Wheel wear profiles are interesting for both economic and performance reasons. A good wheel profile design should be able to resist wear and to allow stable vehicle running. The ability to resist wear reduces the wheel reprofiling and replacement cost. The ability to allow stable vehicle running is important for safety and ride quality. In this work, a wear model based upon the work done in the wheel/rail contact patch is used to predict wheel wear profiles. The effects of train dynamic response, random rail alignment and the non-linearity of wheel/rail contact geometry are included The distribution of contact patch work is obtained by discretized method and applied to the wheel wear problem. Using the contact patch work wear model, consecutive wheel wear profiles for tread contact and slight flange contact are predicted. These analytical wear profiles match well with experimental results and other analytical approaches. / Master of Science

A method is presented for the prediction of the wear history of a train wheel by a numerical simulation. The method consists of three fundamental steps. First, the wheel/rail contact geometry is characterized. Contact points, Herzian contact patch area and creep coefficients are determined as functions of the wheelset lateral position. Second, a time history of the wheelset positions and velocities is determined from a simulation of the vehicle response to a specified track input. Finally, a wear algorithm dependent on the geometry and the dynamics is used to compute the amounts of material to be removed at the discrete points describing the wheel profile. The process is repeated recurrently to simulate the gradual wearing of the wheel. The method has been tested with several different wear models and it has been found that worn profiles are relatively insensitive to the selection of wear model. A parametric study on the effect of creep coefficient and payload on wear rate has been used to differentiate the wear models. Results include predictions of AAR and CN worn wheel profiles. The predictions show that the CN profile wears parallel to the new profile. This trend has been observed in practice. / M.S.

Orientador: Paulo Roberto Mei / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-16T10:24:52Z (GMT). No. of bitstreams: 1 VillasBoas_RenatoLyra_M.pdf: 13424471 bytes, checksum: c7a6d60275922ab9255b8f8e74fd29e1 (MD5) Previous issue date: 2010 / Resumo: Neste trabalho foi desenvolvido um aço microligado com 0,7% de carbono para fabricação de rodas ferroviárias. Tomou-se como base um aço classe C da norma AAR M-107 e adicionou-se nióbio e molibdênio. A pesquisa foi realizada em duas etapas distintas. A primeira etapa estudou-se o efeito da adição de nióbio e molibdênio no aço com 0,7% de carbono antes e após a deformação por laminação, simulando o forjamento real das rodas ferroviárias produzidas na MWL Brasil. Com os dados disponíveis passou-se à segunda etapa da pesquisa onde foram fabricadas e ensaiadas rodas ferroviárias na MWL Brasil usando um aço com composição química semelhante à utilizada na primeira etapa para observar o efeito do nióbio e molibdênio nas mesmas. Os aços foram austenitizados a 1250 °C para solubilização do nióbio na austenita e deformados a partir de 1200 °C. Na primeira etapa o aço foi laminado em 4 passes sofrendo uma deformação total na espessura de 67% e resfriado ao ar. Na segunda etapa, o aço foi forjado pelo processo de fabricação usado pela MWL Brasil. Após o tratamento térmico, foram realizados ensaios de dureza da perlita, tração, impacto, tenacidade à fratura, além de microscopia ótica e medida do tamanho de grão austenítico. Observou-se aumento no limite de escoamento (8,5%), ductilidade (15%), energia de impacto (29%), tenacidade à fratura (33%) e temperabilidade pela microadição de nióbio e molibdênio, mostrando que esses elementos podem melhorar o desempenho das rodas ferroviárias atualmente produzidas. / Abstract: In this work it was developed a microalloyed steel with 0.7% carbon to manufacture railway wheels. It was taken as basis a steel class C of standard AAR M-107 and added niobium and molybdenum. The research was conducted in two stages. The first step was studied the effect of the addition of niobium and molybdenum on 0.7% C steel before and after deformation by rolling, simulating the actual forging of railroad wheels process in MWL Brasil. With the available data the second stage of the research was conducted, manufacturing and testing railway wheels in MWL Brasil, using a steel with similar chemical composition to that was used in the first step to observe the effect of niobium and molybdenum in them. The steels were austenitized at 1250 °C for niobium solubilization in austenite and deformed from 1200 °C. In the first stage, the steels were rolled at 4 passes undergoing a total deformation of 67% in thickness and aircooled. In the second step, the steels were forged by MWL Brasil manufacturing process. After heat treatment, tests on pearlite hardness, tensile, impact, fracture toughness were performed. Microstructure was observed by optical microscopy and the austenite grain size was measured. It was observed an increasing on the yield strength (8,5%), ductility (15%), impact energy (29%), fracture toughness (33%) and hardenability by niobium and molybdenum microalloying, showing that these elements can improve the performance of railway wheels nowadays produced by MWL Brasil. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

This work addresses the advanced probabilistic modeling of the stochastic nature of microgrinding in the machining of high-aspect ratio, ceramic micro-features. The heightened sensitivity of such high-fidelity workpieces to excessive grit cutting force drives a need for improved stochastic modeling. Statistical propagation is used to generate a comprehensive analytic probabilistic model for static wheel topography. Numerical simulation and measurement of microgrinding wheels show the model accurately predicts the stochastic nature of the topography when exact wheel specifications are known. Investigation into the statistical scale affects associated microgrinding wheels shows that the decreasing number of abrasives in the wheel increases the relative statistical variability in the wheel topography although variability in the wheel concentration number dominates the source of variance. An in situ microgrinding wheel measurement technique is developed to aid in the calibration of the process model to improve on the inaccuracy caused by wheel specification error. A probabilistic model is generated for straight traverse and infeed microgrinding dynamic wheel topography. Infeed microgrinding was shown to provide a method of measuring individual grit cutting forces with constant undeformed chip thickness within the grind zone. Measurements of the dynamic wheel topography in infeed microgrinding verified the accuracy of the probabilistic model.

