Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 64-66.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / King, William Paul, Committee Chair ; Henderson, Clifford L, Committee Co-Chair ; Gall, Ken, Committee Member.

Thesis (M.S.)--University of North Texas, May, 2007. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "September 2006." Includes bibliographical references (p. [243]-256). Also available via the World Wide Web.

Orientador: Luís Rocha / Banca: José Humberto Dias da Silva / Banca: Carlos Nelson Elias / Resumo: O titânio e suas ligas são amplamente utilizados em diversas aplicações biomédicas devido às suas propriedades, nomeadamente a alta resistência à corrosão e elevada biocompatibilidade. A elevada resistência à corrosão advém da capacidade de o titânio formar na sua superfície uma camada de óxido amorfo estável com espessura de alguns nanômetros (filme passivo). As propriedades dos filmes passivos nas ligas de titânio são sensíveis à microestrutura (fases presentes e sua proporção relativa) e às condições ambientais que levam à formação desse filme. Por outro lado, a espessura, morfologia e composição do filme de óxido nativo podem ser manipuladas de forma a obter propriedades diferentes. O presente trabalho teve como objetivo o desenvolvimento de superfícies nanoestruturadas nanotubos em titânio comercialmente puro e na liga de Ti-2,5Zr através da técnica de anodização. Fez-se a análise da influência da voltagem aplicada à célula eletrolítica e do tempo de anodização nas características das superfícies produzidas (morfologia e estrutura). Os mecanismos de formação e crescimento dos nanotubos de dióxido de titânio (TiO2) foram analisados em função da voltagem e do tempo de anodização, os resultados obtidos mostraram que a morfologia da superfície, nomeadamente o diâmetro dos nanotubos formados, é fortemente dependente tanto das condições de anodização quanto do substrato a partir do qual os nanotubos são formados / Abstract: Titanium and is alloys are widely used in various biomedical applications because of their properties, namely high corrosion resistance and high biocompatibility. The high corrosion resistance results from the ability of the titanium to form on its surface a layer of stable amorphous oxide with a thickness of a few nanometers (passive film). The properties of the passive films in the titanium alloys are sensitive to the microsctructure (present phases and their relative proportion) and the environmental conditions that lead to the formulation of this film. On the other hand, the thickness, morphology and composition of the native oxide film can be mainipulated in order to obtain different properties. The present work aimed to the development of nano-structured nanotube surfaces in commercially pure titanium and Ti- 2,5Zr alloy by anodizing technique. The influence of the voltage applied to the electrolytic cell and the anodizing time on the characteristic of the produced surfaces (morphology and structure) were analyzed. The formation and growth mechanisms of titanium dioxide (TiO2) nanotubes were analyzed as a function of voltage and time of anodization, the results showed that the surface morphology, namely the diameter of the nanotubes formed, is strongly dependent on both the conditions of anodizing and of the substrate from which the nanotubes are formed / Mestre

This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon the crystal structure and orientation of the plane of indentation. Nanoindentation, Nanovision, scanning electron microscopy, electron dispersive spectroscopy and electron backscattered diffraction techniques were used to determine the sample composition and crystal orientation. Surface topographical features like indentation pile-ups and sink-ins were measured and the effect of crystal orientation on them was studied. The results show that pile-up formation is not a random phenomenon, but is quite characteristic of the material. It depends on the type of stress imposed by a specific indenter, the depth of penetration, the microstructure and orientation of the plane of indentation. Pile-ups are formed along specific directions on a plane and this formation as well as the pile-up height and the contact radii with the indenter is dependant on the aforesaid parameters. These pile-ups affect the mechanical properties like elastic modulus and hardness measurements which are pivotal variables for specific applications in micro and nano scale devices.

