Browsing by Subject "interface"
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Item Applications of the thermodynamics of elastic, crystalline materials(Texas A&M University, 2006-10-30) Si, XiuhuaThe 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.Item Developing a Framework for a New Visual-Based Interface Design in Autodesk Maya(2012-10-19) Withers, Timothy ClaytonIn this thesis, I develop an efficient and user-friendly node-based interface to be used in the creation of a particle system in Autodesk Maya. Maya's interface inconsistencies were identified and solutions were designed based on research in a number of fields related to human-computer interaction (HCI) as well as taking design queues from other highly successful 3D programs that employ a node-based interface. This research was used to guide the design of the interface in terms of organizing the data into logical chunks of information, using color to help the user develop working mental models of the system, and also using simple, easy to identify, graphical representations of a particle system. The result is an easy-to-use and intuitive interface that uses a visual-based approach in creating a particle system in Maya. By following guidelines laid out by previous researchers in the field of HCI, the interface should be a less frustrating to use and more organized version of Maya's current interface.Item Interfacial Interactions between Biomolecules and Materials(2012-10-19) Rocha-Zapata, AracelyThis research investigates the interfacial interactions between biological entities and synthetic materials at two length scales: bulk and nanometer size. At the bulk scale, biomolecule adhesion is key for synthetic material incorporation in the body. Quantifying the adhesion strength becomes necessary. For the nanometer scale, the nanoparticles are generally delivered through the blood stream and their effect on the blood flow must be studied. An experimental approach was taken to study interaction at both material length scales. The cell/protein adhesion strength to bulk-sized materials was studied. The goal was to identify the most influential factor affecting adhesion: chemistry or surface roughness. The effects of nanoparticles on the viscosity of protein and amino acid solutions were measured. A statistical thermodynamic analysis was focused on the entropy change induced by the addition of gold nanoparticles to protein/amino acid solutions. Rheological studies were applied. A rheometer with a parallel plate was used to quantify the adhesion strength of cells and proteins to synthetic surfaces at the bulk scale. The adhesion strength depends on the applied shear stress and the radius of cells or proteins that remained attached to the surface after testing. At the nanometer scale, the viscosity of the nanoparticle enhanced protein or amino acid solutions were measured with a cone and plate. The adhesion studies were conducted with the following biological entities: fibroblasts, egg-white protein, and neurons. The fibroblast adhesion to poly(carbonate) and poly(methyl methacrylate) demonstrate fibroblasts are strongly attached to highly polar materials. Protein adhesion to titanium and chromium nitride coatings showed that chemical composition is the most influential factor. The neuron adhesion to poly-D-lysine coated glass demonstrated that neuron strengthening was due to an increase in adhesion molecules at the neuron/material interface. For nanoparticulates, it was found that the charged nanoparticles affect the protein and amino acid conformation and the potential energy of the solutions. Quantifying biomolecule adhesion to surfaces and predicting the behavior of nanoparticles inside a biological system are crucial for material selection and application. The major impact of this research lies in observing the interaction mechanisms at the interfaces of material-biological entities.Item Investigation of Interfaces Under Mechanical and Thermal Loading Using a Cohesive Zone Model(2014-04-28) Ozsoy, Ovul OzguFailures of structures is a great concern of engineering for longer and safer service life. The ability to predict a damage and failure depends on understanding the deformation and stress that develop in the material. Damage (micro level failures) and failures often initiate at material interfaces. Interactions between different material phases, as well as crack initiation and propagation, make fracture and damage processes very difficult to analyze. The interfaces between dissimilar layers in the functionally graded hybrid material (FGHC) are the most critical for reliability. The use of different processes and materials to fabricate a hybrid material induce mismatch strains, making interfacial failure a primary damage mechanism. As advanced materials are introduced in load bearing structures in aerospace applications to improve performance, maintenance, and manufacturing, designing safe interfaces becomes a paramount goal. Creating seamless interfaces and mechanical locking between metal and polymer matrix composite layers is possible by fabricating a metal surface with various surface features. One of the joining methods is using carbon nano tube grown on the fabric surface, with the subsequent