Relevant bibliographies by topics / Coefficient Of Friction (COF)

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Academic literature on the topic 'Coefficient Of Friction (COF)'

Author: Grafiati
Published: 4 June 2021
Last updated: 7 September 2023

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Journal articles on the topic "Coefficient Of Friction (COF)"

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Tan, Adin Ming, Yehuda Weizman, Firoz Alam, and Franz Konstantin Fuss. "The Coefficient of Friction of Soccer Balls." Proceedings 49, no. 1 (June 15, 2020): 92. http://dx.doi.org/10.3390/proceedings2020049092.

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Nine soccer balls were tested for their friction against a leather sheet, using a force plate. An average normal force of 63.6 N was applied and the movement of the ball had an average velocity of 15 mm/s. Each test was repeated 15 times and the average Coefficient of Friction (COF) was reported. The following results were obtained: Jabulani (COF: 0.62 ± 0.05); Fracas (COF: 0.41 ± 0.01); Ordem 3 (COF: 0.63 ± 0.02); Teamgeist (COF: 0.38 ± 0.01); Brazuca (COF: 0.45 ± 0.01); Kopanya (COF: 0.39 ± 0.01); React (COF: 0.37 ± 0.01); Finale 15 (COF: 0.39 ± 0.06); Vintage T-panel leather ball (COF: 0.41 ± 0.02). Overall, the COF of all balls tested ranged between 0.37 and 0.62. The Finale 15 ball showed a decreasing COF trend with repeated trials and the React ball produced pronounced slip-stick phenomenon.
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Fiagbe, Yesuenyeagbe A. K., and Emmanuel W. Ramde. "FRICTION COEFFICIENT OF MUNICIPAL SOLID WASTE COMPONENTS." International Journal of Engineering Technologies and Management Research 7, no. 7 (July 7, 2020): 1–7. http://dx.doi.org/10.29121/ijetmr.v7.i7.2020.702.

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Engineering properties of materials includes coefficient of friction (COF) which are basic in design performance of engineering systems. The COF can be considered as very important in design of handling tools. Various types of handling tools and equipment are used at various stages of disposal and treatment of MSW and COF is one critical property. This paper presents estimate of COF of municipal solid waste components. The components of the municipal solid waste are paper, plastic, organic and others. The estimation of the COF was done using an inclino-tribometer. Waste from 16 sample locations were used with 6 surfaces which are considered to be of relevant. It was estimated that Formica surface has the least COF values and range from 0.269 and 0.312 with ‘others’ – formica surface tribosystem being the least. It was also found that paint application on wooden surface with oil paint would increase COF as compared to applying emulsion on same wooden surface. The study pointed out that polishing with vanish is the best way to reduce COF in wood surfaces. It was also observed that painting metal surfaces with oil paint will increase the COF than when the same metal was left unpolished or unpainted.
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Varriale, Francesco, Stefano Candeo, Gabriele Riva, Jens Wahlström, and Yezhe Lyu. "A Brake System Coefficient of Friction Estimation Using 3D Friction Maps." Lubricants 10, no. 7 (June 23, 2022): 134. http://dx.doi.org/10.3390/lubricants10070134.

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The coefficient of friction (COF) is one of the core factors in the evaluation of brake system performance. It is challenging to predict the COF, since it is strongly influenced by several parameters such as contact pressure (p), slip rate (v) and temperature (T) that depend on the driving conditions. There is a need for better models to describe how the brake friction varies under different driving conditions. The purpose of this research is to study the possibility of using 3D friction pvT-maps to estimate the COF of a disc brake system under different driving conditions. The 3D friction pvT-maps are created by filtering results of material tests conducted in a mini-dyno inertia bench. The COF measured under different driving cycles in an inertia dyno bench with the full brake system are compared with the COF estimated by the friction maps coming from the reduced scale dyno bench to investigate the validity of the simulation approach. This study shows that mini dyno bench is suitable to obtain a tribological characterization of the friction pad–disc rotor contact pair and is able to replace the full inertia dyno bench to investigate the brake system performance.
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Fang, Kun. "Frictional Performance of Polyphenyl Ester Modified Polytetrafluoroethylene." Materials Science Forum 1080 (January 30, 2023): 33–39. http://dx.doi.org/10.4028/p-g7gf9i.

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This paper mainly studied the coefficient of friction (COF), wear performance and frictional vibration performance of polyphenyl ester modified polytetrafluoroethylene under dry friction and water lubrication friction conditions. Polyphenyl ester modified polytetrafluoroethylene composites were prepared by blending 20% polyphenyl ester with polytetrafluoroethylene, and the COF, wear performance and frictional vibration properties of such composites were tested. The results showed that: (1) Under dry friction conditions, as the specific pressure between the friction pairs increased, the volume of wear and the thickness of the wear increased, the COF decreased at first and then increased, the frictional vibration increased and stabilized after the pressure of 0.5 MPa. (2) Under water-lubricated friction conditions, as the specific pressure between the friction pairs increased, the COF increased, and the frictional vibration increased and stabilized after the pressure of 0.5 MPa; (3) The wear resistance of polyphenyl ester modified polytetrafluoroethylene composite under water-lubricated friction was better than that under dry friction, the COF was less than that under dry friction, and the total level of frictional vibration was slightly lower than that under dry friction. Therefore, in order to reduce frictional vibration and improve service life, the working pressure should be reduced, and the lubrication performance between the friction surfaces should be improved. Under water-lubricated friction, the maximum working pressure of the polyphenyl ester modified polytetrafluoroethylene composite system is recommended not to exceed 0.8 MPa.
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Eun, Jinsu, Jaejin Ryue, Sangsoo Park, and Kikwang Lee. "A Novel Method to Measure the Static Coefficient of Friction for Socks." Sensors 22, no. 15 (July 25, 2022): 5525. http://dx.doi.org/10.3390/s22155525.

