The lowest natural frequencies of thin-walled noncircular fiber-reinforced composite cylinders, specifically cylinders with elliptical cross sections, are investigated. Of interest is the variation of the lowest natural frequency, the so-called fundamental frequency, as a function of wall laminate properties, cross-sectional eccentricity and other cylinder geometric parameters. Both simple and clamped support boundary conditions are investigated. Laminate properties that are uniform with circumferential location and laminate properties that vary with circumferential location, by way of varying laminate fiber angle with circumferential location, are considered. As the radius of curvature of a noncircular cylinder varies with circumferential location, it is logical to consider the influence of circumferentially varying fiber orientation on the fundamental frequency. The analysis for predicting the fundamental frequency is based on Donnell shell theory, linear elastic properties, and the use of Hamilton's Principle in conjunction with the Rayleigh-Ritz technique. By use of a so-called shape factor, the magnitude of cylinder normal displacements are modulated to be larger in the regions of the cross section with the largest radius of curvatures and smaller in the regions with the smallest radius of curvature. The final equations for predicting the fundamental frequency are quite complex, but a series of approximations results in a hierarchy of simpler equations, the simplest being referred to as Lo's approximation. The prediction of the fundamental frequencies is spot checked by comparing the results as predicted by the various levels of approximation with predictions of a shell-based finite element model. Considering uniform laminate properties, comparisons between the developed analysis and the finite element model are good for all levels of simpler equations, and excellent in some cases. The developed analysis is subsequently used for parameter studies. It is found that compared to a circular cylinder of the same circumference and with uniform laminate properties, the fundamental frequency of an elliptical cylinder is always less. Surprisingly, based on the results obtained, it appears that for a given cylinder geometry the fundamental frequency is not particularly sensitive to wall lamination sequence, though the wave number in the circumferential direction of the mode shape associated with the fundamental frequency is sensitive to lamination sequence. Considering cylinders with circumferentially varying fiber orientation, comparisons between the developed analysis and the finite element model for most of the cases studied are good. However, the developed equations are limited since it is difficult to find a set of known functions to describe the deformation of an arbitrary lamination sequence when applying the Rayleigh-Ritz technique. In general, in can be concluded that the effect of varying fiber orientation on the fundamental frequency is much less than the influence of cylinder aspect ratio. It can also be concluded that the developed analysis would be an excellent tool for design purposes, as the calculation of the fundamental frequency is done quickly, and design trade-offs studies would be easy. / Ph. D.

Because of a very variable geological composition of the Czech Republic, there is a various scale of all genetic types of rocks that are used for the production of crushed stone. The most often used group of rocks are effusive magmatic rocks, which represent about 34 % of crushed stone marketed (Starý et al. 2010). These rocks are used for all kinds of construction purposes including roads. The experimental material of crushed stone used in this thesis was sampled from 40 active quarries in the Czech Republic. The studied volcanic rocks originated from Neoproterozoic and Paleozoic complexes of Barrandien, Carboniferous and Permian of Krkonose Piedmont Basin, Carboniferous and Permian of Intrasudetic basin, area of ordovician Železné Hory, from the main volcanic center of Bohemian Massif in the north-west Bohemia (České středohoří Mts. and Doupov Mts.), Neovolcanic area of Czech Cretaceous basin and area of Neovolcanic East and West Sudeten. Petrographic study was carried out in a form of standard petrographic analysis of thin sections and chemical analysis, which helped inclusion of rocks to a classified systems. The whole suite of volcanic rocks was separated to five petrographic-technologic subgroups defined as: (1) rhyolites / porphyres, (2) phonolites, (3) basalts s.l., (4) spilites and (5)...

