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Sample records for coefficient of friction

  1. Apparatus for measurement of coefficient of friction

    Science.gov (United States)

    Slifka, A. J.; Siegwarth, J. D.; Sparks, L. L.; Chaudhuri, Dilip K.

    1990-01-01

    An apparatus designed to measure the coefficient of friction in certain controlled atmospheres is described. The coefficient of friction observed during high-load tests was nearly constant, with an average value of 0.56. This value is in general agreement with that found in the literature and also with the initial friction coefficient value of 0.67 measured during self-mated friction of 440C steel in an oxygen environment.

  2. 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

  3. The coefficient of friction, particularly of ice

    International Nuclear Information System (INIS)

    Mills, Allan

    2008-01-01

    The static and dynamic coefficients of friction are defined, and values from 0.3 to 0.6 are quoted for common materials. These drop to about 0.15 when oil is added as a lubricant. Water ice at temperatures not far below 0 °C is remarkable for low coefficients of around 0.05 for static friction and 0.04–0.02 for dynamic friction, but these figures increase as the temperature diminishes. Reasons for the slipperiness of ice are summarized, but they are still not entirely clear. One hypothesis suggests that it is related to the transient formation of a lubricating film of liquid water produced by frictional heating. If this is the case, some composition melting a little above ambient temperatures might provide a skating rink that did not require expensive refrigeration. Various compositions have been tested, but an entirely satisfactory material has yet to be found

  4. Prediction of friction coefficients for gases

    Science.gov (United States)

    Taylor, M. F.

    1969-01-01

    Empirical relations are used for correlating laminar and turbulent friction coefficients for gases, with large variations in the physical properties, flowing through smooth tubes. These relations have been used to correlate friction coefficients for hydrogen, helium, nitrogen, carbon dioxide and air.

  5. Micro- and macroscale coefficients of friction of cementitious materials

    International Nuclear Information System (INIS)

    Lomboy, Gilson; Sundararajan, Sriram; Wang, Kejin

    2013-01-01

    Millions of metric tons of cementitious materials are produced, transported and used in construction each year. The ease or difficulty of handling cementitious materials is greatly influenced by the material friction properties. In the present study, the coefficients of friction of cementitious materials were measured at the microscale and macroscale. The materials tested were commercially-available Portland cement, Class C fly ash, and ground granulated blast furnace slag. At the microscale, the coefficient of friction was determined from the interaction forces between cementitious particles using an Atomic Force Microscope. At the macroscale, the coefficient of friction was determined from stresses on bulk cementitious materials under direct shear. The study indicated that the microscale coefficient of friction ranged from 0.020 to 0.059, and the macroscale coefficient of friction ranged from 0.56 to 0.75. The fly ash studied had the highest microscale coefficient of friction and the lowest macroscale coefficient of friction. -- Highlights: •Microscale (interparticle) coefficient of friction (COF) was determined with AFM. •Macroscale (bulk) COF was measured under direct shear. •Fly ash had the highest microscale COF and the lowest macroscale COF. •Portland cement against GGBFS had the lowest microscale COF. •Portland cement against Portland cement had the highest macroscale COF

  6. Coefficient of Friction of Human Corneal Tissue.

    Science.gov (United States)

    Wilson, Tawnya; Aeschlimann, Rudolf; Tosatti, Samuele; Toubouti, Youssef; Kakkassery, Joseph; Osborn Lorenz, Katherine

    2015-09-01

    A novel property evaluation methodology was used to determine the elusive value for the human corneal coefficient of friction (CoF). Using a microtribometer on 28 fresh human donor corneas with intact epithelia, the CoF was determined in 4 test solutions (≥5 corneas/solution): tear-mimicking solution (TMS) in borate-buffered saline (TMS-PS), TMS in phosphate-buffered saline (TMS-PBS), TMS with HEPES-buffered saline (TMS-HEPES), and tear-like fluid in PBS (TLF-PBS). Mean (SD) CoF values ranged from 0.006 to 0.015 and were 0.013 (0.010) in TMS-PS, 0.006 (0.003) in TMS-PBS, 0.014 (0.005) in TMS-HEPES, and 0.015 (0.009) in TLF-PBS. Statistically significant differences were shown for TMS-PBS versus TLF (P = 0.0424) and TMS-PBS versus TMS-HEPES (P = 0.0179), but not for TMS-PBS versus TMS-PS (P = 0.2389). Successful measurement of the fresh human corneal tissue CoF was demonstrated, with values differing in the evaluated buffer solutions, within this limited sample size.

  7. Asymmetrical slip propensity: required coefficient of friction.

    Science.gov (United States)

    Seo, Jung-suk; Kim, Sukwon

    2013-07-31

    Most studies in performing slips and falls research reported their results after the ipsilateral leg of subjects (either right foot or left foot) was guided to contact the contaminated floor surface although many studies indicated concerns for asymmetries of legs in kinematic or kinetic variables. Thus, the present study evaluated if dominant leg's slip tendency would be different from non-dominant leg's slip tendency by comparing the Required Coefficient of Friction (RCOF) of the two lower limbs. Forty seven health adults participated in the present study. RCOF was measured when left or right foot of subjects contacted the force platforms respectively. Paired t-test was performed to test if RCOF and heel velocity (HCV) of dominant legs was different from that of non-dominant legs. It was suggested that the asymmetry in RCOFs and HCV between the two lower limbs existed. The RCOFs of non-dominant legs were higher than that of dominant legs. The results indicated that asymmetry in slip propensity, RCOF, was existed in lower extremity. The results from the study suggested that it would be benefit to include a variable, such as asymmetry, in slips and falls research.

  8. Friction coefficients of PTFE bearing liner

    Science.gov (United States)

    Daniels, C. M.

    1979-01-01

    Data discusses frictional characteristics of PTFE (polytetrafluoroethylene) under temperature extremes and in vacuum environment. Tests were also run on reduced scale hardware to determine effects of vacuum. Data is used as reference by designers of aircraft-control system rod-end bearings and for bearings used in polar regions.

  9. A Simple Measurement of the Sliding Friction Coefficient

    Science.gov (United States)

    Gratton, Luigi M.; Defrancesco, Silvia

    2006-01-01

    We present a simple computer-aided experiment for investigating Coulomb's law of sliding friction in a classroom. It provides a way of testing the possible dependence of the friction coefficient on various parameters, such as types of materials, normal force, apparent area of contact and sliding velocity.

  10. Chondroitin sulfate reduces the friction coefficient of articular cartilage.

    Science.gov (United States)

    Basalo, Ines M; Chahine, Nadeen O; Kaplun, Michael; Chen, Faye H; Hung, Clark T; Ateshian, Gerard A

    2007-01-01

    The objective of this study was to investigate the effect of chondroitin sulfate (CS)-C on the frictional response of bovine articular cartilage. The main hypothesis is that CS decreases the friction coefficient of articular cartilage. Corollary hypotheses are that viscosity and osmotic pressure are not the mechanisms that mediate the reduction in the friction coefficient by CS. In Experiment 1, bovine articular cartilage samples (n=29) were tested in either phosphate buffered saline (PBS) or in PBS containing 100mg/ml of CS following 48h incubation in PBS or in PBS+100mg/ml CS (control specimens were not subjected to any incubation). In Experiment 2, samples (n=23) were tested in four different solutions: PBS, PBS+100mg/ml CS, and PBS+polyethylene glycol (PEG) (133 or 170mg/ml). In Experiment 3, samples (n=18) were tested in three solutions of CS (0, 10 and 100mg/ml). Frictional tests (cartilage-on-glass) were performed under constant stress (0.5MPa) for 3600s and the time-dependent friction coefficient was measured. Samples incubated or tested in a 100mg/ml CS solution exhibited a significantly lower equilibrium friction coefficient than the respective PBS control. PEG solutions delayed the rise in the friction coefficient relative to the PBS control, but did not reduce the equilibrium value. Testing in PBS+10mg/ml of CS did not cause any significant decrease in the friction coefficient. In conclusion, CS at a concentration of 100mg/ml significantly reduces the friction coefficient of bovine articular cartilage and this mechanism is neither mediated by viscosity nor osmolarity. These results suggest that direct injection of CS into the joint may provide beneficial tribological effects.

  11. Anticipating the friction coefficient of friction materials used in automobiles by means of machine learning without using a test instrument

    OpenAIRE

    TİMUR, Mustafa; AYDIN, Fatih

    2013-01-01

    The most important factor for designs in which friction materials are used is the coefficient of friction. The coefficient of friction has been determined taking such variants as velocity, temperature, and pressure into account, which arise from various factors in friction materials, and by analyzing the effects of these variants on friction materials. Many test instruments have been produced in order to determine the coefficient of friction. In this article, a study about the use ...

  12. Measurement of Dynamic Friction Coefficient on the Irregular Free Surface

    International Nuclear Information System (INIS)

    Yeom, S. H.; Seo, K. S.; Lee, J. H.; Lee, K. H.

    2007-01-01

    A spent fuel storage cask must be estimated for a structural integrity when an earthquake occurs because it freely stands on ground surface without a restriction condition. Usually the integrity estimation for a seismic load is performed by a FEM analysis, the friction coefficient for a standing surface is an important parameter in seismic analysis when a sliding happens. When a storage cask is placed on an irregular ground surface, measuring a friction coefficient of an irregular surface is very difficult because the friction coefficient is affected by the surface condition. In this research, dynamic friction coefficients on the irregular surfaces between a concrete cylinder block and a flat concrete slab are measured with two methods by one direction actuator

  13. Nitrogen ion implantation effect on friction coefficient of tool steel

    International Nuclear Information System (INIS)

    Velichko, N.I.; Udovenko, V.F.; Markus, A.M.; Presnyakova, G.N.; Gamulya, G.D.

    1988-01-01

    Effect of nitrogen molecular ion implantation into KhVSG steel on the friction coefficient in the air and vacuum is investigated. Irradiation is carried out by the N 2 + beam with energy 120 keV and flux density 5 μ/cm 2 at room temperature in vacuum 5x10 -4 Pa. The integral dose of irradiation is 10 17 particle/cm 2 . Nitrogen ion implantation is shown to provide the formation of the modified layer changing friction properties of steel. The friction coefficient can either increase or decrease depending on implantation and test conditions. 4 refs.; 2 figs

  14. Friction coefficient of skin in real-time.

    Science.gov (United States)

    Sivamani, Raja K; Goodman, Jack; Gitis, Norm V; Maibach, Howard I

    2003-08-01

    Friction studies are useful in quantitatively investigating the skin surface. Previous studies utilized different apparatuses and materials for these investigations but there was no real-time test parameter control or monitoring. Our studies incorporated the commercially available UMT Series Micro-Tribometer, a tribology instrument that permits real-time monitoring and calculation of the important parameters in friction studies, increasing the accuracy over previous tribology and friction measurement devices used on skin. Our friction tests were performed on four healthy volunteers and on abdominal skin samples. A stainless steel ball was pressed on to the skin with at a pre-set load and then moved across the skin at a constant velocity of 5 mm/min. The UMT continuously monitored the friction force of the skin and the normal force of the ball to calculate the friction coefficient in real-time. Tests investigated the applicability of Amonton's law, the impact of increased and decreased hydration, and the effect of the application of moisturizers. The friction coefficient depends on the normal load applied, and Amonton's law does not provide an accurate description for the skin surface. Application of water to the skin increased the friction coefficient and application of isopropyl alcohol decreased it. Fast acting moisturizers immediately increased the friction coefficient, but did not have the prolonged effect of the slow, long lasting moisturizers. The UMT is capable of making real-time measurements on the skin and can be used as an effective tool to study friction properties. Results from the UMT measurements agree closely with theory regarding the skin surface.

  15. Apparent Coefficient of Friction of Wheat on Denim.

    Science.gov (United States)

    Schwab, Charles V

    2017-07-31

    Calculation of the extraction force for a grain entrapment victim requires a coefficient of friction between the grain and the surface of the victim. Because denim is a common fabric for the work clothes that cover entrapment victims, the coefficient of friction between grain and denim becomes necessary. The purpose of this research was to calculate the apparent coefficient of friction of wheat on denim fabric using a proven procedure. The expectation is to improve the current understanding of conditions that influence extraction forces for victims buried in wheat. The apparent coefficient of friction of wheat on denim fabric was calculated to be 0.167 with a standard deviation of ±0.013. The wheat had a moisture content of 10.7% (w.b.) and bulk density of 778.5 kg m-3. The apparent coefficient of friction of wheat on denim was not significantly affected by pull speeds of 0.004, 0.008, and 0.021 mm s-1 nor normal grain pressures of 3.2, 4.8, 6.3, 7.9, and 11.1 kPa. This is a beginning of understanding the conditions that influence the extraction forces for grain entrapment victims. Copyright© by the American Society of Agricultural Engineers.

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

    International Nuclear Information System (INIS)

    Liu, Huaiju; Zhu, Caichao; Sun, Zhangdong; Zhang, Yuanyuan; Song, Chaosheng

    2016-01-01

    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.

  17. 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

  18. Influence of roughness parameters on coefficient of friction under ...

    Indian Academy of Sciences (India)

    S¯adhan¯a Vol. 33, Part 3, June 2008, pp. ... Surface texture and thus roughness parameters influence coefficient of friction during sliding. ..... tural irregularities and complexities of the natural system, fractal is widely used to explain the natural ...

  19. Evaluation of coefficient of friction in bulk metal forming

    NARCIS (Netherlands)

    Solhjoo, Soheil

    In this study an upper bound analysis for cylindrical "Barrel Compression Test" (BCT) is developed. BCT method is a very simple method which can be utilized in order to evaluate quantitatively the coefficient of friction by means of just one cylindrical specimen in an upsetting test. The method is

  20. Determination of the Static Friction Coefficient from Circular Motion

    Science.gov (United States)

    Molina-Bolívar, J. A.; Cabrerizo-Vílchez, M. A.

    2014-01-01

    This paper describes a physics laboratory exercise for determining the coefficient of static friction between two surfaces. The circular motion of a coin placed on the surface of a rotating turntable has been studied. For this purpose, the motion is recorded with a high-speed digital video camera recording at 240 frames s[superscript-1], and the…

  1. Preload, Coefficient of Friction, and Thread Friction in an Implant-Abutment-Screw Complex.

    Science.gov (United States)

    Wentaschek, Stefan; Tomalla, Sven; Schmidtmann, Irene; Lehmann, Karl Martin

    To examine the screw preload, coefficient of friction (COF), and tightening torque needed to overcome the thread friction of an implant-abutment-screw complex. In a customized load frame, 25 new implant-abutment-screw complexes including uncoated titanium alloy screws were torqued and untorqued 10 times each, applying 25 Ncm. Mean preload values decreased significantly from 209.8 N to 129.5 N according to the number of repetitions. The overall COF increased correspondingly. There was no comparable trend for the thread friction component. These results suggest that the application of a used implant-abutment-screw complex may be unfavorable for obtaining optimal screw preload.

  2. Evaluation of coefficient of friction in bulk metal forming

    OpenAIRE

    Solhjoo, Soheil

    2014-01-01

    In this study an upper bound analysis for cylindrical "Barrel Compression Test" (BCT) is developed. BCT method is a very simple method which can be utilized in order to evaluate quantitatively the coefficient of friction by means of just one cylindrical specimen in an upsetting test. The method is checked by a series of finite element method (FEM) simulations and by means of the results of FEM simulations the method is modified.

  3. Modeling and data analysis of the NASA-WSTF frictional heating apparatus - Effects of test parameters on friction coefficient

    Science.gov (United States)

    Zhu, Sheng-Hu; Stoltzfus, Joel M.; Benz, Frank J.; Yuen, Walter W.

    1988-01-01

    A theoretical model is being developed jointly by the NASA White Sands Test Facility (WSTF) and the University of California at Santa Barbara (UCSB) to analyze data generated from the WSTF frictional heating test facility. Analyses of the data generated in the first seconds of the frictional heating test are shown to be effective in determining the friction coefficient between the rubbing interfaces. Different friction coefficients for carobn steel and Monel K-500 are observed. The initial condition of the surface is shown to affect only the initial value of the friction coefficient but to have no significant influence on the average steady-state friction coefficient. Rotational speed and the formation of oxide film on the rotating surfaces are shown to have a significant effect on the friction coefficient.

  4. [Determination of a Friction Coefficient for THA Bearing Couples].

    Science.gov (United States)

    Vrbka, M; Nečas, D; Bartošík, J; Hartl, M; Křupka, I; Galandáková, A; Gallo, J

    2015-01-01

    The wear of articular surfaces is considered one of the most important factors limiting the life of total hip arthroplasty (THA). It is assumed that the particles released from the surface of a softer material induce a complex inflammatory response, which will eventually result in osteolysis and aseptic loosening. Implant wear is related to a friction coefficient which depends on combination of the materials used, roughness of the articulating surfaces, internal clearance, and dimensions of the prosthesis. The selected parameters of the bearing couples tested were studied using an experimental device based on the principle of a pendulum. Bovine serum was used as a lubricant and the load corresponded to a human body mass of 75 kg. The friction coefficient was derived from a curve of slowdown of pendulum oscillations. Roughness was measured with a device working on the principle of interferometry. Clearance was assessed by measuring diameters of the acetabular and femoral heads with a 3D optical scanner. The specimens tested included unused metal-on-highly cross-linked polyethylene, ceramic-on-highly cross-linked polyethylene and ceramic-on-ceramic bearing couples with the diameters of 28 mm and 36 mm. For each measured parameter, an arithmetic mean was calculated from 10 measurements. 1) The roughness of polyethylene surfaces was higher by about one order of magnitude than the roughness of metal and ceramic components. The Protasul metal head had the least rough surface (0.003 μm). 2) The ceramic-on-ceramic couples had the lowest clearance. Bearing couples with polyethylene acetabular liners had markedly higher clearances ranging from 150 μm to 545 μm. A clearance increased with large femoral heads (up to 4-fold in one of the couple tested). 3) The friction coefficient was related to the combination of materials; it was lowest in ceramic-on-ceramic surfaces (0.11 to 0.12) and then in ceramic-on-polyethylene implants (0.13 to 0.14). The friction coefficient is

  5. Determination of friction coefficient in unconfined compression of brain tissue.

    Science.gov (United States)

    Rashid, Badar; Destrade, Michel; Gilchrist, Michael D

    2012-10-01

    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 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 μ 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 μ was equal to 0.09±0.03, 0.18±0.04, 0.18±0.04 and 0.20±0.02 at strain rates of 1, 30, 60 and 90/s, respectively. Additional tests were also performed to analyze brain tissue under lubricated and bonded conditions, with and without initial contact of the top platen with the brain tissue, with different specimen aspect ratios and with different lubricants (Phosphate Buffer Saline (PBS), Polytetrafluoroethylene (PTFE) and Silicone). The test conditions (lubricant used, biological tissue, loading velocity) adopted in this study were similar to the studies conducted by other research groups. This study will help to understand the amount of friction generated during unconfined compression of brain tissue for strain rates of up to 90/s. Copyright © 2012 Elsevier Ltd. All rights reserved.

  6. The coefficient of friction of chrysotile gouge at seismogenic depths

    Science.gov (United States)

    Moore, Diane E.; Lockner, D.A.; Tanaka, H.; Iwata, K.

    2004-01-01

    We report new strength data for the serpentine mineral chrysotile at effective normal stresses, ??sn between 40 and 200 MPa in the temperature range 25??-280??C. Overall, the coefficient of friction, ?? (= shear stress/effective normal stress) of water-saturated chrysotile gouge increases both with increasing temperature and ??sn, but the rates vary and the temperature-related increases begin at ???100??C. As a result, a frictional strength minimum (?? = 0.1) occurs at low ??sn at about 100??C. Maximum strength (?? = 0.55) results from a combination of high normal stress and high temperature. The low-strength region is characterized by velocity strengthening and the high-strength region by velocity-weakening behavior. Thoroughly dried chrysotile has ?? = 0.7 and is velocity-weakening. The frictional properties of chrysolite can be explained in its tendency to adsorb large amounts of water that acts as a lubricant during shear. The water is progressively driven off the fiber surfaces with increasing temperature and pressure, causing chrysotile to approach its dry strength. Depth profiles for a chrysotile-lined fault constructed from these data would pass through a strength minimum at ???3 km depth, where sliding should be stable. Below that depth, strength increases rapidly as does the tendency for unstable (seismic) slip. Such a trend would not have been predicted from the room-temperature data. These results therefore illustrate the potential hazards of extrapolating room-temperature friction data to predict fault zone behavior at depth. This depth profile for chrysotile is consistent with the pattern of slip on the Hayward fault, which creeps aseismically at shallow depths but which may be locked below 5 km depth. ?? 2004 by V. H. Winston and Son, Inc. All rights reserved.

  7. A study on a characteristic of stem friction coefficient for motor operated flexible wedge gate valve

    International Nuclear Information System (INIS)

    Kim, Dae-Woong; Park, Sung-Geun; Lee, Sang-Guk; Kang, Shin-Cheul

    2009-01-01

    Stem friction coefficient is a coefficient that represents friction between thread leads of the stem and stem nut. It is an important factor to determine output thrust delivered from the actuator to the valve stem in assessing performance of motor operated valves. This study analyzes the effects of changes in differential pressure on stem friction coefficient, and determines the bounding value of stem friction coefficient. A dynamic test was conducted on multiple flexible wedge gate valves in various differential pressure conditions, and the test data was statistically analyzed to determine the bounding value. The results show that stem friction coefficient in middle and high differential pressure is influenced by fluid pressure, while stem friction coefficient in low differential pressure is almost not affected by fluid pressure. In addition, it is found that the bounding value of stem friction coefficient is higher in a closing stroke than in an opening stroke.

  8. Pendulum mass affects the measurement of articular friction coefficient.

    Science.gov (United States)

    Akelman, Matthew R; Teeple, Erin; Machan, Jason T; Crisco, Joseph J; Jay, Gregory D; Fleming, Braden C

    2013-02-01

    Friction measurements of articular cartilage are important to determine the relative tribologic contributions made by synovial fluid or cartilage, and to assess the efficacy of therapies for preventing the development of post-traumatic osteoarthritis. Stanton's equation is the most frequently used formula for estimating the whole joint friction coefficient (μ) of an articular pendulum, and assumes pendulum energy loss through a mass-independent mechanism. This study examines if articular pendulum energy loss is indeed mass independent, and compares Stanton's model to an alternative model, which incorporates viscous damping, for calculating μ. Ten loads (25-100% body weight) were applied in a random order to an articular pendulum using the knees of adult male Hartley guinea pigs (n=4) as the fulcrum. Motion of the decaying pendulum was recorded and μ was estimated using two models: Stanton's equation, and an exponential decay function incorporating a viscous damping coefficient. μ estimates decreased as mass increased for both models. Exponential decay model fit error values were 82% less than the Stanton model. These results indicate that μ decreases with increasing mass, and that an exponential decay model provides a better fit for articular pendulum data at all mass values. In conclusion, inter-study comparisons of articular pendulum μ values should not be made without recognizing the loads used, as μ values are mass dependent. Copyright © 2012 Elsevier Ltd. All rights reserved.

  9. Load dependency of the coefficient of friction of oral mucosa

    NARCIS (Netherlands)

    Prinz, J.F.; Wijk, de R.A.; Huntjens, L.

    2007-01-01

    Frictional conditions in the mouth are thought by food scientists to be critical to the perception of important food attributes such as astringency, smoothness, roughness, slipperiness, etc. This ability to detect friction probably evolved to avoid foods that could wear the teeth excessively. In

  10. Frictional coefficient depending on active friction radius with BPV ...

    African Journals Online (AJOL)

    Frictional coefficient depending on active friction radius with BPV and BTV in automobile disc braking system. ... International Journal of Engineering, Science and Technology. Journal Home · ABOUT ... AJOL African Journals Online. HOW TO ...

  11. Influence of surface modification on friction coefficient of the titanium-elastomer couple.

    Science.gov (United States)

    Chladek, Wiesław; Hadasik, Eugeniusz; Chladek, Grzegorz

    2007-01-01

    This paper presents the results of a study of the friction coefficient of titanium-elastomer couple. The study was carried out with a view to potential future utilization of its results for constructing retentive elements of implanted prostheses. Changes in the friction force were recorded while removing titanium specimens placed between two silicone counter specimens made of Ufi Gel. The influence of the titanium specimen movement speed in relation that of to the counter specimens and the influence of clamping force on the friction force were assessed. Additionally, the surface roughness of titanium specimens differed; in one case, titanium was coated with polyethylene. The effect of introducing artificial saliva between the cooperating surfaces on the friction force and friction coefficient was analyzed as well. Based on the characteristics recorded, the possibilities of shaping the friction coefficient have been assessed, since it is the friction coefficient that determines effective operation of a friction couple through increasing the titanium specimen roughness. The artificial saliva being introduced between the specimens reduces considerably the friction coefficient through a change of the phenomenon model. An increase in the pressure force for the specimens of high roughness entails a reduction of the friction coefficient. The study carried out allows us to identify the roughness parameters, which in turn will enable obtaining the prescribed retention force for friction/membrane couplings.

  12. Prediction of Sliding Friction Coefficient Based on a Novel Hybrid Molecular-Mechanical Model.

    Science.gov (United States)

    Zhang, Xiaogang; Zhang, Yali; Wang, Jianmei; Sheng, Chenxing; Li, Zhixiong

    2018-08-01

    Sliding friction is a complex phenomenon which arises from the mechanical and molecular interactions of asperities when examined in a microscale. To reveal and further understand the effects of micro scaled mechanical and molecular components of friction coefficient on overall frictional behavior, a hybrid molecular-mechanical model is developed to investigate the effects of main factors, including different loads and surface roughness values, on the sliding friction coefficient in a boundary lubrication condition. Numerical modelling was conducted using a deterministic contact model and based on the molecular-mechanical theory of friction. In the contact model, with given external loads and surface topographies, the pressure distribution, real contact area, and elastic/plastic deformation of each single asperity contact were calculated. Then asperity friction coefficient was predicted by the sum of mechanical and molecular components of friction coefficient. The mechanical component was mainly determined by the contact width and elastic/plastic deformation, and the molecular component was estimated as a function of the contact area and interfacial shear stress. Numerical results were compared with experimental results and a good agreement was obtained. The model was then used to predict friction coefficients in different operating and surface conditions. Numerical results explain why applied load has a minimum effect on the friction coefficients. They also provide insight into the effect of surface roughness on the mechanical and molecular components of friction coefficients. It is revealed that the mechanical component dominates the friction coefficient when the surface roughness is large (Rq > 0.2 μm), while the friction coefficient is mainly determined by the molecular component when the surface is relatively smooth (Rq < 0.2 μm). Furthermore, optimal roughness values for minimizing the friction coefficient are recommended.

  13. An eight-legged tactile sensor to estimate coefficient of static friction.

    Science.gov (United States)

    Wei Chen; Rodpongpun, Sura; Luo, William; Isaacson, Nathan; Kark, Lauren; Khamis, Heba; Redmond, Stephen J

    2015-08-01

    It is well known that a tangential force larger than the maximum static friction force is required to initiate the sliding motion between two objects, which is governed by a material constant called the coefficient of static friction. Therefore, knowing the coefficient of static friction is of great importance for robot grippers which wish to maintain a stable and precise grip on an object during various manipulation tasks. Importantly, it is most useful if grippers can estimate the coefficient of static friction without having to explicitly explore the object first, such as lifting the object and reducing the grip force until it slips. A novel eight-legged sensor, based on simplified theoretical principles of friction is presented here to estimate the coefficient of static friction between a planar surface and the prototype sensor. Each of the sensor's eight legs are straight and rigid, and oriented at a specified angle with respect to the vertical, allowing it to estimate one of five ranges (5 = 8/2 + 1) that the coefficient of static friction can occupy. The coefficient of friction can be estimated by determining whether the legs have slipped or not when pressed against a surface. The coefficients of static friction between the sensor and five different materials were estimated and compared to a measurement from traditional methods. A least-squares linear fit of the sensor estimated coefficient showed good correlation with the reference coefficient with a gradient close to one and an r(2) value greater than 0.9.

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

    International Nuclear Information System (INIS)

    Linjun, Xie; Guohong, Xue; Ming, Zhang

    2016-01-01

    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 f of the HDS is obtained. So, the

  15. 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

  16. Characterization of skin friction coefficient, and relationship to stratum corneum hydration in a normal Chinese population.

    Science.gov (United States)

    Zhu, Y H; Song, S P; Luo, W; Elias, P M; Man, M Q

    2011-01-01

    Studies have demonstrated that some cutaneous biophysical properties vary with age, gender and body sites. However, the characteristics of the skin friction coefficient in different genders and age groups have not yet been well established. In the present study, we assess the skin friction coefficient in a larger Chinese population. A total of 633 subjects (300 males and 333 females) aged 0.15-79 years were enrolled. A Frictiometer FR 770 and Corneometer CM 825 (C&K MPA 5) were used to measure the skin friction coefficient and stratum corneum hydration, respectively, on the dorsal surface of the hand, the forehead and the canthus. In the females, the maximum skin friction coefficients on both the canthus and the dorsal hand skin were observed around the age of 40 years. In the males, the skin friction coefficient on the dorsal hand skin gradually increased from 0 to 40 years of age, and changed little afterward. Skin friction coefficients on some body sites were higher in females than in age-matched males in some age groups. On the canthus and the dorsal hand skin of females, a positive correlation was found between skin friction coefficient and stratum corneum hydration (p skin friction coefficient was positively correlated with stratum corneum hydration on the forehead and the dorsal hand skin (p skin friction coefficient varies with age, gender and body site, and positively correlates with stratum corneum hydration on some body sites. Copyright © 2010 S. Karger AG, Basel.

  17. The friction coefficient and its relation to the contact fatigue characteristics of materials

    International Nuclear Information System (INIS)

    Fedorov, S.V.

    1995-01-01

    The process of friction has been treated within the framework of an ergodynamic concept of deformable bodies. Equations of the friction energy balance are derived and a structure-energy interpretation of the friction process proposed. The friction parameter ranges within the domain of compatibility have been computed for tribosystems. The friction coefficient is shown to be a characteristic of the fatigue, wear resistance, and order (disorder) parameter of a tribosystem. Equations of state of a tribosystem and universal friction constants have been proposed. 31 refs.; 2 figs.; 3 tabs

  18. Experimental rig to estimate the coefficient of friction between tire and surface in airplane touchdown simulations.

    Science.gov (United States)

    Li, Chengwei; Zhan, Liwei

    2015-08-01

    To estimate the coefficient of friction between tire and runway surface during airplane touchdowns, we designed an experimental rig to simulate such events and to record the impact and friction forces being executed. Because of noise in the measured signals, we developed a filtering method that is based on the ensemble empirical mode decomposition and the bandwidth of probability density function of each intrinsic mode function to extract friction and impact force signals. We can quantify the coefficient of friction by calculating the maximum values of the filtered force signals. Signal measurements are recorded for different drop heights and tire rotational speeds, and the corresponding coefficient of friction is calculated. The result shows that the values of the coefficient of friction change only slightly. The random noise and experimental artifact are the major reason of the change.

  19. Shape optimization in 2D contact problems with given friction and a solution-dependent coefficient of friction

    Czech Academy of Sciences Publication Activity Database

    Haslinger, J.; Outrata, Jiří; Pathó, R.

    2012-01-01

    Roč. 20, č. 1 (2012), s. 31-59 ISSN 1877-0533 R&D Projects: GA AV ČR IAA100750802 Institutional research plan: CEZ:AV0Z10750506 Institutional support: RVO:67985556 Keywords : shape optimization * Signorini problem * model with given frinction * solution-dependent coefficient of friction * mathematical probrams with equilibrium constraints Subject RIV: BA - General Mathematics Impact factor: 1.036, year: 2012 http://library.utia.cas.cz/separaty/2012/MTR/outrata-shape optimization in 2d contact problems with given friction and a solution-dependent coefficient of friction .pdf

  20. Rotational friction coefficient of a permeable cylinder in a viscous fluid

    NARCIS (Netherlands)

    Wiegel, F.W.

    1979-01-01

    An exact expression is derived for the rotational friction coefficient of a cylinder of infinite length and constant permeability immersed in an incompressible viscous fluid. An asymptotic expression for the translational friction coefficient of a permeable cylinder moving in a sheet of viscous

  1. Static coefficient of friction between stainless steel and PMMA used in cemented hip and knee implants.

    Science.gov (United States)

    Nuño, N; Groppetti, R; Senin, N

    2006-11-01

    Design of cemented hip and knee implants, oriented to improve the longevity of artificial joints, is largely based on numerical models. The static coefficient of friction between the implant and the bone cement is necessary to characterize the interface conditions in these models and must be accurately provided. The measurement of this coefficient using a repeatable and reproducible methodology for materials used in total hip arthroplasty is missing from the literature. A micro-topographic surface analysis characterized the surfaces of the specimens used in the experiments. The coefficient of friction between stainless steel and bone cement in dry and wet conditions using bovine serum was determined using a prototype computerized sliding friction tester. The effects of surface roughness (polished versus matt) and of contact pressure on the coefficient of friction have also been investigated. The serum influences little the coefficient of friction for the matt steel surface, where the mechanical interactions due to higher roughness are still the most relevant factor. However, for polished steel surfaces, the restraining effect of proteins plays a very relevant role in increasing the coefficient of friction. When the coefficient of friction is used in finite element analysis, it is used for the debonded stem-cement situation. It can thus be assumed that serum will propagate between the stem and the cement mantle. The authors believe that the use of a static coefficient of friction of 0.3-0.4, measured in the present study, is appropriate in finite element models.

  2. Internal friction and linear expansion coefficient in zirconium and cobalt within the range of phase transitions

    International Nuclear Information System (INIS)

    Boyarskij, S.V.

    1986-01-01

    Experimental results are presented for internal friction and linear expansion coefficient at zirconium and cobalt in the temperature range from 440 K to the point of the phase transition of the first kind (1138 K for Zr and 706 for Co). Anomalous changes of the internal friction and linear expansion coefficient in the phase transition region are found. Theoretical considerations are given to explain the sharp decrease of the internal friction as temperature approaches the phase transition point

  3. Wettability and friction coefficient of micro-magnet arrayed surface

    Science.gov (United States)

    Huang, Wei; Liao, Sijie; Wang, Xiaolei

    2012-01-01

    Surface coating is an important part of surface engineering and it has been successfully used in many applications to improve the performance of surfaces. In this paper, magnetic arrayed films with different thicknesses were fabricated on the surface of 316 stainless steel disks. Controllable colloid - ferrofluids (FF) was chosen as lubricant, which can be adsorbed on the magnetic surface. The wettability of the micro-magnet arrayed surface was evaluated by measuring the contract angle of FF drops on surface. Tribological experiments were carried out to investigate the effects of magnetic film thickness on frictional properties when lubricated by FF under plane contact condition. It was found that the magnetic arrayed surface with thicker magnetic films presented larger contract angle. The frictional test results showed that samples with thicker magnetic films could reduce friction and wear more efficiently at higher sliding velocity under the lubrication of FF.

  4. Estimation of Road Friction Coefficient in Different Road Conditions Based on Vehicle Braking Dynamics

    Science.gov (United States)

    Zhao, You-Qun; Li, Hai-Qing; Lin, Fen; Wang, Jian; Ji, Xue-Wu

    2017-07-01

    The accurate estimation of road friction coefficient in the active safety control system has become increasingly prominent. Most previous studies on road friction estimation have only used vehicle longitudinal or lateral dynamics and often ignored the load transfer, which tends to cause inaccurate of the actual road friction coefficient. A novel method considering load transfer of front and rear axles is proposed to estimate road friction coefficient based on braking dynamic model of two-wheeled vehicle. Sliding mode control technique is used to build the ideal braking torque controller, which control target is to control the actual wheel slip ratio of front and rear wheels tracking the ideal wheel slip ratio. In order to eliminate the chattering problem of the sliding mode controller, integral switching surface is used to design the sliding mode surface. A second order linear extended state observer is designed to observe road friction coefficient based on wheel speed and braking torque of front and rear wheels. The proposed road friction coefficient estimation schemes are evaluated by simulation in ADAMS/Car. The results show that the estimated values can well agree with the actual values in different road conditions. The observer can estimate road friction coefficient exactly in real-time and resist external disturbance. The proposed research provides a novel method to estimate road friction coefficient with strong robustness and more accurate.

  5. Friction coefficient dependence on electrostatic tribocharging

    Science.gov (United States)

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

    2013-01-01

    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. PMID:23934227

  6. Friction coefficient dependence on electrostatic tribocharging.

    Science.gov (United States)

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

    2013-01-01

    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.

  7. Coefficient of Friction at the Fingertips in Type II Diabetics Compared to Healthy Adults.

    Science.gov (United States)

    Thames, Beatriz H; Gorniak, Stacey L

    2017-07-01

    Clinical observations suggest that type II diabetes patients are more susceptible to skin changes, which may be associated with reduced coefficient of friction at the fingertips. Reduced coefficient of friction may explain recent reports of fine motor dysfunction in diabetic patients. Coefficient of friction was evaluated using slip force evaluation in a cross-sectional cohort of diabetic patients and age- and sex-matched healthy controls. Covariates of tactile sensation, disease duration, glycated hemoglobin, and clinical diagnosis of peripheral neuropathy were also assessed. A significant decrease in fingertip coefficient of friction in the diabetic group was found as compared to controls. Health state covariates did not alter the strength of between-group differences in statistical analyses. This finding of between-group differences for fingertip frictional properties suggests that causative factors of reported manual motor dysfunction lie in both the distal and proximal portions of the nervous system.

  8. The coefficient of friction in Parkinson's disease gait.

    Science.gov (United States)

    Kleiner, Ana; Galli, M; Franceschini, M; De Pandis, M F; Stocchi, F; Albertini, G; de Barros, Ricardo Machado Leite

    This study aimed to characterize the coefficient of friction (COF) curves of patients with Parkinson's disease (PD) during barefoot gait and to evaluate the relationships between this variable and functional scales. Twenty-two subjects with PD (ON phase of levodopa) and 22 healthy subjects participated in this study. The participants walked barefoot along a pathway that went over two force plates embedded in the floor of the data collection room. The instantaneous COF was calculated as the ratio between the horizontal and vertical components of the ground reaction forces. Two-sample t-tests applied to every 1% of the support phase of the COF curve were used to compare the groups and to identify the phases in which the two groups were different. Specifically, three COF areas were computed: Area 1 (for the loading response phase), Area 2 (for the midstance phase) and Area 3 (for the terminal stance phase). Pearson's tests were applied to assess the associations between the COF curve areas and the clinical scales. The subjects with PD exhibited lower COF values during the loading response and terminal stance phases and higher COF values during the mid-stance phase compared with the control group. A strong positive correlation was observed between Area 1 and the Timed Up and Go Test (90.3%). In conclusion, the patients' COFs exhibited patterns that were different from those of the control group. Moreover, during the loading response phase, these differences were well-correlated with the Timed Up and Go Test scale data; Timed Up and Go Test data can be used to identify the risk of falls among PD patients.

  9. The effect of chalk on the finger-hold friction coefficient in rock climbing.

    Science.gov (United States)

    Amca, Arif Mithat; Vigouroux, Laurent; Aritan, Serdar; Berton, Eric

    2012-11-01

    The main purpose of this study was to examine the effect of chalk on the friction coefficient between climber's fingers and two different rock types (sandstone and limestone). The secondary purpose was to investigate the effects of humidity and temperature on the friction coefficient and on the influence of chalk. Eleven experienced climbers took part in this study and 42 test sessions were performed. Participants hung from holds which were fixed on a specially designed hang board. The inclination of the hang board was progressively increased until the climber's hand slipped from the holds. The angle of the hang board was simultaneously recorded by using a gyroscopic sensor and the friction coefficient was calculated at the moment of slip. The results showed that there was a significant positive effect of chalk on the coefficient of friction (+18.7% on limestone and +21.6% on sandstone). Moreover sandstone had a higher coefficient of friction than limestone (+15.6% without chalk, +18.4% with chalk). These results confirmed climbers' belief that chalk enhances friction. However, no correlation with humidity/temperature and friction coefficient was noted which suggested that additional parameters should be considered in order to understand the effects of climate on finger friction in rock climbing.

  10. Measurement of the friction coefficient between UO2 and cladding tube

    International Nuclear Information System (INIS)

    Tachibana, Toshimichi; Narita, Daisuke; Kaneko, Hiromitsu; Honda, Yutaka

    1978-01-01

    Most of fuel rods used for light water reactors or fast reactors consist of the cladding tubes filled with UO 2 -PuO 2 pellets. The measurement was made on the coefficient of static friction and the coefficient of dynamic friction in helium under high contact load on UO 2 /Zry-2 and UO 2 /SUS 316 combined samples at the temperature ranging from room temperature to 400 deg. C and from room temperature to 600 deg. C, respectively. The coefficient of static friction for Zry-2 tube and UO 2 pellets was 0.32 +- 0.08 at room temperature and 0.47 +- 0.07 at 400 deg. C, and increased with temperature rise in this temperature range. The coefficient of static friction between 316 stainless steel tube and UO 2 pellets was 0.29 +- 0.04 at room temperature and 1.2 +- 0.2 at 600 deg. C, and increased with temperature rise in this temperature range. The coefficient of dynamic friction for both UO 2 /Zry-2 and UO 2 /SUS 316 combinations seems to be equal to or about 10% excess of the coefficient of static friction. The coefficient of static friction for UO 2 /SUS 316 combination decreased with the increasing number of repetition, when repeating slip several times on the same contact surfaces. (Kobatake, H.)

  11. Tribology of skin : review and analysis of experimental results for the friction coefficient of human skin

    NARCIS (Netherlands)

    Derler, S.; Gerhardt, L.C.

    2012-01-01

    In this review, we discuss the current knowledge on the tribology of human skin and present an analysis of the available experimental results for skin-friction coefficients. Starting with an overview on the factors influencing the friction behaviour of skin, we discuss the up-to-date existing

  12. Estimation of the friction coefficient between wheel and rail surface using traction motor behaviour

    International Nuclear Information System (INIS)

    Zhao, Y; Liang, B; Iwnicki, S

    2012-01-01

    The friction coefficient between a railway wheel and rail surface is a crucial factor in maintaining high acceleration and braking performance of railway vehicles thus monitoring this friction coefficient is important. Restricted by the difficulty in directly measuring the friction coefficient, the creep force or creepage, indirect methods using state observers are used more frequently. This paper presents an approach using a Kalman filter to estimate the creep force and creepage between the wheel and rail and then to identify the friction coefficient using the estimated creep force-creepage relationship. A mathematic model including an AC motor, wheel and roller is built to simulate the driving system. The parameters are based on a test rig at Manchester Metropolitan University. The Kalman filter is designed to estimate the friction coefficient based on the measurements of the simulation model. Series of residuals are calculated through the comparison between the estimated creep force and theoretical values of different friction coefficient. Root mean square values of the residuals are used in the friction coefficient identification.

  13. Scaling of mesoscale simulations of polymer melts with the bare friction coefficient

    NARCIS (Netherlands)

    Kindt, P.; Kindt, P.; Briels, Willem J.

    2005-01-01

    Both the Rouse and reptation model predict that the dynamics of a polymer melt scale inversely proportional with the Langevin friction coefficient (E). Mesoscale Brownian dynamics simulations of polyethylene validate these scaling predictions, providing the reptational friction (E)R=(E)+(E)C is

  14. Influence of self-affine roughness on the friction coefficient of rubber at high sliding velocity

    NARCIS (Netherlands)

    Palasantzas, G

    2004-01-01

    In this work we investigate the influence of self-affine roughness on the friction coefficient of a rubber body onto a solid surface at high speeds. The roughness is characterized by the rms amplitude w, the correlation length xi, and the roughness exponent H. It is shown that the friction

  15. The Impact of One Heat Treated Contact Element on the Coefficient of Static Friction

    Directory of Open Access Journals (Sweden)

    P. Todorović, , , , , ,

    2013-12-01

    Full Text Available The subject of the paper includes theoretical considerations, the conducting of experimental tests, and the analysis of exposed test results related to determination of the coefficient of static friction of previously heat-treated contact pairs. One contact element is previously, before the procedure of determining the coefficient of static friction, heated at temperatures in the range of ambient temperature to 280°C and then cooled down to ambient temperature. The results of experimental tests of five different materials show that depending on the heat treatment of one contact element, there is a significant decrease in the coefficient of static friction. The authors of the paper consider that the reasons for the decreasing coefficient of static friction are related to oxide formation and changes in the surface layer of the contact element which is previously heat-treated.

  16. A methodology to quantify the stochastic distribution of friction coefficient required for level walking.

    Science.gov (United States)

    Chang, Wen-Ruey; Chang, Chien-Chi; Matz, Simon; Lesch, Mary F

    2008-11-01

    The required friction coefficient is defined as the minimum friction needed at the shoe and floor interface to support human locomotion. The available friction is the maximum friction coefficient that can be supported without a slip at the shoe and floor interface. A statistical model was recently introduced to estimate the probability of slip and fall incidents by comparing the available friction with the required friction, assuming that both the available and required friction coefficients have stochastic distributions. This paper presents a methodology to investigate the stochastic distributions of the required friction coefficient for level walking. In this experiment, a walkway with a layout of three force plates was specially designed in order to capture a large number of successful strikes without causing fatigue in participants. The required coefficient of friction data of one participant, who repeatedly walked on this walkway under four different walking conditions, is presented as an example of the readiness of the methodology examined in this paper. The results of the Kolmogorov-Smirnov goodness-of-fit test indicated that the required friction coefficient generated from each foot and walking condition by this participant appears to fit the normal, log-normal or Weibull distributions with few exceptions. Among these three distributions, the normal distribution appears to fit all the data generated with this participant. The average of successful strikes for each walk achieved with three force plates in this experiment was 2.49, ranging from 2.14 to 2.95 for each walking condition. The methodology and layout of the experimental apparatus presented in this paper are suitable for being applied to a full-scale study.

  17. Measurement of Turbulent Skin Friction Drag Coefficients Produced by Distributed Surface Roughness of Pristine Marine Coatings

    DEFF Research Database (Denmark)

    Zafiryadis, Frederik; Meyer, Knud Erik; Gökhan Ergin, F.

    drag coefficients as well as roughness Reynolds numbers for the various marine coatings across the range of Rex by fitting of the van Driest profile. The results demonstrate sound agreement with the present ITTC method for determining skin friction coefficients for practically smooth surfaces at low...... Reynolds numbers compared to normal operation mode for the antifouling coatings. Thus, better estimates for skin friction of rough hulls can be realised using the proposed method to optimise preliminary vessel design....

  18. Measuring principles of frictional coefficients in cartilaginous tissues and its substitutes

    NARCIS (Netherlands)

    Huyghe, J.M.R.J.; Janssen, C.F.; Donkelaar, van C.C.; Lanir, Y.

    2002-01-01

    The frictional properties of cartilaginous tissues, such as the hydraulic permeability, the electro-osmotic permeability, the diffusion coefficients of various ions and solutes, and the electrical conductance, are vital data to characterise the extracellular environment in which chondrocytes reside.

  19. Microscopic calculation of friction coefficients for use in heavy-ion reaction

    International Nuclear Information System (INIS)

    Iwamoto, A.; Harada, K.; Yoshida, S.

    1981-01-01

    A microscopic calculation has been done for the friction coefficient for use in the deep-inelastic collision of heavy nuclei. We adopted the formalism of the linear response theory as a basis and used the adiabatic base of the two-center shell model. Several reaction channels with the total mass numbers of 236 and 260 systems were investigated. The friction coefficients for the radial and deforming motions including the coupling term were calculated as a function of the distance between two nuclei and deformation of the two nuclei for each channel. The general feature of the friction coefficient, its strength and form factor, was clarified in this model and comparison with the results of other models were done. It was found that our model gives a physically plausible value for the friction coefficient as a whole. (orig.)

  20. Friction coefficient of spruce pine on steel -- a note on lubricants

    Science.gov (United States)

    Charles W. McMillin; Truett J. Lemoine; Floyd G. Manwiller

    1970-01-01

    Generally, the introduction of water and ethanol increased the friction coefficient for ovendry samples but decreased the coeffecient when the samples were saturated. Octanoic acid decreased the coefficient when samples were wet. In the entire experiment, coefficients ranged from 0.14 to 0.78.

  1. Determination of the frictional coefficient of the implant-antler interface: experimental approach.

    Science.gov (United States)

    Hasan, Istabrak; Keilig, Ludger; Staat, Manfred; Wahl, Gerhard; Bourauel, Christoph

    2012-10-01

    The similar bone structure of reindeer antler to human bone permits studying the osseointegration of dental implants in the jawbone. As the friction is one of the major factors that have a significant influence on the initial stability of immediately loaded dental implants, it is essential to define the frictional coefficient of the implant-antler interface. In this study, the kinetic frictional forces at the implant-antler interface were measured experimentally using an optomechanical setup and a stepping motor controller under different axial loads and sliding velocities. The corresponding mean values of the static and kinetic frictional coefficients were within the range of 0.5-0.7 and 0.3-0.5, respectively. An increase in the frictional forces with increasing applied axial loads was registered. The measurements showed an evidence of a decrease in the magnitude of the frictional coefficient with increasing sliding velocity. The results of this study provide a considerable assessment to clarify the suitable frictional coefficient to be used in the finite element contact analysis of antler specimens.

