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Oliver, William B. "An experimental investigation of the static coefficient of friction for sheetpile interlocks." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/104522.
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Lång, Marcus. "Static Friction in Slip Critical Bolt Joints : Coefficient of Friction in Steel, Aluminium and ED Coated Steel." Thesis, Karlstads universitet, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-55223.
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This project was performed together with ÅF Industry AB in Trollhättan, Sweden. ÅF’s expertise in Trollhättan is oriented towards the automotive industry. It was conducted within the section of CAE and safety where they, for instance, dimension bolt joints in the cars. Bolt joints play an important role in the automotive industry. Slip critical bolt joints are used widely throughout the vehicles. With lack of good test data, the bolt joints need to be dimensioned conservatively. This may lead to that bolt joints are over-dimensioned, adding more mass to the car. On the contrary, the availability of reliable test data enables designers to optimize joint dimensions to achieve a safe design with minimized mass. A mechanical testing configuration has been designed as well as a testing procedure for a test to determine the static friction value between mating surfaces in bolt joints. The testing configuration has been used to perform tests to find the static friction coefficient in different materials. The study contains varied combinations of steel, aluminium and ED-Coated steel. The study resulted in tables with levels of probability. The developed test configuration is robust and relatively simple to use and is recommended for further use. For improved statistical significance, it was noted that more samples should be used than was used in this study. The aluminium has a smoother surface finish and that could be the reason why its coefficient of friction is lower than steel. It is therefore considered important to also include surface roughness when presenting coefficient of friction results.
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Kinsella, Mary E. "Ejection forces and static friction coefficients for rapid tooled injection mold inserts." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092660338.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xvi, 206 p.; also includes graphics (some col.). Includes bibliographical references (p. 167-173). Available online via OhioLINK's ETD Center
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Längkvist, Martin. "Online Identification of Friction Coefficients in an Industrial Robot." Thesis, Linköping University, Department of Electrical Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-19269.
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All mechanical systems with moving parts are affected by friction, including industrial robots. Being able to design an accurate friction model would further increase the performance of todays robots. Friction is a complex dynamic phenomena that is constantly changing depending on the state and environment of the robot. It is therefore beneficial to update the parameters of the friction model online. An estimate of the friction will be made using the feedback control signal with the help of a feedforward control scheme in a two axis simulation setup. The friction estimate is then used for an offline identification of three friction model parameters in a static Lugre friction model. Improvements on the identification will be done by introducing some shut-off rules that will improve the estimate. The normalized least mean square method (NLMS) will then be used to update the parameters online. A simulation of friction compensation with a fixed friction model, and with an adaptive friction model will be studied. The method will also be simulated using experimental data taken from a real industrial robot.
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Hutama, Chapin. "Effect of Inclusion of Nanofibers on Rolling Resistance and Friction of Silicone Rubber." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1556118372072796.
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Fasol, Christian. "Hydrodynamique et transfert de chaleur dans un mélangeur statique Sulzer SMX avec des fluides rhéologiquement complexes." Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL031N.
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Les mélangeurs statiques sont, grâce à leurs multiples avantages, de plus en plus utilisés dans l'industrie, en particulier lorsque les procédés font intervenir des fluides rhéologiquement complexes. Cette utilisation est cependant essentiellement basée sur l'empirisme et le savoir-faire. Nous avons étudié l'hydrodynamique, via la distribution des temps de séjour (DTS) et la perte de charge, et le transfert de chaleur, éventuellement couplés dans un type de mélangeur particulièrement adapté aux fluides visqueux: le mélangeur statique Sulzer SMX. Nous proposons un modèle de DTS basé sur l'association en parallèle pour chaque élément de mélangeur statique d'un écoulement piston et d'un réacteur parfaitement agité ; les deux paramètres à ajuster de ce modèle sont des fonctions d'un nombre de Reynolds généralisé qui tient compte de la rhéologie des fluides qui circulent dans le mélangeur. Nous proposons une corrélation pour le facteur de frottement en fonction de ce même nombre de Reynolds généralisé ; cette corrélation est valable qu'il y ait ou non couplage avec le transfert de chaleur. Le transfert de chaleur a été étudié de deux façons. D’une part par une approche globale et d'autre part par une approche prenant en compte l'hydrodynamique dans le mélangeur statique (connaissance de la DTS). Les corrélations obtenues concernant le coefficient de transfert de chaleur sont tout à fait comparables. Ce travail a été complété par deux études préliminaires: l'une a montré qualitativement l'efficacité du mélangeur à disperser du gaz dans des milieux rhéologiquement complexes ; l'autre a mis en évidence le caractère chaotique du mélange dans ce type de mélangeur
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Griffiths, Peter Robert. "Static and Dynamic Components of Droplet Friction." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4897.
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As digital microfluidics has continued to mature since its advent in the early 1980's, an increase in new and novel applications of this technology have been developed. However, even as this technology has become more common place, a consensus on the physics and force models of the motion of the contact line between the fluid, substrate, and ambient has not been reached. This uncertainty along with the dependence of the droplet geometry on the force to cause its motion has directed much of the research at specific geometries and droplet actuation methods.
The goal of this thesis is to help characterize the components of the friction force which opposes droplet motion as a one dimensional system model based upon simple system parameters independent from the actuation method. To this end, the force opposing the motion of a droplet under a thin rectangular glass cover slip was measured for varying cover slip dimensions (widths, length), gap height between the cover slip and substrate, and bulk droplet velocity. The stiffness of the droplet before droplet motion began, the force at which the motion initiated, and the steady-state force opposing the droplet motion were measured. The data was then correlated to hypothesized equations and compared to simple models accounting for the forces due to the contact angle hysteresis, contact line friction, and viscous losses.
It was found that the stiffness, breakaway force, and steady-state force of the droplet could be correlated to with an error standard deviation of 8 %, 14%, and 10 % respectively. Much of the error was due to an unexpected height dependence for the breakaway and steady-state forces and testing error associated with the velocity. The models for the stiffness and breakaway force over predicted the results by 36% and 16% respectively. During testing,
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stability issues with the cover slip were observed and simple dye testing was conducted to visualize the droplet flow field.
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Grzeskiewicz, Ronald. "Effect of hydrogen on the coefficient of friction of iron." Thesis, This resource online, 1988. http://scholar.lib.vt.edu/theses/available/etd-04122010-083727/.
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Dorton, David W. "Experimental evaluation of effective friction coefficient for liquid ring seals." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08042009-040326/.
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Peterson, Eric W. "Tire-Road Friction Coefficient Estimation Using a Multi-scale, Physics-based Model." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/51148.
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The interaction between a tire and road surface is of critical importance as the motion of a car in both transient and steady-state maneuvers is predicated on the friction forces generated at the tire-road interface. A general method for predicting friction coefficients for an arbitrary asphalt pavement surface would be an invaluable engineering tool for designing many vehicle safety and performance features, tire design, and improving asphalt-aggregate mixtures used for pavement surfaces by manipulating texture. General, physics-based methods for predicting friction are incredibly difficult, if not impossible to realize—However, for the specific case of rubber sliding across a rough surface, the primary physical mechanisms responsible for friction, notably rubber hysteresis, can be modeled.
The objective of the subsequent research is to investigate one such physics model, referred to as Persson Theory, and implement the constitutive equations into a MatLab® code to be solved numerically. The model uses high-resolution surface measurements, along with some of the physical properties of rubber as inputs and outputs the kinetic friction coefficient. The Persson model was successfully implemented into MatLab® and high resolution measurements (from optical microscopy and imaging software) were obtained for a variety of surfaces. Friction coefficients were calculated for each surface and compared with measured friction values obtained from British Pendulum testing. The accuracy and feasibility of the Persson model are discussed and results are compared with a simpler, semi-empirical indenter model. A brief discussion of the merits and drawbacks of the Persson model are offered along with recommendations for future research based on the information acquired from the present study.Master of Science
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Lee, Edward Chungjen. "A study of the static to kinetic friction transition of polymers." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-07282008-135807/.
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Sista, Sri Narasimha Bhargava. "Dry Static Friction in Metals: Experiments and Micro-Asperity Based Modeling." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1416579128.
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Koubek, Radek, and Karolina Dedicova. "Friction of wood on steel." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-35094.
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This thesis deals with the experimental description of friction between steel and wood materials, specifically laminated veneer lumber (LVL) and pine wood with two types of annual rings. It studies the influence of a number of different parameters on the coefficient of friction such as contact pressure, moisture content, fiber orientation in relation to the load direction, steel surface roughness, and horizontal load rate. First, the theoretical mechanical and physical properties as well as the coefficient of friction itself are described. This is followed by the description of the test setup including the test method and how the obtained data is exported, handled and processed and how the coefficient of friction is determined. The results study the influence of different parameters and show that the coefficients of friction for the smooth sliding plate tests vary in between 0.1 and 0.3, whereas tests with the rough sliding plate vary around 0.7. Factors influencing the coefficient of friction were found to be the different moisture content under all tested pressures, the different fiber direction under low contact pressure, the contact pressure itself, though under higher pressures the influence was found to be low, and the horizontal load rate under low pressures. The outcomes are further discussed in the discussion chapter.
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Pažítková, Monika. "Tření v tvářecích procesech." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-416430.
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This thesis deals with tests of forming operations, which are used to determine coefficient of friction. In the theoretical part of thesis, the individual tests are described in details, with the greatest emphasis on the upsetting test. In the experimental part of thesis was perform upsetting test on the cylindrical and ring samples. Coefficient of friction of the cylindrical samples was determined by a calculation method and ring samples were evaluated using diagram of calibration. The thesis includes comparison of the result received on lubricant and unlubricated samples and method for determined coefficient of friction. Graphite Delta 144 was used as a lubricant. This result show that the lubricant has a positive effect on forming process.
