Dissertations / Theses on the topic 'Angel of internal friction'

The phenomenon of internal friction most generally defined as the dissipation of mechanical energy inside a gaseous, liquid or solid medium. It is basically different from “friction” in the tribological sense, i.e., the resistance against the motion of two solid surfaces relative to each other (“external friction”).

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-08-23T13:35:50Z No. of bitstreams: 1 DANIEL BESERRA COSTA - DISSERTAÇÃO (PPGECA) 2018.pdf: 3178699 bytes, checksum: cdb4fe8ec72383894c5c447ebe2853ae (MD5)<br>Made available in DSpace on 2018-08-23T13:35:50Z (GMT). No. of bitstreams: 1 DANIEL BESERRA COSTA - DISSERTAÇÃO (PPGECA) 2018.pdf: 3178699 bytes, checksum: cdb4fe8ec72383894c5c447ebe2853ae (MD5) Previous issue date: 2018-02-21<br>Capes<br>A deformação permanente é definida como o acúmulo de pequenas quantidades de deformação não recuperáveis resultante da aplicação das cargas dos veículos. A deformação permanente na camada de revestimento asfáltico pode ser oriunda por três mecanismos: deformação permanente por densificação, por uso e por fluência da mistura. Dado que as temperaturas de serviço da camada de revestimento estão em torno de 40 a 60 °C, a mistura asfáltica nesse intervalo de temperatura se comporta como um material sólido. Sendo assim, é razoável supor que os mecanismos de falha aplicáveis aos materiais sólidos sejam válidos para as misturas de asfálticas. Sendo o critério Mohr-Coulomb amplamente utilizado para descrever as características de cisalhamento de materiais sólidos, poderá ser utilizado para obtenção do ângulo de atrito interno da mistura, bem como o seu intercepto coesivo. Este trabalho teve como objetivo a determinação de ângulos de atrito internos de diferentes misturas asfálticas e sua influência no comportamento mecânico, em especifico, na resistência à deformação permanente destas misturas. Como forma de atingir o objetivo da pesquisa foi desenvolvido um programa experimental visando à avaliação das propriedades mecânicas relacionadas ao ângulo de atrito interno das misturas asfálticas com CAP 50/70 e E – 55/75. Foi possível executar análises em laboratório a partir da determinação de parâmetros de ruptura por cisalhamento, com o auxílio da teoria de Mohr-Coulomb, tendo como inferência o desempenho de misturas estudadas em campo. Verificou-se que, a cada acréscimo de 5% de partículas graúdas em uma faixa granulométrica, as misturas estudadas apresentaram, em geral, um ganho de 1° (Grau) no ângulo de atrito interno para cada faixa estudada. Entretanto, deve ser observado o limite de 30 a 35% de partículas graúdas para cada mistura. Pode-se concluir que: os parâmetros de ruptura por cisalhamento, ângulo de atrito interno e intercepto coesivo são fatores determinantes no desempenho a deformação permanente de misturas asfálticas. Para os ligantes utilizados os resultados indicaram que o acréscimo do ângulo de atrito interno resulta numa maior resistência a deformação permanente.<br>Permanent deformation is defined as the accumulation of small amounts of non-recoverable deformation resulting from the application of vehicle loads. The permanent deformation in the surface layer of asphalt pavements can come from three mechanisms: permanent deformation by densification, by use and by creep of the mixture. Since the service temperatures of the pavement surface layer are around 40 and 60 ºC, the asphalt mixture, in this temperature range, behaves as a solid material. Therefore, it is reasonable to assume that failure mechanisms applicable to solid materials are valid for asphalt mixtures. As the Mohr-Coulomb criterion is widely used to describe the shear characteristics of solid materials, it can be used to obtain the internal friction angle of the asphalt mixture as well as to estimate its cohesive intercept. This work had as objective to determine the internal angles of friction of different asphalt mixtures and their influence on the mechanical behavior, in particular, on the resistance to permanent deformation of these mixtures. In order to achieve the objective of this research, an experimental program was developed to evaluate the mechanical properties related to the internal angle of friction of asphalt mixtures with the 50/70 asphalt binder and the E 55/75 asphalt binder. It was possible to perform laboratory analyses from the determination of shear rupture parameters, supported by the Mohr-Coulomb's theory, inferred by the performance of mixtures studied in the field. It was verified that, at each increment of 5% of coarse particles in a particle size range, the studied mixtures presented, in general, a gain of 1° (degree) in the internal angle of friction for each size range studied. However, the limit of 30 to 35% of coarse particles should be observed for each mixture. It can be concluded that: the parameters of shear rupture, internal angle of friction and cohesive intercept are determining factors in the permanent deformation performance of asphalt mixtures. For the asphalt binders used, the results indicated that the increment of the internal angle of friction results in a greater resistance to permanent deformation.

Thesis (M.S.)--Texas A & M University, 2003.<br>"Major Subject: Mechanical Engineering." Title from author supplied metadata (automated record created on Jul. 18, 2005.). Vita. Abstract. Includes bibliographical references.

This thesis deals with a study of methods sufficient to describe the behavior of bulk materials (homogeneous and non-homogeneous) during their transport by bucket elevators in the application focused on the optimization of the bucket shape and also on the optimization of operating parameters of whole elevator. More specifically, this thesis is based on the studying and creating analytical and numerical computational models which are used for description of flows and deformations especially of particulate materials. Firstly, the thesis is focused on the process of discharging the bucket – the relationship among the shape of the surface of a particulate material and geometry, position and movement of the bucket. The beginning and way of discharge of the bucket will be determined. Secondly, the thesis includes the overall computational model of a bucket elevator which is based on discrete element method and presented in the case study. The goal is to determine the limits of some classical physical and mathematical descriptions.

Past studies on sands have shown that the shear strength measured in plane strain tests was higher than that measured in triaxial tests. It was observed that this difference changed with the friction angle &amp<br>#966<br>cv at constant volume related to the mineralogical composition. In order to investigate the difference in strength measured in the wedge shear test, which approaches the plane strain condition, in the triaxial test, and in the shear box test, Anatolian sands were obtained from different locations in Turkey. Mineralogical analyses, identification tests, wedge shear tests (cylindrical wedge shear tests (cylwests) and prismatic wedge shear tests (priswests)), triaxial tests, and shear box tests were performed on these samples. In all shear tests, the shear strength measured was found to increase with the inclination &amp<br>#948<br>of the shear plane to the bedding planes. Thus, cylwests (&amp<br>#948<br>= 60o) iii yielded higher values of internal friction &amp<br>#966<br>by about 3.6o than priswests (&amp<br>#948<br>= 30o) under normal stresses between 17 kPa and 59 kPa. Values of &amp<br>#966<br>measured in cylwests were about 1.08 times those measured in triaxial tests (&amp<br>#948<br>&amp<br>#8776<br>65o), a figure close to the corresponding ratio of 1.13 found by past researchers between actual plane strain and triaxial test results. There was some indication that the difference between cylwest and triaxial test results increased with the &amp<br>#966<br>cv value of the samples. With the smaller &amp<br>#948<br>values (30o and 40o), priswests yielded nearly the same &amp<br>#966<br>values as those obtained in triaxial tests under normal stresses between 20 kPa and 356 kPa. Shear box tests (&amp<br>#948<br>=0o) yielded lower values of &amp<br>#966<br>than cylwests (by about 7.9o), priswests (by about 4.4o), and triaxial tests (by about 4.2o) under normal stresses between 17 kPa and 48 kPa. It was shown that the shear strength measured in shear box tests showed an increase when &amp<br>#948<br>was increased from 30o to 60o<br>this increase (about 4.2o) was of the order of the difference (about 3.6o) between priswest (&amp<br>#948<br>= 30o) and cylwest (&amp<br>#948<br>= 60o) results mentioned earlier. Shear box specimens with &amp<br>#948<br>= 60o, prepared from the same batch of any sample as the corresponding cylwests, yielded &amp<br>#966<br>values very close to those obtained in cylwests.

