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1
Ledezma, Rodríguez Javier Andre. "Technology progress, credit market frictions and labor market friction." Tesis, Universidad de Chile, 2014. http://www.repositorio.uchile.cl/handle/2250/117059.
Testo completoAbstract (sommario):
Magíster en Economía Aplicada<br>Este trabajo modela la interacción entre progreso tecnológico (PT), fricciones en el mercado laboral y fricciones en el mercado del crédito, con el objetivo de estudiar cómo la respuesta del mercado laboral frente al aumento del PT se encuentra mediada por el grado de desarrollo del mercado del crédito. La hipótesis principal apunta al hecho que economías con fricciones en el mercado del crédito responden de manera diferente al PT que aquellas economías sin fricciones en dicho mercado, lo que determinaría finalmente el efecto sobre el mercado laboral. Acemoglu (2001) plantea que un mecanismo de este estilo podría servir como explicación alternativa al milagro del empleo en EEUU respecto a Europa durante la década del 80. Con este propósito se desarrolla un modelo teórico de búsqueda para modelar las imperfecciones en ambos mercados, siguiendo el esquema propuesto por Pissarides (1998), aplicado en etapas sucesivas como en Wasmer y Weil (2004). En el modelo, un empresario sigue tres etapas antes de iniciar la producción de su idea de negocio: i) Recauda los fondos necesarios desde el mercado del crédito que le permita iniciar su empresa; ii) Busca un trabajador en el mercado laboral para iniciar la producción de la firma y iii) Produce el bien, el que luego se transa en un mercado de bienes competitivos. Debido a las fricciones, las dos primeras etapas toman tiempo y necesitan recursos. Cuando se inicia la producción, la firma adquiere la tecnología más avanzada disponible cuya productividad es la más alta de la economía. Esta productividad se mantiene constante hasta que el empresario decide adoptar una nueva tecnología con mayor productividad, lo que implica la destrucción de la relación laboral, y también en este modelo, la destrucción de la relación de préstamo. Los principales hallazgos muestran que a medida que crece el PT el valor del trabajo para un empresario disminuye al igual que su vida útil, no obstante, existen dos posibles efectos sobre la congestión de equilibrio del mercado laboral y sobre el desempleo. El sentido de estos efectos depende del costo total involucrado en el proceso de abrir una vacante, el que a su vez se relaciona con las fricciones del mercado del crédito. Un aumento del PT en economías donde el costo total asociado a abrir vacantes es menor que la pérdida del valor del trabajo asociado al PT, incentiva al empresario a destruir las actuales relaciones de trabajo y préstamo, disminuyendo la congestión del mercado laboral. De esta manera, en equilibrio, un aumento del PT induciría mayor reasignación laboral y mayor desempleo. No obstante, economías donde abrir una vacante es un proceso costoso mayor a la pérdida del valor de un trabajo asociada al aumento en el PT, los empresarios prefieren mantener la firma en producción hasta que sea rentable y evitan la transición al mercado del crédito. En equilibrio, la congestión del mercado laboral aumenta y existe una mayor reasignación laboral, sin embargo, el efecto sobre el desempleo depende si el efecto positivo del PT en la congestión de mercado laboral supera, o no, a una fracción del efecto negativo que el PT tiene sobre la vida óptima del trabajo. Respecto a la eficiencia del mercado del crédito, entendida como la habilidad de unir a prestamistas con prestatarios, una economía con una alta probabilidad de encuentro entre estos agentes, presenta menores tiempos de vida de las relaciones de trabajo y una mayor congestión de equilibrio del mercado laboral. Lo primero, dado que encontrar financiamiento se hace más probable, mientras que lo segundo ocurre ya que en equilibrio se ofrecerán más vacantes en busca de trabajadores. No obstante, el efecto sobre el desempleo depende de cómo se balancean estas fuerzas.
2
Stratton, Daryl A. "Characterizing the Frictional Interface in Friction Stir Welding." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1757.pdf.
Testo completo
3
Omam, Alan Frederic. "Internal friction." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Cerca il testo completoAbstract (sommario):
The phenomenon of internal friction most generally defined as the dissipation of mechanical energy inside a gaseous, liquid or solid medium. It is basically different from “friction” in the tribological sense, i.e., the resistance against the motion of two solid surfaces relative to each other (“external friction”).
4
Roa, Julio Alberto. "Evaluation of International Friction Index and High-Friction Surfaces." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/36277.
Testo completoAbstract (sommario):
State highway agencies have an obligation to provide users with optimal surface conditions under various weather conditions throughout the year. A satisfactory pavement surface should exhibit good friction and texture depth to reduce roadway highway accidents. This is why friction is starting to receive increased attention in the pavement management process.
There have been numerous research efforts by different countries and agencies to better understand the behavior of different friction testing devices and the influence of texture, speed, and other external conditions on their measurements.
The first part of this thesis presents a research effort to compare and harmonize texture and skid resistance measurements taken with various devices on 24 pavement sections with a wide range of textures. Measurements were compared and the International Friction Index (IFI) calculated following PIARC and ASTM steps.
The results revealed discrepancies in the IFI values calculated for the different devices, suggesting that the coefficients A, B, and C proposed by PIARC may need to be adjusted for each device considered before the IFI can be implemented by the surface properties consortium participating agencies. In this research the A, B, and C coefficients were then recalculated, and the predicted values of friction using these revised coefficients are presented. The coefficients developed were also used to obtain IFI values for high-friction surfaces (HFS).
It has been found that under different conditions, different parameters and coefficients will result. It is strongly recommended equipment comparison experiments (like the NASA and Smart Road programs) continue to better determine the coefficients necessary for harmonization.
HFS have emerged as viable high-friction pavement alternatives that mitigate the consequences of driver error, poor geometric alignment of the roadway, and insufficient friction at the tire-pavement interaction, especially during wet weather. This thesis presents a study of the HFS available in the U.S. market and their performance (friction and texture) in different applications, under different weather conditions, and in various locations. This thesis also presents the results of the benefit-cost analysis for the studied HFS.<br>Master of Science
5
Hu, Yuan. "Friction-Stir Riveting: Mechanical Testing of Friction-Stir Riveting." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1430393133.
Testo completo
6
REDDA, BOYNA ROHITH. "IMPACT OF FRICTION TEST SCALE ON BRAKE FRICTION PERFORMANCE." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2051.
Testo completoAbstract (sommario):
It is well known that the friction performance is a system property. The coefficient of friction and its stability, wear rate and the propensity to vibration and noise are always characteristics of a system and it is not easy to predict their performance based on smaller scale friction tests. This paper discusses the relation between performances of different-scale testers and possibility to model the friction performance of real systems in small simpler testers. It addressed the application of “scaling laws,” the application of typically adopted scaling strategies in friction industry and the testing strategies based on understanding of phenomena on the friction surface and in the friction systems. Full scale AKM standard dyno test and small tester (Bruker UMT) are related and the testing strategy is suggested. It is concluded that in spite of the fact that the scaling and simulations do not allow for a perfect prediction of performance (friction is a system property), it is still possible to make educated decisions on the research and development stage, when proper testing strategy on a smaller scale is adopted.
