter 2.4.2.1 --- Indexing Diffraction Patterns --- p.52 / Chapter 2.4.2.2 --- Energy Dispersive X-Ray Analysis --- p.53 / Chapter 2.4.2.3 --- Electron Energy Loss Spectroscopy --- p.53 / Figures --- p.55 / References --- p.62 / Chapter Chapter 3: --- Dependence of the Mechanical Properties of FesoC2o Network Alloys on the Addition of Ni --- p.63 / Chapter 3.1 --- Abstract --- p.63 / Chapter 3.2 --- Introduction --- p.64 / Chapter 3.3 --- Experimental --- p.64 / Chapter 3.4 --- Results --- p.66 / Chapter 3.5 --- Discussions --- p.74 / Chapter 3.6 --- Conclusions --- p.79 / Tables --- p.80 / Figures --- p.82 / References --- p.100 / Bibliography --- p.101

The highly optimized hierarchical structure of trabecular bone is a major contributor to its remarkable mechanical properties. At the micro-scale level, individual plate-like and rod-like trabeculae are interconnected, forming a complex trabecular architecture. It is widely believed that bone strength, an important mechanical characteristic that describes the capability of bone to resist fracture, is largely determined by the tissue-level material properties of these microscopic trabecular elements. However, due to the complicated microstructure and irregular morphology of trabecular bone, a link between the tissue-level and the apparent level mechanics in trabecular bone has never been established. Thus, the goal of this thesis is to examine the tissue-level material properties of trabecular bone and their contribution to apparent-level bone mechanics, and ultimately to improve our fundamental understanding and assessment of bone strength in diseased and healthy patients. At the micro-scale level, plate-like and rod-like trabeculae are distinctly aligned along different orientations on the anatomical axis of the skeleton. Also, the highly organized underlying ultrastructure of bone tissue suggests trabecular bone might possess an anisotropic tissue modulus, i.e. different modulus in the axial and lateral cross-section of a trabecula. In this thesis, we studied this tissue-level anisotropy by examining mechanical properties of individual trabecular plates and rods aligned longitudinally, obliquely, and transversely on the anatomical axis using micro-indentation. We discovered that, despite the different orientations of trabeculae, tissue moduli are higher in the axial direction than in the lateral direction for both plates and rods. We also discovered that plates have a higher tissue modulus than rods, suggesting different degrees of mineralization. Furthermore, the tissue mineral density correlated strongly but distinctly with tissue modulus in the axial and lateral directions, providing descriptions on how spatially heterogeneous mineralization at the tissue level affects the tissue modulus. After characterization of the anisotropic and heterogeneous modulus of trabecular bone at the tissue level, we then sought to investigate its contribution to apparent-level mechanical properties, including apparent Young’s modulus and yield strength. Non-linear FE voxel models incorporating experimentally determined anisotropy and heterogeneity were created from micro-computed tomography (µCT) images of healthy trabecular bone samples. Apparent Young's modulus and yield strength predicted by the models were compared to and correlated with gold standard mechanical testing measurements, as well as to the same FE models without incorporation of anisotropy and/or heterogeneity. We discovered that the anisotropic model prediction was highly correlated and indistinguishable from mechanical testing measurements. However, the prediction power of the model was not enhanced by incorporating anisotropy and heterogeneity (compared to a homogeneous and isotropic model), suggesting that variances in tissue-level material properties contribute minimally to the apparent level bone behaviors in healthy bone. However, the possibility remained that a more substantial contribution could arise in diseased bone, particularly diseases in which tissue-level properties are compromised. Therefore, we studied trabecular bone in two diseased conditions – subchondral bone in human knees affected by osteoarthritis and pelvic bone affected by adolescent idiopathic sclerosis – to see how disease can alter the tissue-level and, consequently, apparent-level bone mechanics. In OA bone, we found a significant decrease in tissue modulus in the subchondral bone under severely damaged cartilage compared to control, which provides an explanation for a minimal increase in apparent stiffness with an almost doubled bone volume fraction. In AIS bone, no differences were found in tissue-level or apparent level Young’s modulus compared to control. However, the mineral density was found to play a distinct role in the modulus of growing bone tissue compared to mature bone.