La presente tesis evalúa el comportamiento mecánico de un suelo arcilloso mezclado con PET triturado. El uso potencial de este material plástico en aplicaciones geotécnicas puede reducir el problema de la eliminación inadecuada y mejorar las características de resistencia y deformación del suelo. Se empleó Tereftalato de polietileno, PET, y suelo arcilloso proveniente de la provincia de Tarapoto. Los parámetros de resistencia al corte que definen las características mecánicas del suelo son el ángulo de fricción y la cohesión. En la ejecución de una obra civil, estos parámetros generalmente no se ajustan a los requerimientos del proyecto, por tal razón se debe buscar una solución para la estabilidad del suelo implicado en cualquier construcción. Esta tesis se realizó en tres etapas, la primera fue la recolección de información, la segunda la fase de laboratorio, llevándose a cabo ensayos de Proctor estándar (densidad – humedad), corte directo (ángulo de fricción y cohesión), limite líquido, limite plástico y granulometría; y por último el análisis de los resultados. El suelo arcilloso utilizado fue mezclado con 5%, 10% y 20% de PET triturado en peso seco. Los porcentajes de PET aumentaron la capacidad de soporte del suelo.<br>This thesis evaluates the mechanical behavior of a clay soil mixed with crushed PET. The potential use of this waste material in geotechnical applications may ultimately reduce the problem of improper disposal and improve the strength and deformation characteristics of the soil. Polyethylene terephthalate, PET, and clayey soil from the province of Tarapoto were used. The shear strength parameters that define the mechanical properties of soil are the internal friction angle and cohesion. While constructing any civil engineering structure, those parameters usually do not adjust to the requirements of the Project, therefore, there must be a solution for the soil stability in any civil work. This thesis was carried out in three stages, the first was the collection of information, the second the laboratory phase, carrying out standard Proctor tests (density - humidity), direct cutting (angle of friction and cohesion), liquid limit, limit plastic and granulometry; and finally the analysis of the results. The clayey soil used was mixed with 5%, 10% and 20% of crushed PET by dry weight. The percentages of PET increased the soil support capacity.<br>Tesis

Road safety is a very important topic for research and development divisions in the automotive industry. As the tyre is the only link between road surface and vehicle, it plays a very significant role in accident mitigation and prevention. This thesis investigates the influence of internal tyre pressure on the brake distance both experimentally and theoretically. Brake tests were performed using a robotic system and a winch was used to pull a car with locked wheels. For both experiments, the tyre pressures were changed. A rubber friction law is presented which can be used for tyre and vehicle dynamics calculations. The friction law was tested by comparing numerical results to the full rubber friction theory of Persson and to experimental data. A two-dimensional (2D) tyre model is introduced that combines the rubber friction law with a simple mass-spring description of the tyre body. The tyre model is very flexible and can be applied to different manoeuvres. It can be used to calculate μ-slip curves, self aligning-torque, braking, and cornering, or combined motion (e.g. braking during cornering). The theoretical predictions have been compared to measured data from indoor tyre testing on sandpaper substrate. Additionally simulations of anti-lock braking system (ABS) using two different control algorithms are presented. In addition a method for rapidly changing the tyre inflation pressure while a vehicle is in motion is presented. This method can be used for novel safety system approaches.

Diploma thesis describes design and function verification of device for filling tap hole of electric arc furnace with tap hole diameter from 190 mm to 250 mm. The theses includes drive design calculation of chute swinging movement and bearing calculations. Another part of the thesis deals with verification of device functions which it is completed with process description of creating DEM simulation in program YADE. The thesis also includes basic experiments for determination angle of internal friction, angle of repose, coefficient of restitution and angle of material friction on a steel surface. Drawing documentation of selected assemblies is part of the thesis.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>Includes bibliographical references (p. 113-115).<br>Piston ring friction losses account for approximately 20% of the total mechanical losses in modern internal combustion engines. A reduction in piston ring friction would therefore result in higher efficiency, lower fuel consumption and reduced emissions. The goal of this study was to develop low-friction piston ring designs to improve engine efficiency, without adversely affecting oil consumption, blowby, wear, or cost. These are desirable objectives for today's engine manufacturers as they strive to improve engine performance while trying to meet increasingly stringent emissions regulations. Using an existing piston ring friction and lubrication model, the main contributors to friction in modern internal combustion engines were identified as the top ring around top dead center of the compression/expansion strokes and the oil control ring throughout the engine cycle. Model predictions indicated that the top ring friction could be reduced by implementing a skewed barrel profile design or an upward piston groove tilt design, and oil control ring friction could be reduced by decreasing ring tension. An increase in groove wear was predicted to occur with the upward piston groove tilt design, which could be eliminated by the introduction of a positive static twist on the top ring. An increase in oil consumption was predicted to occur with the low-tension oil control ring design, which could be mitigated either by the introduction of a negative static twist on the second ring, or by the implementation of the skewed barrel top ring design. Model predictions indicated that by combining the low-friction designs, a reduction in piston ring pack friction of 30-35% could be achieved, without an increase in blowby, wear, or oil consumption.<br>(cont.) Experimental results conducted on a full-scale natural gas power generation engine supported the model predictions for the low-tension oil control ring design. The predicted reduction in piston ring friction would translate to a 0.5-1% increase in brake thermal efficiency, which would result in a significant improvement in fuel economy and a substantial reduction in emissions over the life of the engine.<br>by Grant Smedley.<br>S.M.

This work examines the detailed flow characteristics of direct measuring skin friction gages with computational methods. This type of device uses a small movable head mounted flush to a wall such that the head is assumed to be exposed to the same shear stress from the flow as the surrounding wall. The force caused by the action of the shear stress on the head deflects a flexure system monitored by instruments such as strain gages mounted at the base of a beam. The goal of the study was to develop an understanding of the effects that the geometric design and installation parameters of the sensor have on the surrounding flow and the ability of the sensor to reflect the undisturbed shear stress value. Disruption of the external flow due to poor design and/or improper installation of the sensor can take the form of intrusion into the flow, recession into the wall, and/or tilted alignment of the sensor such that the head is not flat in the plane of the wall, as well as flow into or out of the small gap surrounding the sensing head. Further, the performance of a direct measuring skin friction sensor in the presence of a pressure gradient has always been a concern. These effects are studied here with a three-dimensional, Navier-Stokes code based on a finite element method technique. Numerical solutions for cases in which one or more design parameters were varied are shown for a variety of flow situations. These situations include: (a) a laminar fully-developed channel flow at a low Reynolds number, (b) a turbulent flat plate boundary layer flow at a high Reynolds number, and (c) strong favorable and adverse pressure gradient turbulent boundary layer flows created by converging and diverging channels at high Reynolds number. Reported results for all cases include detailed flow visualization and stress field imagery, and total surface forces on the sensing head and gage flexure. Under ideal circumstances, these total forces should reflect as accurately as possible the average value of undisturbed shear stress times the exposed sensing head area (the friction force). Any deviation from this value was considered an â errorâ in the simulated measurement. The laminar channel flow case with a strong favorable pressure gradient showed the importance of proper alignment of the sensor. Protrusion or recession of the sensing head proved to be the dominant effect on resulting forces seen by the gage, changing the output by up to 15% for head protrusion and 10% for head recession for misalignments up to +/-1% of the head diameter. The thickness of the lip on the edge of the head also proved to have a significant effect on the output, with a smaller lip thickness generally showing better performance than a large one. Zero lip thickness indicated accuracy to within 1% of the desired wall shear result, since the pressure differences had little influence on the sensing head. Finally, the assumption of a linear pressure variation from the surface to the cavity along the lip as has been suggested in the past was investigated. The results indicate that the linear assumption works well only for large ratios of lip thickness to gap size, a fact which is correlated with previous experimental results. For the turbulent external flat plate case, misalignment remained the dominant effect on the sensor response. Results indicated that, in general, protrusion is more costly than the same level of recession, and a protrusion of +1% of the head diameter was shown to cause in excess of 100% error in indicated wall shear output. Both protrusion and recession produced large variations in both force and moment on the sensing flexure, but the outcome was that for protrusion the errors caused by these two effects tended to sum together, while for recession they tended to partially cancel out. The gap size played an increased role in the high Reynolds number boundary layer cases. Gap sizes of 1.67% up to 6.67% of the head diameter were studied and were shown to produce output errors between 4% and 22% (with larger errors corresponding to larger gap sizes), thus showing the importance of minimizing the gap for high Reynolds number flows. The lip was shown to have no significant effect for a flow without a pressure gradient. Finally, the favorable and adverse pressure gradient flows showed reasonable performance of the skin friction gage. Errors in output were shown to be -6% for the favorable pressure gradient case and 17% for the adverse pressure gradient case. Only the baseline gage design was studied for these situations, but the results from the two cases indicate that further reducing the lip thickness may not improve the performance of the gage. The error in output was caused almost entirely by applied moment for the adverse pressure gradient, while the applied force and applied moment had a cancellation effect in the favorable pressure gradient case. As a general result, the use of computational fluid dynamics has been shown to be an effective tool in the design and analysis of skin friction gages. Using a computational approach has the advantage of being able to resolve the small, confined gap regions of the gage, providing information that has been shown to be unavailable from previous experimental studies. This work has contributed to a much better understanding of the detailed flow over, in, and around skin friction gages. This will lead to improved gage design and reduced uncertainty in these important measurements.<br>Ph. D.

