Orientadores: João Domingos Biagi, Antonio Carlos de Oliveira Ferraz / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-12T05:33:01Z (GMT). No. of bitstreams: 1 Fraiha_Marcos_D.pdf: 1875565 bytes, checksum: a372a466eacf5e49b82f4cdc2d006270 (MD5) Previous issue date: 2008 / Resumo: O objetivo geral deste trabalho foi determinar os efeitos da taxa de cisalhamento, temperatura e pressão gerados no processo de extrusão de alimentos para animais sobre a viabilidade de esporos bacterianos. Baseado na fundamentação teórica de reologia de materiais, foi possível a construção de um reômetro fundamental utilizando materiais e operações simples de tornearia. Para caracterizar o comportamento reológico de alimentos para animais, uma mistura de grãos de milho e soja na proporção 70:30 (massa:massa) foi submetida ao reômetro capilar sob 3 níveis de temperatura e umidade da massa, e 4 taxas de cisalhamento aparente: 80, 120 e 160°C, 26,5±0,08; 30,4±0,31 e 33,4±0,05%; 30,4; 72,9; 304,3 e 728,6 s-1 respectivamente. Diferentes taxas de deformação e dimensões da matriz foram utilizadas para obtenção das taxas de cisalhamento acima. Os efeitos de umidade e temperatura da massa, e taxa de cisalhamento sobre a mistura de milho e soja foram ajustados para uma expressão única (P<0.001, R2 = 0.93): ?=18.769,7 (?) -0,86 e (-9,34U+935T), onde (?) é a taxa de cisalhamento, U é a teor de água na amostra e T é o inverso da temperatura na massa, em escala Kelvin. Como esperado, a mistura moída de milho e soja apresentou comportamento pseudoplástico. Outro experimento objetivou determinar os parâmetros de destruição térmica de esporos de Bacillus sterothermophilus ATCC 7953 e a estimativa de suas dimensões. Os valores de D121,1°C e z para os esporos suspensos em solução salina foram 8,8 min e 12,8 °C, respectivamente. Para aqueles suspensos em mistura milho e soja, D121,1°C e z foram 14,2 min e 23,7 °C , respectivamente. As micrografias indicaram que os esporos apresentam-se como bastonetes, homogêneos em forma e dimensão, cujos comprimento e diâmetro foram estimados em 2 e 1 µm, respectivamente. Outro experimento visou determinar o efeito da taxa de cisalhamento sobre a viabilidade de esporos de B. stearothermophilus sob escoamento viscométrico em reômetro capilar. Os esporos foram inoculados em mistura de milho e soja para contagem e umidade de 106 UFC/5g, e 30,0±0,30%, respectivamente. As amostras foram submetidas às taxas de cisalhamento aparentes variando de 728,6 a 3.643,0 s-1, sob 80°C. As contagens microbiológicas foram menores quando comparadas ao controle (P < 0,001). Baseados nos parâmetros termobacteriológicos dos esporos, a redução de viabilidade observada não pode ser explicada pelo efeito do calor isoladamente, e confirma a hipótese do efeito do fenômeno mecânico sobre a redução celular. Outro trabalho visou determinar o efeito do calor, pressão e taxa de cisalhamento sobre a viabilidade de esporos termodúricos em ração animal submetida ao processo de extrusão. Os esporos foram semeados em mistura de grãos moídos de milho e soja, para contagem final de 106 UFC/5g e umidade de 30%, e submetidos ao processo em extrusora de rosca simples. A pressão estática não influenciou a viabilidade, porém temperatura e tensão cisalhante reduziram a viabilidade dos microorganismos. O percentual da redução da viabilidade dos microorganismos está diretamente relacionado ao volume de material submetido ao gradiente de velocidade de escoamento. / Abstract: The overall objective of this thesis was to determine the effects of mass temperature, pressure and shear rate on the viability of bacterial spores. The first paper describes the design and construction of a capillary rheometer attached to an universal testing machine used to characterize feed ingredients. To characterize the rheological behavior of animal feed under viscometric flow, a 70:30 (mass:mass) mixture of ground corn and soybean grains was submitted to a capillary rheometer at 3 temperatures and moisture levels, and 4 shear rates: 80, 120 and 160 °C, 26.5±0.08; 30.4±0.31 and 33.4±0.05%; 30.4; 72.9; 304.3 and 728.6 s-1 respectively. Based on experimental data, moisture content, mass temperature and shear rate effects on apparent shear viscosity of corn-soy mix were fitted to a single expression (P<0.001, R2 = 0.93): ?