7
Kietzig, Anne-Marie. "Microscopic ice friction." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23322.
Testo completoAbstract (sommario):
Microscopic ice friction was studied systematically across all to ice friction relevant friction regimes using several metallic interfaces. A rheometer with a newly designed fixture for friction measurements was used in these studies. The investigations focus on the influence of material properties, such as surface wettability, roughness, surface structure, surface nanopatterning, and thermal conductivity.
Using a femtosecond laser process certain dual scale roughness structures were created to mimic the lotus leaf on the surface of inherently hydrophilic metal alloys. After laser irradiation the samples show initially superhydrophilic behavior with complete wetting of the structured surface. However, over time these surfaces become hydrophobic to superhydrophobic. The change in wetting behavior correlates with the amount of carbon found on the structured surface. The explanation for the time dependency of the surface wettability lies in the combined effect of surface morphology and surface chemistry.
With regard to ice friction this controlled lotus-like roughness significantly increases the coefficient of friction at low sliding speeds and temperatures well below the ice melting point. However, at temperatures close to the melting point and relatively higher speeds, roughness and hydrophobicity significantly decrease ice friction. This decrease in friction is mainly due to the suppression of capillary bridges.
The influence of surface structure on ice friction was also investigated isolated from the effect of surface roughness. It is shown that grooves oriented in the sliding direction also significantly decrease friction in the low velocity range compared to scratches and grooves randomly distributed over a surface.
The isolated effect of thermal conductivity on ice friction is investigated by thermally insulating the slider and the friction fixture with fiberglass. A decrease of the friction coefficient in the boundary friction regime and an earlier onset of the mixed friction regime in terms of sliding velocity are reported. Furthermore, the dependence of the ice friction coefficient on sliding velocity is compared for different sliding materials. It was concluded that the influence of thermal conductivity decreases with increasing sliding velocity.
8
Chou, Danielle 1981. "Dahl friction modeling." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32826.
Testo completoAbstract (sommario):
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>Includes bibliographical references (p. 22).<br>The drive behind improved friction models has been better prediction and control of dynamic systems. The earliest model was of classical Coulomb friction; however, the discontinuity during force reversal of the Coulomb friction model has long been a point of contention since such a discontinuity does not accurately portray the behavior of real systems. Other models have been suggested, but variations of the Dahl solid friction model remain some of the simplest yet most useful. Dahl's original theory proposed that friction behaved as a stress acting upon the quantum mechanical bonds at the interface. Thus, the relationship between frictional force and position would be analogous to a stress-strain curve, complete with hysteresis should there be permanent displacement akin to plastic deformation in materials. This project reviews the variations of Dahl friction models popular in the literature and then demonstrates it both analytically via Matlab and Simulink simulations and experimentally by observing the behavior of a limited angle torque motor.<br>by Danielle Chou.<br>S.B.
9
Gerde, Eric Stendahl. "Fracture and friction /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008334.
Testo completo
10
Quignon, Benoit. "Investigations of the frictional behaviour of nanotextured surfaces by friction force microscopy." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685551.
Testo completoAbstract (sommario):
Friction is omnipresent in our daily life, and although this phenomenon has been studied for centuries, the fundamental understanding on tribological processes as a whole is still lacking. Reducing friction is beneficial in many applications, from mediating wear to improving the life span of devices, hence improving our knowledge of the parameters affecting frictional forces is of paramount importance. In particular, the miniaturisation of modern devices implies that their reliability and durability become friction limited. Recent advances in the fabrication of nanostructured surfaces with tuneable topographic properties, along with advances in metrological tools such as the atomic force microscope (AFM), now provide the means to systematically study friction on well-defined nanostructured surfaces. This research project is focused on the lubricated and un lubricated frictional behaviour of nanotextured surfaces using the AFM with conventional and colloidal probes. The frictional properties of nanotextured surfaces bearing aluminium oxide nanodomes and zinc oxide nanorods of varying topographic properties in air, as well as the frictional properties in aqueous solutions of ionic and nonionic surfactants on flat and textured surfaces of titanium oxide, are reported. The results show that for the nanodomed-textured surfaces, the ancient Amontons laws of dry friction are obeyed; however, the friction coefficient was insufficient to fully characterise the frictional behaviour of such nanotextured surfaces. Pronounced stick-slip frictional characteristics were observed, with the amplitude of the stick-slip varying linearly with the applied load. On nanorod-textured surfaces, the friction-applied load linear relationship was however lost, due to the bending contributions of the rods to the lateral force experienced by the probe. Finally, the results obtained on flat and pillar-textured titanium oxide surfaces showed that ionic surfactants could mediate effective boundary lubrication with the existence of two frictional regimes, due to load- and shear-induced structural changes in the nanofilms of the adsorbed surfactant molecules.
11
Kuzmin, Leonid. "Interfacial kinetic ski friction." Doctoral thesis, Mittuniversitetet, Institutionen för teknik och hållbar utveckling, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-11525.
Testo completoAbstract (sommario):
It is no doubt, that the ski glide over the snow is a very complicated object of research. However, ski glide is just a one area of many other areas of human knowledge. As a rule, the scientists and practitioners, who work in these areas, operate with some publicly expressed more or less solid hypotheses. These researchers work with one hypothesis until another and a better one comes up. Our literature studies and our own observations regarding modern skis preparations, did not give us any solid hypotheses, which are able to explain the actual form and content of this procedure. The present work is an attempt to reveal such hypotheses. Conclusion: To achieve an optimal glide on skis with the base (the ski sole) made of some high hydrophobic durable polymer, e.g. UHMWPE, PTFE; we only have to create an adequate topography (texture) on the ski running surface, adequate to the actual snow conditions.
12
Ujvari, Szerena Krisztina. "Journal Bearing Friction Optimization." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60669.
Testo completoAbstract (sommario):
Engine downsizing, improving fuel efficiency while satisfying the environmental legislations are one of the main driving forces in developing new solutions for passenger cars.Engine main bearings, are journal bearings which support the crankshaft and operate principally in full film lubrication. Defining the optimum design parameters of the bearings which can provide low friction and high durability for automobiles represents a multi-variable problem.Being the supporters of the main shaft driven by the internal combustion engine, main bearings are subjected to strenuous operating conditions. These include high loads and pressures amongst others. The trend in lubricant selection for these components is shifting towards choosing engine oils with lower viscosity to further reduce fuel consumption. Simultaneously with the shift in oil, new solutions for controlling the geometry and the topography on the micro-scale are becoming available. Three main bearing top layers plated on a conventional aluminum alloy containing tin and silicon were selected for the study. The top layers, one bismuth based and two newly developed polymer based, were investigated for their frictional and wear performance.In order to study experimentally the influence of different design parameters on bearing performance a test rig and a methodology was developed. The selected engine main bearings were tested in lubricated condition with two oils having different viscosity. Pre - and post test analysis of the shaft surface roughness was performed using white light interferometry. The wear performance of the bearings was measured both as mass loss and surface topography.The results suggest that the developed test rig can be used to simulate close to running condition testing. The measurement method and set up shows good consistency at a load of 2000 N, but indicates inconsistency in set up at 500 N.It is found that the newly developed engine main bearing top layers have promising frictional and wear performance, providing a reduction in friction by up to 20%.