Orientador: Eduardo Carlos Bianchi / Coorientador: Luiz Eduardo de Angelo Sanchez / Banca: Hamilton José de Mello / Banca: Alessandro Roger Rodrigues / Resumo: A aplicação de ferro fundido nodular perlítico na indústria vem se destacando devido a sua elevada resistência mecânica e possibilidade de fácil manufatura, uma vez que sua alta fluidez permite fundir peças com dimensões próximas à final. Entretanto, em componentes que exigem elevada precisão dimensional, como eixos virabrequins, pistões e bielas, por exemplo, é indispensável a utilização do processo de retificação. A indústria desenvolveu diversos tipos de grãos abrasivos de óxido de alumínio para essa aplicação. Todavia, o desenvolvimento de novos grãos abrasivos visa readequar o seguimento, de modo a aplicar no mercado uma nova classe de grãos abrasivos de nitreto de boro cúbico (CBN), suprindo uma lacuna existente no desenvolvimento industrial. Desta forma, foram desenvolvidos diversos tipos de grãos abrasivos de CBN com diferentes níveis de friabilidade, visando assim um melhor desempenho de acordo com determinado processo. Embora a retificação de ferro fundido nodular perlítico seja ampla na indústria, são escassos os estudos pertinentes ao assunto, sendo exíguo sua aplicação quando relacionado a friabilidade de grãos abrasivos. Portanto, vislumbrou-se o estudo do tema a partir da iniciativa da indústria, fabricante de rebolos de CBN, para o entendimento dos fenômenos relacionados ao processo, catalogando o funcionamento dos rebolos e estabelecendo relações em prol do seu desempenho durante o processo de retificação. Deste modo, a rugosidade média aritmética, desvios de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The application of pearlitic ductile cast iron in the industrial sector has been outstanding due to its high mechanical resistance and possibility of easy manufacture, since its high fluidity allows melting pieces with dimensions close to the end. However, for components requiring high dimensional precision, such as crankshafts, pistons and connecting rods, for example, it is essential to use the grinding process. The industry has developed various types of aluminum oxide abrasive grains for this application. Thereby, the development of new abrasive grains aims at re-adjusting the follow-up, so that a new class of cubic boron nitride (CBN) abrasive grains is available on the market, supplying a gap in industrial development. Thus, different types of CBN abrasive grains with different levels of friability were developed, aiming at a better performance according to a certain process. Although the grinding of pearlitic ductile cast iron is ample in the industry, the pertinent studies are rare, and its application is scarce when related to the friability of abrasive grains. Therefore, the study of the theme was glimpsed from the initiative of the industry, manufacturer of CBN grinding wheels, to understand the phenomena related to the process, cataloging the grinding of the grinding wheels and establishing relationships in favor of its performance during the grinding process. In this way, the average surface roughness, roundness deviation, diametrical wear wheel, G-ratio, electri... (Complete abstract click electronic access below) / Mestre

Thesis (Ph.D.)--Ohio University, June, 2009. / Release of full electronic text on OhioLINK has been delayed until June 1, 2012. Includes bibliographical references (leaves 371-443)

Thesis (Ph.D.)--Ohio University, June, 2009. / Title from PDF t.p. Release of full electronic text on OhioLINK has been delayed until June 1, 2012. Includes bibliographical references (leaves 371-443)

This doctoral thesis extends analytical terramechanic modelling for small lightweight mobile robots operating on sandy soil. Previous terramechanic models were designed to capture and predict the mean values of the forces and sinkage that a wheel may experience. However, these models do not capture the fluctuations in the forces and sinkage that were observed in experimental data. The model developed through the course of this research enhances existing terramechanic models by proposing and validating a new pressure-sinkage relationship. The resulting two-dimensional model was validated with a unique high fidelity single-wheel testbed (SWTB) which was installed on a Blohm Planomat 408 computer-numerically controlled creepfeed grinding machine. The new SWTB translates the terrain in the horizontal direction while the drivetrain and wheel support systems are constrained in the horizontal direction but allowed to freely move in the vertical direction. The design of the SWTB allowed for a counterbalance to be installed and, as a result, low normal loads could be examined. The design also took advantage of the grinding machine's high load capacity and precise velocity control. Experiments were carried out with the new SWTB and predictable repeating ridges were found in the track of a smooth rigid wheel operating in sandy soil. To ensure that these ridges were not an artifact of the new SWTB a mobile robot was used to validate the SWTB findings, which it did. The new SWTB is a viable method for investigating fundamental terramechanic issues. A series of experiments at different slip ratios and normal loads were carried out on the SWTB to validate the new pressure-sinkage relationship which explicitly captures and predicts the oscillations about the mean values for the forces and sinkage values for both a smooth wheel and a wheel with grousers. The new pressure-sinkage relationship adds two new dimensionless empirical factors to the well known pressure-sinkage relationship for a rigid wheel. The first new factor accounts for changes in the local density of the terrain around the wheel and the second factor accounts for the effects grousers have on the forces and sinkage.

Thesis (M.J.) - Carleton University, 2002. / Includes bibliographical references (p. 190-203). Also available in electronic format on the Internet.

Thesis--Copenhagen. / Summary in Danish. Includes bibliographical references and index.