Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Rubber is the main component of the pneumatic tire. When rubber is put under cyclic loading, like when a tire is rolled, heat is generated and stored in the rubber, due to hysteresis. Heat stored in the tire is increased by factors like under-inflation, overloading, speeding and defects in the tire. The heat causes high temperatures in the tire due to the poor thermal conductivity of rubber. When the temperature in the rubber increases to 185 °C, pyrolysis and thermo-oxidation starts and can cause the tire to eventually explode. A numerical model of a rolling passenger vehicle tire was developed to calculate the temperature distribution inside the tire and analyse the effect of different operating conditions on the temperature. Operating conditions include loading, inflation pressure, rolling velocity and ambient temperature. The tire was modelled by a single rubber type, using the Mooney-Rivlin material model. The bead wire was modelled using an isotropic material model, while the body and steel cord plies were modelled as rebars. The cavity, used to inflate the tire, included the pressure increase due to the volume change, when the tire is loaded. The numerical model was validated using experimental data from tests done on an actual tire. These tests included deformation and contact stress analysis, as well as surface temperature measurements. Numerical results showed an increase in temperature when the load, rolling velocity and the ambient temperature were increased, as well as when the inflation pressure was decreased. The trends of the numerical data matched the trends of the experimental data. However, the values of the numerical model were not consistent with the experimental data due to material properties from literature being used to model the tire. / AFRIKAANSE OPSOMMING: Rubber is die hoofkomponent in die pneumatiese band. As rubber onder ’n sikliese las geplaas word, soos wanneer ’n band rol, word hitte gegenereer en in die rubber gestoor as gevolg van histerese. Die hitte wat in die band gestoor word, word verhoog deur faktore soos lae inflasiedruk, hoë las, hoë rol snelhede en gebreke in die band. Die hitte veroorsaak hoë temperature in die band weens die swak termiese geleiding van rubber. As die temperatuur in die band hoër as 185 °C raak, vind piroliese en termo-oksidasie plaas en die band kan uiteindelik ontplof. ’n Numeriese model van ’n passasiersmotorband is ontwikkel om die temperatuurverspreiding te bepaal, asook om die effek van verskillende werkstoestande op die temperatuur te analiseer. Die band is gemodelleer met een tipe rubber en die Mooney-Rivlin materiaal-model is gebruik om die rubber te beskryf. Die spanrand van die band is deur ’n isotropiese materiaalmodel gemodelleer, terwyl die hoof- en staalkoordlae as bewapening gemodelleer is. Die holte wat gebruik word om die band op te blaas, neem die druk toename as gevolg van die verandering in volume in ag wanneer die band belas word. Die numeriese model was bekragtig met eksperimentele data wat deur toetse op ’n werklike band onttrek is. Die toetse sluit die volgende in: vervormingen kontakspanninganalises, asook temperature wat op die oppervlak van die band gemeet is. Die numeriese resultate toon ’n toename in temperatuur wanneer die las, rolsnelheid en omgewingstemperatuur verhoog word, asook waneer die inflasiedruk verlaag word. Die numeriese model se tendense stem ooreen met die eksperimentele data, maar die waardes van die numeriese model is nie in ooreenstemmig met die eksperimentele data nie. Die verskil is as gevolg van die materiaaleienskappe wat uit die literatuur geneem is.

<p>The aim of this thesis is to increase the understanding of wear in rolling/sliding contacts such as the wheel-rail contact for railroads and the roller-washer contact for roller bearings.</p><p>The Stockholm commuter train network has been the subject of papers A and B in this thesis in which the wear and surface cracks on rails has been observed for a period of three years. By comparing the wear depth with the crack length, equilibrium between these two damage mechanisms was found for a lubricated rail. By using a lubricant with friction modifiers the stresses was low enough to prevent crack propagation; at the same time, the rail was hard enough to reduce the wear rate. This is probably the most favourable state in terms of rail maintenance cost.</p><p>Roller bearings subjected to lubricant borne particles have been the subject of papers C, D and E in this thesis. Particles in the lubricating oil can have a significant impact on the wear in lubricated contacts. Even at low concentration levels can self-generated particles cause significant wear. The here presented results shows that filtration during run-in can significantly reduce both the mass loss and the number of self generated particles. A series of experiments has been carried out to study the wear of roller bearings by ingested lubricant borne hard particles. The form of the worn profile and the length of wear scratches correspond closely to the sliding within the contact. A count of the number of wear scratches on the rolling element surface indicates that the contact concentrates particles. A novel wear model based on the observation of a single point on the contacting surface when a concentration of particles passes through it has been developed and the necessary data for the model has been determined from the experiments. Comparison of the simulation results with the experimental results shows good qualitative agreement for the form change of the washer surfaces.</p>

No description available.

