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Sample records for average friction coefficient

  1. Self-Excited Vibrations in Turning: Efforts Torsor and Average Friction Coefficient Analysis

    CERN Document Server

    Gérard, Alain; Zapciu, Miron

    2009-01-01

    An experimental device in turning including, in particular, a six-component dynamometer is exploited to measure the complete torque of cutting forces in a case of self-excited vibrations. For the tests, the tool used is type TNMA 16 04 12 carbide not covered (nuance carbide-SUMITIMO ELECTRIC), without chip breeze. The machined material is an alloy of chrome molybdenum type 42 CrMo24. The test-tubes are cylindrical with a diameter of 120 mm and a length of 30 mm. The effort of analysis relates to the moments. In particular, to the tool tip point, when feed rate increases the friction coefficient of swivelling is increasing while that of bearing is decreasing. Innovative remarks on the evolution of the average friction coefficient for various depths of cut and feed rate are presented

  2. Energy Balance of Friction and Friction Coefficient in Energetical Interpretation

    Directory of Open Access Journals (Sweden)

    S.V. Fedorov

    2015-09-01

    Full Text Available Sliding friction energy model is proposed. In this model, generalized mechanism of transformation and dissipation of energy under friction the model of elastic-plastic deformation and fracture contact volumes is considered. Energy model of the process of plastic deformation and destruction of solid bodies is based on the concept of ergodynamic of deformable bodies. Equations of energy balance of friction within the structural and energetic interpretation of deformation are proposed. The energy interpretation of the coefficient of friction is showed. From this position the friction coefficient is the most informative characteristic of the process. Experimental friction curves have been generalized. As a result of the energy analysis of friction, the energy diagram of the structural evolution of the friction surfaces is suggested.

  3. Friction coefficient dependence on electrostatic tribocharging

    Science.gov (United States)

    Burgo, Thiago A. L.; Silva, Cristiane A.; Balestrin, Lia B. S.; Galembeck, Fernando

    2013-08-01

    Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro- and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro- and nanoscale friction coefficients in PTFE and probably in other insulating polymers.

  4. Graphite friction coefficient for various conditions

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The friction coefficient the graphite used in the Tsinghua University 10MW High Tem-perature Gas-Cooled Reactor was analyzed for various conditions. The variation of the graphitefriction coefficient was measured for various sliding velocities, sliding distances, normal loads, en-vironments and temperatures. A scanning elector microscope (SEM) was used to analyze the fric-tion surfaces.

  5. High Speed Friction Microscopy and Nanoscale Friction Coefficient Mapping

    OpenAIRE

    Bosse, James L.; Lee, Sungjun; Huey, Bryan D; Andersen, Andreas Sø; Sutherland, Duncan S

    2014-01-01

    As mechanical devices in the nano/micro length scale are increasingly employed, it is crucial to understand nanoscale friction and wear especially at technically relevant sliding velocities. Accordingly, a novel technique has been developed for Friction Coefficient Mapping (FCM), leveraging recent advances in high speed AFM. The technique efficiently acquires friction versus force curves based on a sequence of images at a single location, each with incrementally lower loads. As a result, true...

  6. Friction analysis of kinetic schemes : the friction coefficient

    NARCIS (Netherlands)

    Lolkema, Juke S.

    1995-01-01

    Friction analysis is proposed as the application of general control analysis to single enzymes to describe the control of elementary kinetic steps on the overall catalytic rate. For each transition, a friction coefficient is defined that measures the sensitivity of the turnover rate to the free ener

  7. FRICTION ANALYSIS OF KINETIC SCHEMES - THE FRICTION COEFFICIENT

    NARCIS (Netherlands)

    LOLKEMA, JS

    1995-01-01

    Friction analysis is proposed as the application of general control analysis to single enzymes to describe the control of elementary kinetic steps on the overall catalytic rate. For each transition, a friction coefficient is defined that measures the sensitivity of the turnover rate to the free ener

  8. Kinetic Friction Coefficient of Ice,

    Science.gov (United States)

    1985-03-01

    For the hardest ice tested (xi = 0.33 described by Rabinowicz (1965), where To is inter- mm, H, = 1525 kPa), the calculated values of a preted as...material with a low elastic pressures. The frictional force was measured at modulus ( Rabinowicz 1965). It has been observed the application point of...tion 10, pp. 8-16. Barnes, P. and D. Tabor (1966) Plastic flow and Rabinowicz , E. (1965) Friction and Wear of Mate- pressure melting in the deformation

  9. Study on the Friction Coefficient in Grinding

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The friction between the abrasive grains and workpi ec e is a crutial factor determining the main grinding output. Few studies have bee n carried out investigating the values of the friction coefficient in grinding, due to the difficulty of direct measurement. In this paper, a mathematical model of the friction coefficient in grinding has been established with the aid of a new grinding parameter C ge, which has close relations to wheel wear rate Z s, metal removal rate Z w, specific energy u and gr...

  10. Monomeric Friction Coefficient of Metalnanodispersible Polymeric Systems

    Directory of Open Access Journals (Sweden)

    B.B. Kolupayev

    2016-12-01

    Full Text Available Influence of a nanodispersible metal excipient in number of 0    5,0 vol.% Cu for the size of a monomeric friction coefficient of polyvinylchloride (PVC systems in temperature range 298  Т  (Tg + 10 K is investigated. It is shown that various types of coordination movements of building blocks are described by a friction coefficient which serves as a measure of influence of external fields and ingredients on viscoelastic behavior of a composite. The analysis of processes of a relaxation on the basis of the theory of flexible chains taking into account power and entropic factors is carried out.

  11. Friction Experiments for Dynamical Coefficient Measurement

    Directory of Open Access Journals (Sweden)

    J. J. Arnoux

    2011-01-01

    Full Text Available An experimental study, including three experimental devices, is presented in order to investigate dry friction phenomena in a wide range of sliding speeds for the steel on steel contact. A ballistic setup, with an air gun launch, allows to estimate the friction coefficient between 20 m/s and 80 m/s. Tests are completed by an adaptation of the sensor on a hydraulic tensile machine (0.01 m/s to 3 m/s and a pin-on-disk tribometer mounted on a CNC lathe (1 to 30 m/s. The interactions at the asperity scale are characterized by a white light interferometer surface analysis.

  12. Measurement of friction coefficient in aluminum sheet warm forming

    Institute of Scientific and Technical Information of China (English)

    GUO Zheng-hua; LI Zhi-gang; HUANG Chong-jiu; DONG Xiang-huai

    2005-01-01

    Aluminum alloy sheets are used more and more to manufacture auto panels. Because the friction behavior is very complicated, it is necessary to study the friction during the aluminum sheet warm forming process. The author has designed a new probe sensor based on an online tribotest method which directly measures friction coefficient in the forming process. Experiments of cup drawing have been conducted and the friction coefficients under different forming conditions have been measured. The results indicate that the forming parameters, such as forming temperature, blankholding force and lubrication status have great effect upon the friction coefficient.

  13. The Frictional Coefficient of Bovine Knee Articular Cartilage

    Institute of Scientific and Technical Information of China (English)

    Qian Shan-hua; Ge Shi-rong; Wang Qing-liang

    2006-01-01

    The normal displacement of articular cartilage was measured under load and in sliding, and the coefficient of friction during sliding was measured using a UMT-2 Multi-Specimen Test System. The maximum normal displacement under load and the start-up frictional coefficient have similar tendency of variation with loading time. The sliding speed does not significantly influence the frictional coefficient of articular cartilage.

  14. Experimental investigation of friction coefficient in tube hydroforming

    Institute of Scientific and Technical Information of China (English)

    Hyae Kyung YI; Hong Sup YIM; Gun Yeop LEE; Sung Mun LEE; Gi Suk CHUNG; Young-Hoon MOON

    2011-01-01

    The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.

  15. Friction Coefficient of UHMWPE During Dry Reciprocating Sliding

    Directory of Open Access Journals (Sweden)

    F. Zivic

    2014-09-01

    Full Text Available This paper deals with the friction coefficient behaviour during dry reciprocating sliding of UHMWPE in contact with alumina (Al2O3, within a range of velocities typical for hip implants. Five values of normal force (100 - 1000 mN and three values of sliding speed (4 - 12 mm/s have been observed. Real time diagrams of the friction coefficient as a function of the sliding cycles were recorded for each test. Dynamic friction coefficient curves exhibited rather uniform behavior for all test conditions. Somewhat larger values of friction coefficient could be observed during the running-in period in case of low loads (100 - 250 mN and the lowest velocity (4 mm/s. In case of high loads and speeds, friction coefficient reached steady state values shortly after the beginning of the test.

  16. The Relationship between the Friction Coefficient and the Asperities Original Inclination Angle

    Directory of Open Access Journals (Sweden)

    Guan Cheng-yao

    2013-07-01

    Full Text Available Because of the contact deformation, the inclination angle of the contact face is decreased gradually when contact and deformation. Base on the change of inclination angle of the contact surface, the concept “friction repose angle” set out. The tangent of the initial inclination angle of two asperities is three time of the tangent of the “friction repose angle”. The relationship set up a bridge between the initial surface geometric configuration (can be detect and the configuration which after the deformation (can not be detect. Static Friction Coefficient is the max value of Kinetic Friction Coefficient before the deformation process of instantaneous contact surface. The Ratio of Kinetic and Static Friction Coefficient distribute from 0.771 to 0.9117 and were inversely proportional to the inclination angle of the contact face .Kinetic Friction Coefficient is the average friction coefficient of the deformation process of instantaneous contact surface. In the sandstone, the value of Kinetic Friction Coefficient which more than 0.5546 is because of the coupling of different classes zigzag-shape surface asperities mostly. The study puts forward the new ideas “dynamic deformation tribology” which will promote the development of the Tribology.

  17. Temperature dependent effective friction coefficient estimation in friction stir welding with the bobbin tool

    Directory of Open Access Journals (Sweden)

    Mijajlović Miroslav M.

    2016-01-01

    Full Text Available The friction coefficient in many friction stir welding researches is generally used as an effective, constant value without concern on the adaptable and changeable nature of the friction during welding sequence. This is understandable because the main problem in analyzing friction in friction stir welding are complex nature of the friction processes, case-dependent and time dependent contact between the bodies, influence of the temperature, sliding velocity, etc. This paper is presenting a complex experimental-numerical-analytical model for estimating the effective friction coefficient on contact of the bobbin tool and welding plates during welding, considering the temperature at the contact as the most influencing parameter on friction. The estimation criterion is the correspondence of the experimental temperature and temperature from the numerical model. The estimation procedure is iterative and parametric - the heat transport parameters and friction coefficient are adapted during the estimation procedure in a realistic manner to achieve relative difference between experimental and model’s temperature lower than 3%. The results show that friction coefficient varies from 0.01 to 0.21 for steel-aluminium alloy contact and temperature range from 406°C to 22°C.

  18. Effects of lubricant's friction coefficient on warm compaction powder metallurgy

    Institute of Scientific and Technical Information of China (English)

    LI Yuan-yuan; NGAI Tungwai Leo; WANG Shng-lin; ZHU Min; CHEN Wei-ping

    2005-01-01

    The correct use of lubricant is the key of warm compaction powder metallurgy.Different lubricants produce different lubrication effects and their optimal application temperature will be different.Three different lubricants were used to study the effects of friction coefficient on warm compaction process.Friction coefficients of these lubricants were measured at temperatures ranging from ambient temperature to 200 ℃.Iron-base samples were prepared using different processing temperatures and their green compact densities were studied.

  19. Coefficient of friction of a starved lubricated spur gear pair

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Huaiju; Zhu, Caichao; Sun, Zhangdong; Zhang, Yuanyuan; Song, Chaosheng [Chongqing University, Chongqing (China)

    2016-05-15

    The frictional power loss issue of gear pairs becomes an important concern in both industry and academia due to the requirement of the energy saving and the improvement of power density of gear drives. A thermal starved elastohydrodynamic lubrication model is developed to study the tribological performance of a spur gear pair under starved lubrication conditions. The contact pressure, the film thickness, the temperature rise, the frictional power loss, as well as the coefficient of friction are evaluated by considering the variation of the curvature radius, the sliding/rolling motion, and the load distribution of gear tooth within the meshing period. Effects of lubrication starvation condition, load and speed on the coefficient of friction are studied.

  20. Wobble friction coefficient in post-stressed concrete

    Directory of Open Access Journals (Sweden)

    Diego Ernesto Dueñas Puentes

    2010-04-01

    Full Text Available This work was aimed at establishing a wobble friction coefficient (K from records regarding some post-stressed bridges built in Colombia. Such records were arranged and analysed together with stress diagrams resulting from the corres-ponding plans, calculations and reports. Suitable records were produced from this review to make the analysis. Once the records had been selected, the probable wobble friction coefficient (K was then calculated for each case and this coefficient was related to the length of the cable and the total area of the strands composing the cable. These records and their results were subsequently grouped according to the type of bridge to produce a wobble friction coefficient (K for each specific structure. The study indicated that the wobble friction coefficient was lower than that indicated by the Colombian Seismic Bridge Design Code, Instituto Nacional De Vías, 1995]. The influence of tensioning equipment, materials and labour suggested a format for recording tensioning to reduce inaccuracy when readings are being taken. A reduction in the costs of tensioning would arise from taking the forgoing into account.

  1. Effect of electrostatic field on dynamic friction coefficient of pistachio

    Directory of Open Access Journals (Sweden)

    M. H Aghkhani

    2016-04-01

    Full Text Available Introduction: Separation and grading of agricultural products from the production to supply, has notable importance. The separation can be done based on physical, electrical, magnetic, optical properties and etc. It is necessary for any development of new systems to study enough on the properties and behavior of agricultural products. Some characteristics for separation are size (length, width and thickness, hardness, shape, density, surface roughness, color, speed limit, aerodynamic properties, electrical conductivity, elasticity and coefficient of static friction point. So far, the friction properties of agricultural products used in the separating process, but the effect of electrostatic charging on static and dynamic coefficients of friction for separation had little attention. The aim of this study was to find out the interactions between electrostatic and friction properties to find a way to separate products that separation is not possible with conventional methods or not sufficiently accurate. In this paper, the separation of close and smiley pistachios by electrostatic charging was investigated. Materials and Methods: Kallehghoochi pistachio cultivar has the top rank in production in Iran. Therefore, it was used as a sample. The experimental design that used in this study, had moisture content at three levels (24.2, 14.5 and 8.1 percent, electric field intensity at three levels (zero, 4000 and 7000 V, speed of movement on the surface at three levels (1300, 2500 and 3300 mm per minute, friction surface (galvanized sheet iron, aluminum and flat rubber and pistachio type at two levels (filled splits and closed that was measured and analyzed in completely randomized factorial design. A friction measuring device (built in Ferdowsi University of Mashhad used to measure the friction force. It has a removable table that can move in two directions with adjustable speed. The test sample put into the vessel with internal dimensions of 300 × 150

  2. Road Friction Coefficient Real-Time Identification Based on the Tire Dynamic Friction Model

    Institute of Scientific and Technical Information of China (English)

    FAN Xiao-bin; DENG Pan; JIANG Yu; FAN Bing-xu

    2013-01-01

    Road friction coefficient real-time estimation methods is an important issue and problem in automotive active safety con-trol system development. First a fixed feedback gain sliding mode observer of road adhesion coefficient is designed through the es-tablishment of tire/road dynamic friction model in this article. The simulation results shows that the observer can well real-time iden-tify the current road adhesion characteristics. And more importantly, the observer only need wheel speed signal and the braking torque (brake pressure) signal, so the system is low cost, and its adaptability is good. There is no doubt this estimation method has a good application prospect.

  3. Interpretation of the Friction Coefficient During Reciprocating Sliding of Ti6Al4V Alloy Against Al2O3

    Directory of Open Access Journals (Sweden)

    S. Mitrovic

    2011-03-01

    Full Text Available Tribological behaviour of Ti6Al4V alloy, during linear reciprocating sliding against alumina, at nanotribometer (ball-on-flat type of contact was investigated. Experiments were carried out for sliding in Ringer's solution, over a range of loads (100 - 1000 mN and speeds (4 - 12 mm/s. Friction behaviour of the contact pairs was investigated by analysis of the dynamic friction coefficient plots and effective root mean square (rms coefficient of friction, COFrms. Presented mathematical envelopes of dynamic coefficient of friction curves and averaged envelope signals provided additional explanation of one calculated COFrms value. Envelopes of dynamic coefficient of friction enabled easier determination of different periods during sliding, which were further related to wear mechanisms.

  4. Use of a Correlation Coefficient for Conditional Averaging.

    Science.gov (United States)

    1997-04-01

    data. Selection of the sine function period and a correlation coefficient threshold are discussed. Also examined are the effects of the period and...threshold level on the number of ensembles captured for inclusion for conditional averaging. Both the selection of threshold correlation coefficient and the...A method of collecting ensembles for conditional averaging is presented that uses data collected from a plane mixing layer. The correlation

  5. Determination of Friction Coefficient in Unconfined Compression of Brain Tissue

    CERN Document Server

    Rashid, Badar; Gilchrist, Michael; 10.1016/j.jmbbm.2012.05.001

    2013-01-01

    Unconfined compression tests are more convenient to perform on cylindrical samples of brain tissue than tensile tests in order to estimate mechanical properties of the brain tissue because they allow for homogeneous deformations. The reliability of these tests depends significantly on the amount of friction generated at the specimen/platen interface. Thus, there is a crucial need to find an approximate value of the friction coefficient in order to predict a possible overestimation of stresses during unconfined compression tests. In this study, a combined experimental-computational approach was adopted to estimate the dynamic friction coefficient mu of porcine brain matter against metal platens in compressive tests. Cylindrical samples of porcine brain tissue were tested up to 30% strain at variable strain rates, both under bonded and lubricated conditions in the same controlled environment. It was established that mu was equal to 0.09 +/- 0.03, 0.18 +/- 0.04, 0.18 +/- 0.04 and 0.20 +/- 0.02 at strain rates of...

  6. Experimental Study on Friction Coefficient Between Concrete and the Top Surface of Rubble Mound Foundation

    Institute of Scientific and Technical Information of China (English)

    LI Yan-bao; JIANG Xue-lian; GUO Hong-yi

    2005-01-01

    Experimental studies on the friction coefficient between concrete and the top surface of a rubble mound foundation in China are reviewed. Through comparison of different test results, the development of this research is comprehensively analyzed. An experiment is carried out in the condition similar to prototype. The process curve of friction coefficient with the test block sliding is analyzed and a standard for determination of the friction coefficient is defined. The variation features of the friction coefficient are analyzed on the basis of the present experimental results and other studies in China. It is shown that the friction coefficient between concrete and the top surface of a rubble mound foundation decreases with the increase of the foundation pressure, and the friction coefficient for a very fine leveling bed is smaller than that for a fine leveling bed.

  7. Identification of Maximum Road Friction Coefficient and Optimal Slip Ratio Based on Road Type Recognition

    Institute of Scientific and Technical Information of China (English)

    GUAN Hsin; WANG Bo; LU Pingping; XU Liang

    2014-01-01

    The identification of maximum road friction coefficient and optimal slip ratio is crucial to vehicle dynamics and control. However, it is always not easy to identify the maximum road friction coefficient with high robustness and good adaptability to various vehicle operating conditions. The existing investigations on robust identification of maximum road friction coefficient are unsatisfactory. In this paper, an identification approach based on road type recognition is proposed for the robust identification of maximum road friction coefficient and optimal slip ratio. The instantaneous road friction coefficient is estimated through the recursive least square with a forgetting factor method based on the single wheel model, and the estimated road friction coefficient and slip ratio are grouped in a set of samples in a small time interval before the current time, which are updated with time progressing. The current road type is recognized by comparing the samples of the estimated road friction coefficient with the standard road friction coefficient of each typical road, and the minimum statistical error is used as the recognition principle to improve identification robustness. Once the road type is recognized, the maximum road friction coefficient and optimal slip ratio are determined. The numerical simulation tests are conducted on two typical road friction conditions(single-friction and joint-friction) by using CarSim software. The test results show that there is little identification error between the identified maximum road friction coefficient and the pre-set value in CarSim. The proposed identification method has good robustness performance to external disturbances and good adaptability to various vehicle operating conditions and road variations, and the identification results can be used for the adjustment of vehicle active safety control strategies.

  8. Research on friction coefficient of nuclear Reactor Vessel Internals Hold Down Spring: Stress coefficient test analysis method

    Energy Technology Data Exchange (ETDEWEB)

    Linjun, Xie, E-mail: linjunx@zjut.edu.cn [College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014 (China); Guohong, Xue; Ming, Zhang [Shanghai Nuclear Engineering Research & Design Institute, Shanghai 200233 (China)

    2016-08-01

    Graphical abstract: HDS stress coefficient test apparatus. - Highlights: • This paper performs mathematic deduction to the physical model of Hold Down Spring (HDS), establishes a mathematic model of axial load P and stress, stress coefficient and friction coefficient and designs a set of test apparatuses for simulating the pretightening process of the HDS for the first time according to a model similarity criterion. • The mathematical relation between the load and the strain is obtained about the HDS, and the mathematical model of the stress coefficient and the friction coefficient is established. So, a set of test apparatuses for obtaining the stress coefficient is designed according to the model scaling criterion and the friction coefficient of the K1000 HDS is calculated to be 0.336 through the obtained stress coefficient. • The relation curve between the theoretical load and the friction coefficient is obtained through analysis and indicates that the change of the friction coefficient f would influence the pretightening load under the condition of designed stress. The necessary pretightening load in the design process is calculated to be 5469 kN according to the obtained friction coefficient. Therefore, the friction coefficient and the pretightening load under the design conditions can provide accurate pretightening data for the analysis and design of the reactor HDS according to the operations. - Abstract: This paper performs mathematic deduction to the physical model of Hold Down Spring (HDS), establishes a mathematic model of axial load P and stress, stress coefficient and friction coefficient and designs a set of test apparatuses for simulating the pretightening process of the HDS for the first time according to a model similarity criterion. By carrying out tests and researches through a stress testing technique, P–σ curves in loading and unloading processes of the HDS are obtained and the stress coefficient k{sub f} of the HDS is obtained. So, the

  9. Wave Attenuation and Friction Coefficient on the Coral-Reef Flat

    Institute of Scientific and Technical Information of China (English)

    朱良生; 黎满球; 张洪生; 隋世峰

    2004-01-01

    Several sets of S4 direction-wave-current-tide meters have been deployed on the coral-reef flat of Yongshu Reef in the sea area of Nansha Islands. Based on the observational sea wave data, the attenuation characteristics of the waves propagating on the coral reef flat, the bottom friction coefficients and the transfer of wave energy are discussed in the paper. The results show that, in the relative depths of 0. 0613 ~ 0. 0867, the wave height attenuation per unit distance of wave propagation is 22.09 % ~ 46.56 %, with an average of 31.35 %; the wave energy attenuation coefficient, 33.74%~ 53.22%, with an average of 43.61%. The average of the bottom friction coefficients on the coral-reef flat is 0. 1346,which is about 10 times that on the sand or silt bottom. In the course of propagation on the reef flat, the waves sustain more loss in high frequency than in low frequency and the spectral energy transfers to the low frequency. These resuhs may be used for reference in island and reef engineering.

  10. Enhanced surface friction coefficient and hydrophobicity of TPE substrates using an APPJ system

    Energy Technology Data Exchange (ETDEWEB)

    Sainz-García, Elisa, E-mail: elisa.sainzg@unirioja.es; Alba-Elías, Fernando, E-mail: fernando.alba@unirioja.es; Múgica-Vidal, Rodolfo, E-mail: rodolfo.mugica@alum.unirioja.es; González-Marcos, Ana, E-mail: ana.gonzalez@unirioja.es

    2015-02-15

    Highlights: • Coatings on thermoplastic elastomers by atmospheric pressure plasma jet. • Study of influence of APTES and FLUSI percentage on the coating's properties. • The best sample (AF{sub 75}) used 75% of APTES and 25% of FLUSI as precursor mixture. • Sample AF{sub 75} reduced a 51.5% the FC and increased a 4.4% the WCA. - Abstract: An APPJ system was used to deposit a coating that combines a low friction coefficient with a high water contact angle (WCA) on a thermoplastic elastomer substrate (TPE) that is used in automotive profiling. The main drawback of this research is that groups that improve the hydrophobicity of the surface worsen its tribological properties. To overcome this, this study explored the use of various mixtures of differing proportions of two precursors. They were a siloxane, aminopropyltriethoxysilane (APTES) that was used to reduce the friction coefficient by its content of SiO{sub x} and a fluorinated compound, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (FLUSI) that was used to improve the water-repellency characteristics, due to the presence of CF{sub 2} long chains. The coatings were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), dynamic Water Contact Angle (WCA), stability tests and tribological tests. It was found that an increase of the absorbance area under the SiOSi peak and inorganic groups is related to lower friction coefficients. On the other hand, the higher the CF{sub 2} percentage is, the higher the WCA is. The sample that was coated with 25% of FLUSI and 75% of APTES combined the improvements of both functional properties, the friction coefficient and the WCA. It has an average friction coefficient that is (0.530 ± 0.050) 51.5% lower and a WCA that is (θ{sub adv} = 119.8° ± 4.75) 4.4% higher than the uncoated TPE sample. A satisfactory

  11. Dependence of the osmotic coefficients and average ionic activity coefficients on hydrophobic hydration in solutions

    Science.gov (United States)

    Sergievskii, V. V.; Rudakov, A. M.

    2016-08-01

    The model that considers the nonideality of aqueous solutions of electrolytes with allowance for independent contributions of hydration of ions of various types and electrostatic interactions was substantiated using the cluster ion model. The empirical parameters in the model equations were found to be the hydrophilic and hydrophobic hydration numbers of ions in the standard state and the dispersion of their distribution over the stoichiometric coefficients. A mathematically adequate description of the concentration dependences of the osmotic coefficients and average ion activity coefficients of electrolytes was given for several systems. The difference in the rate of the decrease in the hydrophilic and hydrophobic hydration numbers of ions leads to extremum concentration dependences of the osmotic coefficients, which were determined by other authors from isopiestic data for many electrolytes and did not find explanation.

  12. A coefficient average approximation towards Gutzwiller wavefunction formalism.

    Science.gov (United States)

    Liu, Jun; Yao, Yongxin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-06-24

    Gutzwiller wavefunction is a physically well-motivated trial wavefunction for describing correlated electron systems. In this work, a new approximation is introduced to facilitate the evaluation of the expectation value of any operator within the Gutzwiller wavefunction formalism. The basic idea is to make use of a specially designed average over Gutzwiller wavefunction coefficients expanded in the many-body Fock space to approximate the ratio of expectation values between a Gutzwiller wavefunction and its underlying noninteracting wavefunction. To check with the standard Gutzwiller approximation (GA), we test its performance on single band systems and find quite interesting properties. On finite systems, we noticed that it gives superior performance over GA, while on infinite systems it asymptotically approaches GA. Analytic analysis together with numerical tests are provided to support this claimed asymptotical behavior. Finally, possible improvements on the approximation and its generalization towards multiband systems are illustrated and discussed.

  13. A coefficient average approximation towards Gutzwiller wavefunction formalism

    Science.gov (United States)

    Liu, Jun; Yao, Yongxin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-06-01

    Gutzwiller wavefunction is a physically well-motivated trial wavefunction for describing correlated electron systems. In this work, a new approximation is introduced to facilitate the evaluation of the expectation value of any operator within the Gutzwiller wavefunction formalism. The basic idea is to make use of a specially designed average over Gutzwiller wavefunction coefficients expanded in the many-body Fock space to approximate the ratio of expectation values between a Gutzwiller wavefunction and its underlying noninteracting wavefunction. To check with the standard Gutzwiller approximation (GA), we test its performance on single band systems and find quite interesting properties. On finite systems, we noticed that it gives superior performance over GA, while on infinite systems it asymptotically approaches GA. Analytic analysis together with numerical tests are provided to support this claimed asymptotical behavior. Finally, possible improvements on the approximation and its generalization towards multiband systems are illustrated and discussed.

  14. Adhesion energy between mica surfaces: Implications for the frictional coefficient under dry and wet conditions

    Science.gov (United States)

    Sakuma, Hiroshi

    2013-12-01

    frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones.

  15. Prediction and determination of both friction coefficient and forming force on sheet metal deep—drawing

    Institute of Scientific and Technical Information of China (English)

    Junxiang; YonglinKang; 等

    2002-01-01

    On the basis of the criterion of no-wrinkle,the principle and method of prediction and determination of both friction coefficient and forming force on sheet metal deep-drawing are put forward,and proved it's expedience and practicability.They are suitable for as sessment of lubricant properties.Friction coefficient and forming force are a function of material parameter,design parameter and process parameter,especially relative prevent wrinkle blank-holder force.Product of both friction coefficient and prevent wrinkle blank-holder force is only function of process parameter η after determining material parameter and design parameter.

  16. The frictional coefficient of the temporomandibular joint and its dependency on the magnitude and duration of joint loading.

    Science.gov (United States)

    Tanaka, E; Kawai, N; Tanaka, M; Todoh, M; van Eijden, T; Hanaoka, K; Dalla-Bona, D A; Takata, T; Tanne, K

    2004-05-01

    In synovial joints, friction between articular surfaces leads to shear stress within the cartilaginous tissue, which might result in tissue rupture and failure. Joint friction depends on synovial lubrication of the articular surfaces, which can be altered due to compressive loading. Therefore, we hypothesized that the frictional coefficient of the temporomandibular joint (TMJ) is affected by the magnitude and duration of loading. We tested this by measuring the frictional coefficient in 20 intact porcine TMJs using a pendulum-type friction tester. The mean frictional coefficient was 0.0145 (SD 0.0027) after a constant loading of 50 N during 5 sec. The frictional coefficient increased with the length of the preceding loading duration and exceeded 0.0220 (SD 0.0014) after 1 hr. Application of larger loading (80 N) resulted in significantly larger frictional coefficients. In conclusion, the frictional coefficient in the TMJ was proportional to the magnitude and duration of joint loading.

  17. Anomalous low friction coefficient in shear thickening suspensions

    Science.gov (United States)

    Clavaud, Cecile; Berut, Antoine; Metzger, Bloen; Forterre, Yoel; GEP Team

    2016-11-01

    We study the frictional behavior of classical and shear thickening suspensions under low confining pressure, by measuring the pile slope-angle in rotating drum flow experiments. We show that, at low rotation rates, the pile angle of the shear thickening suspension is about 8 .5° , which is much lower than pile angles observed with classical suspensions in the same conditions ( 25°). We then study the frictional behavior of silica powders in water, and show that we can switch from low to high pile angle by changing the salinity of the suspension. These results support a recent scenario for the shear-thickening transition in such non-Brownian systems, where inter particle repulsive forces suppress friction at low confining pressure. ERC PlantMove.

  18. Effect of Tension on Friction Coefficient Between Lining and Wire Rope with Low Speed Sliding

    Institute of Scientific and Technical Information of China (English)

    PENG Yu-xing; ZHU Zhen-cai; CHEN Guo-an; CAO Guo-hua

    2007-01-01

    In order to obtain the exact friction coefficient between lining and wire rope, the tension of wire rope is studied as a factor which affects this coefficient. A mechanical model of a wire rope subjected to axial load was established to determine the torque of the wire rope. The contact motion between lining and wire rope was regarded as a screw rotation and the axial force of the lining resulting from the torque of the wire rope was analyzed. Theoretical formulas relating tension of the wire rope and the friction coefficient was obtained. Experiments between lining and wire rope with low sliding speed were carried out with friction tester made by us. Experimental results show that increment of the friction coefficient is proportional to that of the tension of the wire rope with a low sliding speed. The experimental results agree with the theoretical calculation; the errors are less than 6%, which proves the validity of the theoretical model.

  19. Study on the testing methods of friction coefficient in metal sheet deep drawing

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A more suitable method is introduced about testing friction coefficient on deep drawingcondition. It is pointed out that many ways to mesture friction coefficient. However, if a study of thefriction and lubrication in sheet metal deep drawing process is made, the testing method recom-mended in this paper should be used. As it is identical with the actual working condition accordingto its testing principle and state of stress.

  20. Prediction and determination of both friction coefficient and forming force on sheet metal deep-drawing

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    On the basis of the criterion of no-wrinkle, the principle and method of prediction and determination of both friction coefficientand forming force on sheet metal deep-drawing are put forward, and proved it's expedience and practicability. They are suitable for assessment of lubricant properties. Friction coefficient and forming force are a function of material parameter, design parameter and process parameter, especially relative prevent wrinkle blank-holder force. Product of both friction coefficient and prevent wrinkle blank-holder force isonly function of process parameter after determining material parameter and design parameter.

  1. The measurement of friction coefficient down to 1.8 K for LHC Magnets

    CERN Document Server

    Artoos, K; Poncet, Alain; Savary, F; Veness, R J M

    1994-01-01

    The Large Hadron Collider (LHC) proposed for construction at CERN consists of a series of high field superconducting dipole magnet operating at 1.8K. The mechanical structure of these magnets contains many components in close contact. A knowledge of the friction coefficient between these components is required. Indeed, during assembly and cool down of the magnets, prestresses must be transferred to the superconducting coils. During operation, frictional heating may provoke loss of superconductivity. A machine has been built at CERN to measure the coefficient of friction from room temperature down to 1.8K. This paper describes the cryogenic tribometer and the results collected to date.

  2. Influence of the Previous Preheating Temperature on the Static Coefficient of Friction with Lubrication

    Directory of Open Access Journals (Sweden)

    M. Živković

    2016-12-01

    Full Text Available Experimental investigations static coefficient of friction in lubricated conditions and pre-heating of the sample pin at high temperatures is discussed in this paper. The static coefficient of friction was measured in the sliding steel copper pins per cylinder of polyvinylchloride. Pins are previously heated in a special chamber from room temperature to a temperature of 800 oC with a step of 50 °C. Tribological changes in the surface layer of the pins caused by pre-heating the pins at high temperatures and cooling systems have very significantly influenced the increase in the coefficient of static friction. The results indicate the possibility of improving the friction characteristics of metal materials based on their thermal treatment at elevated temperatures.

  3. Development and assessment of atomistic models for predicting static friction coefficients

    Science.gov (United States)

    Jahangiri, Soran; Heverly-Coulson, Gavin S.; Mosey, Nicholas J.

    2016-08-01

    The friction coefficient relates friction forces to normal loads and plays a key role in fundamental and applied areas of science and technology. Despite its importance, the relationship between the friction coefficient and the properties of the materials forming a sliding contact is poorly understood. We illustrate how simple relationships regarding the changes in energy that occur during slip can be used to develop a quantitative model relating the friction coefficient to atomic-level features of the contact. The slip event is considered as an activated process and the load dependence of the slip energy barrier is approximated with a Taylor series expansion of the corresponding energies with respect to load. The resulting expression for the load-dependent slip energy barrier is incorporated in the Prandtl-Tomlinson (PT) model and a shear-based model to obtain expressions for friction coefficient. The results indicate that the shear-based model reproduces the static friction coefficients μs obtained from first-principles molecular dynamics simulations more accurately than the PT model. The ability of the model to provide atomistic explanations for differences in μs amongst different contacts is also illustrated. As a whole, the model is able to account for fundamental atomic-level features of μs, explain the differences in μs for different materials based on their properties, and might be also used in guiding the development of contacts with desired values of μs.

  4. A hierarchical estimator development for estimation of tire-road friction coefficient

    Science.gov (United States)

    Zhang, Xudong; Göhlich, Dietmar

    2017-01-01

    The effect of vehicle active safety systems is subject to the friction force arising from the contact of tires and the road surface. Therefore, an adequate knowledge of the tire-road friction coefficient is of great importance to achieve a good performance of these control systems. This paper presents a tire-road friction coefficient estimation method for an advanced vehicle configuration, four-motorized-wheel electric vehicles, in which the longitudinal tire force is easily obtained. A hierarchical structure is adopted for the proposed estimation design. An upper estimator is developed based on unscented Kalman filter to estimate vehicle state information, while a hybrid estimation method is applied as the lower estimator to identify the tire-road friction coefficient using general regression neural network (GRNN) and Bayes' theorem. GRNN aims at detecting road friction coefficient under small excitations, which are the most common situations in daily driving. GRNN is able to accurately create a mapping from input parameters to the friction coefficient, avoiding storing an entire complex tire model. As for large excitations, the estimation algorithm is based on Bayes' theorem and a simplified “magic formula” tire model. The integrated estimation method is established by the combination of the above-mentioned estimators. Finally, the simulations based on a high-fidelity CarSim vehicle model are carried out on different road surfaces and driving maneuvers to verify the effectiveness of the proposed estimation method. PMID:28178332

  5. Interpreting Bivariate Regression Coefficients: Going beyond the Average

    Science.gov (United States)

    Halcoussis, Dennis; Phillips, G. Michael

    2010-01-01

    Statistics, econometrics, investment analysis, and data analysis classes often review the calculation of several types of averages, including the arithmetic mean, geometric mean, harmonic mean, and various weighted averages. This note shows how each of these can be computed using a basic regression framework. By recognizing when a regression model…

  6. Indirect Estimations of Frictional Coefficients of Fractures in Sandstones for Analysis of Injection Induced Microseismicity

    Science.gov (United States)

    Jo, Y.; Chang, C.; Koh, H. J.

    2014-12-01

    The frictional coefficient of fractures, a fundamental parameter needed to analyze a variety of geomechanical problems for microseismicity, is normally determined from laboratory shear tests. However, recovered rock cores are rarely available because of difficulties and high cost in getting undisturbed core samples. In that case, the frictional coefficient should be either assumed or estimated indirectly. We investigate the frictional property of fractures of various sandstones in laboratory tests and attempt to correlate that with other properties measureable relatively readily even without cores. We use various sandstones obtained from different depths of a 1 km deep borehole drilled for coal bed methane development in a Paleozoic sedimentary basin, South Korea. The sandstones have various physical properties (e.g. P-wave velocity (VP) of 2253-5038 m/s) and chemical compositions in terms of clay content (5-31%). We conduct direct shear tests in an artificial saw-cut fracture in the sandstones and determined frictional coefficients in a range of 0.36-0.57. The frictional coefficients have an inverse-linear correlation with clay contents measured from XRD analysis. These results are also quite consistent with those from previous clay gouge experiments (Takahashi et al., 2007; Tembe et al., 2010; Kohli & Zoback, 2013). They also have a linear correlation with VP. Our study demonstrates that frictional coefficients can be estimated empirically from such properties. To check feasibility of such an approach, we apply the obtained empirical relation to the borehole where cores were recovered. The clay contents in sandstone formations are estimated from the borehole gamma ray log calibrated using the XRD clay content data. Clay content estimated from gamma ray varies significantly with depth in a range of 0-45%. This range of clay content corresponds to frictional coefficients of 0.25-0.58. Comparison between estimated and measured frictional coefficients shows a

  7. Measuring the Coefficient of Friction of a Small Floating Liquid Marble

    Science.gov (United States)

    Ooi, Chin Hong; Nguyen, Anh Van; Evans, Geoffrey M.; Dao, Dzung Viet; Nguyen, Nam-Trung

    2016-12-01

    This paper investigates the friction coefficient of a moving liquid marble, a small liquid droplet coated with hydrophobic powder and floating on another liquid surface. A floating marble can easily move across water surface due to the low friction, allowing for the transport of aqueous solutions with minimal energy input. However, the motion of a floating marble has yet to be systematically characterised due to the lack of insight into key parameters such as the coefficient of friction between the floating marble and the carrier liquid. We measured the coefficient of friction of a small floating marble using a novel experimental setup that exploits the non-wetting properties of a liquid marble. A floating liquid marble pair containing a minute amount magnetite particles were immobilised and then released in a controlled manner using permanent magnets. The capillarity-driven motion was analysed to determine the coefficient of friction of the liquid marbles. The “capillary charge” model was used to fit the experimental results. We varied the marble content and carrier liquid to establish a relationship between the friction correction factor and the meniscus angle.

  8. Tuning apparent friction coefficient by controlled patterning bulk metallic glasses surfaces

    Science.gov (United States)

    Li, Ning; Xu, Erjiang; Liu, Ze; Wang, Xinyun; Liu, Lin

    2016-12-01

    Micro-honeycomb structures with various pitches between adjacent cells were hot-embossed on Zr35Ti30Cu8.25Be26.75 bulk metallic glass surface. The effect of pitch geometry on the frictional behavior of metallic glass surface was systematically investigated. The results revealed that all textured metallic glass surfaces show a reduction in friction coefficient compared to smooth surface. More intriguingly, the friction coefficient first decreased and then increased gradually with increasing pitches. Such unique behavior can be understood fundamentally from the perspective of competing effects between contact area and local stress level with increasing pitches. This finding not only enhance the in-depth understanding of the mechanism of the significant role of surface topography on the frictional behavior of metallic glass surface, but also opens a new route towards other functional applications for bulk metallic glasses.

  9. Investigation on tribology behavior of lubricants using the coefficient of friction test method

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This test method is used to determine the property of lubricants by measure the pa-rameters such as the coefficient of friction, wear value and seizure load on the Four Ball Wear TestMachine. Experiments were conducted using ASTM D5183-95 Standard Test Method (StandardTest Method For Determination Of The Coefficient of Friction of Lubricants Using the Four BallWear Test Machine) to measure the friction reducing ability , antiwear property and ex-treme-pressure property of different type of lubricants, the additives are also been studied at thesame time. From the test result, this test method can distinguish not only the property of differenttype of lubricants rapidly, sensitively and effectively but also can reflect the friction reducingability , antiwear property and extreme-pressure property of various additive formula.

  10. A Tactile Sensor Using Piezoresistive Beams for Detection of the Coefficient of Static Friction.

    Science.gov (United States)

    Okatani, Taiyu; Takahashi, Hidetoshi; Noda, Kentaro; Takahata, Tomoyuki; Matsumoto, Kiyoshi; Shimoyama, Isao

    2016-05-18

    This paper reports on a tactile sensor using piezoresistive beams for detection of the coefficient of static friction merely by pressing the sensor against an object. The sensor chip is composed of three pairs of piezoresistive beams arranged in parallel and embedded in an elastomer; this sensor is able to measure the vertical and lateral strains of the elastomer. The coefficient of static friction is estimated from the ratio of the fractional resistance changes corresponding to the sensing elements of vertical and lateral strains when the sensor is in contact with an object surface. We applied a normal force on the sensor surface through objects with coefficients of static friction ranging from 0.2 to 1.1. The fractional resistance changes corresponding to vertical and lateral strains were proportional to the applied force. Furthermore, the relationship between these responses changed according to the coefficients of static friction. The experimental result indicated the proposed sensor could determine the coefficient of static friction before a global slip occurs.

  11. Study for reasonable value of friction coefficient between main cable and saddle

    Institute of Scientific and Technical Information of China (English)

    Deng Ting; Luo Xiheng

    2012-01-01

    The value of friction coefficient between the main cable and saddle, relates to not only the anti-slippage stability of three-tower suspension bridge, but also the reasonable stiffness of the middle tower and the magnitude of rigidity of the whole bridge. First, the paper does some comparative studies about the relevant provisions of international norms, and then, summarizes the relevant load test results both at home and abroad. Finally, the paper draws the appropriate anti-slippage safety factor for the most unfavorable load in accordance with international load standards, and discusses the rationality and feasibility of the friction coefficient of 0.2 between main cable and saddle.

  12. A comparison of two methods of measuring static coefficient of friction at low normal forces: a pilot study.

    Science.gov (United States)

    Seo, Na Jin; Armstrong, Thomas J; Drinkaus, Philip

    2009-01-01

    This study compares two methods for estimating static friction coefficients for skin. In the first method, referred to as the 'tilt method', a hand supporting a flat object is tilted until the object slides. The friction coefficient is estimated as the tangent of the angle of the object at the slip. The second method estimates the friction coefficient as the pull force required to begin moving a flat object over the surface of the hand, divided by object weight. Both methods were used to estimate friction coefficients for 12 subjects and three materials (cardboard, aluminium, rubber) against a flat hand and against fingertips. No differences in static friction coefficients were found between the two methods, except for that of rubber, where friction coefficient was 11% greater for the tilt method. As with previous studies, the friction coefficients varied with contact force and contact area. Static friction coefficient data are needed for analysis and design of objects that are grasped or manipulated with the hand. The tilt method described in this study can easily be used by ergonomic practitioners to estimate static friction coefficients in the field in a timely manner.

  13. Effective assessment of tyre-road friction coefficient using a hybrid estimator

    Science.gov (United States)

    Ren, Hongbin; Chen, Sizhong; Shim, Taehyun; Wu, Zhicheng

    2014-08-01

    Vehicle stability and active safety control depend heavily on tyre forces available on each wheel of a vehicle. Since tyre forces are strongly affected by the tyre-road friction coefficient, it is crucial to optimise the use of the adhesion limits of the tyres. This study presents a hybrid method to identify the road friction limitation; it contributes significantly to active vehicle safety. A hybrid estimator is developed based on the three degrees-of-freedom vehicle model, which considers longitudinal, lateral and yaw motions. The proposed hybrid estimator includes two sub-estimators: one is the vehicle state information estimator using the unscented Kalman filter and another is the integrated road friction estimator. By connecting two sub-estimators simultaneously, the proposed algorithm can effectively estimate the road friction coefficient. The performance of the proposed estimation algorithm is validated in CarSim/Matlab co-simulation environment under three different road conditions (high-μ, low-μ and mixed-μ). Simulation results show that the proposed estimator can assess vehicle states and road friction coefficient with good accuracy.

  14. Friction Coefficient Between Rolling Tube and Mandrel of Full Floating Mandrel Mill

    Institute of Scientific and Technical Information of China (English)

    ZHAO Zhi-yi; XIE Jian-xin; HE Xiao-ming; DONG Kai; YU Yong; PAN Feng

    2009-01-01

    In the process of steel tube production, continuous tube rolling is the foremost forming procedure and the critical step that decides the dimension precision and the surface quality. In the actual production of the φ140 mm full floating mandrel mill in Steel Tube Branch in Baosteel, steel T91 was chosen to be the typical sample, self-made roll-ing force transducer and mandrel velocity testing equipment were used, and a series of comprehensive tests on rolling parameters including the rolling force and mandrel velocity were carried out. After the experiment, the friction state between rolling tube and mandrel was analyzed. The friction coefficient was calculated and the values of 0.033-0.074 in each mill were obtained. The friction coefficient increases obviously along the rolling direction.

  15. The stochastic distribution of available coefficient of friction on quarry tiles for human locomotion.

    Science.gov (United States)

    Chang, Wen-Ruey; Matz, Simon; Chang, Chien-Chi

    2012-01-01

    The available coefficient of friction (ACOF) for human locomotion is the maximum coefficient of friction that can be supported without a slip at the shoe and floor interface. A statistical model was introduced to estimate the probability of slip by comparing the ACOF with the required coefficient of friction, assuming that both coefficients have stochastic distributions. This paper presents an investigation of the stochastic distributions of the ACOF of quarry tiles under dry, water and glycerol conditions. One hundred friction measurements were performed on a walkway under the surface conditions of dry, water and 45% glycerol concentration. The Kolmogorov-Smirnov goodness-of-fit test was used to determine if the distribution of the ACOF was a good fit with the normal, log-normal and Weibull distributions. The results indicated that the ACOF appears to fit the normal and log-normal distributions better than the Weibull distribution for the water and glycerol conditions. However, no match was found between the distribution of ACOF under the dry condition and any of the three continuous distributions evaluated. Based on limited data, a normal distribution might be more appropriate due to its simplicity, practicality and familiarity among the three distributions evaluated.

  16. Static Coefficient of Rolling Friction at High Contact Temperatures and Various Contact Pressure

    Directory of Open Access Journals (Sweden)

    B. Tadić

    2016-03-01

    Full Text Available The paper theoretically and experimentally analyzes the influence of increased temperature and load contact in the value of the coefficient of rolling friction. Theoretical analyzes show that at temperatures of the order of 200 0C, exist thermal potential necessary to narrow contact zone leads to a redistribution of the contact pressure and an increase in torque performance. Based on the measurement results, established the regression coefficient of friction depending on the temperature, normal load and geometry parameters of contact elements (radius of curvature of the contact elements. Material of examination contact pairs is steel ASTM A-295 hardness 64-66 HRC. The measurement results indicate a very significant impact on the temperature coefficient of friction, normal load and contact geometry (the radius of curvature of the contact elements. According to the authors future research should focus on optimizing the choice of materials that under the given conditions of mechanical and thermal load of contact to ensure a minimum value of the coefficient of rolling friction.

  17. Effect of particle-fiber friction coefficient on ultrafine aerosol particles clogging in nanofiber based filter

    Science.gov (United States)

    Sambaer, Wannes; Zatloukal, Martin; Kimmer, Dusan

    2013-04-01

    Realistic SEM image based 3D filter model considering transition/free molecular flow regime, Brownian diffusion, aerodynamic slip, particle-fiber and particle-particle interactions together with a novel Euclidian distance map based methodology for the pressure drop calculation has been utilized for a polyurethane nanofiber based filter prepared via electrospinning process in order to more deeply understand the effect of particle-fiber friction coefficient on filter clogging and basic filter characteristics. Based on the performed theoretical analysis, it has been revealed that the increase in the fiber-particle friction coefficient causes, firstly, more weaker particle penetration in the filter, creation of dense top layers and generation of higher pressure drop (surface filtration) in comparison with lower particle-fiber friction coefficient filter for which deeper particle penetration takes place (depth filtration), secondly, higher filtration efficiency, thirdly, higher quality factor and finally, higher quality factor sensitivity to the increased collected particle mass. Moreover, it has been revealed that even if the particle-fiber friction coefficient is different, the cake morphology is very similar.

  18. Accurate measurement of the kinetic coefficient of friction between a surface and a granular mass

    NARCIS (Netherlands)

    Rademacher, F.J.C.

    1978-01-01

    A device has been developed for correct measurement of the kinematic coefficient of friction between a cohesionless granular material and a surface. Particle size may range from 0.5 up to about 9 mm, depending somewhat on the desired accuracy. Sliding velocity of the granules with respect to the sur

  19. Inversion for basal friction coefficients with a two-dimensional flow line model using Tikhonov regularization

    Directory of Open Access Journals (Sweden)

    Yuri V. Konovalov

    2012-09-01

    Full Text Available We present results of basal friction coefficient inversion. The inversion was performed by a 2D flow line model for one of the four fast flowing ice streams on the southern side of the Academy of Sciences Ice Cap in the Komsomolets Island, Severnaya Zemlya archipelago. The input data for the performance of both the forward and the inverse problems included synthetic aperture radar interferometry ice surface velocities, ice surface elevations and ice thicknesses obtained by airborne measurements (all were taken from Dowdeswell et al., 2002. Numerical experiments with: i different sea level shifts; and ii randomly perturbed friction coefficient have been carried out in the forward problem. The impact of sea level changes on vertical distribution of horizontal velocity and on shear stress distribution near the ice front has been investigated in experiments with different sea level shifts. The experiments with randomly perturbed friction coefficient have revealed that the modeled surface velocity is weakly sensitive to the perturbations and, therefore, the inverse problem should be considered ill posed. To mitigate ill posedness of the inverse problem, Tikhonov’s regularization was applied. The regularization parameter was determined from the relation of the discrepancy between observed and modeled velocities to the regularization parameter. The inversion was performed for both linear and non-linear sliding laws. The inverted spatial distributions of the basal friction coefficient are similar for both sliding laws. The similarity between these inverted distributions suggests that the changes in the friction coefficient are accompanied by appropriate water content variations at the glacier base.

  20. Local convective heat transfer coefficient and friction factor of CuO/water nanofluid in a microchannel heat sink

    Science.gov (United States)

    Chabi, A. R.; Zarrinabadi, S.; Peyghambarzadeh, S. M.; Hashemabadi, S. H.; Salimi, M.

    2017-02-01

    Forced convective heat transfer in a microchannel heat sink (MCHS) using CuO/water nanofluids with 0.1 and 0.2 vol% as coolant was investigated. The experiments were focused on the heat transfer enhancement in the channel entrance region at Re Hydraulic performance of the MCHS was also estimated by measuring friction factor and pressure drop. Results showed that higher convective heat transfer coefficient was obtained at the microchannel entrance. Maximum enhancement of the average heat transfer coefficient compared with deionized water was about 40 % for 0.2 vol% nanofluid at Re = 1150. Enhancement of the convective heat transfer coefficient of nanofluid decreased with further increasing of Reynolds number.

  1. Diffusion Coefficient of Helium in Mo-Assessed by the Internal Friction Technique

    Institute of Scientific and Technical Information of China (English)

    WANG Weiguo; YANG Junfeng; WANG Xianping; XIE Chunyi; LI Renhong; CHEN Junling; FANG Qianfeng

    2009-01-01

    Diffusion behavior of helium in molybdenum was investigated by means of the in-ternal friction method. An apparent relaxation internal friction peak associated with helium long-range diffusion was observed around 475 K at a resonant frequency of 56 Hz. In terms of the Gorsky relaxation model and the shift of the peak position with the measurement frequency, the activation energy and pre-exponential factor of the diffusion coefficient of the helium atoms in molybdenum were deduced as 0.63 eV and 6.5 cm2/s, respectively.

  2. Coefficient of Friction Measurements for Thermoplastics and Fibre Composites Under Low Sliding Velocity and High Pressure

    DEFF Research Database (Denmark)

    Poulios, Konstantinos; Svendsen, Gustav Winther; Hiller, Jochen

    2013-01-01

    that friction materials which are untypical for brake applications, like thermoplastics and fibre composites, can offer superior performance in terms of braking torque, wear resistance and cost than typical brake linings. In this paper coefficient of friction measurements for various thermoplastic and fibre...... composite materials running against a steel surface are presented. All tests were carried out on a pinon-disc test-rig in reciprocating operation at a fixed sliding speed and various pressure levels for both dry and grease lubricated conditions. Moreover, a generic theoretical framework is introduced...

  3. Improve Simulation of Plain Bearings in Dry and Mixed Lubrication Regime by Defining Locally Resolved Dry Friction Coefficients

    Directory of Open Access Journals (Sweden)

    C. Schneider

    2015-06-01

    Full Text Available Asperity friction is a main indicator for wear and heat conduction [1]. It occurs when thickness of oil film shrinks due to high load or slow speed. Friction is scientifically well known as long as it is dominated by laminar oil film effects. If film thickness shrinks, the friction coefficient depends mainly on surface properties. This inaccuracy is normally preceded in simulation by using friction coefficients defined by Coulomb’s law [2]. To improve simulation results, the simulated friction moment was compared to measurement on a component test rig. Friction moment is produced on every square millimetre of the bearing surface, but can only be measured as an integral. Research findings show that measured results can’t be met by using one global dry friction coefficient for the whole bearing surface, even though it is material dependent. By introducing locally resolved and asperity pressure dependent dry friction coefficients, it was possible to adapt the simulated friction moment to measure one with a deviation of less than 5 percent. By means of simulation it was possible to develop locally resolved results based on integral measurements; and improve modelling the frictional state of mixed lubrication.

  4. Anomalous Velocity Dependence of the Friction Coefficient of an Air Supported Pulley

    Science.gov (United States)

    Crismani, Matteo; Nauenberg, Michael

    2009-11-01

    A standard undergraduate lab exercise to verify Newton's law, F = ma, is to measure the acceleration a of a glider of mass m suspended on an air track. In our experiment the glider is accelerated by a thin tape attached to the glider at one end, and to a weight of mass M at the other end. The weight hangs vertically via a pulley over which the tape is suspended by air pressure. In the absence of friction, the force pulling the glider is F = (M m/(M + m)g, where g is the acceleration of gravity. To the accuracy provided by the fast electronic timers (accurate to 1/10000 second) used in our experiment to measure the velocity and the acceleration of the glider, we verified that the friction due to the air track can be neglected. But we found that this is not the case for the friction due to the air pulley which adds a component -v/T to the force F on the glider, where T is the friction coefficient. We have measured the dependence of this coefficient on v, and found an excellent analytic fit to our data. This fit deviates considerable from the conventional assumption that 1/T is a constant and/or depends linearly on v.

  5. Effect of Lubricant Viscosity and Surface Roughness on Coefficient of Friction in Rolling Contact

    Directory of Open Access Journals (Sweden)

    S.G. Ghalme

    2013-12-01

    Full Text Available The main objective of this paper is to investigate the effect of surface roughness and lubricant viscosity on coefficient of friction in silicon nitride- steel rolling contact. Two samples of silicon nitride with two different values of surface roughness were tested against steel counter face. The test was performed on four ball tester in presence of lubricant with two different values of viscosity. Taguchi technique a methodology in design of experiment implemented to plan the experimentation and same is utilized to evaluate the interacting effect of surface roughness and lubricant viscosity. Analysis of experimental results presents a strong interaction between surface roughness and lubricant viscosity on coefficient of friction in rolling contact.

  6. Studies in molecular dynamics of the friction coefficient and the Lorentz gas

    Energy Technology Data Exchange (ETDEWEB)

    Alley, W.E.

    1979-06-01

    The thesis consists of three hard-sphere molecular dynamics studies. The first describes a modification of Fick's diffusion law, required whenever long-time correlations are present. The second study concerns the mass and size dependence of the friction coefficient as well as its dependence on boundary conditions. The study presents a molecular dynamics method which calculates the infinite-mass friction coefficient of finite size hard-sphere particles. The third study presents the applicability of hydrodynamics to describe fluctuations in fluids on the molecular level. This study shows that the fluctuations present in a system of hard spheres when placed between closely spaced parallel hard walls lead to an acoustical resonance for those wavelengths which correspond to the spacing, or integer fractions thereof.

  7. Coefficient of Friction Measurements for Thermoplastics and Fiber Composites under Low Sliding Velocity and High Pressure

    DEFF Research Database (Denmark)

    Poulios, Konstantinos; Svendsen, G.; Hiller, Jochen

    2012-01-01

    materials which are untypical for brake applications, like thermoplastics and fiber composites, can offer superior performance in terms of braking torque, wear resistance and cost than typical brake linings. In this paper coefficient of friction measurements for various thermoplastic and fiber composite...... materials running against a steel surface are presented. All tests were carried out on a pin-on-disc test-rig at a fixed sliding speed and various pressure levels for both dry and grease lubricated conditions....

  8. On the nature of the coefficient of friction of diamond-like carbon films deposited on rubber

    NARCIS (Netherlands)

    Martinez-Martinez, D.; van der Pal, J. P.; Schenkel, M.; Shaha, K. P.; Pei, Y. T.; De Hosson, J. Th M.

    2012-01-01

    In this paper, the nature of the coefficient of friction (CoF) of diamond-like carbon (DLC)-protected rubbers is studied. The relative importance of the viscoelastic and adhesive contributions to the overall friction is evaluated experimentally by modifying the contact load and the adhesive strength

  9. NGA-West 2 GMPE average site coefficients for use in earthquake-resistant design

    Science.gov (United States)

    Borcherdt, Roger D.

    2015-01-01

    Site coefficients corresponding to those in tables 11.4–1 and 11.4–2 of Minimum Design Loads for Buildings and Other Structures published by the American Society of Civil Engineers (Standard ASCE/SEI 7-10) are derived from four of the Next Generation Attenuation West2 (NGA-W2) Ground-Motion Prediction Equations (GMPEs). The resulting coefficients are compared with those derived by other researchers and those derived from the NGA-West1 database. The derivation of the NGA-W2 average site coefficients provides a simple procedure to update site coefficients with each update in the Maximum Considered Earthquake Response MCER maps. The simple procedure yields average site coefficients consistent with those derived for site-specific design purposes. The NGA-W2 GMPEs provide simple scale factors to reduce conservatism in current simplified design procedures.

