WorldWideScience

Sample records for surface friction velocity

  1. Influence of shear velocity on frictional characteristics of rock surface

    Indian Academy of Sciences (India)

    Friction at the interface of the rock samples was developed by increasing shear strain at a con- stant rate by applying constant velocity using the tribometer. For shaly sandstone, state para- meters (a and b) played a major role in determining the friction values and roughness of the contact surfaces as well. Higher values of b ...

  2. Influence of shear velocity on frictional characteristics of rock surface

    Indian Academy of Sciences (India)

    Friction at the interface of the rock samples was developed by increasing shear strain at a constant rate by applying constant velocity using the tribometer. For shaly sandstone, state parameters ( and ) played a major role in determining the friction values and roughness of the contact surfaces as well. Higher values of  ...

  3. Influence of shear velocity on frictional characteristics of rock surface

    Indian Academy of Sciences (India)

    stress (Pa), μ0 the initial coefficient of friction, a, b the experimentally determined constant, V the displacement rate (m/s), θ the 'state' variables, Dc the critical slip distance and V0 the initial displace- ment rate (m/s). In order to study the velocity effect on fric- tion for shaly sandstone, the two blocks were kept one over the ...

  4. 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.

  5. 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.

  6. Deformations on Hole and Projectile Surfaces Caused By High Velocity Friction During Ballistic Impact

    Science.gov (United States)

    Karamış, M. B.

    2018-01-01

    In this study, the deformations caused by the ballistic impact on the MM composites and on projectile surfaces are examined. The hole section and grain deformation of unreinforced targets are also examined after impact. The relatively high complexity of impact problems is caused by the large number of intervening parameters like relative velocity of projectile and target, shape of colliding objects, relative stiffness and masses, time-dependent surface of contact, geometry and boundary conditions and material characteristics. The material used in this investigation are 2024 and 7075 aluminum alloys as matrix reinforced with SiC and Al2O3 particles. The matrix materials are extensively used in defense applications due to its favorable ballistic properties, moderate strength, high corrosion resistance and super plastic potential. Two different composites were produced; one by casting and the other by lamination. The ballistic tests of the composite targets were carried out according to NIJ Standard-0101.04, Temperature 21 °C, RH=65% with 7.62 mm projectiles. The bullet weight was 9.6 g and their muzzle velocities were in the range of 770–800 m/s. The projectiles consisted of a steel core, copper jacket and lead material. The composite targets were positioned 15 m from the rifle. The interaction between projectiles and the target hole created after impact were examined by light microscopy and photography. Different damage and failure mechanisms such as petalling, cracking, spalling, dishing, etc., were observed on the target body. On the other hand, dramatic wear and damages on the projectile surface were also observed. The targets were supported with Al-5083 backing blocks having 40 mm thickness.

  7. Scaling properties of velocity and temperature spectra above the surface friction layer in a convective atmospheric boundary layer

    Directory of Open Access Journals (Sweden)

    K. G. McNaughton

    2007-06-01

    Full Text Available We report velocity and temperature spectra measured at nine levels from 1.42 meters up to 25.7 m over a smooth playa in Western Utah. Data are from highly convective conditions when the magnitude of the Obukhov length (our proxy for the depth of the surface friction layer was less than 2 m. Our results are somewhat similar to the results reported from the Minnesota experiment of Kaimal et al. (1976, but show significant differences in detail. Our velocity spectra show no evidence of buoyant production of kinetic energy at at the scale of the thermal structures. We interpret our velocity spectra to be the result of outer eddies interacting with the ground, not "local free convection".

    We observe that velocity spectra represent the spectral distribution of the kinetic energy of the turbulence, so we use energy scales based on total turbulence energy in the convective boundary layer (CBL to collapse our spectra. For the horizontal velocity spectra this scale is (zi εo2/3, where zi is inversion height and εo is the dissipation rate in the bulk CBL. This scale functionally replaces the Deardorff convective velocity scale. Vertical motions are blocked by the ground, so the outer eddies most effective in creating vertical motions come from the inertial subrange of the outer turbulence. We deduce that the appropriate scale for the peak region of the vertical velocity spectra is (z εo2/3 where z is height above ground. Deviations from perfect spectral collapse under these scalings at large and small wavenumbers are explained in terms of the energy transport and the eddy structures of the flow.

    We find that the peaks of the temperature spectra collapse when wavenumbers are scaled using (z1/2 zi1/2. That is, the lengths of the thermal structures depend on both the lengths of the

  8. 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.

  9. 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...

  10. 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...

  11. Friction surfaced Stellite6 coatings

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-08-15

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

  12. Friction surfaced Stellite6 coatings

    International Nuclear Information System (INIS)

    Rao, K. Prasad; Damodaram, R.; Rafi, H. Khalid; Ram, G.D. Janaki; Reddy, G. Madhusudhan; Nagalakshmi, R.

    2012-01-01

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

  13. Contact Dependence and Velocity Crossover in Friction between Microscopic Solid/Solid Contacts.

    Science.gov (United States)

    McGraw, Joshua D; Niguès, Antoine; Chennevière, Alexis; Siria, Alessandro

    2017-10-11

    Friction at the nanoscale differs markedly from that between surfaces of macroscopic extent. Characteristically, the velocity dependence of friction between apparent solid/solid contacts can strongly deviate from the classically assumed velocity independence. Here, we show that a nondestructive friction between solid tips with radius on the scale of hundreds of nanometers and solid hydrophobic self-assembled monolayers has a strong velocity dependence. Specifically, using laterally oscillating quartz tuning forks, we observe a linear scaling in the velocity at the lowest accessed velocities, typically hundreds of micrometers per second, crossing over into a logarithmic velocity dependence. This crossover is consistent with a general multicontact friction model that includes thermally activated breaking of the contacts at subnanometric elongation. We find as well a strong dependence of the friction on the dimensions of the frictional probe.

  14. Friction of atomically stepped surfaces

    NARCIS (Netherlands)

    Dikken, R.J.; Thijsse, B.J.; Nicola, L.

    2017-01-01

    The friction behavior of atomically stepped metal surfaces under contact loading is studied using molecular dynamics simulations. While real rough metal surfaces involve roughness at multiple length scales, the focus of this paper is on understanding friction of the smallest scale of roughness:

  15. Nonlinear friction dynamics on polymer surface under accelerated movement

    Directory of Open Access Journals (Sweden)

    Yuuki Aita

    2017-04-01

    Full Text Available Nonlinear phenomena on the soft material surface are one of the most exciting topics of chemical physics. However, only a few reports exist on the friction phenomena under accelerated movement, because friction between two solid surfaces is considered a linear phenomenon in many cases. We aim to investigate how nonlinear accelerated motion affects friction on solid surfaces. In the present study, we evaluate the frictional forces between two polytetrafluoroethylene (PTFE resins using an advanced friction evaluation system. On PTFE surfaces, the normalized delay time δ, which is the time lag in the response of the friction force to the accelerated movement, is observed in the pre-sliding friction process. Under high-velocity conditions, kinetic friction increases with velocity. Based on these experimental results, we propose a two-phase nonlinear model including a pre-sliding process (from the beginning of sliding of a contact probe to the establishment of static friction and a kinetic friction process. The present model consists of several factors including velocity, acceleration, stiffness, viscosity, and vertical force. The findings reflecting the viscoelastic properties of soft material is useful for various fields such as in the fabrication of clothes, cosmetics, automotive materials, and virtual reality systems as well as for understanding friction phenomena on soft material surfaces.

  16. Friction tensor concept for textured surfaces

    Indian Academy of Sciences (India)

    Depending on the sliding direction the coefficient of friction varies between maximum and minimum for textured surfaces. For random surfaces without any texture the friction coefficient becomes independent of the sliding direction. This paper proposes the concept of a friction tensor analogous to the heat conduction tensor ...

  17. Ice friction: The effects of surface roughness, structure, and hydrophobicity

    Science.gov (United States)

    Kietzig, Anne-Marie; Hatzikiriakos, Savvas G.; Englezos, Peter

    2009-07-01

    The effect of surface roughness, structure, and hydrophobicity on ice friction is studied systematically over a wide range of temperature and sliding speeds using several metallic interfaces. Hydrophobicity in combination with controlled roughness at the nanoscale is achieved by femtosecond laser irradiation to mimic the lotus effect on the slider's surface. The controlled roughness significantly increases the coefficient of friction at low sliding speeds and temperatures well below the ice melting point. However, at temperatures close to the melting point and relatively higher speeds, roughness and hydrophobicity significantly decrease ice friction. This decrease in friction is mainly due to the suppression of capillary bridges in spite of the presence of surface asperities that facilitate their formation. Finally, grooves oriented in the sliding direction also significantly decrease friction in the low velocity range compared to scratches and grooves randomly distributed over a surface.

  18. Drop friction on liquid-infused surfaces

    Science.gov (United States)

    Gas, Armelle; Keiser, Ludovic; Clanet, Christophe; Quere, David

    2017-11-01

    Trapping a thin liquid film in the roughness of a textured material creates a surface that is partially solid and partially liquid, referred to as a lubricant-impregnated surface. Those surfaces have recently raised a great interest for their promising industrial applications. Indeed, they proved to drastically reduce adhesion of a broad range of liquids, leading to enhanced mobility, and strong anti-biofouling, anti-icing and anti-fogging properties. In our talk we discuss the nature of the friction generated as a drop glides on a textured material infused by another liquid. Different regimes are observed, depending on the viscosities of both liquids. While a viscous drop is simply opposed by a Stokes-type friction, the force opposing a drop moving on a viscous substrate becomes non-linear in velocity. A liquid on an infused material is surrounded by a meniscus, and this specific feature is proposed to be responsible for the special observed frictions, on both adhesive and nonadhesive substrates.

  19. Effect of surface pattern on the adhesive friction of elastomers.

    Science.gov (United States)

    Wu-Bavouzet, Fanny; Cayer-Barrioz, Juliette; Le Bot, Alain; Brochard-Wyart, Françoise; Buguin, Axel

    2010-09-01

    We present experimental results for the friction of a flat surface against a hexagonally patterned surface, both being made of PolyDiMethylSiloxane. We simultaneously measure forces of range 10 mN and observe the contact under sliding velocities of about 100 μm/s. We observe adhesive friction on three different pattern heights (80, 310, and 2100 nm). Two kinds of contacts have been observed: the flat surface is in close contact with the patterned one (called intimate contact, observed for 80 nm) or only suspended on the tops on the asperities (called laid contact, observed for 2100 nm). In the range of velocities used, the contact during friction is similar to the static one. Furthermore, our experimental system presents a contact transition during friction for h=310 nm.

  20. Static friction between rigid fractal surfaces.

    Science.gov (United States)

    Alonso-Marroquin, Fernando; Huang, Pengyu; Hanaor, Dorian A H; Flores-Johnson, E A; Proust, Gwénaëlle; Gan, Yixiang; Shen, Luming

    2015-09-01

    Using spheropolygon-based simulations and contact slope analysis, we investigate the effects of surface topography and atomic scale friction on the macroscopically observed friction between rigid blocks with fractal surface structures. From our mathematical derivation, the angle of macroscopic friction is the result of the sum of the angle of atomic friction and the slope angle between the contact surfaces. The latter is obtained from the determination of all possible contact slopes between the two surface profiles through an alternative signature function. Our theory is validated through numerical simulations of spheropolygons with fractal Koch surfaces and is applied to the description of frictional properties of Weierstrass-Mandelbrot surfaces. The agreement between simulations and theory suggests that for interpreting macroscopic frictional behavior, the descriptors of surface morphology should be defined from the signature function rather than from the slopes of the contacting surfaces.

  1. Friction velocity estimation using Reynolds shear stress profile data

    Science.gov (United States)

    Volino, Ralph; Schultz, Michael

    2017-11-01

    A method for using profiles of the mean streamwise velocity and the Reynolds shear stress to estimate the friction velocity, uτ, is presented. The Reynolds averaged two-dimensional streamwise momentum equation is solved for the Reynolds shear stress term. The remaining terms in the equation are separated into those which depend on the local gradient of the mean streamwise velocity profile and those which do not. Using only the terms retained with the Couette flow assumption, the Reynolds shear stress profile can be matched in the inner 10 percent of the boundary layer with the appropriate choice of uτ. Including the other terms which do not depend on the streamwise velocity profile gradient, the fit can be extended to the inner 30 percent of the boundary layer. Using all terms the full Reynolds shear stress profile can be fit. The method is verified using laminar solutions for zero and non-zero pressure gradient boundary layers, and with ZPG turbulent DNS results. It is then applied to zero, favorable and adverse pressure gradient experimental data from smooth and rough walls. Results obtained for local friction velocities agree well with those obtained by other techniques. The method may prove useful when other methods are not practical or fully appropriate. Sponsored by the Office of Naval Research.

  2. 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

  3. Friction tensor concept for textured surfaces

    Indian Academy of Sciences (India)

    This paper proposes the concept of a friction tensor analogous to the heat conduc- tion tensor in anisotropic media. This implies that there exists two principal friction coefficients μ1,2 analogous to the principal conductivities k1,2. For symmetrically textured surfaces the principal directions are orthogonal with atleast one ...

  4. Reducing Friction with a Liquid Film on the Body Surface

    Directory of Open Access Journals (Sweden)

    Nikolay Klyuev

    2018-03-01

    Full Text Available A flow of a thin layer of liquid is simulated on a flat surface of a body located in a stream of air. Liquid film on the surface of the body reduces frictional resistance and can be used as a boundary layer control element. The paper presents a mathematical model of the film flow on a half-plane, located at an angle to the horizon. The fluid flow is determined by the force of gravity and friction from the external air current. A model of an incompressible viscous fluid is used in the boundary-layer approximation. The terms of the motion equation are averaged over the film thickness according to the Leibniz rule. In the cross section of the film, a quadratic law is adopted for the distribution of the longitudinal velocity, taking into account friction on the film surface. An analytical solution of the problem is obtained in the form of series in powers of the small parameter for determining the film thickness and the average longitudinal velocity along the length of the plate. It is shown that the friction decreases with flow around a half-plane with a film of liquid on the surface.

  5. Surface Imaging Skin Friction Instrument and Method

    Science.gov (United States)

    Brown, James L. (Inventor); Naughton, Jonathan W. (Inventor)

    1999-01-01

    A surface imaging skin friction instrument allowing 2D resolution of spatial image by a 2D Hilbert transform and 2D inverse thin-oil film solver, providing an innovation over prior art single point approaches. Incoherent, monochromatic light source can be used. The invention provides accurate, easy to use, economical measurement of larger regions of surface shear stress in a single test.

  6. Friction Surfacing In Steel 304

    OpenAIRE

    S. Godwin Barnabas; Anantharam; Shyam sundar; B.S.Aravind T.Prabhu

    2016-01-01

    Surface engineering deals with the surface of the solid matter and it is sub-discipline of The surface phase of a solid interacts with the surrounding environment. This interaction can degrade the surface phase over time, may result in loss of material from its surface. Environmental degradation of the surface phase over time can be caused by wear, corrosion, creep, fatigue loads, shear loads, tensile loads, cutting forces or when exposed to higher temperature. Wear can be minimiz...

  7. 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...

  8. Friction properties and deformation mechanisms of halite(-mica) gouges from low to high sliding velocities

    NARCIS (Netherlands)

    Buijze, L.; Niemeijer, A.R.; Han, R.; Shimamoto, T.; Spiers, C.J.

    2017-01-01

    The evolution of friction as a function of slip rate is important in understanding earthquake nucleation and propagation. Many laboratory experiments investigating friction of fault rocks are either conducted in the low velocity regime (10−8–10−4 ms−1) or in the high velocity regime (0.01–1 m s−1).

  9. Friction velocity and aerodynamic roughness of conventional and undercutter tillage within the Columbia Plateau, USA

    Science.gov (United States)

    Friction velocity and aerodynamic roughness are characteristics of the soil-plant-atmosphere interface which affect wind erosion. Although exchange of momentum at the interface can be altered by land management practices, no attempts have been made to quantify the effect of tillage on friction veloc...

  10. Dynamic permeability of simulated fault induced by intermediate velocity friction test

    Science.gov (United States)

    Tanikawa, W.

    2017-12-01

    , because viscosity of fluid through slip surface might have decreased during sliding due to frictional heating. High velocity friction test caused anomalous temperature increase to nearly 100 oC, which can increase 2 orders of magnitude of viscosity, and this 2 orders of magnitude is consistent with the permeability reduction at high velocity test.

  11. 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.

  12. Experimental results of a hydrodynamic friction behaviour of a linear contact at low sliding velocity

    Science.gov (United States)

    Bouzana, A.; Guermat, A.; Belarifi, F.

    2018-01-01

    We propose in this work the experimental results of the lubricated friction behavior of linear contact (finite length) in isoviscous hydrodynamic regime. This study was made on a tribometer Plint - Cameron TE77, using a pure mineral oil lubricant (N175). without additives for three loads 20, 40 and 80 Newton. and a velocity, range varying from 0.05 to 0.4 ms-1, trials are held in pure sliding mode for a total distance of displacement L = 15mm. The studied contact is a cylinder/cylinder. The geometry of test pieces is part of a piston ring and a liner of a real engine. The first cylinder represents the male part with material of MKJet nuance having undergoes a surface coating by thermal projection (HVOF). the second cylinder represents the female part whose material is cast iron of nuance FGL, without surface treatment, and whose dimensions were adapted to minimize the computational error on the speed of sliding and the force of friction which is lower than 5%. Processing the results recorded for ten cycles with four hundred points per cycle to the extraction of average curves, enables us to plot the curves of friction according to velocity and thereafter the curve of Stribeck. The results show that we can get a total isoviscous regime for loads 20 and 40N, however for load 80N, this regime is partial, as it comes off the final curve from a speed value 0.1 m / s. the values of the friction coefficient varies for the three loads used between 0.004 and 0.017. These results show the possibility of obtaining a hydrodynamic regime with high load and low speed, with treatments suitable surfaces and are made to reduce wear and increase the lifetime of the mechanism.

  13. Experiment Evaluation of Skin Friction Drag by Surface Tailoring

    Science.gov (United States)

    Manigandan, S.; Gopal krishna, K.; Gagan Kumar, K.; Gunasekar, P.; Nithya, S.

    2017-08-01

    Reduction of drag is an important role of aerodynamic specialist in real time world. The performance of forward moving object improved when the drag is reduced. Skin friction drag caused when the fluid tending to shear along the surface of the body and it is dependent on energy expenditure. Initial research concluded that nearly 20 to 40% of total drag is skin friction drag, based on flight forward velocity. This means a lot of fuel burned. In this paper we investigate a methodology to reduce the skin friction drag by implementing different kinds of exterior treatments. The ideology inspired from the world fastest moving oceanic creature. Structures are fabricated based on the replica of scales of the oceanic creature. The outer skin of the aerofoil NACA0012 is modified like shark scales. Then it is tested using open type sub sonic wind tunnel. In addition to that, the leading edge thickness effect also studied. The turbulent flow phenomenon is validated at different velocities and compared with numerical results using STAR CCM+. From the plots and graphical results, it is found that the skin friction drag is generated less due to reduction of transverse shear stress present in turbulent flow and skin friction drag depends on boundary layer thickness and on the percentage of chord of flow separation. In addition to this, the result delivers that the ordinary polished surface produces more drag than the modified scales. The outlook of this technology is excrescence for different applications. This open section wind tunnel testing produces 10-15% reduction in drag and can be turn to high values when the experiment is conducted in closed section wind tunnel with real time atmospheric conditions, which can be done as a future work.

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

    Science.gov (United States)

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

    2014-03-04

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

  15. High velocity properties of the dynamic frictional force between ductile metals

    International Nuclear Information System (INIS)

    Hammerberg, James Edward; Hollan, Brad L.; Germann, Timothy C.; Ravelo, Ramon J.

    2010-01-01

    The high velocity properties of the tangential frictional force between ductile metal interfaces seen in large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations are characterized by interesting scaling behavior. In many cases a power law decrease in the frictional force with increasing velocity is observed at high velocities. We discuss the velocity dependence of the high velocity branch of the tangential force in terms of structural transformation and ultimate transition, at the highest velocities, to confined fluid behavior characterized by a critical strain rate. The particular case of an Al/Al interface is discussed.

  16. Apparent Dependence of Rate- and State-Dependent Friction Parameters on Loading Velocity and Cumulative Displacement Inferred from Large-Scale Biaxial Friction Experiments

    Science.gov (United States)

    Urata, Yumi; Yamashita, Futoshi; Fukuyama, Eiichi; Noda, Hiroyuki; Mizoguchi, Kazuo

    2017-06-01

    We investigated the constitutive parameters in the rate- and state-dependent friction (RSF) law by conducting numerical simulations, using the friction data from large-scale biaxial rock friction experiments for Indian metagabbro. The sliding surface area was 1.5 m long and 0.5 m wide, slid for 400 s under a normal stress of 1.33 MPa at a loading velocity of either 0.1 or 1.0 mm/s. During the experiments, many stick-slips were observed and those features were as follows. (1) The friction drop and recurrence time of the stick-slip events increased with cumulative slip displacement in an experiment before which the gouges on the surface were removed, but they became almost constant throughout an experiment conducted after several experiments without gouge removal. (2) The friction drop was larger and the recurrence time was shorter in the experiments with faster loading velocity. We applied a one-degree-of-freedom spring-slider model with mass to estimate the RSF parameters by fitting the stick-slip intervals and slip-weakening curves measured based on spring force and acceleration of the specimens. We developed an efficient algorithm for the numerical time integration, and we conducted forward modeling for evolution parameters ( b) and the state-evolution distances (L_{{c}}), keeping the direct effect parameter ( a) constant. We then identified the confident range of b and L_{{c}} values. Comparison between the results of the experiments and our simulations suggests that both b and L_{{c}} increase as the cumulative slip displacement increases, and b increases and L_{{c}} decreases as the loading velocity increases. Conventional RSF laws could not explain the large-scale friction data, and more complex state evolution laws are needed.

  17. Sliding Friction on Liquid-Infused Surfaces

    Science.gov (United States)

    Rashed, Ziad; Habibi, Mohammad; Boreyko, Jonathan

    2017-11-01

    Slippery porous liquid-infused surfaces (SLIPS) are well-known for their ability to stably minimize the hysteresis of a wide variety of liquids. However, whether SLIPS could also reduce the sliding friction of solid objects has not been given much consideration. Here, we measure the friction force associated with dragging an aluminum cube across an array of ordered silicon micropillars impregnated with silicone oil. The solid fraction of the micropillars was either 0.025 or 0.25, while the viscosity of the silicone oil was 10, 100, or 1,000 cSt. Non-intuitively, it was observed that the sliding friction decreased with increasing lubricant viscosity or increasing solid fraction. These findings suggest that the key parameter is therefore the hydraulic resistance of the alleys between the micropillars, which should be as large as possible to minimize lateral oil drainage from underneath the sliding body. This would indicate that scaling down to nano-roughness would be optimal for minimizing the sliding friction, which was confirmed by additional experiments on a disordered nanostructured substrate.

  18. The Investigations of Friction under Die Surface Vibration in Cold Forging Process

    DEFF Research Database (Denmark)

    Jinming, Sha

    of the application of ultrasonic vibration on drawing, rolling and other metal forming process show that the load and friction coefficient would be decreased with the presence of ultrasonic vibration. Investigations on forging processes and under low frequency, especially the quantitative analysis of friction......The objective of this thesis is to fundamentally study the influence of die surface vibration on friction under low frequency in metal forging processes. The research includes vibrating tool system design for metal forming, theoretical and experimental investigations, and finite element simulations...... on die surface vibration in forging process. After a general introduction to friction mechanisms and friction test techniques in metal forming, the application of ultrasonic vibration in metal forming, the influence of sliding velocity on friction is described. Some earlier investigations...

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  20. Kwik Bond Polymers(R) high friction surface treatment.

    Science.gov (United States)

    2015-12-01

    High friction surface treatment (HFST) was applied to two on-ramps in the Seattle urban area to improve : friction resistance. The ramps were high accident locations. The system applied was polyester resin binder and : calcined bauxite aggregate. Tes...

  1. Velocity dependence of joint friction in robotic manipulators with gear transmissions

    NARCIS (Netherlands)

    Waiboer, R.R.; Aarts, Ronald G.K.M.; Jonker, Jan B.