  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......Friction materials for typical brake applications are normally designed considering thermal stability as the major performance criterion. There are, however, brake applications with very limited sliding velocities, where the generated heat is insignificant. In such cases it is possible...... in order to interpret the changes of friction observed during the running-in phase....

  3. 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.

  4. A comparison of roughness parameters and friction coefficients of aesthetic archwires.

    Science.gov (United States)

    Rudge, Philippa; Sherriff, Martyn; Bister, Dirk

    2015-02-01

    Compare surface roughness of 'aesthetic' nickel-titanium (NiTi) archwires with their dynamic frictional properties. Archwires investigated were: four fully coated tooth coloured [Forestadent: Biocosmetic (FB) and Titanol Cosmetic (FT); TOC Tooth Tone (TT); and Hawley Russell Coated Superelastic NiTi (HRC)]; two partially coated tooth coloured [DB Euroline Microcoated (DB) and TP Aesthetic NiTi (TP)]; two rhodium coated [TOC Sentalloy (TS) and Hawley Russell Rhodium Coated Superelastic NiTi (HRR)]; and two controls: stainless steel [Forestadent Steel (FS)] and NiTi archwire [Forestadent Titanol Superelastic (FN)]. Surface roughness [profilometry (Rugosurf)] was compared with frictional coefficients for archwire/bracket/ligature combinations (n = 10). Analysis of variance, Sidak's multiple comparison of means, and Spearman's correlation coefficient were used for analysis. Roughness coefficients were from low to high: FB; FN; TT; FS; TS; HRR; FT; DB; TP; HRC. Friction coefficients were from low to high: TP; FS; FN; HRR; FT; DB; FB; HRC; TS; TT. Coated archwires generally exhibited higher friction than uncoated controls. TP had the lowest friction but this was not statistically significant (P < 0.05). Friction of tooth coloured coated archwires were significantly different for some wires. Spearman's correlation did not demonstrate consistency between surface roughness (R a) and dynamic friction. Aesthetic archwires investigated had either low surface roughness or low frictional resistance but not both properties simultaneously. Causes for friction are likely to be multifactorial and do not appear to be solely determined by surface roughness (measured by profilometry). For selecting the most appropriate aligning archwire, both surface roughness and frictional resistance need to be considered. © The Author 2014. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  5. 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.

  6. Coefficient of friction and wear rate effects of different composite nanolubricant concentrations on Aluminium 2024 plate

    Science.gov (United States)

    Zawawi, N. N. M.; Azmi, W. H.; Redhwan, A. A. M.; Sharif, M. Z.

    2017-10-01

    Wear of sliding parts and operational machine consistency enhancement can be avoided with good lubrication. Lubrication reduce wear between two contacting and sliding surfaces and decrease the frictional power losses in compressor. The coefficient of friction and wear rate effects study were carried out to measure the friction and anti-wear abilities of Al2O3-SiO2 composite nanolubricants a new type of compressor lubricant to enhanced the compressor performances. The tribology test rig employing reciprocating test conditions to replicate a piston ring contact in the compressor was used to measure the coefficient of friction and wear rate. Coefficient of friction and wear rate effects of different Al2O3-SiO2/PAG composite nanolubricants of Aluminium 2024 plate for 10-kg load at different speed were investigated. Al2O3 and SiO2 nanoparticles were dispersed in the Polyalkylene Glycol (PAG 46) lubricant using two-steps method of preparation. The result shows that the coefficient friction and wear rate of composite nanolubricants decreased compared to pure lubricant. The maximum reduction achievement for friction of coefficient and wear rate by Al2O3-SiO2 composite nanolubricants by 4.78% and 12.96% with 0.06% volume concentration. Therefore, 0.06% volume concentration is selected as the most enhanced composite nanolubricants with effective coefficient of friction and wear rate reduction compared to other volume concentrations. Thus, it is recommended to be used as the compressor lubrication to enhanced compressor performances.

  7. Friction Coefficient Determination by Electrical Resistance Measurements

    Science.gov (United States)

    Tunyagi, A.; Kandrai, K.; Fülöp, Z.; Kapusi, Z.; Simon, A.

    2018-01-01

    A simple and low-cost, DIY-type, Arduino-driven experiment is presented for the study of friction and measurement of the friction coefficient, using a conductive rubber cord as a force sensor. It is proposed for high-school or college/university-level students. We strongly believe that it is worthwhile planning, designing and performing Arduino…

  8. Translational friction coefficient of a permeable cylinder in a sheet of viscous fluid

    NARCIS (Netherlands)

    Wiegel, F.W.

    1979-01-01

    The author calculates the translational friction coefficient and the translational diffusion coefficient of a permeable cylinder moving in a sheet of fluid which is embedded on both sides in a fluid of much lower viscosity. The result, which is an asymptotic expression valid in the limit of small

  9. 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.

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

    Directory of Open Access Journals (Sweden)

    Xudong Zhang

    Full Text Available 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.

  11. Determination of the coefficient of dynamic friction between coatings of alumina and metallic materials

    Science.gov (United States)

    Santos, A.; Córdoba, E.; Ramírez, Z.; Sierra, C.; Ortega, Y.

    2017-12-01

    This project aims to determine the coefficient of dynamic friction between micrometric size coatings of alumina and metallic materials (Steel and aluminium); the methodology used to achieve the proposed objective consisted of 4 phases, in the first one was developed a procedure that allowed, from a Pin on Disk machine built based on the specifications given by the ASTM G99-05 standard (Standard test method for wear tests with a Pin on Disk machine), to determine the coefficient of dynamic friction between two materials in contact; subsequently the methodology was verified through tests between steel-steel and steel-aluminium, due to these values are widely reported in the literature; as a third step, deposits of alumina particles of micrometric size were made on a steel substrate through thermal spraying by flame; finally, the tests were carried out between pins of steel of aluminium and alumina coating to determine the coefficients of dynamic friction between these two surfaces. The results of the project allowed to verify that the developed methodology is valid to obtain coefficients of dynamic friction between surfaces in contact since the percentages of error were of 3.5% and 2.1% for steel-steel and aluminium-steel, respectively; additionally, it was found that the coefficient of friction between steel-alumina coatings is 0.36 and aluminium-alumina coating is 0.25.

  12. 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

    2016-12-02

    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.

  13. The development of the friction coefficient inspection equipment for skin using a load cell.

    Science.gov (United States)

    Song, Han Wook; Park, Yon Kyu; Lee, Sung Jun; Woo, Sam Yong; Kim, Sun Hyung; Kim, Dal Rae

    2008-01-01

    The skin is an indispensible organ for human because it contributes to the metabolism using its own biochemical functions as well as it protects the human body from the exterior stimuli. Recently, the friction coefficient have been used as the decision index of the progress for the bacterial aliments in the field of the skin physiology and the importance of friction coefficient have been increased in the skin care market because of the needs of the well being times. In addition, the usage of friction coefficient is known to have the big discrimination ability in classification of human constitutions, which is utilized in the alternative medicine. In this study, we designed a system which used the multi axes load cell and hemi-circular probe and tried to measure the friction coefficient of hand skins repeatedly. Using this system, the relative repeatability error for the measurement of the friction coefficient was below 4 %. The coefficient is not concerned in curvatures of tips. Using this system, we will try to establish the standard for classification of constitutions.

  14. 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

    2016-01-01

    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. PMID:27213374

  15. 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.

  16. Numerical Study of Tire Hydroplaning Based on Power Spectrum of Asphalt Pavement and Kinetic Friction Coefficient

    OpenAIRE

    Shengze Zhu; Xiuyu Liu; Qingqing Cao; Xiaoming Huang

    2017-01-01

    Hydroplaning is a driving phenomenon threating vehicle’s control stability and safety. It happens when tire rolls on wet pavement with high speed that hydrodynamic force uplifts the tire. Accurate numerical simulation to reveal the mechanism of hydroplaning and evaluate the function of relevant factors in this process is significant. In order to describe the friction behaviors of tire-pavement interaction, kinetic friction coefficient curve of tire rubber and asphalt pavement was obtained by ...

  17. Coefficients of sliding friction of single crystals of high explosives under different rubbing conditions

    International Nuclear Information System (INIS)

    Wu, Y Q; Chaudhri, M Munawar

    2013-01-01

    The coefficients of sliding friction of single crystals of commonly used high explosives pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX) and beta-cyclotetramethylene tetranitramine (β-HMX) under several rubbing configurations and at a relative sliding speed of 0.22 mm s -1 were measured. The sliding configurations were (1) crystal-polished steel pairs, (2) like-crystal pairs and (3) unlike-crystal pairs. For every rubbing configuration the friction force showed oscillations, which are thought to be caused by the formation and shearing of the adhesive junctions formed at the surface of the rubbing crystals. This shearing of the adhesive junctions led to the formation of microscopic and sub-microscopic particles, which were confirmed by an environmental scanning electron microscope study. For every rubbing configuration and for relatively high normal loads pressing the rubbing crystals together, the coefficient of friction was generally in the range 0.2-0.25 and it has been concluded that the coefficient of friction is controlled by the adhesion with almost negligible contribution from the ploughing component. From a knowledge of the coefficient of friction and the uniaxial yield stress values of single crystals of RDX and β-HMX, the shear strength of these crystals were determined to be ∼13.4 MPa and ∼16.8 MPa, respectively.

  18. 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.

  19. Slip Control of Electric Vehicle Based on Tire-Road Friction Coefficient Estimation

    Directory of Open Access Journals (Sweden)

    Gaojian Cui

    2017-01-01

    Full Text Available The real-time change of tire-road friction coefficient is one of the important factors that influence vehicle safety performance. Besides, the vehicle wheels’ locking up has become an important issue. In order to solve these problems, this paper comes up with a novel slip control of electric vehicle (EV based on tire-road friction coefficient estimation. First and foremost, a novel method is proposed to estimate the tire-road friction coefficient, and then the reference slip ratio is determined based on the estimation results. Finally, with the reference slip ratio, a slip control based on model predictive control (MPC is designed to prevent the vehicle wheels from locking up. In this regard, the proposed controller guarantees the optimal braking torque on each wheel by individually controlling the slip ratio of each tire within the stable zone. Theoretical analyses and simulation show that the proposed controller is effective for better braking performance.

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

    Science.gov (United States)

    Sainz-García, Elisa; Alba-Elías, Fernando; Múgica-Vidal, Rodolfo; González-Marcos, Ana

    2015-02-01

    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 SiOx 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 CF2 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 CF2 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 (θadv = 119.8° ± 4.75) 4.4% higher than the uncoated TPE sample. A satisfactory stability in humid ambient for twelve months showed a slight decrease of WCA (4.4%) for this sample. The results of this study permit one to realize the effectiveness of using fluorinated precursors to avoid a significant decrease in the WCA when applying a precursor to anti-friction improvement.

  1. Coefficient of Friction Between Carboxymethylated Hyaluronic Acid-Based Polymer Films and the Ocular Surface.

    Science.gov (United States)

    Colter, Jourdan; Wirostko, Barbara; Coats, Brittany

    2017-12-01

    Hyaluronic acid-based polymer films are emerging as drug-delivery vehicles for local and continuous drug administration to the eye. The highly lubricating hyaluronic acid increases comfort, but displaces films from the eye, reducing drug exposure and efficacy. Previous studies have shown that careful control of the surface interaction of the film with the eye is critical for improved retention. In this study, the frictional interaction of a carboxymethylated, hyaluronic acid-based polymer (CMHA-S) with and without methylcellulose was quantified against ovine and human sclera at three axial loads (0.3, 0.5, and 0.7 N) and four sliding velocities (0.3, 1.0, 10, and 30 mm/s). Static coefficients of friction significantly increased with rate (P Friction became more rate-dependent when methylcellulose was added to CMHA-S. Kinetic coefficient of friction was not affected by rate, and averaged 0.15 ± 0.1. Methylcellulose increased CMHA-S static and kinetic friction by 60% and 80%, respectively, but was also prone to wear during testing. These data suggest that methylcellulose can be used to create a friction differential on the film, but a potentially increased degradation rate with the methylcellulose must be considered in the design.

  2. 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.

  3. Wood variables affecting the friction coefficient of spruce pine on steel

    Science.gov (United States)

    Truett J. Lemoine; Charles W. McMillin; Floyd G. Manwiller

    1970-01-01

    Wood of spruce pine, Pinus glabra Walk., was factorially segregated by moisture content (0, 10, and 18 percent), specific gravity (less than 0.45 and more than 0.45), and extractive content (unextracted and extractive-freE), and the kinetic coefficient of friction on steel (having surface roughness of 9 microinches RMS) determined for tangential...

  4. Wear Potential of Dental Ceramics and its Relationship with Microhardness and Coefficient of Friction.

    Science.gov (United States)

    Freddo, Rafael Augusto; Kapczinski, Myriam Pereira; Kinast, Eder Julio; de Souza Junior, Oswaldo Baptista; Rivaldo, Elken Gomes; da Fontoura Frasca, Luis Carlos

    2016-10-01

    To evaluate, by means of pin-on-disk testing, the wear potential of different dental ceramic systems as it relates to friction parameters, surface finish, and microhardness. Three groups of different ceramic systems (Noritake EX3, Eris, Empress II) with 20 disks each (10 glazed, 10 polished) were used. Vickers microhardness (Hv) was determined with a 200-g load for 30 seconds. Friction coefficients (μ) were determined by pin-on-disk testing (5 N load, 600 seconds, and 120 rpm). Wear patterns were assessed by scanning electron microscopy (SEM). The results were analyzed using one-way ANOVA and Tukey's test, with the significance level set at α = 0.05. The coefficients of friction were as follows: Noritake EX3 0.28 ± 0.12 (polished), 0.33 ± 0.08 (glazed); Empress II 0.38 ± 0.08 (polished), 0.45 ± 0.05 (glazed); Eris 0.49 ± 0.05 (polished), 0.49 ± 0.06 (glazed). Microhardness measurements were as follows: Noritake EX3 530.7 ± 8.7 (polished), 525.9 ± 6.2 (glazed); Empress II 534.1 ± 8 (polished), 534.7 ± 4.5 (glazed); Eris, 511.7 ± 6.5 (polished), 519.5 ± 4.1 (glazed). The polished and glazed Noritake EX3 and polished and glazed Eris specimens showed statistically different friction coefficients. SEM image analysis revealed more surface changes, such as small cracks and grains peeling off, in glazed ceramics. Wear potential may be related to the coefficient of friction in Noritake ceramics, which had a lower coefficient than Eris ceramics. Within-group analysis showed no differences in polished or glazed specimens. The differences observed were not associated with microhardness. © 2015 by the American College of Prosthodontists.

  5. The Effect of a Variable Disc Pad Friction Coefficient for the Mechanical Brake System of a Railway Vehicle.

    Science.gov (United States)

    Lee, Nam-Jin; Kang, Chul-Goo

    2015-01-01

    A brake hardware-in-the-loop simulation (HILS) system for a railway vehicle is widely applied to estimate and validate braking performance in research studies and field tests. When we develop a simulation model for a full vehicle system, the characteristics of all components are generally properly simplified based on the understanding of each component's purpose and interaction with other components. The friction coefficient between the brake disc and the pad used in simulations has been conventionally considered constant, and the effect of a variable friction coefficient is ignored with the assumption that the variability affects the performance of the vehicle braking very little. However, the friction coefficient of a disc pad changes significantly within a range due to environmental conditions, and thus, the friction coefficient can affect the performance of the brakes considerably, especially on the wheel slide. In this paper, we apply a variable friction coefficient and analyzed the effects of the variable friction coefficient on a mechanical brake system of a railway vehicle. We introduce a mathematical formula for the variable friction coefficient in which the variable friction is represented by two variables and five parameters. The proposed formula is applied to real-time simulations using a brake HILS system, and the effectiveness of the formula is verified experimentally by testing the mechanical braking performance of the brake HILS system.

  6. The Effect of a Variable Disc Pad Friction Coefficient for the Mechanical Brake System of a Railway Vehicle

    Science.gov (United States)

    Lee, Nam-Jin; Kang, Chul-Goo

    2015-01-01

    A brake hardware-in-the-loop simulation (HILS) system for a railway vehicle is widely applied to estimate and validate braking performance in research studies and field tests. When we develop a simulation model for a full vehicle system, the characteristics of all components are generally properly simplified based on the understanding of each component’s purpose and interaction with other components. The friction coefficient between the brake disc and the pad used in simulations has been conventionally considered constant, and the effect of a variable friction coefficient is ignored with the assumption that the variability affects the performance of the vehicle braking very little. However, the friction coefficient of a disc pad changes significantly within a range due to environmental conditions, and thus, the friction coefficient can affect the performance of the brakes considerably, especially on the wheel slide. In this paper, we apply a variable friction coefficient and analyzed the effects of the variable friction coefficient on a mechanical brake system of a railway vehicle. We introduce a mathematical formula for the variable friction coefficient in which the variable friction is represented by two variables and five parameters. The proposed formula is applied to real-time simulations using a brake HILS system, and the effectiveness of the formula is verified experimentally by testing the mechanical braking performance of the brake HILS system. PMID:26267883

  7. Use of the lognormal distribution for the coefficients of friction and wear

    International Nuclear Information System (INIS)

    Steele, Clint

    2008-01-01

    To predict the reliability of a system, an engineer might allocate a distribution to each input. This raises a question: how to select the correct distribution? Siddall put forward an evolutionary approach that was intended to utilise both the understanding of the engineer and available data. However, this method requires a subjective initial distribution based on the engineer's understanding of the variable or parameter. If the engineer's understanding is limited, the initial distribution will be misrepresentative of the actual distribution, and application of the method will likely fail. To provide some assistance, the coefficients of friction and wear are considered here. Basic tribology theory, dimensional issues and the central limit theorem are used to argue that the distribution for each of the coefficients will typically be like a lognormal distribution. Empirical evidence from other sources is cited to lend support to this argument. It is concluded that the distributions for the coefficients of friction and wear would typically be lognormal in nature. It is therefore recommended that the engineer, without data or evidence to suggest differently, should allocate a lognormal distribution to the coefficients of friction and wear

  8. High speed friction microscopy and nanoscale friction coefficient mapping

    International Nuclear Information System (INIS)

    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 maps of the coefficient of friction can be uniquely calculated for heterogeneous surfaces. These parameters are determined at a scan velocity as fast as 2 mm s −1 for microfabricated SiO 2 mesas and Au coated pits, yielding results that are identical to traditional speed measurements despite being ∼1000 times faster. To demonstrate the upper limit of sliding velocity for the custom setup, the friction properties of mica are reported from 200 µm s −1 up to 2 cm s −1 . While FCM is applicable to any AFM and scanning speed, quantitative nanotribology investigations of heterogeneous sliding or rolling components are therefore uniquely possible, even at realistic velocities for devices such as MEMS, biological implants, or data storage systems. (paper)

  9. Contribution of gait parameters and available coefficient of friction to perceptions of slipperiness.

    Science.gov (United States)

    Chang, Wen-Ruey; Lesch, Mary F; Chang, Chien-Chi; Matz, Simon

    2015-01-01

    Perceived slipperiness rating (PSR) has been widely used to assess walkway safety. In this experiment, 29 participants were exposed to 5 floor types under dry, wet and glycerol conditions. The relationship between their PSR and objective measurements, including utilized coefficient of friction (UCOF), gait kinematics and available coefficient of friction (ACOF), was explored with a regression analysis using step-wise backward elimination. The results showed that UCOF and ACOF, as well as their difference, were the major predictors of the PSR under wet and glycerol conditions. Under wet conditions, the participants appeared to rely on the potential for foot slip to form their PSR. Under glycerol conditions, some kinematic variables also became major predictors of PSR. The results show how different proprioceptive responses and ACOF contributed to the prediction of PSR under different surface conditions. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

  10. The stochastic distribution of available coefficient of friction for human locomotion of five different floor surfaces.

    Science.gov (United States)

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

    2014-05-01

    The maximum coefficient of friction that can be supported at the shoe and floor interface without a slip is usually called the available coefficient of friction (ACOF) for human locomotion. The probability of a slip could be estimated using a statistical model by comparing the ACOF with the required coefficient of friction (RCOF), assuming that both coefficients have stochastic distributions. An investigation of the stochastic distributions of the ACOF of five different floor surfaces under dry, water and glycerol conditions is presented in this paper. One hundred friction measurements were performed on each floor surface under each surface condition. 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 distributions had a slightly better match with the normal and log-normal distributions than with the Weibull in only three out of 15 cases with a statistical significance. The results are far more complex than what had heretofore been published and different scenarios could emerge. Since the ACOF is compared with the RCOF for the estimate of slip probability, the distribution of the ACOF in seven cases could be considered a constant for this purpose when the ACOF is much lower or higher than the RCOF. A few cases could be represented by a normal distribution for practical reasons based on their skewness and kurtosis values without a statistical significance. No representation could be found in three cases out of 15. Copyright © 2013 Elsevier Ltd and The Ergonomics Society. All rights reserved.

  11. The friction coefficient of shoulder joints remains remarkably low over 24 h of loading.

    Science.gov (United States)

    Jones, Brian K; Durney, Krista M; Hung, Clark T; Ateshian, Gerard A

    2015-11-05

    The frictional response of whole human joints over durations spanning activities of daily living has not been reported previously. This study measured the friction of human glenohumeral joints during 24 h of reciprocal loading in a pendulum testing device, at moderate (0.2 mm/s, 4320 cycles) and low (0.02 mm/s, 432 cycles) sliding speeds, under a 200 N load. The effect of joint congruence was also investigated by testing human humeral heads against significantly larger mature bovine glenoids. Eight human joints and six bovine joints were tested in four combinations: human joints tested at moderate (hHCMS, n=6) and low speed (hHCLS, n=3), human humeral heads tested against bovine glenoids at moderate speed (LCMS, n=3), and bovine joints tested at moderate speed (bHCMS, n=3). In the first half hour the mean±standard deviation of the friction coefficient was hHCMS: 0.0016±0.0011, hHCLS: 0.0012±0.0002, LCMS: 0.0008±0.0002 and bHCMS: 0.0024±0.0008; in the last four hours it was hHCMS: 0.0057±0.0025, hHCLS: 0.0047±0.0017, LCMS: 0.0012±0.0003 and bHCMS: 0.0056±0.0016. The initial value was lower than the final value (pfriction coefficient of natural human shoulders remains remarkably low (averaging as little as 0.0015 and no greater than 0.006) for up to 24 h of continuous loading. The sustained low friction coefficients observed in incongruent joints (~0.001) likely represent rolling rather than sliding friction. Copyright © 2015. Published by Elsevier Ltd.

  12. The Friction Coefficient of Shoulder Joints Remains Remarkably Low Over 24 h of Loading

    Science.gov (United States)

    Jones, Brian K.; Durney, Krista M.; Hung, Clark T.; Ateshian, Gerard A.

    2015-01-01

    The frictional response of whole human joints over durations spanning activities of daily living has not been reported previously. This study measured the friction of human glenohumeral joints during 24 h of reciprocal loading in a pendulum testing device, at moderate (0.2 mm/s, 4320 cycles) and low (0.02 mm/s, 432 cycles) sliding speeds, under a 200 N load. The effect of joint congruence was also investigated by testing human humeral heads against significantly larger mature bovine glenoids. Six human joints and six bovine joints were tested in four combinations: human joints tested at moderate (hHCMS, n=6) and low speed (hHCLS, n=3), human humeral heads tested against bovine glenoids at moderate speed (LCMS, n=3), and bovine joints tested at moderate speed (bHCMS, n=3). In the first half hour the mean ± standard deviation of the friction coefficient was hHCMS: 0.0016±0.0011, hHCLS: 0.0012±0.0002, LCMS: 0.0008±0.0002 and bHCMS: 0.0024±0.0008; in the last four hours it was hHCMS: 0.0057±0.0025, hHCLS: 0.0047±0.0017, LCMS: 0.0012±0.0003 and bHCMS: 0.0056±0.0016. The initial value was lower than the final value (pfriction coefficient of natural human shoulders remains remarkably low (averaging as little as 0.0015 and no greater than 0.006) for up to 24 h of continuous loading. The sustained low friction coefficients observed in incongruent joints (~0.001) likely represent rolling rather than sliding friction. PMID:26472306

  13. 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.

  14. 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.

  15. Prediction of static friction coefficient in rough contacts based on the junction growth theory

    Science.gov (United States)

    Spinu, S.; Cerlinca, D.

    2017-08-01

    The classic approach to the slip-stick contact is based on the framework advanced by Mindlin, in which localized slip occurs on the contact area when the local shear traction exceeds the product between the local pressure and the static friction coefficient. This assumption may be too conservative in the case of high tractions arising at the asperities tips in the contact of rough surfaces, because the shear traction may be allowed to exceed the shear strength of the softer material. Consequently, the classic frictional contact model is modified in this paper so that gross sliding occurs when the junctions formed between all contacting asperities are independently sheared. In this framework, when the contact tractions, normal and shear, exceed the hardness of the softer material on the entire contact area, the material of the asperities yields and the junction growth process ends in all contact regions, leading to gross sliding inception. This friction mechanism is implemented in a previously proposed numerical model for the Cattaneo-Mindlin slip-stick contact problem, which is modified to accommodate the junction growth theory. The frictionless normal contact problem is solved first, then the tangential force is gradually increased, until gross sliding inception. The contact problems in the normal and in the tangential direction are successively solved, until one is stabilized in relation to the other. The maximum tangential force leading to a non-vanishing stick area is the static friction force that can be sustained by the rough contact. The static friction coefficient is eventually derived as the ratio between the latter friction force and the normal force.

  16. Study on Material Parameters Identification of Brain Tissue Considering Uncertainty of Friction Coefficient

    Science.gov (United States)

    Guan, Fengjiao; Zhang, Guanjun; Liu, Jie; Wang, Shujing; Luo, Xu; Zhu, Feng

    2017-10-01

    Accurate material parameters are critical to construct the high biofidelity finite element (FE) models. However, it is hard to obtain the brain tissue parameters accurately because of the effects of irregular geometry and uncertain boundary conditions. Considering the complexity of material test and the uncertainty of friction coefficient, a computational inverse method for viscoelastic material parameters identification of brain tissue is presented based on the interval analysis method. Firstly, the intervals are used to quantify the friction coefficient in the boundary condition. And then the inverse problem of material parameters identification under uncertain friction coefficient is transformed into two types of deterministic inverse problem. Finally the intelligent optimization algorithm is used to solve the two types of deterministic inverse problems quickly and accurately, and the range of material parameters can be easily acquired with no need of a variety of samples. The efficiency and convergence of this method are demonstrated by the material parameters identification of thalamus. The proposed method provides a potential effective tool for building high biofidelity human finite element model in the study of traffic accident injury.

  17. Friction coefficient and limiter load test analysis by flexibility coefficient model of Hold-Down Spring of nuclear reactor vessel internals

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Linjun [Zhejiang Univ. of Technology, Hangzhou (China). College of Mechanical Engineering; Xue, Guohong; Zhang, Ming [Shanghai Nuclear Engineering Research and Design Institute, Shanghai (China)

    2017-11-15

    The friction force between the contact surfaces of a reactor internal hold-down spring (HDS) and core barrel flanges can directly influence the axial stiffness of an HDS. However, friction coefficient cannot be obtained through theoretical analysis. This study performs a mathematical deduction of the physical model of an HDS. Moreover, a mathematical model of axial load P, displacement δ, and flexibility coefficient is established, and a set of test apparatuses is designed to simulate the preloading process of the HDS. According to the experimental research and theoretical analysis, P-δ curves and the flexibility coefficient λ are obtained in the loading processes of the HDS. The friction coefficient f of the M1000 HDS is further calculated as 0.224. The displacement limit load value (4,638 kN) can be obtained through a displacement limit experiment. With the friction coefficient considered, the theoretical load is 4,271 kN, which is relatively close to the experimental result. Thus, the friction coefficient exerts an influence on the displacement limit load P. The friction coefficient should be considered in the design analysis for HDS.

  18. Friction coefficient and limiter load test analysis by flexibility coefficient model of Hold-Down Spring of nuclear reactor vessel internals

    International Nuclear Information System (INIS)

    Xie, Linjun

    2017-01-01

    The friction force between the contact surfaces of a reactor internal hold-down spring (HDS) and core barrel flanges can directly influence the axial stiffness of an HDS. However, friction coefficient cannot be obtained through theoretical analysis. This study performs a mathematical deduction of the physical model of an HDS. Moreover, a mathematical model of axial load P, displacement δ, and flexibility coefficient is established, and a set of test apparatuses is designed to simulate the preloading process of the HDS. According to the experimental research and theoretical analysis, P-δ curves and the flexibility coefficient λ are obtained in the loading processes of the HDS. The friction coefficient f of the M1000 HDS is further calculated as 0.224. The displacement limit load value (4,638 kN) can be obtained through a displacement limit experiment. With the friction coefficient considered, the theoretical load is 4,271 kN, which is relatively close to the experimental result. Thus, the friction coefficient exerts an influence on the displacement limit load P. The friction coefficient should be considered in the design analysis for HDS.

  19. Comparison of different methods to extract the required coefficient of friction for level walking.

    Science.gov (United States)

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

    2012-01-01

    The required coefficient of friction (RCOF) is an important predictor for slip incidents. Despite the wide use of the RCOF there is no standardised method for identifying the RCOF from ground reaction forces. This article presents a comparison of the outcomes from seven different methods, derived from those reported in the literature, for identifying the RCOF from the same data. While commonly used methods are based on a normal force threshold, percentage of stance phase or time from heel contact, a newly introduced hybrid method is based on a combination of normal force, time and direction of increase in coefficient of friction. Although no major differences were found with these methods in more than half the strikes, significant differences were found in a significant portion of strikes. Potential problems with some of these methods were identified and discussed and they appear to be overcome by the hybrid method. No standard method exists for determining the required coefficient of friction (RCOF), an important predictor for slipping. In this study, RCOF values from a single data set, using various methods from the literature, differed considerably for a significant portion of strikes. A hybrid method may yield improved results.

  20. Flow Function of Pharmaceutical Powders Is Predominantly Governed by Cohesion, Not by Friction Coefficients.

    Science.gov (United States)

    Leung, Lap Yin; Mao, Chen; Srivastava, Ishan; Du, Ping; Yang, Chia-Yi

    2017-07-01

    The purpose of this study was to demonstrate that the flow function (FFc) of pharmaceutical powders, as measured by rotational shear cell, is predominantly governed by cohesion but not friction coefficients. Driven by an earlier report showing an inverse correlation between FFc and the cohesion divided by the corresponding pre-consolidation stress (Wang et al. 2016. Powder Tech. 294:105-112), we performed analysis on a large data set containing 1130 measurements from a ring shear tester and identified a near-perfect inverse correlation between the FFc and cohesion. Conversely, no correlation was found between FFc and friction angles. We also conducted theoretical analysis and estimated such correlations based on Mohr-Coulomb failure model. We discovered that the correlation between FFc and cohesion can sustain as long as the angle of internal friction at incipient flow is not significantly larger than the angle of internal friction at steady-state flow, a condition covering almost all pharmaceutical powders. The outcome of this study bears significance in pharmaceutical development. Because the cohesion value is strongly influenced by the interparticle cohesive forces, this study effectively shows that it is more efficient to improve the pharmaceutical powder flow by lowering the interparticle cohesive forces than by lowering the interparticle frictions. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  1. 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

  2. Pleural liquid and kinetic friction coefficient of mesothelium after mechanical ventilation.

    Science.gov (United States)

    Bodega, Francesca; Sironi, Chiara; Porta, Cristina; Zocchi, Luciano; Agostoni, Emilio

    2015-01-15

    Volume and protein concentration of pleural liquid in anesthetized rabbits after 1 or 3h of mechanical ventilation, with alveolar pressure equal to atmospheric at end expiration, were compared to those occurring after spontaneous breathing. Moreover, coefficient of kinetic friction between samples of visceral and parietal pleura, obtained after spontaneous or mechanical ventilation, sliding in vitro at physiological velocity under physiological load, was determined. Volume of pleural liquid after mechanical ventilation was similar to that previously found during spontaneous ventilation. This finding is contrary to expectation of Moriondo et al. (2005), based on measurement of lymphatic and interstitial pressure. Protein concentration of pleural liquid after mechanical ventilation was also similar to that occurring after spontaneous ventilation. Coefficient of kinetic friction after mechanical ventilation was 0.023±0.001, similar to that obtained after spontaneous breathing. Copyright © 2014 Elsevier B.V. All rights reserved.

  3. Experimental Investigation of Friction Coefficient and Wear Rate of Composite Materials Sliding Against Smooth and Rough Mild Steel Counterfaces

    Directory of Open Access Journals (Sweden)

    M.A. Chowdhury

    2013-12-01

    Full Text Available In the present study, friction coefficient and wear rate of gear fiber reinforced plastic (gear fiber and glass fiber reinforced plastic (glass fiber sliding against mild steel are investigated experimentally. In order to do so, a pin on disc apparatus is designed and fabricated. Experiments are carried out when smooth or rough mild steel pin slides on gear fiber and glass fiber disc. Experiments are conducted at normal load 10, 15 and 20 N, sliding velocity 1, 1.5 and 2 m/s and relative humidity 70%. Variations of friction coefficient with the duration of rubbing at different normal loads and sliding velocities are investigated. Results show that friction coefficient is influenced by duration of rubbing, normal load and sliding velocity. In general, friction coefficient increases for a certain duration of rubbing and after that it remains constant for the rest of the experimental time. The obtained results reveal that friction coefficient decreases with the increase in normal load for gear fiber and glass fiber mating with smooth or rough mild steel counterface. On the other hand, it is also found that friction coefficient increases with the increase in sliding velocity for both of the tested materials. Moreover, wear rate increases with the increase in normal load and sliding velocity. The magnitudes of friction coefficient and wear rate are different depending on sliding velocity and normal load for both smooth and rough counterface pin materials.

  4. RADIAL FORCE IMPACT ON THE FRICTION COEFFICIENT AND TEMPERATURE OF A SELF-LUBRICATING PLAIN BEARING

    Directory of Open Access Journals (Sweden)

    Nada Bojić

    2017-12-01

    Full Text Available Self-lubricating bearings are available in spherical, plain, flanged journal, and rod end bearing configurations. They were originally developed to eliminate the need for re-lubrication, to provide lower torque and to solve application problems where the conventional metal-to-metal bearings would not perform satisfactorily, for instance, in the presence of high frequency vibrations. Among the dominant tribological parameters of the self-lubricating bearing, two could be singled out: the coefficient of friction and temperature. To determine these parameters, an experimental method was applied in this paper. By using this method, the coefficient of friction and temperature were identified and their correlation was established. The aim of this research was to determine the effect of radial force on tribological parameters in order to predict the behavior of sliding bearings with graphite in real operating conditions.

  5. Required coefficient of friction during turning at self-selected slow, normal, and fast walking speeds.

    Science.gov (United States)

    Fino, Peter; Lockhart, Thurmon E

    2014-04-11

    This study investigated the relationship of required coefficient of friction to gait speed, obstacle height, and turning strategy as participants walked around obstacles of various heights. Ten healthy, young adults performed 90° turns around corner pylons of four different heights at their self selected normal, slow, and fast walking speeds using both step and spin turning strategies. Kinetic data was captured using force plates. Results showed peak required coefficient of friction (RCOF) at push off increased with increased speed (slow μ=0.38, normal μ=0.45, and fast μ=0.54). Obstacle height had no effect on RCOF values. The average peak RCOF for fast turning exceeded the OSHA safety guideline for static COF of μ>0.50, suggesting further research is needed into the minimum static COF to prevent slips and falls, especially around corners. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. Influence of the Friction Coefficient on the Trajectory Performance for a Car-Like Robot

    Directory of Open Access Journals (Sweden)

    Francisco Valero

    2017-01-01

    Full Text Available A collision-free trajectory planner for a car-like mobile robot moving in complex environments is introduced and the influence of the coefficient of friction on important working parameters is analyzed. The proposed planner takes into account not only the dynamic capabilities of the robot but also the behaviour of the tire. This planner is based on sequential quadratic programming algorithms and the normalized time method. Different values for the coefficient of friction have been taken following a normal Gaussian distribution to see its influence on the working parameters. The algorithm has been applied to several examples and the results show that computation times are compatible with real-time work, so the authors call them efficient generated trajectories as they avoid collisions. Besides, working parameters such as the minimum trajectory time, the maximum vehicle speed, computational time, and consumed energy have been monitored and some conclusions have been reached.

  7. Friction coefficient determination by electrical resistance measurements

    Science.gov (United States)

    Tunyagi, A.; Kandrai, K.; Fülöp, Z.; Kapusi, Z.; Simon, A.

    2018-05-01

    A simple and low-cost, DIY-type, Arduino-driven experiment is presented for the study of friction and measurement of the friction coefficient, using a conductive rubber cord as a force sensor. It is proposed for high-school or college/university-level students. We strongly believe that it is worthwhile planning, designing and performing Arduino and compatible sensor-based experiments in physics class in order to ensure a better understanding of phenomena, develop theoretical knowledge and multiple experimental skills.

  8. Predictive multiscale computational model of shoe-floor coefficient of friction.

    Science.gov (United States)

    Moghaddam, Seyed Reza M; Acharya, Arjun; Redfern, Mark S; Beschorner, Kurt E

    2018-01-03

    Understanding the frictional interactions between the shoe and floor during walking is critical to prevention of slips and falls, particularly when contaminants are present. A multiscale finite element model of shoe-floor-contaminant friction was developed that takes into account the surface and material characteristics of the shoe and flooring in microscopic and macroscopic scales. The model calculates shoe-floor coefficient of friction (COF) in boundary lubrication regime where effects of adhesion friction and hydrodynamic pressures are negligible. The validity of model outputs was assessed by comparing model predictions to the experimental results from mechanical COF testing. The multiscale model estimates were linearly related to the experimental results (p < 0.0001). The model predicted 73% of variability in experimentally-measured shoe-floor-contaminant COF. The results demonstrate the potential of multiscale finite element modeling in aiding slip-resistant shoe and flooring design and reducing slip and fall injuries. Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.

  9. [The appraisal of mechanical properties and friction coefficient of PVA hydro-gel].

    Science.gov (United States)

    Chen, Liqi; Zhang, Dekun; Zhang, Jinsong

    2009-10-01

    Gelatin and hydroxyapatite were introduced to polyvinyl alcohol (PVA) hydrogel with an attempt to enhance the performances of PVA hydrogel. Through a reiterative freezing-thawing methods, three kinds of PVA composite hydrogels were prepared. The mechanical performances of these composite hydrogels with the same PVA and HA content but varying gelatin content, such as tensile strength, elasticity modulus, creep curve, relaxation curve and friction coefficient were evaluated by using a computer-controlled universal electronic mechanical testing machine and a UMT-II frictional testing machine. The additional effects of hydroxylapatite and varying gelatin on the performances of composite PVA hydro-gels were analyzed. It was found that the gelatin content directly influenced the physical performances of PVA composite hydrogels; but no linear relationship was recorded. PVA composite hydrogel containing 2wt-% gelatin gave optimal results, i.e. tensile strength of 5.5MPa, compressive elastical modulus of 1.48MPa, creeping rate of 31% in 45 minutes, stress relaxing rate of 40.3%, and the starting friction coefficient of 0.332.

  10. The impact of surface and geometry on coefficient of friction of artificial hip joints.

    Science.gov (United States)

    Choudhury, Dipankar; Vrbka, Martin; Mamat, Azuddin Bin; Stavness, Ian; Roy, Chanchal K; Mootanah, Rajshree; Krupka, Ivan

    2017-08-01

    Coefficient of friction (COF) tests were conducted on 28-mm and 36-mm-diameter hip joint prostheses for four different material combinations, with or without the presence of Ultra High Molecular Weight Polyethylene (UHMWPE) particles using a novel pendulum hip simulator. The effects of three micro dimpled arrays on femoral head against a polyethylene and a metallic cup were also investigated. Clearance played a vital role in the COF of ceramic on polyethylene and ceramic on ceramic artificial hip joints. Micro dimpled metallic femoral heads yielded higher COF against a polyethylene cup; however, with metal on metal prostheses the dimpled arrays significantly reduced the COF. In situ images revealed evidence that the dimple arrays enhanced film formation, which was the main mechanism that contributed to reduced friction. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Effect of Friction Coefficient on the Small Punch Creep Behavior of AISI 316L Stainless Steel

    International Nuclear Information System (INIS)

    Kim, Bum-Joon; Cho, Nam-Hyuck; Kim, Moon-K; Lim, Byeong-Soo

    2011-01-01

    Small punch creep testing has received attention due to the convenience of using smaller specimens than those of conventional uniaxial creep tests, which enables creep testing on developing or currently operational components. However, precedent studies have shown that it is necessary to consider friction between the punch and specimen when computing uniaxial equivalent stress from a finite element model. In this study, small punch creep behaviors of AISI 316L stainless steel, which is widely used in high temperature-high pressure machineries, have been compared for the two different ceramic balls such as Si 3 N 4 and Al 2 O 3 . The optimal range of the friction coefficient is 0.4⁓0.5 at 650°C for the best fit between experimental and simulation data of AISI 316 L stainless steel. The higher the friction coefficient, the longer the creep rupture time is. Therefore, the type of ceramic ball used must be specified for standardization of small punch creep testing.

  12. Modelling the stochastic nature of the available coefficient of friction at footwear-floor interfaces.

    Science.gov (United States)

    Gragg, Jared; Klose, Ellison; Yang, James

    2017-07-01

    The available coefficient of friction (ACOF) is a measure of the friction available between two surfaces, which for human gait would be the footwear-floor interface. It is often compared to the required coefficient of friction (RCOF) to determine the likelihood of a slip in gait. Both the ACOF and RCOF are stochastic by nature meaning that neither should be represented by a deterministic value, such as the sample mean. Previous research has determined that the RCOF can be modelled well by either the normal or lognormal distributions, but previous research aimed at determining an appropriate distribution for the ACOF was inconclusive. This study focuses on modelling the stochastic nature of the ACOF by fitting eight continuous probability distributions to ACOF data for six scenarios. In addition, the data were used to study the effect that a simple housekeeping action such as sweeping could have on the ACOF. Practitioner Summary: Previous research aimed at determining an appropriate distribution for the ACOF was inconclusive. The study addresses this issue as well as looking at the effect that an act such as sweeping has on the ACOF.

  13. Synthesis and characterization of a zwitterionic hydrogel blend with low coefficient of friction.

    Science.gov (United States)

    Osaheni, Allen O; Finkelstein, Eric B; Mather, Patrick T; Blum, Michelle M

    2016-12-01

    Hydrogels display a great deal of potential for a wide variety of biomedical applications. Often times the performance of these biomimetic materials is limited due to inferior friction and wear properties. This manuscript presents a method inspired by the tribological phenomena observed in nature for enhancing the lubricious properties of poly(vinyl alcohol) (PVA) hydrogels. This was achieved by blending PVA with various amounts of zwitterionic polymer, poly([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide) (pMEDSAH). Our results indicate that pMEDSAH acts as an effective boundary lubricant, allowing for reduction in coefficient of friction by more than 80%. This reduction in friction coefficient was achieved while maintaining comparable mechanical and physical properties to that of the neat material. Also, these zwitterionic blends were found to be cytocompatible. Analysis of the structure to property relationships within this system indicate that the zwitterionic polymer served as a boundary lubricant and promoted a reduction in friction through hydration lubrication. This novel approach provides a promising platform for further investigations enhancing the tribological properties of hydrogels for biomedical applications. The novelty of this work stems from showing that zwitterionic polymers can be used as an extremely effective hydrogel boundary lubricant. This work will have significant scientific impact because to date, design of hydrogels has emphasized replication of mechanical properties, but in order for these types of materials to be fully utilized as biomaterials it is imperative that they possess improved tribological and lubrication properties, because ignoring the surface and boundary lubrication mechanism, make these potential load-bearing substitutes incompatible with other natural articulating surfaces, leading the constructs to wear, fail, and damage healthy tissue. Our work also provides unique insight to the structure

  14. The influence of friction coefficient and wheel/rail profiles on energy dissipation in the wheel/rail contact

    NARCIS (Netherlands)

    Idarraga Alarcon, G.A.; Burgelman, N.D.M.; Meza Meza, J.; Toro, A.; Li, Z.

    2015-01-01

    This work investigates the energy dissipation in a wheel/rail system through friction work modeling. In order to identify the effect of the friction coefficient on the energy dissipation in the wheel/rail contact, several simulations were performed using a 3D multibody model of a railway vehicle

  15. Experimental Measurement of the Static Coefficient of Friction at the Ti-Ti Taper Connection in Total Hip Arthroplasty.

    Science.gov (United States)

    Bitter, T; Khan, I; Marriott, T; Schreurs, B W; Verdonschot, N; Janssen, D

    2016-03-01

    The modular taper junction in total hip replacements has been implicated as a possible source of wear. The finite-element (FE) method can be used to study the wear potential at the taper junction. For such simulations it is important to implement representative contact parameters, in order to achieve accurate results. One of the main parameters in FE simulations is the coefficient of friction. However, in current literature, there is quite a wide spread in coefficient of friction values (0.15 - 0.8), which has a significant effect on the outcome of the FE simulations. Therefore, to obtain more accurate results, one should use a coefficient of friction that is determined for the specific material couple being analyzed. In this study, the static coefficient of friction was determined for two types of titanium-on-titanium stem-adaptor couples, using actual cut-outs of the final implants, to ensure that the coefficient of friction was determined consistently for the actual implant material and surface finish characteristics. Two types of tapers were examined, Biomet type-1 and 12/14, where type-1 has a polished surface finish and the 12/14 is a microgrooved system. We found static coefficients of friction of 0.19 and 0.29 for the 12/14 and type-1 stem-adaptor couples, respectively.

  16. The Influence of Natural Frequency of the Experimental Set-up on the Friction Coefficient of Stainless Steel-304

    Directory of Open Access Journals (Sweden)

    M. A. Chowdhury

    2010-03-01

    Full Text Available The present paper investigates experimentally the effect of natural frequency of the experimental set-up on friction property of stainless steel-304. To do so, a pin-on-disc apparatus having facility of vibrating the test samples at different directions, amplitudes and frequencies was designed and fabricated. The natural frequency of the set-up was varied by adding dead loads of the setup from 0 kg to 50 kg. At each added load the friction coefficient has been measured. Results show that both the natural frequency and friction coefficient decrease with the increase of added loads. It has been also observed that the coefficient of friction increases with the increase of natural frequency of the experimental setup. The experimental results are also compared with those available in literature and simple physical explanations are provided.

  17. Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress

    Science.gov (United States)

    Whitney, G. A.; Mansour, J. M.; Dennis, J. E.

    2015-01-01

    The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy. PMID:25691395

  18. Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress.

    Science.gov (United States)

    Whitney, G A; Mansour, J M; Dennis, J E

    2015-09-01

    The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy.

  19. Numerical Study of Tire Hydroplaning Based on Power Spectrum of Asphalt Pavement and Kinetic Friction Coefficient

    Directory of Open Access Journals (Sweden)

    Shengze Zhu

    2017-01-01

    Full Text Available Hydroplaning is a driving phenomenon threating vehicle’s control stability and safety. It happens when tire rolls on wet pavement with high speed that hydrodynamic force uplifts the tire. Accurate numerical simulation to reveal the mechanism of hydroplaning and evaluate the function of relevant factors in this process is significant. In order to describe the friction behaviors of tire-pavement interaction, kinetic friction coefficient curve of tire rubber and asphalt pavement was obtained by combining pavement surface power spectrum and complex modulus of tread rubber through Persson’s friction theory. Finite element model of tire-fluid-pavement was established in ABAQUS, which was composed of a 225-40-R18 radial tire and three types of asphalt pavement covered with water film. Mechanical responses and physical behaviors of tire-pavement interaction were observed and compared with NASA equation to validate the applicability and accuracy of this model. Then contact force at tire-pavement interface and critical hydroplaning speed influenced by tire inflation pressure, water film thickness, and pavement types were investigated. The results show higher tire inflation pressure, thinner water film, and more abundant macrotexture enhancing hydroplaning speed. The results could be applied to predict hydroplaning speed on different asphalt pavement and improve pavement skid resistance design.