infusion of resin. This method makes use of grown forest of carbon nano tubes using carbon vapor deposition. Experimental techniques are well established for determining interlaminar fracture in composite material systems. The mode I interlaminar fracture toughness can be obtained by the mode I test standard, which uses double cantilever beam specimen. Similarly, mode II and mixed-mode properties are extracted by designated test standards, such as end-notch flexure test and mixed mode bending test. Double cantilever beam test is conducted to explore fracture toughness of hybrid interfacesmodi ed by carbon nanotube grown on carbon fabric and Ti-foil as a function of temperature to assess its potential use within FGHC. It is seen that fracture toughness of modi ed interfaces in mode I is higher than the unmodified ed interfaces. In the present study, computational assessment of joining a metal laminate to carbon ber reinforced polymer (CFRP) laminate was undertaken to investigate interlaminar response and mode I and II delamination toughness. The objective of the present research was to develop a computational model to study delamination in laminated composite plates subjected to bending and extensional loads, and to study di erent joining techniques, as well as to predict the thermomechanical interfacial response. This model incorporates extreme environment conditions, such as high temperature to study these joining techniques. Experimental data of DCB tests were obtained in collaboration with Dr. Ochoa's group in order to validate and verify the computational solutions. The results of this study are expected to provide a better understanding of interface mechanical behavior, thereby provide both materials scientists and designers in selecting alternate material systems and interfaces so that enhanced structural properties such as interfacial strength and durability of the joints subject to out-of-plane bending, impact, and fatigue loading are realized.Item Mechanical Properties and Radiation Tolerance of Metallic Multilayers(2011-08-08) Li, NanHigh energy neutron and proton radiation can induce serious damage in structural metals, including void swelling and embrittlement. Hence the design of advanced metallic materials with significantly enhanced radiation tolerance is critical for the application of advanced nuclear energy systems. The goals of this dissertation are to examine the fundamental physical mechanisms that determine the responses of certain metallic multilayers, with ultra-high density interface structures, to plastic deformation and high fluence He ion irradiation conditions. This dissertation focuses on the investigation of mechanical and radiation responses of Al/Nb and Fe/W multilayers. Radiation induced microstructural evolution in Cu and Cu/Mo multilayer films are briefly investigated for comparisons. Al/Nb multilayer films were synthesized by magnetron sputtering at room temperature. The interface is of Kurdjumov-Sachs orientation relationship. In situ nanoindentation inside a transmission electron microscope (TEM) reveal that interfaces act as strong barriers for dislocation transmission and dislocations climb along the Al/Nb interfaces at a much higher velocity than in bulk. The evolution of microstructure and mechanical properties of Al/Nb multilayers has been investigated after helium ion irradiations: 100 keV He+ ions with a dose of 6x10^16/cm2. When layer thickness, h, is greater than 25 nm, hardness barely changes, whereas radiation hardening is more significant at smaller h. This study shows that miscible fcc/bcc interface with large positive heat of mixing is not stable during ion irradiation. In parallel we investigate sputtered Fe/W multilayers. Film hardness increases with decreasing h, and approaches a maximum of 12.5 GPa when h = 1 nm. After radiation, radiation hardening is observed in specimens when h >/= 5 nm, however, hardness barely changes in irradiated Fe/W 1 nm specimens due to intermixing. In comparison, Cu/Mo 5 nm multilayers with immiscible interface has also been investigated after helium ion irradiations. Interfaces exhibit significantly higher helium solubility than bulk. He/vacancy ratio affects the formation and distribution of He bubbles. The greater diameter of He bubbles in Cu than Mo originates from the ease of bubble growth in Cu via punching of interstitial loops. Finally, helium bubble migration and growth mechanisms were investigated in irradiated Cu (100) single crystal films via in situ heating inside a TEM. The activation energy for bubble growth is ~ 0.02 eV at low temperature. At higher temperatures, the activation energy for bubble coalescence is ~ 0.22 eV inside crystal, and 0.34 eV close to surface. The migration mechanisms of helium bubbles involve continuous as well as Brownian movement.Item Nanoengineered Thin Films for Solid Oxide Fuel Cells(2013-11-21) Su, QingSolid oxide fuel cells (SOFCs) are very attractive as energy generation devices because of their high energy efficiency, flexible fuel selections and clean energy conversion. To avoid cell cracking and formation of non-conducting compounds at electrolyte/electrode interfaces issues caused by high operating temperatures (~1000 ?C for conventional