    2005-01-01

    This paper analyses the problem of modelling joint friction in robotic manipulators with gear transmissions at joint velocities varying from close to zero until their maximum appearing values. It is shown that commonly used friction models that incorporate Coulomb, (linear) viscous and Stribeck

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

    DEFF Research Database (Denmark)

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

    2013-01-01

    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...... 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...... of this linear plot as the stick-slip amplitude coefficient (SSAC). We suggest that such stick-slip behaviors are characteristics of surfaces with nanotextures and that such local frictional instabilities have important implications to surface damage and wear. We thus propose that the shear characteristics...

  3. 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....

  4. 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

  5. Early Life And In Service Friction Characteristics Of Runway Surface

    OpenAIRE

    Widyatmoko, I.; Fergusson, C.

    2012-01-01

    This paper presents friction data gathered from seven regional and major international airports in the UK, covering different surface courses, from the time of installation to in service. The wet friction monitoring at these airports was carried out by using Continuous Friction Measurement Equipments (CFME) over 4 years in service. Some materials showed reduction in the wet friction values during a few days after installation but then followed by a steady increase in the values, even without ...

  6. 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.

  7. Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

    Energy Technology Data Exchange (ETDEWEB)

    Puli, Ramesh, E-mail: rameshpuli2000@gmail.com; Janaki Ram, G.D.

    2012-12-15

    Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener-Hollomon parameter during friction surfacing. - Highlights: Black-Right-Pointing-Pointer Dynamic recrystallization in alloy 316L friction surfaced coatings is examined. Black-Right-Pointing-Pointer Friction surfacing leads to discontinuous dynamic recrystallization in alloy 316L. Black-Right-Pointing-Pointer Strain rates in friction surfacing exceed 400 s{sup -1}. Black-Right-Pointing-Pointer Estimated grain size matches well with experimental observations in 316L coatings.

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

    DEFF Research Database (Denmark)

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

    2013-01-01

    Friction forces have long been associated with the famous Amontons' rule that states that the friction force is linearly dependent on the applied normal load, with the proportionality constant being known as the friction coefficient. Amontons' rule is however purely phenomenological and does...... not in itself provide any information on why the friction coefficient is different for different material combinations. In this study, friction forces between a colloidal probe and nanostructured particle coated surfaces in an aqueous environment exhibiting different roughness length scales were measured...... by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All...

  9. 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.

  10. CRITICAL VELOCITY OF CONTROLLABILITY OF SLIDING FRICTION BY NORMAL OSCILLATIONS IN VISCOELASTIC CONTACTS

    Directory of Open Access Journals (Sweden)

    Mikhail Popov

    2016-12-01

    Full Text Available Sliding friction can be reduced substantially by applying ultrasonic vibration in the sliding plane or in the normal direction. This effect is well known and used in many applications ranging from press forming to ultrasonic actuators. One of the characteristics of the phenomenon is that, at a given frequency and amplitude of oscillation, the observed friction reduction diminishes with increasing sliding velocity. Beyond a certain critical sliding velocity, there is no longer any difference between the coefficients of friction with or without vibration. This critical velocity depends on material and kinematic parameters and is a key characteristic that must be accounted for by any theory of influence of vibration on friction. Recently, the critical sliding velocity has been interpreted as the transition point from periodic stick-slip to pure sliding and was calculated for purely elastic contacts under uniform sliding with periodic normal loading. Here we perform a similar analysis of the critical velocity in viscoelastic contacts using a Kelvin material to describe viscoelasticity. A closed-form solution is presented, which contains previously reported results as special cases. This paves the way for more detailed studies of active control of friction in viscoelastic systems, a previously neglected topic with possible applications in elastomer technology and in medicine.

  11. Skin Friction Reduction Characteristics of Nonsmooth Surfaces Inspired by the Shapes of Barchan Dunes

    Directory of Open Access Journals (Sweden)

    Xiao-wen Song

    2017-01-01

    Full Text Available A new type of nonsmooth surface inspired by the shape of barchan dunes has been proposed and is intended to reduce skin friction, a major cause of overall drag. Simulations were carried out to obtain skin friction reduction characteristics for the nonsmooth surface using the commercial computational fluid dynamics software Fluent. A realizable k-ε model was employed to assess the influence of the nonsmooth structure on turbulent flow and velocity fields. The numerical simulation results showed that the new nonsmooth surface possesses the desired skin friction reduction effect and that the maximum skin friction reduction percentage reached 33.63% at a fluid speed of 30 m/s. Various aspects of the skin friction reduction mechanism were discussed, including the distribution of velocity vectors and shear stress contours and the variations in boundary layer thickness. The accuracy of the flow field for the nonsmooth unit was further verified by particle image velocimetry test results. The new bionic nonsmooth surface, which exceeds the limitations of existing nonsmooth bionic structures, can effectively reduce skin friction and should provide insights into engineering applications in the future.

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

    DEFF Research Database (Denmark)

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

    2012-01-01

    materials which are untypical for brake applications, like thermoplastics and fiber composites, can offer superior performance in terms of braking torque, wear resistance and cost than typical brake linings. In this paper coefficient of friction measurements for various thermoplastic and fiber composite......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 friction...

  13. 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

  14. Friction of hydrogels with controlled surface roughness on solid flat substrates.

    Science.gov (United States)

    Yashima, Shintaro; Takase, Natsuko; Kurokawa, Takayuki; Gong, Jian Ping

    2014-05-14

    This study investigated the effect of hydrogel surface roughness on its sliding friction against a solid substrate having modestly adhesive interaction with hydrogels under small normal pressure in water. The friction test was performed between bulk polyacrylamide hydrogels of varied surface roughness and a smooth glass substrate by using a strain-controlled rheometer with parallel-plates geometry. At small pressure (normal strain 1.4-3.6%), the flat surface gel showed a poor reproducibility in friction. In contrast, the gels with a surface roughness of 1-10 μm order showed well reproducible friction behaviors and their frictional stress was larger than that of the flat surface hydrogel. Furthermore, the flat gel showed an elasto-hydrodynamic transition while the rough gels showed a monotonous decrease of friction with velocity. The difference between the flat surface and the rough surface diminished with the increase of the normal pressure. These phenomena are associated with the different contact behaviors of these soft hydrogels in liquid, as revealed by the observation of the interface using a confocal laser microscope.

  15. Friction tensor concept for textured surfaces

    Indian Academy of Sciences (India)

    friction coefficients of Mg and Al-Mg alloy pins sliding over EN8 steel flats. The sliding angle was varied between 0 and 90 degrees and morphology of ... has explained friction based on energy dissipation mechanisms initiated in the early history of tribology by Rabinowicz (1951). Despite the spatio-temporal complexity in ...

  16. Stick-slip friction of gecko-mimetic flaps on smooth and rough surfaces.

    Science.gov (United States)

    Das, Saurabh; Cadirov, Nicholas; Chary, Sathya; Kaufman, Yair; Hogan, Jack; Turner, Kimberly L; Israelachvili, Jacob N

    2015-03-06

    The discovery and understanding of gecko 'frictional-adhesion' adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick-slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick-slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick-slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  17. Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces

    Science.gov (United States)

    Das, Saurabh; Cadirov, Nicholas; Chary, Sathya; Kaufman, Yair; Hogan, Jack; Turner, Kimberly L.; Israelachvili, Jacob N.

    2015-01-01

    The discovery and understanding of gecko ‘frictional-adhesion’ adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick–slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick–slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick–slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems. PMID:25589569

  18. 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 ...

  19. 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

  20. A note on the stochastic nature of particle cohesive force and implications to threshold friction velocity for aerodynamic dust entrainment

    Science.gov (United States)

    There is considerable interest to determine the threshold for aeolian dust emission on Earth and Mars. Existing schemes for threshold friction velocity are all deterministic in nature, but observations show that in the dust particle size range the threshold friction velocity scatters strongly due t...

  1. Rubber friction on road surfaces: Experiment and theory for low sliding speeds

    Energy Technology Data Exchange (ETDEWEB)

    Lorenz, B.; Persson, B. N. J. [PGI, FZ Jülich, 52425 Jülich (Germany); Oh, Y. R.; Nam, S. K.; Jeon, S. H. [Hankook Tire Co. LTD., 112 Gajeongbuk-ro, Yuseong-gu, Daejeon 305-725 (Korea, Republic of)

    2015-05-21

    We study rubber friction for tire tread compounds on asphalt road surfaces. The road surface topographies are measured using a stylus instrument and atomic force microscopy, and the surface roughness power spectra are calculated. The rubber viscoelastic modulus mastercurves are obtained from dynamic mechanical analysis measurements and the large-strain effective modulus is obtained from strain sweep data. The rubber friction is measured at different temperatures and sliding velocities, and is compared to the calculated data obtained using the Persson contact mechanics theory. We conclude that in addition to the viscoelastic deformations of the rubber surface by the road asperities, there is an important contribution to the rubber friction from shear processes in the area of contact. The analysis shows that the latter contribution may arise from rubber molecules (or patches of rubber) undergoing bonding-stretching-debonding cycles as discussed in a classic paper by Schallamach.

  2. 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.

  3. Friction reduction using discrete surface textures: principle and design

    Science.gov (United States)

    Hsu, Stephen M.; Jing, Yang; Hua, Diann; Zhang, Huan

    2014-08-01

    There have been many reports on the use of dimples, grooves, and other surface textures to control friction in sliding interfaces. The effectiveness of surface textures in friction reduction has been demonstrated in conformal contacts under high speed low load applications such as mechanical seals and automotive water pump seals, etc., resulting in reduced friction and longer durability. For sliding components with higher contact pressures or lower speeds, conflicting results were reported. Reasons for the inconsistency may be due to the differences in texture fabrication techniques, lack of dimple size and shape uniformity, and different tester used. This paper examines the basic principles on which surface textural patterns influence friction under the three principle lubrication regimes: hydrodynamic, elastohydrodynamic, and boundary lubrication regimes. Our findings suggest that each regime requires specific dimple size, shape, depth, and areal density to achieve friction reduction. Control experiments were also conducted to explore mechanisms of friction reduction. The dimple geometric shape and the dimple's orientation with respect to the sliding direction influence friction significantly. The underlying mechanisms for friction control via textures are discussed.

  4. Friction reduction using discrete surface textures: principle and design

    International Nuclear Information System (INIS)

    Hsu, Stephen M; Jing, Yang; Hua, Diann; Zhang, Huan

    2014-01-01

    There have been many reports on the use of dimples, grooves, and other surface textures to control friction in sliding interfaces. The effectiveness of surface textures in friction reduction has been demonstrated in conformal contacts under high speed low load applications such as mechanical seals and automotive water pump seals, etc., resulting in reduced friction and longer durability. For sliding components with higher contact pressures or lower speeds, conflicting results were reported. Reasons for the inconsistency may be due to the differences in texture fabrication techniques, lack of dimple size and shape uniformity, and different tester used. This paper examines the basic principles on which surface textural patterns influence friction under the three principle lubrication regimes: hydrodynamic, elastohydrodynamic, and boundary lubrication regimes. Our findings suggest that each regime requires specific dimple size, shape, depth, and areal density to achieve friction reduction. Control experiments were also conducted to explore mechanisms of friction reduction. The dimple geometric shape and the dimple's orientation with respect to the sliding direction influence friction significantly. The underlying mechanisms for friction control via textures are discussed. (paper)

  5. Evaluation of Tyregrip(R) high-friction surfacing.

    Science.gov (United States)

    2012-06-01

    This report describes the installation of Tyregrip, a high friction surface, on a high accident location to reduce accident : rates. Tyregrip is a thin polymer overlay system that uses a two part epoxy binder and calcined bauxite aggregate. Postc...

  6. Alternative aggregates and materials for high friction surface treatments.

    Science.gov (United States)

    2016-05-01

    The State of Florida has used high friction surface treatments (HFSTs) since 2006 to reduce wet weather crashes on : tight curves and intersections and to maintain bridge decks; however, the Florida Department of Transportation : (FDOT) has reported ...

  7. Evaluation of high friction surface locations in Kansas.

    Science.gov (United States)

    2016-05-01

    In 2009, the Kansas Department of Transportation entered into an agreement with the Federal Highway : Administration to fulfill the requirements of the High Friction Surface Materials Enhancing Safety at Horizontal : Curves on the National Highway Sy...

  8. Public satisfaction survey of high friction surface treatment.

    Science.gov (United States)

    2017-04-01

    Missouri adults in Callaway County were surveyed to capture their satisfaction with a local high friction surface treatment on : westbound US 54. This treatment was implemented in Project J5P3012. The results are weighted proportionally to the county...

  9. An integrated approach to friction surfacing process optimisation

    OpenAIRE

    Voutchkov, I.I.; Jaworski, B.; Vitanov, V.I.; Bedford, G.M.

    2001-01-01

    This paper discusses the procedures for data collection, management and optimisation of the friction surfacing process. Experimental set-up and characteristics of measuring equipment are found to match the requirements for accurate and unbiased data signals. The main friction surfacing parameters are identified and the first stage of the optimisation process is achieved by visually assessing the coatings and introducing the substrate speed vs. force map. The optimum values from this first sta...

  10. Influence of normal loads and sliding velocities on friction properties of engineering plastics sliding against rough counterfaces

    Science.gov (United States)

    Nuruzzaman, D. M.; Chowdhury, M. A.; Rahaman, M. L.; Oumer, A. N.

    2016-02-01

    Friction properties of plastic materials are very important under dry sliding contact conditions for bearing applications. In the present research, friction properties of engineering plastics such as polytetrafluoroethylene (PTFE) and nylon are investigated under dry sliding contact conditions. In the experiments, PTFE and nylon slide against different rough counterfaces such as mild steel and stainless steel 316 (SS 316). Frictional tests are carried out at low loads 5, 7.5 and 10 N, low sliding velocities 0.5, 0.75 and 1 m/s and relative humidity 70%. The obtained results reveal that friction coefficient of PTFE increases with the increase in normal loads and sliding velocities within the observed range. On the other hand, frictional values of nylon decrease with the increase in normal loads and sliding velocities. It is observed that in general, these polymers show higher frictional values when sliding against SS 316 rather than mild steel. During running-in process, friction coefficient of PTFE and nylon steadily increases with the increase in rubbing time and after certain duration of rubbing, it remains at steady level. At identical operating conditions, the frictional values are significantly different depending on normal load, sliding velocity and material pair. It is also observed that in general, the influence of normal load on the friction properties of PTFE and nylon is greater than that of sliding velocity.

  11. Measurements of skin friction in water using surface stress sensitive films

    International Nuclear Information System (INIS)

    Crafton, J W; Fonov, S D; Jones, E G; Goss, L P; Forlines, R A; Fontaine, A

    2008-01-01

    The measurement of skin friction on hydrodynamic surfaces is of significant value for the design of advanced naval technology, particularly at high Reynolds numbers. Here we report on the development of a new sensor for measurement of skin friction and pressure that operates in both air and water. This sensor is based on an elastic polymer film that deforms under the action of applied normal and tangential loads. Skin friction and pressure gradients are determined by monitoring these deformations and then solving an inverse problem using a finite element model of the elastic film. This technique is known as surface stress sensitive films. In this paper, we describe the development of a sensor package specifically designed for two-dimensional skin friction measurements at a single point. The package has been developed with the goal of making two-dimensional measurements of skin friction in water. Quantitative measurements of skin friction are performed on a high Reynolds number turbulent boundary layer in the 12 inch water tunnel at Penn State University. These skin friction measurements are verified by comparing them to measurements obtained with a drag plate as well as by performing two-dimensional velocity measurements above the sensor using a laser Doppler velocimetry system. The results indicate that the sensor skin friction measurements are accurate to better than 5% and repeatable to better than 2%. The directional sensitivity of the sensor is demonstrated by positioning the sensor at several orientations to the flow. A final interesting feature of this sensor is that it is sensitive to pressure gradients, not to static pressure changes. This feature should prove useful for monitoring the skin friction on a seafaring vessel as the operating depth is changed

  12. A 2-D model for friction of complex anisotropic surfaces

    Science.gov (United States)

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

    2018-03-01

    The friction force observed at macroscale is the result of interactions at various lower length scales that are difficult to model in a combined manner. For this reason, simplified approaches are required, depending on the specific aspect to be investigated. In particular, the dimensionality of the system is often reduced, especially in models designed to provide a qualitative description of frictional properties of elastic materials, e.g. the spring-block model. In this paper, we implement for the first time a two dimensional extension of the spring-block model, applying it to structured surfaces and investigating by means of numerical simulations the frictional behaviour of a surface in the presence of features like cavities, pillars or complex anisotropic structures. We show how friction can be effectively tuned by appropriate design of such surface features.

  13. Development of a Constitutive Friction Law based on the Frictional Interaction of Rough Surfaces

    Directory of Open Access Journals (Sweden)

    F. Beyer

    2015-12-01

    Full Text Available Friction has a considerable impact in metal forming. This is in particular true for sheet-bulk metal-forming (SBMF in which local highly varying contact loads occur. A constitutive friction law suited to the needs of SBMF is necessary, if numerical investigations in SBMF are performed. The identification of the friction due to adhesion and ploughing is carried out with an elasto-plastic half-space model. The normal contact is verified for a broad range of normal loads. In addition, the model is used for the characterization of the occurring shear stress. Ploughing is determined by the work which is necessary to plastically deform the surface asperities of the new area that gets into contact during sliding. Furthermore, the surface patches of common half-space models are aligned orthogonally to the direction in which the surfaces approach when normal contact occurs. For a better reflection of the original surfaces, the element patches become inclined. This leads to a geometric share of lateral forces which also contribute to friction. Based on these effects, a friction law is derived which is able to predict the contact conditions especially for SBMF.

  14. Experimental Analysis of Grease Friction Properties on Sliding Textured Surfaces

    Directory of Open Access Journals (Sweden)

    Xijun Hua

    2017-10-01

    Full Text Available There is comprehensive work on the tribological properties and lubrication mechanisms of oil lubricant used on textured surfaces, however the use of grease lubrication on textured surfaces is rather new. This research article presents an experimental study of the frictional behaviours of grease lubricated sliding contact under mixed lubrication conditions. The influences of surface texture parameters on the frictional properties were investigated using a disc-on-ring tribometer. The results showed that the friction coefficient is largely dependent on texture parameters, with higher and lower texture density resulting in a higher friction coefficient at a fixed texture depth. The sample with texture density of 15% and texture depth of 19 μm exhibited the best friction properties in all experimental conditions because it can store more grease and trap wear debris. The reduction of friction is mainly attributable to the formation of a stable grease lubrication film composed of oil film, transfer film and deposited film, and the hydrodynamic pressure effect of the surface texture, which increases the mating gap and reduces the probability of asperity contact. This result will help in understanding the tribological behaviour of grease on a textured surface and in predicting the lubrication conditions of sliding bearings for better operation in any machinery.

  15. 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.

  16. 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.

  17. Atomic-scale friction on stepped surfaces of ionic crystals.

    Science.gov (United States)

    Steiner, Pascal; Gnecco, Enrico; Krok, Franciszek; Budzioch, Janusz; Walczak, Lukasz; Konior, Jerzy; Szymonski, Marek; Meyer, Ernst

    2011-05-06

    We report on high-resolution friction force microscopy on a stepped NaCl(001) surface in ultrahigh vacuum. The measurements were performed on single cleavage step edges. When blunt tips are used, friction is found to increase while scanning both up and down a step edge. With atomically sharp tips, friction still increases upwards, but it decreases and even changes sign downwards. Our observations extend previous results obtained without resolving atomic features and are associated with the competition between the Schwöbel barrier and the asymmetric potential well accompanying the step edges.

  18. 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.

    Skin friction drag coefficients are determined for marine antifouling coatings in pristine condition by use of Constant Temperature Anemometry (CTA) with uni-directionalhot-wires. Mean flow behaviour for varying surface roughness is analysed in zero pressure gradient, flat plate, turbulentboundary...... 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...... layers for Reynolds numbers from Rex =1:91x105 to Rex = 9:54x105. The measurements were conducted at the Technical University of Denmark in a closed-loop wind tunnel redesigned for investigations as this. Ensemble averages of the boundary layer velocity profiles allowed for determination of skin friction...

  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. Alternative methods to model frictional contact surfaces using NASTRAN

    Science.gov (United States)

    Hoang, Joseph

    1992-01-01

    Elongated (slotted) holes have been used extensively for the integration of equipment into Spacelab racks. In the past, this type of interface has been modeled assuming that there is not slippage between contact surfaces, or that there is no load transfer in the direction of the slot. Since the contact surfaces are bolted together, the contact friction provides a load path determined by the normal applied force (bolt preload) and the coefficient of friction. Three alternate methods that utilize spring elements, externally applied couples, and stress dependent elements are examined to model the contacted surfaces. Results of these methods are compared with results obtained from methods that use GAP elements and rigid elements.

  1. Estimating Discharge, Depth and Bottom Friction in Sand Bed Rivers Using Surface Currents and Water Surface Elevation Observations

    Science.gov (United States)

    Simeonov, J.; Czapiga, M. J.; Holland, K. T.

    2017-12-01

    We developed an inversion model for river bathymetry estimation using measurements of surface currents, water surface elevation slope and shoreline position. The inversion scheme is based on explicit velocity-depth and velocity-slope relationships derived from the along-channel momentum balance and mass conservation. The velocity-depth relationship requires the discharge value to quantitatively relate the depth to the measured velocity field. The ratio of the discharge and the bottom friction enter as a coefficient in the velocity-slope relationship and is determined by minimizing the difference between the predicted and the measured streamwise variation of the total head. Completing the inversion requires an estimate of the bulk friction, which in the case of sand bed rivers is a strong function of the size of dune bedforms. We explored the accuracy of existing and new empirical closures that relate the bulk roughness to parameters such as the median grain size diameter, ratio of shear velocity to sediment fall velocity or the Froude number. For given roughness parameterization, the inversion solution is determined iteratively since the hydraulic roughness depends on the unknown depth. We first test the new hydraulic roughness parameterization using estimates of the Manning roughness in sand bed rivers based on field measurements. The coupled inversion and roughness model is then tested using in situ and remote sensing measurements of the Kootenai River east of Bonners Ferry, ID.

  2. 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.

  3. Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1986-01-01

    An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

  4. Using eddy covariance to measure the dependence of air–sea CO2 exchange rate on friction velocity

    Directory of Open Access Journals (Sweden)

    S. Landwehr

    2018-03-01

    Full Text Available Parameterisation of the air–sea gas transfer velocity of CO2 and other trace gases under open-ocean conditions has been a focus of air–sea interaction research and is required for accurately determining ocean carbon uptake. Ships are the most widely used platform for air–sea flux measurements but the quality of the data can be compromised by airflow distortion and sensor cross-sensitivity effects. Recent improvements in the understanding of these effects have led to enhanced corrections to the shipboard eddy covariance (EC measurements.Here, we present a revised analysis of eddy covariance measurements of air–sea CO2 and momentum fluxes from the Southern Ocean Surface Ocean Aerosol Production (SOAP study. We show that it is possible to significantly reduce the scatter in the EC data and achieve consistency between measurements taken on station and with the ship underway. The gas transfer velocities from the EC measurements correlate better with the EC friction velocity (u* than with mean wind speeds derived from shipboard measurements corrected with an airflow distortion model. For the observed range of wind speeds (u10 N = 3–23 m s−1, the transfer velocities can be parameterised with a linear fit to u*. The SOAP data are compared to previous gas transfer parameterisations using u10 N computed from the EC friction velocity with the drag coefficient from the Coupled Ocean–Atmosphere Response Experiment (COARE model version 3.5. The SOAP results are consistent with previous gas transfer studies, but at high wind speeds they do not support the sharp increase in gas transfer associated with bubble-mediated transfer predicted by physically based models.

  5. Friction and diffusion dynamics of adsorbates at surfaces

    NARCIS (Netherlands)

    Fusco, C.

    2005-01-01

    A theoretical study of the motion of adsorbates (e. g. atoms, molecules or clusters) on solid surfaces is presented, with a focus on surface diffusion and atomic-scale friction. These two phenomena are inextricably linked, because when an atomic or molecular adsorbate diffuses, or is pulled, it

  6. Friction of Droplets Sliding on Microstructured Superhydrophobic Surfaces.

    Science.gov (United States)

    Qiao, Shasha; Li, Shen; Li, Qunyang; Li, Bo; Liu, Kesong; Feng, Xi-Qiao

    2017-11-28

    Liquid transport is a fundamental process relevant to a wide range of applications, for example, heat transfer, anti-icing, self-cleaning, drag reduction, and microfluidic systems. For these applications, a deeper understanding of the sliding behavior of water droplets on solid surfaces is of particular importance. In this study, the frictional behavior of water droplets sliding on superhydrophobic surfaces decorated with micropillar arrays was studied using a nanotribometer. Our experiments show that surfaces with a higher solid area fraction generally exhibited larger friction, although friction might drop when the solid area fraction was close to unity. More interestingly, we found that the sliding friction of droplets was enhanced when the dimension of the microstructures increased, showing a distinct size effect. The nonmonotonic dependence of friction force on solid area fraction and the apparent size effect can be qualitatively explained by the evolution of two governing factors, that is, the true length of the contact line and the coordination degree of the depinning events. The mechanisms are expected to be generally applicable for other liquid transport processes involving the dynamic motion of a three-phase contact line, which may provide a new means of tuning liquid-transfer behavior through surface microstructures.

