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Ces travaux de thèse concernent l'étude du contact à grande vitesse pouvant intervenir entre le pied de l'aube et l'alvéole du disque (tous deux en Ti6Al4V) de la soufflante du turboréacteur CFM56. Le comportement et les modes d'endommagement associés à ce type d'événements restent méconnus et peu traités dans la littérature. L'utilisation d'un tribomètre spécifique adapté sur un banc balistique, d'un thermocouple feuille-pièce et de modélisations numériques (éléments finis) ont permis d'étudier les liens existants entre vitesse, pression, température et efforts de frottement. Les endommagements induits ont ensuite été analysés en étudiant l'usure et l'évolution de la microstructure en sous surface (MEB, Imagerie 3D et EBSD). Une modélisation semi-analytique basée sur le cisaillement adiabatique des aspérités a été développée pour étudier l'évolution de la taille de la surface réelle de contact. En associant ce modèle à deux essais expérimentaux, des enveloppes inférieures et supérieures de l'évolution du coefficient de frottement pour une large gamme de vitesse de glissement ont été calculées. Ce travail de thèse est le fruit d'une collaboration entre la société Snemca, le LaBPS (Laboratoire de mécanique, Biomécanique, Polymères et Structure) et le LEM3 (Laboratoire d'étude des Microstructures et de Mécanique des Matériaux) / In case of exceptional events in aircraft engines (bird ingestion or blade disassembly), blade motions induce sliding at the interlock between the blade root and the slot of the fan rotor. The interface then undergoes quasi-instantaneous sliding under high normal pressure. This thesis work was initiated to investigate this phenomena and deals therefore with extreme sliding interactions for a Ti6Al4V tribopair (aircraft engine CFM56). Interface behavior and wear modes associated to these extreme thermomechanical loads remain poorly studied in literature. Links between velocity, pressure, temperature and friction force have been investigated by using a specific tribometer adapted on a ballistic bench, a foil-workpiece thermocouple and finite elements analysis. Induced damage were then analyzed by studying wear and microstructure evolutions (SEM, nanotomography and EBSD). A semi-analytical model, based on adiabatic shearing of asperities, has been proposed to evaluate the evolution of the real area of contact. By associated the latter with two experimental tests, upper and lower estimations of the mean friction force for a large velocity range can be calculated. This work is the result of collaboration between aircraft manufacturer Snecma, the LaBPS (Laboratory of Mechanics, Biomechanics, Polymers and Structures) and the LEM3 (Laboratory of Microstructure and Mechanics of Materials)

FSW is a welding technique invented and patented by The Welding Institute in 1991. This welding technique utilises the benefits of solid-state welding to materials regarded as difficult to weld by fusion processes. The productivity of the process was not optimised as the real-time dynamics of the material and tool changes were not considered. Furthermore, the process has a plastic weld region where no traditional modelling describing the interaction between the tool and work piece is available. Fuzzy logic technology is one of the artificial intelligent strategies used to improve the control of the dynamics of industrial processes. Fuzzy control was proposed as a viable solution to improve the productivity of the FSW process. The simulations indicated that FLC can use feed rate and welding speed to adaptively regulate the feed force and tool temperature respectively, irrespective of varying tool and material change. The simulations presented fuzzy logic technology to be robust enough to regulate FSW process in the absence of accurate mathematical models.

Orientadores: Cecilia Amelia de Carvalho Zavaglia, Marcelo de Carvalho Reis / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T01:42:37Z (GMT). No. of bitstreams: 1 Bavaresco_VanessaPetrilli_D.pdf: 14276021 bytes, checksum: d5ab24900afcc34fe160b1d9a55fa2bd (MD5) Previous issue date: 2004 / Resumo: O desenvolvimento de próteses articulares com superfície complacente, capaz de favorecer ou permitir a lubrificação entre os componentes das juntas artificiais, como acontece nas juntas naturais, vem despertando grande interesse visto que diminui o coeficiente de atrito entre as superfícies, favorecendo o deslizamento entre as mesmas e minimizando o desgaste. A proposta deste trabalho foi estudar e melhorar as propriedades mecânicas de hidrogéis poliméricos de poli (metacrilato de 2-hidroxietila) (pREMA) e poli (álcool vinílico) (PVA) reconhecidamente utilizados no estudo de reparadores da cartilagem articular natural. Para tanto foram obtidos copolímeros de pREMA e n-vinil pirrolidona (NVP) (polímero hidrofílico de reforço) variando-se a concentração de agente de reticulação e blendas de poliHEMA com o copolímero poli(metacrilato de metila-co-ácido acrílico) (75:25) enquanto que, os hidrogéis a base de poli (álcool vinílico) foram reticulados com radiação ionizante de feixe de elétrons. O estudo envolveu a caracterização térmica, mecânica e morfológica desses materiais bem como sua caracterização quanto ao desgaste em um equipamento do tipo PIN-ON-DISK com uma contra-superficie de metal em condições próximas à fisiológica com movimento relativo rotativo e, ainda, com movimento recíproco ou alternado / Abstract: There is an increasing interest in the development of soft layered articular prostheses, which favour sliding between components, as natural joints do, thus reducing contact stresses and wear. The purpose of this work was to characterize and improve the mechanical properties of poly (2-hydroxyethyl metacrylate) (pHEMA) and polyvinyl alcohol (PVA) hydrogels. These hydrogels are extensively studied for articular cartilage repair. Samples of pHEMA and n-vinyl pirrolidone (NVP) copolymers with different amounts of trimethylol propane trimethacrylate (TMPTMMA) crosslinking agent, and samples of pHEMA/poly (methyl metacrylate-co-acrylic acid) blends were prepared by thermal polymerization. Additionally, PVA based hydrogels were prepared by means of electron beam ionizing radiation. Hydrogel samples were characterized by indentation creep test, equilibrium water content (EWC) and Differential Scanning Calorimetry (DSC). The tribological characterization of hydrogels was performed under nearly looading physiological conditions at room temperature on a pin-on-disc equipment, Plint TE67, using a stainless steel 316L disc counter surface / Doutorado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