13
Sloan, Michael. "Eco-efficient friction materials." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/42237.
Testo completoAbstract (sommario):
Automotive friction materials are multi component composites in which fibrous materials play a fundamental role. Modern friction formulations have been developed around asbestos fibres, a heavily used material before legislation outlawed its use in the 1980’s. The replacement adopted by the friction industry was aramid, a high performance, high cost synthetic fibre. The work in this thesis investigates the role of aramid fibres in an economy friction material from the early mixing stages in manufacture using mechanical and optical analysis techniques through to the friction and wear performance of brake pads by employing instrumented friction and wear machines. Experimental procedures were designed and employed to quantify the performance of aramid pulp within the friction formulation as a function of volume fraction. Investigation showed a hierarchal fibre structure produced by an inherent molecular structure that encourages fibrillation producing complex fibre morphologies. This physical structure has been identified as fundamental to the success of aramid pulp in friction materials as the fibre network readily entraps small particles aiding the manufacturing process of friction materials. A structural model has been developed to describe both the particle retention performance of aramid fibres and the bulk structure of the pulp as a function of fibre geometry. A dynamic mechanical test was used to measure the bulk elastic properties of fibre networks to assess their suitability as processing fibres in friction materials and providing a novel analytical technique for the friction industry. Hemp, flax and jute are examples of high performance natural fibres that offer a significant cost saving over aramid, representing candidate replacements. Various natural fibres were trialled in friction formulations as direct replacements and also blended with aramid pulp. The results are compared to the baseline specification produced for aramid pulp allowing the suitability of natural fibres in friction materials to be discussed.
14
Gearing, Brian P. (Brian Paul) 1972. "Friction in sheet forming." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9413.
Testo completo
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Newby, William Robert. "Environmentally acceptable friction composites." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/15032.
Testo completoAbstract (sommario):
Currently, the production of most non-asbestos organic (NAO) friction materials depends on a long and energy intensive manufacturing process and an unsustainable supply of synthetic resins and fibres; it is both expensive and bad for the environment. In this research, a new, more energy efficient, manufacturing process was developed which makes use of a naturally derived resin and natural plant fibres. The new process is known as 'cold moulding' and is fundamentally different from the conventional method. It was used to develop a new brake pad for use in low temperature (<400 °C) applications, such as rapid urban rail transit (RURT) trains. A commercially available resin based upon cashew nut shell liquid (CNSL) was analysed and found to have properties suitable for cold moulding. In addition, hemp fibre was identified as a suitable composite reinforcement. This was processed to improve its morphology and blended with aramid to improve its thermal stability. Each stage of cold mould manufacture was thoroughly investigated and the critical process parameters were identified. The entire procedure was successfully scaled up to produce an industrially sized 250 kg batch of material and the resultant composites were found to have appropriate thermal and mechanical properties for use in a rail brake pad. The tribological performance of these composites was iteratively developed through a rigorous testing and evaluation procedure. This was performed on both sub- and full-scale dynamometers. By adding various abrasives, lubricants, and fillers to the formulation it was possible to produce a brake pad with similar friction characteristics to the current market material, but with a 60% lower wear rate. In addition, this brake pad caused 15% less wear to the brake disc. A detailed examination of both halves of the friction couple found that cold moulded composites exhibit a different wear mechanism from the current market material, which was suggested to be the reason for their superior properties. Cold moulding is 3.5x faster and uses 400% less energy than the conventional method.
16
Torres, Josette Annmarie. "Bodies Degraded by Friction." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/77491.
Testo completoAbstract (sommario):
Bodies Degraded by Friction is a collection of poetry existing in finite spaces. The first section, “A Moment and a Moment and a Moment," attempts to capture in words small passages of time as simple as clicking through a Facebook photo album and as destructive as new love. The second section, “It’s Complicated," is a manuscript in progress detailing a year in the life of an “other woman" negotiating an interpersonal relationship role underrepresented in self-help books and mass media. Several themes run throughout the book: the consequences of the use of technology-mediated communication as digital isolationist mechanisms, the collisions of real/virtual identity and real/virtual place, disruption as a poetic device, and the idea that love is a fleeting and ultimately impermanent state.<br>Master of Fine Arts
17
Björling, Marcus. "Friction in Elastohydrodynamic Lubrication." Doctoral thesis, Luleå tekniska universitet, Maskinelement, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17478.
Testo completoAbstract (sommario):
Today, with increasing demands on industry to reduce energy consumption and emissions, the strive to increase the efficiency of machine components is maybe bigger than ever. This PhD thesis focus on friction in elastohydrodynamic lubrication (EHL), found in, among others, gears, bearings and cam followers. Friction in such contacts is governed by a complex interaction of material, surface and lubricant parameters as well as operating conditions. In this work, experimental studies have been conducted that show how friction varies over a wide range of running conditions when changing parameters like lubricant viscosity, base oil type, surface roughness and lubricant temperature. These measurements have also been used to predict the friction behaviour in a real gear application. Numerical modeling of elastohydrodynamic (EHD) friction and film thickness are important for increased understanding of the field of EHL. Due to the high pressure and shear normally found in EHD contacts it is crucial that appropriate rheological models are used. An investigation has been carried out in order to assess the friction prediction capabilities of some of the most well founded rheological models. A numerical model was used to predict friction coefficients through the use of lubricant transport properties. Experiments were then performed that matches the predicted results rather well, and the deviations are discussed. The numerical model in combination with experimental measurements are used to investigate the friction reducing effect of diamond like carbon (DLC) coatings in EHL. A new mechanism of friction reduction through thermal insulation is proposed as an alternative to the current hypothesis of solid-liquid slip. These findings opens up for new families of coatings where thermal properties are in focus that may be both cheaper, and more effective in reducing friction in certain applications than DLC coatings of today.<br>Godkänd; 2014; 20140825 (marbjo); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Marcus Björling Ämne: Maskinelement/Machine Elements Avhandling: Friction in Elastohydrodynamic Lubrication Opponent: Professor H P Evans, Cardiff School of Engineering, Cardiff University, Cardiff, Wales, UK Ordförande: Professor Roland Larsson, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Torsdag den 2 oktober 2014, kl 09.00 Plats: E231, Luleå tekniska universitet
18
Mahdi, Duale A. M. "Aspects of shaving friction." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/808507/.