  7. Skin friction and velocity profile family for compressible turbulent boundary layers

    Science.gov (United States)

    Huang, P. G.; Bradshaw, P.; Coakley, T. J.

    1993-01-01

    The paper presents a general approach to constructing mean velocity profiles for compressible turbulent boundary layers with isothermal or adiabatic walls. The theory is based on a density-weighted transformation that allows the extension of the incompressible similarity laws of the wall to the compressible regions. The velocity profile family is compared to a range of experimental data, and excellent agreement is obtained. A self-consistent skin friction law, which satisfies the proposed velocity profile family, is derived and compared with the well-known Van Driest II theory for boundary layers in zero pressure gradient. The results are found to be at least as good as those obtained by using the Van Driest II transformation.

  8. Technique for measuring very high surface velocities

    International Nuclear Information System (INIS)

    Maron, Y.

    1977-01-01

    An interferometric technique for measuring displacements of surfaces moving at velocities in the range of a few millimeters per microsecond is presented. The Doppler shift of frequency of light scattered from such surfaces is too high to be detectable by known devices. The present technique is based upon monitoring the signal resulting from the interference between two beams reflected from the surface at different incidence angles. Measurement systems for specularly as well as diffusely reflecting surfaces are described. Light source with very modest temporal coherence delivering about 100 mw power is required. The accuracy of the technique is discussed. (author)

  9. Canonical treatment of the rocket with friction linear in the velocity

    International Nuclear Information System (INIS)

    Campos, I; Jimenez, J L; Valle, G del

    2003-01-01

    We show that the problem of the rocket with friction linear in the velocity can be treated by canonical methods. In order to achieve this we must abandon the restriction to natural Lagrangians of the form L = T - V, and use the method of S-equivalent Lagrangians. We also solve the problem with constant gravity. This example may be useful for the teaching of the application of canonical methods to dissipative systems, as well as to the teaching of the use of the method of S-equivalent Lagrangians

  10. Intermonolayer friction and surface shear viscosity of lipid bilayer membranes

    NARCIS (Netherlands)

    den Otter, Wouter K.; Shkulipa, S.

    2007-01-01

    The flow behavior of lipid bilayer membranes is characterized by a surface viscosity for in-plane shear deformations, and an intermonolayer friction coefficient for slip between the two leaflets of the bilayer. Both properties have been studied for a variety of coarse-grained double-tailed model

  11. Performance Improvement of Friction Stir Welds by Better Surface Finish

    Science.gov (United States)

    Russell, Sam; Nettles, Mindy

    2015-01-01

    The as-welded friction stir weld has a cross section that may act as a stress concentrator. The geometry associated with the stress concentration may reduce the weld strength and it makes the weld challenging to inspect with ultrasound. In some cases, the geometry leads to false positive nondestructive evaluation (NDE) indications and, in many cases, it requires manual blending to facilitate the inspection. This study will measure the stress concentration effect and develop an improved phased array ultrasound testing (PAUT) technique for friction stir welding. Post-welding, the friction stir weld (FSW) tool would be fitted with an end mill that would machine the weld smooth, trimmed shaved. This would eliminate the need for manual weld preparation for ultrasonic inspections. Manual surface preparation is a hand operation that varies widely depending on the person preparing the welds. Shaving is a process that can be automated and tightly controlled.

  12. Friction behaviors of rough chromium surfaces under starving lubrication conditions

    Science.gov (United States)

    Liu, Derong; Yan, Bo; Shen, Bin; Liu, Lei; Hu, Wenbin

    2018-01-01

    Surface texturing has become an effective method for improving the tribological properties of mechanical components under the oil lubrication. In this study, a rough surface, with the bumps arranged in a random array, was prepared by means of electrodeposition. A post-grinding and polishing processing was employed to fabricate flat areas for tribological tests under conformal contact. Compared with the smooth surfaces, the rough surface improves the load capacity of coatings at high loads. The effects of rough surfaces on friction reduction become more pronounced at higher speeds and lower normal loads due to the transition of lubricant regime from the boundary to mixed lubrication.

  13. Surface Velocities and Hydrology at Engabreen

    DEFF Research Database (Denmark)

    Messerli, Alexandra

    Recent studies have likened the seasonal observations of ice flow at the marginal regions of the Greenland Ice Sheet (GrIS) to those found on smaller alpine and valley counterparts. These similarities highlight the need for further small scale studies of seasonal evolution in the hydrological...... on surface velocities recorded at the site. The Svartisen Subglacial Laboratory (SSL) under Engabreen, augmented by additional subglacial pressure and hydrological measurements, provides a invaluable observations for detailed process-oriented studies. However, the lack of complementary surface velocity data...... and dynamic structure of valley glaciers, to aid interpretation of observations from the margins of the GrIS. This thesis aims to collate a large suit of glacio-hydrological data from the outlet glacier Engabreen, Norway, in order to better understand the role the subglacial drainage configuration has...

  14. Enhancement of Friction against a Rough Surface by a Ridge-Channel Surface Microstructure.

    Science.gov (United States)

    Bai, Ying; Hui, Chung-Yuen; Levrard, Benjamin; Jagota, Anand

    2015-07-14

    We report on a study of the sliding friction of elastomeric surfaces patterned with ridges and channels (and unstructured flat controls), against both smooth and roughened spherical indenters. Against the smooth spherical indenter, all of the structured surfaces have highly reduced sliding friction due to the reduction in actual area of contact. Against roughened spherical indenters, however, the sliding force for structured samples can be up to 50% greater than that of an unstructured flat control. The mechanism of enhanced friction against a rough surface is due to a combination of increased actual area of contact, interlocking between roughness and the surface structure, and attendant dynamic instabilities that dissipate energy.

  15. Plasticity under rough surface contact and friction

    NARCIS (Netherlands)

    Sun, F.

    2016-01-01

    The ultimate objective of this work is to gain a better understanding of the plastic behavior of rough metal surfaces under contact loading. Attention in this thesis focuses on the study of single and multiple asperities with micrometer scale dimensions, a scale at which plasticity is known to be

  16. Comparison of three different methods for assessing in situ friction velocity: A case study from Loch Etive, Scotland

    DEFF Research Database (Denmark)

    Inoue, Tetsunori; Glud, Ronnie N.; Stahl, Henrik

    2011-01-01

    Three approaches, Eddy Correlation (EC), Turbulent Kinetic Energy (TKE), and Inertial Dissipation (ID) methods, were compared to evaluate their potential for estimation of friction velocity in a Scottish sea loch. As an independent assessment parameter, we used simultaneous O2 recordings of the d......Three approaches, Eddy Correlation (EC), Turbulent Kinetic Energy (TKE), and Inertial Dissipation (ID) methods, were compared to evaluate their potential for estimation of friction velocity in a Scottish sea loch. As an independent assessment parameter, we used simultaneous O2 recordings...

  17. 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

  18. Cohesive delamination and frictional contact on joining surface via XFEM

    Directory of Open Access Journals (Sweden)

    Francesco Parrinello

    2018-02-01

    Full Text Available In the present paper, the complex mechanical behaviour of the surfaces joining two differentbodies is analysed by a cohesive-frictional interface constitutive model. The kinematical behaviouris characterized by the presence of discontinuous displacement fields, that take place at the internalconnecting surfaces, both in the fully cohesive phase and in the delamination one. Generally, in order tocatch discontinuous displacement fields, internal connecting surfaces (adhesive layers are modelled bymeans of interface elements, which connect, node by node, the meshes of the joined bodies, requiringthe mesh to be conforming to the geometry of the single bodies and to the relevant connecting surface.In the present paper, the Extended Finite Element Method (XFEM is employed to model, both fromthe geometrical and from the kinematical point of view, the whole domain, including the connectedbodies and the joining surface. The joining surface is not discretized by specific finite elements, butit is defined as an internal discontinuity surface, whose spatial position inside the mesh is analyticallydefined. The proposed approach is developed for two-dimensional composite domains, formed by twoor more material portions joined together by means of a zero thickness adhesive layer. The numericalresults obtained with the proposed approach are compared with the results of the classical interfacefinite element approach. Some examples of delamination and frictional contact are proposed withlinear, circular and curvilinear adhesive layer.

  19. On the prediction of threshold friction velocity of wind erosion using soil reflectance spectroscopy

    Science.gov (United States)

    Li, Junran; Flagg, Cody B.; Okin, Gregory S.; Painter, Thomas H.; Dintwe, Kebonye; Belnap, Jayne

    2015-01-01

    Current approaches to estimate threshold friction velocity (TFV) of soil particle movement, including both experimental and empirical methods, suffer from various disadvantages, and they are particularly not effective to estimate TFVs at regional to global scales. Reflectance spectroscopy has been widely used to obtain TFV-related soil properties (e.g., moisture, texture, crust, etc.), however, no studies have attempted to directly relate soil TFV to their spectral reflectance. The objective of this study was to investigate the relationship between soil TFV and soil reflectance in the visible and near infrared (VIS–NIR, 350–2500 nm) spectral region, and to identify the best range of wavelengths or combinations of wavelengths to predict TFV. Threshold friction velocity of 31 soils, along with their reflectance spectra and texture were measured in the Mojave Desert, California and Moab, Utah. A correlation analysis between TFV and soil reflectance identified a number of isolated, narrow spectral domains that largely fell into two spectral regions, the VIS area (400–700 nm) and the short-wavelength infrared (SWIR) area (1100–2500 nm). A partial least squares regression analysis (PLSR) confirmed the significant bands that were identified by correlation analysis. The PLSR further identified the strong relationship between the first-difference transformation and TFV at several narrow regions around 1400, 1900, and 2200 nm. The use of PLSR allowed us to identify a total of 17 key wavelengths in the investigated spectrum range, which may be used as the optimal spectral settings for estimating TFV in the laboratory and field, or mapping of TFV using airborne/satellite sensors.

  20. Surface deformation and friction characteristic of nano scratch at ductile-removal regime for optical glass BK7.

    Science.gov (United States)

    Li, Chen; Zhang, Feihu; Ding, Ye; Liu, Lifei

    2016-08-20

    Nano scratch for optical glass BK7 based on the ductile-removal regime was carried out, and the influence rule of scratch parameters on surface deformation and friction characteristic was analyzed. Experimental results showed that, with increase of normal force, the deformation of burrs in the edge of the scratch was more obvious, and with increase of the scratch velocity, the deformation of micro-fracture and burrs in the edge of the scratch was more obvious similarly. The residual depth of the scratch was measured by atomic force microscope. The experimental results also showed that, with increase of normal force, the residual depth of the scratch increased linearly while the elastic recovery rate decreased. Furthermore, with increase of scratch velocity, the residual depth of the scratch decreased while the elastic recovery rate increased. The scratch process of the Berkovich indenter was divided into the cutting process of many large negative rake faces based on the improved cutting model, and the friction characteristic of the Berkovich indenter and the workpiece was analyzed. The analysis showed that the coefficient of friction increased and then tended to be stable with the increase of normal force. Meanwhile, the coefficient of friction decreased with the increase of scratch velocity, and the coefficients, k ln(v) and μ0, were introduced to improve the original formula of friction coefficient.

  1. Frictional Performance Assessment of Cemented Carbide Surfaces Textured by Laser

    Science.gov (United States)

    Fang, S.; Llanes, L.; Klein, S.; Gachot, C.; Rosenkranz, A.; Bähre, D.; Mücklich, F.

    2017-10-01

    Cemented carbides are advanced engineering materials often used in industry for manufacturing cutting tools or supporting parts in tribological system. In order to improve service life, special attention has been paid to change surface conditions by means of different methods, since surface modification can be beneficial to reduce the friction between the contact surfaces as well as to avoid unintended damage. Laser surface texturing is one of the newly developed surface modification methods. It has been successfully introduced to fabricate some basic patterns on cemented carbide surfaces. In this work, Direct Laser Interference Patterning Technique (DLIP) is implemented to produce special line-like patterns on a cobalt (Co) and nickel (Ni) based cemented tungsten carbide grade. It is proven that the laser-produced patterns have high geometrical precision and quality stability. Furthermore, tribology testing using a nano-tribometer unit shows that friction is reduced by the line-like patterns, as compared to the polished one, under both lubricated and dry testing regimes, and the reduction is more pronounced in the latter case.

  2. Vehicle Velocity and Roll Angle Estimation with Road and Friction Adaptation for Four-Wheel Independent Drive Electric Vehicle

    Directory of Open Access Journals (Sweden)

    Linhui Zhao

    2014-01-01

    Full Text Available Vehicle velocity and roll angle are important information for active safety control systems of four-wheel independent drive electric vehicle. In order to obtain robustness estimation of vehicle velocity and roll angle, a novel method is proposed based on vehicle dynamics and the measurement information provided by the sensors equipped in modern cars. The method is robust with respect to different road and friction conditions. Firstly, the dynamic characteristics of four-wheel independent drive electric vehicle are analyzed, and a four-degree-of-freedom nonlinear dynamic model of vehicle and a tire longitudinal dynamic equation are established. The relationship between the longitudinal and lateral friction forces is derived based on Dugoff tire model. The unknown input reconstruction technique of sliding mode observer is used to achieve longitudinal tire friction force estimation. A simple observer is designed for the estimation of the roll angle of the vehicle. And then using the relationship, the estimated longitudinal friction forces and roll angle, a sliding mode observer for vehicle velocity estimation is provided, which does not need to know the tire-road friction coefficient and road angles. Finally, the proposed method is evaluated experimentally under a variety of maneuvers and road conditions.

  3. Seasonal dynamics of threshold friction velocity and dust emission in Central Asia.

    Science.gov (United States)

    Xi, Xin; Sokolik, Irina N

    2015-02-27

    An improved model representation of mineral dust cycle is critical to reducing the uncertainty of dust-induced environmental and climatic impact. Here we present a mesoscale model study of the seasonal dust activity in the semiarid drylands of Central Asia, focusing on the effects of wind speed, soil moisture, surface roughness heterogeneity, and vegetation phenology on the threshold friction velocity ( u *t ) and dust emission during the dust season of 1 March to 31 October 2001. The dust model WRF-Chem-DuMo allows us to examine the uncertainties in seasonal dust emissions due to the selection of dust emission scheme and soil grain size distribution data. To account for the vegetation effects on the u *t , we use the Moderate Resolution Imaging Spectroradiometer monthly normalized difference vegetation index to derive the dynamic surface roughness parameters required by the physically based dust schemes of Marticorena and Bergametti (1995, hereinafter MB) and Shao et al. (1996, hereinafter Shao). We find the springtime u *t is strongly enhanced by the roughness effects of temperate steppe and desert ephemeral plants and, to less extent, the binding effects of increased soil moisture. The u *t decreases as the aboveground biomass dies back and soil moisture depletes during summer. The u *t dynamics determines the dust seasonality by causing more summer dust emission, despite a higher frequency of strong winds during spring. Due to the presence of more erodible materials in the saltation diameter range of 60-200 µm, the dry-sieved soil size distribution data lead to eight times more season-total dust emission than the soil texture data, but with minor differences in the temporal distribution. On the other hand, the Shao scheme produces almost the same amount of season-total dust emission as the MB scheme, but with a strong shift toward summer due to the strong sensitivity of the u *t to vegetation. By simply averaging the MB and Shao model experiments, we obtain

  4. Friction Evaluation of Laser Textured Tool Steel Surfaces

    Directory of Open Access Journals (Sweden)

    Šugárová Jana

    2017-06-01

    Full Text Available Surface textures can be defined as a regularly arranged micro-depressions or grooves with defined shape and dimensions. These textures, if they are manufactured by laser ablation process, contribute to a significant improvement of the tribological, optical or various biological properties. The aim of this paper is to analyze the influence of the surface textures prepared by laser surface texturing (LST at the friction coefficient value measured on the tool (90MnCrV8 steel – workpiece (S235JRG1 steel interface. Planar frontal surfaces of compression platens have been covered by parabolic dimple-like depressions with different dimensions. The morphological analysis of such manufactured depressions has been performed by laser scanning microscopy. Influence of such created textures on the tribological properties of the contact pair has been analyzed by the ring compression test method in the terms of hydrodynamic lubrication regime. The experimental research shown that by applying of surface textures with defined shape and dimensions and using an appropriate liquid lubricant at the same time, the coefficient of contact friction can be reduced nearly to the half of its original value.

  5. Slip velocity has major impact on the frictional strength and microstructure of quartz-muscovite gouges under hydrothermal conditions

    Science.gov (United States)

    Niemeijer, Andre R.

    2015-04-01

    Previous friction experiments on rock analogue experiments of mixtures of salt and phyllosilicates, demonstrated the possibility of producing mylonitic fault rocks through the simultaneous operation of pressure solution and frictional sliding. This frictional-viscous flow process produces a strong velocity-dependence of friction, with friction values dropping from 0.8 to ~0.2-0.3 over just one order of magnitude decrease in sliding velocity. Here, we present the results of rotary shear experiments on simulated fault gouges of 80 wt% quartz and 20 wt% muscovite. Sliding experiments using a four orders of magnitude range of constant velocities (0.03 - 300 μm/s) to a displacement of 30 mm were done at 500 ° C, 120 MPa effective normal stress and 80 MPa fluid pressure to verify the mechanism at hydrothermal conditions and to link the produced microstructure to the observed strength. At the lowest sliding velocity tested, final friction reached a value of ~0.3, which is lower than that of pure muscovite under similar conditions. With increasing sliding velocity, friction increases, reaching a maximum of ~0.9 at 3 μm/s after which it decreases mildly to ~0.8 at 300 μm/s. The bulk microstructure of the sample sheared at 0.03 μm/s shows an anastomosing foliation of muscovite grain intervened by asymmetrical quartz clasts, with an average grain size of about 20 μm, slightly lower than the median starting size (~49 μm). In contrast, the grains of the sample deformed at 300 micron/s are very small, many of them smaller than distinguishable in the light microscope (i.e. orientations, possibly indicating a Crystallographic Preferred Orientation. These zones of uniform extinction can be found in all samples and their thickness decreases monotonically with decreasing sliding velocity. The microstructure observed at low velocity, in the frictional-viscous regime, is similar to numerous examples from natural fault rocks (e.g. the Median Tectonic Line and the Zuccale Fault

  6. Influence of shear velocity on frictional characteristics of rock surface

    Indian Academy of Sciences (India)

    Author Affiliations. T N Singh1 A K Verma2 Tanmay Kumar3 Avi Dutt3. Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai 400 056, India. CeRES, The Energy and Resources Institute, Darbari Seth Block, IHC Complex, Lodhi Road, New Delhi 110 003, India. Institute of Technology, Banaras Hindu ...

  7. Turbulent friction drag reduction using electroactive polymer and electromagnetically driven surfaces

    Science.gov (United States)

    Gouder, Kevin; Potter, Mark; Morrison, Jonathan F.

    2013-01-01

    This work reports aerodynamic testing of two spanwise-oscillating surfaces fabricated out of electroactive polymers (EAPs) in the dielectric form of actuation, and of an electromagnetic-driven linear motor. Hot-wire and PIV measurements of velocity and direct measurement of friction drag using a drag balance are presented. A maximum of 16 % surface friction reduction, as calculated by the diminution of the wall-normal streamwise velocity gradient, was obtained. Among other quantities, the spatial dependence of the drag reduction was investigated. When this spatial transient and portions which are static are accounted for, the direct drag measurements complement the hot-wire data. PIV measurements, where the laser beam was parallel to the oscillating surface at y + ≈ 15, support the hot-wire data. The two actuators are original in design, and significant contributions have been made to the development of EAPs. This experiment is the first to aerodynamically test EAP actuators at such a large scale and at a relatively moderate Re.

  8. The transition of dynamic rupture styles in elastic media under velocity-weakening friction

    KAUST Repository

    Gabriel, A.-A.

    2012-09-01

    Although kinematic earthquake source inversions show dominantly pulse-like subshear rupture behavior, seismological observations, laboratory experiments and theoretical models indicate that earthquakes can operate with different rupture styles: either as pulses or cracks, that propagate at subshear or supershear speeds. The determination of rupture style and speed has important implications for ground motions and may inform about the state of stress and strength of active fault zones. We conduct 2D in-plane dynamic rupture simulations with a spectral element method to investigate the diversity of rupture styles on faults governed by velocity-and-state-dependent friction with dramatic velocity-weakening at high slip rate. Our rupture models are governed by uniform initial stresses, and are artificially initiated. We identify the conditions that lead to different rupture styles by investigating the transitions between decaying, steady state and growing pulses, cracks, sub-shear and super-shear ruptures as a function of background stress, nucleation size and characteristic velocity at the onset of severe weakening. Our models show that small changes of background stress or nucleation size may lead to dramatic changes of rupture style. We characterize the asymptotic properties of steady state and self-similar pulses as a function of background stress. We show that an earthquake may not be restricted to a single rupture style, but that complex rupture patterns may emerge that consist of multiple rupture fronts, possibly involving different styles and back-propagating fronts. We also demonstrate the possibility of a super-shear transition for pulse-like ruptures. Finally, we draw connections between our findings and recent seismological observations.

  9. Solid Lubrication Fundamentals and Applications. Properties of Clean Surfaces: Adhesion, Friction, and Wear

    Science.gov (United States)

    Miyoshi, Kazuhisa

    1998-01-01

    This chapter presents the adhesion, friction, and wear behaviors of smooth, atomically clean surfaces of solid-solid couples, such as metal-ceramic couples, in a clean environment. Surface and bulk properties, which determine the adhesion, friction, and wear behaviors of solid-solid couples, are described. The primary emphasis is on the nature and character of the metal, especially its surface energy and ductility. Also, the mechanisms of friction and wear for clean, smooth surfaces are stated.

  10. Possible stibnite transformation at the friction surface of the semi-metallic friction composites designed for car brake linings

    Science.gov (United States)

    Matějka, V.; Lu, Y.; Matějková, P.; Smetana, B.; Kukutschová, J.; Vaculík, M.; Tomášek, V.; Zlá, S.; Fan, Y.

    2011-12-01

    After a friction process several changes in phase composition of friction composites are often registered. High temperature, accompanied by high pressure induced during braking can cause initiation of chemical reactions which do not run at room or elevated temperatures under the atmospheric pressure. Most of the studies in the field of tribochemistry at friction surfaces of automotive semi-metallic brake linings deal with phenolic resin degradation and corrosion of metallic components. The paper addresses the formation of elemental antimony as well as the alloying process of iron with antimony observed on the surface of laboratory prepared semi-metallic friction composites containing stibnite. The role of alumina abrasives in the process of stibnite transformation is also discussed and mechanism of stibnite transformation was outlined.

  11. Effect of the Surface Texture on Friction Thrust Bearing Performance

    Directory of Open Access Journals (Sweden)

    Suárez-Bustamante F.A.

    2012-01-01

    Full Text Available This paper shows a theoretical model which stablishes relations among the operational conditions of a thrust bearing, its conditioned microtopography and the friction coeficient when it works under Hydrodynamic Lubrication conditions. Among the most outstanding results obtained from an exploration made with the model are: building of a map where the performance of these components is characterized and the obtention of some relations among several adimentional groups that show the possiblility to enhance the hydrodynamic lubrication regime for this sort of bearings by artificial conditioning of their surfaces.

  12. frictiOns - the software-surface-rubbing game

    Directory of Open Access Journals (Sweden)

    Endi Tupja

    2018-01-01

    Full Text Available Smartphone usage has drastically changed the way images are produced and contemplated, creating thus fertile ground for a virtual environment blurring information exchange with entertainment. In the experimental film frictiOns, virtuality and interaction have been reconsidered under an analogue perspective.  Disobeying assumptions on device and virtuality by challenging the concept of surface and interface. An analysis of art games and the binome (iphone-entertainment, examines the prospective of users as players, highlighting cultural determining factors such as flattening and soft power.