The research reported in the thesis addresses questions of how engine fuel consumption and carbon dioxide emissions are can be reduced through improvements in thermal management, lubricant design, and energy recovery. The investigations are based on simulation studies using computational models and sub-models developed or revised during the work, and results provided by complementary experimental studies carried out by collaborating investigators. The brake thermal efficiency of the internal combustion engines (ICE) used in cars and light duty commercial vehicles is reduced by frictional losses. These losses vary with engine design, lubricant formulation and thermal state. They are most significant when the engine is running cold or partially warm. Over the New European Drive Cycle (NEDC), engine friction losses raise vehicle fuel consumption by several percentage points. A version of the computational model, PROMETS, has been developed and applied in studies of thermal behaviour, friction and engine lubricant to investigate the performance of a 2.0l, I4 GTDI spark ignition engine and in particular, how these influence fuel consumption over the NEDC. Core parts of PROMETS include a physics-based, empirically calibrated friction model, a cycle averaged description of gas-to-structure heat transfer and a lumped capacity description of thermal behaviour of the engine block and cylinder head. In the thesis, revisions to the description of friction and interactions between friction, local thermal conditions and lubricant are reported. It is shown that the bulk temperature of coolant rather than oil has the stronger influence on friction at the piston-liner interface, whilst bulk oil temperature more strongly influences friction in crankshaft bearings and other lower engine components. However, local oil film temperatures have a direct influence on local friction contribution. To account for this, local values of oil temperature and viscosity are used in describing local friction contributions. Implementation required an oil system model to be developed; an iterative model of the frictional dissipation within the main bearings, and a prediction of piston cooling jet heat transfer coefficients have been added to the oil circuit. Simulations of a range of scenarios and design changes are presented and analysed in the thesis. The size of the fuel savings that could potentially be made through improved thermal management has been demonstrated to be 4.5% for the engine being simulated. Model results show that of the friction contributing surfaces, the piston group is responsible for the highest levels of friction, and also exhibits the largest absolute reduction in friction as the temperature of the engine rises. The relatively low warm-up rate of the lower engine structure gives a correspondingly slow reduction in friction in crankshaft bearings from their cold start values. Measures to accelerate this reduction by raising oil temperature have limited effect unless the strong thermal links between the oil and the surrounding metal are broken. When additional heating is applied to the engine oil, only around 30% is retained to raise the oil temperature due to these thermal links.

Low friction lubricant development provides a worthwhile contribution to vehicle CO₂ emission reduction. Conventional low friction lubricant development focuses on empirical processes using out dated engine technology and old test methods. This strategy is inefficient and restricts the lubricant's potential. A new method proposed in the present research combines tribological simulations with rig, engine and vehicle tests. This approach provides insights undocumented until now. The contribution to CO₂ emission reduction from individual engine components on vehicle drive cycles that include warm-up is predicted using lubricants down to the new SAE 8 viscosity grade. A bearing model is used to design the lubricant's non Newtonian characteristics to achieve friction reduction. An isoviscous lubricant with a viscosity of 4.6 cSt is shown to achieve the minimum friction in the bearing. The research shows that by starting with lubricants having kinematic viscosities higher than this value, it is possible to improve lubricant performance by lowering viscosity index (VI), introducing shear thinning, or reducing the density and pressure viscosity coefficient. Conversely, for lubricants with lower starting viscosities it is shown that higher VI values, more shear-stable lubricants and higher densities and pressure viscosity coefficients are required. The model predicts that high oil film pressures occur in the bearing and cause significant local lubricant viscosity increase (300&percnt;), indicating that the lubricant's pressure viscosity behaviour is important here, despite the contact being conformal. Simulation and motored engine testing establishes lubricant behaviour in the piston-to-bore conjunction. This analysis identifies a poor correlation between measured and predicted values at low engine speeds. A rig-on-liner tribometer shows that this error is attributable to a deficiency in the simulation's characterisation of boundary regime friction. An oil pump test determines how a modern variable displacement oil pump (and its control system) responds to lowering viscosity. The hypothesis that low viscosity lubricants cause the parasitic load from this component to increase is disproven using this component-level rig test. Chassis dynamometer testing compares the CO₂ reduction performance of lubricant thermal management systems to the values achieved by reducing the viscosity grade. CO₂ reductions of between 0.4&percnt; and 1.0&percnt; are identified using a cold-start new European drive cycle (NEDC) with a 5W-30 preheated to 60&deg;C and 90&deg;C respectively. Reductions in CO₂ emissions between 0.4&percnt; and 1.2&percnt; are found on the NEDC by lowering the oil fill volume from 5.1 L to 2.1 L. For the unmodified case, a 3.7&percnt; reduction in CO₂ emissions is reported by reducing the viscosity grade from a 5W 30 to an SAE 8 in the NEDC. The performance of a novel external oil reservoir is simulated to understand its ability to retain oil temperature during the vehicle cool-down procedure. An oil temperature of 65&deg;C at the end of the soak period (following a prior test where the oil was assumed to reach 90&deg;C) is predicted by installing insulation to the reservoir and indicates that a viable method to achieve the CO₂ benefits identified through lubricant preheating tests exists. A full vehicle model combines the outputs from each of these sub-models to predict lubricant performance on the NEDC the new World-wide harmonized light duty test cycle (WLTC). This new approach provides a tool that enables next generation low friction lubricants to be developed. The model predicts that an SAE 8 lubricant can reduce CO2 emissions by 2.8&percnt; on the NEDC and 1.9&percnt; on the WLTC compared to a 5W-30. A theoretical experiment, where all lubricant related friction was deleted from the simulation, predicts that lubricant-related CO₂ emissions are 8.7&percnt; on the NEDC and reduce to 6.3&percnt; on the WLTC. These results indicate that the planned adoption of the WLTC in September 2017 reduces the potential contribution to CO₂ emission reduction from lubricants by 28&percnt;.

In this thesis, we study the dynamics of an elastic body, whose shape and position evolve due to the gravitational forces exerted by a pointlike planet whose position is fixed in space. The first result of this thesis is that, if any internal deformation of the body dissipates some energy, then the dynamics of the system has only three possible final behaviors: (i) the satellite is expelled to infinity, (ii) the satellite falls on the planet, (iii) the satellite is captured in a synchronous orbit. By item (iii) we mean that the shape of the body reaches a final configuration, that a principal axis of inertia is directed towards the attracting planet and that the center of mass of the satellite moves on a circle of constant radius. Secondly, we study the stability of the synchronous orbit. Restricting to the quadrupole approximation and assuming that the body is very rigid, we prove that such an orbit is (locally) asymtotically stable, both in the case of a triaxial satellite and in the case of a satellite with spherical symmetry. Some additional results on the dynamics of the body close to the synchronous orbit and some new kinematical results are also present in the thesis.