  20. Effect of the coefficient of friction of a running surface on sprint time in a sled-towing exercise.

    Science.gov (United States)

    Linthorne, Nicholas P; Cooper, James E

    2013-06-01

    This study investigated the effect of the coefficient of friction of a running surface on an athlete's sprint time in a sled-towing exercise. The coefficients of friction of four common sports surfaces (a synthetic athletics track, a natural grass rugby pitch, a 3G football pitch, and an artificial grass hockey pitch) were determined from the force required to tow a weighted sled across the surface. Timing gates were then used to measure the 30-m sprint time for six rugby players when towing a sled of varied weight across the surfaces. There were substantial differences between the coefficients of friction for the four surfaces (micro = 0.21-0.58), and in the sled-towing exercise the athlete's 30-m sprint time increased linearly with increasing sled weight. The hockey pitch (which had the lowest coefficient of friction) produced a substantially lower rate of increase in 30-m sprint time, but there were no significant differences between the other surfaces. The results indicate that although an athlete's sprint time in a sled-towing exercise is affected by the coefficient offriction of the surface, the relationship relationship between the athlete's rate of increase in 30-m sprint time and the coefficient of friction is more complex than expected.

  1. Estimation of coefficient of rolling friction by the evolvent pendulum method

    Science.gov (United States)

    Alaci, S.; Ciornei, F. C.; Ciogole, A.; Ciornei, M. C.

    2017-05-01

    The paper presents a method for finding the coefficient of rolling friction using an evolvent pendulum. The pendulum consists in a fixed cylindrical body and a mobile body presenting a plane surface in contact with a cylindrical surface. The mobile body is placed over the fixed one in an equilibrium state; after applying a small impulse, the mobile body oscillates. The motion of the body is video recorded and afterwards the movie is analyzed by frames and the decrease with time of angular amplitude of the pendulum is found. The equation of motion is established for oscillations of the mobile body. The equation of motion, differential nonlinear, is integrated by Runge-Kutta method. Imposing the same damping both to model’s solution and to theoretical model, the value of coefficient of rolling friction is obtained. The last part of the paper presents results for actual pairs of materials. The main advantage of the method is the fact that the dimensions of contact regions are small, of order a few millimeters, and thus is substantially reduced the possibility of variation of mechanical characteristic for the two surfaces.

  2. Regulation of the friction coefficient of articular cartilage by TGF-beta1 and IL-1beta.

    Science.gov (United States)

    DuRaine, Grayson; Neu, Corey P; Chan, Stephanie M T; Komvopoulos, Kyriakos; June, Ronald K; Reddi, A Hari

    2009-02-01

    Articular cartilage functions to provide a low-friction surface for joint movement for many decades of life. Superficial zone protein (SZP) is a glycoprotein secreted by chondrocytes in the superficial layer of articular cartilage that contributes to effective boundary lubrication. In both cell and explant cultures, TGF-beta1 and IL-1beta have been demonstrated to, respectively, upregulate and downregulate SZP protein levels. It was hypothesized that the friction coefficient of articular cartilage could also be modulated by these cytokines through SZP regulation. The friction coefficient between cartilage explants (both untreated and treated with TGF-beta1 or IL-1beta) and a smooth glass surface due to sliding in the boundary lubrication regime was measured with a pin-on-disk tribometer. SZP was quantified using an enzyme-linked immunosorbant assay and localized by immunohistochemistry. Both TGF-beta1 and IL-1beta treatments resulted in the decrease of the friction coefficient of articular cartilage in a location- and time-dependent manner. Changes in the friction coefficient due to the TGF-beta1 treatment corresponded to increased depth of SZP staining within the superficial zone, while friction coefficient changes due to the IL-1beta treatment were independent of SZP depth of staining. However, the changes induced by the IL-1beta treatment corresponded to changes in surface roughness, determined from the analysis of surface images obtained with an atomic force microscope. These findings demonstrate that the low friction of articular cartilage can be modified by TGF-beta1 and IL-1beta treatment and that the friction coefficient depends on multiple factors, including SZP localization and surface roughness.

  3. Changes in condylar coefficient of friction after osteochondral graft transplantation and modulation with hyaluronan.

    Science.gov (United States)

    Lane, John; Healey, Robert; Amiel, David

    2009-12-01

    To better understand the changes in the cartilage coefficient of friction (COF) after an osteochondral repair, an assessment of dynamic loads has been developed using a goat knee model. The application of hyaluronan (HA) was also assessed for its lubricative properties and the resulting COF of the knee after osteochondral repair. A total of 18 caprine knees were dissected and mounted into an Instron load frame (Instron, Norwood, MA) for testing. The COF was measured in 10 knees relative to the normal, unaltered joint and then calibrated to account for friction of the system. These experimental knees were tested in 5 modes: normal; empty 4.5-mm defect; and osteochondral repairs that were elevated, flush, or depressed relative to the cartilage surface. Saline solution lavage kept the knees moist during testing. The effect of HA was evaluated after mechanical testing. Eight knees were used to study the effect of lavage on the joints because of the significant increase in the COF that it produced. Whereas all modes increased the COF from normal levels, the most significant changes occurred when there was proud placement. Increases of 4 times the normal friction levels were measured. Increases in the COF were also associated with saline solution lavage (0.006 to 0.046). There was a significant reduction in friction after HA injection, which reduced the COF to near-normal levels. There is a significant increase in the COF associated with saline solution lavage and an osteochondral plug being left proud, which can be temporarily reduced with a lubricative material such as HA. Dramatic increases in the COF can potentially damage chondrocytes when the patient begins articulating the joint after surgery. Such injuries may affect the ability of the cartilage to heal fully. Reducing the elevated COF with lubricating materials, such as HA, is recommended based on the results of this study.

  4. Effects of the friction coefficient on the torque characteristics of a hydraulic cam-rotor vane motor

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Qiankun; Wang, Xuyong; Yuan, Fan; Chen, Liang Shen; Tao, Jian Feng [School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai (China); Miao, Zhong Hua [School of Mechatronic Engineering and Automation, Shanghai University, Shanghai (China)

    2016-08-15

    The friction coefficient between the vane and the slot is one of the most critical factors that affects the performance of a continuous rotary hydraulic cam-rotor vane motor. To study the effects of this coefficient on the torque characteristics of the motor, the mathematical model for the normal force and the disturbing torque between the cam rotors and the vanes of the motor was established by analyzing the forces exerted on the vanes. The mathematical model was simulated with MATLAB, and simulation results show that an increase in the friction coefficient would simultaneously decrease the normal force and increase the disturbing torque, which would negatively affect the performance of the motor. Further experimental research indicated that the low-speed performance of the hydraulic cam-rotor motor was significantly improved when the friction coefficient was reduced by controlling the parallelism tolerance, flatness and roughness between the vanes and the slots.

  5. 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.

  6. Friction coefficient of an intact free liquid jet moving in air

    Science.gov (United States)

    Comiskey, P. M.; Yarin, A. L.

    2018-04-01

    Here, we propose a novel method of determining the friction coefficient of intact free liquid jets moving in quiescent air. The middle-size jets of this kind are relevant for such applications as decorative fountains, fiber-forming, fire suppression, agriculture, and forensics. The present method is based on measurements of trajectories created using a straightforward experimental apparatus emulating such jets at a variety of initial inclination angles. Then, the trajectories are described theoretically, accounting for the longitudinal traction imposed on such jets by the surrounding air. The comparison of the experimental data with the theoretical predictions shows that the results can be perfectly superimposed with the friction coefficient {C_{{fd}}}=5R{e_d}^{{ - 1/2 ± 0.05}}, in the 621 ≤ R{e_d} ≤ 1289 range, with Red being the Reynolds number based on the local cross-sectional diameter of the jet. The results also show that the farthest distance such jets can reach corresponds to the initial inclination angle α =35° which is in agreement with already published data.

  7. Changes in the surface roughness and friction coefficient of orthodontic bracket slots before and after treatment.

    Science.gov (United States)

    Liu, Xiaomo; Lin, Jiuxiang; Ding, Peng

    2013-01-01

    In this study, we tested the surface roughness of bracket slots and the friction coefficient between the bracket and the stainless steel archwire before and after orthodontic treatment. There were four experimental groups: groups 1 and 2 were 3M new and retrieved brackets, respectively, and groups 3 and 4 were BioQuick new and retrieved brackets, respectively. All retrieved brackets were taken from patients with the first premolar extraction and using sliding mechanics to close the extraction space. The surface roughness of specimens was evaluated using an optical interferometry profilometer, which is faster and nondestructive compared with a stylus profilometer, and provided a larger field, needing no sample preparation, compared with atomic force microscopy. Orthodontic treatment resulted in significant increases in surface roughness and coefficient of friction for both brands of brackets. However, there was no significant difference by brand for new or retrieved brackets. These retrieval analysis results highlight the necessity of reevaluating the properties and clinical behavior of brackets during treatment to make appropriate treatment decisions. © Wiley Periodicals, Inc.

  8. Estimation of sediment friction coefficient from heating upon APC penetration during the IODP NanTroSEIZE

    Science.gov (United States)

    Kinoshita, M.; Kawamura, K.; Lin, W.

    2015-12-01

    During the Nankai Trough Seismogenic Zone Experiments (NanTroSEIZE) of the Integrated Ocean Drilling Program (IODP), the advanced piston corer temperature (APC-T) tool was used to determine in situ formation temperatures while piston coring down to ~200 m below sea floor. When the corer is fired into the formation, temperature around the shoe abruptly increases due to the frictional heating. The temperature rise due to the frictional heat at the time of penetration is 10 K or larger. We found that the frictional temperature rise (=maximum temperature) increases with increasing depth, and that its intersection at the seafloor seems non-zero. Frictional heat energy is proportional to the maximum temperature rise, which is confirmed by a FEM numerical simulation of 2D cylindrical system. Here we use the result of numerical simulation to convert the observed temperature rise into the frictional heat energy. The frictional heat energy is represented as the product of the shooting length D and the shear stress (τ) between the pipe and the sediment. Assuming a coulomb slip regime, the shear stress is shows as: τ= τ0 + μ*(Sv-Pp), where τ0 is the cohesive stress, μ the dynamic frictional coefficient between the pipe and the sediment, Sv the normal stress at the pipe, and Pp the pore pressure. This can explain the non-zero intersection as well as depth-dependent increase for the frictional heating observed in the APC-T data. Assuming a hydrostatic state and by using the downhole bulk density data, we estimated the friction coefficient for each APC-T measurement. For comparison, we used the vane-shear strength measured on core samples to estimate the friction coefficients. The frictional coefficients μ were estimated as ranging 0.01 - 0.06, anomalously lower than expected for shallow marine sediments. They were lower than those estimated from vane-shear data, which range 0.05 to 0.2. Still, both estimates exhibit a significant increase in the friction coefficient at

  9. Effect of Polypropylene Modification by Impregnation with Oil on Its Wear and Friction Coefficient at Variable Load and Various Friction Rates

    Directory of Open Access Journals (Sweden)

    Paweł Sędłak

    2017-01-01

    Full Text Available Laboratorial two-body wear testing was carried out in order to assess effects of polypropylene modification by impregnating it with oils on friction coefficient and wear in comparison to those parameters of unmodified polypropylene, Teflon, and polyamide during operation under conditions of sliding friction without lubrication. Wear behaviour of the tested specimens was investigated using ASTM G77-98 standard wear test equipment. Recording program made it possible to visualise and record the following parameters: rotational speed and load, linear wear, friction coefficient, temperature of the specimen, and ambient temperature. In addition, wear mechanisms of the analysed materials were determined with use of scanning electron microscopy. In the case of the remaining tested polymers, the most important mechanism of wear was adhesion (PP, PTFE, PA 6.6, and PA MoS2, microcutting (PTFE, PA 6.6, and PA MoS2, fatigue wear (PTFE, forming “roll-shaped particles” combined with plastic deformation (PA 6.6 and PA MoS2, and thermal wear (PP. Impregnation of polypropylene with engine oil, gear oil, or RME results in significant reduction of friction coefficient and thus of friction torque, in relation to not only unmodified polypropylene but also the examined polyamide and Teflon.

  10. A study on the determination of diffusion coefficient of carbon in 304 austenitic stainless steels by internal friction method

    International Nuclear Information System (INIS)

    Kim, K.S.; Kim, T.H.

    1982-01-01

    Internal friction peaks associated with the presence of carbon in 18-8 type 304 stainless steel have been observed from measurements with a torsion pendulum. The temperature for maximum internal friction lies between 250degC and 300degC with a frequency of vibration. The height of the peak rises and the position of the peak shifts to a lower temperature with an increase of the carbon content. And a comparison of the activation energy and the diffusion coefficient determined by internal friction methods with those measured in conventional macro-diffusion experiments reveals that the diffusion data measured by internal friction method and the diffusion data measured by conventional method exist in the same line. It follows from the above fact that observed internal friction peak is associated with the stress-induced diffusion of carbon in face-centered cubic alloys. (Author)

  11. Slip safety risk analysis of surface properties using the coefficients of friction of rocks.

    Science.gov (United States)

    Çoşkun, Gültekin; Sarıışık, Gencay; Sarıışık, Ali

    2017-12-19

    This study was conducted to determine the most appropriate surface processing techniques (SPT), environmental conditions (EC) and surface roughness (SR) to minimize the risk of slipping when pedestrians walk on a floor covering of rocks barefoot and with shoes. Coefficients of friction (COFs) and values of SR were found using five different types of rocks, four SPT and two (ramp and pendulum) tests. Results indicate that the parameters which affect the COF values of rocks include SR, EC and SPT. Simple linear regression was performed to examine the relationship between the values of the COF and the SR. The value of the COF was identified as R 2  ≥ 0.864. Statistical results, which are based on experimental measurements, show that rocks are classified according to their safe use areas depending on their COF and SR values.

  12. [Tribological assessment of articular cartilage. A system for the analysis of the friction coefficient of cartilage, regenerates and tissue engineering constructs; initial results].

    Science.gov (United States)

    Schwarz, M L R; Schneider-Wald, B; Krase, A; Richter, W; Reisig, G; Kreinest, M; Heute, S; Pott, P P; Brade, J; Schütte, A

    2012-10-01

    Values for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.

  13. EFFECTS OF TIN ON HARDNESS, WEAR RATE AND COEFFICIENT OF FRICTION OF CAST CU-NI-SN ALLOYS

    Directory of Open Access Journals (Sweden)

    S. ILANGOVAN

    2013-02-01

    Full Text Available An investigation was carried out to understand the effects of Sn on hardness, wear rate and the coefficient of friction of spinodal Cu-Ni-Sn alloys. Alloys of appropriate compositions were melted in a crucible furnace under argon atmosphere and cast into sand moulds. Solution heat treated and aged specimens were tested for hardness, wear rate and the coefficient of friction. It was found that the hardness increases when the Sn content increases from 4% to 8% in the solution heat treated conditions. The peak aging time is found to decrease with an increase in the Sn content. Further, the coefficient of friction is independent of hardness whereas the wear rate decreases linearly with hardness irrespective of Sn content.

  14. Intelligent tires for identifying coefficient of friction of tire/road contact surfaces using three-axis accelerometer

    International Nuclear Information System (INIS)

    Matsuzaki, Ryosuke; Kamai, Kazuto; Seki, Ryosuke

    2015-01-01

    Intelligent tires equipped with sensors as well as the monitoring of the tire/road contact conditions are in demand for improving vehicle control and safety. With the aim of identifying the coefficient of friction of tire/road contact surfaces during driving, including during cornering, we develop an identification scheme for the coefficient of friction that involves estimation of the slip angle and applied force by using a single lightweight three-axis accelerometer attached on the inner surface of the tire. To validate the developed scheme, we conduct tire-rolling tests using an accelerometer-equipped tire with various slip angles on various types of road surfaces, including dry and wet surfaces. The results of these tests confirm that the estimated slip angle and applied force are reasonable. Furthermore, the identified coefficient of friction by the developed scheme agreed with that measured by standardized tests. (paper)

  15. Sliding motion modulates stiffness and friction coefficient at the surface of tissue engineered cartilage.

    Science.gov (United States)

    Grad, S; Loparic, M; Peter, R; Stolz, M; Aebi, U; Alini, M

    2012-04-01

    Functional cartilage tissue engineering aims to generate grafts with a functional surface, similar to that of authentic cartilage. Bioreactors that stimulate cell-scaffold constructs by simulating natural joint movements hold great potential to generate cartilage with adequate surface properties. In this study two methods based on atomic force microscopy (AFM) were applied to obtain information about the quality of engineered graft surfaces. For better understanding of the molecule-function relationships, AFM was complemented with immunohistochemistry. Bovine chondrocytes were seeded into polyurethane scaffolds and subjected to dynamic compression, applied by a ceramic ball, for 1h daily [loading group 1 (LG1)]. In loading group 2 (LG2), the ball additionally oscillated over the scaffold, generating sliding surface motion. After 3 weeks, the surfaces of the engineered constructs were analyzed by friction force and indentation-type AFM (IT-AFM). Results were complemented and compared to immunohistochemical analyses. The loading type significantly influenced the mechanical and histological outcomes. Constructs of LG2 exhibited lowest friction coefficient and highest micro- and nanostiffness. Collagen type II and aggrecan staining were readily observed in all constructs and appeared to reach deeper areas in loaded (LG1, LG2) compared to unloaded scaffolds. Lubricin was specifically detected at the top surface of LG2. This study proposes a quantitative AFM-based functional analysis at the micrometer- and nanometer scale to evaluate the quality of cartilage surfaces. Mechanical testing (load-bearing) combined with friction analysis (gliding) can provide important information. Notably, sliding-type biomechanical stimuli may favor (re-)generation and maintenance of functional articular surfaces and support the development of mechanically competent engineered cartilage. Copyright © 2012 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights

  16. Cationic agent contrast-enhanced computed tomography imaging of cartilage correlates with the compressive modulus and coefficient of friction.

    Science.gov (United States)

    Lakin, B A; Grasso, D J; Shah, S S; Stewart, R C; Bansal, P N; Freedman, J D; Grinstaff, M W; Snyder, B D

    2013-01-01

    The aim of this study is to evaluate whether contrast-enhanced computed tomography (CECT) attenuation, using a cationic contrast agent (CA4+), correlates with the equilibrium compressive modulus (E) and coefficient of friction (μ) of ex vivo bovine articular cartilage. Correlations between CECT attenuation and E (Group 1, n = 12) and μ (Group 2, n = 10) were determined using 7 mm diameter bovine osteochondral plugs from the stifle joints of six freshly slaughtered, skeletally mature cows. The equilibrium compressive modulus was measured using a four-step, unconfined, compressive stress-relaxation test, and the coefficients of friction were determined from a torsional friction test. Following mechanical testing, samples were immersed in CA4+, imaged using μCT, rinsed, and analyzed for glycosaminoglycan (GAG) content using the 1,9-dimethylmethylene blue (DMMB) assay. The CECT attenuation was positively correlated with the GAG content of bovine cartilage (R(2) = 0.87, P coefficients of friction: CECT vs μ(static) (R(2) = 0.71, P = 0.002), CECT vs μ(static_equilibrium) (R(2) = 0.79, P coefficient of friction. Copyright © 2012 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

  17. Lowering coefficient of friction in Cu alloys with stable gradient nanostructures.

    Science.gov (United States)

    Chen, Xiang; Han, Zhong; Li, Xiuyan; Lu, K

    2016-12-01

    The coefficient of friction (COF) of metals is usually high, primarily because frictional contacts induce plastic deformation underneath the wear surface, resulting in surface roughening and formation of delaminating tribolayers. Lowering the COF of metals is crucial for improving the reliability and efficiency of metal contacts in engineering applications but is technically challenging. Refining the metals' grains to nanoscale cannot reduce dry-sliding COFs, although their hardness may be elevated many times. We report that a submillimeter-thick stable gradient nanograined surface layer enables a significant reduction in the COF of a Cu alloy under high-load dry sliding, from 0.64 (coarse-grained samples) to 0.29, which is smaller than the COFs of many ceramics. The unprecedented stable low COF stems from effective suppression of sliding-induced surface roughening and formation of delaminating tribolayer, owing to the stable gradient nanostructures that can accommodate large plastic strains under repeated sliding for more than 30,000 cycles.

  18. Simple and Reliable Method to Estimate the Fingertip Static Coefficient of Friction in Precision Grip.

    Science.gov (United States)

    Barrea, Allan; Bulens, David Cordova; Lefevre, Philippe; Thonnard, Jean-Louis

    2016-01-01

    The static coefficient of friction (µ static ) plays an important role in dexterous object manipulation. Minimal normal force (i.e., grip force) needed to avoid dropping an object is determined by the tangential force at the fingertip-object contact and the frictional properties of the skin-object contact. Although frequently assumed to be constant for all levels of normal force (NF, the force normal to the contact), µ static actually varies nonlinearly with NF and increases at low NF levels. No method is currently available to measure the relationship between µ static and NF easily. Therefore, we propose a new method allowing the simple and reliable measurement of the fingertip µ static at different NF levels, as well as an algorithm for determining µ static from measured forces and torques. Our method is based on active, back-and-forth movements of a subject's finger on the surface of a fixed six-axis force and torque sensor. µ static is computed as the ratio of the tangential to the normal force at slip onset. A negative power law captures the relationship between µ static and NF. Our method allows the continuous estimation of µ static as a function of NF during dexterous manipulation, based on the relationship between µ static and NF measured before manipulation.

  19. A technique for measuring dynamic friction coefficient under impact loading.

    Science.gov (United States)

    Lin, Y L; Qin, J G; Chen, R; Zhao, P D; Lu, F Y

    2014-09-01

    We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m(2)/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.

  20. Measurements of the static friction coefficient between bone and muscle tissues.

    Science.gov (United States)

    Shacham, Sharon; Castel, David; Gefen, Amit

    2010-08-01

    This study aimed at measuring the static coefficient of friction (mu) between bone and skeletal muscle tissues in order to support finite element (FE) modeling in orthopaedic and rehabilitation research, where such contact conditions need to be defined. A custom-made friction meter (FM) that employs the load cell and motion-controlled loading arm of a materials testing machine was designed for this study. The FM was used to measure mu between fresh ulna bones and extensor muscles surrounding the ulna, which were harvested from five young adult pigs. Mean bone-muscle mu were between 0.36 and 0.29, decreased with the increase in loads applied on the bone (p<0.05) and plateaued at a mean approximately 0.3 for loads exceeding 4 N. Hence, for FE modeling of bone-muscle contacts through which loads with magnitudes of kgs to 10s-of-kgs are transferred, assuming mu of approximately 0.3 appears to be appropriate.

  1. The effects of microhardnesses and friction coefficients of GCr15 and Cr4Mo4V bearing materials by ion implantation

    International Nuclear Information System (INIS)

    Yang Qifa; Xiang Deguang; Lu Haolin

    1988-01-01

    Some experimental results of microhardnesses and friction coefficients of GCr15 and Cr4Mo4V bearing materials which were implanted with Cr, Mo, N and B ions are reported in this paper. It is found that the microhardnesses are increased and the friction coefficients are reduced by Cr, Mo, N and B ion implantation for two materials. The friction coefficients of Cr + Mo + N , Cr + Mo + B ion implanted samples are reduced to 1/3 of the unimplanted samples

  2. Using Plasticine (TM) to Measure the Rolling Friction Coefficient.

    Science.gov (United States)

    Castellvi, Francesc; And Others

    1995-01-01

    Presents an experiment that makes manifest the energy lost to friction of an iron ball moving along an inclined iron rail, which allows students to compute the rolling friction coefficient. Uses a method based on measurement of deformation produced in a piece of Plasticine by an inelastic collision with the ball and combines mechanical concepts…

  3. Effects of self-affine surface roughness on the friction coefficient of rubbers in the presence of a liquid interlayer

    NARCIS (Netherlands)

    Palasantzas, G; De Hosson, JTM

    2004-01-01

    In this article, we investigate how the friction coefficient is affected by the presence of a liquid layer in between a self-affine rough surface and a sliding rubber surface. The liquid layer will reduce energy dissipation from the small surface asperities and cavities of lateral sizes smaller than

  4. The Required Coefficient of Friction for evaluating gait alterations in people with Multiple Sclerosis during gait.

    Science.gov (United States)

    Pacifici, Ilaria; Galli, Manuela; Kleiner, Ana Francisca Rozin; Corona, Federica; Coghe, Giancarlo; Marongiu, Elisabetta; Loi, Andrea; Crisafulli, Antonio; Cocco, Eleonora; Marrosu, Maria Giovanna; Pau, Massimiliano

    2016-11-01

    Required Coefficient of Friction (RCOF) is one of the most critical gait parameters associated to the occurrence of slipping in individuals affected by neurological disorders characterized by balance impairments. This study aims to calculate RCOF in people with Multiple Sclerosis (MS) on the basis of three-dimensional Gait Analysis (GA) data. This study enrolls 22 people with MS (pwMS) who were characterized by an Expanded Disability Status Score in the range 1.5-6 and 10 healthy controls (HC). All participants underwent to three-dimensional GA from which we extracted kinematic and kinetic data (i.e. the Ground Reaction Forces, GRF, and joint moments and powers in the sagittal plane). RCOF was calculated as the ratio of the shear to normal GRF components during the stance phase of gait cycle, and normalized by the walking velocity. Thus, the following variables were extracted: first peak (named P1COF), valley (named V1COF), and second peak (named P2COF) in RCOF curve; also computating the maximum ankle dorsi-plantarflexion moment (MOMmax) and the maximum ankle joint power (PWRmax). Our data revealed that P2COF results are significantly lower in pwMS when compared to HC (p=0.043; Z=-2.025). In pwMS, the study found a moderate, positive correlation between V1COF and MOMmax (r=0.558; pFriction during mid stance and push off phases is critically important to determine whether the frictional capabilities of foot/floor interface are sufficient to prevent slips in pwMS. The impaired ankle moment in MS group causes increased P2COF in comparison to HC, increasing the risk of slipping in the critical phase of transmission of the developed forces to kinematic chain. Also, the correlation analysis among RCOF values and kinetic variables describe the interplay between V1COF and MOMmax: the higher V1COF is, the higher is MOMmax; and the different correlation the study found between COF and kinetic parameters in MS and HC group highlightes the different gait patterns of the two

  5. Clinical assessment of dynamic coefficient of friction effects in shoe-sole trituration of patients with drop foot.

    Science.gov (United States)

    Nima, Jamshidi; Firooz, Salami

    2012-06-01

    The aim of this study was examining the effect of human factors such as plantar friction, contact period time, and impulse on shoe-sole trituration of drop foot patients. Twenty-five patients with drop foot and twenty normal subjects were recruited in the study. The force plate and its related software's recorded human factor (coefficient of friction, ground reaction force, time of stance phase) as time dependent parameters. Dynamic coefficient of friction patterns were categorized based on their magnitude versus time when the longitudinal axis of the sole was plotted as the Y-axis and the transverse axis of the sole as X-axis during stance phase. The result of this research indicated that the average coefficient of friction among drop foot patients is 77.53 % (p value <0.05) lower than the normal subjects. Also the time of stance phase among drop foot patients is 7.56 % (p value <0.05) greater than normal subjects. There is no difference in the peaks, of vertical ground reaction force between normal and control group. The findings of this research revealed that the time of stance phase has a key role in shoe-sole trituration of patients with drop foot.

  6. The Influence of Natural Frequency of the Experimental Set-up on the Friction Coefficient of Stainless Steel-304

    OpenAIRE

    M. A. Chowdhury; Md. M. Helali

    2010-01-01

    The present paper investigates experimentally the effect of natural frequency of the experimental set-up on friction property of stainless steel-304. To do so, a pin-on-disc apparatus having facility of vibrating the test samples at different directions, amplitudes and frequencies was designed and fabricated. The natural frequency of the set-up was varied by adding dead loads of the setup from 0 kg to 50 kg. At each added load the friction coefficient has been measured. Results show that both...

  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. Incorporation of velocity-dependent restitution coefficient and particle surface friction into kinetic theory for modeling granular flow cooling.

    Science.gov (United States)

    Duan, Yifei; Feng, Zhi-Gang

    2017-12-01

    Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009)10.1209/0295-5075/86/60007]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.

  9. 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

  10. 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.

  11. The Application of Vibration Accelerations in the Assessment of Average Friction Coefficient of a Railway Brake Disc

    Directory of Open Access Journals (Sweden)

    Sawczuk Wojciech

    2017-06-01

    Full Text Available Due to their wide range of friction characteristics resulting from the application of different friction materials and good heat dissipation conditions, railway disc brakes have long replaced block brakes in many rail vehicles. A block brake still remains in use, however, in low speed cargo trains. The paper presents the assessment of the braking process through the analysis of vibrations generated by the components of the brake system during braking. It presents a possibility of a wider application of vibroacoustic diagnostics (VA, which aside from the assessment of technical conditions (wear of brake pads also enables the determination of the changes of the average friction coefficient as a function of the braking onset speed. Vibration signals of XYZ were measured and analyzed. The analysis of the results has shown that there is a relation between the values of the point measures and the wear of the brake pads.

  12. Evaluation of the friction coefficient, the radial stress, and the damage work during needle insertions into agarose gels.

    Science.gov (United States)

    Urrea, Fabián A; Casanova, Fernando; Orozco, Gustavo A; García, José J

    2016-03-01

    Agarose hydrogels have been extensively used as a phantom material to mimic the mechanical behavior of soft biological tissues, e.g. in studies aimed to analyze needle insertions into the organs producing tissue damage. To better predict the radial stress and damage during needle insertions, this study was aimed to determine the friction coefficient between the material of commercial catheters and hydrogels. The friction coefficient, the tissue damage and the radial stress were evaluated at 0.2, 1.8, and 10mm/s velocities for 28, 30, and 32 gauge needles of outer diameters equal to 0.36, 0.31, and 0.23mm, respectively. Force measurements during needle insertions and retractions on agarose gel samples were used to analyze damage and radial stress. The static friction coefficient (0.295±0.056) was significantly higher than the dynamic (0.255±0.086). The static and dynamic friction coefficients were significantly smaller for the 0.2mm/s velocity compared to those for the other two velocities, and there was no significant difference between the friction coefficients for 1.8 and 10mm/s. Radial stress averages were 131.2±54.1, 248.3±64.2, and 804.9±164.3Pa for the insertion velocity of 0.2, 1.8, and 10mm/s, respectively. The radial stress presented a tendency to increase at higher insertion velocities and needle size, which is consistent with other studies. However, the damage work did not show to be a good predictor of tissue damage, which appears to be due to simplifications in the analytical model. Differently to other approaches, the method proposed here based on radial stress may be extended in future studies to quantity tissue damage in vivo along the entire needle track. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Analytical study of friction coefficients of pomegranate seed as essential parameters in design of post-harvest equipment

    Directory of Open Access Journals (Sweden)

    S.M. Shafaei

    2016-09-01

    Full Text Available Friction coefficients (static friction coefficient (SFC and dynamic friction coefficient (DFC of pomegranate seed on different structural surfaces (glass, aluminum, plywood, galvanized steel and rubber as affected by moisture content (4–21.9% (d. b. and sliding velocity (1.4–16 (cm/s were investigated. Analysis of variance (ANOVA was performed to determine the effect of main treatments and their interactions on SFC and DFC. Significance of single or multiple effect of the main treatments with five levels was assessed using Duncan’s multiple range test (DMRT. To predict SFC and DFC, multiple linear regression (MLR modeling technique was applied for each type of structural surface. The goodness of fit of each MLR model was evaluated using statistical parameters: coefficient of determination, root mean square error and mean relative deviation modulus. Results showed that the minimum and maximum SFC or DFC were in minimum and maximum moisture content on glass and rubber surface, respectively. ANOVA table indicated the significant effect of main treatments and their interactions on SFC and DFC at significance level of 1% (P < 0.01. According to DMRT results, SFC linearly increased as moisture content increased and DFC increased also linearly as individual or simultaneous increment of moisture content and sliding velocity occurred, for all experimental conditions. According to the obtained statistical parameters, both SFC and DFC were properly predicted by means of MLR modeling technique.

  14. Required coefficient of friction in the anteroposterior and mediolateral direction during turning at different walking speeds.

    Science.gov (United States)

    Yamaguchi, Takeshi; Suzuki, Akito; Hokkirigawa, Kazuo

    2017-01-01

    This study investigated the required coefficient of friction (RCOF) and the tangent of center of mass (COM)-center of pressure (COP) angle in the mediolateral (ML) and anteroposterior (AP) directions during turning at different walking speeds. Sixteen healthy young adults (8 males and 8 females) participated in this study. The participants were instructed to conduct trials of straight walking and 90° step and spin turns to the right at each of three self-selected speeds (slow, normal, and fast). The ML and AP directions during turning gait were defined using the orientation of the pelvis to construct a body-fixed reference frame. The RCOF values and COM-COP angle tangent in the ML direction during turning at weight acceptance phase were higher than those during straight walking, and those values increased with increasing walking speed. The ML component of the RCOF and COM-COP tangent values during weight acceptance for step turns were higher than those for spin turns. The mean centripetal force during turning tended to increase with an increase in walking speed and had a strong positive correlation with the RCOF values in the ML direction (R = 0.97 during the weight acceptance phase; R = 0.95 during the push-off phase). Therefore, turning, particularly step turn, is likely to cause lateral slip at weight acceptance because of the increased centripetal force compared with straight walking. Future work should test at-risk population and compare with the present results.

  15. 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.

  16. Required coefficient of friction in the anteroposterior and mediolateral direction during turning at different walking speeds.

    Directory of Open Access Journals (Sweden)

    Takeshi Yamaguchi

    Full Text Available This study investigated the required coefficient of friction (RCOF and the tangent of center of mass (COM-center of pressure (COP angle in the mediolateral (ML and anteroposterior (AP directions during turning at different walking speeds. Sixteen healthy young adults (8 males and 8 females participated in this study. The participants were instructed to conduct trials of straight walking and 90° step and spin turns to the right at each of three self-selected speeds (slow, normal, and fast. The ML and AP directions during turning gait were defined using the orientation of the pelvis to construct a body-fixed reference frame. The RCOF values and COM-COP angle tangent in the ML direction during turning at weight acceptance phase were higher than those during straight walking, and those values increased with increasing walking speed. The ML component of the RCOF and COM-COP tangent values during weight acceptance for step turns were higher than those for spin turns. The mean centripetal force during turning tended to increase with an increase in walking speed and had a strong positive correlation with the RCOF values in the ML direction (R = 0.97 during the weight acceptance phase; R = 0.95 during the push-off phase. Therefore, turning, particularly step turn, is likely to cause lateral slip at weight acceptance because of the increased centripetal force compared with straight walking. Future work should test at-risk population and compare with the present results.

  17. Determination of the friction coefficient via the force autocorrelation function. A molecular dynamics investigation for a dense Lennard-Jones fluid

    International Nuclear Information System (INIS)

    Vogelsang, R.; Hoheisel, C.

    1987-01-01

    For a large region of dense fluid states of a Lennard-Jones system, they have calculated the friction coefficient by the force autocorrelation function of a Brownian-type particle by molecular dynamics (MD). The time integral over the force autocorrelation function showed an interesting behavior and the expected plateau value when the mass of the Brownian particle was chosen to be about a factor of 100 larger than the mass of the fluid particle. Sufficient agreement was found for the friction coefficient calculated by this way and that obtained by calculations of the self-diffusion coefficient using the common relation between these coefficients. Furthermore, a modified friction coefficient was determined by integration of the force autocorrelation function up to the first maximum. This coefficient can successfully be used to derive a reasonable soft part of the friction coefficient necessary for the Rice-Allnatt approximation for the shear velocity and simple liquids

  18. Influence of the processing variables on the performance of MAGCLA(TM): friction coefficient and radius of the particles

    International Nuclear Information System (INIS)

    Augusto, Paulo A; Castelo-Grande, Teresa; Barbosa, Domingos; Estevez, A M

    2007-01-01

    This work presents simulation results for the behaviour of different particles in a new magnetic-classifier (MAGCLA(TM)), which is capable of separating and classifying particles according to their magnetic susceptibilities. In a previous article the results for a blank simulation were reported. In this paper the blank simulation is compared with the results obtained for the variation of two of the main processing variables: friction coefficient, μ, and the radius of the particles, r part , in the outcome results

  19. Does Increased Coefficient of Friction of Highly Porous Metal Increase Initial Stability at the Acetabular Interface?

    Science.gov (United States)

    Goldman, Ashton H; Armstrong, Lucas C; Owen, John R; Wayne, Jennifer S; Jiranek, William A

    2016-03-01

    Highly porous metal acetabular components illustrate a decreased rate of aseptic loosening in short-term follow-up compared with previous registry data. This study compared the effect of component surface roughness at the bone-implant interface and the quality of the bone on initial pressfit stability. The null hypothesis is that a standard porous coated acetabular cup would show no difference in initial stability as compared with a highly porous acetabular cup when subjected to a bending moment. Second, would bone mineral density (BMD) be a significant variable under these test conditions. In a cadaveric model, acetabular cup micromotion was measured during a 1-time cantilever bending moment applied to 2 generations of pressfit acetabular components. BMD data were also obtained from the femoral necks available for associated specimen. The mean bending moment at 150 μm was not found to be significantly different for Gription (24.6 ± 14.0 N m) cups vs Porocoat (25 ± 10.2 N m; P > .84). The peak bending moment tolerated by Gription cups (33.9 ± 20.3 N m) was not found to be significantly different from Porocoat (33.5 ± 12.2 N m; P > .92). No correlation between BMD and bending moment at 150 μm of displacement could be identified. The coefficient of friction provided by highly porous metal acetabular shells used in this study did not provide better resistance to migration under bending load when compared with a standard porous coated component. Copyright © 2016 Elsevier Inc. All rights reserved.

  20. 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...

  1. 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.

  2. Comparison of the Friction-Loss Coefficient for the Gap of Two Contact Surfaces and a Crack

    International Nuclear Information System (INIS)

    Nam, Ho Yun; Choi, Byoung Hae; Kim, Jong Bum; Lee, Young Bum

    2011-01-01

    A leak-detection method has been developed by measuring the pressure variation between the inner and outer heat transfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers

  3. The effects of silver coating on friction coefficient and shear bond strength of steel orthodontic brackets.

    Science.gov (United States)

    Arash, Valiollah; Anoush, Keivan; Rabiee, Sayed Mahmood; Rahmatei, Manuchehr; Tavanafar, Saeid

    2015-01-01

    Aims of the present study was to measure frictional resistance between silver coated brackets and different types of arch wires, and shear bond strength of these brackets to the tooth. In an experimental clinical research 28 orthodontic brackets (standard, 22 slots) were coated with silver ions using electroplate method. Six brackets (coated: 3, uncoated: 3) were evaluated with Scanning Electron Microscopy and Atomic Force Microscopy. The amount of friction in 15 coated brackets was measured with three different kinds of arch wires (0.019 × 0.025-in stainless steel [SS], 0.018-in stainless steel [SS], 0.018-in Nickel-Titanium [Ni-Ti]) and compared with 15 uncoated steel brackets. In addition, shear bond strength values were compared between 10 brackets with silver coating and 10 regular brackets. Universal testing machine was used to measure shear bond strength and the amount of friction between the wires and brackets. SPSS 18 was used for data analysis with t-test. SEM and AFM results showed deposition of a uniform layer of silver, measuring 8-10 μm in thickness on bracket surfaces. Silver coating led to higher frictional forces in all the three types of arch wires, which was statistically significant in 0.019 × 0.025-in SS and 0.018-in Ni-Ti, but it did not change the shear bond strength significantly. Silver coating with electroplating method did not affect the bond strength of the bracket to enamel; in addition, it was not an effective method for decreasing friction in sliding mechanics. © Wiley Periodicals, Inc.

  4. Determination of oral mucosal Poisson's ratio and coefficient of friction from in-vivo contact pressure measurements.

    Science.gov (United States)

    Chen, Junning; Suenaga, Hanako; Hogg, Michael; Li, Wei; Swain, Michael; Li, Qing

    2016-01-01

    Despite their considerable importance to biomechanics, there are no existing methods available to directly measure apparent Poisson's ratio and friction coefficient of oral mucosa. This study aimed to develop an inverse procedure to determine these two biomechanical parameters by utilizing in vivo experiment of contact pressure between partial denture and beneath mucosa through nonlinear finite element (FE) analysis and surrogate response surface (RS) modelling technique. First, the in vivo denture-mucosa contact pressure was measured by a tactile electronic sensing sheet. Second, a 3D FE model was constructed based on the patient CT images. Third, a range of apparent Poisson's ratios and the coefficients of friction from literature was considered as the design variables in a series of FE runs for constructing a RS surrogate model. Finally, the discrepancy between computed in silico and measured in vivo results was minimized to identify the best matching Poisson's ratio and coefficient of friction. The established non-invasive methodology was demonstrated effective to identify such biomechanical parameters of oral mucosa and can be potentially used for determining the biomaterial properties of other soft biological tissues.

  5. 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

    -placements, internal diameter and thickness of the rings are measured during the tests. Viscoelastic andstructural relaxation behaviour of the glass are implemented into the ABAQUS FEM software through aFORTRAN material subroutine (UMAT) and the FE model is validated with a sandwich seal test. Then, byFE simulation...... of the ring compression test and comparison of the experimental creep with the simulatedone in an iterative procedure, viscoelastic parameters of the glass material are characterized. Finally,interfacial glass/mould friction coefficients at different temperatures are determined through FEM basedfriction...... curves combined with experimental data points. The obtained viscoelastic parameters and inter-facial friction coefficients can later be employed for prediction of the final shape/size as well as the stressdistribution in the glass wafer during a real wafer based precision glass moulding process. © 2014...

  6. Variation of the Friction Coefficient for a Cylinder Rolling down an Inclined Board

    Science.gov (United States)

    Yan, Zixiang; Xia, Heming; Lan, Yueheng; Xiao, Jinghua

    2018-01-01

    A cylinder rolling down an inclined board is a commonly seen and interesting object to study and it is also easy to experiment with and model. Following what has become a popular practice, we use smartphones to measure the angular acceleration of a cylinder rolling down a plane of different inclining angles. The friction force deviates from the…

  7. Effect of T6 treatment on the coefficient of friction of Al25Mg2Si2Cu4Fe alloy

    Science.gov (United States)

    Sondur, D. G.; Mallapur, D. G.; Udupa, K. Rajendra

    2018-04-01

    Effect of T6 treatment on the coefficient of friction of Al25Mg2Si2Cu4Fe alloy was evaluated by conducting wear test on pin on disc wear testing machine. Wear test parameters such as the load and the speed were varied by keeping one constant and varying the other respectively. It was observed that the coefficient of friction is high for as cast condition due to the brittle microstructure. After T6 heat treatment the precipitates formed such as the Chinese scripts and the Mg2Si blocks got modified that lead to improvement in the hardness and the wear resistance. This reduces the coefficient of friction.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    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 Al 2 O 3 and TiO 2 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 Al 2 O 3 and TiO 2 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 Al 2 O 3 and TiO 2 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.

  9. A GENERALIZED COEFFICIENT OF FRICTION FOR ASSESSING ENERGY EFFICIENCY OF BEARING SYSTEMS

    OpenAIRE

    Al-Bender, Farid

    2011-01-01

    Environmental impact estimations, often carried out in the framework of Life Cycle Assessment (LCA) on production machines and machine tools, show that a significant (if not the greatest) part of the environmental impact is related to the use-phase of the machine. A closer analysis reveals that the energy efficiency of the bearing systems, i.e. their friction loss, is the main culprit in this. Cost reduction and maintenance savings were the main motivations that initiated tribology as a s...

  10. EXPERIMENTAL STUDY ON HEAT TRANSFER COEFFICIENT AND FRICTION FACTOR OF Al2O3 NANOFLUID IN A PACKED BED COLUMN

    Directory of Open Access Journals (Sweden)

    G. Srinivasa Rao

    2011-12-01

    Full Text Available The forced convection heat transfer coefficient and friction factor are determined for the flow of water and nanofluid in a vertical packed bed column. The analysis is undertaken in the laminar and transition Reynolds number range. The column is filled with spherical glass beads as the bed material. The heat transfer coefficients with Al2O3 nanofluid increased by 12% to 15% with the increase of volume concentration from 0.02% to 0.5% compared with water. The experimental values of axial temperature are in good agreement with the NTU-ε method proposed by Schumann’s model.

  11. 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.

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

    Science.gov (United States)

    Alajmi, Mahdi; Shalwan, Abdullah

    2015-07-08

    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.

  13. Effect of the coefficient of friction and tightening speed on the preload induced at the dental implant complex with the finite element method.

    Science.gov (United States)

    Bulaqi, Haddad Arabi; Mousavi Mashhadi, Mahmoud; Geramipanah, Farideh; Safari, Hamed; Paknejad, Mojgan

    2015-05-01

    To prevent screw loosening, a clear understanding of the factors influencing secure preload is necessary. The purpose of this study was to investigate the effect of coefficient of friction and tightening speed on screw tightening based on energy distribution method with exact geometric modeling and finite element analysis. To simulate the proper boundary conditions of the screw tightening process, the supporting bone of an implant was considered. The exact geometry of the implant complex, including the Straumann dental implant, direct crown attachment, and abutment screw were modeled with Solidworks software. Abutment screw/implant and implant/bone interfaces were designed as spiral thread helixes. The screw-tightening process was simulated with Abaqus software, and to achieve the target torque, an angular displacement was applied to the abutment screw head at different coefficients of friction and tightening speeds. The values of torque, preload, energy distribution, elastic energy, and efficiency were obtained at the target torque of 35 Ncm. Additionally, the torque distribution ratio and preload simulated values were compared to theoretically predicted values. Upon reducing the coefficient of friction and enhancing the tightening speed, the angle of turn increased at the target torque. As the angle of turn increased, the elastic energy and preload also increased. Additionally, by increasing the coefficient of friction, the frictional dissipation energy increased but the efficiency decreased, whereas the increase in tightening speed insignificantly affected efficiency. The results of this study indicate that the coefficient of friction is the most influential factor on efficiency. Increasing the tightening speed lowered the response rate to the frictional resistance, thus diminishing the coefficient of friction and slightly increasing the preload. Increasing the tightening speed has the same result as reducing the coefficient of friction. Copyright © 2015

  14. The influence of heel height on utilized coefficient of friction during walking.

    Science.gov (United States)

    Blanchette, Mark G; Brault, John R; Powers, Christopher M

    2011-05-01

    Wearing high heel shoes has been associated with an increased potential for slips and falls. The association between wearing high heels and the increased potential for slipping suggests that the friction demand while wearing high heels may be greater when compared to wearing low heel shoes. The purpose of this study was to determine if heel height affects utilized friction (uCOF) during walking. A secondary purpose of this study was to compare kinematics at the ankle, knee, and hip that may explain uCOF differences among shoes with varied heel heights. Fifteen healthy women (mean age 24.5±2.5yrs) participated. Subjects walked at self-selected velocity under 3 different shoe conditions that varied in heel height (low: 1.27cm, medium: 6.35cm, and high: 9.53cm). Ground reaction forces (GRFs) were recorded using a force platform (1560Hz). Kinematic data were obtained using an 8 camera motion analysis system (120Hz). Utilized friction was calculated as the ratio of resultant shear force to vertical force. One-way repeated measures ANOVAs were performed to test for differences in peak uCOF, GRFs at peak uCOF and lower extremity joint angles at peak uCOF. On average, peak uCOF was found to increase with heel height. The increased uCOF observed in high heel shoes was related to an increase in the resultant shear force and decrease in the vertical force. Our results signify the need for proper public education and increased footwear industry awareness of how high heel shoes affect slip risk. Copyright © 2011 Elsevier B.V. All rights reserved.

  15. Impact of higher-order flows in the moment equations on Pfirsch-Schlüter friction coefficients

    Energy Technology Data Exchange (ETDEWEB)

    Honda, M., E-mail: honda.mitsuru@jaea.go.jp [Japan Atomic Energy Agency, Naka, Ibaraki 311-0193 (Japan)

    2014-09-15

    The impact of the higher-order flows in the moment approach on an estimate of the friction coefficients is numerically examined. The higher-order flows are described by the lower-order hydrodynamic flows using the collisional plasma assumption. Their effects have not been consistently taken into account thus far in the widely used neoclassical transport codes based on the moment equations in terms of the Pfirsch-Schlüter flux. Due to numerically solving the friction-flow matrix without using the small-mass ratio expansion, it is clearly revealed that incorporating the higher-order flow effects is of importance especially for plasmas including multiple hydrogenic ions and other lighter species with similar masses.

  16. Temperature and Water Vapor Pressure Effects on the Friction Coefficient of Hydrogenated Diamondlike Carbon Films

    Science.gov (United States)

    2009-07-01

    FA9550- 04-1-0367. References 1 Erdemir, A., Eryilmaz, O. L., Nilufer, I. B., and Fenske , G. R., 2000, “Syn- thesis of Superlow-Friction Carbon... Fenske , G. R., 2000, “Effect of Source Gas Chemistry on Tribological Performance of Diamond-Like Car- bon Films,” Diamond Relat. Mater., 9, pp. 632–637...ASME J. Tribol., 127, pp. 82–88. 12 Johnson, J. A., Woodford, J. B., Erdemir, A., and Fenske , G. R., 2003, “Near- Surface Characterization of

  17. Experimental Investigation of Friction Coefficient and Wear Rate of Composite Materials Sliding Against Smooth and Rough Mild Steel Counterfaces

    OpenAIRE

    M.A. Chowdhury; D.M. Nuruzzaman; B.K. Roy; S. Samad; R. Sarker; A.H.M. Rezwan

    2013-01-01

    In the present study, friction coefficient and wear rate of gear fiber reinforced plastic (gear fiber) and glass fiber reinforced plastic (glass fiber) sliding against mild steel are investigated experimentally. In order to do so, a pin on disc apparatus is designed and fabricated. Experiments are carried out when smooth or rough mild steel pin slides on gear fiber and glass fiber disc. Experiments are conducted at normal load 10, 15 and 20 N, sliding velocity 1, 1.5 and 2 m/s and relative h...