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Monk, Stuart. "The role of friction coefficient on launch conditions in high-loft angle golf clubs." Thesis, University of Birmingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433489.
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Koller, Anton W. "The friction coefficient of soft contact lens surfaces in relation to comfort and performance." Thesis, City University London, 2014. http://openaccess.city.ac.uk/13791/.
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The soft contact lenses of today are made from a variety of hydrogel materials. These materials have different properties in terms of water content, monomers, hardness and other tensile characteristics. It is likely that the frictional properties also vary between materials. It is known that constituents of the tear film interact with contact lens materials to form a biofilm on the lens surface. The hypothesis of this research is that although the frictional properties of lens materials may vary these properties do not affect the comfort and performance of the lenses in vivo. A tribometer is a device to measure the coefficient of friction of materials. There was no commercially available tribometer designed specifically for use with contact lens materials, so one was constructed and validated against standard solid materials. The same equipment was used to determine the friction coefficients of five contemporary soft lens materials under different conditions of lubrication but, unlike other tribometers, this unique design simulated human blinking as far as possible. The experimental friction coefficients varied widely from 0.27 to 5.89 under different conditions of lubrication. The largest variation between materials was seen using the most viscous lubricant. For the in vivo studies the author coordinated the manufacture of 250 contact lenses, which were lathe cut and polished to a standard design, achieving exceptionally tight tolerances, using the same five materials. This rigourous process was carried out to minimise variations in the geometry of each contact lens. Subjects were screened to minimise ocular heterogeneities between subjects. Clinical performance of each lens was assessed using comfort, contrast sensitivity, visual acuity, entoptic phenomena, non-invasive tear break-up time and lens movement on the eye. In a clinical environment none of these parameters showed any associations with the coefficients of friction found in vitro, apart from a moderate correlation (rho = 0.5) between lens movement and the coefficient of friction under borderline friction conditions. In conclusion, the findings of this research support the hypothesis that frictional properties of soft lenses do not affect comfort and performance in vivo.
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Ashaju, D. I. "Experimental and theoretical analysis of coefficient of friction and redundant deformation in tube sinking process." Thesis, City University London, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382795.
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Al-Kawaz, Ammar. "Development and rheological analysis of a surface polymer nanocomposite anti-friction." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE025/document.
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L'objectif de cette thèse est l'identification de couplages (nanoparticules / matrice de poly(methyl-methacrylate) PMMA) qui renforcent la rigidité de surface du PMMA tout en conservant le maximum de transparence. Le choix s'est porté sur trois type de nanoparticules carbonées : du graphène multicouches (FLG), de l'oxyde de graphène (GO) et des nanotubes de carbones (MWCNT). Une première décrit la préparation et la fonctionnalisation de ces trois types de nanoparticules pour assurer une meilleure dispersion dans la matrice. Deux méthodes ont été retenues pour réaliser ces matériaux composites : la polymérisation en masse et le mélange en solution. Une seconde partie présente la caractérisation des propriétés mécaniques de ces revêtements en trois étapes : en volume, en surface et sous forme de revêtement en couches minces (15-20µm). Les résultats majeurs montrent que les nano-composites réalisés retardent l'apparition de la plasticité comparé à un PMMA pur, même à faible pourcentage, et permettent ainsi de limiter les effets de rayures de surfaces. Le faible pourcentage de renfort permet de conserver la transparence et plus l'épaisseur diminue plus on peut augmenter ce taux de renfort sans dégrader les propriétés mécaniques du revêtement. Les nanoparticules choisies comme agents de renfort de la matrice polymère s'avèrent être également de très bons candidats pour la diminution du frottement comparée à un plastifiant type ErucamideThe goal of this thesis is the identification of couplings (nanoparticles / matrix poly (methyl methacrylate) PMMA) which ensure PMMA surface rigidity while maintaining maximum transparency. The choice fell on three types of carbonaceous nanoparticles: Few layer graphene (FLG), graphene oxide (GO) and carbon nanotubes (MWCNT). A first part describes the preparation and functionalization of these three types of nanoparticles to provide a better dispersion in the matrix. Two methods were used to prepare nanocomposite materials: bulk polymerization and solution blending. A second part presents the characterization of the mechanical properties of these coatings in three stages: volume, surface and thin layer coating (15-20μm). The main results show that nanocomposites made delay the onset of plasticity compared with pure PMMA, even at a low percentage, and help to limit the effects of surface scratches. The small percentage of reinforcement keeps the transparency and the more the thickness decreases the more the rate of reinforcement can increase without degrading the mechanical properties of the coating. Moreover, nanoparticles chosen as the polymer matrix of reinforcing agents prove to be very good candidates for reduction in friction compared to a plasticizer such Erucamide
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Wiggers, Frank Norbert. "The flow and drainage of foams and films." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368426.
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The behaviour of gas-liquid foams has been the subject of extensive research in the past century because of the usefulness of liquid foams in industry. In this work we present new experimental and theoretical developments concerning flow and drainage behaviour of surfactant based liquid foams and films. The flow of free films and foam was studied in vertical tubes for different liquid properties. Measurements of the thickness of the lubricating layer on the wall and CFD simulation shows a relationship between the liquid thickness, liquid viscosity and pressure drop for the flow of free films. For foam flow, friction factors were determined for all systems and data lied remarkably on a unique line on the friction factor-Reynolds number plot and has a practical significance in that pressure drop can be calculated using a constant friction factor along a pipe of a constant cross section in any flow regime. An improved ER technique has been developed for accurate measurements of foam resistance, which includes the liquid layer at the wall. Traditional ER-methods for characterising the drainage of a wall-confined static foams do not take into consideration the effects of a substantial liquid layer established on the wall during drainage which transports a substantial amount of liquid. A method is proposed for the estimation of temporal as well axial variations of the wall liquid thickness inferred from the measurements of the local liquid holdup. A theoretical model is proposed for foam drainage based on the analogy of liquid flow through a packed bed of solid particles. A good agreement is obtained between theory and experiment on the basis of judicious estimations of foam cell size and shape factor.
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Satam, Sayali S. "Optimization of Wet Friction Systems Based on Rheological, Adsorption, Lubricant and Friction Material Characterization." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1503358825451407.
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Han, Han. "Determination of Flow Stress and Coefficient of Friction for Extruded Anisotropic Materials under Cold Forming Conditions." Licentiate thesis, KTH, Production Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1498.
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The work material in metal working operations always showssome kind of anisotropy. In order to simplify the theoreticalanalysis, especially considering bulk deformation processes,anisotropy is usually neglected and the material is assumed tobe isotropic. On the other hand, the analysis that consideredthe influence of anisotropy seldom incorporates the influenceof friction. For predicting the material flow during plasticdeformation and for predicting the final material properties ofthe product, adequate descriptions of both flow stress curvesand coefficients of friction have to be developed.
In the present work a number of experimental methods fordetermining the anisotropy have been utilized and compared:Yield loci, strain ratios (R-values) and establishing flowstress-curves in different directions. The results show thatthe yield loci measurements are weak in predicting anisotropywhen the material strain hardening is different in differentdirections. It is concluded that also the strain ration(R-value) measurements are unreliable for describinganisotropy. The most trustable and useful results were foundfrom multi-direction determinations of the flow stresses.
Three typical cases of ring upsetting conditions wereanalyzed by theory (3D-FEM) and experiments:
An anisotropic ring, oriented 900 to the axis ofrotational symmetrical anisotropy. The friction coefficientwas the same in all directions
An isotropic ring. The friction coefficient was differentin different directions
An anisotropic ring oriented 00 to the axis of rotationalsymmetrical anisotropy. The friction coefficient was the samein all directions
The cases 1) and 2) reveal that the influence of anisotropyon the ring deformation is quite similar to that obtained bychanging the frictional condition. The case 3) exposes that ifthe material flow caused by anisotropy is incorrectly referredto friction, the possible error of the friction coefficient canbe as high as 80% for a pronounced anisotropic material. Amodified two-specimen method (MTSM) has been establishedaccording to an inverse method. Experiments were carried ascylinder upsetting. Here both ordinary cylinders were used aswell as so-called Rastegaev specimen. Also plane straincompression tests were utilized. The results show that MTSM isable to evaluate the validity of a selected mathematical modelwhen both the friction coefficient and the flow stress areunknown for a certain process. MTSM can also be used toestimate the friction coefficient and flow stress provided thatthe selected mathematical model is adequate.
Key words:Anisotropy, friction coefficient, flowstress, modified two-specimen method and FE-analysis
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Aretusini, Stefano. "Frictional processes of clay-rich gouges at seismic slip rates." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/frictional-processes-of-clayrich-gouges-at-seismic-slip-rates(1d6fca4a-86d2-4139-a431-f1e24d8ede8a).html.