SOFCs), intermediate temperature SOFCs (ITSOFCs) in the range of 500-700 ?C have attracted extensive research interests. However, the polarization loss of cathode and ohmic loss of electrolyte significantly increases under reduced temperatures which lead to decreased cell performance and power output. To address the above issues, the efforts in this work are focused on engineering microstructure of cathode, electrolyte and their interface to achieve high performance. First, a bi-layer method has been developed to prepare La0.5Sr0.5CoO3 (LSCO) cathode by combining a pulsed laser deposition (PLD) technique and a screen printing method. It provides a cost-effective approach to fabricate thick and high quality cathode films and the method could also be applied to many other cathode systems. Second, detailed PLD interlayer thickness effect is investigated. The mechanical and electrochemical properties of those hybrid cathodes are examined and correlated with the microstructure of the cells with different interlayer thicknesses. Third, partial oxygen pressure AC impedance study has been carried on those bi-layer cathodes with different interlayer thicknesses. The guidelines for designing high-performance bi-layer cathodes with optimum performance and low cost are proposed. Fourth, the design of a La0.8Sr0.2MnO3-?/Zr0.92Y0.08O2 thin interlayer with a vertically-aligned nanocomposite (VAN) structure between the electrolyte and oxygen electrode is demonstrated for solid oxide reversible fuel cells. The VAN structure significantly improves the overall cell performance and also acts as a transition layer that improves adhesion and relieves both thermal stress and lattice strain. Fifth, Two-phase (Ce0.9Gd0.1O1.95)0.5/(Zr0.92Y0.08O1.96)0.5 nanocomposite thin films with vertically aligned structure are grown as the electrolyte for thin film solid oxide fuel cells (TFSOFCs). More than 50% increase in overall power density is achieved compared with that of the cells without VAN electrolyte.Item Specific Ion Effects on Interfacial Phenomena(2012-02-14) Flores Araujo, SarahA new interdisciplinary facet of chemistry has developed, as we attempt to comprehend complex interfacial phenomena in which ions play crucial roles. Understanding the mechanisms by which ions affect water at surfaces and interact with the molecules dissolved in it, pose a ubiquitous challenge with enormous implications for biological and physical sciences. These represent steps towards unraveling mechanisms in protein folding and crystallization, protein-protein interactions, enzymatic activity, implant biocompatibility, atmospheric chemistry phenomena, and even in more inorganic processes like metal oxide dissolution and corrosion; all of them fundamental technological challenges. In this thesis, the specific ion effects on interfacial water structure adjacent to air/water and solid/water interfaces were explored using vibrational sum frequency spectroscopy. At the air/water interface, monolayers of bovine serum albumin, elastin-like peptides, and surfactants, were analyzed in presence of subphases that consisted of different sodium salts and varying pH value. The results suggested that anions interact directly with the protein?s surface, and their effects on water structure are dominated by the charge state of the interfacial layer, rather than the detailed chemical structure of the macromolecules. At the solid/liquid interface, water structure at surfaces like quartz, octadecyltrichlorosilane-covered quartz, and titanium oxide, confirmed that the propensities of anions to adsorb at an interface are favored for more polarizable anions, following the Hofmeister order, and disproving the notion that the order of the interaction can be inverted with changes in charge sign or degree of hydrophobicity of the surface. Similarly, by analyzing interfacial water structure we performed one of the very first systematic studies on the interactions of cations with metal oxide surfaces. The results showed that specific cation effects were quite prominent at low concentration and high pH value, following a direct Hofmeister series, which can be explained in terms of charge density, polarizability, and basicity of the oxide surfaces. Our findings are of interest, since they provide with essential information not only to understand protein phenomena associated with neurodegenerative conditions like Alzheimer, but also by proving the generality of ion interactions beyond biological, we can even influence the development of the next generations of microprocessors and beyond.Item Structure of gas-liquid interface and hydrophobic interface for urea aqueous solution: a computer simulation study(2009-05-15) Yu, MengUrea aqueous solution is ubiquitously used to denature protein. Regardless of its extensive use, the mechanism is still unclear and remains an active field of study. There have been two proposed mechanisms, the direct and indirect. The indirect mechanism, which attributes the ability of urea of changing water structure, is susceptible since many research works show that there is little effect of urea on water structure. The current study provided evidence for the indirect mechanism by demonstrating that the introduction of