  18. On development of analytical closure relationships for local wall friction, heat and mass transfer coefficients for sub-channel codes

    International Nuclear Information System (INIS)

    Kornienko, Y.

    2000-01-01

    The purpose has been to describe an approach suggested for constructing generalized closure relationships for local and subchannel wall friction, heat and mass transfer coefficients, with not only axial and transversal parameters taken into account, but azimuthal substance transfer effects as well. These constitutive relations that are primary for description of one- and two-phase one-dimensional flow models can be derived from the initial 3-D drift flux formulation. The approach is based on the Reynolds flux, boundary layer and generalized coefficient of substance transfer. One more task has been to illustrate the validity of the 'conformity principle' for the limiting cases. The method proposed is based on the similarity theory, boundary layer model, and a phenomenological description of the regularities of the substance transfer (momentum, heat, and mass), as well as on an adequate simulation of the forms of flow structure by a generalized approach to build (an integrated in form and semi-empirical in maintenance structure) analytical relationships for wall friction, heat and mass transfer coefficients. (author)

  19. Stochastic distribution of the required coefficient of friction for level walking--an in-depth study.

    Science.gov (United States)

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

    2012-01-01

    This study investigated the stochastic distribution of the required coefficient of friction (RCOF) which is a critical element for estimating slip probability. Fifty participants walked under four walking conditions. The results of the Kolmogorov-Smirnov two-sample test indicate that 76% of the RCOF data showed a difference in distribution between both feet for the same participant under each walking condition; the data from both feet were kept separate. The results of the Kolmogorov-Smirnov goodness-of-fit test indicate that most of the distribution of the RCOF appears to have a good match with the normal (85.5%), log-normal (84.5%) and Weibull distributions (81.5%). However, approximately 7.75% of the cases did not have a match with any of these distributions. It is reasonable to use the normal distribution for representation of the RCOF distribution due to its simplicity and familiarity, but each foot had a different distribution from the other foot in 76% of cases. The stochastic distribution of the required coefficient of friction (RCOF) was investigated for use in a statistical model to improve the estimate of slip probability in risk assessment. The results indicate that 85.5% of the distribution of the RCOF appears to have a good match with the normal distribution.

  20. Effect of Substrate Bias on Friction Coefficient, Adhesion Strength and Hardness of TiN-COATED Tool Steel

    Science.gov (United States)

    Hamzah, Esah; Ali, Mubarak; Toff, Mohd Radzi Hj. Mohd

    In the present study, TiN coatings have been deposited on D2 tool steel substrates by using cathodic arc physical vapor deposition technique. The objective of this research work is to determine the usefulness of TiN coatings in order to improve the micro-Vickers hardness and friction coefficient of TiN coating deposited on D2 tool steel, which is widely used in tooling applications. A Pin-on-Disc test was carried out to study the coefficient of friction versus sliding distance of TiN coating deposited at various substrate biases. The standard deviation parameter during tribo-test result showed that the coating deposited at substrate bias of -75 V was the most stable coating. A significant increase in micro-Vickers hardness was recorded, when substrate bias was reduced from -150 V to zero. Scratch tester was used to compare the critical loads for coatings deposited at different bias voltages and the adhesion achievable was demonstrated with relevance to the various modes, scratch macroscopic analysis, critical load, acoustic emission and penetration depth. A considerable improvement in TiN coatings was observed as a function of various substrate bias voltages.

  1. Static and kinetic friction coefficients of Scots pine (Pinus sylvestris L., parallel and perpendicular to grain direction

    Directory of Open Access Journals (Sweden)

    Aira, J. R.

    2014-09-01

    Full Text Available In this study the static (µe and kinetic (µd coefficients of friction were obtained for Pinus sylvestis L. sawn timber of Spanish origin. Friction between transverse surfaces sliding perpendicular to the grain (tangential direction and radial surfaces sliding parallel to the grain was analyzed. A specifically designed device was used for tests, which makes it possible to apply contact pressure and measure displacements and applied loads simultaneously. Coefficients of friction between transverse surfaces (µe = 0,24; µd = 0,17 were about twice of the coefficients of friction between radial surfaces (µe = 0,12; µd = 0,08. Furthermore, these values are located within normal values of those commonly reported for softwood. The results are considered preliminary due to the small number of specimens.En este estudio se determinaron los coeficientes de rozamiento, estático (µe y dinámico (µd, en madera aserrada de Pinus sylvestris L. de procedencia española, diferenciando si se produce el contacto entre secciones de corte transversal con deslizamiento en dirección perpendicular a la fibra (en dirección tangencial, o entre secciones de corte radial con deslizamiento paralelo a la fibra. Para la realización de los ensayos se ha utilizado un dispositivo, diseñado específicamente, que posibilita la aplicación de una presión de contacto y la medición del desplazamiento y de la fuerza aplicada de manera simultánea, permitiendo la obtención de los coeficientes de rozamiento estático y dinámico. Los coeficientes de rozamiento obtenidos entre secciones transversales (µe = 0.24; µd = 0.17 fueron del orden del doble de los coeficientes de rozamiento entre secciones radiales (µe = 0.12; µd = 0.08. Además, estos valores se encuentran dentro de los valores que aparecen habitualmente en la bibliografía para madera de coníferas. Debido al escaso tamaño de la muestra los resultados se consideran preliminares.

  2. 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.

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

    KAUST Repository

    Calo, Victor M.; Collier, Nathan; Gehre, Matthias; Jin, Bangti; Radwan, Hany G.; Santillana, Mauricio

    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.

  4. A comprehensive investigation on static and dynamic friction coefficients of wheat grain with the adoption of statistical analysis.

    Science.gov (United States)

    Shafaei, S M; Kamgar, S

    2017-07-01

    This paper deals with studying and modeling static friction coefficient (SFC) and dynamic friction coefficient (DFC) of wheat grain as affected by several treatments. Significance of single effect (SE) and dual interaction effect (DIE) of treatments (moisture content and contact surface) on SFC and, SE, DIE, and triple interaction effect (TIE) of treatments (moisture content, contact surface and sliding velocity) on DFC were determined using statistical analysis methods. Multiple linear regression (MLR) modeling was employed to predict SFC and DFC on different contact surfaces. Predictive ability of developed MLR models was evaluated using some statistical parameters (coefficient of determination ( R 2 ), root mean square error (RMSE), and mean relative deviation modulus (MRDM)). Results indicated that significant increasing DIE of treatments on SFC was 3.2 and 3 times greater than significant increasing SE of moisture content and contact surface, respectively. In case of DFC, the significant increasing TIE of treatments was 8.8, 3.7, and 8.9 times greater than SE of moisture content, contact surface, and sliding velocity, respectively. It was also found that the SE of contact surface on SFC was 1.1 times greater than that of moisture content and the SE of contact surface on DFC was 2.4 times greater than that of moisture content or sliding velocity. According to the reasonable average of statistical parameters ( R 2  = 0.955, RMSE = 0.01788 and MRDM = 3.152%), the SFC and DFC could be successfully predicted by suggested MLR models. Practically, it is recommended to apply the models for direct prediction of SFC and DFC, respective to each contact surface, based on moisture content and sliding velocity.

  5. 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.

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

    KAUST Repository

    Mayo, Talea; Butler, Troy; Dawson, Clint N.; Hoteit, Ibrahim

    2014-01-01

    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.

  7. Coefficient of friction of dry slash pine and southern red oak on three tension-grip facings

    Science.gov (United States)

    Truett J. Lemoine; Peter Koch

    1974-01-01

    A urethane material proved to have nine times higher static friction coefficient (0.9) than smooth steel (0.1) on radial and tangential wood surfaces pulled parallel to the grain. It is probably superior to 220-grit garnet paper or sand coatings for tension-grip facings in lumber testing machines.

  8. Does the third mutual friction coefficient B'' exist

    International Nuclear Information System (INIS)

    Mathieu, P.; Placais, B.; Simon, Y.

    1985-01-01

    Precise measurements of the attenuation of a second-sound wave propagation axially in rotating He II at first sight suggest that the third mutual-friction coefficient B'' has a non-zero value (B'' = 0.021 at 1.9 K). But the observation of metastable states associated with various levels of attenuation is not reconcilable with the semi-classical model of the vortex line [fr

  9. Investigation of the Maximum Spin-Up Coefficients of Friction Obtained During Tests of a Landing Gear Having a Static-Load Rating of 20,000 Pounds

    Science.gov (United States)

    Batterson, Sidney A.

    1959-01-01

    An experimental investigation was made at the Langley landing loads track to obtain data on the maximum spin-up coefficients of friction developed by a landing gear having a static-load rating of 20,000 pounds. The forward speeds ranged from 0 to approximately 180 feet per second and the sinking speeds, from 2.7 feet per second to 9.4 feet per second. The results indicated the variation of the maximum spin-up coefficient of friction with forward speed and vertical load. Data obtained during this investigation are also compared with some results previously obtained for nonrolling tires to show the effect of forward speed.

  10. Coefficient of friction and wear of sputtered a-C thin coatings containing Mo

    Czech Academy of Sciences Publication Activity Database

    Novák, P.; Musil, Jindřich; Čerstvý, R.; Jäger, Aleš

    2010-01-01

    Roč. 205, č. 5 (2010), s. 1486-1490 ISSN 0257-8972. [International Conference on Metallurgical Coatings and Thin Films /37./. San Diego, CA, 26.04.2010-30.04.2010] Institutional research plan: CEZ:AV0Z10100520 Keywords : Mo-C coating * mechanical properties * friction * wear * magnetron sputtering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.135, year: 2010

  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. Copyright © 2015 Elsevier Ltd and The Ergonomics Society. All rights reserved.

  12. Average Skin-Friction Drag Coefficients from Tank Tests of a Parabolic Body of Revolution (NACA RM-10)

    Science.gov (United States)

    Mottard, Elmo J; Loposer, J Dan

    1954-01-01

    Average skin-friction drag coefficients were obtained from boundary-layer total-pressure measurements on a parabolic body of revolution (NACA rm-10, basic fineness ratio 15) in water at Reynolds numbers from 4.4 x 10(6) to 70 x 10(6). The tests were made in the Langley tank no. 1 with the body sting-mounted at a depth of two maximum body diameters. The arithmetic mean of three drag measurements taken around the body was in good agreement with flat-plate results, but, apparently because of the slight surface wave caused by the body, the distribution of the boundary layer around the body was not uniform over part of the Reynolds number range.

  13. 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

    Friction materials for typical brake applications are normally designed considering thermal stability as the major performance criterion. There are however brake applications with very limited sliding velocities, where the generated heat is insignificant. In such cases it is possible that frictio...

  14. Shape Optimization in Contact Problems with Coulomb Friction and a Solution-Dependent Friction Coefficient

    Czech Academy of Sciences Publication Activity Database

    Beremlijski, P.; Outrata, Jiří; Haslinger, Jaroslav; Pathó, R.

    2014-01-01

    Roč. 52, č. 5 (2014), s. 3371-3400 ISSN 0363-0129 R&D Projects: GA ČR(CZ) GAP201/12/0671 Grant - others:GA MŠK(CZ) CZ.1.05/1.1.00/02.0070; GA MŠK(CZ) CZ.1.07/2.3.00/20.0070 Institutional support: RVO:67985556 ; RVO:68145535 Keywords : shape optimization * contact problems * Coulomb friction * solution-dependent coefficient of friction * mathematical programs with equilibrium constraints Subject RIV: BA - General Mathematics Impact factor: 1.463, year: 2014 http://library.utia.cas.cz/separaty/2014/MTR/outrata-0434234.pdf

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

    KAUST Repository

    Sraj, Ihab; Mandli, Kyle T.; Knio, Omar; Dawson, Clint N.; Hoteit, Ibrahim

    2014-01-01

    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.

  16. 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.

  17. Experimental research on friction coefficient between grain bulk and bamboo clappers

    Science.gov (United States)

    Tang, Gan; Sun, Ping; Zhao, Yanqi; Yin, Lingfeng; Zhuang, Hong

    2017-12-01

    A silo is an important piece of storage equipment, especially in the grain industry. The internal friction angle and the friction coefficient between the grain and the silo wall are the main parameters needed for calculating the lateral pressure of the silo wall. Bamboo is used in silo walls, but there are no provisions about the friction coefficient between bulk grain and bamboo clappers in existing codes. In this paper, the material of the silo wall is bamboo. The internal friction of five types of grain and the friction coefficient between the grain and the bamboo clappers were measured with an equal-strain direct shear apparatus. By comparing the experimental result values with the code values, the friction coefficient between the grain bulk and bamboo clappers is lower than that between grain and steel wall and that between grain and concrete wall. The differences in value are 0.21 and 0.09, respectively.

  18. Calculation of Friction Coefficient and Analysis of Fluid Flow in a Stepped Micro-Channel for Wide Range of Knudsen Number Using Lattice Boltzmann (MRT Method

    Directory of Open Access Journals (Sweden)

    Y. Bakhshan

    2015-01-01

    Full Text Available Micro scale gas flows has attracted significant research interest in the last two decades. In this research, the fluid flow of gases in the stepped micro-channel at a wide range of Knudsen number has been analyzed with using the Lattice Boltzmann (MRT method. In the model, a modified second-order slip boundary condition and a Bosanquet-type effective viscosity are used to consider the velocity slip at the boundaries and to cover the slip and transition regimes of flow and to gain an accurate simulation of rarefied gases. It includes the slip and transition regimes of flow. The flow specifications such as pressure loss, velocity profile, streamline and friction coefficient at different conditions have been presented. The results show good agreement with available experimental data. The calculation shows that the friction coefficient decreases with increasing the Knudsen number and stepping the micro-channel has an inverse effect on the friction coefficient. Furthermore, a new correlation is suggested for calculation of the friction coefficient in the stepped micro-channel as below: C_f Re  = 3.113+2.915/(1 +2 Kn+ 0.641 exp⁡(3.203/(1 + 2 Kn

  19. Measurements of Heat-Transfer and Friction Coefficients for Helium Flowing in a Tube at Surface Temperatures up to 5900 Deg R

    Science.gov (United States)

    Taylor, Maynard F.; Kirchgessner, Thomas A.

    1959-01-01

    Measurements of average heat transfer and friction coefficients and local heat transfer coefficients were made with helium flowing through electrically heated smooth tubes with length-diameter ratios of 60 and 92 for the following range of conditions: Average surface temperature from 1457 to 4533 R, Reynolds numbe r from 3230 to 60,000, heat flux up to 583,200 Btu per hr per ft2 of heat transfer area, and exit Mach numbe r up to 1.0. The results indicate that, in the turbulent range of Reynolds number, good correlation of the local heat transfer coefficients is obtained when the physical properties and density of helium are evaluated at the surface temperature. The average heat transfer coefficients are best correlated on the basis that the coefficient varies with [1 + (L/D))(sup -0,7)] and that the physical properties and density are evaluated at the surface temperature. The average friction coefficients for the tests with no heat addition are in complete agreement with the Karman-Nikuradse line. The average friction coefficients for heat addition are in poor agreement with the accepted line.

  20. Effect of the Contact Pressure on the Friction Loss Coefficient in a Micro Gap

    International Nuclear Information System (INIS)

    Nam, Ho Yun; Kim, Jong Man; Kim, Jong Bum; Lee, Yong Bum

    2010-01-01

    As one way to improve the reliability of a steam generator for a sodium-cooled fast reactor, a double-wall tube steam generator is being developed. The current development of the DWTSG focuses on the improvement of heat transfer capability for a double-wall tube and the development of a proper leak detection method for the double-wall tube during the operation of a reactor. In the conventional double wall tubes(DWT), the inner tube and the outer tube are made of the same material. When the temperature difference between the inner tube and the outer tube increases, the heat transfer efficiency decreases. To improve the heat transfer capability of a double wall tube, the inner tube is made of a material with a thermal expansion coefficient which is about 10 to 15% greater than that of the outer tube . For the on-line and real-time detection of whether the heat transfer tube is damaged or not, a detection method was developed by combining the heat transfer tube gaps and the detection holes meeting with a one-to-one correspondence in the lower tubesheet. In the pre-stressed DWT, there is a very small space due to the surface roughness of the inner wall and outer wall. Thus, if the outer wall is broken, the helium gas (2MPa) in the very narrow space is ejected into the sodium (0.1MPa), and if the inner wall is broken, the superheated gas (16.5MPa) is ejected into the space filled with helium gas. If the four grooves with 0.2-04mm depths are dug in the inner surface of the outer wall in order for the helium gas to flow easily, we can detect the leakage by checking the change of gas volume in the online groove

  1. Experimental Investigation of Average Heat-Transfer and Friction Coefficients for Air Flowing in Circular Tubes Having Square-Thread-Type Roughness

    Science.gov (United States)

    Sams, E. W.

    1952-01-01

    An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through electrically heated Inconel tubes having various degrees of square-thread-type roughness, an inside diameter of 1/2 inch, and a length of 24 inches. were obtained for tubes having conventional roughness ratios (height of thread/radius of tube) of 0 (smooth tube), 0.016, 0.025, and 0.037 over ranges of bulk Reynolds numbers up to 350,000, average inside-tube-wall temperatures up to 1950deg R, and heat-flux densities up to 115,000 Btu per hour per square foot. Data The experimental data showed that both heat transfer and friction increased with increase in surface roughness, becoming more pronounced with increase in Reynolds number; for a given roughness, both heat transfer and friction were also influenced by the tube wall-to-bulk temperature ratio. Good correlation of the heat-transfer data for all the tubes investigated was obtained by use of a modification of the conventional Nusselt correlation parameters wherein the mass velocity in the Reynolds number was replaced by the product of air density evaluated at the average film temperature and the so-called friction velocity; in addition, the physical properties of air were evaluated at the average film temperature. The isothermal friction data for the rough tubes, when plotted in the conventional manner, resulted in curves similar to those obtained by other investigators; that is, the curve for a given roughness breaks away from the Blasius line (representing turbulent flow in smooth tubes) at some value of Reynolds number, which decreases with increase in surface roughness, and then becomes a horizontal line (friction coefficient independent of Reynolds number). A comparison of the friction data for the rough tubes used herein indicated that the conventional roughness ratio is not an adequate measure of relative roughness for tubes having a square-thread-type element. The present data, as well

  2. On a model for the prediction of the friction coefficient in mixed lubrication based on a load-sharing concapt with measured surface roughness

    NARCIS (Netherlands)

    Akchurin, Aydar; Bosman, Rob; Lugt, Pieter Martin; van Drogen, Mark

    2015-01-01

    A new model was developed for the simulation of the friction coefficient in lubricated sliding line contacts. A half-space-based contact algorithm was linked with a numerical elasto-hydrodynamic lubrication solver using the load-sharing concept. The model was compared with an existing asperity-based

  3. The possibility of modifying the elements of the bearing assembly with nanoparticles in order to reduce the friction coefficient

    Science.gov (United States)

    Stankevich, P.; Mironovs, V.; Vasilyeva, E.; Breki, A.; Tolochko, O.

    2017-10-01

    Recent study considers the tribological characteristics of the sintered bushings used in the connecting nodes brake lever system of railway cars. Particular attention is paid sleeves low content of alloying elements. Bushings had been prepared by powder metallurgy route by using low alloyed powders of Fe-Cu-C system. Porosity after sintering was about 20%. Generally, before using material was impregnated by industrial mineral oil in order to improve friction condition. In the recent study we use new lubricating compositions for impregnating in sintered bodies. Such compositions consist of basic mineral oil with addition of 4 wt.% of layered tungsten dichalcogenides (WS2 and WSe2) nanoparticles, which were ultrasonically dispersed. Tungsten disulphide nanoparticles have spherical shape with the diameter of 30-50 nm, and diselenide nanoparticles have a flat shape with the mean dimensions of 5x70 nm. Tribological testing of the product was provided. Sintered bushings impregnated with commercial oil and suspension of nanoparticles were tested in the spinning friction conditions in the couple with bearing steel at the load of 210 N and spinning rate of 200 rpm. The friction test in couple with steel exhibited the value of friction moment to be about 2 times less as compared with commercial oil. The additions of tungsten disulphide nanoparticles also significantly decrease oscillations the friction torque.

  4. Friction coefficient and effective interference at the implant-bone interface.

    Science.gov (United States)

    Damm, Niklas B; Morlock, Michael M; Bishop, Nicholas E

    2015-09-18

    Although the contact pressure increases during implantation of a wedge-shaped implant, friction coefficients tend to be measured under constant contact pressure, as endorsed in standard procedures. Abrasion and plastic deformation of the bone during implantation are rarely reported, although they define the effective interference, by reducing the nominal interference between implant and bone cavity. In this study radial forces were analysed during simulated implantation and explantation of angled porous and polished implant surfaces against trabecular bone specimens, to determine the corresponding friction coefficients. Permanent deformation was also analysed to determine the effective interference after implantation. For the most porous surface tested, the friction coefficient initially increased with increasing normal contact stress during implantation and then decreased at higher contact stresses. For a less porous surface, the friction coefficient increased continually with normal contact stress during implantation but did not reach the peak magnitude measured for the rougher surface. Friction coefficients for the polished surface were independent of normal contact stress and much lower than for the porous surfaces. Friction coefficients were slightly lower for pull-out than for push-in for the porous surfaces but not for the polished surface. The effective interference was as little as 30% of the nominal interference for the porous surfaces. The determined variation in friction coefficient with radial contact force, as well as the loss of interference during implantation will enable a more accurate representation of implant press-fitting for simulations. Copyright © 2015 Elsevier Ltd. All rights reserved.

  5. The effect of load in a contact with boundary lubrication. [reduction of coefficient of friction

    Science.gov (United States)

    Georges, J. M.; Lamy, B.; Daronnat, M.; Moro, S.

    1978-01-01

    The effect of the transition load on the wear in a contact with boundary lubrication was investigated. An experimental method was developed for this purpose, and parameters affecting the boundary lubrication under industrial operating conditions were identified. These parameters are the adsorbed boundary film, the contact microgeometry (surface roughness), macrogeometry, and hardness of materials used. It was found that the curve of the tops of the surface protrustion affect the transition load, and thus the boundary lubrication. The transition load also depends on the chemical nature of the contact and its geometrical and mechanical aspects.

  6. Effect of laceration and trimming of a tendon on the coefficient of friction along the A2 pulley: an in vitro study on turkey tendon.

    Science.gov (United States)

    Hajipour, L; Gulihar, A; Dias, J

    2010-08-01

    We carried out lacerations of 50%, followed by trimming, in ten turkey flexor tendons in vitro and measured the coefficient of friction at the tendon-pulley interface with loads of 200 g and 400 g and in 10 degrees , 30 degrees, 50 degrees and 70 degrees of flexion. Laceration increased the coefficient of friction from 0.12 for the intact tendon to 0.3 at both the test loads. Trimming the laceration reduced the coefficient of friction to 0.2. An exponential increase in the gliding resistance was found at 50 degrees and 70 degrees of flexion (p = 0.02 and p = 0.003, respectively) following trimming compared to that of the intact tendon. We concluded that trimming partially lacerated flexor tendons will reduce the gliding resistance at the tendon-pulley interface, but will lead to fragmentation and triggering of the tendon at higher degrees of flexion and loading. We recommend that higher degrees of flexion be avoided during early post-operative rehabilitation following trimming of a flexor tendon.

  7. Determination of friction factors and heat transfer coefficients for flow past artificially roughened surfaces

    International Nuclear Information System (INIS)

    Hodge, S.A.

    1979-12-01

    Because convective heat transfer is enhanced in flow past rough surfaces, much experimental and analytical effort over the past several decades has been devoted to the evaluation of artificial roughening for potential application to the heat transfer surfaces of gas-cooled reactors. Unfortunately, much of the analytical development in this field has been inadequately explained in the literature; this has led to misinterpretation of some of the subsequent experimental findings, compounding the uncertainty. This work provides a critical review of the underlying assumptions, theoretical foundations, and supporting experimental evidence for the analytical procedures in current use for the evaluation of roughness effects. It is a concise presentation of the available formulations with recommendations concerning their applicability to rough rod bundles

  8. Hair-on-hair static friction coefficient can be determined by tying a knot.

    Science.gov (United States)

    Chevalier, Nicolas R

    2017-11-01

    Characterizing the tribological properties of the hair-hair interface is important to quantify the manageability of hair and to assess the performance of hair care products. Audoly et al. (Phys. Rev. Lett. 99, 164301, 2007) derived an equation relating the self-friction coefficient of an elastic fiber to the dimensions of a simple, relaxed overhand knot made from this fiber. I experimentally tested and validated their equation using nylon thread and an independent measurement of its self-friction coefficient. I show that this methodology can be applied to provide high-throughput data on the static self-friction coefficient of single hair fibers in various conditions and to quantitatively assess how hair care treatments (conditioner, relaxant) alter frictional properties. I find that treatment of hair with 1M sodium hydroxide leads to a quick, irreversible self-friction coefficient increase; the resulting fine frictional fibers can be used to form very small knots for microsurgical vessel and organ ligature in medicine or embryology. The relaxed overhand knot method can more generally be used to measure the self-friction coefficients of a wide range of elastic fibers from the nano- (e.g. proteins, nanotubes) to the macro-scale (e.g. textile fiber, fiberglass). Copyright © 2017 Elsevier B.V. All rights reserved.

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

    DEFF Research Database (Denmark)

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

    2012-01-01

    Purpose - The purpose of this paper is to determine the magnitude and spatial distribution of the heat transfer coefficient between the workpiece and the backingplate in a friction stir welding process using inverse modelling. Design/methodology/approach - The magnitude and distribution of the heat...... in an inverse modeling approach to determine the heat transfer coefficient in friction stir welding. © Emerald Group Publishing Limited....

  10. Frictional coefficient depending on active friction radius with BPV ...

    African Journals Online (AJOL)

    www.ajol.info/index.php/ijest ... parameters acquired using the braking system and predetermined values. ... subjected to the variations in the incompressibility of the hydraulic brake fluid, introducing air can have detrimental effects on the ... process. Degestein et al. (2006) concluded that uniform surface pressing occurs due ...

  11. Calculation of skin-friction coefficients for low Reynolds number turbulent boundary layer flows. M.S. Thesis - California Univ. at Davis

    Science.gov (United States)

    Barr, P. K.

    1980-01-01

    An analysis is presented of the reliability of various generally accepted empirical expressions for the prediction of the skin-friction coefficient C/sub f/ of turbulent boundary layers at low Reynolds numbers in zero-pressure-gradient flows on a smooth flat plate. The skin-friction coefficients predicted from these expressions were compared to the skin-friction coefficients of experimental profiles that were determined from a graphical method formulated from the law of the wall. These expressions are found to predict values that are consistently different than those obtained from the graphical method over the range 600 Re/sub theta 2000. A curve-fitted empirical relationship was developed from the present data and yields a better estimated value of C/sub f/ in this range. The data, covering the range 200 Re/sub theta 7000, provide insight into the nature of transitional flows. They show that fully developed turbulent boundary layers occur at Reynolds numbers Re/sub theta/ down to 425. Below this level there appears to be a well-ordered evolutionary process from the laminar to the turbulent profiles. These profiles clearly display the development of the turbulent core region and the shrinking of the laminar sublayer with increasing values of Re/sub theta/.

  12. Minimizing of the boundary friction coefficient in automotive engines using Al{sub 2}O{sub 3} and TiO{sub 2} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Ali, Mohamed Kamal Ahmed, E-mail: eng.m.kamal@mu.edu.eg; Xianjun, Hou, E-mail: houxj@whut.edu.cn; Elagouz, Ahmed [Wuhan University of Technology, Hubei Key Laboratory of Advanced Technology for Automotive Components (China); Essa, F.A. [Kafrelsheikh University, Mechanical Engineering Department, Faculty of Engineering (Egypt); Abdelkareem, Mohamed A. A. [Wuhan University of Technology, Hubei Key Laboratory of Advanced Technology for Automotive Components (China)

    2016-12-15

    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 Al{sub 2}O{sub 3} and TiO{sub 2} 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 Al{sub 2}O{sub 3} and TiO{sub 2} 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 Al{sub 2}O{sub 3} and TiO{sub 2} 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.

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

    DEFF Research Database (Denmark)

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

    2013-01-01

    to sustained frictional instabilities, effectively with no contact frictional sliding. The amplitude of the stick-slip oscillations, σf, was found to correlate with the topographic properties of the surfaces and scale linearly with the applied load. In line with the friction coefficient, we define the slope......-defined nanodomes comprising densely packed prolate spheroids, of diameters ranging from tens to hundreds of nanometers. Our results show that the average lateral force varied linearly with applied load, as described by Amontons' first law of friction, although no direct correlation between the sample topographic...... properties and their measured friction coefficients was identified. Furthermore, all the nanodomed textures exhibited pronounced oscillations in the shear traces, similar to the classic stick-slip behavior, under all the shear velocities and load regimes studied. That is, the nanotextured topography led...

  14. 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.

  15. Tire-to-Surface Friction-Coefficient Measurements with a C-123B Airplane on Various Runway Surfaces

    Science.gov (United States)

    Sawyer, Richard H.; Kolnick, Joseph J.

    1959-01-01

    An investigation was conducted to obtain information on the tire-to-surface friction coefficients available in aircraft braking during the landing run. The tests were made with a C-123B airplane on both wet and dry concrete and bituminous pavements and on snow-covered and ice surfaces at speeds from 12 to 115 knots. Measurements were made of the maximum (incipient skidding) friction coefficient, the full-skidding (locked wheel) friction coefficient, and the wheel slip ratio during braking.

  16. Investigation of Shear-Thinning Behavior on Film Thickness and Friction Coefficient of Polyalphaolefin Base Fluids With Varying Olefin Copolymer Content

    Energy Technology Data Exchange (ETDEWEB)

    Zolper, Thomas J.; He, Yifeng; Delferro, Massimiliano; Shiller, Paul; Doll, Gary; LotfizadehDehkordi, Babak; Ren, Ning; Lockwood, Frances; Marks, Tobin J.; Chung, Yip-Wah; Greco, Aaron; Erdemir, Ali; Wang, Qian

    2016-08-11

    This study investigates the rheological properties, elastohydrodynamic (EHD) film-forming capability, and friction coefficients of low molecular mass poly-alpha-olefin (PAO) base stocks with varying contents of high molecular mass olefin copolymers (OCPs) to assess their shear stability and their potential for energy-efficient lubrication. Several PAO-OCP mixtures were blended in order to examine the relationship between their additive content and tribological performance. Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy were used to characterize the molecular masses and structures, respectively. Density, viscosity, EHD film thickness, and friction were measured at 303 K, 348 K, and 398 K. Film thickness and friction were studied at entrainment speeds relevant to the boundary, mixed, and full-film lubrication regimes. The PAO-OCP mixtures underwent temporary shear-thinning resulting in decreases in film thickness and hydrodynamic friction. These results demonstrate that the shear characteristics of PAO-OCP mixtures can be tuned with the OCP content and provide insight into the effects of additives on EHD characteristics.

  17. Showing Area Matters: A Work of Friction

    Science.gov (United States)

    Van Domelen, David

    2010-01-01

    Typically, we teach the simplified friction equation of the form F[subscript s] = [mu][subscript s]N for static friction, where F[subscript s] is the maximum static friction, [mu][subscript s] is the coefficient of static friction, and "N" is the normal force pressing the surfaces together. However, this is a bit too simplified, and…

  18. Friction dampers, the positive side of friction

    NARCIS (Netherlands)

    Lopez Arteaga, I.; Nijmeijer, H.; Busturia, J.M.; Sas, P.; Munck, de M.

    2004-01-01

    Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised or controlled. In this work one of the positive sides of friction is investigated: friction damping. Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of

  19. Adaptive Neuro-Fuzzy Computing Technique for Determining Turbulent Flow Friction Coefficient

    Directory of Open Access Journals (Sweden)

    Mohammad Givehchi

    2013-08-01

    Full Text Available Estimation of the friction coefficient in pipes is very important in many water and wastewater engineering issues, such as distribution of velocity and shear stress, erosion, sediment transport and head loss. In analyzing these problems, knowing the friction coefficient, can obtain estimates that are more accurate. In this study in order to estimate the friction coefficient in pipes, using adaptive neuro-fuzzy inference systems (ANFIS, grid partition method was used. For training and testing of neuro-fuzzy model, the data derived from the Colebrook’s equation was used. In the neuro-fuzzy approach, pipe relative roughness and Reynolds number are considered as input variables and friction coefficient as output variable is considered. Performance of the proposed approach was evaluated by using of the data obtained from the Colebrook’s equation and based on statistical indicators such as coefficient determination (R2, root mean squared error (RMSE and mean absolute error (MAE. The results showed that the adaptive nerou-fuzzy inference system with grid partition method and gauss model as an input membership function and linear as an output function could estimate friction coefficient more accurately than other conditions. The new proposed approach in this paper has capability of application in the practical design issues and can be combined with mathematical and numerical models of sediment transfer or real-time updating of these models.

  20. PEBBLES Simulation of Static Friction and New Static Friction Benchmark

    International Nuclear Information System (INIS)

    Cogliati, Joshua J.; Ougouag, Abderrafi M.

    2010-01-01

    Pebble bed reactors contain large numbers of spherical fuel elements arranged randomly. Determining the motion and location of these fuel elements is required for calculating certain parameters of pebble bed reactor operation. This paper documents the PEBBLES static friction model. This model uses a three dimensional differential static friction approximation extended from the two dimensional Cundall and Strack model. The derivation of determining the rotational transformation of pebble to pebble static friction force is provided. A new implementation for a differential rotation method for pebble to container static friction force has been created. Previous published methods are insufficient for pebble bed reactor geometries. A new analytical static friction benchmark is documented that can be used to verify key static friction simulation parameters. This benchmark is based on determining the exact pebble to pebble and pebble to container static friction coefficients required to maintain a stable five sphere pyramid.

  1. 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

    2017-08-01

    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.

  2. 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.

  3. On the Brownian motion of a massive sphere suspended in a hard-sphere fluid. II. Molecular dynamics estimates of the friction coefficient

    International Nuclear Information System (INIS)

    Bocquet, L.; Hansen, J.P.; Piasecki, J.

    1994-01-01

    The friction coefficient γ exerted by a hard-sphere fluid on an infinitely massive Brownian sphere is calculated for several size ratios Σ/σ where Σ and σ are the diameters of the Brownian and fluid spheres, respectively. The exact microscopic expression derived in part I of this work from kinetic theory is transformed and shown to be proportional to the time integral of the autocorrelation function of the momentum transferred from the fluid to the Brownian sphere during instantaneous collisions. Three different methods are described to extract the friction coefficient from molecular dynamics simulations carried out on finite systems. The three independent methods lead to estimates of γ which agree within statistical errors (typically 5%). The results are compared to the predictions of Enskog theory and of the hydrodynamic Stokes law. The former breaks down as the size ratio and/or the packing fraction of the fluid increase. Somewhat surprisingly, Stokes' law is found to hold with stick boundary conditions, in the range 1 ≤ Σ/σ ≤ 4.5 explored in the present simulations, with a hydrodynamic diameter d=Σ. The analysis of the molecular dynamics data on the basis of Stokes' law with slip boundary conditions is less conclusive, although the right trend is found as Σ/σ increases

  4. Influence of Nitrogen Flow Rate on Friction Coefficient and Surface Roughness of TiN Coatings Deposited on Tool Steel Using Arc Method

    Science.gov (United States)

    Hamzah, Esah; Ourdjini, Ali; Ali, Mubarak; Akhter, Parvez; Hj. Mohd Toff, Mohd Radzi; Abdul Hamid, Mansor

    In the present study, the effect of various N2 gas flow rates on friction coefficient and surface roughness of TiN-coated D2 tool steel was examined by a commercially available cathodic arc physical vapor deposition (CAPVD) technique. A Pin-on-Disc test was carried out to study the Coefficient of friction (COF) versus sliding distance. A surface roughness tester measured the surface roughness parameters. The minimum values for the COF and surface roughness were recorded at a N2 gas flow rate of 200 sccm. The increase in the COF and surface roughness at a N2 gas flow rate of 100 sccm was mainly attributed to an increase in both size and number of titanium particles, whereas the increase at 300 sccm was attributed to a larger number of growth defects generated during the coating process. These ideas make it possible to optimize the coating properties as a function of N2 gas flow rate for specific applications, e.g. cutting tools for automobiles, aircraft, and various mechanical parts.

  5. Friction pressure drop and heat transfer coefficient of two-phase flow in helically coiled tube once-through steam generator for integrated type marine water reactor

    International Nuclear Information System (INIS)

    Nariai, Hideki; Kobayashi, Michiyuki; Matsuoka, Takeshi.

    1982-01-01

    Two-phase friction pressure drop and heat transfer coefficients in a once-through steam generator with helically coiled tubes were investigated with the model test rig of an integrated type marine water reactor. As the dimensions of the heat transfer tubes and the thermal-fluid conditions are almost the same as those of real reactors, the data applicable directly to the real reactor design were obtained. As to the friction pressure drop, modified Kozeki's prediction which is based on the experimental data by Kozeki for coiled tubes, agreed the best with the experimental data. Modified Martinelli-Nelson's prediction which is based on Martinelli-Nelson's multiplier using Ito's equation for single-phase flow in coiled tube, agreed within 30%. The effect of coiled tube on the average heat transfer coefficients at boiling region were small, and the predictions for straight tube could also be applied to coiled tube. Schrock-Grossman's correlation agreed well with the experimental data at the pressures of lower than 3.5 MPa. It was suggested that dryout should be occurred at the quality of greater than 90% within the conditions of this report. (author)

  6. Real-Time Dynamic Observation of Micro-Friction on the Contact Interface of Friction Lining

    Science.gov (United States)

    Zhang, Dekun; Chen, Kai; Guo, Yongbo

    2018-01-01

    This paper aims to investigate the microscopic friction mechanism based on in situ microscopic observation in order to record the deformation and contact situation of friction lining during the frictional process. The results show that friction coefficient increased with the shear deformation and energy loss of the surfacee, respectively. Furthermore, the friction mechanism mainly included adhesive friction in the high-pressure and high-speed conditions, whereas hysteresis friction was in the low-pressure and low-speed conditions. The mixed-friction mechanism was in the period when the working conditions varied from high pressure and speed to low pressure and speed. PMID:29498677

  7. Application of a non-dynamometric method to the measurement of the coefficient of static friction in cold and hot water between stainless steel and two alloys of zirconium

    International Nuclear Information System (INIS)

    D'Agraives, B.C.; Toornvliet, J.

    1977-01-01

    A method is proposed to perform comparative measurements of the coefficient of friction, either in cold water (25 0 C) or in hot pressurized water (240 0 C). For the purpose, a pin-on-disc tribometer, working with no force transducer, in which the coefficient of friction μ is measured through an angle 0, and given by μ=K sin 0 is used. The method is presently applied to the determination of the incipient friction along a distance of few millimetres. At low speed (1 mm/s) and with light contacts loads (from 50 to 150 g), two different friction mechanisms are observed for the following couples of materials; Zircalloy 2/304L stainless steel, Zirconium Niobium 2.5/304L stainless steel, 304L stainless steel/304L stainless steel. The first mechanism, which is observed essentially in cold conditions, is characterized by a regular sliding since friction starts, whereas the second appears mostly in hot conditions and shows peaks of friction with irregular and scattered values of μ. These two mechanisms seem to be related to intermetallic affinity of the mating materials, and also to the existence of preoxydized surface layers, and, to a large extent, to the change in the water viscosity. In such conditions, it appears that it is not possible to replace friction experiments in hot water by easier experiments in cold water

  8. 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

  9. Tactile friction of topical formulations.

    Science.gov (United States)

    Skedung, L; Buraczewska-Norin, I; Dawood, N; Rutland, M W; Ringstad, L

    2016-02-01

    The tactile perception is essential for all types of topical formulations (cosmetic, pharmaceutical, medical device) and the possibility to predict the sensorial response by using instrumental methods instead of sensory testing would save time and cost at an early stage product development. Here, we report on an instrumental evaluation method using tactile friction measurements to estimate perceptual attributes of topical formulations. Friction was measured between an index finger and an artificial skin substrate after application of formulations using a force sensor. Both model formulations of liquid crystalline phase structures with significantly different tactile properties, as well as commercial pharmaceutical moisturizing creams being more tactile-similar, were investigated. Friction coefficients were calculated as the ratio of the friction force to the applied load. The structures of the model formulations and phase transitions as a result of water evaporation were identified using optical microscopy. The friction device could distinguish friction coefficients between the phase structures, as well as the commercial creams after spreading and absorption into the substrate. In addition, phase transitions resulting in alterations in the feel of the formulations could be detected. A correlation was established between skin hydration and friction coefficient, where hydrated skin gave rise to higher friction. Also a link between skin smoothening and finger friction was established for the commercial moisturizing creams, although further investigations are needed to analyse this and correlations with other sensorial attributes in more detail. The present investigation shows that tactile friction measurements have potential as an alternative or complement in the evaluation of perception of topical formulations. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  10. 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.

  11. 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.

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

    International Nuclear Information System (INIS)

    Garza, I.A.

    1996-01-01

    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

  13. Flight Measurements of Average Skin-Friction Coefficients on a Parabolic Body of Revolution (NACA RM-10) at Mach Numbers from 1.0 to 3.7

    Science.gov (United States)

    Loposer, J. Dan; Rumsey, Charles B.

    1954-01-01

    Measurement of average skin-friction coefficients have been made on six rocket-powered free-flight models by using the boundary-layer rake technique. The model configuration was the NACA RM-10, a 12.2-fineness-ratio parabolic body of revolution with a flat base. Measurements were made over a Mach number range from 1 to 3.7, a Reynolds number range 40 x 10(exp 6) to 170 x 10(exp 6) based on length to the measurement station, and with aerodynamic heating conditions varying from strong skin heating to strong skin cooling. The measurements show the same trends over the test ranges as Van Driest's theory for turbulent boundary layer on a flat plate. The measured values are approximately 7 percent higher than the values of the flat-plate theory. A comparison which takes into account the differences in Reynolds number is made between the present results and skin-friction measurements obtained on NACA RM-10 scale models in the Langley 4- by 4-foot supersonic pressure tunnel, the Lewis 8- by 6-foot supersonic tunnel, and the Langley 9-inch supersonic tunnel. Good agreement is shown at all but the lowest tunnel Reynolds number conditions. A simple empirical equation is developed which represents the measurements over the range of the tests.

  14. A study on the stem friction coefficient with differential pressure conditions for the motor operated flexible wedge gate valve

    International Nuclear Information System (INIS)

    Kim, Dae Woong; Park, Sung Keun; Kim, Yang Seok; Lee, Do Hwan

    2008-01-01

    Stem friction coefficient is very important parameter for the evaluation of valve performance. In this study, the characteristics of stem friction coefficient is analyzed, and the bounding value is determined. The hydraulic testing is performed for flexible wedge gate valves in the plant and statistical method is applied to the determination of bounding value. According to the results of this study, stem friction coefficient is not effected in low differential pressure condition, but it is showed different distribution in medium and high differential pressure condition. And the bounding value of closing stroke is higher than that of opening stroke

  15. On the skin friction coefficient in viscoelastic wall-bounded flows

    International Nuclear Information System (INIS)

    Housiadas, Kostas D.; Beris, Antony N.

    2013-01-01

    Highlights: ► We decompose the skin friction coefficient to its individual contributions. ► The contributions are evaluated using simulation results in turbulent channel flow. ► We present a fitting curve for the drag reduction. ► A new formula for the skin friction coefficient is also developed. ► The results agree well with experimental data from the literature. -- Abstract: Analysis of the skin friction coefficient for wall bounded viscoelastic flows is performed by utilizing available direct numerical simulation (DNS) results for viscoelastic turbulent channel flow. The Oldroyd-B, FENE-P and Giesekus constitutive models are used. First, we analyze the friction coefficient in viscous, viscoelastic and inertial stress contributions, as these arise from suitable momentum balances, for the flow in channels and pipes. Following Fukagata et al. (Phys. Fluids, 14, p. L73, 2002) and Yu et al. (Int. J. Heat. Fluid Flow, 25, p. 961, 2004) these three contributions are evaluated averaging available numerical results, and presented for selected values of flow and rheological parameters. Second, based on DNS results, we develop a universal function for the relative drag reduction as a function of the friction Weissenberg number. This leads to a closed-form approximate expression for the inverse of the square root of the skin friction coefficient for viscoelastic turbulent pipe flow as a function of the friction Reynolds number involving two primary material parameters, and a secondary one which also depends on the flow. The primary parameters are the zero shear-rate elasticity number, El 0 , and the limiting value for the drag reduction at high Weissenberg number, LDR, while the secondary one is the relative wall viscosity, μ w . The predictions reproduce both types A and B of drag reduction, as first introduced by Virk (Nature, 253, p. 109, 1975), corresponding to partially and fully extended polymer molecules, respectively. Comparison of the results for the

  16. Self-affine roughness influence on the friction coefficient for rubbers onto solid surfaces

    NARCIS (Netherlands)

    Palasantzas, G

    2004-01-01

    In this paper we investigate the influence of self-affine roughness on the friction coefficient mu(f) of a rubber body under incomplete contact onto a solid surface. The roughness is characterized by the rms amplitude w, the correlation length xi, and the roughness exponent H. It is shown that with

  17. Steady sliding frictional contact problem for a 2d elastic half-space with a discontinuous friction coefficient and related stress singularities

    Science.gov (United States)

    Ballard, Patrick

    2016-12-01

    The steady sliding frictional contact problem between a moving rigid indentor of arbitrary shape and an isotropic homogeneous elastic half-space in plane strain is extensively analysed. The case where the friction coefficient is a step function (with respect to the space variable), that is, where there are jumps in the friction coefficient, is considered. The problem is put under the form of a variational inequality which is proved to always have a solution which, in addition, is unique in some cases. The solutions exhibit different kinds of universal singularities that are explicitly given. In particular, it is shown that the nature of the universal stress singularity at a jump of the friction coefficient is different depending on the sign of the jump.

  18. Increased friction coefficient and superficial zone protein expression in patients with advanced osteoarthritis.

    Science.gov (United States)

    Neu, C P; Reddi, A H; Komvopoulos, K; Schmid, T M; Di Cesare, P E

    2010-09-01

    To quantify the concentration of superficial zone protein (SZP) in the articular cartilage and synovial fluid of patients with advanced osteoarthritis (OA) and to further correlate the SZP content with the friction coefficient, OA severity, and levels of proinflammatory cytokines. Samples of articular cartilage and synovial fluid were obtained from patients undergoing elective total knee replacement surgery. Additional normal samples were obtained from donated body program and tissue bank sources. Regional SZP expression in cartilage obtained from the femoral condyles was quantified by enzyme-linked immunosorbent assay (ELISA) and visualized by immunohistochemistry. Friction coefficient measurements of cartilage plugs slid in the boundary lubrication system were obtained. OA severity was graded using histochemical analyses. The concentrations of SZP and proinflammatory cytokines in synovial fluid were determined by ELISA. A pattern of SZP localization in knee cartilage was identified, with load-bearing regions exhibiting high SZP expression. SZP expression patterns were correlated with friction coefficient and OA severity; however, SZP expression was observed in all samples at the articular surface, regardless of OA severity. SZP expression and aspirate volume of synovial fluid were higher in OA patients than in normal controls. Expression of cytokines was elevated in the synovial fluid of some patients. Our findings indicate a mechanochemical coupling in which physical forces regulate OA severity and joint lubrication. The findings of this study also suggest that SZP may be ineffective in reducing joint friction in the boundary lubrication mode at an advanced stage of OA, where other mechanisms may dominate the observed tribological behavior.

  19. Regression models to predict the behavior of the coefficient of friction of AISI 316L on UHMWPE under ISO 14243-3 conditions.