Measuring structural damping due to internal friction in deposited thin films can provide useful guidelines for the design of high-Q micro/nanomechanical resonators utilized used for sensing, communications and vibration energy harvesting. Such measurements can also generate valuable insights into the effects of size and confinement on the mechanisms of damping in these films. Typically, these measurements are carried out by depositing a thin film on a relatively thick cantilevered substrate and measuring the change in damping in the substrate/film composite. However, the measured damping is due to losses from several sources including support losses, clamping losses, thermoelastic damping (TED) and internal friction losses in the substrate/film composite. Accurately identifying the magnitude of internal friction in the film has been a long-standing difficulty in this field. This thesis presents the design and development of a silicon microcantilever platform to resolve this difficulty. At the core of the platform is the ability to reduce the damping in single crystal silicon microcantilevers to low levels of damping approaching the fundamental limits of dissipation established by thermoelastic damping (TED). This demonstrates that all other sources of damping (viscous losses, support losses and internal friction losses) are sufficiently low. These cantilevers can then be coated with the thin film of interest and the damping in the substrate/film composite measured. The measured damping is comprised of the thermoelastic damping in the substrate/film composite and the internal friction in the film. The former can be calculated using accurate models and the initial damping can be substracted from the measured damping in the composite to obtain an accurate estimate of the internal friction in the film. In this dissertation, single crystal silicon cantilevers ranging from 8 to 130 micrometers in thickness, and fundamental frequencies ranging from 80 Hz to 40 kHz were fabricated. Using the measurement platform, these beams are demonstrated to have low damping with values approaching the TED limit. Subsets of these beams are then used to carry out the first calibrated measurements on the effects of thickness and frequency on internal friction in thin films of aluminum, gold and silver at room temperature. The films ranged in thickness from 60 nm to 450 nm and were studied over frequencies from 100 Hz to 1.5 kHz. The results of this study provide two valuable guidelines for the design of low dissipation (high Q) layered composite resonators: gold leads to a smaller increase in damping than either aluminum or silver, and damping in the composite resonators can be decreased by reducing the film thickness. As a third design guideline, a strategy to control and minimize the damping by selective patterning of thin films on the resonator is described. In this work, a simple model is developed to predict the damping in partially metalized cantilevered beams and experimentally validated using the platform. The silicon microcantilever platform, and the results obtained using this platform establish a foundation for studying internal friction in thin films.<br>Mesurer l'amortissement structurel causé par friction interne dans les films minces déposés permet d'établir des recommandations pour le design de résonateurs micro/nanomécaniques ayant un facteur de qualité élevé, ainsi qu'apporter une meilleure compréhension de l'effet de la taille et du confinement sur le mécanisme d'amortissement de ces films minces. Ce type de résonateurs est utilisé dans les microsystèmes électromécaniques de détection, de communication et de récupération d'énergie vibratoire. Ces mesures d'amortissement sont réalisées en déposant un film mince sur un substrat ayant une forme de poutre en porte-à-faux et d'épaisseur relativement élevée, et en mesurant le changement d'amortissement de l'ensemble substrat/film. Cependant, l'amortissement global a des origines multiples, notamment des pertes provenant du support, du système de fixation, de l'amortissement thermoélastique, et de la friction interne dans l'ensemble substrat/film. Identifier avec précision l'amplitude de la friction interne dans le film est une difficulté de connue de longue date dans le milieu de la recherche scientifique. Cette thèse présente le design et le développement d'une plateforme en silicium ayant une micro-poutre en porte-à-faux afin de résoudre ce problème. L'intérêt principal de cette plateforme est que l'amortissement dans les micro-poutres en porte-à-faux faites en silicium monocristallin est réduit à un faible niveau approchant les limites théoriques de la dissipation établies par les lois de l'amortissement thermoélastique. Cela démontre que les autres sources d'amortissement (amortissement visqueux, pertes liées au support ou à la friction interne du substrat) sont suffisamment faibles. Par la suite, ces poutres peuvent être recouvertes par le film mince étudié et l'amortissement de l'ensemble substrat/film est mesuré. Cette mesure provient à la fois de l'amortissement thermoélastique dans l'ensemble substrat/film et de la friction interne dans le film mince. Cette dernière peut être calculée grâce à ces modèles précis, et l'amortissement initial du substrat peut être soustrait de l'amortissement mesuré pour l'ensemble substrat/film afin d'en déduire une estimation précise de la friction interne dans le film mince uniquement.Les poutres en porte-à-faux en silicium monocristallin fabriquées dans le cadre de cette thèse avaient une épaisseur comprise entre 8 et 130 µm, et une fréquence fondamentale comprise entre 80 Hz et 40 kHz. En utilisant la plateforme de mesure évoquée précédemment, le faible amortissement approchant la limite thermoélastique théorique de ces poutres est démontré. Ce type de poutres est ensuite utilisé pour mener les premières mesures calibrées portant sur l'effet de l'épaisseur et de la fréquence sur la friction interne dans les films minces d'aluminium, d'or, et d'argent à température ambiante. Les films minces avaient une épaisseur comprise entre 60 nm et 450 nm, et furent testés à des fréquences comprises entre 100 Hz et 1,5 kHz. Les résultats de cette étude établissent deux recommandations pour le design de résonateurs à couches minces à faible dissipation (haut facteur de qualité) : l'or induit une augmentation de l'amortissement qui est plus faible que celle induite par l'aluminium ou l'argent, et l'amortissement des résonateurs peut être diminué en réduisant l'épaisseur de la couche mince. Une troisième recommandation est donnée sous la forme d'une stratégie pour contrôler et minimiser l'amortissement en déposant le film mince sur le résonateur selon un certain motif au lieu d'une couche continue. Dans ce travail de recherche, un modèle simple est développé pour prédire l'amortissement des poutres en porte-à-faux partiellement recouvertes de métal. Ce modèle est ensuite validé expérimentalement grâce à la plateforme en silicium. Cette plateforme ainsi que les résultats obtenus en l'utilisant établissent les fondements de l'étude de la friction interne dans les films minces.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 88-91).<br>With the increasing interest in decreasing the environmental impact from internal combustion engines as well as increasing the fuel efficiency has led to deeper investigation into the components of the engine. The mechanical friction in an engine is a major concern, any improvements or reductions in friction can have large implication on the' efficiency of the engines. This thesis focuses on the piston/ ring pack assembly and its contribution to friction. It investigates several key components and trends in friction for the piston/ ring pack assembly, specifically the trends related to the oil control ring and the liner surface. The Floating Liner Engine is used in this study to isolate results from different components. The data collected can be used for comparative analysis and to identify trends in the friction trace. The thesis starts with describing the Floating Liner Engine system at MIT in detail. Both the data collection and the hardware systems are described as well as the test capabilities of the Floating Liner Engine. The results used in the thesis have been collected using the motoring condition. The oil control ring plays a key role in controlling the supply of oil to the top two rings and hence has a higher tension that the top two rings. This leads to the oil control ring having a significant contribution to the total friction of the system. The two most prevalent oil control rings used in the industry are the twin land oil control ring (TLOCR) and the three piece oil control ring (TPOCR). The thesis investigates the effect of changing liner roughness on the friction of the TLOCR. A comparison between the TLOCR and the TPOCR is also performed using the same liner surfaces. The results from these studies show a marked difference between the friction traces from the two oil control rings.<br>by Sarthak Vaish.<br>S.M.