  13. Frictional Properties of Sediments from Nankai Trough IODP Expedition 316: Results from an Intermediate-Velocity Test

    Science.gov (United States)

    Tsutsumi, A.; Fabbri, O.; Ujiie, K.; Andreani, M.; 314/315/316 Scientific Party, I.

    2008-12-01

    Shear deformation experiments were performed on discrete core samples from NanTroSEIZE drilling sites C0004 and C0006 (Exp.316), at normal stresses of 1.0 to 5.0 MPa and at slip rates from 0.0026 to 26 mm/s, with a rotary-shear, intermediate- to high-velocity friction apparatus at Kyoto University. To be used in the experiments, collected discrete samples were disaggregated, oven dried at 90 ° C for 24 hours and then sieved to eliminate clasts larger than about 0.1 mm. The experimental fault is composed of thin layer (< 1.0 mm) of the disaggregated materials, which is put between a pair of 24.8 mm diameter granite cylinders. A Teflon ring surrounds the fault in order to avoid a leak of the sheared material during the experiment. Our preliminary results show that the level of friction recorded for the tested samples are generally low, from about 0.1 to 0.3, over the range of experimental conditions used in this study. The velocity dependence of friction of the tested samples is complex and it varies for different samples. For example, sample from C0004D-26R-1 at 260.5 mbsf exhibits strong velocity strengthening behavior at slower velocities (0.0026 to 2.6 mm/s) and almost no or a weak velocity weakening behavior at the fastest velocities tested in this study (2.6 to 26.0 mm/s). In contrast, sample from C0006E-31X-4 at 232.7 mbsf exhibits a weak velocity weakening behavior to a step change in loading velocity at velocities from 0.0026 to 0.26 mm/s, with a transition to a subtle dependence of friction at velocities from 0.26 to 26 mm/s. Such transitions in velocity dependence with the increase of slip rate might affect the mode of sliding of faults within a shallow portion of the Nankai subduction zone. Additional work to examine associations between the velocity dependence and the composition of the tested materials over a wide range of experimental conditions is needed.

  14. A new state-of-the-art tool to investigate rock friction under extreme slip velocities and accelerations: SHIVA

    Science.gov (United States)

    Niemeijer, André; di Toro, Giulio; Nielsen, Stefan; Scarlato, Piergiorgio; Romeo, Gianni; di Stefano, Giuseppe; Smith, Steven; di Felice, Fabio; Mariano, Sofia

    2010-05-01

    Despite considerable effort over the past several decades, the mechanics of earthquakes rupture remain largely unknown. In order to complement fault drilling projects and field and seismological observations, recent friction experiments strive to reproduce as closely as possible in-situ (natural) conditions of slip velocity and acceleration on intact and fault rocks. In this contribution, we present a novel state-of-the-art experimental rotary shear apparatus (SHIVA or Slow to HIgh Velocity Apparatus) capable of shearing samples at sliding velocities up to 10 m/s, accelerations of ~ 40 m/s2 and normal stresses up to 50 MPa. In comparison with existing high speed friction machines, this apparatus extends the range of sliding velocities, normal stresses, sample size and, more importantly, accelerations. The apparatus consists of a pair of brushless electric motors (a low velocity motor, 10-6-10-3 m/s, power 5 kW, and a high velocity motor, 10-3 - 10 m/s, power 270 kW), that are connected by a gear system that allows a switch between motors without loss of velocity and force. The motors drive a rotary shaft which clamps ring-shaped samples (diameter 40- 50 mm). On the other side of the rotary shaft, a stationary shaft holds the other half of the sample assembly. The shaft is held stationary by a pair of stainless steel arms, one of which is attached to the side of the concrete-filled base where torque is measured by a tension cell. Axial force (maximum 37 kN) is applied on this side by a piston-cylinder couple with an arm to increase the force. The entire machine measures by 3.5 by 1.2 meters and weighs 3700 kg. We aim to perform experiments on rock samples of a variety of compositions using slip velocities and accelerations that simulate slip velocity functions that occur during earthquakes. In addition, we plan to develop a pore fluid system and a pressure vessel in order to perform experiments that include the physical-chemical processes that occur during slow

  15. Friction of ice. [on Ganymede, Callisto, and Europa surfaces

    Science.gov (United States)

    Beeman, M.; Durham, W. B.; Kirby, S. H.

    1988-01-01

    Frictional sliding experiments were performed on saw-cut samples of laboratory-made polycrystalline water ice, prepared in the same way as the material used by Kirby et al. (1987) in ice deformation experiments. The data show that the maximum frictional stress is a function of the normal stress but is not measurably dependent on temperature or sliding rate over the ranges covered in these experiments (77-115 K and 0.0003-0.03 mm/s, respectively). The sliding behavior was invariably stick slip, with the sliding surfaces exhibiting only minor gouge development. In samples with anomalously low strength, a curious arrangement of densely packed short vertical fractures was observed. The results of these experiments were applied to a model of near-surface tectonic activity on Ganymede, one of Jupiter's icy moons. The results indicate that a global expansion on Ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 + or - 3 km.

  16. Influence of surface roughness on the friction property of textured surface

    Directory of Open Access Journals (Sweden)

    Yuankai Zhou

    2015-02-01

    Full Text Available In contrast with dimple textures, surface roughness is a texture at the micro-scale, essentially which will influence the load-bearing capacity of lubricant film. The numerical simulation was carried out to investigate the influence of surface roughness on friction property of textured surface. The lubricant film pressure was obtained using the method of computational fluid dynamics according to geometric model of round dimple, and the renormalization-group k–ε turbulent model was adopted in the computation. The numerical simulation results suggest that there is an optimum dimensionless surface roughness, and near this value, the maximum load-bearing capacity can be achieved. The load-bearing capacity is determined by the surface texture, the surface roughness, and the interaction between them. To get information of friction coefficient, the experiments were conducted. This experiment was used to evaluate the simulation. The experimental results show that for the frequency of 4 and 6 Hz, friction coefficient decreases at first and then increases with decreasing surface roughness, which indicates that there exists the optimum region of surface roughness leading to the best friction reduction effect, and it becomes larger when area fractions increase from 2% to 10%. The experimental results agree well with the simulation results.

  17. A Physics-Based Rock Friction Constitutive Law: Steady State Friction

    Science.gov (United States)

    Aharonov, Einat; Scholz, Christopher H.

    2018-02-01

    Experiments measuring friction over a wide range of sliding velocities find that the value of the friction coefficient varies widely: friction is high and behaves according to the rate and state constitutive law during slow sliding, yet markedly weakens as the sliding velocity approaches seismic slip speeds. We introduce a physics-based theory to explain this behavior. Using conventional microphysics of creep, we calculate the velocity and temperature dependence of contact stresses during sliding, including the thermal effects of shear heating. Contacts are assumed to reach a coupled thermal and mechanical steady state, and friction is calculated for steady sliding. Results from theory provide good quantitative agreement with reported experimental results for quartz and granite friction over 11 orders of magnitude in velocity. The new model elucidates the physics of friction and predicts the connection between friction laws to independently determined material parameters. It predicts four frictional regimes as function of slip rate: at slow velocity friction is either velocity strengthening or weakening, depending on material parameters, and follows the rate and state friction law. Differences between surface and volume activation energies are the main control on velocity dependence. At intermediate velocity, for some material parameters, a distinct velocity strengthening regime emerges. At fast sliding, shear heating produces thermal softening of friction. At the fastest sliding, melting causes further weakening. This theory, with its four frictional regimes, fits well previously published experimental results under low temperature and normal stress.

  18. Contact splitting and the effect of dimple depth on static friction of textured surfaces.

    Science.gov (United States)

    Greiner, Christian; Schäfer, Michael; Popp, Uwe; Gumbsch, Peter

    2014-06-11

    The morphological texturing of surfaces has demonstrated its high potential to maximize adhesion as well as to reduce friction and wear. A key to understanding such phenomena is a principle known as contact splitting. Here, we extend this concept to the static friction behavior of dimpled surfaces. Our results indicate that contact splitting does exist for such structures and that with certain dimple sizes and depths static friction values significantly exceeding those of untextured surfaces can be obtained. These results can be applied to all surfaces where friction forces are to be tuned, from nanoelectromechanical systems up to combustion engines.

  19. A comparative study of frictional resistance and surface roughness between orthodontic bracket and arch wire

    OpenAIRE

    Kazuro, SATOH; Masaru, ISHIGAME; Yukiko, NAKAMURA; Kazushi, OGASAWARA; Shigeru, TANAKA; Hiroyuki, MIURA; Department of Orthodontics, School of Dentistry, Iwate Medical University; Department of Orthodontics, School of Dentistry, Iwate Medical University; Department of Orthodontics, School of Dentistry, Iwate Medical University; Department of Orthodontics, School of Dentistry, Iwate Medical University; Department of Orthodontics, School of Dentistry, Iwate Medical University; Department of Orthodontics, School of Dentistry, Iwate Medical University

    2003-01-01

    The frictional resistance between an orthodontic bracket and arch wire is closely related to the efficiency of tooth movement in sliding mechanics. Frictional resistance may arise from the materials, geometrical configuration between the orthodontic bracket and arch wire, ligation system and its force, wire stiffness, direction and degree of orthodontic force, and surface roughness of bracket and wire. This study examined the relationship between the frictional resistance and surface roughnes...

  20. Influence of surface roughness on the friction property of textured surface

    OpenAIRE

    Yuankai Zhou; Hua Zhu; Wenqian Zhang; Xue Zuo; Yan Li; Jianhua Yang

    2015-01-01

    In contrast with dimple textures, surface roughness is a texture at the micro-scale, essentially which will influence the load-bearing capacity of lubricant film. The numerical simulation was carried out to investigate the influence of surface roughness on friction property of textured surface. The lubricant film pressure was obtained using the method of computational fluid dynamics according to geometric model of round dimple, and the renormalization-group k–ε turbulent model was adopted in ...

  1. Self-Organization during Friction in Complex Surface Engineered Tribosystems

    Directory of Open Access Journals (Sweden)

    Ben D. Beake

    2010-02-01

    Full Text Available Self-organization during friction in complex surface engineered tribosystems is investigated. The probability of self-organization in these complex tribosystems is studied on the basis of the theoretical concepts of irreversible thermodynamics. It is shown that a higher number of interrelated processes within the system result in an increased probability of self-organization. The results of this thermodynamic model are confirmed by the investigation of the wear performance of a novel Ti0.2Al0.55Cr0.2Si0.03Y0.02N/Ti0.25Al0.65Cr0.1N (PVD coating with complex nano-multilayered structure under extreme tribological conditions of dry high-speed end milling of hardened H13 tool steel.

  2. 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.

  3. 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

  4. 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.

  5. Experimental and Numerical Simulation of the Dynamic Frictional Contact between an Aircraft Tire Rubber and a Rough Surface

    Directory of Open Access Journals (Sweden)

    Iulian Rosu

    2016-08-01

    Full Text Available This paper presents a numerical simulation of an aircraft tire in contact with a rough surface using a variable friction coefficient dependent on temperature and contact pressure. A sliding facility was used in order to evaluate this dependence of the friction coefficient. The temperature diffusion throughout the tire cross-section was measured by means of thermocouples. Both frictional heating and temperature diffusion were compared to numerical two- and three- dimensional simulations. An adequate temperature prediction could be obtained. In future simulations, wear should be taken into account in order to have a more accurate simulation especially in the case of high pressures and slipping velocities. A 3D finite element model for a rolling tire at a velocity of 37.79 knots (19.44 m/s and in a cornering phase was investigated using a variable friction coefficient dependent on temperature and pressure. The numerical simulation tended to predict the temperature of the tire tread after a few seconds of rolling in skidding position, the temperature of the contact zone increases to 140 °C. Further investigations must be carried out in order to obtain the evolution of the temperature observed experimentally. The authors would like to point out that for confidentiality reasons, certain numerical data could not be revealed.

  6. Controlling friction in a manganite surface by resistive switching

    OpenAIRE

    Schmidt, Hendrik; Krisponeit, Jon-Olaf; Samwer, Konrad; Volkert, Cynthia A.

    2016-01-01

    We report a significant change in friction of a $\\rm La_{0.55}Ca_{0.45}MnO_3$ thin film measured as a function of the materials resistive state under ultrahigh vacuum conditions at room temperature by friction force microscopy. While friction is high in the insulating state, it clearly changes to lower values if the probed local region is switched to the conducting state via nanoscale resistance switching. Thus we demonstrate active control of friction without having to change the temperature...

  7. Velocity Profiles and Skin Friction on a Ribletted Flat Plate in Adverse Pressure Gradient

    National Research Council Canada - National Science Library

    Branam, Richard

    1997-01-01

    .... The skin friction drag coefficients were calculated using a numerical integration technique to determine an average value and scaled to the platform area of the plate to compare results with smooth plate values...

  8. Surface Wave Velocity-Stress Relationship in Uniaxially Loaded Concrete

    DEFF Research Database (Denmark)

    Shokouhi, Parisa; Zoëga, Andreas; Wiggenhauser, Herbert

    2012-01-01

    loading cycles revealed that the velocities show a stress-memory effect in good agreement with the Kaiser effect. Comparing the velocities measured during loading and unloading, the effects of stress and damage on the measured velocities could be differentiated. Moreover, the stress dependency of surface......The sonic surface wave (or Rayleigh wave) velocity measured on prismatic concrete specimens under uniaxial compression was found to be highly stress-dependent. At low stress levels, the acoustoelastic effect and the closure of existing microcracks results in a gradual increase in surface wave...... velocities. At higher stress levels, concrete suffers irrecoverable damage: the existing microcracks widen and coalesce and new microcracks form. This progressive damage process leads first to the flattening and eventually the drop in the velocity-stress curves. Measurements on specimens undergoing several...

  9. Influence of Laser Shock Texturing on W9 Steel Surface Friction Property

    Science.gov (United States)

    Fan, Yujie; Cui, Pengfei; Zhou, Jianzhong; Dai, Yibin; Guo, Erbin; Tang, Deye

    2017-09-01

    To improve surface friction property of high speed steel, micro-dent arrays on W9Mo3Cr4V surface were produced by laser shock processing. Friction test was conducted on smooth surface and texturing surface and effect of surface texturing density on friction property was studied. The results show that, under the same condition, friction coefficient of textured surface is lower than smooth surface with dent area density less than 6%, wear mass loss, width and depth of wear scar are smaller; Wear resistance of the surface is the best and the friction coefficient is the smallest when dent area density is 2.2%; Friction coefficient, wear mass loss, width and depth of wear scar increase correspondingly as density of dent area increases when dent area density is more than 2.2%. Abrasive wear and adhesive wear, oxidative wear appear in the wear process. Reasonable control of geometric parameters of surface texturing induced by laser shock processing is helpful to improve friction performance.

  10. Friction and surface chemistry of some ferrous-base metallic glasses

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1982-01-01

    The friction properties of some ferrous-base metallic glasses were measured both in argon and in vacuum to a temperature of 350 C. The alloy surfaces were also analyzed with X-ray photoelectron spectroscopy to identify the compounds and elements present on the surface. The results of the investigation indicate that even when the surfaces of the amorphous alloys, or metallic glasses, are atomically clean, bulk contaminants such as boric oxide and silicon dioxide diffuse to the surfaces. Friction measurements in both argon and vacuum indicate that the alloys exhibit higher coefficients of friction in the crystalline state than they do in the amorphous state.

  11. Experimental Study of Reciprocating Friction between Rape Stalk and Bionic Nonsmooth Surface Units

    Directory of Open Access Journals (Sweden)

    Zheng Ma

    2015-01-01

    Full Text Available Background. China is the largest producer of rape oilseed in the world; however, the mechanization level of rape harvest is relatively low, because rape materials easily adhere to the cleaning screens of combine harvesters, resulting in significant cleaning losses. Previous studies have shown that bionic nonsmooth surface cleaning screens restrain the adhesion of rape materials, but the underlying mechanisms remain unclear. Objective. The reciprocating friction between rape stalk and bionic nonsmooth metal surface was examined. Methods. The short-time Fourier transform method was used to discriminate the stable phase of friction signals and the stick-lag distance was defined to analyze the stable reciprocating friction in a phase diagram. Results. The reciprocating friction between rape stalk and metal surface is a typical stick-slip friction, and the bionic nonsmooth metal surfaces with concave or convex units reduced friction force with increasing reciprocating frequency. The results also showed that the stick-lag distance of convex surface increased with reciprocating frequency, which indicated that convex surface reduces friction force more efficiently. Conclusions. We suggest that bionic nonsmooth surface cleaning screens, especially with convex units, restrain the adhesion of rape materials more efficiently compared to the smooth surface cleaning screens.

  12. Influence of the surface finishing on ultrasound velocity in wood

    Directory of Open Access Journals (Sweden)

    Tomáš Špaček

    2008-01-01

    Full Text Available Non-destructive diagnostic methods are very useful for monumental buildings. This paper deals with one of these technique, namely with ultrasound testing and influence of surface finishing on ultrasound velocity measured by means of device the Arborsonic Decay Detector. Surface finishing (Primalex – thick synthetic film of the surface finishing, Luxol – Extra – thin synthetic film of the surface finishing and Impranal Profi SL – thick acryl film the surface finishing were selected and tested in this research. The transmittion time was measured and velocity was converted from it. This was compared before and after application of surface finishing.

  13. 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.

  14. Predicting the Wear of High Friction Surfacing Aggregate

    Directory of Open Access Journals (Sweden)

    David Woodward

    2017-05-01

    Full Text Available High friction surfacing (HFS is a specialist type of road coating with very high skid resistance. It is used in the UK at locations where there is significant risk of serious or fatal accidents. This paper considers the aggregate used in HFS. Calcined bauxite is the only aggregate that provides the highest levels of skid resistance over the longest period. No naturally occurring aggregate has been found to give a comparable level of in-service performance. This paper reviews the historical development of HFS in the UK relating to aggregate. In-service performance is predicted in the laboratory using the Wear test which subjects test specimens to an estimated 5–8 years simulated trafficking. Examples are given of Wear test data. They illustrate why calcined bauxite performs better than natural aggregate. They show how the amount of calcined bauxite can be reduced by blending with high skid resistant natural aggregates. Data from the Wear test can be related to every HFS laboratory experiment and road trial carried out in the UK for over the last 50 years. Anyone considering the prediction of HFS performance needs to carefully consider the data given in this paper with any other test method currently being considered or used to investigate HFS.

  15. 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.

  16. General contact mechanics theory for randomly rough surfaces with application to rubber friction

    OpenAIRE

    Scaraggi, Michele; Persson, Bo N. J.

    2015-01-01

    We generalize the Persson contact mechanics and rubber friction theory to the case where both surfaces have surface roughness. The solids can be rigid, elastic or viscoelastic, and can be homogeneous or layered. We calculate the contact area, the viscoelastic contribution to the friction force, and the average interfacial separation as a function of the sliding speed and the nominal contact pressure. We illustrate the theory with numerical results for a rubber block sliding on a road surface....

  17. Formation of Composite Surface during Friction Surfacing of Steel with Aluminium

    OpenAIRE

    Janakiraman, S.; Bhat, K. Udaya

    2012-01-01

    Commercial pure aluminium was deposited on medium carbon steel using friction surfacing route. An aluminium rod was used as the consumable tool. Normal load and tool rotation speed were the variables. Under certain combinations of load and speed the deposition was continuous and uniform. The deposit consisted of Al embedded with fine particles of iron. The interface between substrate material and deposited material was smooth and relatively small. A mechanism is discussed for formation of a ...

  18. Contact mechanics and rubber friction for randomly rough surfaces with anisotropic statistical properties.

    Science.gov (United States)

    Carbone, G; Lorenz, B; Persson, B N J; Wohlers, A

    2009-07-01

    In this paper we extend the theory of contact mechanics and rubber friction developed by one of us (B.N.J. Persson, J. Chem. Phys. 115, 3840 (2001)) to the case of surfaces with anisotropic surface roughness. As an application we calculate the viscoelastic contribution to the rubber friction. We show that the friction coefficient may depend significantly on the sliding direction, while the area of contact depends weakly on the sliding direction. We have carried out experiments for rubber blocks sliding on unidirectionally polished steel surfaces. The experimental data are in a good qualitative agreement with the theory.

  19. Friction surfacing for enhanced surface protection of marine engineering components: erosion-corrosion study

    Science.gov (United States)

    Rajakumar, S.; Balasubramanian, V.; Balakrishnan, M.

    2016-08-01

    Good mechanical properties combined with outstanding corrosion-resistance properties of cast nickel-aluminum bronze (NAB) alloy lead to be a specific material for many marine applications, including ship propellers. However, the erosion-corrosion resistance of cast-NAB alloy is not as good as wrought NAB alloy. Hence, in this investigation, an attempt has been made to improve the erosion-corrosion resistance of cast NAB alloy by depositing wrought (extruded) NAB alloy applying the friction surfacing (FS) technique. Erosion-corrosion tests were carried out in slurries composed of sand particles of 3.5% NaCl solution. Silica sand having a nominal size range of 250-355 μm is used as an erodent. Specimens were tested at 30° and 90° impingement angles. It is observed that the erosion and erosion-corrosion resistance of friction surfaced NAB alloy exhibited an improvement as compared to cast NAB alloy. Scanning electron microscope (SEM) analysis showed that the erosion tracks developed on the cast NAB alloy were wider and deeper than those formed on the friction surfaced extruded NAB alloy.

  20. 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

  1. Surface Velocities of Taylor Glacier, Antarctica, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains surface velocities of Taylor Glacier, Antarctica, for the year 2003. Measurement period was approximately 12 months. There are approximately...

  2. Interferometric method for measuring high velocities of diffuse surfaces

    International Nuclear Information System (INIS)

    Maron, Y.

    1978-01-01

    An interferometric method for measuring the displacement of diffuse surfaces moving with velocities of a few microsecond is presented. The method utilizes the interference between two light beams reflected from a constant area of the moving surface at two different angles. It enables the detection of high rate velocity variations. Light source of a fairly low temporal coherence and power around 100mW is needed. (author)

  3. Estimating propagation velocity through a surface acoustic wave sensor

    Science.gov (United States)

    Xu, Wenyuan; Huizinga, John S.

    2010-03-16

    Techniques are described for estimating the propagation velocity through a surface acoustic wave sensor. In particular, techniques which measure and exploit a proper segment of phase frequency response of the surface acoustic wave sensor are described for use as a basis of bacterial detection by the sensor. As described, use of velocity estimation based on a proper segment of phase frequency response has advantages over conventional techniques that use phase shift as the basis for detection.

  4. 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

    In this paper, we discuss the nature of the static and kinetic friction, and of (thermally activated) creep.We focus on boundary lubrication at high confining pressure (∼1GPa), as is typical for hard solids, where one or at most two layers of confined molecules separates the sliding surfaces. We......, the system exhibits a very small static friction, and a (low velocity) kinetic friction which increases with increasing sliding velocity. On the other hand, if the springs are soft enough, strong elastic instabilities occur during sliding, resulting in a large static friction force Fs, and a kinetic friction...... force Fk equal to the static friction force at low sliding velocities. In this case rapid slip events occur at the interface, characterized by velocities much higher and independent of the drive velocity v. In the MD simulations we observe that, for incommensurate systems (at low temperature), only when...

  5. Depression storage and infiltration effects on overland flow depth-velocity-friction at desert conditions: field plot results and model

    Directory of Open Access Journals (Sweden)

    M. J. Rossi

    2012-09-01

    Full Text Available Water infiltration and overland flow are relevant in considering water partition among plant life forms, the sustainability of vegetation and the design of sustainable hydrological models and management. In arid and semi-arid regions, these processes present characteristic trends imposed by the prevailing physical conditions of the upper soil as evolved under water-limited climate. A set of plot-scale field experiments at the semi-arid Patagonian Monte (Argentina were performed in order to estimate the effect of depression storage areas and infiltration rates on depths, velocities and friction of overland flows. The micro-relief of undisturbed field plots was characterized at z-scale 1 mm through close-range stereo-photogrammetry and geo-statistical tools. The overland flow areas produced by controlled water inflows were video-recorded and the flow velocities were measured with image processing software. Antecedent and post-inflow moisture were measured, and texture, bulk density and physical properties of the upper soil were estimated based on soil core analyses. Field data were used to calibrate a physically-based, mass balanced, time explicit model of infiltration and overland flows. Modelling results reproduced the time series of observed flow areas, velocities and infiltration depths. Estimates of hydrodynamic parameters of overland flow (Reynolds-Froude numbers are informed. To our knowledge, the study here presented is novel in combining several aspects that previous studies do not address simultaneously: (1 overland flow and infiltration parameters were obtained in undisturbed field conditions; (2 field measurements of overland flow movement were coupled to a detailed analysis of soil microtopography at 1 mm depth scale; (3 the effect of depression storage areas in infiltration rates and depth-velocity friction of overland flows is addressed. Relevance of the results to other similar desert areas is justified by the accompanying

  6. Surface friction measurements of fine-graded asphalt mixtures : final report, June 2008.

    Science.gov (United States)

    2008-06-01

    Skid resistance is generated by the development of friction between the vehicle tire and : roadway surface, and is partially dependent upon the characteristics of the pavement : texture. Microtexture and macrotexture are the critical components of pa...