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Mechanical testers have commonly been used to measure the frictional properties of socks. However, the friction values may be susceptible to the level of stretchiness of tested fabrics or human variability. Thus, the aim of this study was to propose a novel method that enables friction measurement of socks in a sock-wearing condition with less human variability effects. Five socks with different frictional properties were chosen. Three experimental ramp tests were performed with an artificial structure shaped like the foot-ankle complex (last) and a ramp tester to quantify the static coefficient of friction (COF) at the foot against sock, at the sock against an insole, and the foot wearing socks against the insole, respectively. The angle where the last slipped while the ramp surface was gradually inclined was used to compute the static COF values for each sock. The reliability was 0.99, and COF values ranged from 0.271 to 0.861 at the foot-sock interface, 0.342 to 0.639 at the sock-insole interface, and 0.310 to 0.614 in the third test. Socks with different frictional properties were successfully distinguished each other. Thus, the suggested protocol could be a reliable option for measuring the static COF values in the tension similar with it found in a sock-waring condition with reduced effects of human variability.
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Schanner, Jonathan, Roman Funke, Andreas Schubert, and Alexander Hasse. "Investigating the Friction Behavior of Turn-Milled High Friction Surface Microstructures under Different Tribological Influence Factors." Journal of Manufacturing and Materials Processing 6, no. 6 (November 15, 2022): 143. http://dx.doi.org/10.3390/jmmp6060143.

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The coefficient of friction (COF) is an important parameter for mechanical engineers to consider when designing frictional connections. Previous work has shown that a surface microstructuring of the harder friction partner leads to a significant increase in the COF. However, the impact of the changes in the tribological system on the COF are not known in detail. In this study, the tribological influence factors such as the nominal surface pressure, the material pairing, lubrication, and the surface properties of the counterbody are investigated. Microstructuring is applied by turn-milling of an annular contact surface of cylindrical specimens. A torsional test bench is used to measure the torque depending on the displacement of the two specimens, thus enabling the determination of the COF. All tests with the microstructured specimens result in higher COF than the reference test with unstructured samples. The manufacturing process of the counterbody surface, the nominal surface pressure, and the materials in contact have a significant influence on the COF. While lubrication reduces friction in the case of unstructured specimens, the COF does not change significantly for microstructured samples. This proves that the deformative friction component dominates over the adhesive. Microstructuring the harder friction partner increases the transmittable torque in frictional connections and reduces the sensitivity towards possible contamination with lubricants.
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do Vale, Joao Luiz, Carlos Henrique da Silva, and Giuseppe Pintaude. "Energetic coefficient of friction applied to cylinder liners lab tests." Industrial Lubrication and Tribology 72, no. 9 (December 18, 2019): 1103–8. http://dx.doi.org/10.1108/ilt-08-2019-0324.

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Purpose This paper aims to present a proposal for evaluating the coefficient of friction (COF), under a reciprocating test that considers the energy dissipated by the friction force. In addition, this new parameter is compared to average COF, which is often used to evaluate COF in reciprocating tests. Design/methodology/approach Samples of compacted graphite iron were extracted directly from an internal combustion engine block. The piston ring used was a nitrided martensitic stainless steel with an asymmetrical profile, and the lubricant oil was the SAE 30 CF, controlled at 40°C. Different testing conditions were carried out in a CETR-UMT-Bruker tribometer, varying loads between 25-125 N, frequencies between 1-12.5 Hz and track length between 3-10 mm. Three maps comparing the average COF and the energetic definition were built, allowing to discuss their similarities. Findings In general, both parameters had similarities especially for low frequencies and small tracks. However, for test conditions that imposed higher accelerations (i.e. longer track lengths and higher frequencies), the energetic COF (COFe) was lower than the average COF (COFa) and presented better agreement in Stribeck-like curves – independent on the experienced lubrication regime along the stroke. As the COFe can be interpreted as a weighted average of instantaneous COF in relation to in-track displacements, an immediate consequence is that instantaneous COF closest to mid-stroke is considered more significant. Furthermore, perturbations associated with the intrinsic accelerations of the movement test are minimized in the COFe formulation. Originality/value The energetic COF parameter (COFe) is presented and compared to the average COF. The new parameter presented less data dispersion and is attractive to evaluate the COF behavior in reciprocating tests, as its formulation minimizes perturbations associated with the intrinsic accelerations of the movement (mainly in the initial and final part of the track where the acceleration has its greatest magnitude). Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0324
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Swensen, Eric E., Jerry L. Purswell, Robert E. Schlegel, and Ronald L. Stanevich. "Coefficient of Friction and Subjective Assessment of Slippery Work Surfaces." Human Factors: The Journal of the Human Factors and Ergonomics Society 34, no. 1 (February 1992): 67–77. http://dx.doi.org/10.1177/001872089203400108.

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Research was conducted to determine how well subjects could distinguish between surfaces with different coefficient of friction (COF) values and to evaluate how well subjective ratings of slipperiness correlated with the actual COF values. Thirty-three ironworkers experienced in working and walking on steel surfaces and 23 university students inexperienced with these tasks participated in the study. Subjective slipperiness ratings for a variety of climbing and walking conditions were obtained from the subjects. It was found that subjects could identify differences in the slipperiness of four types of steel coatings tested in the study. There was a high correlation between the subjective ratings and the measured COF values. Subjects did not slip at a COF of 0.41 but did lose footing at a COF of 0.20.
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Chen, Xiang, Zhong Han, Xiuyan Li, and K. Lu. "Lowering coefficient of friction in Cu alloys with stable gradient nanostructures." Science Advances 2, no. 12 (December 2016): e1601942. http://dx.doi.org/10.1126/sciadv.1601942.