=18.769,7 (?) -0,86 e (-9,34U+935T), where (?) is the shear rate, U is the sample moisture and T is the sample reciprocal temperature in Kelvin scale. In order to determine thermobacteriological parameters for B. stearothermophilus spores, they were suspended in saline solution medium (0,85%, pH 6,7) and in ground corn-soy mix to a final count of 106 CFU/mL and 106 CFU/5g, respectively, distributed to TDT tubes and submitted to heat, from 100 to 126 °C, for a period of time varying from 0 to 40 min. D121,1°C and z values for these spores, as determined in the saline solution, were 8.8 min and 12.8 °C, respectively. D121,1°C and z values determined in the corn-soy mix were 14.2 min and 23.7 °C, respectively. The micrographs indicated that the spores are homogeneous in shape and size, which length and diameters are 2 and 1 µm, respectively. Another experiment aimed to determine shear effects on the viability of bacterial spores under viscometric flow. The spores were inoculated in the feed mixture to a final count of 106 CFU/5g, and 30.0±0.30% moisture. Samples were submitted to apparent shear rates varying from 728.6 to 3,643.0 s-1 at 80 °C in a capillary rheometer. Microbial counts were lower after treatments compared to control (P<0.001). A final work determined the heat, pressure and shear rate effects on the viability of the spores sowed into feed, submitted to extrusion. Bacillus stearothermophilus spores were sowed into corn and soy grain mixture to 106 CFU/5g and moisture of 30%, and then submitted to the extrusion process in a single screw extruder. Static pressure had no effect, but heat and shear stress reduced microbial count. The higher shear rate due to rotational speed increase of screw did not affect cell viability. It was concluded that static pressure level did not affect the viability of Bacillus stearothermophilus spores but heat and shear stress did. These conclusions indicated that the volume of feed under a velocity gradient during mass flow through the screw channel remained unchanged in the last case, what resulted in the same percentage of spores submitted to shear stress. / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola

Orientador: Rubens Caram Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-25T20:28:46Z (GMT). No. of bitstreams: 1 Mello_MarianaGerardi_M.pdf: 7703668 bytes, checksum: e57388ff91b2ed6bded8b3ae1daee175 (MD5) Previous issue date: 2014 / Resumo: O aumento da expectativa de vida e as melhorias sempre necessárias na área da saúde conferem grande importância ao desenvolvimento de biomateriais. Ligas de Ti contendo elementos ? estabilizadores são atrativas para uso como biomaterial devido a sua alta resistência específica, elevada resistência à corrosão e incomum biocompatibilidade, além de menor módulo de elasticidade, o que é benéfico para os tecidos ósseos próximos ao implante. Este trabalho trata do estudo de estabilidade de fases em ligas tipo ? no sistema Ti-Mo-Sn processadas sob diferentes condições e foi realizado por meio das seguintes etapas: (a) Estudo do efeito do teor de Sn na estabilidade de fases após resfriamento ao forno e em água em ligas Ti-Mo; (b) Estudo do efeito do teor de Sn na supressão da formação das fases ? e ?¿¿; (c) Estudo do efeito do teor de Sn na precipitação da fase ? por meio de envelhecimento; (d) Estudo das propriedades mecânicas das amostras processadas sob diferentes condições. Tal trabalho foi desenvolvido a partir da preparação de ligas em forno a arco sob atmosfera controlada, tratamento térmico de homogeneização, deformação plástica por meio de laminação a quente e caracterização utilizando-se microscopia óptica, microscopia eletrônica de varredura e transmissão, difração de raios-X e calorimetria exploratória diferencial. As amostras foram também submetidas a tratamentos térmicos de envelhecimento. As propriedades mecânicas das amostras foram avaliadas por meio de ensaios de tração e medidas de módulo de elasticidade usando técnicas acústicas. Os resultados sugerem que o Sn se comporta como um elemento de liga supressor da formação das fases ? e ?