  7. Wear of Polished Steel Surfaces in Dry Friction Linear Contact on Polimer Composites with Glass Fibres

    Directory of Open Access Journals (Sweden)

    D. Rus

    2013-12-01

    Full Text Available It is generally known that the friction and wear between polymers and polished steel surfaces has a special character, the behaviour to friction and wear of a certain polymer might not be valid for a different polymer, moreover in dry friction conditions. In this paper, we study the reaction to wear of certain polymers with short glass fibres on different steel surfaces, considering the linear friction contact, observing the friction influence over the metallic surfaces wear. The paper includes also its analysis over the steel’s wear from different points of view: the reinforcement content influence and tribological parameters (load, contact pressure, sliding speed, contact temperature, etc.. Thus, we present our findings related to the fact that the abrasive component of the friction force is more significant than the adhesive component, which generally is specific to the polymers’ friction. Our detections also state that, in the case of the polyamide with 30% glass fibres, the steel surface linear wear rate order are of 10-4 mm/h, respectively the order of volumetric wear rate is of 10-6 cm3 /h. The resulting volumetric wear coefficients are of the order (10-11 – 10-12 cm3/cm and respectively linear wear coefficients of 10-9 mm/cm.

  8. Forces and friction between hydrophilic and hydrophobic surfaces: influence of oleate species.

    Science.gov (United States)

    Theander, Katarina; Pugh, Robert J; Rutland, Mark W

    2007-09-15

    The atomic force microscope has been used to investigate normal surface forces and lateral friction forces at different concentrations of sodium oleate, a frequently used fatty acid in the deinking process. The measurements have been performed using the colloidal probe technique with bead materials consisting of cellulose and silica. Cellulose was used together with a printing ink alkyd resin and mica, whereas silica was used with a hydrophobized silica wafer. The cellulose-alkyd resin system showed stronger double layer repulsion and the friction was reduced with increasing surfactant concentration. The adhesive interaction disappeared immediately on addition of sodium oleate. The normal surface forces for cellulose-mica indicated no apparent adsorption of the sodium oleate however, the friction coefficient increased on addition of sodium oleate, which we ascribe to some limited adsorption increasing the effective surface roughness. The silica-hydrophobic silica system showed a completely different surface force behavior at the different concentrations. An attractive hydrophobic interaction was evident since the surfaces jumped into adhesive contact at a longer distance than the van der Waals forces would predict. The strong adhesion was reflected in the friction forces as a nonlinear relationship between load and friction and a large friction response at zero applied load. Indirect evidence of adsorption to the hydrophilic silica surface was also observed in this case, and QCM studies were performed to confirm the adsorption of material to both surfaces.

  9. Formation of Composite Surface during Friction Surfacing of Steel with Aluminium

    Directory of Open Access Journals (Sweden)

    S. Janakiraman

    2012-01-01

    Full Text Available Commercial pure aluminium was deposited on medium carbon steel using friction surfacing route. An aluminium rod was used as the consumable tool. Normal load and tool rotation speed were the variables. Under certain combinations of load and speed the deposition was continuous and uniform. The deposit consisted of Al embedded with fine particles of iron. The interface between substrate material and deposited material was smooth and relatively small. A mechanism is discussed for formation of a composite surface on the steel substrate.

  10. Friction and adhesion of gecko-inspired PDMS flaps on rough surfaces.

    Science.gov (United States)

    Yu, Jing; Chary, Sathya; Das, Saurabh; Tamelier, John; Turner, Kimberly L; Israelachvili, Jacob N

    2012-08-07

    Geckos have developed a unique hierarchical structure to maintain climbing ability on surfaces with different roughness, one of the extremely important parameters that affect the friction and adhesion forces between two surfaces. Although much attention has been paid on fabricating various structures that mimic the hierarchical structure of a gecko foot, yet no systematic effort, in experiment or theory, has been made to quantify the effect of surface roughness on the performance of the fabricated structures that mimic the hierarchical structure of geckos. Using a modified surface forces apparatus (SFA), we measured the adhesion and friction forces between microfabricated tilted PDMS flaps and optically smooth SiO(2) and rough SiO(2) surfaces created by plasma etching. Anisotropic adhesion and friction forces were measured when sliding the top glass surface along (+y) and against (-y) the tilted direction of the flaps. Increasing the surface roughness first increased the adhesion and friction forces measured between the flaps and the rough surface due to topological matching of the two surfaces but then led to a rapid decrease in both of these forces. Our results demonstrate that the surface roughness significantly affects the performance of gecko mimetic adhesives and that different surface textures can either increase or decrease the adhesion and friction forces of the fabricated adhesives.

  11. Investigations on femtosecond laser modified micro-textured surface with anti-friction property on bearing steel GCr15

    Science.gov (United States)

    Yang, Lijun; Ding, Ye; Cheng, Bai; He, Jiangtao; Wang, Genwang; Wang, Yang

    2018-03-01

    This work puts forward femtosecond laser modification of micro-textured surface on bearing steel GCr15 in order to reduce frictional wear and enhance load capacity during its application. Multi pulses femtosecond laser ablation experiments are established for the confirmation of laser spot radius as well as single pulse threshold fluence and pulse incubation coefficient of bulk material. Analytical models are set up in combination with hydrodynamics lubrication theory. Corresponding simulations are carried out on to explore influences of surface and cross sectional morphology of textures on hydrodynamics lubrication effect based on Navier-Stokes (N-S) equation. Technological experiments focus on the impacts of femtosecond laser machining variables, like scanning times, scanning velocity, pulse frequency and scanning gap on morphology of grooves as well as realization of optimized textures proposed by simulations, mechanisms of which are analyzed from multiple perspectives. Results of unidirectional rotating friction tests suggest that spherical texture with depth-to-width ratio of 0.2 can significantly improve tribological properties at low loading and velocity condition comparing with un-textured and other textured surfaces, which also verifies the accuracy of simulations and feasibility of femtosecond laser in modification of micro-textured surface.

  12. Friction wear cast iron casting surface hardened by concentrated source of heat

    Directory of Open Access Journals (Sweden)

    W. Orlowicz

    2009-04-01

    Full Text Available In this study surface fusion by the GTAW (in argon atmosphere surfacing process on plate of cast iron with electric arc advance speedsfrom 200 to 800 mm/min and current range I=300A were performed. The geometry, microstructure, hardness, friction wear intensity weremeasured. A stepwise regression method was used to develop relationships between the electric arc advance speed, parameters of fusion geometry, microhardness and friction wear intensity.

  13. Surface shear stress dependence of gas transfer velocity parameterizations using DNS

    Science.gov (United States)

    Fredriksson, S. T.; Arneborg, L.; Nilsson, H.; Handler, R. A.

    2016-10-01

    Air-water gas-exchange is studied in direct numerical simulations (DNS) of free-surface flows driven by natural convection and weak winds. The wind is modeled as a constant surface-shear-stress and the gas-transfer is modeled via a passive scalar. The simulations are characterized via a Richardson number Ri=Bν/u*4 where B, ν, and u* are the buoyancy flux, kinematic viscosity, and friction velocity respectively. The simulations comprise 0water gas-exchange, (ii) determine, for a given buoyancy flux, the wind speed at which gas transfer becomes primarily shear driven, and (iii) find an expression for the gas-transfer velocity for flows driven by both convection and shear. The evaluated gas transfer-velocity parametrizations are based on either the rate of turbulent kinetic energy dissipation, the surface flow-divergence, the surface heat-flux, or the wind-speed. The parametrizations based on dissipation or divergence show an unfavorable Ri dependence for flows with combined forcing whereas the parametrization based on heat-flux only shows a limited Ri dependence. The two parametrizations based on wind speed give reasonable estimates for the transfer-velocity, depending however on the surface heat-flux. The transition from convection- to shear-dominated gas-transfer-velocity is shown to be at Ri≈0.004. Furthermore, the gas-transfer is shown to be well represented by two different approaches: (i) additive forcing expressed as kg,sum =AShearu*|Ri/Ric+1| 1/4Sc-n where Ric=|AShear/ABuoy|4, and (ii) either buoyancy or shear dominated expressed as, kg=ABuoy|Bν| 1/4Sc-n, Ri>Ric or kg=AShearu*Sc-n, Riwater surface-characteristics.

  14. Surface science. Adhesion and friction in mesoscopic graphite contacts.

    Science.gov (United States)

    Koren, Elad; Lörtscher, Emanuel; Rawlings, Colin; Knoll, Armin W; Duerig, Urs

    2015-05-08

    The weak interlayer binding in two-dimensional layered materials such as graphite gives rise to poorly understood low-friction characteristics. Accurate measurements of the adhesion forces governing the overall mechanical stability have also remained elusive. We report on the direct mechanical measurement of line tension and friction forces acting in sheared mesoscale graphite structures. We show that the friction is fundamentally stochastic in nature and is attributable to the interaction between the incommensurate interface lattices. We also measured an adhesion energy of 0.227 ± 0.005 joules per square meter, in excellent agreement with theoretical models. In addition, bistable all-mechanical memory cell structures and rotational bearings have been realized by exploiting position locking, which is provided solely by the adhesion energy. Copyright © 2015, American Association for the Advancement of Science.

  15. Methods of preparing internal combustion engine cylinder bore surfaces for frictional improvement

    Directory of Open Access Journals (Sweden)

    Chung Hwa Kong

    2017-01-01

    Full Text Available Frictional losses piston to cylinder bore contact is a major sources of mechanical losses in an internal combustion engine (ICE. Traditional plateau honing produces a relatively rough cylinder bore surface with many valleys for oil retention and plateau surfaces that are usually has micro roughness's that causes mechanical friction to act as a bearing surface. A smooth polished dimpled surface is more ideal to achieve low friction and wear in an ICE. Alternative methods to create a smooth dimpled surface on a hypereutectic aluminum ADC12 substrate for frictional improvements are evaluated in this study using an oscillating wear tester (OWT. The methods include casting in the dimples in the aluminum matrix, sandblasting as well as embossing the pits. The texture samples are evaluated by examining the surface properties, measuring frictional coefficient as well as wear characteristics. It was found that the samples embossed with #320 grit sandpaper and sandblasted with #240 sieve sand samples had a reduced coefficient of friction (μ of 23% at low sliding speeds before hydrodynamic lubrication mode and 6.9% in the fully hydrodynamic lubrication region.

  16. 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.

  17. Characterization of holding brake friction pad surface after pin-on-plate wear test

    DEFF Research Database (Denmark)

    Drago, N.; Gonzalez Madruga, D.; De Chiffre, L.

    2018-01-01

    This article concerns the metrological characterization of the surface on a holding brake friction material pin after a pin-on-plate (POP) wear test. The POP test induces the formation of surface plateaus that affect brake performances such as wear, friction, noise and heat. Three different...... materials’ surfaces have been characterized after wear from data obtained with a focus variation 3D microscope. A new surface characterization approach with plateau identification is proposed, using the number of plateau on the surface, equivalent diameter, length and breadth as measurands...

  18. Measuring surface flow velocity with smartphones: potential for citizen observatories

    Science.gov (United States)

    Weijs, Steven V.; Chen, Zichong; Brauchli, Tristan; Huwald, Hendrik

    2014-05-01

    Stream flow velocity is an important variable for discharge estimation and research on sediment dynamics. Given the influence of the latter on rating curves (stage-discharge relations), and the relative scarcity of direct streamflow measurements, surface velocity measurements can offer important information for, e.g., flood warning, hydropower, and hydrological science and engineering in general. With the growing amount of sensing and computing power in the hands of more outdoorsy individuals, and the advances in image processing techniques, there is now a tremendous potential to obtain hydrologically relevant data from motivated citizens. This is the main focus of the interdisciplinary "WeSenseIt" project, a citizen observatory of water. In this subproject, we investigate the feasibility of stream flow surface velocity measurements from movie clips taken by (smartphone-) cameras. First results from movie-clip derived velocity information will be shown and compared to reference measurements.

  19. 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.

  20. Temperature processes at two sliding surfaces subjected to dry friction

    Czech Academy of Sciences Publication Activity Database

    Půst, Ladislav; Pešek, Luděk; Cibulka, Jan; Bula, Vítězslav

    2012-01-01

    Roč. 63, 5/6 (2012), s. 277-292 ISSN 0039-2472 R&D Projects: GA ČR GA101/09/1166 Institutional support: RVO:61388998 Keywords : dry friction * vibration damping * experimental set * increase of temperature * lost energy Subject RIV: BI - Acoustics

  1. An investigation of coseismic OSL / TL time zeroing of quartz gouge based on low- to high-velocity friction experiments

    Science.gov (United States)

    Akasegawa, K.; Oohashi, K.; Hasebe, N.; Miura, K.

    2016-12-01

    To determine an age of coseismic event of an active fault, we generally examine crosscutting relationship between faults and overlying strata by trenching. However, we could not apply this method in case there are no overlying young strata in the vicinity of the fault zones. The alternative is a dating of fault zone materials whose age experienced resetting with seismic fault slip (for example, the ESR method;. Ikeya et al,1982; the OSL and TL methods). The idea behinds to the OSL (optically stimulated luminescence) and TL (thermoluminescence) dating methods for a determination of paleo-earthquake event is the accumulated natural radiation damage becomes to zero (time zeroing) by the frictional heating and grinding. However, physical and geological conditions required to induce time zeroing is not well understood because there is only few experimental investigations under the limited conditions (Hiraga et al,2004;. Kim et al, 2014) . In this study, we conduct low- to high-velocity friction experiments using quartz gouge under various experimental conditions (e.g., normal stress, displacement, moisture content) to establish an empirical relationship and physical and geological conditions of coseismic OSL time zeroing. In this experiment, we carry out the friction experiments using quartz in Tsushigawa granite taken from the east wall of the Nojima fault Ogura trench site, which was excavated in 2015. Samples were taken from the most distant position from the fault in the trench site. The samples were clashed using a mortar and sieved to a grain size of treatment. The residual is user for the friction experiments after having known radiation dose using an artificial gamma-ray source. In this presentation, we show results of the friction experiments and dating of the quartz gouge and discuss physical and geological conditions of OSL time zeroing. References Okumura, T., and Shitaoka, Y., 2011. Engineering Geology of Japan, No. 1, 5-17. Hiraga, S., Yoshimoto, A., and

  2. Laser surface graphitization to control friction of diamond-like carbon coatings

    Science.gov (United States)

    Komlenok, Maxim S.; Kononenko, Vitaly V.; Zavedeev, Evgeny V.; Frolov, Vadim D.; Arutyunyan, Natalia R.; Chouprik, Anastasia A.; Baturin, Andrey S.; Scheibe, Hans-Joachim; Shupegin, Mikhail L.; Pimenov, Sergei M.

    2015-11-01

    To study the role of laser surface graphitization in the friction behavior of laser-patterned diamond-like carbon (DLC) films, we apply the scanning probe microscopy (SPM) in the lateral force mode (LFM) which allows to obtain simultaneously the lateral force and topography images and to determine local friction levels in laser-irradiated and original surface areas. Based on this approach in the paper, we report on (1) laser surface microstructuring of hydrogenated a-C:H and hydrogen-free ta-C films in the regime of surface graphitization using UV laser pulses of 20-ns duration and (2) correlation between the structure and friction properties of the laser-patterned DLC surface on micro/nanoscale using SPM/LFM technique. The SPM/LFM data obtained for the surface relief gratings of graphitized microstructures have evidenced lower friction forces in the laser-graphitized regions. For the hydrogenated DLC films, the reversible frictional behavior of the laser-graphitized micropatterns is found to take place during LFM imaging at different temperatures (20 and 120 °C) in ambient air. It is revealed that the lateral force distribution in the laser-graphitized areas is shifted to higher friction levels (relative to that of the unirradiated surface) at temperature 120 °C and returned back to the lower friction during the sample cooling to 20 °C, thus confirming an influence of adsorbed water layers on the nanofriction properties of laser-graphitized micropatterns on the film surface.

  3. Surface integrity analysis of abrasive water jet-cut surfaces of friction stir welded joints

    Czech Academy of Sciences Publication Activity Database

    Kumar, R.; Chattopadhyaya, S.; Dixit, A. R.; Bora, B.; Zeleňák, Michal; Foldyna, Josef; Hloch, Sergej; Hlaváček, Petr; Ščučka, Jiří; Klich, Jiří; Sitek, Libor; Vilaca, P.

    2017-01-01

    Roč. 88, č. 5 (2017), s. 1687-1701 ISSN 0268-3768 R&D Projects: GA MŠk(CZ) LO1406; GA MŠk ED2.1.00/03.0082 Institutional support: RVO:68145535 Keywords : friction stir welding (FSW) * abrasive water jet (AWJ) * optical profilometer * topography * surface roughness Subject RIV: JQ - Machines ; Tools OBOR OECD: Mechanical engineering Impact factor: 2.209, year: 2016 http://link.springer.com/article/10.1007/s00170-016-8776-0

  4. Technology of wear resistance increase of surface elements of friction couples using solid lubricants

    Science.gov (United States)

    Morgunov, A. P.; Masyagin, V. B.; Derkach, V. V.; Matveev, N. A.

    2017-06-01

    Based on the results of experimental investigations in wear resistance increase using lamellar solid lubricants the technology of wear resistance increase of surface elements of friction couples by applying solid lubricants is developed with the following surface plastic deformation providing enough bond strength of solid lubricant with an element surface and increasing operational life.

  5. Gradient nanostructured surface of a Cu plate processed by incremental frictional sliding

    DEFF Research Database (Denmark)

    Hong, Chuanshi; Huang, Xiaoxu; Hansen, Niels

    2015-01-01

    The flat surface of a Cu plate was processed by incremental frictional sliding at liquid nitrogen temperature. The surface treatment results in a hardened gradient surface layer as thick as 1 mm in the Cu plate, which contains a nanostructured layer on the top with a boundary spacing of the order...

  6. Probing the surface profile and friction behavior of heterogeneous polymers: a molecular dynamics study

    Science.gov (United States)

    Dai, L.; Sorkin, V.; Zhang, Y. W.

    2017-04-01

    We perform molecular dynamics simulations to investigate molecular structure alternation and friction behavior of heterogeneous polymer (perfluoropolyether) surfaces using a nanoscale probing tip (tetrahedral amorphous carbon). It is found that depending on the magnitude of the applied normal force, three regimes exist: the shallow depth-sensing (SDS), deep depth-sensing (DDS), and transitional depth-sensing (TDS) regimes; TDS is between SDS and DDS. In SDS, the tip is floating on the polymer surface and there is insignificant permanent alternation in the polymer structure due to largely recoverable atomic deformations, and the surface roughness profile can be accurately measured. In DDS, the tip is plowing through the polymer surface and there is significant permanent alternation in the molecular structure. In this regime, the lateral friction force rises sharply and fluctuates violently when overcoming surface pile-ups. In SDS, the friction can be described by a modified Amonton’s law including the adhesion effect; meanwhile, in DDS, the adhesion effect is negligible but the friction coefficient is significantly higher. The underlying reason for the difference in these regimes rests upon different contributions by the repulsion and attraction forces between the tip and polymer surfaces to the friction force. Our findings here reveal important insights into lateral depth-sensing on heterogeneous polymer surfaces and may help improve the precision of depth-sensing devices.

  7. Transitions from nanoscale to microscale dynamic friction mechanisms on polyethylene and silicon surfaces

    International Nuclear Information System (INIS)

    Niederberger, S.; Gracias, D. H.; Komvopoulos, K.; Somorjai, G. A.

    2000-01-01

    The dynamic friction mechanisms of polyethylene and silicon were investigated for apparent contact pressures and contact areas in the ranges of 8 MPa-18 GPa and 17 nm2-9500 μm2, respectively. Friction force measurements were obtained with a friction force microscope, scanning force microscope, and pin-on-disk tribometer. Silicon and diamond tips with a nominal radius of curvature between 100 nm and 1.2 mm were slid against low- and high-density polyethylene and Si(100) substrates under contact loads in the range of 5 nN-0.27 N. The low friction coefficients obtained with all material systems at low contact pressures indicated that deformation at the sliding interface was primarily elastic. Alternatively, the significantly higher friction coefficients at higher contact pressures suggested that plastic deformation was the principal mode of deformation. The high friction coefficients of polyethylene observed with large apparent contact areas are interpreted in terms of the microstructure evolution involving the rearrangement of crystalline regions (lamellae) nearly parallel to the sliding direction, which reduces the surface resistance to plastic shearing. Such differences in the friction behavior of polyethylene resulting from stress-induced microstructural changes were found to occur over a relatively large range of the apparent contact area. The friction behavior of silicon was strongly affected by the presence of a native oxide film. Results are presented to demonstrate the effect of the scale of deformation at the contact interface on the dynamic friction behavior and the significance of contact parameters on the friction measurements obtained with different instruments. (c) 2000 American Institute of Physics

  8. Friction as a probe of surface properties of a polymer glass

    OpenAIRE

    Bureau, Lionel

    2007-01-01

    We probe the temperature dependence of friction at the interface between a glassy poly(methylmethacrylate) lens and a flat substrate coated with a methyl-terminated self-assembled monolayer. The monolayer exhibits density defects which act as pinning sites for the polymer chains. We show that the shear response of such an interface supports the existence, at the surface of the glassy polymer, of a nanometer-thick layer of mobile chains. Friction can be ascribed to the interplay between viscou...

  9. Consolidation of Surface Coatings by Friction Stir Techniques

    Science.gov (United States)

    2010-09-01

    4] Morisada, Fujii, Mizuno, Abe, Nagaoka, Fukusumi, 2010, “Modification of Thermally Sprayed Cemented Carbide Layer by Friction Stir Processing...Affected Zone SEM Scanning Electron Microscope SiC Silicon Carbide SZ Stir Zone TMAZ Thermo=Mechanically Affected Zone Ti Titanium TWI The...tool plastically deforms the metals in the weld zone (WZ), heating the material and then traverses along the butted edges. Since the welding

  10. 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.

  11. Frictional melting of gabbro under extreme experimental conditions of normal stress, acceleration, and sliding velocity

    NARCIS (Netherlands)

    Niemeijer, A.; Di Toro, G.; Nielsen, S.; Di Felice, F.

    2011-01-01

    With the advent of high‐velocity shear apparatus, several experimental studies have been performed in recent years, improving our understanding of the evolution of fault strength during seismic slip. However, these experiments were conducted under relatively low normal stress (<20 MPa) and using

  12. Estimating Stream Surface Flow Velocities from Video Clips

    Science.gov (United States)

    Weijs, S. V.; Brauchli, T.; Chen, Z.; Huwald, H.

    2014-12-01

    Measuring surface flow velocities in streams can provide important information on discharge. This information is independent of water level, the most commonly used proxy for discharge and therefore has significant potential to reduce uncertainties. Advances in cheap and commonly used imaging devices (e.g. smartphone cameras) and image processing techniques offer new opportunities to get velocity information. Short video clips of streams can be used in combination with optical flow algorithms to get proxies for stream surface velocities. Here some initial results are presented and the main challenges are discussed, especially in view of using these techniques in a citizen science context (specifically the "WeSenseIt" project, a citizen observatory of water), where we try to minimize the need for site preparation and additional equipment needed to take measurements.

  13. Near-Surface Seismic Velocity Data: A Computer Program For ...

    African Journals Online (AJOL)

    A computer program (NESURVELANA) has been developed in Visual Basic Computer programming language to carry out a near surface velocity analysis. The method of analysis used includes: Algorithms design and Visual Basic codes generation for plotting arrival time (ms) against geophone depth (m) employing the ...