In diesem Beitrag werden neben der detaillierten Betrachtung der Wandervorgänge von Lagerringen primär die Simulationsmethodik bezüglich elastischer Zwischenschichten sowie die Ergebnisse einer FE-Parameterstudie präsentiert. Der Fokus liegt dabei auf Wälzlageraußenringen von Radiallagern unter Punktlast.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

No description available.

An investigation into an adaptable morphing concept for enhancing aircraft control and performance is described in this thesis. The impetus for the work was multi-legend. Initially, the work involved identifying and optimizing winglets on a swept wing baseline configuration to enhance the controllability and aerodynamic efficiency of unmanned aerial vehicles. Moreover, the other objective was to develop a realistic skin for a morphing aircraft concept that would allow subtle, more efficient shape changes to improve aircraft efficiency. In this regard, preliminary computations were performed with Athena Vortex Lattice modelling in which varying degrees of twist, swept and dihedral angle were considered. The results from this work indicated that if adaptable winglets were employed on small scale UAVs improvements in both aircraft control and performance could be achieved. Subsequent to this computational study, novel morphing wing and/or winglet mechanisms were developed to provide efficient shape changing as well as to develop a novel alternative method for a morphing skin. This new technique was numerically optimized in ANSYS Mechanical, experimentally investigated in a wind tunnel, and also compared with a baseline aileron configuration. Afterwards, flight testing was performed with an Extra 300 78 inch remote controller aircraft with the results being compared against existing fixed wing configurations. After evaluating numerical results, from various winglet configurations investigated in AVL, selected cases were found to provide good evidence that adaptable winglets, through morphing, could provide benefits for small scale aircraft control and performance as well as offering an acceptable alternative aircraft control methodology to the current discrete, 3-axis control philosophies. Using ANSYS Mechanical for structural analysis, rib configurations were also optimised in terms of weight, stress, and displacement, as well as required twist deformation magnitudes (±6° of twist achieved). Furthermore, the skin was found to be rigid with a low rate of surface wrinkling promoting a low drag surface. Ultimately, the viability of this novel concept mechanism was validated through flight testing with similar roll authority achieved compared to traditional aileron configuration. Finally, a morphing concept also provided potential shape changing performance with smooth aerodynamic surface finish. Leading to the possibility of the concept is being a viable skin for morphing application.

The effect of high temperature, high strain rate deformation on the evolution of second phase particles in commercial aluminium alloys has been investigated. Three model alloys provided by Novelis have been examined, and the evolution of particles during deformation has been examined for the alloy that most closely resembles the composition of alloys used in commercial applications. The effect of deformation mechanisms was expected to be an enhancement of diffusion controlled processes; therefore the first part of the work was to develop a heat treatment that would produce a fine distribution of dispersoid particles. This heat treatment was then used to prepare material for torsion testing, at strain rates similar to those found during the hot rolling stage of commercial production. Testing was performed at both the end of heat treatment temperature, to remove thermal effects, and at a lower temperature which more closely represents the temperature during commercial rolling. Material was examined by optical microscopy, FEGSEM and TEM and the particle populations were characterised by backscattered FEGSEM imaging and image analysis. This demonstrated that the disperoid particle population develops in multiple ways. Along with the enhancement of coarsening there is a significant shape change to the dispersoid particles, suggesting a change in the character of their interface. It has also been demonstrated that there is nucleation of new particles, despite a long prior hold time, in material deformed at the same temperature as the heat treatment. Material deformed at lower temperatures also demonstrated a larger increase in the volume fraction of dispersoid than material with the same thermal history. A constitutive model for diffusion enhancement and a model for particle evolution have been combined to simulate the effects of thermomechanical processing on the particle population.