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The coefficient of friction (COF) of metals is usually high, primarily because frictional contacts induce plastic deformation underneath the wear surface, resulting in surface roughening and formation of delaminating tribolayers. Lowering the COF of metals is crucial for improving the reliability and efficiency of metal contacts in engineering applications but is technically challenging. Refining the metals’ grains to nanoscale cannot reduce dry-sliding COFs, although their hardness may be elevated many times. We report that a submillimeter-thick stable gradient nanograined surface layer enables a significant reduction in the COF of a Cu alloy under high-load dry sliding, from 0.64 (coarse-grained samples) to 0.29, which is smaller than the COFs of many ceramics. The unprecedented stable low COF stems from effective suppression of sliding-induced surface roughening and formation of delaminating tribolayer, owing to the stable gradient nanostructures that can accommodate large plastic strains under repeated sliding for more than 30,000 cycles.
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Li, Kai Way, Hsuan Cheng Lin, Ching Chung Chen, Li Wen Liu, and Chih Yong Chen. "Measurements of Friction Coefficient on Kitchen Floors in Restaurants." Applied Mechanics and Materials 303-306 (February 2013): 773–76. http://dx.doi.org/10.4028/www.scientific.net/amm.303-306.773.

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Friction measurements in the field were conducted in twelve restaurants in Taiwan. Four restaurants for each of the Chinese style, western style, and western style fast food restaurant were visited. The Brungraber Mark II slipmeter was adopte to measure the coefficient of friction (COF) in three areas in each of the restaurant. The results showed that three, two Chinese style and one western style, of the restaurants had mean COF lower than 0.5, a safety standard commonly adopted in the USA. Engineering/managerial interventions are required for those restaurants as far as employee safety is concerned. The fast food restaurants had more consistent COF levels than those of the other two types of restaurants as these restaurants only operate down-stream food preparation in the store. The Chinese style restaurants had significantly (p<0.05) lower COF than those of the western style restaurants. This was consistent with the commonly belief that Chinese style cuisine is much greasy, in general, as compared to those of western cooking.
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Dissertations / Theses on the topic "Coefficient Of Friction (COF)"

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Cardoso, Ana Paula Domingos. "Aços galvanizados com aplicação de pós-tratamento para melhoria da estampabilidade em processos de conformação na indústria automobilística." Universidade do Estado de Santa Catarina, 2013. http://tede.udesc.br/handle/handle/1651.

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The present work aims to develop and characterize galvanized steels with chemical post-treatment application, which provides to the metal forming improvement properties. The main reason for this development is related with the fact that the most of zinc coatings problems are related with their sensitivity for abrasion wear during forming process. In view of these difficulties, related with coating steel forming, the Arcelormittal group has been developing Pos-Treatment solutions known as NIT (New Treatment Innorganic) and Pre-phosphate with the main function to promote the improvement of forming properties in deep stamping process through the lubricating properties. The propose solutions was applied over the standard steels known as IF, and galvanized with GI and GA zinc coatings. The forming improvement were evaluated through wear tests by plane friction and pin on disc tribometer, with aim to determine the friction coefficient behaviour for these materials in front of contacts pressure (MPa) application and distance (m). In addition, cracking potential analysis was done through Erichsen and weight loss methods to evaluate the powdering failure possibility. The post-treatment microstructure was evaluated through MEV and FEG-EDS analysis. As a complement study was simulated remobility tests to reproduce one step of the automotive process that can be negative influenced by post treatment application waste on the strip after forming and was evaluated the material corrosion potential in humidity tests cycles
O presente trabalho tem o objetivo de desenvolver e caracterizar aços galvanizados com aplicação de pós-tratamento químico, que visam proporcionar ao metal melhoria de conformabilidade. A justificativa principal deste estudo esta no fato de que o principal problema de revestimentos à base de zinco vêm a ser a sua sensibilidade ao processo de desgaste por abrasão, podendo danificar tanto a peça revestida, como as ferramentas das prensas de estampagem, principalmente no processamento de peças críticas voltados para aplicações da indústria automotiva. Diante destas dificuldades, o grupo ArcelorMittal tem desenvolvido a aplicação de soluções de pós-tratamento do tipo NIT (New Innorganic Treatment) e pré-fosfato , com a função de promover ao aço galvanizado, melhoria de conformabilidade e , através da propriedade de lubrificação, durante processos de estampagem de peças de alta criticidade. As soluções propostas foram aplicadas sobre os aços convencionais do tipo IF, galvanizados com revestimento base Zn denominados GI e GA. Os ganhos de conformação foram avaliados por ensaios de desgaste realizados em tribômetros de fricção planar e pino sobre disco, a fim de avaliar o comportamento do coeficiente de atrito destes materiais diante da aplicação de determinadas pressões de contato (MPa) e distância percorrida (m). Além disto, foram realizados ensaios de avaliação de potencial de fratura do material através de testes em prensa de embutimento Erichsen e Perda de Massa, método este que visa avaliar a possibilidade de ocorrência de fragilizações por Powdering. Com intuito de conhecer a microestrutura dos filmes de póstratamento depositados sobre o aço revestido foram realizadas análises metalográficas via MEV e FEG-EDS. Como complemento ao trabalho foram realizados ensaios de remobilidade dos filmes aplicados, simulações de uma das etapas de processos da indústria automotiva que podem vir a sofrer influência do pós-tratamento após estampagem do material e avaliação do potencial de corrosão em ciclos de câmara úmida.
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Paes, Eliel dos Santos. "Ultra baixo coeficiente de atrito no deslizamento de Si3N4-Al2O3. Efeitos da força aplicada, velocidade de deslizamento e temperatura do ensaio." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-16112012-115902/.