¿¿ em ligas Ti-Mo. Além disso, propicia o refinamento da fase ? precipitada, o que resulta em aumento da resistência mecânica / Abstract: The increase in life expectancy and the always necessary healthcare improvements attach great importance to the development of biomaterials. Ti alloys containing ? stabilizing elements are prone to be used as biomaterials due to their high specific strength, high corrosion resistance, unusual biocompatibility and low modulus of elasticity, which is very beneficial to the bone tissues near the implant. This study deals with the phase stability in ? type alloys in the Ti-Mo-Sn system processed under different conditions and was carried out through the following steps: (a) Study of the effect of the Sn content on the phase stability in Ti-Mo alloys; (b) Study of the effect of the Sn content on the suppression of the ? and ?'' phases precipitation; (c) Study of the effect of the Sn content on the precipitation of the ? phase by aging; (d) Study of the mechanical properties of samples processed under different conditions. This study was developed through the preparation of alloys by using arc furnace under controlled atmosphere, homogenization heat treatment, plastic deformation through hot rolling and characterization using optical microscopy, scanning and transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. Samples were also submitted to aging heat treatments. The mechanical properties of the samples were evaluated by tensile test and measurement of elastic modulus using acoustic techniques. The results suggest that Sn acts as a suppressor alloying element in the formation of the ? e ?¿¿ phases in the Ti-Mo system. Moreover, Sn addition provides refinement of ? phase particles, which provides an increase in the mechanical strength / Mestrado / Materiais e Processos de Fabricação / Mestra em Engenharia Mecânica

Bien que les organes creux (intestins, etc.) puissent être lésés lors d’accidents automobiles, les recherches biomécaniques passées se sont principalement intéressées aux organes pleins. Deux axes de recherche ont été explorés dans cette étude : - le comportement mécanique du mésentère humain, qui est le principal moyen de fixité de l’intestin grêle, a été caractérisé lors d’essais de traction sur échantillons. Le mésentère s’est comporté comme un matériau anisotrope sensible à la vitesse de déformation. Des valeurs de raideur et déformation à rupture ont été proposées. - les effets des conditions aux limites entre organes sur les réponses interne et externe de l’abdomen ont été étudiés par simulation. Des modélisations permettant ou non le glissement entre un solide représentant les intestins, les organes pleins et la cavité abdominale ont été implémentées dans trois modèles éléments finis qui ont été soumis à des impacts correspondant à une étude de la littérature. Les relations force-déflexion, et les cinématiques internes et externes étaient très similaires pour les trois modèles. Les déformations prédites dans un mésentère très simplifié étaient supérieures aux déformations à rupture obtenues expérimentalement sur échantillons. Toutefois, aucune lésion du mésentère n’était décrite dans l’étude de référence. Ce résultat pourrait remettre en cause la représentation des intestins par un solide unique typiquement utilisée dans les modèles existants ainsi que celle du mésentère utilisée dans cette étude. En l’absence de données internes sur les organes et le mésentère lors d’un choc, il est difficile de savoir comment ces modélisations devraient évoluer. / While hollow organs (intestines, etc.) can be injured during automotive accidents, past biomechanical research were largely focused on solid organs. Two research topics were developed in the current study: - the mechanical response of the human mesentery – which is the main attach point of the small intestines – was characterized during tensile tests conducted on samples. The mesentery behaved like an anisotropic strain rate sensitive material. Stiffness and failure strain values were proposed. - the effects of the boundary conditions between organs on the internal and external response of the abdomen were studied using simulations. Different modelling approaches allowing or not sliding between a solid component representing the intestines, the solid organs and the abdominal cavity were implemented in three finite element models that were subjected impacts derived from a literature study. The relationship between force and deflection, and the internal and external kinematics were very similar for all models. The strains predicted in a very simplified mesentery were larger than the failure strains observed in testing. However, no mesenteric injuries were described in the reference study. This questions both the choice of a single solid component for the intestines typically used existing finite element models and the simplified representation of the mesentery of the current study. In the absence of internal data on organ and mesenteric kinematics during an impact, it is difficult to define which strategy should be used in future modelling efforts.