The present work contains two parts: nanofluids and bioheat transport, both involving multiscales and sharing some common features. The former centers on addressing the three key issues of nanofluids research: (i) what is the macroscale manifestation of microscale physics, (ii) how to optimize microscale physics for the optimal system performance, and (iii) how to effectively manipulate at microscale. The latter develops an analytical theory of bioheat transport that includes: (i) identification and contrast of the two approaches for developing macroscale bioheat models: the mixture-theory (scaling-down) and porous-media (scaling-up) approaches, (ii) rigorous development of first-principle bioheat model with the porous-media approach, (iii) solution-structure theorems of dual-phase-lagging (DPL) bioheat equations, (iv) practical case studies of bioheat transport in skin tissues and during magnetic hyperthermia, and (v) rich effects of interfacial convective heat transfer, blood velocity, blood perfusion and metabolic reaction on blood and tissue macroscale temperature fields. Nanofluids, fluid suspensions of nanostructures, find applications in various fields due to their unique thermal, electronic, magnetic, wetting and optical properties that can be obtained via engineering nanostructures. The present numerical simulation of structure-property correlation for fourteen types of two/three-dimensional nanofluids signifies the importance of nanostructure’s morphology in determining nanofluids’ thermal conductivity. The success of developing high-conductive nanofluids thus depends very much on our understanding and manipulation of the morphology. Nanofluids with conductivity of upper Hashin-Shtrikman bounds can be obtained by manipulating structures into an interconnected configuration that disperses the base fluid and thus significantly enhancing the particle-fluid interfacial energy transport. The numerical simulation also identifies the particle’s radius of gyration and non-dimensional particle-fluid interfacial area as two characteristic parameters for the effect of particles’ geometrical structures on the effective thermal conductivity. Predictive models are developed as well for the thermal conductivity of typical nanofluids. A constructal approach is developed to find the constructal microscopic physics of nanofluids for the optimal system performance. The approach is applied to design nanofluids with any branching level of tree-shaped microstructures for cooling a circular disc with uniform heat generation and central heat sink. The constructal configuration and system thermal resistance have some elegant universal features for both cases of specified aspect ratio of the periphery sectors and given the total number of slabs in the periphery sectors. The numerical simulation on the bubble formation in T-junction microchannels shows: (i) the mixing enhancement inside liquid slugs between microfluidic bubbles, (ii) the preference of T-junctions with small channel width ratio for either producing smaller microfluidic bubbles at a faster speed or enhancing mixing within the liquid phase, and (iii) the existence of a critical value of nondimensional gas pressure for bubble generation. Such a precise understanding of two-phase flow in microchannels is necessary and useful for delivering the promise of microfluidic technology in producing high-quality and microstructure-controllable nanofluids. Both blood and tissue macroscale temperatures satisfy the DPL bioheat equation with an elegant solution structure. Effectiveness and features of the developed solution structure theorems are demonstrated via examining bioheat transport in skin tissues and during magnetic hyperthermia. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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This study describes the biomechanics of the foot and ankle during the transitional and steady state skating strides using kinematic, kinetic, and myoelectric measures. A data set for five collegiate hockey players was completed (mean +/- SD: age = 21.8 +/- 1.9 years, height = 1.81 +/- 0.05 m, mass = 83.3 +/- 8.0 kg). Three acceleration strides and a constant velocity stride were examined on ice. An electrogoniometer at the ankle was used to measure angular displacement and velocity values. Myoelectric activation patterns were measured at the vastus medialis, tibialis anterior, peroneus longus, and medial gastrocnemius of the right lower limb. Kinetic pressure profiles were measured using piezo resistive fabric sensors providing accurate pressure measurement within the narrow confines of the skate boot-to-foot/ankle interface. Sixteen flexible piezo-resistive sensors (1.2 cm x 1.8 cm x 0.2 cm thick) were taped to discrete anatomical surfaces of the plantar, dorsal, medial and lateral surface of the foot, as well as to the posterior aspect of heel and leg. Repeated measures ANOVAs and Tukey post hoc tests found few significant differences among stride variables; however insights into the mechanics of ice hockey skating at the foot and ankle are given.

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