  10. Electromechanical imitator of antilock braking modes of wheels with pneumatic tire and its application for the runways friction coefficient measurement

    Science.gov (United States)

    Putov, A. V.; Kopichev, M. M.; Ignatiev, K. V.; Putov, V. V.; Stotckaia, A. D.

    2017-01-01

    In this paper it is considered a discussion of the technique that realizes a brand new method of runway friction coefficient measurement based upon the proposed principle of measuring wheel braking control for the imitation of antilock braking modes that are close to the real braking modes of the aircraft chassis while landing that are realized by the aircraft anti-skid systems. Also here is the description of the model of towed measuring device that realizes a new technique of runway friction coefficient measuring, based upon the measuring wheel braking control principle. For increasing the repeatability accuracy of electromechanical braking imitation system the sideslip (brake) adaptive control system is proposed. Based upon the Burkhard model and additive random processes several mathematical models were created that describes the friction coefficient arrangement along the airstrip with different qualitative adjectives. Computer models of friction coefficient measuring were designed and first in the world the research of correlation between the friction coefficient measuring results and shape variations, intensity and cycle frequency of the measuring wheel antilock braking modes. The sketch engineering documentation was designed and prototype of the latest generation measuring device is ready to use. The measuring device was tested on the autonomous electromechanical examination laboratory treadmill bench. The experiments approved effectiveness of method of imitation the antilock braking modes for solving the problem of correlation of the runway friction coefficient measuring.

  11. Determination of coefficient of friction for self-expanding stent-grafts.

    Science.gov (United States)

    Vad, Siddharth; Eskinazi, Amanda; Corbett, Timothy; McGloughlin, Tim; Vande Geest, Jonathan P

    2010-12-01

    Migration of stent-grafts (SGs) after endovascular aneurysm repair of abdominal aortic aneurysms is a serious complication that may require secondary intervention. Experimental, analytical, and computational studies have been carried out in the past to understand the factors responsible for migration. In an experimental setting, it can be very challenging to correctly capture and understand the interaction between a SG and an artery. Quantities such as coefficient of friction (COF) and contact pressures that characterize this interaction are difficult to measure using an experimental approach. This behavior can be investigated with good accuracy using finite element modeling. Although finite element models are able to incorporate frictional behavior of SGs, the absence of reliable values of coefficient of friction make these simulations unreliable. The aim of this paper is to demonstrate a method for determining the coefficients of friction of a self-expanding endovascular stent-graft. The methodology is demonstrated by considering three commercially available self-expanding SGs, labeled as A, B, and C. The SGs were compressed, expanded, and pulled out of polymeric cylinders of varying diameters and the pullout force was recorded in each case. The SG geometries were recreated using computer-aided design modeling and the entire experiment was simulated in ABAQUS 6.8/STANDARD. An optimization procedure was carried out for each SG oversize configuration to determine the COF that generated a frictional force corresponding to that measured in the experiment. The experimental pullout force and analytically determined COF for SGs A, B, and C were in the range of 6-9 N, 3-12 N, and 3-9 N and 0.08-0.16, 0.22-0.46, and 0.012-0.018, respectively. The computational model predicted COFs in the range of 0.00025-0.0055, 0.025-0.07, and 0.00025-0.006 for SGs A, B, and C, respectively. Our results suggest that for SGs A and B, which are exoskeleton based devices, the pullout forces

  12. Optimization of method a load cell calibration for the measurement of coefficient of friction

    Science.gov (United States)

    Castro, R. M.; Pereira, M.; Sousa, A. R.; Curi, E. I. M.; Izidoro, C. L.; Correa, L. C.

    2016-07-01

    The instrumentation of equipment for mechanical testing is used to optimize the time to deliver a result, besides minimizing errors associated with manual measurements. Given this context, this work aims to present a calibration method for a load cell to determine the measurement results of force and friction coefficient, developed from on rotary pin-on-disk tribometer. The results indicate that the procedure provides measurements reliable for the tribological phenomena, resulting in with proximity the values provided by the ASTM G99-04.

  13. Relationship Between Measured Friction Coefficients and Two Tread Groove Design Parameters for Footwear Pads

    Institute of Scientific and Technical Information of China (English)

    LI Kai Way; CHEN Chin Jung; LIN Ching-Hua; HSU Yao Wen

    2006-01-01

    The shoe sole geometrical design parameters are believed to be important factors affecting the coefficient of friction (COF) between the shoe/floor interface. This study is concerned with the relationship between the measured COF and the tread groove orientation and width on the footwear pad. Friction measurements using the Brungraber Mark Ⅱ slipmeter were conducted. Six tread groove width/orientations designs on the footwear pads under 27 footwear material/floor/contamination conditions were tested. The results show that tread orientation and width affect the measured COF significantly. Wider grooved footwear pads result in higher COF values and footwear pads with tread grooves perpendicular to the friction measurement direction have higher COF values. A regression model using measured COF as the dependent variable and tread groove width, groove orientation, footwear material, floor, and contamination conditions as independent variables was established. The models are significant at p<0.0001 with R2 of 0.97, which may be used in predicting the COF at the shoe-floor interface.

  14. On the Effect of Counterface Materials on Interface Temperature and Friction Coefficient of GFRE Composite Under Dry Sliding Contact

    Directory of Open Access Journals (Sweden)

    N. S.M. El-Tayeb

    2005-01-01

    Full Text Available Nowadays, there is an increase interest in polymeric composite materials for high-performance in many industrial applications. In other words, the tribo-studies on polymeric materials are growing fast to enhance the polymeric products such as bearings, seals, ring and bushes. The current work presents an attempt to study the correlation between the type of counterface material and frictional heating at the interface surfaces for different, normal loads (23N, 49N and 72N, sliding velocities (0.18, 1.3 and 5.2 m sˉ1 and interval time (0-720 sec. Sliding friction experiments are performed on a pin-on-ring (POR tribometer under dry contact condition. Interface temperature and friction force were measured simultaneously during sliding of glass fiber reinforced epoxy (GFRE composite against three different counter face materials, hardened steel (HS, cast iron (CI and Aluminum alloy (Al. Experimental results showed that the type of counterface material greatly influences both interface temperature and friction coefficient. Higher temperature and friction coefficient were evident when sliding took place against HS surface, compared to sliding against CI and Al under same condition. When sliding took place against HS, the friction coefficient of GFRE composite was about an order of magnitude higher than sliding the GFRE composite against the other counter face materials. Based on the optical microscope graphs, the friction and induced temperature results of GFRE composite are analyzed and discussed.

  15. A hybrid PSO-SVM-based method for predicting the friction coefficient between aircraft tire and coating

    Science.gov (United States)

    Zhan, Liwei; Li, Chengwei

    2017-02-01

    A hybrid PSO-SVM-based model is proposed to predict the friction coefficient between aircraft tire and coating. The presented hybrid model combines a support vector machine (SVM) with particle swarm optimization (PSO) technique. SVM has been adopted to solve regression problems successfully. Its regression accuracy is greatly related to optimizing parameters such as the regularization constant C , the parameter gamma γ corresponding to RBF kernel and the epsilon parameter \\varepsilon in the SVM training procedure. However, the friction coefficient which is predicted based on SVM has yet to be explored between aircraft tire and coating. The experiment reveals that drop height and tire rotational speed are the factors affecting friction coefficient. Bearing in mind, the friction coefficient can been predicted using the hybrid PSO-SVM-based model by the measured friction coefficient between aircraft tire and coating. To compare regression accuracy, a grid search (GS) method and a genetic algorithm (GA) are used to optimize the relevant parameters (C , γ and \\varepsilon ), respectively. The regression accuracy could be reflected by the coefficient of determination ({{R}2} ). The result shows that the hybrid PSO-RBF-SVM-based model has better accuracy compared with the GS-RBF-SVM- and GA-RBF-SVM-based models. The agreement of this model (PSO-RBF-SVM) with experiment data confirms its good performance.

  16. AN INEQUALITY BETWEEN THE WEIGHTED AVERAGE AND THE ROWWISE CORRELATION-COEFFICIENT FOR PROXIMITY MATRICES

    NARCIS (Netherlands)

    KRIJNEN, WP

    1994-01-01

    De Vries (1993) discusses Pearson's product-moment correlation, Spearman's rank correlation, and Kendall's rank-correlation coefficient for assessing the association between the rows of two proximity matrices. For each of these he introduces a weighted average variant and a rowwise variant. In this

  17. Choosing the best index for the average score intraclass correlation coefficient.

    Science.gov (United States)

    Shieh, Gwowen

    2016-09-01

    The intraclass correlation coefficient (ICC)(2) index from a one-way random effects model is widely used to describe the reliability of mean ratings in behavioral, educational, and psychological research. Despite its apparent utility, the essential property of ICC(2) as a point estimator of the average score intraclass correlation coefficient is seldom mentioned. This article considers several potential measures and compares their performance with ICC(2). Analytical derivations and numerical examinations are presented to assess the bias and mean square error of the alternative estimators. The results suggest that more advantageous indices can be recommended over ICC(2) for their theoretical implication and computational ease.

  18. PROPERTIES OF CP: COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS, AND REACTION TO SPARK, FRICTION AND IMPACT

    Energy Technology Data Exchange (ETDEWEB)

    Weese, R K; Burnham, A K

    2005-09-28

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear and isothermal heating, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Differential scanning calorimetry, DSC, was used to monitor CP decomposition at linear heating rates of 1-7 C min{sup -1} in perforated pans and of 0.1-1.0 C min{sup -1} in sealed pans. The kinetic triplet was calculated using the LLNL code Kinetics05, and predictions for 210 and 240 C are compared to isothermal thermogravimetric analysis (TGA) experiments. Values are also reported for spark, friction, and impact sensitivity.

  19. Shear-­induced segregation of granular particles with different friction coefficients

    Science.gov (United States)

    Gillemot, Katalin; Somfai, Ellák; Börzsönyi, Tamás

    2016-04-01

    Segregation plays a major role in a large number of geological mechanisms, including sediment transport, bedsurface and bedload dynamics. Segregation induced by size or density difference of the particles was widely studied, but less attention has been given to the effects of surface friction of the particles. In the current study we address both experimentally and numerically the question of shear-induced segregation of a two component granular mixture, when the friction coefficients of the particles differ. For a system under gravity, we found both in the experiments and with the help of discreet element simulations that particles having a smoother surface tend to sink downwards. This is similar to the well described kinetic sieving of smaller or denser particles. In our case the smooth particles are more likely to fall into holes created by the shearing then the rough ones. Removing the gravitational field (simulations only) segregation persists and can be related to the distribution of the granular temperature in the system. Understanding the driving mechanisms may help us to better describe the more complex segregation patterns found in real life.

  20. EFFECT OF MOISTURE CONTENT AND PARTICLE SIZE ON BULK DENSITY, POROSITY, PARTICLE DENSITY AND COEFFICIENT OF FRICTION OF COIR PITH

    Directory of Open Access Journals (Sweden)

    Dr.I.Neethi Manickam,

    2011-04-01

    Full Text Available Coir pith can be used as fuel in loose form or in briquettes. Bulk density, coefficient of friction, porosity and particle density affects densification and combustion of coir pith. The moisture content and particle size ranges were 10.1 to 60.2%w.b. and 0.098 to 0.925mm respectively. Porosity was varied from 0.623 to 0.862 and the particle density was varied from 0.939 to 0.605 gm/cc for the above ranges of moisture content and particle size. Bulk density was in the range of 0.097 to 0.341gm/cc. The coefficient of friction against mild steel was in the range of 0.5043 to 0.6332. Models were developed to find out bulk density, porosity, particle density and coefficient of friction for different moisture content and particle size.

  1. Portable Tester Friction (PFT). Mesures du coefficient de frottement dynamique de revêtements de sol

    OpenAIRE

    Marchal, P.; Jacques, M.

    2014-01-01

    Le Portable Tester Friction (PFT) est un appareil destiné à mesurer le coefficient de frottement dynamique d’un revêtement de sol en laboratoire et sur site. Ce document décrit le protocole de mesure avec le PFT et les résultats de mesures effectuées sur un panel de quinze revêtements de sol de caractéristiques différentes (matériaux, états de surface) réalisées en présence de deux polluants (huile et solution d’eau). Le PFT présente une très bonne sensibilité et une très bonne répétabilité. ...

  2. A Study on Bottom Friction Coefficient in the Bohai, Yellow, and East China Sea

    Directory of Open Access Journals (Sweden)

    Daosheng Wang

    2014-01-01

    Full Text Available The adjoint tidal model based on the theory of inverse problem has been applied to investigate the effect of bottom friction coefficient (BFC on the tidal simulation. Using different schemes of BFC containing the constant, different constant in different subdomain, depth-dependent form, and spatial distribution obtained from data assimilation, the M2 constituent in the Bohai, Yellow, and East China Sea (BYECS is simulated by assimilating TOPEX/Poseidon altimeter data, respectively. The simulated result with spatially varying BFC obtained from data assimilation is better than others. Results and analysis of BFC in BYECS indicate that spatially varying BFC obtained from data assimilation is the best fitted one; meanwhile it could improve the accuracy in the simulation of M2 constituent. Through the analysis of the best fitted one, new empirical formulas of BFC in BYECS are developed with which the commendable simulated results of M2 constituent in BYECS are obtained.

  3. Velocity dependence of coefficient of friction of diamond like carbon coatings

    Science.gov (United States)

    Sharma, Neha; Kumar, Niranjan; Dash, S.; Tyagi, A. K.

    2012-06-01

    The velocity dependence of coefficient of friction (CoF) of hydrogen-free and hydrogenated Diamond Like Carbon (DLC) coatings was studied on sliding. In low velocity regime, CoF of hydrogen-free DLC was found to increase which may be linked to a thermally activated pre-mature breaking of the surface asperities. However, CoF of hydrogenated DLC was found to decrease due to formation of graphite like lubricious layer and sustainability of cross-linked network of H-bonded atoms. In high velocity regime, CoF of hydrogen free DLC increases marginally due to an inefficient transfer of thermal energy while that of hydrogenated DLC increases due to rapid formation and rupture of atomic bonds.

  4. Influence of the tool temperature increment on the coefficient of friction behavior on the deep drawing process of HSS

    Science.gov (United States)

    Gil, I.; Galdos, L.; Mugarra, E.; Mendiguren, J.; Saenz de Argandoña, E.

    2016-11-01

    The use of High Strength Steels (HSS) in the deep drawing processes has an impact on the temperature that is achieved on the die surfaces. Due to the heat that is created through the deformation of the material and the friction itself, the tools temperature increase considerably up to approximately 100°C. This temperature increment has an effect on both the wear of the surface and also the coefficient of friction (COF). In this work the influence of the tool temperature on the coefficient of friction is studied. For that, Strip Drawing Tests have been carried out at different tool temperatures with a DP780, High Strength Steel. Moreover, different contact pressures have been considered in the study to analyse the combined effect of the contact pressure with the temperature increment. It has been proved that the temperature increment has to be taken into account to predict accurately the behavior of the coefficient of friction between the sheet and the tool. This change in the coefficient of friction has a high impact on the prediction of the deep drawing process.

  5. The friction coefficient evolution of a MoS2/WC multi-layer coating system during sliding wear

    Science.gov (United States)

    Chan, T. Y.; Hu, Y.; Gharbi, Mohammad M.; Politis, D. J.; Wang, L.

    2016-08-01

    This paper discusses the evolution of friction coefficient for the multi-layered Molybdenum Disulphide (MoS2) and WC coated substrate during sliding against Aluminium AA 6082 material. A soft MoS2 coating was prepared over a hard WC coated G3500 cast iron tool substrate and underwent friction test using a pin-on-disc tribometer. The lifetime of the coating was reduced with increasing load while the Aluminium debris accumulated on the WC hard coating surfaces, accelerated the breakdown of the coatings. The lifetime of the coating was represented by the friction coefficient and the sliding distance before MoS2 coating breakdown and was found to be affected by the load applied and the wear mechanism.

  6. STRESS ANALYSIS IN CUTTING TOOLS COATED TiN AND EFFECT OF THE FRICTION COEFFICIENT IN TOOL-CHIP INTERFACE

    Directory of Open Access Journals (Sweden)

    Kubilay ASLANTAŞ

    2003-02-01

    Full Text Available The coated tools are regularly used in today's metal cutting industry. Because, it is well known that thin and hard coatings can reduce tool wear, improve tool life and productivity. Such coatings have significantly contributed to the improvements cutting economies and cutting tool performance through lower tool wear and reduced cutting forces. TiN coatings have especially high strength and low friction coefficients. During the cutting process, low friction coefficient reduce damage in cutting tool. In addition, maximum stress values between coating and substrate also decrease as the friction coefficient decreases. In the present study, stress analysis is carried out for HSS (High Speed Steel cutting tool coated with TiN. The effect of the friction coefficient between tool and chip on the stresses developed at the cutting tool surface and interface of coating and HSS is investigated. Damage zones during cutting process was also attempted to determine. Finite elements method is used for the solution of the problem and FRANC2D finite element program is selected for numerical solutions.

  7. Efficiencies and coefficients of performance of heat engines, refrigerators, and heat pumps with friction: a universal limiting behavior.

    Science.gov (United States)

    Bizarro, João P S; Rodrigues, Paulo

    2012-11-01

    For work-producing heat engines, or work-consuming refrigerators and heat pumps, the percentage decrease caused by friction in their efficiencies, or coefficients of performance (COP's), is approximately given by the ratio W(fric)/W between the work spent against friction forces and the work performed by, or delivered to, the working fluid. This universal scaling, which applies in the limit of small friction (W(fric)/W heat-engine efficiencies), allows a simple and quick estimate of the impact that friction losses can have on the FOM's of thermal engines and plants, or of the level of those losses from the observed and predicted FOM's. In the case of refrigerators and heat pumps, if W(fric)/W heat engines), the COP percentage decrease due to friction approaches asymptotically (W(fric)/W)/(1+W(fric)/W) instead of W(fric)/W. Estimates for the level of frictional losses using the Carnot (or, for heat engines and power plants only, the Curzon-Ahlborn) predictions and observed FOM's of real power plants, heat engines, refrigerators, and heat pumps show that they usually operate in domains where these behaviors are valid.

  8. Use of the quartz crystal microbalance to determine the monomeric friction coefficient of polyimides

    Science.gov (United States)

    Bechtold, Mary M.

    1995-01-01

    When a thin film of polymer is coated on to a quartz crystal microbalance (QCM), the QCM can be used to detect the rate of increase in weight of the polymer film as the volatile penetrant diffuses into the polymer. From this rate information the diffusion coefficient of the penetrant into the polymer can be computed. Calculations requiring this diffusion coefficient lead to values which approximate the monomeric friction coefficient of the polymer. This project has been concerned with the trial of crystal oscillating circuits suitable for driving polymer coated crystals in an atmosphere of penetrant. For these studies done at room temperature, natural rubber was used as an easily applied polymer that is readily penetrated by toluene vapors, qualities anticipated with polyimides when they are tested at T(g) in the presence of toluene. Three quartz crystal oscillator circuits were tested. The simplest circuit used +/- 5 volt dc and had a transistor to transistor logic (TTL) inverter chip that provides a 180 deg phase shift via a feed back loop. This oscillator circuit was stable but would not drive the crystal when the crystal was coated with polymer and subjected to toluene vapors. Removal of a variable resistor from this circuit increased stability but did not otherwise increase performance. Another driver circuit tested contained a two stage differential input, differential output, wide band video amplifier and also contain a feed back loop. The circuit voltage could not be varied and operated at +/- 5 volts dc; this circuit was also stable but failed to oscillate the polymer coated crystal in an atmosphere saturated with toluene vapors. The third oscillator circuit was of similar construction and relied on the same video amplifier but allowed operation with variable voltage. This circuit would drive the crystal when the crystal was submerged in liquid toluene and when the crystal was coated with polymer and immersed in toluene vapors. The frequency readings

  9. Estimation of tire-road friction coefficient based on frequency domain data fusion

    Science.gov (United States)

    Chen, Long; Luo, Yugong; Bian, Mingyuan; Qin, Zhaobo; Luo, Jian; Li, Keqiang

    2017-02-01

    Due to the noise of sensing equipment, the tire states, such as the sideslip angle and the slip ratio, cannot be accurately observed under the conditions with small acceleration, which results in the inapplicability of the time domain data based tire-road friction coefficient (TRFC) estimation method. In order to overcome this shortcoming, frequency domain data fusion is proposed to estimate the TRFC based on the natural frequencies of the steering system and the in-wheel motor driving system. Firstly, a relationship between TRFC and the steering system natural frequency is deduced by investigating its frequency response function (FRF). Then the lateral TRFC is determined by the steering natural frequency which is only identified using the information of the assist motor current and the steering speed of the column. With spectral comparison between the steering and driving systems, the data fusion is carried out to get a comprehensive TRFC result, using the different frequency information of the longitudinal and lateral value. Finally, simulations and experiments on different road surfaces validated the correctness of the steering system FRF and the effectiveness of the proposed approach.

  10. Laser texturing of Hastelloy C276 alloy surface for improved hydrophobicity and friction coefficient

    Science.gov (United States)

    Yilbas, B. S.; Ali, H.

    2016-03-01

    Laser treatment of Hastelloy C276 alloy is carried out under the high pressure nitrogen assisting gas environment. Morphological and metallurgical changes in the laser treated layer are examined using the analytical tools including, scanning electron and atomic force microscopes, X-ray diffraction, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. Microhardness is measured and the residual stress formed in the laser treated surface is determined from the X-ray data. The hydrophibicity of the laser treated surface is assessed using the sessile drop method. Friction coefficient of the laser treated layer is obtained incorporating the micro-tribometer. It is found that closely spaced laser canning tracks create a self-annealing effect in the laser treated layer and lowers the thermal stress levels through modifying the cooling rates at the surface. A dense structure, consisting of fine size grains, enhances the microhardness of the surface. The residual stress formed at the surface is compressive and it is in the order of -800 MPa. Laser treatment improves the surface hydrophobicity significantly because of the formation of surface texture composing of micro/nano-pillars.

  11. Low friction coefficient coatings Ni-Cr by magnetron sputtering, DC

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Hernandez, J.; Mandujano-Ruiz, A.; Torres-Gonzalez, J.; Espinosa-Beltran, F. J.; Herrera-Hernandez, H.

    2015-07-01

    Magnetron Sputter Deposition technique with DC was used for the deposition of Ni-Cr coatings on AISI 316 SS like substrate. The cathode with a nominal composition Ni-22 at% Cr was prepared by Mechanical Alloying (MA) technique, with a maximum milling time of 16 hours and, with a high energy SPEX 8000 mill. The coatings were made under Argon atmosphere at room temperature with a power of 100 W at different times of growth. Chemical composition, microstructure, topography, nano hardness and wear of the coatings were evaluated using the techniques of microanalysis by energy dispersive X-ray analyzer (EDAX), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Nano-indentation and pin-on-Disk, respectively. After milling, was not detected contamination in the mixtures. XRD analysis revealed that the microstructure of the Ni-Cr alloy was maintained in the coatings with respect to MA powders, with some degree of recrystallization. Nano hardness values were in the order of 8.8 GPa with a Youngs modulus of 195 GPa. The adhesion of the films was evaluated according to their resistance to fracture when these were indented at different loads using Vickers microhardness. The wear test results showed a decrease in the friction coefficient with respect to the increase of thickness films, getting a minimum value of 0.08 with a thickness of 1 μm and which correspond with the maximum growing time. (Author)

  12. Micromachined strain gauges for the determination of liquid flow friction coefficients in microchannels

    Science.gov (United States)

    Baviere, R.; Ayela, F.

    2004-02-01

    In this research program, we have performed and tested cupro-nickel (Cu-Ni) strain gauges micromachined on different sorts of silicon nitride (Si3N4) membranes. The design of the gauges obeys an electrical Wheatstone bridge configuration. We have found a good agreement between the expected electromechanical response of the bridge and the experimental signals. The results have displayed sensitivity to static pressure ranging from 50 to 100 µV V-1 bar-1 as a function of the thickness and of the diameter of the membranes. This is part of a study devoted to determining liquid flow friction coefficients in silicon-Pyrex microchannels. Preliminary attempts (Reynolds number up to 300) made using global pressure measurements and with very simple local pressure probes are discussed. Further experiments using Cu-Ni strain gauges are described. Their micromachining, characterization and integration along silicon microchannels are presented. These sensors permitted us to perform the first local and reliable pressure drop measurements in a 7.5 µm deep microchannel. The results are in good agreement with the classical laminar theory for a Reynolds number ranging from 0.2 to 3.

  13. Measurement of Vehicle Tire-to-Road Coefficient of Friction with a Portable Microcomputerized Transducer.

    Science.gov (United States)

    1982-08-01

    Rabinowicz , E.,Friction and Wear of Materials, John Wiley & Sons, New York, 1965. C24) Calcote, L. R., "A Comparison of High-Speed Photo- graphy and...May 1981. [23] Rabinowicz , E.,Friction and Wear of Materials, John Wiley & Sons, New Yo-, 5-7 [24] Calcote, L. R., "A Comparison of High-Speed Photo

  14. Sustained frictional instabilities on nanodomed surfaces: Stick-slip amplitude coefficient

    DEFF Research Database (Denmark)

    Quignon, Benoit; Pilkington, Georgia A.; Thormann, Esben

    2013-01-01

    of the nanodomed surfaces cannot be fully described by the framework of Amontons' laws of friction and that additional parameters (e.g., σf and SSAC) are required, when their friction, lubrication, and wear properties are important considerations in related nanodevices. © 2013 American Chemical Society....

  15. A Method to Estimate Friction Coefficient from Orientation Distribution of Meso-scale Faults: Applications to Faults in Forearc Sediment and Underplated Tectonic Mélange

    Science.gov (United States)

    Sato, K.

    2015-12-01

    Friction coefficients along faults control the brittle strength of the earth's upper crust, although it is difficult to estimate them especially of ancient geological faults. Several previous studies tried to determine the friction coefficient of meso-scale faults from their orientation distribution as follows. Fault-slip analysis through stress tensor inversion techniques gives principal stress axes and a stress ratio, which allows us to draw a normalized Mohr's circle. Assuming that a faulting occurs when the ratio of shear stress to normal stress on it, i.e., the slip tendency, exceeds the friction coefficient, one can find a linear boundary of distribution of points corresponding to faults on Mohr diagram. The slope of the boundary (friction envelope) provides the friction coefficient. This method has a difficulty in graphically and manually recognizing the linear boundary of distribution on the Mohr diagram. This study automated the determination of friction coefficient by considering the fluctuations of fluid pressure and differential stress. These unknown factors are expected to make difference in density of points representing faults on the Mohr diagram. Since the density is controlled by the friction coefficient, we can optimize the friction coefficient so as to explain the density distribution. The method was applied to two examples of natural meso-scale faults. The first example is from the Pleistocene Kazusa Group, central Japan, which filled a forearc basin of the Sagami Trough. Stress inversion analysis showed WNW-ENE trending tensional stress with a low stress ratio. The friction coefficient was determined to be around 0.66, which is typical value for sandstone. The Second example is from an underplated tectonic mélange in the Cretaceous to Paleogene Shimanto accretionary complex in southwest Japan along the Nankai Trough. The stress condition was determined to be an axial compression perpendicular to the foliation of shale matrix. The friction

  16. Morphology characterization and friction coefficient determination of sputtered V{sub 2}O{sub 5} films

    Energy Technology Data Exchange (ETDEWEB)

    Kluensner, T.; Shen, Q.; Hlawacek, G. [Institute of Physics, University of Leoben, Franz-Josef-Strasse 18, A-8700 Leoben (Austria); Teichert, C., E-mail: teichert@unileoben.ac.a [Institute of Physics, University of Leoben, Franz-Josef-Strasse 18, A-8700 Leoben (Austria); Fateh, N.; Fontalvo, G.A.; Mitterer, C. [Department of Physical Metallurgy and Materials Testing, University of Leoben, Franz-Josef-Strasse 18, A-8700 Leoben (Austria)

    2010-12-01

    The morphology of V{sub 2}O{sub 5} low-friction coatings on MgO (001) substrates synthesized by unbalanced reactive magnetron sputtering was investigated using atomic force microscopy. Analyzing the height-height correlation function, the evolution of the surface roughness parameters root mean square roughness (rms), lateral correlation length, and the Hurst parameter were determined. Studying samples of V{sub 2}O{sub 5} grown at temperatures from 25 {sup o}C to 300 {sup o}C, a transition from amorphous to crystalline growth at 80 {sup o}C was observed. The rms roughness increased from 0.7 nm at 26 {sup o}C to 21 nm at 300 {sup o}C. Furthermore, a method to quantitatively determine friction coefficients via friction force microscopy was applied. The surface contact forces were calculated via the cantilever's spring constants determined using the Sader method. At scan speeds of 1.25 {mu}m/s and 3.13 {mu}m/s, friction coefficients of 0.60 {+-} 0.02 and 0.63 {+-} 0.01, respectively, have been obtained.

  17. Physical properties of elongated magnetic particles: magnetization and friction coefficient anisotropies.

    Science.gov (United States)

    Vereda, Fernando; de Vicente, Juan; Hidalgo-Alvarez, Roque

    2009-06-02

    Anisotropy counts: A brief review of the main physical properties of elongated magnetic particles (EMPs) is presented. The most important characteristic of an EMP is the additional contribution of shape anisotropy to the total anisotropy energy of the particle, when compared to spherical magnetic particles. The electron micrograph shows Ni-ferrite microrods fabricated by the authors.We present an overview of the main physical properties of elongated magnetic particles (EMPs), including some of their more relevant properties in suspension. When compared to a spherical magnetic particle, the most important characteristic of an EMP is an additional contribution of shape anisotropy to the total anisotropy energy of the particle. Increasing aspect ratios also lead to an increase in both the critical single-domain size of a magnetic particle and its resistance to thermally activated spontaneous reversal of the magnetization. For single-domain EMPs, magnetization reversal occurs primarily by one of two modes, coherent rotation or curling, the latter being facilitated by larger aspect ratios. When EMPs are used to prepare colloidal suspensions, other physical properties come into play, such as their anisotropic friction coefficient and the consequent enhanced torque they experience in a shear flow, their tendency to align in the direction of an external field, to form less dense sediments and to entangle into more intricate aggregates. From a more practical point of view, EMPs are discussed in connection with two interesting types of magnetic colloids: magnetorheological fluids and suspensions for magnetic hyperthermia. Advances reported in the literature regarding the use of EMPs in these two systems are included. In the final section, we present a summary of the most relevant methods documented in the literature for the fabrication of EMPs, together with a list of the most common ferromagnetic materials that have been synthesized in the form of EMPs.

  18. HEAT TRANSFER COEFFICIENT AND FRICTION FACTOR CHARACTERISTICS OF A GRAVITY ASSISTED BAFFLED SHELL AND HEAT-PIPE HEAT EXCHANGER

    Directory of Open Access Journals (Sweden)

    P. Raveendiran

    2015-06-01

    Full Text Available The heat transfer coefficients and friction factors of a baffled shell and heat pipe heat exchanger with various inclination angles were determined experimentally; using methanol as working fluid and water as heat transport fluid were reported. Heat pipe heat exchanger reported in this investigation have inclination angles varied between 15o and 60o for different mass flow rates and temperature at the shell side of the heat exchanger. All the required parameters like outlet temperature of both hot and cold side of heat exchanger and mass flow rate of fluids were measured using an appropriate instrument. Different tests were performed from which condenser side heat transfer coefficient and friction factor were calculated. In all operating conditions it has been found that the heat transfer coefficient increases by increasing the mass flow rate and angle of inclination. The reduction in friction factor occurs when the Reynolds number is increased. The overall optimum experimental effectiveness of GABSHPHE has found to be 42% in all operating conditioning at ψ = 45o.

  19. Minimizing of the boundary friction coefficient in automotive engines using Al2O3 and TiO2 nanoparticles

    Science.gov (United States)

    Ali, Mohamed Kamal Ahmed; Xianjun, Hou; Elagouz, Ahmed; Essa, F. A.; Abdelkareem, Mohamed A. A.

    2016-12-01

    Minimizing of the boundary friction coefficient is critical for engine efficiency improvement. It is known that the tribological behavior has a major role in controlling the performance of automotive engines in terms of the fuel consumption. The purpose of this research is an experimental study to minimize the boundary friction coefficient via nano-lubricant additives. The tribological characteristics of Al2O3 and TiO2 nano-lubricants were evaluated under reciprocating test conditions to simulate a piston ring/cylinder liner interface in automotive engines. The nanoparticles were suspended in a commercially available lubricant in a concentration of 0.25 wt.% to formulate the nano-lubricants. The Al2O3 and TiO2 nanoparticles had sizes of 8-12 and 10 nm, respectively. The experimental results have shown that the boundary friction coefficient reduced by 35-51% near the top and bottom dead center of the stroke (TDC and BDC) for the Al2O3 and TiO2 nano-lubricants, respectively. The anti-wear mechanism was generated via the formation of protective films on the worn surfaces of the ring and liner. These results will be a promising approach for improving fuel economy in automotive.

  20. The Relationship between the Friction Coefficient and the Asperities Original Inclination Angle

    OpenAIRE

    Guan Cheng-yao; Qi Jia-fu; Qiu Nan-sheng; Zhao Guo-chun; Zhang Hou-he; Yang Qiao; Bai Xiang-dong; Wang Chao

    2013-01-01

    Because of the contact deformation, the inclination angle of the contact face is decreased gradually when contact and deformation. Base on the change of inclination angle of the contact surface, the concept “friction repose angle” set out. The tangent of the initial inclination angle of two asperities is three time of the tangent of the “friction repose angle”. The relationship set up a bridge between the initial surface geometric configuration (can be detect) and the configuration which afte...

  1. Correlation between Mechanical Properties with Specific Wear Rate and the Coefficient of Friction of Graphite/Epoxy Composites

    Directory of Open Access Journals (Sweden)

    Mahdi Alajmi

    2015-07-01

    Full Text Available The correlation between the mechanical properties of Fillers/Epoxy composites and their tribological behavior was investigated. Tensile, hardness, wear, and friction tests were conducted for Neat Epoxy (NE, Graphite/Epoxy composites (GE, and Data Palm Fiber/Epoxy with or without Graphite composites (GFE and FE. The correlation was made between the tensile strength, the modulus of elasticity, elongation at the break, and the hardness, as an individual or a combined factor, with the specific wear rate (SWR and coefficient of friction (COF of composites. In general, graphite as an additive to polymeric composite has had an eclectic effect on mechanical properties, whereas it has led to a positive effect on tribological properties, whilst date palm fibers (DPFs, as reinforcement for polymeric composite, promoted a mechanical performance with a slight improvement to the tribological performance. Statistically, this study reveals that there is no strong confirmation of any marked correlation between the mechanical and the specific wear rate of filler/Epoxy composites. There is, however, a remarkable correlation between the mechanical properties and the friction coefficient of filler/Epoxy composites.

  2. A STUDY OF THE PROPERTIES OF CP: COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS AND REACTION TO SPARK, FRICTION AND IMPACT

    Energy Technology Data Exchange (ETDEWEB)

    Weese, R K; Burnham, A K; Fontes, A T

    2005-03-30

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear heating rates, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Using differential scanning calorimetry, DSC, CP was decomposed at linear heating rates of 1, 3, and 7 C/min and the kinetic triplet calculated using the LLNL code Kinetics05. Values are also reported for spark, friction, and impact sensitivity.

  3. Adsorption Behavior of Heat Modified Soybean Oil via Boundary Lubrication Coefficient of Friction Measurements

    Science.gov (United States)

    The frictional behaviors of soybean oil and heat modified soybean oils with different Gardner scale viscosities as additives in hexadecane have been examined in a boundary lubrication test regime (steel contacts) using Langmuir adsorption model. The free energy of adsorption (delta-Gads) of various...

  4. Low friction coefficient coatings Ni-Cr by magnetron sputtering, DC

    Directory of Open Access Journals (Sweden)

    Morales-Hernández, Jorge

    2015-09-01

    Full Text Available Magnetron Sputter Deposition technique with DC was used for the deposition of Ni-Cr coatings on AISI 316 SS like substrate. The cathode with a nominal composition Ni-22 at% Cr was prepared by Mechanical Alloying (MA technique, with a maximum milling time of 16 hours and, with a high energy SPEX 8000 mill. The coatings were made under Argon atmosphere at room temperature with a power of 100 W at different times of growth. Chemical composition, microstructure, topography, nanohardness and wear of the coatings were evaluated using the techniques of microanalysis by energy dispersive X-ray analyzer (EDAX, X-Ray Diffraction (XRD, Atomic Force Microscopy (AFM, Nano-indentation and pin-on-Disk, respectively. After milling, was not detected contamination in the mixtures. XRD analysis revealed that the microstructure of the Ni-Cr alloy was maintained in the coatings with respect to MA powders, with some degree of recrystallization. Nanohardness values were in the order of 8.8 GPa with a Young’s modulus of 195 GPa. The adhesion of the films was evaluated according to their resistance to fracture when these were indented at different loads using Vickers microhardness. The wear test results showed a decrease in the friction coefficient with respect to the increase of thickness’ films, getting a minimum value of 0.08 with a thickness of 1 μm and which correspond with the maximum growing time.La técnica de Deposición por Chisporroteo Magnético (Magnetron Sputtering con el proceso DC, fue usado para la deposición de los recubrimientos de Ni-Cr sobre acero inoxidable AISI 316 como sustrato. El cátodo con una composición nominal Ni-22 at% Cr fue preparado por la técnica de Aleado Mecánico (AM, con un tiempo máximo de molienda de 16 horas y con un molino de alta energía tipo SPEX 8000. Las películas se realizaron bajo una atmósfera de argón a temperatura ambiente con una potencia de 100 W a diferentes tiempos de crecimiento. La composición qu

  5. The Determinants of Gini Coefficient in Iran Based on Bayesian Model Averaging

    OpenAIRE

    Mohsen Mehrara; Mojtaba Mohammadian

    2015-01-01

    This paper has tried to apply BMA approach in order to investigate important influential variables on Gini coefficient in Iran over the period 1976-2010. The results indicate that the GDP growth is the most important variable affecting the Gini coefficient and has a positive influence on it. Also the second and third effective variables on Gini coefficient are respectively the ratio of government current expenditure to GDP and the ratio of oil revenue to GDP which lead to an increase in inequ...

  6. Evaluation of the viscoelastic behaviour and glass/mould interface friction coefficient in the wafer based precision glass moulding

    DEFF Research Database (Denmark)

    Sarhadi, Ali; Hattel, Jesper Henri; Hansen, Hans Nørgaard

    2014-01-01

    Recent improvements in the manufacturing process of camera lenses have introduced the use of a newtechnology involving wafer based precision glass moulding. The utilization of this technology has someimportant advantages such as cost reduction, supply chain simplification and higher image quality...... paper deals with characterization of the interfacial glass/mould friction coefficient andviscoelastic behaviour of the L-BAL42 glass material above the glass transition temperature. Several glassrings are pressed at three different temperatures to various thicknesses and the experimental force, dis-placements...

  7. Approximate analytical solutions and approximate value of skin friction coefficient for boundary layer of power law fluids

    Institute of Scientific and Technical Information of China (English)

    SU Xiao-hong; ZHENG Lian-cun; JIANG Feng

    2008-01-01

    This paper presents a theoretical analysis for laminar boundary layer flow in a power law non-Newtonian fluids.The Adomian analytical decomposition technique is presented and an approximate analytical solution is obtained.The approximate analytical solution can be expressed in terms of a rapid convergent power series with easily computable terms.Reliability and efficiency of the approximate solution are verified by comparing with numerical solutions in the literature.Moreover,the approximate solution can be successfully applied to provide values for the skin friction coefficient of the laminar boundary layer flow in power law non-Newtonian fluids.

  8. The Determinants of Gini Coefficient in Iran Based on Bayesian Model Averaging

    Directory of Open Access Journals (Sweden)

    Mohsen Mehrara

    2015-03-01

    Full Text Available This paper has tried to apply BMA approach in order to investigate important influential variables on Gini coefficient in Iran over the period 1976-2010. The results indicate that the GDP growth is the most important variable affecting the Gini coefficient and has a positive influence on it. Also the second and third effective variables on Gini coefficient are respectively the ratio of government current expenditure to GDP and the ratio of oil revenue to GDP which lead to an increase in inequality. This result is corresponding with rentier state theory in Iran economy. Injection of massive oil revenue to Iran's economy and its high share of the state budget leads to inefficient government spending and an increase in rent-seeking activities in the country. Economic growth is possibly a result of oil revenue in Iran economy which has caused inequality in distribution of income.

  9. Gradient-based estimation of Manning's friction coefficient from noisy data

    CERN Document Server

    Calo, Victor M; Gehre, Matthias; Jin, Bangti; Radwan, Hany

    2012-01-01

    We study the numerical recovery of Manning's roughness coefficient for the diffusive wave approximation of the shallow water equation. We describe a conjugate gradient method for the numerical inversion. Numerical results for one-dimensional model are presented to illustrate the feasibility of the approach. Also we provide a proof of the differentiability of the weak form with respect to the coefficient as well as the continuity and boundedness of the linearized operator under reasonable assumptions using the maximal parabolic regularity theory.

  10. Gradient-based estimation of Manning's friction coefficient from noisy data

    KAUST Repository

    Calo, Victor M.

    2013-01-01

    We study the numerical recovery of Manning\\'s roughness coefficient for the diffusive wave approximation of the shallow water equation. We describe a conjugate gradient method for the numerical inversion. Numerical results for one-dimensional models are presented to illustrate the feasibility of the approach. Also we provide a proof of the differentiability of the weak form with respect to the coefficient as well as the continuity and boundedness of the linearized operator under reasonable assumptions using the maximal parabolic regularity theory. © 2012 Elsevier B.V. All rights reserved.

  11. Effects of flooring on required coefficient of friction: Elderly adult vs. middle-aged adult barefoot gait.

    Science.gov (United States)

    Rozin Kleiner, Ana Francisca; Galli, Manuela; Araujo do Carmo, Aline; Barros, Ricardo M L

    2015-09-01

    The aim of this study was to investigate the effect of flooring on barefoot gait according to age and gender. Two groups of healthy subjects were analyzed: the elderly adult group (EA; 10 healthy subjects) and the middle-aged group (MA; 10 healthy subjects). Each participant was asked to walk at his or her preferred speed over two force plates on the following surfaces: 1) homogeneous vinyl (HOV), 2) carpet, 3) heterogeneous vinyl (HTV) and 4) mixed (in which the first half of the pathway was covered by HOV and the second by HTV). Two force plates (Kistler 9286BA) embedded in the data collection room floor measured the ground reaction forces and friction. The required coefficient of friction (RCOF) was analyzed. For the statistical analysis, a linear mixed-effects model for repeated measures was performed. During barefoot gait, there were differences in the RCOF among the flooring types during the heel contact and toe-off phases. Due to better plantar proprioception during barefoot gait, the EA and MA subjects were able to distinguish differences among the flooring types. Moreover, when the EA were compared with the MA subjects, differences could be observed in the RCOF during the toe-off phase, and gender differences in the RCOF could also be observed during the heel contact phase in barefoot gait.

  12. Data assimilation within the Advanced Circulation (ADCIRC) modeling framework for the estimation of Manning's friction coefficient

    KAUST Repository

    Mayo, Talea

    2014-04-01

    Coastal ocean models play a major role in forecasting coastal inundation due to extreme events such as hurricanes and tsunamis. Additionally, they are used to model tides and currents under more moderate conditions. The models numerically solve the shallow water equations, which describe conservation of mass and momentum for processes with large horizontal length scales relative to the vertical length scales. The bottom stress terms that arise in the momentum equations can be defined through the Manning\\'s n formulation, utilizing the Manning\\'s n coefficient. The Manning\\'s n coefficient is an empirically derived, spatially varying parameter, and depends on many factors such as the bottom surface roughness. It is critical to the accuracy of coastal ocean models, however, the coefficient is often unknown or highly uncertain. In this work we reformulate a statistical data assimilation method generally used in the estimation of model state variables to estimate this model parameter. We show that low-dimensional representations of Manning\\'s n coefficients can be recovered by assimilating water elevation data. This is a promising approach to parameter estimation in coastal ocean modeling. © 2014 Elsevier Ltd.

  13. Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding

    DEFF Research Database (Denmark)

    Larsen, Anders; Stolpe, Mathias; Hattel, Jesper Henri

    2012-01-01

    of the spatial distribution of the heat transfer coefficient are analysed and a simple, two parameter distribution is found to give good results. Originality/value - The heat transfer from workpiece to backingplate is important for the temperature field in the workpiece, and in turn the mechanical properties...

  14. Uncertainty quantification and inference of Manning's friction coefficients using DART buoy data during the Tōhoku tsunami

    KAUST Repository

    Sraj, Ihab

    2014-11-01

    Tsunami computational models are employed to explore multiple flooding scenarios and to predict water elevations. However, accurate estimation of water elevations requires accurate estimation of many model parameters including the Manning\\'s n friction parameterization. Our objective is to develop an efficient approach for the uncertainty quantification and inference of the Manning\\'s n coefficient which we characterize here by three different parameters set to be constant in the on-shore, near-shore and deep-water regions as defined using iso-baths. We use Polynomial Chaos (PC) to build an inexpensive surrogate for the G. eoC. law model and employ Bayesian inference to estimate and quantify uncertainties related to relevant parameters using the DART buoy data collected during the Tōhoku tsunami. The surrogate model significantly reduces the computational burden of the Markov Chain Monte-Carlo (MCMC) sampling of the Bayesian inference. The PC surrogate is also used to perform a sensitivity analysis.

  15. Numerical estimation on balance coefficients of central difference averaging method for quench detection of the KSTAR PF coils

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jin Sub; An, Seok Chan; Ko, Tae Kuk [Yonsei University, Seoul (Korea, Republic of); Chu, Yong [National Fusion Research Institute(NFRI), Daejeon (Korea, Republic of)

    2016-09-15

    A quench detection system of KSTAR Poloidal Field (PF) coils is inevitable for stable operation because normal zone generates overheating during quench occurrence. Recently, new voltage quench detection method, combination of Central Difference Averaging (CDA) and Mutual Inductance Compensation (MIK) for compensating mutual inductive voltage more effectively than conventional voltage detection method, has been suggested and studied. For better performance of mutual induction cancellation by adjacent coils of CDA+MIK method for KSTAR coil system, balance coefficients of CDA must be estimated and adjusted preferentially. In this paper, the balance coefficients of CDA for KSTAR PF coils were numerically estimated. The estimated result was adopted and tested by using simulation. The CDA method adopting balance coefficients effectively eliminated mutual inductive voltage, and also it is expected to improve performance of CDA+MIK method for quench detection of KSTAR PF coils.

  16. CONSTRUCTION OF POLYNOMIAL MATRIX USING BLOCK COEFFICIENT MATRIX REPRESENTATION AUTO-REGRESSIVE MOVING AVERAGE MODEL FOR ACTIVELY CONTROLLED STRUCTURES

    Institute of Scientific and Technical Information of China (English)

    LI Chunxiang; ZHOU Dai

    2004-01-01

    The polynomial matrix using the block coefficient matrix representation auto-regressive moving average (referred to as the PM-ARMA) model is constructed in this paper for actively controlled multi-degree-of-freedom (MDOF) structures with time-delay through equivalently transforming the preliminary state space realization into the new state space realization. The PM-ARMA model is a more general formulation with respect to the polynomial using the coefficient representation auto-regressive moving average (ARMA) model due to its capability to cope with actively controlled structures with any given structural degrees of freedom and any chosen number of sensors and actuators. (The sensors and actuators are required to maintain the identical number.) under any dimensional stationary stochastic excitation.

  17. Study on the Friction Direction Angle of Equivalent Friction Coefficient of V-belt%影响V带当量摩擦因数的摩擦力方向角研究

    Institute of Scientific and Technical Information of China (English)

    廖林清; 蔺朝莉; 屈翔; 谢明

    2011-01-01

    根据V带传动的实际情况,分析传动带在主动轮和从动轮动弧区内任意位置的周向变形和径向变形,给出摩擦力方向角的计算公式;并运用Matlab软件绘制出动弧角和方向角的关系图.通过分析摩擦力方向角对当量摩擦因数的影响,得出从动轮处当量摩擦因数随摩擦力方向角增大而减小,主动轮处当量摩擦因数随摩擦力方向角绝对值的增大而增大;根据主动轮当量摩擦因数μv≥μ/(sinθ/2),再结合这极限打滑转矩的公式,可以解释实际的极限打滑转矩大于理论上的极限打滑转矩现象.%According to the actual situation of v- belt drive, the radial deformation and circular deformation of any position of dynamic arc area of driving wheel and driven wheel are analyzed, and the calculation formula of friction direction angle is given, the relational graph of dynamic arc angle and direction angle are obtained by using Matlab. Through the analysis of the influence of friction direction angle on equivalent friction coefficient, the regular of the e-quivalent friction coefficient of that the equivalent friction coefficient of driven wheel decrease with the increase of direction angle, the equivalent friction coefficient of driving wheel increase with the increase of absolute of direction angle. According to the equivalent friction coefficient of the driving wheel μv≧μ/sinθ/2 and combining the formula oflimit skid torque, the number of actual limit skid torque larger than the number of theory limit skid torque can be explained.

  18. 影响井下防喷器胶筒与套管间摩擦因数的因素%Influence Factors of Friction Coefficient between Sealing Rubber of Downhole Bop and Casing Pipe

    Institute of Scientific and Technical Information of China (English)

    付玉坤; 刘清友; 王娟

    2012-01-01

    The influences of positive pressure, relative sliding rate and lubrication condition on friction coefficient between sealing rubber of downhole bop and casing pipe were studied by friction test. The results show that the friction coefficient increased with the sliding rate increasing at the same positive pressure without lubricant or water lubrication, but decreased in oil lubrication because the growth of sliding rate made contribution to the formation of lubricating film. At the same pressure and relative rate, the average friction coefficient in oil lubrication was the smallest, followed by that in water lubrication and the greatest was given without lubricant. The effect of positive pressure had no regularity.%通过摩擦试验,研究了正压力、相对滑动速度以及润滑条件对井下防喷器胶筒与套管间摩擦因数的影响。结果表明:相同正压力下,无润滑剂和水润滑摩擦时,两者间的摩擦因数随着滑动速度的增加而增加,在油润滑时,滑动速度的增加有利于润滑膜的形成,使摩擦因数降低;在相同正压力和相对滑动速度下,油润滑摩擦因数均值最小,水润滑时次之,无润滑剂时最大;正压力的影响无规律性。

  19. Analytical solutions for the coefficient of variation of the volume-averaged solute concentration in heterogeneous aquifers

    Science.gov (United States)

    Kabala, Z. J.

    1997-08-01

    Under the assumption that local solute dispersion is negligible, a new general formula (in the form of a convolution integral) is found for the arbitrary k-point ensemble moment of the local concentration of a solute convected in arbitrary m spatial dimensions with general sure initial conditions. From this general formula new closed-form solutions in m=2 spatial dimensions are derived for 2-point ensemble moments of the local solute concentration for the impulse (Dirac delta) and Gaussian initial conditions. When integrated over an averaging window, these solutions lead to new closed-form expressions for the first two ensemble moments of the volume-averaged solute concentration and to the corresponding concentration coefficients of variation (CV). Also, for the impulse (Dirac delta) solute concentration initial condition, the second ensemble moment of the solute point concentration in two spatial dimensions and the corresponding CV are demonstrated to be unbound. For impulse initial conditions the CVs for volume-averaged concentrations axe compared with each other for a tracer from the Borden aquifer experiment. The point-concentration CV is unacceptably large in the whole domain, implying that the ensemble mean concentration is inappropriate for predicting the actual concentration values. The volume-averaged concentration CV decreases significantly with an increasing averaging volume. Since local dispersion is neglected, the new solutions should be interpreted as upper limits for the yet to be derived solutions that account for local dispersion; and so should the presented CVs for Borden tracers. The new analytical solutions may be used to test the accuracy of Monte Carlo simulations or other numerical algorithms that deal with the stochastic solute transport. They may also be used to determine the size of the averaging volume needed to make a quasi-sure statement about the solute mass contained in it.

  20. Numerical study on spatially varying bottom friction coefficient of a 2D tidal model with adjoint method

    Science.gov (United States)

    Lu, Xianqing; Zhang, Jicai

    2006-10-01

    Based on the simulation of M2 tide in the Bohai Sea, the Yellow Sea and the East China Sea, TOPEX/Poseidon altimeter data are assimilated into a 2D tidal model to study the spatially varying bottom friction coefficient (BFC) by using the adjoint method. In this study, the BFC at some grid points are selected as the independent BFC, while the BFC at other grid points can be obtained through linear interpolation with the independent BFC. Two strategies for selecting the independent BFC are discussed. In the first strategy, one independent BFC is uniformly selected from each 1°×1° area. In the second one, the independent BFC are selected based on the spatial distribution of water depth. Twin and practical experiments are carried out to compare the two strategies. In the twin experiments, the adjoint method has a strong ability of inverting the prescribed BFC distributions combined with the spatially varying BFC. In the practical experiments, reasonable simulation results can be obtained by optimizing the spatially varying independent BFC. In both twin and practical experiments, the simulation results with the second strategy are better than those with the first one. The BFC distribution obtained from the practical experiment indicates that the BFC in shallow water are larger than those in deep water in the Bohai Sea, the North Yellow Sea, the South Yellow Sea and the East China Sea individually. However, the BFC in the East China Sea are larger than those in the other areas perhaps because of the large difference of water depth or bottom roughness. The sensitivity analysis indicates that the model results are more sensitive to the independent BFC near the land.

  1. Coefficients of Friction, Lubricin, and Cartilage Damage in the Anterior Cruciate Ligament-Deficient Guinea Pig Knee

    Science.gov (United States)

    Teeple, Erin; Elsaid, Khaled A.; Fleming, Braden C.; Jay, Gregory D.; Aslani, Koosha; Crisco, Joseph J.; Mechrefe, Anthony P.

    2009-01-01

    The coefficient of friction (COF) of articular cartilage is thought to increase with osteoarthritis (OA) progression, and this increase may occur due to a decrease in lubricin concentration. The objectives of this study were to measure the COF of guinea pig tibiofemoral joints with different stages of OA, and to establish relationships between COF, lubricin concentrations in synovial fluid, and degradation status using the Hartley guinea pig model. Both hind limbs from 24 animals were harvested: seven 3-month-old (no OA), seven 12-month-old (mild OA), and ten that were euthanized at 12-months of age after undergoing unilateral anterior cruciate ligament (ACL) transection at 3-months of age (moderate OA). Contralateral knees served as age matched controls. COFs of the tibiofemoral joints were measured using a pendulum apparatus. Synovial fluid lavages were analyzed to determine the concentration and integrity of lubricin using ELISA and western blot, and the overall articular cartilage status was evaluated by histology. The results showed that the mean COF in the ACL-deficient knees was significantly greater than that of the 3-month knees (p<0.01) and the 12-month knees (p<0.01). Lubricin concentrations in the ACL-deficient knees were significantly lower than that of the 3-month knees (p<0.01) and 12-month knees (p<0.01). No significant differences in COF or lubricin concentration were found between the 3-month and the 12-month knees. Histology verified the extent of cartilage damage in each group. Conclusion COF values increased and lubricin levels decreased with cartilage damage following ACL transection. PMID:17868097

  2. Charts Adapted from Van Driest's Turbulent Flat-plate Theory for Determining Values of Turbulent Aerodynamic Friction and Heat-transfer Coefficients

    Science.gov (United States)

    Lee, Dorothy B; Faget, Maxime A

    1956-01-01

    A modified method of Van Driest's flat-plate theory for turbulent boundary layer has been found to simplify the calculation of local skin-friction coefficients which, in turn, have made it possible to obtain through Reynolds analogy theoretical turbulent heat-transfer coefficients in the form of Stanton number. A general formula is given and charts are presented from which the modified method can be solved for Mach numbers 1.0 to 12.0, temperature ratios 0.2 to 6.0, and Reynolds numbers 0.2 times 10 to the 6th power to 200 times 10 to the 6th power.

  3. Micromechanical study of macroscopic friction and dissipation in idealised granular materials: the effect of interparticle friction

    NARCIS (Netherlands)

    Kruyt, N.P.; Rothenburg, L.; Gutkowski, Witold; Kowalewski, Tomasz A.

    2004-01-01

    Using Discrete Element Method (DEM) simulations with varying interparticle friction coefficient, the relation between interparticle friction coefficient and macroscopic continuum friction and dissipation is investigated. As expected, macroscopic friction and dilatancy increase with interparticle fri

  4. Tire-Road Friction Coefficients Estimation Base on Slip Rate%基于滑移率的路面附着系数估计

    Institute of Scientific and Technical Information of China (English)

    李宣政

    2014-01-01

    Wheel Tire-Road Friction Coefficients for vehicle active safety control system is very important, such as collision avoidance, adaptive cruise and other auxiliary systems, such as the vehicle's longitudinal security depends on the road surface friction coefficient, such as vehicle status information in real time, accurate estimates. This paper focuses on the vehicle's longitudinal dynamics model, Proposed a level road adhesion coefficient for non-traffic estimation algorithm. The use of tire longitudinal force and slip ratio, the relationship between the road surface friction coefficient and slip rate, by recursive least squares algorithm to achieve a real-time estimation of the road surface friction coefficient. Finally, the use of Matlab/Simulink simulation environment for recursive least squares estimation algorithm was validated simulation results demonstrate the effectiveness of the algorithm.%轮胎要路面附着系数对于车辆主动安全控制系统十分重要,如主动避撞、自适应巡航等车辆纵向安全辅助系统等,依赖于路面附着系数等车辆状态信息实时、准确的估计。本文重点分析了车辆纵向动力学模型,提出了一种针对非水平路况的路面附着系数估计算法。利用轮胎纵向力与滑移率,路面附着系数与滑移率的关系,通过递推最小二乘算法实现了路面附着系数的实时估计。最后利用Matlab/Simulink仿真环境对递推最小二乘估计算法进行了验证,仿真结果验证了算法的有效性。

  5. 鞋底摩擦系数测控系统的设计%Design of Monitoring and Controlling System of Footwear Sole Coefficient of Friction

    Institute of Scientific and Technical Information of China (English)

    杨永杰; 林贤贤; 吕冬华; 张小美

    2012-01-01

    Slip resistance of footwear sole affects the comfort and safety of shoes directly, and slip resistance is mainly expressed by the coefficient of friction. Within a certain range, the greater the coefficient of friction, the better the slip resistance. In order to determine the safety performance of shoes, the system will obtain the coefficient of friction by measuring the tension and pressure put on shoes, so it's very important to do the measurement precisely. Monitoring — controlling System of footwear sole friction will transmit the tension and pressure via serial communication to the software, which execute real—time processing, displaying, drawing and saving, finally on the basis of the system test, the coefficient of several kinds of material is corresponding to international standard, which verify the correctness of the software and measurement accuracy.%鞋底的止滑性直接影响着鞋子穿用时的舒适性和安全性,止滑性主要由摩擦系数来表示,在一定范围内,摩擦系数越大,止滑性越好;系统通过测量作用于鞋的拉力和压力,求得摩擦系数,从而来判断各种鞋子的安全性能,因此对拉力压力的测量显得十分重要;鞋底摩擦系数测控系统通过串口将采集到的拉力和压力数据发送给上位机实时处理、显示、绘图并保存;最后对系统进行了测试,所测得的各种材质的摩擦系数符合国际标准,验证了它的正确性且测量精度高.