Testo completoAbstract (sommario):
Shaving is an everyday act for many people and Gillette is at the forefront of this market. The complex process of designing a razor involves understanding the interaction between the cartridge and the face which are complicated systems in their own right. Wet shaving is a complex tribological process for which the mechanisms and parameters are not well understood. The time and high cost associated with designing razors are a major driving force for developing a technical model of shaving. Friction has been identified as an important parameter influencing consumer relevant attributes such glide and comfort. This thesis focused on breaking the problem down into two key areas, skin friction and hair cutting friction. By combining in-vivo and in-vitro testing capabilities, the key parameters affecting skin friction were determined and quantified. Due to the limited knowledge of the relative contribution of adhesion and deformation friction to total friction in the biotribology field, this thesis has confirmed past results and expanded on previous knowledge regarding the relative proportion of adhesion and deformation in three lubrication cases, namely, dry, water and oil contacts. Empirical models of skin friction for these three cases were developed to estimate the relative proportion of adhesion and deformation friction. The primary parameters affecting relative proportion of adhesion and deformation included the contact lubrication, probe material, sliding speed, and probe geometry. Further, the results indicated for the oil contact case, for high normal loads and sliding speeds, deformation friction contributed as much as 50% of the total friction. Hair cutting friction was also investigated focusing on two parameters, hair density and hair cutting profile. These two parameters significantly affected hair cutting friction, where increasing hair density and the area under the curve (hair cutting profile) increased hair cutting friction significantly. Two case studies were considered that combined data from skin friction and hair cutting to estimate the relative proportion of adhesion, deformation and hair cutting friction to shaving friction. The results showed, for contacts with water as a lubricant, hair cutting and adhesion friction contribute on average the same proportion (40-40%) and depends on the type of hair cutting profile considered. For contacts with oil as a lubricant, relative contribution of hair cutting friction significantly increases and can be as high as 80% of the shaving friction depending on the hair cutting profile considered.
19
Edmunds, Rorie. "Parallel folding with friction." Thesis, University of Bath, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412346.
Testo completo
20
Clain-Burckbuchler, Juliette. "Friction sèche et mouillée." Paris 6, 2004. http://www.theses.fr/2004PA066383.
Testo completo
21
Parkanyi, Tamas. "Rubber friction on ice : investigation of frictional heating and melt water film thickness." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/18751.
Testo completoAbstract (sommario):
Friction on ice is important for many different fields such as winter sports and vehicle traction. In vehicle handling, maximising the friction coefficient between tyres and the ice surface is key to safety. The friction coefficient between tyre rubber and ice has been observed to be as high as unity at low temperatures and as little as 0.05 close to the ice melting temperature. The observed low friction is due to thin water films generated through frictional heating. Little is known about the formation and behaviour of this fluid film and its thickness has been difficult to measure. Previous attempts included techniques such as capacitance, conductivity and fluorescence spectroscopy, however results have been inconsistent. The primary aim of this study was to develop a measurement technique for this lubricating layer, establishing its thickness and the conditions under which its presence results in low friction. This was done by designing a micro-scale linear tribometer (microtribometer) to measure the friction coefficient (μ) on ice under a microscope. Clear ice, and ice with fluorescent particles of various sizes were created. The two ice types were then joined and tested on. During a friction test on the microtribometer, the particles displaced in the direction of sliding due to melt water presence. Images of the ice surface were taken before and after a friction measurement was made, and the amount of particle movement was assessed. The size and displacement of particles were correlated to the range of melt water thickness for a given sliding condition. This study is the first direct measurement method for the melt water layer on ice. Frictional heating is generated through the physical contact of rubber and ice asperities. By conducting friction measurements with rubbers of varying shear modulus (G*) and surface roughness (Ra) on both the microtribometer and on our large–scale tribometer, FRIMA, analysis of the contact can be made over a range of length scales. Further insight into the interfacial effects was provided by surface roughness measurements of both ice and rubber before and ice after microtribometer tests and in FRIMA. Finally, the use of differential interference contrast in reflected light microscopy with ice friction measurements provided visual evidence of the melt water presence. It was found that the melt water thickness based on particle displacement was between 0.1 to 2μm, for a velocity of 4.3 ⇥ 10−4 ms−1 and 0.5MPa nominal load, between –6°C to 0°C. A decreasing film thickness was found with decreasing temperature and the friction coefficient increased with decreasing temperature. At higher temperatures, the differences between the rubbers on both FRIMA and the microtribometer were found to be negligible because of the lubricating layer. Increasing the rubber surface roughness was found to increase at high and decrease friction significantly at low temperatures. These phenomena can be explained by the decreasing amount of solid-solid contact. A simple analytical approach to interpret the results suggests that the rubber compresses significantly and the surface roughness is smoothened upon contact with ice. Furthermore, simple hydrodynamic shear calculations show that pure liquid shear is insufficient to account for the measured low μ values close to melting temperatures. The combined effect of the increasing melt water presence reducing the real contact area and the significant deformation of the rubber asperities failing to compensate for this reduced contact area can account for the results. It is anticipated that these results provide direction for finding ways to improve solid-solid contact between rubber and ice, as there is some viscoelastic dissipation even at conditions close to the melting temperature. Some topics for example are: improving the thermal conductivity of tyre compounds or further investigating the surface roughness of rubber and ice separately and with the thin liquid film in between.
22
Najafi, Shahriar. "Evaluation of Continuous Friction Measuring Equipment (CFME) for Supporting Pavement Friction Management Programs." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/51244.
Testo completoAbstract (sommario):
It is the responsibility of pavement engineers to design pavements that provide safe and smooth riding surfaces over their entire life cycle. Each year many people around the world lose their lives in vehicle crashes, which are one of the leading causes of death in the United States (US). One of the contributing factors in many of these crashes is inappropriate friction between tires and the pavement. To minimize the impact of this factor, state Departments of Transportation (DOTs) must monitor the friction of their pavement networks systematically and regularly. Several devices are used around the world for measuring friction. Locked-wheel skid trailers are the predominant technology for roadways in the U.S. However, Continues Friction Measuring Equipment (CFME) is emerging as a practical alternative, especially for network-level monitoring. This type of technology has been used for monitoring runway friction for many years and is starting to be used also for measuring roadway friction.
This thesis evaluates the different operational characteristics of CFME to provide guidelines for highway agencies interested in using this technology for supporting their friction management programs. It follows a manuscript format and is composed of two papers. The first part of the thesis presents a methodology to objectively synchronize and compare CFME measurements using cross-correlation. This methodology allows for comparing the “shape” of the friction profiles, instead of only the average friction values. The methodology is used for synchronizing friction measurements and assessing the repeatability and reproducibility of the CFME using friction measurements taken on a wide range of surfaces at the Virginia Smart Road. The proposed approach provides highway agencies with a rigorous method to process CFME measurements.
