Internal friction has been known to be a cause of whirl instability in built-up rotors since the early 1900's. This internal damping tends to make the rotor whirl at shaft speeds greater than a critical speed, the whirl speed usually being equal to the critical speed. Over the years of research, though models have been developed to explain instabilities due to internal friction, its complex and unpredictable nature has made it extremely difficult to come up with a set of equations or rules that can be used to predict instabilities accurate enough for design. This thesis deals with suggesting improved methods for predicting the effects of shrink fits on threshold speeds of instability. A supporting objective is to quantify the internal friction in the system by measurements. Experimental methods of determining the internal damping with non-rotating tests are investigated, and the results are correlated with appropriate mathematical models for the system. Rotating experiments were carried out and suggest that subsynchronous vibration in rotating machinery can have numerous sources or causes. Also, subsynchronous whirl due to internal friction is not a highly repeatable phenomenon.

Les films minces de polymères font désormais partie intégrante de notre vie quotidienne sous forme par exemple d’adhésifs et de lubrifiants. Les macromolécules qui les composent présentent de nombreux paramètres modulables tels que leur nature chimique, leur masse moléculaire ou encore leur flexibilité, permettant d’atteindre des performances très contrastées et d’envisager un large domaine d’applications, notamment dans le secteur des nanotechnologies. Ces nouveaux développements nécessitent cependant de maîtriser la stabilité de ces couches minces de polymère. En effet, que ce soit dans le cadre de la tendance à la miniaturisation nécessitant de structurer les films à des échelles nanométriques ou dans le cadre d’applications tribologiques faisant appel aux propriétés mécaniques des polymères, leur stabilité est un critère essentiel qui conditionne leurs performances. De nombreuses propriétés des systèmes polymères sont directement déterminées par les interfaces du matériau dont l’étude est commodément réalisée par l’intermédiaire d’un confinement des chaînes. Dans ce contexte, nous étudions dans une première partie les conséquences de la nature chimique d’un polymère à l’état vitreux soumis à une contrainte mécanique appliquée en surface. Nous montrons tout d’abord que la cristallisation permet d’obtenir une structuration hiérarchique de la surface des films. Sur base de ces travaux, nous avons ensuite réalisé une structuration de surface par l’intermédiaire d’un microscope à force atomique (nanorubbing) qui permet un contrôle extrêmement précis des déformations imposées. Enfin, nous tâcherons d’apporter une contribution à la controverse sur la mobilité des chaînes polymères au sein de films minces. La seconde partie de notre travail s’intéresse au comportement rhéologique de longues chaînes de polymères confinées que nous étudions grâce au processus de démouillage de films minces, une conséquence directe de l’influence des interfaces sur la stabilité des films. Les propriétés des fluides viscoélastiques sont détaillées afin de mettre en évidence l’importance de paramètres physiques trop souvent négligés tels que le stress résiduel. Nous démontrons enfin que l’étude de l’interface associée aux dynamiques de retrait du film permet de caractériser la relaxation de chaînes confinées et d’en déduire la stabilité du système étudié.

Applications relying on a high static friction include various types of fixtures, couplings, bolted joints, torsion joints, etc. The common characteristic of these applications is that they rely on the friction force to maintain the relative position of two mating surfaces. Also applications relying on high dynamic friction are common, the main example being brakes, where a low friction could be devastating. The plateau model for the friction of brakes has been refined. By using advanced electron microscopy, it has been shown that during braking a partly amorphous friction film, comprising nanosized iron oxide agglomerates, dissipates the friction energy. The film is only about 100 nm thick. It is separated from the underlying less mobile material by a thin boundary. The actual braking power is thus localised to this very thin film, leading to remarkably high power densities. In a typical case it was estimated to 40 GW/dm3. Squeal and vibrations are critical problems for brakes. The present work has shown that a textured disc pattern may counteract squeal efficiently. The most successful pattern has spiral shaped arms in which wear resistant ceramic particles are embedded. The different wear characteristics of treated and untreated disc surface lead to an elevation of the patterned area above the rest of the disc. In a related experiment, laser technique was used to inject the particles deeper into the disc surface, and thus prolonging the time of silence. Textured diamond surfaces have been used to study the influence of load, repeated scratching and surface roughness on the static coefficient of friction. It was shown that these surfaces were remarkably stable at high friction levels. A maximum load limit was found above which the coefficient of friction falls. This and a number of other factors were found important for the successful design of high-friction joints.