    Science.gov (United States)

    Garcia-Garcia, A L; Alvarez-Vera, M; Montoya-Santiyanes, L A; Dominguez-Lopez, I; Montes-Seguedo, J L; Sosa-Savedra, J C; Barceinas-Sanchez, J D O

    2018-06-01

    Friction is the natural response of all tribosystems. In a total knee replacement (TKR) prosthetic device, its measurement is hindered by the complex geometry of its integrating parts and that of the testing simulation rig operating under the ISO 14243-3:2014 standard. To develop prediction models of the coefficient of friction (COF) between AISI 316L steel and ultra-high molecular weight polyethylene (UHMWPE) lubricated with fetal bovine serum dilutions, the arthrokinematics and loading conditions prescribed by the ISO 142433: 2014 standard were translated to a simpler geometrical setup, via Hertz contact theory. Tribological testing proceeded by loading a stainless steel AISI 316L ball against the surface of a UHMWPE disk, with the test fluid at 37 °C. The method has been applied to study the behavior of the COF during a whole walking cycle. On the other hand, the role of protein aggregation phenomena as a lubrication mechanism has been extensively studied in hip joint replacements but little explored for the operating conditions of a TKR. Lubricant testing fluids were prepared with fetal bovine serum (FBS) dilutions having protein mass concentrations of 5, 10, 20 and 36 g/L. The results were contrasted against deionized, sterilized water. The results indicate that even at protein concentration as low as 5 g/L, protein aggregation phenomena play an important role in the lubrication of the metal-on-polymer tribopair. The regression models of the COF developed herein are available for numerical simulations of the tribological behavior of the aforementioned tribosystem. In this case, surface stress rather than film thickness should be considered. Copyright © 2018 Elsevier Ltd. All rights reserved.

  20. Tyre-road friction coefficient estimation based on tyre sensors and lateral tyre deflection: modelling, simulations and experiments

    Science.gov (United States)

    Hong, Sanghyun; Erdogan, Gurkan; Hedrick, Karl; Borrelli, Francesco

    2013-05-01

    The estimation of the tyre-road friction coefficient is fundamental for vehicle control systems. Tyre sensors enable the friction coefficient estimation based on signals extracted directly from tyres. This paper presents a tyre-road friction coefficient estimation algorithm based on tyre lateral deflection obtained from lateral acceleration. The lateral acceleration is measured by wireless three-dimensional accelerometers embedded inside the tyres. The proposed algorithm first determines the contact patch using a radial acceleration profile. Then, the portion of the lateral acceleration profile, only inside the tyre-road contact patch, is used to estimate the friction coefficient through a tyre brush model and a simple tyre model. The proposed strategy accounts for orientation-variation of accelerometer body frame during tyre rotation. The effectiveness and performance of the algorithm are demonstrated through finite element model simulations and experimental tests with small tyre slip angles on different road surface conditions.

  1. Origins of Rolling Friction

    Science.gov (United States)

    Cross, Rod

    2017-01-01

    When a hard object rolls on a soft surface, or vice versa, rolling friction arises from deformation of the soft object or the soft surface. The friction force can be described in terms of an offset in the normal reaction force or in terms of energy loss arising from the deformation. The origin of the friction force itself is not entirely clear. It…

  2. Experimental friction coefficients for bovine cartilage measured with a pin-on-disk tribometer: testing configuration and lubricant effects.

    Science.gov (United States)

    Shi, Liu; Sikavitsas, Vassilios I; Striolo, Alberto

    2011-01-01

    The friction coefficient between wet articular cartilage surfaces was measured using a pin-on-disk tribometer adopting different testing configurations: cartilage-on-pin vs. alumina-on-disk (CA); cartilage-on-pin vs. cartilage-on-disk (CC); and alumina-on-pin vs. cartilage-on-disk (AC). Several substances were dissolved in the phosphate buffered saline (PBS) solution to act as lubricants: 10,000 molecular weight (MW) polyethylene glycol (PEG), 100,000 MW PEG, and chondroitin sulfate (CS), all at 100 mg/mL concentration. Scanning electron microscopy photographs of the cartilage specimens revealed limited wear due to the experiment. Conducting the experiments in PBS solutions we provide evidence according to which a commercial pin-on-disk tribometer allows us to assess different lubrication mechanisms active in cartilage. Specifically, we find that the measured friction coefficient strongly depends on the testing configuration. Our results show that the friction coefficient measured under CC and AC testing configurations remains very low as the sliding distance increases, probably because during the pin displacement the pores present in the cartilage replenish with PBS solution. Under such conditions the fluid phase supports a large load fraction for long times. By systematically altering the composition of the PBS solution we demonstrate the importance of solution viscosity in determining the measured friction coefficient. Although the friction coefficient remains low under the AC testing configuration in PBS, 100 mg/mL solutions of both CS and 100,000 MW PEG in PBS further reduce the friction coefficient by ~40%. Relating the measured friction coefficient to the Hersey number, our results are consistent with a Stribeck curve, confirming that the friction coefficient of cartilage under the AC testing configuration depends on a combination of hydrodynamic, boundary, and weep bearing lubrication mechanisms.

  3. Effect of Process Parameters on Friction Model in Computer Simulation of Linear Friction Welding

    Directory of Open Access Journals (Sweden)

    A. Yamileva

    2014-07-01

    Full Text Available The friction model is important part of a numerical model of linear friction welding. Its selection determines the accuracy of the results. Existing models employ the classical law of Amonton-Coulomb where the friction coefficient is either constant or linearly dependent on a single parameter. Determination of the coefficient of friction is a time consuming process that requires a lot of experiments. So the feasibility of determinating the complex dependence should be assessing by analysis of effect of approximating law for friction model on simulation results.

  4. CORROSION AND SURFACE PROTECTION IN MACHINE MATERIALS FRICTION HAVE DIFFERENT SURFACE PAIRS EXPERIMENTAL INVESTIGATION OF FACTORS

    OpenAIRE

    Senai YALCINKAYA

    2017-01-01

    Friction force, normal force, linear change. The normal force varies with the loads on the friction object. In order to determine the friction force and the friction coefficient, the friction object and the friction speed are used. The experimental work was carried out in three stages. In the first stage, the effect of normal force on the friction force was studied. In the second step, the friction force of the friction surface area is influenced. The effect of the change of the s...

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

    NARCIS (Netherlands)

    Kruyt, Nicolaas P.; Gutkowski, Witold; Rothenburg, L.; 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

  6. Characterization of friction and wear behavior of friction modifiers used in wheel-rail contacts

    NARCIS (Netherlands)

    Oomen, M. A.; Bosman, R.; Lugt, P. M.

    2017-01-01

    Reliable traction between wheel and rail is an important issue in the railway industry. To reduce variations in the coefficient of friction, so-called “friction modifiers” (carrier with particles) are used. Twin-disk tests were done with three commercial friction modifiers, based on different

  7. Friction of elastomer-on-glass system and direct observation of its frictional interface

    International Nuclear Information System (INIS)

    Okamoto, Yoshihiro; Nishio, Kazuyuki; Sugiura, Jun-ichi; Hirano, Motohisa; Nitta, Takahiro

    2007-01-01

    We performed a study on the static friction of PDMS elastomers with well-defined surface topography sliding over glass. An experimental setup for simultaneous measurements of friction force and direct observations of frictional interface has been developed. The static friction force was nearly proportional to normal load. The static friction force was independent of stick time. The simultaneous measurements revealed that the static friction force was proportional to the total area of contact. The coefficient was nearly independent of the surface topography of PDMS elastomers

  8. Accelerated and Decelerated Flows in a Circular Pipe : 1st Report, Velocity Profile and Friction Coefficient

    OpenAIRE

    Kurokawa, Junichi; Morikawa, Masahiro

    1986-01-01

    In order to determine the flow characteristics of a transient flow in a circular pipe, an accelerated and a decelerated flow are studied, and effects of acceleration upon the formation of a velocity profile, transition and a friction coefficient are determined for a wide range of accelerations. The results of the accelerated flow show that there are two patterns in the formation of a sectional velocity profile and transition, one of which is observed when the acceleration is relatively large ...

  9. On the nature of the static friction, kinetic friction and creep

    DEFF Research Database (Denmark)

    Persson, B. N. J.; Albohr, O.; Mancosu, F.

    2003-01-01

    of capillary bridges. However, there is no single value of the static friction coefficient, since it depends upon the initial dwell time and on rate of starting.We argue that the correct basis for the Coulomb friction law, which states that the friction force is proportional to the normal load...

  10. Reynolds number and friction coefficient for axial-parallel flow through complex cross-sections

    International Nuclear Information System (INIS)

    Markfort, D.

    1975-01-01

    Thermal and hydraulic lay-out of reactor fuel elements and other heat transfer equipment makes use of established functional relationship between dimensionless characters, the former being transferred from circular tube to more complex geometries. The stringent requirement (from theory) for 'geometrical similarity' is bypassed by defining 'equivalent diameters'. But dimensionless numbers may be derived from 'flow-integral-conditions' while the geometrical components contained therein reduce if not completely abolish the requirement for geometrical similarity. The derivation is demonstrated by using the Reynolds number. A friction coefficient valid for any kind of flow regime can be defined using integral-conditions. Correlations of friction coefficient and Reynolds number using universal-velocity profiles confirm the analysis when compared to well known experimental data. (orig.) [de

  11. Application of laws of diagramic logic to calculation of middle coefficient of friction for turbulent boundary layer

    International Nuclear Information System (INIS)

    Denisov, A.S.

    1994-01-01

    Canonical formalization of an phenomenon of reasoning by images consists of eight laws of diagramic logic, providing an structural diagram of exploring object as main unit of operating. That laws are divided into three groups: (1) The first channel of application for structural diagrams is the deduction of necessary result from previous theorems of author. (2) The second channel of application for structural diagrams is the deduction of necessary result from parallel theorems of other author. (3) The third channel of application for structural diagrams is the deduction of necessary result by means of modification of nuclear theory

  12. Kinetic Friction of Sport Fabrics on Snow

    Directory of Open Access Journals (Sweden)

    Werner Nachbauer

    2016-03-01

    Full Text Available After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier’s friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction of different fabrics of ski garments with respect to roughness, speed, and contact pressure. Three types of fabrics were investigated: a commercially available ski overall, a smooth downhill racing suit, and a dimpled downhill racing suit. Friction was measured for fabrics taped on a short ski using a linear tribometer. The fabrics’ roughness was determined by focus variation microscopy. Friction coefficients were between 0.19 and 0.48. Roughness, friction coefficient, and friction force were highest for the dimpled race suit. The friction force of the fabrics was higher for the higher contact pressure than for the lower one at all speeds. It was concluded that the main friction mechanism for the fabrics was dry friction. Only the fabric with the roughest surface showed friction coefficients, which were high enough to sufficiently decelerate a sliding skier on beginner and intermediate slopes.

  13. The effect of friction in coulombian damper

    Science.gov (United States)

    Wahad, H. S.; Tudor, A.; Vlase, M.; Cerbu, N.; Subhi, K. A.

    2017-02-01

    The study aimed to analyze the damping phenomenon in a system with variable friction, Stribeck type. Shock absorbers with limit and dry friction, is called coulombian shock-absorbers. The physical damping vibration phenomenon, in equipment, is based on friction between the cushioning gasket and the output regulator of the shock-absorber. Friction between them can be dry, limit, mixture or fluid. The friction is depending on the contact pressure and lubricant presence. It is defined dimensionless form for the Striebeck curve (µ friction coefficient - sliding speed v). The friction may damp a vibratory movement or can maintain it (self-vibration), depending on the µ with v (it can increase / decrease or it can be relative constant). The solutions of differential equation of movement are obtained for some work condition of one damper for automatic washing machine. The friction force can transfer partial or total energy or generates excitation energy in damper. The damping efficiency is defined and is determined analytical for the constant friction coefficient and for the parabolic friction coefficient.

  14. A Strain-Based Method to Detect Tires’ Loss of Grip and Estimate Lateral Friction Coefficient from Experimental Data by Fuzzy Logic for Intelligent Tire Development

    Directory of Open Access Journals (Sweden)

    Jorge Yunta

    2018-02-01

    Full Text Available Tires are a key sub-system of vehicles that have a big responsibility for comfort, fuel consumption and traffic safety. However, current tires are just passive rubber elements which do not contribute actively to improve the driving experience or vehicle safety. The lack of information from the tire during driving gives cause for developing an intelligent tire. Therefore, the aim of the intelligent tire is to monitor tire working conditions in real-time, providing useful information to other systems and becoming an active system. In this paper, tire tread deformation is measured to provide a strong experimental base with different experiments and test results by means of a tire fitted with sensors. Tests under different working conditions such as vertical load or slip angle have been carried out with an indoor tire test rig. The experimental data analysis shows the strong relation that exists between lateral force and the maximum tensile and compressive strain peaks when the tire is not working at the limit of grip. In the last section, an estimation system from experimental data has been developed and implemented in Simulink to show the potential of strain sensors for developing intelligent tire systems, obtaining as major results a signal to detect tire’s loss of grip and estimations of the lateral friction coefficient.

  15. A Strain-Based Method to Detect Tires' Loss of Grip and Estimate Lateral Friction Coefficient from Experimental Data by Fuzzy Logic for Intelligent Tire Development.

    Science.gov (United States)

    Yunta, Jorge; Garcia-Pozuelo, Daniel; Diaz, Vicente; Olatunbosun, Oluremi

    2018-02-06

    Tires are a key sub-system of vehicles that have a big responsibility for comfort, fuel consumption and traffic safety. However, current tires are just passive rubber elements which do not contribute actively to improve the driving experience or vehicle safety. The lack of information from the tire during driving gives cause for developing an intelligent tire. Therefore, the aim of the intelligent tire is to monitor tire working conditions in real-time, providing useful information to other systems and becoming an active system. In this paper, tire tread deformation is measured to provide a strong experimental base with different experiments and test results by means of a tire fitted with sensors. Tests under different working conditions such as vertical load or slip angle have been carried out with an indoor tire test rig. The experimental data analysis shows the strong relation that exists between lateral force and the maximum tensile and compressive strain peaks when the tire is not working at the limit of grip. In the last section, an estimation system from experimental data has been developed and implemented in Simulink to show the potential of strain sensors for developing intelligent tire systems, obtaining as major results a signal to detect tire's loss of grip and estimations of the lateral friction coefficient.

  16. Age differences in the required coefficient of friction during level walking do not exist when experimentally-controlling speed and step length.

    Science.gov (United States)

    Anderson, Dennis E; Franck, Christopher T; Madigan, Michael L

    2014-08-01

    The effects of gait speed and step length on the required coefficient of friction (COF) confound the investigation of age-related differences in required COF. The goals of this study were to investigate whether age differences in required COF during self-selected gait persist when experimentally-controlling speed and step length, and to determine the independent effects of speed and step length on required COF. Ten young and 10 older healthy adults performed gait trials under five gait conditions: self-selected, slow and fast speeds without controlling step length, and slow and fast speeds while controlling step length. During self-selected gait, older adults walked with shorter step lengths and exhibited a lower required COF. Older adults also exhibited a lower required COF when walking at a controlled speed without controlling step length. When both age groups walked with the same speed and step length, no age difference in required COF was found. Thus, speed and step length can have a large influence on studies investigating age-related differences in required COF. It was also found that speed and step length have independent and opposite effects on required COF, with step length having a strong positive effect on required COF, and speed having a weaker negative effect.

  17. Investigations of the applicability of a model-supported friction coefficient prediction model in a moving vehicle; Untersuchungen zum Einsatz eines modellunterstuetzten Reibwertvorhersagemodells im fahrenden Fahrzeug

    Energy Technology Data Exchange (ETDEWEB)

    Klempau, F. [TU Darmstadt, Fachgebiet Fahrzeugtechnik (Germany)

    2000-07-01

    In recent years driving-stability- and driver-assistance systems have become more and more common in new cars. Along with this development there is a growing demand for a system predicting the actual friction potential in the tyre contact patch. Within the European research project VERT (VEhicle Road Tyre Interaction) a big number of friction measurements were carried out to define the main influencing parameters of the tyre-road-friction-process. With the help of empirical and physical models it was possible to describe the effect of these main influencing parameters on friction values. The aim of the research work in this project is to implement these models in driving simulations as well as to consider the feasibility to implement them into real cars. This paper presents the possibilities developing a friction prediction model for implementation in a moving vehicle. (orig.) [German] U.a. wegen der zunehmenden Verbreitung von Fahrdynamik- und Fahrerassistenz - Systemen wird der Wunsch nach Kenntnis des Reibwertpotentials zwischen Reifen und Fahrbahn immer dringender. Zur Bestimmung der Einfluesse auf den Reibwert wurden im Rahmen des europaeischen Forschungsprojekts VERT, dessen Partner fzd ist, eine Vielzahl von Messungen durchgefuehrt. Ihre Auswertung ermoeglichte die Bestimmung von Haupteinflussgroessen und die Beschreibung ihrer Auswirkungen auf den Reibwert mittels empirischer und physikalischer (orig.)

  18. Experimental Measurement of the Static Coefficient of Friction at the Ti-Ti Taper Connection in Total Hip Arthroplasty

    NARCIS (Netherlands)

    Bitter, T.; Khan, I.; Marriott, T.; Schreurs, B.W.; Verdonschot, Nicolaas Jacobus Joseph; Janssen, D.

    2016-01-01

    The modular taper junction in total hip replacements has been implicated as a possible source of wear. The finite-element (FE) method can be used to study the wear potential at the taper junction. For such simulations it is important to implement representative contact parameters, in order to

  19. Device measures static friction of magnetic tape

    Science.gov (United States)

    Cole, P. T.

    1967-01-01

    Device measures the coefficient of static friction of magnetic tape over a range of temperatures and relative humidities. It uses a strain gage to measure the force of friction between a reference surface and the tape drawn at a constant velocity of approximately 0.0001 inch per second relative to the reference surface.

  20. Measurement of friction coefficient for various thin films using millimeter-size movers driven by electro-static force. Seiden kudogata bisho mover wo mochiita usumaku no masatsu keisoku

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, M; Watanabe, S; Yoshimura, N [Akita Univ., Akita (Japan); Fujita, H [The University of Tokyo, Tokyo (Japan)

    1992-12-20

    Discussions were given on measurements of coefficients for static friction between different types of thin films. A small light-weight mover of a millimeter size was driven electrostatically to measure friction in a condition close to operation of a micromachine. The thin film materials were fabricated using a sol-gel process, sputtering, vacuum deposition and a CVD process. The materials include Ni, Ti, Al, SiO2, SiNx, Si wafers and glasses. The measured values for Ni-Ni, Al-Al and Ni-Al were larger by from 0.1 to 0.2 than values for bulk. The reason for this would be because of the friction generating mechanisms being different and the sample weight being lighter. Measured values for different types of thin films on silicon wafers were higher. This may be because OH groups are formed on the wafer surface causing high adhesiveness. Values for glasses are small in general. Friction coefficients for SiO2 thin films are small on the whole. However, SiO2-SiO2 showed larger values. This indicates that SiO2 is a useful material for micromechatronics, but proper selection of contacting opponents is important. 7 refs., 4 figs., 7 tabs.

  1. Bottom friction models for shallow water equations: Manning’s roughness coefficient and small-scale bottom heterogeneity

    Science.gov (United States)

    Dyakonova, Tatyana; Khoperskov, Alexander

    2018-03-01

    The correct description of the surface water dynamics in the model of shallow water requires accounting for friction. To simulate a channel flow in the Chezy model the constant Manning roughness coefficient is frequently used. The Manning coefficient nM is an integral parameter which accounts for a large number of physical factors determining the flow braking. We used computational simulations in a shallow water model to determine the relationship between the Manning coefficient and the parameters of small-scale perturbations of a bottom in a long channel. Comparing the transverse water velocity profiles in the channel obtained in the models with a perturbed bottom without bottom friction and with bottom friction on a smooth bottom, we constructed the dependence of nM on the amplitude and spatial scale of perturbation of the bottom relief.

  2. 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....

  3. Phalanx force magnitude and trajectory deviation increased during power grip with an increased coefficient of friction at the hand-object interface.

    Science.gov (United States)

    Enders, Leah R; Seo, Na Jin

    2011-05-17

    This study examined the effect of friction between the hand and grip surface on a person's grip strategy and force generation capacity. Twelve young healthy adults performed power grip exertions on an instrumented vertical cylinder with the maximum and 50% of maximum efforts (far above the grip force required to hold the cylinder), while normal and shear forces at each phalanx of all five fingers in the direction orthogonal to the gravity were recorded. The cylinder surface was varied for high-friction rubber and low-friction paper coverings. An increase in surface friction by replacing the paper covering with the rubber covering resulted in 4% greater mean phalanx normal force (perpendicular to the cylinder surface) and 22% greater mean phalanx shear force in either the proximal or distal direction of the digits (pfriction with the rubber surface compared to the paper surface was associated with a 20% increase in the angular deviation of the phalanx force from the direction normal to the cylinder surface (p<0.05). This study demonstrates that people significantly changed the magnitude and direction of phalanx forces depending on the surface they gripped. Such change in the grip strategy appears to help increase grip force generation capacity. This finding suggests that a seemingly simple power grip exertion involves sensory feedback-based motor control, and that people's power grip capacity may be reduced in cases of numbness, glove use, or injuries resulting in reduced sensation. Copyright © 2011 Elsevier Ltd. All rights reserved.

  4. Frictional properties of jointed welded tuff

    International Nuclear Information System (INIS)

    Teufel, L.W.

    1981-07-01

    The results of the experiments on simulated joints in welded tuff from the Grouse Canyon Member of the Belted Range Tuff warrant the following conclusions: (1) The coefficient of friction of the joints is independent of normal stress at a given sliding velocity. (2) The coefficient of friction increases with both increasing time of stationary contact and decreasing sliding velocity. (3) Time and velocity dependence of friction is due to an increase in the real area of contact on the sliding surface, caused by asperity creep. (4) Joints in water-saturated tuff show a greater time and velocity dependence of friction than those in dehydrated tuff. (5) The enhanced time and velocity dependence of friction with water saturation is a result of increased creep at asperity contacts, which is in turn due to a reduction in the surface indentation hardness by hydrolytic weakening and/or stress corrosion cracking

  5. Effect of the yarn pull-out velocity of shear thickening fluid-impregnated Kevlar fabric on the coefficient of friction

    Energy Technology Data Exchange (ETDEWEB)

    Aikarami, Sh [Dept. of Mechanical and Aerospace Engineering, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Kordani, N. [Dept. of Mechanical Engineering, University of Mazandaran, Mazandaran (Iran, Islamic Republic of); Sadough, Vanini A. [Dept. of Mechanical Engineering, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Amiri, H. [Technical Campus, Tehran South Branch, Islamic Azad University, Tehran(Iran, Islamic Republic of)

    2016-08-15

    This study explains the yarn pull-out process behavior of woven fabrics in relation to their mechanical properties. Empirical research on the relationship between the yarn pull-out behavior and fabric properties are evaluated, along with a detailed comparison of friction between the fabric fibers in static and dynamic modes. Samples are tested in three modes, namely, neat, dissolved liquid, and silica particle- based Shear thickening fluid (STF)-treated fabric. Accordingly, the presence of STF increases friction between the fabrics and the warp and weft yarns, as well as prevents the displacement of the yarns. Increased friction also leads to an increase in the energy absorption of the yarn pull-out process. In this research, the pull-out test has been performed at three different velocities: 50, 250 and 500 mm/min. Results show that increases in the pull-out velocity increase the pull-out force of the neat and dissolved liquid samples. By contrast, the behavior is completely opposite in the STF-treated sample. Comparing the yarn pull-out values indicates that the STF-treated samples have the highest value, which is approximately three times higher than that of the neat sample.

  6. Effect of the yarn pull-out velocity of shear thickening fluid-impregnated Kevlar fabric on the coefficient of friction

    International Nuclear Information System (INIS)

    Aikarami, Sh; Kordani, N.; Sadough, Vanini A.; Amiri, H.

    2016-01-01

    This study explains the yarn pull-out process behavior of woven fabrics in relation to their mechanical properties. Empirical research on the relationship between the yarn pull-out behavior and fabric properties are evaluated, along with a detailed comparison of friction between the fabric fibers in static and dynamic modes. Samples are tested in three modes, namely, neat, dissolved liquid, and silica particle- based Shear thickening fluid (STF)-treated fabric. Accordingly, the presence of STF increases friction between the fabrics and the warp and weft yarns, as well as prevents the displacement of the yarns. Increased friction also leads to an increase in the energy absorption of the yarn pull-out process. In this research, the pull-out test has been performed at three different velocities: 50, 250 and 500 mm/min. Results show that increases in the pull-out velocity increase the pull-out force of the neat and dissolved liquid samples. By contrast, the behavior is completely opposite in the STF-treated sample. Comparing the yarn pull-out values indicates that the STF-treated samples have the highest value, which is approximately three times higher than that of the neat sample

  7. Method for producing ceramic composition having low friction coefficient at high operating temperatures

    Science.gov (United States)

    Lankford, Jr., James

    1988-01-01

    A method for producing a stable ceramic composition having a surface with a low friction coefficient and high wear resistance at high operating temperatures. A first deposition of a thin film of a metal ion is made upon the surface of the ceramic composition and then a first ion implantation of at least a portion of the metal ion is made into the near surface region of the composition. The implantation mixes the metal ion and the ceramic composition to form a near surface composite. The near surface composite is then oxidized sufficiently at high oxidizing temperatures to form an oxide gradient layer in the surface of the ceramic composition.

  8. Friction Properties of Carbon Fiber Brush

    OpenAIRE

    大塚, 由佳; 月山, 陽介; 野老山, 貴行; 梅原, 徳次; OHTSUKA, Yuka; TSUKIYAMA, Yosuke; TOKOROYAMA, Takayuki; UMEHARA, Noritsugu

    2011-01-01

    直径数μmのカーボンファイバーを束ねたカーボンファイバーブラシ材料と金属材料のすべり摩擦におけるすべり出しの摩擦及び平均摩擦特性と,金属同士のそれらの摩擦特性の相違を調べ,カーボンファイバーブラシ材料の摩擦の特異性を明らかにした. Friction properties as initial and average friction coefficient were investigated for carbon brush materials. Experimental results shows that static friction coefficient of carbon fiber brush is smaller than kinetic friction after a macro slip. This phenomena is different from the usual friction properties between metals. I...

  9. CORROSION AND SURFACE PROTECTION IN MACHINE MATERIALS FRICTION HAVE DIFFERENT SURFACE PAIRS EXPERIMENTAL INVESTIGATION OF FACTORS

    Directory of Open Access Journals (Sweden)

    Senai YALCINKAYA

    2017-05-01

    Full Text Available Friction force, normal force, linear change. The normal force varies with the loads on the friction object. In order to determine the friction force and the friction coefficient, the friction object and the friction speed are used. The experimental work was carried out in three stages. In the first stage, the effect of normal force on the friction force was studied. In the second step, the friction force of the friction surface area is influenced. The effect of the change of the shear rate in step 3 on the friction force was investigated. At the last stage, the experimental study of the effect of the material selection on the friction force was made and it was seen that the aluminum / brass surface pair had the smallest friction coefficient as a result of the opening. The greatest coefficient of friction is found in the pair of glass / felt objects.

  10. Correlations for heat transfer coefficient and friction factor for turbulent flow of air through square and hexagonal ducts with twisted tape insert

    Science.gov (United States)

    Yadav, Rupesh J.; Kore, Sandeep S.; Joshi, Prathamesh S.

    2018-05-01

    The experimental and numerical Nusselt number and friction factor investigation for turbulent flow through a non-circular duct with twisted-tape inserts have been presented. The non-circular ducts include square, hexagonal duct. The results of non-circular ducts are compared with circular duct. All the ducts have same equivalent diameter. The twist ratios used for the experiment are Y = 3.5, 4.5, 5.5 and 6.5. Experiments were carried out on square duct, hexagonal duct and circular duct. The Reynolds number lied between 10,000 and 1, 05,000. The present study is restricted to the flow of air at Pr = 0.7 only and within a narrow temperature range of 40 to 75 ΟC, within which the compressible nature of air can be neglected. The results reveal that, both Nusselt number and friction factor increases as the side of non-circular duct increases. Maximum Nusselt number and friction factor is obtained in case of circular duct with twisted tape. Further the correlations of Nu and f are given for different non circular duct with twisted tape insert for engineering applications for the turbulent regime. Since the thermal performance factor (η) is observed to be within the range of 0.8 to 1.13 for both circular and noncircular ducts, the overall benefit of using twisted tape in the flow field shall nevertheless be marginal.

  11. The fuel-cladding interfacial friction coefficient in water-cooled reactor fuel rods

    International Nuclear Information System (INIS)

    Smith, E.

    1979-01-01

    A central problem in the development of cladding failure criteria and of effective operational, design or material remedies is to know whether the cladding stress is enhanced significantly near cladding ridges, pellet chips or fuel pellet cracks; the latter may also be coincident with cladding ridges at pellet-pellet interfaces. As regards the fuel pellet crack source of cladding stress concentration, the magnitude of the uranium dioxide-Zircaloy interfacial friction coefficient μ governs the magnitude and distribution of the enhanced cladding stress. Considerable discussion, particularly at a Post-Conference Seminar associated with the SMIRT 4 Conference, has focussed on the value of μ, the author taking the view that it is unlikely to be large (< 0.5). The reasoning behind this view is as follows. A fuel pellet should fracture during a power ramp when the tensile hoop stress within the pellet exceeds the fuel's fracture stress. Since the preferred position for a fuel pellet crack to form is at the fuel-cladding interface midway between existing fuel cracks, where the interfacial shear stress changes sign, the pellet segment size after a power ramp provides a limit to the magnitude of the interfacial shear stresses and consequently to the value of μ. With this argument as a basis, the author's early work used the Gittus fuel rod model, in which there is a symmetric distribution of fuel pellet cracks and symmetric interfacial slippage, to show that μ < 0.5 if it is assumed that the average hoop stress within the cladding attains yield levels. It was therefore suggested that a high interfacial friction coefficient is unlikely to be operative during a power ramp; this result was used to support the view that interfacial friction effects do not play a dominant role in stress corrosion crack formation within the cladding. (orig.)

  12. Amontonian frictional behaviour of nanostructured surfaces.

    Science.gov (United States)

    Pilkington, Georgia A; Thormann, Esben; Claesson, Per M; Fuge, Gareth M; Fox, Oliver J L; Ashfold, Michael N R; Leese, Hannah; Mattia, Davide; Briscoe, Wuge H

    2011-05-28

    With nanotextured surfaces and interfaces increasingly being encountered in technological and biomedical applications, there is a need for a better understanding of frictional properties involving such surfaces. Here we report friction measurements of several nanostructured surfaces using an Atomic Force Microscope (AFM). These nanostructured surfaces provide well defined model systems on which we have tested the applicability of Amontons' laws of friction. Our results show that Amontonian behaviour is observed with each of the surfaces studied. However, no correlation has been found between measured friction and various surface roughness parameters such as average surface roughness (R(a)) and root mean squared (rms) roughness. Instead, we propose that the friction coefficient may be decomposed into two contributions, i.e., μ = μ(0) + μ(g), with the intrinsic friction coefficient μ(0) accounting for the chemical nature of the surfaces and the geometric friction coefficient μ(g) for the presence of nanotextures. We have found a possible correlation between μ(g) and the average local slope of the surface nanotextures. This journal is © the Owner Societies 2011

  13. Study on friction behaviour of brake shoe materials for mining hoist

    Science.gov (United States)

    Ungureanu, M.; Ungureanu, N. S.; Crăciun, I.

    2017-02-01

    The friction coefficient in the brake linkages has an important influence on the braking efficiency and safety of machines. The paper presents a method for the study of the friction coefficient of the friction couple brake shoe-drum for mining hoist. In this context, it is interesting to define the friction coefficient, not just according to the materials in contact, but according to the entire ensemble of tribological factors of the friction couple.

  14. Friction dependence of shallow granular flows from discrete particle simulations

    NARCIS (Netherlands)

    Thornton, Anthony Richard; Weinhart, Thomas; Luding, Stefan; Bokhove, Onno

    2011-01-01

    A shallow-layer model for granular flows is completed with a closure relation for the macroscopic bed friction or basal roughness obtained from micro-scale discrete particle simulations of steady flows. We systematically vary the bed friction by changing the contact friction coefficient between

  15. Status of Stellite 6 friction testing

    International Nuclear Information System (INIS)

    Watkins, J.C.; DeWall, K.G.

    1998-01-01

    For the past several years, researchers at the Idaho National Engineering and Environmental Laboratory, under the sponsorship of the US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, have been investigating the performance of motor-operated valves subjected to design basis flow and pressure loads. Part of this research addresses the friction that occurs at the interface between the valve disc and the valve body seats during operation of a gate valve. In most gate valves, these surfaces are hardfaced with Stellite 6, a cobalt-based alloy. Analytical methods exist for predicting the thrust needed to operate these valves at specific pressure conditions. To produce accurate valve thrust predictions, the analyst must have a reasonably accurate, though conservative, estimate of the coefficient of friction at the disc-to-seat interface. One of the questions that remains to be answered is whether, and to what extent, aging of the disc and seat surfaces effects the disc-to-seat coefficient of friction. Specifically, does the environment in a nuclear plants piping system cause the accumulation of an oxide film on these surfaces that increases the coefficient of friction; and if so, how great is the increase? This paper presents results of specimen tests addressing this issue, with emphasis on the following: (1) the characteristics and thickness of the oxide film that develops on Stellite 6 as it ages; (2) the change in the friction coefficient of Stellite 6 as it ages, including the question of whether the friction coefficient eventually reaches a plateau; and (3) the effect in-service cycling has on the characteristics and thickness of the oxide film and on the friction coefficient

  16. Friction characteristics for density of micro dimples using photolithography

    International Nuclear Information System (INIS)

    Chae, Young Jun; Kim, Seock Sam

    2005-01-01

    Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple

  17. Chemical origins of frictional aging.

    Science.gov (United States)

    Liu, Yun; Szlufarska, Izabela

    2012-11-02

    Although the basic laws of friction are simple enough to be taught in elementary physics classes and although friction has been widely studied for centuries, in the current state of knowledge it is still not possible to predict a friction force from fundamental principles. One of the highly debated topics in this field is the origin of static friction. For most macroscopic contacts between two solids, static friction will increase logarithmically with time, a phenomenon that is referred to as aging of the interface. One known reason for the logarithmic growth of static friction is the deformation creep in plastic contacts. However, this mechanism cannot explain frictional aging observed in the absence of roughness and plasticity. Here, we discover molecular mechanisms that can lead to a logarithmic increase of friction based purely on interfacial chemistry. Predictions of our model are consistent with published experimental data on the friction of silica.

  18. Internal Friction And Instabilities Of Rotors

    Science.gov (United States)

    Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

    1992-01-01

    Report describes study of effects of internal friction on dynamics of rotors prompted by concern over instabilities in rotors of turbomachines. Theoretical and experimental studies described. Theoretical involved development of nonlinear mathematical models of internal friction in three joints found in turbomachinery - axial splines, Curvic(TM) splines, and interference fits between smooth cylindrical surfaces. Experimental included traction tests to determine the coefficients of friction of rotor alloys at various temperatures, bending-mode-vibration tests of shafts equipped with various joints and rotordynamic tests of shafts with axial-spline and interference-fit joints.

  19. Micromechanical simulation of frictional behaviour in metal forming

    International Nuclear Information System (INIS)

    Zhang, S.; Hodgson, P.D.; Cardew-Hall, M.J.; Kalyanasundaram, S.

    2000-01-01

    Friction is a critical factor for Sheet Metal Forming (SMF). The Coulomb friction model is usually used in most Finite Element (FE) simulation for SMF. However, friction is a function of the local contact deformation conditions, such as local pressure, roughness and relative velocity. This paper will present a micromechanical model that accounts for the local frictional behaviour through finite element simulations performed at the micromechanical level. Frictional behaviour between contact surfaces can be based on three cases: boundary, hydrodynamic and mixed lubrication. In our microscopic friction model based on FEM, the case of boundary lubrication contact between sheet and tool has been considered. In the view of microscopic geometry, roughness depends upon amplitude and wavelength of surface asperities of sheet and tool. The mean pressure applied on the surface differs from the pressure over the actual contact area. The effect of roughness (microscopic geometric condition) and relative speed of contact surfaces on friction coefficient was examined in the FE model for the microscopic friction behaviour. The analysis was performed using an explicit finite element formulation. In this study, it was found that the roughness of deformable sheet decreases during sliding and the coefficient of friction increases with increasing roughness of contact surfaces. The coefficient of friction increases with the increase of relative velocity and adhesive friction coefficient between contact surfaces. (author)

  20. Friction characteristics of hardfacing materials in high temperature sodium

    International Nuclear Information System (INIS)

    Mizobuchi, Syotaro; Kano, Shigeki; Nakayama, Kohichi; Atsumo, Hideo

    1980-01-01

    Friction and self-welding test were conducted on several materials used for the contacting and sliding components of a sodium cooled fast breeder reactor. In the present study, the friction and self-welding characteristics of each material were evaluated through measuring the kinetic and breakaway friction coefficients. The influence of oscillating rotation and vertical reciprocating motion on the friction mode was also investigated. The results obtained are as follows: (1) Colmonoy No.6, the nickel base hardfacing alloy, indicated the lowest kinetic friction coefficient of all the materials in the present study. Also, Cr 3 C 2 /Ni-Cr material prepared by a detonation gun showed the most stable friction behavior. (2) The breakaway friction coefficient of each material was dependent upon dwelling time in a sodium environment. (3) The friction behavior of Cr 3 C 2 /Ni-Cr material was obviously related with the finishing roughness of the friction surface. It was anticipated that nichrome material as the binder of the chrome carbide diffused and exuded to the friction surface by sliding in sodium. (4) The friction coefficient in sliding mode of vertical reciprocating was lower than that of oscillating rotation. (author)

  1. Surface Friction of Polyacrylamide Hydrogel Particles

    Science.gov (United States)

    Cuccia, Nicholas; Burton, Justin

    Polyacrylamide hydrogel particles have recently become a popular system for modeling low-friction, granular materials near the jamming transition. Because a gel consists of a polymer network filled with solvent, its frictional behavior is often explained using a combination of hydrodynamic lubrication and polymer-surface interactions. As a result, the frictional coefficient can vary between 0.001 and 0.03 depending on several factors such as contact area, sliding velocity, normal force, and the gel surface chemistry. Most tribological measurements of hydrogels utilize two flat surfaces, where the contact area is not well-defined. We have built a custom, low-force tribometer to measure the single-contact frictional properties of spherical hydrogel particles on flat hydrogel surfaces under a variety of measurement conditions. At high velocities (> 1 cm/s), the friction coefficient depends linearly on velocity, but does not tend to zero at zero velocity. We also compare our measurements to solid particles (steel, glass, etc.) on hydrogel surfaces, which exhibit larger frictional forces, and show less dependence on velocity. A physical model for the friction which includes the lubrication layer between the deformed surfaces will be discussed. National Science Foundation Grant No. 1506446.

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

    International Nuclear Information System (INIS)

    Kang, Won Seok; Choi, Chan Kyu; Yoo, Hong Hee

    2015-01-01

    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.

  4. The effects of friction on the compressive behaviour of high strength steels

    International Nuclear Information System (INIS)

    Ashton, M.; Parry, D.J.

    1997-01-01

    An investigation, covering a wide range of strain rate and temperature, has been performed into the effects of interfacial friction on the compressive properties of an armour plate steel. In order to calculate the coefficient of friction, ring tests were carried out and the Avitzur analysis applied. In general, coefficients of friction decreased with increasing temperature and strain rate. Other specimen observations indicated the same friction trends. It is essential that friction corrections be applied if meaningful results are to be obtained. (orig.)

  5. Anisotropic Friction of Wrinkled Graphene Grown by Chemical Vapor Deposition.

    Science.gov (United States)

    Long, Fei; Yasaei, Poya; Yao, Wentao; Salehi-Khojin, Amin; Shahbazian-Yassar, Reza

    2017-06-21

    Wrinkle structures are commonly seen on graphene grown by the chemical vapor deposition (CVD) method due to the different thermal expansion coefficient between graphene and its substrate. Despite the intensive investigations focusing on the electrical properties, the nanotribological properties of wrinkles and the influence of wrinkle structures on the wrinkle-free graphene remain less understood. Here, we report the observation of anisotropic nanoscale frictional characteristics depending on the orientation of wrinkles in CVD-grown graphene. Using friction force microscopy, we found that the coefficient of friction perpendicular to the wrinkle direction was ∼194% compare to that of the parallel direction. Our systematic investigation shows that the ripples and "puckering" mechanism, which dominates the friction of exfoliated graphene, plays even a more significant role in the friction of wrinkled graphene grown by CVD. The anisotropic friction of wrinkled graphene suggests a new way to tune the graphene friction property by nano/microstructure engineering such as introducing wrinkles.

  6. Friction measurements of steel on refractory bricks

    International Nuclear Information System (INIS)

    Eiselstein, L.E.

    1981-08-01

    During startup or shutdown of a pool-type LMFBR, substantial shear stresses may arise between the base of the steel reactor vessel and the refractory brick support base. The magnitude of these stresses, which result from differences in thermal expansion, can be estimated if the friction coefficient is known. This report describes experiments to determine friction coefficients between 2 1/4 Cr-1Mo steel and several refractory materials and to examine effects to contact pressure, temperature, sliding velocity, lubricants, and surface condition

  7. Friction

    Science.gov (United States)

    Matsuo, Yoshihiro; Clarke, Daryl D.; Ozeki, Shinichi

    Friction materials such as disk pads, brake linings, and clutch facings are widely used for automotive applications. Friction materials function during braking due to frictional resistance that transforms kinetic energy into thermal energy. There has been a rudimentary evolution, from materials like leather or wood to asbestos fabric or asbestos fabric saturated with various resins such as asphalt or resin combined with pitch. These efforts were further developed by the use of woven asbestos material saturated by either rubber solution or liquid resin binder and functioned as an internal expanding brake, similar to brake lining system. The role of asbestos continued through the use of chopped asbestos saturated by rubber, but none was entirely successful due to the poor rubber heat resistance required for increased speeds and heavy gearing demands of the automobile industry. The use of phenolic resins as binder for asbestos friction materials provided the necessary thermal resistance and performance characteristics. Thus, the utility of asbestos as the main friction component, for over 100 years, has been significantly reduced in friction materials due to asbestos identity as a carcinogen. Steel and other fibrous components have displaced asbestos in disk pads. Currently, non-asbestos organics are the predominate friction material. Phenolic resins continue to be the preferred binder, and increased amounts are necessary to meet the requirements of highly functional asbestos-free disk pads for the automotive industry. With annual automobile production exceeding 70 million vehicles and additional automobile production occurring in developing countries worldwide and increasing yearly, the amount of phenolic resin for friction material is also increasing (Fig. 14.1). Fig. 14.1 Worldwide commercial vehicle production In recent years, increased fuel efficiency of passenger car is required due to the CO2 emission issue. One of the solutions to improve fuel efficiency is to

  8. 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

    Based on the concepts of the friction theory (f-theory) for viscosity modeling, a procedure is introduced for predicting the viscosity of hydrocarbon mixtures rich in one component, which is the case for natural gases. In this procedure, the mixture friction coefficients are estimated with mixing...... 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...... coefficients of the other components are estimated by the one-parameter general f-theory model. The viscosity predictions are performed with the SRK, the PR, and the PRSV equations of state, respectively. For recently measured viscosities of natural gases, the resultant AAD (0.5 to 0.8%) is in excellent...

  9. 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.

  10. Elaboration of high-temperature friction polymer material and study of its wear aspects

    International Nuclear Information System (INIS)

    Gventsadze, L.

    2009-01-01

    High-temperature friction composite material is elaborated and its physical, mechanical and tribologic features are studied. It is shown, that addition to the friction material composition of filling material having nanopores -diatomite-and its modification with polyethilensilan leads to friction materials friction coefficient stability and wear resistance increase at high temperatures (400-600 ℃). (author)

  11. Gas desorption during friction of amorphous carbon films

    International Nuclear Information System (INIS)

    Rusanov, A; Fontaine, J; Martin, J-M; Mogne, T L; Nevshupa, R

    2008-01-01

    Gas desorption induced by friction of solids, i.e. tribodesorption, is one of the numerous physical and chemical phenomena, which arise during friction as result of thermal and structural activation of material in a friction zone. Tribodesorption of carbon oxides, hydrocarbons, and water vapours may lead to significant deterioration of ultra high vacuum conditions in modern technological equipment in electronic, optoelectronic industries. Therefore, knowledge of tribodesorption is crucial for the performance and lifetime of vacuum tribosystems. Diamond-like carbon (DLC) coatings are interesting materials for vacuum tribological systems due to their high wear resistance and low friction. Highly hydrogenated amorphous carbon (a-C:H) films are known to exhibit extremely low friction coefficient under high vacuum or inert environment, known as 'superlubricity' or 'superlow friction'. However, the superlow friction period is not always stable and then tends to spontaneous transition to high friction. It is supposed that hydrogen supply from the bulk to the surface is crucial for establishing and maintaining superlow friction. Thus, tribodesorption can serve also as a new technique to determine the role of gases in superlow friction mechanisms. Desorption of various a-C:H films, deposited by PECVD, ion-beam deposition and deposition using diode system, has been studied by means of ultra-high vacuum tribometer equipped with a mass spectrometer. It was found that in superlow friction period desorption rate was below the detection limit in the 0-85 mass range. However, transition from superlow friction to high friction was accompanied by desorption of various gases, mainly of H 2 and CH 4 . During friction transition, surfaces were heavily damaged. In experiments with DLC films with low hydrogen content tribodesorption was significant during the whole experiment, while low friction was not observed. From estimation of maximum surface temperature during sliding contact it

  12. The influence of the friction coefficients, the power and the flowrate on the two-phase flow instabilities in natural circulation

    International Nuclear Information System (INIS)

    Kerris, A.M.

    1987-04-01

    A study of non-linear effects of a two phases flow instabilities has been done using theoretical and experimental models. The experimental model is based on a boiling channel placed in a water loop of natural convection. Studies of stability, with introduction of fluctuations over different parameters, have been achieved using the two models. The results of the experimental model agree with those of the theoretical model. It was found that the head loss coefficients K I and K E of the inlet and outlet channel respectively, had an influence over the stability of the system. An increase in the former produces an increase in the stability while an increase in the latter has the effect of increasing the instability. In the experiment, oscillations of the flow rate were observed. Two types of oscillations were noticed: (1) small oscillations called pressure drop oscillations, (2) large oscillations called density wave oscillations. A study of the variation of these two types of oscillations with power and the coefficient K I and K E had been achieved. It was found that pressure drop oscillations disappeared with the increase of power and the density waves oscillations increased with the increase of power

  13. 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.

  14. Dry friction of microstructured polymer surfaces inspired by snake skin

    OpenAIRE

    Martina J. Baum; Lars Heepe; Elena Fadeeva; Stanislav N. Gorb

    2014-01-01

    Summary The microstructure investigated in this study was inspired by the anisotropic microornamentation of scales from the ventral body side of the California King Snake (Lampropeltis getula californiae). Frictional properties of snake-inspired microstructured polymer surface (SIMPS) made of epoxy resin were characterised in contact with a smooth glass ball by a microtribometer in two perpendicular directions. The SIMPS exhibited a considerable frictional anisotropy: Frictional coefficients ...

  15. 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)

  16. Identification of GMS friction model without friction force measurement

    International Nuclear Information System (INIS)

    Grami, Said; Aissaoui, Hicham

    2011-01-01

    This paper deals with an online identification of the Generalized Maxwell Slip (GMS) friction model for both presliding and sliding regime at the same time. This identification is based on robust adaptive observer without friction force measurement. To apply the observer, a new approach of calculating the filtered friction force from the measurable signals is introduced. Moreover, two approximations are proposed to get the friction model linear over the unknown parameters and an approach of suitable filtering is introduced to guarantee the continuity of the model. Simulation results are presented to prove the efficiency of the approach of identification.

  17. 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…

  18. Effect of time derivative of contact area on dynamic friction

    OpenAIRE

    Arakawa, Kazuo

    2015-01-01

    This study investigated dynamic friction during oblique impact of a golf ball by evaluating the ball’s angular velocity, contact force, and the contact area between the ball and target. The effect of the contact area on the angular velocities was evaluated, and the results indicated that the contact area plays an important role in dynamic friction. In this study, the dynamic friction force F was given by F= μN+μη.dA/dt, where μ is the coefficient of friction, N is the contact force, dA/dt is ...

  19. 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.

  20. Friction enhancement in concertina locomotion of snakes

    Science.gov (United States)

    Marvi, Hamidreza; Hu, David L.

    2012-01-01

    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. PMID:22728386

  1. Frictional behaviour of high performance fibrous tows: Friction experiments

    NARCIS (Netherlands)

    Cornelissen, Bo; Rietman, Bert; Akkerman, Remko

    2013-01-01

    Tow friction is an important mechanism in the production and processing of high performance fibrous tows. The frictional behaviour of these tows is anisotropic due to the texture of the filaments as well as the tows. This work describes capstan experiments that were performed to measure the

  2. On friction of Nb-Nb pair in He1 and He2

    International Nuclear Information System (INIS)

    Zinenko, S.A.; Karapetyan, S.S.; Silin, A.A.

    1990-01-01

    Peculiarities of manifestation of the effect of anomalous friction of superconductors (AFS) in He1 and He2 are studied. Helium thermodynamic state effect on the character of friction interaction of Nb-Nb pair velocity and reduction ratio for friction coefficient is studied. The intensity of heat removal released from friction contact region is estimated, the necessary and sufficient conditions for AFC effect manifestation are ascertained using characteristic relaxation time concept. Dependences for Nb-Nb pair friction coefficient in a superconducting state on the time of friction interaction in gaseous helium, He1, He2 are presented

  3. Frictional strength of wet and dry montmorillonite

    Science.gov (United States)

    Morrow, C. A.; Moore, D. E.; Lockner, D. A.

