The thermodynamic behaviors of multicomponent, elastic, crystalline solids under stress and electro-magnetic fields are developed, including the extension of Euler’s equation, Gibbs equation, Gibbs-Duhem equation, the conditions to be expected at equilibrium, and an extension of the Gibbs phase rule. The predictions of this new phase rule are compared with experimental observations. The stress deformation behaviors of the single martensitic crystal with and without magnetic fields were studied with the stress deformation equation derived by Slattery and Si (2005). One coherent interfacial condition between two martensitic variants was developed and used as one boundary condition of the problem. The dynamic magnetic actuation process of the single crystal actuator was analyzed. The extension velocity and the actuation time of the single crystal actuator are predicted. The relationship between the external stress and the extension velocity and the actuation time with the presence of a large external magnetic field was studied. The extended Gibbs-Duhem equation and Slattery-Lagoudas stress-deformation expression for crystalline solids was used. Interfacial constraints on the elastic portion of stress for crystalline-crystalline interfaces and crystalline-fluids or crystallineamorphous solids interfaces were derived and tested by the oxidation on the exterior of a circular cylinder, one-sided and two-sided oxidation of a plate. An experiment for measuring solid-solid interface surface energies was designed and the silicon-silicon dioxide surface energy was estimated. A new generalized Clausius-Clapeyron equation has been derived for elastic crystalline solids as well as fluids and amorphous solids. Special cases are pertinent to coherent interfaces as well as the latent heat of transformation.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 97-108). Also available in print.

Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Kumar, Satish; Committee Member: Garmestani, Hamid; Committee Member: Graham, Samuel; Committee Member: Griffin, Anselm; Committee Member: Shofner, Meisha. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This dissertation introduces a new approach to measure the mechanical properties of soft tissues. A laser-induced microbubble, created by focusing a single nanosecond laser pulse with a custom-made objective lens, was created at desired locations inside a tissue sample. An acoustic radiation force was generated by a low frequency transducer to displace the microbubble. A custom-built high pulse repetition frequency (PRF) ultrasound system, consisting of two 25 MHz single element transducers, was used to track the dynamics of the microbubble. Reconstruction of the mechanical properties at the specific location in a tissue sample was performed using a theoretical model, which calculated the dynamics of a microbubble under an externally applied force in a viscoelastic medium. The theoretical model and the high PRF ultrasound system were successfully validated in both gelatin phantoms and ex vivo bovine crystalline lenses. Age-related sclerosis of the crystalline lenses from bovine was clearly detected, which might be linked to changes in the crystalline. Location-dependent variation explained that the outer cortex and the inner nucleus had different mechanical properties. In the old and young porcine vitreous humors, age-related changes were not found. However, local variations of the mechanical properties were discovered, which may coincide with the different distributions of the molecular compositions. The laser-induced microbubble approach shows potential for future research into the origin of physiological phenomena and the development of inherent disorders in the eye. I hope that further studies – in the development of a more suitable theoretical model for the microbubble dynamics, in extension to in vivo applications, and in defining the relationship of the mechanical properties to molecular components in the eye – may provide a plan for the therapeutic treatment of eye-related diseases. / text

Semi-crystalline polymers have shown increased crystalline order and size when confined in multilayered films by coextrusion1. The resulting large crystals lead to dramatic improvements in gas barrier properties. Ordered polymers whose characteristics are between that of the liquid phase and the crystalline phase are known as liquid crystalline polymers. The highly ordered mesogens in liquid crystalline polymers contribute to their exceptional bulk properties. In this research, side-chain liquid crystalline polymers were confined in multilayered films, made by either multilayer coextrusion or spin coating, with a non-liquid crystalline polymer in an attempt to improve the ordering of the liquid crystalline mesogens. The liquid crystalline behavior and morphology was studied to understand the correlation between the confinement size and the properties of the multilayer films. Commercial main chain liquid crystalline polymers and hydrogen bonded liquid crystalline polymers were also explored in this research for their use in multilayer coextrusion. / text

Polyetheretherketone (PEEK), a polymer with mechanical strength comparable to human bone, is gaining popularity in the orthopedic field because it can potentially relieve the clinical complications, such as stress shielding effect and inevitable implantation failure, which are caused by the mismatch of the mechanical strength between the current metallic implants and the implantation sites. However, it is bio-inert and requires supplementary modification. Plasma immersion ion implantation (PIII) has been well documented that it is a good way to improve the bioactivity of a biomaterial. It is a method that introduces new elements to the biomaterial, generating bio-functional groups on the material surface without altering its mechanical properties. Hence, the aim of this study is to improve the bioactivity of PEEK by modifying its surface chemistry with the use of water (H2O) and ammonia (NH3) plasma immersion ion implantation (PIII) without altering its mechanical properties. After PIII treatment, a series of surface characterization tests that provide information about the surface properties, such as surface energy, roughness, surface chemical composition and crystallinity of PIII-treated PEEK were carried out. Results show that both H2O PIII and NH3 PIII-treated PEEK had significantly higher surface energy and roughness than untreated PEEK. There was also no significant change in the crystallinity of the PIII-treated PEEK, indicating that PIII treatment will not alter the mechanical properties of PEEK. Improvement in wetting properties of PEEK samples suggest the formation of polar functional groups on the PIII-treated PEEK materials, while the increased in surface roughness may be due to the energetic bombardments of plasma ions on the material surface. The in vitro bioactivity of plasma-treated PEEK was investigated and confirmed with hMSC-TERT. Initial cell attachment, cell spreading area, cell proliferation and differentiation were studied. Cell adhesion and cell spreading were enhanced on PIII-treated PEEK, and higher cell viability was observed on PIII-treated PEEK. Moreover, cell proliferation was promoted on early time point and cell differentiation was also enhanced particularly on day 7 by measuring the alkaline phosphatase activity. Therefore, H2O-PIII and NH3-PIII treatments were able to promote the bioactivity of PEEK samples. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