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Smectite clay minerals are among the most common minerals in subduction zone megathrusts faults at shallow depth and in landslide decollements. Consequently, deformation processes at seismic slip rates (ca. 1 m/s) in smectites contribute to control the mechanics of megathrust earthquakes and landslide collapses. To investigate the deformation processes, rotary shear experiments on smectite-rich gouge layers (70/30 wt.% Ca-montmorillonite/opal) were performed. The experiments were conducted at ambient temperature and at 5 MPa normal stress. The gouges were sheared under vacuum (<0.001 mbar) and room humidity (i.e., water depleted) or in the presence of liquid water (i.e., water rich) conditions, at slip rates of 0.0003 <V <1.5 m/s and displacements of 0.1 <d <30 m. The temperature evolution with slip was measured with thermocouples and modelled numerically. Permeability of the gouge layer was measured with the pore pressure oscillation method prior to the rotary experiments. Before and after the experiments, the mineral and amorphous material content in wt.% were determined via quantitative X-ray powder diffraction and the microstructures investigated via scanning and transmission electron microscopy. The activation of deformation processes was strongly controlled by the water content of the gouge layers. Under water depleted conditions, grainsize reduction producing nanoparticles controlled the evolution of the friction coefficient f at all slip rates. Coseismic dynamic weakening (f = 0.2 - 0.3) occurred by combined thermal decomposition or melting (with decreasing water content) and pressurization of water released by dehydration of smectite interlayer. Under water rich conditions, grain size reduction was minor and development of nano-foliations occurred. At all slip rates, the friction coefficient rapidly decreased at the onset of slip. The large initial weakening (to f <0.15) was due to the presence of a film of water lubricating the surfaces of the sub-parallel smectite grains forming the nano-foliation in combination with shear-enhanced water pressurization. Then, friction coefficient evolved depending on the balance between dissipation of pore pressures, dehydration of smectite interlayer and thickening of the nano-foliation layers. At higher displacement and slip rates, sustained dynamic weakening was aided by vaporization of pore water. Expulsion of water determined a switch to deformation processes typical of water depleted conditions. In nature, the presence of liquid water in smectites has a lubricating effect, pressurizes the slipping zone and renders the smectite-rich gouges prone to accommodate large seismic slips. During megathrust earthquakes, such lubricating effect may result in the easy propagation of seismic ruptures in smectite- and water-rich sediments at shallow depths. Similarly, the presence of water can promote large displacements during landslide collapse.
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Kleiner, Ana Francisca Rozin 1982. "The required coefficient of friction in normal and pathological gait : friction and gait = Coeficiente de atrito requerido na marcha normal e patológica: atrito e marcha." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/274676.
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Orientador: Ricardo Machado Leite de BarrosTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Educação Física
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Resumo: O objetivo principal desta tese foi analisar o coeficiente de atrito requerido (RCOF) na marcha de idosos, pacientes com acidente vascular cerebral (AVC) e com doença de Parkinson (DP). Esta tese contém seis capítulos. No Primeiro Capítulo a revisão de literatura sobre Tribologia (o estudo do atrito) e RCOF na marcha é apresentada. Atrito é a resistência ao movimento durante o deslizar ou girar que acontece quando um corpo sólido se move tangencialmente sobre outro corpo com o qual esta em contato. Na marcha, o RCOF é o atrito requerido entre o sapato e o chão para realizar vários tipos de atividades. O Segundo Capítulo discute a metodologia para calcular o RCOF baseada nas forças de reação do solo (FRS). Para calcular o RCOF os dados de FRS durante a marcha são adquiridos. Para isso, o participante é instruído a andar descalço em sua velocidade preferida ao longo de uma passarela, sob a qual duas plataformas de força estão embutidas no chão da sala de coleta de dados. Após coletados, os dados de GRF são normalizados pelo peso corporal do sujeito e em função da percentagem da fase de suporte. Em seguida, o RCOF é calculado como a razão entre as componentes horizontais de FRS (resultante das FRS lateral e antero-posterior) e a FRS vertical. Com esta metodologia foram realizados os estudos apresentados nos Terceito, Quarto, Quinto e Sexto Capítulos desta tese. No Terceiro e no Quarto Capítulos são apresentadas investigações os efeitos de diferentes superfícies no RCOF durante a marcha normal e patológica. Para isso, o participante foi orientado a caminhar sobre as seguintes superfícies: 1) piso vinílico (HOV); 2) carpete; 3) revestimento vinílico (HTV); 4) mista (a primeira parte da passarela foi coberta por HOV e a segunda por HTV). Todas as quatro superfícies apresentavam coeficiente de atrito estático seguro (que varia 0,44-0,55) e são amplamente utilizadas em residências e instalações públicas. Os principais resultados destes estudos foram: na marcha descalça indivíduos saudáveis apresentaram diferenças no RCOF entre os tipos de superfície nas fases de contato inicial e apoio terminal. Além disso, o RCOF na marcha dos pacientes com AVC foi alterada na fase apoio terminal devido as quatro superfícies testadas. No Quinto e no Sexto Capítulos, a análise da curva do RCOF em pacientes com AVC e DP foi apresentada, respectivamente. O RCOF dos pacientes com AVC e DP apresentaram padrões diferentes aos do grupo controle. Em pacientes com AVC o contato inicial, a fase de rolamento e o apoio terminal são as fases mais críticas para a incidência de quedas. Os pacientes com DP apresentaram valores RCOF mais baixos durante o contato inicial e a fase de apoio terminal em comparação com o grupo controle. Estas análises representam a primeira tentativa de explorar as características da curva RCOF durante a análise da marcha; além disso, esta variável também pode ser utilizada na predição da queda dos pacientes com AVC e DP
Abstract: The main goal of this thesis was to analyze the required coefficient of friction (RCOF) on elderly, stroke and parkinsonian gait. This thesis is presented in six chapters. In the First Chapter the literature review of Tribology (the study of friction) and the RCOF during the gait are presented. Friction is the resistance to motion during sliding or rolling that is experienced when a solid body moves tangentially over another with which it is in contact. During the gait, the RCOF is the friction required at the shoe and floor interface to support different types of human activities. The Second Chapter discusses the methodology to calculate the RCOF based on the ground reaction forces (GRF). To calculate the RCOF the GRF data during the participant¿s gait analysis is acquired. For this the participant is ask to walk barefoot, at his or her selected speed, along a pathway, beneath which two force platforms embedded in the data collection room floor. After this the GRF data is normalized by the subject¿s body weight and it is expressed as a function of the percentage of the support phase. Then, the instantaneous RCOF is calculated as the ratio between the shear of the horizontal GRF components (resultant of lateral and anterior posterior GRF) and the vertical GRF. With this methodology the studies presented in the Third, Fourth, Fifth and Sixth chapters were design. The Third and the Fourth chapters the studies about the effects of flooring in RCOF during normal and pathological gait were discussed. For this, the participant was oriented to walk on the following flooring: 1) homogeneous vinyl (HOV); 2) carpet; 3) heterogeneous vinyl (HTV); 4) mixed (the first half part of the pathway were covered by HOV and the second by HTV). All the four surfaces presented safe static coefficient of friction (ranging from 0.44-0.55) and they are widely used in residences and public facilities. The main results of these studies were: in healthy subjects¿ barefoot gait, there were differences in the RCOF among the flooring types in the heel contact and toe-off phases. Moreover, the RCOF of stroke patients was altered on the toe off phase due to the four flooring tested. In the fifth and sixth chapters, studies about the instantaneous RCOF curve analysis in patients with Stroke and PD were presented respectively. The RCOF of patients with stroke and PD exhibited patterns that were different than those of the healthy subjects. In patients with stroke the initial contact, the mid stance and the terminal stance seem to be critical phases for the incidence of slips. The patients with PD performed lower RCOF values during the loading response and terminal stance phases in comparison with the control group. These analyses represent the first attempt to explore the RCOF curve parameters during the gait analysis; moreover, its might be used in the prediction of the real fall propensity of patients with stroke and PD
Doutorado
Biodinamica do Movimento e Esporte
Doutora em Educação Física
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Mohamed, Iqbal Amir Asyraf. "CHARACTERIZATION AND TRIBOLOGICAL PERFORMANCE OF AUTOMOTIVE BRAKE PADS WITH DIFFERENT RAW MATERIALS." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2127.
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Over the years, numerous studies have been conducted for the development of alternative materials for better performance of brake pads. With a huge selection of materials, automobile manufacturers must prioritize the performance standards, safety, cost and environmental factors of the brake pads. To improve the friction performance of brake pads, maintain customers comfort level and environment safety, design engineers test and verify the best materials to satisfy the federal performance standards. Raw materials of brake pads compose of different categories such as organic, semi metallic and low-metallic. Besides the difference in composition, these materials affect the brake pads in terms of friction properties, wear rates and noise levels. It is crucial for engineers and manufacturers to improve friction stability while minimizing vibration by manipulating the composition of different raw materials and additive materials. Automotive brake pads normally consist of numerous metallic and composite materials that are formed by hot compression which can result in various mechanical properties [14]. This research proposes to investigate different composition of metallic raw materials and how their frictional performance is affected under different environmental testing standards. This research investigates the frictional performance of six types of raw materials with different mechanical properties and morphology using a universal mechanical tester (Bruker UMT). This paper examines the overall friction performance, coefficient of friction and creep groan behavior of six different raw materials under different humidity levels. By scrutinizing the static and kinetic coefficient of friction(COF) at different humidity levels, humidity-induced friction instability at low speed is studied and presented in this paper. After performing friction tests for each material, it was concluded that the friction performance and kinetic coefficient of friction of the brake pad samples were drastically affected by longer exposure to humid air.
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Masilela, Sipho Rudolph. "Assessment of the friction behaviour of selected base oils under oscillatory sliding conditions." Diss., University of Pretoria, 2009. http://hdl.handle.net/2263/67797.
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The ability of a lubricating oil to reduce friction in mechanical surfaces which are in relative sliding motion depends on the base oil behaviour. Previous studies have demonstrated that temperature has a significant influence on the friction behaviour of mineral and synthetic base oils by using a laboratory based friction testing machine. However, the effect of a constantly changing load under different temperature conditions has not been explored fully. In this study, the effect of an increasing load on the friction behaviour of four six different mineral base oils and a polyalphaolefin (PAO) base oil were studied using the SRV4® tribometer. The sliding surfaces were AISI 52100 steel ball and disc. The average loads (range: 50 – 250 N), temperatures (range: 40 – 120 oC), relative humidity of 20 % and a sliding speed of 0.2 m.s-1 were selected as the test conditions. The seven base oils were selected from four API base oil groups. Stribeck curves were used as a tool to characterize the friction behaviour of the base oils.