  6. On the Effect of Counterface Materials on Interface Temperature and Friction Coefficient of GFRE Composite Under Dry Sliding Contact

    OpenAIRE

    N. S. M. EL-TAYEB; B. F. Yousif; P. V. Brevern

    2005-01-01

    Nowadays, there is an increase interest in polymeric composite materials for high-performance in many industrial applications. In other words, the tribo-studies on polymeric materials are growing fast to enhance the polymeric products such as bearings, seals, ring and bushes. The current work presents an attempt to study the correlation between the type of counterface material and frictional heating at the interface surfaces for different, normal loads (23N, 49N and 72N), sliding velocities (...

  7. Approach to estimation of vehicle-road longitudinal friction coefficient%一种道路纵向附着系数估计方法

    Institute of Scientific and Technical Information of China (English)

    宋翔; 李旭; 张为公; 陈伟; 徐启敏

    2013-01-01

    According to the road adaptive requirements for the vehicle longitudinal safety assistant system an estimation method of the road longitudinal friction coefficient is proposed.The method can simultaneously be applied to both the high and the low slip ratio conditions. Based on the simplified magic formula tire model the road longitudinal friction coefficient is preliminarily estimated by the recursive least squares method.The estimated friction coefficient and the tires model parameters are considered as extended states. The extended Kalman filter algorithm is employed to filter out the noise and adaptively adjust the tire model parameters. Then the final road longitudinal friction coefficient is accurately and robustly estimated. The Carsim simulation results show that the proposed method is better than the conventional algorithm. The road longitudinal friction coefficient can be quickly and accurately estimated under both the high and the low slip ratio conditions.The error is less than 0.1 and the response time is less than 2 s which meets the requirements of the vehicle longitudinal safety assistant system.%针对汽车纵向安全辅助系统道路自适应的要求,提出了一种道路纵向附着系数估计方法.该方法能够同时适应高滑移率和低滑移率工况.首先基于简化魔术轮胎模型,利用递归最小二乘方法实时初步估计出纵向附着系数,然后将所估计出的附着系数与轮胎模型参数作为扩充状态,利用扩展卡尔曼滤波算法,滤除信号噪声,实现轮胎模型系数的自适应调整,最终实时获取准确的道路纵向附着系数估计,并通过车辆动力学软件Carsim仿真验证了算法的有效性和可行性.结果表明该算法优于传统算法,在高滑移率和低滑移率工况下都能够快速、准确地估计出道路附着系数,误差小于0.1,响应时间小于1 s,满足车辆纵向安全辅助系统的需要.

  8. Synthetic modeling of a fluid injection-induced fault rupture with slip-rate dependent friction coefficient

    Science.gov (United States)

    Urpi, Luca; Rinaldi, Antonio Pio; Rutqvist, Jonny; Cappa, Frédéric; Spiers, Christopher J.

    2016-04-01

    Poro-elastic stress and effective stress reduction associated with deep underground fluid injection can potentially trigger shear rupture along pre-existing faults. We modeled an idealized CO2 injection scenario, to assess the effects on faults of the first phase of a generic CO2 aquifer storage operation. We used coupled multiphase fluid flow and geomechanical numerical modeling to evaluate the stress and pressure perturbations induced by fluid injection and the response of a nearby normal fault. Slip-rate dependent friction and inertial effects have been aken into account during rupture. Contact elements have been used to take into account the frictional behavior of the rupture plane. We investigated different scenarios of injection rate to induce rupture on the fault, employing various fault rheologies. Published laboratory data on CO2-saturated intact and crushed rock samples, representative of a potential target aquifer, sealing formation and fault gouge, have been used to define a scenario where different fault rheologies apply at different depths. Nucleation of fault rupture takes place at the bottom of the reservoir, in agreement with analytical poro-elastic stress calculations, considering injection-induced reservoir inflation and the tectonic scenario. For the stress state here considered, the first triggered rupture always produces the largest rupture length and slip magnitude, correlated with the fault rheology. Velocity weakening produces larger ruptures and generates larger magnitude seismic events. Heterogeneous faults have been considered including velocity-weakening or velocity strengthening sections inside and below the aquifer, while upper sections being velocity-neutral. Nucleation of rupture in a velocity strengthening section results in a limited rupture extension, both in terms of maximum slip and rupture length. For a heterogeneous fault with nucleation in a velocity-weakening section, the rupture may propagate into the overlying velocity

  9. Friction phenomena and their impact on the shear behaviour of granular material

    Science.gov (United States)

    Suhr, Bettina; Six, Klaus

    2016-06-01

    In the discrete element simulation of granular materials, the modelling of contacts is crucial for the prediction of the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g. contact normal load or temperature to name only two. In discrete element method (DEM) simulations the usage of Coulomb's law of friction is state of the art in modelling particle-particle contacts. Usually in Coulomb's law, for all contacts only one constant coefficient of friction is used, which needs to reflect all tribological effects. Thus, whenever one of the influence factors of friction varies over a wide range, it can be expected that the usage of only one constant coefficient of friction in Coulomb's law is an oversimplification of reality. For certain materials, e.g. steel, it is known that a dependency of the coefficient of friction on the contact normal load exists. A more tribological tangential contact law is implemented in DEM, where the interparticle friction coefficient depends on the averaged normal stress in the contact. Simulations of direct shear tests are conducted, using steel spheres of different size distributions. The strong influence of interparticle friction on the bulk friction is shown via a variation of the constant interparticle friction coefficient. Simulations with constant and stress-dependent interparticle friction are compared. For the stress-dependent interparticle friction, a normal stress dependency of the bulk friction is seen. In the literature, measurements of different granular materials and small normal loads also show a stress dependency of the bulk friction coefficient. With increasing applied normal stress, the bulk friction coefficient reduces both in the experiments and in the simulations.

  10. Friction phenomena and their impact on the shear behaviour of granular material

    Science.gov (United States)

    Suhr, Bettina; Six, Klaus

    2017-01-01

    In the discrete element simulation of granular materials, the modelling of contacts is crucial for the prediction of the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g. contact normal load or temperature to name only two. In discrete element method (DEM) simulations the usage of Coulomb's law of friction is state of the art in modelling particle-particle contacts. Usually in Coulomb's law, for all contacts only one constant coefficient of friction is used, which needs to reflect all tribological effects. Thus, whenever one of the influence factors of friction varies over a wide range, it can be expected that the usage of only one constant coefficient of friction in Coulomb's law is an oversimplification of reality. For certain materials, e.g. steel, it is known that a dependency of the coefficient of friction on the contact normal load exists. A more tribological tangential contact law is implemented in DEM, where the interparticle friction coefficient depends on the averaged normal stress in the contact. Simulations of direct shear tests are conducted, using steel spheres of different size distributions. The strong influence of interparticle friction on the bulk friction is shown via a variation of the constant interparticle friction coefficient. Simulations with constant and stress-dependent interparticle friction are compared. For the stress-dependent interparticle friction, a normal stress dependency of the bulk friction is seen. In the literature, measurements of different granular materials and small normal loads also show a stress dependency of the bulk friction coefficient. With increasing applied normal stress, the bulk friction coefficient reduces both in the experiments and in the simulations.

  11. Experimental Validation of Strategy for the Inverse Estimation of Mechanical Properties and Coefficient of Friction in Flat Rolling

    Science.gov (United States)

    Yadav, Vinod; Singh, Arbind Kumar; Dixit, Uday Shanker

    2016-06-01

    Flat rolling is one of the most widely used metal forming processes. For proper control and optimization of the process, modelling of the process is essential. Modelling of the process requires input data about material properties and friction. In batch production mode of rolling with newer materials, it may be difficult to determine the input parameters offline. In view of it, in the present work, a methodology to determine these parameters online by the measurement of exit temperature and slip is verified experimentally. It is observed that the inverse prediction of input parameters could be done with a reasonable accuracy. It was also assessed experimentally that there is a correlation between micro-hardness and flow stress of the material; however the correlation between surface roughness and reduction is not that obvious.

  12. Dry Friction Coefficient of Oil Pumping Polished Rod%抽油机光杆干摩擦系数的研究

    Institute of Scientific and Technical Information of China (English)

    雷改丽; 李飞舟; 韩玉强

    2012-01-01

    The wear resistance of pumping polished rod is comparatively low, for those reasons cause the technical bottleneck to used pumping unit. The wear properties of 40MnVB were studied by mating with TC4 alloy, GCr15 steel and Si4N3 cramic. The change relation between velocity and mass loss rate of wear or friction coefficient or morphology pography of wear mark were studied. The wear mechanism of 40MnVB alloy was discussed by SEM and EDS. The results show that the friction coefficient of the alloy experiences two phases which are advancing wear stage and stable wear stage. The wear mark of 40MnVB alloy is furrow morphology. The wear mechanism of GCr15 steel and Si4N3 ceramic are delamination abrasion, adhesive abrasion and oxidation abrasion at room temperature. But mating with TC4 alloy, the friction coefficient changes little, and the wear mark of 40MnVB alloy is furrow, and the wear machanism is fatigue abrasion and delamination abrasion.%抽油机光杆材质的耐磨性已成为制约抽油机的技术瓶颈.采用SEM和EDS等手段对抽油机光杆40MnVB在不同压力和速度下,与TC4、GCr15和Si4N3配副对磨的摩擦磨损性能进行研究,分析了摩擦系数和磨痕形貌、摩擦速度和压力变化的规律,探讨了磨损机理.结果表明:在室温范围内,40MnVB与对磨材料GCr15和Si4N3陶瓷的摩擦系数较高,磨痕主要呈氧化磨损、犁沟形貌,磨损经历了预磨损和稳定磨损两个阶段,磨损机理为剥层磨损、粘着磨损和氧化磨损.与对磨材料TC4对磨的摩擦系数较低,磨痕主要呈犁沟形貌,磨损机理为剥层磨损、疲劳磨损.

  13. Evaluation of existing EPRI and INEL test data to determine the worm to worm gear coefficient of friction in Limitorque actuators

    Energy Technology Data Exchange (ETDEWEB)

    Garza, I.A.

    1996-12-01

    About the last sizing parameter for motor operated valves which has not been determined by utility or NRC sponsored testing is actuator efficiency. A by-product of EPRI testing for valve factors is the measurement of the actuator efficiencies. Motor sizing in this testing provides efficiency testing for motors running near synchronous speed. INEL testing, sponsored by the NRC, for stem factors and rate of loading provides complimentary data for motors loaded down to zero speed. This paper analyzes the data from these two test programs to determine the coefficient of friction for the worm to worm gear interface. This allowed the development of an algorithm for determining the efficiency of actuators which have not been tested. This paper compares the results of this algorithm to the test data to provide a measure of the accuracy of this method for calculating actuator efficiency.

  14. Friction in total hip joint prosthesis measured in vivo during walking.

    Directory of Open Access Journals (Sweden)

    Philipp Damm

    Full Text Available Friction-induced moments and subsequent cup loosening can be the reason for total hip joint replacement failure. The aim of this study was to measure the in vivo contact forces and friction moments during walking. Instrumented hip implants with Al2O3 ceramic head and an XPE inlay were used. In vivo measurements were taken 3 months post operatively in 8 subjects. The coefficient of friction was calculated in 3D throughout the whole gait cycle, and average values of the friction-induced power dissipation in the joint were determined. On average, peak contact forces of 248% of the bodyweight and peak friction moments of 0.26% bodyweight times meter were determined. However, contact forces and friction moments varied greatly between individuals. The friction moment increased during the extension phase of the joint. The average coefficient of friction also increased during this period, from 0.04 (0.03 to 0.06 at contralateral toe off to 0.06 (0.04 to 0.08 at contralateral heel strike. During the flexion phase, the coefficient of friction increased further to 0.14 (0.09 to 0.23 at toe off. The average friction-induced power throughout the whole gait cycle was 2.3 W (1.4 W to 3.8 W. Although more parameters than only the synovia determine the friction, the wide ranges of friction coefficients and power dissipation indicate that the lubricating properties of synovia are individually very different. However, such differences may also exist in natural joints and may influence the progression of arthrosis. Furthermore, subjects with very high power dissipation may be at risk of thermally induced implant loosening. The large increase of the friction coefficient during each step could be caused by the synovia being squeezed out under load.

  15. Predictability of tracer dilution in large open channel flows: Analytical solution for the coefficient of variation of the depth-averaged concentration

    Science.gov (United States)

    Pannone, Marilena

    2014-03-01

    A large-time analytical solution is proposed for the spatial variance and coefficient of variation of the depth-averaged concentration due to instantaneous, cross sectionally uniform solute sources in pseudorectangular open channel flows. The mathematical approach is based on the use of the Green functions and on the Fourier decomposition of the depth-averaged velocities, coupled with the method of the images. The variance spatial trend is characterized by a minimum at the center of the mass and two mobile, decaying symmetrical peaks which, at very large times, are located at the inflexion points of the average Gaussian distribution. The coefficient of variation, which provides an estimate of the expected percentage deviation of the depth-averaged point concentrations about the section-average, exhibits a minimum at the center which decays like t-1 and only depends on the river diffusive time scale. The defect of cross-sectional mixing quickly increases with the distance from the center, and almost linearly at large times. Accurate numerical Lagrangian simulations were performed to validate the analytical results in preasymptotic and asymptotic conditions, referring to a particularly representative sample case for which cross-sectional depth and velocity measurements were known from a field survey. In addition, in order to discuss the practical usefulness of computing large-time concentration spatial moments in river flows, and resorting to directly measured input data, the order of magnitude of section-averaged concentrations and corresponding coefficients of variation was estimated in field conditions and for hypothetical contamination scenarios, considering a unit normalized mass impulsively injected across the transverse section of 81 U.S. rivers.

  16. 碳/碳材料与石棉/酚醛间热摩擦系数试验%Experiment of Thermal Friction Coefficient Between Carbon/Carbon and Asbestos Phenolic Material

    Institute of Scientific and Technical Information of China (English)

    刘芹; 生志斐; 史宏斌; 陈慧; 刘曙光

    2012-01-01

    This paper presents the experimental results of thermal friction coefficient between the carbon/ carbon material and moulded asbestos/phenolic material by SRV high temperature friction wear testing machine.The test design and specimen sampling are based on the real work conditions.The variation regularity of friction coefficient with temperature,contact load and friction speed are generalized.The test results show that increasing the temperature may decrease the thermal friction coefficient between the carbon/carbon material and moulded asbestos/phenolic material;the friction coefficient of the throat component with glue is larger than the component without glue significantly.Increasing the load may reduce the friction coefficient obscurely.With the friction speed enhanced,the coefficient increases obviously.The test results can provide some helpful reference value to the modification of nozzle thermal structure analysis model with high precision calculation.%根据固体火箭发动机喉部结构的实际工况,取样并设计试验,采用SRV高温摩擦磨损试验机测试了碳/碳与模压石棉/酚醛材料间的热摩擦系数,总结了这两类材料间的摩擦系数随温度、接触载荷及摩擦速度的变化规律。试验结果表明,碳/碳与模压石棉/酚醛材料间的热摩擦系数随温度升高呈非线性单调下降趋势;含胶层的两材料组件间摩擦系数明显高于无胶层组件间摩擦系数;温度一定条件下,载荷增加使得摩擦系数小幅降低;随着摩擦速度的提高,摩擦系数呈增大趋势。

  17. Bounce- and MLT-averaged diffusion coefficients in a physics-based magnetic field geometry obtained from RAM-SCB for the 17 March 2013 storm

    Science.gov (United States)

    Zhao, Lei; Yu, Yiqun; Delzanno, Gian Luca; Jordanova, Vania K.

    2015-04-01

    Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth's magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth's ring current and provides a realistic modeling of the Earth's magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (˜1 MeV) and ring current (˜100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth's magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons.

  18. Research on Friction Coefficient of Spur Gears Based on Carreau Rheological Model%基于Carreau流变模型的渐开线齿轮摩擦因数研究∗

    Institute of Scientific and Technical Information of China (English)

    邹玉静; 常德功

    2015-01-01

    结合载荷分担概念和弹流润滑理论,研究润滑剂的流变性对渐开线齿轮油膜厚度、摩擦因数等润滑特性的影响;分别采用Carreau流变模型和Doolittle⁃Tait自由体积黏度模型描述润滑剂的剪切稀化特性及黏压关系,研究齿轮载荷、转速、表面粗糙度和润滑剂压黏系数对摩擦因数的影响。研究结果表明:不同的润滑剂剪切稀化特性不同,因此油膜厚度、油膜承载比例和摩擦因数均不同;摩擦因数随着转矩的增大先显著增大,当超过某一转矩值时,摩擦因数开始缓慢变化;摩擦因数随着转速的增加先显著减小,当转速增加至某一值时摩擦因数又随之增大;随着表面粗糙度和润滑剂压黏系数的增大,摩擦因数均明显增大。%Study on the friction coefficient of the tooth surface plays an important role on reducing friction loss and im⁃proving the system transmission performance.The effects of the rheological behavior of lubricants on the film thickness and the friction coefficient along the line of action of involute spur gear were studied by employing the load sharing concept and elastohydrodynamic lubrication theory.Carreau rheological model was used to describe the shearing thinning behavior and the Doolittle’s free volume equation was used to represent the pressure⁃viscous relation.The effects of the load,rotational speed and surface roughness of gear and the pressure⁃viscous coefficient of lubricants on the friction coefficient were also studied,and comparisons between the results from two different lubricants were given. The results show that shearing thinning behavior affects the oil film thickness,the oil film load scaling factor and the friction coefficient significantly.The torque,rotational speed and surface roughness of gear and the pressure⁃viscous coefficient have a great influence on the friction coefficient. With the increasing of input torque, the friction

  19. Research of optimization method for friction coefficient model in cold rolling process%冷轧轧制过程摩擦系数模型优化方法研究

    Institute of Scientific and Technical Information of China (English)

    高雷; 郭立伟; 李书昌; 陈丹; 何绪铃

    2014-01-01

    The friction coefficient model in cold rolling process is a nonlinear polynomial. In order to get the parameters of friction coefficient model which can better reflect the real rolling condition,we perform regression analysis on the parameters through optimized method by making full use of the ac-tual process data. The practical application proves that it can improve the calculation precision of the friction coefficient model in cold rolling process and provide a basis for high accuracy rolling.%冷轧轧制过程摩擦系数模型为非线性多项式,为了获得更能反应实际轧制工况的摩擦系数模型参数,充分利用实际工艺数据,通过优化的方法对模型参数进行回归分析。实际应用证明,该方法可以提高轧制过程摩擦系数模型设定精度,为高精度轧制提供基础。

  20. 宽V带无级变速器中当量摩擦因数的研究%Study on the Equivalent Friction Coefficient of Wide V- Belt CVT

    Institute of Scientific and Technical Information of China (English)

    莫帅; 李振亮; 李亚; 许玮

    2012-01-01

    The operational principle of wide V - belt CVT is introduced, the importance of the calculation of e-quivalent friction coefficient of V - belt is elaborated drive in the overall wide V - belt CVT design,some drawbacks of the existing formula are analyzed. Based on Euler formula of flat belt and the actual performance of wide V - belt CVT, the periphery friction and radial friction are taken into consideration,puts forward another formula of the equivalent friction coefficient of wide V - belt CVT is put forward, and three kind of different direction angles of friction are discussed.%介绍了宽V带无级变速器的工作原理,阐述了V带当量摩擦因数的计算对于整个宽V带无级变速器设计的重要性,分析了现有的V带传动中当量摩擦因数计算公式的不足,根据平带传动的欧拉公式并结合宽V带无级变速器中V带传动的实际情况,考虑了周向摩擦力和径向摩擦力,提出了摩擦力方向角,推导出了宽V带无级变速器中V带传动的当量摩擦因数的计算公式,并就摩擦力方向角的3种情况分别进行了讨论.

  1. Friction Properties of Bio-mimetic Nano-fibrillar Arrays

    Institute of Scientific and Technical Information of China (English)

    CHEN Shao-Hua; MI Chun-Hui

    2009-01-01

    Nano-fibrillar arrays are fabricated using polystyrene materials. The average diameter of each fiber is about 300 nm.Experiments show that such a fibrillar surface possesses a relatively hydrophobic feature with a water contact angle of 142°.Nanoscale friction properties are mainly focused on.It is found that the friction force of polystyrene nano-fibrillar surfaces is obviously enhanced in contrast to polystyrene smooth surfaces.The apparent coefficient of friction increases with the applied load, but is independent of the scanning speed.An interesting observation is that the friction force increases almost linearly with the real contact area, which abides by the fundamental Bowden-Tabor law of nano-scale friction.

  2. 转换波AVO反演速度比各横波反射系数%Converted wave AVO inversion for average velocity ratio and shear wave reflection coefficient

    Institute of Scientific and Technical Information of China (English)

    魏修成; 陈天胜; 季玉新

    2008-01-01

    Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the relations between the extrema position and amplitude, average velocity ratio across the interface, and shear wave reflection coefficient are derived. The extrema position is a monotonically decreasing function of average velocity ratio, and the extrema amplitude is a function of average velocity ratio and shear wave reflection coefficient. For theoretical models, the average velocity ratio and shear wave reflection coefficient are inverted from the extrema position and amplitude obtained from fitting a power function to converted wave AVO curves. Shear wave reflection coefficient sections have clearer physical meaning than conventional converted wave stacked sections and establish the theoretical foundation for geological structural interpretation and event correlation. 'The method of inverting average velocity ratio and shear wave reflection coefficient from the extrema position and amplitude obtained from fitting a power function is applied to real CCP gathers. The inverted average velocity ratios are consistent with those computed from compressional and shear wave well logs.

  3. Experimental study of the friction factor of liquid laminar flows in micro-tubes; Etude experimentale du coefficient de frottement d'ecoulements laminaires en microtubes

    Energy Technology Data Exchange (ETDEWEB)

    Brutin, D.; Tadrist, L. [Ecole Polytechnique Universitaire de Marseille: Lab. IUSTI-U.M.R. 6595, 13 - Marseille (France)

    2003-07-01

    We highlight an original method to determine precisely the friction factor of laminar flows in capillaries. The experiments are performed at Reynolds numbers ranging from 10 to 1000 using a transient method. We carry out a set of experiments and develop a specific treatment method. The friction factor obtained for capillary diameters ranging from 50 to 530 {mu}m is experimentally determined. Experiments are also developed for two fluids: distilled and tap water. Experimental results for tap water and fused silica surfaces indicate a deviation to the Moody's theory. An increase of the friction factor is observed for decreasing diameters using tap water. This result seems to be to due to the fluid's ionic composition (Electric Double Layer). (authors)

  4. Steady and transient sliding under rate-and-state friction

    Science.gov (United States)

    Putelat, Thibaut; Dawes, Jonathan H. P.

    2015-05-01

    eventually stopping, while in the second basin of attraction the sliding motion continues indefinitely. We show that a second definition of μs is possible, compatible with the first one, as the weighted average of the rate-and-state friction coefficient over the time the block is in motion.

  5. Experimental study on effect of slope angle on equivalent friction coefficient of agricultural V-belt%农用V型带当量摩擦系数影响角的试验

    Institute of Scientific and Technical Information of China (English)

    朱琳; 王金武; 郑大宇; 王玺

    2011-01-01

    The existed equation of equivalent friction coefficient of V belt has drawback due to the neglect to the deviation of the circumferential friction from the tension of the belt. It's an effective way to calculate the equivalent friction coefficient by taking the slope angle into account. By adopting the displacement fiber optic sensors in the experiment to measure the radial displacement of V belt, the trajectory of the belt and the value of the slope angle were acquired, and then the equivalent friction coefficient of V belt was obtained. The results showed that from the entry to the exit point when the belt contacted the driving pulley, the slope angle firstly decreased gradually and then increased backward, the absolute value of the slope angle was less than 4.5° when the angular velocity of the pulley was smaller or equal to 1500 r/min; the equivalent coefficient of friction increased from 0.9594 to 1.0596 when the angular velocity of the pulley was 600 r/min, which increased from 0.9529 to 1.0601 when the angular velocity was 1500 r/min. To calculate the equivalent friction coefficient of V belt accurately can make the foundation of evaluating the capacity and service life and reasonable selection of V belt used in the agricultural machinery.%为解决现有公式因忽略周向摩擦力与拉力不共线而导致V带当量摩擦系数计算不准确的问题,引入当量摩擦系数影响角.通过试验设计,采用补偿式位移型光纤传感器系统精确测量传动过程中带的径向位移,描绘V带真实运动轨迹,求得V带当量摩擦系数影响角,进而准确计算出V带当量摩擦系数.结果表明,在V带绕进到绕出主动轮的过程中,影响角值先逐渐减小而后又反向增大,当带轮角速度≤1 500 r/min时,影响角的绝对值<4.5°;当V带角速度为600 r/min时,V带当量摩擦系数从0.9594增大到1.0596,当V带角速度为1 500 r/min时,V带当量摩擦系数从0.9529增大到1.0601.准确计算V带当量

  6. Influence of Heat Flux and Friction Coefficient on Thermal Stresses in Risers of Drum Boilers under Dynamic Conditions of Steam Demand

    Directory of Open Access Journals (Sweden)

    M. A. Habib

    2013-01-01

    Full Text Available Boiler swing rate, which is the rate at which the boiler load is changed, has significant influence on the parameters of the boiler operating conditions such as drum water pressure and level, steam quality in the riser tubes, wall temperatures of riser tubes, and the associated thermal stresses. In this paper, the thermal stresses developed in boiler tubes due to elevated rates of heat transfer and friction are presented versus thermal stresses developed in tubes operated under normal conditions. The differential equations comprising the nonlinear model and governing the flow inside the boiler tubes were formulated to study different operational scenarios in terms of resulting dynamic response of critical variables. The experimental results and field data were obtained to validate the present nonlinear dynamic model. The calculations of the heat flux and the allowable steam quality were used to determine the maximum boiler swing rates at different conditions of riser tube of friction factor and heat flux. Diagrams for the influence of friction factor of the boiler tubes and the heat flux, that the tube is subjected to, on the maximum swing rate were examined.

  7. 和谐型大功率内燃机车高摩合成闸瓦的研制%Development of Composite Brake Shoes with High Friction Coefficient for High Power Diesel Locomotive (HXN)

    Institute of Scientific and Technical Information of China (English)

    裴顶峰; 张国文; 党佳; 贺春江

    2012-01-01

    Nitrile butadiene rubber modified phenolic resin was used as adhesive. Graphite, bauxite, potash feldspar powder, reduced ferrous powder and precipitated barium sulfate were used as filler. Steel fiber and sepiolite fiber were used as reinforcing fibers. The friction material of composite brake shoe with high friction coefficient was constituted by the blend of the above materials. Composite brake shoe with high friction coefficient for high power diesel locomotive was developed through optimizing technology and formula by trial and error. Test results show that all the physical, mechanical, braking, friction and wear properties of the developed composite brake shoe with high friction coefficient meet the technical requirements of high power diesel locomotive (HXN). The impact strength and compression modulus reaches 3. 8 kJ ? M-2 and 460 Mpa respectively. Tests of 1 : 1 Train braking dynamic test stand also show that, at the speed of 120 km ? H-1, the braking distance of the loaded car, the maximum temperature of wheel tread and abrasion loss is 817 m, 215 °C and 0. 87 cm3 ? MJ-1 respectively, which can fully meet the operating requirements of emergency braking distance less than 1100 m, the maximum temperature of wheel tread less than 400 t and the braking abrasion loss of loaded car less than 1. 5 cm3 ? MJ-1 at the speed of 120 km ? H-1. The compressive properties of composite brake shoes with high friction coefficient have reached the level of the same type foreign products.%以丁腈橡胶改性酚醛树脂为黏合剂,石墨、铝矾土、钾长石粉、还原铁粉和沉淀硫酸钡等为填料,钢纤维和海泡石纤维为增强纤维,混合构成了高摩合成闸瓦的摩擦材料;通过反复实验,优化配方及工艺,研制出适合我国和谐型大功率内燃机车运用需求的高摩合成闸瓦.测试结果显示:研制的高摩合成闸瓦的各项物理力学性能及制动摩擦磨损性能符合和谐型大功率

  8. 水分对猪牙表面硬度和摩擦系数的影响%Effect of Water Content on the Hardness and Friction Coefficient of Swine Teeth Enamel

    Institute of Scientific and Technical Information of China (English)

    华李成; 郑靖; 周仲荣

    2013-01-01

    本文采用猪牙为研究对象,通过干燥和浸泡处理来控制猪牙釉质中的水分含量,利用维氏硬度仪和纳米压痕/划痕仪,研究了水分对离体生物硬组织力学性能和摩擦学特性的影响.结果表明:水含量能引起猪牙釉质表层硬度和摩擦系数的恢复性变化.猪牙表层硬度会随着水分的减少而升高,在水分再次增加后回落.猪牙表面摩擦系数随着水分的减少而降低,在水分再次增加后回升.%The mechanical properties and micro-friction behavior of swine tooth were investigated after various drying treatments,using Vicker's indentation test machine and nano-hardness/scratch tester.Moreover,the recovery of swine tooth's mechanical properties in water was investigated by immersing the dried enamel specimens in deionized water.The objective of this study is to explore the effect of water on biological hard tissue.The results show that the hardness and friction coefficient of swine tooth enamel were associated with its water content.The surface hardness of swine tooth enamel increased with the reduction of water,but the friction coefficient of swine tooth enamel decreased,and they were recovered significantly after water-immersing treatment.

  9. Experimental Study on Friction Characteristics of Caragana korshinskii Kom

    Institute of Scientific and Technical Information of China (English)

    Xiao LlU; Yuming GUO

    2015-01-01

    Caragana korshinski Kom, which is a kind of excel ent shrubs, has strong resistance to windstorms, and it is also a kind of forage that is of high nutritional value as wel as a forming fuel conversion resource that is of high caloric. Cara-gana korshinski Kom is of high lignifications after growing for a few years and the toughness of it is considerably high. Currently in China, equipments of harvesting and processing for ripe crops can hardly finish the mechanized production for Cara-gana korshinski Kom. Friction characteristics of woody material for Caragana kor-shinski Kom under different conditions should be given when the relevant operation machinery is designed, which can provide physical parameters for transportation of Caragana korshinski Kom as wel as the designing of relevant machinery. The pa-per bases on the research of friction characteristics between Caragana korshinski Kom whose diameter of 7, 10, and 13 mm under sampling directions of 0° , 45° , and 90° and machinery materials that are commonly used such as steel plate, rub-ber sheet and so on, and meanwhile the test considers factors such as different conditions of Caragana korshinski Kom, different materials of machines, different angles and so on. The data strongly suggests that the average static, dynamic fric-tion coefficient between Caragana korshinski Kom and steel plate is 0.399 711 and 0.353 022, respectively; The average static and dynamic friction coefficient between Caragana korshinski Kom and rubber sheet is 0.965 178 and 0.883 667, respec-tively. The maximum of static and dynamic friction coefficients is when the angle between the direction of sampling and the direction of movement is vertical. As the angle increased, the dynamic and static friction coefficient decreased. The friction coefficient between Caragana korshinski Kom and steel plate were increased with the increase of the diameter of Caragana korshinski Kom, but the diameter have no effect on the dynamic friction

  10. Experimental Study on the Impact of External Geometrical Shape on Free and Forced Convection Time Dependent Average Heat Transfer Coefficient during Cooling Process

    Directory of Open Access Journals (Sweden)

    Sundus Hussein Abd

    2012-01-01

    Full Text Available In this research, an experimental study was conducted to high light the impact of the exterior shape of a cylindrical body on the forced and free convection heat transfer coefficients when the body is hold in the entrance of an air duct. The impact of changing the body location within the air duct and the air speed are also demonstrated. The cylinders were manufactured with circular, triangular and square sections of copper for its high thermal conductivity with appropriate dimensions, while maintaining the surface area of all shapes to be the same. Each cylinder was heated to a certain temperature and put inside the duct at certain locations. The temperature of the cylinder was then monitored. The heat transfer coefficient were then calculated for forced convection for several Reynolds number (4555-18222.The study covered free convection impact for values of Rayleigh number ranging between (1069-3321. Imperical relationships were obtained for all cases of forced and free convection and compared with equations of circular cylindrical shapes found in literature. These imperical equations were found to be in good comparison with that of other sources.

  11. 矩形通道内两相脉动流平均摩擦压降实验研究%Experimental Study on Average Frictional Pressure Drop of Gas-liquid Two-phase Pulsatile Flow

    Institute of Scientific and Technical Information of China (English)

    周豹; 高璞珍; 谭思超; 田竞达; 张虹

    2013-01-01

    通过对截面为40 mm ×3 mm窄矩形通道内不同正弦脉动周期、振幅、平均流量工况下氮气-水两相流(平均分液相雷诺数 Rel<10000,平均分气相雷诺数 Reg <800)进行实验研究,发现两相脉动流与单相水脉动流的规律不同,平均压差对脉动周期、振幅不敏感。应用各经验公式计算的脉动工况下平均摩擦压降的偏差与稳态工况的计算偏差在数值和分布上均无明显差异,且计算值分布在测量值两侧、相对偏差基本小于20%。其中,Mishima-Hibiki方法和Lee-Lee方法的计算结果与测量结果吻合良好,相对偏差在10%以内,说明两相流摩擦压降经验公式同样适用于脉动工况下平均摩擦压降的计算。%The gas-liquid two-phase pulsatile flow was studied in a rectangular channel with 40 mm × 3 mm cross section under different periods ,flow rate amplitudes and its mean values (mean Rel < 10 000 ,mean Reg < 800) .There was difference between the single phase pulsatile flow and the gas-liquid two-phase pulsatile flow ,and pulsation period and amplitude were not sensitive for the average frictional pressure drop .There was no significant difference on the values and distribution between the calculation deviations in pulsatile flow and the calculation deviations in steady flow by using different empirical formulas .Almost all of the relative deviations were less than 20% , and the relative deviations of Mishima-Hibiki method and Lee-Lee method were less than 10% .The results show that the empirical formulas for the two-phase steady flow frictional pressure drop are also suitable for the calculation of the average value of two-phase pulsatile flow .

  12. 低附着路面条件的EPS控制策略%Electric Power Steering on Low Friction Coefficient Road

    Institute of Scientific and Technical Information of China (English)

    赵林峰; 陈无畏; 秦炜华; 杨军

    2011-01-01

    On the slippery road surface, the alignment torque decreases evidently and the conventional control strategy of electric power steering(EPS) can not respond to this particular situation equally in time. Moreover, this status leads to poor steering-wheel returnability and false road feeling, and even results in incorrect handling. The EPS model based on a whole vehicle dynamics is established to obtain the self alignment torque on the current road based on the electric motor current and torque value measured by the torque sensor. Then the ratio of self alignment torque and nominal alignment torque are used to estimate the road friction, which is divided into three levels: high, middle and low, and a new assistant torque control strategy based on the road friction estimation and a time-varying sliding mode return control strategy are proposed. The simulation results show that the new control strategy can improve road feeling and steering-wheel returnability on the slippery road. The Labview PXI hardware-in-the-loop test platform for EPS is established, the assistant torque control strategy based on road friction and the time-varying sliding mode return control strategy are validated on the platform. The test result is consistent with the simulation result.%低附着路面上,车辆自回正力矩显著降低,传统电动助力转向控制策略不能很好地克服这一不利影响,导致车辆回正性能降低,路感丧失甚至带来驾驶员对车辆的误操纵,或导致车辆不能及时回正;在建立基于整车动力学的电动助力转向系统模型的基础上,经电动机电流和转矩传感器测得转矩值,拟合得到当前路面条件下的自回正力矩,同时通过转向盘转角信息计算理想路面条件下的名义自回正力矩,结合路面估计算法,将被识别的路面附着系数等级分为高、中、低,设计基于路面附着系数的助力电流控制策略和基于时变滑模变结构控制的回正控制策略,仿真

  13. A thermodynamic model of sliding friction

    Directory of Open Access Journals (Sweden)

    Lasse Makkonen

    2012-03-01

    Full Text Available A first principles thermodynamic model of sliding friction is derived. The model predictions are in agreement with the observed friction laws both in macro- and nanoscale. When applied to calculating the friction coefficient the model provides a quantitative agreement with recent atomic force microscopy measurements on a number of materials.

  14. 基于统计的润滑剂摩擦因数测试方法研究%Study on the Test Method for the Determination of the Friction Coefficient of Lubricants Based on Statistical Theory

    Institute of Scientific and Technical Information of China (English)

    林福严; 杨建华; 张志华; 李静敏

    2011-01-01

    润滑剂摩擦因数测试具有很大的误差,ASTM D5183-05和SH/T0762-05标准的数据重复性和再现性误差都分别为20%和49%.根据数学理论导出在一定置信度下的试验数据误差估算式;通过多次抽样测试认为四球摩擦因数测试的重复性误差可以控制在1%~5%以内;提出根据试验数据方差来预计试验次数的计算公式,并指出为保证试验结果的可靠性除了保证必要的测试次数外还要确保实际测试精度.%The test error in the determination of the friction coefficient of lubricants is rather large.The data repeatability and reproducibility of ASTM D5183-05 and SH/T0762-05 are 20% and 49% respectively.An expression for the test error estimation with given confidence level was deduced from statistical theory.With duplicate tests, the repeatability for the determination of the friction coefficient of lubricants using four-ball wear test machine can be reduced to 1% ~ 5%.A formula for estimating the number of duplicate tests by the variance of test data was proposed.To ensure the reliability of test result,the number of duplicate tests and the calculated precision of tests must be ensured.

  15. Calculation procedure to determine average mass transfer coefficients in packed columns from experimental data for ammonia-water absorption refrigeration systems

    Energy Technology Data Exchange (ETDEWEB)

    Sieres, Jaime; Fernandez-Seara, Jose [University of Vigo, Area de Maquinas y Motores Termicos, E.T.S. de Ingenieros Industriales, Vigo (Spain)

    2008-08-15

    The ammonia purification process is critical in ammonia-water absorption refrigeration systems. In this paper, a detailed and a simplified analytical model are presented to characterize the performance of the ammonia rectification process in packed columns. The detailed model is based on mass and energy balances and simultaneous heat and mass transfer equations. The simplified model is derived and compared with the detailed model. The range of applicability of the simplified model is determined. A calculation procedure based on the simplified model is developed to determine the volumetric mass transfer coefficients in the vapour phase from experimental data. Finally, the proposed model and other simple calculation methods found in the general literature are compared. (orig.)

  16. Transition Path Time Distribution, Tunneling Times, Friction, and Uncertainty

    Science.gov (United States)

    Pollak, Eli

    2017-02-01

    A quantum mechanical transition path time probability distribution is formulated and its properties are studied using a parabolic barrier potential model. The average transit time is well defined and readily calculated. It is smaller than the analogous classical mechanical average transit time, vanishing at the crossover temperature. It provides a direct route for determining tunneling times. The average time may be also used to define a coarse grained momentum of the system for the passage from one side of the barrier to the other. The product of the uncertainty in this coarse grained momentum with the uncertainty in the location of the particle is shown under certain conditions to be smaller than the ℏ/2 formal uncertainty limit. The model is generalized to include friction in the form of a bilinear interaction with a harmonic bath. Using an Ohmic friction model one finds that increasing the friction, increases the transition time. Only moderate values of the reduced friction coefficient are needed for the quantum transition time and coarse grained uncertainty to approach the classical limit which is smaller than ℏ/2 when the friction is not too small. These results show how one obtains classical dynamics from a pure quantum system without invoking any further assumptions, approximations, or postulates.

  17. Friction in surface micromachined microengines

    Energy Technology Data Exchange (ETDEWEB)

    Miller, S.L.; Sniegowski, J.J.; LaVigne, G.; McWhorter, P.J.

    1996-03-01

    Understanding the frictional properties of advanced Micro-Electro- Mechanical Systems (MEMS) is essential in order to develop optimized designs and fabrication processes, as well as to qualify devices for commercial applications. We develop and demonstrate a method to experimentally measure the forces associated with sliding friction of devices rotating on a hub. The method is demonstrated on the rotating output gear of the microengine recently developed at Sandia National Laboratories. In-situ measurements of an engine running at 18300 rpm give a coefficient of friction of 0.5 for radial (normal) forces less than 4 {mu}N. For larger forces the effective coefficient of friction abruptly increases, suggesting a fundamental change in the basic nature of the interaction between the gear and hub. The experimental approach we have developed to measure the frictional forces associated with the microengine is generically applicable to other MEMS devices.

  18. Friction laws for lubricated nanocontacts

    Science.gov (United States)

    Buzio, R.; Boragno, C.; Valbusa, U.

    2006-09-01

    We have used friction force microscopy to probe friction laws for nanoasperities sliding on atomically flat substrates under controlled atmosphere and liquid environment, respectively. A power law relates friction force and normal load in dry air, whereas a linear relationship, i.e., Amontons' law, is observed for junctions fully immersed in model lubricants, namely, octamethylciclotetrasiloxane and squalane. Lubricated contacts display a remarkable friction reduction, with liquid and substrate specific friction coefficients. Comparison with molecular dynamics simulations suggests that load-bearing boundary layers at junction entrance cause the appearance of Amontons' law and impart atomic-scale character to the sliding process; continuum friction models are on the contrary of limited predictive power when applied to lubrication effects. An attempt is done to define general working conditions leading to the manifestation of nanoscale lubricity due to adsorbed boundary layers.

  19. Postoperative changes in in vivo measured friction in total hip joint prosthesis during walking.

    Directory of Open Access Journals (Sweden)

    Philipp Damm

    Full Text Available Loosening of the artificial cup and inlay is the most common reasons for total hip replacement failures. Polyethylene wear and aseptic loosening are frequent reasons. Furthermore, over the past few decades, the population of patients receiving total hip replacements has become younger and more active. Hence, a higher level of activity may include an increased risk of implant loosening as a result of friction-induced wear. In this study, an instrumented hip implant was used to measure the contact forces and friction moments in vivo during walking. Subsequently, the three-dimensional coefficient of friction in vivo was calculated over the whole gait cycle. Measurements were collected from ten subjects at several time points between three and twelve months postoperative. No significant change in the average resultant contact force was observed between three and twelve months postoperative. In contrast, a significant decrease of up to 47% was observed in the friction moment. The coefficient of friction also decreased over postoperative time on average. These changes may be caused by 'running-in' effects of the gliding components or by the improved lubricating properties of the synovia. Because the walking velocity and contact forces were found to be nearly constant during the observed period, the decrease in friction moment suggests an increase in fluid viscosity. The peak values of the contact force individually varied by 32%-44%. The friction moment individually differed much more, by 110%-129% at three and up to 451% at twelve months postoperative. The maximum coefficient of friction showed the highest individual variability, about 100% at three and up to 914% at twelve months after surgery. These individual variations in the friction parameters were most likely due to different 'running-in' effects that were influenced by the individual activity levels and synovia properties.

  20. Scale effects in sliding friction: An experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Blau, P.J.

    1991-07-24

    Solid friction is considered by some to be a fundamental property of two contacting materials, while others consider it to be a property of the larger tribosystem in which the materials are contained. A set of sliding friction experiments were designed to investigate the hypothesis that the unlubricated sliding friction between two materials is indeed a tribosystems-related property and that the relative influence of the materials properties or those of the machine on friction varies from one situation to another. Three tribometers were used: a friction microprobe (FMP), a typical laboratory-scale reciprocating pin-on-flat device, and a heavy-duty commercial wear tester. The slider material was stainless steel (AISI 440C) and the flat specimen material was an ordered alloy of Ni{sub 3}Al (IC-50). Sphere-on-flat geometry was used at ambient conditions and at normal forces ranging from 0.01 N to 100 N and average sliding velocities of 0.01 to 100.0 mm/s. The nominal, steady-state sliding friction coefficient tended to decrease with increases in normal force for each of the three tribometers, and the steady state value of sliding friction tended to increase as the mass of the machine increased. The variation of the friction force during sliding was also a characteristic of the test system. These studies provide further support to the idea that the friction of both laboratory-scale and engineering tribosystems should be treated as a parameter which may take on a range of characteristic values and not conceived as having a single, unique value for each material pair.

  1. Distance estimation of trench wet snow avalanche based on equivalent friction coefficient%基于等价摩擦系数的沟槽式湿雪雪崩抛程预测

    Institute of Scientific and Technical Information of China (English)

    段书苏; 姚令侃; 郭海强

    2016-01-01

    Wet snow avalanche is one of the main types of snow disaster in China,and it is also a common natural disaster in the late winter and early spring.The Palongzangbu river basin is in typical subtropical monsoon moist climate.Dense snow avalanches are formed because of heavy snowfall.The avalanche runout distance is the key aspect concerning avalanche risk to the traffic road.So it is often required for hazard zoning or planning of mitigation measures.Many of the prevailing avalanche models are either tend to underestimate or overestimate the runout distances,for the reason that almost all the models were relatively to the microtopography along their path.However,the micro topographies are different enormously among the different avalanche paths.Through the comparison between landslides and snow avalanches,both the two phenomenon are the formation sliding surface due to dramatic changes of water content Therefore,the Equivalent friction coefficient can be used to estimate the avalanche distance.36 typical trench medium wet snow avalanche paths are selected in the Palongcangbu river basin,and Plot the relationship between the equivalent friction coefficient and formation area.The statistic shows that:there is a good linear relation between the equivalent friction coefficient and the formation area (the correlation coefficient is R2 =0.425).Based on this relationship,the relationship between avalanche distance and the formation area,the maximum height is Hmax=Lmax 0.1586In (S) + 0.66454 in the Palongcangbu river basin.%湿雪雪崩是我国危害性较大的雪崩类型之一,也是在降雪充沛山区冬末春初一种常见的自然灾害.西藏帕隆藏布江流域处于亚热带季风温润气候,大量降雪形成了密集的雪崩,公路两侧雪崩抛程是能否影响到线路的关键要素.通过比较山体崩塌和雪崩之间的异同点,认为两者都是因为含水量的剧烈变化而形成滑动面,可以基于等价摩擦系数对雪崩抛程进行

  2. FACTORS INFLUENCING FRICTION OF PHOSPHATE COATINGS,

    Science.gov (United States)

    surface roughness, crystalline structure , and velocity. The coefficients of friction for manganese phosphate coatings did not differ to any practical...The coefficient of friction was independent of the applied load. Velocity during dynamic testing, surface finish, and crystalline structure influenced

  3. Skin Friction Gage for Measurements in Hypersonic Flow

    Institute of Scientific and Technical Information of China (English)

    Francois Falempin; Marat Goldfeld; Roman Nestoulia

    2003-01-01

    A description and results of tests of a new small-scale gage for direct measurement of skin friction force are presented in the paper. The gage design provides separated measurement of longitudinal and transversal component of friction force. Application of this scheme provides high sensitivity and necessary high-frequency response of the gage. The tests of the gage were carried out in a blow down wind tunnel at Mach numbers of 2 and 4 within the range of Reynolds numbers Rex from 0.8 to 5 million and in the hot-shot wind tunnel at Mach number 6 and Reynolds numbers Rex= 2.5-10 million. The measurements of skin friction were carried out on a flat plate and on a ramp beyond the shock wave. Simultaneously with the direct measurement of friction in the blow down wind tunnel, the measurements of profiles of average velocities and mass flow rate pulsations were realised. Analysis of measurement errors has shown that the friction gage permits to measure skin friction coefficient on a flat plate with mistake not more than 10%.

  4. Frictional torque numbers for ball cup and journal bearings

    OpenAIRE

    Ligterink, D.J.

    1982-01-01

    Plastic bearing material wears in ball cup and journal bearings. Contact areas in the ball cup and the journal bearing increase. The frictional torque needed to rotate the ball or journal also increases. When the coefficient of friction is assumed to be constant during wearing out, the frictional torque increases to a maximum of 1.273 times the frictional torque at zero wear.

  5. 渤黄东海底摩擦系数数值研究%Numerical Study on the Bottom Friction Coefficient of the Bohai, Yellow and East China Seas

    Institute of Scientific and Technical Information of China (English)

    张继才; 祝建国; 吕咸青

    2006-01-01

    使用伴随同化方法探讨了四种底摩擦系数处理方法并模拟了渤黄东海的M2分潮.理想实验表明:伴随同化方法有很强的反演底摩擦系数的能力;为了得到较好的反演结果,反演策略必须与给定的分布一致;如果给定分布很复杂,则需要复杂的反演策略.实际实验表明,底摩擦效应与地形密切相关,而海洋地形十分复杂,故需要较多的独立的底摩擦系数才能得到较好的模拟结果.本文的第四种方法将每一点均作为独立的底摩擦系数,在实验中获得了成功,验证了这种方法的合理性和有效性.%Based on the simulation of the M2 tide in the Bohai, Yellow and East China Seas, numerical experiments are made to study 4 strategies on the bottom friction coefficient (BFC) in a numerical adjoint model. In order to make a better simulation, the strategy must be consistent with the given BFC distribution. The real bottom friction decided by ocean topography is very complicated and an independent BFC is required. The fourth method which takes the BFC in each grid point as an independent BFC simulates practical experiments best and demonstrates the reasonability and efficiency of this method.

  6. Friction coefficient and microhardness of anodized aluminum alloys under different elaboration conditions%不同加工条件下阳极化铝合金的摩擦因数和显微硬度

    Institute of Scientific and Technical Information of China (English)

    M GUEZMIL; W BENSALAH; A KHALLADI; K ELLEUCH; M DEPETRIS-WERY; HF AYEDI

    2015-01-01

    研究电解液、电流密度和温度等阳极化条件对在Al 5745和Al 1050A基质上形成的氧化膜层摩擦因数和维氏硬度的影响。采用DELTALAB HVS−1000维氏硬度计和旋转销盘摩擦试验机测量样品的硬度和摩擦性能。结果表明:当草酸浓度为10 g/L、电流密度为3 A/dm2及温度为5°C时,样品获得最高的维氏硬度(>HV 400)和最低的摩擦因数(HV 400) and the lowest friction coefficient (<0.4) were obtained with the oxalic acid addition of 10 g/L at high current density of 3 A/dm2 and low temperature of 5 °C. The presence of oxidized Mg through the anodic oxide layer formed on Al 5754 was examined using glow-discharge optical emission spectroscopy (GDOES). The MgO was found to act negatively on the mechanical property of the layer. Finally, the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM) were used to characterize the anodic layer before and after friction tests. It is found that the wear mechanism is related to many aspects of the initial morphology, chemical composition of the layer (C, S and Mg), porosity and internal stress.

  7. Friction and friction-generated temperature at a polymer-metal interface

    Science.gov (United States)

    Price, H. L.; Burks, H. D.

    1974-01-01

    Results of friction and thermal tests of molded polyimide and pyrrone polymers are presented. The coefficient of sliding friction up to surface velocities of 2 m/sec and the coefficient of thermal expansion from 300 to 500 K were measured. An apparatus was constructed to measure simultaneously the coefficient of sliding friction and the friction-generated temperature. Measurements were made at a nominal pressure-velocity product of 0.25 MN/msec and at temperatures between 300 and 500 K.

  8. FEM simulation of friction testing method based on combined forward rod-backward can extrusion

    DEFF Research Database (Denmark)

    Nakamura, T; Bay, Niels; Zhang, Z. L

    1997-01-01

    A new friction testing method by combined forward rod-backward can extrusion is proposed in order to evaluate frictional characteristics of lubricants in forging processes. By this method the friction coefficient mu and the friction factor m can be estimated along the container wall and the conic...... in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm the analysis resulting in reasonable values for the friction coefficient and the friction factor....

  9. Experimental investigation on friction and squeezing of roof structure key blocks corner upon long-wall face

    Institute of Scientific and Technical Information of China (English)

    Qingxiang Huang

    2005-01-01

    The coefficients of friction and squeezing of the key blocks corner in the roof structure of underground coalface are key factors to roof structure stability quantitative analysis. In this paper, through the special test of three-type corner friction and squeezing of real rock specimens, and physical simulation test on the roof key blocks of roof structure as well as the finite element calculation of the corner stress distribution and failure mechanism, the characteristics of friction and squeezing of the roof key blocks corner are revealed. It is found that the friction angle of the roof key blocks corner is the residual friction angle, and the frictional angle of the roof key blocks is 22-32° (average 27°), so the friction coefficient is determined as 0.5. It also found the squeezing strength is less than the uniaxial strength, and the squeezing coefficient of the roof blocks corner is determined as 0.4. Based on the results, the ground control theory can be updated from qualitative analysis to quantitative analysis.

  10. 温挤压下钛白粉对铝合金摩擦系数影响研究%Effect of Titanium Dioxide on Friction Coefficient of Aluminum Alloy Under Warm Extrusion

    Institute of Scientific and Technical Information of China (English)

    刘胜濠; 张星

    2012-01-01

    On the basis of analyzing the lubricant for warm extrusion of aluminum alloy, the lubricating impact of titanium dioxide under different temperature was experimentally studied. The results show that titanium dioxide has lubricating impact in aluminum alloy warm extrusion. The minimum friction coefficient of titanium dioxide is at 350°C . However, its lubricating effect is still not more ideal than graphite. The idea of using titanium dioxide instead of graphite as the lubricant of aluminum alloy is temporarily not feasible.%在分析铝合金温挤压用润滑剂的基础上,实验研究了不同温度下钛白粉的润滑效果.结果表明,钛白粉在铝合金温挤压成形中具有一定的润滑作用.在350℃下摩擦系数最小,可是润滑效果仍然没有石墨的理想.使用钛白粉代替石墨作为铝合金的润滑剂的设想暂时行不通.

  11. Benchmarking of direct and indirect friction tests in micro forming

    DEFF Research Database (Denmark)

    Eriksen, Rasmus Solmer; Calaon, Matteo; Arentoft, M.

    2012-01-01

    The sizeable increase in metal forming friction at micro scale, due to the existence of size effects, constitutes a barrier to the realization of industrial micro forming processes. In the quest for improved frictional conditions in micro scale forming operations, friction tests are applied...... to qualify the tribological performance of the particular forming scenario. In this work the application of a simulative sliding friction test at micro scale is studied. The test setup makes it possible to measure the coefficient of friction as a function of the sliding motion. The results confirm a sizeable...... increase in the coefficient of friction when the work piece size is scaled down. © (2012) Trans Tech Publications....

  12. Friction Effects in Pedestrian Headform Impacts with Engine Hoods

    Institute of Scientific and Technical Information of China (English)

    LIU Qi; XIA Yong; ZHOU Qing

    2009-01-01

    In the pedestrian headform impact test mandated by the European pedestrian safety requirements, the contact friction between the headform and the engine hood affects the headform kinematics and head injury criterion (HIC) to some extent. This study shows that the friction effect is more significant with child headform impact than with adult headform impact and the relative angle between the headform impact di-rection and the hood surface greatly affects the headform impact sensitivity to the friction coefficient. The sensitivity of the headform kinematics to the friction coefficient is also analyzed. The results show that ac-curate friction coefficients are needed to improve predictions of pedestrian headform impacts with hoods.

  13. Low friction wear resistant graphene films

    Science.gov (United States)

    Sumant, Anirudha V.; Berman, Diana; Erdemir, Ali

    2017-02-07

    A low friction wear surface with a coefficient of friction in the superlubric regime including graphene and nanoparticles on the wear surface is provided, and methods of producing the low friction wear surface are also provided. A long lifetime wear resistant surface including graphene exposed to hydrogen is provided, including methods of increasing the lifetime of graphene containing wear surfaces by providing hydrogen to the wear surface.

  14. Rolling Friction on a Wheeled Laboratory Cart

    Science.gov (United States)

    Mungan, Carl E.

    2012-01-01

    A simple model is developed that predicts the coefficient of rolling friction for an undriven laboratory cart on a track that is approximately independent of the mass loaded onto the cart and of the angle of inclination of the track. The model includes both deformation of the wheels/track and frictional torque at the axles/bearings. The concept of…

  15. State Averages

    Data.gov (United States)

    U.S. Department of Health & Human Services — A list of a variety of averages for each state or territory as well as the national average, including each quality measure, staffing, fine amount and number of...

  16. Stochastic modeling of friction force and vibration analysis of a mechanical system using the model

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Won Seok; Choi, Chan Kyu; Yoo, Hong Hee [Hanyang University, Seoul (Korea, Republic of)

    2015-09-15

    The squeal noise generated from a disk brake or chatter occurred in a machine tool primarily results from friction-induced vibration. Since friction-induced vibration is usually accompanied by abrasion and lifespan reduction of mechanical parts, it is necessary to develop a reliable analysis model by which friction-induced vibration phenomena can be accurately analyzed. The original Coulomb's friction model or the modified Coulomb friction model employed in most commercial programs employs deterministic friction coefficients. However, observing friction phenomena between two contact surfaces, one may observe that friction coefficients keep changing due to the unevenness of contact surface, temperature, lubrication and humidity. Therefore, in this study, friction coefficients are modeled as random parameters that keep changing during the motion of a mechanical system undergoing friction force. The integrity of the proposed stochastic friction model was validated by comparing the analysis results obtained by the proposed model with experimental results.

  17. THE FRICTION OF QUARTZ IN HIGH VACUUM

    Science.gov (United States)

    the effects of surface cleanliness . Ultra-high vacuums (to 10 to the minus 10th power torr) and high temperatures (to 350 deg C) were combined with...chemical cleaning and careful handling techniques to produce the maximum surface cleanliness . The coefficient of static friction under varying...on 30-40 mesh glass balls. The coefficient of friction of smooth quartz was found to vary from 0.1 to 1.0 depending on the surface cleanliness . The

  18. Frictional torque numbers for ball cup and journal bearings

    NARCIS (Netherlands)

    Ligterink, D.J.

    1982-01-01

    Plastic bearing material wears in ball cup and journal bearings. Contact areas in the ball cup and the journal bearing increase. The frictional torque needed to rotate the ball or journal also increases. When the coefficient of friction is assumed to be constant during wearing out, the frictional t

  19. Investigation of Friction-induced Damage to the Pig Cornea

    NARCIS (Netherlands)

    da Cruz Barros, Raquel; Van Kooten, Theo G.; Veeregowda, Deepak Halenahally

    2015-01-01

    Mechanical friction causes damage to the cornea. A friction measurement device with minimal intervention with the pig cornea tear film revealed a low friction coefficient of 0.011 in glycerine solution. Glycerine molecules presumably bind to water, mucins, and epithelial cells and therewith improve

  20. Milled Die Steel Surface Roughness Correlation with Steel Sheet Friction

    DEFF Research Database (Denmark)

    Berglund, J.; Brown, C.A.; Rosén, B.-G.

    2010-01-01

    This work investigates correlations between the surface topography ofmilled steel dies and friction with steel sheet. Several die surfaces were prepared by milling. Friction was measured in bending under tension testing. Linear regression coefficients (R2) between the friction and texture...

  1. Friction and wear behaviour of self lubricating bearing liners

    Science.gov (United States)

    Gay, Russell

    The thesis describes a numerical model for evaluating the variation of friction and wear of a self lubricating bearing liner over its useful wear life. Self-lubricating bearings have been in widespread use since the mid-1950s, particularly in the aerospace industry where they have the advantage of being low maintenance components. They are commonly used in relatively low speed, reciprocating applications such as control surface actuators, and usually consist of a spherical bearing with the inner and outer elements separated by a composite textile resin-bonded liner. A finite element model has been developed to predict the local stiffness of a particular liner at different states of wear. Results obtained using the model were used to predict the overall friction coefficient as it evolves due to wear, which is a novel approach. Experimental testing was performed on a bespoke flat-on-flat wear test rig with a reciprocating motion to validate the results of the friction model.. These tests were carried out on a commercially-available bearing liner, predominantly at a high contact pressure and an average sliding speed of 0.2 ms-1. Good agreement between predicted and experimentally measured wear was obtained when appropriate coefficients of friction were used in the friction model, and when the reciprocating sliding distance was above a critical value. A numerical wear model was also developed to predict the trend of backlash development in real bearing geometries using a novel approach. Results from the wear model were validated against full-scale bearing tests carried out elsewhere by the sponsoring company. Good agreement was obtained between the model predictions and the experimental results for the first 80% of the bearing wear life, and explanations for the discrepancy during the last 20% of the wear life have been proposed..