  14. Determination of the Basic Friction Angle of Rock Surfaces by Tilt Tests

    Science.gov (United States)

    Jang, Hyun-Sic; Zhang, Qing-Zhao; Kang, Seong-Seung; Jang, Bo-An

    2018-04-01

    Samples of Hwangdeung granite from Korea and Berea sandstone from USA, both containing sliding planes, were prepared by saw-cutting or polishing using either #100 or #600 grinding powders. Their basic friction angles were measured by direct shear testing, triaxial compression testing, and tilt testing. The direct shear tests and triaxial compression tests on the saw-cut, #100, and #600 surfaces indicated that the most reliable results were obtained from the #100 surface: basic friction angle of 29.4° for granite and 34.1° for sandstone. To examine the effect of surface conditions on the friction angle in tilt tests, the sliding angles were measured 50 times with two surface conditions (surfaces cleaned and not cleaned after each measurement). The initial sliding angles were high regardless of rock type and surface conditions and decreased exponentially as measurements continued. The characteristics of the sliding angles, differences between tilt tests, and dispersion between measurements in each test indicated that #100 surface produced the most reliable basic friction angle measurement. Without cleaning the surfaces, the average angles for granite (32 measurements) and sandstone (23 measurements) were similar to the basic friction angle. When 20-50 measurements without cleaning were averaged, the basic friction angle was within ± 2° for granite and ± 3° for sandstone. Sliding angles using five different tilting speeds were measured but the average was similar, indicating that tilting speed (between 0.2° and 1.6°/s) has little effect on the sliding angle. Sliding angles using four different sample sizes were measured with the best results obtained for samples larger than 8 × 8 cm.

  15. Numerical Studies of Friction Between Metallic Surfaces and of its Dependence on Electric Currents

    Science.gov (United States)

    Meintanis, Evangelos; Marder, Michael

    2009-03-01

    We will present molecular dynamics simulations that explore the frictional mechanisms between clean metallic surfaces. We employ the HOLA molecular dynamics code to run slider-on-block experiments. Both objects are allowed to evolve freely. We recover realistic coefficients of friction and verify the importance of cold-welding and plastic deformations in dry sliding friction. We also find that plastic deformations can significantly affect both objects, despite a difference in hardness. Metallic contacts have significant technological applications in the transmission of electric currents. To explore the effects of the latter to sliding, we had to integrate an electrodynamics solver into the molecular dynamics code. The disparate time scales involved posed a challenge, but we have developed an efficient scheme for such an integration. A limited electrodynamic solver has been implemented and we are currently exploring the effects of currents in the friction and wear of metallic contacts.

  16. Fluoride influences nickel-titanium orthodontic wires' surface texture and friction resistance.

    Science.gov (United States)

    Abbassy, Mona Aly

    2016-01-01

    The aim of this study was to investigate the effects exerted by the acidulated fluoride gel on stainless steel and nickel-titanium (Ni-Ti) orthodontic wires. Sixty stainless steel and Ni-Ti orthodontic archwires were distributed into forty archwires used for in vitro study and twenty for in situ study. Fluoride was applied for 1 h in the in vitro experiment while it was applied for 5 min in the in situ experiment. The friction resistance of all wires with ceramic brackets before/after topical fluoride application was measured using a universal testing machine at 1 min intervals of moving wire. Moreover, surface properties of the tested wires before/after fluoride application and before/after friction test were examined by a scanning electron microscope (SEM). Dunnett's t -test was used to compare frictional resistance of as-received stainless steel wires and Ni-Ti wires to the wires treated by fluoride in vitro and in situ ( P wire on friction resistance in vitro and in situ ( P wires recorded significantly high friction resistance after fluoride application when compared to stainless steel wires in vitro , P wires in situ , P wires after fluoride application in vitro and in situ . The in vitro fluoride application caused an increase in friction resistance of Ni-Ti wires when compared to stainless steel wires. In vitro and in situ fluoride application caused deterioration in surface properties of Ni-Ti wires.

  17. Velocity profiles and surface roughness under breaking waves

    Science.gov (United States)

    Craig, Peter D.

    1996-01-01

    Recent measurements under wave-breaking conditions in the ocean, lakes, and tanks reveal a layer immediately below the surface in which dissipation decays as depth to the power -2 to -4 and downwind velocities are approximately linear with depth. This behavior is consistent with predictions of a conventional, one-dimensional, level 2.5 turbulence closure model, in which the influence of breaking waves is parameterized as a surface source of turbulent kinetic energy. The model provides an analytic solution which describes the near-surface power law behavior and the deeper transition to the "law of the wall." The mixing length imposed in the model increases linearly away from a minimum value, the roughness length, at the surface. The surface roughness emerges as an important scaling factor in the wave-enhanced layer but is the major unknown in the formulation. Measurements in the wave-affected layer are still rare, but one exceptional set, both in terms of its accuracy and proximity to the surface, is that collected by Cheung and Street [1988] in the Stanford wind tunnel. Their velocity profiles first confirm the accuracy of the model, and, second, allow estimation, via a best fit procedure, of roughness lengths at five different wind speeds. Conclusions are tentative but indicate that the roughness length increases with wind speed and appears to take a value of approximately one sixth the dominant surface wavelength. A more traditional wall-layer model, which ignores the flux of turbulent kinetic energy, will also accurately reproduce the measured velocity profiles. In this case, enhanced surface turbulence is forced on the model by the assumption of a large surface roughness, three times that required by the full model. However, the wall-layer model cannot predict the enhanced dissipation near the surface.

  18. Prediction of fluid velocity slip at solid surfaces

    DEFF Research Database (Denmark)

    Hansen, Jesper Schmidt; Todd, Billy; Daivis, Peter

    2011-01-01

    methods, it allows us to directly compute the intrinsic wall-fluid friction coefficient rather than an empirical friction coefficient that includes all sources of friction for planar shear flow. The slip length predicted by our method is in excellent agreement with the slip length obtained from direct...

  19. Adhesive friction for elastic-plastic contacting rough surfaces considering asperity interaction

    International Nuclear Information System (INIS)

    Sahoo, Prasanta

    2006-01-01

    The paper describes a theoretical study of adhesive friction at the contact between rough surfaces taking asperity interaction into consideration and using an elastic-plastic model of contact deformation that is based on an accurate finite element analysis of an elastic-plastic single asperity contact. The micro-contact model of asperity interactions, developed by Zhao and Chang, is integrated into the improved elastic-plastic rough surface adhesive contact analysis to consider the adhesive friction behaviour of rough surfaces. The model considers a large range of interference values from fully elastic through elastic-plastic to fully plastic regimes of contacting asperities. Two well-established adhesion indices are used to consider different conditions that arise as a result of varying load, surface and material parameters. Results are obtained for the coefficient of friction against applied load for various combinations of these parameters. The results show that the coefficient of friction depends strongly on the applied load for the no-interaction case while it becomes insensitive to the load for interaction consideration. Moreover, the inclusion of elastic-plastic asperities further reduces the friction coefficient

  20. Surface wave phase velocities between Bulgaria and the Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Gaždová, Renata; Kolínský, Petr; Popova, I.; Dimitrova, L.

    2011-01-01

    Roč. 18, č. 2 (2011), s. 16-23 ISSN 1803-1447. [OVA´11 – New Knowledge and Measurements in Seismology, Engineering Geophysics and Geotechnics. Ostrava, 12.04.2011-14.04.2011] R&D Projects: GA ČR GA205/09/1244 Institutional research plan: CEZ:AV0Z30460519 Keywords : surface waves * phase velocity * shear wave velocity Subject RIV: DC - Siesmology, Volcanology, Earth Structure http://www.caag.cz/egrse/2011-2/03%20gazdova_ova.pdf

  1. Velocity profiles of fluid flow close to a hydrophobic surface

    Science.gov (United States)

    Fialová, Simona; Pochylý, František; Kotek, Michal; Jašíková, Darina

    The results of research on viscous liquid flow upon a superhydrophobic surface are presented in the paper. In the introduction, the degrees of surface hydrophobicity in correlation with an adhesion coefficient are defined. The usage of the adhesion coefficient for the definition of a new boundary condition is employed for expressing the slip of the liquid over the superhydrophobic surface. The slip of the liquid was identified on a special experimental device. The essence of the device consists of a tunnel of rectangular cross section whose one wall is treated with a superhydrophobic layer. The other walls are made of transparent organic glass whose surface is hydrophilic. Velocity profiles are measured by PIV. The methodology is drawn so that it allows the speed determination at the closest point to the wall. The measurements were performed for different Reynolds numbers for both laminar and turbulent flow. Based on the measured velocity profiles, marginal terms of use have been verified, expressing slippage of the liquid on the wall. New forms of velocity profiles considering superhydrophobic surfaces are shown within the work.

  2. Influence of surface topography on friction, film breakdown and running-in in the mixed lubrication regime

    NARCIS (Netherlands)

    Lugt, Pieter Martin; Severt, R.W.M.; Fogelström, J.; Tripp, J.H.

    2001-01-01

    The influence of surface topography on the lubricant film build-up ability and the friction characteristics of potential rolling bearing surfaces has been investigated by experiments on two-disc rigs. Traction-friction torque measurements were made for a variety of surface combinations, together

  3. The Influence of the Tool Surface Texture on Friction and the Surface Layers Properties of Formed Component

    Directory of Open Access Journals (Sweden)

    Jana Šugárová

    2018-03-01

    Full Text Available The morphological texturing of forming tool surfaces has high potential to reduce friction and tool wear and also has impact on the surface layers properties of formed material. In order to understand the effect of different types of tool textures, produced by nanosecond fibre laser, on the tribological conditions at the interface tool-formed material and on the integrity of formed part surface layers, the series of experimental investigations have been carried out. The coefficient of friction for different texture parameters (individual feature shape, including the depth profile of the cavities and orientation of the features relative to the material flow was evaluated via a Ring Test and the surface layers integrity of formed material (surface roughness and subsurface micro hardness was also experimentally analysed. The results showed a positive effect of surface texturing on the friction coefficients and the strain hardening of test samples material. Application of surface texture consisting of dimple-like depressions arranged in radial layout contributed to the most significant friction reduction of about 40%. On the other hand, this surface texture contributed to the increase of surface roughness parameters, Ra parameter increased from 0.49 μm to 2.19 μm and the Rz parameter increased from 0.99 μm to 16.79 μm.

  4. On the thermo-mechanical events during friction surfacing of high speed steels

    OpenAIRE

    Bedford, G.M.; Vitanov, V.I.; Voutchkov, I.I.

    2001-01-01

    This paper is concerned with the friction surfacing of high-speed steels, BM2, BT15 and ASP30 onto plain carbon steel plate. The events that the matrix and carbides experience as the coating material pass from the coating rod to the substrate, in forming the coating, is described. The coating is observed to harden automatically within a few seconds of being deposited onto the cold substrate. This autohardening is observed to be an inherent feature of the friction surfacing process and the onl...

  5. Elastomeric friction

    Science.gov (United States)

    Vorvolakos, Katherine

    This dissertation examines the tribology of PDMS (polydimethylsiloxane) elastomers from a practical and a fundamental perspective. We examine the adhesive, energetic, and tribological properties of several commercial biofouling release coatings, and show that adhesive (and bioadhesive) release from an elastomer depends on the friction of its surface. Having shown that friction is an obstacle to release, we lubricate a model PDMS network by incorporating linear unreactive PDMS oils varying in molecular weight (0.8--423 kg/mol). Surface segregation upon curing depends on molecular weight and mass percentage. Atomic Force Microscopy (AFM) is used to detect the thickness of the lubricant layer. Surprisingly, high-viscosity oils lubricate better than low-viscosity oils, indicating a non-hydrodynamic lubrication. Applying this technology to a commercial elastomer, we see an improvement in bioadhesive release capabilities, as evidenced by a reduced tenacity of mussel adhesive protein. In comparing entangled polymer melts to crosslinked elastomers, we encountered an opportunity to study the tribology of the latter. We studied the effects of molecular weight, velocity, and temperature on the friction of crosslinked PDMS elastomers sliding against two model surfaces: a self-assembled monolayer (SAM) of n-hexadecylsilane, and a thin (˜100mum) film of polystyrene (PS). The change from smooth to stick-slip (unstable) interfacial sliding occurs at a distinct velocity on each surface, implying that it's not necessarily attributable to a bulk glass transition of the PDMS, as popularly believed. The peak shear stress attained immediately before stick-slip sliding is found to be linear with the shear modulus raised to an exponent n of ¾, in contrast with the predictions of Chernyak and Leonov ( n = 1). Low-velocity behavior differs greatly between the SAM and the PS, implying a mechanistic difference. Whereas on the SAM, sliding likely proceeds purely by stochastic adsorption and

  6. Probing the surface properties of a polymer glass with macroscopic friction

    International Nuclear Information System (INIS)

    Bureau, Lionel

    2007-01-01

    We show how macroscopic friction can be used as a sensitive probe of chain dynamics at the surface of a glassy polymer. We present experiments in which a smooth poly(methylmethacrylate) (PMMA) solid slides on flat surfaces presenting different densities of pinning sites available for polymer/substrate bond formation. These experiments indicate that: (i) at high pinning level, frictional dissipation occurs through the sudden flips of molecular-sized bistable regions localized in a nm-thick layer of confined chains, which responds to shear as an elasto-plastic solid, and (ii) in situations of weak pinning, dissipation appears to be governed by a process akin to that proposed for rubber friction. This suggests that some 'glass-to-rubber' transition occurs at the polymer surface when its interaction with the substrate goes from strong to weak. The temperature-dependence of friction provides further support for the presence of a nm-thick layer at the polymer surface, which exhibits a rubberlike response in situation of weak interaction with the countersurface. This behavior results from the interplay between viscous flow in this surface layer, and shear induced depinning of adsorbed surface chains. Moreover, a quantitative analysis of the results indicates that the pinning dynamics of polymer chains is controlled by localized β rotational motions at the interface

  7. On the nature of surface roughness with application to contact mechanics, sealing, rubber friction and adhesion

    International Nuclear Information System (INIS)

    Persson, B N J; Albohr, O; Tartaglino, U; Volokitin, A I; Tosatti, E

    2005-01-01

    Surface roughness has a huge impact on many important phenomena. The most important property of rough surfaces is the surface roughness power spectrum C(q). We present surface roughness power spectra of many surfaces of practical importance, obtained from the surface height profile measured using optical methods and the atomic force microscope. We show how the power spectrum determines the contact area between two solids. We also present applications to sealing, rubber friction and adhesion for rough surfaces, where the power spectrum enters as an important input. (topical review)

  8. Reduction of Friction of Metals Using Laser-Induced Periodic Surface Nanostructures

    Directory of Open Access Journals (Sweden)

    Zhuo Wang

    2015-10-01

    Full Text Available We report on the effect of femtosecond-laser-induced periodic surface structures (LIPSS on the tribological properties of stainless steel. Uniform periodic nanostructures were produced on AISI 304L (American Iron and Steel Institute steel grade steel surfaces using an 800-nm femtosecond laser. The spatial periods of LIPSS measured by field emission scanning electron microscopy ranged from 530 to 570 nm. The tribological properties of smooth and textured surfaces with periodic nanostructures were investigated using reciprocating ball-on-flat tests against AISI 440C balls under both dry and starved oil lubricated conditions. The friction coefficient of LIPSS covered surfaces has shown a lower value than that of the smooth surface. The induced periodic nanostructures demonstrated marked potential for reducing the friction coefficient compared with the smooth surface.

  9. Surface enhancement of cold work tool steels by friction stir processing with a pinless tool

    Science.gov (United States)

    Costa, M. I.; Verdera, D.; Vieira, M. T.; Rodrigues, D. M.

    2014-03-01

    The microstructure and mechanical properties of enhanced tool steel (AISI D2) surfaces produced using a friction stir welding (FSW) related procedure, called friction stir processing (FSP), are analysed in this work. The surface of the tool steel samples was processed using a WC-Co pinless tool and varying processing conditions. Microstructural analysis revealed that meanwhile the original substrate structure consisted of a heterogeneous distribution of coarse carbides in a ferritic matrix, the transformed surfaces consisted of very small carbides, homogenously distributed in a ferrite- bainite- martensite matrix. The morphology of the surfaces, as well as its mechanical properties, evaluated by hardness and tensile testing, were found to vary with increasing tool rotation speed. Surface hardness was drastically increased, relative to the initial hardness of bulk steel. This was attributed to ferrite and carbide refinement, as well as to martensite formation during solid state processing. At the highest rotation rates, tool sliding during processing deeply compromised the characteristics of the processed surfaces.

  10. 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.

  11. Water Surface and Velocity Measurement-River and Flume

    Directory of Open Access Journals (Sweden)

    J. H. Chandler

    2014-06-01

    Full Text Available Understanding the flow of water in natural watercourses has become increasingly important as climate change increases the incidence of extreme rainfall events which cause flooding. Vegetation in rivers and streams reduce water conveyance and natural vegetation plays a critical role in flood events which needs to be understood more fully. A funded project at Loughborough University is therefore examining the influence of vegetation upon water flow, requiring measurement of both the 3-D water surface and flow velocities. Experimental work therefore requires the measurement of water surface morphology and velocity (i.e. speed and direction in a controlled laboratory environment using a flume but also needs to be adaptable to work in a real river. Measuring the 3D topographic characteristics and velocity field of a flowing water surface is difficult and the purpose of this paper is to describe recent experimental work to achieve this. After reviewing past work in this area, the use of close range digital photogrammetry for capturing both the 3D water surface and surface velocity is described. The selected approach uses either two or three synchronised digital SLR cameras in combination with PhotoModeler for data processing, a commercial close range photogrammetric package. One critical aspect is the selection and distribution of appropriate floating marker points, which are critical if automated and appropriate measurement methods are to be used. Two distinct targeting approaches are available: either large and distinct specific floating markers or some fine material capable of providing appropriate texture. Initial work described in this paper uses specific marker points, which also provide the potential measuring surface velocity. The paper demonstrates that a high degree of measurement and marking automation is possible in a flume environment, where lighting influences can be highly controlled. When applied to a real river it is apparent that

  12. Using IR Imaging of Water Surfaces for Estimating Piston Velocities

    Science.gov (United States)

    Gålfalk, M.; Bastviken, D.; Arneborg, L.

    2013-12-01

    The transport of gasses dissolved in surface waters across the water-atmosphere interface is controlled by the piston velocity (k). This coefficient has large implications for, e.g., greenhouse gas fluxes but is challenging to quantify in situ. At present, empirical k-wind speed relationships from a small number of studies and systems are often extrapolated without knowledge of model performance. It is therefore of interest to search for new methods for estimating k, and to compare the pros and cons of existing and new methods. Wind speeds in such models are often measured at a height of 10 meters. In smaller bodies of water such as lakes, wind speeds can vary dramatically across the surface through varying degrees of wind shadow from e.g. trees at the shoreline. More local measurements of the water surface, through wave heights or surface motion mapping, could give improved k-estimates over a surface, also taking into account wind fetch. At thermal infrared (IR) wavelengths water has very low reflectivity (depending on viewing angle) than can go below 1%, meaning that more than 99% is heat radiation giving a direct measurement of surface temperature variations. Using an IR camera at about 100 frames/s one could map surface temperature structures at a fraction of a mm depth even with waves present. In this presentation I will focus on IR imaging as a possible tool for estimating piston velocities. Results will be presented from IR field measurements, relating the motions of surface temperature structures to k calculated from other simultaneous measurements (flux chamber and ADV-Based Dissipation Rate), but also attempting to calculate k directly from the IR surface divergence. A relation between wave height and k will also be presented.

  13. Curve identification for high friction surface treatment (HFST) installation recommendation : final report.

    Science.gov (United States)

    2016-09-01

    The objectives of this study are to develop and deploy a means for cost-effectively extracting curve information using the widely available GPS and GIS data to support high friction surface treatment (HFST) installation recommendations (i.e., start a...

  14. Friction and Surface Dynamics of Polymers on the Nanoscale by AFM

    NARCIS (Netherlands)

    Schönherr, Holger; Schónherr, Holger; Samori, Paolo; Tocha, E.; Vancso, Gyula J.

    2008-01-01

    In this article the measurement and understanding of friction forces and surface dynamics of polymers on the one hand and the importance of molecular relaxation processes and viscoelasticity in polymers for advanced micro- and nanoscale applications on the other hand are discussed. Particular

  15. 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

  16. WEAR OF THE FRICTION SURFACES PARTS IN THE PRESENSE OF SOLID PARTICLES CONTACTING ZONE

    Directory of Open Access Journals (Sweden)

    B. M. Musaibov

    2015-01-01

    Full Text Available The problems of intensity of wear of details of the cars working in the oil polluted by abrasive particles, depending on mechanical properties of material of details and abrasive particles, their sizes, a form and concentration, loading, temperature of a surface of friction, speed of sliding, quality of lubricant are considered. 

  17. Circular mode: a new scanning probe microscopy method for investigating surface properties at constant and continuous scanning velocities.

    Science.gov (United States)

    Nasrallah, Hussein; Mazeran, Pierre-Emmanuel; Noël, Olivier

    2011-11-01

    In this paper, we introduce a novel scanning probe microscopy mode, called the circular mode, which offers expanded capabilities for surface investigations especially for measuring physical properties that require high scanning velocities and/or continuous displacement with no rest periods. To achieve these specific conditions, we have implemented a circular horizontal displacement of the probe relative to the sample plane. Thus the relative probe displacement follows a circular path rather than the conventional back and forth linear one. The circular mode offers advantages such as high and constant scanning velocities, the possibility to be combined with other classical operating modes, and a simpler calibration method of the actuators generating the relative displacement. As application examples of this mode, we report its ability to (1) investigate the influence of scanning velocity on adhesion forces, (2) measure easily and instantly the friction coefficient, and (3) generate wear tracks very rapidly for tribological investigations. © 2011 American Institute of Physics

  18. Low Friction Surfaces for Low Temperature Applications, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Lunar and other extraterrestrial environments put extreme demands on moving mechanical components. Gears must continue to function and surfaces must continue to...

  19. Friction and Adhesion Forces of Bacillus thuringiensis Spores on Planar Surfaces in Atmospheric Systems

    Energy Technology Data Exchange (ETDEWEB)

    Kweon, Hyojin [Georgia Inst. of Technology, Atlanta, GA (United States); Yiacoumi, Sotira [Georgia Inst. of Technology, Atlanta, GA (United States); Tsouris, Costas [Georgia Inst. of Technology, Atlanta, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2011-11-07

    The kinetic friction force and the adhesion force of Bacillus thuringiensis spores on planar surfaces in atmospheric systems were studied using atomic force microscopy. The influence of relative humidity (RH) on these forces varied for different surface properties including hydrophobicity, roughness, and surface charge. The friction force of the spore was greater on a rougher surface than on mica, which is atomically flat. As RH increases, the friction force of the spores decreases on mica whereas it increases on rough surfaces. The influence of RH on the interaction forces between hydrophobic surfaces is not as strong as for hydrophilic surfaces. The friction force of the spore is linear to the sum of the adhesion force and normal load on the hydrophobic surface. In conclusion, the poorly defined surface structure of the spore and the adsorption of contaminants from the surrounding atmosphere are believed to cause a discrepancy between the calculated and measured adhesion forces.

  20. Negentropy Generation and Fractality in the Dry Friction of Polished Surfaces

    Directory of Open Access Journals (Sweden)

    Mordecai Segall

    2010-03-01

    Full Text Available We consider the Robin Hood model of dry friction to study entropy transfer during sliding. For the polished surface (steady state we study the probability distribution of slips and find an exponential behavior for all the physically relevant asperity interaction-distance thresholds. In addition, we characterize the time evolution of the sample by its spatial fractal dimension and by its entropy content. Starting from an unpolished surface, the entropy decreases during the Robin Hood process, until it reaches a plateau; thereafter the system fluctuates above the critical height. This validates the notion that friction increases information in the neighborhood of the contacting surface at the expense of losing information in remote regions. We explain the practical relevance of these results for engineering surface processing such as honing.

  1. Ultralow friction induced by tribochemical reactions: a novel mechanism of lubrication on steel surfaces.

    Science.gov (United States)

    Li, Ke; Amann, Tobias; Walter, Michael; Moseler, Michael; Kailer, Andreas; Rühe, Jürgen

    2013-04-30

    The tribological properties of two steel surfaces rubbing against each other are measured while they are in contact with 1,3-diketones of varying structure. Such systems show after a short running-in period ultralow friction properties with a coefficient of friction of as low as μ = 0.005. It is suggested that the extremely favorable friction properties are caused by a tribochemical reaction between the 1,3-diketones and the steel surfaces, leading to formation of a chelated iron-diketo complex. The influence of temperature and the molecular structure of the 1,3 diketo-lubricants onto the friction properties of the system is elucidated under both static and dynamic conditions. With progression of the tribochemical reaction, the sliding surfaces become very conformal and smooth, so that the pressure is greatly reduced and further wear is strongly reduced. All iron particles potentially generated by wear during the initial running-in period are completely dissolved through complex formation. It is proposed that the tribochemical polishing reaction causes a transition from boundary lubrication to fluid lubrication.