Doctorat en kinésithérapie et réadaptation / info:eu-repo/semantics/nonPublished

Four silicon nitride powder blends vary in starting powder characteristics, glass chemistry, and phase composition. This work focuses on how these properties influence densification behavior, microstructural development, and the resulting mechanical performance of dense ceramics. Previous work completed on alpha-rich, low oxide containing (8 wt%), and fine silicon nitride powder (GS-44) showed high hardness equiaxed with grained ceramic. GS-44 served as an excellent precursor for the matrix phase material in graphene reinforced composites, which resulted in 235% increase in toughness and high hardness retention [1] with the addition of 1.5 vol% graphene. As the GS-44 powder is no longer in production, investigative work into other commercial powders and customization of powder blends was initiated. Commercial blends were selected based on availability, high alpha content, fine particle size, and additive chemistry (Al2O3, MgO, and Y2O3). The objective was to understand which powder characteristics led to a ceramic design that contained high hardness, strength, and toughness properties in order to increase the use of silicon nitride in extreme temperature environments. One such example is aerospace and structural applications that require a high-performance material that is lightweight and good thermal stability. Strong covalent bonding in silicon nitride make densification of powders extremely difficult; thereby, sintering additives are necessary to promote liquid phase sintering processes. Compaction of ceramic powders was carried out using a spark plasma sintering (SPS) furnace by utilizing a pulsed direct current through a conductive graphite die that encapsulates the sample powder. SPS was preferred over other conventional sintering methods owing to its high heating rate and short dwell times at the sintering target temperature. Thus, SPS provides superior control for tailoring the final silicon nitride properties by producing a hard alpha-phase and tough beta-phase microstructures. The custom blend developed had an appreciable amount of media wear included during the milling process that increased the additive content. Development of the custom blend was used to understand the effect of a larger additive content. Commercial GS-44 blend was used as the control to track the effect of adjusting specific surface area and oxide content in silicon nitride powder systems (HCS-M, C-R3, and UA-SN). The mechanical results for the four matrix systems, showed that toughness increased with grain coarsening and minimization of alumina content in beta silicon nitride. Based on these findings it is important to determine tradeoffs (i.e. balance of high hardness, toughness, and strength) to engineer an optimal ceramic that can be used for structural and aerospace applications.

No description available.

Le vrillage est un mode de retour élastique particulier, qui se produit suite à la mise en forme par emboutissage de pièces allongées, à savoir dont une des dimensions est grande devant les deux autres. Le vrillage est caractérisé par la torsion de la pièce autour d’un axe parallèle à la plus grande dimension. D’un point de vue expérimental, le vrillage représente un véritable défi, du fait de la grande dimension, de l’ordre du mètre, des pièces industrielles et de la grande dispersion des valeurs caractéristiques de vrillage obtenues pour un même procédé et un même matériau. En conséquence, l’étude du vrillage en utilisant une échelle réduite sur l’ensemble des dimensions outils et pièce est retenue pour ce travail de thèse, avec un intérêt particulier pour l’influence de l’alignement tôle/outils sur l’intensité du vrillage.L’objectif général de ce travail de thèse est l’étude expérimentale et numérique du vrillage de pièces en forme de U, à partir de flans de longueur 100 mm et d’épaisseur 0,15 mm. Une première partie concerne la caractérisation et modélisation du comportement mécanique du matériau, un acier inoxydable. Des essais mécaniques de traction et cisaillement simple ont été réalisés, avec une mesure locale sans contact du champ de déformation. L’écrouissage ainsi que l’évolution de la pente à la décharge ont été caractérisés, et les paramètres d’un modèle élasto-plastique avec écrouissage mixte et dépendance du module d’Young avec la déformation plastique équivalente ont été identifiés à partir de ces essais.Afin de constituer une base expérimentale sur le vrillage, un dispositif spécifique a été conçu et usiné dans le cadre de cette thèse. Des