Aluminum and Zinc oxide powder were blended by friction stir processing (FSP) with threaded pin of 6mm in diameter under conditions of traverse speed, 1mm/sec and rotation speed, 1500rpm. Different thermal analysis (DTA) was conducted to reveal that the melting point of the stir zone decreased to 592oC from 660oC of the green compact specimen containing 20wt%ZnO. X-ray diffraction (XRD) identified that Zn from ZnO dissolved into Al matrix, and did not resolve redox products, alomina. Scanning electron microscopy (SEM) with filed emission gun was employed with EDS analysis. It is interesting to note that many redoxed products with oxygen concentration higher than that of the matrix can be seen as dark and gray phases in BSE images. Evidently, a chemical reaction in Al/ZnO system is possible during FSP and results of the reduced Zn dissolving into the Al matrix and the expected but not detectable nanoscale alumina uniformly being dispersed into the matrix can be attributed to the excellent 22% elongation, and 350 MPa tensile strength in the stir zone from stirred Al-25wt% ZnO.

In this paper, Friction Stir Welding(FSW) experiments are conducted using similar and dissimilar metals of 6061-T6 Aluminum alloy, AZ-31 Magnesium alloy, JISC-1100 pure copper as specimens. Thermalcouples of type D are used to measure temperature history at different postions of workpiece duing Fsw. Form the temperature history, the preheating temperature and the tool rotation and tool moving speed can be found for a successful welding process. The experimental results show that the temperature ranges for the tool starting to move after preheating are 250-2500C, 200-2500C and 300-3500C for silimar metals of Al alloy, Mg alloy and pure copper and that for of dissimilar of Al alloy and Mg alloy is 200-2500C. Vickers hardness test and tensile test of the welded products are also conducted. The hardness testing results show that the vickers hardness of similar Al alloy, Mg alloy and pure copper sheets beforing weldig are about, 102, 70 and 105HV, respectively. The hardness of the nugget region of similar Al alloy, Mg alloy and pure copper sheets after welding are about 60, 62 and 65 HV, respectively and that for dissimilar of Al alloy and Mg alloy sheets is 138HV. The tensile testing results shows that for similar of Al alloy, Mg alloy and pure copper sheets beforing weldig are about, 320, 300 and 280MPa, respectively. The tensile strenghts of similar Al alloy, Mg alloy and pure copper sheets after welding, are about 160, 250 and 200 MPa, respectively, and that for dissimilar Al and Mg alloys is 100 MPa. The above experimental results can provide information for Fsw of Al, Mg alloys and pure copper. Keywords¡GFriction Stir Welding¡Fthermalcouple¡Ftemperature career

Coatings are often used on critical components in machines and engines to reduce wear and to provide low friction in order to reduce energy losses and the environmental impact. A triboactive coating not only provides this desired performance, it also actively maintains the low friction by a structural or chemical change in a very thin top layer of these already micrometer thin coatings. This so-called tribofilm is often 5-50 nm thick and can be formed either from the coating itself or by a reaction with the counter surface or the surrounding atmosphere, i.e. gas, fuel, oil, etc. The tribofilm will maintain the wanted performance for as long as the system is not chemically disturbed. This thesis provides a detailed overview of the functionality of triboactive low-friction coatings, in many different systems. The majority of the tribofilms discussed, formed in very different environments, are built up by tungsten disulfide (WS2), which is a material similar to graphite, with a lamellar structure where strongly bonded atomic planes may slip over each other almost without resistance. The major difference is that WS2 is an intrinsically triboactive material, while graphite is not. However, graphite and other carbon-based materials can be made triboactive in certain atmospheres or by addition of other elements, such as hydrogen. The remarkable affinity and driving force to form such WS2 low-friction tribofilms, regardless of the initial states of the sulfur and tungsten, and even when the forming elements are present only at ppm levels, is a recurrent observation in the thesis. Addition of an alloying element to sputtered coatings of WS2 can improve its mechanical and frictional properties significantly. Several promising attempts have been made to find good candidates, out of which a few important ones are investigated in this thesis. Their achievable potential in friction reductions is demonstrated. By reducing friction, energy losses can be avoided, which also results in lower particle and exhaust emissions, which directly reduces the environmental impact. Triboactive coatings are shown to be a promising route to significantly improve tribological applications and allow more environmental friendly and energy efficient vehicles.