Paper and board are hydrophobized (sized) to control the spreading and absorption of waterbased inks and retard the absorption and edge penetration of liquid packaging by aqueous liquids. Alkenyl ketene dimers (AKD) and alkenyl succinic anhydride (ASA) are synthetic sizing agents that are generally used under neutral or slightly alkaline papermaking conditions. The overall objective of this thesis is to improve understanding of the internal sizing of paper and board by AKD and ASA by establishing a link between the sizing mechanism on one hand, and properties of sized papers, such as surface chemistry, wettability and friction, on the other. Fundamental research has been conducted in parallel with more applied research on laboratory and pilot papers. Significant effort has been expended to study the spreading behavior of AKD. The main instrument to characterize the surface chemical composition of AKD and ASA sized papers was X-ray photoelectron spectroscopy (XPS). By combination with time-of-flight secondary ion mass spectrometry (ToF-SIMS) we have been able to determine the lateral distribution and the chemical state of the sizing agent at the paper surface. Combined with contact angle measurements using liquids with different surface tensions, and other methods to analyze the amounts of size in paper, this has enabled us to obtain a deeper knowledge of the sizing mechanisms of AKD and ASA. The results indicate a definitive relationship between the redistribution of AKD at the surface of pilot papers and the drying profile used during papermaking. However, the spreading was not complete, as also seen on a model surface. Further spreading of AKD was shown to occur via surface diffusion in the form of an autophobic monolayer precursor. The spreading rate increased linearly with temperature and showed an inverse proportionality with respect to the melting point of the AKD. This monolayer spreading is relatively slow the diffusion coefficient being of the order 10-11 m2/s. AKD spreading was not hindered by hydrolyzed AKD (ketone) that spread as well. Moreover, AKD spread on the surface of crystalline calcium carbonate. In laboratory papers, the extractives present on CTMP fiber surfaces appeared to have enhanced the spreading of AKD when the fibers were in water. In spite of a slightly lower retention, ASA covered the surface of unfilled and PCC-filled pilot papers to a significantly higher extent than AKD. The ASA sized papers, however demonstrated slightly lower resistance to water. This was attributed to formation of hydrolyzed ASA products. The results obtained confirm the proposed sizing mechanism for ASA, where the hydrolyzed ASA plays a key role. The sizing level of these papers stored wrapped in aluminium foil at 23 °C and 5O %RH was nearly unchanged over prolonged storage time. In contrast, the papers exposed to ambient conditions suffered from sizing loss, most likely due to hydrolysis and migration. The reduction of the sizing degree was higher for the AKD than ASA sized unfilled papers and the catalytic effect of PCC contributed to the hydrolysis of AKD in PCC-filled papers. As expected, the use of sizing agent reduced the surface energy of paper. The higher the sizing degree of paper the lower the surface energy, and thus the higher the resistance to wetting. This was particularly seen in the contact angles with ethylene glycol having a lower surface tension than water. AKD significantly decreased the friction between unfilled papers, whereas ASA had no impact. This difference was attributed to surface chemical composition. Friction reduction for the AKD sized papers started at the AKD coverage normally found in paper produced for low water absorption. As expected, PCC filler increased paper-to-paper friction.<br>Papper och kartong hydrofoberas (limmas) för att kontrollera spridning och absorption avvattenbaserade tryckfärger och hindra kantinträngning av vattenbaserade vätskor ivätskekartong. Alkylketendimer (AKD) och alkylbärnstensyra anhydrid (ASA) är syntetiskahydrofoberingsmedel som allmänt används under neutrala eller något alkaliska förhållandenvid papperstillverkning.Arbetets övergripande målsättning var att förbättra förståelse för mäldhydrofobering avpapper och kartong med AKD och ASA genom att upprätta ett samband mellanhydrofoberingsmekanism på ena sida och ytkemi hos hydrofoberat papper och dessvätningsförmåga och friktion på den andra sidan. Grundläggande studier parallellt med mertillämpade undersökningar på laboratorie- och pilotpapper har utförts. En betydande strävanhar använts för att studera spridning av AKD. Huvudinstrumentet för att karakterisera kemisksammansättning av ytan av pilotpapper hydrofoberade med AKD och ASA var röntgenfotoelektron spektroskopi (XPS). Genom att kombinera det med sekundär jonmasspektrometri (ToF-SIMS) har lateral fördelning och kemiskt tillstånd av AKD och ASAvid en yta av papper kunnat bestämmas. Kombinerat med mätningar av kontaktvinkel medvätskor med olika ytspänning och andra metoder för att analysera halten avhydrofoberinsgmedel i papper har gjort det möjligt att erhålla djupare kunskap omhydrofoberingsmekanismer av AKD och ASA.Resultaten indikerar en klar koppling mellan omfördelning av AKD på ytan av pilotpapperoch torkningsprofil vid papperstillverkning. Emellertid, spridningen var inte fullständig, vilketvar fallet även på modellytor. Fortsatt spridning av AKD visades ske som ytdiffusion i formav ett autofobiskt monoskikt (precursor film). Spridningshastigheten ökade linjärt medtemperatur och visade omvänd proportionalitet med avseende på AKD:s smältpunkt. Dennamonoskiktspridning är relativt långsam, diffusionshastighet är i storleksordningen 10-11 m2/s.Hydrolyserat AKD (keton) hindrade inte AKD:s spridning utan spred även den. Dessutomspred AKD på ytan av kristallina kalciumkarbonat. I laboratoriepapper är extraktivämnennärvarande på ytor av CTMP fiber och tycktes ha förbättrat AKD:s spridning när fibrerna varunder vatten.ivTrots något lägre retention täckte ASA ytan av icke-fyllda och PCC-fyllda papper tillsignifikant högre grad än AKD. ASA-papperen visade dock något lägre motstånd mot vatten.Detta var hänvisat till bildning av hydrolyserade ASA-produkter. De uppnådda resultatenbekräftar den föreslagna hydrofoberingsmekanismen för ASA, där hydrolyserat ASA spelaren avgörande roll. Hydrofoberingsgraden av papper lagrade inlindade i aluminiumfolie vid23 °C och 50 RH var nästan oändrad över den förlängda lagringstiden. Som motsatsgenomgick papperen som exponerats mot omgivande atmosfärsförhållanden genomgick enminskning av hydrofoberingsgraden, troligen på grund av hydrolys och migrering. Minskningav hydrofoberingsgraden var större för icke-fyllda papper av AKD än av ASA. PCC:skatalytiska effekt bidrog till hydrolys av AKD i PCC-fyllda papper.Som förväntat reducerade användning av hydrofoberingsmedel reducerade ytenergin avpapper. Ju högre hydrofoberingsgrad desto lägre var ytenergin och därmed desto högremotstånd mot vätning. Detta sågs särskilt i kontaktvinklar med etylenglykol som har lägreytspänning än vatten.AKD minskade signifikant friktionen mellan icke-fyllda papper, medan ASA inte hadeinverkan. Denna skillnad hänfördes till skillnad i ytsammansättning. Minskning av friktion förAKD-hydrofoberade papperen påbörjades vid en sådan yttäckning av AKD som är normaltför papper tillverkat för låg vattenabsorption. Som förväntat ökade PCC-fyllmedel friktionenmellan papperen.<br>QC 20100817

Aircraft engine manufacturers strive for greater performance and efficiency by continually increasing the turbine inlet temperature. High turbine inlet temperatures significantly degrade the lifetime of components in the turbine. Modern gas turbines operate with turbine inlet temperatures well above the melting temperature of key turbine components. Without active cooling schemes, modern turbines would fail catastrophically. This study will evaluate a novel cooling scheme for turbine airfoils, called microcircuit cooling, in which small cooling channels are located extremely close to the surface of a turbine airfoil. Coolant bled from the compressor passes through the microcircuits and exits through film cooling slots. On further cooling benefit is that the microcircuit passages are filled with irregular pin fin features that serve to increase convective cooling through the channels. Results from this study indicate a strong interaction between the internal microcircuit features and the external film-cooling from the slot exit. Asymmetric cooling patterns downstream of the slot resulted from the asymmetric pin fin design within the microcircuit. Adiabatic effectiveness levels were found to be optimum for the slot design at a blowing ratio of 0.37. The pin fin arrangement along with the impingement cooling at the microcircuit entrance increased the area-averaged heat transfer by a factor of three, relative to an obstructed channel, over a Reynolds range of 5,000 to 15,000.<br>Master of Science