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Foram realizados ensaios tribológicos de deslizamento do par Si3N4-Al2O3, lubrificado com água, na configuração esfera contra disco, sendo a esfera de nitreto de silício e o disco de alumina para investigar a influência da velocidade de deslizamento, da carga aplicada e da temperatura no coeficiente de atrito. As esferas de nitreto de silício e os discos de alumina foram caracterizados determinando-se: densidades, dureza Vickers, módulo de elasticidade e tenacidade à fratura. Os ensaios foram realizados com rugosidade inicial nos discos de Rrms = 352 nm. O regime de ultra baixo coeficiente de atrito (UBCA, μ < 0,01) foi atingido após um período de running-in de aproximadamente uma hora e o coeficiente de atrito ficou na faixa de μ = 0,008 a μ = 0,002. Os resultados mostraram que este sistema deslizante tem características hidrodinâmicas, pois o coeficiente de atrito diminuiu com o aumento da velocidade de deslizamento. Uma variação suave da carga aplicada fez com que o coeficiente de atrito permanecesse no regime de UBCA, com a carga aplicada variando de 54 N até 94 N. Em temperaturas menores ou iguais a 11°C o sistema não atingiu o regime de UBCA e o coeficiente de atrito final ficou da ordem de centésimos. Foi observado o fenômeno de UBCA em temperaturas de 30 e 40°C. No entanto, nestas temperaturas, a baixa viscosidade da água não deveria permitir que o sistema atingisse o regime de UBCA. A análise dos dados possibilitou inferir que durante o regime de UBCA o sistema desliza num regime de lubrificação mista, sendo lubrificação hidrodinâmica, devido ao filme de água, somada a lubrificação limite, devido às camadas hidratadas formadas nas superfícies das cerâmicas. Os resultados mostraram que a temperatura influencia no desgaste das cerâmicas. A determinação do volume desgastado possibilitou observar que durante os ensaios a alumina sofre menos desgaste que o nitreto de silício e que o desgaste de ambas cerâmicas aumenta com o aumento da temperatura.
Tribological tests were conducted in a ball on disk setup, using water as lubricant. Were used a silicon nitride ball and alumina disk. The tests were conducted to investigate the effects of sliding speed, applied load and temperature on friction coefficient. The silicon nitride balls and alumina disks were characterized by determining density, Vickers hardness, elastic modulus and fracture toughness. The tests were conducted with initial roughness on the disk surface of 352 nm. The ultra low friction coefficient regime (ULFC, μ < 0.01) was reached after a running-in period of approximately one hour and the friction coefficient remains in the range of μ = 0.008 a μ = 0.002 during this steady state regime. The results showed that this sliding system has hydrodynamic characteristics, because the friction coefficient decreased with increasing of the sliding speed. With an smooth variation of the applied load the system remained in the ULFC regime, when the applied load varied from 54 N up to 94 N. At temperatures below or equal to 11°C the system did not reach the ULFC regime and the final friction coefficient was the order of hundredths. We observed the ULFC phenomenon at temperatures of 30 and 40°C. However, at these temperatures, the water viscosity is low and should not allow the system to reach the ULFC regime. The data analysis allowed infer that during the ULFC regime the system slides with a mixed lubrication regime, hydrodynamic plus limitrofe, the first due to water film and the second due to the hydrated layer formed on the ceramics surfaces. The results showed a influences of temperature in the ceramics wear. The results of the worn volume allowed to observe that during the tests alumina suffers less wear than the silicon nitride, and the ceramics wear increases with increasing temperature.
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Ogata, Paulo Henrique. "Compósitos ferro-grafita para componentes de motores com propriedades tribológicas melhoradas." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-16112015-155422/.

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A constante busca por motores com maior eficiência energética, requer a introdução de novos materiais ou inovações nas rotas de fabricação dos materiais existentes. O presente trabalho busca, a partir de rotas de tratamento térmico, soluções para minimizar o desgaste originado no contato entre corpos metálicos em componentes submetidos a altas pressões de contato em regime lubrificado. A modificação microestrutural a partir de tratamentos térmicos originou matriz martensítica relativamente dura com uma dispersão refinada de nódulos esféricos de grafita, que atuariam como lubrificantes sólidos. O estudo baseou-se em dois ferros fundidos (cinzento e branco) submetidos a tratamentos de austenitização seguidos de tempera em óleo e revenimento em diferentes tempos. Ensaios de dilatometria foram efetuados nos dois materiais para estudar a cinética de grafitização secundaria sob diferentes condições de tratamento térmico. As propriedades mecânicas foram avaliadas por medidas de dureza Vickers das amostras tratadas termicamente. Amostras de ferro fundido cinzento e de branco modificado por tratamentos térmicos foram ensaiadas em teste de desgaste por deslizamento, com intuito de avaliar a influência de modificações na superfície no coeficiente de atrito.
The constant search for engines with higher energy efficiency requires the development of new materials or manufacturing innovations on the routes of existing materials. In the present work, heat treatment routs were investigated to minimize wear originated at the contact between metallic bodies into components subjected to high contact pressures in lubricated regime. Microstructural modification from heat treatments yielded relatively hard martensitic matrix with a fine dispersion of spherical graphite nodules, which act as solid lubricants. The study was based on two cast iron (gray and white) undergoing treatments of soaking (austenitizing) followed by quenching in oil and tempering at different times. Dilatometry tests were performed on both materials to study the kinetics of secondary graphitization under different heat treatment conditions. Mechanical properties were evaluated from Vickers hardness of the thermally treated samples. Samples of gray cast iron and white modified by heat treatments were tested in sliding wear test, in order to assess the influence of changes in the surface friction coefficient.
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Balarini, Junior Roberto. "Ultra baixo coeficiente de atrito no deslizamento de Si3N4 Al2O3 em água: estudo ab initio do running-in." Universidade Federal do Espírito Santo, 2013. http://repositorio.ufes.br/handle/10/6236.