In most robot applications, the control of the manipulators end-effector along a specified desired trajectory is the main concern. In these applications, the end-effector (tip) of the manipulator is required to follow a given trajectory. Several methods have been so far proposed for the motion control of robot manipulators. However, most of these control methods ignore either joint friction or joint elasticity which can be caused by the transmission systems (e.g. belts and gearboxes). This study aims at development of a comprehensive control strategy for the tip-trajectory tracking of flexible-joint robot manipulators. While the proposed control strategy takes into account the effect of the friction and the elasticity in the joints, it also provides a highly accurate motion for the manipulators end-effector. During this study several approaches have been developed, implemented and verified experimentally/numerically for the tip trajectory tracking of robot manipulators. To compensate for the elasticity of the joints two methods have been proposed; they are a composite controller whose design is based on the singular perturbation theory and integral manifold concept, and a swarm controller which is a novel biologically-inspired controller and its concept is inspired by the movement of real biological systems such as flocks of birds and schools of fishes. To compensate for the friction in the joints two new approaches have been also introduced. They are a composite compensation strategy which consists of the non-linear dynamic LuGre model and a Proportional-Derivative (PD) compensator, and a novel friction compensation method whose design is based on the Work-Energy principle. Each of these proposed controllers has some advantages and drawbacks, and hence, depending on the application of the robot manipulator, they can be employed. For instance, the Work-Energy method has a simpler form than the LuGre-PD compensator and can be easily implemented in industrial applications, yet it provides less accuracy in friction compensation. In addition to design and develop new controllers for flexible-joint manipulators, another contribution of this work lays in the experimental verification of the proposed control strategies. For this purpose, experimental setups of a two-rigid-link flexible-joint and a single-rigid-link flexible-joint manipulators have been employed. The proposed controllers have been experimentally tested for different trajectories, velocities and several flexibilities of the joints. This ensures that the controllers are able to perform effectively at different trajectories and speeds. Besides developing control strategies for the flexible-joint manipulators, dynamic modeling and vibration suppression of flexible-link manipulators are other parts of this study. To derive dynamic equations for the flexible-link flexible-joint manipulators, the Lagrange method is used. The simulation results from Lagrange method are then confirmed by the finite element analysis (FEA) for different trajectories. To suppress the vibration of flexible manipulators during the manoeuvre, a collocated sensor-actuator is utilized, and a proportional control method is employed to adjust the voltage applied to the piezoelectric actuator. Based on the controllability of the states and using FEA, the optimum location of the piezoelectric along the manipulator is found. The effect of the controllers gain and the delay between the input and output of the controller are also analyzed through a stability analysis.

Traditional tribology is based on the surface with random micro structures due to limitations of manufacturing technology. The modern manufacturing technology now promises to fabricate surfaces with regular micro structures (or asperities). The word asperity refers to a single physical entity on the surface of a material, contributing to a concept called roughness in traditional tribology. Regular asperity surfaces imply that all asperities on the surface of a material have the same shape and size, and a deterministic distribution over the surface. The emergence of regular asperity surfaces will have a transformative impact to the discipline of tribology.<p> The overall objective of this thesis is to study how the regular asperity would affect the tribological behavior. Specifically, this thesis develops a computational model to demonstrate and characterize the effect of the surface with regular anisotropic asperities (RAA) on the directional friction behavior when the surface is in a fully lubricated state. By directional friction, it is meant that friction force changes its magnitude with the change of the relative motion direction. By anisotropic asperity, it is meant that the geometry of the asperity is not symmetrical along the motion direction.<p> This thesis presents a detailed development of the computational model by employing computational fluid dynamics (CFD) techniques. In particular, the model takes the Navier-Stokes (NS) equation as a governing equation and the Half-Sommerfeld Condition (HSC) to represent fluid behavior in the cavitation region; as such the model is named NS-HSC for short. Verification of the NS-HSC model is conducted with the information available in literature. A theory is proposed to explain the relationship between directional friction behavior and specific RAA structures. The thesis concludes: (1) the NS-HSC model is more accurate than the existing model in the literature and can be used to predict directional friction behavior and to design RAA surfaces, and (2) the proposed theory is excellent consistent with the NS-HSC model and thus useful to analysis and design of RAA surfaces for directional friction.<p> The major contributions of this thesis are: (1) the first model in the field of tribology to predict the directional friction behavior for RAA surfaces under a fully lubricated status, (2) the first investigation, in the field of CFD, into combining the NS and HSC for modeling a laminar flow with cavitation, and (3) the first theory in the field of tribology for directional friction on fully lubricated RAA surfaces.