Increasing demand for improved fuel economy 'and environmental protection has meant that there has been increased focus on the implementation of non-ferrous materials and coatings which have excellent tribological properties for automotive applications. Since all . . commercially. available lubricants are typically optimised for ferrous materials, it is therefore expected that lubricants will not perform in an optimised way on alternative surfaces: It is therefore crucial to understand how the existing lubricants interact with non- . . ferrous coatings to be able to sensibly approach the design of new additives for non-ferrous surfaces. In this study, CrN and DLC coatings which have excellent generic tribological properties, chosen for a full evaluation of their tribochemistry using both model and fully formulated oils. Tribological tests were performed using three test rigs, namely pin-on-plate, min~ traction machine (MTM) and cam/follower rig. The pin-on-plate tests were performed to evaluate friction, wear and fturability of CrN and DLC coatings under boundary lubrication .. conditions. Based on the results obtained from pin-on-plate tests, a' few coatings were chosen for cam/follower tests. In addition, MTM tests were performed to investigate the effect of slidelroll ratio and lubrication regime on the tribologicalltribochemical performance of a particular DLC coating. Based on the MTM results, the link between the results obtained from pin-on-plate and cam/follower rigs were assessed. Using the state-of-the-art surface analysis techniques such as atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS), both physical and chemical characterisation of tribofilms formed by lubricant additives on CrN and DLC coatings have been characterised. Finally, they are correlated with the tribological results and also compared with those observed in conventional ferrous systems. This study has shown that the tribological performance of CrN and DLC coatings are oil dependent. The physical and chemical analyses of tribofilms suggest that the CrN coating responds in a similar manner to steel surfaces to the conventional additives. Optimisation 'of lubricant additives has been found to be immensely important, especially for the effective lubrication of110n/low-hydrogenated DLC coatings.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 117-120).<br>The recent worldwide quest to increase the fuel efficiency of internal combustion engines has led to great effects to reduce friction of many of the components in these engines. One area of major concern pertaining to this area is the friction of the piston/ring pack assembly. Because of the importance and necessity of this component to the internal combustion engine, any improvements can have relatively large implications for friction reduction. The purpose of this paper is to investigate several key components of the piston/ring pack assembly and how they influence friction levels. Specifically, experimental friction trends related to the oil control ring, piston skirt, liner surface and lubricant will be discussed. The Floating Liner Engine is used in this study in both the motored and fired configuration to isolate results from components and provide data for comparative analysis. The oil control ring (OCR) controls the supply of lubricating oil to the top two rings of the ring pack and has a significant contribution to friction of the system. This study investigates the two most prevalent types of OCR in the automotive market: the twin land oil control ring (TLOCR) and three piece oil control ring (TPOCR). The effect of changing the land width and spring tension on different liner surfaces for the TLOCR is investigated, and distinct trends are identified. A comparison is then done between the TLOCR and TPOCR on different liner surfaces. Results showed the TPOCR displayed different patterns of friction compared the TLOCR in certain cases. The piston skirt is also an important contributor of friction in the piston assembly. This thesis discusses the investigation into low friction coatings on the piston skirt. A brief study of piston skirt patterns is presented, with little gains being made by applying patterns the piston skirt coating. Next the roughness of the piston skirt coating is analyzed, and results show that reducing piston skirt roughness can have positive effects on friction reduction. Finally, an introductory study into the profile of the piston skirt is presented, with the outcome being that friction reduction is possible by optimizing the skirt profile. The final section of this thesis discusses the effects of lubricants pertaining to friction in the piston assembly. The effects of changing lubricant viscosity through both temperature and formulation are presented, as well as results from testing the effects of select anti-wear additives in the oil. The results identify new developments related to lubricant/additive effects on the liner surface, and how these effects can influence friction.<br>by Zach Westerfield.<br>S.M.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-06-22Bitstream added on 2014-06-13T18:41:33Z : No. of bitstreams: 1 souza_ac_dr_bauru.pdf: 4889412 bytes, checksum: b1b5556d4915022278e65a9a1b120315 (MD5)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>O desenvolvimento científico e tecnológico na área de novos materiais contribui para diversas aplicações do nióbio e suas ligas nas indústrias aeroespacial, aeronáutica, automobilística, naval, usinas nucleares, etc. O Brasil lidera o cenário mundial na oferta de nióbio, atingindo uma participação de 92,4% da produção mundial, justificando, assim, o interesse no estudo desse metal. Este trabalho tem dois objetivos: o primeiro é garantir a introdução do nitrogênio em solução sólida intersticial na matriz metálica Nb sob pressão parcial na ordem de 'X POT.-4' Torr e temperatura na ordem de 173 K, com diferentes tempos de dopagens; e, o segundo é caracterizar a liga Nb-1,0%pZr em termos de suas propriedades anelásticas, com diferentes concentrações de nitrogênio em solução sólida, tendo como referência padrão o metal nióbio. Pelo emprego do método de Espectroscopia Mecânica com base na técnia de atrito interno, que fornece informações sobre as interações Gás-Metal e outras técnicas auxiliares, como Difração de Raios X e Microscopia Eletrônica, foi possível mostrar a introdução de nitrogênio em solução em nióbio sob baixas condições de temperatura e pressão. Além disso, foi efetuada a caracterização anelástica da liga Nb-1,0%pZr em função do aumento da concentração de nitrogênio em solução sólida.<br>The scientific and technological development in the area of new materials has contributed to severa applications of niobium and its alloys to the aerospatial, aeronautical, automotive and naval industries, nuclear power stations, among others. Brazil is a worldwide leader in the supply of supply of niobium, reaching 92.4% share in the world production, thus justifying the interest in the study of that metal. In the present paper, there are two objectives: the first is to guarantee the introduction of nitrogen in an interstitial solid solution of niobium under partial pressure of 10-4 Torr and at a temperature of aound 1373 K, with different doping times. The second one is to characterize a Nb-1,0%Zr alloy according to its anelastic relaxation properties, with different nitrogen concentration in a solid solution, having niobium as a reference. By using Mechanical Spectroscopy, and bases on the internal friction technique - which provides information on Metal-Gas interactions and others auxiliary techniques, such as X-Ray Diffraction and Scanning Electron Microscopy - it was possible to show the introduction of nitrogen in a solid solution in niobium at a low temperature and pressure conditions. In addition, the anelastic characterization of the Nb-1,0%Zr alloy was performed in therms of the nitrogen concentration in a solid solution, showing complex anelastic relaxation structures, which were decomposed into their component relaxation processes due to stress-induced ordering of oxygen and nitrogen atoms around niobium and zirconium atoms.

Esta dissertação mostra a análise da interação de intersticiais pesados como oxigênio e nitrogênio em amostras policristalinas de nióbio e monocristalinas de nióbio e tânalo. Os dados experimentais foram obtidos através de medidas de atrito interno e freqüência de oscilação do pêndulo em função da temperatura, utilizando-se um pêndulo de torção invertido tipo Kê. Os resultados mostram estruturas de relaxação atribuídas à reorientação induzida por tensão de átomos intersticiais em torno de átomos da matriz metálica. Estas estruturas forma analisadas através de dois métodos: subtrações sucessivas e tempo de relaxação. A partir das medidas de atrito interno foram identificados os processos de relaxações Nb-O, Nb-N e Ta-O. Esses mesmos processos de relaxação foram confirmados por meio das medidas de freqüência de oscilação do pendulo usando um método proposto nesta dissertação, o qual relaciona o quadrado dessa freqüência medida e o inverso da temperatura.<br>This dissertation shows the analysis of heavy interstitials interaction, such as oxygen and nitrogen, in a policrystalline niobium sample and single crystal samples of niobium and tantalum. The experimental data were obtained by internal friction and oscillation frequency measurements as a function of temperature, using a Kê-type inverted torsion pendulum. The results show relaxation structures attributed to stress induced ordering of interstitial atoms around the mettalic matrix atoms. These structures were analysed by two methods: sucessive subtraction and relaxation time. From internal friction measurements, Nb-O, Nb-N and Ta-O relaxation processes were identified. These same relaxation processes were confirmed by oscillation frequency measurements, using a method proposed here, which relates squared frequency with inverse of temperature.

Resumo: O desenvolvimento científico e tecnológico na área de novos materiais contribui para diversas aplicações do nióbio e suas ligas nas indústrias aeroespacial, aeronáutica, automobilística, naval, usinas nucleares, etc. O Brasil lidera o cenário mundial na oferta de nióbio, atingindo uma participação de 92,4% da produção mundial, justificando, assim, o interesse no estudo desse metal. Este trabalho tem dois objetivos: o primeiro é garantir a introdução do nitrogênio em solução sólida intersticial na matriz metálica Nb sob pressão parcial na ordem de 'X POT.-4' Torr e temperatura na ordem de 173 K, com diferentes tempos de dopagens; e, o segundo é caracterizar a liga Nb-1,0%pZr em termos de suas propriedades anelásticas, com diferentes concentrações de nitrogênio em solução sólida, tendo como referência padrão o metal nióbio. Pelo emprego do método de Espectroscopia Mecânica com base na técnia de atrito interno, que fornece informações sobre as interações Gás-Metal e outras técnicas auxiliares, como Difração de Raios X e Microscopia Eletrônica, foi possível mostrar a introdução de nitrogênio em solução em nióbio sob baixas condições de temperatura e pressão. Além disso, foi efetuada a caracterização anelástica da liga Nb-1,0%pZr em função do aumento da concentração de nitrogênio em solução sólida.<br>Abstract: The scientific and technological development in the area of new materials has contributed to severa applications of niobium and its alloys to the aerospatial, aeronautical, automotive and naval industries, nuclear power stations, among others. Brazil is a worldwide leader in the supply of supply of niobium, reaching 92.4% share in the world production, thus justifying the interest in the study of that metal. In the present paper, there are two objectives: the first is to guarantee the introduction of nitrogen in an interstitial solid solution of niobium under partial pressure of 10-4 Torr and at a temperature of aound 1373 K, with different doping times. The second one is to characterize a Nb-1,0%Zr alloy according to its anelastic relaxation properties, with different nitrogen concentration in a solid solution, having niobium as a reference. By using Mechanical Spectroscopy, and bases on the internal friction technique - which provides information on Metal-Gas interactions and others auxiliary techniques, such as X-Ray Diffraction and Scanning Electron Microscopy - it was possible to show the introduction of nitrogen in a solid solution in niobium at a low temperature and pressure conditions. In addition, the anelastic characterization of the Nb-1,0%Zr alloy was performed in therms of the nitrogen concentration in a solid solution, showing complex anelastic relaxation structures, which were decomposed into their component relaxation processes due to stress-induced ordering of oxygen and nitrogen atoms around niobium and zirconium atoms.<br>Orientador: Carlos Roberto Grandini<br>Coorientador: Odila Florêncio<br>Banca: Carlos Alberto Soufen<br>Banca: Luis Rogério de Oliveira Hein<br>Banca: Tomaz Toshimi Ishikawa<br>Banca: Antonio Jorge Abdalla<br>O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp<br>Doutor