  2. The effect of irrigation time and type of irrigation fluid on cartilage surface friction.

    Science.gov (United States)

    Stärke, F; Awiszus, F; Lohmann, C H; Stärke, C

    2018-01-01

    It is known that fluid irrigation used during arthroscopic procedures causes a wash-out of lubricating substances from the articular cartilage surface and leads to increased friction. It was the goal of this study to investigate whether this effect depends on the time of irrigation and type of fluid used. Rabbit hind legs were used for the tests. The knees were dissected and the friction coefficient of the femoral cartilage measured against glass in a boundary lubrication state. To determine the influence of irrigation time and fluid, groups of 12 knees received either no irrigation (control), 15, 60 or 120min of irrigation with lactated Ringer's solution or 60min of irrigation with normal saline or a sorbitol/mannitol solution. The time of irrigation had a significant effect on the static and kinetic coefficient of friction (CoF), as had the type of fluid. Longer irrigation time with Ringer's solution was associated with increased friction coefficients (relative increase of the kinetic CoF compared to the control after 15, 60 and 120min: 16%, 76% and 88% respectively). The sorbitol/mannitol solution affected the static and kinetic CoF significantly less than either Ringer's or normal saline. The washout of lubricating glycoproteins from the cartilage surface and the associated increase of friction can be effectively influenced by controlling the time of irrigation and type of fluid used. The time of exposure to the irrigation fluid should be as short as possible and monosaccharide solutions might offer a benefit compared to salt solutions in terms of the resultant friction. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. Effects of pavement surface texture on noise and frictional characteristics.

    Science.gov (United States)

    1987-02-01

    An experimental modification of the transverse groove : surface texture of a section of an urban interstate highway was : performed by the Iowa Department of Transportation. Transverse : groove texturing is a design feature required by the Federal : ...

  4. Microstructures of friction surfaced coatings. A TEM study; Gefuege durch Reibauftragschweissen aufgetragener Beschichtungen. Eine TEM-Untersuchung

    Energy Technology Data Exchange (ETDEWEB)

    Akram, Javed; Kalvala, Prasad Rao; Misra, Mano [Utah Univ., Salt Lake City, UT (United States). Dept. of Metallurgical Engineering; Dilip, J. John Samuel [Louisville Univ., KY (United States). Dept. of Industrial Engineering; Pal, Deepankar; Stucker, Brent [Louisville Univ., KY (United States). Dept. of Industrial Engineering; 3D Sim, Park City, UT (United States)

    2016-05-15

    The microstructures of dissimilar metal welds between 9Cr-1Mo (Modified) (P91) and austenitic stainless steel (AISI 304) with Ni-based alloy interlayers (Inconel 625, Inconel 600 and Inconel 800H) are reported. These interlayers were deposited by the friction surfacing method one over the other on P91 alloy, which was finally friction welded to AISI 304. In this paper, the results of microstructural evolution in the friction surfaced coated interlayers (Inconel 625, 600, 800H) are reported. For comparative purposes, the microstructures of consumable rods (Inconel 625, 600, 800H) and dissimilar metal base metals (P91 and AISI 304) were also reported. Friction surfaced coatings exhibited dynamic recrystallization. In friction surfaced coatings, the carbide particles were found to be finer and distributed uniformly throughout the matrix, compared to their rod counterparts.

  5. Static or breakloose friction for lubricated contacts: the role of surface roughness and dewetting

    International Nuclear Information System (INIS)

    Lorenz, B; Persson, B N J; Krick, B A; Sawyer, W G; Rodriguez, N; Mangiagalli, P

    2013-01-01

    We present experimental data for the static or breakloose friction for lubricated elastomer contacts, as a function of the time of stationary contact. Due to fluid squeeze-out from the asperity contact regions, the breakloose friction force increases continuously with the time of stationary contact. We consider three different cases: (a) PDMS rubber balls against flat smooth glass surfaces, (b) PDMS cylinder ribs against different substrates (glass, smooth and rough PMMA and an inert polymer) and (c) application to syringes. Due to differences in the surface roughness and contact pressures the three systems exhibit very different time dependences of the breakloose friction. In case (a) for rough surfaces the dry contact area A is a small fraction of the nominal contact area A 0 , and the fluid squeeze-out is fast. In case (b) the dry contact area is close to the nominal contact area, A/A 0 ≈ 1, and fluid squeeze-out is very slow due to percolation of the contact area. In this case, remarkably, different fluids with very different viscosities, ranging from 0.005 Pa s (water–glycerol mixture) to 1.48 Pa s (glycerol), give very similar breakloose friction forces as a function of the time of stationary contact. In case (c) the contact pressure and the surface roughness are larger than in case (b), and the squeeze-out is very slow so that even after a very long time the area of real contact is below the percolation threshold. For all cases (a)–(c), the increase in the breakloose friction is mainly due to the increase in the area of real contact with increasing time, because of the fluid squeeze-out and dewetting. (paper)

  6. Static or breakloose friction for lubricated contacts: the role of surface roughness and dewetting.

    Science.gov (United States)

    Lorenz, B; Krick, B A; Rodriguez, N; Sawyer, W G; Mangiagalli, P; Persson, B N J

    2013-11-06

    We present experimental data for the static or breakloose friction for lubricated elastomer contacts, as a function of the time of stationary contact. Due to fluid squeeze-out from the asperity contact regions, the breakloose friction force increases continuously with the time of stationary contact. We consider three different cases: (a) PDMS rubber balls against flat smooth glass surfaces, (b) PDMS cylinder ribs against different substrates (glass, smooth and rough PMMA and an inert polymer) and (c) application to syringes. Due to differences in the surface roughness and contact pressures the three systems exhibit very different time dependences of the breakloose friction. In case (a) for rough surfaces the dry contact area A is a small fraction of the nominal contact area A0, and the fluid squeeze-out is fast. In case (b) the dry contact area is close to the nominal contact area, A/A0 ≈ 1, and fluid squeeze-out is very slow due to percolation of the contact area. In this case, remarkably, different fluids with very different viscosities, ranging from 0.005 Pa s (water–glycerol mixture) to 1.48 Pa s (glycerol), give very similar breakloose friction forces as a function of the time of stationary contact. In case (c) the contact pressure and the surface roughness are larger than in case (b), and the squeeze-out is very slow so that even after a very long time the area of real contact is below the percolation threshold. For all cases (a)–(c), the increase in the breakloose friction is mainly due to the increase in the area of real contact with increasing time, because of the fluid squeeze-out and dewetting.

  7. The influence of surface topography on the forming friction of automotive aluminum sheet

    Energy Technology Data Exchange (ETDEWEB)

    Kramer, Pamela Ann [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

    1998-05-01

    Interest in utilizing aluminum alloys in automobiles has increased in recent years as a result of the desire to lower automobile weight and, consequently, increase fuel economy. While aluminum alloy use in cast parts has increased, outer body panel applications are still being investigated. The industry is interested in improving the formability of these sheet alloys by a combination of alloy design and processing. A different avenue of improving the formability of these alloys may be through patterning of the sheet surface. Surface patterns hold the lubricant during the forming process, with a resulting decrease in the sheet-die surface contact. While it has been speculated that an optimum surface pattern would consist of discrete cavities, detailed investigation into the reduction of forming friction by utilizing discrete patterns is lacking. A series of discrete patterns were investigated to determine the dependence of the forming friction of automotive aluminum alloys on pattern lubricant carrying capacity and on material strength. Automotive aluminum alloys used in outer body panel applications were rolled on experimental rolls that had been prepared with a variety of discrete patterns. All patterns for each alloy were characterized before and after testing both optically and, to determine pattern lubricant capacity, using three dimensional laser profilometry. A draw bead simulation (DBS) friction tester was designed and fabricated to determine the forming friction of the patterned sheets. Tensile testing and frictionless DBS testing were performed to ascertain the material properties of each sheet. The most striking result of this work was the inversely linear dependence of forming friction on the lubricant carrying capacity of the discrete patterns.

  8. Fabrication and characterization of stable superhydrophobic surface with good friction-reducing performance on Al foil

    Energy Technology Data Exchange (ETDEWEB)

    Li, Peipei [Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004 (China); Chen, Xinhua, E-mail: xuc0374@hotmail.com [College of Chemistry and Chemical Engineering, Xuchang University, Xuchang 461000 (China); Yang, Guangbin; Yu, Laigui [Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004 (China); Zhang, Pingyu, E-mail: pingyu@henu.edu.cn [Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004 (China)

    2014-05-01

    Graphical abstract: A lotus-leaf-like hierarchical structure was successfully created on Al foil by a facile three-step solution–immersion method. As-obtained etched-immersed Al/STA rough surface contains interconnected convex–concave micro-structure and uniformly distributed nano-sheets that endow the surface with excellent superhydrophobicity (WCA: 164.2°; WSA: below 5°). Besides, the as-prepared etched-immersed Al/STA superhydrophobic surface on Al foil exhibits good friction-reducing ability and stable superhydrophobicity. - Highlights: • A stable superhydrophobic surface was created on aluminum foil by a facile three-step solution–immersion method. • A lotus-leaf-like hierarchical structure consists of interconnected convex–concave micro-structure and uniformly distributed nano-sheets has been constructed on the aluminum surface. • The superhydrophobic surfaces on aluminum substrate showing effective friction-reducing performance and self-cleaning ability. - Abstract: A lotus-leaf-like hierarchical structure with superhydrophobicity was created on Al foil by a facile three-step solution–immersion method involving etching in hydrochloric acid solution and immersing in hot water as well as surface-modification by stearic acid (denoted as STA). As-prepared etched-immersed Al/STA rough surface was characterized by means of scanning electron microscopy and X-ray photoelectron spectroscopy. Moreover, the water contact angles and water sliding angles of as-prepared etched-immersed Al/STA rough surface were measured, and the friction-reducing performance and self-cleaning ability of the as-prepared surface were also evaluated. Results indicate that the etched-immersed Al/STA rough surface consists of interconnected convex–concave micro-structure and uniformly distributed nano-sheets. Besides, it exhibits stable superhydrophobicity and good friction-reducing ability. Namely, it has a contact angle of water as high as 164.2° and a water sliding

  9. Characterization of boron carbide particulate reinforced in situ copper surface composites synthesized using friction stir processing

    Energy Technology Data Exchange (ETDEWEB)

    Sathiskumar, R., E-mail: sathiscit2011@gmail.com [Department of Mechanical Engineering, Coimbatore Institute of Technology, Coimbatore, 641 014 Tamil Nadu (India); Murugan, N., E-mail: murugan@cit.edu.in [Department of Mechanical Engineering, Coimbatore Institute of Technology, Coimbatore, 641 014 Tamil Nadu (India); Dinaharan, I., E-mail: dinaweld2009@gmail.com [Department of Mechanical Engineering, V V College of Engineering, Tisaiyanvilai, 627 657 Tamil Nadu (India); Vijay, S.J., E-mail: vijayjoseph@karunya.edu [Centre for Research in Metallurgy (CRM), School of Mechanical Sciences, Karunya University, Coimbatore, 641 114 Tamil Nadu (India)

    2013-10-15

    Friction stir processing has evolved as a novel solid state technique to fabricate surface composites. The objective of this work is to apply the friction stir processing technique to fabricate boron carbide particulate reinforced copper surface composites and investigate the effect of B{sub 4}C particles and its volume fraction on microstructure and sliding wear behavior of the same. A groove was prepared on 6 mm thick copper plates and packed with B{sub 4}C particles. The dimensions of the groove was varied to result in five different volume fractions of B{sub 4}C particles (0, 6, 12, 18 and 24 vol.%). A single pass friction stir processing was done using a tool rotational speed of 1000 rpm, travel speed of 40 mm/min and an axial force of 10 kN. Metallurgical characterization of the Cu/B{sub 4}C surface composites was carried out using optical microscope and scanning electron microscope. The sliding wear behavior was evaluated using a pin-on-disk apparatus. Results indicated that the B{sub 4}C particles significantly influenced the area, dispersion, grain size, microhardness and sliding wear behavior of the Cu/B{sub 4}C surface composites. When the volume fraction of B{sub 4}C was increased, the wear mode changed from microcutting to abrasive wear and wear debris was found to be finer. Highlights: • Fabrication of Cu/B{sub 4}C surface composite by friction stir processing • Analyzing the effect of B{sub 4}C particles on the properties of Cu/B4C surface composite • Increased volume fraction of B{sub 4}C particles reduced the area of surface composite. • Increased volume fraction of B{sub 4}C particles enhanced the microhardness and wear rate. • B{sub 4}C particles altered the wear mode from microcutting to abrasive.

  10. Self-adaptive surface texture design for friction reduction across the lubrication regimes

    Science.gov (United States)

    Hsu, Stephen M.; Jing, Yang; Zhao, Fei

    2016-03-01

    Surface texturing has been shown to reduce friction and improve durability in mechanical face seals and metal forming operations, and lightly loaded thrust bearings. However, the success has been limited to conformal contacts and low load high speed operating conditions, i.e. hydrodynamic lubrication dominated regime. Both experiments and numerical simulations have shown that textural patterns, under higher loading and/or slower speeds may increase friction and even cause the lubrication film collapse. Specific designs of surface texture pattern, as its shape, depth and density, are required for different lubrication regimes. Our own study has shown (Hsu et al 2014 J. Phys. D: Appl. Phys. 47 335307) that large/shallow dimple reduces friction in hydrodynamic lubrication regime, whereas small/deep dimple shows benefit in mixed/boundary lubrication regimes (if the textural designs can provides hydrodynamic/hydrostatic lift forces to reduce the machine loading). In considering an engine component typically experiences duty cycles that may cross various lubrication regimes, a multiscale surface texture design appears attractive. This type of mixed shape texturing combines textures designed for low load, high speed operating conditions and the textures that are designed for high load, low speed operations. In this paper, two types of multiscale surface texture designs are presented. Ball-on-three-flats (BOTF) wear tester (under high loading conditions) is used to evaluate the performance of these multiscale texture designs along with the baselines of un-textured surfaces under the same surface preparation procedures. Two texture designs with only a single shape dimples are included in the study. Results suggest that multiscale surface texture design not only further reduces friction in comparison to the textures with single shape dimples, but also shows the effectiveness across hydrodynamic regimes to the mixed lubrication regimes.

  11. High friction on ice provided by elastomeric fiber composites with textured surfaces

    Science.gov (United States)

    Rizvi, R.; Naguib, H.; Fernie, G.; Dutta, T.

    2015-03-01

    Two main applications requiring high friction on ice are automobile tires and footwear. The main motivation behind the use of soft rubbers in these applications is the relatively high friction force generated between a smooth rubber contacting smooth ice. Unfortunately, the friction force between rubber and ice is very low at temperatures near the melting point of ice and as a result we still experience automobile accidents and pedestrian slips and falls in the winter. Here, we report on a class of compliant fiber-composite materials with textured surfaces that provide outstanding coefficients of friction on wet ice. The fibrous composites consist of a hard glass-fiber phase reinforcing a compliant thermoplastic polyurethane matrix. The glass-fiber phase is textured such that it is aligned transversally and protruding out of the elastomer surface. Our analysis indicates that the exposed fiber phase exhibits a "micro-cleat" effect, allowing for it to fracture the ice and increase the interfacial contact area thereby requiring a high force to shear the interface.

  12. Surface effects in adhesion, friction, wear, and lubrication

    National Research Council Canada - National Science Library

    Buckley, Donald H

    1981-01-01

    ... for carbon bodies to improve their wear resistance in high altitude aircraft generator applications. Basic researchers found that moisture in the carbon was critical t o its lubrication. Therefore, the presence of moisture o n the surface of the carbon was important. With it present, the carbon lubricated very effectively and very low wear was ...

  13. General contact mechanics theory for randomly rough surfaces with application to rubber friction

    Science.gov (United States)

    Scaraggi, M.; Persson, B. N. J.

    2015-12-01

    We generalize the Persson contact mechanics and rubber friction theory to the case where both surfaces have surface roughness. The solids can be rigid, elastic, or viscoelastic and can be homogeneous or layered. We calculate the contact area, the viscoelastic contribution to the friction force, and the average interface separation as a function of the sliding speed and the nominal contact pressure. We illustrate the theory with numerical results for the classical case of a rubber block sliding on a road surface. We find that with increasing sliding speed, the influence of the roughness on the rubber block decreases to the extent that only the roughness of the stiff counter face needs to be considered.

  14. Toward understanding whether superhydrophobic surfaces can really decrease fluidic friction drag.

    Science.gov (United States)

    Su, Bin; Li, Mei; Lu, Qinghua

    2010-04-20

    Superhydrophobic surfaces in nature such as legs of water striders can get an extra supporting force from the deformed water surface they contact, leading to an anticipation of using water-repellent surfaces on ship and even submarine hulls to reduce friction drag. Here, we first fabricate superhydrophobic coatings with microstructures on glass balls by introducing hydrophobic silica nanoparticles into a polyethylene terephthalate (PET) film. Then, the movement of a superhydrophobic ball on and below water surface is investigated and compared with that of a highly hydrophilic normal glass ball. The results reveal that a superhydrophobic ball can fall more slowly under water compared with a normal glass ball, because the dense microbubbles trapped at the solid/water interface around the superhydrophobic ball act not as a reducer, but as an enhancer for the friction drag. In contrast, the faster movement of a superhydrophobic ball on the water surface can be mainly attributed to the great reduction of skin friction owing to the increased area of the solid/atmosphere interface.

  15. Friction stir processed Al - Metal oxide surface composites: Anodization and optical appearance

    DEFF Research Database (Denmark)

    Gudla, Visweswara Chakravarthy; Jensen, Flemming; Canulescu, Stela

    2014-01-01

    Multiple-pass friction stir processing (FSP) was employed to impregnate metal oxide (TiO2, Y2O3 and CeO2) particles into the surface of an Aluminium alloy. The surface composites were then anodized in a sulphuric acid electrolyte. The effect of anodizing parameters on the resulting optical...... appearance was studied. Microstructural and morphological characterization was performed using transmission electron microscopy (TEM). The surface appearance was analysed using an integrating sphere-spectrometer setup. Increasing the anodizing voltage changed the surface appearance of the composites from...

  16. Equilibrium without Friction of a Particle on a Mobile Surface with Bilateral Constraints

    Directory of Open Access Journals (Sweden)

    Nicolae–Doru Stănescu

    2015-09-01

    Full Text Available In this paper we will study the equilibrium of a particle on a mobile surface in the case characterized by bilateral constraints between the particle and the surface, and the absence of friction. Based on our previous work, the conditions for the equilibrium are obtained. We prove that the positions of equilibrium on a mobile surface are no longer the same with those obtained for a fixed surface, the system could have either other equilibrium positions, completely different, or some more equilibrium positions, or no equilibrium position.

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

    Directory of Open Access Journals (Sweden)

    Thiago Fontoura de Andrade

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

  18. Surface chemistry, microstructure and friction properties of some ferrous-base metallic glasses at temperatures to 750 C

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1982-01-01

    X-ray photoelectron spectroscopy analysis, transmission electron microscopy, diffraction studies, and sliding friction experiments were conducted with ferrous-base metallic glasses in sliding contact with aluminum oxide at temperatures from room to 750 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on the friction properties, surface chemistry, and microstructure of metallic glasses. The relative concentrations of the various constituents at the surface of the sputtered specimens were very different from the normal bulk compositions. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and silicon oxide at 350 C and boron nitride above 500 C. The coefficient of friction increased with increasing temperature to 350 C. Above 500 C the coefficient of friction decreased rapidly. The segregation of contaminants may be responsible for the friction behavior.

  19. Friction in volcanic environments

    Science.gov (United States)

    Kendrick, Jackie E.; Lavallée, Yan

    2016-04-01

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

  20. Three-dimensional flow of a nanofluid over a permeable stretching/shrinking surface with velocity slip: A revised model

    Science.gov (United States)

    Jusoh, R.; Nazar, R.; Pop, I.

    2018-03-01

    A reformulation of the three-dimensional flow of a nanofluid by employing Buongiorno's model is presented. A new boundary condition is implemented in this study with the assumption of nanoparticle mass flux at the surface is zero. This condition is practically more realistic since the nanoparticle fraction at the boundary is latently controlled. This study is devoted to investigate the impact of the velocity slip and suction to the flow and heat transfer characteristics of nanofluid. The governing partial differential equations corresponding to the momentum, energy, and concentration are reduced to the ordinary differential equations by utilizing the appropriate transformation. Numerical solutions of the ordinary differential equations are obtained by using the built-in bvp4c function in Matlab. Graphical illustrations displaying the physical influence of the several nanofluid parameters on the flow velocity, temperature, and nanoparticle volume fraction profiles, as well as the skin friction coefficient and the local Nusselt number are provided. The present study discovers the existence of dual solutions at a certain range of parameters. Surprisingly, both of the solutions merge at the stretching sheet indicating that the presence of the velocity slip affects the skin friction coefficients. Stability analysis is carried out to determine the stability and reliability of the solutions. It is found that the first solution is stable while the second solution is not stable.

  1. Biomimetic patterned surfaces for controllable friction in micro- and nanoscale devices

    Science.gov (United States)

    Singh, Arvind; Suh, Kahp-Yang

    2013-12-01

    Biomimetics is the study and simulation of biological systems for desired functional properties. It involves the transformation of underlying principles discovered in nature into man-made technologies. In this context, natural surfaces have significantly inspired and motivated new solutions for micro- and nano-scale devices (e.g., Micro/Nano-Electro-Mechanical Systems, MEMS/NEMS) towards controllable friction, during their operation. As a generic solution to reduce friction at small scale, various thin films/coatings have been employed in the last few decades. In recent years, inspiration from `Lotus Effect' has initiated a new research direction for controllable friction with biomimetic patterned surfaces. By exploiting the intrinsic hydrophobicity and ability to reduce contact area, such micro- or nano-patterned surfaces have demonstrated great strength and potential for applications in MEMS/NEMS devices. This review highlights recent advancements on the design, development and performance of these biomimetic patterned surfaces. Also, we present some hybrid approaches to tackle current challenges in biomimetic tribological applications for MEMS/NEMS devices.

  2. Boundary lubrication of heterogeneous surfaces and the onset of cavitation in frictional contacts.

    Science.gov (United States)

    Savio, Daniele; Pastewka, Lars; Gumbsch, Peter

    2016-03-01

    Surfaces can be slippery or sticky depending on surface chemistry and roughness. We demonstrate in atomistic simulations that regular and random slip patterns on a surface lead to pressure excursions within a lubricated contact that increase quadratically with decreasing contact separation. This is captured well by a simple hydrodynamic model including wall slip. We predict with this model that pressure changes for larger length scales and realistic frictional conditions can easily reach cavitation thresholds and significantly change the load-bearing capacity of a contact. Cavitation may therefore be the norm, not the exception, under boundary lubrication conditions.

  3. Deposition of Coatings for Raising the Wear Resistance of Friction Surfaces of Spherical Sliding Bearings

    Science.gov (United States)

    Gorlenko, A. O.; Davydov, S. V.

    2018-01-01

    The process of finishing plasma hardening with deposition of a multilayer amorphous coating of the Si - O - C - N system is considered as applied to hardening of the friction surfaces of spherical sliding bearings. The microrelief, the submicrorelief, and the tribological characteristics of the deposited wear-resistant antifriction amorphous coating, which are responsible for the elevated wear resistance of spherical sliding bearings, are investigated.

  4. Skin Friction Measurements Using Luminescent Oil Films

    Science.gov (United States)

    Husen, Nicholas M.