essais d’emboutissage de flans rectangulaires, de dimensions 100 x 28 mm2, pour atteindre une forme de U de profondeur 7 mm, ont été réalisés. L’alignement de l’éprouvette avec le poinçon et la matrice a été particulièrement contrôlé et deux orientations ont été étudiées : l’éprouvette est soit alignée avec le poinçon, soit désalignée de 2° par rapport à son centre. La forme finale des éprouvettes a été mesurée avec un scanner laser. Le vrillage est caractérisé par le rapport de l’angle entre le fond de deux sections extrêmes sur leur distance respective. Un vrillage de 11°.m-1 a été mesuré pour les éprouvettes désalignées, tandis que pour les éprouvettes alignées, aucun vrillage significatif n’a été obtenu. L’étude des sections transversales de l’éprouvette montre une corrélation entre l’asymétrie du retour élastique causée par l’asymétrie de la géométrie de l’éprouvette, dans le cas désaligné, et le vrillage. Le glissement de l’éprouvette sous le poinçon au cours de l’essai affecte également le vrillage quelque soit l’orientation de l’éprouvette.Finalement, la simulation numérique de la mise en forme d’un flan en forme de U a été effectuée avec le code de calcul Abaqus®. Un solveur explicite est utilisé pour l’étape d’emboutissage et un solveur implicite pour le retour élastique. L’influence de la taille de maillage, ainsi que celle de la loi de comportement du matériau ont été étudiées. Les résultats de la simulation numérique sont alors confrontés aux résultats expérimentaux. / Twisting of metallic sheets is one particular mode of springback that occurs after drawing of elongated parts, i.e. with one dimension much larger than the two others. Twisting is usually characterized by the disorientation angle between the two end sections which turn around an axis parallel to the greatest dimension. From experimental point of view, twisting is very challenging because a lot of data were obtained on industrial-type parts, with one dimension of the order of the meter. These data are usually very dispersed and with the same process parameters, material and geometry, very different values for the twisting parameter can be obtained. As a consequence, the study of twisting phenomenon by using a reduced scale for all the dimensions of the tools and blank is retained in this work of. The influence of the blank alignment with the tools on the intensity of the twisting parameter was particular investigated.The objective of the thesis is the experimental and numerical study of the twisting of U-shaped part, obtained from stainless steel blanks with a length of 100 mm and thickness of 0.15 mm. The first part relates to the characterization and modeling of the material mechanical behavior. Conventional tests such as tension and simple shear were performed. The kinematic contribution to the hardening and the evolution of the loading-unloading slope with the plastic deformation were carried out. The parameters of an elastic-plastic model based on a mixed hardening and degradation of Young’s modulus with the equivalent plastic strain have been identified from these tests.In order to establish an experimental database for twisting, a dedicated device for drawing U-shaped elongated parts was designed and manufactured. Deep-drawing of rectangular blanks, of dimensions 100 x 28 mm2, to achieve a U-shape rail of 7 mm of depth was performed. Two different orientations of the part with respect to the tools were chosen: either aligned with the tools, or purposefully misaligned by 2°. The geometry of the part after springback was laser scanned. Twisting is characterized by the disorientation angle in-between the two end sections of the part over the distance. Several samples were drawn for each configuration, leading to the conclusion that almost no twisting occurs in the first case whereas a twisting parameter of 11°.m-1 corresponded to the second one. The analysis of the geometry of cross sections has shown a correlation between twisting and asymmetry of springback, like the opening of the U-shaped rail, caused by the asymmetry of the blank in the misaligned case. The sliding of the blank beneath the punch during the process also affects twisting whatever its orientation. Finally, finite element simulation of the drawing process, for the two configurations of the blank, within the explicit framework for drawing and implicit one for springback, were carried out using Abaqus® software. The influences of the mesh size as well as the material behavior law on the intensity of twisting parameter were studied. Numerical predictions were compared with experiments.