We examine various models of soft matter, and one model of quasicrystals, focusing on abrupt changes as density is varied. We consider in detail two models, one of granular matter and another of confined wires, showing that the models become ordered as density is increased, with crystalline order observed in the former and nematic order observed in the latter. We associate the phenomenon of random close packing with the onset of crystalline order in our granular model, and we conjecture that crumpled wires should exhibit a nematic transition with increasing compaction. We also consider two other models of granular matter: one which describes dilatancy onset as a second order phase transition, and one which describes random loose packing as a precise, well- defined density. Finally, we examine an equilibrium model of quasicrystals with a first order phase transition to a solid phase without any crystalline order. / text

With the continuing trend towards miniaturization, micro milling plays an increasingly important role in fabrication of freeform and high-accuracy micro parts or components directly and cost-effectively. The technology is in kinematics scaled down from the conventional milling, however, existing knowledge and experiences are limited and comprehensive studies on the micro tooling performance are essential and much needed particularly for the process planning and optimization. The cutting performance of micro tools is largely dependent on the dynamic performance of machine tools, tooling characteristics, work material properties and process conditions, and the latter three aspects will be focused in the study. The state of the art of micro milling technology with respect to the tooling performance has been critically reviewed, together with modelling work for performance prediction as well as metrology and instrumentation for the performance characterization. A novel 3D finite element method taking into account the geometry of a micro tool, including the tool diameter, rake angle, relief angle, cutting edge radius and helix angle, has been proposed for modelling and simulation of the micro milling process. Validation through well-designed micro milling trials demonstrates that the approach is capable of characterizing the milling process effectively. With the support of FEM simulation developed, the tooling geometrical effects, including those from helix angle, rake angle and cutting edge radius with influences on cutting forces, tool stresses, tool temperatures, milling chip formation and temperatures have been comprehensively studied and compared for potential micro tool design and optimization purposes. In an effort to prolong the tool life and enhance the tooling efficiency, DLC and NCD coatings have been deposited on micro end mills by PE-CVD and HF-CVD processes respectively. Corresponding cutting performance of these coated tools have been assessed and compared with those of WC micro tools in both dry and wet cutting conditions so as for better understanding of the coating influence on micro tools. Furthermore, the cutting characteristics of the DLC coated and uncoated tools have been analysed through verified plane-strain simulations. The effects of coating friction coefficient, coating thickness and UCT have been determined and evaluated by design of simulation method. Mechanical, chemical and physical properties of a work material have a direct influence on its micro-machinability. Five most common engineering materials including Al 6061-T6, C101, AISI 1045, 304 and P20, have been experimentally investigated and their micro milling behaviours in terms of the cutting forces, tool wear, surface roughness, and micro-burr formation have been compared and characterized. Feed rate, cutting speed and axial depth of cut constitute the complete set of process variables and they have significant effects on the tooling performance. Fundamental understanding of their influences is essential for production engineers to determine optimum cutting parameters so as to achieve the maximum extension of the tool life. 3D FE-based simulations have been carried out to predict the process variable effects on the cutting forces, tool stresses, tool temperatures as well as micro milling chip formation and temperatures. Furthermore, experimental approach has been adopted for the surface roughness characterization. Suggestions on selecting practical cutting variables have been provided in light of the results obtained. Conclusions with respect to the holistic investigation on the tooling performance in micro milling have been drawn based on the research objectives achieved. Recommendations for future work have been pointed out particularly for further future research in the research area.

Crystalline silicon solar cells translate energy from the sun into electrical energy via the photoelectric effect. This technology has the potential to simultaneously reduce carbon emissions and our dependence on fossil fuels. The cost of photovoltaic energy, however, is still higher than the cost of electricity off of the grid which hampers this technologies adoption. Raising solar cell efficiency without significantly raising the cost is crucial to lowering the cost of photovoltaic produced energy. One technology which holds promise to increase solar cell efficiency is a selective emitter solar cell. In this work the benefit of selective emitter solar cells is quantified through numerical modeling. Further, the use of ultraviolet laser to create a laser doped selective emitter solar cell is explored. Through optimization of the laser doping process to minimize laser induced defects it is shown that this process can increase solar cell efficiency to over 19.1%. Additionally, 2D and 3D numerical modeling are performed to determine the limitations screen printed interdigitated back contact solar cells and the practical efficiency limit for crystalline Si solar cells.

We numerically investigate crystalline order on negative Gaussian curvature capillary bridges. In agreement with the experimental results in [W. Irvine et al., Nature, Pleats in crystals on curved surfaces, 2010, 468, 947] we observe for decreasing integrated Gaussian curvature, a sequence of transitions, from no defects to isolated dislocations, pleats, scars and isolated sevenfold disclinations. We especially focus on the dependency of topological charge on the integrated Gaussian curvature, for which we observe, again in agreement with the experimental results, no net disclination for an integrated curvature down to −10, and an approximately linear behavior from there on until the disclinations match the integrated curvature of −12. In contrast to previous studies in which ground states for each geometry are searched for, we here show that the experimental results, which are likely to be in a metastable state, can be best resembled by mimicking the experimental settings and continuously changing the geometry. The obtained configurations are only low energy local minima. The results are computed using a phase field crystal approach on catenoid-like surfaces and are highly sensitive to the initialization.