The results show that for all the base oils, the coefficient of friction and the Stribeck parameter decrease gradually with the increase in applied normal load under constant temperature conditions. The increase in temperature increased the coefficient of friction and decreased the Stribeck parameter at each load stage. The external friction mechanisms dominated the friction behaviour under all test conditions. Viscosity showed a strong influence on the film forming characteristics of the seven base oils only at 40 and 60 oC. Between 80 and 120 oC, the oil-surface interactions were predominant. The results further demonstrated that effect of an increasing temperature on the coefficient of friction was bigger between 80 and 100 oC for all Group III base oils and was consistent between 40 and 120 oC for the Group III+ and PAO base oil. The highly saturated (PAO and Group III+) base oils have demonstrated good thermal stability and less reactivity compared to the less saturated base oils (GI and GIII) under all test conditions. The friction behaviour of the PAO base oil was the most affected by the presence of dissolved water. The presence of water proved to increase the friction at the sliding steel interfaces.Dissertation (MEng)--University of Pretoria, 2018.
Chemical Engineering
MEng
Unrestricted
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Wolf, Juraj. "Analýza koeficientu tření obtokového ventilu turbodmychadla." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-402560.
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Aim of the diploma thesis is set to present a new method for evaluation of the friction coefficient of the wastegate valve system. A test fixture was designed and manufactured for this purpose. Simulations in ANSYS and MSC Adams support test results. The developed method provides an accurate and affordable solution for investigating of friction coefficient for various valves of turbochargers wastegate.
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Prausa, Jeffrey Nathaniel. "Heat Transfer Coefficient and Adiabatic Effectiveness Measurements for an Internal Turbine Vane Cooling Feature." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/76790.
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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.Master of Science
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Ghosh, Amrita. "Naviers-Stokes equations with Navier boundary condition." Thesis, Pau, 2018. http://www.theses.fr/2018PAUU3021/document.
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Le titre de ma thèse de doctorat est "Equations de Stokes et de Navier-Stokes avec la con- dition de Navier", où j’ai considéré l’écoulement d’un fluide newtonien visqueux, incompressible dans un domaine borné de R3. L’écoulement du fluide est décrit par les équations bien connues de Navier-Stokes, données par le système suivant ∂t − ∆u + (u • ∇)u + ∇π = 0, div u = 0 dans Ω × (0, T )u • n = 0, 2[(Du)n]τ + αuτ = 0 sur Γ × (0, T )u(0) = u0 dans Ω (0.1) dans un domaine borné Ω ⊂ R3 de frontière Γ, éventuellement non simplement connexe, de classe C1,1. La vitesse initiale u0 et le coefficient de friction α, scalaire, sont des fonctions don- nées. Les vecteurs unitaires normal extérieur et tangents à Γ sont notés n et τ respectivement et Du = 1 (∇u + ∇uT ) est le tenseur des déformations. Les fonctions u et π décrivent respective- ment les champs de vitesses et de pression du fluide dans Ω satisfaisant la condition aux limites (0.1.2).Cette condition aux limites, proposée par H. Navier en 1823, a été abondamment étudiée ces dernières années, qui pour de nombreuses raisons convient parfois mieux que la condition aux limites de Dirichlet sans glissement : elle offre plus de liberté et est susceptible de fournir une solution physiquement acceptable au moins pour certains des phénomènes paradoxaux résultant de la condition de non-glissement, comme par exemple le paradoxe de D’Alembert ou le paradoxe de non-collision.Ma thèse comporte trois parties. Dans la première, je cherche à savoir si le problème (0.1) est bien posé en théorie Lp, en particulier l’existence, l’unicité de solutions faibles, fortes dans W 1,p(Ω) et W 2,p(Ω) pour tout p ∈ (1, ∞), en considérant la régularité minimale du coefficient de friction α. Ici α est une fonction, pas simplement une constante qui reflète les diverses propriétés du fluide et/ou de la frontière, ce qui nous permet d’analyser le comportement de la solution par rapport au coefficient de frottement.Utilisant le fait que les solutions sont bornées indépendamment de α, on montre que la solution des équations de Navier-Stokes avec la condition de Navier converge fortement vers une solution des équations de Navier-Stokes avec la condition de Dirichlet, correspondant à la même donnée initiale dans l’espace d’énergie lorsque α → ∞. Des résultats similaires ont été obtenus pour le cas stationnaire.Le dernier chapitre concerne les estimations pour le problème de Robin pour le laplacien : l’opérateur elliptique de second ordre suivant, sous forme divergentielle dans un domaine bornéΩ ⊂ Rn de classe C1, avec la condition aux limites de Robin a été considéré div(A∇)u = divf + F dans Ω, ∂u+ αu = f n + g sur Γ.∂n (0.2) Les coefficients de la matrice symétrique A sont supposés appartenir à l’espace V MO(R3). Aussi α est une fonction appartenant à un certain espace Lq . En plus de prouver l’existence, l’unicité de solutions faibles et fortes, nous obtenons une borne sur u, uniforme par rapport à α pour α suffisamment large, en norme Lp. Pour plus de clarté, nous avons étudié séparément les deux cas: l’estimation intérieure et l’estimation au bordMy PhD thesis title is "Navier-Stokes equations with Navier boundary condition" where I have considered the motion of an incompressible, viscous, Newtonian fluid in a bounded do- main in R3. The fluid flow is described by the well-known Navier-Stokes equations, given by thefollowing system 1 )t − L1u + (u ⋅ ∇)u + ∇n = 0, div u = 01u ⋅ n = 0, 2[(IDu)n]r + aur = 0 in Q × (0, T )on Γ × (0, T ) (0.1) 11lu(0) = u0 in Qin a bounded domain Q ⊂ R3 with boundary Γ, possibly not connected, of class C1,1. The initialvelocity u0 and the (scalar) friction coefficient a are given functions. The unit outward normal and tangent vectors on Γ are denoted by n and r respectively and IDu = 1 (∇u + ∇uT ) is the rate of strain tensor. The functions u and n describe respectively the velocity2 and the pressure of a fluid in Q satisfying the boundary condition (0.1.2).This boundary condition, first proposed by H. Navier in 1823, has been studied extensively in recent years, among many reasons due to its contrast with the no-slip Dirichlet boundary condition: it offers more freedom and are likely to provide a physically acceptable solution at least to some of the paradoxical phenomenons, resulting from the no-slip condition, for example, D’Alembert’s paradox or no-collision paradox.My PhD work consists of three parts. primarily I have discussed the Lp -theory of well-posedness of the problem (0.1), in particular existence, uniqueness of weak and strong solutions in W 1,p (Q) and W 2,p (Q) for all p ∈ (1, ∞) considering minimal regularity on the friction coefficienta. Here a is a function, not merely a constant which reflects various properties of the fluid and/or of the boundary. Moreover, I have deduced estimates showing explicitly the dependence of u on a which enables us to analyze the behavior of the solution with respect to the friction coefficient.Using this fact that the solutions are bounded with respect to a, we have shown the solution of the Navier-Stokes equations with Navier boundary condition converges strongly to a solution of the Navier-Stokes equations with Dirichlet boundary condition corresponding to the sameinitial data in the energy space as a → ∞. The similar results have also been deduced for thestationary case.The last chapter is concerned with estimates for a Laplace-Robin problem: the following second order elliptic operator in divergence form in a bounded domain Q ⊂ Rn of class C1, withthe Robin boundary condition has been considered1div(A∇)u = divf + F in Q, 11 )u + u = f ⋅ n + g on Γ. (0.2) 2The coefficient matrix A is symmetric and belongs to V MO(R3). Also a is a function belonging to some Lq -space. Apart from proving existence, uniqueness of weak and strong solutions, we obtain the bound on u, uniform in a for a sufficiently large, in the Lp -norm. We have separately studied the two cases: the interior estimate and the boundary estimate to make the main idea clear in the simple set up
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Svedberg, Ida, and Christopher Holmqvist. "Analys av friktionskoefficient och sättningsgrad i gummipackningar : Analysis of the friction coefficient and setting ratio of rubber gaskets." Thesis, Linnéuniversitetet, Institutionen för teknik, TEK, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-19412.