D.Ing. / Unbound granular material has and is still being used with great success in the construction of road pavements in South Africa and many other countries around the world. Often this material is used in the main structural layers of the pavement with very little protection provided against high traffic induced stresses by way of a surface treatment or thin asphalt concrete layer. The performance of unbound granular pavement layers depend mainly on the level of densification and degree of saturation of the material in addition to the stress levels to which the layers are subjected. The main form of distress of unbound granular layers is the permanent deformation of the layer, either through the gradual deformation or rapid shear failure of the layer. Design engineers need accurate and appropriate design procedures to safeguard the road against such rapid shear failure and to ensure that the road has sufficient structural capacity to support the traffic loading over the structural design period. The recent trend in pavement design has been to move away from empirical design methods towards rational mechanistic-empirical design methods that attempt to relate cause and effect. Although a mechanistic-empirical pavement design method has been available in South Africa since the midseventies, increasing criticism has been levelled against the method recently. The models for characterising the resilient response and shear strength and estimating the structural capacity of unbound material have been of particular concern. The purpose of the research reported in this thesis was therefore to develop an improved mechanistic-empirical design model, reflecting the characteristics and behaviour of unbound granular material. The new design model consists of three components namely a resilient modulus, yield strength and plastic deformation damage model with each model including the effects of the density and moisture content of the material unbound granular where appropriate. The models were calibrated for a range of unbound materials from fine-grained sand and calcrete mixture to commercial crushed stone products using the results from static and dynamic tri-axial tests. An approximation of the suction pressure of partially saturated unbound material was introduced in the yield strength model and was validated with independent matric suction measurements on the sand and calcrete mixture. The yield strength model which is a function of the density and moisture conditions as well as the confinement pressure was calibrated for the individual materials with a high accuracy. A single plastic strain damage model was calibrated for the combined plastic strain data from all the crushed stone materials but a single model could not be calibrated for the plastic strain data of the natural gravels as these materials vary too much in terms of particle size distribution and the properties of the fines found in these materials. The formulation of the plastic strain damage model includes the density and degree of saturation of the material. A single resilient modulus model was calibrated for the combined resilient modulus data from all the materials excluding the data from a limited number of tests during which large plastic strain occurred. The resilient modulus model again ii incorporates the density, degree of saturation and the stress dependency of unbound granular material and is on an effective stress formulation for the bulk stress. Finally, the yield strength, resilient modulus and plastic strain damage models are combined in a mechanistic-empirical design model for partially saturated unbound granular material. Results from the proposed design method seem more realistic than results from the current design model and the model is not as sensitive to variation in the design inputs as the current design model is. In addition to this, the effects of the density and moisture content of the partially saturated, unbound granular material on the resilient response and performance of the material is explicitly included in the formulation of the proposed design model.

M.Ing. (Mechanical Engineering) / Titanium and its alloys have the potential to serve as a strategic economic driver of the South African economy. The manufacture and use of high strength, lightweight materials such as titanium alloys have become of great importance in the aerospace and biomedical industries over the past few decades. The manufacturing costs of titanium alloy components however, are considered high due to the poor machinability of the material. Furthermore, as with all metals during machining, surface residual stresses are induced into the material. These are of particular interest in the aerospace industry as they can be either detrimental or beneficial to the performance and fatigue life of materials. The aim of this investigation is therefore to examine the effect that machining parameters have on the magnitude, sign and distribution of residual stresses induced in Grade 4 and 5 titanium alloys during high performance machining (turning). The effect of these machining parameters is investigated by residual stress measurements conducted with X-ray diffraction and grain structure analysis of the machined surfaces by optical microscopy. Results show that cutting speed and depth of cut have a significant effect on the residual stresses. At low cutting speeds, the surface residual stresses are largely compressive, becoming more tensile with an increase in cutting speed. An increase in depth of cut also introduces more compressive residual stresses into the material. The microstructural analysis of the alloys shows that grain deformation decreases with an increase in cutting speed and cutting depth.

M.Ing. / This dissertation investigates the fatigue and monotonic tensile properties of cast aluminium alloy wheels in various post cast conditions. It was found that monotonic tensile properties could be used in the original universal slopes method of Manson to predict the fatigue properties as a conservative first approximation for A356 cast aluminium alloy wheels. Using finite element analysis and the predicted fatigue properties the fatigue life of A356 aluminium alloy wheels could be determined. Further work is required on the surface effect of paint on the wheel and residual stress on the surface of the wheel.