Title from PDF of title page. / Document formatted into pages; contains 78 pages. / Thesis (M.S.M.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: This thesis focuses on identifying hard material pairs with low roughness, high coefficient of static friction, high wear resistance and high modulus of elasticity, suitable for sliding in dry friction conditions under a normal load. A wide range of materials including various steels, various coatings on tool steels deposited by various deposition techniques and different ceramics were examined and considered for tribological testing. Procedures and sequences were developed for conducting tribology tests on the material pairs. High endurance - low cycle tests were conducted and based on the performance of material pairs with respect to friction, wear and surface roughness a small set of material pairs and coatings was selected for further testing. High endurance - high cycle tests were performed on an additional seventeen pairs of material pairs selected for long term sliding. / ABSTRACT: Material pairs were selected for low endurance tests based on high corrosion resistance along with all the above specified design parameters. Low endurance tests were conducted to identify material pairs sliding for a short distance in humid environments. Results are tabulated and pictures of the material pairs after wear tests are presented. It was found that four material pairs for high endurance applications and two pairs for the low endurance applications performed very well in regard of design specifications. These material pairs find a major application in friction clamps of an Inchworm motor resulting in enhancement of force output of the motor. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

This thesis deals with the experimental description of friction between steel and wood materials, specifically laminated veneer lumber (LVL) and pine wood with two types of annual rings. It studies the influence of a number of different parameters on the coefficient of friction such as contact pressure, moisture content, fiber orientation in relation to the load direction, steel surface roughness, and horizontal load rate. First, the theoretical mechanical and physical properties as well as the coefficient of friction itself are described. This is followed by the description of the test setup including the test method and how the obtained data is exported, handled and processed and how the coefficient of friction is determined. The results study the influence of different parameters and show that the coefficients of friction for the smooth sliding plate tests vary in between 0.1 and 0.3, whereas tests with the rough sliding plate vary around 0.7. Factors influencing the coefficient of friction were found to be the different moisture content under all tested pressures, the different fiber direction under low contact pressure, the contact pressure itself, though under higher pressures the influence was found to be low, and the horizontal load rate under low pressures. The outcomes are further discussed in the discussion chapter.

Friction is one of the important parameters in metal forming processes since it affects metal flow in the die, forming load, strain distribution, tool and die life, surface quality of the product etc. The range of coefficient of friction in different metal forming applications is not well known and the factors affecting variation are ambiguous. Commercially available FEA packages input the coefficient of friction as constant among the whole process which is not a realistic approach. In this study, utility of user-subroutines is integrated into MSC SuperForm v.2004 and MSC Marc v.2003 FEA packages, to apply a variable coefficient of friction depending on the contact interface conditions. Instead of using comparatively simple friction models such as Coulomb, Shear (constant) models, friction models proposed by Wanheim-Bay and Levanov were used to simulate some cold forging operations. The FEA results are compared with the experimental results available in literature for cylinder upsetting. Results show that, large variation on the coefficient of friction is possible depending on the friction model used, the part geometry and the ratio of contact normal pressure to equivalent yield stress. For the ratio of contact normal pressure to equivalent yield stress values above 4, coefficient of friction values are approximately same for both friction models.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Rick Neu; Committee Member: Itzhak Green; Committee Member: Jeffrey Streator

Um processo alternativo à solda por arco para aplicação em materiais de difícil junção ou em ambientes submersos é a solda por fricção. Neste trabalho foi desenvolvido um equipamento de solda por fricção para pesquisas e determinação de parâmetros ótimos de soldagem em diferentes meios. Para verificar o desempenho do equipamento foi utilizado o processo de solda por fricção de pinos consumíveis. Os registros das variáveis de soldagem permite avaliar o comportamento do sistema para a faixa de operação utilizada. Diferentes uniões de aço de baixo carbono e aço de baixa liga foram obtidas. Mediante análises macrográficas da junta foi avaliada a zona afetada pelo calor e a presença de regiões com possível falta de preenchimento. O controle servohidráulico desenvolvido apresenta uma resposta dinâmica adequada para esta aplicação, no entanto são apresentadas algumas propostas de melhorias. / An alternative process to the conventional arc welding for mating difficult-to-join materials or in underwater environment is friction welding. During this work a friction welding equipment was developed for research and determination of optimum welding parameters under different environments. To evaluate the equipment performance the friction hydro pillar processing method was used. Data acquisition of the welding parameters allows assessing the system behavior within the operational range. Joints of low carbon and low alloy steels have been obtained. Macrographic analyses of the weld joint were performed to evaluate the heat affected zone and the presence of unfilled regions. The servohydraulic control developed have shown an adequate dynamic response for this application, nevertheless some improvements are proposed.