The second part of the thesis evaluates the impact of several operational characteristics on the CFME measurements using a field experiment. The results of the experiment confirmed that the measurements are significantly affected by (1) the direction of testing while testing on sections of road with a significant grade, (2) water film thickness, and (3) testing speed. The experiment showed that measurements taken downhill on a 6% grade were significantly higher than those taken uphill. The analysis also verified that, consistent with previous studies, the measured friction decreases with higher water depth and testing speeds. It also showed that the change of friction with speed is approximately linear over the range of speeds used in the experiment.
In general, the thesis results suggest that CFME can provide repeatable and reproducible friction profiles that can be used to support friction management programs and other asset management business functions. However, care should be taken with regard to the operational conditions during testing since the measurements are affected by several factors. Further research is needed to (1) quantify the effect of these, and potentially other, operational factors; and (2) establish standard testing condition and approaches for correcting measurements taken under other conditions.<br>Master of Science
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Pereira, De Matos Rafael. "Molecular dynamics simulations of amine-based friction modifiers : diffusion, adsorption and friction behaviors." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC013.
Testo completoAbstract (sommario):
Les amines grasses sont présentes dans la formulation de lubrifiants automobiles, en tant que modificateurs de frottement organiques (MFO), afin d'atténuer les effets négatifs entraînés par le frottement et l'usure induits au sein des pièces sujettes aux conditions limites (c'est-à-dire, sous haute pression et basse vitesse de glissement). Outre leurs propriétés de lubrification, ces additifs présentent l'avantage d'être compatibles avec les systèmes de dépollution des gaz d'échappement, puisque leur composition organique est exempte d'éléments nocifs, tels que le soufre, le phosphore et certains métaux. Ainsi, un protocole de calcul en dynamique moléculaire classique a été mis en place et utilisé pour étudier, à l'échelle moléculaire, les propriétés des surfactants. En particulier, trois mécanismes d'action ont été considérés, à savoir : leur diffusion dans un milieu liquide, leur adsorption sur des substrats solides, et leur comportement en frottement. Dans ce contexte, différents facteurs associés à la structure des constituants des lubrifiants ont été analysés, notamment leur effet sur la performance des MFO. Les simulations révèlent que : (i) Diffusion – le coefficient de diffusion des composés aminés sont considérablement impactées par les caractéristiques de l'huile de base (exemple: leur polarité et masse moléculaire), sachant que les modèles de solvant les plus polaires et les plus lourds provoquent le ralentissement du flux diffusif des MFO ; par ailleurs, la structure des additifs jouent également un rôle dans leur diffusion, où les molécules les plus petites et les moins polaires s'avèrent relativement les plus mobiles. (ii) Adsorption – les amines primaires réagissent chimiquement avec une surface d'oxyde de fer, en formant des monocouches auto-assemblées, dont l'organisation et l'épaisseur augmentent avec leur taux de recouvrement. (iii) Frottement – les films adsorbés contenant d'amines constituées d'une chaîne hydrocarbonée C18 linéaire et saturée sont capables de réduire le frottement d'un système modèle représentant un nano-contact en régime limite ; en plus, leur efficacité dépend de la microstructure développée par les amines adsorbées sur les substrats sous compression et cisaillement ; d'ailleurs, les films permettant la formation de(s) plan(s) de glissement bien défini(s) entre les molécules organiques confinées sont davantage disposés à diminuer la résistance de glissement. Par conséquent, ces études ont permis de confirmer l'intérêt de l'apport d'une approche numérique complémentaire aux techniques expérimentales dans le but de comprendre les phénomènes élémentaires des systèmes tribologiques<br>Fatty amines and their derivatives are employed as organic friction modifiers (OFM) in lubricant oils in order to mitigate the negative effects of friction and wear, both induced by the moving and rubbing components of an internal combustion engine that are subjected to boundary lubrication conditions (i.e., high contact pressure and low sliding velocity). In addition to their tribological performance, these additives exhibit the benefit of being compatible with exhaust aftertreatment systems that equip the current light-duty vehicles, owing to their sulfur- and phosphorus-free chemical composition. For these reasons, we have developed a computational protocol, composed of equilibrium and non-equilibrium (classical) molecular dynamics simulations, in order to gain a deeper understanding into their mechanisms of action at nanoscale, and in particular into their diffusion, adsorption and friction behaviors. In this context, the influence of different molecular structure factors – related to lubricant constituents – on OFM working performance were investigated. The obtained results have shown that: (i) Diffusion – OFM diffusivity is substantially affected by the base oil structure and chemistry (e.g., polarity and molar mass), where solvents with relatively larger and higher polar groups tend to slow down their diffusive rate; besides, the OFM dynamics in liquid phase is also impacted by their own composition, being the molecules with relatively smaller and less polar structure the most mobile additives. (ii) Adsorption – primary alkyl amines do chemisorb onto iron-oxide substrates, thereby forming molecular films whose packing order and thickness increase with increasing surface coverage. (iii) Friction – adsorbed layers containing primary amines with linear, saturated, C18 hydrocarbon tails are able to reduce friction in a single-asperity, boundary nano-contact model, where their efficiency is dependent on their molecular ordering under confinement and shear; in addition, the organic films allowing the formation of well-defined slippage interface(s) with little molecular interdigitation are more prone to diminish the sliding resistance of solid substrates in relative motion.Therefore, those findings are expected to foster the exploration and development of computational simulation approaches, as a complement of experimental techniques, to investigate the fundamental phenomena present in tribological-relevant engineering systems
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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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Raftari, Maryam. "Investigation of the frictional behaviour of end-grafted polymer layers using friction force microscopy." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/7001/.
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Cora, Omer Necati. "Friction Analysis In Cold Forging." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605674/index.pdf.
Testo completoAbstract (sommario):
Friction is one of the important parameters in metal forming processes since it affects metal flow in the die, forming load, strain distribution, tool and die life, surface quality of the product etc. The range of coefficient of friction in different metal forming applications is not well known and the factors affecting variation are ambiguous. Commercially available FEA packages input the coefficient of friction as constant among the whole process which is not a realistic approach.
In this study, utility of user-subroutines is integrated into MSC SuperForm v.2004 and MSC Marc v.2003 FEA packages, to apply a variable coefficient of friction depending on the contact interface conditions. Instead of using comparatively simple friction models such as Coulomb, Shear (constant) models, friction models proposed by Wanheim-Bay and Levanov were used to simulate some cold forging operations. The FEA results are compared with the experimental results available in literature for cylinder upsetting. Results show that, large variation on the coefficient of friction is possible depending on the friction model used, the part geometry and the ratio of contact normal pressure to equivalent yield stress. For the ratio of contact normal pressure to equivalent yield stress values above 4, coefficient of friction values are approximately same for both friction models.
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Söderberg, Anders. "Interface modeling - friction and wear." Doctoral thesis, KTH, Maskinkonstruktion (Avd.), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9861.