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Examensarbetet har varit förlagt på SwePart Transmission AB i Liatorp. Företaget tillverkar kugghjul och kan även ge helhetslösningar för växellådor. SwePart Transmission AB har uppmärksammat problem i form av läckage vid delningsplanet i sina växellådor. Företaget har föraningar om att konstruktionen utsätts för glidning i delningsplanet där packningen är placerad. För att glidning inte ska förekomma krävs att packningens friktionskoefficient och fästelementens förspänningsförluster är kända vid konstruktionsstadiet. Packningens friktionskoefficient är idag osäker och har kontrollerats. Detta har gjorts genom tester där vi placerade packningarna i ett friktionsförband och gjorde mätningar i ett dragprov. Med erhållna mätvärden kunde vi på matematisk väg erhålla en ny friktionskoefficient. Testerna utfördes med tre olika ytjämnheter i förbandet för att se om det hade någon inverkan på friktionskoefficienten. Efter testerna kunde vi påvisa en skillnad i friktionskoefficient mellan olika ytjämnheter på anliggningsytorna mot packningen. Vi kunde även se skillnad på friktionskoefficienten för oljad respektive torr yta. Förbandets förmåga att glida bestäms av förspänningen i skruven som minskar radikalt om stora sättningar förkommer. Sättningar kommer att förekomma och det vet man, men utsträckningen är okänd. Då packningen är förbandets mjukaste del kommer den att dominera förbandets sättningsbeteende. I våra tester har vi mätt hur stora sättningar packningen gav upphov till som funktion av tiden. Testet gjordes genom att klämma en packning med känd förspänningskraft. Därefter mättes förbandtjockleksförändringen under de första 25 minuterna. Sättningstestet gjordes för att anmärkningar ifrån kunder kommit på att skruvarna som håller ihop växellådshusen tappar sin förspänning efter en okänd tid i drift, vilket kan härledas till sättningar. Enligt mätvärdena från testet förekommer det inte några större sättningar i vårt testförband vilket kan bero på att vår anliggningsarea skiljer sig ifrån den verkliga. Rapporten kommer beröra sättningsgrad och friktionskoefficient för gummipackningar där tester och bakomliggande teori kommer redovisas. Testerna som gjorts har vi utvecklat och testkört med hjälp av expertis ifrån Linnéuniversitet.This degree project was located at SwePart Transmission AB in Liatorp. The company manufactures gears and do also provide total solutions for gearing. SwePart Transmission AB has noticed problems with leakage in the division plane in their gearboxes. The company has premonitions that the structure is subject to sliding in the division plane where the gasket is placed. To prevent sliding it’s required that the friction coefficient between the gasket and division plane and the preload of the fasteners is known at the design stage. The gaskets friction coefficient is currently uncertain and has been checked. This was done by tests in which we placed the gasket in a friction joint and then made measurements in a tensile testing machine. With the obtained measurement values we could mathematically obtain a new coefficient of friction. The tests were performed with three different surface finishes in the joint to see if it had any effect on the friction coefficient. After the tests, we could see a difference in coefficient of friction between different surface finishes on the contact surfaces to the gasket. We could also see a difference in coefficient of friction of oiled and dry surface. The joints capability of sliding is determined by the preload in the screws that is dramatically reduced if large settings occur. It’s known that settings will occur, but the extent is unknown. Since the gasket is the softest part in the bolted joint, it will dominate the joints setting behavior. In our tests we have measured the amount of settings caused by the gasket as a function of time. The test was made by sandwiching a gasket with a certain load. After that the change in thickness was measured during 25 minutes. This test was performed because the company had received complains from customers concerning preload losses in the screws after an unknown time in use. The preload losses can be traced to settings in the gasket. According the measurements from the test, there are no major settings in our test joint, which can be explained by the difference in contact area between our test and the “real” design. This report will concern the setting rate and friction coefficient of rubber gaskets where tests and underlying theories will be presented. The test has been developed and performed with help of expertise form Linnaeus University.
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Ezhilan, Madhumitha. "Commissioning a Commercial Laser Induced Fluorescence System for Characterization of Static Mixer Performance." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1499793560290147.
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Lim, Wei Jun. "Frictional Properties of Carbon-Carbon Composites and Their Relation to Fiber Architecture and Microstructure." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2055.
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The use of carbon-carbon (C/C) composites for clutch application requires a basic understanding of the structural characteristics of the composites that control their frictional and engineering properties. These are related to the microstructure of the matrix and fiber architecture, with the character of fiber/matrix interface and type of defects, porosity and microcracks being the most relevant. The purpose of this study is to examine and characterize the relation between the fiber architecture of selected C/C composites and its relation to their frictional properties when subjected to different normal forces and relative humidity. Friction tests is conducted using a Brüker Universal Friction Tester (UFT). This study also seeks to characterize and analyze the microstructure and fiber architecture through Polarized Light Microscopy, X-Ray Diffraction and Ultrasound Scans. This study shows that the Coefficient of Friction (COF) at constant normal force and RPM are always slightly lower for the samples with surface fibers orientated at 45° relative to the direction of rotation compared to samples with surface fibers orientated 0/90° at 50% relative humidity. The percent difference ranges from 1.62% to 15.30%. However, at 85% relative humidity, the average COF at the constant normal force and RPM are always slightly higher for the 45° compared to 0/90° samples for Rotor samples, while in contrast the average COF are always lower for the 45° samples compared to 0/90° samples for Stator samples. The percent difference ranges from 3.14% to 35.46%. This study found significant differences between the 0/90° samples and the 45° samples. There is indication that the fiber orientation can cause differences between frictional properties even if the clutches are made from the same material. The change in humidity also significantly changes the resulting COF.
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Figueiredo, Tiago Petermann. "Effect of lubricant propertieson the friction coefficient under different temperatures, speeds and loads using a ball-on-disc test." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-16032017-102949/.
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The present study has the objective of evaluating the effect of lubricant features on the friction coefficient by using three different lubricants (two synthetics and one mineral), which are used in automotive transmissions. In order to perform experiments, it was used a ball-on-disc system. The disc was manufactured with the same mechanical properties as transmission gears and the ball was made of 52100 SAE steel. The test parameters were defined based on a dynamic analysis conducted using \"ISOCAD\" which takes into account the geometry of the gear and vehicle dynamics (applied force and speed) during the tribological experiments. In order to set the temperature parameter, the lubricant testing temperature of a standard fuel economy was used. Experiments were conducted in two different lubrication conditions: i (starved) and ii (fully flooded). After the parameters were defined, it was possible to calculate the oil film thickness and, thus define the lubrication regime reached in each condition. Mixed and/or boundary lubrication was obtained in all the tests. Results showed the relationship between the speed and the specific oil film using a Khonsari and Masjedi formulation (2014), which takes into account the effect of surface roughness and, it is based on Downson and Higginson\'s (1981) formulation. The chemical analysis of the lubricant showed a relationship between friction coefficient and the additives used in lubricants. These results also showed the oil performance under different temperatures, speeds and loads. The best results were obtained for a synthetic lubricant.O presente estudo tem o objetivo de avaliar o efeito de propriedades dos lubrificantes sobre o coeficiente de atrito. Para tanto foram testados três lubrificantes diferentes (dois sintéticos e um mineral), que são utilizados em transmissões automotivas. Os experimentos foram conduzidos utilizando um sistema tribológico denominado \"ball-on-disc\". Os discos foram fabricados com as mesmas propriedades mecânicas das engrenagens de transmissão, já as esferas foram fabricadas com aço SAE 52100. Os parâmetros de teste foram definidos com base na análise dinâmica conduzida utilizando o software \"ISOCAD\", que leva em conta a geometria da engrenagem e a dinâmica do veículo (força aplicada e velocidade) durante os ensaios tribológicos. Para definir os parâmetros de temperatura, foram utilizadas as mesmas temperaturas encontradas durante o ensaio de economia de combustível padronizado. Experimentos foram realizados em duas condições de lubrificação diferentes: i) fornecimento limitado de lubrificante, ou \"Starved\" e ii) condição de lubrificação imersa, ou \"Fully flooded\". Depois dos parâmetros definidos, foi possível calcular a espessura de filme de óleo, de forma a definir o regime de lubrificação alcançado em cada condição. Lubrificação mista e limítrofe foi obtida todas as condições de testes. Os resultados mostraram a relação entre a velocidade e o filme de óleo específico usando uma formulação de Khonsari e Masjedi (2014), que leva em conta o efeito da rugosidade da superfície e baseia-se na formulação de Downson e Higginson (1981). A análise química do lubrificante mostrou que existe uma relação entre o coeficiente de atrito e os aditivos utilizados nos lubrificantes. Estes resultados também mostram o desempenho dos lubrificantes em diferentes temperaturas, velocidades e cargas. Os melhores resultados foram obtidos para um lubrificante sintético.
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Punna, Harshitha. "Impact of stiffness and damping capacity using two different rubbers on friction coefficient and noise levels of brake materials." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/theses/2773.
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Friction contact with both external and internal environments can significantly influence its efficiency, which could cause friction instabilities, vibration, and noise. Focusing on the effects that troubles brake pad, rotor, and friction-induced NVH, the main motivation for this study is to understand its drawbacks for some extent in a braking system. By proper study on applied statistics, an experimental design is planned. The design has friction tests that are performed by scaling down real test properties used in dynamometer to scaled-down properties in a subscale tester by using scaling law of physics. The test has two different types of rubbers with different humidity conditions with respect to two different brake pads in a small-scale tester, the Universal Mechanical Tester (UMT). This friction experiment helps in determining how different rubbers impact its stiffness on the coefficient of friction and noise levels, also to evaluate which scenario has the better damping capacity. The effect on the coefficient of friction and noise levels with and without rubbers is also compared. The results are subjected to the Design of Experiments analyses test know the statistical relationship between factors affecting the process and output of that process at different controllable variables namely humidity and temperature.
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Lin, Zhan-Jun. "Design of a Tribometer to Study Friction inThreaded Fastener Interfaces." Thesis, KTH, Maskinkonstruktion (Inst.), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-281707.