Over the years, numerous studies have been conducted for the development of alternative materials for better performance of brake pads. With a huge selection of materials, automobile manufacturers must prioritize the performance standards, safety, cost and environmental factors of the brake pads. To improve the friction performance of brake pads, maintain customers comfort level and environment safety, design engineers test and verify the best materials to satisfy the federal performance standards. Raw materials of brake pads compose of different categories such as organic, semi metallic and low-metallic. Besides the difference in composition, these materials affect the brake pads in terms of friction properties, wear rates and noise levels. It is crucial for engineers and manufacturers to improve friction stability while minimizing vibration by manipulating the composition of different raw materials and additive materials. Automotive brake pads normally consist of numerous metallic and composite materials that are formed by hot compression which can result in various mechanical properties [14]. This research proposes to investigate different composition of metallic raw materials and how their frictional performance is affected under different environmental testing standards. This research investigates the frictional performance of six types of raw materials with different mechanical properties and morphology using a universal mechanical tester (Bruker UMT). This paper examines the overall friction performance, coefficient of friction and creep groan behavior of six different raw materials under different humidity levels. By scrutinizing the static and kinetic coefficient of friction(COF) at different humidity levels, humidity-induced friction instability at low speed is studied and presented in this paper. After performing friction tests for each material, it was concluded that the friction performance and kinetic coefficient of friction of the brake pad samples were drastically affected by longer exposure to humid air.

Um processo alternativo à solda por arco para aplicação em materiais de difícil junção ou em ambientes submersos é a solda por fricção. Neste trabalho foi desenvolvido um equipamento de solda por fricção para pesquisas e determinação de parâmetros ótimos de soldagem em diferentes meios. Para verificar o desempenho do equipamento foi utilizado o processo de solda por fricção de pinos consumíveis. Os registros das variáveis de soldagem permite avaliar o comportamento do sistema para a faixa de operação utilizada. Diferentes uniões de aço de baixo carbono e aço de baixa liga foram obtidas. Mediante análises macrográficas da junta foi avaliada a zona afetada pelo calor e a presença de regiões com possível falta de preenchimento. O controle servohidráulico desenvolvido apresenta uma resposta dinâmica adequada para esta aplicação, no entanto são apresentadas algumas propostas de melhorias. / An alternative process to the conventional arc welding for mating difficult-to-join materials or in underwater environment is friction welding. During this work a friction welding equipment was developed for research and determination of optimum welding parameters under different environments. To evaluate the equipment performance the friction hydro pillar processing method was used. Data acquisition of the welding parameters allows assessing the system behavior within the operational range. Joints of low carbon and low alloy steels have been obtained. Macrographic analyses of the weld joint were performed to evaluate the heat affected zone and the presence of unfilled regions. The servohydraulic control developed have shown an adequate dynamic response for this application, nevertheless some improvements are proposed.

L'optimisation de nombreux procédés technologiques requiert une compréhension approfondie des phénomènes de frottement des papiers. Nous avons donc cherché à mieux comprendre ces phénomènes pour tenter d'améliorer la séparation des enveloppes dans les machines à affranchir. Les méthodes normalisées de mesure du frottement papier-papier se sont tout d'abord avérées limitées en termes de répétabilité et de conditions expérimentales. Nous avons donc développé deux méthodes de mesure, l'une à faible et l'autre à haute vitesses. Nous avons aussi adapté la mesure du frottement aux différents contacts papier rencontrés dans les machines à affranchir. Dans un second temps, nous avons utilisé ces méthodes pour étudier les mécanismes responsables du frottement avec le matériau papier. Nous avons notamment étudié (i) la dépendance du frottement papier-papier à la direction et longueur du déplacement, (ii) l'influence de la température et de l'humidité sur le frottement papier-papier et (iii) les principales caractéristiques frictionnelles des contacts enveloppe-enveloppe, papier-rouleau et papier-patin. Dans un troisième temps, nous avons développé un modèle complet de la séparation des enveloppes dans une machine à affranchir. Cette séparation vise à déplacer, sans l'abimer, l'enveloppe inférieure d'une pile – et uniquement cette enveloppe. Le modèle a permis d'identifier, de caractériser et de proposer une optimisation des principaux paramètres de ce procédé. / The improvement of numerous technological processes requires a deep understanding of the paper friction phenomena. Thus, we tried to obtain a better understanding of those phenomena to improve the envelopes separation in franking machines. The standad methods for measuring the paper-on-paper friction force appeared to be limited in terms of repeatability and experimental conditions. Thus, we developed two experimental methods, at low and high speeds, respectively. We also adapted the friction measurement methods to the different contacts found in franking machines. We then used those methods to study the mechanisms responsible for the friction with the paper materials. In particular, we studied (i) the dependency of the paper-on-paper friction to the direction and length of the displacement, (ii) the influence of temperature and humidity on the paper-on-paper friction, and (iii) the main frictional properties of the envelope-on-envelope, rollers-on-paper, and pads-on-paper contacts, respectively. To finish with, we developed a model of the envelopes separation inside a franking machine. This process aims at displacing - with no damage - the bottommost envelope of a stack - and only this envelope. The model allowed us to identify, to characterize, and to propose an optimization of the main process parameters.