Orientador: Carlos Roberto Grandini<br>Banca: Alfredo Gonçalves Cunha<br>Banca: Paulo Noronha Lisboa Filho<br>O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp<br>Resumo: Desde a descoberta dos supercondutores com alta Tc, vários trabalhos têm sido efetuados sobre as diferentes propriedades destes materiais. As cerâmicas Y'BA IND.2' "C IND.U 'IND.3' 'O IND. 7-'delta' mostraram que tem suas propriedades supercondutoras fortemente afetadas pela quantidade de oxigênio. Mais recentemente, medidas de relaxações anelásticas em 'LA IND.2'CU 'O IND. 4+'delta' mostraram que a remoção deste elemento pode ser relacionada com dois eventos. Um deles é o decréscimo na mobilidade entre dois planos adjacentes CuO e o outro, é o aumento no número de padrões de mobilidade para os octaedros CU 'O IND. 6'. Para SM'BA IND.2' "C IND.U 'IND.3' 'O IND. 7-'delta' (SBCO), a possibilidade de uma estequiometria de oxigênio variável e sua alta mobilidade nos planos... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: Since the discovery of the high Tc superconductors, several works have been made about the different propoerties of these materials. Y'BA IND.2' "C IND.U 'IND.3' 'O IND. 7-'delta' ceramic showed to have its superconducting properties strongly affected by the oxygen content. More recently, anelastic relaxation measurements in 'LA IND.2'CU 'O IND. 4+'delta', showed that the remotion of this element can be related to two events. One is the decrease in mobility between two adjacent CuO planes, and the other is the increase in the number of tilting patterns of the Cu 'O IND. 6' octahedra. For SM'BA IND.2' "C IND.U 'IND.3' 'O IND. 7-'delta' (SBCO), the possibility of variable stoichiometry and the high mobility of oxygen in the... (Complete abstract, click electronic access below)<br>Mestre

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 107-109).<br>Nowadays, a rapid growth of internal combustion (IC) engines is considered to be a major contributor to energy crisis. About 20% of the mechanical loss in internal combustion engines directly goes to the friction loss between piston ring pack and liner finish. A twin-land oil control ring (TLOCR) deterministic model was developed by Chen et al. and it helps the automotive companies investigate the effects of liner finish, rings, and lubricants on friction and oil control of the TLOCR [2]. This work focuses on application of the TLOCR model and extension of the deterministic model to the top two rings. First, there are some practical challenges in the application of Chen's TLOCR deterministic model. Due to different wear condition on the same liner, surface roughness varies from spot to spot. A small patch of measurement cannot provide enough information and the change of plateau roughness makes the contact model unreliable. As a result, a multi-point correlation method was proposed to combine the information of different spots from the same liner and this method was shown to give better match to the experimental results. A top-two-ring lubrication cycle model was developed based on the multiphase deterministic model by Li. et al [30] and previous top-two-ring lubrication model by Chen. Et al [2][31]. The model is composed with two parts. First, the deterministic model is used to generate a correlation between the hydrodynamic pressure/friction and the minimum clearance with prescribed oil supply from the deterministic oil control ring model. It was found that within reasonable accuracy, the gas pressure effect on the hydrodynamic lubrication of the top two rings can be decoupled from the hydrodynamic lubrication. Thus, only single-phase deterministic model was needed to generate the correlation. This decoupling significantly reduces the computation time. Then, a cycle model was developed utilizing the correlation of hydrodynamic pressure/friction and the minimum clearance. The cycle model considers the effect of gas pressure variations in different ring pack regions as well as the dynamic twist of the top two rings. Finally, the models were used to examine the friction and lubrication of three different liner finishes in an actual engine running cycle.<br>by Yang Liu.<br>S.M.