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Este trabalho é uma investigação tribológica envolvendo o par cerâmico composto por esferas de nitreto de silício (Si3N4) deslizando contra discos de óxido de alumínio (Al2O3) em água. No total, dez ensaios foram conduzidos com a intenção de reproduzir o fenômeno de Ultra Baixo Coeficiente de Atrito (UBCA) em laboratório, o qual é caracterizado pela obtenção de valores de coeficiente de atrito (μ) da ordem dos milésimos (μ < 0,01) no regime estacionário. Uma vez alcançado os valores de UBCA, o objetivo principal deste trabalho foi o de investigar o período de running-in, através de uma série de análises em relação ao comportamento do coeficiente de atrito durante o regime transitório, incluindo correlações com algumas variáveis, como rugosidade superficial, erros de batimento axial, íons formados durante o deslizamento e desgaste das cerâmicas. Para isto, as curvas de coeficiente de atrito por tempo foram expandidas para intervalos de tempos pré-determinados e o comportamento de μ em cada um destes intervalos foi investigado e comparado entre os ensaios realizados, sendo que o caráter oscilatório do coeficiente de atrito foi inserido nas análises do período transitório. Em geral, foi comprovado que maiores valores de rugosidade superficial resultaram em maiores períodos de running-in e que existe uma tendência de aumento de desgaste com o aumento do tempo de transição. Para todos os ensaios, a taxa de desgaste das esferas de Si3N4 foi superior à dos discos de Al2O3. Em adição, através de comparações entre a medida da soma das rugosidades das superfícies desgastadas com a espessura mínima do filme lubrificante, este trabalho confirma a hipótese de que é necessário um regime de lubrificação misto (hidrodinâmico e limítrofe) para a obtenção do regime de UBCA, sendo que, para a eficácia do modo de lubrificação esperado, estima-se que é necessário concentrações de íons de silício (Si) superiores a 1,3 mg/l, aproximadamente. Esta quantidade de íons Si é supostamente a mínima necessária para a formação de uma camada de sílica adequada para conferir a parcela de lubrificação limítrofe necessária para a obtenção do regime de UBCA
This work is a tribological investigation involving the ceramic pair composed by balls of silicon nitride (Si3N4) sliding against disks of aluminum oxide (Al2O3) under water. A total of ten tests were conducted in order to reproduce the phenomenon of Ultra Low Friction Coefficient (ULFC) in laboratory, which is characterized by obtaining values of friction coefficient (μ) below of 0,01 in the steady state. Once reached these values, the main objective of this study was to investigate the running-in period by a series of analyses in relation to the behavior of the friction coefficient during the running-in period, including correlations with some variables such as surface roughness, axial parallelism errors, ions formed during the sliding and wear of samples. For this reason, the curves of friction coefficient versus time were expanded for some predetermined intervals and the behavior of μ for each one of these intervals was investigated and compared between themselves, and the oscillatory behavior of the friction coefficient was inserted into the analysis of the running-in period. In general, it was concluded that higher values of surface roughness resulted in longer periods of running-in and that there is a trend of increasing wear with increasing time of transition. For all tests, the wear rate of the silicon nitride balls was higher than alumina disks. In addition, by comparing the measure of the sum of the roughness of the worn surfaces with minimum thickness of the lubricant film, the present work confirms the hypothesis that it is necessary a mixed lubrication (hydrodynamic combined with boundary) to obtain the regime of ULFC and for effective lubrication expected mode it is estimated that is required an ions concentration of silicon (Si) higher than 1.3 mg/l approximately. This amount of ions Si is supposed to be the minimum necessary for the formation of a silica layer enable to confer the boundary lubrication participation for obtaining the ULFC
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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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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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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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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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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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Books on the topic "Coefficient Of Friction (COF)"

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Forland, Kathryn A. Kinetic friction coefficient of ice. [Hanover, N.H.]: US Army Corps of Engineers, Cold Regions Research & Engineering Laboratory, 1985.

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B, Oswald Fred, Townsend Dennis P, and United States. National Aeronautics and Space Administration., eds. Measurement of gear tooth dynamic friction. [Washington, DC]: National Aeronautics and Space Administration, 1996.

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Healy, Alan Gerard. An investigation of methods of measuring the coefficient of friction of roadstone. [London]: Queen Mary and Westfield College, 1997.

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Nagel, F. A method for the approximate calculation of the skin friction coefficient of horizontal wavy plates. Rhode Saint Genese, Belgium: von Karman Institute for Fluid Dynamics, 1987.

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Miyoshi, Kazuhisa. Durability evaluation of selected solid lubricating films. [Cleveland, Ohio]: National Aeronautics and Space Administration, Glenn Research Center, 2001.

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L, Thom R., and George C. Marshall Space Flight Center., eds. Database for the tribological properties of self-lubricating materials. Marshall Space Flight Center, Ala: National Aeronautics and Space Administration, Marshall Space Flight Center, 1998.

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L, Thom R., and George C. Marshall Space Flight Center., eds. Database for the tribological properties of self-lubricating materials. Marshall Space Flight Center, Ala: National Aeronautics and Space Administration, Marshall Space Flight Center, 1998.

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Zaharioudakis, Nikolaos I. An investigation of performance of aggregate mixtures by measuring their skid-resistance and coefficient of friction. [London]: Queen Mary and Westfield College, 1998.

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Miyoshi, Kazuhisa. Surface chemistry, friction, and wear properties of untreated and laser-annealed surfaces of pulsed-laser-deposited WS₂ coatings. [Washington, D.C: National Aeronautics and Space Administration, 1996.

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Miyoshi, Kazuhisa. Surface chemistry, friction, and wear properties of untreated and laser-annealed surfaces of pulsed-laser-deposited WS₂ coatings. [Washington, D.C: National Aeronautics and Space Administration, 1996.

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Book chapters on the topic "Coefficient Of Friction (COF)"

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Ahmad, Norazrin Azwani, Masine Md. Tap, Ardiyansyah Syahrom, and Jafri Mohd. Rohani. "The Relationship Between Coefficient of Friction (COF) with Floor Slipperiness and Roughness." In Quantitative and Qualitative Factors that Leads to Slip and Fall Incidents, 21–31. Singapore: Springer Singapore, 2016. http://dx.doi.org/10.1007/978-981-10-3286-8_3.

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Blau, Peter J. "Friction Coefficient." In Encyclopedia of Tribology, 1304–6. Boston, MA: Springer US, 2013. http://dx.doi.org/10.1007/978-0-387-92897-5_169.

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Gooch, Jan W. "Friction Coefficient." In Encyclopedic Dictionary of Polymers, 327–28. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_5316.

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Gooch, Jan W. "Coefficient of Friction." In Encyclopedic Dictionary of Polymers, 151. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_2533.

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Man, George, and Mao-Qiang Man. "Skin Friction Coefficient." In Agache's Measuring the Skin, 203–10. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-32383-1_20.

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Shang, De-Yi, and Liang-Cai Zhong. "Skin-Friction Coefficient." In Heat and Mass Transfer, 81–90. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-94403-6_7.