  2. Friction anisotropy in boronated graphite

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, N., E-mail: niranjan@igcar.gov.in [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Radhika, R. [Crystal Growth Centre, Anna University, Chennai (India); Kozakov, A.T. [Research Institute of Physics, Southern Federal University, Rostov-on-Don (Russian Federation); Pandian, R. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Chakravarty, S. [UGC-DAE CSR, Kalpakkam (India); Ravindran, T.R.; Dash, S.; Tyagi, A.K. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India)

    2015-01-01

    Graphical abstract: - Highlights: • Friction anisotropy in boronated graphite is observed in macroscopic sliding condition. • Low friction coefficient is observed in basal plane and becomes high in prismatic direction. • 3D phase of boronated graphite transformed into 2D structure after friction test. • Chemical activity is high in prismatic plane forming strong bonds between the sliding interfaces. - Abstract: Anisotropic friction behavior in macroscopic scale was observed in boronated graphite. Depending upon sliding speed and normal loads, this value was found to be in the range 0.1–0.35 in the direction of basal plane and becomes high 0.2–0.8 in prismatic face. Grazing-incidence X-ray diffraction analysis shows prominent reflection of (0 0 2) plane at basal and prismatic directions of boronated graphite. However, in both the wear tracks (1 1 0) plane become prominent and this transformation is induced by frictional energy. The structural transformation in wear tracks is supported by micro-Raman analysis which revealed that 3D phase of boronated graphite converted into a disordered 2D lattice structure. Thus, the structural aspect of disorder is similar in both the wear tracks and graphite transfer layers. Therefore, the crystallographic aspect is not adequate to explain anisotropic friction behavior. Results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy shows weak signature of oxygen complexes and functional groups in wear track of basal plane while these species dominate in prismatic direction. Abundance of these functional groups in prismatic plane indicates availability of chemically active sites tends to forming strong bonds between the sliding interfaces which eventually increases friction coefficient.

  3. Design of new frictional testing machine for shallow fault materials

    Science.gov (United States)

    Tadai, O.; Tanikawa, W.; Hirose, T.; Sakaguchi, M.; Lin, W.

    2009-12-01

    Subduction thrust faults at shallow depth mainly consist of granular and clay-rich materials which strengths are influenced by the presence of pore water. Dilatation and pore pressure generation of fault zones by the dynamic friction will increase the volumetric water content in fault zone, which can assist the fault weakening by acoustic fluidization or hydrodynamic lubrication mechanism. Therefore the evaluation of rheology for clay minerals rich in pore water is critical for understanding of seismic behaviors at shallow depth. Here, we introduce a new testing apparatus for the purpose of accurate evaluation of friction behavior for incohesive fault rock materials. Our machine can shear granular materials up to 80 mm of outer diameter and maximum thickness of 40 mm. The capacities of axial load, torque, and motor are 100kN, 500Nm and 30kW, respectively, and pore pressure is increased up to 50 MPa. Maximum rotation speed is 660 rpm, which is equivalent to 1 m/s of the average slip velocity when sample diameter is 60 mm. We can monitor the dynamic changes of pore pressure and temperature at sliding surface during the friction tests. We can also control the pore pressure, axial load, pore pressure and temperature independently. All parameters can be held at targeted values and be generated at constant incremental velocity. We can control the rotation more sensitively to program the complicated rotation history that slip velocity and acceleration change during the rotation. We used powdered smectite and illite in our friction tests. We measured normal stress dependence on shear stress at normal stress up to 25 MPa with a constant rotation speed from 0.01 to 1 rpm. Normal stress is proportional to shear stress for dry clay minerals, and the friction coefficients are from 0.3 to 0.5. On the other hand, very low friction is observed in clay minerals saturated by water, and shear strength is nearly constant at various normal stresses. Our results suggest that clay

  4. Comparative Frictional Analysis of Automobile Drum and Disc Brakes

    Directory of Open Access Journals (Sweden)

    H.P. Khairnar

    2016-03-01

    Full Text Available In the present work, a comparative frictional behaviour of drum brakes and disc brakes in automobiles has been investigated. The influential factors; contact force and friction radius were modeled for the estimation of the friction coefficient for drum as well as disc brakes. The effect of contact force and friction radius is studied with varying conditions of parameters; longitudinal force, caliper force and torque on piston side as well as non-piston side. The numerical results obtained have been compared with the similar obtained from virtual Matlab/Simulink models for drum and disc brakes. The results evidenced that friction radius predominantly affects brake pressure and thus the friction coefficient, also the increase in contact force resulted with decrease in friction coefficient both for drum and disc brakes. Further it has been found that disc brakes exhibit gradual decrease of friction coefficient due to the equitable distribution of braking effort while drum brake presents sudden variations in friction coefficient. It can be revealed that frictional behaviour of disc brake is more consistent than drum brake.

  5. Frictional Forces Required for unrestrained locomotion in dairy cattle

    NARCIS (Netherlands)

    Tol, van der P.P.J.; Metz, J.H.M.; Noordhuizen-Stassen, E.N.; Back, W.; Braam, C.R.

    2005-01-01

    Most free-stall housing systems in the Netherlands are equipped with slatted or solid concrete floors with manure scrapers. A slipping incident occurs when the required coefficient of friction (RCOF) exceeds the coefficient of friction (COF) at the claw–floor interface. An experiment was conducted t

  6. Friction and stick-slip in a telescope construction

    NARCIS (Netherlands)

    Hammerschlag, R.H.

    1986-01-01

    Stick-slip in high resolution telescopes should be avoided. The contact places where stick-slip can occur are described. Some contact places require a high friction coefficient, others a low friction coefficient. Some experiments have been carried out to find lubricants for contact places which comb

  7. Optimizing snake locomotion in the plane. II. Large transverse friction

    CERN Document Server

    Alben, Silas

    2013-01-01

    We determine analytically the form of optimal snake locomotion when the coefficient of transverse friction is large, the typical regime for biological and robotic snakes. We find that the optimal snake motion is a retrograde traveling wave, with a wave amplitude that decays as the -1/4 power of the coefficient of transverse friction. This result agrees well with our numerical computations.

  8. Thermal activation in boundary lubricated friction

    Energy Technology Data Exchange (ETDEWEB)

    Michael, P.C. [Francis Bitter National Magnet Lab. and Dept. of Mechanical Engineering, Massachusetts Inst. of Tech., Cambridge, MA (United States); Rabinowicz, E. [Francis Bitter National Magnet Lab. and Dept. of Mechanical Engineering, Massachusetts Inst. of Tech., Cambridge, MA (United States); Iwasa, Y. [Francis Bitter National Magnet Lab. and Dept. of Mechanical Engineering, Massachusetts Inst. of Tech., Cambridge, MA (United States)

    1996-05-01

    The friction coefficients for copper pairs lubricated with fatty acids and fluorinated fatty acids have been measured over a wide range of sliding speeds and temperatures. Sliding speeds in the range 10{sup -7}-10{sup -2} m s{sup -1} and temperatures in the range 4.2-300 K were used. The friction coefficients near 300 K are generally low and increase with sliding speed, while the friction coefficients at low temperatures are markedly higher and relatively independent of velocity. Each lubricant`s friction vs. velocity behavior over the temperature range 150-300 K can be described by a friction-velocity master curve derived from a thermal activation model for the lubricant`s shear strength. The activation energies deduced from this friction model are identical to those obtained in the same temperature range for a vibrational mode associated with low temperature mechanical relaxations in similarly structured polymers. These results suggest that thermally activated interfacial shear is responsible for the fatty acids` positive-sloped friction vs. velocity characteristics at low sliding speeds near room temperature. (orig.)

  9. Sliding without slipping under Coulomb friction: opening waves and inversion of frictional force

    CERN Document Server

    Yastrebov, Vladislav A

    2015-01-01

    An elastic layer slides on a rigid flat governed by Coulomb's friction law. We demonstrate that if the coefficient of friction is high enough, the sliding localizes within stick-slip pulses, which transform into opening waves propagating at intersonic speed in the direction of sliding or, for high Poisson's ratios, at supersonic speed in the opposite one. This sliding mode, characterized by small frictional dissipation, rapidly relaxes the shear elastic energy via stress waves and enables the contact surface slide ahead of the top one, resulting in inversion of the frictional force direction.

  10. Device for Measuring Sliding Friction on Highloft Nonwovens

    Directory of Open Access Journals (Sweden)

    Stephen Michielsen

    2006-08-01

    Full Text Available When measuring the sliding friction on highly compliant materials such as fabric batting and foam rubber, a substantial portion of the apparent friction is due to the deformation of the substrate. A new friction instrument consisting of a sled within a sled has been developed that eliminates the contribution of this deformation and provides the true sliding friction as well as the force required to deform the substrate. The friction coefficient as measured using a conventional steel sled sliding on high loft polyester batts increased as the number of polyester batts increased. Using the new, guarded friction sled, the friction coefficient was independent of the number of supporting batts, thus separating the deformation forces from the sliding forces.

  11. Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces

    DEFF Research Database (Denmark)

    Hansson, Petra M; Claesson, Per M.; Swerin, Agne;

    2013-01-01

    by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All...... the particle coated surfaces exhibited similar friction coefficients, from which it may be concluded that the surface geometry, and not the roughness amplitude per se, influenced the measured friction. During measurements with hydrophobic surfaces, strong adhesive forces related to the formation of a bridging...... air cavity were evident from both normal force and friction force measurements. In contrast to the frictional forces between the hydrophilic surfaces, the friction coefficient for hydrophobic surfaces was found to depend on the surface structure and we believe that this dependence is related...

  12. Thermodynamic aspects of rock friction

    CERN Document Server

    Mitsui, Noa

    2013-01-01

    Rate- and state-dependent friction law for velocity-step tests is analyzed from a thermodynamic point of view. A simple macroscopic non-equilibrium thermodynamic model with a single internal variable reproduces instantaneous jump and relaxation. Velocity weakening appears as a consequence of a plasticity related nonlinear coefficient. Permanent part of displacement corresponds to plastic strain, and relaxation effects are analogous to creep in thermodynamic rheology.

  13. Solvent friction effects propagate over the entire protein molecule through low-frequency collective modes.

    Science.gov (United States)

    Moritsugu, Kei; Kidera, Akinori; Smith, Jeremy C

    2014-07-24

    Protein solvation dynamics has been investigated using atom-dependent Langevin friction coefficients derived directly from molecular dynamics (MD) simulations. To determine the effect of solvation on the atomic friction coefficients, solution and vacuum MD simulations were performed for lysozyme and staphylococcal nuclease and analyzed by Langevin mode analysis. The coefficients thus derived are roughly correlated with the atomic solvent-accessible surface area (ASA), as expected from the fact that friction occurs as the result of collisions with solvent molecules. However, a considerable number of atoms with higher friction coefficients are found inside the core region. Hence, the influence of solvent friction propagates into the protein core. The internal coefficients have large contributions from the low-frequency modes, yielding a simple picture of the surface-to-core long-range damping via solvation governed by collective low-frequency modes. To make use of these findings in implicit-solvent modeling, we compare the all-atom friction results with those obtained using Langevin dynamics (LD) with two empirical representations: the constant-friction and the ASA-dependent (Pastor-Karplus) friction models. The constant-friction model overestimates the core and underestimates the surface damping whereas the ASA-dependent friction model, which damps protein atoms only on the solvent-accessible surface, reproduces well the friction coefficients for both the surface and core regions observed in the explicit-solvent MD simulations. Therefore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.

  14. On Sliding Friction of PEEK Based Composite Coatings

    Institute of Scientific and Technical Information of China (English)

    H. Liao; G. Zhang; C. Mateus; H. Li; C. Coddet

    2004-01-01

    Polyetheretherketone (PEEK) based composite materials become of great interest to applications as bearing and slider materials due to their excellent tribological performance. In present work, graphite and MoS2 (7%, wt) filled PEEK coatings were prepared using serigraph technique. Employing a uniform design experiment, the friction behavior of the composite coatings was systematically investigated under dry sliding conditions on a ball-on-disc arrangement. The evolution mechanism of coating friction coefficient was discussed. Correlation of coatings friction coefficient with sliding velocity and applied load was accomplished usingstepwise regression method. The results indicate that friction coefficients of PEEK + MoS2 and PEEK + graphite coating decrease while increasing applied load. Moreover, friction coefficient of PEEK + MoS2 coating increases with increasing sliding velocity.

  15. On Sliding Friction of PEEK Based Composite Coatings

    Institute of Scientific and Technical Information of China (English)

    H.Liao; G.Zhang; C.Mateus; H.Li; C.Coddet

    2004-01-01

    Polyetheretherketone (PEEK) based composite materials become of great interest to applications as bearing and slider materials due to their excellent tribological performance. In present work, graphite and MoS2(7%,wt) filled PEEK coatings were prepared using serigraph technique. Employing a uniform design experiment, the friction behavior of the composite coatings was systematically investigated under dry sliding conditions on a ball-on-disc arrangement. The evolution mechanism of coating friction coefficient was discussed. Correlation of coatings friction coefficient with sliding velocity and applied load was accomplished using stepwise regression method. The results indicate that friction coefficients of PEEK+MoS2 and PEEK+graphite coating decrease while increasing applied load. Moreover, friction coefficient of PEEK+MoS2 coating increases with increasing sliding velocity.

  16. Quantized friction across ionic liquid thin films

    Science.gov (United States)

    Smith, Alexander M.; Lovelock, Kevin R. J.; Gosvami, Nitya Nand; Welton, Tom; Perkin, Susan

    Ionic liquids, salts in the liquid state under ambient conditions, are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers. Multiple friction-load regimes emerge, each corresponding to a different number of ion layers in the film. In contrast to molecular liquids, the friction coefficients differ for each layer due to their varying composition.

  17. Coordinated Water Under Confinement Eases Sliding Friction

    Science.gov (United States)

    Defante, Adrian; Dhopotkar, Nishad; Dhinojwala, Ali

    Water is essential to a number of interfacial phenomena such as the lubrication of knee joints, protein folding, mass transport, and adsorption processes. We have used a biaxial friction cell to quantify underwater friction between a hydrophobic elastomeric lens and a hydrophobic self-assembled monolayer in the presence of surfactant solutions. To gain an understanding of the role of water in these processes we have coupled this measurement with surface sensitive sum frequency generation to directly probe the molecular constitution of the confined contact interface. We observe that role of confined coordinated water between two hydrophobic substrates covered with surfactants is the key to obtaining a low coefficient of friction.

  18. Quantized friction across ionic liquid thin films.

    Science.gov (United States)

    Smith, Alexander M; Lovelock, Kevin R J; Gosvami, Nitya Nand; Welton, Tom; Perkin, Susan

    2013-10-07

    Ionic liquids - salts in the liquid state under ambient conditions - are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers. Multiple friction-load regimes emerge, each corresponding to a different number of ion layers in the film. In contrast to molecular liquids, the friction coefficients differ for each layer due to their varying composition.

  19. Acoustics of friction.

    Science.gov (United States)

    Akay, Adnan

    2002-04-01

    This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of

  20. 小冲杆试验中摩擦系数及试样厚度对载荷-位移曲线及断裂位置的影响%Effect of friction coefficient and specimen thickness on L-D curve and fracture position in small punch test

    Institute of Scientific and Technical Information of China (English)

    张广哲; 徐一飞; 关凯书

    2012-01-01

    ABAQUS was adopted to establish SPT model. The test process was simulated based on the ductile elasto-plastic damage theory of Gurson. A comparison of L-D curve between simulation and test with the specimen thickness 0. 5mm has been done to ensure the validity of parameters. The results show that both the friction coefficient and the specimen thickness have some effect on the L-D curve and fracture position, the friction coefficient also influences the final stage of the L-D curve.%基于Gurson弹塑性损伤理论,应用大型有限元软件ABAQUS对小冲杆试验全过程进行模拟,通过0.5mm厚试样载荷-位移曲线的模拟值与试验值对比,确保有限元模型参数的准确性,进而得出钢珠与试样间的摩擦作用对载荷位移曲线及断裂位置的影响,以及试样厚度对断裂位置的影响.

  1. Role of Friction in Cold Ring Rolling

    Institute of Scientific and Technical Information of China (English)

    He YANG; Lianggang GUO; Mei ZHAN

    2005-01-01

    Cold ring rolling is an advanced but complex metal forming process under coupled effects with multi-factors, such as geometry sizes of rolls and ring blank, material, forming process parameters and friction, etc. Among these factors,friction between rolls and ring blank plays animportant role in keeping the stable forming of cold ring rolling. An analytical method was firstly presented for proximately determining the critical friction coefficient of stable forming and then a method was proposed to determine thecritical friction coefficient by combining analytical method with numerical simulation. And the influence of friction coefficient on the quality of end-plane and side spread of ring,rolling force, rolling moment and metal flow characteristic in the cold ring rolling process have been explored using the three dimensional (3D) numerical simulation based on the elastic-plastic dynamic finite element method (FEM)under the ABAQUS software environment, and the results show that increasing the friction on the contact surfaces between rolls and ring blank is useful not only for improving the stability of cold ring rolling but also for improving the geometry and dimension precision of deformed ring.

  2. Low temperature friction force microscopy

    Science.gov (United States)

    Dunckle, Christopher Gregory

    The application of friction force techniques within atomic force microscopy (AFM) allows for direct measurements of friction forces at a sliding, single-asperity interface. The temperature dependence of such single-asperity contacts provides key insight into the comparative importance of dissipative mechanisms that result in dry sliding friction. A variable temperature (VT), ultrahigh vacuum (UHV) AFM was used with an interface consisting of a diamond coated AFM tip and diamond-like carbon sample in a nominal sample temperature range of 90 to 275K. The results show that the coefficient of kinetic friction, mu k, has a linear dependence that is monotonically increasing with temperature varying from 0.28 to 0.38. To analyze this data it is necessary to correlate the sample temperature to the interface temperature. A detailed thermal model shows that the sample temperature measured by a macroscopic device can be very different from the temperature at the contact point. Temperature gradients intrinsic to the design of VT, UHV AFMs result in extreme, non-equilibrium conditions with heat fluxes on the order of gigawatts per squared meter through the interface, which produce a discontinuous step in the temperature profile due to thermal boundary impedance. The conclusion from this model is that measurements acquired by VT, UHV AFM, including those presented in this thesis, do not provide meaningful data on the temperature dependence of friction for single-asperities. Plans for future work developing an isothermal AFM capable of the same measurements without the introduction of temperature gradients are described. The experimental results and thermal analysis described in this thesis have been published in the Journal of Applied Physics, "Temperature dependence of single-asperity friction for a diamond on diamondlike carbon interface", J. App. Phys., 107(11):114903, 2010.

  3. Energy coefficients for a propeller series

    DEFF Research Database (Denmark)

    Olsen, Anders Smærup

    2004-01-01

    The efficiency for a propeller is calculated by energy coefficients. These coefficients are related to four types of losses, i.e. the axial, the rotational, the frictional, and the finite blade number loss, and one gain, i.e. the axial gain. The energy coefficients are derived by use of the poten......The efficiency for a propeller is calculated by energy coefficients. These coefficients are related to four types of losses, i.e. the axial, the rotational, the frictional, and the finite blade number loss, and one gain, i.e. the axial gain. The energy coefficients are derived by use...... of the potential theory with the propeller modelled as an actuator disk. The efficiency based on the energy coefficients is calculated for a propeller series. The results show a good agreement between the efficiency based on the energy coefficients and the efficiency obtained by a vortex-lattice method....

  4. The role of adsorbed water on the friction of a layer of submicron particles

    Science.gov (United States)

    Sammis, Charles G.; Lockner, David A.; Reches, Ze’ev

    2011-01-01

    Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near μ = 0.6 at low slip speeds to a coefficient near μ = 0.3 at higher slip speeds is attributed to competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer enables the otherwise rough particles to rotate, the coefficient of friction will drop to μ = 0.3, appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100°C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to μ = 0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1 nm thick layer of adsorbed water, with a minimum particle radius of approximately 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and the range of velocities over which it occurs decrease with increasing normal stress, as predicted by the model. Moreover, the analysis predicts that this high-speed weakening mechanism should operate only for particles with radii smaller than approximately 1 μm. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

  5. Friction laws from dimensional-analysis point of view

    CERN Document Server

    Hatano, Takahiro

    2015-01-01

    Friction laws, which are a key to the understanding of the diversity of earthquakes, are considered theoretically. Using dimensional analysis, the logarithmic dependence of the friction coefficient on the slip velocity and the state variable is derived without any knowledge of the underlying physical processes on the frictional surface. This is based on a simple assumption that the friction coefficient is expressed as the difference from a reference state. Therefore, the functional form of the rate and state dependent friction law itself does not necessarily mean that thermal activation processes dominate friction. It is also shown that, if there are two (or more) state variables having the same dimension, we need not assume the logarithmic dependence on the state variables.

  6. Self-Organization during Friction of Slide Bearing Antifriction Materials

    Directory of Open Access Journals (Sweden)

    Iosif S. Gershman

    2015-12-01

    Full Text Available This article discusses the peculiarities of self-organization behavior and formation of dissipative structures during friction of antifriction alloys for slide bearings against a steel counterbody. It shows that during self-organization, the moment of friction in a tribosystem may be decreasing with the load growth and in the bifurcations of the coefficient of friction with respect to load. Self-organization and the formation of dissipative structures lead to an increase in the seizure load.

  7. Modeling and Calculation of Impact Friction Caused by Corner Contact in Gear Transmission

    Institute of Scientific and Technical Information of China (English)

    ZHOU Changjiang; CHEN Siyu

    2014-01-01

    Corner contact in gear pair causes vibration and noise, which has attracted many attentions. However, teeth errors and deformation make it difficulty to determine the point situated at corner contact and study the mechanism of teeth impact friction in the current researches. Based on the mechanism of corner contact, the process of corner contact is divided into two stages of impact and scratch, and the calculation model including gear equivalent error-combined deformation is established along the line of action. According to the distributive law, gear equivalent error is synthesized by base pitch error, normal backlash and tooth profile modification on the line of action. The combined tooth compliance of the first point lying in corner contact before the normal path is inversed along the line of action, on basis of the theory of engagement and the curve of tooth synthetic compliance & load-history. Combined secondarily the equivalent error with the combined deflection, the position standard of the point situated at corner contact is probed. Then the impact positions and forces, from the beginning to the end during corner contact before the normal path, are calculated accurately. Due to the above results, the lash model during corner contact is founded, and the impact force and frictional coefficient are quantified. A numerical example is performed and the averaged impact friction coefficient based on the presented calculation method is validated. This research obtains the results which could be referenced to understand the complex mechanism of teeth impact friction and quantitative calculation of the friction force and coefficient, and to gear exact design for tribology.

  8. On Surface Structure and Friction Regulation in Reptilian Limbless Locomotion

    CERN Document Server

    Abdel-Aal, Hisham A

    2012-01-01

    One way of controlling friction and associated energy losses is to engineer a deterministic structural pattern on the surface of the rubbing parts (i.e., texture engineering). Custom texturing enhances the quality of lubrication, reduces friction, and allows the use of lubricants of lower viscosity. To date, a standardized procedure to generate deterministic texture constructs is virtually non-existent. Many engineers, therefore, study natural species to explore surface construction and to probe the role surface topography assumes in friction control. Snakes offer rich examples of surfaces where topological features allow the optimization and control of frictional behavior. In this paper, we investigate the frictional behavior of a constrictor type reptile, Python regius. The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional response of snakesk...

  9. Friction measurement in MEMS using a new test structure

    Energy Technology Data Exchange (ETDEWEB)

    Crozier, B.T.; De Boer, M.P.; Redmond, J.M.; Bahr, D.F.; Michalske, T.A.

    1999-12-09

    A MEMS test structure capable of measuring friction between polysilicon surfaces under a variety of test conditions has been refined from previous designs. The device is applied here to measuring friction coefficients of polysilicon surfaces under different environmental, loading, and surface conditions. Two methods for qualitatively comparing friction coefficients ({mu}) using the device are presented. Samples that have been coated with a self-assembled monolayer of the lubricating film perfluorinated-decyltrichorosilane (PFTS) have a coefficient of friction that is approximately one-half that of samples dried using super-critical CO{sub 2} (SCCO{sub 2}) drying. Qualitative results indicate that {mu} is independent of normal pressure. Wear is shown to increase {mu} for both supercritically dried samples and PFTS coated samples, though the mechanisms appear to be different. Super critically dried surfaces appear to degrade continuously with increased wear cycles, while PFTS coated samples reach a steady state friction value after about 10{sup 4} cycles.

  10. Guide for the estimation of the {alpha} and {beta} coefficients in the Average enrichment equation as burnt function by fuel type; Guia para la estimacion de los coeficientes {alpha} y {beta} en la ecuacion de enriquecimiento promedio como funcion del quemado por tipo de combustible

    Energy Technology Data Exchange (ETDEWEB)

    Montes T, J.L.; Cortes C, C.C. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

    1992-08-15

    The objective of the report is to determine manually or by means of a calculation sheet, the coefficients {alpha} and {beta} of the average enrichment equation as function of the fuel burnt (B) using the Lineal Reactivity Pattern, with information generated by the RECORD code of the FMS package. (Author00.

  11. A Damping Characteristics Calculation Method of Metal Dry Friction Isolators

    Institute of Scientific and Technical Information of China (English)

    JIANG Hong-yuan; HAO De-gang; XIA Yu-hong; ULANOV A M; PONOMAREV Yu K

    2008-01-01

    The dry friction ring-type vibration isolator is considered as an isotropic continuous medium. A method of dry friction hysteresis loop calculation is proposed based on friction force analysis of contact beam. The friction force is modeled as an equivalent distributed moment to use the finite element method (FEM) to calculate the dry friction vibration isolator hysteresis loop, so the damping characteristics can be obtained. A comparison of the hysteresis loop calculation results and the experimental results shows the average relative error is 2.7%, it proves the calculation method is feasible.

  12. Predicting vibration-induced displacement for a resonant friction slider

    DEFF Research Database (Denmark)

    Fidlin, A.; Thomsen, Jon Juel

    2001-01-01

    A mathematical model is set up to quantify vibration-induced motions of a slider, sandwiched between friction layers with different coefficients of friction, and equipped with an imbedded resonator that oscillates at high frequency and small amplitude. This model is highly nonlinear, involving non...... of the full equations of motion. The expressions are used to estimate and explain the influence of system parameters....

  13. The Static Ladder Problem with Two Sources of Friction

    Science.gov (United States)

    Bennett, Jonathan; Mauney, Alex

    2011-01-01

    The problem of a ladder leaning against a wall in static equilibrium is a classic example encountered in introductory mechanics texts. Most discussions of this problem assume that the static frictional force between the ladder and wall can be ignored. A few authors consider the case where the static friction coefficients between ladder/wall…

  14. Frictional characteristics of granular system under high pressure

    Institute of Scientific and Technical Information of China (English)

    曹秒艳; 彭雅新; 赵长财; 董国疆; 杜冰

    2016-01-01

    In order to reveal the force transmission features of the granules in the solid granule medium forming (SGMF) technology, the frictional characteristics of the non-metallic granule medium (NGM) under high pressure were investigated by tests and simulations. And the relevant changing curves of the internal friction coefficient of the granular system under different normal pressures were obtained by self-designed shear test. By the granule volume compression test, the accurate discrete element simulation parameters were obtained, based on this, the discrete element method (DEM) was adopted to reveal the evolution law of the NGM granules movement in the sample shear process from the microscopic view. Based on the DEM, the influence of granule diameter, surface friction coefficient, normal pressure and shear velocity on the internal friction coefficient of the granular system were studied. And the parameters were conducted to be dimensionless by introducing the inertia coefficient. Finally, the expression showing power-law relationship of inertia coefficient, surface friction coefficient and internal friction coefficient is obtained.

  15. Comparative evaluation of frictional characteristics of coated low friction ligatures - Super Slick Ties™ with conventional uncoated ligatures

    Directory of Open Access Journals (Sweden)

    Deepu Leander

    2011-01-01

    Conclusions: SST produced lower levels of friction (11% for all archwire materials when compared to conventional uncoated ligatures (Dispense-A-Stix and both conventional uncoated ligatures and coated ligatures gave a rank order of coefficient of kinetic friction (μkf among archwires, with stainless steel archwires exhibiting the least and TMA TM showing the highest.

  16. Adhesion and friction of thin metal films

    Science.gov (United States)

    Buckley, D. H.

    1976-01-01

    Sliding friction experiments were conducted in vacuum with thin films of titanium, chromium, iron, and platinum sputter deposited on quartz or mica substrates. A single crystal hemispherically tipped gold slider was used in contact with the films at loads of 1.0 to 30.0 and at a sliding velocity of 0.7 mm/min at 23 C. Test results indicate that the friction coefficient is dependent on the adhesion of two interfaces, that between the film and its substrate and the slider and the film. There exists a relationship between the percent d bond character of metals in bulk and in thin film form and the friction coefficient. Oxygen can increase adhesive bonding of a metal film (platinum) to a substrate.

  17. Static and dynamic friction of hierarchical surfaces

    Science.gov (United States)

    Costagliola, Gianluca; Bosia, Federico; Pugno, Nicola M.

    2016-12-01

    Hierarchical structures are very common in nature, but only recently have they been systematically studied in materials science, in order to understand the specific effects they can have on the mechanical properties of various systems. Structural hierarchy provides a way to tune and optimize macroscopic mechanical properties starting from simple base constituents and new materials are nowadays designed exploiting this possibility. This can be true also in the field of tribology. In this paper we study the effect of hierarchical patterned surfaces on the static and dynamic friction coefficients of an elastic material. Our results are obtained by means of numerical simulations using a one-dimensional spring-block model, which has previously been used to investigate various aspects of friction. Despite the simplicity of the model, we highlight some possible mechanisms that explain how hierarchical structures can significantly modify the friction coefficients of a material, providing a means to achieve tunability.

  18. Effect of Interface Modified by Graphene on the Mechanical and Frictional Properties of Carbon/Graphene/Carbon Composites

    Directory of Open Access Journals (Sweden)

    Wei Yang

    2016-06-01

    Full Text Available In this work, we developed an interface modified by graphene to simultaneously improve the mechanical and frictional properties of carbon/graphene/carbon (C/G/C composite. Results indicated that the C/G/C composite exhibits remarkably improved interfacial bonding mode, static and dynamic mechanical performance, thermal conductivity, and frictional properties in comparison with those of the C/C composite. The weight contents of carbon fibers, graphene and pyrolytic carbon are 31.6, 0.3 and 68.1 wt %, respectively. The matrix of the C/G/C composite was mainly composed of rough laminar (RL pyrocarbon. The average hardness by nanoindentation of the C/G/C and C/C composite matrices were 0.473 and 0.751 GPa, respectively. The flexural strength (three point bending, interlaminar shear strength (ILSS, interfacial debonding strength (IDS, internal friction and storage modulus of the C/C composite were 106, 10.3, 7.6, 0.038 and 12.7 GPa, respectively. Those properties of the C/G/C composite increased by 76.4%, 44.6%, 168.4% and 22.8%, respectively, and their internal friction decreased by 42.1% in comparison with those of the C/C composite. Owing to the lower hardness of the matrix, improved fiber/matrix interface bonding strength, and self-lubricating properties of graphene, a complete friction film was easily formed on the friction surface of the modified composite. Compared with the C/C composite, the C/G/C composite exhibited stable friction coefficients and lower wear losses at simulating air-plane normal landing (NL and rejected take-off (RTO. The method appears to be a competitive approach to improve the mechanical and frictional properties of C/C composites simultaneously.

  19. MODIFICATION OF FLAKE REINFORCED FRICTION BRAKE COMPOSITE MATERIAL

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    According to the recent development trend and need of the friction brake material, the flake reinforced friction brake material has been made out by adjusting the recipe and techniques. The two-dimensional flake vermiculite is selected as the reinforced stuffing of the material; the modified resin is used as the basal bed of the material. The tests manifest that the properties of mechanics are high, the friction coefficients are suitable and stable,and especially in high temperatures the wear is low. It is an excellent friction brake material.

  20. Friction Properties of Inkjet and Flexographic Prints on Different Papers

    Directory of Open Access Journals (Sweden)

    Simona Grigaliūnienė

    2015-03-01

    Full Text Available Friction between different papers, inkjet and flexographic prints has been experimentally investigated. Flexographic prints have been made using an anilox roller, and inkjet prints have been produced covering paper with one and four toner layers. Static (SCOF and kinetic (KCOF friction coefficients between paper and paper, paper and prints, prints and prints have been determined. Friction properties have been discovered to be different in flexographic and laser prints. The dependence of SCOF and KCOF on pressure (both decrease together with roughness measurements enables to conclude that the friction of prints is mainly governed by adhesion forces.

  1. Uniform Design of Optimizing Formulation of Friction Materials with Composite Mineral Fiber (CMF) and Their Friction and Wear Behavior

    Science.gov (United States)

    Yang, Yazhou; Jiang, Man; Xu, Jie; Ma, Yunhai; Tong, Jin

    2012-04-01

    In this work, the uniform design method was applied to arrange the experimental scheme for optimizing formulation of friction materials. The friction and wear of the friction materials based on the optimized formulation was carried out on a constant speed friction tester (JF150D-II), using pad-on-disc contact mode against gray cast iron disc. The worn surfaces of the friction materials were examined by scanning electron microscopy (JSM5310) and the friction mechanism was discussed. The results showed that the uniform design method was appropriate for finding the optimum formulation of the friction materials with better properties. Compared with two conventional friction materials, the friction materials based on the optimized formulation possessed higher and stable friction coefficient and higher wear resistance, even at the disc temperature of 350°C. The adhesion, strain fatigue and abrasive wear were the main wear mechanisms of the friction materials. Tribo-chemical phenomenon and plastic deformation existed on the worn surface layer.

  2. Friction Compensation in the Upsetting of Cylindrical Test Specimens

    DEFF Research Database (Denmark)

    Christiansen, Peter; Martins, P. A. F.; Bay, Niels Oluf

    2016-01-01

    This manuscript presents a combined numerical andexperimental methodology for determining the stress-straincurve of metallic materials from the measurements of forceand displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens....... The methodology is based on minimizing the errorbetween the average surface pressure obtained from the experimental measurements of the force and displacement and thatobtained from the slab method of analysis of metal plasticity.Three different friction models based on Coulomb friction, the constant friction...... model or combined friction models are utilized .Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction...

  3. 动态摩擦因数对蝶式制动器温度场影响的试验和模拟研究%Experimental and Simulation Research on the Influence of Dynamic Friction Coefficient to the Temperature Field of Disc Brake

    Institute of Scientific and Technical Information of China (English)

    周俊峰; 王伟; 张晨; 刘焜

    2016-01-01

    To research into temperature field of disc brake, as needed, a constant speed braking bench is developed to simulate the braking condition of motorcycle under long slope by similarity principle. The disc fixed on rotating shaft, which is clamped by three jaw chuck of lathe, rotate with constant speed. The disc is clamped by inner pad and outward pad though hydraulic pressure. Temperature evolution of certain point on outward pad, braking torque evolution, mean value of braking pressure, temperature evolution on the frictional area of disc are measured by thermal couple, pressure sensor, piezometer, thermal imager respectively. The braking bench could realize the dynamic test of all variables under different rational speed and different braking pressure. The maximum temperature is chosen as variable to research the evolution of friction coefficient with temperature increasing. Based on experiment, simulation and analysis are did by ABAQUS. Simulation models are made from actual model by the ratio 1:1, load and boundary conditions are the same as reality, the evolution of friction coefficient with increasing temperature is put into contact condition, finally, the evolutions of the temperature fields of disc and pad are obtained. Compare to the simulation result and experimental result, it shows that the contact model with dynamic friction coefficient is better fit into the actual braking condition.%针对蝶式制动器制动过程中温度场研究的需要,利用相似原理研制定速制动试验台,用以模拟摩托车匀速下长坡时的制动工况。制动试验台用车床的三爪卡盘控制固定在旋转轴上的制动盘做定速旋转运动,内外摩擦片通过液压力夹紧制动盘,使制动盘与摩擦片发生摩擦运动,通过热电偶、拉压力传感器、压力表、热成像仪分别测出定速制动50 s的摩擦片上固定点的温度变化、制动扭矩(经计算得出)的动态变化、制动力的均值、制动盘摩

  4. New Micro- and Macroscopic Models of Contact and Friction

    Science.gov (United States)

    1992-11-01

    T., and Rabinowicz , E., "The Nature of the Coefficient of Friction," .Journ. Appl. Phys., 24, 2, pp. 136-139, 1953. 23. Bush, A. W., Gibson, R. D...Nonlinear Friction Laws," International Journal of Engineering Science, Vol. 24, No. 11, pp. 1755-1768, 1986. 76. Rabinowicz , E., "The Nature of the...Static and Kinetic Coefficients of Friction," Journ. AppL. Physics, 11, 22, pp. 1373-1379, 1951. 77. Rabinowicz , E., "The Intrinsic Variables Affecting

  5. Viscosity Prediction of Natural Gas Using the Friction Theory

    DEFF Research Database (Denmark)

    Zeberg-Mikkelsen, Claus Kjær; Cisneros, Sergio; Stenby, Erling Halfdan

    2002-01-01

    rules based on the values of the pure component friction coefficients. Since natural gases contain mainly methane, two f-theory models are combined, where the friction coefficients of methane are estimated by a seven-constant f-theory model directly fitted to methane viscosities, and the friction...... agreement with the experimental uncertainty (+/-1.0%). The AAD is found to be higher for older measurements (around 3.5%), due mainly to the higher experimental uncertainties and problems with some of the measurements. Overall, the results are satisfactory for most industrial applications related to natural...

  6. Friction behavior of Al-Cu-Fe-B polycrystalline quasicrystals

    Institute of Scientific and Technical Information of China (English)

    周细应; 李培耀; 罗军明; 钱士强; 童建华

    2004-01-01

    Dry sliding friction between the polycrystalline Al59 Cu25.5 Fe12.5 B3 quasicrystals(QCs) and coating of thediamond-like carbon(DLC) was carried out by self-made tribometer under different conditions. The influences of four parameters(temperature, sliding velocity, applied load, atmosphere) on friction of quasicrystal surface were studied. Microstructure of quasicrystal, morphology of worn surface, and wear debris were observed by scanning electron microscope(SEM). The results show that for QCs, the friction coefficient and the roughness of worn surface is influenced by the parameters, especially greatly by the temperature. With increasing the applied load and sliding velocity, the friction coefficient decreases. The dominant wear mechanism at 350 ℃ is delamination for QCs. The cracks forms on the worn surface during friction. Moreover, phase transformation is not observed on worn surface of QCs at 350 ℃.

  7. Study of lubrication behavior of pure water for hydrophobic friction pair

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The perfluorooctyltrichlorosilane molecular layer was self-assembled on glass plate. The tribological properties of the molecular layer in water were studied with the method of ball on disk. An interesting phenomenon was found that low friction coefficients of 0.02―0.08 were obtained when the friction pair was lubricated with only a water droplet. Whereas, when the friction pair was encircled with large amount of water or fully immersed in water, the friction coefficient was higher than that under a droplet lubrication. A mechanism of water droplet lubrication was proposed that the surface tension caused by the solid-liquid-air three-phase interface makes water molecules enter into the contact zone, which separates the two friction surfaces and provides a low friction coefficient. However, water film can hardly form when more water encircles the friction pair, due to the attraction between water molecules.

  8. Friction characteristics of floppy disks

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This note presents the principle and structure of a tribological measure for floppy disks.The precision of the force measuring system is 1 mN in loading and 3×10-6 N in friction.The resolution of the film thickness between head and floppy disk is 0.5 nm in the vertical and 1.5 nm in the horizontal direction.In order to investigate the tribological characteristics of floppy disks,six types of floppy disks have been tested and the floating properties of these disks are also studied with film measuring system.The experimental results of the surface morphology and friction coefficient of these floppy disks using the atomic force microscope/friction force mcroscope (AFM/FFM) are in accordance with the conclusion made by our own measuring system.The experimental results show that the air film thickness between head and disk is of the same order as the surface roughness of floppy disks.

  9. Theory of noncontact friction for atom-surface interactions

    Science.gov (United States)

    Jentschura, U. D.; Janke, M.; DeKieviet, M.

    2016-08-01

    The noncontact (van der Waals) friction is an interesting physical effect, which has been the subject of controversial scientific discussion. The direct friction term due to the thermal fluctuations of the electromagnetic field leads to a friction force proportional to 1 /Z5 (where Z is the atom-wall distance). The backaction friction term takes into account the feedback of thermal fluctuations of the atomic dipole moment onto the motion of the atom and scales as 1 /Z8 . We investigate noncontact friction effects for the interactions of hydrogen, ground-state helium, and metastable helium atoms with α -quartz (SiO2), gold (Au), and calcium difluorite (CaF2). We find that the backaction term dominates over the direct term induced by the thermal electromagnetic fluctuations inside the material, over wide distance ranges. The friction coefficients obtained for gold are smaller than those for SiO2 and CaF2 by several orders of magnitude.

  10. Variables influencing the frictional behaviour of in vivo human skin.

    Science.gov (United States)

    Veijgen, N K; Masen, M A; van der Heide, E

    2013-12-01

    In the past decades, skin friction research has focused on determining which variables are important to affect the frictional behaviour of in vivo human skin. Until now, there is still limited knowledge on these variables. This study has used a large dataset to identify the effect of variables on the human skin, subject characteristics and environmental conditions on skin friction. The data are obtained on 50 subjects (34 males and 16 females). Friction measurements represent the friction between in vivo human skin and an aluminium sample, assessed on three anatomical locations. The coefficient of friction increased significantly (pskin and the height of the subject. Other outcome variables in this study were the hydration of the skin and the skin temperature.

  11. Surface defects and temperature on atomic friction

    Energy Technology Data Exchange (ETDEWEB)

    Fajardo, O Y; Mazo, J J, E-mail: yovany@unizar.es [Departamento de Fisica de la Materia Condensada and Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain)

    2011-09-07

    We present a theoretical study of the effect of surface defects on atomic friction in the stick-slip dynamical regime of a minimalistic model. We focus on how the presence of defects and temperature change the average properties of the system. We have identified two main mechanisms which modify the mean friction force of the system when defects are considered. As expected, defects change the potential profile locally and thus affect the friction force. But the presence of defects also changes the probability distribution function of the tip slip length and thus the mean friction force. We corroborated both effects for different values of temperature, external load, dragging velocity and damping. We also show a comparison of the effects of surface defects and surface disorder on the dynamics of the system. (paper)

  12. Torsional friction damper optimization

    Science.gov (United States)

    Ye, Shaochun; Williams, Keith A.

    2006-06-01

    A new approach for the analysis of friction dampers is presented in this work. The exact form of the steady-state solution for a friction damper implemented on a primary system is developed and numerical solutions are used to determine the optimum friction in a friction damper applied to a specific primary system. When compared to classical results presented by earlier authors, the new approach provides a more optimal solution. In addition, viscous damping in the primary system may be included with the new analysis approach. The ability to optimize a friction damper when viscous damping is included in the primary system is a significant improvement over earlier methods and shows potential for serving as a guide to realizing a more accurate estimate of the optimal damping for friction dampers.

  13. Study of Composite Hardcoat Anodizing of Aluminum Alloy 6063 and Its Friction Behaviors

    Institute of Scientific and Technical Information of China (English)

    LIU Shi-yong; ZHANG Hui-chen; GAO Xue-min; LIU Wei; SHI Ya-qin

    2004-01-01

    A composite hard-anodized coating containing micro PTFE (polytetrafluoroethylene) particles on aluminum alloy 6063 was produced by adding micro PTFE particles into the traditional hardcoat anodizing solution. The size of the PTFE particles is around 2 μ m in diameter and the content of the PTFE particles in the composite coating is within 2%-3% by area percentage. Thickness of the composite coating can reach up to 70 μ m after one hour's anodizing. Surface hardness of the composite coating is between 400-480 HV0.1. The average friction coefficient of the composite coating against steel under dry friction test is 0.11, which is 17% lower than that obtained by traditional hardcoat anodizing.

  14. Study of Composite Hardcoat Anodizing of Aluminum Alloy 6063 and Its Friction Behaviors

    Institute of Scientific and Technical Information of China (English)

    LIUShi-yong; ZHANGHui-chen; GAOXue-min; LIUWei; SHIYa-qin

    2004-01-01

    A composite hard-anodized coating containing micro PTFE (polytetrafluoroethylene) particles on aluminum alloy 6063 was produced by adding micro PTFE particles into the traditional hardcoat anodizing solution. The size of the PTFE particles is around 2μm in diameter and the content of the PTFE particles in the composite coating is within 2%-3% by area percentage. Thickness of the composite coating cart reach up to 70μm after one hour's anodizing. Surface hardness of the composite coating is between 4(RI-480 HV0.1, The average friction coefficient of the composite coating against steel under dry friction tost is 0.11, which is 17% lower than that obtained by traditional hardcoat anodizing.

  15. Experimental determination of heat transfer and friction in helically-finned tubes

    Energy Technology Data Exchange (ETDEWEB)

    Zdaniuk, Gregory J. [Ramboll Whitbybird Ltd., 60 Newman Street, London W1T 3DA (United Kingdom); Chamra, Louay M.; Mago, Pedro J. [Department of Mechanical Engineering, Mississippi State University, 210 Carpenter Engineering Building, P.O. Box ME, Mississippi State, MS 39762-5925 (United States)

    2008-01-15

    Heat transfer coefficients and friction factors were determined experimentally for eight helically-finned tubes and one smooth tube using liquid water at Reynolds numbers ranging from 12,000 to 60,000. The helically-finned tubes tested in this investigation have helix angles between 25 and 48 , number of fin starts between 10 and 45, and fin height-to-diameter ratios between 0.0199 and 0.0327. An uncertainty analysis was completed and plain-tube results were compared to the Blasius and Dittus-Boelter equations with satisfactory agreement. Power-law correlations for Fanning friction and Colburn j-factors were developed using a least-squares regression. The performance of the correlations was evaluated with data of other researchers with average prediction errors between 30% and 40%. (author)

  16. Energy based optimization of viscous-friction dampers on cables

    Science.gov (United States)

    Weber, F.; Boston, C.

    2010-04-01

    This investigation optimizes numerically a viscous-friction damper connected to a cable close to one cable anchor for fastest reduction of the total mechanical cable energy during a free vibration decay test. The optimization parameters are the viscous coefficient of the viscous part and the ratio between the friction force and displacement amplitude of the friction part of the transverse damper. Results demonstrate that an almost pure friction damper with negligibly small viscous damping generates fastest cable energy reduction over the entire decay. The ratio between the friction force and displacement amplitude of the optimal friction damper differs from that derived from the energy equivalent optimal viscous damper. The reason for this is that the nonlinearity of the friction damper causes energy spillover from the excited to higher modes of the order of 10%, i.e. cables with attached friction dampers vibrate at several frequencies. This explains why the energy equivalent approach does not yield the optimal friction damper. Analysis of the simulation data demonstrates that the optimally tuned friction damper dissipates the same energy per cycle as if each modal component of the cable were damped by its corresponding optimal linear viscous damper.

  17. Friction and wear of single-crystal manganese-zinc ferrite

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1979-01-01

    Sliding friction experiments were conducted with single-crystal manganese-zinc ferrite in contact with itself and with transition metals. Results indicate mating highest atomic density directions (110 line type) on matched crystallographic planes exhibit the lowest coefficient of friction indicating that direction is important in the friction behavior of ferrite. Matched parallel high atomic density planes and crystallographic directions at the interface exhibit low coefficients of friction. The coefficients of friction for ferrite in contact with various metals are related to the relative chemical activity of these metals. The more active the metal, the higher the coefficient of friction. Cracking and the formation of hexagon- and rectangular-shaped platelet wear debris due to cleavages are observed on the ferrite surfaces as a result of sliding.

  18. Skin friction on a flat perforated acoustic liner

    Science.gov (United States)

    Boldman, D. R.; Brinich, P. F.

    1976-01-01

    The report concerns the measurement of friction coefficients of a typical perforated acoustic liner installed in the side of a wind tunnel. The results are compared with measured friction coefficients of a smooth hard wall for the same mean flow velocities in a wind tunnel. At a velocity of 61 m/sec, an increase in the local skin coefficient of only a few percent was observed, but at the highest velocity of 213 m/sec an increase of about 20% was obtained. This velocity is a realistic velocity for turbo-machinery components utilizing such liners, so a loss in performance is to be expected. Some tests were also performed to see if changes in the mean boundary layer induced by imposed noise would result in friction increase, but only at low velocity levels was such an increase in friction noted.

  19. Modeling of the voltage-controlled friction effect

    Institute of Scientific and Technical Information of China (English)

    孟永钢; 蒋洪军; 常秋英; 黄柏林

    2002-01-01

    A phenomenological model of the dependence of friction coefficient on external voltage is proposed based on experimental results of friction and electric current of three different trbopairs, Si3N4-ball/steel-disc, Si3N4-ball/brass-disc and SiO2-ball/steel-disc, lubricated with zinc strearate suspension. It was found that the variation of friction coefficient correlates with the variation of electric current for all of the three tribopairs. The change in electric current is considered to be caused by the rate of electrochemical reactions occurring on the rubbing surface. By taking the electrochemical reaction into account in the total energy consumption, an expression for describing the relationship between the rates of friction coefficient and electric current is derived, and the constants included in the expression are determined through curve fitting of experimental data.

  20. The Influence of Normal Load and Sliding Speed on Frictional Properties of Skin

    Institute of Scientific and Technical Information of China (English)

    Wei Tang; Shi-rong Ge; Hua Zhu; Xi-chuan Cao; Ning Li

    2008-01-01

    The study of frictional properties of human skin is important for medical research, skin care products and textile exploitation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carried out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N,normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of fiiction. When sliding speed increases from 0.5 mm·s-1 to 4 mm·s-1,the friction coefficient increases and "stick-slip" phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was interpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.

  1. Effect of ZrSiO4 on the Friction Performance of Automotive Brake Friction Materials

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy (SEM), and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements (ZrSiO4) before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements (ZrSiO4). With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed.However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0,5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.

  2. Friction and wear behavior of carbon fiber reinforced brake materials

    Institute of Scientific and Technical Information of China (English)

    Du-qing CHENG; Xue-tao WANG; Jian ZHU; Dong-bua QIU; Xiu-wei CHENG; Qing-feng GUAN

    2009-01-01

    A new composite brake material was fabri-cated with metallic powders, barium sulphate and modified phenolic resin as the matrix and carbon fiber as the reinforced material. The friction, wear and fade character-istics of this composite were determined using a D-MS friction material testing machine. The surface structure of carbon fiber reinforced friction materials was analyzed by scanning electronic microscopy (SEM). Glass fiber-reinforced and asbestos fiber-reinforced composites with the same matrix were also fabricated for comparison. The carbon fiber-reinforced friction materials (CFRFM) shows lower wear rate than those of glass fiber- and asbestos fiber-reinforced composites in the temperature range of 100℃-300℃. It is interesting that the frictional coefficient of the carbon fiber-reinforced friction materials increases as frictional temperature increases from 100℃ to 300℃, while the frictional coefficients of the other two composites decrease during the increasing temperatures. Based on the SEM observation, the wear mechanism of CFRFM at low temperatures included fiber thinning and pull-out. At high temperature, the phenolic matrix was degraded and more pull-out enhanced fiber was demonstrated. The properties of carbon fiber may be the main reason that the CFRFM possess excellent tribological performances.

  3. Friction in orthodontics

    Science.gov (United States)

    Prashant, P. S.; Nandan, Hemant; Gopalakrishnan, Meera

    2015-01-01

    Conventional wisdom suggests that resistance to sliding (RS) generated at the wire-bracket interface has a bearing on the force transmitted to the teeth. The relative importance of static and kinetic friction and also the effect of friction on anchorage has been a topic of debate. Lot of research work has been done to evaluate the various factors that affect friction and thus purportedly retards the rate of tooth movement. However, relevancy of these studies is questionable as the methodology used hardly simulates the oral conditions. Lately studies have concluded that more emphasis should be laid on binding and notching of archwires as these are considered to be the primary factors involved in retarding the tooth movement. This article reviews the various components involved in RS and the factors affecting friction. Further, research work should be carried out to provide cost effective alternatives aimed at reducing friction. PMID:26538873

  4. Friction enhancement in concertina locomotion of snakes.

    Science.gov (United States)

    Marvi, Hamidreza; Hu, David L

    2012-11-07

    Narrow crevices are challenging terrain for most organisms and biomimetic robots. Snakes move through crevices using sequential folding and unfolding of their bodies in the manner of an accordion or concertina. In this combined experimental and theoretical investigation, we elucidate this effective means of moving through channels. We measure the frictional properties of corn snakes, their body kinematics and the transverse forces they apply to channels of varying width and inclination. To climb channels inclined at 60°, we find snakes use a combination of ingenious friction-enhancing techniques, including digging their ventral scales to double their frictional coefficient and pushing channel walls transversely with up to nine times body weight. Theoretical modelling of a one-dimensional n-linked crawler is used to calculate the transverse force factor of safety: we find snakes push up to four times more than required to prevent sliding backwards, presumably trading metabolic energy for an assurance of wall stability.

  5. Hyperstaticity and loops in frictional granular packings

    Science.gov (United States)

    Tordesillas, Antoinette; Lam, Edward; Metzger, Philip T.

    2009-06-01

    The hyperstatic nature of granular packings of perfectly rigid disks is analyzed algebraically and through numerical simulation. The elementary loops of grains emerge as a fundamental element in addressing hyperstaticity. Loops consisting of an odd number of grains behave differently than those with an even number. For odd loops, the latent stresses are exterior and are characterized by the sum of frictional forces around each loop. For even loops, the latent stresses are interior and are characterized by the alternating sum of frictional forces around each loop. The statistics of these two types of loop sums are found to be Gibbsian with a "temperature" that is linear with the friction coefficient μ when μ<1.

  6. Fractional trajectories: Decorrelation versus friction

    Science.gov (United States)

    Svenkeson, A.; Beig, M. T.; Turalska, M.; West, B. J.; Grigolini, P.

    2013-11-01

    The fundamental connection between fractional calculus and subordination processes is explored and affords a physical interpretation of a fractional trajectory, that being an average over an ensemble of stochastic trajectories. Heretofore what has been interpreted as intrinsic friction, a form of non-Markovian dissipation that automatically arises from adopting the fractional calculus, is shown to be a manifestation of decorrelations between trajectories. We apply the general theory developed herein to the Lotka-Volterra ecological model, providing new insight into the final equilibrium state. The relaxation time to achieve this state is also considered.

  7. FEM simulation of a friction testing method based on combined forward conical can-backward straight can extrusion

    DEFF Research Database (Denmark)

    Nakamura, T; Bay, Niels

    1998-01-01

    A new friction testing method based on combined forward conical can-backward straight can extrusion is proposed in order to evaluate friction characteristics in severe metal forming operations. By this method the friction coefficient along the conical punch surface is determined knowing...... the friction coefficient along the die wall. The latter is determined by a combined forward and backward can extrusion of straight cans. Calibration curves determining the relationship between punch travel, can heights, and friction coefficient for the two rests are calculated based on a rigid-plastic FEM...... analysis. Experimental friction tests are carried out in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm that the theoretical analysis results irt reasonable values for the friction coefficient....

  8. Experimental Investigation on Heat Transfer and Frictional Characteristics of Shell-and-tube Heat exchangers with Different Baffles and Tubes

    Science.gov (United States)

    Wang, C.; Zhu, J. G.; Sang, Z. F.

    2010-03-01

    In this study, the heat transfer and tube frictional characteristics of the helixchangers (shell-and-tube heat exchanger with helical baffles) with spirally corrugated and smooth tubes and the conventional shell-and-tube heat exchanger with smooth tubes were experimentally obtained. The results show that the helixchangers with the spirally corrugated tube and the smooth tubes enhance the total heat transfer coefficient about 26% and 7% on the average than the segmental baffled heat exchanger. In the tube side, the spirally corrugated tube leads to about 28% average increase on convective heat transfer performance and about 24% average increase on pressure drop than the smooth tube, but its conversion efficiency is still higher. The helical baffle could enhance the shell-side condensation coefficient by 13%, and the spirally corrugated tube could help the helixchanger with it enhance remarkably the condensation performance by 53% than the segmental baffled heat exchanger.

  9. Approximate equations at breaking for nearshore wave transformation coefficients

    Digital Repository Service at National Institute of Oceanography (India)

    Chandramohan, P.; Nayak, B.U.; SanilKumar, V.

    Based on small amplitude wave theory approximate equations are evaluated for determining the coefficients of shoaling, refraction, bottom friction, bottom percolation and viscous dissipation at breaking. The results obtainEd. by these equations...

  10. Quantifying the Frictional Forces between Skin and Nonwoven Fabrics

    Science.gov (United States)

    Jayawardana, Kavinda; Ovenden, Nicholas C.; Cottenden, Alan

    2017-01-01

    When a compliant sheet of material is dragged over a curved surface of a body, the frictional forces generated can be many times greater than they would be for a planar interface. This phenomenon is known to contribute to the abrasion damage to skin often suffered by wearers of incontinence pads and bed/chairbound people susceptible to pressure sores. Experiments that attempt to quantify these forces often use a simple capstan-type equation to obtain a characteristic coefficient of friction. In general, the capstan approach assumes the ratio of applied tensions depends only on the arc of contact and the coefficient of friction, and ignores other geometric and physical considerations; this approach makes it straightforward to obtain explicitly a coefficient of friction from the tensions measured. In this paper, two mathematical models are presented that compute the material displacements and surface forces generated by, firstly, a membrane under tension in moving contact with a rigid obstacle and, secondly, a shell-membrane under tension in contact with a deformable substrate. The results show that, while the use of a capstan equation remains fairly robust in some cases, effects such as the curvature and flaccidness of the underlying body, and the mass density of the fabric can lead to significant variations in stresses generated in the contact region. Thus, the coefficient of friction determined by a capstan model may not be an accurate reflection of the true frictional behavior of the contact region. PMID:28321192

  11. Frictional Characteristics of Thrust Bearing in Scroll Compressor

    Science.gov (United States)

    Sato, Hajime; Itoh, Takahide; Kobayashi, Hiroyuki

    This paper presents frictional characteristics of thrust bearing in scroll compressor focusing on the behavior of sliding portion which affects the generation of oil film. The coefficient of friction and tilt angle of sliding portion in the thrust bearing are obtained through both elemental friction test and cylinder pressure measurement of actual scroll compressor. Both tests showed that the coefficient of friction in low contact pressure rose with increase of tilt angle of sliding portion. The value of contact pressure which the coefficient of friction turns into increase was in agreement of the value which tilt angle become to increase. Numerical analysis using mixed lubrication theory was also performed. Analytical result indicated the same characteristics as the experiments, and the correlation between the coefficient of friction and the behavior of sliding portion was confirmed. Based on the experimental and the analytical results obtained here, the optimization of thrust bearing for commercial scroll compressor was applied. 2% improvement of total efficiency in rated condition was archived by optimization of thrust bearing.