Les travaux de cette thèse concernent le développement d’un modèle par éléments discrets du comportement thermo-mécanique d’un alliage d’aluminium et de son évolution microstructurale lorsqu’il est soumis à des conditions de grandes déformations et/ou de grandes vitesses de déformation (soudage par friction-malaxageou FSW). Le procédé de « soudage par friction malaxage » (Friction Stir Welding,FSW) est un procédé de soudage récent, inventé en 1991 par « The Welding Institute (TWI) ». Ce procédé se distingue des autres par sa capacité à souder la matière à l’état visqueux, sans atteindre le point de fusion. Le principe est relativement simple et comparable à une opération de fraisage, si ce n’est que l’outil coupant est remplacé par un outil malaxant composé d’un pion et d’un épaulement. Ce procédé revêt un fort intérêt pour l’industrie aéronautique, car il offre la possibilité de souder des alliages d’aluminium des séries 2XXX et 7XXX, réputés difficiles à souder par d’autres procédés.Le soudage par friction-malaxage étant un procédé récent, il demeure encore un sujet de recherche actif, pour mieux appréhender certains points comme l’écoulement de la matière, l’influence des paramètres du procédé (vitesse de rotation, forme de l’outil, ...)et la modification de la microstructure. Ce dernier point est particulièrement important pour les alliages à durcissement structural comme ceux des séries 2XXX et 7XXX. Pour ces alliages d’aluminium, les propriétés mécaniques dépendent étroitement de leur état de précipitation, lui-même influencé par l’apport de chaleur généré lors du soudage.L’optimisation des paramètres de soudage par rapport aux propriétés mécaniques passe obligatoirement par la prédiction de l’état de la précipitation le long du joint soudé. Le travail de la thèse vise à mettre en place des modèles à l’échelle de la microstructure permettant de prévoir la modification des propriétés de la matière liées aux paramètres du procédé. / The work of this thesis concerns the development of a model using the discrete element method, for the thermo-mechanical behavior of an aluminum alloy and its microstructural evolution when exposed to conditions of large deformations and/or high deformation rates (Friction StirWelding or FSW). Friction stir welding is a recent welding process invented in 1991 by "The welding Institute" (TWI). This process is different from the others by its ability to weld material in the viscous state, without reaching the melting point. The principle is relatively simple and similar to a milling process except that the cutting tool is replaced by a rotary tool composed of a pin and a shoulder. This process is of great interest in the aircraft industry because it offers the possibility to weld aluminum alloys 2XXX and 7XXX series, known to be difficult to weld by other processes. Since friction stir welding is a recent process, it still remains a subject of active research, to better understand certain issues such as material flow, influence of process parameters (rotation speed, tool shape, ...) and the modification of the microstructure. This last point is particularly important for structural hardening alloys such as those of the 2XXX and 7XXX series. For these aluminum alloys, the mechanical properties are highly dependent on their state of precipitation, which is itself influenced by the heat generated during thewelding. The optimization ofwelding parameters in order to obtain good mechanical properties requires the prediction of precipitation state along thewelded joint. Thework of this thesis is to develop required models at the scale of microstructure allowing to predict the modification of material properties related to the process parameters

Um processo alternativo à solda por arco para aplicação em materiais de difícil junção ou em ambientes submersos é a solda por fricção. Neste trabalho foi desenvolvido um equipamento de solda por fricção para pesquisas e determinação de parâmetros ótimos de soldagem em diferentes meios. Para verificar o desempenho do equipamento foi utilizado o processo de solda por fricção de pinos consumíveis. Os registros das variáveis de soldagem permite avaliar o comportamento do sistema para a faixa de operação utilizada. Diferentes uniões de aço de baixo carbono e aço de baixa liga foram obtidas. Mediante análises macrográficas da junta foi avaliada a zona afetada pelo calor e a presença de regiões com possível falta de preenchimento. O controle servohidráulico desenvolvido apresenta uma resposta dinâmica adequada para esta aplicação, no entanto são apresentadas algumas propostas de melhorias. / An alternative process to the conventional arc welding for mating difficult-to-join materials or in underwater environment is friction welding. During this work a friction welding equipment was developed for research and determination of optimum welding parameters under different environments. To evaluate the equipment performance the friction hydro pillar processing method was used. Data acquisition of the welding parameters allows assessing the system behavior within the operational range. Joints of low carbon and low alloy steels have been obtained. Macrographic analyses of the weld joint were performed to evaluate the heat affected zone and the presence of unfilled regions. The servohydraulic control developed have shown an adequate dynamic response for this application, nevertheless some improvements are proposed.