Diversos tipos de defeitos superficiais estão presentes em barras laminadas (e produtos longos) e a presença destes defeitos pode ser muito prejudicial ao desempenho de peças, principalmente, quando se trata de aços para aplicação na cadeia automotiva, onde os níveis de exigência durante o forjamento da peça e durante a sua aplicação são extremamente elevados. Neste trabalho buscou-se determinar as condições operacionais mais apropriadas para a melhoria da qualidade superficial do produto laminado bruto com conseqüente redução de refugo e retrabalho ao longo de toda a cadeia de produção. O objetivo do trabalho é mostrar os defeitos de superficiais de dobra e escama como conseqüência de condições operacionais inapropriadas. Para isto aplicou-se uma metodologia que envolve a análise dos principais pontos de geração de defeitos, possibilitando um levantamento das causas. Com as ações propostas, buscou-se tornar o processo mais estável. Obtiveram-se melhorias significativas na qualidade superficial do material com acentuada redução no refugo por qualidade de aço produzido. / Several types of defects are present in rolled bars and their effects can be very harmful to the performance of mechanical parts, especially in the case of steels for application in the automotive industry, where quality requirements during forging and during its application are high. In this study we sought to determine the most appropriate operating conditions for the reduction of scrap caused by defects that originate in the rolling process, the analyzed defects were the so called overlap of rolling, scales and risks. For this a methodology that involved the analysis of the main points of generation of defects, allowing a survey of the causes was applied. With the proposed actions it was aimed at making the process more stable. This led to a significant improvement in surface quality of the material with marked reduction in scrap for each kind of steel.

Orientador: Marcelo dos Santos Pereira / Banca: Ana Paula Rosifini Alves Claro / Banca: Rafael Humberto Mota de Siqueira / Resumo: Os fabricantes de latas vêm se tornando cada vez mais exigentes na qualidade e propriedades dos materiais utilizados na confecção de seus produtos. Um dos metais mais usados na indústria de manufatura de componentes obtidos através de estampagem e estiramento, como na fabricação de corpo de latas de bebidas, trata-se da liga de Alumínio AA3104. Isto se deve às suas propriedades mecânicas, estampabilidade, entre outra. Ela pertence ao grupo 3XXX, sendo que seu principal elemento de liga é o manganês (em pequenas quantidades / teores). Trata-se de uma liga não tratável termicamente, sendo que suas propriedades mecânicas são melhoradas a partir da formação de solução sólida e / ou deformação à frio. Desta forma, o presente estudo teve como objetivo avaliar de maneira detalhada a influência de duas diferentes condições de laminação à frio sobre o comportamento mecânico e microestrutural da liga de Alumínio AA3104: laminação à frio com tempo de resfriamento intermediário e sem tempo de resfriamento intermediário entre passes. A análise mecânica, por meio do Ensaio de Tração, mostrou que os materiais laminados com tempo de resfriamento intermediário obtiveram maiores valores de Limite de Escoamento (283,1 MPa) e Limite de Resistência a Tração (309,3 MPa) do que aqueles materiais laminados sem este tempo de resfriamento intermediário (273,2 e 300,0 MPa, respectivamente). Isto foi justificado pelo aumento da quantidade de partículas de segunda fase precipitados na matriz da liga, que... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The manufacturers of cans have become increasingly demanding in quality and in the properties of the materials used to make their products. One of the most used metals in the manufacturing industry of components obtained by stamping, as in the manufacture of beverage cans body, is the AA3104 Alloy. This is due to its mechanical properties, stampatability, among others. It belongs to the 3XXX group, and its main alloying element is manganese (in small amounts / contents). It is an alloy not thermally treatable, where its mechanical properties are improved from the formation of solid solution and / or cold forming. Therefore, the present study had as objective to evaluate in detail the influence of two different conditions of cold rolling on the mechanical and microstructural behavior of the aluminum alloy AA3104: cold rolling with intermediate cooling time and without intermediate cooling time between passes. The mechanical analysis, through the Tensile Test, showed that rolled materials with intermediate cooling time obtained higher values of Yield Strength (283,1 MPa) and Ultimate Tensile Strength (309,3 MPa) than those laminated materials without this intermediate cooling time (273,2 and 300,0 MPa, respectively). This was justified by the increase in the amount of second phase particles and precipitated dispersions in the alloy matrix, which made difficult the movement of dislocations, making the material more resistant / Mestre