The development of new technologies in the production of concrete over time is allowing increase its compressive strength, workability and durability. Despite their many advantages, concrete has limitations related to its fragile behavior in the presence of tensile loads. An alternative to solve this problem is the use of fibers in the concrete, getting a composite material that has different characteristics of the original material. Seeking collaborate with the evaluation about the efficiency of different fiber types, this work analyses the behavior of fluid concrete reinforced with steel fibers, subjected to tensile loads, evaluating the influence of shape factor and volumetric fraction. The ability of flow has served as a reference for concrete can be used on parts with high rates of reinforcement, whose compacting is not fully efficient. However, because it is a cementitious matrix, the concentration of tensile strength on these points of high rates of reinforcement, may trigger a harmful process of cracking. Are analyzed in this work the effects of the incorporation of steel fibers in the workability, the incorporated air content, the compressive strength, the tensile strength and modulus of elasticity. Additionally, a comparison is made between the relationship of the compression strength and tensile of the experimental results with the theoretical relationships of the tensile strength found in the literature , and finally, was seek by the mixture rules evaluate whose parameters of the study are more influents on the behavior of the new composite. For this, were used specimens tests cylindrical of dimensions of 10cm x 20cm of fluid concrete with regular resistance, with percentage of steel fiber of 0,4% and 0,8% of the cement mass and shape factors of 33, 50 and 80, for each of the percentage, in tests of tensile by diametrical compression. Obtained results allowed display, from changes in shape factor and volumetric fraction added to fluid cementitious matrix, that fibers with larger shape factor and higher volumetric fraction tend to be more efficient in the tensile strength of fluid composites. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O desenvolvimento de novas tecnologias na produção do concreto ao longo do tempo vem permitindo elevar a sua resistência à compressão, trabalhabilidade e durabilidade. Apesar de suas muitas vantagens, o concreto apresenta limitações relacionadas ao seu comportamento frágil quando na presença de esforços de tração. Uma alternativa para contornar este problema é a utilização de fibras no concreto, obtendo-se assim um material compósito que possui características diferentes do material original. Buscando colaborar na avaliação da eficiência de diferentes tipos de fibras, o presente trabalho analisa o comportamento de concretos fluidos reforçados com fibras de aço, submetidos à tensões de tração, avaliando a influência do fator de forma e da fração volumétrica. A capacidade de fluir tem servido de referência para que o concreto possa ser utilizado em peças com altas taxas de armadura, cujo adensamento não é totalmente eficiente. Entretanto, por se tratar de uma matriz cimentícia, a concentração de tensões de tração nesses pontos de alta taxa de armadura pode desencadear um processo nocivo de fissuração. São analisados no trabalho os efeitos da incorporação de fibras de aço na trabalhabilidade, no teor de ar incorporado, na resistência à compressão, na resistência à tração e no módulo de elasticidade. Adicionalmente, é executada uma comparação entre a relação das resistências à compressão e à tração dos resultados experimentais com a relação teórica da resistência à tração encontrada na literatura, e por fim, buscou-se através da regra das misturas avaliar quais os parâmetros de estudos são mais influentes no comportamento do novo compósito. Para isso, foram utilizados corpos-de-prova cilíndricos de dimensões de 10cm x 20cm de concreto fluido de resistência usual, com teor de fibras de aço de 0,4% e 0,8% da quantidade de cimento em massa e com fatores de forma de 33, 50 e 80, para cada um dos teores, em ensaios de tração por compressão diametral. Os resultados obtidos permitiram visualizar, a partir das modificações no fator de forma e na fração volumétrica adicionadas a matriz cimentícia fluida, que fibras com maior fator de forma e maior fração volumétrica tendem a ser mais eficientes na resistência à tração dos compósitos fluidos.

Solving of this diploma thesis is evaluation porosity in sequence on mechanical properties from different Al alloys. Castings were made by gravity casting to the iron-mould or gravity casting to the sand. Measurements (mechanical properties, porosity, DAS - dendrite arm spacing, shape factors and sphericity) were statistically analysed and dependencies which were detected were processed to the graphs.

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Literature does not provide a satisfactory answer to maximum and minimum particle size or the particle size of the mortar phase especially for optimal porosity of concrete. To overcome the shortcomings of the design methods were thought to design a new method for design of concrete mix. This idea is based on a complex analysis of powder materials (determination of granular properties, shape factor of fillers, porosity, packing of powder materials, surface area, etc.) and subsequently to assess the influence to pore system of concrete and physical and mechanical properties in hardened state of concrete. In this work are presented and analyzed two types of fillers – fly ash and limestone dust.