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Bolts and nuts are one of most common joining methods since they are simple and low-cost to connect parts. Appropriate clamp force from bolted joint remains resultant joints secured, but higher/lower preload on bolted joint increases risk of the failure of mechanism. Therefore, achieving accurate clamp force in bolted joint is always the aim of tightening process. Torque control tightening tool are the most common tightening tool present in the market. The clamp force obtained from torque control tightening is highly dependent upon friction. Only small part of applied torque is transferred into the effective torque that turns in to clamp forces because most of applied torque is consumed by friction forces under bolt /nut head and in a thread interface. However, friction coefficient does not remain constant during tightening process and it relates to many factors such as tightening speed, speed profile, tightening time, joint’s material, etc. Hence, it changes the distribution ratio and leads to an error in estimation of clamp force between the components. This project aims to develop a tribometer which is capable of operating in different speeds and load conditions corresponding to different tightening process. A new concept of pin-on-disc tribometer is proposed and the speed and load profile are achieved by using closed loop control in the linear actuator and the motor. The test rig was built up and the several validation tests were done.Skruv och mutter tillhör bland de vanligaste medlen att binda ihop två ytor med varandra då det är ett billigt och enkelt sätt att uppnå det önskade resultatet. Det är viktigt att rätt klämkraft uppnås i skruvförbandet, vid för låg/hög klämkraft är risken för haveri i konstruktionen stor. Därför är att uppnå korrekt klämkraft i ett skruvförband alltid målet i en åtdragningsprocess. Skruvdragare som drar åt med ett förinställt moment (torque control) är för tillfället det vanligaste verktyget på marknaden för att uppnå rätt klämkraft. Klämkraften som uppstår vid åtdragning av ett skruvförband med ett sådant verktyg är i största del beroende på friktionskraften i skruvförbandet för korrekt moment. Endast en liten del av momentet som påverkar skruven övergår till effektivt fasthållande moment i skruvförbandet, det mesta momentet går åt för att övervinna friktionen mellan skruv och mutter. Friktionskoefficitenten håller sig inte konstant vid ett åtdragande moment utan beror på flera faktorer såsom åtdragningshastighet, profilhastighet, åtdragningstid och vilket material skruvförbandet är gjort av bland annat. Eftersom friktionskoeffiecienten ständigt ändrar sig leder detta till ett fel då man ska uppskatta klämkraften mellan två ytor. Detta examensarbete ämnar till att bygga en tribometer som är kapabel till att fungera vid olika hastigheter och kraftförhållanden som korresponderar till olika åtdragningsprocesser. Ett koncept på en ny pin-on-disc tribometer föreslås och hastighets samt kraftprofiler skapas genom ett closed-loop reglertekniksystem i ett linjärt ställdon och motorn. Testriggen konstruerades och flertalet utvärderingstester utfördes.
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Lee, Hyunwook. "A Polynomial Chaos Approach for Stochastic Modeling of Dynamic Wheel-Rail Friction." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77195.
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Accurate estimation of the coefficient of friction (CoF) is essential to accurately modeling railroad dynamics, reducing maintenance costs, and increasing safety factors in rail operations. The assumption of a constant CoF is popularly used in simulation studies for ease of implementation, however many evidences demonstrated that CoF depends on various dynamic parameters and instantaneous conditions. In the real world, accurately estimating the CoF is difficult due to effects of various uncertain parameters, such as wheel and rail materials, rail roughness, contact patch, and so on. In this study, the newly developed 3-D nonlinear CoF model for the dry rail condition is introduced and the CoF variation is tested using this model with dynamic parameters estimated from the wheel-rail simulation model. In order to account for uncertain parameters, a stochastic analysis using the polynomial chaos (poly-chaos) theory is performed using the CoF and wheel-rail dynamics models.
The wheel-rail system at a right traction wheel is modeled as a mass-spring-damper system to simulate the basic wheel-rail dynamics and the CoF variation. The wheel-rail model accounts for wheel-rail contact, creepage effect, and creep force, among others. Simulations are performed at train speed of 20 m/s for 4 sec using rail roughness as a unique excitation source. The dynamic simulation has been performed for the deterministic model and for the stochastic model. The dynamics results of the deterministic model provide the starting point for the uncertainty analysis. Six uncertain parameters have been studied with an assumption of 50% uncertainty, intentionally imposed for testing extreme conditions. These parameters are: the maximum amplitude of rail roughness (MARR), the wheel lateral displacement, the track stiffness and damping coefficient, the sleeper distance, and semi-elliptical contact lengths. A symmetric beta distribution is assumed for these six uncertain parameters. The PDF of the CoF has been obtained for each uncertain parameter study, for combinations of two different uncertain parameters, and also for combinations of three different uncertain parameters.
The results from the deterministic model show acceptable vibration results for the body, the wheel, and the rail. The introduced CoF model demonstrates the nonlinear variation of the total CoF, the stick component, and the slip component. In addition, it captures the maximum CoF value (initial peak) successfully. The stochastic analysis results show that the total CoF PDF before 1 sec is dominantly affected by the stick phenomenon, while the slip dominantly influences the total CoF PDF after 1 sec. Although a symmetric distribution has been used for the uncertain parameters considered, the uncertainty in the response obtained displayed a skewed distribution for some of the situations investigated. The CoF PDFs obtained from simulations with combinations of two and three uncertain parameters have wider PDF ranges than those obtained for only one uncertain parameter.
FFT analysis using the rail displacement has been performed for the qualitative validation of the stochastic simulation result due to the absence of the experimental data. The FFT analysis of the deterministic rail displacement and of the stochastic rail displacement with uncertainties demonstrates consistent trends commensurate with loss of tractive efficiency, such as the bandwidth broadening, peak frequency shifts, and side band occurrence. Thus, the FFT analysis validates qualitatively that the stochastic modeling with various uncertainties is well executed and is reflecting observable, real-world results.
In conclusions, the development of an effective model which helps to understand the nonlinear nature of wheel-rail friction is critical to the progress of railroad component technology and rail safety. In the real world, accurate estimation of the CoF at the wheel-rail interface is very difficult since it is influenced by several uncertain parameters as illustrated in this study. Using the deterministic CoF value can cause underestimation or overestimation of CoF values leading to inaccurate decisions in the design of the wheel-rail system. Thus, the possible PDF ranges of the CoF according to key uncertain parameters must be considered in the design of the wheel-rail system.Ph. D.
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Bhagwat, Pushkaraj. "A Computational Study of the Effects of Plasticity and Damage Models in Microscopic and Macroscopic Static Metal Friction." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1461593775.
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Carbone, Laura. "Interface behaviour of geosynthetics in landfill cover systems under static and seismic loading conditions." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU006/document.
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Les Installations de Stockage de Déchets actuelles sont munies de barrieres de confinement composites géosynthétiques et minerales. En couverture, les interfaces entre composants de ces systèmes installés sur forte pente peuvent constituer des surfaces de glissement préférentiel. L'étude de ces interfaces est donc cruciale pour l'évaluation de la stabilité des barrières de ces installations. Le comportement de ces interfaces, en particuliers des interfaces géosynthétique - géosynthétique se révèle complexe: il va dépendre de la nature des polymères, de l'endommagement , de la vitesse de glissement relatif, de la température. Les conditions de chargement sont aussi primordiales, statiques ou dynamiques (cas de seisme). L'originalité du travail effectué dans le cadre de la présente étude tient d'abord aux dispositifs expérimentaux utilisés en parallèle, un Plan incliné et une Table Vibrante, les deux permettant de simuler les conditions réelles sur site, sous faible contrainte normale, en conditions d'une part statiques, d'autre part dynamiques. Des procédures d'essai nouvelles ont permis une interprétation fine des résultats d'essais. En particulier la variation du frottement en fonction de la cinétique d'essai est clairement démontrée, et le couplage des résultats obtenus dans les deux configurations d'essai permet de montrer que leur interprétation est complexe et ne peut se limiter à celle proposée par la norme européenne. En particulier, le niveau du déplacement relatif et la vitesse de déplacement influent significativement sur les résultats. Une étude spécifique de l'endommagement est aussi présentéeModern landfills are equipped with multi-layered liners, including geosynthetic-geosynthetic and soil-geosynthetic interfaces. The interfaces represent weakness surfaces where the shear strength is a crucial aspect for the landfill stability. The behaviour of each interface can be different depending on the interactions of the materials in contact under the different load conditions (i.e. static and seismic loading). Nevertheless, the assessment of the geosynthetic interface shear strength can be difficult depending on different factors such as mechanical damage, time-dependent processes (ageing), stress dependent processes (such as repeated loading), coupled effects of both time and stress-strain dependent processes (creep or relaxation). In the present work, the static and the dynamic behaviour of typical geosynthetic - geosynthetic interfaces is investigated by means of the Inclined Plane and the Shaking Table tests since both devices permit to simulate experimental conditions close to them expected in landfill cover systems (low normal stress, small and large deformations). Two new test procedures are proposed and applied in order to assess the interface friction at both devices during all the phases of the tests. Taking advantage of the complementarity of both facilities, an innovative interpretation of test results considering the evolution of the shear strength parameters, passing from the static to the dynamic loading conditions, from small to large displacements is carried out. Furthermore, the dependence of the interface friction on different parameters such as the kinematic conditions, the normal stress and the mechanical damage is also investigated. In light of test results, it has been demonstrated that the variation of the interface friction could be significant, depending on the loading conditions (static or dynamic), on the actual kinematic conditions and on the level of deformation at which the interface is subjected
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Thiyagarajan, Kamesh. "Conceptual development of brake friction estimation strategies." Thesis, KTH, Fordonsdynamik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285677.
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The thesis work investigates brake friction estimation strategies. The friction between the brake disc and brake pads is not constant during the braking application and contributes to the amount of brake torque achieved at the wheels. In this study, it is considered that any change in the brake torque between the requested and achieved values is only due to the varying brake friction coefficient. The work gives three different approaches to estimate the brake friction coefficient using two prominent state estimation strategies, Unscented Kalman Filter and Moving Horizon Estimation. The inputs to the estimators are obtained from a Vehicle model, which is built using the wheel balance equations. The estimators have been tuned to minimize the estimation error in nominal conditions and tested for their robustness through a wide analysis, where the sensitivity of the strategies is checked against a spectra of potential system parameters and boundary conditions. Throughout all the analysis, the developed models estimate the brake friction coefficient within an acceptable error range. This work opens up opportunities for further studies that can be performed using the built estimator models.Detta examensarbete studerar strategier för skattning av bromsfriktion. Friktionen mellan bromsskivan och bromsbeläggen är inte konstant under bromsförloppet och det är denna som genererar bromsmomentet för varje hjul. I detta arbete så antas att förändringen i bromsmoment mellan begärd och uppnått endast är på grund av varierande bromsfriktion mellan bromsbelägg och bromsskiva. Arbetet presenterar tre olika sätt att skatta bromsfriktionen genom användning av två kända skattningsmetoder, Uncented Kalman Filter och Moving Horizon Estimation. Ingående värden till skattningsmetoderna fås från en fordonsmodell som är byggd med hjälp av hjulbalansekvationer. Skattningsmetoderna har justerats så att de minimerar skattningsfelet i nominella fall och de är testade för robusthet genom en bred analys där känsligheten hos metoderna testas genom en flora av potentiella systemparametrar och gränsvärden. Genom hela analysen så uppnår de utvecklade skattningsmetoderna bromsfriktionsvärden med acceptabla felnivåer. Detta arbete öppnar upp för möjligheter för vidare analyser där de utvecklade metoderna kan användas.