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Shang, De-Yi, and Liang-Cai Zhong. "Skin-Friction Coefficient." In Heat Transfer of Laminar Mixed Convection of Liquid, 129–38. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-27959-6_9.

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Man, George, and Mao-Qiang Man. "Skin Friction Coefficient." In Agache’s Measuring the Skin, 1–8. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-26594-0_20-1.

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Gooch, Jan W. "Coefficient of Friction, Kinetic." In Encyclopedic Dictionary of Polymers, 151. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_2534.

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Gooch, Jan W. "Coefficient of Friction, Static." In Encyclopedic Dictionary of Polymers, 151. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_2535.

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Conference papers on the topic "Coefficient Of Friction (COF)"

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Cummings, Scott, Tom McCabe, Glenn Guelde, and Dan Gosselin. "Brake Shoe Coefficient of Friction Variation." In ASME 2009 Rail Transportation Division Fall Technical Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/rtdf2009-18022.

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A series of dynamometer tests were conducted by the Wheel Defect Prevention Research Consortium (WDPRC) to quantify the amount of expected variation in brake shoe coefficient of friction (COF) and resulting wheel temperature throughout the life of an individual brake shoe. Variations in brake shoe COF within an individual railcar are one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. High friction composition and tread conditioning brake shoes were installed in the “as manufactured” condition with no wear-in or machining at the beginning of the test matrix which consisted of seventeen stop tests and twelve grade tests. For each brake shoe tested, the average COF and maximum wheel temperature were recorded during eleven identical light grade tests interspersed throughout the test matrix.
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Marinack, Martin C., Patrick S. M. Dougherty, and C. Fred Higgs. "Single Particle Interaction Properties: Investigations on the Coefficient of Restitution and Coefficient of Friction." In ASME/STLE 2012 International Joint Tribology Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ijtc2012-61165.

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Understanding granular flows has always been important for predicting natural phenomena such as rockslides and soil erosion, as well as industrial processes such as coal-based fossil fuel systems and solids processing. As such, it becomes important to understand granular flows from both a classical granular flow and tribological perspective. Inherently important in the study of granular flows is the study of the individual particle level interactions, which define the global behavior of the flow. The current work examines both the coefficient of restitution (COR) and coefficient of friction (COF) for various material combinations. COR and tribological experiments are performed on various sphere and plate (disk) materials, such as low carbon steel, tungsten carbide (WC), and NITINOL 60.
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Lee, HyunWook, Corina Sandu, Carvel Holton, and Mehdi Ahmadian. "An Empirical Approach to Modeling the Friction Coefficient for Wheel-Rail Contact." In ASME 2009 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/detc2009-86429.

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The coefficient of friction (CoF) is one of the most important parameters for the contact between the wheel and the rail. Accurate estimation or measurement of the CoF has a very important role, both in terms of modeling the train dynamics and in terms of reducing operational costs in the long-term. For ease of implementation, since the nature of the wheel-rail contact dynamics is very complex, the assumption of a constant CoF is still used in most theoretical studies. Nevertheless, experimental work indicates that the CoF depends on dynamic changes in various wheel-rail conditions, like sliding velocity, contact patch shape and size for stick and sliding region, wheel and rail geometry, wheel vibration, rail surface roughness and/or lubrication, etc. In this paper we present the proposed equation to model the nonlinear dry friction coefficient at the wheel-rail contact. The friction coefficient is calculated at the three different values for change in the damping ratio while maintaining all the other conditions the same. As expected, the analysis performed to estimate the dry friction coefficient based on the proposed equation and using NUCARS® simulation results shows that the coefficient of friction has a highly nonlinear dependence on its parameters.
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Ishida, Makoto, Fusayoshi Aoki, Yasutomo Sone, Takumi Ban, and Kensuke Shirouzu. "Rail Corrugations Caused by Low Coefficient of Friction in a Submarine Railway Tunnel." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-64346.

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One of some types of rail corrugations is caused on railway rail surface in a submarine tunnel. It poses a large problem from the aspects of railway vehicle and railway track deterioration. In this paper, the mechanism of the rail corrugations was studied with the focus placed on roll-slip of wheel and rail interface. Traction and vertical force interacting between wheel and rail were investigated by a vehicle/track interaction model, and the coefficient of friction (COF) on rail surface was measured. Also, the rail surface was analysed with infrared to understand the chemical composition of surface layer influenced by salty and very humid atmosphere in the submarine tunnel. β-FeOOH was found out as a cause of reducing COF on rail surface.
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Waikar, R. A., and Y. B. Guo. "The Effect of Machining Induced White Layer on Frictional and Wear Performance at Dry and Lubricated Sliding Contact." In ASME/STLE 2009 International Joint Tribology Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/ijtc2009-15112.

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A white layer on a machined surface is often produced at abusive machining conditions. However, the effect of white layer on frictional and wear performance has received little attention. This study has shown that the existence of a turned white layer slightly decreases the coefficient of friction (COF), while a ground white layer significantly increases COF at dry conditions. At lubricated conditions, the turned white layer only slightly increases COF while the ground white layer slightly reduces it. The third body wear debris may act as solid lubricants leading to reduced friction.
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Lorenço, Marcelo A., Paulo R. Barbosa, Adilson R. Costa, Rafael H. M. Siqueira, and Milton S. F. Lima. "Effects of a laser surface treatment in a press-hardened steel on the coefficient of friction." In Latin America Optics and Photonics Conference. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/laop.2022.m4c.4.

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Singh, Gurjeet, and Kurt Beschorner. "Influence of Hydrodynamic Fluid Pressure and Shoe Tread Depth on Available Coefficient of Friction." In ASME/STLE 2012 International Joint Tribology Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ijtc2012-61173.