    2017-05-01

    Montmorillonite is a common mineral in fault zones, and its low strength relative to other common gouge minerals is important in many models of fault rheology. However, the coefficient of friction, μ, varies with degree of saturation and is not well constrained in the literature due to the difficulty of establishing fully drained or fully dried states in the laboratory. We measured μ of both saturated and oven-dried montmorillonite at normal stresses up to 700 MPa. Care was taken to shear saturated samples slowly enough to avoid pore fluid overpressure. For saturated samples, μ increased from 0.10 to 0.28 with applied effective normal stress, while for dry samples μ decreased from 0.78 to 0.45. The steady state rate dependence of friction, (a - b), was positive, promoting stable sliding. The wide disparity in reported frictional strengths can be attributed to experimental procedures that promote differing degrees of partial saturation or overpressured pore fluid conditions.

  4. Determination of the Frictional Behavior at Compaction of Powder Materials Consisting of Spray-Dried Granules

    Science.gov (United States)

    Staf, Hjalmar; Olsson, Erik; Lindskog, Per; Larsson, Per-Lennart

    2018-03-01

    The frictional behavior during powder compaction and ejection is studied using an instrumented die with eight radial sensors. The average friction over the total powder pillar is used to determine a local friction coefficient at each sensor. By comparing forces at compaction with forces at ejection, it can be shown that the Coulomb's friction coefficient can be described as a function of normal pressure. Also stick phenomena has been investigated in order to assess its influence on the determination of the local friction coefficient.

  5. Transport properties under the influence of finite friction

    Institute of Scientific and Technical Information of China (English)

    展永; 赵同军; 于慧; 宋艳丽

    2002-01-01

    Using the Langevin Monte Carlo method, the influence of friction on the directed motion of a Brownian particle driven by an external noise source is investigated. The results show that the existence and change of the environment friction influence the establishment and development of the steady motion of a Brownian particle derived by non- equilibrium fluctuation. The most probable correlation time, which corresponds to the maximum current, is inversely proportional to the friction coefficient. The abnormal transition of the current with different friction appears because of the coupling between the effective ratchet potential and coloured noise intensity.

  6. Effects of antimony trisulfide (Sb2S3) on sliding friction of automotive brake friction materials

    Science.gov (United States)

    Lee, Wan Kyu; Rhee, Tae Hee; Kim, Hyun Seong; Jang, Ho

    2013-09-01

    The effect of antimony trisulfide (Sb2S3) on the tribological properties of automotive brake friction materials was investigated using a Krauss type tribometer and a 1/5 scale dynamometer with a rigid caliper. Results showed that Sb2S3 improved fade resistance by developing transfer films on the disc surface at elevated temperatures. On the other hand, the rubbing surfaces of the friction material exhibited contact plateaus with a broader height distribution when it contained Sb2S3, indicating fewer contact junctions compared to the friction material with graphite. The friction material with Sb2S3 also exhibited a lower stick-slip propensity than the friction material with graphite. The improved fade resistance with Sb2S3 is attributed to its lubricating capability sustained at high temperatures, while the lower stick-slip propensity of the friction material with Sb2S3 is associated with the slight difference between its static and kinetic coefficients of friction and high normal stiffness.

  7. Skin friction related behaviour of artificial turf systems.

    Science.gov (United States)

    Tay, Sock Peng; Fleming, Paul; Hu, Xiao; Forrester, Steph

    2017-08-01

    The occurrence of skin friction related injuries is an issue for artificial turf sports pitches and remains a barrier to their acceptance. The purpose of this study was to evaluate the current industry standard Securisport® Sports Surface Tester that measures skin surface related frictional behaviour of artificial turf. Little research has been published about the device and its efficacy, despite its widespread use as a standard FIFA test instrument. To achieve a range of frictional behaviours, several "third generation" (3G) carpet and infill combinations were investigated; friction time profiles throughout the Securisport rotations were assessed in combination with independent measurements of skin roughness before and after friction testing via 3D surface scanning. The results indicated that carpets without infill had greatest friction (coefficients of friction 0.97-1.20) while those completely filled with sand or rubber had similar and lower values independent of carpet type (coefficient of friction (COF) ≈0.57). Surface roughness of a silicone skin (s-skin) decreased after friction testing, with the largest change on sand infilled surfaces, indicating an "abrasive" polishing effect. The combined data show that the s-skin is damaged in a surface-specific manner, thus the Securisport COF values appear to be a poor measure of the potential for skin abrasion. It is proposed that the change in s-skin roughness improves assessment of the potential for skin damage when players slide on artificial turf.

  8. Frictional properties of single crystals HMX, RDX and PETN explosives

    International Nuclear Information System (INIS)

    Wu, Y.Q.; Huang, F.L.

    2010-01-01

    The frictional properties of single crystals of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) secondary explosives are examined using a sensitive friction machine. The explosive crystals used for the measurements are at least 3.5 mm wide. The friction coefficients between crystals of the same explosive (i.e., HMX on HMX, etc.), crystals of different explosives (i.e., HMX on RDX, etc.), and each explosive and a well-polished gauge steel surface are determined. The frictional surfaces are also studied under an environmental scanning electron microscope (ESEM) to analyze surface microstructural changes under increasing loading forces. The friction coefficients vary considerably with increasing normal loading forces and are particularly sensitive to slider shapes, crystal roughness and the mechanical properties of both the slider and the sample. With increasing loading forces, most friction experiments show surface damage, consisting of grooves, debris, and nano-particles, on both the slider and sample. In some cases, a strong evidence of a localized molten state is found in the central region of the friction track. Possible mechanisms that affect the friction coefficient are discussed based on microscopic observations.

  9. Frictional performance of ball screw

    International Nuclear Information System (INIS)

    Nakashima, Katuhiro; Takafuji, Kazuki

    1985-01-01

    As feed screws, ball screws have become to be adopted in place of trapezoidal threads. The structure of ball screws is complex, but those are the indispensable component of NC machine tools and machining centers, and are frequently used for industrial robots. As the problems in the operation of ball screws, there are damage, life and the performance related to friction. As to the damage and life, though there is the problem of the load distribution on balls, the results of the research on rolling bearings are applied. The friction of ball screws consists of the friction of balls and a spiral groove, the friction of a ball and a ball, the friction in a ball-circulating mechanism and the viscous friction of lubricating oil. It was decided to synthetically examine the frictional performance of ball screws, such as driving torque, the variation of driving torque, efficiency, the formation of oil film and so on, under the working condition of wide range, using the screws with different accuracy and the nuts of various circuit number. The experimental setup and the processing of the experimental data, the driving performance of ball screws and so on are reported. (Kako, I.)

  10. Psychophysical evaluation of a variable friction tactile interface

    Science.gov (United States)

    Samur, Evren; Colgate, J. Edward; Peshkin, Michael A.

    2009-02-01

    This study explores the haptic rendering capabilities of a variable friction tactile interface through psychophysical experiments. In order to obtain a deeper understanding of the sensory resolution associated with the Tactile Pattern Display (TPaD), friction discrimination experiments are conducted. During the experiments, subjects are asked to explore the glass surface of the TPaD using their bare index fingers, to feel the friction on the surface, and to compare the slipperiness of two stimuli, displayed in sequential order. The fingertip position data is collected by an infrared frame and normal and translational forces applied by the finger are measured by force sensors attached to the TPaD. The recorded data is used to calculate the coefficient of friction between the fingertip and the TPaD. The experiments determine the just noticeable difference (JND) of friction coefficient for humans interacting with the TPaD.

  11. Frictional behaviour of polymer films under mechanical and electrostatic loads

    International Nuclear Information System (INIS)

    Ginés, R; Christen, R; Motavalli, M; Bergamini, A; Ermanni, P

    2013-01-01

    Different polymer foils, namely polyimide, FEP, PFA and PVDF were tested on a setup designed to measure the static coefficient of friction between them. The setup was designed according to the requirements of a damping device based on electrostatically tunable friction. The foils were tested under different mechanically applied forces and showed reproducible results for the static coefficient of friction. With the same setup the measurements were performed under an electric field as the source of the normal force. Up to a certain electric field the values were in good agreement. Beyond this field discrepancies were found. (paper)

  12. Evaluation of deep drawing force under different friction conditions

    Directory of Open Access Journals (Sweden)

    Lăzărescu Lucian

    2017-01-01

    Full Text Available The purpose of this study is to investigate the variation of the required punch load during the deep drawing process under different friction conditions. In this regards, several deep-drawing tests of cylindrical cups were conducted under four friction conditions at the tool–blank interface. The first case was the dry deep-drawing, considered as a reference friction condition, while in the other three cases hydraulic oil, lithium-based grease and animal fat were used as lubricants. For each friction case, three levels of blank holding force were adopted, namely 10, 20 and 25 kN. The finite element simulation of the deep-drawing process was used to generate a set of calibration curves. By overlapping the experimental load-stroke curves on the calibration curves, the friction coefficient was estimated for each friction case.

  13. The coefficient of friction of UHMWPE along an entire walking cycle using a ball-on-disc tribometer under arthrokinematics and loading conditions prescribed by ISO 14243-3:2014.

    Science.gov (United States)

    Barceinas-Sanchez, J D O; Alvarez-Vera, M; Montoya-Santiyanes, L A; Dominguez-Lopez, I; Garcia-Garcia, A L

    2017-01-01

    The observation of tribological phenomena occurring in total knee replacement (TKR) simulators may be obscured by the intrinsic complexity of their operation: the dynamics and kinematics prescribed by the ISO 14243-3:2014 standard, and the geometry of the surfaces involved. On the other hand, evaluating the individual performance of the tribosystem elements may be carried out in simpler apparatuses. An experimental method is presented here, by means of which the arthrokinematics and loading conditions prescribed by the said standard are adapted to a ball-on-disc configuration in order to observe the behavior of the coefficient of friction along an entire walking cycle, using the contact point of an AISI 316L stainless steel ball rolling/sliding on an ultra-high molecular weight polyethylene (UHMWPE) disc, lubricated by a solution of fetal bovine serum, at 37°C. The method was tried on two different testing fluids prepared with protein concentrations of 20g/L, according to the said standard, and 36g/L, as received. The statistical model obtained for the behavior of the COF during the entire walking cycle may be used in numerical simulations of UHMWPE wear, under the conditions established by ISO 14243-3:2014. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Frictional Heating with Time-Dependent Specific Power of Friction

    Directory of Open Access Journals (Sweden)

    Topczewska Katarzyna

    2017-06-01

    Full Text Available In this paper analytical solutions of the thermal problems of friction were received. The appropriate boundary-value problems of heat conduction were formulated and solved for a homogeneous semi–space (a brake disc heated on its free surface by frictional heat fluxes with different and time-dependent intensities. Solutions were obtained in dimensionless form using Duhamel's theorem. Based on received solutions, evolution and spatial distribution of the dimensionless temperature were analyzed using numerical methods. The numerical results allowed to determine influence of the time distribution of friction power on the spatio-temporal temperature distribution in brake disc.

  15. Energy based optimization of viscous–friction dampers on cables

    International Nuclear Information System (INIS)

    Weber, F; Boston, C

    2010-01-01

    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

  16. Fretting friction and wear characteristics of magnetorheological fluid under different magnetic field strengths

    International Nuclear Information System (INIS)

    Zhang, P.; Lee, K.H.; Lee, C.H.

    2017-01-01

    A magnetorheological fluid (MRF) performs differently under different magnetic field strength. This study examined the fretting friction and wear characteristics of MRFs under a range of magnetic field strengths and oscillation frequencies. The fretting friction and wear behaviors of MRF are investigated using a fretting friction and wear tester. The surfaces of specimen are examined by optical microscopy and 3D surface profilometer before and after the tests and wear surface profiles, the wear volume loss and wear coefficient for each magnetic field strength are evaluated. The results show that the friction and wear properties of MRF change according to the magnetic field strength and oscillation frequency. - Highlights: • Fretting friction and wear characteristics of MRF is examined. • The friction coefficients increased with increasing magnetic field strength. • The coefficient of friction decreased with increasing oscillation frequency. • Wear volume and coefficient become worse with increasing magnetic field strength.

  17. Size scaling of static friction.

    Science.gov (United States)

    Braun, O M; Manini, Nicola; Tosatti, Erio

    2013-02-22

    Sliding friction across a thin soft lubricant film typically occurs by stick slip, the lubricant fully solidifying at stick, yielding and flowing at slip. The static friction force per unit area preceding slip is known from molecular dynamics (MD) simulations to decrease with increasing contact area. That makes the large-size fate of stick slip unclear and unknown; its possible vanishing is important as it would herald smooth sliding with a dramatic drop of kinetic friction at large size. Here we formulate a scaling law of the static friction force, which for a soft lubricant is predicted to decrease as f(m)+Δf/A(γ) for increasing contact area A, with γ>0. Our main finding is that the value of f(m), controlling the survival of stick slip at large size, can be evaluated by simulations of comparably small size. MD simulations of soft lubricant sliding are presented, which verify this theory.

  18. Slow rupture of frictional interfaces

    OpenAIRE

    Sinai, Yohai Bar; Brener, Efim A.; Bouchbinder, Eran

    2011-01-01

    The failure of frictional interfaces and the spatiotemporal structures that accompany it are central to a wide range of geophysical, physical and engineering systems. Recent geophysical and laboratory observations indicated that interfacial failure can be mediated by slow slip rupture phenomena which are distinct from ordinary, earthquake-like, fast rupture. These discoveries have influenced the way we think about frictional motion, yet the nature and properties of slow rupture are not comple...

  19. A Pedagogical Model of Static Friction

    OpenAIRE

    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.

  20. Characterization of the dynamic friction of woven fabrics: Experimental methods and benchmark results

    NARCIS (Netherlands)

    Sachs, Ulrich; Akkerman, Remko; Fetfatsidis, K.; Vidal-Sallé, E.; Schumacher, J.; Ziegmann, G.; Allaoui, S.; Hivet, G.; Maron, B.; Vanclooster, K.; Lomov, S.V.

    2014-01-01

    A benchmark exercise was conducted to compare various friction test set-ups with respect to the measured coefficients of friction. The friction was determined between Twintex®PP, a fabric of commingled yarns of glass and polypropylene filaments, and a metal surface. The same material was supplied to

  1. Development of a New Method to Investigate the Dynamic Friction Behavior of Interfaces Using a Kolsky Tension Bar

    International Nuclear Information System (INIS)

    Sanborn, B.; Song, B.; Nishida, E.

    2017-01-01

    In order to understand interfacial interaction of a bi-material during an impact loading event, the dynamic friction coefficient is one of the key parameters that must be characterized and quantified. In this study, a new experimental method to determine the dynamic friction coefficient between two metals was developed by using a Kolsky tension bar and a custom-designed friction fixture. Polyvinylidene fluoride (PVDF) force sensors were used to measure the normal force applied to the friction tribo pairs and the friction force was measured with conventional Kolsky tension bar method. To evaluate the technique, the dynamic friction coefficient between 4340 steel and 7075-T6 aluminum was investigated at an impact speed of approximately 8 m/s. Additionally, the dynamic friction coefficient of the tribo pairs with varied surface roughness was also investigated. The data suggest that higher surface roughness leads to higher friction coefficients at the same speed of 8 m/s.

  2. Optimization of wheel-rail interface friction using top-of-rail friction modifiers: State of the art

    Science.gov (United States)

    Khan, M. Roshan; Dasaka, Satyanarayana Murty

    2018-05-01

    High Speed Railways and Dedicated Freight Corridors are the need of the day for fast and efficient transportation of the ever growing population and freight across long distances of travel. With the increase in speeds and axle loads carried by these trains, wearing out of rails and train wheel sections are a common issue, which is due to the increase in friction at the wheel-rail interfaces. For the cases where the wheel-rail interface friction is less than optimum, as in case of high speed trains with very low axle loads, wheel-slips are imminent and loss of traction occurs when the trains accelerate rapidly or brake all of a sudden. These vast variety of traction problems around the wheel-rail interface friction need to be mitigated carefully, so that the contact interface friction neither ascents too high to cause material wear and need for added locomotive power, nor be on the lower side to cause wheel-slips and loss of traction at high speeds. Top-of-rail friction modifiers are engineered surface coatings applied on top of rails, to maintain an optimum frictional contact between the train wheels and the rails. Extensive research works in the area of wheel-rail tribology have revealed that the optimum frictional coefficients at wheel-rail interfaces lie at a value of around 0.35. Application of top-of-rail (TOR) friction modifiers on rail surfaces add an extra layer of material coating on top of the rails, with a surface frictional coefficient of the desired range. This study reviews the common types of rail friction modifiers, the methods for their application, issues related with the application of friction modifiers, and a guideline on selection of the right class of coating material based on site specific requirements of the railway networks.

  3. Local skin friction coefficients and boundary layer profiles obtained in flight from the XB-70-1 airplane at Mach numbers up to 2.5

    Science.gov (United States)

    Fisher, D. F.; Saltzman, E. J.

    1973-01-01

    Boundary-layer and local friction data for Mach numbers up to 2.5 and Reynolds numbers up to 3.6 x 10 to the 8th power were obtained in flight at three locations on the XB-70-1 airplane: the lower forward fuselage centerline (nose), the upper rear fuselage centerline, and the upper surface of the right wing. Local skin friction coefficients were derived at each location by using (1) a skin friction force balance, (2) a Preston probe, and (3) an adaptation of Clauser's method which derives skin friction from the rake velocity profile. These three techniques provided consistent results that agreed well with the von Karman-Schoenherr relationship for flow conditions that are quasi-two-dimensional. At the lower angles of attack, the nose-boom and flow-direction vanes are believed to have caused the momentum thickness at the nose to be larger than at the higher angles of attack. The boundary-layer data and local skin friction coefficients are tabulated. The wind-tunnel-model surface-pressure distribution ahead of the three locations and the flight surface-pressure distribution ahead of the wing location are included.

  4. 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.

  5. Fingerprints are unlikely to increase the friction of primate fingerpads.

    Science.gov (United States)

    Warman, Peter H; Ennos, A Roland

    2009-07-01

    It is generally assumed that fingerprints improve the grip of primates, but the efficiency of their ridging will depend on the type of frictional behaviour the skin exhibits. Ridges would be effective at increasing friction for hard materials, but in a rubbery material they would reduce friction because they would reduce contact area. In this study we investigated the frictional performance of human fingertips on dry acrylic glass using a modified universal mechanical testing machine, measuring friction at a range of normal loads while also measuring the contact area. Tests were carried out on different fingers, fingers at different angles and against different widths of acrylic sheet to separate the effects of normal force and contact area. The results showed that fingertips behaved more like rubbers than hard solids; their coefficients of friction fell at higher normal forces and friction was higher when fingers were held flatter against wider sheets and hence when contact area was greater. The shear stress was greater at higher pressures, suggesting the presence of a biofilm between the skin and the surface. Fingerprints reduced contact area by a factor of one-third compared with flat skin, however, which would have reduced the friction; this casts severe doubt on their supposed frictional function.

  6. Measurements of average heat-transfer and friction coefficients for subsonic flow of air in smooth tubes at high surface and fluid temperatures

    Science.gov (United States)

    Humble, Leroy V; Lowdermilk, Warren H; Desmon, Leland G

    1951-01-01

    An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through smooth tubes for an over-all range of surface temperature from 535 degrees to 3050 degrees r, inlet-air temperature from 535 degrees to 1500 degrees r, Reynolds number up to 500,000, exit Mach number up to 1, heat flux up to 150,000 btu per hour per square foot, length-diameter ratio from 30 to 120, and three entrance configurations. Most of the data are for heat addition to the air; a few results are included for cooling of the air. The over-all range of surface-to-air temperature ratio was from 0.46 to 3.5.

  7. Chirality-dependent friction of bulk molecular solids.

    Science.gov (United States)

    Yang, Dian; Cohen, Adam E

    2014-08-26

    We show that the solid-solid friction between bulk chiral molecular solids can depend on the relative chirality of the two materials. In menthol and 1-phenyl-1-butanol, heterochiral friction is smaller than homochiral friction, while in ibuprofen, heterochiral friction is larger. Chiral asymmetries in the coefficient of sliding friction vary with temperature and can be as large as 30%. In the three compounds tested, the sign of the difference between heterochiral and homochiral friction correlated with the sign of the difference in melting point between racemate (compound or conglomerate) and pure enantiomer. Menthol and ibuprofen each form a stable racemic compound, while 1-phenyl-1-butanol forms a racemic conglomerate. Thus, a difference between heterochiral and homochiral friction does not require the formation of a stable interfacial racemic compound. Measurements of chirality-dependent friction provide a unique means to distinguish the role of short-range intermolecular forces from all other sources of dissipation in the friction of bulk molecular solids.

  8. The role of frictional strength on plate coupling at the subduction interface

    KAUST Repository

    Tan, Eh; Lavier, Luc L.; Van Avendonk, Harm J. A.; Heuret, Arnauld

    2012-01-01

    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

  9. Friction and wear properties of ZrO2/SiO2 composite nanoparticles

    International Nuclear Information System (INIS)

    Li Wei; Zheng Shaohua; Cao Bingqiang; Ma Shiyu

    2011-01-01

    In this article, the lubrication properties of ZrO 2 /SiO 2 composite nanoparticles modified with aluminum zirconium coupling agent as additives in lubricating oil under variable applied load and concentration fraction were reported. It was demonstrated that the modified nanoparticles as additives in lubrication can effectively improve the lubricating properties. Under an optimized concentration of 0.1 wt%, the average friction coefficient was reduced by 16.24%. This was because the nanoparticles go into the friction zone with the flow of lubricant, and then the sliding friction changed to rolling friction with a result of the reduction of the friction coefficient.

  10. Study on the friction of κ-carrageenan hydrogels in air and aqueous environments.

    Science.gov (United States)

    Kozbial, Andrew; Li, Lei

    2014-03-01

    Understanding the friction mechanism of polysaccharide hydrogels, which is the key component of human cartilage that has very low friction coefficient, is critical to develop next generation artificial joint replacement materials. In this study, the friction of the polysaccharide κ-carrageenan hydrogel was investigated to elucidate the effect of external load, cross-linking density, velocity, and environment on friction. Our experimental results show that (1) coefficient of friction (COF) decreases with normal load in air and remains constant in water, (2) increasing cross-linking density concurrently increases friction and is proportional to Young's modulus, (3) COF increases with testing velocity in both air and water, and (4) friction is reduced in aqueous environment due to the lubricating effect of water. The underlying frictional mechanism is discussed on the basis of water transport from bulk to surface and a previously proposed "repulsion-adsorption" model. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. The friction wear of electrolytic composite coatings

    International Nuclear Information System (INIS)

    Starosta, R.

    2002-01-01

    The article presents the results of investigation of wear of galvanic composite coatings Ni-Al 2 O 3 and Ni-41%Fe-Al 2 O 3 . The diameter of small parts of aluminium oxide received 0.5; 3; 5 μm. Investigations of friction sliding were effected on PT3 device at Technical University of Gdansk. Counter sample constituted a funnel made of steel NC6 (750 HV). Increase of wear coatings together with the rise of iron content in matrix is observed. The rise of sizes of ceramic particles caused decrease of wear of composite coatings, but rise of steel funnel wear. The friction coefficient increased after ceramic particle s were built in coatings. The best wear resistance characterized Ni-41%Fe-Al 2 O 3 coatings containing 2.2x10 6 mm -2 ceramic particles. (author)

  12. A study of kinetic friction: The Timoshenko oscillator

    Science.gov (United States)

    Henaff, Robin; Le Doudic, Gabriel; Pilette, Bertrand; Even, Catherine; Fischbach, Jean-Marie; Bouquet, Frédéric; Bobroff, Julien; Monteverde, Miguel; Marrache-Kikuchi, Claire A.

    2018-03-01

    Friction is a complex phenomenon that is of paramount importance in everyday life. We present an easy-to-build and inexpensive experiment illustrating Coulomb's law of kinetic friction. The so-called friction, or Timoshenko, oscillator consists of a plate set into periodic motion through the competition between gravity and friction on its rotating supports. The period of such an oscillator gives a measurement of the coefficient of kinetic friction μk between the plate and the supports. Our prototype is mainly composed of a motor, LEGO blocks, and a low-cost microcontroller, but despite its simplicity, the results obtained are in good agreement with values of μk found in the literature (enhanced online).

  13. Skin friction under pressure. The role of micromechanics

    Science.gov (United States)

    Leyva-Mendivil, Maria F.; Lengiewicz, Jakub; Limbert, Georges

    2018-03-01

    The role of contact pressure on skin friction has been documented in multiple experimental studies. Skin friction significantly raises in the low-pressure regime as load increases while, after a critical pressure value is reached, the coefficient of friction of skin against an external surface becomes mostly insensitive to contact pressure. However, up to now, no study has elucidated the qualitative and quantitative nature of the interplay between contact pressure, the material and microstructural properties of the skin, the size of an indenting slider and the resulting measured macroscopic coefficient of friction. A mechanistic understanding of these aspects is essential for guiding the rational design of products intended to interact with the skin through optimally-tuned surface and/or microstructural properties. Here, an anatomically-realistic 2D multi-layer finite element model of the skin was embedded within a computational contact homogenisation procedure. The main objective was to investigate the sensitivity of macroscopic skin friction to the parameters discussed above, in addition to the local (i.e. microscopic) coefficient of friction defined at skin asperity level. This was accomplished via the design of a large-scale computational experiment featuring 312 analyses. Results confirmed the potentially major role of finite deformations of skin asperities on the resulting macroscopic friction. This effect was shown to be modulated by the level of contact pressure and relative size of skin surface asperities compared to those of a rigid slider. The numerical study also corroborated experimental observations concerning the existence of two contact pressure regimes where macroscopic friction steeply and non-linearly increases up to a critical value, and then remains approximately constant as pressure increases further. The proposed computational modelling platform offers attractive features which are beyond the reach of current analytical models of skin

  14. Slow rupture of frictional interfaces

    Science.gov (United States)

    Bar Sinai, Yohai; Brener, Efim A.; Bouchbinder, Eran

    2012-02-01

    The failure of frictional interfaces and the spatiotemporal structures that accompany it are central to a wide range of geophysical, physical and engineering systems. Recent geophysical and laboratory observations indicated that interfacial failure can be mediated by slow slip rupture phenomena which are distinct from ordinary, earthquake-like, fast rupture. These discoveries have influenced the way we think about frictional motion, yet the nature and properties of slow rupture are not completely understood. We show that slow rupture is an intrinsic and robust property of simple non-monotonic rate-and-state friction laws. It is associated with a new velocity scale cmin, determined by the friction law, below which steady state rupture cannot propagate. We further show that rupture can occur in a continuum of states, spanning a wide range of velocities from cmin to elastic wave-speeds, and predict different properties for slow rupture and ordinary fast rupture. Our results are qualitatively consistent with recent high-resolution laboratory experiments and may provide a theoretical framework for understanding slow rupture phenomena along frictional interfaces.

  15. Improvement of the mechanical and frictional properties of steels by continuous and pulsed ion irradiation

    International Nuclear Information System (INIS)

    Romanov, I.G.

    1992-01-01

    Effect of continuous and powerful pulsed ion beams (PIB) on structural, mechanical, tribological properties and surface morphology of steels were investigated. The results obtained demonstrate the significant influence of ion irradiation type on microhardness, friction coefficient, wear resistance and surface roughness characteristics. Friction coefficient variation in irradiated steels is interpreted within the framework of an adhesion-deformation model

  16. Effect of Friction Model and Tire Maneuvering on Tire-Pavement Contact Stress

    OpenAIRE

    Haichao Zhou; Guolin Wang; Yangmin Ding; Jian Yang; Chen Liang; Jing Fu

    2015-01-01

    This paper aims to simulate the effects of different friction models on tire braking. A truck radial tire (295/80R22.5) was modeled and the model was validated with tire deflection. An exponential decay friction model that considers the effect of sliding velocity on friction coefficients was adopted for analyzing braking performance. The result shows that the exponential decay friction model used for evaluating braking ability meets design requirements of antilock braking system (ABS). The ti...

  17. [Evaluation of orthodontic friction using a tribometer with alternating movement].

    Science.gov (United States)

    Pernier, C M; Jablonska-Mazanek, E D; Ponsonnet, L; Grosgogeat, B

    2005-12-01

    It is essential for orthodontists to control the complex phenomenon of friction. The in vitro techniques, usually dynamometers or tensile testing machines, used to measure the frictional resistance between arch wires and brackets are linear and unidirectional and can be criticised because tooth movements, such as tipping and uprighting, as well everyday oral activities, primarily chewing, are not uni-dimensional but more closely resemble the small amplitude oscillatory phenomena known as fretting. We therefore decided to develop a fretting machine not with linear but with alternating movements better suited to evaluate the frictional behaviour of orthodontic bracket-wire combinations. Once we had completed construction of this device, we proceeded to measure the frictional resistance between one stainless steel bracket (MicroArch GAC) and five wires currently used in orthodontics (Two nickel-titanium shape memory alloys: Neo Sentalloy and Neo Sentalloy with Ionguard GAC--Three titanium-molybdenum alloys: TMA and Low Friction TMA Ormco and Resolve GAC). We were able to set up a classification of the wires according to their coefficient of friction, demonstrating the inefficacy of ion implantation and quantifying the increase in the coefficient of friction which occurs when Resolve wires are placed in the oral environment for approximately one year.

  18. Dry friction of microstructured polymer surfaces inspired by snake skin

    Directory of Open Access Journals (Sweden)

    Martina J. Baum

    2014-07-01

    Full Text Available The microstructure investigated in this study was inspired by the anisotropic microornamentation of scales from the ventral body side of the California King Snake (Lampropeltis getula californiae. Frictional properties of snake-inspired microstructured polymer surface (SIMPS made of epoxy resin were characterised in contact with a smooth glass ball by a microtribometer in two perpendicular directions. The SIMPS exhibited a considerable frictional anisotropy: Frictional coefficients measured along the microstructure were about 33% lower than those measured in the opposite direction. Frictional coefficients were compared to those obtained on other types of surface microstructure: (i smooth ones, (ii rough ones, and (iii ones with periodic groove-like microstructures of different dimensions. The results demonstrate the existence of a common pattern of interaction between two general effects that influence friction: (1 molecular interaction depending on real contact area and (2 the mechanical interlocking of both contacting surfaces. The strongest reduction of the frictional coefficient, compared to the smooth reference surface, was observed at a medium range of surface structure dimensions suggesting a trade-off between these two effects.

  19. Dry friction of microstructured polymer surfaces inspired by snake skin.

    Science.gov (United States)

    Baum, Martina J; Heepe, Lars; Fadeeva, Elena; Gorb, Stanislav N

    2014-01-01

    The microstructure investigated in this study was inspired by the anisotropic microornamentation of scales from the ventral body side of the California King Snake (Lampropeltis getula californiae). Frictional properties of snake-inspired microstructured polymer surface (SIMPS) made of epoxy resin were characterised in contact with a smooth glass ball by a microtribometer in two perpendicular directions. The SIMPS exhibited a considerable frictional anisotropy: Frictional coefficients measured along the microstructure were about 33% lower than those measured in the opposite direction. Frictional coefficients were compared to those obtained on other types of surface microstructure: (i) smooth ones, (ii) rough ones, and (iii) ones with periodic groove-like microstructures of different dimensions. The results demonstrate the existence of a common pattern of interaction between two general effects that influence friction: (1) molecular interaction depending on real contact area and (2) the mechanical interlocking of both contacting surfaces. The strongest reduction of the frictional coefficient, compared to the smooth reference surface, was observed at a medium range of surface structure dimensions suggesting a trade-off between these two effects.

  20. Friction tensor concept for textured surfaces

    Indian Academy of Sciences (India)

    Directionality of grinding marks influences the coefficient of friction ... Menezes et al (2006a,b) studied the effect of roughness parameters and grinding angle on ... as coefficient of friction, sliding velocity, normal load, hardness and thermal.

  1. 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

  2. Machine Learning of Fault Friction

    Science.gov (United States)

    Johnson, P. A.; Rouet-Leduc, B.; Hulbert, C.; Marone, C.; Guyer, R. A.

    2017-12-01

    We are applying machine learning (ML) techniques to continuous acoustic emission (AE) data from laboratory earthquake experiments. Our goal is to apply explicit ML methods to this acoustic datathe AE in order to infer frictional properties of a laboratory fault. The experiment is a double direct shear apparatus comprised of fault blocks surrounding fault gouge comprised of glass beads or quartz powder. Fault characteristics are recorded, including shear stress, applied load (bulk friction = shear stress/normal load) and shear velocity. The raw acoustic signal is continuously recorded. We rely on explicit decision tree approaches (Random Forest and Gradient Boosted Trees) that allow us to identify important features linked to the fault friction. A training procedure that employs both the AE and the recorded shear stress from the experiment is first conducted. Then, testing takes place on data the algorithm has never seen before, using only the continuous AE signal. We find that these methods provide rich information regarding frictional processes during slip (Rouet-Leduc et al., 2017a; Hulbert et al., 2017). In addition, similar machine learning approaches predict failure times, as well as slip magnitudes in some cases. We find that these methods work for both stick slip and slow slip experiments, for periodic slip and for aperiodic slip. We also derive a fundamental relationship between the AE and the friction describing the frictional behavior of any earthquake slip cycle in a given experiment (Rouet-Leduc et al., 2017b). Our goal is to ultimately scale these approaches to Earth geophysical data to probe fault friction. References Rouet-Leduc, B., C. Hulbert, N. Lubbers, K. Barros, C. Humphreys and P. A. Johnson, Machine learning predicts laboratory earthquakes, in review (2017). https://arxiv.org/abs/1702.05774Rouet-LeDuc, B. et al., Friction Laws Derived From the Acoustic Emissions of a Laboratory Fault by Machine Learning (2017), AGU Fall Meeting Session S025

  3. 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.

  4. The effects of aging on friction of MOVs

    International Nuclear Information System (INIS)

    Hunt, T.H.; Sinha, U.P.

    1991-01-01

    This report studied the effect of three aging mechanisms: corrosion, erosion, and deposition on the friction coefficients of the sliding surfaces of motor-operated valves (MOVs) used in nuclear plant systems. The US Nuclear Regulatory Commission (NRC) sponsored the study, and it was performed following the guidelines of their Nuclear Plant Aging Research (NPAR) program. The authors reached three general conclusions: corrosion and deposition should not prevent valve operation by obstructing the mechanical tolerances of the MOVs; the aging mechanisms may increase the friction coefficients due to roughening the surfaces with age; and the codes and standards defining MOV surveillance requirements need review to include methods for detecting aging degradation

  5. How brucite may affect the frictional properties of serpentinite

    Science.gov (United States)

    Moore, Diane E.; Lockner, David A.; Iwata, K.; Tanaka, H.; Byerlee, J.D.

    2001-01-01

    The frictional strength of brucite gouge has been measured at hydrothermal conditions to 450°C. At room temperature, brucite has a coefficient of friction, μ ≈ 0.30, making it one of the weakest minerals identified to date. With increasing temperature at a constant effective normal stress, the coefficient of friction of brucite decreases to a minimum of μ ≈ 0.20 near 300°C, and μ ≈ 0.22–0.24 in the temperature range 350–450°C. Brucite has a sheeted crystal structure, and its low frictional strength may be attributed to the relatively weak bonds between the layers. In addition, the temperature dependence of μ to ≈300°C can be explained in terms of the anomalously large coefficient of thermal expansion of brucite, which will further weaken the interlayer bonds. Brucite is a common constituent of serpentinite, and at ≈300°C, where brucite is weakest, all the major serpentine minerals have μ ≥ 0.5. The maximum expected brucite content of a serpentinite is close to 20% by weight or volume. That amount of disseminated brucite will lower the coefficient of friction of serpentinite by ≤10–15% in the deeper parts of the seismogenic zone. However, the effect will be much greater if shear can be concentrated along brucite-lined slip surfaces in the serpentinite body.

  6. Reduction of friction stress of ethylene glycol by attached hydrogen ions

    Science.gov (United States)

    Li, Jinjin; Zhang, Chenhui; Deng, Mingming; Luo, Jianbin

    2014-01-01

    In the present work, it is shown that the friction stress of ethylene glycol can decrease by an order of magnitude to achieve superlubricity if there are hydrogen ions attached on the friction surfaces. An ultra-low friction coefficient (μ = 0.004) of ethylene glycol between Si3N4 and SiO2 can be obtained with the effect of hydrogen ions. Experimental result indicates that the hydrogen ions adsorbed on the friction surfaces forming a hydration layer and the ethylene glycol in the contact region forming an elastohydrodynamic film are the two indispensable factors for the reduction of friction stress. The mechanism of superlubricity is attributed to the extremely low shear strength of formation of elastohydrodynamic film on the hydration layer. This finding may introduce a new approach to reduce friction coefficient of liquid by attaching hydrogen ions on friction surfaces. PMID:25428584

  7. Friction and wear behaviour of ion beam modified ceramics

    International Nuclear Information System (INIS)

    Lankford, J.; Wei, W.; Kossowsky, R.

    1987-01-01

    In the present study, the sliding friction coefficients and wear rates of carbide, oxide, and nitride materials for potential use as sliding seals (ring/liner) were measured under temparature, environmental, velocity, and loading conditions representative of a diesel engine. In addition, silicon nitride and partially stabilized zirconia discs were modified by ion mixing with TiNi, nickel, cobalt and chromium, and subsequently run against carbide pins, with the objective of producing reduced friction via solid lubrication at elevated temperature. Unmodified ceramic sliding couples were characterized at all temperatures by friction coefficients of 0.24 and above. However, the coefficient at 800 0 C in an oxidizing environment was reduced to below 0.1, for certain material combinations, by the ion implantation of TiNi or cobalt. This beneficial effect was found to derive from lubricious titanium, nickel, and cobalt oxides. (author)

  8. Friction and wear behaviour of ion beam modified ceramics

    Science.gov (United States)

    Lankford, J.; Wei, W.; Kossowsky, R.

    1987-01-01

    In the present study, the sliding friction coefficients and wear rates of carbide, oxide, and nitride materials for potential use as sliding seals (ring/liner) were measured under temperature, environmental, velocity, and loading conditions representative of a diesel engine. In addition, silicon nitride and partially stabilized zirconia discs were modified by ion mixing with TiNi, nickel, cobalt and chromium, and subsequently run against carbide pins, with the objective of producing reduced friction via solid lubrication at elevated temperature. Unmodified ceramic sliding couples were characterized at all temperatures by friction coefficients of 0.24 and above. However, the coefficient at 800 C in an oxidizing environment was reduced to below 0.1, for certain material combinations, by the ion implantation of TiNi or cobalt. This beneficial effect was found to derive from lubricious titanium, nickel, and cobalt oxides.

  9. Effect of hexagonal boron nitride and calcined petroleum coke on friction and wear behavior of phenolic resin-based friction composites

    International Nuclear Information System (INIS)

    Yi Gewen; Yan Fengyuan

    2006-01-01

    Calcined petroleum coke (CPC) and hexagonal boron nitride (h-BN) were used as the friction modifiers to improve the friction and wear properties of phenolic resin-based friction composites. Thus, the composites with different relative amounts of CPC and h-BN as the friction modifiers were prepared by compression molding. The hardness and bending strength of the friction composites were measured. The friction and wear behaviors of the composites sliding against cast iron at various temperatures were evaluated using a pin-on-disc test rig. The worn surfaces and wear debris of the friction composites were analyzed by means of scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. It was found that the hybrid of the two friction modifiers was effective to significantly decrease the wear rate and stabilize the friction coefficient of the friction composites at various temperatures by forming a uniform lubricating and/or transferred film on the rubbing surfaces. The uniform and durable transfer films were also able to effectively diminish the direct contact between the friction composite and the cast iron counterpart and hence prevent severe wear of the latter as well. The effectiveness of the hybrid of CPC and h-BN in improving the friction and wear behavior of the phenolic resin-based friction modifiers could be attributed to the complementary action of the 'low temperature' lubricity of CPC and the 'high temperature' lubricity of h-BN. The optimum ratio of the two friction modifiers CPC and h-BN in the friction composites was suggested to be 1:1, and the corresponding friction composite showed the best friction-reducing and antiwear abilities

  10. 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.

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

    International Nuclear Information System (INIS)

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

    2011-01-01

    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 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Aal, H A [Arts et Metier ParisTech, Rue Saint Dominique BP 508, 51006 Chalons-en-Champagne (France); Vargiolu, R; Zahouani, H [Laboratoire de Tribology et Dynamique des Systemes, UMR CNRS 5513, ENI Saint Etienne - Ecole Centrale de Lyon -36 Avenue Guy de Collongue, 69131 Ecully cedex. France (France); Mansori, M El, E-mail: Hisham.abdel-aal@ensam.eu [Ecole Nationale Superieure d' Arts et Metiers, 2, cours des Arts et Metiers - 13617 Aix en Provence cedex 1 (France)

    2011-08-19

    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.

  13. [Study of friction and loosening in hip endoprostheses].

    Science.gov (United States)

    Dovzak Bajs, Ivana; Cvjetko, Ivan; Car, Dolores; Kokić, Visnja

    2002-01-01

    Like any other operative procedure, the implantation of hip prosthesis is associated with certain complications, which diminishes the value and purpose of such a procedure. One of the complications in artificial hip implantation is loosening of the alloplastic material. Therefore, the aim of this study was to examine the effect of lubrication on the torsional moment and its role in the loosening of the femoral component, using an experimental mechanical model. The following hypothesis was tested: the magnitude of torsional loading in the "bone-endoprosthesis-bone cement system" is similar to any other known loading. The testing device was constructed with the possibility of simulation of positions similar to original performances in the implanted hip prosthesis. It refers primarily to the possibilities of achieving definite forces and velocities. The intention was to point quantitatively to the role of friction moment between the acetabular and femoral endoprosthesis part. Trials were conducted by combining 7 types of loading and 4 kinds of lubrication: dry, water, plasma, and light oil. The testing joint (Ring's prosthesis) was connected through tensometric measuring shaft upon the working forepart oscillating mechanism. Graded by the changeable static loading by means of the pendulum and via lever mechanism the testing joint was loaded by force from 610 to 7137 N. As the cause of friction resistance in the moving joint, torque deformaties of the measuring shaft occurred. The testing joint enabled oscillating movement using a four-part mechanism. In this way, it was possible to define not only the maximum values of the frictional moment (or the coefficient of friction) during one movement cycle but also to examine its relation to the kind of lubrication. Change in the measuring torsional moment were computer recorded. Before each trial, the gauging of the complete outfit was performed. Thereafter, cleaning of the frictional surfaces of the whole outfit was done

  14. 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 conical...... curves are obtained by rigid-plastic FEM simulations in a combined forward rod-backward can extrusion process for a reduction in area R-b = 25, 50 and 70 percent in the backward can extrusion. It is confirmed that the friction factor m(p) on the punch nose in the backward cart extrusion has almost...... 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....

  15. Friction, Free Axes of Rotation and Entropy

    Directory of Open Access Journals (Sweden)

    Alexander Kazachkov

    2017-03-01

    Full Text Available Friction forces acting on rotators may promote their alignment and therefore eliminate degrees of freedom in their movement. The alignment of rotators by friction force was shown by experiments performed with different spinners, demonstrating how friction generates negentropy in a system of rotators. A gas of rigid rotators influenced by friction force is considered. The orientational negentropy generated by a friction force was estimated with the Sackur-Tetrode equation. The minimal change in total entropy of a system of rotators, corresponding to their eventual alignment, decreases with temperature. The reported effect may be of primary importance for the phase equilibrium and motion of ubiquitous colloidal and granular systems.

  16. Experimental study of flow friction characteristics of integral pin-fin tubes

    International Nuclear Information System (INIS)

    Ding Ming; Yan Changqi; Sun Licheng

    2007-01-01

    Friction characteristics of integral pin-fin tubes, through which lubricating-oil flowed vertically, were studied experimentally. Effects of the pitch, the height of fins and the machining direction on friction coefficient were analyzed. The experimental results showed that the friction coefficient of the integral pin-fro tube was obviously lager than that of smooth tube. Compared with other influential factors, the effect of the height of fins was dominant. Because the three-dimensional pin fin could disturb and destroy the boundary layer, when the Reynolds Number reached 200-300, the friction coefficient curve began to bend, that was, a turning point was appeared in the friction coefficient curve. (authors)

  17. Friction and wear of some ferrous-base metallic glasses

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1984-01-01

    Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminium oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

  18. Investigation into the Friction and Roughness Properties of Prints Using Conventional and UV Inks

    Directory of Open Access Journals (Sweden)

    Giedrė Giraitytė

    2015-03-01

    Full Text Available The article experimentally investigates the properties of offset print friction and determines static and kinetic coeffi­cients of friction. Conventional and UV inks have been found to increase the static friction coefficient and re­duce the kinetic friction coefficient between paper and print. The roughness pro­perties of two different types of paper and prints using conventional and UV inks have been examined and compared thus determining that conventional inks strongly increase the roughness of print surface and that the influence of UV inks depend on the type of paper.

  19. Friction Properties of Surface-Fluorinated Carbon Nanotubes

    Science.gov (United States)

    Wal, R. L. Vander; Miyoshi, K.; Street, K. W.; Tomasek, A. J.; Peng, H.; Liu, Y.; Margrave, J. L.; Khabashesku, V. N.

    2005-01-01

    Surface modification of the tubular or sphere-shaped carbon nanoparticles through chemical treatment, e.g., fluorination, is expected to significantly affect their friction properties. In this study, a direct fluorination of the graphene-built tubular (single-walled carbon nanotubes) structures has been carried out to obtain a series of fluorinated nanotubes (fluoronanotubes) with variable C(n)F (n =2-20) stoichiometries. The friction coefficients for fluoronanotubes, as well as pristine and chemically cut nanotubes, were found to reach values as low as 0.002-0.07, according to evaluation tests run in contact with sapphire in air of about 40% relative humidity on a ball-on-disk tribometer which provided an unidirectional sliding friction motion. These preliminary results demonstrate ultra-low friction properties and show a promise in applications of surface modified nanocarbons as a solid lubricant.

  20. Friction and wear properties of diamonds and diamond coatings

    International Nuclear Information System (INIS)

    Hayward, I.P.

    1991-01-01

    The recent development of chemical vapor deposition techniques for diamond growth enables bearings to be designed which exploit diamond's low friction and extreme resistance to wear. However, currently produced diamond coatings differ from natural diamond surfaces in that they are polycrystalline and faceted, and often contain appreciable amounts of non-diamond material (i.e. graphitic or amorphous carbon). Roughness, in particular, influences the friction and wear properties; rough coatings severely abrade softer materials, and can even wear natural diamond sliders. Nevertheless, the best available coatings exhibit friction coefficients as low as those of natural diamond and are highly resistant to wear. This paper reviews the tribological properties of natural diamond, and compares them with those of chemical vapor deposited diamond coatings. Emphasis is placed on the roles played by roughness and material transfer in controlling frictional behavior. (orig.)

  1. Frictional properties of self-adaptive chromium doped tungsten–sulfur–carbon coatings at nanoscale

    Energy Technology Data Exchange (ETDEWEB)

    Zekonyte, J., E-mail: j.zekonyte@soton.ac.uk [National Centre for Advanced Tribology, Faculty of Engineering and Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Cavaleiro, A. [SEG-CEMUC – Department of Mechanical Engineering, University of Coimbra, Rua Luís Reis Santos, P-3030 788 Coimbra (Portugal); Polcar, T. [National Centre for Advanced Tribology, Faculty of Engineering and Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, Prague 6 (Czech Republic)

    2014-06-01

    Transition metal dichalcogenides (TMD) are excellent dry lubricants forming thin (∼10 nm) tribolayer that simultaneously protects the coating from environmental attack and provides low friction. In this paper, we focus on nanoscale frictional properties of chromium doped tungsten–sulfur–carbon (WSC–Cr) coatings with various Cr content. Friction force microscopy was used to investigate friction force as a function of load. A non-linear contact area dependence on the normal force was observed. The calculated interfacial shear strength was relatively low in the region of 70–99 MPa. Friction coefficient decreased with increased applied load independently of chromium content in the coatings.

  2. Tribological characterization of the drill collars and casing friction couples

    Science.gov (United States)

    Ripeanu, R. G.; Badicioiu, M.; Caltaru, M.; Dinita, A.; Laudacescu, E.

    2018-01-01

    Drill collars are special pipes used in the drilling of wells for weighting the drill bit, enabling it to drill through the rock. In the drilling process, the drill collars are exposed to an intensive wear due to friction on inner surface of casing wall. In order to evaluate the tribological behaviour of this friction couple, paper presents the drill collars parent material, reconditioned and casing pipe chemical composition, microstructures, hardness and friction tests. For friction tests were prepared samples extracted from new and reconditioned drill collars and from casing pipes and tested on a universal tribometer. Were used plane-on-disk surface friction couples and tests were conducted at two sliding speeds and three normal loads for each materials couple. Plane static partner samples were extracted from casing pipes and disks samples were extracted from new and reconditioned drill collars. Were obtained friction coefficients values and also the temperatures increasing values due to friction working tests parameters. The temperature increasing values were obtained by measuring it with an infrared thermographic camera.