Testo completoAbstract (sommario):
The general trend toward increased use of computer models and simulations during product development calls for accurate and reliable product models. The function of many products relies on contact interfaces between interacting components. Simulating the behavior of such products requires accurate models of both components and interfaces. Depending on the purpose of the simulation, interface models of different degrees of detail are needed. In simulating very large systems with many interfaces, it might be computationally expensive to integrate detailed models of each individual interface. Condensed models, or abstractions, that describe the interface properties with the fewest degrees of freedom are therefore required. This thesis deals with the modeling and simulation of mechanical interfaces in a systems context. The five appended papers discuss the issue from both the simulation and tribological points of view. The aim is to study how friction and wear can be modeled in the behavioral simulation of technical systems and to discuss the convenience and applicability of using different types of models as building blocks of a system model in simulations. Paper A reviews existing friction models of sliding contacts under different running conditions. Paper B uses a simplified contact model, the elastic foundation model, to model friction in a boundary-lubricated rolling and sliding contact. The model is integrated into a dynamic rigid body model of a mechanical system, and the system behavior is simulated. Paper C discusses the application of the elastic foundation model to rough surface contact problems and investigates how the error in its results depends on surface roughness. Papers D and E address how the wear of the contact surfaces at the pad-to-rotor interface in a passenger car disc brake can be simulated using finite element analysis (FEA).<br>QC 20100811
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Colegrove, Paul Andrew. "Modelling of friction stir welding." Thesis, University of Cambridge, 2004. https://www.repository.cam.ac.uk/handle/1810/240576.
Testo completoAbstract (sommario):
This thesis investigates the modelling of friction stir welding (FSW). FSW is a relatively new welding process where a rotating non-consumable tool is used to join two materials through high temperature deformation. The aim of the thesis is the development of a numerical model to improve process understanding and to assist in the design of new tools. The early part of the thesis describes the process, defines the modelling problem and describes why a computational fluid dynamics package (FLUENT) was selected for the subsequent work. A systematic series of friction stir welding experiments in 7075 aluminium alloy, used to provide validation data for a numerical model of the process, are described in chapter 2. The trials examined how the welding conditions and tool type affected the weld temperature and heat input. From this data a thermal model of the welds was developed that included the convective heat flow due to material mixing. Chapters 3 to 6 describe the model development, from a preliminary model of a standard tool, to a detailed analysis of 2 dimensional profiles incorporating a novel slip boundary condition, and finally to a full 3 dimensional model of a new tool design, including material slip. The preliminary model with a standard tool assumed that the material stuck to the tool surface and included features such as the tool tilt, heat generation and heat flow. The model captured many of the real process characteristics, but gave poor predictions of the welding forces and heat generation. This identified the need for a more complex treatment of the tool-material interface that allowed material slip. The slip model was first implemented in a 2 dimensional study of flow around profiled tooling (chapter 4). This enabled a first order visualisation of the flow and the quantitative comparison of different 2 dimensional pin profiles. In chapter 5 an optimised 2 dimensional pin profile was determined by selecting the shape that minimised the traversing force. Two prototype tools based on this profile were manufactured: the plain 'Trivex™' and the threaded 'MX-Trivex™'. These were tested against a conventional 'MX-Triflute™' tool with the results showing that the traversing force was reduced by 18-25%. Chapter 6 describes 3 dimensional models of the 'Trivex™' and 'Triflute™' tools, which extended the slip model to 3 dimensions. The model correctly predicted that the Trivex™ tool had lower traversing and down forces than its Triflute™ counterpart, as observed experimentally. The thesis successfully demonstrates the application of fluid dynamics modelling to friction stir welding, enhancing visualisation of the flow, and guiding the development of new tooling.
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Bartels, Guido. "Mesoscopic Aspects of Solid Friction." Gerhard-Mercator-Universitaet Duisburg, 2006. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-01272006-083621/.
Testo completoAbstract (sommario):
The phenomenon of friction is on the one hand useful, for example for walking, which would not be so easy without friction, and on the other hand disturbing, for example in wheel bearings, where it slows down desired motion. Therefore, the origin and effect of friction is under intense research. One main point in this work is the analytic investigation of the coupling between friction force and (torsion) friction torque of a sliding and spinning disk. The local friction force at a contact area element was chosen to be an algebraic function of the local relative velocity with an exponent α > 0. It could be shown, that for α < 1 sliding and torsion friction dynamically reduce each other, while for α > 1 they amplify each other. In case of α = 1 sliding and torsion friction are decoupled. With respect to the velocity ratio of sliding and angular velocity, the final motion mode has been investigated, i.e. whether both motions stop together or whether one motion gets dominant. For α < 1 both motions stop together, while for α > 1 it depends on the initial velocity ratio. The mass distribution and contact area radius, which are encoded in the key parameter C of the corresponding differential equation, are the second important influence on the final motion mode. A phase diagram shows for given values C and α the possible final motion modes. The influence of an inhomogenous pressure distribution within the contact area on the coupling was investigated exemplarily for α = 0 with a cylinder as object. In contrast to the disk (homogenous pressure distribution) the cylinder is deflected from its initial sliding direction. In this context the motion of a curling rock on ice is discussed, as it is deflected towards the opposite direction compared to that of the cylinder. Another focal point is the investigation of the role of friction torques (rolling and torsion friction) in the compaction of nano-powders. For this three dimensional contact dynamics simulations with phenomenologically chosen contact laws were performed. With this it could be shown that torsion and rolling friction contribute significantly to the final porosity. Furthermore, these contributions of torsion and rolling friction are independent of each other and can be represented by a sum. In the chapter Conclusions and Outlook a brief introduction on recent research of atomic scale torsion friction is presented.
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Garoff, Niklas. "The Friction between Paper Surfaces." Doctoral thesis, Stockholm, 2002. http://www.diva-portal.org/kth/theses/abstract.xsql?dbid=3415.
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Vairis, Achilles. "High frequency linear friction welding." Thesis, Online version, 1997. http://ethos.bl.uk/OrderDetails.do?did=1&uin=uk.bl.ethos.389136.
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de, Silveira Glynis. "Friction of paper and board." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606347.
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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.
Testo completoAbstract (sommario):
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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Awawdeh, Mohammed Adel. "An investigation of orthodontic friction." Thesis, Queen's University Belfast, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431404.
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Hwang, Kuo-Lun. "Friction in unsteady pipe flows." Thesis, University of Dundee, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413174.
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Sehmbi, Jatinder Singh. "The dynamics of friction oscillators." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248042.
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Motamedi, Farshad. "Interfacial friction in fabric mechanics." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47577.