  12. Association between friction and wear in diarthrodial joints lacking lubricin

    Science.gov (United States)

    Jay, Gregory D; Torres, Jahn R; Rhee, David K; Helminen, Heikki J; Hytinnen, Mika M; Cha, Chung-Ja; Elsaid, Khaled; Kim, Kyung-Suk; Cui, Yajun; Warman, Matthew L

    2007-01-01

    Objective The glycoprotein lubricin (encoded by the gene Prg4) is secreted by surface chondrocytes and synovial cells, and has been shown to reduce friction in vitro. In contrast to man-made bearings, mammalian diarthrodial joints must endogenously produce friction-reducing agents. This study was undertaken to investigate whether friction is associated with wear. Methods The lubricating ability of synovial fluid (SF) samples from humans with genetic lubricin deficiency was tested in vitro. The coefficient of friction in the knee joints of normal and lubricin-null mice was measured ex vivo; these joints were also studied by light and electron microscopy. Atomic force microscopy was used to image and measure how lubricin reduces friction in vitro. Results SF lacking lubricin failed to reduce friction in the boundary mode. Joints of lubricin-null mice showed early wear and higher friction than joints from their wild-type counterparts. Lubricin self-organized and reduced the work of adhesion between apposing asperities. Conclusion These data show that friction is coupled with wear at the cartilage surface in vivo. They imply that acquired lubricin degradation occurring in inflammatory joint diseases predisposes the cartilage to damage. Lastly, they suggest that lubricin, or similar biomolecules, will have applications in man-made devices in which reducing friction is essential. PMID:17968947

  13. Classical shear cracks drive the onset of dry frictional motion.

    Science.gov (United States)

    Svetlizky, Ilya; Fineberg, Jay

    2014-05-08

    Frictional processes entail the rupture of the ensemble of discrete contacts defining a frictional interface. There are a variety of views on how best to describe the onset of dry frictional motion. These range from modelling friction with a single degree of freedom, a 'friction coefficient', to theoretical treatments using dynamic fracture to account for spatial and temporal dynamics along the interface. We investigated the onset of dry frictional motion by performing simultaneous high-speed measurements of the real contact area and the strain fields in the region surrounding propagating rupture tips within the dry (nominally flat) rough interfaces formed by brittle polymer blocks. Here we show that the transition from 'static' to 'dynamic' friction is quantitatively described by classical singular solutions for the motion of a rapid shear crack. We find that these singular solutions, originally derived to describe brittle fracture, are in excellent agreement with the experiments for slow propagation, whereas some significant discrepancies arise as the rupture velocity approaches the Rayleigh wave speed. In addition, the energy dissipated in the fracture of the contacts remains nearly constant throughout the entire range in which the rupture velocity is less than the Rayleigh wave speed, whereas the size of the dissipative zone undergoes a Lorentz-like contraction as the rupture velocity approaches the Rayleigh wave speed. This coupling between friction and fracture is critical to our fundamental understanding of frictional motion and related processes, such as earthquake dynamics.

  14. Water-vapor effects on friction of magnetic tape in contact with nickel-zinc ferrite

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1984-01-01

    The effects of humidity of moist nitrogen on the friction and deformation behavior of magnetic tape in contact with a nickel-zinc ferrite spherical pin were studied. The results indicate that the coefficient of friction is markedly dependent on the ambient relative humidity. Although the coefficient of friction remains low below 40-percent relative humidity, it increases rapidly with increasing relative humidity above 40 percent. The general ambient environment of the tape does not have any effect on the friction behavior if the area where the tape is in sliding contact with the ferrite pin is flooded with controlled nitrogen. The response time for the friction of the tape to humidity changes is about 10 sec. The effect of friction as a function of relative humidity on dehumidifying is very similar to that on humidifying. A surface softening of the tape due to water vapor increases the friction of the tape.

  15. Frictional velocity-weakening in landslides on Earth and on other planetary bodies.

    Science.gov (United States)

    Lucas, Antoine; Mangeney, Anne; Ampuero, Jean Paul

    2014-03-04

    One of the ultimate goals in landslide hazard assessment is to predict maximum landslide extension and velocity. Despite much work, the physical processes governing energy dissipation during these natural granular flows remain uncertain. Field observations show that large landslides travel over unexpectedly long distances, suggesting low dissipation. Numerical simulations of landslides require a small friction coefficient to reproduce the extension of their deposits. Here, based on analytical and numerical solutions for granular flows constrained by remote-sensing observations, we develop a consistent method to estimate the effective friction coefficient of landslides. This method uses a constant basal friction coefficient that reproduces the first-order landslide properties. We show that friction decreases with increasing volume or, more fundamentally, with increasing sliding velocity. Inspired by frictional weakening mechanisms thought to operate during earthquakes, we propose an empirical velocity-weakening friction law under a unifying phenomenological framework applicable to small and large landslides observed on Earth and beyond.

  16. The effects of porosity in friction performance of brake pad using waste tire dust

    Directory of Open Access Journals (Sweden)

    İbrahim Mutlu

    2015-10-01

    Full Text Available Abstract This research is focused on the effect of porosity on the friction-wear properties of automotive brake pads. Waste Tire Dust (WTD was used as a new friction material in brake pads. Newly formulated brake pad materials with five different components have been produced by conventional techniques. In the experimental studies, the change of the friction coefficient, the temperature of the friction surface, the specific wear rate, and the hardness, density and porosity were measured. In addition, the micro-structural characterizations of brake pads are determined using Scanning Electron Microscopy (SEM. The mean coefficient of friction, porosity and specific wear are increased due to a WTD rate increases, on the other hand, hardness and density are decreased. As a result, WTD can be considered as an alternative to revalorize this kind of waste products in the brake pads and the amount of porosity of the brake pad affected the friction coefficient and wear behavior of the pad.

  17. Iliotibial band friction syndrome.

    Science.gov (United States)

    Lavine, Ronald

    2010-07-20

    Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for iliotibial band friction syndrome; and (4) the rationale behind these methods and the clinical outcome studies that support their efficacy.

  18. Polymer friction Molecular Dynamics

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, Vladimir N.; Persson, Bo N. J.

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively...... independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to the squeezing pressure and finite at zero load, indicating an adhesional contribution to the friction force....

  19. The behaviour of molybdenum dialkyldithiocarbamate friction modifier additives

    CERN Document Server

    Graham, J C H

    2001-01-01

    In recent years there has been growing concern to produce energy-efficient lubricated components and modem engine oil specifications require lubricants to demonstrate fuel efficiency in standardised engine tests. One important method of producing low friction and thus fuel-efficient lubricants is to use oil-soluble, molybdenum-containing, friction modifier additives. In optimal conditions these additives are able to produce very low friction coefficients, in the range 0.045 to 0.075 in boundary lubrication conditions. Very little is known about the chemical and physical mechanisms by which oil soluble molybdenum additives form low friction films in tribological contacts. Information about their activity could lead to optimal use of these additives in lubricants and, therefore, more efficient engine running. The work outlined in this thesis investigated the behaviour of oil-soluble molybdenum additives and showed that these additives were able to effectively reduce friction in the absence of other additives su...

  20. Study on the cutting plane friction law of sandstone

    Institute of Scientific and Technical Information of China (English)

    ZHAI Ying-da (翟英达); KANG Li-xun(康立勋)

    2003-01-01

    The friction characteristics of rock damage plane have important impact on the stability of block structure formed after the stratum is broken. The mechanics properties of rock damage plane are described by parameters such as roughness coefficient, wall compress strength and basic friction angle. These three coefficients for fine grain sandstone and medium-granular sandstone and grit sandstone are test. The friction stress is researched at the condition of different normal compressive stress acting on the tension damage plane. The friction law of tension damage plane of sandstone abided by is summed up. This law will provide scientific basis for block structure stability judging in basic roof stratum and roof pressure intensity calculating.

  1. Science 101: What Causes Friction?

    Science.gov (United States)

    Robertson, Bill

    2014-01-01

    Defining friction and asking what causes it might seem like a trivial question. Friction seems simple enough to understand. Friction is a force between surfaces that pushes against things that are moving or tending to move, and the rougher the surfaces, the greater the friction. Bill Robertson answers this by saying, "Well, not exactly".…

  2. Studies of the frictional heating of polycrystalline diamond compact drag tools during rock cutting

    Energy Technology Data Exchange (ETDEWEB)

    Ortega, A.; Glowka, D.A.

    1982-06-01

    A numerical-analytical model is developed to analyze temperatures in polycrystalline diamond compact (PDC) drag tools subject to localized frictional heating at a worn flat area and convective cooling at exposed lateral surfaces. Experimental measurements of convective heat transfer coefficients of PDC cutters in a uniform crossflow are presented and used in the model to predict temperatures under typical drilling conditions with fluid flow. The analysis compares favorably with measurements of frictional temperatures in controlled cutting tests on Tennessee marble. It is found that average temperatures at the wearflat contact zone vary directly with frictional force per unit area and are proportional to the one-half power of the cutting speed at the velocities investigated. Temperatures are found to be much more sensitive to decreases in the dynamic friction by lubrication than to increases in convective cooling rates beyond currently achievable levels with water or drilling fluids. It is shown that use of weighted drilling fluids may actually decrease cooling rates compared to those achieved with pure water. It is doubtful that tool temperatures can be kept below critical levels (750/sup 0/C) if air is employed as the drilling fluid. The degree of tool wear is found to have a major influence on the thermal response of the friction contact zone, so that for equal heating per contact area, a worn tool will run much hotter than a sharp tool. It is concluded that tool temperatures may be kept below critical levels with conventional water or mud cooling as long as the fluid provides good cutter-rock lubrication.

  3. Friction stir welding tool

    Science.gov (United States)

    Tolle; Charles R. , Clark; Denis E. , Barnes; Timothy A.

    2008-04-15

    A friction stir welding tool is described and which includes a shank portion; a shoulder portion which is releasably engageable with the shank portion; and a pin which is releasably engageable with the shoulder portion.

  4. Pressure-viscosity coefficient of biobased lubricants

    Science.gov (United States)

    Film thickness is an important tribological property that is dependent on the combined effect of lubricant properties, material property of friction surfaces, and the operating conditions of the tribological process. Pressure-viscosity coefficient (PVC) is one of the lubricant properties that influe...

  5. Friction and Wear of Sintered Alumina at High Temperature

    OpenAIRE

    Senda, Tetsuya; TAKAHASHl, Chiori; UEMATSU, Susumu; Amada, Shigeyasu

    1991-01-01

    The frictional behavior of alumina ceramics was investigated at various temperatures up to 1200℃. The coefficient of friction decreased with increasing temperature and this temperature dependency became more pronounced as higher contact pressures were applied. Wear loss at room temperature could be interpreted as being caused by one of either two different behavior modes. These have a rate difference of a factor of ten. At temperatures higher than 800℃, the wear loss was far less than that at...

  6. Anisotropic friction and wear of single-crystal manganese-zinc ferrite in contact with itself

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1978-01-01

    Sliding friction experiments were conducted with manganese-zinc ferrite (100), (110), (111), and (211) planes in contact with themselves. Mating the highest-atomic-density directions, (110), of matched crystallographic planes resulted in the lowest coefficients of friction. Mating matched (same) high-atomic-density planes and matched (same)crystallographic directions resulted in low coefficients of friction. Mating dissimilar crystallographic planes, however, did not give significantly different friction results from those with matched planes. Sliding caused cracking and the formation of hexagonal- and rectangular-platelet wear debris on ferrite surfaces, primarily from cleavage of the (110) planes.

  7. Superlow friction behavior of diamond-like carbon coatings: Time and speed effects

    Science.gov (United States)

    Heimberg, J. A.; Wahl, K. J.; Singer, I. L.; Erdemir, A.

    2001-04-01

    The friction behavior of a diamond-like carbon coating was studied in reciprocating sliding contact at speeds from 0.01 to 5 mm/s, in dry nitrogen. "Superlow" friction coefficients of 0.003-0.008 were obtained in continuous sliding at the higher speeds (>1 mm/s). However, friction coefficients rose to values typical of diamond-like carbon in dry and ambient air (0.01-0.1) at lower speeds (sustained, suppressed, and recovered as a function of exposure time, demonstrating that duty cycle cannot be ignored when predicting performance of superlow friction coatings in devices.

  8. Improving friction performance of cast iron by laser shock peening

    Science.gov (United States)

    Feng, Xu; Zhou, Jianzhong; Huang, Shu; Sheng, Jie; Mei, Yufen; Zhou, Hongda

    2015-05-01

    According to different purpose, some high or low friction coefficient of the material surface is required. In this study, micro-dent texture was fabricated on cast iron specimens by a set of laser shock peening (LSP) experiments under different laser energy, with different patterns of micro dimples in terms of the depth over diameter. The mechanism of LSP was discussed and surface morphology of the micro dimples were investigated by utilizing a Keyence KS-1100 3D optical surface profilometer. The tests under the conditions of dry and lubricating sliding friction were accomplished on the UMT-2 apparatus. The performance of treated samples during friction and wear tests were characterized and analyzed. Based on theoretical analysis and experimental study, friction performance of textured and untextured samples were studied and compared. Morphological characteristics were observed by scanning electron microscope (SEM) and compared after friction tests under dry condition. The results showed that friction coefficient of textured samples were obvious changed than smooth samples. It can be seen that LSP is an effective way to improve the friction performance of cast iron by fabricating high quality micro dimples on its surface, no matter what kind of engineering application mentioned in this paper.

  9. Effect of Al2O3 on the friction performance of P/M composite materials for friction applications

    Science.gov (United States)

    Ivǎnuş, R. C.; ǎnuş, D., IV; Cǎlmuc, F.

    2010-06-01

    Bronze bearings are one of most used friction materials. In those applications where higher mechanical properties are needed, iron base bearings can be an alternative to bronze base materials, or other alloying elements added to bronze. The paper presents the results obtained in metal matrix composites field with friction characteristics, for automotive brakes, by P/M. The scope of these researches was the improvement of wear resistance and friction properties of metal matrix composites. Friction-wear properties of the Al2O3 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested.Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy (SEM), and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820°C. Density of the final samples decreased with increasing the amount of reinforcing elements (Al2O3) before presintering. However after sintering, there is no change in density of the samples including reinforcing elements (Al2O3). With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0,5% reinforced Al2O3. The SEM images of the sample indicated that while bronze-based break lining material without Al2O3 showed abrasive wear behaviour, increasing the amount of Al2O3 resulted in a change of abrasive to adhesive wear mechanism. With increasing the amount of reinforcing Al2O3, wear resistance of the samples was increased. However samples reinforced with 5% and 6% Al2O3 showed the best results.

  10. Spectroscopic signatures of quantum friction

    Science.gov (United States)

    Klatt, Juliane; Bennett, Robert; Buhmann, Stefan Yoshi

    2016-12-01

    We present a formula for the spectroscopically accessible level shifts and decay rates of an atom moving at an arbitrary angle relative to a surface. Our Markov formulation leads to an intuitive analytic description whereby the shifts and rates are obtained from the coefficients of the Heisenberg equation of motion for the atomic flip operators but with complex Doppler-shifted (velocity-dependent) transition frequencies. Our results conclusively demonstrate that for the limiting case of parallel motion the shifts and rates are quadratic or higher in the atomic velocity. We show that a stronger, linear velocity dependence is exhibited by the rates and shifts for perpendicular motion, thus opening the prospect of experimentally probing the Markovian approach to the phenomenon of quantum friction.

  11. Friction in volcanic environments

    Science.gov (United States)

    Kendrick, Jackie E.; Lavallée, Yan

    2016-04-01

    Volcanic landscapes are amongst the most dynamic on Earth and, as such, are particularly susceptible to failure and frictional processes. In rocks, damage accumulation is frequently accompanied by the release of seismic energy, which has been shown to accelerate in the approach to failure on both a field and laboratory scale. The point at which failure occurs is highly dependent upon strain-rate, which also dictates the slip-zone properties that pertain beyond failure, in scenarios such as sector collapse and pyroclastic flows as well as the ascent of viscous magma. High-velocity rotary shear (HVR) experiments have provided new opportunities to overcome the grand challenge of understanding faulting processes during volcanic phenomena. Work on granular ash material demonstrates that at ambient temperatures, ash gouge behaves according to Byerlee's rule at low slip velocities, but is slip-weakening, becoming increasingly lubricating as slip ensues. In absence of ash along a slip plane, rock-rock friction induces cataclasis and heating which, if sufficient, may induce melting (producing pseudotachylyte) and importantly, vesiculation. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The shear-thinning behaviour and viscoelasticity of frictional melts yield a tendency for extremely unstable slip, and occurrence of frictional melt fragmentation. This velocity-dependence acts as an important feedback mechanism on the slip plane, in addition to the bulk composition, mineralogy and glass content of the magma, that all influence frictional behaviour. During sector collapse events and in pyroclastic density currents it is the frictional properties of the rocks and ash that, in-part, control the run-out distance and associated risk. In addition, friction plays an important role in the eruption of viscous magmas: In the conduit, the rheology of magma is integral

  12. Road Friction Estimation under Complicated Maneuver Conditions for Active Yaw Control

    Institute of Scientific and Technical Information of China (English)

    LI Liang; LI Hongzhi; SONG Jian; YANG Cai; WU Hao

    2009-01-01

    Road friction coefficient is a key factor for the stability control of the vehicle dynamics in the critical conditions. Obviously the vehicle dynamics stability control systems, including the anti-lock brake system(ABS), the traction control system(TCS), and the active yaw control(AYC) system, need the accurate tire and road friction information. However, the simplified method based on the linear tire and vehicle model could not obtain the accurate road friction coefficient for the complicated maneuver of the vehicle. Because the active braking control mode of AYC is different from that of ABS, the road friction coefficient cannot be estimated only with the dynamics states of the tire. With the related dynamics states measured by the sensors of AYC, a comprehensive strategy of the road friction estimation for the active yaw control is brought forward with the sensor fusion technique. Firstly, the variations of the dynamics characteristics of vehicle and tire, and the stability control mode in the steering process are considered, and then the proper road friction estimation methods are brought forward according to the vehicle maneuver process. In the steering maneuver without braking, the comprehensive road friction from the four wheels may be estimated based on the multi-sensor signal fusion method. The estimated values of the road friction reflect the road friction characteristic. When the active brake involved, the road friction coefficient of the braked wheel may be estimated based on the brake pressure and tire forces, the estimated values reflect the road friction between the braked wheel and the road. So the optimal control of the wheel slip rate may be obtained according to the road friction coefficient. The methods proposed in the paper are integrated into the real time controller of AYC, which is matched onto the test vehicle. The ground tests validate the accuracy of the proposed method under the complicated maneuver conditions.

  13. Reflections on Friction in Quantum Mechanics

    Directory of Open Access Journals (Sweden)

    Yair Rezek

    2010-08-01

    Full Text Available Distinctly quantum friction effects of three types are surveyed: internalfriction, measurement-induced friction, and quantum-fluctuation-induced friction. We demonstrate that external driving will lead to quantum internal friction, and critique the measurement-based interpretation of friction. We conclude that in general systems will experience internal and external quantum friction over and beyond the classical frictional contributions.

  14. Volume Averaging Theory (VAT) based modeling and closure evaluation for fin-and-tube heat exchangers

    Science.gov (United States)

    Zhou, Feng; Catton, Ivan

    2012-10-01

    A fin-and-tube heat exchanger was modeled based on Volume Averaging Theory (VAT) in such a way that the details of the original structure was replaced by their averaged counterparts, so that the VAT based governing equations can be efficiently solved for a wide range of parameters. To complete the VAT based model, proper closure is needed, which is related to a local friction factor and a heat transfer coefficient of a Representative Elementary Volume (REV). The terms in the closure expressions are complex and sometimes relating experimental data to the closure terms is difficult. In this work we use CFD to evaluate the rigorously derived closure terms over one of the selected REVs. The objective is to show how heat exchangers can be modeled as a porous media and how CFD can be used in place of a detailed, often formidable, experimental effort to obtain closure for the model.

  15. Modelling of aircraft braking coefficient from IMAG friction measurements

    OpenAIRE

    GERTHOFFERT, Jonathan; GROSJEAN, Cyrielle; Cerezo, Véronique; Do, Minh Tan

    2014-01-01

    Les performances de freinage des avions sont fortement dépendantes de l’état de surface des pistes, qui peut être sévèrement dégradé lorsque les conditions météorologiques sont mauvaises. Les appareils de mesure du frottement sont un outil largement utilisé pour caractériser cet état de surface. Afin de pouvoir fournir aux équipages des informations pertinentes pour calculer leurs performances opérationnelles, les résultats de mesure des appareils de mesure du frottement doivent être re...

  16. Compressible Friction Coefficients in a Simulated Heat Pipe.

    Science.gov (United States)

    1987-12-01

    injection and decrease with suction. 5 4 FROMM Kinney and Sparrow (6) used an analytical model to in- - -~ vestigate the effects of surface suction on...Therefore, two models were used in the num- erical simulation: an incompressible model for Mach numbers less than 0.01, and a compressible model for Mach

  17. Friction coefficient measurements of silencers on specialized duct tract

    Directory of Open Access Journals (Sweden)

    Sehnalek Stanislav

    2016-01-01

    Full Text Available This article describes test methods on air duct track in Laboratory of Environmental Engineering. It focuses on measurement of silencer parameter like is pressure loss coeffcient. Firstly, the paper describe the measurement apparatus with description of calculation method by standard ISO 7235 and energy equation. Then the paper presents three ways how to accomplish measurement because such way is not covered by procedure in standard. Then follows the evaluation of results of measurements on three types of silencer designed for HVAC applications. The article is concluded with discussion over measured data with outline for further research.

  18. Analysis of Wear Mechanisms in Low Friction, Nanocomposite AlMgB14-TiB2 Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Cook, Bruce A [Ames Laboratory; Harringa, J [Ames Laboratory; Anderegg, A [Ames Laboratory; Russell, A M [Iowa State University; Qu, Jun [ORNL; Blau, Peter Julian [ORNL; Higdon, Clifton [Eaton Corporation; Elmoursi, Alaa A [Eaton Corporation

    2010-01-01

    Recent developments in coating science and technology offer new opportunities to enhance the energy-efficiency and performance of industrial machinery such as hydraulic fluid pumps and motors. The lubricated friction and wear characteristics of two wear-resistant coatings, diamond-like carbon and a nanocomposite material based on AlMgB{sub 14}-50 vol.% TiB{sub 2}, were compared in pin-on-disk tribotests using Mobil DTE-24{trademark} oil as the lubricant. In each case, the pins were fixed 9.53 mm diameter spheres of AISI 52100 steel, the load was 10 N, and the speed 0.5 m/s in all tests. Average steady-state friction coefficient values of 0.10 and 0.08 were measured for the DLC and nanocomposite, respectively. The coatings and their 52100 steel counterfaces were analyzed after the tests by X-ray photoelectron and Auger spectroscopy for evidence of material transfer or tribo-chemical reactions. The low-friction behavior of the boride nanocomposite coating is due to the formation of lubricative boric acid, B(OH){sub 3}. In contrast, the low-friction behavior of the DLC coating is related to the relatively low dielectric constant of the oil-based lubricant, leading to desorption of surface hydrogen from the coating.

  19. A study on the frictional response of reptilian shed skin

    Science.gov (United States)

    Abdel-Aal, H. A.; Vargiolu, R.; Zahouani, H.; El Mansori, M.

    2011-08-01

    Deterministic surfaces are constructs of which profile, topography and textures are integral to the function of the system they enclose. They are designed to yield a predetermined tribological response. Developing such entities relies on controlling the structure of the rubbing interface so that, not only the surface is of optimized topography, but also is able to self-adjust its tribological behaviour according to the evolution of sliding conditions. In seeking inspirations for such designs, many engineers are turning toward the biological world to study the construction and behaviour of bio-analogues, and to probe the role surface topography assumes in conditioning of frictional response. That is how a bio-analogue can self-adjust its tribological response to adapt to habitat constraints. From a tribological point of view, Squamate Reptiles, offer diverse examples where surface texturing, submicron and nano-scale features, achieves frictional regulation. In this paper, we study the frictional response of shed skin obtained from a snake (Python regius). The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional response of snakes. The coefficient of friction depends on the direction of sliding: the value in forward motion is lower than that in the backward direction. Diagonal and side winding motion induces a different value of the friction coefficient. We discuss the origin of such a phenomenon in relation to surface texturing and study the energy constraints, implied by anisotropic friction, on the motion of the reptile.

  20. Finger pad friction and its role in grip and touch

    Science.gov (United States)

    Adams, Michael J.; Johnson, Simon A.; Lefèvre, Philippe; Lévesque, Vincent; Hayward, Vincent; André, Thibaut; Thonnard, Jean-Louis

    2013-01-01

    Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanisms. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counterintuitively, the coefficient of friction can increase by an order of magnitude in a period of tens of seconds when in contact with an impermeably smooth surface, such as glass. In contrast, the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first-order kinetics. Surprisingly, the sensitivity of the coefficient of friction to the normal load and sliding velocity is comparatively of second order, yet these dependencies provide the main basis of theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick–slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function. PMID:23256185

  1. Friction and Wear Behavior of GCr15 Under Multiple Movement Condition

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Friction and wear of GCr15 under cross-sliding condition is tested on a ball-on-disc wear test machine. This result shows that the cross-sliding of friction pair leads to different friction and wear behavior. For the condition described in this paper, the friction coefficients with ball reciprocating are smaller than that without ball reciprocating. The friction coefficients increase with the increase of reciprocating frequency.. The wear weight loss of the ball subjected reciprocating sliding decreases, however, the wear weight loss of disc against the reciprocating ball increases. In cross-sliding friction, the worn surfaces of the ball show crinkle appearance along the circumferential sliding traces. Delaminating of small strip debris is formed along the plowing traces on the disc worn surface. The plowing furrow on the disc surfaces looks deeper and wider than that without reciprocating sliding. The size of wear particles from cross-sliding wear is larger than those without reciprocating sliding.

  2. Analysis of friction effects on satellite antenna driving mechanism with clearance joints

    Science.gov (United States)

    Bai, Z. F.; Chen, J.; Bian, S.; Shi, X.

    2017-01-01

    The existence of clearance in joints of mechanism is inevitable. In this paper, the friction effects in clearance joints on dynamic responses of driving mechanism of satellite antenna are studied. Considering clearances in joints, the contact force model in clearance joints is established using a nonlinear continuous contact force model and the friction effect is considered by using a modified Coulomb friction model. Then the dual-axis driving mechanism of satellite antenna with clearance joints is used as the application example. The numerical simulation of dual-axis driving mechanism with clearance joints is presented. The friction effects of clearance joint on dynamic responses of the dual-axis driving mechanism are discussed and analyzed quantitatively for four cases with different friction coefficients. The investigation results show that the increase of friction coefficient will decrease the vibration amplitude of the driving mechanism system.

  3. Friction behavior of 304 stainless steel of varying hardness lubricated with benzene and some benzyl structures

    Science.gov (United States)

    Buckley, D. H.

    1974-01-01

    The lubricating properties of some benzyl and benzene structures were determined by using 304 stainless steel surfaces strained to various hardness. Friction coefficients and wear track widths were measured with a Bowden-Leben type friction apparatus by using a pin-on-disk specimen configuration. Results obtained indicate that benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol resulted in the lowest friction coefficients for 304 stainless steel, while benzyl ether provided the least surface protection and gave the highest friction. Strainhardening of the 304 stainless steel prior to sliding resulted in reduced friction in dry sliding. With benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol changes in 304 stainless steel hardness had no effect upon friction behavior.

  4. Study of relationship between performance of emulsion and friction coefficient and its practical model in cold tandem mill%乳化液性能对摩擦系数影响机理及工程实用模型的研究

    Institute of Scientific and Technical Information of China (English)

    白振华; 陈浩; 王瑞; 高明磊; 崔亚亚; 吴首民

    2014-01-01

    以往现场对冷连轧过程中摩擦系数的研究主要偏重于带钢特性、轧制工艺以及工艺润滑制度,乳化液的 pH 值、铁粉含量、皂化值等性能参数对摩擦系数的影响以定性研究为主且不能定量分析,本文以某冷轧薄板厂1220五机架冷连轧机组为研究对象,在大量的现场实验与理论研究的基础上,充分结合冷连轧机组的设备与工艺特点,定量研究了乳化液性能对摩擦系数的影响,建立了相应的工程实用模型,并将其应用到生产实践,使得轧制压力的预报精度控制在15%以内。%In the past, the research on friction coefficient in the process of cold tandem rolling mainly focused on strip steel character, rolling technology and technological lubrication system to pH value of emulsion, iron powder content, saponification value and other performance parameters, which have been mainly studied qualitative but not quantitatively. Taking the 1220 five-rack cold tandem mills of some cold sheet rolling plant as example, after a large number of field experiments and theoretical studies, fully integrated with equipment and process features of cold tandem mills, the influence mechanic of emulsion performance on fiction coefficient are studied quantitatively and an practical engineering model is established. What's more, the model is applied to pro-duction and the forecasting accuracy of rolling force is controlled within 15%.

  5. Interfacial Friction and Adhesion of Polymer Brushes

    KAUST Repository

    Landherr, Lucas J. T.

    2011-08-02

    A bead-probe lateral force microscopy (LFM) technique is used to characterize the interfacial friction and adhesion properties of polymer brushes. Our measurements attempt to relate the physical structure and chemical characteristics of the brush to their properties as thin-film, tethered lubricants. Brushes are synthesized at several chain lengths and surface coverages from polymer chains of polydimethylsiloxane (PDMS), polystyrene (PS), and a poly(propylene glycol)-poly(ethylene glycol) block copolymer (PPG/PEG). At high surface coverage, PDMS brushes manifest friction coefficients (COFs) that are among the lowest recorded for a dry lubricant film (μ ≈ 0.0024) and close to 1 order of magnitude lower than the COF of a bare silicon surface. Brushes synthesized from higher molar mass chains exhibit higher friction forces than those created using lower molar mass polymers. Increased grafting density of chains in the brush significantly reduces the COF by creating a uniform surface of stretched chains with a decreased surface viscosity. Brushes with lower surface tension and interfacial shear stresses manifest the lowest COF. In particular, PDMS chains exhibit COFs lower than PS by a factor of 3.7 and lower than PPG/PEG by a factor of 4.7. A scaling analysis conducted on the surface coverage (δ) in relation to the fraction (ε) of the friction force developing from adhesion predicts a universal relation ε ∼ δ4/3, which is supported by our experimental data. © 2011 American Chemical Society.

  6. High fidelity frictional models for MEMS.

    Energy Technology Data Exchange (ETDEWEB)

    Carpick, Robert W. (University of Wisconsin, Madison, WI); Reedy, Earl David, Jr.; Bitsie, Fernando; de Boer, Maarten Pieter; Corwin, Alex David; Ashurst, William Robert (Auburn University, Auburn, AL); Jones, Reese E.; Subhash, Ghatu S. (Michigan Technological Institute, Houghton, MI); Street, Mark D. (University of Wisconsin, Madison, WI); Sumali, Anton Hartono; Antoun, Bonnie R.; Starr, Michael James; Redmond, James Michael; Flater, Erin E. (University of Wisconsin, Madison, WI)

    2004-10-01

    The primary goals of the present study are to: (1) determine how and why MEMS-scale friction differs from friction on the macro-scale, and (2) to begin to develop a capability to perform finite element simulations of MEMS materials and components that accurately predicts response in the presence of adhesion and friction. Regarding the first goal, a newly developed nanotractor actuator was used to measure friction between molecular monolayer-coated, polysilicon surfaces. Amontons law does indeed apply over a wide range of forces. However, at low loads, which are of relevance to MEMS, there is an important adhesive contribution to the normal load that cannot be neglected. More importantly, we found that at short sliding distances, the concept of a coefficient of friction is not relevant; rather, one must invoke the notion of 'pre-sliding tangential deflections' (PSTD). Results of a simple 2-D model suggests that PSTD is a cascade of small-scale slips with a roughly constant number of contacts equilibrating the applied normal load. Regarding the second goal, an Adhesion Model and a Junction Model have been implemented in PRESTO, Sandia's transient dynamics, finite element code to enable asperity-level simulations. The Junction Model includes a tangential shear traction that opposes the relative tangential motion of contacting surfaces. An atomic force microscope (AFM)-based method was used to measure nano-scale, single asperity friction forces as a function of normal force. This data is used to determine Junction Model parameters. An illustrative simulation demonstrates the use of the Junction Model in conjunction with a mesh generated directly from an atomic force microscope (AFM) image to directly predict frictional response of a sliding asperity. Also with regards to the second goal, grid-level, homogenized models were studied. One would like to perform a finite element analysis of a MEMS component assuming nominally flat surfaces and to include the

  7. A new transducer for local load measurements of friction and roll pressure in cold flat rolling

    DEFF Research Database (Denmark)

    Lagergren, J.; Wanheim, Tarras; Precz, W.

    2006-01-01

    selected from a steady state with no disturbance from the material flow. The transducer was able to simultaneously measure both the normal pressure and the friction stress. An estimation of the coefficient of friction was accordingly performed. The new transducer works very well, it was seen to be robust...... and able to avoid signal disturbance. The pressure and friction stress distribution results was as expected by the authors and showed good reproducibility, together with a proven agreement between recorded and simulated signals....

  8. Dry friction and wear properties of intermetallics MoSi2

    Institute of Scientific and Technical Information of China (English)

    张厚安; 刘心宇; 陈平; 唐果宁

    2001-01-01

    The dry friction and wear properties of intermetallics MoSi2 against 45 steel under different loads were investigated with M-2 type friction and wear tester. Scanning electric microscope (SEM) equipment with microprobe was employed to analyze the morphology of the friction surface. Results show that the dry friction and wear properties are deeply affected by load. The wear rate of MoSi2 at the load of 80 N is the maximum which is 36.1 μg/m. On the condition of the load of 150 N, MoSi2 material has the better friction and wear properties: friction coefficient is 0.28 and wear rate is 10.6μg/m. With the load increasing, the main friction mechanisms change from microslip and plastic deformation to adhesive effect, and the main wear mechanisms change from plough-groove wear and oxidation-fatigue wear to adhesive wear.

  9. Calculating frictional force with considering material microstructure and potential on contact surfaces

    Institute of Scientific and Technical Information of China (English)

    XU Zhongming; HUANG Ping

    2007-01-01

    A method based on the energy dissipation mechanism of an Independent Oscillator model is used to calculate the frictional force and the friction coefficient of interfacial friction. The friction work is calculated with considering the potential change of contact surfaces during sliding. The potential change can be gained by a universal adhesive energy function. The relationships between frictional force and parameters of a tribo-system, such as surface energy and microstructure of interfacial material, are set up. The calculation results of the known experimental data denote that the frictional force is nearly proportional to the surface energy of the material, nearly inversely proportional to the scaling length, and independent of the lattice constant. The results agree with that of adhesion friction equations. They also agree with the experimental results performed with an atomic-force microscope under the ultra high vacuum condition.

  10. The Effects of Contact Interface on the Friction Characteristics of Self-assembly Monolayers

    Institute of Scientific and Technical Information of China (English)

    ZHANGHui-chen; GAOYu-zhou; YANLi

    2004-01-01

    The effects of different contact interfaces on the friction characteristics of OTS self-assembled monolayers were investigated by a universal micro-tribometer in different sliding velocities. The results indicate that there exist lower friction coefficients between OTS SAMs and Ti, Ni and Cu films deposited on GCrl5 steel balls than those between OTS SAMs and GCr15 steel ball. The friction coefftcient between OTS SAMs and Ti film is the largest, and the friction coefficient between OTS SAMs and Cu film is the least in these three films, which depends the iatrinsic characteristics of the materials. The friction coefficients between OTS SAMs and GCrI5 steel balland three nanometer films increase with the sliding velachy increasing, which can be explained by the relaxationcharacteristics of OTS molecules.

  11. Friction Wear Property of Brake Materials by Copper-based Powder Metallurgy With Various Brake Speeds

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-xiu; GAO Hong-xia; WEI Xiu-lan

    2004-01-01

    The experiment is conducted on MM-1000 friction test machine, which tests friction wear property of copper-based brake materials by powder metallurgy at different brake speeds. It shows that the coefficient of friction and wear volume are greatly influenced by brake speed. When the brake speed is 4000 r/min, which is a bit higher, the material still has a higher coefficient of friction with 0.47. When the brake speed is over 4000r/min, the coefficient of friction decreased rapidly. When the brake speed is 3000r/min, the material's wear is in its minimum. That is to say no matter how higher or lower the brake speed is the wear volume is bigger relatively. With the brake speed of the lower one it mainly refers to fatigue wear; while of higher one it mainly refers to abradant and oxidation wear.

  12. Friction and wear of human hair fibres

    Science.gov (United States)

    Bowen, James; Johnson, Simon A.; Avery, Andrew R.; Adams, Michael J.

    2016-06-01

    An experimental study of the tribological properties of hair fibres is reported, and the effect of surface treatment on the evolution of friction and wear during sliding. Specifically, orthogonally crossed fibre/fibre contacts under a compressive normal load over a series of 10 000 cycle studies are investigated. Reciprocating sliding at a velocity of 0.4 mm s-1, over a track length of 0.8 mm, was performed at 18 °C and 40%-50% relative humidity. Hair fibres retaining their natural sebum were studied, as well as those stripped of their sebum via hexane cleaning, and hair fibres conditioned using a commercially available product. Surface topography modifications resulting from wear were imaged using scanning electron microscopy and quantified using white light interferometry. Hair fibres that presented sebum or conditioned product at the fibre/fibre junction exhibited initial coefficients of friction at least 25% lower than those that were cleaned with hexane. Coefficients of friction were observed to depend on the directionality of sliding for hexane cleaned hair fibres after sufficient wear cycles that cuticle lifting was present, typically on the order 1000 cycles. Cuticle flattening was observed for fibre/fibre junctions exposed to 10 mN compressive normal loads, whereas loads of 100 mN introduced substantial cuticle wear and fibre damage.

  13. Biomechanics of iliotibial band friction syndrome in runners.

    Science.gov (United States)

    Orchard, J W; Fricker, P A; Abud, A T; Mason, B R

    1996-01-01

    We propose a biomechanical model to explain the pathogenesis of iliotibial band friction syndrome in distance runners. The model is based on a kinematic study of nine runners with iliotibial band friction syndrome, a cadaveric study of 11 normal knees, and a literature review. Friction (or impingement) occurs near footstrike, predominantly in the foot contact phase, between the posterior edge of the iliotibial band and the underlying lateral femoral epicondyle. The study subjects had an average knee flexion angle of 21.4 degrees +/- 4.3 degrees at footstrike, with friction occurring at, or slightly below, the 30 degrees of flexion traditionally described in the literature. In the cadavers we examined, there was substantial variation in the width of the iliotibial bands. This variation may affect individual predisposition to iliotibial band friction syndrome. Downhill running predisposes the runner to iliotibial band friction syndrome because the knee flexion angle at footstrike is reduced. Sprinting and faster running on level ground are less likely to cause or aggravate iliotibial band friction syndrome because, at footstrike, the knee is flexed beyond the angles at which friction occurs.

  14. Intelligent Flow Friction Estimation

    Directory of Open Access Journals (Sweden)

    Dejan Brkić

    2016-01-01

    Full Text Available Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with respect to the friction factor (λ. In the present study, a noniterative approach using Artificial Neural Network (ANN was developed to calculate the friction factor. To configure the ANN model, the input parameters of the Reynolds Number (Re and the relative roughness of pipe (ε/D were transformed to logarithmic scales. The 90,000 sets of data were fed to the ANN model involving three layers: input, hidden, and output layers with, 2, 50, and 1 neurons, respectively. This configuration was capable of predicting the values of friction factor in the Colebrook equation for any given values of the Reynolds number (Re and the relative roughness (ε/D ranging between 5000 and 108 and between 10−7 and 0.1, respectively. The proposed ANN demonstrates the relative error up to 0.07% which had the high accuracy compared with the vast majority of the precise explicit approximations of the Colebrook equation.

  15. Gravitomagnetic dynamical friction

    CERN Document Server

    Cashen, Benjamin; Kesden, Michael

    2016-01-01

    A supermassive black hole moving through a field of stars will gravitationally scatter the stars, inducing a backreaction force on the black hole known as dynamical friction. In Newtonian gravity, the axisymmetry of the system about the black hole's velocity $\\mathbf{v}$ implies that the dynamical friction must be anti-parallel to $\\mathbf{v}$. However, in general relativity the black hole's spin $\\mathbf{S}$ need not be parallel to $\\mathbf{v}$, breaking the axisymmetry of the system and generating a new component of dynamical friction similar to the Lorentz force $\\mathbf{F} = q\\mathbf{v} \\times \\mathbf{B}$ experienced by a particle with charge $q$ moving in a magnetic field $\\mathbf{B}$. We call this new force gravitomagnetic dynamical friction and calculate its magnitude for a spinning black hole moving through a field of stars with Maxwellian velocity dispersion $\\sigma$, assuming that both $v$ and $\\sigma$ are much less than the speed of light $c$. We use post-Newtonian equations of motion accurate to $...

  16. Skin tribology: Science friction?

    NARCIS (Netherlands)

    Heide, van der E.; Zeng, X.; Masen, M.A.

    2013-01-01

    The application of tribological knowledge is not just restricted to optimizing mechanical and chemical engineering problems. In fact, effective solutions to friction and wear related questions can be found in our everyday life. An important part is related to skin tribology, as the human skin is fre

  17. Contact Pressure Effect on Frictional Characteristics of Steel Sheet for Autobody

    Science.gov (United States)

    Han, S. S.; Kim, D. J.

    2011-08-01

    The high strength steel (HSS) is widely used in auto body part due to its advantage of weight reduction. The usage of HSS extends the range of contact pressure than that of mild steel's and makes it is not disregardable fact that the effect of contact pressure on frictional characteristics of steel sheet. To investigate the influence of contact pressure on frictional behavior of steel sheet, the flat type friction test with high strength bare steel sheet was conducted under various contact pressures. According to the test result, the relationship between contact pressure and friction coefficient shows U shape. When the contact pressure is lower than 10 MPa, the friction coefficient was slightly decreased as contact pressure was increased. However the amount of decrement was very small. Above 10 MPa contact pressure the friction coefficient was increased as the contact pressure was increased and the amount of increment of friction coefficient was not negligible. This study shows that the effect of contact pressure on frictional behavior of steel sheet is very big, especially on HSS stamping which has the wide range of contact pressure.

  18. Network Theory, Cracking and Frictional Sliding

    CERN Document Server

    Ghaffari, H O

    2012-01-01

    We have developed different network approaches to complex patterns of frictional interfaces (contact areas developments). Here, we analyze the dynamics of static friction. We found, under the correlation measure, the fraction of triangles correlates with the detachment fronts. Also, for all types of the loops (such as triangles), there is a universal power law between nodes' degree and motifs where motifs frequency follow a power law. This shows high energy localization is characterized by fast variation of the loops fraction. Also, this proves that the congestion of loops occurs around hubs. Furthermore, the motif distributions and modularity space of networks -in terms of within-module degree and participation coefficient- show universal trends, indicating an in common aspect of energy flow in shear ruptures. Moreover, we confirmed that slow ruptures generally hold small localization, while regular ruptures carry a high level of energy localization. We proposed that assortativity, as an index to correlation...

  19. Dependence of friction on roughness, velocity, and temperature.

    Science.gov (United States)

    Sang, Yi; Dubé, Martin; Grant, Martin

    2008-03-01

    We study the dependence of friction on surface roughness, sliding velocity, and temperature. Expanding on the classic treatment of Greenwood and Williamson, we show that the fractal nature of a surface has little influence on the real area of contact and the static friction coefficient. A simple scaling argument shows that the static friction exhibits a weak anomaly mu ~ A(0)(-chi/4), where A0 is the apparent area and chi is the roughness exponent of the surface. We then develop a method to calculate atomic-scale friction between a microscopic asperity, such as the tip of a friction force microscope (FFM) and a solid substrate. This method, based on the thermal activation of the FFM tip, allows a quantitative extraction of all the relevant microscopic parameters and reveals a universal scaling behavior of atomic friction on velocity and temperature. This method is extended to include a soft atomic substrate in order to simulate FFM scans more realistically. The tip is connected with the support of the cantilever by an ideal spring and the substrate is simulated with a ball-spring model. The tip and substrate are coupled with repulsive potentials. Simulations are done at different temperatures and scanning velocities on substrates with different elastic moduli. Stick-slip motion of the tip is observed, and the numerical results of the friction force and distribution of force maxima match the theoretical framework.

  20. Frictional action at lower limb/prosthetic socket interface.

    Science.gov (United States)

    Zhang, M; Turner-Smith, A R; Roberts, V C; Tanner, A

    1996-04-01

    The frictional action at stump/socket interface is discussed by a simplified model and finite element model analyses and clinical pressure measurements. The friction applied to the stump skin produces stresses within tissue and these stresses may damage the tissues and affect their normal functions. The combination of normal and shear stresses is considered to be a critical factor leading to amputee's discomfort and tissue damage. However, friction at the stump/socket interface has a beneficial action. A simplified residual limb model and a finite element model using real geometry have been developed to analyse the support action of friction. Both results show that the friction plays a critical role both in supporting the load of the amputee's body during the support phase of the gait cycle and in preventing the prosthesis from slipping off the limb during swing phase. Pressure at the below-knee socket during walking were measured with conditions of different friction. The results reveal that a larger pressures was produced at the lubricated interface than at the normal interface. A proper choice of coefficient of friction will balance the requirements of relief of load stress and reduction of slip with the general ability to support loads.

  1. Talc as friction reducing additive to lubricating oil

    Science.gov (United States)

    Rudenko, Pavlo; Bandyopadhyay, Amit

    2013-07-01

    Reduction of friction and wear by colloidal suspensions of ceramic powders in lubricating oils is an approach that can allow to formulate environment friendly energy saving lubricants. Commercial talc powder was evaluated as an extreme pressure additive to a lubricating oil under different temperatures and concentrations. The best lubricity was achieved at the temperature of 100 °C and the concentration of 0.15 wt% when dynamic and static friction coefficients were reduced by over 30% in comparison to reference lubricating oil alone. At high temperature, talc forms transfer film on metal surface, which reduce both friction and wear behavior in mating surfaces. However, at room temperature, film formation was not observed. Results are explained using pressure and temperature induced lamellar dehydration mechanism when products of dehydration form oxide transfer films on the friction surface.

  2. Nanoscience friction and rheology on the nanometer scale

    CERN Document Server

    Meyer, E; Gyalog, T; Overney, R M

    1998-01-01

    Friction force microscopy is an important analytical tool in the field of tribology on the nanometer-scale. The contact area between the probing tip and the sample is reduced to some square nanometers, corresponding to the ideal of a single asperity contact. Traditional concepts, such as friction coefficients, adhesion and elasticity and stick-slip are re-examined with this novel technique. New concepts based upon classical and quantum mechanics are investigated.Contents: Introduction and Motivation; Instruments; Normal Forces at the Atomic Scale; Understanding of Lateral Forces; Dissipation Mechanisms; Nanorheology and Nanoconfinement; Generation of Ultrasonic Waves in Sliding Friction; Friction Force Microscopy Experiments; Appendix: Instrumental Aspects of Force Microscopy.Readership: Graduate and researchers in physics, chemistry and materials science.

  3. Influence of various base oils on friction and power loss in gears; Einfluss verschiedener Grundoele auf Reibung und Verlustleistung in Zahnradgetrieben

    Energy Technology Data Exchange (ETDEWEB)

    Doleschel, A.; Michaelis, K.; Hoehn, B.R.

    2001-03-01

    The frictional behaviour of synthetic lubricants was systematically investigated in a twin disc test rig and a back-to-back gear test rig. For 22 lubricants (mineral oil, polyalfaolefin (PAO), polyglycol (PG), ester and mixtures) the coefficient of friction was measured in the twin disc test rig, dependant on pressure, oil temperature, rolling and sliding velocity. In the gear test rig pressure and velocity was varied for 9 lubricants. The mineral oil shows an estimated coefficient of friction of about {mu} >> 0.045, the synthetic lubricants have a lower coefficient of friction. In the twin disc test rig the lowest coefficient of friction with PG as low as 20% of the coefficient of mineral oil was measured, depending on the mixture of EO:PO. In the gear test rig such low coefficients of friction were not measured, but still values of 60% compared to mineral oil were obtained. Esters show in the twin disc test rig a coefficient of friction in the range of 30% to 100% of the coefficient of friction of mineral oil, in the gear test rig in the range of 60% to 100%. From these investigations a calculation method for the coefficient of friction in disc and gear contacts was derived. With these equations the power loss and efficiency of transmissions in practice, lubricated with synthetic gear oils can be evaluated. (orig.)

  4. Influence of loading and rotation speed on Friction and Wear properties of CuAlBi Alloy

    Institute of Scientific and Technical Information of China (English)

    Liu Rongchang; Dong Litao; Li Xingyuan; Chen Xiuhong

    2007-01-01

    The variation of the friction coefficient of the CuAlBi alloy at different connecting loading and friction speed were investigated by using MMU-5G sliding friction-wear tester, besides, the wear mass loss of the CuAlBi alloy was measured, and the influence of loading and rotation speed on friction and wear properties of CuAlBi alloy was also discussed. The results show that the friction coefficient increase then decrease with increase of connecting loading as well as decreases with increase of friction speed, and the wear loss mass increases with increase of connecting loading and friction speed. As a result, the wear failure form of CuAlBi alloy is mainly ploughing.

  5. Fault Wear and Friction Evolution: Experimental Analysis

    Science.gov (United States)

    Boneh, Y.; Chang, J. C.; Lockner, D. A.; Reches, Z.

    2011-12-01

    Wear is an inevitable product of frictional sliding of brittle rocks as evidenced by the ubiquitous occurrence of fault gouge and slickenside striations. We present here experimental observations designed to demonstrate the relationship between wear and friction and their governing mechanisms. The experiments were conducted with a rotary shear apparatus on solid, ring-shaped rock samples that slipped for displacements up to tens of meters. Stresses, wear and temperature were continuously monitored. We analyzed 86 experiments of Kasota dolomite, Sierra White granite, Pennsylvania quartzite, Karoo gabbro, and Tennessee sandstone at slip velocities ranging from 0.002 to 0.97 m/s, and normal stress from 0.25 to 6.9 MPa. We conducted two types of runs: short slip experiments (slip distance mechanisms; and long slip experiments (slip distance > 3 m) designed to achieve mature wear conditions and to observe the evolution of wear and friction as the fault surfaces evolved. The experiments reveal three wear stages: initial, running-in, and steady-state. The initial stage is characterized by (1) discrete damage striations, the length of which is comparable to total slip , and local pits or plow features; (2) timing and magnitude of fault-normal dilation corresponds to transient changes of normal and shear stresses; and (3) surface roughness increasing with the applied normal stress. We interpret these observations as wear mechanisms of (a) plowing into the fresh rock surfaces; (b) asperity breakage; and (c) asperity climb. The running-in stage is characterized by (1) intense wear-rate over a critical wear distance of Rd = 0.3-2 m; (2) drop of friction coefficient over a weakening distance of Dc = 0.2-4 m; (3) Rd and Dc display positive, quasi-linear relation with each other. We interpret these observations as indicating the organizing of newly-created wear particles into a 'three-body' structure that acts to lubricate the fault (Reches & Lockner, 2010). The steady

  6. Effects of water-vapor on friction and deformation of polymeric magnetic media in contact with a ceramic oxide

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1984-01-01

    The effects of humidity (water-vapor) in nitrogen on the friction and deformation behavior of magnetic tape in contact with a Ni-Zn ferrite spherical pin were studied. The coefficient of friction is markedly dependent on the ambient relative humidity. In elastic contacts the coefficient of friction increased linearly with increasing humidity; it decreased linearly when humidity was lowered. This effect is the result of changes in the chemistry and interaction of tape materials such as degradation of the lubricant. In plastic contacts there was no effect of humidity on friction below 40 percent relative humidity. There is no effect on friction associated with the breakthrough of the adsorbed water-vapor film at the interface of the tape and Ni-Zn ferrite. The coefficient of friction, however, increased rapidly with increasing relative humidity above 40 percent in plastic contacts.

  7. Study Friction Distribution during the Cold Rolling of Material by Matroll Software

    Science.gov (United States)

    Abdollahi, H.; Dehghani, K.

    2007-04-01

    Rolling process is one of the most important ways of metal forming. Since the results of this process are almost finished product, therefore controlling the parameters affecting this process is very important in order to have cold rolling products with high quality. Among the parameters knowing the coefficient of friction within the roll gap is known as the most significant one. That is because other rolling parameters such as rolling force, pressure in the roll gap, forward slip, surface quality of sheet, and the life of work rolls are directly influenced by friction. On the other hand, in rolling calculation due to lake of a true amount for coefficient of friction a supposed value is considered for it. In this study, a new software (Matroll), is introduced which can determine the coefficient of friction (COF) and plot the friction hills for an industrial mill. Besides, based on rolling equations, it offers about 30 rolling parameters as outputs. Having the rolling characteristics as inputs, the software is able to calculate the coefficient of friction. Many rolling passes were performed on real industrial aluminum mill. The coefficient of friction was obtained for all passes. The results are in good agreement with the findings of the other researchers.

  8. PAMPS-PAAM凝胶的启动摩擦学性能%Start-up friction properties of PAMPS-PAAM hydrogel

    Institute of Scientific and Technical Information of China (English)

    鲍磊; 张有忱

    2013-01-01

    目的 PAMPS-PAAM凝胶是应用前景较好的关节软骨替代物.前期试验表明,其压缩强度已达到关节软骨的平均压缩强度,但对其摩擦学性能的研究还较少.方法 本文选用2-丙烯酰胺-2-甲基丙磺酸(2-acrylamide-2-methylpro panesulfonic acid,AMPS)凝胶和丙烯酰胺(acrylamide,AAM)溶液制备PAMPS-PAAM互穿网络凝胶,在自制销-盘式摩擦试验机上通过PAMPS-PAAM凝胶与不锈钢试样的对磨,测试加载时间和滑行速率对材料的启动摩擦因数的影响.结果 影响PAMPS-PAAM互穿网络凝胶的启动摩擦因数的主要因素为加载时间,加载时间越长,启动摩擦因数越大.加载时间在15 min以内,启动摩擦因数随加载时间的增长急剧变化,加载时间超过15 min,启动摩擦因数的变化趋势变缓.滑行速率的变化与启动摩擦因数的大小无明显关联,且在不同的滑行速率下,启动摩擦因数的数值相差不大.结论 PAMPS-PAAM凝胶具有与软骨相近的启动摩擦性能.%Objective PAMPS-PAAM hydrogel is a substitute of articular cartilage with a good prospect of application.The compression strength of hydrogel reaches the average compression strength of articular cartilage in the former test.However,the research on the friction properties of hydrogel is in need.Methods This article adopts PAMPS-PAAM interpenetrating polymer network hydrogel which is made by AMPS hydrogel and AAM solution to launch the friction between PAMPS-PAAM hydrogel and stainless steel model with a home-made pin-plate testing machine.In the tests,the influence of loading duration and sliding velocity on the start-up friction properties are measured.Results The major factor that can influence the start-up friction coefficient of PAMPS-PAAM hydrogel is loading duration.The longer the loading duration is,the larger the start-up friction coefficient is.When the loading duration is within 15 mins,the start-up friction coefficient changes rapidly versus loading

  9. AFM friction and adhesion mapping of the substructures of human hair cuticles

    Energy Technology Data Exchange (ETDEWEB)

    Smith, James R., E-mail: james.smith@port.ac.uk [School of Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael' s Building, White Swan Road, Portsmouth, PO1 2DT (United Kingdom); Tsibouklis, John; Nevell, Thomas G. [School of Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael' s Building, White Swan Road, Portsmouth, PO1 2DT (United Kingdom); Breakspear, Steven [School of Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael' s Building, White Swan Road, Portsmouth, PO1 2DT (United Kingdom); Global R and D–Hair Beauty Laboratory, Kao Corporation, 2-1-3, Bunka Sumida-ku, Tokyo, 131-8501 (Japan)

    2013-11-15

    Using atomic force microscopy, values of the microscale friction coefficient, the tip (silicon nitride) - surface adhesion force and the corresponding adhesion energy, for the substructures that constitute the surface of human hair (European brown hair) have been determined from Amonton plots. The values, mapped for comparison with surface topography, corresponded qualitatively with the substructures’ plane surface characteristics. Localised maps and values of the frictional coefficient, extracted avoiding scale edge effects, are likely to inform the formulation of hair-care products and treatments.

  10. Friction in rail guns

    Science.gov (United States)

    Kay, P. K.

    1984-01-01

    The influence of friction is included in the present equations describing the performance of an inductively driven rail gun. These equations, which have their basis in an empirical formulation, are applied to results from two different experiments. Only an approximate physical description of the problem is attempted, in view of the complexity of details in the interaction among forces of this magnitude over time periods of the order of milisecs.

  11. Tribological Investigation of SiC/Al Composite under Dry Sliding Friction

    Directory of Open Access Journals (Sweden)

    DAI Liquan

    2016-12-01

    Full Text Available The effect of sliding distances on aluminum matrix composite reinforced by silicon carbide particle with volume fraction of 9% was investigated. Friction behavior and wear resistance of the composite with distances of 5000 r, 10000 r and 20000 r were studied under dry sliding conditions of the same speed and load(200 r/min, 45 N. The results show that the friction coefficient in long-range sliding process displays three stages:wearing zone, stable zone and accelerating zone. The matrix surface produces severe adhesion because of the rising temperature and then leads plastic areas, in which both friction coefficient and wear rate are increased.

  12. The effect of friction in the hold down post spherical bearings on hold down post loads

    Science.gov (United States)

    Richardson, James A.

    1990-01-01

    The effect of friction at the connection of the Solid Rocket Booster (SRB) aft skirt and the mobile launch platform (MLP) hold down posts was analyzed. A simplified model of the shuttle response during the Space Shuttle Main Engine (SSME) buildup was constructed. The model included the effect of stick-slip friction for the rotation of the skirt about the spherical bearing. Current finite element models assume the joint is completely frictionless in rotation and therefore no moment is transferred between the skirt and the hold down posts. The model was partially verified against test data and preliminary parameter studies were performed. The parameter studies indicated that the coefficient of friction strongly influenced the moment on the hold down posts. The coefficient of friction had little effect on hold down post vertical loads, however. Further calibration of the model is necessary before the effect of friction on the hold down post horizontal loads can be analyzed.

  13. Electronic friction at the atomic scale: Conduction, electrostatic and magnetic effects

    Science.gov (United States)

    Krim, Jacqueline; Altfeder, Igor

    2013-03-01

    We have performed a magnetic probe microscopy study of levitation and atomic-scale friction for Fe on YBCO (Tc = 92.5K) in the temperature range 65 - 293 K, to explore electronic contributions to friction at the atomic scale. The samples were prepared with oxygen-depleted surfaces, with thin semiconducting surface layers present atop the bulk. Below Tc, the friction coefficient was observed to be constant at 0.19 and exhibited no correlation with the strength of superconducting levitation forces observed below Tc. The friction coefficient exhibited a change in slope within experimental error of Tc that increased progressively above Tc and reached 0.33 by room temperature. The results were analyzed within the context of underlying atomic-scale electronic and phononic mechanisms that give rise to friction we conclude that contact electrification and static electricity play a significant role above Tc. Supported by NSF and AFOSR.

  14. Theory of friction based on brittle fracture

    Science.gov (United States)

    Byerlee, J.D.