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Rizzo, Giuseppe, Antonino Bonanno, Giorgio Paolo Massarotti, Luca Pastorello, Mariarosa Raimondo, Federico Veronesi, and Magda Blosi. "Energy efficiency improvement by the application of nanostructured coatings on axial piston pump slippers." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-200187.
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Axial piston pumps and motors are widely used in heavy-duty applications and play a fundamental role in hydrostatic and power split drives. The mechanical power losses in hydraulic piston pumps come from the friction between parts in relative motion. The improvement, albeit marginal, in overall efficiency of these components may significantly impact the global efficiency of the machine. The friction between slipper and swash plate is a functional key in an axial piston pump, especially when the pump (at low rotational speed or at partial displacement) works in the critical areas where the efficiency is low.
The application of special surface treatments have been exploited in pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers. The potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Due to the difficulty to reproduce the real working conditions of axial piston pump slippers, it has been made a hydraulic test bench properly designed in order to compare the performance of nano-coated slippers with respect to standard ones. The nano-coated and standard slippers have been subjected to the following working conditions: a test at variable pressure and constant rotational speed, a test at constant pressure and variable rotational speed. The comparison between standard and nanocoated slippers, for both working conditions, shows clearly that more than 20% of friction reduction can be achieved using the proposed nano-coating methodology.
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Cummings, Patrick. "Modeling the Locked-Wheel Skid Tester to Determine the Effect of Pavement Roughness on the International Friction Index." Scholar Commons, 2010. https://scholarcommons.usf.edu/etd/1604.
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Pavement roughness has been found to have an effect on the coefficient of friction measured with the Locked-Wheel Skid Tester (LWT) with measured friction decreasing as the long wave roughness of the pavement increases. However, the current pavement friction standardization model adopted by the American Society for Testing and Materials (ASTM), to compute the International Friction Index (IFI), does not account for this effect. In other words, it had been previously assumed that the IFI's speed constant (SP), which defines the gradient of the pavement friction versus speed relationship, is an invariant for any pavement with a given mean profile depth (MPD), regardless of its roughness. This study was conducted to quantify the effect of pavement roughness on the IFI's speed constant. The first phase of this study consisted of theoretical modeling of the LWT using a two-degree of freedom vibration system. The model parameters were calibrated to match the measured natural frequencies of the LWT. The calibrated model was able to predict the normal load variation during actual LWT tests to a reasonable accuracy. Furthermore, by assuming a previously developed skid number (SN) versus normal load relationship, even the friction profile of the LWT during an actual test was predicted reasonably accurately. Because the skid number (SN) versus normal load relationship had been developed previously using rigorous protocol, a new method that is more practical and convenient was prescribed in this work. This study concluded that higher pavement long-wave roughness decreases the value of the SP compared to a pavement with identical MPD but lower roughness. Finally, the magnitude of the loss of friction was found to be governed by the non-linear skid number versus normal load characteristics of a pavement.
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Wondimu, Nahom Abebe. "SIMULATED AND EXPERIMENTAL SLIDING MODE CONTROL OF A HYDRAULIC POSITIONING SYSTEM." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1145419922.
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Sandu, Sebastian. "Developing a power dissipation model for planetary roller screws." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI096.
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Les vis à rouleaux convertissent la rotation en translation de manière très efficace et sont utilisées dans des nombreuses industries. Mais même s'il présente beaucoup d'avantages, le mécanisme reste complexe et relativement difficile à comprendre. Le principal but de cette thèse est de quantifier la puissance dissipée par les vis à rouleaux standard et inversées, qui est un résultat important pour toute étude liée à l'efficacité ou la distribution de température. De plus, il s'agit d'un critère de conception dans le choix de paramètres optimaux pour une certaine application. À cause des travaux peu nombreux en termes de recherche et des hypothèses restrictives faites dans la littérature courante, ce mémoire commence avec une analyse géométrique de base du mécanisme et envisage de généraliser les équations des surfaces filetées pour les différents types de profils et conditions de jeu. La position des points de contact peut ensuite être déduite avec un algorithme de type Newton-Raphson très rapide. Cette information est cruciale pour toute étude ultérieure de force. Après, les équations classiques de Hertz sont adaptées à des contacts peu conformes pour déterminer la forme, les dimensions et l'orientation des ellipses de contact rouleau-vis et rouleau-douille. Il est prouvé que les directions principales de courbure obtenues ici par géométrie différentielle sont différentes de celles supposées dans les précédents travaux de recherche. Ensuite, la cinématique du mécanisme est étudiée avec un modèle stationnaire, qui établit des liens entre les mouvements uniformes de tous les composants et permet de calculer d'une manière simplifiée le champ de vitesse de glissement en tout point de l'aire de contact. Le mouvement local apparaît comme une combinaison de spin et de glissement uniforme. Le modèle est calibré sur un seul degré de liberté qui prend la forme d'un quotient de glissement, qui dépend de conditions de lubrification et équations d'équilibre dynamique. Un banc expérimental est conçu pour mesurer ce quotient et permettre donc la comparaison avec des valeurs numériques, ainsi que les quelques modèles analytiques disponibles dans la littérature. Les résultats montrent que les mesures sont très proches des conditions de fonctionnement idéales, ce qui fait que les propriétés du lubrifiant et les coefficients de frottement deviennent les paramètres les plus influents dans le peu de marge disponible pour l'amélioration cinématique. Finalement, un modèle numérique en forces est développé et permet de calculer la puissance dissipée pendant l'équilibre stationnaire. L'algorithme itératif détermine d'abord le quotient de glissement atteint à l'équilibre et utilise ensuite le résultat pour déduire les autres variables cinématiques et dynamiques liées au calcul. Une étude paramétrique est réalisée dans le but d'identifier les facteurs importants pour l'efficacité et la puissance dissipée, ainsi que leur contribution relativeRoller screws are highly efficient rotation-translation converters used in a variety of industries. Despite its numerous advantages, the mechanism remains complex and rather difficult to understand. The main goal of this thesis is to quantify the amount of power dissipated by standard and inverted roller screws, which is an important result for any study related to efficiency or temperature distribution. Furthermore, it is used as a design criterion in choosing optimal parameters for a given application. Due to the limited amount of available research and the restrictive assumptions made in current literature, this memoir starts with a basic geometric analysis of the mechanism and attempts to generalize threaded surface equations for different types of profiles and backlash conditions. The contact point locations can then be deduced using a very fast Newton-Raphson algorithm. This information is crucial for any subsequent force analysis. Classic Hertzian equations are then adapted to slightly conforming contacts in order to calculate the shape, size and orientation of the roller-screw and roller-nut contact ellipses. It is shown that the principal directions of curvature obtained here by differential geometry are different from the ones assumed by previous research. Next, the mechanism kinematics is investigated using a stationary model, which relates the steady-state movement of all the different components and allows a simplified calculation of the sliding velocity field at any point within the contact areas. The local motion proves to be a combination of spin and uniform sliding. The model is set to have only one degree of freedom in the form of a slip ratio, which depends on lubrication conditions and force balance equations. An experimental setup is designed to measure this ratio and thus allow comparison to numerical values, as well as the few analytical models available in the literature. Results show that measurements are very close to ideal operating conditions, which makes lubricant properties and friction coefficients the most influential parameters in the little room available for kinematic improvement. Finally, a numerical force model is developed, which calculates the power dissipated during the steady-state regime. The iterative algorithm first determines the value of the slip ratio reached during stationary equilibrium and then uses the result to deduce the other kinematic and dynamic unknowns involved. A parametric study is conducted to identify the important factors in efficiency and power dissipation, as well as their relative influence
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Zhao, Lei. "Dynamics and Statics of Three-Phase Contact Line." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/102649.
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Wetting, which addresses either spontaneous or forced spreading of liquids on a solid surface, is a ubiquitous phenomenon in nature and can be observed by us on a daily basis, e.g., rain drops falling on a windshield and lubricants protecting our corneas. The study of wetting phenomena can be traced back to the observation of water rising in a capillary tube by Hauksbee in 1706 and still remains as a hot topic, since it lays the foundation for a wide spectrum of applications, such as fluid mechanics, surface chemistry, micro/nanofluidic devices, and phase change heat transfer enhancement. Generally, wetting is governed by the dynamic and static behaviors of the three-phase contact line. Therefore, a deep insight into the dynamics and statics of three-phase contact line at nanoscale is necessary for the technological advancement in nanotechnology and nanoscience. This dissertation aims to understand the dynamic wetting under a molecular kinetic framework and resolve the reconfiguration of liquid molecules at the molecular region of contact line.