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Liao, Kai Ph D. Massachusetts Institute of Technology. "Factors affecting piston ring friction." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82499.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.<br>This thesis was scanned as part of an electronic thesis pilot project.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 153-156).<br>The piston ring pack friction is a major contributor to the internal combustion engine mechanical friction loss. The oil control ring decides the oil supply to the top two rings in addition to being the major friction contributor in the ring pack. This work concentrated on the oil control ring friction. A large range of ring land widths and tensions, liner finish, and oil viscosity were investigated both experimentally and numerically to reveal how different factors affect the piston ring friction. A floating liner engine (FLE) was modified for motoring tests. The engine system repeatability and self-consistency were demonstrated. The thesis then discussed proper methods to select and measure the rings, liners and oil, which were important to generating meaningful results from the experiment. The ranges of engine speeds and liner temperatures were designed to ensure that all the lubrication modes, namely, boundary, mixed and hydrodynamic, can become dominant in both the instantaneous friction over a cycle and the FMEP over the engine speed range for any combination of rings, liners and lubricants. A parallel modeling effort was made to the experiments. The work showed that with careful preparation of adequate information on rings, liners and lubricants, the model can match the friction trends observed in the experiment over a large range of operating parameters and designs on the ring, liner finish and lubricant viscosity. The ring friction change over the liner break-in was studied using liners covering a wide range of surface roughness. The hydrodynamic pressure generation ability of the liner appears to be decided by the large surface structure. Therefore, the break-in process, which removes individual asperities from the plateau, does not affect pure hydrodynamic lubrication, and only the mixed lubrication is affected by the plateau roughness change. By keeping the same hydrodynamic pressure - ring/liner clearance (P-h) correlation and changing the plateau roughness, the model can predict the ring friction change over different lubrication regimes during the break-in. Compared to the current industry norm, a new engine power cylinder system design using a smaller land width twin land oil control ring with a lower ring tension and accompanied by a smoother liner surface gives lower friction and better oil control at the same time.<br>by Kai Liao.<br>Ph.D.
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Ella, Samantha. "Rubber snow interface and friction." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/17941.
Testo completoAbstract (sommario):
Tyres are used in everyday life for a variety of practical and recreational tasks. Frictional behaviour of tyres on any surface is important for vehicle safety and control; this behaviour becomes more important when that surface is snow. The interaction of rubber and a snow surface is complex and a deeper understanding of both is needed in order to help develop better tyres. Outdoor full scale tyre test results were compared to results from indoor laboratory tests using a linear tribometer and a surface of compacted artificial snow; these were in excellent correlation allowing a systematic and comprehensive study of rubber friction on snow to be conducted in the laboratory. Rubber samples of varied rubber compositions and geometries were used to gain an understanding of friction on snow. Samples with varying glass transition temperature (Tg), dynamic rigidity (G*) and Payne effect (dependence of the dynamic moduli on the amplitude of the applied strain) were investigated along with samples with and without sipes. The rubber friction coefficient (μ) was measured as a function of velocity and temperature. The siped samples exhibited a higher μ than those without sipes. FE simulations, rubber friction tests for varying contact pressures and steel blade force tests were performed to evaluate contributions from ‘surface’ friction and ploughing separately. The increased μ was attributed to the ploughing force from the front edges of the ‘subblocks’ created by the sipes. Although it is well known in the industry that siped tyres grip well, this is the first time it has been explained how sipes grip effectively through a combination of ploughing and rubber snow interaction. A comprehensive study of varying rubber properties (Tg, G* and Payne effect) was conducted to better understand their impact on snow friction. The findings were evaluated using the WLF shift factor to account for the running frequency of the rubber from the snow surface roughness. G* was found to be the dominant parameter for rubber μ when considering running frequency. Increased μ values were exhibited by rubbers with a lower G*. The decreased G* makes the rubber more compliant, thus increasing the contact area between the rubber and the snow, in turn increasing μ. A better knowledge of the surface roughness of snow will aid the understanding of the interaction between rubber and snow for tyres. A method was developed to characterise the artificial snow surface utilising sectioning and imaging of chemically stabilised snow samples. From images of the snow surface before friction testing the average indentor size can be found, this is used to analyse the running frequency of the rubber. Qualitatively comparing the surfaces before and after rubber friction testing shows a decrease in surface profile aggressivity after a test; this is attributed to melting of the snow from frictional heating and snow grain fracture. Friction tests were conducted to directly compare rubber friction on snow and ice using round edged samples. Again it was found that the rubber with the decreased G* exhibited higher friction; this was seen on both snow and ice confirming G* as the dominant rubber property for both surfaces, regardless of the surface roughness change. It was found that at low temperatures ice had a higher μ than snow, while at high temperatures snow exhibited a higher μ than ice. It is hypothesised that this intriguing switch is due to the surface roughness change leading to differing contact areas both with and without melt water. This switch is not seen when a simple heat transfer model is used, confirming the effect as a surface roughness change. The use of a modified Hertz model shows that indentation is the dominant mechanism at low velocities on snow. It is hypothesised that at high velocities melt water dominates on both snow and ice while adhesion may have a more significant role on ice at low velocities. These findings provide knowledge that can be used in the design of tyres for snow and ice in the future.
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Pereira, Diogo Jorge O. A. "Friction surfacing of aluminium alloys." Master's thesis, Faculdade de Ciências e Tecnologia, 2012. http://hdl.handle.net/10362/8758.
Testo completoAbstract (sommario):
Dissertação para a obtenção do grau de Mestre em Engenharia Mecânica<br>Friction surfacing is a solid state joining process that has attracted much interest in the past decades. This technology allows joining dissimilar metallic materials while avoiding the brittle intermetallic formations, involving temperatures bellow melting point and producing like forged metal structures.
Much research using different steels has been made but the same does not happen with aluminium alloys, specially using different aluminium alloys.
Friction surface coatings using consumable rods of AA6082-T6 were produced on AA2024-T3 plates using a wide range of parameters. Coatings were examined to assure the best set of parameters according to the physical properties, such as: bonding width and thickness. Coatings were characterized metallurgical and mechanically. Besides metallurgical techniques, hardness, tensile, bending and wear tests were carried out.
From this study, it was shown that high rotation speeds reduce the coating thickness and improve bonding to the substrate, while the applied load is the key parameter to obtain a good bonding width. Travel speed controls the deposition rate and the coating thickness. For the tested parameters a fine grain structure was obtained. The coatings have similar properties to the as-received rods but with higher ultimate tensile strength (UTS), elongation and wear resistance.
Finally, an assessment of power and material consumption was performed revealing that Friction Surfacing is quite competitive when compared to other surface coating technologies.
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Wu-Bavouzet, Fangnien. "Friction sur surfaces à plots." Paris 6, 2008. http://www.theses.fr/2008PA066383.
Testo completoAbstract (sommario):
L'objet de cette thèse est l'adhésion et la friction de lentilles millimétriques d'élastomères sur un substrat décoré de plots micrométriques de hauteur variable. A cette fin, nous avons utilisé un AFM géant permettante mesurer les forces normales et tangentielles appliquées à la lentille et d'observer le contact. Il permet d'explorer des vitesses de glissement de l'ordre de 100 µm/s, et des forces de l'ordre de 10-3 N. Nous avons observé deux types de contact selon la hauteur h des plots : intime (h<hc) et posé (h>hc). Les régimes de glissement observés dépendent de la dureté de l'élastomère : avec une lentille dure (module d'Young E ~ 1 MPa), on observe du glissement stable, tandis qu'on met en évidence des ondes de Schallamach et de stick-slip avec des lentilles molles (E ~ 0. 1 MPa). Dans les deux cas, nous avons étudié la force de friction, l'aire de contact et la contrainte tangentielle en fonction de la hauteur des plots, de la vitesse de glissement, et de la force normale.