  3. Study on the property of low friction complex graphite-like coating containing tantalum

    Science.gov (United States)

    Wang, Zuoping; Feng, Lajun; Shen, Wenning

    2018-03-01

    In order to enhance equipment lifetime under low oil or even dry conditions, tantalum was introduced into the graphite-like coating (GLC) by sputtering mosaic targets. The results showed that the introduction of Ta obviously reduced the friction coefficient and hardness of the GLC, while improved the wearability. When the atomic percentage of Ta was larger than 3%, the steady friction coefficient was lower than 0.01, suggesting the coating exhibited super lubricity. When the content of Ta was about 5.0%, the average friction coefficient was 0.02 by a sliding friction test under load of 20 N in unlubricated condition. Its average friction coefficient reduced by 75%, compared with that of control GLC (0.0825).

  4. A multivariable model for predicting the frictional behaviour and hydration of the human skin.

    Science.gov (United States)

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

    2013-08-01

    The frictional characteristics of skin-object interactions are important when handling objects, in the assessment of perception and comfort of products and materials and in the origins and prevention of skin injuries. In this study, based on statistical methods, a quantitative model is developed that describes the friction behaviour of human skin as a function of the subject characteristics, contact conditions, the properties of the counter material as well as environmental conditions. Although the frictional behaviour of human skin is a multivariable problem, in literature the variables that are associated with skin friction have been studied using univariable methods. In this work, multivariable models for the static and dynamic coefficients of friction as well as for the hydration of the skin are presented. A total of 634 skin-friction measurements were performed using a recently developed tribometer. Using a statistical analysis, previously defined potential influential variables were linked to the static and dynamic coefficient of friction and to the hydration of the skin, resulting in three predictive quantitative models that descibe the friction behaviour and the hydration of human skin respectively. Increased dynamic coefficients of friction were obtained from older subjects, on the index finger, with materials with a higher surface energy at higher room temperatures, whereas lower dynamic coefficients of friction were obtained at lower skin temperatures, on the temple with rougher contact materials. The static coefficient of friction increased with higher skin hydration, increasing age, on the index finger, with materials with a higher surface energy and at higher ambient temperatures. The hydration of the skin was associated with the skin temperature, anatomical location, presence of hair on the skin and the relative air humidity. Predictive models have been derived for the static and dynamic coefficient of friction using a multivariable approach. These

  5. Friction and wear performance of low-friction carbon coatings under oil lubrication

    International Nuclear Information System (INIS)

    Kovalchenko, A.; Ajayi, O. O.; Erdemir, A.; Fenske, G. R.

    2001-01-01

    Amorphous carbon coatings with very low friction properties were recently developed at Argonne National Laboratory. These coatings have shown good promise in mitigating excessive wear and scuffing problems associated with low-lubricity diesel fuels. To reduce the negative effect of sulfur and other lubricant additives in poisoning the after-treatment catalyst, a lubricant formulation with a low level of sulfur may be needed. Exclusion of proven sulfur-containing extreme pressure (EP) and antiwear additives from oils will require other measures to ensure durability of critical lubricated components. The low-friction carbon coating has the potential for such applications. In the present study, we evaluated the friction and wear attributes of three variations of the coating under a boundary lubrication regime. Tests were conducted with both synthetic and mineral oil lubricants using a ball-on-flat contact configuration in reciprocating sliding. Although the three variations of the coating provided modest reductions in friction coefficient, they all reduced wear substantially compared to an uncoated surface. The degradation mode of oxidative wear on the uncoated surface was replaced by a polishing wear mode on the coated surfaces

  6. 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....

  7. Friction characteristics of the curved sidewall surfaces of a rotary MEMS device in oscillating motion

    International Nuclear Information System (INIS)

    Wu, Jie; Wang, Shao; Miao, Jianmin

    2009-01-01

    A MEMS device with a configuration similar to that of a micro-bearing was developed to study the friction behavior of the curved sidewall surfaces. This friction-testing device consists of two sets of actuators for normal motion and rotation, respectively. Friction measurements were performed at the curved sidewall surfaces of single-crystal silicon. Two general models were developed to determine the equivalent tangential stiffness of the bush-flexure assembly at the contact point by reducing a matrix equation to a one-dimensional formulation. With this simplification, the motions of the contacting surfaces were analyzed by using a recently developed quasi-static stick-slip model. The measurement results show that the coefficient of static friction exhibits a nonlinear dependence on the normal load. The true coefficient of static friction was determined by fitting the experimental friction curve

  8. Assessment of friction between a rolling cylindrical element and a ...

    African Journals Online (AJOL)

    A cost-effective friction coefficient measuring technique was developed and tested. The technique involved the mounting of two sensing elements on the surface of rolls, in a manner that sought to measure simultaneously the normal and the tangential stresses during rolling. The instrumented roll termed “SGRoll” was ...

  9. Systematic Breakdown of Amontons' Law of Friction for an Elastic Object Locally Obeying Amontons' Law

    Science.gov (United States)

    Otsuki, Michio; Matsukawa, Hiroshi

    2013-01-01

    In many sliding systems consisting of solid object on a solid substrate under dry condition, the friction force does not depend on the apparent contact area and is proportional to the loading force. This behaviour is called Amontons' law and indicates that the friction coefficient, or the ratio of the friction force to the loading force, is constant. Here, however, using numerical and analytical methods, we show that Amontons' law breaks down systematically under certain conditions for an elastic object experiencing a friction force that locally obeys Amontons' law. The macroscopic static friction coefficient, which corresponds to the onset of bulk sliding of the object, decreases as pressure or system length increases. This decrease results from precursor slips before the onset of bulk sliding, and is consistent with the results of certain previous experiments. The mechanisms for these behaviours are clarified. These results will provide new insight into controlling friction. PMID:23545778

  10. Systematic breakdown of Amontons' law of friction for an elastic object locally obeying Amontons' law.

    Science.gov (United States)

    Otsuki, Michio; Matsukawa, Hiroshi

    2013-01-01

    In many sliding systems consisting of solid object on a solid substrate under dry condition, the friction force does not depend on the apparent contact area and is proportional to the loading force. This behaviour is called Amontons' law and indicates that the friction coefficient, or the ratio of the friction force to the loading force, is constant. Here, however, using numerical and analytical methods, we show that Amontons' law breaks down systematically under certain conditions for an elastic object experiencing a friction force that locally obeys Amontons' law. The macroscopic static friction coefficient, which corresponds to the onset of bulk sliding of the object, decreases as pressure or system length increases. This decrease results from precursor slips before the onset of bulk sliding, and is consistent with the results of certain previous experiments. The mechanisms for these behaviours are clarified. These results will provide new insight into controlling friction.

  11. Experimental Investigation on Friction and Wear Properties of Different Steel Materials

    Directory of Open Access Journals (Sweden)

    M.A. Chowdhury

    2013-03-01

    Full Text Available Friction coefficient and wear rate of different steel materials are investigated and compared in this study. In order to do so, a pin on disc apparatus is designed and fabricated. Experiments are carried out when different types of disc materials such as stainless steel 314 (SS 314, stainless steel 202 (SS 202 and mild steel slide against stainless steel 314 (SS 314 pin. Experiments are conducted at normal load 10, 15 and 20 N, sliding velocity 1, 1.5 and 2 m/s and relative humidity 70%. At different normal loads and sliding velocities, variations of friction coefficient with the duration of rubbing are investigated. The obtained results show that friction coefficient varies with duration of rubbing, normal load and sliding velocity. In general, friction coefficient increases for a certain duration of rubbing and after that it remains constant for the rest of the experimental time. The obtained results reveal that friction coefficient decreases with the increase in normal load for all the tested materials. It is also found that friction coefficient increases with the increase in sliding velocity for all the materials investigated. Moreover, wear rate increases with the increase in normal load and sliding velocity for SS 314, SS 202 and mild steel. In addition, at identical operating condition, the magnitudes of friction coefficient and wear rate are different for different materials depending on sliding velocity and normal load.

  12. Nano-friction behavior of phosphorene.

    Science.gov (United States)

    Bai, Lichun; Liu, Bo; Srikanth, Narasimalu; Tian, Yu; Zhou, Kun

    2017-09-01

    Nano-friction of phosphorene plays a significant role in affecting the controllability and efficiency of applying strain engineering to tune its properties. So far, the friction behavior of phosphorene has not been studied. This work studies the friction of single-layer and bilayer phosphorene on an amorphous silicon substrate by sliding a rigid tip. For the single-layer phosphorene, it is found that its friction is highly anisotropic, i.e. the friction is larger along the armchair direction than that along the zigzag direction. Moreover, pre-strain of the phosphorene also exhibits anisotropic effects. The friction increases with the pre-strain along the zigzag direction, but decreases with that along the armchair direction. Furthermore, the strong adhesion between the phosphorene and its substrate increases the friction between the phosphorene and the tip. For bilayer phosphorene, its friction highly depends on its stacking mode, which determines the contact interface with a commensurate or incommensurate pattern. This friction behavior is quite unique and greatly differs from that of graphene and molybdenum disulfide. Detailed analysis reveals that this behavior results from the combination effect of the friction contact area, the potential-energy profile of phosphorene, and its unique elongation.

  13. Attenuation coefficients of soils

    International Nuclear Information System (INIS)

    Martini, E.; Naziry, M.J.

    1989-01-01

    As a prerequisite to the interpretation of gamma-spectrometric in situ measurements of activity concentrations of soil radionuclides the attenuation of 60 to 1332 keV gamma radiation by soil samples varying in water content and density has been investigated. A useful empirical equation could be set up to describe the dependence of the mass attenuation coefficient upon photon energy for soil with a mean water content of 10%, with the results comparing well with data in the literature. The mean density of soil in the GDR was estimated at 1.6 g/cm 3 . This value was used to derive the linear attenuation coefficients, their range of variation being 10%. 7 figs., 5 tabs. (author)

  14. Frictional strength and heat flow of southern San Andreas Fault

    Science.gov (United States)

    Zhu, P. P.

    2016-01-01

    Frictional strength and heat flow of faults are two related subjects in geophysics and seismology. To date, the investigation on regional frictional strength and heat flow still stays at the stage of qualitative estimation. This paper is concentrated on the regional frictional strength and heat flow of the southern San Andreas Fault (SAF). Based on the in situ borehole measured stress data, using the method of 3D dynamic faulting analysis, we quantitatively determine the regional normal stress, shear stress, and friction coefficient at various seismogenic depths. These new data indicate that the southern SAF is a weak fault within the depth of 15 km. As depth increases, all the regional normal and shear stresses and friction coefficient increase. The former two increase faster than the latter. Regional shear stress increment per kilometer equals 5.75 ± 0.05 MPa/km for depth ≤15 km; regional normal stress increment per kilometer is equal to 25.3 ± 0.1 MPa/km for depth ≤15 km. As depth increases, regional friction coefficient increment per kilometer decreases rapidly from 0.08 to 0.01/km at depths less than ~3 km. As depth increases from ~3 to ~5 km, it is 0.01/km and then from ~5 to 15 km, and it is 0.002/km. Previously, frictional strength could be qualitatively determined by heat flow measurements. It is difficult to obtain the quantitative heat flow data for the SAF because the measured heat flow data exhibit large scatter. However, our quantitative results of frictional strength can be employed to investigate the heat flow in the southern SAF. We use a physical quantity P f to describe heat flow. It represents the dissipative friction heat power per unit area generated by the relative motion of two tectonic plates accommodated by off-fault deformation. P f is called "fault friction heat." On the basis of our determined frictional strength data, utilizing the method of 3D dynamic faulting analysis, we quantitatively determine the regional long-term fault

  15. Coefficients of viscosity for heavy impurity element in tokamak

    Energy Technology Data Exchange (ETDEWEB)

    El-Sharif, R N; Bekhit, A M [Plasma Physics dept., NRC, Atomic energy Authority, Cairo, (Egypt)

    1997-12-31

    The transport of heavy impurity element in to tokamak was studied theoretically. The viscosity coefficients of chromium impurities has been calculated in 13 and 21 moment approximation, in the limit of strong fields where is the gyrofrequency of species it was found that the off diagonal coefficient approximately tends to zero. This means that the friction force in the off-diagonal direction is very small, for the perpendicular viscosity coefficient the two approximation coincide to each other. 3 figs.

  16. Friction, adhesion and wear properties of PDMS films on silicon sidewalls

    International Nuclear Information System (INIS)

    Penskiy, I; Gerratt, A P; Bergbreiter, S

    2011-01-01

    This paper demonstrates the first tests of friction, adhesion and wear properties of thin poly(dimethylsiloxane) (PDMS) films on the sidewalls of silicon-on-insulator structures. The test devices were individually calibrated using a simple method that included optical and electrical measurements. The static coefficient of friction versus normal pressure curves were obtained for PDMS–PDMS, PDMS–silicon and silicon–silicon sidewall interfaces. The effects of aging on friction and adhesion properties of PDMS were also evaluated. The results of friction tests showed that the static coefficient of friction follows the JKR contact model, which means that the friction force depends on the apparent area of contact. The wear tests showed high resistance of PDMS to abrasion over millions of cycles.

  17. Influence of the heat flux and of the gas on heat transfer and friction coefficients in a smooth cylindrical tube; Influence du flux de chaleur et de la nature du gaz sur les coefficients d'echange et le frottement dans un tube cylindrique lisse

    Energy Technology Data Exchange (ETDEWEB)

    Delpont, J P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1962-12-15

    The stainless steel tube used for the experiments is heated by means of d.c current; its inside diameter is 40 mm; its length is about 5.80 meters. Special core has been taken (heated rocket) to avoid heat loss and to provide very accurate measurements. The cooling gases tested are air and carbon dioxide at a pressure of 2.6 to 19 psi; the Reynolds number ranges from 70,000 to 10{sup 6}, the wall temperature and the heat flux reach respectively 430 deg C and 16 watts/cm{sup 2}. The Reynolds number Re{sub m}, Stanton number M{sub m} and friction coefficient f are computed by evaluating the physical properties of the gases at the mean temperature T{sub m}. For a given Reynolds number, a decrease of M{sub m} and of f is observed hen the heat flux increases, this decrease reaches 10 per cent in the experiments described. A formulation is proposed to express this effect in terms of a heat flow parameter (T{sub m} - T{sub m}) / T{sub p} used as a corrective factor (T{sub p} = wall temperature). The correlation formulae are: M{sub m} = 0.0168 Re{sub m}{sup -0.18} P{sub m}{sup -0.6} (1 - 0.4 [(T{sub p} - T{sub m}) / T{sub p}]) for air f = f{sub 0} (1 0.25 [(T{sub p} - T{sub m}) / T{sub p}]) for air M{sub m} = 0.0171 Re{sub m}{sup -0.18} P{sub m}{sup -0.6} (1 - 0.2 [(T{sub p} - T{sub m}) / T{sub p}]) for carbon dioxide f = f{sub 0} (1 - 0.20 [(T{sub p} - T{sub m}) / T{sub p}]) for carbon dioxide where f{sub 0} = the friction coefficient for isotherm flow. (author) [French] Le tube utilite a un diametre interieur de 40 mm; sa longueur est de 5,80 m environ; il est en acier inoxydable et chauffe par un courant continu. Des precautions particulieres (enceinte chauffante exterieure) ont ete prises pour eviter tout echange de chaleur avec le milieu exterieur et permettre des mesures extremement precises. Les gaz de refroidissement experimentes sont l'air et le gaz corbonique sous une pression de 1,8 a 13 hpz; les nombres de Reynolds vont de 70 000 a 10{sup 6}, la temperature de

  18. Generalization of proposed tendon friction correlation and its application to PCCV structural analysis

    International Nuclear Information System (INIS)

    Kashiwase, Takako; Nagasaka, Hideo

    2000-01-01

    The present paper dealt with the extension of tendon friction coefficient correlation as a function of loading end load and circumferential angle, proposed in the former paper. The extended correlation further included the effects of the number of strands contacted with sheath, tendon diameter, politicization of tendon and tendon local curvature. The validity of the correlation was confirmed by several published measured data. The structural analysis of middle cylinder part of 1/4 PCCV (Prestressed Concrete Containment Vessel) model was conducted using the present friction coefficient correlation. The results were compared with the analysis using constant friction coefficient, focused on the tendon tension force distribution. (author)

  19. Avaliação do coeficiente de atrito de braquetes metálicos e estéticos com fios de aço inoxidável e beta-titânio Evaluation of the friction coefficient of metal and esthetic brackets with stainless steel and beta-titanium wires

    Directory of Open Access Journals (Sweden)

    Cristine Pritsch Braga

    2004-12-01

    Full Text Available Um fator importante que define a eficácia dos aparelhos ortodônticos fixos é o atrito existente entre as superfícies de fios e braquetes. Assim, este estudo teve como objetivo investigar o coeficiente de atrito estático entre fios de aço inoxidável e beta-titânio (TP Orthodontics e braquetes de aço inoxidável (Dynalock® - Unitek, braquetes estéticos com slot de aço inoxidável (Clarity® - Unitek e estéticos convencionais (Allure® - GAC. Para tanto, construiu-se um equipamento no Departamento de Engenharia Mecânica e Mecatrônica da PUCRS. Antes de serem iniciados os testes, foi quantificado o erro de método e constatou-se que não houve interferência significante (p>0,05 do fator operador nas medições. Então, pôde-se calcular o valor do coeficiente de atrito, obtido pela divisão da força de atrito pela carga normal. O método estatístico utilizado neste estudo foi Análise de Variância (ANOVA e teste de Comparações Múltiplas (Tukey. Constatou-se que: 1 a combinação com menor coeficiente de atrito foi composta pelo fio de aço inoxidável e braquete Dynalock® e a que apresentou maior coeficiente foi a do braquete Allure® com o fio de beta-titânio; 2 o fio de beta-titânio apresentou coeficiente de atrito significativamente maior do que o fio de aço inoxidável; 3 o braquete Dynalock® não apresentou diferenças significativas em relação ao coeficiente de atrito do braquete Clarity® quando o fio utilizado foi de beta-titânio. No entanto, quando o fio testado foi de aço inoxidável, apresentou coeficiente de atrito significativamente menor. O braquete Clarity® apresentou coeficiente de atrito significativamente menor do que o braquete Allure®.An important factor that defines the effectiveness of the appliances is the friction between the surfaces of wires and brackets. Thus, that study was developed in order to investigate the static friction coefficient between stainless steel and beta-titanium wires (TP

  20. Proximity friction reexamined

    International Nuclear Information System (INIS)

    Krappe, H.J.

    1989-01-01

    The contribution of inelastic excitations to radial and tangential friction form-factors in heavy-ion collisions is investigated in the frame-work of perturbation theory. The dependence of the form factors on the essential geometrical and level-density parameters of the scattering system is exhibited in a rather closed form. The conditions for the existence of time-local friction coefficients are discussed. Results are compared to form factors from other models, in particular the transfer-related proximity friction. For the radial friction coefficient the inelastic excitation mechanism seems to be the dominant contribution in peripheral collisions. (orig.)

  1. Flat friction tests applied to austenic stainless steels with several surface finish. Analysis of adhesion conditions in friction

    International Nuclear Information System (INIS)

    Coello, J.; Miguel, V.; Ferrer, C.; Calatatyd, A.; Martinez, A.

    2008-01-01

    The main purpose of this work is to evaluate the tribological behaviour of austenic stainless steels AISI 304 with bright surface finishing (B). The assays have been carried out in flat faced dies system with mineral oil of 200 cts viscosity, S 2 Mo grease and in dry conditions. The relationship between friction coefficient and pressure and velocity has been established for the mineral oil as lubricant. In these conditions, a strong adhesive tendency has been found in boundary lubrication regime. The results obtained here, show us that S 2 Mo grease leads to lowest values for the friction coefficient. A minor adhesive behaviour tendency for AISI 316 steel, harder than 304 grades, has been found. A relevant plowing phenomena has been observed for the more critical friction conditions tried out. A surface hardener is produced as a consequence of that. (Author) 19 refs

  2. Investigation of Dynamic Friction Induced by Shock Loading Conditions

    International Nuclear Information System (INIS)

    Juanicotena, A.; Szarzynski, S.

    2006-01-01

    Modeling the frictional sliding of one surface against another under high pressure is often required to correctly describe the response of complex systems to shock loading. In order to provide data for direct code and model comparison, a new friction experiment investigating dry sliding characteristics of metal on metal at normal pressures up to 10 GPa and sliding velocities up to 400 m/s has been developed. The test consists of a specifically designed target made of two materials. A plane shock wave generated by plate impact results in one material sliding against the other. The material velocity of the rear surface of the target is recorded versus time by Doppler Laser Interferometry. The dynamic friction coefficient μ is then indirectly determined by comparison with results of numerical simulations involving the conventional Coulomb law. Using this new experimental configuration, three dynamic friction experiments were performed on AA 5083-Al (H111) / AISI 321 stainless steel tribo-pair. Results suggest a decrease in the friction coefficient with increasing sliding velocity

  3. Physical and Frictional Properties of NERICA

    Directory of Open Access Journals (Sweden)

    2016-11-01

    Full Text Available Some physical and frictional properties of the seeds and husks of New Rice for Africa (NERICA were studied at varying moisture contents of 13%, 17%, and 20% (w.b. In the study, four varieties of NERICA namely; FARO 44, FARO 51, FARO 52 and FARO 57 were selected to represent the different size ranges common to NERICA. The physical properties of NERICA such as shape, size, volume, moisture contents, density, weights, surface area, aspect ratio and sphericity were obtained through physical measurement of the grains samples of each of the four varieties. Results of the physical measurements indicate that the size ranges for the varieties are as follows: FARO 44; 3.653mm to 3.858mm, FARO 51; 3.685mm to 3.916mm, FARO 52; 3.674mm to 3.863mm and FARO 57; 3.924mm to 4.019mm. Results of the frictional properties, shows that plywood material has the highest value of 28.4(1.36 = 33.0(1.41, 29.9(1.38 = 35.2(1.45 and 30.4(1.28 = 37.6(1.51 at 13%, 17% and 20% (w.b respectively, while plastic material has the lowest coefficient of friction value of 20.8(1.21 = 17.7(1.14, 19.4(1.17 = 21.8(1.24 and 21.3(1.24 = 22.9(1.26 at 13%, 17% and 20% (w.b respectively.

  4. Existence of solutions for quasistatic problems of unilateral contact with nonlocal friction for nonlinear elastic materials

    Directory of Open Access Journals (Sweden)

    Alain Mignot

    2005-09-01

    Full Text Available This paper shows the existence of a solution of the quasi-static unilateral contact problem with nonlocal friction law for nonlinear elastic materials. We set up a variational incremental problem which admits a solution, when the friction coefficient is small enough, and then by passing to the limit with respect to time we obtain a solution.

  5. Effect of grafted oligopeptides on friction.

    Science.gov (United States)

    Iarikov, Dmitri D; Ducker, William A

    2013-05-14

    Frictional and normal forces in aqueous solution at 25 °C were measured between a glass particle and oligopeptide films grafted from a glass plate. Homopeptide molecules consisting of 11 monomers of either glutamine, leucine, glutamic acid, lysine, or phenylalanine and one heteropolymer were each "grafted from" an oxidized silicon wafer using microwave-assisted solid-phase peptide synthesis. The peptide films were characterized using X-ray photoelectron spectroscopy and secondary ion mass spectrometry. Frictional force measurements showed that the oligopeptides increased the magnitude of friction compared to that on a bare hydrophilic silicon wafer but that the friction was a strong function of the nature of the monomer unit. Overall we find that the friction is lower for more hydrophilic films. For example, the most hydrophobic monomer, leucine, exhibited the highest friction whereas the hydrophilic monomer, polyglutamic acid, exhibited the lowest friction at zero load. When the two surfaces had opposite charges, there was a strong attraction, adhesion, and high friction between the surfaces. Friction for all polymers was lower in phosphate-buffered saline than in pure water, which was attributed to lubrication via hydrated salt ions.

  6. Nonlinear friction model for servo press simulation

    Science.gov (United States)

    Ma, Ninshu; Sugitomo, Nobuhiko; Kyuno, Takunori; Tamura, Shintaro; Naka, Tetsuo

    2013-12-01

    The friction coefficient was measured under an idealized condition for a pulse servo motion. The measured friction coefficient and its changing with both sliding distance and a pulse motion showed that the friction resistance can be reduced due to the re-lubrication during unloading process of the pulse servo motion. Based on the measured friction coefficient and its changes with sliding distance and re-lubrication of oil, a nonlinear friction model was developed. Using the newly developed the nonlinear friction model, a deep draw simulation was performed and the formability was evaluated. The results were compared with experimental ones and the effectiveness was verified.

  7. Chemically triggered ejection of membrane tubules controlled by intermonolayer friction.

    Science.gov (United States)

    Fournier, J-B; Khalifat, N; Puff, N; Angelova, M I

    2009-01-09

    We report a chemically driven membrane shape instability that triggers the ejection of a tubule growing exponentially toward a chemical source. The instability is initiated by a dilation of the exposed monolayer, which is coupled to the membrane spontaneous curvature and slowed down by intermonolayer friction. Our experiments are performed by local delivery of a basic pH solution to a giant vesicle. Quantitative fits of the data give an intermonolayer friction coefficient b approximately 2x10;{9} J s/m;{4}. The exponential growth of the tubule may be explained by a Marangoni stress yielding a pulling force proportional to its length.

  8. The effects of shear and normal stress paths on rock friction

    International Nuclear Information System (INIS)

    Olsson, W.A.

    1990-01-01

    The effect of variable normal stress on the coefficient of friction of smooth artificial surfaces in welded tuff was studied. The shear stress response to changes in normal stress during constant-velocity sliding suggests that friction depends on the history of the normal stress; or, more generally, the path in shear/normal stress space. 6 refs., 5 figs

  9. Investigation of squeal noise under positive friction characteristics condition provided by friction modifiers

    Science.gov (United States)

    Liu, Xiaogang; Meehan, Paul A.

    2016-06-01

    Field application of friction modifiers on the top of rail has been shown to effectively curb squeal and reduce lateral forces, but performance can be variable, according to other relevant research. Up to now, most investigations of friction modifiers were conducted in the field, where it is difficult to control or measure important parameters such as angle of attack, rolling speed, adhesion ratio etc. In the present investigation, the effect of different friction modifiers on the occurrence of squeal was investigated on a rolling contact two disk test rig. In particular, friction-creep curves and squeal sound pressure levels were measured under different rolling speeds and friction modifiers. The results show friction modifiers can eliminate or reduce the negative slope of friction-creep curves, but squeal noise still exists. Theoretical modelling of instantaneous creep behaviours reveals a possible reason why wheel squeal still exists after the application of friction modifiers.

  10. Mathematical models of viscous friction

    CERN Document Server

    Buttà, Paolo; Marchioro, Carlo

    2015-01-01

    In this monograph we present a review of a number of recent results on the motion of a classical body immersed in an infinitely extended medium and subjected to the action of an external force. We investigate this topic in the framework of mathematical physics by focusing mainly on the class of purely Hamiltonian systems, for which very few results are available. We discuss two cases: when the medium is a gas and when it is a fluid. In the first case, the aim is to obtain microscopic models of viscous friction. In the second, we seek to underline some non-trivial features of the motion. Far from giving a general survey on the subject, which is very rich and complex from both a phenomenological and theoretical point of view, we focus on some fairly simple models that can be studied rigorously, thus providing a first step towards a mathematical description of viscous friction. In some cases, we restrict ourselves to studying the problem at a heuristic level, or we present the main ideas, discussing only some as...

  11. Mechanical and tribological properties of ceramic-matrix friction materials with steel fiber and mullite fiber

    International Nuclear Information System (INIS)

    Wang, Fahui; Liu, Ying

    2014-01-01

    Highlights: • Interaction of mixing the steel and mullite fibers can improve the mechanical properties. • Mixing the steel and mullite fibers can also improve friction stability. • Friction coefficient increases with increasing additional mullite fiber content. • Ceramic-matrix friction material shows sever fade due to mullite fibers agglomerated. - Abstract: The purpose of the present work was to investigate and compare the mechanical and tribological behaviors of ceramic-matrix friction material (CMFM) with steel fiber (SF), mullite fiber (MF), and mixing SF and MF. The CMFM was prepared by hot-pressing sintering, and the tribological behaviors were determined using a constant speed friction tester. The worn surfaces and wear debris were observed by a scanning electron microscopy (SEM). Experiment results show that the combination of SF and MF can improve the mechanical properties that each single fiber does not have. The sever fade for the specimen reinforced by single MF during the whole friction testing can be attributed to the poor interface cohesive strength between MF and matrix. Mixing the SF and MF can improve the friction stability, and the friction coefficients for friction material with a mixture of the SF and MF increases with increasing MF content. For all specimens, increasing in the friction temperatures result in the increase of wear rates

  12. Performance Characteristics of a Wood By-Product as Base Friction ...

    African Journals Online (AJOL)

    The resulting friction brake lining materials were additionally subjected to thermal cycles and associated baking and curing. The final products were thereafter subjected to laboratory and road performance tests which included investigations of the effects of temperature and pressure on the friction lining coefficients, the ...

  13. An atomistic investigation of the effect of strain on frictional properties of suspended graphene

    Directory of Open Access Journals (Sweden)

    Qingshun Bai

    2016-05-01

    Full Text Available We performed molecular dynamics (MD simulations of a diamond probe scanned on a suspended graphene to reveal the effect of strain on the frictional properties of suspended graphene. The graphene was subjected to some certain strain along the scanning direction. We compared the friction coefficient obtained from different normal loads and strain. The results show that the friction coefficient can be decreased about one order of magnitude with the increase of the strain. And that can be a result of the decreased asymmetry of the contact region which is caused by strain. The synthetic effect of potential energy and the fluctuation of contact region were found to be the main reason accounting for the fluctuation of the friction force. The strain can reduce the fluctuation of the contact region and improve the stability of friction.

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

    International Nuclear Information System (INIS)

    Smith, James R.; Tsibouklis, John; Nevell, Thomas G.; Breakspear, Steven

    2013-01-01

    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.

  15. Slip Morphology of Elastic Strips on Frictional Rigid Substrates.

    Science.gov (United States)

    Sano, Tomohiko G; Yamaguchi, Tetsuo; Wada, Hirofumi

    2017-04-28

    The morphology of an elastic strip subject to vertical compressive stress on a frictional rigid substrate is investigated by a combination of theory and experiment. We find a rich variety of morphologies, which-when the bending elasticity dominates over the effect of gravity-are classified into three distinct types of states: pinned, partially slipped, and completely slipped, depending on the magnitude of the vertical strain and the coefficient of static friction. We develop a theory of elastica under mixed clamped-hinged boundary conditions combined with the Coulomb-Amontons friction law and find excellent quantitative agreement with simulations and controlled physical experiments. We also discuss the effect of gravity in order to bridge the difference in the qualitative behaviors of stiff strips and flexible strings or ropes. Our study thus complements recent work on elastic rope coiling and takes a significant step towards establishing a unified understanding of how a thin elastic object interacts vertically with a solid surface.

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

    International Nuclear Information System (INIS)

    Abdollahi, H.; Dehghani, K.

    2007-01-01

    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

  17. ANALYSIS OF THE MAGNETIZED FRICTION FORCE.

    Energy Technology Data Exchange (ETDEWEB)

    FEDOTOV, A.V.; BRUHWILER, D.L.; SIDORIN, A.O.

    2006-05-29

    A comprehensive examination of theoretical models for the friction force, in use by the electron cooling community, was performed. Here, they present their insights about the models gained as a result of comparison between the friction force formulas and direct numerical simulations, as well as studies of the cooling process as a whole.

  18. The role of friction in tow mechanics

    NARCIS (Netherlands)

    Cornelissen, Bo

    2013-01-01

    Friction plays and important role in the processing of fibrous materials: during production of tow materials, during textile manufacturing and during preforming operations for composite moulding processes. One of the poorly understood phenomena in these processes is the dynamic frictional behaviour

  19. Adaptive friction compensation: a globally stable approach

    NARCIS (Netherlands)

    Verbert, K.A.; Tóth, R.; Babuska, R.

    2016-01-01

    In this paper, an adaptive friction compensation scheme is proposed. The friction force is computed as a timevarying friction coefficient multiplied by the sign of the velocity and an on-line update law is designed to estimate this coefficient based on the actual position and velocity errors.

  20. High-velocity frictional properties of gabbro

    Science.gov (United States)

    Tsutsumi, Akito; Shimamoto, Toshihiko

    High-velocity friction experiments have been performed on a pair of hollow-cylindrical specimens of gabbro initially at room temperature, at slip rates from 7.5 mm/s to 1.8 m/s, with total circumferential displacements of 125 to 174 m, and at normal stresses to 5 MPa, using a rotary-shear high-speed friction testing machine. Steady-state friction increases slightly with increasing slip rate at slip rates to about 100 mm/s (velocity strengthening) and it decreases markedly with increasing slip rate at higher velocities (velocity weakening). Steady-state friction in the velocity weakening regime is lower for the non-melting case than the frictional melting case, due perhaps to severe thermal fracturing. A very large peak friction is always recognized upon the initiation of visible frictional melting, presumably owing to the welding of fault surfaces upon the solidification of melt patches. Frictional properties thus change dramatically with increasing displacement at high velocities, and such a non-linear effect must be incorporated into the analysis of earthquake initiation processes.

  1. Large Friction Anisotropy of a Polydiacetylene Monolayer

    International Nuclear Information System (INIS)

    Burns, A.R.; Carpick, R.W.; Sasaki, D.Y.

    1999-01-01

    Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties

  2. A graded nano-TiN coating on biomedical Ti alloy: Low friction coefficient, good bonding and biocompatibility

    Energy Technology Data Exchange (ETDEWEB)

    Cui, Wenfang [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819 (China); Qin, Gaowu, E-mail: qingw@smm.neu.edu.cn [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819 (China); Duan, Jingzhu; Wang, Huan [Spinal surgery, Shengjing Hospital, China Medical University, Shenyang 110004 (China)

    2017-02-01

    In order to solve wear resistance of Ti alloy biomaterials, the concept of a graded nano-TiN coating has been proposed. The coating was prepared on Ti-6Al-4V bio-alloy by DC reactive magnetron sputtering. The wear performance of the coated specimens was measured in Hank's solution under the load of 10 N, and the biocompatibility was evaluated according to ISO-10993-4 standard. The results show that the gradient coating exhibits a gradual change in compositions and microstructures along the direction of film growth. Nano-TiN with the size of several to dozens nanometers and Ti{sub 4}N{sub 3−x} transitional phase with variable composition form a graded composite structure, which significantly improves adhesion strength (L{sub c1} = 80 N, L{sub c2} = 120 N), hardness (21 GPa) and anti-wear performance (6.2 × 10{sup −7} mm{sup 3}/Nm). The excellent bonding and wear resistance result from a good match of mechanical properties at substrate/coating interface and the strengthening and toughening effects of the nanocrystalline composite. The nano-TiN coating has also been proved to have good biocompatibility through in-vitro cytotoxicity, hemocompatibility and general toxicity tests. And thus, the proposed graded nano-TiN coating is a good candidate improving wear resistance of many implant medical devices. - Highlights: • A graded nano-TiN coating was prepared on biomedical Ti alloy by PVD. • The combination of hard and soft phase increases hardness and toughness. • The coating exhibits high bonding, low coefficient of friction and wear rate. • The new coating has good bio-safety and great clinical application prospect.

  3. On the geometric phenomenology of static friction.

    Science.gov (United States)

    Ghosh, Shankar; Merin, A P; Nitsure, Nitin

    2017-09-06

    In this note we introduce a hierarchy of phase spaces for static friction, which give a graphical way to systematically quantify the directional dependence in static friction via subregions of the phase spaces. We experimentally plot these subregions to obtain phenomenological descriptions for static friction in various examples where the macroscopic shape of the object affects the frictional response. The phase spaces have the universal property that for any experiment in which a given object is put on a substrate fashioned from a chosen material with a specified nature of contact, the frictional behaviour can be read off from a uniquely determined classifying map on the control space of the experiment which takes values in the appropriate phase space.

  4. Effect of humidity and interlayer cation on frictional strength of montmorillonite

    Science.gov (United States)

    Tetsuka, H.; Katayama, I.; Sakuma, H.; Tamura, K.

    2016-12-01

    Smectite has been ubiquitously seen in fault gouge (Schleicher et al., 2006; Kuo et al., 2009; Si et al., 2014; Kameda, 2015) and is characteristic by low frictional coefficient (Saffer et al., 2001; Ikari et al., 2007); consequently, it has a key role in fault dynamics. The frictional strength of montmorillonite (a typical type of smectite) is affected by mainly two factors, 1) hydration state and 2) interlayer cation. Previous laboratory experiments have shown that the frictional strength of montmorillonite changes with hydration state (Ikari et al., 2007) and with interlayer cation (Behnsen and Faulkner, 2013). However, experimental study for frictional strengths of interlayer cation-exchanged montmorillonite under controlled hydration state has not been reported. We are developing humidity control system in biaxial friction testing machine and try to investigate the effect of relative humidity and interlayer cation on frictional strength of montmorillonite. The humidity control system consists of two units, 1) the pressure vessel (core holder) unit controlled by a constant temperature and 2) the vapor generating unit controlled by variable temperature. We control relative humidity around sample, which is calculated from the temperature around sample and the vapor pressure at vapor generating unit. Preliminary experiments under controlled humidity show frictional coefficient of montmorillonite decrease with increasing relative humidity. In the meeting, we will report the systematic study of frictional coefficient as function of relative humidity and interlayer cation species.

  5. Trial manufacture of rotary friction tester and frictional force measurement of metals

    CERN Document Server

    Abe, T; Kanari, M; Tanzawa, S

    2002-01-01

    In the plasma confinement type fusion reactor, in-vessel structures such as a blanket module slide at the joints each other when plasma disruption occurs, and then frictional heat is generated there. Therefore, for the selection of material and the use as the design data, it is important to understand the frictional characteristics of metals and ceramic films in the vacuum. In the present study, we have manufactured a prototype of rotary friction tester and examined the performances of the tester. The frictional characteristics of metals in the room air was measured using the friction tester, and the results obtained are as follows. A drifting friction force for a constant time and a friction force during the idling were 98 mN and 225 mN, respectively. These values were sufficiently small as compared to pressing load (9.8 - 57.8 N) used in the friction test. In a friction force measurement of stainless steel, dynamic friction force obeyed Amontons' law which indicated that dynamic friction force is not depend...

  6. Friction and wear properties of Ti6Al4V/WC-Co in cold atmospheric plasma jet

    International Nuclear Information System (INIS)

    Xu Wenji; Liu Xin; Song Jinlong; Wu Libo; Sun Jing

    2012-01-01

    Highlights: ► Cold plasma jet can effectively reduce the friction coefficients of Ti6Al4V/WC-Co friction pairs. ► Cold plasma jet can easily form nitrides on the surface of Ti6Al4V and on new surfaces generated by tool wear. ► The nitrides can reduce the friction coefficients and protect the friction surface. - Abstract: The friction and wear properties of Ti6Al4V/WC-Co friction pair were studied using an autonomous atmospheric pressure bare electrode cold plasma jet generating device and block-on-ring friction/wear tester, respectively. The study was conducted under air, air jet, nitrogen jet, air cold plasma jet, and nitrogen cold plasma jet atmospheres. Both nitrogen cold and air cold plasma jets effectively reduced the friction coefficients of the friction pairs and decreased friction temperature. The friction coefficient in the nitrogen cold plasma jet decreased to almost 60% compared with that in the air. The scanning electron microscope, energy-dispersive X-ray spectroscope, and X-ray diffraction analyses illustrated that adhesive wear was relieved and the friction surfaces of Ti6Al4V were smoother, both in the nitrogen cold and air cold plasma jets. The roughness value R a of the Ti6Al4V friction surfaces can reach 1.107 μm. A large number of nitrogen particles in the ionic and excited states contained by cold plasma jets reacts easily on the friction surface to produce a large amount of nitrides, which can excellently reduce the wear of Ti6Al4V/WC-Co friction pairs in real-time.

  7. Application of the Dahl friction model in the dynamics analysis of grab cranes

    Directory of Open Access Journals (Sweden)

    Urbaś A.

    2016-01-01

    Full Text Available The paper presents dynamics analysis of grab cranes. The cranes can be built out of any number of links, however, only selected links have their own drive that is considered in the flexible form. The cranes are mounted to the ground by means of any number of flexible supports. Joint coordinates and homogeneous transformation matrices are used to describe the cranes’ geometry. Equations of motion are derived using Lagrange equations. Friction phenomenon is taken into account in all joints. The joint forces and torques used to calculate friction torques in the revolute joints and friction forces in the prismatic joints are determined using the recursive Newton-Euler algorithm. Models of revolute and prismatic joints are worked out. Friction coefficients are defined using the Dahl friction model. The results of numerical calculations present the influence of friction on the driving torques, force and behaviour of the load.

  8. Computational Study of Low Interlayer Friction in Tin+1Cn (n = 1, 2, and 3) MXene.

    Science.gov (United States)

    Zhang, Difan; Ashton, Michael; Ostadhossein, Alireza; van Duin, Adri C T; Hennig, Richard G; Sinnott, Susan B

    2017-10-04

    The friction of adjacent Ti n+1 C n (n = 1, 2, and 3) MXene layers is investigated using density functional theory (DFT) calculations and classical molecular dynamics simulations with ReaxFF potentials. The calculations reveal the sliding pathways in all three MXene systems with low energy barriers. The friction coefficients for interlayer sliding are evaluated using static calculations. Both DFT and ReaxFF methods predict friction coefficients between 0.24 and 0.27 for normal loads less than 1.2 GPa. The effect of titanium (Ti) vacancies in sublayers and terminal oxygen (O) vacancies at surfaces on the interlayer friction is further investigated using the ReaxFF potential. These defects are found to increase the friction coefficients by increasing surface roughness and creating additional attractive forces between adjacent layers. However, these defective MXenes still maintain friction coefficients below 0.31. We also consider functionalized Ti 3 C 2 MXene terminated with -OH and -OCH 3 and find that compared to the -O-terminated surface both groups further reduce the interlayer friction coefficient to 0.10-0.14.

  9. Direct measurement of friction of a fluctuating contact line.

    Science.gov (United States)

    Guo, Shuo; Gao, Min; Xiong, Xiaomin; Wang, Yong Jian; Wang, Xiaoping; Sheng, Ping; Tong, Penger

    2013-07-12

    We report a direct measurement of the friction coefficient of a fluctuating (and slipping) contact line using a thin vertical glass fiber of diameter d with one end glued onto a cantilever beam and the other end touching a liquid-air interface. By measuring the broadening of the resonant peak of the cantilever system with varying liquid viscosity η, we find the friction coefficient of the contact line has a universal form, ξ(c)≃0.8πdη, independent of the liquid-solid contact angle. The obtained scaling law is further supported by the numerical simulation based on the phase field model under the generalized Navier boundary conditions.

  10. 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.

  11. The behaviour of molybdenum dialkyldithiocarbamate friction modifier additives

    International Nuclear Information System (INIS)

    Graham, Jocelyn Claire Herries

    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 such as ZnDTP. Their activity was shown to be highly concentration and temperature dependent and was also found to be sensitive to the roughness of the contacting surfaces. Raman spectroscopy was used to analyse the chemical nature of molybdenum-containing reaction films and found that friction reduction indubitably arises from the local formation of platelets (diameter 30-50 nm) of MoS 2 . The formation of MoS 2 -rich films was found to occur only during direct asperity-asperity rubbing of the contacting surfaces (this type of contact being especially prevalent in pure sliding contacts). At elevated temperatures and in the presence of oxidising gases the consumption of MoDTC was monitored. MoDTC concentration dropped until the total value fell below a critical level to reduce friction. The study showed that decay rate of molybdenum-containing species was reduced by the addition of peroxide-decomposing antioxidants. (author)

  12. Frictional ageing from interfacial bonding and the origins of rate and state friction.

    Science.gov (United States)

    Li, Qunyang; Tullis, Terry E; Goldsby, David; Carpick, Robert W

    2011-11-30

    Earthquakes have long been recognized as being the result of stick-slip frictional instabilities. Over the past few decades, laboratory studies of rock friction have elucidated many aspects of tectonic fault zone processes and earthquake phenomena. Typically, the static friction of rocks grows logarithmically with time when they are held in stationary contact, but the mechanism responsible for this strengthening is not understood. This time-dependent increase of frictional strength, or frictional ageing, is one manifestation of the 'evolution effect' in rate and state friction theory. A prevailing view is that the time dependence of rock friction results from increases in contact area caused by creep of contacting asperities. Here we present the results of atomic force microscopy experiments that instead show that frictional ageing arises from the formation of interfacial chemical bonds, and the large magnitude of ageing at the nanometre scale is quantitatively consistent with what is required to explain observations in macroscopic rock friction experiments. The relative magnitude of the evolution effect compared with that of the 'direct effect'--the dependence of friction on instantaneous changes in slip velocity--determine whether unstable slip, leading to earthquakes, is possible. Understanding the mechanism underlying the evolution effect would enable us to formulate physically based frictional constitutive laws, rather than the current empirically based 'laws', allowing more confident extrapolation to natural faults.

  13. Assembling of carbon nanotubes film responding to significant reduction wear and friction on steel surface

    Science.gov (United States)

    Zhang, Bin; Xue, Yong; Qiang, Li; Gao, Kaixong; Liu, Qiao; Yang, Baoping; Liang, Aiming; Zhang, Junyan

    2017-11-01

    Friction properties of carbon nanotubes have been widely studied and reported, however, the friction properties of carbon nanotubes related on state of itself. It is showing superlubricity under nanoscale, but indicates high shear adhesion as aligned carbon nanotube film. However, friction properties under high load (which is commonly in industry) of carbon nanotube films are seldom reported. In this paper, carbon nanotube films, via mechanical rubbing method, were obtained and its tribology properties were investigated at high load of 5 to 15 N. Though different couple pairs were employed, the friction coefficients of carbon nanotube films are nearly the same. Compared with bare stainless steel, friction coefficients and wear rates under carbon nanotube films lubrication reduced to, at least, 1/5 and 1/(4.3-14.5), respectively. Friction test as well as structure study were carried out to reveal the mechanism of the significant reduction wear and friction on steel surface. One can conclude that sliding and densifying of carbon nanotubes at sliding interface contribute to the sufficient decrease of friction coefficients and wear rates.

  14. 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.

  15. Rubber contact mechanics: adhesion, friction and leakage of seals.

    Science.gov (United States)

    Tiwari, A; Dorogin, L; Tahir, M; Stöckelhuber, K W; Heinrich, G; Espallargas, N; Persson, B N J

    2017-12-13

    We study the adhesion, friction and leak rate of seals for four different elastomers: Acrylonitrile Butadiene Rubber (NBR), Ethylene Propylene Diene (EPDM), Polyepichlorohydrin (GECO) and Polydimethylsiloxane (PDMS). Adhesion between smooth clean glass balls and all the elastomers is studied both in the dry state and in water. In water, adhesion is observed for the NBR and PDMS elastomers, but not for the EPDM and GECO elastomers, which we attribute to the differences in surface energy and dewetting. The leakage of water is studied with rubber square-ring seals squeezed against sandblasted glass surfaces. Here we observe a strongly non-linear dependence of the leak rate on the water pressure ΔP for the elastomers exhibiting adhesion in water, while the leak rate depends nearly linearly on ΔP for the other elastomers. We attribute the non-linearity to some adhesion-related phenomena, such as dewetting or the (time-dependent) formation of gas bubbles, which blocks fluid flow channels. Finally, rubber friction is studied at low sliding speeds using smooth glass and sandblasted glass as substrates, both in the dry state and in water. The measured friction coefficients are compared to theory, and the origin of the frictional shear stress acting in the area of real contact is discussed. The NBR rubber, which exhibits the strongest adhesion both in the dry state and in water, also shows the highest friction both in the dry state and in water.

  16. Friction behavior of cobalt base and nickel base hardfacing materials in high temperature sodium

    International Nuclear Information System (INIS)

    Mizobuchi, Syotaro; Kano, Shigeki; Nakayama, Kohichi; Atsumo, Hideo

    1980-01-01

    A friction behavior of the hardfacing materials such as cobalt base alloy ''Stellite'' and nickel base alloy ''Colmonoy'' used in the sliding components of a sodium cooled fast breeder reactor was investigated in various sodium environments. Also, friction tests on these materials were carried out in argon environment. And they were compared with those in sodium environment. The results obtained are as follows: (1) In argon, the cobalt base hardfacing alloy showed better friction behavior than the nickel base hardfacing alloy. In sodium, the latter was observed to have the better friction behavior being independent of the sodium temperature. (2) The friction coefficient of each material tends to become lower by pre-exposure in sodium. Particularly, this tendency was remarkable for the nickel base hardfacing alloy. (3) The friction coefficient between SUS 316 and one of these hardfacing materials was higher than that between latter materials. Also, some elements of hardfacing alloys were recognized to transfer on the friction surface of SUS 316 material. (4) It was observed that each tested material has a greater friction coefficient with a decrease of the oxygen content in sodium. (author)

  17. Frictional sliding and fracture behavior of some Nevada test site tuffs

    International Nuclear Information System (INIS)

    Morrow, C.; Byerlee, J.