    1967-01-01

    A theory of friction is presented that may be more applicable to geologic materials than the classic Bowden and Tabor theory. In the model, surfaces touch at the peaks of asperities and sliding occurs when the asperities fail by brittle fracture. The coefficient of friction, ??, was calculated from the strength of asperities of certain ideal shapes; for cone-shaped asperities, ?? is about 0.1 and for wedge-shaped asperities, ?? is about 0.15. For actual situations which seem close to the ideal model, observed ?? was found to be very close to 0.1, even for materials such as quartz and calcite with widely differing strengths. If surface forces are present, the theory predicts that ?? should decrease with load and that it should be higher in a vacuum than in air. In the presence of a fluid film between sliding surfaces, ?? should depend on the area of the surfaces in contact. Both effects are observed. The character of wear particles produced during sliding and the way in which ?? depends on normal load, roughness, and environment lend further support to the model of friction presented here. ?? 1967 The American Institute of Physics.

  15. Comparison of tribological properties of industrial low friction coatings

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    MX2 (M=Mo, W; X=S, Se) and DLC (a-C: H and WC/C) are the two kinds of typical low friction coatings widely used in industry. The friction and wear properties of these two kinds of coatings marked as MOVIC, MOST, MoSe2/Ni, WSe2, a-C: H and WC/C coatings were determined by fretting tests in ambient air of different humidity. The results show that the coefficient of friction of MX2 coatings increases when the relative humidity of air increases whereas the coefficient of friction DLC coatings decreases with the increasing of relative humidity. MOVIC and WSe2 coatings have a poor friction and wear resistance because of non-basal planes (100) and (101) parallel to the surface in the MOVIC coating, or the rough and porous surface of WSe2 coatings. Among these six coatings, MoSe2/Ni and WC/C coatings have the highest wear resistance which seems to be unaffected by the relative humidity.

  16. Investigation of friction and wear characteristics of cast iron material under various conditions

    Energy Technology Data Exchange (ETDEWEB)

    Joo, Ji Hoon; Kim, Chang Lae; Oh, Jeong Taek; Kim, Dae Eun [Yonsei University, Seoul (Korea, Republic of); Nemati, Narguess [School of Materials and Metallurgy, University of Tehran, Tehran (Iran, Islamic Republic of)

    2015-08-15

    Cast iron is widely used in fields such as the transport and heavy industries. For parts where contact damage is expected to occur, it is necessary to understand the friction and wear characteristics of cast iron. In this study, we use cast iron plates as the specimens to investigate their friction and wear characteristics. We perform various experiments using a reciprocating type tribotester. We assess the frictional characteristics by analyzing the friction coefficient values that were obtained during the sliding tests. We observe the wear surfaces of cast iron and steel balls using a scanning electron microscope, confocal microscope, and 3D profiler. We investigate the friction and wear characteristics of cast iron by injecting sand and alumina particles having various sizes. Furthermore, we estimate the effect of temperature on the friction and wear characteristics. The results obtained are expected to aid in the understanding of the tribological characteristics of cast iron in industry.

  17. A method to change frictional characteristics based on ultrasonic micro driving technique

    Institute of Scientific and Technical Information of China (English)

    CHEN Weishan; ZHANG Fan; LIU Junkao

    2006-01-01

    In order to reduce friction force and eliminate stick-slip phenomenon of a mechanic system at a low velocity, a method based on the ultrasonic micro driving technique to change the frictional characteristics is proposed. Exciting clockwise and anticlockwise microscopic elliptical motion of driving points on the ultrasonic actuator's two longitudinal bolt-clamped vibrators will generate ultrasonic lubrication action; furthermore, the friction can be actively controlled by adjusting the vibrators' vibrating amplitude. An experimental installation for friction control is designed using aerostatic guide, force sensors and a low speed moment motor.Fuzzy control theory is applied into this system. The experiments indicate the friction force has been reduced largely and the motion of the experimental system is stable. The friction coefficient is only about 0.0053 when the total mass of the ultrasonic actuator and load is3.8 kg and the motor's driving velocity is 0.5 mm/s.

  18. Solid friction between soft filaments

    CERN Document Server

    Ward, Andrew; Schwenger, Walter; Welch, David; Lau, A W C; Vitelli, Vincenzo; Mahadevan, L; Dogic, Zvonimir

    2015-01-01

    Any macroscopic deformation of a filamentous bundle is necessarily accompanied by local sliding and/or stretching of the constituent filaments. Yet the nature of the sliding friction between two aligned filaments interacting through multiple contacts remains largely unexplored. Here, by directly measuring the sliding forces between two bundled F-actin filaments, we show that these frictional forces are unexpectedly large, scale logarithmically with sliding velocity as in solid-like friction, and exhibit complex dependence on the filaments' overlap length. We also show that a reduction of the frictional force by orders of magnitude, associated with a transition from solid-like friction to Stokes' drag, can be induced by coating F-actin with polymeric brushes. Furthermore, we observe similar transitions in filamentous microtubules and bacterial flagella. Our findings demonstrate how altering a filament's elasticity, structure and interactions can be used to engineer interfilament friction and thus tune the prop...

  19. Friction surfaced Stellite6 coatings

    Energy Technology Data Exchange (ETDEWEB)

    Rao, K. Prasad; Damodaram, R. [Department of Metallurgical and Materials Engineering - Indian Institute of Technology Madras, Chennai 600 036 (India); Rafi, H. Khalid, E-mail: khalidrafi@gmail.com [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India); Ram, G.D. Janaki [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India); Reddy, G. Madhusudhan [Metal Joining Group, Defence Metallurgical Research Laboratory (DMRL) Kanchanbagh, Hyderabad 500 058 (India); Nagalakshmi, R. [Welding Research Institute, Bharat Heavy Electricals Limited, Tiruchirappalli 620 014 (India)

    2012-08-15

    Solid state Stellite6 coatings were deposited on steel substrate by friction surfacing and compared with Stellite6 cast rod and coatings deposited by gas tungsten arc and plasma transferred arc welding processes. Friction surfaced coatings exhibited finer and uniformly distributed carbides and were characterized by the absence of solidification structure and compositional homogeneity compared to cast rod, gas tungsten arc and plasma transferred coatings. Friction surfaced coating showed relatively higher hardness. X-ray diffraction of samples showed only face centered cubic Co peaks while cold worked coating showed hexagonally close packed Co also. - Highlights: Black-Right-Pointing-Pointer Stellite6 used as coating material for friction surfacing. Black-Right-Pointing-Pointer Friction surfaced (FS) coatings compared with casting, GTA and PTA processes. Black-Right-Pointing-Pointer Finer and uniformly distributed carbides in friction surfaced coatings. Black-Right-Pointing-Pointer Absence of melting results compositional homogeneity in FS Stellite6 coatings.

  20. Theory of noncontact friction for atom-surface interactions

    CERN Document Server

    Jentschura, U D; DeKieviet, M

    2016-01-01

    The noncontact (van der Waals) friction is an interesting physical effect which has been the subject of controversial scientific discussion. The "direct" friction term due to the thermal fluctuations of the electromagnetic field leads to a friction force proportional to 1/Z^5 where Z is the atom-wall distance). The "backaction" friction term takes into account the feedback of thermal fluctuations of the atomic dipole moment onto the motion of the atom and scales as 1/Z^8. We investigate noncontact friction effects for the interactions of hydrogen, ground-state helium and metastable helium atoms with alpha-quartz (SiO_2), gold (Au) and calcium difluorite (CaF_2). We find that the backaction term dominates over the direct term induced by the thermal electromagnetic fluctuations inside the material, over wide distance ranges. The friction coefficients obtained for gold are smaller than those for SiO_2 and CaF_2 by several orders of magnitude.

  1. Dynamic friction of self-affine surfaces

    Science.gov (United States)

    Schmittbuhl, Jean; Vilotte, Jean-Pierre; Roux, Stéphane

    1994-02-01

    We investigate the velocity dependence of the friction between two rigid blocks limited by a self-affine surface such as the one generated by a crack. The upper solid is subjected either to gravity or to an external elastic stiffness, and is driven horizontally at constant velocity, V, while the lower solid is fixed. For low velocities, the apparent friction coefficient is constant. For high velocities, the apparent friction is shown to display a velocity weakening. The weakening can be related to the variation of the mean contact time due to the occurrence of jumps during the motions. The cross-over between these two regimes corresponds to a characteristic velocity which depends on the geometry of the surfaces and on the mean normal force. In the case of simple gravity loading, the velocity dependence of the apparent friction at high velocities is proportional to 1/V^2 where V is the imposed tangential velocity. In the case of external elastic stiffness, two velocity weakening regimes can be identified, the first is identical to the gravity case with a 1/V^2 dependence, the second appears at higher velocities and is characterized by a 1/V variation. The characteristic velocity of this second cross-over depends on the roughness and the elastic stiffness. The statistical distribution of ballistic flight distances is analysed, and is shown to reveal in all cases the self-affinity of the contacting surfaces. Nous analysons la dépendence en vitesse du frottement entre deux solides limités par une surface rugueuse auto-affine comme celle d'une surface de fracture. Le solide supérieur est soumis soit à la gravité, soit à une raideur élastique externe, et est entraîné à vitesse horizontale constante V sur le solide inférieur fixe. A faible vitesse, le coefficient de friction apparent, est constant. A forte vitesse, le coefficient de friction apparent devient inversement proportionnel à la vitesse. Cette dépendance peut être reliée à la variation du temps

  2. A novel polyvinyl alcohol hydrogel functionalized with organic boundary lubricant for use as low-friction cartilage substitute: synthesis, physical/chemical, mechanical, and friction characterization.

    Science.gov (United States)

    Blum, Michelle M; Ovaert, Timothy C

    2012-10-01

    A novel material design was developed by functionalizing polyvinyl alcohol hydrogel with an organic low-friction boundary lubricant (molar ratios of 0.2, 0.5, and 1.0 moles of lauroyl chloride). The hydrogels were fabricated using two different techniques. First, the boundary lubricant was initially functionalized to the polymer, then the hydrogels were created by physically crosslinking the reacted polymer. Second, hydrogels were initially created by crosslinking pure polyvinyl alcohol, with the functionalization reaction performed on the fully formed gel. After the reaction, Fourier transform infrared spectroscopy and attenuated total reflectance spectra revealed a clear ester peak, the diminishment of the alcohol peak, and the amplification of the alkyl peaks, which confirmed attachment of the hydrocarbon chains to the polymer. Additional chemical characterization occurred through elemental analysis where an average increase of 22% carbon and 40% hydrogen provided further confirmation of attachment. Physical characterization of the boundary lubricant functionalized hydrogels was performed by water content and contact angle measurements. Water content dependency showed that method 1 had a direct relationship with boundary lubricant concentration, and method 2 displayed an inverse relationship. The contact angle increased as boundary lubricant concentration increased for the pure matrix material for both processing methods, suggesting that the hydrocarbons produced surface properties that mimic natural cartilage, and contact behavior of the biphasic system was dependent on processing method. Friction tests demonstrated a significant decrease in friction coefficient, with a maximum decrease of 70% and a minimum decrease of 24% for boundary lubricant functionalized hydrogels compared with nonfunctionalized polyvinyl alcohol hydrogels.

  3. Determination of basic friction angle using various laboratory tests.

    Science.gov (United States)

    Jang, Bo-An

    2016-04-01

    The basic friction angle of rock is an important factor of joint shear strength and is included within most shear strength criteria. It can be measured by direct shear test, triaxial compression test and tilt test. Tilt test is mostly used because it is the simplest method. However, basic friction angles measured using tilt test for same rock type or for one sample are widely distributed and often do not show normal distribution. In this research, the basic friction angles for the Hangdeung granite form Korea and Berea sandstone from USA are measured accurately using direct shear test and triaxial compression test. Then basic friction angles are again measured using tilt tests with various conditions and are compared with those measured using direct shear test and triaxial compression test to determine the optimum condition of tilt test. Three types of sliding planes, such as planes cut by saw and planes polished by #100 and #600 grinding powders, are prepared. When planes are polished by #100 grinding powder, the basic friction angles measured using direct shear test and triaxial compression test are very consistent and show narrow ranges. However, basic friction angles show wide ranges when planes are cut by saw and are polished by #600 grinding powder. The basic friction angle measured using tilt test are very close to those measured using direct shear test and triaxial compression test when plane is polished by #100 grinding powder. When planes are cut by saw and are polished by #600 grinding powder, basic friction angles measured using tilt test are slightly different. This indicates that tilt test with plane polished by #100 grinding powder can yield an accurate basic friction angle. In addition, the accurate values are obtained not only when planes are polished again after 10 times of tilt test, but values are averaged by more 30 times of tests.

  4. Friction and wear calculation methods

    CERN Document Server

    Kragelsky, I V; Kombalov, V S

    1981-01-01

    Friction and Wear: Calculation Methods provides an introduction to the main theories of a new branch of mechanics known as """"contact interaction of solids in relative motion."""" This branch is closely bound up with other sciences, especially physics and chemistry. The book analyzes the nature of friction and wear, and some theoretical relationships that link the characteristics of the processes and the properties of the contacting bodies essential for practical application of the theories in calculating friction forces and wear values. The effect of the environment on friction and wear is a

  5. Friction and hardness of gold films deposited by ion plating and evaporation

    Science.gov (United States)

    Miyoshi, K.; Spalvins, T.; Buckley, D. H.

    1983-01-01

    Sliding friction experiments were conducted with ion-plated and vapor-deposited gold films on various substrates in contact with a 0.025-mm-radius spherical silicon carbide rider in mineral oil. Hardness measurements were also made to examine the hardness depth profile of the coated gold on the substrate. The results indicate that the hardness is influenced by the depth of the gold coating from the surface. The hardness increases with an increase in the depth. The hardness is also related to the composition gradient in the graded interface between the gold coating and the substrate. The graded interface exhibited the highest hardness resulting from an alloy hardening effect. The coefficient of friction is inversely related to the hardness, namely, the load carrying capacity of the surface. The greater the hardness that the metal surface possesses, the lower is the coefficient of friction. The graded interface exhibited the lowest coefficient of friction.

  6. The effect of friction on simulated containment of underground nuclear explosions

    Energy Technology Data Exchange (ETDEWEB)

    Attia, A.V.

    1990-11-01

    The strength of the residual stress field is used as an important indicator in assessing the containment of underground nuclear explosions. Containment analysis using the COTTAGE geology shows considerable cracking in the hard Paleozoic layer, just below the cavity. The coefficient of friction is the ratio of total shear stress applied to a closed fracture surface to normal applied compressive total stress. Without any friction, the Paleozoic residual stress field is weakest. As the friction coefficient is increased from 0 to 0.5, the Paleozoic residual stress field is strengthened. A further increase of the friction coefficient from 0.5 to 0.8 shows strengthened where cracks are closed and weakening where cracks remain open. 4 refs., 4 figs., 1 tab.

  7. Friction or Closure

    DEFF Research Database (Denmark)

    Lundahl, Mikela

    2014-01-01

    . The anthropologist Anna Tsing has developed the concept-metaphor friction as a way to discuss the energy created when various actors narrate “the same” event(s) in different ways, and see the other participants’ accounts as fantasies or even fabrications. I will use my position as researcher and my relations...... is Stone Town in Zanzibar and the de-velopment and dissolution going on under the shadow of the UNESCO World Heritage flag; a growing tourism; a global and local increase in islamisation; and the political tension within the Tanzanian union. My main focus is narratives of the identity of Zanzibar since...

  8. The hysteretic contribution of friction for the polished rubber on the concrete surface

    Science.gov (United States)

    Feshanjerdi, M.; Khorrami, M.; Masoudi, A. A.; Razzaghi Kashani, M.

    2017-02-01

    The rubber friction coefficient, and the contact area during stationary sliding is calculated, for the contact of a polished rubber block and a concrete surface, when both surfaces are rough. The calculation is based on an extended version of Persson's contact mechanics theory. Compared to only the substrate being rough, when both of the surfaces are rough but their cross correlation is zero, the friction coefficient is larger. Introducing a positive correlation decreases the friction coefficient, while introducing a negative correlation increases the friction coefficient. To support these theoretical arguments, some experiments have been performed. We have produced roughness on the rubber surface, using abrasive paper, and measured the surface topographies for the concrete and the polished rubber surfaces. The auto spectral density functions for the both surfaces have been calculated, and the rubber viscoelastic modulus mastercurve has been obtained. We have measured the rubber friction at different sliding velocities, when the rubber surfaces are rough and smooth, and compared it to the theoretical results. It is seen that when the rubber surface is rough, the rubber friction coefficient is larger compared to the case the rubber surface is smooth. The theoretical results are in good agreement with experimental observation.

  9. Model coupling friction and adhesion for steel-concrete interfaces

    CERN Document Server

    Raous, Michel

    2010-01-01

    The interface behaviour between steel and concrete, during pull-out tests, is numerically investigated using an interface model coupling adhesion and Coulomb friction. This model, first developed by Raous, Cang\\'emi, Cocou and Monerie (RCCM), is based on the adhesion intensity variable, introduced by Fr\\'emond, which is a surface damage variable. The RCCM model is here completed by taking a variable friction coefficient to simulate the slip weakening of the interface when sliding occurs. Identification of the parameters and validation of the model are carried on pull out experiments conducted at the INSA of Toulouse on steel-concrete interface of reinforced concrete.

  10. Discontinuous transformations and averaging for vibro-impact analysis

    DEFF Research Database (Denmark)

    Thomsen, Jon Juel; Fidlin, A.

    2004-01-01

    Certain vibro-impact problems can be conveniently solved by discontinuous transformations combined with averaging. We briefly outline the background for this, and then focus on illustrating the procedure for specific examples: A self-excited friction oscillator with one- or two-sided stops, and a...

  11. Low friction in mixed-mu superconducting bearings

    Science.gov (United States)

    Hull, J. R.; Hilton, E. F.; Mulcahy, T. M.; Yang, Z. J.; Lockwood, A.; Strasik, M.

    1995-12-01

    Individual magnetic steel rotors were levitated by combining the attractive force between permanent magnets and the steel with the repulsive force between high-temperature superconductors and the steel. The free spindown of several rotors was observed, and the effective coefficient of friction for the bearing was calculated as a function of geometry. Low-speed coefficients of <10-8 were observed, and the velocity dependence of MnZn ferrite rotors suggest that coefficients of <10-6 are attainable at bearing rim velocities of 100 m/s.

  12. Influence of the electrical sliding speed on friction and wear processes in an electrical contact copper stainless steel

    Science.gov (United States)

    Bouchoucha, A.; Chekroud, S.; Paulmier, D.

    2004-02-01

    Among the various parameters that influence the friction and wear behaviour of a copper-stainless steel couple crossed by an electrical current and in a dry contact is the sliding speed. The tests were carried out under ambient environment and the sliding speed was in the range of 0.2-8 ms -1. The electrical current intensity was varied from 0 to 40 A and held constant during each experiment. The normal load was maintained constant corresponding to an average Hertzian stress of 10 7 Pa. It appears that the friction coefficient and the wear rate increase at first with the speed, reach their maximums, then slowly decrease and tend to constant values. Over the entire range of sliding speeds two types of wear are observed. These latters are essentially mild wear as long as hard debris do not appear at the interface and severe wear when debris consisting of oxides or oxide metal mixture become big enough, they are removed from the surface and have abrasive effect. The results are discussed in terms of observations of wear debris size and composition, wear track study, metallographic study of worn surfaces and friction and electrical contact resistance records.

  13. Aggregation and Averaging.

    Science.gov (United States)

    Siegel, Irving H.

    The arithmetic processes of aggregation and averaging are basic to quantitative investigations of employment, unemployment, and related concepts. In explaining these concepts, this report stresses need for accuracy and consistency in measurements, and describes tools for analyzing alternative measures. (BH)

  14. On Averaging Rotations

    DEFF Research Database (Denmark)

    Gramkow, Claus

    1999-01-01

    In this article two common approaches to averaging rotations are compared to a more advanced approach based on a Riemannian metric. Very offten the barycenter of the quaternions or matrices that represent the rotations are used as an estimate of the mean. These methods neglect that rotations belong...... approximations to the Riemannian metric, and that the subsequent corrections are inherient in the least squares estimation. Keywords: averaging rotations, Riemannian metric, matrix, quaternion...

  15. Slow frictional waves

    Science.gov (United States)

    Viswanathan, Koushik; Sundaram, Narayan; Chandrasekar, Srinivasan

    Stick-slip, manifest as intermittent tangential motion between two dry solid surfaces, is a friction instability that governs diverse phenomena from automobile brake squeals to earthquakes. We show, using high-speed in situ imaging of an adhesive polymer interface, that low velocity stick-slip is fundamentally of three kinds, corresponding to passage of three different surface waves -- separation pulses, slip pulses and the well-known Schallamach waves. These waves, traveling much slower than elastic waves, have clear distinguishing properties. Separation pulses and Schallamach waves involve local interface separation, and propagate in opposite directions while slip pulses are characterized by a sharp stress front and do not display any interface detachment. A change in the stick-slip mode from separation to slip pulse is effected simply by increasing the normal force. Together, these three waves constitute all possible stick-slip modes in adhesive friction and are shown to have direct analogues in muscular locomotory waves in soft bodied invertebrates. A theory for slow wave propagation is also presented which is capable of explaining the attendant interface displacements, velocities and stresses.

  16. Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.

    2008-01-01

    Friction stir welding (FSW) is a solid state welding process invented in 1991 at The Welding Institute in the United Kingdom. A weld is made in the FSW process by translating a rotating pin along a weld seam so as to stir the sides of the seam together. FSW avoids deleterious effects inherent in melting and promises to be an important welding process for any industries where welds of optimal quality are demanded. This article provides an introduction to the FSW process. The chief concern is the physical effect of the tool on the weld metal: how weld seam bonding takes place, what kind of weld structure is generated, potential problems, possible defects for example, and implications for process parameters and tool design. Weld properties are determined by structure, and the structure of friction stir welds is determined by the weld metal flow field in the vicinity of the weld tool. Metal flow in the vicinity of the weld tool is explained through a simple kinematic flow model that decomposes the flow field into three basic component flows: a uniform translation, a rotating solid cylinder, and a ring vortex encircling the tool. The flow components, superposed to construct the flow model, can be related to particular aspects of weld process parameters and tool design; they provide a bridge to an understanding of a complex-at-first-glance weld structure. Torques and forces are also discussed. Some simple mathematical models of structural aspects, torques, and forces are included.

  17. The influence of high temperatures on the tribological properties of automotive friction materials

    Science.gov (United States)

    Savage, Luke

    Temperatures of over 800C can be generated at the frictional interface within the brake systems of large vehicles, such high temperatures result in severe wear at the frictional interface, and can also lead to a very dangerous condition known as brake fade, characterised by a sharp fall in the coefficient of friction between the pad and disc, resulting in a catastrophic loss of braking efficiency. Common friction materials are very specialised composites often containing up to 15 components bound together within a phenolic resin matrix. The high temperature behaviour of the various constituents of friction materials were investigated using thermogravimetric analysis, focusing in particular on the thermal decomposition of the phenolic resin matrix material, where it has been firmly established that the thermal decomposition products of phenolic resin are the primary cause of brake fade. This has lead to the development of a novel approach for reducing fade in conventional resin based friction materials, involving a partial carbonisation to 400C. The high temperature wear characteristics of both modified and conventional friction materials were examined using standard dynamometer tests, as well as a 'continuous drag' type test machine, equipped with a heating facility. During this study a number of factors were identified as the main influences on the overall wear behaviour of friction materials. These included test temperature, sample test history, and the various effects of friction films, which were the subject of a detailed analysis. The formation of friction films was found to be an important facet of a successful friction material, producing a reduction in wear at the frictional interface. Films were examined and analysed using EDX, SEM, and X-ray diffraction techniques, which revealed the presence of a high proportion of magnetite (Fe3O4), containing iron which originated from the disc surface. It was established that the incorporation of iron in friction

  18. Elastic model of dry friction

    Energy Technology Data Exchange (ETDEWEB)

    Larkin, A. I.; Khmelnitskii, D. E., E-mail: dekl2@cam.ac.uk [Landau Institute for Theoretical Physics (Russian Federation)

    2013-09-15

    Friction of elastic bodies is connected with the passing through the metastable states that arise at the contact of surfaces rubbing against each other. Three models are considered that give rise to the metastable states. Friction forces and their dependence on the pressure are calculated. In Appendix A, the contact problem of elasticity theory is solved with adhesion taken into account.

  19. Corrosion effects on friction factors

    Energy Technology Data Exchange (ETDEWEB)

    Magleby, H.L.; Shaffer, S.J.

    1996-03-01

    This paper presents the results of NRC-sponsored material specimen tests that were performed to determine if corrosion increases the friction factors of sliding surfaces of motor-operated gate valves, which could require higher forces to close and open safety-related valves when subjected to their design basis differential pressures. Friction tests were performed with uncorroded specimens and specimens subjected to accelerated corrosion. Preliminary tests at ambient conditions showed that corrosion increased the friction factors, indicating the need for additional tests duplicating valve operating parameters at hot conditions. The additional tests showed friction factors of corroded specimens were 0.1 to 0.2 higher than for uncorroded specimens, and that the friction factors of the corroded specimens were not very dependent on contact stress or corrosion film thickness. The measured values of friction factors for the three corrosion films tested (simulating three operating times) were in the range of 0.3 to 0.4. The friction factor for even the shortest simulated operating time was essentially the same as the others, indicating that the friction factors appear to reach a plateau and that the plateau is reached quickly.

  20. Controlling vortex motion and vortex kinetic friction

    Science.gov (United States)

    Nori, Franco; Savel'ev, Sergey

    2006-05-01

    We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.

  1. Partial squeeze film levitation modulates fingertip friction.

    Science.gov (United States)

    Wiertlewski, Michaël; Fenton Friesen, Rebecca; Colgate, J Edward

    2016-08-16

    When touched, a glass plate excited with ultrasonic transverse waves feels notably more slippery than it does at rest. To study this phenomenon, we use frustrated total internal reflection to image the asperities of the skin that are in intimate contact with a glass plate. We observed that the load at the interface is shared between the elastic compression of the asperities of the skin and a squeeze film of air. Stroboscopic investigation reveals that the time evolution of the interfacial gap is partially out of phase with the plate vibration. Taken together, these results suggest that the skin bounces against the vibrating plate but that the bounces are cushioned by a squeeze film of air that does not have time to escape the interfacial separation. This behavior results in dynamic levitation, in which the average number of asperities in intimate contact is reduced, thereby reducing friction. This improved understanding of the physics of friction reduction provides key guidelines for designing interfaces that can dynamically modulate friction with soft materials and biological tissues, such as human fingertips.

  2. An Improved Algorithm for Calculating Friction Force and Torque in Involute Helical Gears

    Directory of Open Access Journals (Sweden)

    Lin Han

    2013-01-01

    Full Text Available Time varying frictional force and torque are one of the main exciting sources of vibration in helical gears. This paper presents an approach to determine the friction force and torque in involute helical gears considering nonuniform load distribution along contact lines. An analytical load distribution model is employed and extended to obtain the load per unit of length along contact lines. Friction force and torque models under nonuniform assumption are derived. Comparisons of the determined friction force and torque with the results from uniform assumption are made. In addition, the differences between constant friction coefficient and varying coefficient are revealed. Moreover, two typical design cases of helical gears are studied. Results show that the fluctuations of friction force and torque under uniform assumption are more significant than those under nonuniform assumption in sample I for a single tooth, but less significant for the sum of those of the three teeth, while in sample II, the fluctuations under uniform assumption are less significant than those under nonuniform assumption. The friction coefficient induced difference is negligible compared with the difference induced by load distribution assumptions.

  3. Development and validation of a new method for measuring friction between skin and nonwoven materials.

    Science.gov (United States)

    Cottenden, A M; Wong, W K; Cottenden, D J; Farbrot, A

    2008-07-01

    A new method for measuring the coefficient of friction between nonwoven materials and the curved surface of the volar forearm has been developed and validated. The method was used to measure the coefficient of static friction for three different nonwoven materials on the normal (dry) and over-hydrated volar forearms of five female volunteers (ages 18-44). The method proved simple to run and had good repeatability: the coefficient of variation (standard deviation expressed as a percentage of the mean) for triplets of repeat measurements was usually (80 per cent of the time) less than 10 per cent. Measurements involving the geometrically simpler configuration of pulling a weighted fabric sample horizontally across a quasi-planar area of volar forearm skin proved experimentally more difficult and had poorer repeatability. However, correlations between values of coefficient of static friction derived using the two methods were good (R = 0.81 for normal (dry) skin, and 0.91 for over-hydrated skin). Measurements of the coefficient of static friction for the three nonwovens for normal (dry) and for over-hydrated skin varied in the ranges of about 0.3-0.5 and 0.9-1.3, respectively. In agreement with Amontons' law, coefficients of friction were invariant with normal pressure over the entire experimental range (0.1-8.2 kPa).

  4. Bamboo Fibre-reinforced Semi-Metallic Brake Friction Materials for Automotive Applications

    Directory of Open Access Journals (Sweden)

    Talib R. J.

    2016-01-01

    Full Text Available Three friction material formulations composed of bamboo fiber along with binder, friction modifiers and filler have been prepared through powder metallurgy process. Sample F1 and F2 are composed of 10 wt. % of copper and barium, respectively, while the other ingredients in both formulations have the same wt. %. The wt. % of bamboo fiber in sample F3 is, however, increased by 100%, while the compositions of the other ingredients are proportionally decreased. The samples were examined for their porosity, hardness, and friction and wear properties using hot bath, Rockwell hardness tester, and CHASE friction dynamometer, respectively. The test results are compared with those of a commercial sample as the benchmark. Normal and hot frictions of all the three samples developed comply with the requirements specified by Automotive Manufacturer Equipment Companies Agency (AMECA. However, sample F3 which is composed of 20 wt. % of bamboo fiber does not comply with the minimum requirement of friction coefficient. Whereas, sample F2, which is composed of 10 wt. % of bamboo fiber and 10 wt. % of barium, has lower friction coefficient than the commercial sample, and has a sudden drop in friction coefficient at a temperature of 500°F. Out of three developed samples, sample F1, which is composed of 10 wt. % of bamboo fiber and 10 wt. % of copper, complies with all the requirements and has higher friction coefficient than the commercial sample, and has higher fade resistance. Thus, it could be postulated that bamboo fiber could be used as a reinforcing fiber with composition of 10 wt. %.

  5. Wear and Friction Behavior of Metal Impregnated Microporous Carbon Composites

    Science.gov (United States)

    Goller, Gultekin; Koty, D. P.; Tewari, S. N.; Singh, M.; Tekin, A.

    1996-01-01

    Metal-matrix composites have been prepared by pressure-infiltration casting of copper-base alloy melts into microporous carbon preforms. The carbon preforms contained varying proportions of amorphous carbon and graphite. Load dependence of the wear and friction behavior of the composite pins has been examined under ambient conditions against cast-iron plates, using a pin-on-plate reciprocating wear tester. The wear resistance of the composite is significantly improved, as compared with the base alloy. Contrary to the normally expected behavior, the addition of graphite to the amorphous carbon does not reduce the friction coefficient, especially at high loads. The wear and friction behavior of the composites is very sensitive to the size and distribution of the microstructural constituents.

  6. Functional-Friction Networks: New Insights on the Laboratory Earthquakes

    CERN Document Server

    Ghaffari, H O

    2013-01-01

    We formulate the universality of regular precursor rupture fronts in functional network parameter space, in light of recent analysis of acoustics emissions-coupled friction experimental results. Furthermore, using a phenomenological approach based on friction networks, we propose that the energy of the ruptures can be extended in terms of networks motifs and the transition from regular rupture to slow deformation can have a third production from the critical rupture class, comparable with the direct observations of this phenomena in the transparent samples . Based on this model, the transition from slow ruptures (i.e., creep pulse) to the critical speeds of ruptures is possible. In addition, the evolution of arrested rupture fronts is inspected through a statistical-network modelling which sheds light on the communities evolution. We propose a phase diagram for the friction networks which depends on the scaling coefficients of scalar parameters and can show a transition towards the capturing of the links by a...

  7. Suitable Friction Sliding Materials for Base Isolation of Masonry Buildings

    Directory of Open Access Journals (Sweden)

    Radhikesh P. Nanda

    2012-01-01

    Full Text Available A feasibility study of friction base isolation system for seismic protection has been performed. Four different sliding interfaces, namely, green marble/High Density Poly Ethylene (HDPE, green marble/green marble, green marble/geosynthetic, and green marble/ rubber layers have been studied through experimental and analytical investigations. The experimental investigations show that the coefficient of friction values of these interfaces lies in the desirable range for seismic protection, i.e., 0.05 to 0.15. The analytical investigation reveals that most of these sliding interfaces are effective in reducing spectral accelerations up to 50% and the sliding displacement is restricted within plinth projection of 75 mm (3 in. Green marble and geosynthetic are found to be better alternatives for use in friction isolation system with equal effectiveness of energy dissipation and limiting the earthquake energy transmission to super structure during strong earthquake leading to a low cost, durable solution for earthquake protection of masonry buildings.

  8. Reducing Sliding Friction with Liquid-Impregnated Surfaces

    Science.gov (United States)

    Habibi, Mohammad; Collier, C. Patrick; Boreyko, Jonathan; Nature Inspired Fluids; Interfaces Team; CenterNanophase Materials Sciences Team

    2015-11-01

    Liquid-impregnated surfaces are fabricated by infusing a lubricating liquid into the micro/nano roughness of a textured substrate, such that the surface is slippery for any deposited liquid immiscible with the lubricant. To date, liquid-impregnated surfaces have almost exclusively focused on repelling liquids by minimizing the contact angle hysteresis. Here, we demonstrate that liquid-impregnated surfaces are also capable of reducing sliding friction for solid objects. Ordered arrays of silicon micropillars were infused with lubricating liquids varying in viscosity by two orders of magnitude. Five test surfaces were used: two different micropillared surfaces with and without liquid infusion and a smooth, dry control surface. The static and kinetic coefficients of friction were measured using a polished aluminum cube as the sliding object. Compared to the smooth control surface, the sliding friction was reduced by at least a factor of two on the liquid-impregnated surfaces.

  9. Fault Frictional Stability in a Nuclear Waste Repository

    Science.gov (United States)

    Orellana, Felipe; Violay, Marie; Scuderi, Marco; Collettini, Cristiano

    2016-04-01

    Exploitation of underground resources induces hydro-mechanical and chemical perturbations in the rock mass. In response to such disturbances, seismic events might occur, affecting the safety of the whole engineering system. The Mont Terri Rock Laboratory is an underground infrastructure devoted to the study of geological disposal of nuclear waste in Switzerland. At the site, it is intersected by large fault zones of about 0.8 - 3 m in thickness and the host rock formation is a shale rock named Opalinus Clay (OPA). The mineralogy of OPA includes a high content of phyllosilicates (50%), quartz (25%), calcite (15%), and smaller proportions of siderite and pyrite. OPA is a stiff, low permeable rock (2×10-18 m2), and its mechanical behaviour is strongly affected by the anisotropy induced by bedding planes. The evaluation of fault stability and associated fault slip behaviour (i.e. seismic vs. aseismic) is a major issue in order to ensure the long-term safety and operation of the repository. Consequently, experiments devoted to understand the frictional behaviour of OPA have been performed in the biaxial apparatus "BRAVA", recently developed at INGV. Simulated fault gouge obtained from intact OPA samples, were deformed at different normal stresses (from 4 to 30 MPa), under dry and fluid-saturated conditions. To estimate the frictional stability, the velocity-dependence of friction was evaluated during velocity steps tests (1-300 μm/s). Slide-hold-slide tests were performed (1-3000 s) to measure the amount of frictional healing. The collected data were subsequently modelled with the Ruina's slip dependent formulation of the rate and state friction constitutive equations. To understand the deformation mechanism, the microstructures of the sheared gouge were analysed. At 7 MPa normal stress and under dry conditions, the friction coefficient decreased from a peak value of μpeak,dry = 0.57 to μss,dry = 0.50. Under fluid-saturated conditions and same normal stress, the

  10. Friction properties of amorphous carbon ultrathin films deposited by filtered cathodic vacuum arc and radio-frequency sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Matlak, J.; Komvopoulos, K., E-mail: kyriakos@me.berkeley.edu

    2015-03-31

    The friction properties of ultrathin films of amorphous carbon (a-C) deposited on Si(100) substrates by filtered cathodic vacuum arc and radio-frequency sputtering were investigated by surface force microscopy. Deposition parameters yielding a-C films with high sp{sup 3} content were used to deposit films of thickness between 5 and 35 nm. The coefficient of friction of both types of a-C films was measured with a 1-μm-radius conical diamond tip and normal loads in the range of 20–640 μN. The results show a strong dependence of the friction properties on the surface roughness, thickness, and structure of the a-C films, which are influenced by the intricacies of the deposition method. The dependence of the coefficient of friction on normal load and the dominance of adhesion and plowing friction mechanisms are interpreted in terms of the through-thickness variation of carbon atom hybridization of the a-C films. - Highlights: • Comparison of nanoscale friction properties of ultrathin amorphous carbon films. • Friction dependence on film roughness, thickness, and structure (hybridization). • Effect of through-thickness changes in carbon atom hybridization on film friction. • Explanation of film friction trends in terms of competing friction mechanisms.

  11. Effect of Coulomb friction on orientational correlation and velocity distribution functions in a sheared dilute granular gas.

    Science.gov (United States)

    Gayen, Bishakhdatta; Alam, Meheboob

    2011-08-01

    From particle simulations of a sheared frictional granular gas, we show that the Coulomb friction can have dramatic effects on orientational correlation as well as on both the translational and angular velocity distribution functions even in the Boltzmann (dilute) limit. The dependence of orientational correlation on friction coefficient (μ) is found to be nonmonotonic, and the Coulomb friction plays a dual role of enhancing or diminishing the orientational correlation, depending on the value of the tangential restitution coefficient (which characterizes the roughness of particles). From the sticking limit (i.e., with no sliding contact) of rough particles, decreasing the Coulomb friction is found to reduce the density and spatial velocity correlations which, together with diminished orientational correlation for small enough μ, are responsible for the transition from non-gaussian to gaussian distribution functions in the double limit of small friction (μ→0) and nearly elastic particles (e→1). This double limit in fact corresponds to perfectly smooth particles, and hence the maxwellian (gaussian) is indeed a solution of the Boltzmann equation for a frictional granular gas in the limit of elastic collisions and zero Coulomb friction at any roughness. The high-velocity tails of both distribution functions seem to follow stretched exponentials even in the presence of Coulomb friction, and the related velocity exponents deviate strongly from a gaussian with increasing friction.

  12. Student figures in friction

    DEFF Research Database (Denmark)

    Nielsen, Gritt B.

      This thesis analyses how ‘the student', as a contested figure, is negotiated and enacted in a period of extensive university reform in Denmark. Through a combination of historical and anthropological research, it focuses on students' changing participation in the shaping of Danish society......, students' room for participation in their own learning, influenced by demands for efficiency, flexibility and student-centred education. The thesis recasts the anthropological endeavour as one of ‘figuration work'. That is, ‘frictional events' are explored as moments when conflicting figures......, the university and their own education. Detailed studies explore, first, politically active students' various attempts to influence national educational policies; second, student participation in the development of the university, especially regarding debates over consumer conduct versus co-ownership; and third...

  13. Anti-wear and friction performance of ZrO2 nanoparticles as lubricant additive

    Institute of Scientific and Technical Information of China (English)

    Shiyu Ma; Shaohua Zheng; Duxia Cao; Hongna Guo

    2010-01-01

    The surface of ZrO2 nanoparticles was modified with silane coupling agent KH-560 by dispersing the nanoparticles in 20# machine oil.The tribological performance of the 20# machine oil with ZrO2 nanoparticles was evaluated by a four-ball tester and a thrust-ring machine.The loss of the thrust-ring weight was measured by an electronic balance with a precision of 0.0001 g.The worn surface was examined under a metallographic microscope with 400-times magnification.The results showed that the average friction coefficient decreased by 27.34%,and that the weight loss of the thrust-ring indicated no wear or nega-tive wear,the wear loss after six loads tests being-0.0163 g.The anti-wear(AW)and reducing friction(RF)abilities of the oil with ZrO2 nanoparticles addition were considerably improved,maximizing at an additive concentration of 0.5 wt%.

  14. Structure and Friction Behavior of CrNx/a-C:H Nanocomposite Films

    Directory of Open Access Journals (Sweden)

    Lunlin Shang

    2014-01-01

    Full Text Available CrN and CrNx/a-C:H nanocomposite films were deposited on Si substrates by the magnetron sputtering technique. The structure, chemical state, and friction behavior of the CrNx/a-C:H films prepared at various CH4 content were studied systematically. The CrN film shows strong (111 and (220 orientation, while the CrNx/a-C:H films consist of the nanocrystalline CrNx or Cr particles embedded in an amorphous hydrocarbon (a-C:H matrix and show weak diffraction peaks, which is in accordance with the XPS analysis results. The typical Raman D and G peaks are observed, indicating that the separated amorphous carbon or CNx phase appears in the CrNx/a-C:H films. However, no chromium carbide was observed in all the as-deposited samples. From the SEM graphs, all the deposited films depicted a dense and compact microstructure with well-attached interface with the substrate. The average friction coefficient of the CrNx/a-C:H films largely decreased with increasing CH4 content.

  15. Your Average Nigga

    Science.gov (United States)

    Young, Vershawn Ashanti

    2004-01-01

    "Your Average Nigga" contends that just as exaggerating the differences between black and white language leaves some black speakers, especially those from the ghetto, at an impasse, so exaggerating and reifying the differences between the races leaves blacks in the impossible position of either having to try to be white or forever struggling to…

  16. On Averaging Rotations

    DEFF Research Database (Denmark)

    Gramkow, Claus

    2001-01-01

    In this paper two common approaches to averaging rotations are compared to a more advanced approach based on a Riemannian metric. Very often the barycenter of the quaternions or matrices that represent the rotations are used as an estimate of the mean. These methods neglect that rotations belong...

  17. Inertial Lévy Flight with Nonlinear Friction

    Institute of Scientific and Technical Information of China (English)

    L(U) Yan; BAO Jing-Dong

    2011-01-01

    Lévy Bight with nonlinear friction is studied. Due to the occurrence of extremely long jumps Levy flights often possess infinite variance and are physically problematic if describing the dynamics of a particle of finite mass. However, by introducing nonlinear friction, we show that the stochastic process subject to Levy noise exhibits finite variance, leading to a well-defined .kinetic energy. In the force-free fiIeld, normal diffusion behavior is observed and the diffusion coefficient decreases with Levy index μ. Furthermore, we find a kinetic resonance of the particle in the harmonic potential to the external oscillating field in the generally underdamped region and the value of the linear friction γo determines whether resonance occurs or not.%Lévy flight with nonlinear friction is studied.Due to the occurrence of extremely long jumps Lévy flights often possess infinite variance and are physically problematic if describing the dynamics of a particle of finite mass.However,by introducing nonlinear friction,we show that the stochastic process subject to Lévy noise exhibits finite variance,leading to a well-defined kinetic energy.In the force-free field,normal diffusion behavior is observed and the diffusion coefficient decreases with Lévy index μ.Furthermore,we find a kinetic resonance of the particle in the harmonic potential to the external oscillating field in the generally underdamped region and the value of the linear friction γ0 determines whether resonance occurs or not.The stable Lévy process,often called the Lévy flight,is used to model various phenomena such as self-diffusion in micelle systems,[1] special problems in reaction dynamics,[2] and even the flight of an albatross.

  18. Dry Friction and Wear Characteristics of Impregnated Graphite in a Corrosive Environment

    Institute of Scientific and Technical Information of China (English)

    JIA Qian; YUAN Xiaoyang; ZHANG Guoyuan; DONG Guangneng; ZHAO Weigang

    2014-01-01

    Tribological properties of impregnated graphite are greatly influenced by preparation technology and working conditions and it’s highly susceptible to corrosion environmental impacts, but the experimental research about it are few. In this paper, three kinds of impregnated graphite samples are prepared with different degree of graphitization, the tribological properties of these samples in the dry friction environment and in a corrosive environment are analyzed and contrasted. The tribo-test results show that the friction coefficient of samples is reduced and the amount of wear of samples increase when the graphitization degree of samples increases in dry friction condition. While in a corrosive environment (samples are soaked N2O4), the friction coefficient and amount of wear are changed little if the graphitization degree of samples are low. If the degree of graphitization increase, the friction coefficient and amount of wear of samples increase too, the amount of wear is 2 to 3 times as the samples tested in the non-corrosive environment under pv value of 30 MPa•m/s. The impregnated graphite, which friction coefficient is stable and graphitization degree is in mid level, such #2, is more appropriate to have a work in the corrosion conditions. In this paper, preparation and tribological properties especially in corrosive environment of the impregnated graphite is studied, the research conclusion can provide an experimental and theoretical basis for the selection and process improvement of graphite materials, and also provide some important design parameters for contact seal works in a corrosive environment.

  19. Estimation of friction parameters in gravity currents by data assimilation in a model hierarchy

    Directory of Open Access Journals (Sweden)

    A. Wirth

    2011-01-01

    Full Text Available This paper is the last in a series of three investigating the friction laws and their parametrisation in idealised gravity currents in a rotating frame. Results on the dynamics of a gravity current (Wirth, 2009 and on the estimation of friction laws by data assimilation (Wirth and Verron, 2008 are combined to estimate the friction parameters and discriminate between friction laws in non-hydrostatic numerical simulations of gravity current dynamics, using data assimilation and a reduced gravity shallow water model.

    I demonstrate, that friction parameters and laws in gravity currents can be estimated using data assimilation. The results clearly show that friction follows a linear Rayleigh law for small Reynolds numbers and the estimated value agrees well with the analytical value obtained for non-accelerating Ekman layers. A significant and sudden departure towards a quadratic drag law at an Ekman layer based Reynolds number of around 800 is shown, in agreement with classical laboratory experiments. The drag coefficient obtained compare well to friction values over smooth surfaces. I show that data assimilation can be used to determine friction parameters and discriminate between friction laws and that it is a powerful tool in systematically connection models within a model hierarchy.

  20. Estimation of friction parameters in gravity currents by data assimilation in a model hierarchy

    Directory of Open Access Journals (Sweden)

    A. Wirth

    2011-04-01

    Full Text Available This paper is the last in a series of three investigating the friction laws and their parametrisation in idealised gravity currents in a rotating frame. Results on the dynamics of a gravity current (Wirth, 2009 and on the estimation of friction laws by data assimilation (Wirth and Verron, 2008 are combined to estimate the friction parameters and discriminate between friction laws in non-hydrostatic numerical simulations of gravity current dynamics, using data assimilation and a reduced gravity shallow water model.

    I demonstrate, that friction parameters and laws in gravity currents can be estimated using data assimilation. The results clearly show that friction follows a linear Rayleigh law for small Reynolds numbers and the estimated value agrees well with the analytical value obtained for non-accelerating Ekman layers. A significant and sudden departure towards a quadratic drag law at an Ekman layer based Reynolds number of around 800 is shown, in agreement with classical laboratory experiments. The drag coefficient obtained compares well to friction values over smooth surfaces. I show that data assimilation can be used to determine friction parameters and discriminate between friction laws and that it is a powerful tool in systematically connecting models within a model hierarchy.

  1. The Research on Friction Characteristics of Non Smooth Bionic Mesoscopic Surface

    Directory of Open Access Journals (Sweden)

    Su Chunjian

    2014-12-01

    Full Text Available The application of using friction to transmit power and prevent slippage is very widely used, many animals have very strong adhesion climbing ability, and it has important theoretical significance and wide application prospect to research and the prepare bionic surface to increase transmission friction using the bionic technology. In recent years, the research of foot structure of climbing animals shows that their surface morphology has both macro and micro scale features, and only study from the macro to the micro scale surface structure can be better elucidate the mechanism of increasing-friction of climbing animal. This paper will study bionic surface structure on mesoscopic scale from micron to millimeter level, research the influence of foot structure of climbing animal under mesoscopic scale on characteristics of increasing friction using bionic technology, prepare the bionic non-smooth surface of convex or concave using bionic manufacturing technology, establish the friction model of non-smooth surface, investigate the increasing-friction mechanism of the bionic surface morphology on mesoscopic scales, reveals the influence of surface morphology, layout, size and material properties on the friction characteristics, provide the design of bionic friction surface and calculation method of friction coefficient and provide reliable theoretical basis for engineering application.

  2. Effect of surface finishing on friction and wear of Poly-Ether-Ether-Ketone (PEEK under oil lubrication

    Directory of Open Access Journals (Sweden)

    Thiago Fontoura de Andrade

    Full Text Available Abstract The tribological properties of poly-ether-ether-ketone (PEEK containing 30% of carbon fiber were studied in an oil-lubricated environment and different surface finishing of the metallic counterbody. Four different finishing processes, commonly used in the automotive industry, were chosen for this study: turning, grinding, honing and polishing. The test system used was tri-pin on disc with pins made of PEEK and counterbody made of steel; they were fully immersed in ATF Dexron VI oil. Some test parameters were held constant, such as the apparent pressure of 2 MPa, linear velocity of 2 m/s, oil temperature at 85 °C, and the time - 120 minutes. The lubrication regime for the apparent pressure of 1 MPa to 7 MPa range was also studied at different sliding speeds. A direct correlation was found between the wear rate, friction coefficient and the lubrication regime, wherein wear under hydrodynamic lubrication was, on average, approximately 5 times lower, and the friction coefficient 3 times lower than under boundary lubrication.

  3. Bottom friction optimization for a better barotropic tide modelling

    Science.gov (United States)

    Boutet, Martial; Lathuilière, Cyril; Son Hoang, Hong; Baraille, Rémy

    2015-04-01

    At a regional scale, barotropic tides are the dominant source of variability of currents and water heights. A precise representation of these processes is essential because of their great impacts on human activities (submersion risks, marine renewable energies, ...). Identified sources of error for tide modelling at a regional scale are the followings: bathymetry, boundary forcing and dissipation due to bottom friction. Nevertheless, bathymetric databases are nowadays known with a good accuracy, especially over shelves, and global tide models performances are better than ever. The most promising improvement is thus the bottom friction representation. The method used to estimate bottom friction is the simultaneous perturbation stochastic approximation (SPSA) which consists in the approximation of the gradient based on a fixed number of cost function measurements, regardless of the dimension of the vector to be estimated. Indeed, each cost function measurement is obtained by randomly perturbing every component of the parameter vector. An important feature of SPSA is its relative ease of implementation. In particular, the method does not require the development of tangent linear and adjoint version of the circulation model. Experiments are carried out to estimate bottom friction with the HYbrid Coordinate Ocean Model (HYCOM) in barotropic mode (one isopycnal layer). The study area is the Northeastern Atlantic margin which is characterized by strong currents and an intense dissipation. Bottom friction is parameterized with a quadratic term and friction coefficient is computed with the water height and the bottom roughness. The latter parameter is the one to be estimated. Assimilated data are the available tide gauge observations. First, the bottom roughness is estimated taking into account bottom sediment natures and bathymetric ranges. Then, it is estimated with geographical degrees of freedom. Finally, the impact of the estimation of a mixed quadratic/linear friction

  4. Friction and Shear Strength at the Nanowire–Substrate Interfaces

    Directory of Open Access Journals (Sweden)

    Gu Yi

    2009-01-01

    Full Text Available Abstract The friction and shear strength of nanowire (NW–substrate interfaces critically influences the electrical/mechanical performance and life time of NW-based nanodevices. Yet, very few reports on this subject are available in the literature because of the experimental challenges involved and, more specifically no studies have been reported to investigate the configuration of individual NW tip in contact with a substrate. In this letter, using a new experimental method, we report the friction measurement between a NW tip and a substrate for the first time. The measurement was based on NW buckling in situ inside a scanning electron microscope. The coefficients of friction between silver NW and gold substrate and between ZnO NW and gold substrate were found to be 0.09–0.12 and 0.10–0.15, respectively. The adhesion between a NW and the substrate modified the true contact area, which affected the interfacial shear strength. Continuum mechanics calculation found that interfacial shear strengths between silver NW and gold substrate and between ZnO NW and gold substrate were 134–139 MPa and 78.9–95.3 MPa, respectively. This method can be applied to measure friction parameters of other NW–substrate systems. Our results on interfacial friction and shear strength could have implication on the AFM three-point bending tests used for nanomechanical characterisation.

  5. Regularized friction and continuation: Comparison with Coulomb's law

    Science.gov (United States)

    Vigué, Pierre; Vergez, Christophe; Karkar, Sami; Cochelin, Bruno

    2017-02-01

    Periodic solutions of systems with friction are difficult to investigate because of the non-smooth nature of friction laws. This paper examines periodic solutions and most notably stick-slip, on a simple one-degree-of-freedom system (mass, spring, damper, and belt), with Coulomb's friction law, and with a regularized friction law (i.e. the friction coefficient becomes a function of relative speed, with a stiffness parameter). With Coulomb's law, the stick-slip solution is constructed step by step, which gives a usable existence condition. With the regularized law, the Asymptotic Numerical Method and the Harmonic Balance Method provide bifurcation diagrams with respect to the belt speed or normal force, and for several values of the regularization parameter. Formulations from the Coulomb case give the means of a comparison between regularized solutions and a standard reference. With an appropriate definition, regularized stick-slip motion exists, its amplitude increases with respect to the belt speed and its pulsation decreases with respect to the normal force.

  6. On the Friction and Wear Behaviors of Dental Machinable Porcelain

    Institute of Scientific and Technical Information of China (English)

    YU Hai-yang; ZHOU Zhong-rong; CAI Zhen-Bing

    2004-01-01

    In order to well design tribosystems of dental CAD-CAM restorations, an understanding of the tribological mechanisms of dental machinable porcelain are essential. The friction and wear behavior of new generation industrially prefabricated Cerec Vitablocs Mark Ⅱ against uniform Si3N4 ball has been performed using a small amplitude reciprocating apparatus under simulating oral conditions. The loads of 10-40 N, reciprocating amplitudes of 100-500 μm, frequencies of 1-4 Hz and two lubrications (no / artificial saliva lubrication) were selected. Tests lasting up to 10 000 cycles were conducted. The results show that Cerec Vitablocs Mark Ⅱ record a friction coefficient of 0.55-0.84. Artificial saliva plays a lubricant effect during wear process. Among three parameters of the test on friction coefficient and wear depth of dental machinable porcelains, the load effect is prominent. Abrasive wear is the main wear mechanism, but brittle cracks and delamination are more popular especially under unlubricated friction.

  7. On the Friction and Wear Behaviors of Dental Machinable Porcelain

    Institute of Scientific and Technical Information of China (English)

    YUHai-yang; ZHOUZhong-rong; CAIZhen-Bing

    2004-01-01

    In order to well design tribosystems of dental CAD-CAM restorations, an understanding of the tribological mechanisms of dental machinable porcelain are essential. The friction and wear behavior of new generation industrially prefabricated Cerec Vitablocs Mark II against uniform Si3N4ball has been performed using a small amplitude reciprocating apparatus under simulating oral conditions. The loads of 10-40N, reciprocating amplitudes of 100-500μm, frequencies of 1-4Hz and two lubrications (no / artificial saliva lubrication) were selected. Tests lasting up to 10 000 cycles were conducted. The results show that Cerec Vitablocs Mark Ⅱ record a friction coefficient of 0.55-0.84. Artificial saliva plays a lubricant effect during wear process. Among three parameters of the test on friction coefficient and wear depth of dental machinable porcelains, the load effect is prominent. Abrasive wear is the main wear mechanism, but brittle cracks and delamination are more popular especially under unlubricated friction.

  8. Circuit racing, track texture, temperature and rubber friction

    Science.gov (United States)

    Sharp, R. S.; Gruber, P.; Fina, E.

    2016-04-01

    Some general observations relating to tyre shear forces and road surfaces are followed by more specific considerations from circuit racing. The discussion then focuses on the mechanics of rubber friction. The classical experiments of Grosch are outlined and the interpretations that can be put on them are discussed. The interpretations involve rubber viscoelasticity, so that the vibration properties of rubber need to be considered. Adhesion and deformation mechanisms for energy dissipation at the interface between rubber and road and in the rubber itself are highlighted. The enquiry is concentrated on energy loss by deformation or hysteresis subsequently. Persson's deformation theory is outlined and the material properties necessary to apply the theory to Grosch's experiments are discussed. Predictions of the friction coefficient relating to one particular rubber compound and a rough surface are made using the theory and these are compared with the appropriate results from Grosch. Predictions from Persson's theory of the influence of nominal contact pressure on the friction coefficient are also examined. The extent of the agreement between theory and experiment is discussed. It is concluded that there is value in the theory but that it is far from complete. There is considerable scope for further research on the mechanics of rubber friction.

  9. Heterogeneity in friction strength of an active fault by incorporation of fragments of the surrounding host rock

    Science.gov (United States)

    Kato, Naoki; Hirono, Tetsuro

    2016-07-01

    To understand the correlation between the mesoscale structure and the frictional strength of an active fault, we performed a field investigation of the Atera fault at Tase, central Japan, and made laboratory-based determinations of its mineral assemblages and friction coefficients. The fault zone contains a light gray fault gouge, a brown fault gouge, and a black fault breccia. Samples of the two gouges contained large amounts of clay minerals such as smectite and had low friction coefficients of approximately 0.2-0.4 under the condition of 0.01 m s-1 slip velocity and 0.5-2.5 MP confining pressure, whereas the breccia contained large amounts of angular quartz and feldspar and had a friction coefficient of 0.7 under the same condition. Because the fault breccia closely resembles the granitic rock of the hangingwall in composition, texture, and friction coefficient, we interpret the breccia as having originated from this protolith. If the mechanical incorporation of wall rocks of high friction coefficient into fault zones is widespread at the mesoscale, it causes the heterogeneity in friction strength of fault zones and might contribute to the evolution of fault-zone architectures.

  10. Frictional properties of confined polymers

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, Vladimir N; Persson, Bo N J

    2008-01-01

    We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively...... independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to the squeezing pressure and finite at zero load, indicating an adhesional contribution to the friction force...

  11. Labor Supply and Optimization Frictions

    DEFF Research Database (Denmark)

    Søgaard, Jakob Egholt

    2015-01-01

    In this paper I investigate the nature of optimization frictions by studying the labor market of Danish students. This particular labor market is an interesting case study as it features a range of special institutional settings that affect students’ incentive to earn income and comparing outcomes...... across these setting effectively allow you to distinguish between different types of frictions. I find that the considered labor market is significantly affected by optimizations frictions, which masks the bunching at kink points normally associated with a positive labor supply elasticity under standard...

  12. Multimodal Friction Ignition Tester

    Science.gov (United States)

    Davis, Eddie; Howard, Bill; Herald, Stephen

    2009-01-01

    The multimodal friction ignition tester (MFIT) is a testbed for experiments on the thermal and mechanical effects of friction on material specimens in pressurized, oxygen-rich atmospheres. In simplest terms, a test involves recording sensory data while rubbing two specimens against each other at a controlled normal force, with either a random stroke or a sinusoidal stroke having controlled amplitude and frequency. The term multimodal in the full name of the apparatus refers to a capability for imposing any combination of widely ranging values of the atmospheric pressure, atmospheric oxygen content, stroke length, stroke frequency, and normal force. The MFIT was designed especially for studying the tendency toward heating and combustion of nonmetallic composite materials and the fretting of metals subjected to dynamic (vibrational) friction forces in the presence of liquid oxygen or pressurized gaseous oxygen test conditions approximating conditions expected to be encountered in proposed composite material oxygen tanks aboard aircraft and spacecraft in flight. The MFIT includes a stainless-steel pressure vessel capable of retaining the required test atmosphere. Mounted atop the vessel is a pneumatic cylinder containing a piston for exerting the specified normal force between the two specimens. Through a shaft seal, the piston shaft extends downward into the vessel. One of the specimens is mounted on a block, denoted the pressure block, at the lower end of the piston shaft. This specimen is pressed down against the other specimen, which is mounted in a recess in another block, denoted the slip block, that can be moved horizontally but not vertically. The slip block is driven in reciprocating horizontal motion by an electrodynamic vibration exciter outside the pressure vessel. The armature of the electrodynamic exciter is connected to the slip block via a horizontal shaft that extends into the pressure vessel via a second shaft seal. The reciprocating horizontal

  13. Onset of frictional sliding of rubber-glass contact under dry and lubricated conditions

    Science.gov (United States)

    Tuononen, Ari J.