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Ляшенко, Яків Олександрович, Яков Александрович Ляшенко, and Yakiv Oleksandrovych Liashenko. "Friction force for boundary lubrication." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20362.
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Opanasyuk, S. "Nanotribology: microscopic mechanisms of friction." Thesis, Вид-во СумДУ, 2007. http://essuir.sumdu.edu.ua/handle/123456789/17441.
Testo completoAbstract (sommario):
Nanotribology is the science of surfaces in relative motion. It is of great theoretical interest and huge practical significance.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/17441
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Li, Yang. "Single Molecule Spintronics and Friction." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou151561792063398.
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Laine, Antoine. "Sliding Friction at the nanoscale." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7076.
Testo completoAbstract (sommario):
Dans ce manuscrit, nous utilisons des méthodes dérivées de la microscopie à force atomique afin de mesurer, à l'échelle nanométrique, la réponse mécanique de différents systèmes. L'accent est porté sur la mise en lumière de la réponse frictionnelle et des mécanismes de dissipation à l'échelle du contact unique, où matières molle et condensée se confondent.Nous présentons premièrement le développement d'un nouvel outil expérimental permettant des mesures de nano-rhéologie et de nano-tribologie en environnement contrôlé. L'étude des propriétés mécaniques de liquides ioniques nano-confinés, avec cet instrument, nous révèle le caractère vitreux de ces électrolytes denses aux interfaces métalliques.Nous étudions par la suite les phénomènes de dissipation à l'échelle ultime, pour des jonctions métalliques de quelques atomes de diamètre. De l'absence de défauts découle une réponse plastique aux antipodes de notre expérience macroscopique.In fine, nous mettons l'accent sur l'étude de la dynamique d'une interface métallique de quelques atomes et développons de nouvelles stratégies expérimentales afin de résoudre la réponse frictionnelle du système soumis à une contrainte harmonique. Nos mesures, quantitativement reproduites numériquement, révèlent un mécanisme de friction quantifiée à l'échelle atomique<br>In this manuscript, we use methodes inherited from Atomic Force Microscopy in order to measure the nanoscale mechanical response of different systems. The focus is put on highlighting the frictional response and dissipation mechanisms taking place at the single asperity level, where soft and hard condensed matter meet.We first present the development of a new experimental tool allowing nanorheology and nanotribology measurement in controlled environment. The study of mechanical properties of nanoconfined RTILs with this apparatus revealed the glassy nature of these dense electrolytes at metallic interfaces.We then study the dissipation phenomena at the ultimate scale for metallic nanojunctions made of a few atoms. The absence of defects rationalizes their unexpected mechanical properties in striking difference with the macroscopic realm.In fine, we focus on the dynamics of a metallic interface made of a few atoms and develop new experimental strategies to probe the frictional response of the interface under harmonic applied stress. Our measurements are quantitatively reproduced numerically and reveal an atomic-scale quantized slip friction mechanism
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Fina, Ernesto. "The friction of racing tyres." Thesis, University of Surrey, 2016. http://epubs.surrey.ac.uk/812823/.
Testo completoAbstract (sommario):
This research investigates the frictional behaviour of racing tyres and compares it to the behaviour of standard road tyres. The analysis is carried out by simulating a racing tyre and a standard tyre rolling on a common track surface. A novel physical tyre model has been developed for this purpose. The model allows a detailed description of the tyre footprint mechanics, the tread compound and road surface physical characteristics. The design and development of the physical tyre model is the result of an in depth literature review, which investigates and critically discusses the main modern theories on rubber friction. In this context, the review singles out the work of Persson (2001a, 2006b), whose approach to mathematically model the complex interactions between road surface and rubber seems a good solution to be implemented in real time applications for tyre models. Persson's theories are replicated within the physical tyre model. The model is then used to calculate the footprint distribution of coefficient of friction and operating temperatures of the racing and standard tyres in order to draw some comparisons. The simulations are limited to pure traction and cornering events carried out on two surfaces with different characteristics. The simulation results highlight the greater sensitivity of racing tyres to variations in operating temperatures and the track surface characteristics. In particular, the physical model simulations show the very narrow range of operating conditions of racing tyres. This explains the variety of tread compounds that are normally used in racing competitions in order for the tyre to suit the different track surfaces and temperatures.
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Carnasciali, Maria-Isabel. "Kinetic friction of nonwetting drops." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22650.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.<br>Committee Chair: Neitzel, G. Paul; Committee Member: Allen, Mark G.; Committee Member: Degertekin, F. Levent; Committee Member: Schatz, Michael; Committee Member: Smith, Marc K.
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Söderberg, Anders. "Interface modeling : friction and wear /." Stockholm : Maskinkonstruktion, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9861.
Testo completo
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Guan, Jian. "Droplets on low friction surfaces." Thesis, Northumbria University, 2017. http://nrl.northumbria.ac.uk/35092/.
Testo completoAbstract (sommario):
Droplet mobility on surfaces is often hampered by the pinning of the droplet’s contact line. External forces would be needed if motion is to continue. The development of Slippery Liquid-Infused Porous Surfaces (SLIPS) or Lubricant-Impregnated Surfaces (LIS) has since enabled the studies of droplets in low friction situations with virtually no contact angle hysteresis. This thesis presents three separate studies of droplet mobility in the absence of contact line pinning, made possible by the use of SLIPS/LIS. Firstly, the first study of evaporation of sessile droplet under true constant contact angle mode was demonstrated. The lack of contact line pinning meant that droplet’s contact line receded smoothly with no stick-slip stepwise retreat as it evaporated. The absence of a contact angle due to the presence of the wetting ridge around the droplet led to the concept of an extrapolated apparent contact angle. The subsequent study saw the experimental realisation of both inward and outward motion of droplet having an apparent contact angle above 90° confined in a wedge geometry formed by a pair of SLIPS/LIS. Out of equilibrium, droplet was free to travel within the wedge until settling at a prescribed location, regardless to its initial position. This enabled the accurate control over the transport and localisation of the droplet by a reconfiguration of the system. The lack of pinning also suggests that the dynamics of the droplet is dictated purely by viscous dissipation. The final study showed that SLIPS/LIS can be created on macro-patterned surfaces. The macro-patterning introduced menisci features in the impregnating liquid layer which interact with the wetting ridge around a droplet. These interactions were used to induce motion to the droplet. It was also found that accurate positioning of the droplet on an otherwise completely slippery surface can be achieved using well-defined surface topography.
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Andreasson, Erik. "Validation of Friction Estimating System." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65393.
Testo completo