In most robot applications, the control of the manipulators end-effector along a specified desired trajectory is the main concern. In these applications, the end-effector (tip) of the manipulator is required to follow a given trajectory. Several methods have been so far proposed for the motion control of robot manipulators. However, most of these control methods ignore either joint friction or joint elasticity which can be caused by the transmission systems (e.g. belts and gearboxes). This study aims at development of a comprehensive control strategy for the tip-trajectory tracking of flexible-joint robot manipulators. While the proposed control strategy takes into account the effect of the friction and the elasticity in the joints, it also provides a highly accurate motion for the manipulators end-effector. During this study several approaches have been developed, implemented and verified experimentally/numerically for the tip trajectory tracking of robot manipulators. To compensate for the elasticity of the joints two methods have been proposed; they are a composite controller whose design is based on the singular perturbation theory and integral manifold concept, and a swarm controller which is a novel biologically-inspired controller and its concept is inspired by the movement of real biological systems such as flocks of birds and schools of fishes. To compensate for the friction in the joints two new approaches have been also introduced. They are a composite compensation strategy which consists of the non-linear dynamic LuGre model and a Proportional-Derivative (PD) compensator, and a novel friction compensation method whose design is based on the Work-Energy principle. Each of these proposed controllers has some advantages and drawbacks, and hence, depending on the application of the robot manipulator, they can be employed. For instance, the Work-Energy method has a simpler form than the LuGre-PD compensator and can be easily implemented in industrial applications, yet it provides less accuracy in friction compensation. In addition to design and develop new controllers for flexible-joint manipulators, another contribution of this work lays in the experimental verification of the proposed control strategies. For this purpose, experimental setups of a two-rigid-link flexible-joint and a single-rigid-link flexible-joint manipulators have been employed. The proposed controllers have been experimentally tested for different trajectories, velocities and several flexibilities of the joints. This ensures that the controllers are able to perform effectively at different trajectories and speeds. Besides developing control strategies for the flexible-joint manipulators, dynamic modeling and vibration suppression of flexible-link manipulators are other parts of this study. To derive dynamic equations for the flexible-link flexible-joint manipulators, the Lagrange method is used. The simulation results from Lagrange method are then confirmed by the finite element analysis (FEA) for different trajectories. To suppress the vibration of flexible manipulators during the manoeuvre, a collocated sensor-actuator is utilized, and a proportional control method is employed to adjust the voltage applied to the piezoelectric actuator. Based on the controllability of the states and using FEA, the optimum location of the piezoelectric along the manipulator is found. The effect of the controllers gain and the delay between the input and output of the controller are also analyzed through a stability analysis.

Traditional tribology is based on the surface with random micro structures due to limitations of manufacturing technology. The modern manufacturing technology now promises to fabricate surfaces with regular micro structures (or asperities). The word asperity refers to a single physical entity on the surface of a material, contributing to a concept called roughness in traditional tribology. Regular asperity surfaces imply that all asperities on the surface of a material have the same shape and size, and a deterministic distribution over the surface. The emergence of regular asperity surfaces will have a transformative impact to the discipline of tribology.<p> The overall objective of this thesis is to study how the regular asperity would affect the tribological behavior. Specifically, this thesis develops a computational model to demonstrate and characterize the effect of the surface with regular anisotropic asperities (RAA) on the directional friction behavior when the surface is in a fully lubricated state. By directional friction, it is meant that friction force changes its magnitude with the change of the relative motion direction. By anisotropic asperity, it is meant that the geometry of the asperity is not symmetrical along the motion direction.<p> This thesis presents a detailed development of the computational model by employing computational fluid dynamics (CFD) techniques. In particular, the model takes the Navier-Stokes (NS) equation as a governing equation and the Half-Sommerfeld Condition (HSC) to represent fluid behavior in the cavitation region; as such the model is named NS-HSC for short. Verification of the NS-HSC model is conducted with the information available in literature. A theory is proposed to explain the relationship between directional friction behavior and specific RAA structures. The thesis concludes: (1) the NS-HSC model is more accurate than the existing model in the literature and can be used to predict directional friction behavior and to design RAA surfaces, and (2) the proposed theory is excellent consistent with the NS-HSC model and thus useful to analysis and design of RAA surfaces for directional friction.<p> The major contributions of this thesis are: (1) the first model in the field of tribology to predict the directional friction behavior for RAA surfaces under a fully lubricated status, (2) the first investigation, in the field of CFD, into combining the NS and HSC for modeling a laminar flow with cavitation, and (3) the first theory in the field of tribology for directional friction on fully lubricated RAA surfaces.