Water spreading on polytetrafluoroethylene surfaces is selected as a classical example to study the dynamic behaviors of three-phase contact line. To accommodate the moving contact line paradox, the excess free energy is considered to be dissipated in the form of molecular dissipation. As-formed contact line friction/dissipation coefficient is calculated for water interacting with PTFE surfaces with varying structures and is found to be on the same order of magnitude with dynamic viscosity. From an ab initio perspective, contact line friction is decomposed into contributions from solid-liquid retarding and viscous damping. A mathematical model is established to generalize the overall friction between a droplet and a solid surface, which is able to clarify the static-to-kinetic transition of solid-liquid friction without introducing contact angle hysteresis. Moreover, drag reduction on lotus-leaf-like surface is accounted for as well. For the first time, the concept of contact line friction is used in the rational design of a superhydrophobic condenser surface for continuous dropwise condensation.
We focus on the transport and reconfiguration of liquid molecules confined by a solid wall to shed light on the morphology of the molecular region of a three-phase contact line. A governing equation, which originates from the free energy analysis of a nonuniform monocomponent system, is derived to describe the patterned oscillations of liquid density. By comparing to the Reynolds transport theorem, we find that the oscillatory profiles of interfacial liquids are indeed governed in a combined manner by self-diffusion, surface-induced convection and shifted glass transition. Particularly for interfacial water, the solid confining effects give rise to a bifurcating configuration of hydrogen bonds. Such unique configuration consists of repetitive layer-by-layer water sheets with intra-layer hydrogen bonds and inter-layer defects. Molecular dynamics simulations on the interfacial configuration of water on solid surfaces reveal a quadratic dependence of adhesion on solid-liquid affinity, which bridges the gap between macroscopic interfacial properties and microscopic parameters.Doctor of Philosophy
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Tertuliano, Iramar da Silva. "Textura superficial: efeito sobre o desempenho de óleos aditivados e não aditivados em ensaios alternados." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-10082017-164633/.
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Neste trabalho foram conduzidos experimentos de laboratório no intuito de avaliar o efeito da textura superficial no desempenho de óleos lubrificantes aditivados e não aditivados. Os materiais envolvidos nos ensaios são referentes a materiais de anel e camisa de motores de combustão interna e as condições de superfície envolveram processamentos de lixamento e retífica, bem como texturização de microcavidades a laser. Os ensaios foram do tipo alternado, com regime limítrofe de lubrificação. Inicialmente foram feitas análises sobre a metodologia utilizada para o cálculo do coeficiente de atrito em ensaios alternados, mostrando que os valores fornecidos diretamente pelo equipamento (aqui chamados de coeficiente de atrito pico a pico) não foram efetivos para este estudo, pois apresentam alta dispersão entre as réplicas dos ensaios e não é representativo em termos de eficiência do tribossistema. Foram geradas microcavidades nas superfícies de alguns blocos de ferro-fundido mediante texturização a laser. Esta texturização gerou rebarbas que foram retiradas por um processo de lixamento. Com isso, uma parte dos resultados avaliou o efeito do lixamento nos parâmetros de rugosidade, no entanto que o processo acaba por aumentar os valores de raio de aspereza e reduzir a altura média dos picos. Por fim, ensaios com óleo sem aditivo tiveram formação de óxido em todas as condições de superfície, com pouca variação do coeficiente de atrito. Já nos ensaios com óleo aditivado, os resultados mostraram pouca influência das microcavidades e maior contribuição das características de picos (raio e altura) na formação de tribofilmes redutores de atrito (neste caso MoS2).This work was conducted by experimental tests in order to evaluate the effect of surface texture on fully formulated oil and base-oil performance. In these tests, the materials were related to the piston ring and cylinder, in which surfaces were sanded, grounded and textured by laser. In addition, the tests were carried out by reciprocating movement and boundary conditions. A coefficient of friction study in reciprocating tests was performed, showing that peak-to-peak methodology does not represent properly the tribosystem efficiency. Burr was generated around the dimples (made by laser surface texturing), in which were removed by sanded process. The results showed that sanded process increased the peak radius and decreased the peak height. The results considering the base oil showed oxide formation on the surface in all the cases, occurring low variation of friction coefficient in the system. On the other hand, in the fully formulated oil results, the dimples had no influence on MoS2 formation; however, it was possible to see a strong relation with the radius and average height of the asperities.
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Furmann, Denis. "Studium vlivu složení synoviální kapaliny na tření kloubní chrupavky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-399378.
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This thesis deals with the study of the effect of the constituents of the model synovial fluid on the frictional properties of articular cartilage. The influence of constituents, concentration, speed and load is observed. Experiments were performed on a commercial tribometer at configuration pin-on-plate. Several types of lubricants containing synovial fluid constituents have been selected for the experiments. Lubricants were prepared at two concentrations, the concentration of healthy individuals and at a concentration typical of for osteoarthritic patients. Speeds 5 and 10 mm/s and 5 and 10 N loads were used for all experiments. It is shown that when using only lubricant containing proteins, no difference in the coefficient of friction is observed and the effect of concentration is also not observed. The addition of hyaluronic acid has a synergistic effect with -globulin, however in the case of lubricants containing albumin, the effect is opposite. After the addition of phospholipids, no significant effect on friction is observed in -globulin containing lubricants. No significant effect of the composition and concentration of the lubricants is observed with the load change.
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Gandhi, Shikha. "Investigation Of The Effect Of Low Molecular Weight Peg On Lysozyme Interactions In Solution Using Composition Gradient Static Light Scattering." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204599050.
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Graviss, Matthew Sheridan. "The influence of a central groove on static and dynamic characteristics of an annular liquid seal with laminar flow." Thesis, Texas A&M University, 2005. http://hdl.handle.net/1969.1/2359.
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This thesis provides experimental static and dynamic results for four pairs of
seals, including a pair of smooth seals and three pairs of centrally grooved seals. The
grooved seals have groove depth to clearance ratios (Dg/C) of 5, 10, and 15. The radial
clearance of each test seal is 0.0891 mm. Test conditions include three shaft rotational
speeds from 4000 to 10000 rpm, three inlet oil pressures from 24 to 70 bars, and seal
dimensionless eccentricities from 0 (centered) to 0.7. For each pair of test seals, dynamic
results include stiffness and damping coefficients; static results include stator position,
attitude angles, and seal leakage. Stiffness, damping, and leakage are compared among
the seal pairs with various groove depths. Results show that all rotordynamic coefficients
consistently decrease with increasing seal groove depths, and seal leakage remains
constant through varying groove depths. Additionally, a comparison is made between
experimental results of all test seals and XLLubeGT. XLLubeGT is a computer model
developed at Texas A&M University, which uses a Reynolds equation + energy equation
model to predict dynamic performance of a grooved seal. It operates on the assumption
that the groove is large enough to create separate lands within the seal, creating a zero or
negligible pressure perturbation across the seal. A comparison with XLLubeGT shows
that even the seal with the largest groove depth tested is not deep enough to agree with
XLLubeGT predictions.
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Huang, Tzung-Tang, and 黃宗堂. "Effects of Surface Characteristics and Fluid Film Thickness on the Coefficient of Static Friction of a Hydrostatic Bearing." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/595ffm.
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碩士國立清華大學
動力機械工程學系
106
Hydrostatic bearings utilize an externally pressurized source that pumps in lubricant to create a film between the moving bearing faces. Hydrostatic bearings have the characteristics of having essentially zero to no wear, low friction, and high damping capabilities. The thickness of this fluid film is affected by the design of the restrictor and bearing, load on the bearing, the source pressure et al. The importance of this is that at small film thicknesses, there may be solid-to-solid contact between the components. Thus, the wear and friction may drastically increase. In general, the thinner the film thickness, the greater the resulting stiffness of the bearing. However, thin film thicknesses may cause solid-to-solid contact of the machine parts. Thus, this study aims to investigate the effects of surface characteristics such as surface roughness and film thickness on the coefficient of static friction of a hydrostatic bearing. This study will utilize a variable capillary restrictor to adjust the film thicknesses to the desired levels and test the amount of force required to induce movement in a linear guide-way carriage, thus, giving a quantitative result about how a small film thickness might affect the performance of the hydrostatic bearing.
49
Lehman, Laura Lynn. "Determination of the friction coefficient of alfalfa." 1989. http://catalog.hathitrust.org/api/volumes/oclc/20730183.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1989.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 59-60).
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Chang, Tei-Lin, and 張得霖. "Implementation of Plastic-Film Friction-Coefficient Tester." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/79912609265951211553.
Full textAbstract:
碩士國立彰化師範大學
電機工程學系
101
This thesis explains the implementation of Plastic-Film Friction-Coefficient Tester to be applied in the static and kinetic coefficients of plastic film and sheet. Since the instrument, imported from foreign makers, is expensive, the manufacturing or purchasing cost is high for small and medium enterprises. Handheld force gauges are often used instead. However, the measurement data by handheld force gauges are unstable and lack of credibility. To reduce the manufacturing or purchasing cost in industry circles, the major purpose of this research is to ensure the reliability of each measurement by well design and tests conforming to ASTM D1894 and calibrated measuring systems. The key introduction of this thesis emphasizes on the design of the friction test platform mechanism, circuit of load cell amplifier and frequency transducer, and the software. This tester can be easily operated with fully automatic measurement. Values will be calculated automatically after test completion, including coefficient and average coefficient of static friction and kinetic frication, and standard deviation. Main features of the software contain test parameter inputs, real-time friction display, and graphics capability of data recording. The experiment tested 5 groups of PVC film with thickness of 0.18 mm, and the test result shows the standard deviation of both static and kinetic friction coefficient is very low, which is 0.034 and 0.004 respectively. It represents a considerable reliability of this test system, which can be applied to the needs of industries. The whole hardware expenditure is only a sixth of a foreign brand, which greatly reducing enterprises’ manufacturing or purchasing costs.