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Slip and fall accidents are a major occupational health concern. Identifying the lubrication mechanisms affecting shoe-floor-contaminant friction under biofidelic (testing conditions that mimic human slipping) conditions is critical to identifying unsafe surfaces and designing a slip-resistant work environment. The purpose of this study is to measure the effects of varying tread design, tread depth and fluid viscosity on underfoot hydrodynamic pressure, the load supported by the fluid (i.e. load carrying capacity), and the coefficient of friction (COF) during a simulated slip. A single vinyl floor material and two shoe types (work shoe and sportswear shoe) with three different tread depths (no tread, half tread and full tread) were tested under two lubrication conditions: 1) 90% glycerol and 10% water (219 cP) and 2) 1.5% Detergent-98.5% (1.8cP) water solutions. Hydrodynamic pressures were measured with a fluid pressure sensor embedded in the floor and a forceplate was used to measure the friction and normal forces used to calculate coefficient of friction. The study showed that hydrodynamic pressure developed when high viscosity fluids were combined with no tread and resulted in a major reduction of COF (0.005). Peak hydrodynamic pressures (and load supported by the fluid) for the no tread-high viscous conditions were 234 kPa (200.5 N) and 87.63 kPa (113.3 N) for the work and sportswear shoe, respectively. Hydrodynamic pressures were negligible when at least half the tread was present or when a low viscosity fluid was used despite the fact that many of these conditions also resulted in dangerously low COF values. The study suggests that hydrodynamic lubrication is only relevant when high viscous fluids are combined with little or no tread and that other lubrication mechanisms besides hydrodynamic effects are relevant to slipping like boundary lubrication.
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Shafiei, M., and A. T. Alpas. "Friction and Wear Behaviour of Nanocrystalline Nickel." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-64315.

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The tribological behaviours of conventional nickel with a grain size of 20±5 μm and nanocrystalline (nc) nickel with a grain size of 15±3 nm were compared. A pin-on-disc tribometer was employed for the friction and wear measurements under unlubricated conditions in ambient air with ∼35% relative humidity. As the grain size was decreased to the nanometer size, a reduction of about 18% was observed in the peak value of coefficient of friction (COF), but the steady-state COF remained almost unchanged. Also it was shown that the wear rate of nc nickel was about 82% lower than that of conventional nickel at 2 N load. This behaviour is mainly attributed to considerable reduction in plastic deformation and microplowing due to increased hardness.
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Lee, HyunWook, Corina Sandu, and Carvel Holton. "Wheel-Rail Dynamic Model and Stochastic Analysis of the Friction in the Contact Patch." In 2010 Joint Rail Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/jrc2010-36229.

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The coefficient of friction (CoF) is one of the most important parameters for characterizing the contact between the wheel and the rail. The assumption of a constant CoF is still used in most theoretical studies, although experimental work indicates that the CoF depends on material and dynamic parameters. In the real world, accurate estimation of the CoF is not simple due to various uncertainties. In this paper we present a new 3D nonlinear dry CoF model at the wheel-rail contact. In addition, a stochastic analysis using the polynomial chaos theory is performed with the CoF model. The maximum amplitude of rail roughness and the lateral displacement of the wheel are considered as uncertain parameters in this study. One of the novelties in this study is that our CoF model captures the maximum CoF value (an initial peak) when the wheel starts to move. The stochastic analysis results show that the CoF probability density function (PDF) of a combination of two uncertain parameters has wider PDF ranges than the PDF obtained for only one uncertain parameter. The current work demonstrates that the CoF is strongly affected by the stochastic variation of dynamic parameters. In reality, the CoF is critical to rail tractive performance and efficiency. Thus, the PDF distribution of the CoF must be accounted for in the design of the wheel-rail system.
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Handoko, Budi Basuki, and Rini Dharmastiti. "Numerical Study on the Effects of Coefficient of Friction to the Dynamic Sliding Contact between Bearing and Talar Components of Metal on Polymer Total Ankle Replacement Implants." In International Conference on Mechanical Engineering. Switzerland: Trans Tech Publications Ltd, 2023. http://dx.doi.org/10.4028/p-s80w27.

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Coefficient of friction (cof) is an important variable when dealing with con-tact between mechanical parts. It depends on various tribological variables and the value can be determined only by experiments. Cof correlates with the wear of material and this is a severe problem in biomedical engineering. This research numerically studied the effects of cof between talar and bear-ing in the total ankle replacement (TAR) implants. The aim is to evaluate the contact situations affected by cof. The TAR models consist of cobalt chrome (CoCr) alloy and ultra high molecular weight polyethylene (UHMWPE) bio-materials. Five cof values of the dry, lubricated and frictionless TAR me-chanical contacts under ankle gait load were examined. The models use a fixed 1 mm element size for UHMWPE bearing component and four element sizes for the talar component, range from 1 mm to 0.4 mm. Results show that, 1) higher cof induces higher contact pressure, 2) contact stress is not af-fected by cof, 3) proper talar element size is 0.4 mm and 4) frictionless model can be used for the TAR contact mechanic computation. Frictionless model calculates equal contact stress and lower contact pressures with an error of 2.68 % compared to the smooth model.
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Reports on the topic "Coefficient Of Friction (COF)"

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Wei, Fulu, Ce Wang, Xiangxi Tian, Shuo Li, and Jie Shan. Investigation of Durability and Performance of High Friction Surface Treatment. Purdue University, 2021. http://dx.doi.org/10.5703/1288284317281.