urea slightly changes the water structure in the hydrophobic interfacial areas. In the current study, the urea aqueous solution systems with either gas-liquid or hydrophobic interface are studied by MD simulations, and the structures of water near the interfacial areas are analyzed in terms of density, orientation and number of hydrogen bonds. For each kind of interface, systems with four different urea concentrations are included, ranging from 0M to 8M. The results show slight change of water structure by the urea solute on the hydrophobic interface in terms of the orientation and number of hydrogen bonds per water molecule.Item The chimaera project: an online database of animal motions(2009-05-15) Gele, Julie KatherineDigital animators will save vast amounts of project time by starting with a completed skeleton and some base animations. This result can be accomplished with Web 2.0 technologies by creating a repository of skeletons and animations that any animator may use for free. While free Maya? skeletons currently exist on the Internet, the websites housing them have only brief features and functions for browsing and interacting with these files. None of these websites contain downloadable animations for the provided skeletons. The Chimaera Project improves the field of Web 2.0 sites offering free rigs by offering many new features and freedoms to the animation community. Users may upload and download Maya? skeletons, share comments and tips with each other, upload animations associated with the skeletons, and search or browse the skeletons in a variety of ways. The skeletons include descriptions and information provided by the creator and are categorized by class, order, and species. Users may access a freely provided script called ?zooXferAnim? to import and export animations into text files to be uploaded and downloaded on the website. Many animations per skeleton may be uploaded. The Chimaera Project extends the Web 2.0 community by creating an interactive resource for animators to contribute and share content in a better, more organized format than previously seen on the Internet.Item The effect of irregular fiber distribution and error in assumed transverse fiber CTE on thermally induced fiber/matrix interfacial stresses(Texas A&M University, 2006-08-16) Zu, Seung-DonThermally induced interfacial stress states between fiber and matrix at cryogenic temperature were studied using three-dimensional finite element based micromechanics. Mismatch of the coefficient of thermal expansion between fiber and matrix, and mismatch of coefficient of thermal expansion between plies with different fiber orientation were considered. In order to approximate irregular fiber distributions and to model irregular fiber arrangements, various types of unit cells, which can represent nonuniformity, were constructed and from the results the worst case of fiber distributions that can have serious stress states were suggested. Since it is difficult to measure the fiber transverse coefficient of thermal expansion at the micro scale, there is an uncertainty problem for stress analysis. In order to investigate the effect of error in assumed fiber transverse coefficient of thermal expansion on thermally induced interfacial stresses, systematic studies were carried out. In this paper, the effect of measurement errors on the local stress states will be studied. Also, in order to determine fiber transverse CTE values from lamina properties, a back calculation method is used for various composite systems.Item Zirconium-doped tantalum oxide high-k gate dielectric films(Texas A&M University, 2005-02-17) Tewg, Jun-YenA new high-k dielectric material, i.e., zirconium-doped tantalum oxide (Zr-doped TaOx), in the form of a sputter-deposited thin film with a thickness range of 5-100 nm, has been studied. Important applications of this new dielectric material include the gate dielectric layer for the next generation metal-oxide-semiconductor field effect transistor (MOSFET). Due to the aggressive device scaling in ultra-large-scale integrated circuitry (ULSI), the ultra-thin conventional gate oxide (SiO2) is unacceptable for many practical reasons. By replacing the SiO2 layer with a high dielectric constant material (high-k), many of the problems can be solved. In this study, a novel high-k dielectric thin film, i.e., TaOx doped with Zr, was deposited and studied. The film?s electrical, chemical, and structural properties were investigated experimentally. The Zr dopant concentration and the thermal treatment condition were studied with respect to gas composition, pressure, temperature, and annealing time. Interface layer formation and properties were studied with or without an inserted thin tantalum nitride (TaNx) layer. The gate electrode material influence on the dielectric properties was also investigated. Four types of gate materials, i.e., aluminum (Al), molybdenum (Mo), molybdenum nitride (MoN), and tungsten nitride (WN), were used in this study. The films were analyzed with ESCA, XRD, SIMS, and TEM. Films were made into MOS capacitors and characterized using I-V and C-V curves. Many promising results were obtained using this kind of high-k film. It is potentially applicable to future MOS devices.