    2016-06-01

    Rubber friction is critical in many applications ranging from automotive tyres to cylinder seals. The process where a static rubber sample transitions to frictional sliding is particularly poorly understood. The experimental and simulation results in this paper show a completely different detachment process from the static situation to sliding motion under dry and lubricated conditions. The results underline the contribution of the rubber bulk properties to the static friction force. In fact, simple Amontons’ law is sufficient as a local friction law to produce the correct detachment pattern when the rubber material and loading conditions are modelled properly. Simulations show that micro-sliding due to vertical loading can release initial shear stresses and lead to a high static/dynamic friction coefficient ratio, as observed in the measurements.

  14. Upset Prediction in Friction Welding Using Radial Basis Function Neural Network

    Directory of Open Access Journals (Sweden)

    Wei Liu

    2013-01-01

    Full Text Available This paper addresses the upset prediction problem of friction welded joints. Based on finite element simulations of inertia friction welding (IFW, a radial basis function (RBF neural network was developed initially to predict the final upset for a number of welding parameters. The predicted joint upset by the RBF neural network was compared to validated finite element simulations, producing an error of less than 8.16% which is reasonable. Furthermore, the effects of initial rotational speed and axial pressure on the upset were investigated in relation to energy conversion with the RBF neural network. The developed RBF neural network was also applied to linear friction welding (LFW and continuous drive friction welding (CDFW. The correlation coefficients of RBF prediction for LFW and CDFW were 0.963 and 0.998, respectively, which further suggest that an RBF neural network is an effective method for upset prediction of friction welded joints.

  15. Adhesion and friction of single-crystal diamond in contact with transition metals

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    An investigation was conducted to examine the adhesion and friction of single-crystal diamond in contact with various transition metals and the nature of metal transfer to diamond. Sliding friction experiments were conducted with diamond in sliding contact with the metals yttrium, titanium, zirconium, vanadium, iron, cobalt, nickel, tungsten, platinum, rhenium and rhodium. All experiments were conducted with loads of 0.05 to 0.3 N, at a sliding velocity of 0.003 m per minute, in a vacuum of 10 to the -8th Pa, at room temperature, and on the (111) plane of diamond with sliding in the 110 line type direction. The results of the investigation indicate that the coefficient of friction for diamond in contact with various metals is related to the relative chemical activity of the metals in high vacuum. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to the surface of diamond in sliding.

  16. Simulation of granular packing of frictional cohesive particles with Gaussian size distribution

    Science.gov (United States)

    Jia, Tao; Gao, Di

    2016-09-01

    The granular packing of frictional cohesive particles with Gaussian distribution is investigated based on distinct element method. Different sliding frictional coefficients are considered in the simulation. Due to the inelastic collision between the particles, the agglomeration of the particles occurs and the packing structure is formed finally. The range of the diameter of the particle is between 50 and 100 μm, and the distribution of the particle diameter is Gaussian. The inelastic interaction is caused by the viscoelastic force and the frictional force. The internal structure of the granular matter is quantified by the coordination number, packing density, and the force distribution. It is found that the increase in the sliding frictional coefficient looses the packing structure, and the distribution range of the contact force is larger than that of the van der Waals force.

  17. Some Aspects Concerning the Behaviour of Friction Materials at Low and Very Low Sliding Speeds

    Directory of Open Access Journals (Sweden)

    N.A. Stoica

    2015-09-01

    Full Text Available The tribological aspects concerning the behaviour of friction materials in the range of low and very low sliding speeds (0.2 – 200 mm/min are essentially different of those in the high sliding speeds range. This paper aims to study the stick-slip phenomenon which occurs in the range of low and very low speeds. Typically, for the stick-slip phenomenon to occur, the static friction coefficient between the two contact surfaces of the friction materials must be larger than the kinetic friction coefficient. For disc brakes, the stick-slip phenomenon is mentioned in many specialized scientific papers. The phenomenon is manifested through self-induced vibrations. The experimental results were obtained on a dedicated testing machine where the parasite stick-slip motion is reduced through the use of bearings.

  18. Simulation of rolling friction in the working stands of wide-strip mills

    Science.gov (United States)

    Garber, E. A.; Samarin, S. N.; Traino, A. I.; Ermilov, V. V.

    2007-04-01

    The energy consumed for rolling friction in the interroll contact area in the working stands of cold-rolling and pinch-pass mils intended for the production of wide steel strips has been analyzed. The coefficients and power of rolling friction are obtained for the first time using the databases of the process control systems of operating mills and simulating these quantities. A statistically reliable regression relation is obtained between the coefficient of rolling friction and the significant parameters of rolling and skin rolling (i.e., the interroll force, the roll speed, and the roll body roughness). The power fraction consumed for rolling friction is found to reach 60 80% of the total power of the main drive of working stands for skin rolling and 30 50% for cold rolling. Therefore, it is necessary to take into account these power losses in designing mills and developing technological cold-rolling conditions.

  19. Investigation of influencing factors on friction during ring test in hot forging using FEM simulation

    Science.gov (United States)

    Sethy, Ritanjali; Galdos, Lander; Mendiguren, Joseba; Sáenz de Argandoña, Eneko

    2016-10-01

    Few studies have been undertaken to understand the friction in hot forming, especially when addressing the issue of varying input parameters. Better understanding of their role is therefore needed in order to obtain accurate results in numerical simulations. This paper numerically investigates the high temperature ring compression test to evaluate how frictional behaviour is affected by variations of input parameters (i.e. press velocity, Heat Transfer Coefficient (HTC), processing time, mesh size, material and tool temperature). The high temperature ring-compression process was simulated by means of Finite Element Modelling (FEM) using FORGE-3D software with the ring made of AISI 304L having ratio of outer diameter, inner diameter and height of 30:15:10. According to the results, the HTC and the press velocity have most significant effects on frictional behavior and the calibration curves needed to calculate the friction coefficients after experimental testing.

  20. Multiple solutions of stick and separation type in the Signorini model with Coulomb friction

    Energy Technology Data Exchange (ETDEWEB)

    Hild, P. [Univ. de Franche-Comte, 25 - Besancon (France). Lab. de Mathematiques

    2005-09-01

    This paper proves the existence of multiple solutions to the Coulomb friction problem with Signorini contact conditions in continuum linear elasticity. We consider a body lying on a rigid foundation and we propose a method in order to exhibit two solutions to the frictional contact problem when the friction coefficient is large enough: one solution which separates from the foundation and another one which remains stuck on the foundation. We apply the method to the simple class of problems with triangular bodies and linear displacement fields and we describe the cases in which such multiple solutions exist. Denoting by {mu} the friction coefficient, we come to the conclusion that such nonuniqueness cases may appear when {mu}>1. (orig.)

  1. A Pedagogical Model of Static Friction

    CERN Document Server

    Pickett, Galen T

    2015-01-01

    While dry Coulombic friction is an elementary topic in any standard introductory course in mechanics, the critical distinction between the kinetic and static friction forces is something that is both hard to teach and to learn. In this paper, I describe a geometric model of static friction that may help introductory students to both understand and apply the Coulomb static friction approximation.

  2. An engineering approach to dry friction behaviour of numerous engineering plastics with respect to the mechanical properties

    Directory of Open Access Journals (Sweden)

    G. Kalacska

    2013-02-01

    Full Text Available Twenty-one different commercial-grade engineering polymers, including virgin and composite types, were selected for testing, based on mechanical engineering practices. Three groups were formed according to typical applications: 1 Sliding machine element materials; 2 Mechanically load-carrying machine element materials that are often subjected to friction and wear effects; and 3 Additional two amorphous materials used as chemically resistant materials that have rare sliding load properties. The friction running-in state was tested using a dynamic pin-on-plate test rig. During steady-state friction tests, two pv regimes (0.8 and 2 MPa"ms–1 were analysed by a pin-on-disc test system. Based on the measured forces on ground structural steel, surface friction coefficients were calculated and analysed with respect to the mechanical effects of friction. The friction results were evaluated by the measured mechanical properties: yield stress, Shore D hardness, Young’s modulus and elongation at the break. The three material groups exhibited different trends in friction with respect to changing mechanical properties. Linear (with varying positive and negative slopes, logarithmic and exponential relationships were observed, and occasionally there were no effects observed. At steady-state friction, the elongation at the break had less effect on the friction coefficients. The dynamic sliding model, which correlates better to real machine element applications, showed that increasing hardness and yield stress decreases friction. During steady-state friction, an increase in pv regime often changed the sign of the linear relationship between the material property and the friction, which agrees with the frictional theory of polymer/steel sliding pairs.

  3. Friction Material Composites Materials Perspective

    CERN Document Server

    Sundarkrishnaa, K L

    2012-01-01

    Friction Material Composites is the first of the five volumes which strongly educates and updates engineers and other professionals in braking industries, research and test labs. It explains besides the formulation of design processes and its complete manufacturing input. This book gives an idea of mechanisms of friction and how to control them by designing .The book is  useful for designers  of automotive, rail and aero industries for designing the brake systems effectively with the integration of friction material composite design which is critical. It clearly  emphasizes the driving  safety and how serious designers should  select the design input. The significance of friction material component like brake pad or a liner as an integral part of the brake system of vehicles is explained. AFM pictures at nanolevel illustrate broadly the explanations given.

  4. The temperature dependence of the friction in the fission

    Energy Technology Data Exchange (ETDEWEB)

    Yamaji, Shuhei [Institute of Physical and Chemical Research, Wako, Saitama (Japan)

    1996-03-01

    We study the slow collective motion at finite excitation on the basis of the linear response theory. The transport coefficients such as friction {gamma}, inertia M and local stiffness C formulated within a locally harmonic approximation are computed along the fission path of {sup 224}Th. It is found that the effective damping rate {eta} = {gamma}/=2{radical}(M|C|)= increases with the temperature T in accord with the fission experiment with the emission of {gamma}-rays. (author)

  5. Negative Average Preference Utilitarianism

    Directory of Open Access Journals (Sweden)

    Roger Chao

    2012-03-01

    Full Text Available For many philosophers working in the area of Population Ethics, it seems that either they have to confront the Repugnant Conclusion (where they are forced to the conclusion of creating massive amounts of lives barely worth living, or they have to confront the Non-Identity Problem (where no one is seemingly harmed as their existence is dependent on the “harmful” event that took place. To them it seems there is no escape, they either have to face one problem or the other. However, there is a way around this, allowing us to escape the Repugnant Conclusion, by using what I will call Negative Average Preference Utilitarianism (NAPU – which though similar to anti-frustrationism, has some important differences in practice. Current “positive” forms of utilitarianism have struggled to deal with the Repugnant Conclusion, as their theory actually entails this conclusion; however, it seems that a form of Negative Average Preference Utilitarianism (NAPU easily escapes this dilemma (it never even arises within it.

  6. Tire/runway friction interface

    Science.gov (United States)

    Yager, Thomas J.

    1990-01-01

    An overview is given of NASA Langley's tire/runway pavement interface studies. The National Tire Modeling Program, evaluation of new tire and landing gear designs, tire wear and friction tests, and tire hydroplaning studies are examined. The Aircraft Landing Dynamics Facility is described along with some ground friction measuring vehicles. The major goals and scope of several joint FAA/NASA programs are identified together with current status and plans.

  7. Peak mass and dynamical friction

    CERN Document Server

    Del Popolo, A

    1995-01-01

    We show how the results given by several authors relatively to the mass of a density peak are changed when small scale substructure induced by dynamical friction are taken into account. The peak mass obtained is compared to the result of Peacock \\& Heavens (1990) and to the peak mass when dynamical friction is absent to show how these effects conspire to reduce the mass accreted by the peak.

  8. Hard and low friction nitride coatings and methods for forming the same

    Science.gov (United States)

    Erdemir, Ali; Urgen, Mustafa; Cakir, Ali Fuat; Eryilmaz, Osman Levent; Kazmanli, Kursat; Keles, Ozgul

    2007-05-01

    An improved coating material possessing super-hard and low friction properties and a method for forming the same. The improved coating material includes the use of a noble metal or soft metal homogeneously distributed within a hard nitride material. The addition of small amounts of such metals into nitrides such as molybdenum nitride, titanium nitride, and chromium nitride results in as much as increasing of the hardness of the material as well as decreasing the friction coefficient and increasing the oxidation resistance.

  9. Friction Properties of Polished Cvd Diamond Films Sliding against Different Metals

    Science.gov (United States)

    Lin, Zichao; Sun, Fanghong; Shen, Bin

    2016-11-01

    Owing to their excellent mechanical and tribological properties, like the well-known extreme hardness, low coefficient of friction and high chemical inertness, chemical vapor deposition (CVD) diamond films have found applications as a hard coating for drawing dies. The surface roughness of the diamond films is one of the most important attributes to the drawing dies. In this paper, the effects of different surface roughnesses on the friction properties of diamond films have been experimentally studied. Diamond films were fabricated using hot filament CVD. The WC-Co (Co 6wt.%) drawing dies were used as substrates. A gas mixture of acetone and hydrogen gas was used as the feedstock gas. The CVD diamond films were polished using mechanical polishing. Polished diamond films with three different surface roughnesses, as well as the unpolished diamond film, were fabricated in order to study the tribological performance between the CVD diamond films and different metals with oil lubrication. The unpolished and polished CVD diamond films are characterized with scanning electron microscope (SEM), atomic force microscope (AFM), surface profilometer, Raman spectrum and X-ray diffraction (XRD). The friction examinations were carried out by using a ball-on-plate type reciprocating friction tester. Low carbide steel, stainless steel, copper and aluminum materials were used as counterpart balls. Based on this study, the results presented the friction coefficients between the polished CVD films and different metals. The friction tests demonstrate that the smooth surface finish of CVD diamond films is beneficial for reducing their friction coefficients. The diamond films exhibit low friction coefficients when slid against the stainless steel balls and low carbide steel ball, lower than that slid against copper ball and aluminum ball, attributed to the higher ductility of copper and aluminum causing larger amount of wear debris adhering to the sliding interface and higher adhesive

  10. Adhesion wear mechanisms under dry friction of titanium alloys in vacuum

    Energy Technology Data Exchange (ETDEWEB)

    Lebedeva, I.L.; Presnyakova, G.N. (Physico-Technical Inst. for Low Temperature Physics and Engineering, Ukrainian Academy of Sciences, Kharkov (Ukrainian SSR))

    1991-08-15

    Physicochemical processes taking place in the surface layers of titanium alloys were studied. For vacuum conditions, a range of external parameters was proved to exist where the alloys have high wear resistance and a low coefficient of friction. The transition from seizure, with tearing of the material at a large depth, to fatigue wear is related to surface hardening due to {alpha} {r reversible} {beta} transitions under friction. Thermodynamic parameters were calculated and the criteria of protective secondary structure formation defined. (orig.).

  11. Slip versus Friction : Modifying the Navier condition

    Science.gov (United States)

    Kotsalis, Evangelos; Walther, Jens; Koumoutsakos, Petros

    2006-03-01

    The modeling of fluid-solid interfaces remains one of the key challenges in fluid mechanics. The prevailing model, attributed to Navier, defines the fluid ``slip'' velocity as proportional to the wall shear and a parameter defined as the slip length. Several works have in turn proposed models for this slip length but no universal model for the slip velocity has been accepted. We present results from large scale molecular dynamics simulations of canonical flow problems, indicating, that the inadequacy of this classic model, stems from not properly accounting for the pressure field. We propose and validate a new model, based on the fundamental observation that the finite ``slip'' velocity is a result of an imbalance between fluid and solid intermolecular forces. An excess force on the fluid elements will lead to their acceleration which in turn may result in a slip velocity at the interface. We formulate the slip velocity in terms of fluid-solid friction Ff and propose a generalized boundary condition: Ff= Fs+ Fp= λuus+ λpp where p denotes the pressure, and λuand λp the viscous and static friction coefficients, for which universal constants are presented. We demonstrate that the present model can overcome difficulties encountered by the classical slip model in canonical flow configurations.

  12. Molecular friction in an actomyosin molecular machine.

    Science.gov (United States)

    Suda, H

    1990-10-07

    In muscle contraction, it has been widely recognized that a binding state exists between myosin and actin in the presence of Mg-ATP. To estimate the magnitude of binding strength, I introduce a concept of frictional phenomena which occurs between two sliding bodies in contact each other. In such cases, the sliding speed can be formulated as a function of the actin-myosin bond strength. In order to validate this, the present theory is applied for the two movement assay systems with no external load; one movement assay of Phalloidin Rhodamine bound F-actin on a myosin coated hydrophobic cover glass and another assay of myosin coated beads along actin cables of Nitella. If a coefficient of 0.005 is applied to the kinetic friction, 1pN for the sliding force per cross-bridge and 10 microns sec-1 for the sliding speed, it is found that the bond strength between actin and one myosin head is about 200 pN in the contracting state.

  13. Evaluation and Description of Friction between an Electro-Deposited Coating and a Ceramic Ball under Fretting Condition

    Directory of Open Access Journals (Sweden)

    Kyungmok Kim

    2015-07-01

    Full Text Available This article describes fretting behavior of zirconia and silicon nitride balls on an electro-deposited coating. Fretting tests are performed using a ball-on-flat configuration. The evolution of the kinetic friction coefficient is determined, along with slip ratio. Experimental results show that the steady-state friction coefficient between ceramic balls (Si3N4 and ZrO2 and an electro-deposited coating is about 0.06, lower than the value between AISI 52100 ball and the coating. After a steady-state sliding, the transition of the friction coefficient is varied with a ball. The friction coefficient for ZrO2 balls became a critical value after higher fretting cycles than those for Si3N4 and AISI 52100 balls. In addition, it is identified that two parameters can describe the transition of the friction coefficient. Finally, the evolution of the friction coefficient is expressed as an exponential or a power-law form.

  14. A new visco-elastic contact model of traveling wave ultrasonic motor with stator frictional layer

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A new contact model of traveling wave ultrasonic motor (TWUSM) with a visco-elastic stator frictional layer was presented. In this model, the initial boundaries were revised, and the rotor revolution speed could be calculated iteratively. This model was compared with compliant slider and rigid stator model. The results of motor characteristics simulations showed that the motors based on this model would gain bigger stall torque. Then the friction and wear characteristics of two models were analyzed. The motors based on this model had lower coefficient of friction and better wear resistance.

  15. Tribological Properties of the Semi-metallic Friction Material with Nano-SiC

    Institute of Scientific and Technical Information of China (English)

    CHENDong; HUANGPing; ZHUWen-jian

    2004-01-01

    The tribological properties of the semi-metallic friction materials with nano-SiC were studied by the contrast experiments. The experimental result indicates that when the nano-SiC powder substitutes the generalSiC powder, the friction coefficient is not obviously improved. On the contrary, the wear rate increases a little.The friction surfaces and the mixed powder were examined by a scanning electron microscope and the experimental data were analysed. The main reason, which leads to the high wear, is found.

  16. Departure of microscopic friction from macroscopic drag in molecular fluid dynamics

    Science.gov (United States)

    Hanasaki, Itsuo; Fujiwara, Daiki; Kawano, Satoyuki

    2016-03-01

    Friction coefficient of the Langevin equation and drag of spherical macroscopic objects in steady flow at low Reynolds numbers are usually regarded as equivalent. We show that the microscopic friction can be different from the macroscopic drag when the mass is taken into account for particles with comparable scale to the surrounding fluid molecules. We illustrate it numerically by molecular dynamics simulation of chloride ion in water. Friction variation by the atomistic mass effect beyond the Langevin regime can be of use in the drag reduction technology as well as the electro or thermophoresis.

  17. Wear of Polished Steel Surfaces in Dry Friction Linear Contact on Polimer Composites with Glass Fibres

    Directory of Open Access Journals (Sweden)

    D. Rus

    2013-12-01

    Full Text Available It is generally known that the friction and wear between polymers and polished steel surfaces has a special character, the behaviour to friction and wear of a certain polymer might not be valid for a different polymer, moreover in dry friction conditions. In this paper, we study the reaction to wear of certain polymers with short glass fibres on different steel surfaces, considering the linear friction contact, observing the friction influence over the metallic surfaces wear. The paper includes also its analysis over the steel’s wear from different points of view: the reinforcement content influence and tribological parameters (load, contact pressure, sliding speed, contact temperature, etc.. Thus, we present our findings related to the fact that the abrasive component of the friction force is more significant than the adhesive component, which generally is specific to the polymers’ friction. Our detections also state that, in the case of the polyamide with 30% glass fibres, the steel surface linear wear rate order are of 10-4 mm/h, respectively the order of volumetric wear rate is of 10-6 cm3 /h. The resulting volumetric wear coefficients are of the order (10-11 – 10-12 cm3/cm and respectively linear wear coefficients of 10-9 mm/cm.

  18. FRICTION MODELING OF Al-Mg ALLOY SHEETS BASED ON MULTIPLE REGRESSION ANALYSIS AND NEURAL NETWORKS

    Directory of Open Access Journals (Sweden)

    Hirpa G. Lemu

    2017-03-01

    Full Text Available This article reports a proposed approach to a frictional resistance description in sheet metal forming processes that enables determination of the friction coefficient value under a wide range of friction conditions without performing time-consuming experiments. The motivation for this proposal is the fact that there exists a considerable amount of factors affect the friction coefficient value and as a result building analytical friction model for specified process conditions is practically impossible. In this proposed approach, a mathematical model of friction behaviour is created using multiple regression analysis and artificial neural networks. The regression analysis was performed using a subroutine in MATLAB programming code and STATISTICA Neural Networks was utilized to build an artificial neural networks model. The effect of different training strategies on the quality of neural networks was studied. As input variables for regression model and training of radial basis function networks, generalized regression neural networks and multilayer networks the results of strip drawing friction test were utilized. Four kinds of Al-Mg alloy sheets were used as a test material.

  19. Improving the Friction Durability of Magnetic Head-Disk Interfaces by Thin Lubricant Films

    Directory of Open Access Journals (Sweden)

    Shojiro Miyake

    2016-01-01

    Full Text Available Nanowear and viscoelasticity were evaluated to study the nanotribological properties of lubricant films of Z-tetraol, D-4OH, and A20H, including their retention and replenishment properties. For A20H and thick Z-tetraol-coated disks, the disk surface partially protrudes, and the phase lag (tan⁡δ increases with friction. This result is consistent with replenishment of the lubricant upon tip sliding. For the D-4OH-coated disk, the tan⁡δ value decreases with tip sliding, similar to the case for the unlubricated disk. The durability of the lubricant-coated magnetic disks was then evaluated by load increase and decrease friction tests. The friction force of the unlubricated disk rapidly increases after approximately 30 reciprocating cycles, regardless of the load. The lubrication state can be estimated by mapping the dependence of friction coefficient on the reciprocating cycle number and load. The friction coefficient can be classified into one of four areas. The lowest friction area constitutes fluid lubrication. The second area constitutes the transition to mixed lubrication. The third area constitutes boundary lubrication. The highest friction of the fourth area results from surface fracture. The boundary lubricating area of the A20H lubricant was wide, because of its good retention and replenishment properties.

  20. Frictional Effects on Gear Tooth Contact Analysis

    OpenAIRE

    Zheng Li; Ken Mao

    2013-01-01

    The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented us...

  1. Research on torsional friction behavior and fluid load support of PVA/HA composite hydrogel.

    Science.gov (United States)

    Chen, Kai; Zhang, Dekun; Yang, Xuehui; Cui, Xiaotong; Zhang, Xin; Wang, Qingliang

    2016-09-01

    Hydrogels have been extensively studied for use as synthetic articular cartilage. This study aimed to investigate (1) the torsional friction contact state and the transformation mechanism of PVA/HA composite hydrogel against CoCrMo femoral head and (2) effects of load and torsional angle on torsional friction behavior. The finite element method was used to study fluid load support of PVA/HA composite hydrogel. Results show fluid loss increases gradually of PVA/HA composite hydrogel with torsional friction time, leading to fluid load support decreases. The contact state changes from full slip state to stick-slip mixed state. As the load increases, friction coefficient and adhesion zone increase gradually. As the torsional angle increases, friction coefficient and slip trend of the contact interface increase, resulting in the increase of the slip zone and the reduction of the adhesion zone. Fluid loss increases of PVA/HA composite hydrogel as the load and the torsional angle increase, which causes the decrease of fluid load support and the increase of friction coefficient.

  2. Effects of the ratio of hardness to Young's modulus on the friction and wear behavior of bilayer coatings

    Science.gov (United States)

    Ni, Wangyang; Cheng, Yang-Tse; Lukitsch, Michael J.; Weiner, Anita M.; Lev, Lenoid C.; Grummon, David S.

    2004-11-01

    We present a study of the effects of the ratio of hardness to Young's modulus on the friction and wear behavior of layered composite coatings. Layered coating structures with the same surface coating but different interlayers were prepared by physical vapor deposition. We found that the ratio of hardness to Young's modulus plays an important role in determining the friction coefficient and wear resistance of layered composite coatings. A low friction coefficient and high wear resistance can be achieved in structures with high ratio of hardness to Young's modulus and moderately high hardness.

  3. Molecular dynamics simulations of metallic friction and of its dependence on electric currents - development and first results

    Science.gov (United States)

    Meintanis, Evangelos Anastasios

    We have extended the HOLA molecular dynamics (MD) code to run slider-on-block friction experiments for Al and Cu. Both objects are allowed to evolve freely and show marked deformation despite the hardness difference. We recover realistic coefficients of friction and verify the importance of cold-welding and plastic deformations in dry sliding friction. Our first data also show a mechanism for decoupling between load and friction at high velocities. Such a mechanism can explain an increase in the coefficient of friction of metals with velocity. The study of the effects of currents on our system required the development of a suitable electrodynamic (ED) solver, as the disparity of MD and ED time scales threatened the efficiency of our code. Our first simulations combining ED and MD are presented.

  4. Friction and wear behaviour of Mo-W doped carbon-based coating during boundary lubricated sliding

    Science.gov (United States)

    Hovsepian, Papken Eh.; Mandal, Paranjayee; Ehiasarian, Arutiun P.; Sáfrán, G.; Tietema, R.; Doerwald, D.

    2016-03-01

    A molybdenum and tungsten doped carbon-based coating (Mo-W-C) was developed in order to provide low friction in boundary lubricated sliding condition at ambient and at high temperature. The Mo-W-C coating showed the lowest friction coefficient among a number of commercially available state-of-the-art DLC coatings at ambient temperature. At elevated temperature (200 °C), Mo-W-C coating showed a significant reduction in friction coefficient with sliding distance in contrast to DLC coatings. Raman spectroscopy revealed the importance of combined Mo and W doping for achieving low friction at both ambient and high temperature. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon debris (from coating) and 'in situ' formed metal sulphides (WS2 and MoS2, where metals were supplied from coating and sulphur from engine oil) in the transfer layer.

  5. Tribological Behavior of Babbitt Alloy Rubbing Against Si3N4 and Steel Under Dry Friction Condition

    Science.gov (United States)

    Ji, Xianbing; Chen, Yinxia

    2016-03-01

    The tribological behavior of Babbitt alloy rubbing with Si3N4 ball and steel ball with various sliding speeds at dry friction condition was investigated. It was found that B88 alloy rubbing with Si3N4 ball and steel ball possesses a low sliding wear resistance at dry friction. The wear rate is above 10-4 mm3/Nm, and the friction coefficient is from 0.2 to 0.4. At low sliding speed of 0.05-0.1 m/s, the mainly wear mechanisms are microgroove and fatigue wear, while at high sliding speed of 0.5 m/s, the wear mechanisms depend on plastic deformation and delamination. The high wear rate indicates that it is needed to prevent Babbitt alloy from working at dry friction conditions, while the low friction coefficient suggests that it is not easy to the occurrence of cold weld.

  6. The role of frictional strength on plate coupling at the subduction interface

    KAUST Repository

    Tan, Eh

    2012-10-01

    At a subduction zone the amount of friction between the incoming plate and the forearc is an important factor in controlling the dip angle of subduction and the structure of the forearc. In this paper, we investigate the role of the frictional strength of sediments and of the serpentinized peridotite on the evolution of convergent margins. In numerical models, we vary thickness of a serpentinized layer in the mantle wedge (15 to 25km) and the frictional strength of both the sediments and serpentinized mantle (friction angle 1 to 15, or static friction coefficient 0.017 to 0.27) to control the amount of frictional coupling between the plates. With plastic strain weakening in the lithosphere, our numerical models can attain stable subduction geometry over millions of years. We find that the frictional strength of the sediments and serpentinized peridotite exerts the largest control on the dip angle of the subduction interface at seismogenic depths. In the case of low sediment and serpentinite friction, the subduction interface has a shallow dip, while the subduction zone develops an accretionary prism, a broad forearc high, a deep forearc basin, and a shallow trench. In the high friction case, the subduction interface is steep, the trench is deeper, and the accretionary prism, forearc high and basin are all absent. The resultant free-air gravity and topographic signature of these subduction zone models are consistent with observations. We believe that the low-friction model produces a geometry and forearc structure similar to that of accretionary margins. Conversely, models with high friction angles in sediments and serpentinite develop characteristics of an erosional convergent margin. We find that the strength of the subduction interface is critical in controlling the amount of coupling at the seismogenic zone and perhaps ultimately the size of the largest earthquakes at subduction zones. © 2012. American Geophysical Union. All Rights Reserved.

  7. Investigation of friction characteristics in segmented piston ring liner assembly of IC engine

    Directory of Open Access Journals (Sweden)

    Tejaskumar Chaudhari

    2016-09-01

    Full Text Available The friction at the piston ring cylinder liner assembly (PRLA is a major contributor in the total friction losses in the I.C. engine. New materials, coatings and high-tech machining processes that previously were considered to be too expensive and therefore only used in complex applications are today becoming more affordable. A significant amount of the total power loss in a modern automotive engine is due to the Friction interaction between the top compression ring and the cylinder liner, especially at the TDC and BDC where boundary lubrication exists. The change in piston speed is accompanied with change the lubrication regime in the cylinder, which results change in friction between the ring and the liner during the entire stroke of the piston. Theoretical modelling of friction force from the various sources of friction will be compared to experimental results for analysing the tribological characteristics. The appropriate sample of piston ring and cylinder liner pair is developed for studying the different tribological parameters on Reciprocating Tribometer. The variable parameters are engine speed, oil viscosity, and load. The experimental results and observations are studied under different operating conditions in speed ranges from 300 rpm to 1500 rpm with constant load of 60 N. It can be seen that as speed increases, the friction force and friction coefficient also decreases.

  8. Influence of composition on friction-wear behavior of composite materials reinforced by brass fibers

    Institute of Scientific and Technical Information of China (English)

    JIA Xian; LING Xiaomei

    2003-01-01

    In the study, for the composite materials reinforced by brass fibers, the influence of dominant ingredients, such as organic adhesion agent, cast iron debris, brass fiber, and graphite powder, on the friction-wear characteristics was investigated. The friction-wear experiment was carried out on the block-on-ring tribometer MM200. The worn surfaces of the friction pair consisting of the composite materials and grey cast iron HT200 under dry sliding friction were examined using scanning electron microscope (SEM), energy dispersive analysis (EDX) and differential thermal analysis-thermogravimetric analysis (DTA-TAG). The experimental results showed that the friction coefficient and the wear loss of the composite material increase obviously with the increase of cast iron debris content, but decrease obviously with the increase of graphite powder content, and increase a little when the mass fraction of brass fiber was over 19%, and the orientation of brass fiber has obvious influence on friction-wear property. When the mass fraction of organic adhesion agent was about 10-11%, the composite materials have an excellent friction-wear performance. The friction heat can pyrolyze organic ingredient in worn surface layer.

  9. Effects of Rare Earths on Properties and Microstructure of Automotive Friction Materials

    Institute of Scientific and Technical Information of China (English)

    Xu Yue; Lu Liguo; Bai Jing

    2007-01-01

    Rare earth compounds as modifiers used widely in modern friction materials can enhance the interracial binding of constituents of materials and improve the comprehensive properties of materials evidently. However, there are still few reports on application of rare earth in automotive friction materials. In order to study the effect mechanism of rare earths in friction materials, a rare earth compound was selected as additive and the effects of materials doped with or without rare earth on friction and wear properties of materials were studied. The microstructure and worn surface morphology were observed by scanning electron microscopy and the macro performance was discussed. Worn surface element constitution of materials was analyzed by energy dispersive spectroscopy. Effect mechanism of rare earths on friction and wear behaviors of friction materials were discussed. The results show that doping rare earths in friction materials can stabilize friction Coefficient, lower the wear rate of materials and increase the impact strength of materials. The flexibility and fracture resistance of materials is greatly improved. Worn surface of materials doped with rare earth is compact and the surface adhesion is greatly enhanced.

  10. Frictional heat transfer regularity of the fluid film in mechanical seals

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The frictional heat transfer regularity in the mechanical seal system consisting of the rotating ring, the stationary ring, the fluid film in the end faces and the sealed medium was investigated. The primary factors affecting the frictional heat transfer regularity, such as the heat transfer coefficients from the rings to the sealed medium, the frictional heat flux, the frictional heat distribution ratio and so on, were discussed. The equations for calculating the temperature field both in the sealing members and in the fluid film were derived. The coupling analysis of the frictional heat of the fluid film and the thermal deformation of the two end faces of the rings was carried out to obtain the separation angle of the two deformed end faces in consideration of the viscosity change of the fluid film. The results indicate that the frictional heat of the fluid film heavily affects its characteristic and the sealing performance of mechanical seals. The frictional heat changes not only the shape of the gap between the end faces but also the viscosity of the fluid film, and thereupon leads to the increase of the leakage rate. The maximum temperature of the system is at the inner radius of the fluid film, and most of the frictional heat is conducted by the rotating ring. Based on the heat transfer analysis method put forward in this paper, the parameterized design of mechanical seals can be realized to determine the best geometrical parameters and to select the appropriate material of the sealing members.

  11. Research on measurement and modeling of the gastro intestine's frictional characteristics

    Science.gov (United States)

    Wang, Kun Dong; Yan, Guo Zheng

    2009-01-01

    The frictional characteristics of an intestine are required basically for the development of a noninvasive endoscope for the human intestine. The frictional force is tested by measuring the current of the motor hauling the frictional coupons at an even speed. A multifunction data acquisition device with model NI-6008 USB is used and the data process is performed on the Labview software. Two kinds of materials with aluminum and copper are used. The surfaces are designed as triangle, rectangular, cylindrical and plane forms. The tested results indicate that the frictional resistance force includes the nominal frictional force and the visco-adhesive force. When the surface contour changes from the triangle to the rectangular, to the cylindrical and finally to the plane, the nominal frictional coefficients will decrease and the visco-adhesive force will increase. The nominal frictional force is related to the elastic restoring force, the real frictional force and the contact angle. The cohesive force is determined by the contact area and the contact angle. This research will provide some preliminary references to the design and the parameter selection of locomotion devices in the human gastro-intestine.

  12. Wave Reflection Coefficient Spectrum

    Institute of Scientific and Technical Information of China (English)

    俞聿修; 邵利民; 柳淑学

    2003-01-01

    The wave reflection coefficient frequency spectrum and directional spectrum for concrete face slope breakwaters and rubble mound breakwaters are investigated through physical model tests in the present study. The reflection coefficients of oblique irregular waves are analyzed by the Modified Two-Point Method (MTPM) proposed by the authors. The results show that the wave reflection coefficient decreases with increasing wave frequency and incident angle or decreasing structure slope. The reflection coefficient frequency spectrum and its variation with Iribarren number are given in this paper. The paper also suggests an empirical 3-dimensional reflection coefficient spectrum, i.e. reflection coefficient directional spectrum, which can be used to illustrate quantitatively the variation of reflection coefficient with the incident angle and the Iribarren number for oblique irregular waves.

  13. Friction and wear measurements of 50 keV N implanted stainless steels

    Science.gov (United States)

    Ikeyama, Masami; Miyagawa, Soji; Clissold, Ronald A.; Wielunski, Leszek S.; Swain, Michael V.

    1997-05-01

    Features of friction, wear and hardness of 50 keV nitrogen implanted 13Cr type, C and V rich stainless steel was studied. The implantation was carried out at room temperature (300 K) or about 800 K to the doses of 1 × 10 18 and 5 × 10 17 ions/cm 2. Friction coefficient was measured using steel or silicon nitride balls with the loads of 98 to 980 mN. Friction coefficient depended on upper contact ball materials and loads, and changed from an initial value of 0.1 to final values between 0.2 and 0.8. After implantation, the surface became softer due to amorphization, however, it became relatively harder around the projected range of implanted N. 800 K implantation reduced the amorphization and enhanced diffusion of nitrogen. For the silicon nitride ball, implanted surfaces showed a lower friction coefficient than unimplanted region, particularly for 800 K implantation. When the friction coefficient increased, a considerable amount of adhered debris was observed on stainless steel surfaces.

  14. Model averaging and muddled multimodel inferences.

    Science.gov (United States)

    Cade, Brian S

    2015-09-01

    Three flawed practices associated with model averaging coefficients for predictor variables in regression models commonly occur when making multimodel inferences in analyses of ecological data. Model-averaged regression coefficients based on Akaike information criterion (AIC) weights have been recommended for addressing model uncertainty but they are not valid, interpretable estimates of partial effects for individual predictors when there is multicollinearity among the predictor variables. Multicollinearity implies that the scaling of units in the denominators of the regression coefficients may change across models such that neither the parameters nor their estimates have common scales, therefore averaging them makes no sense. The associated sums of AIC model weights recommended to assess relative importance of individual predictors are really a measure of relative importance of models, with little information about contributions by individual predictors compared to other measures of relative importance based on effects size or variance reduction. Sometimes the model-averaged regression coefficients for predictor variables are incorrectly used to make model-averaged predictions of the response variable when the models are not linear in the parameters. I demonstrate the issues with the first two practices using the college grade point average example extensively analyzed by Burnham and Anderson. I show how partial standard deviations of the predictor variables can be used to detect changing scales of their estimates with multicollinearity. Standardizing estimates based on partial standard deviations for their variables can be used to make the scaling of the estimates commensurate across models, a necessary but not sufficient condition for model averaging of the estimates to be sensible. A unimodal distribution of estimates and valid interpretation of individual parameters are additional requisite conditions. The standardized estimates or equivalently the t

  15. Model averaging and muddled multimodel inferences

    Science.gov (United States)

    Cade, Brian S.

    2015-01-01

    Three flawed practices associated with model averaging coefficients for predictor variables in regression models commonly occur when making multimodel inferences in analyses of ecological data. Model-averaged regression coefficients based on Akaike information criterion (AIC) weights have been recommended for addressing model uncertainty but they are not valid, interpretable estimates of partial effects for individual predictors when there is multicollinearity among the predictor variables. Multicollinearity implies that the scaling of units in the denominators of the regression coefficients may change across models such that neither the parameters nor their estimates have common scales, therefore averaging them makes no sense. The associated sums of AIC model weights recommended to assess relative importance of individual predictors are really a measure of relative importance of models, with little information about contributions by individual predictors compared to other measures of relative importance based on effects size or variance reduction. Sometimes the model-averaged regression coefficients for predictor variables are incorrectly used to make model-averaged predictions of the response variable when the models are not linear in the parameters. I demonstrate the issues with the first two practices using the college grade point average example extensively analyzed by Burnham and Anderson. I show how partial standard deviations of the predictor variables can be used to detect changing scales of their estimates with multicollinearity. Standardizing estimates based on partial standard deviations for their variables can be used to make the scaling of the estimates commensurate across models, a necessary but not sufficient condition for model averaging of the estimates to be sensible. A unimodal distribution of estimates and valid interpretation of individual parameters are additional requisite conditions. The standardized estimates or equivalently the

  16. Versatile Friction Stir Welding/Friction Plug Welding System

    Science.gov (United States)

    Carter, Robert

    2006-01-01

    A proposed system of tooling, machinery, and control equipment would be capable of performing any of several friction stir welding (FSW) and friction plug welding (FPW) operations. These operations would include the following: Basic FSW; FSW with automated manipulation of the length of the pin tool in real time [the so-called auto-adjustable pin-tool (APT) capability]; Self-reacting FSW (SRFSW); SR-FSW with APT capability and/or real-time adjustment of the distance between the front and back shoulders; and Friction plug welding (FPW) [more specifically, friction push plug welding] or friction pull plug welding (FPPW) to close out the keyhole of, or to repair, an FSW or SR-FSW weld. Prior FSW and FPW systems have been capable of performing one or two of these operations, but none has thus far been capable of performing all of them. The proposed system would include a common tool that would have APT capability for both basic FSW and SR-FSW. Such a tool was described in Tool for Two Types of Friction Stir Welding (MFS- 31647-1), NASA Tech Briefs, Vol. 30, No. 10 (October 2006), page 70. Going beyond what was reported in the cited previous article, the common tool could be used in conjunction with a plug welding head to perform FPW or FPPW. Alternatively, the plug welding head could be integrated, along with the common tool, into a FSW head that would be capable of all of the aforementioned FSW and FPW operations. Any FSW or FPW operation could be performed under any combination of position and/or force control.

  17. Friction and wear of single-crystal and polycrystalline maganese-zinc ferrite in contact with various metals

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Sliding friction experiments were conducted with single-crystal (SCF) and hot-pressed polycrystalline (HPF) manganese-zinc ferrite in contact with various metals. Results indicate that the coefficients of friction for SCF and HPF are related to the relative chemical activity of those metals in high vacuum. The more active the metal, the higher the coefficient of friction. The coefficients of friction for both SCF and HPF were the same and much higher in vacuum than in argon at atmospheric pressure. All the metals tested transferred to the surface of both SCF and HPF in sliding. Both SCF and HPF exhibited cracking and fracture with sliding. Cracking in SCF is dependent on crystallographic characteristics. In HPF, cracking depends on the orientation of the individual crystallites.

  18. Microstructuring the surface of silicon carbide ceramic by laser action for reducing friction losses in rolling bearings

    Science.gov (United States)

    Murzin, Serguei P.; Balyakin, Valeriy B.

    2017-02-01

    A possibility of microstructuring the surface of silicon carbide ceramic by pulse-periodic laser treatment was determined for reducing the coefficient of friction under actual contact stress conditions that occur in elements of the rolling bearing in operation. Temperature rate conditions for the laser treatment with pulse duration in the millisecond range were found, which lead to a change in the surface microrelief of silicon carbide ceramic obtained by diamond grinding after hot isostatic pressing. The determination of the coefficient of sliding friction was conducted with using the ball-on-disk tribometer at normal loads, which corresponds to the values of contact stresses of (0.5-1)×109 Pa. When the load was increased to the upper limit of measuring range, the friction coefficient decrease after laser treatment was more than 30% compared to the initial structure. Significant reduction of friction in rolling bearings up to this level provides an opportunity to improve efficiency of various machines.

  19. Optimal Tuning of Amplitude Proportional Coulomb Friction Damper for Maximum Cable Damping

    DEFF Research Database (Denmark)

    Weber, Felix; Høgsberg, Jan Becker; Krenk, Steen

    2010-01-01

    This paper investigates numerically the optimal tuning of Coulomb friction dampers on cables, where the optimality criterion is maximum additional damping in the first vibration mode. The expression for the optimal friction force level of Coulomb friction dampers follows from the linear viscous...... to higher modes evoked by the amplitude proportional Coulomb friction damper which clamps the cable at its upper and lower positions. The resulting nonsinusoidal cable motion clearly violates the assumption of pure harmonic motion and explains why such dampers have to be tuned differently from optimal...... damper via harmonic averaging. It turns out that the friction force level has to be adjusted in proportion to cable amplitude at damper position which is realized by amplitude feedback in real time. The performance of this adaptive damper is assessed by simulated free decay curves from which the damping...

  20. Origins of Shear Jamming for Frictional Grains

    Science.gov (United States)

    Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert

    2016-11-01

    Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.

  1. Model-based tire-road friction estimation for passenger vehicles

    Energy Technology Data Exchange (ETDEWEB)

    Bian, Ning

    2009-07-01

    Except for aerodynamic force and gravity, all other forces that act on a vehicle have to be transmitted to the road by its tires. Tire-road friction information, in particular, the potential friction coefficient plays a significant role for longitudinal and lateral vehicle dynamics. To obtain high performance of vehicle dynamics control system (VDCS) and driver assistant systems (DAS) such as ABS, TCS, ESC, ACC and so on, the potential friction coefficient is necessary to be provided as a key parameter for such systems. The estimation technique of the potential friction coefficient is mainly based on the three sensor clusters, i.e., in-vehicle standard sensors, tire sensors and environmental sensors. Without any additional or expensive sensor, the approach based on in-vehicle standard sensors can be expected by automobile industry more easily. In this work, the approach has been first studied and then by using the additional IMU sensor. In the thesis, the friction estimator has been at first proposed on horizontal surfaces according to in-vehicle standard sensors. The tire model with the specific parametrization for longitudinal and lateral dynamics has been developed. The stability behavior of observer-based numerical implementation has been analyzed and the observer-based solution to the stability problem has been proposed. Considering practical driving with different tire slip angles of front and real wheels, the improved observer scheme LADE based on lateral dynamics has been proposed to estimate potential friction coefficient for front and rear wheels. The observer scheme LODE has been described to estimate potential friction potential coefficient for each wheel in braking situations and for each rear wheel in accelerating situations. To enhance the estimation performance, based on the basic theory of fault diagnosis the estimation quality monitoring system (EQMS) has been proposed to solve a possibly false convergence problem due to the uncertainties of the

  2. The Reality of Casimir Friction

    CERN Document Server

    Milton, K A; Brevik, I

    2015-01-01

    For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum fluctuations. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Because of the lack of contact with phenomena, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.

  3. The Reality of Casimir Friction

    Directory of Open Access Journals (Sweden)

    Kimball A. Milton

    2016-04-01

    Full Text Available For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum electromagnetic fluctuations, which break time-reversal symmetry. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Partly because of the lack of contact with observations, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here, we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.

  4. Friction of Human Skin against Different Fabrics for Medical Use

    Directory of Open Access Journals (Sweden)

    Luís Vilhena

    2016-03-01

    Full Text Available Knowledge of the tribology of human skin is essential to improve and optimize surfaces and materials in contact with the skin. Besides that, friction between the human skin and textiles is a critical factor in the formation of skin injuries, which are caused if the loads and shear forces are high enough and/or over long periods of time. This factor is of particular importance in bedridden patients, since they are not moving about or are confined to wheelchairs. Decubitus ulcers are one of the most frequently-reported iatrogenic injuries in developed countries. The risk of developing decubitus ulcers can be predicted by using the “Braden Scale for Predicting Pressure Ulcer Risk” that was developed in 1987 and contains six areas of risk (cognitive-perceptual, immobility, inactivity, moisture, nutrition, friction/shear, although there are limitations to the use of such tools. The coefficient of friction of textiles against skin is mainly influenced by: the nature of the textile, skin moisture content and ambient humidity. This study will investigate how skin friction (different anatomical regions varies, rubbing against different types of contacting materials (i.e., fabrics for medical use under different contact conditions and their relationship in the formation and prevention of decubitus ulcers.

  5. Methodology to predict friction pressure drop in drilling fluid flows; Metodologia para previsao de perdas de carga em escoamentos de fluidos de perfuracao

    Energy Technology Data Exchange (ETDEWEB)

    Scheid, Claudia Miriam; Calcada, Luis Americo [Universidade Federal Rural do Rio de Janeiro (UFRRJ). Departamento de Engenharia Quimica (Brazil)], e-mails: scheid@ufrrj.br, calcada@ufrrj.br; Rocha, Daniele Cristine [Centro de Pesquisas da Petrobras (CENPES). Engenharia Basica de Abastecimento - Gas e Energia (Brazil)], e-mail: drocha@petrobras.com.br; Aranha, Pedro Esteves [Centro de Pesquisas da Petrobras (CENPES). Gerencia de Perfuracao e Completacao de Pocos (Brazil)], e-mail: pearanha@petrobras.com.br; Aragao, Atila Fernando Lima [E and P Construcao de Pocos Maritimos. Gerencia de Tecnologia de Fluidos (Brazil)], e-mail: atila_aragao@petrobras.com.br

    2009-12-15

    An extensive experimental study is detailed to evaluate the friction pressure drop resulting from the flow through pipe and annular sections, accessories such as tool joints, bit jets and stabilizers of four different drilling fluids used in deep water operations. After a data analysis process, it was possible to compile a set of equations to predict relevant hydraulic friction pressure loss calculations, such as: hydraulic diameter for annular flows, friction factors for pipe and annular turbulent flows and discharge coefficients for accessories. (author)

  6. The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1979-01-01

    Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh, and W) in contact with single-crystal silicon carbide riders. Results indicate that the coefficient of friction and groove height (corresponding to the wear volume) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease with an increase in solute content of binary alloys. A separate correlation exists between the solute to iron atomic radius ratio and the decreasing rates of change of coefficient of friction and groove height with increasing solute content. These rates of change are minimum at a solute to iron radius ratio of unity. They increase as the atomic ratio increases or decreases linearly from unity. The correlations indicate that atomic size is an important parameter in controlling friction and wear of alloys.

  7. Frictional forces required for unrestrained locomotion in dairy cattle.

    Science.gov (United States)

    van der Tol, P P J; Metz, J H M; Noordhuizen-Stassen, E N; Back, W; Braam, C R; Weijs, W A

    2005-02-01

    Most free-stall housing systems in the Netherlands are equipped with slatted or solid concrete floors with manure scrapers. A slipping incident occurs when the required coefficient of friction (RCOF) exceeds the coefficient of friction (COF) at the claw-floor interface. An experiment was conducted to measure ground reaction forces (GRF) of dairy cows (n = 9) performing various locomotory behaviors on a nonslippery rubber-covered concrete floor. The RCOF was determined as the ratio of the horizontal and vertical components of the GRF. It was shown that during straight walking and walking-a-curve, the RCOF reached values up to the COF, whereas for sudden stop-and-start responses, the RCOF reached values beyond the maximum COF that concrete floors can provide. Our results indicate that concrete floors do not provide enough friction to allow natural locomotory behavior and suggest that tractional properties of floors should be main design criteria in the development of better flooring surfaces for cattle.

  8. Correlation of Preston-tube data with laminar skin friction

    Science.gov (United States)

    Reed, T. D.; Abu-Mostafa, A.; Steinle, F. W., Jr.

    1982-01-01

    Preston-tube data have been obtained on a sharp ten-degree cone in the NASA Ames Eleven-Foot Transonic Wind Tunnel. Data were obtained over a Mach number range of 0.30 to 0.95 and unit Reynolds numbers of 9.84, 13.1, and 16.4 million per meter. The portions of these data, that were obtained within laminar boundary layers, have been correlated with the corresponding values of theoretical skin friction. The rms scatter of skin-friction coefficient about the correlation is of the order of one percent, which is comparable to the reported accuracy for calibrations of Preston-tubes in incompressible pipe-flows. In contrast to previous works on Preston-tube/skin-friction correlations, which are based on the physical height of the probe's face, this very satisfactory correlation for compressible boundary-layer flows is achieved by accounting for the effects of a variable 'effective' height of the probe. The coefficients, which appear in the correlation, are dependent on the particular tunnel environment. The general procedure can be used to define correlations for other wind tunnels.

  9. Friction and wear behaviour of Mo–W doped carbon-based coating during boundary lubricated sliding

    Energy Technology Data Exchange (ETDEWEB)

    Hovsepian, Papken Eh., E-mail: p.hovsepian@shu.ac.uk [Nanotechnology Centre for PVD Research, HIPIMS Research Centre, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB (United Kingdom); Mandal, Paranjayee, E-mail: 200712mum@gmail.com [Nanotechnology Centre for PVD Research, HIPIMS Research Centre, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB (United Kingdom); Ehiasarian, Arutiun P., E-mail: a.ehiasarian@shu.ac.uk [Nanotechnology Centre for PVD Research, HIPIMS Research Centre, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB (United Kingdom); Sáfrán, G., E-mail: safran.gyorgy@ttk.mta.hu [Institute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly-Thegeut 29-33 (Hungary); Tietema, R., E-mail: rtietema@hauzer.nl [IHI Hauzer Techno Coating B.V., Van Heemskerckweg 22, 5928 LL Venlo (Netherlands); Doerwald, D., E-mail: ddoerwald@hauzer.nl [IHI Hauzer Techno Coating B.V., Van Heemskerckweg 22, 5928 LL Venlo (Netherlands)

    2016-03-15

    Graphical abstract: - Highlights: • Novel Mo–W–C coating provides extremely low friction (μ ∼ 0.03) in lubricated condition. • Mo–W–C outperforms existing DLCs in terms of low friction, independent of temperature. • Tribochemical reactions govern the wear mechanism of Mo–W–C coating. • The transfer layer contains graphitic carbon and ‘in situ’ formed WS{sub 2} and MoS{sub 2}. • WS{sub 2} and MoS{sub 2} are the key factors facilitating appreciably low friction and wear rate. - Abstract: A molybdenum and tungsten doped carbon-based coating (Mo–W–C) was developed in order to provide low friction in boundary lubricated sliding condition at ambient and at high temperature. The Mo–W–C coating showed the lowest friction coefficient among a number of commercially available state-of-the-art DLC coatings at ambient temperature. At elevated temperature (200 °C), Mo–W–C coating showed a significant reduction in friction coefficient with sliding distance in contrast to DLC coatings. Raman spectroscopy revealed the importance of combined Mo and W doping for achieving low friction at both ambient and high temperature. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon debris (from coating) and ‘in situ’ formed metal sulphides (WS{sub 2} and MoS{sub 2}, where metals were supplied from coating and sulphur from engine oil) in the transfer layer.

  10. Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale

    Science.gov (United States)

    Tian, Kaiwen; Gosvami, Nitya N.; Goldsby, David L.; Liu, Yun; Szlufarska, Izabela; Carpick, Robert W.

    2017-02-01

    Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds. The role of normal load (and, thus, normal stress) on this interfacial chemical bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.

  11. SURFACE DYNAMIC FRICTION OF POLYMER GELS

    Institute of Scientific and Technical Information of China (English)

    J.P.Gong; G.Kagata; Y.Iwasaki; Y.Osada

    2000-01-01

    The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amonton's law F =μW which well describes the friction of solids. The frictional force and its dependence on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which supported the repulsion-adsorption model proposed by the authors.

  12. The Friction of Saline Ice on Aluminium

    Directory of Open Access Journals (Sweden)

    Christopher Wallen-Russell

    2016-01-01

    Full Text Available The friction of ice on other materials controls loading on offshore structures and vessels in the Arctic. However, ice friction is complicated, because ice in nature exists near to its melting point. Frictional heating can cause local softening and perhaps melting and lubrication, thus affecting the friction and creating a feedback loop. Ice friction is therefore likely to depend on sliding speed and sliding history, as well as bulk temperature. The roughness of the sliding materials may also affect the friction. Here we present results of a series of laboratory experiments, sliding saline ice on aluminium, and controlling for roughness and temperature. We find that the friction of saline ice on aluminium μice-al=0.1 typically, but that this value varies with sliding conditions. We propose physical models which explain the variations in sliding friction.

  13. Friction Properties of OTS SAMs and Silicon Surface under Water Lubrication

    Institute of Scientific and Technical Information of China (English)

    WANG Xin; ZHANG Xiangjun; AHMED Imad; LIU Ying; WEN Shizhu

    2009-01-01

    The friction and wear properties of silicon surface covered with octadecyltrichloro-silane (OTS) self-assembled monolayers (SAMs) were investigated by a UMT-2 microtribometer with and without water as lubricant, and then compared with that of bare silicon surface. Dry friction measurement results show that OTS SAMs have a very low friction coefficient compared to bare silicon surface under lower sliding velocity and normal contact load. However, heavy wear occurs on OTS SAMs under higher contact stress and sliding velocity. Under water lubrication, OTS SAMs can prevent wear obviously and meanwhile present low coefficient of friction even under high velocities.The improved frictional and anti-wear property on OTS SAMs surface is attributed to the hydrophobic property of OTS and hydrodynamic effect of water. Furthermore, a wear critical phase diagram for OTS SAMs with and without water was proposed, which indicates that OTS SAMs working under water lubrication owns a wider range of available load and velocity to reduce friction and prevent wear.

  14. Electric force microscopy of semiconductors: Theory of cantilever frequency fluctuations and noncontact friction

    Energy Technology Data Exchange (ETDEWEB)

    Lekkala, Swapna; Marohn, John A.; Loring, Roger F., E-mail: roger.loring@cornell.edu [Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853 (United States)

    2013-11-14

    An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.

  15. Molecular dynamics simulation of atomic-scale frictional behavior of corrugated nano-structured surfaces.

    Science.gov (United States)

    Kim, Hyun-Joon; Kim, Dae-Eun

    2012-07-01

    Surface morphology is one of the critical parameters that affect the frictional behavior of two contacting bodies in relative motion. It is important because the real contact area as well as the contact stiffness is dictated by the micro- and nano-scale geometry of the surface. In this regard, the frictional behavior may be controlled by varying the surface morphology through nano-structuring. In this study, molecular dynamics simulations were conducted to investigate the effects of contact area and structural stiffness of corrugated nano-structures on the fundamental frictional behavior at the atomic-scale. The nano-structured surface was modeled as an array of corrugated carbon atoms with a given periodicity. It was found that the friction coefficient of the nano-structured surface was lower than that of a smooth surface under specific contact conditions. The effect of applied load on the friction coefficient was dependent on the size of the corrugation. Furthermore, stiffness of the nano-structure was identified to be an important variable in dictating the frictional behavior.

  16. Development of empirical correlation of peak friction angle with surface roughness of discontinuities using tilt test

    Science.gov (United States)

    Serasa, Ailie Sofyiana; Lai, Goh Thian; Rafek, Abdul Ghani; Simon, Norbert; Hussein, Azimah; Ern, Lee Khai; Surip, Noraini; Mohamed, Tuan Rusli

    2016-11-01

    The significant influence of surface roughness of discontinuity surfaces is a quantity that is fundamental to the understanding of shear strength of geological discontinuities. This is due to reason that the shear strength of geological discontinuities greatly influenced the mechanical behavior of a rock mass especially in stability evaluation of tunnel, foundation, and natural slopes. In evaluating the stability of these structures, the study of peak friction angle (Φpeak) of rough discontinuity surfaces has become more prominent seeing that the shear strength is a pivotal factor causing failures. The measurement of peak friction angle however, requires an extensive series of laboratory tests which are both time and cost demanding. With that in mind, this publication presents an approach in the form of an experimentally determined polynomial equation to estimate peak friction angle of limestone discontinuity surfaces by measuring the Joint Roughness Coefficient (JRC) values from tilt tests, and applying the fore mentioned empirical correlation. A total of 1967 tilt tests and JRC measurements were conducted in the laboratory to determine the peak friction angles of rough limestone discontinuity surfaces. A polynomial equation of ɸpeak = -0.0635JRC2 + 3.95JRC + 25.2 that exhibited 0.99 coefficient of determination (R2) were obtained from the correlation of JRC and peak friction angles. The proposed correlation offers a practical method for estimation of peak friction angles of rough discontinuity surfaces of limestone from measurement of JRC in the field.