    1984-01-01

    Deformation studies were performed on tuffaceous rocks from Yucca Mountain, Nevada Test Site to determine the strengths and coefficients of friction under confining pressures from 10 to 50 MPa at room temperature. Frictional strengths of 30 0 sawcut samples increased with pressure and reached values of around 150 MPa at the higher confining pressures. However, the failure strengths of the intact samples were quite unpredictable. The coefficients of friction ranged between 0.7 and 0.9 for all specimens. These data can be used in conjunction with in situ stress measurements at Yucca Mountain, to evaluate the potential for earthquake activity in the region. 1 ref., 7 figs

  18. Friction behavior of a microstructured polymer surface inspired by snake skin.

    Science.gov (United States)

    Baum, Martina J; Heepe, Lars; Gorb, Stanislav N

    2014-01-01

    The aim of this study was to understand the influence of microstructures found on ventral scales of the biological model, Lampropeltis getula californiae, the California King Snake, on the friction behavior. For this purpose, we compared snake-inspired anisotropic microstructured surfaces to other microstructured surfaces with isotropic and anisotropic geometry. To exclude that the friction measurements were influenced by physico-chemical variations, all friction measurements were performed on the same epoxy polymer. For frictional measurements a microtribometer was used. Original data were processed by fast Fourier transformation (FFT) with a zero frequency related to the average friction and other peaks resulting from periodic stick-slip behavior. The data showed that the specific ventral surface ornamentation of snakes does not only reduce the frictional coefficient and generate anisotropic frictional properties, but also reduces stick-slip vibrations during sliding, which might be an adaptation to reduce wear. Based on this extensive comparative study of different microstructured polymer samples, it was experimentally demonstrated that the friction-induced stick-slip behavior does not solely depend on the frictional coefficient of the contact pair.

  19. Friction behavior of a microstructured polymer surface inspired by snake skin

    Directory of Open Access Journals (Sweden)

    Martina J. Baum

    2014-01-01

    Full Text Available The aim of this study was to understand the influence of microstructures found on ventral scales of the biological model, Lampropeltis getula californiae, the California King Snake, on the friction behavior. For this purpose, we compared snake-inspired anisotropic microstructured surfaces to other microstructured surfaces with isotropic and anisotropic geometry. To exclude that the friction measurements were influenced by physico-chemical variations, all friction measurements were performed on the same epoxy polymer. For frictional measurements a microtribometer was used. Original data were processed by fast Fourier transformation (FFT with a zero frequency related to the average friction and other peaks resulting from periodic stick-slip behavior. The data showed that the specific ventral surface ornamentation of snakes does not only reduce the frictional coefficient and generate anisotropic frictional properties, but also reduces stick-slip vibrations during sliding, which might be an adaptation to reduce wear. Based on this extensive comparative study of different microstructured polymer samples, it was experimentally demonstrated that the friction-induced stick-slip behavior does not solely depend on the frictional coefficient of the contact pair.

  20. Experimental quantification of contact forces with impact, friction and uncertainty analysis

    DEFF Research Database (Denmark)

    Lahriri, Said; Santos, Ilmar

    2013-01-01

    and whirl motions in rotor-stator contact investigations. Dry friction coefficient is therefore estimated using two different experimental setups: (a) standard pin-on-disk tests and (b) rotor impact test rig fully instrumented. The findings in both setups indicate that the dry friction coefficient for brass......During rotor-stator contact dry friction plays a significant role in terms of reversing the rotor precession. The frictional force causes an increase in the rotor's tangential velocity in the direction opposite to that of the angular velocity. This effect is crucial for defining ranges of dry whip......-aluminum configuration significantly varies in a range of 0.16-0.83. The rotor enters a full annular contact mode shortly after two impacts with a contact duration of approximately 0.004 s at each location. It is experimentally demonstrated that the friction force is not present when the rotor enters a full annular...

  1. Effects of rolling friction on a spinning coin or disk

    Science.gov (United States)

    Cross, Rod

    2018-05-01

    Experimental and theoretical results are presented concerning the motion of a spinning disk on a horizontal surface. The disk precesses about a vertical axis while falling either quickly or slowly onto the surface depending on the coefficient of rolling friction. The rate of fall also depends on the offset distance, in the rolling direction, between the centre of mass and the line of action of the normal reaction force. Euler’s angular momentum equations are solved to obtain estimates of both the coefficient of friction and the offset distance for a 50.6 mm diameter brass disk spinning on three different surfaces. The fall times varied from about 3 s on P800 emery paper to about 30 s on glass.

  2. Friction and Lubrication of Large Tilting-Pad Thrust Bearings

    Directory of Open Access Journals (Sweden)

    Michał Wasilczuk

    2015-04-01

    Full Text Available Fluid film bearings have been extensively used in the industry because of their unbeatable durability and extremely low friction coefficient, despite a very low coefficient of friction dissipation of energy being noticeable, especially in large bearings. Lubricating systems of large tilting pad thrust bearings utilized in large, vertical shaft hydrogenerators are presented in this paper. A large amount of heat is generated due to viscous shearing of the lubricant large tilting pad thrust bearings, and this requires systems for forced cooling of the lubricant. In the dominant bath lubrication systems, cooling is realized by internal coolers or external cooling systems, with the latter showing some important advantages at the cost of complexity and also, potentially, lower reliability. Substantial losses in the bearings, reaching 1 MW in extreme cases, are a good motivation for the research and development aimed at reducing them. Some possible methods and their potential efficiency, along with some effects already documented, are also described in the paper.

  3. Nonmonotonicity of the Frictional Bimaterial Effect

    Science.gov (United States)

    Aldam, Michael; Xu, Shiqing; Brener, Efim A.; Ben-Zion, Yehuda; Bouchbinder, Eran

    2017-10-01

    Sliding along frictional interfaces separating dissimilar elastic materials is qualitatively different from sliding along interfaces separating identical materials due to the existence of an elastodynamic coupling between interfacial slip and normal stress perturbations in the former case. This bimaterial coupling has important implications for the dynamics of frictional interfaces, including their stability and rupture propagation along them. We show that while this bimaterial coupling is a monotonically increasing function of the bimaterial contrast, when it is coupled to interfacial shear stress perturbations through a friction law, various physical quantities exhibit a nonmonotonic dependence on the bimaterial contrast. In particular, we show that for a regularized Coulomb friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is a nonmonotonic function of the bimaterial contrast and provides analytic insight into the origin of this nonmonotonicity. We further show that for velocity-strengthening rate-and-state friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is also a nonmonotonic function of the bimaterial contrast. Results from simulations of dynamic rupture along a bimaterial interface with slip-weakening friction provide evidence that the theoretically predicted nonmonotonicity persists in nonsteady, transient frictional dynamics.

  4. Protein friction limits diffusive and directed movements of kinesin motors on microtubules.

    Science.gov (United States)

    Bormuth, Volker; Varga, Vladimir; Howard, Jonathon; Schäffer, Erik

    2009-08-14

    Friction limits the operation of macroscopic engines and is critical to the performance of micromechanical devices. We report measurements of friction in a biological nanomachine. Using optical tweezers, we characterized the frictional drag force of individual kinesin-8 motor proteins interacting with their microtubule tracks. At low speeds and with no energy source, the frictional drag was related to the diffusion coefficient by the Einstein relation. At higher speeds, the frictional drag force increased nonlinearly, consistent with the motor jumping 8 nanometers between adjacent tubulin dimers along the microtubule, and was asymmetric, reflecting the structural polarity of the microtubule. We argue that these frictional forces arise from breaking bonds between the motor domains and the microtubule, and they limit the speed and efficiency of kinesin.

  5. Assessment of semi-active friction dampers

    Science.gov (United States)

    dos Santos, Marcelo Braga; Coelho, Humberto Tronconi; Lepore Neto, Francisco Paulo; Mafhoud, Jarir

    2017-09-01

    The use of friction dampers has been widely proposed for a variety of mechanical systems for which applying viscoelastic materials, fluid based dampers or other viscous dampers is impossible. An important example is the application of friction dampers in aircraft engines to reduce the blades' vibration amplitudes. In most cases, friction dampers have been studied in a passive manner, but significant improvements can be achieved by controlling the normal force in the contact region. The aim of this paper is to present and study five control strategies for friction dampers based on three different hysteresis cycles by using the Harmonic Balance Method (HBM), a numerical and experimental analysis. The first control strategy uses the friction force as a resistance when the system is deviating from its equilibrium position. The second control strategy maximizes the energy removal in each harmonic oscillation cycle by calculating the optimal normal force based on the last displacement peak. The third control strategy combines the first strategy with the homogenous modulation of the friction force. Finally, the last two strategies attempt to predict the system's movement based on its velocity and acceleration and our knowledge of its physical properties. Numerical and experimental studies are performed with these five strategies, which define the performance metrics. The experimental testing rig is fully identified and its parameters are used for numerical simulations. The obtained results show the satisfactory performance of the friction damper and selected strategy and the suitable agreement between the numerical and experimental results.

  6. A field theoretic model for static friction

    OpenAIRE

    Mahyaeh, I.; Rouhani, S.

    2013-01-01

    We present a field theoretic model for friction, where the friction coefficient between two surfaces may be calculated based on elastic properties of the surfaces. We assume that the geometry of contact surface is not unusual. We verify Amonton's laws to hold that friction force is proportional to the normal load.This model gives the opportunity to calculate the static coefficient of friction for a few cases, and show that it is in agreement with observed values. Furthermore we show that the ...

  7. Sliding friction and wear behaviors of surface-coated natural serpentine mineral powders as lubricant additive

    International Nuclear Information System (INIS)

    Zhang Baosen; Xu Yi; Gao Fei; Shi Peijing; Xu Binshi; Wu Yixiong

    2011-01-01

    This work aims to investigate the friction and wear properties of surface-coated natural serpentine powders (SP) suspended in diesel engine oil using an Optimal SRV oscillating friction and wear tester. The worn surface was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Results indicated that the additives can improve the wear resistance and decrease friction coefficient of carbon steel friction couples. The 0.5 wt% content of serpentine powders is found most efficient in reducing friction and wear at the load of 50 N. The SEM and XPS analysis results demonstrate that a tribofilm forms on the worn surface, which is responsible for the decrease in friction and wear, mainly with iron oxides, silicon oxides, graphite and organic compounds.

  8. Velocity dependence of friction of confined polymers

    DEFF Research Database (Denmark)

    Sivebæk, Ion Marius; Samoilov, V.N.; Persson, B.N.J.

    2009-01-01

    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. We discuss the velocity dependence of the frictional...... shear stress for both cases. In our simulations, the polymer films are very thin (approx. 3 nm), and the solid walls are connected to a thermostat at a short distance from the polymer slab. Under these circumstances we find that frictional heating effects are not important, and the effective temperature...... in the polymer film is always close to the thermostat temperature. In the first setup (a), for hydrocarbons with molecular lengths from 60 to 1400 carbon atoms, the shear stresses are nearly independent of molecular length, but for the shortest hydrocarbon C20H42 the frictional shear stress is lower. In all...

  9. The temperature dependence of the friction in the fission

    International Nuclear Information System (INIS)

    Yamaji, Shuhei

    1996-01-01

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

  10. The Friction of Vehicle Brake Tandem Master Cylinder

    International Nuclear Information System (INIS)

    Kao, M J; Chang, H; Tsung, T T; Lin, H M

    2006-01-01

    The behaviour of an elastomeric seal for vehicle brake Tandem master cylinder is measured and analyzed in temperature and brake fluids changed. Working conditions are simulated for different piston rod velocity and cylinder supply pressure, in temperature rising, brakefluid boundary and Nanoaluminum oxide brakefluid oxide brakefluid lubrication. The result shows that Nanoaluminum oxide brakefluid with its ball shape can highly reduce friction coefficient to avoid seal excessive wear and reduce slick slip in brake applications

  11. Friction and wear properties of Cu and Fe-based P/M bearing materials

    International Nuclear Information System (INIS)

    Tufekci, Kenan; Kurbanoglu, Cahit; Durak, Ertugrul; Tunay, R. Fatih

    2006-01-01

    The performances of porous bearings under different operating conditions were experimentally investigated in this study. Material groups studied are 90%Cu + 10%Sn bronze and 1%C + % balance Fe iron-based self-lubricating P/M bearings at constant (85%) density. In the experiments, the variation of the coefficient of friction and wear ratio of those two different group materials for different sliding speeds, loads, and temperatures were investigated. As a result, the variation of the friction coefficient - temperature for both constant load, and constant sliding speed, friction coefficient - average bearing pressure, PV - wear loss and temperature-wear loss curves were plotted and compared with each other for two materials, separately. The test results showed that Cu-based bearings have better friction and wear properties than Fe-based bearings

  12. 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.)

  13. THE THEORETICAL FOUNDATIONS OF VIBRATION DAMPERS BY ROLLING FRICTION

    Directory of Open Access Journals (Sweden)

    L. M. Bondarenko

    2015-06-01

    Full Text Available Purpose. There are some unresolved issues in vibration damping – the lack of engineering calculations for the vibration dampers by rolling friction; the absence of evidence of their application appropriateness. Considering this fact, the authors suggest to prove that the dampers based on rolling friction, are similar in rate of oscillation damping by hydraulic shock absorbers. At the same time, they are easier for the hydraulic design, and easily amenable to manual adjustment, both in automatic and manual mode. Methodology. Fixed techniques of practice in order to determine amplitudes of the oscillations of a shock absorber led to a predetermined result and will apply this theory in the calculation of other vibration dampers. Findings. Analysis of the formulas and graphs leads to the following conclusions and recommendations: 1 the nature of the oscillation damping at vibration dampers by rolling friction is close to their decay in the viscous resistance; 2 when conducting the necessary experiments the shock absorber rolling can be recommended as alternatives to hydraulic ones. The research results of this task will help implement the new trend in reduction of dynamic loads in vehicles. Originality. With the help of theoretical curves to determine the coefficients of rolling friction the dependences for determining the amplitudes of the oscillations in the vertical movement of cargo were obtained. At the same time, the previously proposed analytical dependence for determining the coefficient of rolling friction contains only conventional mechanical constants of the contacting bodies and there geometrical dimensions. Practical value. Due to the existing well-known disadvantages of hydraulic shock absorbers it would be logical to apply shock absorbers that are technologically convenient in manufacturing and easy to adjust the damping rate. The proposed theory can be used in the design of shock absorbers rolling as an alternative to the hydraulic

  14. Interfacial Friction and Adhesion of Polymer Brushes

    KAUST Repository

    Landherr, Lucas J. T.; Cohen, Claude; Agarwal, Praveen; Archer, Lynden A.

    2011-01-01

    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

  15. Experimental studies of the magnetized friction force

    International Nuclear Information System (INIS)

    Fedotov, A. V.; Litvinenko, V. N.; Gaalnander, B.; Lofnes, T.; Ziemann, V.; Sidorin, A.; Smirnov, A.

    2006-01-01

    High-energy electron cooling, presently considered as an essential tool for several applications in high-energy and nuclear physics, requires an accurate description of the friction force which ions experience by passing through an electron beam. Present low-energy electron coolers can be used for a detailed study of the friction force. In addition, parameters of a low-energy cooler can be chosen in a manner to reproduce regimes expected in future high-energy operation. Here, we report a set of dedicated experiments in CELSIUS aimed at a detailed study of the magnetized friction force. Some results of the accurate comparison of experimental data with the friction force formulas are presented

  16. Effect of friction on vibrotactile sensation of normal and dehydrated skin.

    Science.gov (United States)

    Chen, S; Ge, S; Tang, W; Zhang, J

    2016-02-01

    Vibrotactile sensation mediated is highly dependent on surface mechanical and frictional properties. Dehydration of skin could change these properties. To investigate the relationship between friction and vibrotactile sensation of normal and dehydrated skin. Vibrations were firstly measured during surface exploration using a biomimetic sensor. Piglet skin was used as human skin model to study frictional properties for both normal and dehydrated skin using an atomic force microscope on nanoscale and a pin-on-disk tribometer on macroscale. Effect of vibrational frequency on friction and vibrotactile perception was also observed on nano and macro scale for normal and dehydrated skin. The result indicated that dehydrated skin was less sensitive than normal skin. The coefficient of friction of dehydrated skin is smaller than that of normal skin on both nano and macro scale. The coefficient of friction increases as increasing scanning frequencies. There is a positive correlation between coefficient of friction and vibrotactile sensation on nanoscale and macroscale. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  17. Friction Welding of Titanium and Carbon Steel

    OpenAIRE

    Atsushi, HASUI; Yoichi, KIRA; Faculty of Science and Technology, Keio University; Ishikawajima-Harima Heavy Industries, Co., Ltd.

    1985-01-01

    Titanium-steel is a combination of dissimilar materials, which are difficult to weld in general, owing to inevitable formation of brittle intermetallic compounds. A prominent feature of friction welding process is ability to weld dissimilar materials in many kinds of combinations. This report deals with friction weldabilily of pure titanium and S25C steel, which are 12 mm in diameter. Main results are summarized as follows; (1) Suitable welding conditions to obtain a sound weld, which has a j...

  18. Fundamentals of Friction and Vapor Phase Lubrication

    National Research Council Canada - National Science Library

    Gellman, Andrew

    2004-01-01

    This is the final report for the three year research program on "Fundamentals of Friction and Vapor Phase Lubrication" conducted at Carnegie Mellon with support from AFOSR grant number F49630-01-1-0069...

  19. Comparisons of friction models in bulk metal forming

    DEFF Research Database (Denmark)

    Tan, Xincai

    2002-01-01

    A friction model is one of the key input boundary conditions in finite element simulations. It is said that the friction model plays an important role in controlling the accuracy of necessary output results predicted. Among the various friction models, which one is of higher accuracy is still...... unknown and controversial. In this paper, finite element analyses applying five different friction models to experiments of upsetting of AA 6082 lubricated with four lubricants are presented. Frictional parameter values are determined by fitness of data of friction area ratio from finite element analysis...... to experimental results. It is found that calibration curves of the friction area ratio for all of the five chosen friction models used in the finite element simulation do fit the experimental results. Usually, calbration curves of the friction area ratio are more sensitive to friction at the tool...

  20. Effects of wall friction on flow in a quasi-2D hopper

    Science.gov (United States)

    Shah, Neil; Birwa, Sumit; Carballo-Ramirez, Brenda; Pleau, Mollie; Easwar, Nalini; Tewari, Shubha

    Our experiments on the gravity-driven flow of spherical particles in a vertical hopper examine how the flow rate varies with opening size and wall friction. We report here on a model simulation using LAMMPS of the experimental geometry, a quasi-2D hopper. Keeping inter-particle friction fixed, the coefficient of friction at the walls is varied from 0.0 to 0.9 for a range of opening sizes. Our simulations find a steady rate of flow at each wall friction and outlet size. The Janssen effect attributes the constant rate of flow of a granular column to the column height independence of the pressure at the base, since the weight of the grains is borne in part by friction at the walls. However, we observe a constant flow regime even in the absence of wall friction, suggesting that wall friction may not be a necessary condition for pressure saturation. The observed velocities of particles near the opening are used to extrapolate their starting positions had they been in free fall. In contrast to scaling predictions, our data suggest that the height of this free-fall arch does not vary with opening size for higher frictional coefficients. We analyze the velocity traces of particles to see the range over which contact interactions remain collisional as they approach the hopper outlet.

  1. The Effect of Thickness and Chemical Reduction of Graphene Oxide on Nanoscale Friction.

    Science.gov (United States)

    Kwon, Sangku; Lee, Kyung Eun; Lee, Hyunsoo; Koh, Sang Joon; Ko, Jae-Hyeon; Kim, Yong-Hyun; Kim, Sang Ouk; Park, Jeong Young

    2018-01-18

    The tribological properties of two-dimensional (2D) atomic layers are quite different from three-dimensional continuum materials because of the unique mechanical responses of 2D layers. It is known that friction on graphene shows a remarkable decreasing behavior as the number of layers increases, which is caused by the puckering effect. On other graphene derivatives, such as graphene oxide (GO) or reduced graphene oxide (rGO), the thickness dependence of friction is important because of the possibilities for technical applications. In this report, we demonstrate unexpected layer-dependent friction behavior on GO and rGO layers. Friction force microscopy measurements show that nanoscale friction on GO does not depend on the number of layers; however, after reduction, friction on rGO shows an inverse thickness dependence compared with pristine graphene. We show that the friction on rGO is higher than that on SiO 2 at low load, and that an interesting crossover behavior at higher load occurs because of the lower friction coefficient and higher adhesion of the rGO. We provide a relevant interpretation that explains the effect of thickness and chemical reduction on nanoscale friction.

  2. Stick-slip friction and wear of articular joints

    Science.gov (United States)

    Lee, Dong Woog; Banquy, Xavier; Israelachvili, Jacob N.

    2013-01-01

    Stick-slip friction was observed in articular cartilage under certain loading and sliding conditions and systematically studied. Using the Surface Forces Apparatus, we show that stick-slip friction can induce permanent morphological changes (a change in the roughness indicative of wear/damage) in cartilage surfaces, even under mild loading and sliding conditions. The different load and speed regimes can be represented by friction maps—separating regimes of smooth and stick-slip sliding; damage generally occurs within the stick-slip regimes. Prolonged exposure of cartilage surfaces to stick-slip sliding resulted in a significant increase of surface roughness, indicative of severe morphological changes of the cartilage superficial zone. To further investigate the factors that are conducive to stick-slip and wear, we selectively digested essential components of cartilage: type II collagen, hyaluronic acid (HA), and glycosaminoglycans (GAGs). Compared with the normal cartilage, HA and GAG digestions modified the stick-slip behavior and increased surface roughness (wear) during sliding, whereas collagen digestion decreased the surface roughness. Importantly, friction forces increased up to 2, 10, and 5 times after HA, GAGs, and collagen digestion, respectively. Also, each digestion altered the friction map in different ways. Our results show that (i) wear is not directly related to the friction coefficient but (ii) more directly related to stick-slip sliding, even when present at small amplitudes, and that (iii) the different molecular components of joints work synergistically to prevent wear. Our results also suggest potential noninvasive diagnostic tools for sensing stick-slip in joints. PMID:23359687

  3. 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 i...

  4. Measuring of heat transfer coefficient

    DEFF Research Database (Denmark)

    Henningsen, Poul; Lindegren, Maria

    Subtask 3.4 Measuring of heat transfer coefficient Subtask 3.4.1 Design and setting up of tests to measure heat transfer coefficient Objective: Complementary testing methods together with the relevant experimental equipment are to be designed by the two partners involved in order to measure...... the heat transfer coefficient for a wide range of interface conditions in hot and warm forging processes. Subtask 3.4.2 Measurement of heat transfer coefficient The objective of subtask 3.4.2 is to determine heat transfer values for different interface conditions reflecting those typically operating in hot...

  5. Friction and wear study of NR/SBR blends with Si3N4Filler

    Science.gov (United States)

    GaneshKumar, A.; Balaganesan, G.; Sivakumar, M. S.

    2018-04-01

    The aim of this paper is to investigate mechanical and frictional properties of natural rubber/styrene butadiene rubber (NR/SBR) blends with and without silicon nitride (Si3N4) filler. The rubber is surface modified by silane coupling agent (Si-69) for enhancing hydrophobic property. The Si3N4of percentage 0 1, 3, 5 and 7, is incorporated into NR/SBR rubber compounds with 20% precipitated silica. The specimens with and without fillers are prepared as per standard for tensile and friction testing. Fourier transform infrared (FTIR) spectroscopy test is conducted and it is inferred that the coupling agent is covalently bonded on the surface of Si3N4 particles and an organic coating layer is formed. The co-efficient of friction and specific wear rate of NR/SBR blends are examined using an in-house built friction tester in a disc-on-plate (DOP) configuration. The specimens are tested to find coefficient of friction (COF) against steel grip antiskid plate under dry, mud, wet and oil environmental conditions. It is found that the increase in tensile strength and modulus at low percentage of Si3N4 dispersion. It is also observed that increase in sliding friction co-efficient and decrease in wear rate for 1% of Si3N4 dispersion in NR/SBR blends. The friction tested surfaces are inspected using Scanning Electron Microscope (SEM) and 3D non contact surface profiler.

  6. Friction of ceramic and metal hip hemi-endoprostheses against cadaveric acetabula.

    Science.gov (United States)

    Müller, L P; Degreif, J; Rudig, L; Mehler, D; Hely, H; Rommens, P M

    2004-12-01

    Studies of hip arthroplasty have dealt mainly with total endoprosthesis, while tribology measurement values of hemi-endoprosthetic implants are rare. The small amount of experimental tribological data concerning materials of hemi-endoprosthetic implants in the form of pendulum trials, animal experiments, in vivo measurements on human hip joints and pin on disc studies report friction coefficients between 0.014 and 0.57; the friction coefficients measured in fresh human cadaver hip joints were determined between 0.001 and 0.08. The HEPFlEx-hip simulator was constructed to test the friction coefficients of unipolar femur head hemi-endoprostheses made of metal or ceramic against fresh cadaveric acetabula. Its plane of movement is uniaxial with a flexion-extension movement of +30/-18 degrees . The force is produced pneumatically dynamic with amounts of 2.5 kN. Newborn calf serum serves as a lubricant. We mounted 20 fresh porcine acetabula and 10 fresh human cadaver acetabula in the HEPFlEx-hip simulator and compared the two unipolar femur head hemi-endoprostheses (metal vs. ceramic). The mean friction coefficients against porcine acetabula were micro=0.017-0.082 for ceramic and micro=0.020-0.101 for metal; against human cadaver acetabula micro=0.017-0.083 for ceramic and micro=0.019-0.118 for metal. The frictional coefficient deltas (metal-ceramic) values of all measurements were Deltamicro=0.004 for porcine acetabula and Deltamicro=0.001 for cadaver acetabula. Box-plots graphics document significantly lower frictional coefficients of the ceramics. The lower frictional coefficients of ceramic compared to metal against fresh cadaveric acetabula may have a clinical impact on the process of the protrusion of the corresponding femoral head through the acetabulum.

  7. Tribo-chemical behavior of eutectoid steel during rolling contact friction

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Y.; Cai, Z.B. [Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu 610031 (China); Peng, J.F. [Tribology Research Institute, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China); Cao, B.B. [Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu 610031 (China); Jin, X.S. [Tribology Research Institute, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China); Zhu, M.H., E-mail: zhuminhao@swjtu.cn [Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu 610031 (China); Tribology Research Institute, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China)

    2016-12-01

    Highlights: • Tribo-chemical behavior was investigated during rolling contact friction. • Tribo-film may weaken the absorptive ability of O/C atoms on the surface. • Tribo-film is related to a low friction coefficient at rolling friction condition. - Abstract: The tribo-chemical behavior of the eutectoid steel during rolling contact friction is investigated via scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and electron probe X-ray microanalysis. The worn surface is divided into three zones: matrix zone (without friction), tribo-film zone (formed during friction) and delamination zone (tribo-film spalling). The different chemical states of atoms between those three zones and the air were investigated using the XPS analysis. The results showed that the matrix zone is composed of Fe{sub 2}O{sub 3}, FeO and metallic Fe, while the tribo-film and delamination zones only contain Fe{sub 2}O{sub 3} and FeO. Where the tribo-film is formed, the absorptive ability of O and C atoms on the top 2–3 atomic layers is probably weakened, while the exposed fresh metal in the delamination zone tends to be continuously oxidized and form tribo-film. The tribo-chemical reaction in the delamination zone is more activated than that in the other two zones. The protective nature of the tribo-film probably maintains a low friction coefficient under rolling contact friction condition.

  8. Modeling Friction Performance of Drill String Torsional Oscillation Using Dynamic Friction Model

    Directory of Open Access Journals (Sweden)

    Xingming Wang

    2017-01-01

    Full Text Available Drill string torsional and longitudinal oscillation can significantly reduce axial drag in horizontal drilling. An improved theoretical model for the analysis of the frictional force was proposed based on microscopic contact deformation theory and a bristle model. The established model, an improved dynamic friction model established for drill strings in a wellbore, was used to determine the relationship of friction force changes and the drill string torsional vibration. The model results were in good agreement with the experimental data, verifying the accuracy of the established model. The analysis of the influence of drilling mud properties indicated that there is an approximately linear relationship between the axial friction force and dynamic shear and viscosity. The influence of drill string torsional oscillation on the axial friction force is discussed. The results indicated that the drill string transverse velocity is a prerequisite for reducing axial friction. In addition, low amplitude of torsional vibration speed can significantly reduce axial friction. Then, increasing the amplitude of transverse vibration speed, the effect of axial reduction is not significant. In addition, by involving general field drilling parameters, this model can accurately describe the friction behavior and quantitatively predict the frictional resistance in horizontal drilling.

  9. 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.

  10. Investigation of Friction Behaviors of Brake Shoe Materials using Metallic Filler

    Directory of Open Access Journals (Sweden)

    E. Surojo

    2015-12-01

    Full Text Available Some vehicles use brake shoe made from semi-metallic materials. Semi-metallic brake shoes are made from a combination of metallic and non-metallic materials. Metallic particles are added in the formulation of brake shoe material to improve composites characteristics. In this paper, friction behaviors of brake shoe material using metallic filler were investigated. Machining chips of cast iron and copper wire of electric motor used were incorporated in composite as metallic fillers with amount 0, 2, and 4 vol. %. Friction testing was performed to measure coefficient of friction by pressing surface specimen against the surface of rotating disc. The results show that cast iron chip and Cu short wire have effect on increasing coefficient of friction of brake shoe material. They form contact plateau at contact surface. At contact surface, the Cu short wires which have parallel orientation to the sliding contact were susceptible to detach from the matrix.

  11. Nonequilibrium Molecular Simulations of New Ionic Lubricants at Metallic Surfaces: Prediction of the Friction.

    Science.gov (United States)

    Mendonça, Ana C F; Pádua, Agílio A H; Malfreyt, Patrice

    2013-03-12

    We report nonequilibrium molecular dynamics of ionic liquids interacting with metallic surfaces. A specific set of interaction parameters for ionic liquids composed of alkylammonium cations and alkylsulfonate anions with an iron surface, which has been previously developed (J. Chem. Theory Comput.2012, 8, 3348) is used here. We develop a procedure for a quantitative prediction of the friction coefficient at different loads and shear rates. The simulated friction coefficient agrees very well with the available experimental ones. The dependence of friction on the load, shear velocity, surface topology, and length of alkyl side chains in the ionic liquid is also investigated. The changes in the frictional forces are explained in terms of the specific arrangements and orientations of groups forming the ionic liquid at the vicinity of the surface.

  12. Velocity Dependence of Friction of Confined Hydrocarbons

    DEFF Research Database (Denmark)

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

    2010-01-01

    We present molecular dynamics friction calculations for confined hydrocarbon “polymer” 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. We discuss the velocity dependence of the f......We present molecular dynamics friction calculations for confined hydrocarbon “polymer” 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. We discuss the velocity dependence...... of the frictional shear stress for both cases. In our simulations, the polymer films are very thin (∼3 nm), and the solid walls are connected to a thermostat at a short distance from the polymer slab. Under these circumstances we find that frictional heating effects are not important, and the effective temperature...... in the polymer film is always close to the thermostat temperature. In the first setup (a), for hydrocarbons with molecular lengths from 60 to 1400 carbon atoms, the shear stresses are nearly independent of molecular length, but for the shortest hydrocarbon C20H42 the frictional shear stress is lower. In all...

  13. Effect of energetic dissipation processes on the friction unit tribological

    Directory of Open Access Journals (Sweden)

    Moving V. V.

    2007-01-01

    Full Text Available In article presented temperature influence on reological and fric-tion unit coefficients cast iron elements. It has been found that surface layer formed in the temperature friction has good rub off resistance. The surface layer structural hardening and capacity stress relaxation make up.

  14. Development of a penetration friction apparatus (PFA) to measure the frictional performance of surgical suture.

    Science.gov (United States)

    Zhang, Gangqiang; Ren, Tianhui; Lette, Walter; Zeng, Xiangqiong; van der Heide, Emile

    2017-10-01

    Nowadays there is a wide variety of surgical sutures available in the market. Surgical sutures have different sizes, structures, materials and coatings, whereas they are being used for various surgeries. The frictional performances of surgical sutures have been found to play a vital role in their functionality. The high friction force of surgical sutures in the suturing process may cause inflammation and pain to the person, leading to a longer recovery time, and the second trauma of soft or fragile tissue. Thus, the investigation into the frictional performance of surgical suture is essential. Despite the unquestionable fact, little is actually known on the friction performances of surgical suture-tissue due to the lack of appropriate test equipment. This study presents a new penetration friction apparatus (PFA) that allowed for the evaluation of the friction performances of various surgical needles and sutures during the suturing process, under different contact conditions. It considered the deformation of tissue and can realize the puncture force measurements of surgical needles as well as the friction force of surgical sutures. The developed PFA could accurately evaluate and understand the frictional behaviour of surgical suture-tissue in the simulating clinical conditions. The forces measured by the PFA showed the same trend as that reported in literatures. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Available friction of ladder shoes and slip potential for climbing on a straight ladder.

    Science.gov (United States)

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

    2005-07-15

    Straight ladder accidents are a major safety problem. As a leading cause of injuries involving straight ladders, slips at the ladder base occur when the required friction exceeds the available friction at the ladder shoe and floor interface. The objectives of this experiment were to measure the available friction at the base of a portable straight ladder in contact with a floor and to estimate the slip potential of the ladder. The results of friction measurements indicated that the measured friction coefficient on the oily surfaces differed among the six commercially available ladder shoes evaluated. A statistical model was used to compare the available friction results from the current study with the friction requirements under different climbing conditions from a previous study based on their stochastic distributions to estimate the slip potential at the base of the ladder. The results showed that different climbing conditions used in the previous study could be supported by available friction on dry surfaces. However, when the ladder was put onto oily surfaces, resulting in a significant reduction in the available friction due to contamination, slip potential was significantly increased.

  16. Influences of thickness, scanning velocity and relative humidity on the frictional properties of WS2 nanosheets

    Science.gov (United States)

    Feng, Dongdong; Peng, Jinfeng; Liu, Sisi; Zheng, Xuejun; Yan, Xinyang; He, Wenyuan

    2018-01-01

    Distinguishing with the traditional cantilever mechanics method, we propose the extended cantilever mechanics method to calibrate the lateral calibration factor by using the normal spring constant obtained from atomic force microscopy (AFM) but not the Young’s modulus and the width of the cantilever, before the influences of thickness, scanning velocity and humidity on the frictional properties are investigated via friction measurement performed by the lateral force mode (LFM) of AFM. Tungsten disulfide (WS2) nanosheets were prepared through hydrothermal intercalation and exfoliation route, and AFM and Raman microscope were used to investigate the frictional properties, thickness and crystalline structure. The friction force and coefficient decrease monotonically with the increase of the nanosheet’s thickness, and the friction coefficient minimum value is close to 0.012 when the thickness larger than 5 nm. The friction property variation on the nanosheet’s thickness can be explained by the puckering effect of tip-sheet adhesion according thickness dependence of bending stiffness in the frame of continuum mechanics. The friction force is a constant value 1.7 nN when the scanning speed larger than the critical value 3.10 μm s-1, while it logarithmically increases for the scanning speed less than the critical value. It is easy to understand through the energy dissipation model and the thermally activated effect. The friction force and friction coefficient increase with the relative humidity at the range of 30%-60%, and the latter is at the range of 0.010-0.013. Influence of relative humidity is discussed via the increasing area of the water monolayer during the water adsorption process. The research can not only enrich nanotribology theory, but also prompt two dimensions materials for nanomechanical applications.

  17. Vibrational Interaction of Two Rotors with Friction Coupling

    Directory of Open Access Journals (Sweden)

    H. Larsson

    2016-01-01

    Full Text Available A lumped parameter model is presented for studying the dynamic interaction between two disks in relative rotational motion and in friction contact. The contact elastic and dissipative characteristics are represented by equivalent stiffness and damping coefficient in the axial as well as torsional direction. The formulation accounts for the coupling between the axial and angular motions by viewing the contact normal force a result of axial behavior of the system. The model is used to investigate stick-slip behavior of a two-disk friction system. In this effort the friction coefficient is represented as an exponentially decaying function of relative angular velocity, varying from its static value at zero relative velocity to its kinetic value at very high velocities. This investigation results in the establishment of critical curve defining two-parameter regions: one in which stick-slip occurs and that in which stick-slip does not occur. Moreover, the onset and termination of stick-slip, when it occurs, are related to the highest component frequency in the system. It is found that stick-slip starts at a period nearly equal to that of the highest component frequency and terminates at a period almost three times that of the highest component frequency.

  18. Finite Element Analysis of the Amontons-Coulomb's Model using Local and Global Friction Tests

    International Nuclear Information System (INIS)

    Oliveira, M. C.; Menezes, L. F.; Ramalho, A.; Alves, J. L.

    2011-01-01

    In spite of the abundant number of experimental friction tests that have been reported, the contact with friction modeling persists to be one of the factors that determine the effectiveness of sheet metal forming simulation. This difficulty can be understood due to the nature of the friction phenomena, which comprises the interaction of different factors connected to both sheet and tools' surfaces. Although in finite element numerical simulations friction models are commonly applied at the local level, they normally rely on parameters identified based on global experimental tests results. The aim of this study is to analyze the applicability of the Amontons-Coulomb's friction coefficient identified using complementary tests: (i) load-scanning, at the local level and (ii) draw-bead, at the global level; to the numerical simulation of sheet metal forming processes.

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

    Science.gov (United States)

    Tuononen, Ari J

    2016-06-13

    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.

  20. Coefficient estimates of negative powers and inverse coefficients for ...

    Indian Academy of Sciences (India)

    and the inequality is sharp for the inverse of the Koebe function k(z) = z/(1 − z)2. An alternative approach to the inverse coefficient problem for functions in the class S has been investigated by Schaeffer and Spencer [27] and FitzGerald [6]. Although, the inverse coefficient problem for the class S has been completely solved ...

  1. Effect of dental tool surface texture and material on static friction with a wet gloved fingertip.

    Science.gov (United States)

    Laroche, Charles; Barr, Alan; Dong, Hui; Rempel, David

    2007-01-01

    Hand injuries are an important cause of pain and disability among dentists and dental hygienists and may be due to the high pinch forces involved in periodontal work. The pinch forces required to perform scaling may be reduced by increasing the friction between the tool and fingers. The purpose of this study was to determine whether modifying the tool material, surface texture, or glove type altered the coefficient of static friction for a wet gloved finger. Seven tools with varying surface topography were machined from 13 mm diameter stainless steel and Delrin and mounted to a 6-component force plate. The textures tested were a fine, medium and coarse diamond knurled pattern and a medium and fine annular pattern (concentric rings). Thirteen subjects pulled their gloved, wet thumb pad along the long axis of the tool while maintaining a normal force of 40 N. Latex and nitrile gloves were tested. The coefficient of static friction was calculated from the shear force history. The mean coefficients of static friction ranged from 0.20 to 0.65. The coefficient of static friction was higher for a smooth tool of Delrin than one of stainless steel. Differences in the coefficient of static friction were observed between the coarse and medium knurled patterns and the fine knurled and annular patterns. Coefficients of static friction were higher for the nitrile glove than the latex glove for tools with texture. These findings may be applied to the design of hand tools that require fine motor control with a wet, gloved hand.

  2. A molecular dynamics (MD simulation on tire-aggregate friction

    Directory of Open Access Journals (Sweden)

    Fengyan Sun

    2017-07-01

    Full Text Available The friction between tire and road surface is fundamentally depending on the molecular forces. In this paper, the nanoscale 3D contact model is employed to investigate the tire-aggregate friction mechanism. The tire and aggregate micro-structure are both constructed to evaluate the microscopic performance of tire-aggregate friction influence. Simulation results show for a high velocity, the energy dissipation of sliding on crystal structure is small, which results in a small friction coefficient; temperature will have influences on the friction coefficient, and with the increasing of velocity, the effect will gradually reduce. Keywords: Tire, Aggregate, Friction coefficient, Microscopic mechanism, MD simulation

  3. Friction characteristics of trocars in laparoscopic surgery.

    Science.gov (United States)

    Alazmani, Ali; Roshan, Rupesh; Jayne, David G; Neville, Anne; Culmer, Peter

    2015-04-01

    This article investigates the friction characteristics of the instrument-trocar interface in laparoscopic surgery for varying linear instrument velocities, trocar seal design and material, and trocar tilt. Furthermore, the effect of applying lubrication at the instrument-trocar seal interface on friction was studied. A friction testing apparatus was designed and built to characterise the resistance force at the instrument-trocar interface as a function of the instrument's linear movement in the 12-mm trocar (at constant velocity) for different design, seal material, and angle of tilt. The resistance force depended on the trocar seal design and material properties, specifically surface roughness, elasticity, hardness, the direction of movement, and the instrument linear velocity, and varied between 0.25 and 8 N. Lubricating the shaft with silicone oil reduced the peak resistance force by 75% for all trocars and eliminated the stick-slip phenomenon evident in non-lubricated cases. The magnitude of fluctuation in resistance force depends on the trocar design and is attributed to stick-slip of the sealing mechanism and is generally higher during retraction in comparison to insertion. Trocars that have an inlet seal made of rubber/polyurethane showed higher resistance forces during retraction. Use of a lubricant significantly reduced frictional effects. Comparisons of the investigated trocars indicate that a low friction port, providing the surgeon with improved haptic feedback, can be designed by improving the tribological properties of the trocar seal interface. © IMechE 2015.

  4. Numerical Studies of the Friction Force for the RHIC Electron Cooler

    CERN Document Server

    Fedotov, Alexei V; Ben-Zvi, Ilan; Bruhwiler, David L; Busby, Richard; Litvinenko, Vladimir N; Schoessow, Paul

    2005-01-01

    Accurate calculation of electron cooling times requires an accurate description of the dynamical friction force. The proposed RHIC cooler will require ~55 MeV electrons, which must be obtained from an RF linac, leading to very high transverse electron temperatures. A strong solenoid will be used to magnetize the electrons and suppress the transverse temperature, but the achievable magnetized cooling logarithm will not be large. Available formulas for magnetized dynamical friction are derived in the logarithmic approximation, which is questionable in this regime. In this paper, we explore the magnetized friction force for parameters of the RHIC cooler, using the VORPAL code.* VORPAL can simulate dynamical friction and diffusion coefficients directly from first principles.** Various aspects of the friction force, such as dependence on magnetic field, scaling with ion charge number and others, are addressed for the problem of high-energy electron cooling in the RHIC regime.

  5. Rubber friction: role of the flash temperature

    International Nuclear Information System (INIS)

    Persson, B N J

    2006-01-01

    When a rubber block is sliding on a hard rough substrate, the substrate asperities will exert time-dependent deformations of the rubber surface resulting in viscoelastic energy dissipation in the rubber, which gives a contribution to the sliding friction. Most surfaces of solids have roughness on many different length scales, and when calculating the friction force it is necessary to include the viscoelastic deformations on all length scales. The energy dissipation will result in local heating of the rubber. Since the viscoelastic properties of rubber-like materials are extremely strongly temperature dependent, it is necessary to include the local temperature increase in the analysis. At very low sliding velocity the temperature increase is negligible because of heat diffusion, but already for velocities of order 10 -2 m s -1 the local heating may be very important. Here I study the influence of the local heating on the rubber friction, and I show that in a typical case the temperature increase results in a decrease in rubber friction with increasing sliding velocity for v>0.01 m s -1 . This may result in stick-slip instabilities, and is of crucial importance in many practical applications, e.g. for tyre-road friction and in particular for ABS braking systems

  6. Critical-like features of stress response in frictional packings

    International Nuclear Information System (INIS)

    Cakir, Abdullah; Silbert, Leonardo E

    2015-01-01

    The mechanical response of static, unconfined, overcompressed face centred cubic, granular arrays is studied using large-scale, discrete element method simulations. Specifically, the stress response due to the application of a localised force perturbation—the Green function technique—is obtained in granular packings generated over several orders of magnitude in both the particle friction coefficient and the applied forcing. We observe crossover behaviour in the mechanical state of the system characterised by the changing nature of the resulting stress response. The transition between anisotropic and isotropic stress response exhibits critical-like features through the identification of a diverging length scale that distinguishes the spatial extent of anisotropic regions from those that display isotropic behaviour. A multidimensional phase diagram is constructed that parameterises the response of the system due to changing friction and force perturbations. (paper)

  7. A study of the static to kinetic friction transition of polymers

    OpenAIRE

    Lee, Edward Chungjen

    1995-01-01

    This study investigates the transition from static to kinetic friction for structural polymers and continues previous research conducted by Dr. N. S. Eiss, B. McCann, and R. Molique. A new test apparatus which simultaneously measures friction, normal load, and relative velocity was developed to study this transition. The polymers used in this study were nylon, ABS, polycarbonate, and fiberglass filled and unfilled polypropylene. Creep effects of polymers on the static coefficie...

  8. Modeling of cryogenic frictional behaviour of titanium alloys using Response Surface Methodology approach

    International Nuclear Information System (INIS)

    El-Tayeb, N.S.M.; Yap, T.C.; Venkatesh, V.C.; Brevern, P.V.

    2009-01-01

    The potential of cryogenic effect on frictional behaviour of newly developed titanium alloy Ti-5Al-4V-0.6Mo-0.4Fe (Ti54) sliding against tungsten carbide was investigated and compared with conventional titanium alloy Ti6Al4V (Ti64). In this study, four models were developed to describe the interrelationship between the friction coefficient (response) and independent variables such as speed, load, and sliding distance (time). These variables were investigated using the design of experiments and utilization of the response surface methodology (RSM). By using this method, it was possible to study the effect of main and mixed (interaction) independent variables on the friction coefficient (COF) of both titanium alloys. Under cryogenic condition, the friction coefficient of both Ti64 and Ti54 behaved differently, i.e. an increase in the case of Ti64 and decrease in the case of Ti54. For Ti64, at higher levels of load and speed, sliding in cryogenic conditions produces relatively higher friction coefficients compared to those obtained in dry air conditions. On contrary, introduction of cryogenic fluid reduces the friction coefficients of Ti54 at all tested conditions of load, speed, and time. The established models demonstrated that the mixed effect of load/speed, time/speed, and load/time consistently decrease the COF of Ti54. However this was not the case for Ti64 whereas the COF increased up to 20% when the Ti64 was tested at higher levels of load and sliding time. Furthermore, the models indicated that interaction of loads and speeds was more effective for both Ti-alloy and have the most substantial influence on the friction. In addition, COF for both alloys behaved linearly with the speed but nonlinearly with the load.

  9. Probabilistic optimization of safety coefficients

    International Nuclear Information System (INIS)

    Marques, M.; Devictor, N.; Magistris, F. de

    1999-01-01

    This article describes a reliability-based method for the optimization of safety coefficients defined and used in design codes. The purpose of the optimization is to determine the partial safety coefficients which minimize an objective function for sets of components and loading situations covered by a design rule. This objective function is a sum of distances between the reliability of the components designed using the safety coefficients and a target reliability. The advantage of this method is shown on the examples of the reactor vessel, a vapour pipe and the safety injection circuit. (authors)

  10. Technique for Determining Lock Coefficient of Differential "Quif"

    Directory of Open Access Journals (Sweden)

    A. B. Fominyh

    2015-01-01

    Full Text Available Increasing the traction qualities of cars on the black ice and snow-covered roads is a relevant task. There are two ways to solve this task, i.e. optimize distribution of the power stream between the driving wheels of the car; introduce a differential (differentials of the increased friction in transmission.Now, an installation of the increased friction differential in transmission is the most widespread measure to increase traction properties of cars. The differential of design "Quif" is one of such differentials. To estimate the efficiency degree of using such a differential is possible either experimentally or theoretically. In case of theoretically determined usefulness of this differential design, as an estimate indicator of the differential installation in transmission a coefficient of lock is accepted.The article considers an algorithm and a technique to calculate a lock coefficient of the differential design "Quif" allowing us to define numeric values of the lock coefficient of such differential at designing stage. It also considers how the lock coefficient depends on the gearing angle and tilt angle of the gear wheel teeth of differential. The given estimating algorithm of designated parameter of differential has more logical and compact structure with regard to the known ones. The lock coefficient values calculated by the offered technique differ from the experimental data by no more than 12%. Taking into account abovementioned, the presented technique for calculating lock coefficient of differential "Quif" is advisable for practical application.

  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. Evaluation of Skin