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The Indiana Department of Transportation (INDOT) completed a total of 25 high friction surface treatment (HFST) projects across the state in 2018. This research study attempted to investigate the durability and performance of HFST in terms of its HFST-pavement system integrity and surface friction performance. Laboratory tests were conducted to determine the physical and mechanical properties of epoxy-bauxite mortar. Field inspections were carried out to identify site conditions and common early HFST distresses. Cyclic loading test and finite element method (FEM) analysis were performed to evaluate the bonding strength between HFST and existing pavement, in particular chip seal with different pretreatments such as vacuum sweeping, shotblasting, and scarification milling. Both surface friction and texture tests were undertaken periodically (generally once every 6 months) to evaluate the surface friction performance of HFST. Crash records over a 5-year period, i.e., 3 years before installation and 2 years after installation, were examined to determine the safety performance of HFST, crash modification factor (CMF) in particular. It was found that HFST epoxy-bauxite mortar has a coefficient of thermal expansion (CTE) significantly higher than those of hot mix asphalt (HMA) mixtures and Portland cement concrete (PCC), and good cracking resistance. The most common early HFST distresses in Indiana are reflective cracking, surface wrinkling, aggregate loss, and delamination. Vacuum sweeping is the optimal method for pretreating existing pavements, chip seal in particular. Chip seal in good condition is structurally capable of providing a sound base for HFST. On two-lane highway curves, HFST is capable of reducing the total vehicle crash by 30%, injury crash by 50%, and wet weather crash by 44%, and providing a CMF of 0.584 in Indiana. Great variability may arise in the results of friction tests on horizontal curves by the use of locked wheel skid tester (LWST) due both to the nature of vehicle dynamics and to the operation of test vehicle. Texture testing, however, is capable of providing continuous texture measurements that can be used to calculate a texture height parameter, i.e., mean profile depth (MPD), not only for evaluating friction performance but also implementing quality control (QC) and quality assurance (QA) plans for HFST.
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Dumas, Alexis, André Bégin-Drolet, and Julien Lépine. Development of a ski testing machine based on the effective friction coefficient for classic cross-country skis. Purdue University, 2022. http://dx.doi.org/10.5703/1288284317548.

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Kedzierski, Mark A., and Donggyu Kang. Horizontal convective boiling of R1234yf, R134a, and R450A within a micro-fin tube :. Gaithersburg, MD: National Institute of Standards and Technology (U.S.), August 2017. http://dx.doi.org/10.6028/nist.tn.1966.

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This report presents local convective boiling heat transfer and Fanning friction factor measurements in a micro-fin tube for R134a and two possible low global warming potential (GWP) refrigerant replacements for R134a: R1234yf and R450A. Test section heating was achieved with water in either counterflow or in parallel flow with the test refrigerant to provide for a range of heat fluxes for each thermodynamic quality. An existing correlation from the literature for single and multi-component mixtures was shown to not satisfactorily predict the convective boiling measurements for flow qualities greater than 40 %. Accordingly, a new correlation was developed specifically for the test fluids of this study so that a fair comparison of the heat transfer performance of the low GWP refrigerants to that of R134a could be made. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting example comparison, for the same operating conditions, showed that the heat transfer coefficient of the multi-component R450A and the single-component R1234yf were, on average, 15 % less and 5 % less, respectively, than that of the single-component R134a. Friction factor measurements were also compared to predictions from an existing correlation. A new correlation for the friction factor was developed to provide a more accurate prediction. The measurements and the new models are important for the evaluation of potential low-GWP refrigerants replacements for R134a.
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4

Cao Romero, Julio A., Jorge Reyes-Avendaño, Julio Soriano, Leonardo Farfan-Cabrera, and Ali Erdemir. A Pin-on-Disc Study on the Electrified Sliding Wear of EVs Powertrain Gears. SAE International, March 2022. http://dx.doi.org/10.4271/2022-01-0320.

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In contrast to conventional powertrains from internal combustion engine vehicles (ICEV), the tribological performance of powertrains of electric vehicles (EVs) must be further evaluated by considering new critical operating conditions such as electrical environments. The operation of any type of electric motor produces shaft voltages and currents due to various hardware configurations and factors. Furthermore, the common application of inverters intensifies this problem. It has been reported that the induced shaft voltages and currents can cause premature failure problems in tribological components such as bearings and gears due to accelerated wear and/or fatigue. It is ascribed to effects of electric discharge machining (EDM), also named, sparking wear caused by shaft currents and poor or increasingly diminishing dielectric strength of lubricants. A great effort has been done to study this problem in bearings, but it has not yet been the case for gears. Considering that EVs powertrains can be configurated with an electric motor coupled to a single-speed or multi-speed transmission, it is expected that shaft currents can also affect gears to some extent. The pin-on-disc test has been widely used to study sliding wear of gear materials under comparable or realistic operating conditions. This accelerated test is effective for screening materials, lubricants and operating conditions allowing evaluations of their friction and wear properties. However, it has not been implemented for studying gear materials under electrified environments. Thus, this paper aims to explore the friction coefficient and wear of gear materials under non-electrified and electrified sliding in a pin-on-disc tester applying typical of EVs powertrain shaft currents during sliding. The tests were carried out at two different DC currents under comparable gear dry and lubricated sliding contact conditions. Friction coefficient, wear volumes and morphologies were evaluated and reported in this work.
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5

EFFECT OF RANDOM PRE-STRESSED FRICTION LOSS ON THE PERFORMANCE OF A SUSPEN-DOME STRUCTURE. The Hong Kong Institute of Steel Construction, March 2022. http://dx.doi.org/10.18057/ijasc.2022.18.1.5.

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The key to the high-efficiency performance of the suspen-dome structure is to apply the pre-stressed design value to the structure accurately. However, engineering practice has found that the use of tensioning hoop cables to apply the pre-stress will produce noticeable pre-stressed friction loss (PFL), which significantly affects the safety performance of the structure. In this paper, based on a 1:10 scaled-down experiment model of a suspen-dome structure with rolling cable-strut joint installed, the random PFL (RPFL) effect of the suspen-dome on structure performance was analyzed through a probability statistics theory. First, aiming at the unequal tensioning force at both sides of the tensioned hoop cable during the tensioning process, a pre-stressed force calculation method is proposed that considers the unequal tensioning control force and RPFL at all cable–strut joints, and the reliability of this method is verified through a tension test. Then, based on the cable-joint tension test carried out in the early stage of the research group, a random mathematical model of the friction coefficient (FC) at the rolling cable–strut joint is established. And then, the cable force calculation method is used to establish the random finite element model, and independent and random changes in the FC at each rolling cable–strut joint can be considered. Subsequently, the Monte Carlo method is used to calculate the random mathematical characteristics of the mechanical performance parameters such as the member stress and joint deformation, and the obtained results are verified through a static loading experiment. In addition, to investigate the effect of random defects on structural stability, other random defects, such as the initial curvature and installation deviation, were continuously introduce based on the random finite element model. As such, we could obtain the law of the effect of multi-defect random variation coupling on the structure’s ultimate bearing capacity.
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