The ability of a lubricating oil to reduce friction in mechanical surfaces which are in relative sliding motion depends on the base oil behaviour. Previous studies have demonstrated that temperature has a significant influence on the friction behaviour of mineral and synthetic base oils by using a laboratory based friction testing machine. However, the effect of a constantly changing load under different temperature conditions has not been explored fully. In this study, the effect of an increasing load on the friction behaviour of four six different mineral base oils and a polyalphaolefin (PAO) base oil were studied using the SRV4® tribometer. The sliding surfaces were AISI 52100 steel ball and disc. The average loads (range: 50 – 250 N), temperatures (range: 40 – 120 oC), relative humidity of 20 % and a sliding speed of 0.2 m.s-1 were selected as the test conditions. The seven base oils were selected from four API base oil groups. Stribeck curves were used as a tool to characterize the friction behaviour of the base oils. The results show that for all the base oils, the coefficient of friction and the Stribeck parameter decrease gradually with the increase in applied normal load under constant temperature conditions. The increase in temperature increased the coefficient of friction and decreased the Stribeck parameter at each load stage. The external friction mechanisms dominated the friction behaviour under all test conditions. Viscosity showed a strong influence on the film forming characteristics of the seven base oils only at 40 and 60 oC. Between 80 and 120 oC, the oil-surface interactions were predominant. The results further demonstrated that effect of an increasing temperature on the coefficient of friction was bigger between 80 and 100 oC for all Group III base oils and was consistent between 40 and 120 oC for the Group III+ and PAO base oil. The highly saturated (PAO and Group III+) base oils have demonstrated good thermal stability and less reactivity compared to the less saturated base oils (GI and GIII) under all test conditions. The friction behaviour of the PAO base oil was the most affected by the presence of dissolved water. The presence of water proved to increase the friction at the sliding steel interfaces. / Dissertation (MEng)--University of Pretoria, 2018. / Chemical Engineering / MEng / Unrestricted

Friction contact with both external and internal environments can significantly influence its efficiency, which could cause friction instabilities, vibration, and noise. Focusing on the effects that troubles brake pad, rotor, and friction-induced NVH, the main motivation for this study is to understand its drawbacks for some extent in a braking system. By proper study on applied statistics, an experimental design is planned. The design has friction tests that are performed by scaling down real test properties used in dynamometer to scaled-down properties in a subscale tester by using scaling law of physics. The test has two different types of rubbers with different humidity conditions with respect to two different brake pads in a small-scale tester, the Universal Mechanical Tester (UMT). This friction experiment helps in determining how different rubbers impact its stiffness on the coefficient of friction and noise levels, also to evaluate which scenario has the better damping capacity. The effect on the coefficient of friction and noise levels with and without rubbers is also compared. The results are subjected to the Design of Experiments analyses test know the statistical relationship between factors affecting the process and output of that process at different controllable variables namely humidity and temperature.

Magnesium is the lightest metal with a very high specific strength. However, its practical applicability is limited by its toughness and reliability. Mg, being HCP has low ductility. This makes the improvement of toughness a grand challenge in Mg alloys. Friction stir processing (FSP) is a thermomechanical technique used to effect microstructural modification. Here, FSP was utilized to affect the toughness of WE43 sheets through microstructural modification. Room temperature Kahn-type tests were conducted to measure the toughness of WE43 sheets. Microscopic techniques (SEM, TEM) was utilized to study the effect of various microstructural factors like grain size, texture, constituent particles, precipitates on crack initiation and propagation. Tensile properties were evaluated by mini-tensile tests. Crack growth in WE43 sheets was also affected by mechanics and digital image correlation (DIC) was utilized to study the plastic zone size. The underlying mechanisms affecting toughness of these sheets were understood which will help in formulating ways in improving it. WE43 nanocomposites were fabricated via FSP. Uniform distribution of reinforcements was obtained in the composites. Improved mechanical properties like that of enhanced strength, increased hardness and stiffness were obtained. But contrary to other metal matrix composites which show reduction in ductility with incorporation of ceramic reinforcements, the nanocomposites showed good strength-ductility combination. The composites were precisely characterized and mechanisms governing this property were studied. The nano-length of the reinforcements was observed to be the main criteria and the dislocation-particle interaction, the main reason behind the strength-ductility property.

The Swedish road network is maintained by the Swedish Transport Administration, municipalities, and entrepreneurs with the goal of keeping the roads in satisfactory condition for traffic. The road operators are responsible for different roads and have several legislations that regulate construction and operation. One important aspect of winter road maintenance is the monitoring of the road situation ahead in order to call out resources for preventive measures. This study is performed at the company NIRA Dynamics with the purpose of going towards more digitized winter road information. The study explores different winter maintenance organizations in Sweden, investigates the importance of the information needed to be able to detect when roads are deemed too risky, and tries to gain an understanding of how the vehicle data provided by NIRA Dynamics best can provide a service for the winter road maintainers. This study is based on eight semi-structured interviews, user-tests aswell as a literature study. The findings of the study show that different winter maintenance organizations can differ a lot depending on the size and governing policies of the municipalities or entrepreneurs. The main differences can be found in their requirements and their method of monitoring the road situation ahead. The findings also show that the vehicle data is promising and has the potential to optimize and improve the overall winter maintenance planning. However, implementing and understanding the vehicle data in a real-world context requires collaboration from the different organizations to fulfill its value.

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