[ES] Con el aumento de la demanda de soluciones más amigables con el medio ambiente en la industria de la automoción, el motor de combustión interna alternativo (MCIA) enfrenta actualmente grandes desafíos para minimizar su consumo de recursos no renovables y especialmente, para reducir sus emisiones contaminantes. Debido a que el aporte de los MCIAs es fundamental para cubrir las necesidades de movilidad y de generación de energía alrededor de todo el mundo, y el hecho de que diferentes alternativas, como los motores eléctricos e hibrido, están y continuaran enfrentado múltiples obstáculos para su implementación masiva en el futuro cercano, la investigación continua en MCIA es fundamental para cumplir con los propósitos de reducción de emisiones. En este aspecto, una aproximación para el aumento de la eficiencia del motor y la reducción del consumo de combustible es mediante la implementación de alternativas dirigidas a reducir las pérdidas mecánicas por fricción. Estas alternativas tribológicas incluyen aquellas que requieren modificaciones en los componentes del motor, como materiales y acabados superficiales, y el uso de formulaciones de aceite lubricante de menor viscosidad o aditivos que mejoren las condiciones de lubricación del motor. Con la contante evolución y mejoras en el MCIA y las condiciones de trabajo cada vez más severas, también surgen nuevas alternativas tribológicas para enfrentar los nuevos desafíos del motor, y por tanto se requiere de investigaciones adicionales en este tema. Durante el desarrollo de esta Tesis, uno de los objetivos consistió en contribuir a la investigación del uso de aceites de baja viscosidad para el ahorro de combustible como un efecto conjunto con las condiciones de conducción del vehículo. Para llevar a cabo este objetivo, se desarrollaron ensayos experimentales bajo condiciones estacionarias en un banco de motor con formulaciones de aceite de diferente viscosidad HTHS, algunas de ellos con aditivo modificador de fricción para expandir el rango de reducción de fricción a condiciones de lubricación más severas. Los mapas de consumo de combustible resultantes de estos ensayos fueron utilizados en un modelo de simulación del vehículo para estimar su consumo de combustible como función del aceite y las condiciones de trabajo de tres ciclos de conducción. Con el objetivo de expandir los conocimientos en los fundamentos de lubricación de los MCIAs y tener la capacidad de evaluar otras alternativas para reducir las pérdidas por fricción, se consideró necesario enfocar la investigación en el conjunto pistón-camisa, que es el par tribológico con mayor aporte a las perdidas por fricción. Para conseguir este objetivo, durante esta Tesis se desarrolló una maqueta específica para el ensamble pistón-camisa, y un modelo teórico para simular la lubricación del segmento de compresión. Para la primera parte, la maqueta se desarrolló basada en el método de camisa flotante, en el cual la camisa fue aislada del resto del motor y la fuerza de fricción generada en la interfaz pistón-camisa pudo ser medida mediante sensores de fuerza. En esta instalación se desarrollaron diferentes ensayos los cuales permitieron llevar a cabo un análisis exhaustivo de los fundamentos de lubricación de este par tribológico como función de diferentes parámetros que tiene impacto en las condiciones de lubricación. Este estudio se complementó con el desarrollo de un modelo de lubricación para el segmento de compresión basado en el método de diferencias finitas. Finalmente, se llevó a cabo una comparativa de resultados experimentales y teóricos para el segmento de compresión, lo cual permitió validar los ensayos experimentales en la maqueta de camisa flotante, así como el modelo de simulación desde el punto de vista de datos de entrada, condiciones de contorno y supuestos.<br>[CA] Amb l'augment de la demanda de solucions més amigables amb el medi ambient en la indústria de l'automoció, el motor de combustió interna alternatiu (MCIA) s'enfronta actualment a grans desafiaments per minimitzar el seu consum de recursos no renovables i especialment, per reduir les seves emissions contaminants . Tenint en compte que l'aportació dels MCIA és fonamental per a cobrir les necessitats de mobilitat i generació d'energia arreu de tot el món, i el fet que diferents alternatives, com els motors elèctrics i híbrids, estan i continuaran enfrontat múltiples obstacles per a la seva implementació massiva al proper futur, la investigació contínua en MCIA és fonamental per complir amb els propòsits de reducció d'emissions. En aquest aspecte, una aproximació per a l'augment de l'eficiència del motor i la reducció de consum de combustible és mitjançant la implementació d'alternatives dirigides a reduir les pèrdues mecàniques per fricció. Aquestes alternatives tribològiques inclouen aquelles que requereixen modificacions de components del motor, com materials i acabats superficials, i l'ús de formulacions d'oli lubricant de menor viscositat o additius que milloren les condicions de lubricació del motor. Amb la constant evolució i millores en el MCIA i les condicions de treball cada vegada més severes, també sorgeixen noves alternatives tribològiques per enfrontar els nous desafiaments del motor, i per tant es requereix d'investigacions addicionals en aquest tema. Durant el desenvolupament d'aquesta Tesi, un dels objectius va consistir a contribuir a la investigació de l'ús d'olis de baixa viscositat per a l'estalvi de combustible com un efecte conjunt amb les condicions de conducció de vehicle. Per dur a terme aquest objectiu, es van desenvolupar assajos experimentals sota condicions estacionàries en un banc de motor amb formulacions d'oli de diferent viscositat HTHS, algunes d'elles amb additiu modificador de fricció per expandir el rang de reducció de fricció a condicions de lubricació més severes . Els mapes de consum de combustible resultants d'aquests assajos van ser utilitzats en un model de simulació del vehicle per estimar el seu consum de combustible com a funció de l'oli i les condicions de treball de tres cicles de conducció. Amb l'objectiu d'expandir els coneixements en els fonaments de lubricació dels MCIAs i tenir la capacitat d'avaluar altres alternatives per reduir les pèrdues per fricció, es va considerar necessari enfocar la recerca al conjunt pistó-camisa, que és el parell tribològic amb major aportació a les perdudes per fricció. Per aconseguir aquest objectiu, durant aquesta Tesi es va desenvolupar una maqueta específica per al acoblament pistó-camisa, i un model teòric per simular la lubricació del segment de compressió. Per a la primera part, la maqueta es va desenvolupar basada en el mètode de camisa flotant, en el qual la camisa va ser aïllada de la resta del motor i la força de fricció generada en la interfície pistó-camisa va poder ser mesurada mitjançant sensors de força. En aquesta instal·lació es van desenvolupar diferents assajos els quals van permetre dur a terme una anàlisi exhaustiva dels fonaments de lubricació d'aquest parell tribològic com a funció de diferents paràmetres que tenen impacte en les condicions de lubricació. Aquest estudi es va complementar amb el desenvolupament d'un model de lubricació per al segment de compressió basat en el mètode de diferències finites. Finalment, es va dur a terme una comparativa de resultats experimentals i teòrics per al segment de compressió, la qual cosa va permetre validar els assajos experimentals a la maqueta de camisa flotant, així com el model de simulació des del punt de vista de dades d'entrada, condicions de contorn i hipòtesis.<br>[EN] With the increasing demand for greener solutions in the automotive industry, the ICE is currently facing great challenges to minimize the consumption of nonrenewable resources and specially to reduce its harmful emissions. Given that the contribution of the ICE is fundamental to cover the actual mobility and power generation needs worldwide, and the fact that different power-train alternatives, such as electric and hybrid vehicles, are and will continue facing multiple obstacles for their large-scale implementation in the near future, the continuous research on the ICE is fundamental in order to meet the emissions reduction targets. In this regard, one approach to increase the engine efficiency and reduce the fuel consumption, is through the implementation of alternatives aimed to reduce the friction mechanical losses. These tribological alternatives include those that require modifications to the engine components, such as materials and surface finishes, and the use of lubricant oil formulation of lower viscosity or additives that improve the lubrication performance of the engine. With the ongoing evolution and improvement of the ICE and the increasingly severe working conditions, new tribological solutions also emerge to face the new challenges in the ICE, and therefore further research is required on this subject. During the development of this Thesis, one of the objectives was to contribute to the research on low viscosity engine oils for fuel economy as a joint effect with the driving conditions of the vehicle. To accomplish this, experimental tests were performed under stationary conditions in an engine bench test for oil formulations of different HTHS viscosity, some of them with friction modifier additive to expand the friction reduction effect to more severe lubrication conditions. The resultant fuel consumption maps were then employed in a vehicle model to estimate the fuel consumption of the vehicle as function of the oil formulation and the working conditions of the three driving cycles. With the aim of expanding the knowledge on the lubrication fundamentals of the engine and to have the capability to assess other alternatives to further reduce the friction mechanical losses, it was deemed necessary to focus the research on the piston-cylinder liner assembly, the tribo-pair of major friction share. In order to achieve this objective, a test rig was developed in this Thesis specific for the piston-liner assembly, and a theoretical model to estimate the lubrication of the piston compression ring. For the first part, the test rig was designed based on the floating liner method, where the cylinder liner was isolated from the rest of the engine and the friction force generated in the piston-liner conjunction could be measured by means of force sensors. Different tests were developed in this test rig which allowed a comprehensive analysis of the piston lubrication fundamentals as function of different parameters having an impact on the lubrication performance of this assembly. This study was complemented with the development of a piston compression ring lubrication model based on the finite differences method. A comparison of experimental and theoretical results was performed for the piston compression ring that helped to validate both the experimental tests in the floating liner and the simulation model from the point of view of input data, boundary conditions and assumptions.<br>Bastidas Moncayo, KS. (2021). Experimental and analytical study of the mechanical friction losses in the piston-cylinder liner tribological pair in internal combustion engines (ICE) [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172188<br>TESIS

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"Hot-tests" form a vital facet towards the end of the production line of modern automotive plants, where the condition of the engine is checked by running it for a short period of time, to ensure its performance under standard operating conditions. The duration of hot-tests for small engines varies from 20-75 seconds. In the conventional procedure, about 10-30 grams of lubricant (for pre-coating) is used with about 650ml of standard oil for engine testing. However, about 1-3 oz. of oil is lost per engine, as it cannot be sucked out of the crankcase after the hot tests. The loss of 1-3 oz. of oil leads to a significant loss in revenue, over the large number of engines manufactured. It also causes a potential safety and environmental hazard due to leakage of lubricant during shipping or upon first use in a particular application. The goal of this project is to conduct "no-oil" hot tests using less than 10 grams of specially formulated lubricants for pretreatment. Implementation of this procedure for conducting the hot tests in the manufacturing facility would save revenue and eliminate potential hazards mentioned above in addition to cutting down on manpower and/or machinery used for handling the engine oil. An experimental study of pre-treatment of interacting interfaces of engine components, with specially formulated lubricants, for no-oil hot tests is presented. This study includes sixteen tests performed on the production line of Tecumseh's small engine manufacturing plant. The formulated lubricants were made up of tribopolymer formers, i.e., monomers, which were used in previous tribopolymerization studies. Tribopolymerization is defined as the planned or intentional formation of protective polymeric films directly and continuously on rubbing surfaces to reduce damage and wear by the use of minor concentrations of selected compounds capable of forming polymeric films in situ. This study entailed the investigation of the anti-wear properties of the formulated lubricants on a high temperature pin-on-disk machine and subsequent selection of lubricants exhibiting superior performance for use in the engine tests. The no-oil hot-tests performed at Virginia Tech and on the assembly line exhibited the superior anti-scuffing/anti-wear properties of the specially formulated lubricants, to warrant their use on the production line in the near future.<br>Master of Science