  17. Friction resistance for gas flow in smooth microtubes

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A new tube-cutting method was used to measure the pressure and Mach number distribution along a microtube of 108.3 μm. Experiments were also performed concerning the average Fanning friction factors of five kinds of microtubes whose diameters range from 80.0 to 166.6 μm. It is found that the pressure distribution in a microtube becomes nonlinear at a high Mach number and the product of measured average Fanning friction factors Cf and Reynolds number Re is higher than 16. Numerical results show that the gas compressibility leads to a variation of the velocity profile from parabolic, and results in a large velocity gradient at the tube inner wall surface. The transition from laminar to turbulence in microtubes also occurs at Re≈2 300, and the phenomenon of early transition is not observed in the experiments.

  18. Friction resistance for gas flow in smooth microtubes

    Institute of Scientific and Technical Information of China (English)

    杜东兴; 李志信; 过增元

    2000-01-01

    A new tube-cutting method was used to measure the pressure and Mach number distribution along a microtube of 108.3 μm. Experiments were also performed concerning the average Fanning friction factors of five kinds of microtubes whose diameters range from 80.0 to 166.6 μm. It is found that the pressure distribution in a microtube becomes nonlinear at a high Mach number and the product of measured average Fanning friction factors 75, and Reynolds number Re is higher than 16. Numerical results show that the gas compressibility leads to a variation of the velocity profile from parabolic, and results in a large velocity gradient at the tube inner wall surface. The transition from laminar to turbulence in microtubes also occurs at Re ≈ 2 300, and the phenomenon of early transition is not observed in the experiments.

  19. Modified Biserial Correlation Coefficients.

    Science.gov (United States)

    Kraemer, Helena Chmura

    1981-01-01

    Asymptotic distribution theory of Brogden's form of biserial correlation coefficient is derived and large sample estimates of its standard error obtained. Its relative efficiency to the biserial correlation coefficient is examined. Recommendations for choice of estimator of biserial correlation are presented. (Author/JKS)

  20. Friction Sensitivity of Primary Explosives

    Science.gov (United States)

    1982-09-01

    potassium dinitrobenzofuroxan none tetrazene 407913 tetrazene 7902454 The mixes which were tested are: NOL 130 (basic lead styphnate , barium nitrate, lead...azide, tetrazene, and antimony sulfide); PA 100 (normal lead styphnate , barium nitrate, tetrazene, lead dioxide, calcium silicide, and antimony...styuhnate, basic lead styphnate , potassium dinitrobenzofuroxan, and tetrazene were tested to determine the- 10% and 50% probability of friction

  1. Friction of atomically stepped surfaces

    Science.gov (United States)

    Dikken, R. J.; Thijsse, B. J.; Nicola, L.

    2017-03-01

    The friction behavior of atomically stepped metal surfaces under contact loading is studied using molecular dynamics simulations. While real rough metal surfaces involve roughness at multiple length scales, the focus of this paper is on understanding friction of the smallest scale of roughness: atomic steps. To this end, periodic stepped Al surfaces with different step geometry are brought into contact and sheared at room temperature. Contact stress that continuously tries to build up during loading, is released with fluctuating stress drops during sliding, according to the typical stick-slip behavior. Stress release occurs not only through local slip, but also by means of step motion. The steps move along the contact, concurrently resulting in normal migration of the contact. The direction of migration depends on the sign of the step, i.e., its orientation with respect to the shearing direction. If the steps are of equal sign, there is a net migration of the entire contact accompanied by significant vacancy generation at room temperature. The stick-slip behavior of the stepped contacts is found to have all the characteristic of a self-organized critical state, with statistics dictated by step density. For the studied step geometries, frictional sliding is found to involve significant atomic rearrangement through which the contact roughness is drastically changed. This leads for certain step configurations to a marked transition from jerky sliding motion to smooth sliding, making the final friction stress approximately similar to that of a flat contact.

  2. Integrated Data Collection and Analysis Project: Friction Correlation Study

    Science.gov (United States)

    2015-08-01

    methods authorized in AOP-7 include Pendulum Friction, Rotary Friction, Sliding Friction (ABL), BAM Friction and Steel/Fiber Shoe Methods. The...environments during their life cycle ; from initial formulation and testing through production, item filling, transport and storage. As such, it is crucial...sensitivity can be obtained by Pendulum Friction, Rotary Friction, Sliding Friction (such as the ABL), BAM Friction and Steel/Fiber Shoe Methods.3, 4 Within

  3. Asbestos free friction composition for brake linings

    Indian Academy of Sciences (India)

    Arnab Ganguly; Raji George

    2008-02-01

    An asbestos free friction material composite for brake linings is synthesized containing fibrous reinforcing constituents, friction imparting and controlling additives, elastomeric additives, fire retarding components and a thermosetting resin. The composite shows exemplary friction characteristics and has great resistance to wear and shows good temperature stability.

  4. Rotary Engine Friction Test Rig Development Report

    Science.gov (United States)

    2011-12-01

    5  4.  Friction Rig Development 7  5.  AutoCAD ...Figure 4. Engine friction test rig AutoCAD model. ........................................................................8  Figure 5. Engine...top dead center. 8 5. AutoCAD Model Development A model of the rotary engine friction test rig was developed to determine the optimal

  5. Microstructures and friction-wear behaviors of cathodic arc ion plated CrC coating at high temperatures

    Science.gov (United States)

    Dejun, Kong; Shouyu, Zhu

    2016-11-01

    A CrC coating was deposited on YT14 cemented carbide cutting tools by a CAIP (cathodic arc ion plating). The surface and interface morphologies, chemical composition, and phases of the obtained coating were analyzed with a field emission scanning electronic microscope (FESEM), energy dispersive spectroscope (EDS), and x-ray diffraction (XRD), respectively. The COFs (coefficient of frictions) and worn morphologies of the CrC coating at 300 °C, 400 °C, and 500 °C were investigated by using a high temperature tribometer, the effects of wear temperatures on the friction-wear properties of the CrC coating were discussed. The results show that the CrC coating exhibits fine dense structure, and the lattice constants of CrC coatings are dependent on processing parameters. The C and Cr elements in the coating are mutually diffused with the W, Co, and Ti in the substrate. The average COF of the coating at 300 °C, 400 °C, and 500 °C is 0.64, 0.63, and 0.40, respectively. The Cr2O3 layer formed on the CrC coating at 500 °C has excellent oxidation resistance, which improves lubrication and wear performance, the wear mechanism is abrasive wear and oxidation wear.

  6. Influence of WS2 Nanopowder Addition on Friction Characteristics of ta-C Coating by FCVA Method

    Directory of Open Access Journals (Sweden)

    Si-Geun Choi

    2015-01-01

    Full Text Available The influence of nano-size WS2 powders on the tribological behavior of ta-C coatings by the filtered cathodic vacuum arc (FCVA method under boundary lubrication conditions has been investigated. In order to characterize and understand tribological behaviors of nano-size WS2 powders added to the synthetic oil (poly-alpha-olefin 6, lubricants with different mixture ratios, ranging from 2 to 8 wt%, have been prepared. ta-C coatings fabricated by FCVA method showed that the G-peak in the obtained Raman spectrum was shifted from 1520 to 1586 cm−1, indicating the sp3 content increased for samples with the thickness of 156 nm. The average friction coefficient decreased proportionally as the nano-size WS2 compositions increased up to 4 wt% in PAO6. After the friction test, structures and particle sizes of WS2 phases were also precisely characterized by using XRD and SEM.

  7. Molecular-dynamics simulation of lateral friction in contact-mode atomic force microscopy of alkane films: The role of molecular flexibility

    DEFF Research Database (Denmark)

    Soza, P.; Hansen, Flemming Yssing; Taub, H.;

    2011-01-01

    Molecular-dynamics simulations are used to investigate lateral friction in contact-mode atomic force microscopy of tetracosane (n-C24H50) films. We find larger friction coefficients on the surface of monolayer and bilayer films in which the long axis of the molecules is parallel to the interface ...

  8. Micro-structure and frictional characteristics of beetle's joint

    Institute of Scientific and Technical Information of China (English)

    DAI; Zhendong; Stanislav; N.; Gorb

    2004-01-01

    Geometric and micro-structure design, tribology properties of beetle joints were experimentally studied, which aimed to enlighten ideas for the joint design of MEMS.The observation by using SEM and microscopy suggested that beetle's joints consist of a concave surface matched with a convex surface. The heads of the beetles, rubbing with flat glass, were tested in fresh and dried statuses and compared with sapphire ball with flat glass. Frictional coefficient of the joint material on glass was significantly lower than that of the sapphire sphere on glass. The material of the joint cuticle for convex surface is rather stiff (the elastic modulus 4.5 Gpa) and smooth. The surface is hydrophobic (the contact angle of distilled water was 88.3° ). It is suggested here that the high stiffness of the joint material and hydrophobicity of the joint surface are parts of the mechanism minimizing friction in insect joints.

  9. Quantum tunneling at zero temperature in the strong friction regime.

    Science.gov (United States)

    Bolivar, A O

    2005-01-21

    In the large damping limit we derive a Fokker-Planck equation in configuration space (the so-called Smoluchowski equation) describing a Brownian particle immersed into a thermal environment and subjected to a nonlinear external force. We quantize this stochastic system and survey the problem of escape over a double-well potential barrier. Our finding is that the quantum Kramers rate does not depend on the friction coefficient at low temperatures; i.e., we predict a superfluidity phenomenon in overdamped open systems. Moreover, at zero temperature we show that the quantum escape rate does not vanish in the strong friction regime. This result, therefore, is in contrast with the work by Ankerhold et al. [Phys. Rev. Lett. 87, 086802 (2001)

  10. The influence of air friction in speed skating.

    Science.gov (United States)

    van Ingen Schenau, G J

    1982-01-01

    With the use of a wind tunnel the air friction force Fw on six speed skaters of different body builds was measured. The dependence of the drag coefficient CD on air velocity v and the influence of different skating postures on drag were investigated. At an air velocity of v = 12 m/sec, an angle between upper and lower leg of 110 degrees and a horizontal trunk position, the measured air friction constant kn(=Fw/V2) of all subjects was calculated from their height l and weight m according to the formula 0.0205 l3 square root m (standard error 2%). CD and as a consequence k appeared to be strongly dependent on air velocity. Expressions to correct k for other velocities and postures were derived and substituted into a power balance by which the influence of posture, ice condition, wind and altitude on performance was predicted.

  11. Dry friction and wear characteristics of MoSi2 against ahoy steels

    Institute of Scientific and Technical Information of China (English)

    CHEN Ping; ZHANG Hou'an; TANG Guoning; LI Songwen

    2005-01-01

    The dry friction and wear characteristics of three kinds of friction couples under different loads, MoSi2/45 tempered steel, MoSi2/45 quenched steel, and MoSi2/CrWMn steel, were investigated by using a friction and wear tester. SEM and X-ray diffraction were employed to analyze the microphotograph of the worn surface and the phase of worn pieces in order to reveal the wear mechanisms of MoSi2 material. The results show that MoSi2/CrWMn steel friction pair has good dry friction and wear properties under the load of 80 N, where the friction coefficient is 0.255 and the wear rate of MoSi2 is only 14.72 mg.km-1. But under the load of 150 N, it is MoSi2/45 tempered steel friction pair that has good tribological properties,MoSi2 under low loads is brittle fracture. With the increase of load, the main wear mechanism of MoSi2 against 45 quenched steel or CrWMn steel is adhesive wear. However, the wear mechanism of MoSi2 against 45 tempered steel is changed from oxidation-fatigue wear to adhesive wear.

  12. Friction and wear properties of pitch/resin densified carbon-carbon composites used for airbrakes

    Institute of Scientific and Technical Information of China (English)

    巩前明; 黄伯云; 黄启忠; 李江鸿; 吴凤秋; 李晔

    2002-01-01

    By use of X-ray diffractometry and scanning electron microscope (SEM), the friction and wear results obtained from MM-1000 dynamometer tests of CVI pitch/resin C/C composites were analyzed. By investigating the factors that affected the friction and wear properties, such as matrix carbon, application environment, graphitization degree and brake pressure, etc, friction and wear mechanism of carbon materials were probed. The results indicate that pitch densified CVI initially treated composite is more graphitizable with its graphitization degree up to 62%, and which results in uniform small debris easier to generate, more smooth friction curves with the coefficient of 0.3~0.4 and relatively higher linear wear and mass loss, compared with CVI/resin C/C composites. It was further proved by SEM observation that tribological behavior of C/C composite was system dependent. Factors determining the friction and wear properties such as the size of debris and its influence on friction and wear, brake pressure, graphization degree and debris film formation interacted and affected each other. The friction and wear mechanism of C/C composites under different high temperature treatments needs further research.

  13. Energy corrugation in atomic-scale friction on graphite revisited by molecular dynamics simulations

    Science.gov (United States)

    Sun, Xiao-Yu; Qi, Yi-Zhou; Ouyang, Wengen; Feng, Xi-Qiao; Li, Qunyang

    2016-08-01

    Although atomic stick-slip friction has been extensively studied since its first demonstration on graphite, the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics (MD) simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding (known as energy corrugation) comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces. For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However, for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.

  14. Lubrication and friction prediction in metal-on-metal hip implants

    Energy Technology Data Exchange (ETDEWEB)

    Wang, F C; Brockett, C; Williams, S; Udofia, I; Fisher, J; Jin, Z M [Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)], E-mail: f.c.wang@bath.ac.uk

    2008-03-07

    A general methodology of mixed lubrication analysis and friction prediction for a conforming spherical bearing in hip implants was developed, with particular reference to a typical metal-on-metal hip replacement. Experimental measurement of frictional torque for a similar implant was carried out to validate the theoretical prediction. A ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup under cyclic operating conditions of representative load and motion. The mixed lubrication model presented in this study was first applied to identify the contact characteristics on the bearing surfaces, consisting of both fluid-film and boundary lubricated regions. The boundary lubricated contact was assumed to occur when the predicted fluid film thickness was less than a typical boundary protein layer absorbed on the bearing surfaces. Subsequently, the friction was predicted from the fluid-film lubricated region with viscous shearing due to both Couette and Poiseuille flows and the boundary protein layer contact region with a constant coefficient of friction. The predicted frictional torque of the typical metal-on-metal hip joint implant was compared with the experimental measurement conducted in a functional hip simulator and a reasonably good agreement was found. The mixed lubrication regime was found to be dominant for the conditions considered. Although the percentage of the boundary lubricated region was quite small, the corresponding contribution to friction was quite large and the resultant friction factor was quite high.

  15. Lubrication and friction prediction in metal-on-metal hip implants.

    Science.gov (United States)

    Wang, F C; Brockett, C; Williams, S; Udofia, I; Fisher, J; Jin, Z M

    2008-03-07

    A general methodology of mixed lubrication analysis and friction prediction for a conforming spherical bearing in hip implants was developed, with particular reference to a typical metal-on-metal hip replacement. Experimental measurement of frictional torque for a similar implant was carried out to validate the theoretical prediction. A ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup under cyclic operating conditions of representative load and motion. The mixed lubrication model presented in this study was first applied to identify the contact characteristics on the bearing surfaces, consisting of both fluid-film and boundary lubricated regions. The boundary lubricated contact was assumed to occur when the predicted fluid film thickness was less than a typical boundary protein layer absorbed on the bearing surfaces. Subsequently, the friction was predicted from the fluid-film lubricated region with viscous shearing due to both Couette and Poiseuille flows and the boundary protein layer contact region with a constant coefficient of friction. The predicted frictional torque of the typical metal-on-metal hip joint implant was compared with the experimental measurement conducted in a functional hip simulator and a reasonably good agreement was found. The mixed lubrication regime was found to be dominant for the conditions considered. Although the percentage of the boundary lubricated region was quite small, the corresponding contribution to friction was quite large and the resultant friction factor was quite high.

  16. Energy corrugation in atomic-scale friction on graphite revisited by molecular dynamics simulations

    Institute of Scientific and Technical Information of China (English)

    Xiao-Yu Sun; Yi-Zhou Qi; Wengen Ouyang; Xi-Qiao Feng; Qunyang Li

    2016-01-01

    Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite, the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics (MD) simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding (known as energy corrugation) comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competi-tion of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces. For relatively low tip-graphite adhesion, friction behaves nor-mally and increases with increasing normal load. However, for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effec-tively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.

  17. Frictional Performance and Temperature Rise of a Mining Nonasbestos Brake Material during Emergency Braking

    Directory of Open Access Journals (Sweden)

    Jiusheng Bao

    2015-01-01

    Full Text Available By simulating emergency braking conditions of mine hoisters, tribological experiments of a mining nonasbestos brake material sliding on E355CC steel friction disc investigated a pad-on-disc friction tester. It is shown that, under combined influence of braking velocity and pressure, the lubricating film and micro-convex-apices on wear surface would have complex physicochemical reactions which make the instant friction coefficient rise gradually while the instant surface temperature rises first and then falls. With the antifriction effect from lubricating film and the desquamating of composite materials, the mean friction coefficient decreases first, then rises, and decreases again with the increasing of initial braking velocity. And with the existence of micro-convex-apices and variation from increment ratio of load and actual contacting area, it rises first and then falls with the increasing of braking pressure. However, the mean surface temperature rises obviously with the increasing of both initial braking velocity and braking pressure for growth of transformed kinetic energy. It is considered that the friction coefficient cannot be considered as a constant when designing brake devices for mine hoisters. And special attention should be paid to the serious influence of surface temperature on tribological performance of brake material during emergency braking.

  18. Friction behaviour of aluminium composites mixed with carbon fibers with different orientations

    Science.gov (United States)

    Caliman, R.

    2016-08-01

    The primary goal of this study work it was to distinguish a mixture of materials with enhanced friction and wearing behaviour. The composite materials may be differentiated from alloys; which can contain two more components but are formed naturally through different processes such as casting. The load applied on the specimen during the tests, is playing a very important role regarding friction coefficient and also the wearing speed. Sintered composites are gaining importance because the reinforcement serves to reduce the coefficient of thermal expansion and increase the strength and modulus. The friction tests are carried out, at the room temperature in dry condition, on a pin-on-disc machine. The exponentially decreasing areas form graphs, represented to the curves coefficient of friction, are attributed to the formation of lubricant transfer film and initial polishing surface samples. The influence of the orientation of the carbon fibers on the friction properties in the sintered polymer composites may be studied by the use of both mechanical wear tests by microscopy and through the use of phenomenological models.

  19. Wind speed scaling and the drag coefficient

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Wind speed scaling in similarity law in wind-generated waves and the drag coefficient are studied. In analyzing the data in the wind wave channel, it is found that the u. scaling greatly reduces the scatter in the U10 scaling. The u. scaling has much less scatter than the scaling using other wind speeds. The friction velocity seems to play a distinctive role in wave growth. The result is important in the applications of the similarity law and in wave modeling. In theory it gives an insight into the mechanism of wind wave interaction. It is found that wave steepness is important in influencing the drag coefficient. The variability of the coefficients in the currently widely used drag form can be explained by the differences in wave steepness in the observations. A drag coefficient model with wind speed and wave steepness as parameters is proposed. An explanation for Kahma' s result that the u. scaling does not reduce the scatter in the U10 scaling is given.

  20. Analysis of the moment caused by friction of cardan joint. Cardan joint no friction kishinryoku kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Ono, K.; Yagi, Shida, T. (Atsugi Unisia Corp., Kanagawa (Japan))

    1990-10-01

    Analyzing the vibromotive force, generated by the friction, in generation morphology, level, dynamical characteristics, etc., through measurement of joint unit friction simulation of frictional vibromotive force and on-platform measurement of propeller shaft in vibromotive force, the present report investigated the influence of friction on the vehicle in sound vibration performance. By a vibromotive force measurement system, internally equipped with a piezoelectric type force meter, frictional vibromotive force could be quantitatively grasped. The friction must be appropriately controlled, because the moment, generated by it, is expected to be put in the vehicle by intermediation of a supporting point and adversely influence the sound vibration performance. Apart from the above, elucidation was made of relation between the ordinal number components of rotation of vibromotive force and friction, calculation of reaction force at the supporting point by the frictional measurement, relation between the joint angle and frictional vibromotive force, second couple force due to the friction, etc. 3 refs., 15 figs.

  1. Friction of tungsten carbide-cobalt coatings obtained by means of plasma spraying

    Energy Technology Data Exchange (ETDEWEB)

    Cartier, M. (Hydromecanique et Frottement, Centre de Recherches, 42 - Andreziux-Boutheon (France)); McDonnell, L.; Cashell, E.M. (CRTC, Cork (Ireland))

    1991-11-29

    A study of the frictional properties of WC-Co-type coatings obtained by plasma spraying was carried out, the influence of the majority of the parameters involved in atmospheric spraying being analysed. This study of the correlations between the tribological behaviour and the compositionl of the coatings shows that friction is mainly determined by the method and degree of decomposition of the carbides. These in turn are linked to the effects of heat and/or oxidation, factors which can change considerably, not only as a function of the method used (plasma power, nature and flow rate of the plasma gases etc.) but also as a function of the coating process and the composition of the original powders. It has been possible to correlate the improvement in the frictional properties (resistance to seizure, reduction in the coefficient of friction) with the presence of free carbon in the coatings, associated with the carbide decomposition process. (orig.).

  2. Numerical Studies of Friction Between Metallic Surfaces and of its Dependence on Electric Currents

    Science.gov (United States)

    Meintanis, Evangelos; Marder, Michael

    2009-03-01

    We will present molecular dynamics simulations that explore the frictional mechanisms between clean metallic surfaces. We employ the HOLA molecular dynamics code to run slider-on-block experiments. Both objects are allowed to evolve freely. We recover realistic coefficients of friction and verify the importance of cold-welding and plastic deformations in dry sliding friction. We also find that plastic deformations can significantly affect both objects, despite a difference in hardness. Metallic contacts have significant technological applications in the transmission of electric currents. To explore the effects of the latter to sliding, we had to integrate an electrodynamics solver into the molecular dynamics code. The disparate time scales involved posed a challenge, but we have developed an efficient scheme for such an integration. A limited electrodynamic solver has been implemented and we are currently exploring the effects of currents in the friction and wear of metallic contacts.

  3. Characterization of the Frictional Response of Squamata Shed Skin in Comparison to Human skin

    CERN Document Server

    Abdel-Aal, H A

    2010-01-01

    Deterministic surfaces are constructs of which profile, topography and textures are integral to the function of the system they enclose. They are designed to yield a predetermined rubbing response. Developing such entities relies on controlling the structure of the rubbing interface so that, not only the surface is of optimized topography, but also is able to self-adjust its behavior according to the evolution of sliding conditions. Inspirations for such designs are frequently encountered in natural species. In particular, and from a tribological point of view, Squamate Reptiles, offer diverse examples where surface texturing, submicron and nano-scale features, achieves frictional regulation. In this paper, we study the frictional response of shed skin obtained from a Python regius snake. The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional re...

  4. An Experimental Study of Turbulent Skin Friction Reduction in Supersonic Flow Using a Microblowing Technique

    Science.gov (United States)

    Hwang, Danny P.

    1999-01-01

    A new turbulent skin friction reduction technology, called the microblowing technique has been tested in supersonic flow (Mach number of 1.9) on specially designed porous plates with microholes. The skin friction was measured directly by a force balance and the boundary layer development was measured by a total pressure rake at the tailing edge of a test plate. The free stream Reynolds number was 1.0(10 exp 6) per meter. The turbulent skin friction coefficient ratios (C(sub f)/C(sub f0)) of seven porous plates are given in this report. Test results showed that the microblowing technique could reduce the turbulent skin friction in supersonic flow (up to 90 percent below a solid flat plate value, which was even greater than in subsonic flow).

  5. A theory of static friction between homogeneous surfaces based on compressible elastic smooth microscopic inclines

    CERN Document Server

    Thun, Freeman Chee Siong; Chan, Kin Sung

    2014-01-01

    We develop a theory of static friction by modeling the homogeneous surfaces of contact as being composed of a regular array of compressible elastic smooth microscopic inclines. Static friction is thought of as the resistance due to having to push the load over these smooth microscopic inclines that share a common inclination angle. As the normal force between the surfaces increases, the microscopic inclines would be compressed elastically. Consequently, the coefficient of static friction does not remain constant but becomes smaller for a larger normal force, since the load would then only need to be pushed over smaller angles. However, a larger normal force would also increase the effective compressed area between the surfaces, as such the pressure is distributed over this larger effective compressed area. The relationship between the normal force and the common angle is therefore non-linear. Overall, static friction is shown to depend on the normal force, apparent contact area, Young's modulus, and the compr...

  6. Wear and friction of oxidation-resistant mechanical carbon graphites at 650 C in air

    Science.gov (United States)

    Allen, G. P.; Wisnader, D. W.

    1975-01-01

    Studies were conducted to determine the friction and wear properties of experimental carbon-graphites. Hemispherically tipped carbon-graphite rider specimens were tested in sliding contact with rotating Inconel X-750 disks in air. A surface speed of 1.33 m/sec, a load of 500 g, and a specimen temperature of 650 C were used. Results indicate: (1) hardness is not a major factor in determining friction and wear under the conditions of these studies. (2) Friction and wear as low as or lower than those observed for a good commercial seal material were attained with some of the experimental materials studied. (3) The inclusion of boron carbide (as an oxidation inhibitor) has a strong influence on wear rate. (4) Phosphate treatment reduces the friction coefficient when boron carbide is not present in the base material.

  7. The Friction and Wear Properties of the Spherical Plain Bearings with Self-lubricating Composite Liner in Oscillatory Movement

    Institute of Scientific and Technical Information of China (English)

    GUOOiang; SONGYun-feng; QIAOHong-bin; LUOWei-li

    2004-01-01

    A test method based on the condition simulation and a friction and wear test machine fecturing oscillatory movement were set up for self-lubricating spherical plain bearings ( SPB).In the machine the condi-tion parameters sueh as load, angle and frequency of oscillation and number of test cycles can be properly con-trolled. The data relating to the tribological properties of the bearing, in terms of friction coefficient, linear wearamount, temperature near friction surface and applied load, can be monitored and recorded simultaneoasly dur-ing test process by a computerized measuring system of the machine. Efforts were made to improve the measurementtechnology of the friction coefficient in oscillating motion. In result, a well-designed bearing torque mechanismwas dzveloped, which could reveal the relation between the friction coefficient and the displneemeat of oscillatingangle in any defined cycle while the curve of friction coefficient vs number of testing cycles was eontinuolusly plotted.The tribologieul properties and service life of four kinds of the bearings, i, e, the sample Ⅰ-Ⅳ with different selffilubricating composite liners, iacluding three kinds of palytetrafluoroethylene (PTFE )fiber weave/epoxy resincomposite liners and a PTFE plasticl copper grid composite liner, were evaluated by testing, and the wear mecha-nisms of the liner materials were analyzed.

  8. Structure and friction of stearic acid and oleic acid films adsorbed on iron oxide surfaces in squalane.

    Science.gov (United States)

    Doig, Michael; Warrens, Chris P; Camp, Philip J

    2014-01-14

    The structure and friction of fatty acid surfactant films adsorbed on iron oxide surfaces lubricated by squalane are examined using large-scale molecular dynamics simulations. The structures of stearic acid and oleic acid films under static and shear conditions, and at various surface coverages, are described in detail, and the effects of unsaturation in the tail group are highlighted. At high surface coverage, the measured properties of stearic acid and oleic acid films are seen to be very similar. At low and intermediate surface coverages, the presence of a double bond, as in oleic acid, is seen to give rise to less penetration of lubricant in to the surfactant film and less layering of the lubricant near to the film. The kinetic friction coefficient is measured as a function of shear rate within the hydrodynamic (high shear rate) lubrication regime. Lubricant penetration and layering are observed to be correlated with friction coefficient. The friction coefficient with oleic acid depends only weakly on surface coverage, while stearic acid admits more lubricant penetration, and its friction coefficient increases significantly with decreasing surface coverage. Connections between film structure and friction are discussed.

  9. Evaluation of Skin Friction Drag for Liner Applications in Aircraft

    Science.gov (United States)

    Gerhold, Carl H.; Brown, Martha C.; Jasinski, Christopher M.

    2016-01-01

    A parameter that is gaining significance in the evaluation of acoustic liner performance is the skin friction drag induced by air flow over the liner surface. Estimates vary widely regarding the amount of drag the liner induces relative to a smooth wall, from less than a 20% increase to nearly 100%, and parameters such as face sheet perforate hole diameter, percent open area, and sheet thickness are expected to figure prominently in the skin friction drag. Even a small increase in liner drag can impose an economic penalty, and current research is focused on developing 'low drag' liner concepts, with the goal being to approach the skin friction drag of a smooth wall. The issue of skin friction drag takes on greater significance as airframe designers investigate the feasibility of putting sound absorbing liners on the non-lifting surfaces of the wings and fuselage, for the purpose of reducing engine noise reflected and scattered toward observers on the ground. Researchers at the NASA Langley Research Center have embarked on investigations of liner skin friction drag with the aims of: developing a systematic drag measurement capability, establishing the drag of current liners, and developing liners that produce reduced drag without compromising acoustic performance. This paper discusses the experimental procedures that have been developed to calculate the drag coefficient based on the change in momentum thickness and the companion research program being carried out to measure the drag directly using a force balance. Liner samples that are evaluated include a solid wall with known roughness and conventional liners with perforated facesheets of varying hole diameter and percent open area.

  10. Transport Coefficients of Fluids

    CERN Document Server

    Eu, Byung Chan

    2006-01-01

    Until recently the formal statistical mechanical approach offered no practicable method for computing the transport coefficients of liquids, and so most practitioners had to resort to empirical fitting formulas. This has now changed, as demonstrated in this innovative monograph. The author presents and applies new methods based on statistical mechanics for calculating the transport coefficients of simple and complex liquids over wide ranges of density and temperature. These molecular theories enable the transport coefficients to be calculated in terms of equilibrium thermodynamic properties, and the results are shown to account satisfactorily for experimental observations, including even the non-Newtonian behavior of fluids far from equilibrium.

  11. Frictional properties of CeO$_{2}$-Al$_{2}$O$_{3}$-ZrO$_{2}$ plasma-sprayed film under mixed and boundary lubricating conditions

    CERN Document Server

    Kita, H; Osumi, K; 10.2109/jcersj.112.615

    2004-01-01

    In order to find a counterpart for reducing the frictional coefficient of Al/sub 2/O/sub 3/-ZrO/sub 2/-CeO/sub 2/ plasma-sprayed film, the sliding properties in mixed and boundary lubricating conditions was investigated. It was found that combination of a CrN- coated cast iron pin and an Al/sub 2/O/sub 3/-ZrO/sub 2/-CeO/sub 2/ plasma sprayed plate provided the lowest frictional coefficient among several combinations chosen from practical materials. The coefficient of friction was much lower than that of the materials combination widely used for piston ring and cylinder liner. It was inferred that the combination of a pin made of hard materials with high density, a smooth surface such as CrN-coated cast iron and a porous plate can reduce the frictional coefficient because less sliding resistance is implemented and porosity retains oil.

  12. Sliding wear and friction behavior of ZA-27 alloy reinforced by Mn-containing intermetallic compounds

    Institute of Scientific and Technical Information of China (English)

    龙雁; 李元元; 张大童; 邱诚; 陈维平

    2002-01-01

    A ZA-27 alloy reinforced with M n-containing intermeta llic compounds was prepared and its tribological behaviors were investigated. By adding Mn, RE, Ti and B into ZA-27 alloy, the test alloy (ZMJ) was fabricated by sand casting. Microstructural analysis shows that considerable amount of Mn-containing intermetallic compounds such as Al5MnZn, Al9(MnZn)2 and Al65 Mn(RE)6Ti4Zn36 are formed. Compared to ZA-27, ZMJ shows better wear resistance, lower friction coefficient and lower temperature rise of worn surface under lubricated sliding condition. ZMJ also shows the lowest steady friction coefficient under dry friction condition. The wear resistance improvement of ZMJ is mainly attributed to the high hardness and good dispersion of these Mn-containing intermetallic compounds. It is indicated that the intermetallic compounds play a dominant role in reducing the sever adhesive and abrasive wear of the ZA-27 alloy.

  13. Friction and wear behavior of single-crystal silicon carbide in sliding contact with various metals

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1978-01-01

    Sliding friction experiments were conducted with single-crystal silicon carbide in contact with various metals. Results indicate the coefficient of friction is related to the relative chemical activity of the metals. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to silicon carbide. The chemical activity of the metal and its shear modulus may play important roles in metal-transfer, the form of the wear debris and the surface roughness of the metal wear scar. The more active the metal, and the less resistance to shear, the greater the transfer to silicon carbide and the rougher the wear scar on the surface of the metal. Hexagon-shaped cracking and fracturing formed by cleavage of both prismatic and basal planes is observed on the silicon carbide surface.

  14. Modeling of friction-induced deformation and microstructures.

    Energy Technology Data Exchange (ETDEWEB)

    Michael, Joseph Richard; Prasad, Somuri V.; Jungk, John Michael; Cordill, Megan J. (University of Minnesota); Bammann, Douglas J.; Battaile, Corbett Chandler; Moody, Neville Reid; Majumdar, Bhaskar Sinha (New Mexico Institure of Mining and Technology)

    2006-12-01

    Frictional contact results in surface and subsurface damage that could influence the performance, aging, and reliability of moving mechanical assemblies. Changes in surface roughness, hardness, grain size and texture often occur during the initial run-in period, resulting in the evolution of subsurface layers with characteristic microstructural features that are different from those of the bulk. The objective of this LDRD funded research was to model friction-induced microstructures. In order to accomplish this objective, novel experimental techniques were developed to make friction measurements on single crystal surfaces along specific crystallographic surfaces. Focused ion beam techniques were used to prepare cross-sections of wear scars, and electron backscattered diffraction (EBSD) and TEM to understand the deformation, orientation changes, and recrystallization that are associated with sliding wear. The extent of subsurface deformation and the coefficient of friction were strongly dependent on the crystal orientation. These experimental observations and insights were used to develop and validate phenomenological models. A phenomenological model was developed to elucidate the relationships between deformation, microstructure formation, and friction during wear. The contact mechanics problem was described by well-known mathematical solutions for the stresses during sliding friction. Crystal plasticity theory was used to describe the evolution of dislocation content in the worn material, which in turn provided an estimate of the characteristic microstructural feature size as a function of the imposed strain. An analysis of grain boundary sliding in ultra-fine-grained material provided a mechanism for lubrication, and model predictions of the contribution of grain boundary sliding (relative to plastic deformation) to lubrication were in good qualitative agreement with experimental evidence. A nanomechanics-based approach has been developed for characterizing the

  15. Analysis Groove Characteristics of Friction Dishes in Wet Speeding Clutch

    Institute of Scientific and Technical Information of China (English)

    HongYue; LiuJin; JinShiliang

    2004-01-01

    The impacts of different groove shapes, numbers, and angle of friction dish on transmitting torque, speed, push pressure in wet speeding clutch are discussed in this paper. Since the wet speeed governing clutch works within hydrodynamic lubrication mixture lubrication. boundary, lubrication and contact situation, the oils combining with a-hydrocarbon or polyester are getting widely used as lubricant.The power-law fluid model with Patir-Cheng average flow model, GT asperity contact model and oil film inertia are applied for average Reynolds equation setting, In order to investigate the relationship between average push pressure within hydrodynamic lubrication and mixture lubrication, average transmitting torque and output speed, the numeral calculation and analysis are presented. According to calculation, it is found that the groove shape, groove angle and groove numbers affect the average transfer torque and push pressure with the speed rate.

  16. Modeling of Instabilities and Self-organization at the Frictional Interface

    Science.gov (United States)

    Mortazavi, Vahid

    The field of friction-induced self-organization and its practical importance remains unknown territory to many tribologists. Friction is usually thought of as irreversible dissipation of energy and deterioration; however, under certain conditions, friction can lead to the formation of new structures at the interface, including in-situ tribofilms and various patterns at the interface. This thesis studies self-organization and instabilities at the frictional interface, including the instability due to the temperature-dependency of the coefficient of friction, the transient process of frictional running-in, frictional Turing systems, the stick-and-slip phenomenon, and, finally, contact angle (CA) hysteresis as an example of solid-liquid friction and dissipation. All these problems are chosen to bridge the gap between fundamental interest in understanding the conditions leading to self-organization and practical motivation. We study the relationship between friction-induced instabilities and friction-induced self-organization. Friction is usually thought of as a stabilizing factor; however, sometimes it leads to the instability of sliding, in particular when friction is coupled with another process. Instabilities constitute the main mechanism for pattern formation. At first, a stationary structure loses its stability; after that, vibrations with increasing amplitude occur, leading to a limit cycle corresponding to a periodic pattern. The self-organization is usually beneficial for friction and wear reduction because the tribological systems tend to enter a state with the lowest energy dissipation. The introductory chapter starts with basic definitions related to self-organization, instabilities and friction, literature review, and objectives. We discuss fundamental concepts that provide a methodological tool to investigate, understand and enhance beneficial processes in tribosystems which might lead to self-organization. These processes could result in the ability of a

  17. Swing Friction Behavior of the Contact Interface Between CoCrMo and UHMWPE Under Dynamic Loading

    Science.gov (United States)

    Chen, Kai; Zhang, Dekun; Yang, Xuehui; Zhang, Xin; Wang, Qingliang; Qi, Jianwei

    2016-12-01

    CoCrMo alloy and UHMWPE have been widely used in knee joint prosthesis implantation materials. In this paper, swing friction behavior of the contact interface between CoCrMo alloy and UHMWPE is studied under dynamic loading. Swing friction characteristic and damage mechanism are discussed. The results show that swing friction coefficients increase with the rising of maximum normal load and swing angular amplitude. Unloading-standing could play alleviative roles in friction and wear to a large degree. As the cycle number gradually increases, the surface roughness of UHMWPE decreases, while the roughness of CoCrMo increases. During the swing friction, the main damage mechanism of CoCrMo is abrasive wear and the main damage mechanisms of UHMWPE are abrasive wear, fatigue wear and plastic deformation. Besides, it is easier to generate surface damages with small angle and heavy load.

  18. Viscous friction between crystalline and amorphous phase of dragline silk.

    Directory of Open Access Journals (Sweden)

    Sandeep P Patil

    Full Text Available The hierarchical structure of spider dragline silk is composed of two major constituents, the amorphous phase and crystalline units, and its mechanical response has been attributed to these prime constituents. Silk mechanics, however, might also be influenced by the resistance against sliding of these two phases relative to each other under load. We here used atomistic molecular dynamics (MD simulations to obtain friction forces for the relative sliding of the amorphous phase and crystalline units of Araneus diadematus spider silk. We computed the coefficient of viscosity of this interface to be in the order of 10(2 Ns/m(2 by extrapolating our simulation data to the viscous limit. Interestingly, this value is two orders of magnitude smaller than the coefficient of viscosity within the amorphous phase. This suggests that sliding along a planar and homogeneous surface of straight polyalanine chains is much less hindered than within entangled disordered chains. Finally, in a simple finite element model, which is based on parameters determined from MD simulations including the newly deduced coefficient of viscosity, we assessed the frictional behavior between these two components for the experimental range of relative pulling velocities. We found that a perfectly relative horizontal motion has no significant resistance against sliding, however, slightly inclined loading causes measurable resistance. Our analysis paves the way towards a finite element model of silk fibers in which crystalline units can slide, move and rearrange themselves in the fiber during loading.

  19. Physical Theories with Average Symmetry

    OpenAIRE

    Alamino, Roberto C.

    2013-01-01

    This Letter probes the existence of physical laws invariant only in average when subjected to some transformation. The concept of a symmetry transformation is broadened to include corruption by random noise and average symmetry is introduced by considering functions which are invariant only in average under these transformations. It is then shown that actions with average symmetry obey a modified version of Noether's Theorem with dissipative currents. The relation of this with possible violat...

  20. Multigrid with FFT smoother for a simplified 2D frictional contact problem

    NARCIS (Netherlands)

    Zhao, J.; Vollebregt, E.A.H.; Oosterlee, C.W.

    2014-01-01

    This paper aims to develop a fast multigrid (MG) solver for a Fredholm integral equation of the first kind, arising from the 2D elastic frictional contact problem. After discretization on a rectangular contact area, the integral equation gives rise to a linear system with the coefficient matrix bein

  1. Effect of temperature on friction and wear behavior of CuO-zirconia composites

    NARCIS (Netherlands)

    Valefi, M.; Rooij, de M.B.; Schipper, D.J.; Winnubst, A.J.A.

    2012-01-01

    Results of wear tests using an alumina ball sliding against 5 wt% copper oxide doped tetragonal zirconia polycrystalline (CuO-TZP) ceramics are reported as a function of temperature up to 700 °C. The specific wear rate and friction coefficient are strongly dependent on temperature. Below a critical

  2. Friction between different wire bracket combinations in artificial saliva: an in vitro evaluation

    Directory of Open Access Journals (Sweden)

    Tatiana Kelly da Silva Fidalgo

    2011-02-01

    Full Text Available OBJECTIVE: The objective this work was to assess the friction coefficient between brackets and wires of different materials under conditions simulating the oral environment. MATERIAL AND METHODS: Stainless steel (SS and titanium-molybdenum alloy (TMA wires of 0.019x0.025-in diameter (American Orthodontics and polycarbonate bracket (American Orthodontics, ceramic bracket (American Orthodontics, and metal bracket (3M Unitek with slots of 0.022x0.030-in were used. The friction coefficient was assessed by means of mechanical traction with the system immersed in artificial saliva. The mean roughness of both wire surface and bracket slots was evaluated by using a surface profilometer. RESULTS: The system using TMA wire and polycarbonate bracket had the highest roughness (p<0.05. SS wire with ceramic bracket had the highest friction coefficient, whereas the use of metallic bracket yielded the lowest (p<0.05. However, it was observed a statistically significant difference in the system using TMA wire and ceramic bracket compared to that using TMA wire and polycarbonate bracket (p=0.038. CONCLUSIONS: Ceramic brackets in association with SS wire should be judiciously used, since this system showed a high friction coefficient.

  3. Frictional properties of high strength; Kokyodo porima sen'i kyoka purasuchikku no masatsu tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Takao, T.; Yoshino, D. [Sophia University, Tokyo (Japan); Kashima, T.; Yamanaka, A. [Toyobo Co., Ltd., Osaka (Japan)

    1999-11-10

    Dyneema fiber reinforced plastic there is the property, which expands with the reduced temperature, and the use as a superconducting coil reel material is examined. In this paper, Zylon fiber reinforced plastic also measured friction coefficient of the surface of ZFRP, and it has the similar property, and possibility of application as a coil reel material of ZFRP is examined. (NEDO)

  4. Investigation of scale effects and directionality dependence on friction and adhesion of human hair using AFM and macroscale friction test apparatus.

    Science.gov (United States)

    LaTorre, Carmen; Bhushan, Bharat

    2006-01-01

    Macroscale testing of human hair tribological properties has been widely used to aid in the development of better shampoos and conditioners. Recently, literature has focused on using the atomic force microscope (AFM) to study surface roughness, coefficient of friction, adhesive force, and wear (tribological properties) on the nanoscale in order to increase understanding about how shampoos and conditioners interact with the hair cuticle. Since there are both similarities and differences when comparing the tribological trends at both scales, it is thus recognized that scale effects are an important aspect of studying the tribology of hair. However, no microscale tribological data for hair exists in literature. This is unfortunate because many interactions between hair-skin, hair-comb, and hair-hair contact takes place at microasperities ranging from a few mum to hundreds of mum. Thus, to bridge the gap between the macro- and nanoscale data, as well as to gain a full understanding of the mechanisms behind the trends, it is now worthwhile to look at hair tribology on the microscale. Presented in this paper are coefficient of friction and adhesive force data on various scales for virgin and chemically damaged hair, both with and without conditioner treatment. Macroscale coefficient of friction was determined using a traditional friction test apparatus. Microscale and nanoscale tribological characterization was performed with AFM tips of various radii. The nano-, micro-, and macroscale trends are compared and the mechanisms behind the scale effects are discussed. Since the coefficient of friction changes drastically (on any scale) depending on whether the direction of motion is along or against the cuticle scales, the directionality dependence and responsible mechanisms are discussed.

  5. Investigation of scale effects and directionality dependence on friction and adhesion of human hair using AFM and macroscale friction test apparatus

    Energy Technology Data Exchange (ETDEWEB)

    LaTorre, Carmen [Nanotribology Laboratory for Information Storage and MEMS/NEMS (NLIM), Ohio State University, Suite 255, 650 Ackerman Road, Columbus, OH 43202 (United States); Bhushan, Bharat [Nanotribology Laboratory for Information Storage and MEMS/NEMS (NLIM), Ohio State University, Suite 255, 650 Ackerman Road, Columbus, OH 43202 (United States)]. E-mail: bhushan.2@osu.edu

    2006-06-15

    Macroscale testing of human hair tribological properties has been widely used to aid in the development of better shampoos and conditioners. Recently, literature has focused on using the atomic force microscope (AFM) to study surface roughness, coefficient of friction, adhesive force, and wear (tribological properties) on the nanoscale in order to increase understanding about how shampoos and conditioners interact with the hair cuticle. Since there are both similarities and differences when comparing the tribological trends at both scales, it is thus recognized that scale effects are an important aspect of studying the tribology of hair. However, no microscale tribological data for hair exists in literature. This is unfortunate because many interactions between hair-skin, hair-comb, and hair-hair contact takes place at microasperities ranging from a few {mu}m to hundreds of {mu}m. Thus, to bridge the gap between the macro- and nanoscale data, as well as to gain a full understanding of the mechanisms behind the trends, it is now worthwhile to look at hair tribology on the microscale. Presented in this paper are coefficient of friction and adhesive force data on various scales for virgin and chemically damaged hair, both with and without conditioner treatment. Macroscale coefficient of friction was determined using a traditional friction test apparatus. Microscale and nanoscale tribological characterization was performed with AFM tips of various radii. The nano-, micro-, and macroscale trends are compared and the mechanisms behind the scale effects are discussed. Since the coefficient of friction changes drastically (on any scale) depending on whether the direction of motion is along or against the cuticle scales, the directionality dependence and responsible mechanisms are discussed.

  6. Linear regression models of floor surface parameters on friction between Neolite and quarry tiles.

    Science.gov (United States)

    Chang, Wen-Ruey; Matz, Simon; Grönqvist, Raoul; Hirvonen, Mikko

    2010-01-01

    For slips and falls, friction is widely used as an indicator of surface slipperiness. Surface parameters, including surface roughness and waviness, were shown to influence friction by correlating individual surface parameters with the measured friction. A collective input from multiple surface parameters as a predictor of friction, however, could provide a broader perspective on the contributions from all the surface parameters evaluated. The objective of this study was to develop regression models between the surface parameters and measured friction. The dynamic friction was measured using three different mixtures of glycerol and water as contaminants. Various surface roughness and waviness parameters were measured using three different cut-off lengths. The regression models indicate that the selected surface parameters can predict the measured friction coefficient reliably in most of the glycerol concentrations and cut-off lengths evaluated. The results of the regression models were, in general, consistent with those obtained from the correlation between individual surface parameters and the measured friction in eight out of nine conditions evaluated in this experiment. A hierarchical regression model was further developed to evaluate the cumulative contributions of the surface parameters in the final iteration by adding these parameters to the regression model one at a time from the easiest to measure to the most difficult to measure and evaluating their impacts on the adjusted R(2) values. For practical purposes, the surface parameter R(a) alone would account for the majority of the measured friction even if it did not reach a statistically significant level in some of the regression models.

  7. Average Convexity in Communication Situations

    NARCIS (Netherlands)

    Slikker, M.

    1998-01-01

    In this paper we study inheritance properties of average convexity in communication situations. We show that the underlying graph ensures that the graphrestricted game originating from an average convex game is average convex if and only if every subgraph associated with a component of the underlyin

  8. Z-plasty lengthening for iliotibial band friction syndrome.

    Science.gov (United States)

    Barber, F Alan; Boothby, Michael H; Troop, Randal L

    2007-10-01

    Iliotibial band friction syndrome presents with lateral knee pain usually in runners. When conservative treatment fails, surgical lengthening, or Z-plasty, can provide symptomatic relief. This retrospective study evaluated the long-term results of iliotibial band Z-plasty for chronic iliotibial band friction syndrome in a consecutive series of patients. Inclusion criteria were failed nonoperative treatment for symptomatic iliotibial band friction syndrome for at least 3 months, minimum age of 17 years, and closed growth plates. Exclusion criteria were history of significant trauma, prior knee surgery, lateral compartment pathology, and anterior or posterior cruciate ligament instability. Postoperative evaluation included annual physical examination consisting of Tegner, Lysholm, Cincinnati, and International Knee Documentation Committee (IKDC) activity scores. Of an initial group of 11 patients, 8 were evaluated an average of 75.6 months postoperatively (range: 59-97 months). Average length of preoperative symptoms was 15.6 months (range: 3-36 months), and average length of nonoperative management was 6.9 months (range: 3-24 months). Postoperatively, mean Cincinnati score was 82.9 (range: 55-95), Tegner score was 4.4 (range: 2-7), Lysholm score was 88.6 (range: 57-100), and IKDC activity score was 2.6 (range: 1-4). No adverse events occurred during surgery. All patients reported complete resolution of lateral knee pain and a full return to preoperative activity levels. Iliotibial Z-plasty was successful for refractory iliotibial band friction syndrome. This improvement was maintained out to 8 years after surgery.

  9. High temperature skin friction measurement

    Science.gov (United States)

    Tcheng, Ping; Holmes, Harlan K.; Supplee, Frank H., Jr.

    1989-01-01

    Skin friction measurement in the NASA Langley hypersonic propulsion facility is described. The sensor configuration utilized an existing balance, modified to provide thermal isolation and an increased standoff distance. For test run times of about 20 sec and ambient-air cooling of the test section and balance, the modified balance performed satisfactorily, even when it was subjected to acoustic and structural vibration. The balance is an inertially balanced closed-loop servo system where the current to a moving-coil motor needed to restore or null the output from the position sensor is a measure of the force or skin friction tending to displace the moving element. The accuracy of the sensor is directly affected by the position sensor in the feedback loop, in this case a linear-variable differential transformer which has proven to be influenced by temperature gradients.

  10. The average free volume model for liquids

    CERN Document Server

    Yu, Yang

    2014-01-01

    In this work, the molar volume thermal expansion coefficient of 59 room temperature ionic liquids is compared with their van der Waals volume Vw. Regular correlation can be discerned between the two quantities. An average free volume model, that considers the particles as hard core with attractive force, is proposed to explain the correlation in this study. A combination between free volume and Lennard-Jones potential is applied to explain the physical phenomena of liquids. Some typical simple liquids (inorganic, organic, metallic and salt) are introduced to verify this hypothesis. Good agreement from the theory prediction and experimental data can be obtained.

  11. Sampling Based Average Classifier Fusion

    Directory of Open Access Journals (Sweden)

    Jian Hou

    2014-01-01

    fusion algorithms have been proposed in literature, average fusion is almost always selected as the baseline for comparison. Little is done on exploring the potential of average fusion and proposing a better baseline. In this paper we empirically investigate the behavior of soft labels and classifiers in average fusion. As a result, we find that; by proper sampling of soft labels and classifiers, the average fusion performance can be evidently improved. This result presents sampling based average fusion as a better baseline; that is, a newly proposed classifier fusion algorithm should at least perform better than this baseline in order to demonstrate its effectiveness.

  12. THE FRICTIONAL RESISTANCE CHARACTERISTICS OF GAS-LIQUID TWO-PHASE FLOW IN HELICAL-COILED TUBES

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This paper deal with the frictional resistance characteristics of gas-liquid two-phase flow in vertical-upward helical-coiled tubes under the system pressure 0.1-0.6MPa.By means of dimension analysis and π theorem, the correlation formulas were obtained for calculating the frictional resistance coefficients of gas-liquid two-phase flow in helical-coiled tubes.The calculated results agree well with the experimental results.

  13. Lawn tennis balls, Rolling friction experiment and Trouton viscosity

    CERN Document Server

    Singh, Ankit; Kulkarni, Kaustubh; Budhraja, Abhishek; Tej, K R Sai; Sankarlingam, Satish; Biswas, Anindya Kumar

    2008-01-01

    Three lawn tennis balls were arbitrarily taken. One ball was new, one was moderately old and another was old. We have fabricated a conveyor belt set-up and measured rolling friction coefficients, $\\mu_{r}$, of the three balls as a function of their angular velocities, $\\omega$. For the new ball, quadratic fit is perfect. For the moderately old ball, linear fit is accurate. In all the three cases, from linear fits, we obtain $k_{rol}$, where, $\\mu_{r}= k_{rol} \\omega + intercept$. We deduce $k_{rol}$ theoretically also, assuming Trouton ratio as three. The experimental results and theoretical estimates are of the same order of magnitude.

  14. Giant Frictional Drag in Double Bilayer Graphene Heterostructures

    Science.gov (United States)

    Lee, Kayoung; Xue, Jiamin; Dillen, David C.; Watanabe, Kenji; Taniguchi, Takashi; Tutuc, Emanuel

    2016-07-01

    We study the frictional drag between carriers in two bilayer graphene flakes separated by a 2-5 nm thick hexagonal boron nitride dielectric. At temperatures (T ) lower than ˜10 K , we observe a large anomalous negative drag emerging predominantly near the drag layer charge neutrality. The anomalous drag resistivity increases dramatically with reducing T , and becomes comparable to the layer resistivity at the lowest T =1.5 K . At low T the drag resistivity exhibits a breakdown of layer reciprocity. A comparison of the drag resistivity and the drag layer Peltier coefficient suggests a thermoelectric origin of this anomalous drag.

  15. Friction and Wear Reduction of Eccentric Journal Bearing Made of Sn-Based Babbitt for Ore Cone Crusher

    OpenAIRE

    Auezhan Amanov; Byungmin Ahn; Moon Gu Lee; Yongho Jeon; Young-Sik Pyun

    2016-01-01

    An anti-friction Babbitt alloy-coated bearing made by a casting process is a journal bearing, which is used in an ore cone crusher eccentric. The main purpose of the Babbitt coated eccentric is to provide a low friction to support and guide a rotating shaft. Despite the fact that the Babbitt-coated eccentric offers a low friction coefficient and can be operated without a continuous supply of lubricant, it suffers from mining environments and short service life. In this study, an ultrasonic na...

  16. Friction and Wear Reduction of Eccentric Journal Bearing Made of Sn-Based Babbitt for Ore Cone Crusher

    Directory of Open Access Journals (Sweden)

    Auezhan Amanov

    2016-11-01

    Full Text Available An anti-friction Babbitt alloy-coated bearing made by a casting process is a journal bearing, which is used in an ore cone crusher eccentric. The main purpose of the Babbitt coated eccentric is to provide a low friction to support and guide a rotating shaft. Despite the fact that the Babbitt-coated eccentric offers a low friction coefficient and can be operated without a continuous supply of lubricant, it suffers from mining environments and short service life. In this study, an ultrasonic nanocrystalline surface modification (UNSM technique was used to further reduce the friction coefficient, to increase the wear resistance, and to extend the service life of the Sn-based Babbitt metal. The friction and wear behavior of the Sn-based Babbitt metal was investigated using a block-on-ring tester under both dry and oil-lubricated conditions. The results of the experiments revealed that the friction and wear behavior of Sn-based Babbitt metal could be improved by the application of the UNSM technique. The friction and wear mechanisms of the specimens were explained and discussed in terms of changes in surface properties—microstructure, surface hardness, surface roughness, etc.

  17. PIV-based investigation of the skin friction of the flow over random fibrous media

    Science.gov (United States)

    Mirbod, Parisa; Gheisari, Reza

    2015-11-01

    Finite Reynolds number (Reflow over fibrous medium inside a rectangular duct was studied using a planar 2D PIV system. Three different fibrous materials with different porosities were used. Fibrous material lined the bottom wall of the duct along the length of the duct. The flow regime for all tests was laminar, and measurements were all done when the flow reached a steady state. Error and uncertainty sources in the experiments were also discussed. Shear rates were estimated at the surface of the fibrous media. As a conclusion to this study skin friction factor were calculated at the interface of all fibrous media at selected Reynolds number. Then using power function, curve fits with the Cf = a/Re form were found which could closely correlate skin friction and Reynolds number. To weaken the effect of near-wall errors in estimated shear rates and consequently skin friction, an average of shear rate estimation in a layer with thickness of 5 mm was calculated which was used to calculate an average skin friction. Correlations of average skin friction with average Reynolds number were also presented.

  18. Design formulas of transmission coefficients for permeable breakwaters

    Directory of Open Access Journals (Sweden)

    Su-xiang ZHANG

    2015-10-01

    Full Text Available New empirical formulas of the transmission coefficient for permeable breakwaters were suggested based on available experimental data regarding the low-crest structure (LCS, including the permeable rubble mound breakwater and pile-type breakwater. The rationality of the present formulas was verified by their comparison with existing empirical and analytical formulas. Numerical flume results were obtained by solving the modified Boussinessq-type wave equations (MBEs, and a new expression relating the friction coefficient to the relative submerged depth was also derived. Comparative analysis shows that the results of the present formulas agree with the numerical flume results as well as available experimental data, and the present formulas are superior to the existing empirical and analytical expressions in estimating the transmission coefficient. The present formulas can provide references for estimation of the transmission coefficient in engineering practice.

  19. Design formulas of transmission coefficients for permeable breakwaters

    Institute of Scientific and Technical Information of China (English)

    Su-xiang ZHANG; Xi LI

    2014-01-01

    Newempirical formulas of the transmission coefficient for permeable breakwaters were suggested based on available experimental data regarding the low-crest structure (LCS), including the permeable rubble mound breakwater and pile-type breakwater. The rationality of the present formulas was verified by their comparison with existing empirical and analytical formulas. Numerical flume results were obtained by solving the modified Boussinessq-type wave equations (MBEs), and a new expression relating the friction coefficientαto the relative submerged depth tsRHwas also derived. Comparative analysis shows that the results of the present formulas agree with the numerical flume results as well as available experimental data, and the present formulas are superior to the existing empirical and analytical expressions in estimating the transmission coefficient. The present formulas can provide references for estimation of the transmission coefficient in engineering practice.

  20. Non-linear friction in reciprocating hydraulic rod seals: Simulation and measurement

    Science.gov (United States)

    Bullock, A. K.; Tilley, D. G.; Johnston, D. N.; Bowen, C. R.; Keogh, P. S.

    2009-08-01

    Non-linear seal friction can impede the performance of hydraulic actuation systems designed for high precision positioning with favourable dynamic response. Methods for predicting seal friction are required to help develop sealing systems for this type of application. Recent simulation techniques have claimed progress, although have yet to be validated experimentally. A conventional reciprocating rod seal is analysed using established elastohydrodynamic theory and the mixed lubrication Greenwood-Williamson-average Reynolds model. A test rig was used to assess the accuracy of the simulation results for both instroke and outstroke. Inverse hydrodynamic theory is shown to predict a U0.5 power law between rod speed and friction. Comparison with experimental data shows the theory to be qualitatively inaccurate and to predict friction levels an order of magnitude lower than those measured. It was not possible to model the regions very close to the inlet and outlet due to the high pressure gradients at the edges of the contact. The mixed lubrication model produces friction levels within the correct order of magnitude, although incorrectly predicts higher friction during instroke than outstroke. Previous experiments have reported higher friction during instroke than outstroke for rectangular seals, suggesting that the mixed lubrication model used could possibly be suitable for symmetric seals, although not for seal tribology in general.