Orientador: Julio Ricardo Sambrano / Banca: Valmor Roberto Mastelaro / Banca: Ricardo Paupitz Barbosa dos Santos / Banca: Aguinaldo Robinson de Souza / Resumo: A modelagem e simulação computacional tem se mostrado como uma ferramenta extremamente útil na pesquisa de novos materiais, pois além de auxiliar e confirmar resultados experimentais, também pode prever e propor novas estruturas. Entre os materiais mais estudados atualmente, podemos destacar o grafeno, que detém ótimas propriedades eletrônicas e mecânicas, com o crescimento do interesse em materiais bidimensionais, foi comprovada a existência de análogos inorgânicos ao grafeno, como por exemplo, o nitreto de boro hexagonal (g-hBN), siliceno(g-Si) e óxido de zinco(g-ZnO); esse leque de estruturas diferentes abriram diversas possibilidades de aplicações, que abrangem desde o desenvolvimento de dispositivos eletrônicos até a biomedicina. A criação de defeitos estruturais (poros) na estrutura pode auxiliar na modulação das propriedades eletrônicas de certos materiais, as quais podem ter formas organizadas e periódicas. Deste modo, esta tese teve como objetivo a modelagem e simulação computacional de superfícies e nanotubos porosos de carbono, nitreto de boro, silício e óxido de zinco, sendo os três últimos propostos pela primeira vez na literatura, aplicando técnicas de modelagem computacional a estruturas cristalinas, tais como a escolha das funções de base e funcionais, otimização da estrutura e de suas propriedades estruturais, eletrônicas, mecânicas e vibracionais. Estas simulações foram executadas aplicando-se a Teoria do Funcional da Densidade combinadas com o funcional híb... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Computational simulations and modeling has been shown to be an extremely useful tool in the research of new materials, since in addition to helping and confirming experimental results, it can also predict and propose new structures. Among the most studied materials today, graphene can be highlighted, which has excellent electronic and mechanical properties, with the growing interest in two-dimensional materials, it has proven the existence of inorganic analogues to the graphene, as for example, the hexagonal boron nitride (g-hBN), silicene (g-Si) and zinc oxide (g-ZnO); this range of structures have opened several possibilities of applications, ranging from the development of electronic devices to biomedicine. The creation of structural defects (pore) in the structure can help to modulate the electronic properties of certain materials, which can have organized and periodic forms. The aim of this thesis was the computational simulation and modeling of porous surfaces and nanotubes of carbon, boron nitride, silicon and zinc oxide, being the last three proposed for the first time in the literature, applying computational modeling techniques to crystalline structures, such as the choice of basis set and functional, optimization of the structure and its structural, electronic, mechanic and vibrational properties. These simulations were performed by applying the Density Functional Theory combined with the B3LYP hybrid function and all-electron basis set functions. Initially we des... (Complete abstract click electronic access below) / Doutor

Surface temperatures generated by friction during osculating/fretting contact were measured using an infrared microscope coupled to a digital data acquisition system developed at Virginia Polytechnic Institute and State University. The contact geometry consisted of a stationary test specimen loaded against a vibrating sapphire disk driven by an electromagnetic shaker. Ceramic materials including zirconium oxide, sapphire, aluminum oxide, and tungsten carbide were used as test specimens since they are inert in air, and generate high surface temperatures when used in the oscillating contact system. Instantaneous fluctuations in surface temperature over a single cycle were measured and recorded. This information was compared with instantaneous friction force and velocity data. The friction force data was measured using semiconductor strain gages connected to a new octagonal ring designed specifically for this research. Zirconium oxide-on-sapphire experiments were performed at various loads, frequencies, and amplitudes. The resulting temperature rises, friction coefficients, heat generation rates, and wear scar sizes were compared. Surface temperature rises were measured as a function of position within the contact region. From this data, and scanning electron micrographs of the wear scars, inferences were made about the size, location, and distribution of real contact areas. Experimental measurements were compared with theoretical predictions obtained using a new numerical model developed by B. Vick and S. J. Foo. / Master of Science

An experimental investigation of surface temperatures generated by dry sliding friction was carried out with the use of an infrared radiometric microscope system that was developed at Virginia Polytechnic Institute and State University. The objective of this study was to investigate the effect of subdividing the apparent contact area on the surface temperature generated by friction. Subdividing the geometric contact resulted in lowering the surface temperatures and followed the trend predicted by theory quite well. The study concluded that the surface temperatures predicted by the Archard and Jaeger theories correctly described the influence of nominal load and sliding velocity on the experimental surface temperatures. A detailing description of the experimental apparatus, the radiation analysis used to convert the radiance output of the microscope to temperature, and the experimental procedure is included. / Master of Science

The objective of this study was to formulate a theoretical model and to develop an efficient and accurate solution method to predict the distribution of frictional heat and resulting temperature rise for simple systems with sliding contact. The solution method developed is a variation of the boundary integral equation method (BIEM) in which a moving, full-space Green's function is used as the fundamental solution. The numerical characteristics and limitations for the solution method are presented, as well as the physical parameters that affect the surface temperature rise. The analysis includes an arbitrary sliding velocity, with special focus on oscillating and unidirectional motion. Since the real contact area is extremely important, the theoretical analysis has the flexibility to handle any arbitrary contact area. Results are presented which display the effect of velocity or Peclet number, the frequency and amplitude of oscillation, and thermal properties. Also, results showing the effect of the number, spacing and orientation of the contact patches are presented. Finally, theoretical calculations corresponding to experiments involving a ball on an oscillating sapphire disk are presented and are found to correlate well with experimental data. / Master of Science