    As aircraft are designed to a greater extent on computers, the need for accurate and fast CFD algorithms has never been greater. The development of CFD algorithms requires experimental data against which CFD output can be validated and from which insight about flow physics can be acquired. Skin friction, in particular, is an important quantity to predict with CFD, and experimental skin friction data sets aid not only with the validation of the CFD predictions, but also in tuning the CFD models to predict specific flow fields. However, a practical experimental technique for collecting spatially and temporally resolved skin friction data on complex models does not yet exist. This dissertation develops and demonstrates a new luminescent oil film skin friction meter which can produce spatially-resolved quantitative steady and unsteady skin friction data on models with complex curvature. The skin friction acting on the surface of a thin film of oil can be approximated by the expression tauw =mu ouh/h, where mu o is the dynamic viscosity of the oil, uh is the velocity of the surface of the oil film, and h is the thickness of the oil film. The new skin friction meter determines skin friction by measuring h and uh. The oil film thickness h is determined by ratioing the intensity of the fluorescent emissions from the oil film with the intensity of the incident light which is scattered from the surface of the model. When properly calibrated, that ratio provides an absolute oil film thickness value. This oil film thickness meter is therefore referred as the Ratioed-Image Film-Thickness (RIFT) Meter. The oil film velocity uh is determined by monitoring the evolution of tagged molecules within the oil film: Photochromic molecules are dissolved into the fluorescent oil and a pattern is written into the oil film using an ultraviolet laser. The evolution of the pattern is recorded, and standard cross-correlation techniques are applied to the resulting sequence of images. This

  5. 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

  6. 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)

  7. Imaging of surface wave phase velocities from array phase observations

    Science.gov (United States)

    Weidle, Christian; Maupin, Valerie

    2010-05-01

    While temporary deployments some 10 years ago were largely based on short-period seismometers, the availability of broadband instruments in instrument pools increased strongly in recent years and as such modern temporary deployments for passive seismological recordings often consist to a large extent, if not exclusively, of broadband instruments. This opens for new analysis approaches as the broadband seismic wavefield is obtained at a relatively high spatial sampling relative to the wavelength. In an attempt to infer surface wave phase velocity anomalies beneath Southern Norway based on data from a temporary network of 41 broadband instruments, we present a new approach to overcome the limitations of two-station phase measurements (on the great circle with the source) and instead exploit the two-dimensional nature of the wavefield by taking into account phase measurements at all stations of the array from a single event. This is based on the assumption that the wavefield is at least piecewise linear within the study region. By triangulation of the network region and linear estimation of the phase gradient in each triangle we get without further a priori assumptions a coarse image of the phase velocity variations within our network. The image can be significantly refined for a single event recording by stacking multiple images based on arbitrary subsets of the available data. Phase velocity anomalies measured from single event recordings can be biased and blurred by non-plane arriving wavefield, reflections and diffractions of heterogeneities. Therefore, by averaging over velocity fields from different events with varying backazimuths, artefacts are reduced and the recovered image significantly improved. Another way to improve the recovered structures is to take into account the spatial variation of the amplitude field. However, while the phase between two neighboring stations may be (at least close to) linear, the amplitude may not, hence estimation of the second

  8. 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.

  9. 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.

  10. The impact of microgeometry pistons with a stepped bearing surface for the friction loss of the internal combustion engine

    Directory of Open Access Journals (Sweden)

    Wroblewski Emil

    2017-01-01

    Full Text Available This paper present the results of experimental piston friction losses on stepped bearing surface microgeometry obtained on the test rig. This test rig is equipped with special temperature control system, which provides better stability to temperature than in standard systems. The results of station tests was discussed. Tests was analyzed depending the moment caused by the friction on the oil temperature in the oil sump. Specified conclusions allow to assess the impact of the stepped profile of the pistons bearing surface microgeometry for different values of engine speed and the oil temperature at the friction losses in the main kinematic engine node which is piston-cylinder.

  11. Rubber friction and force transmission during the shearing process of actively-driven vacuum grippers on rough surfaces

    International Nuclear Information System (INIS)

    Kern, Patrick

    2016-01-01

    Nowadays, vacuum grippers come in many different shapes and sizes. Their stability is guaranteed through specially manufactured metal fittings. These fittings are non-positively and positively connected to the elastic part of the vacuum gripper. The design of the elastic part may vary, though. Elastomer components are used to ensure tightness for the negative pressure in the active cave chamber of the vacuum gripper, as well as for the transfer of shearing forces, which acting parallel to the surface. Some vacuum grippers feature one elastomer for both the sealing function and the transfer of shear forces; other gripper types are equipped with various elastomers for those applications. The vacuum grippers described in this work are equipped with structured rubber friction pads, their tightness being ensured by sealing lips made of a flexible foam rubber. A restraint system consisting of one or several vacuum grippers must be sized prior to its actual practical use. For the transmission of shearing forces, which acting parallel to the surface, it is necessary to take the tribological system, consisting of the suction element's elastomer and the base material, into account since these loads put shearing stress on the vacuum gripper. In practice, however, a standardized value is given for the coefficient of friction μ; i.e. the ratio of transmissible frictional force to the normal force. This does neither include a detailed description of the elastomer used nor of the roughness of the base material. The standardized friction coefficients cannot be applied to the practical design of restraint systems. The present work includes the analysis of the load transmission and the modeling of the friction coefficients μ on rough surfaces during the shearing process of actively-driven vacuum grippers. Based on current theories, the phenomenon of elastomeric friction can be attributed to the two main components of hysteresis and adhesion friction. Both components are

  12. Microstructure and optical appearance of anodized friction stir processed Al - Metal oxide surface composites

    DEFF Research Database (Denmark)

    Gudla, Visweswara Chakravarthy; Jensen, Flemming; Bordo, Kirill

    2014-01-01

    Multiple-pass friction stir processing (FSP) was employed to impregnate Ti, Y and Ce oxide powders into the surface of an Aluminium alloy. The FSP processed surface composite was subsequently anodized with an aim to develop optical effects in the anodized layer owing to the presence of incorporated...... oxide particles which will influence the scattering of light. This paper presents the investigations on relation between microstructure of the FSP zone and optical appearance of the anodized layer due to incorporation of metal oxide particles and modification of the oxide particles due to the anodizing...

  13. A gradient surface produced by combined electroplating and incremental frictional sliding

    DEFF Research Database (Denmark)

    Yu, Tianbo; Hong, Chuanshi; Kitamura, K.

    2017-01-01

    A Cu plate was first electroplated with a Ni layer, with a thickness controlled to be between 1 and 2 mu m. The coated surface was then deformed by incremental frictional sliding with liquid nitrogen cooling. The combined treatment led to a multifunctional surface with a gradient in strain...... processed Cu plate without Ni coating, showing a strong effect of the coated layer on the deformation. The experimental results are followed by an analysis of strengthening mechanisms and a discussion of the applicability of the new technique for increasing the durability and lifetime of components exposed...

  14. A friction test between steel and a brittle material at high contact pressures and high sliding velocities

    Directory of Open Access Journals (Sweden)

    Picart D.

    2012-08-01

    Full Text Available Our aim is to characterize the interface behaviour between an aggregate material and steel. This work focuses on contact pressures and sliding velocities reaching 100 MPa and 10 m/s. The set-up consists in a cylindrical sample of the aggregate material which slips into a steel tube. The tube is both a confinement vessel and a sliding surface. Thanks to confinement, the material can be tested under high stresses without failure. The interface pressure is generated by an axial compression. The sample is pressed on a spring, so it can be simultaneously compressed and rubbed on the tube. The set-up has been tested in the case of a quasi-static loading and the 100 MPa pressure has been reached. Then the set-up was mounted on a Split Hopkinson Pressure Bar device in order to reach higher velocities. Numerical simulations have been realized to check the feasibility and the relevance of this dynamic test. These results are analysed and compared to the experimental ones.

  15. Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part II, Friction, heating, and torque.

    Science.gov (United States)

    Davidson, J A; Schwartz, G; Lynch, G; Gir, S

    1988-04-01

    In Part I, (J.A. Davidson and G. Schwartz, "Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part I, A review," J. Biomed. Mater. Res., 21, 000-000 (1987) it was shown that lubrication of the artificial hip joint was complex and that long-term performance is governed by the combined wear, creep, and to a lesser extent, oxidation degradation of the articulating materials. Importantly, it was shown that a tendency for heating exists during articulation in the hip joint and that elevated temperatures can increase the wear, creep, and oxidation degradation rate of UHMWPE. The present study was performed to examine closely the propensity to generate heat during articulation in a hip joint simulator. The systems investigated were polished Co-Cr-Mo alloy articulating against UHMWPE, polished alumina ceramic against UHMWPE, and polished alumina against itself. Frictional torque was also evaluated for each system at various levels of applied loads. A walking load history was used in both the frictional heating and torque tests. The majority of tests were performed with 5 mL of water lubricant. However, the effect of various concentrations of hyaluronic acid was also evaluated. Results showed frictional heating to occur in all three systems, reaching an equilibrium after roughly 30 min articulation time. Ceramic systems showed reduced levels of heating compared to the cobalt alloy-UHMWPE system. The level of frictional torque for each system ranked similar to their respective tendencies to generate heat. Hyaluronic acid had little effect, while dry conditions and the presence of small quantities of bone cement powder in water lubricant significantly increased frictional torque.

  16. Adhesion and friction in polymer films on solid substrates: conformal sites analysis and corresponding surface measurements.

    Science.gov (United States)

    An, Rong; Huang, Liangliang; Mineart, Kenneth P; Dong, Yihui; Spontak, Richard J; Gubbins, Keith E

    2017-05-21

    In this work, we present a statistical mechanical analysis to elucidate the molecular-level factors responsible for the static and dynamic properties of polymer films. This analysis, which we term conformal sites theory, establishes that three dimensionless parameters play important roles in determining differences from bulk behavior for thin polymer films near to surfaces: a microscopic wetting parameter, α wx , defined as the ratio of polymer-substrate interaction to polymer-polymer interaction; a dimensionless film thickness, H*; and dimensionless temperature, T*. The parameter α wx introduced here provides a more fundamental measure of wetting than previous metrics, since it is defined in terms of intermolecular forces and the atomic structure of the substrate, and so is valid at the nanoscale for gas, liquid or solid films. To test this theoretical analysis, we also report atomic force microscopy measurements of the friction coefficient (μ), adhesion force (F A ) and glass transition temperature (T g ) for thin films of two polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), on two planar substrates, graphite and silica. Both the friction coefficient and the glass transition temperature are found to increase as the film thickness decreases, and this increase is more pronounced for the graphite than for the silica surface. The adhesion force is also greater for the graphite surface. The larger effects encountered for the graphite surface are attributed to the fact that the microscopic wetting parameter, α wx , is larger for graphite than for silica, indicating stronger attraction of polymer chains to the graphite surface.

  17. Atomistic Simulation of Frictional Sliding Between Cellulose Iß Nanocrystals

    Science.gov (United States)

    Xiawa Wu; Robert J. Moon; Ashlie Martini

    2013-01-01

    Sliding friction between cellulose Iß nanocrystals is studied using molecular dynamics simulation. The effects of sliding velocity, normal load, and relative angle between sliding surface are predicted, and the results analyzed in terms of the number of hydrogen bonds within and between the cellulose chains. We find that although the observed friction trends can be...

  18. Static and kinetic friction force and surface roughness of different archwire-bracket sliding contacts.

    Science.gov (United States)

    Carrion-Vilches, Francisco J; Bermudez, María-Dolores; Fructuoso, Paula

    2015-01-01

    The aim of this study was to determine the static and kinetic friction forces of the contact bracket-archwire with different dental material compositions in order to select those materials with lower resistance to sliding. We carried out sliding friction tests by means of a universal testing machine following an experimental procedure as described in ASTM D1894 standard. We determined the static and kinetic friction forces under dry and lubricating conditions using an artificial saliva solution at 36.5ºC. The bracket-archwire pairs studied were: stainless steel-stainless steel; stainless steel-glass fiber composite; stainless steel-Nitinol 60; sapphire-stainless steel; sapphire-glass fiber composite; and sapphire-Nitinol 60. The best performance is obtained for Nitinol 60 archwire sliding against a stainless steel bracket, both under dry and lubricated conditions. These results are in agreement with the low surface roughness of Nitinol 60 with respect to the glass fiber composite archwire. The results described here contribute to establishing selection criteria for materials for dental archwire-brackets.

  19. Structure vs chemistry: friction and wear of Pt-based metallic surfaces.

    Science.gov (United States)

    Caron, A; Louzguine-Luzguin, D V; Bennewitz, R

    2013-11-13

    In comparison of a Pt57.5Cu14.7Ni5.3P22.5 metallic glass with a Pt(111) single crystal we find that wearless friction is determined by chemistry through bond formation alloying, while wear is determined by structure through plasticity mechanisms. In the wearless regime, friction is affected by the chemical composition of the counter body and involves the formation of a liquid-like neck and interfacial alloying. The wear behavior of Pt-based metallic surfaces is determined by their structural properties and corresponding mechanisms for plastic deformation. In the case of Pt(111) wear occurs by dislocation-mediated homogeneous plastic deformation. In contrast the wear of Pt57.5Cu14.7Ni5.3P22.5 metallic glass occurs through localized plastic deformation in shear bands that merge together in a single shear zone above a critical load and corresponds to the shear softening of metallic glasses. These results open a new route in the control of friction and wear of metals and are relevant for the development of self-lubricated and wear-resistant mechanical devices.

  20. Tyre friction behaviour under abrupt wheel torque transients on slippery road surfaces: experimental analysis and modelling

    Science.gov (United States)

    Ivanović, Vladimir; Deur, Joško; Kostelac, Milan; Pentek, Tibor; Hrovat, Davor

    2011-10-01

    The paper shows that, during abrupt wheel torque transients for ice surface and low vehicle speeds, the tyre can develop significantly larger longitudinal force than the peak value of the tyre static curve. This so-called dynamic tyre friction potential (DTFP) effect has many influencing factors such as the rate of change of the wheel torque, the vehicle speed, and the tyre dwell time. The paper presents a detailed analysis of the DTFP behaviour based on the experimental data collected by using an in-wheel motor-based tyre test vehicle. The analysis results and an insight into the brush structure of a tyre model lead to the hypothesis that the different influencing factors may be predominantly explained by the bristle dwell time (BDT) effect. Following this hypothesis, the LuGre model of the tyre friction dynamics is extended with a physical BDT sub-model. The experimental validation results show that the proposed model can accurately capture the low-speed tyre-ice friction behaviour during abrupt wheel torque transients.

  1. The relationship of seismic velocity structure and surface fracture characteristics of basalt outcrops to rippability estimates

    International Nuclear Information System (INIS)

    Kay, S.E.; Dougherty, M.E.; Pelton, J.R.

    1994-01-01

    Seismic velocity has been shown in previous engineering studies to be related to the fracture characteristics and rippability of rock outcrops. However, common methods of measuring seismic velocity in outcrops do not take into account the many possible travel paths for wave propagation and the fact that velocity zones may exist within an outcrop. Presented here are the results of using raytracing inversion of first-arrival travel-time data to map P-velocity structure in basalt outcrops, and also the investigation of the relationship of the mapped velocities to observed surface fractures and hand-sample P-velocities. It is shown that basalt outcrops commonly consist of an irregular near-surface low-velocity zone underlain by higher velocity material; that velocity gradients can exist in outcrops; that hand-sample velocity measurements are typically higher than outcrop-scale measurements; and that the characteristics of surface fractures are empirically related to near-surface P-velocity. All of these findings are relevant to the estimated rippability of rock in geotechnical engineering. The data for this study are derived from eleven sites on basalt outcrops of the Troodos Ophiolite in Cyprus. The basalt types include pillow basalts, massive flows, and a pillow breccia. A commonly available raytracing inversion program (RAYINVR) was used to produce a velocity profile of each outcrop. Different velocity zones were detailed by inverting observed travel times to produce a model of outcrop velocity structure which produces rippability profiles for each outcrop. 16 refs., 9 figs

  2. Surface topography, hardness, and frictional properties of GFRP for esthetic orthodontic wires.

    Science.gov (United States)

    Inami, Toshihiro; Tanimoto, Yasuhiro; Yamaguchi, Masaru; Shibata, Yo; Nishiyama, Norihiro; Kasai, Kazutaka

    2016-01-01

    In our previous study, glass-fiber-reinforced plastics (GFRPs) made from polycarbonate and glass fiber for esthetic orthodontic wires were prepared by using pultrusion. The purpose of the present study was to investigate the surface topography, hardness, and frictional properties of GFRPs. To investigate how fiber diameter affects surface properties, GFRP round wires with a diameter of 0.45 mm (0.018 in.) were prepared incorporating either 13 μm (GFRP-13) or 7 μm (GFRP-7) glass fibers. As controls, stainless steel (SS), cobalt-chromium-nickel alloy, β-titanium (β-Ti) alloy, and nickel-titanium (Ni-Ti) alloy were also evaluated. Under scanning electron microscopy and scanning probe microscopy, the β-Ti samples exhibited greater surface roughness than the other metallic wires and the GFRP wires. The dynamic hardness and elastic modulus of GFRP wires obtained by the dynamic micro-indentation method were much lower than those of metallic wires (p wires and Ni-Ti wire were nearly half as low as those of SS, Co-Cr, and β-Ti wires. In conclusion, there was no significant difference in surface properties between GFRP-13 and GFRP-7; presumably because both share the same polycarbonate matrix. We expect that GFRP wires will deliver superior sliding mechanics with low frictional resistance between the wire and bracket during orthodontic treatment. © 2015 Wiley Periodicals, Inc.

  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. 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.

  5. Atomic force microscopy measurements of topography and friction on dotriacontane films adsorbed on a SiO2 surface

    DEFF Research Database (Denmark)

    Trogisch, S.; Simpson, M.J.; Taub, H.

    2005-01-01

    We report comprehensive atomic force microscopy (AFM) measurements at room temperature of the nanoscale topography and lateral friction on the surface of thin solid films of an intermediate-length normal alkane, dotriacontane (n-C32H66), adsorbed onto a SiO2 surface. Our topographic and frictional...... their location. Above a minimum size, the bulk particles are separated from islands of perpendicularly oriented molecules by regions of exposed parallel layers that most likely extend underneath the particles. We find that the lateral friction is sensitive to the molecular orientation in the underlying...... crystalline film and can be used effectively with topographic measurements to resolve uncertainties in the film structure. We measure the same lateral friction on top of the bulk particles as on the perpendicular layers, a value that is about 2.5 times smaller than on a parallel layer. Scans on top...

  6. Friction characteristics of submicrometre-structured surfaces fabricated by particle-assisted near-field enhancement with femtosecond laser

    International Nuclear Information System (INIS)

    Sakai, Tetsuo; Nedyalkov, Nikolay; Obara, Minoru

    2007-01-01

    We present friction characteristics of sliding textured silicon surfaces at the submicrometre scale. A two-dimensional submicrometre dimple array on the Si surface is fabricated by femtosecond laser processing. Direct femtosecond laser nano-structuring of the Si (1 0 0) substrate by polystyrene particle-assisted near-field enhancement is used. In the investigated hole diameter domain from 229 to 548 nm, an increase in the friction coefficient with the decrease in the hole size is found experimentally. The fabricated submicrometre dimples act evidently as lubricant reservoirs to supply lubricants and traps to capture wear debris. The fluctuation of the friction coefficient is also increased by reducing the dimple size. The lowest friction coefficient of 1.41 x 10 -2 is achieved with the dimple array having a diameter of about 550 nm. This value is 2.6 times lower than that of non-structured substrates

  7. Effective velocity boundary condition at a mixed slip surface

    NARCIS (Netherlands)

    Sbragaglia, M.; Prosperetti, Andrea

    2007-01-01

    This paper studies the nature of the effective velocity boundary condition for liquid flow over a plane boundary on which small free-slip islands are randomly distributed. It is found that an effective Navier partial-slip condition for the velocity emerges from a statistical analysis valid for

  8. Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale

    Directory of Open Access Journals (Sweden)

    Cubillas Pablo

    2009-06-01

    Full Text Available Abstract Lateral Force Microscopy (LFM studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3 or calcite-otavite solid solutions (SS as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0–40 nN, a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

  9. An Investigation of the Influence of Initial Roughness on the Friction and Wear Behavior of Ground Surfaces.

    Science.gov (United States)

    Liang, Guoxing; Schmauder, Siegfried; Lyu, Ming; Schneider, Yanling; Zhang, Cheng; Han, Yang

    2018-02-04

    Friction and wear tests were performed on AISI 1045 steel specimens with different initial roughness parameters, machined by a creep-feed dry grinding process, to study the friction and wear behavior on a pin-on-disc tester in dry sliding conditions. Average surface roughness (Ra), root mean square (Rq), skewness (Rsk) and kurtosis (Rku) were involved in order to analyse the influence of the friction and wear behavior. The observations reveal that a surface with initial roughness parameters of higher Ra, Rq and Rku will lead to a longer initial-steady transition period in the sliding tests. The plastic deformation mainly concentrates in the depth of 20-50 μm under the worn surface and the critical plastic deformation is generated on the rough surface. For surfaces with large Ra, Rq, low Rsk and high Rku values, it is easy to lose the C element in, the reciprocating extrusion.

  10. An Investigation of the Influence of Initial Roughness on the Friction and Wear Behavior of Ground Surfaces

    Science.gov (United States)

    Liang, Guoxing; Schmauder, Siegfried; Lyu, Ming; Schneider, Yanling; Zhang, Cheng; Han, Yang

    2018-01-01

    Friction and wear tests were performed on AISI 1045 steel specimens with different initial roughness parameters, machined by a creep-feed dry grinding process, to study the friction and wear behavior on a pin-on-disc tester in dry sliding conditions. Average surface roughness (Ra), root mean square (Rq), skewness (Rsk) and kurtosis (Rku) were involved in order to analyse the influence of the friction and wear behavior. The observations reveal that a surface with initial roughness parameters of higher Ra, Rq and Rku will lead to a longer initial-steady transition period in the sliding tests. The plastic deformation mainly concentrates in the depth of 20–50 μm under the worn surface and the critical plastic deformation is generated on the rough surface. For surfaces with large Ra, Rq, low Rsk and high Rku values, it is easy to lose the C element in, the reciprocating extrusion. PMID:29401703

  11. An Investigation of the Influence of Initial Roughness on the Friction and Wear Behavior of Ground Surfaces

    Directory of Open Access Journals (Sweden)

    Guoxing Liang

    2018-02-01

    Full Text Available Friction and wear tests were performed on AISI 1045 steel specimens with different initial roughness parameters, machined by a creep-feed dry grinding process, to study the friction and wear behavior on a pin-on-disc tester in dry sliding conditions. Average surface roughness (Ra, root mean square (Rq, skewness (Rsk and kurtosis (Rku were involved in order to analyse the influence of the friction and wear behavior. The observations reveal that a surface with initial roughness parameters of higher Ra, Rq and Rku will lead to a longer initial-steady transition period in the sliding tests. The plastic deformation mainly concentrates in the depth of 20–50 μm under the worn surface and the critical plastic deformation is generated on the rough surface. For surfaces with large Ra, Rq, low Rsk and high Rku values, it is easy to lose the C element in, the reciprocating extrusion.

  12. 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.

  13. Surface Modification by Friction Stir Processing of Low-Carbon Steel: Microstructure Investigation and Wear Performance

    Science.gov (United States)

    Sattari, Behnoosh; Shamanian, Morteza; Salimijazi, Farshid; Salehi, Mehdi

    2018-01-01

    A low-carbon steel sheet with a thickness of 5 mm was subjected to friction stir processing (FSP) by one to four different passes. The microstructures of different regions were characterized using the optical microscopy and electron backscatter diffraction. The Vickers micro-harness was measured at the distance of 200 μm below the processed surfaces. The influence of pass numbers (PNs) on wear resistance was studied in terms of coefficients of friction (CoFs), weight losses and wear rates. SEM topographies of the worn surfaces were also studied to evaluate the wear mechanisms. Microstructure observations showed that Widmänstatten ferrite plates were formed in stir zones (SZs) and heat affected zones. As PN increased, these grains were widened due to the increment of the carbon diffusivity and lengthened because of the high heat input and microstructure anisotropy. Besides, increasing the PN causes increasing of the hardness and wear resistance, simultaneously. Specifically, the wear rate in the SZ was reduced from 2.8 × 10-2 mm3 m-1 in base metal to 0.3 × 10-2 mm3 m-1 in sample which was subjected to 4 FSP passes. However, variation in PN had no considerable effect on CoFs. Oxidative wear mechanism was observed on the worn surface of the steel and the FSPed samples while more debris was formed by increasing the PNs.

  14. Surface Modification by Friction Stir Processing of Low-Carbon Steel: Microstructure Investigation and Wear Performance

    Science.gov (United States)

    Sattari, Behnoosh; Shamanian, Morteza; Salimijazi, Farshid; Salehi, Mehdi

    2018-02-01

    A low-carbon steel sheet with a thickness of 5 mm was subjected to friction stir processing (FSP) by one to four different passes. The microstructures of different regions were characterized using the optical microscopy and electron backscatter diffraction. The Vickers micro-harness was measured at the distance of 200 μm below the processed surfaces. The influence of pass numbers (PNs) on wear resistance was studied in terms of coefficients of friction (CoFs), weight losses and wear rates. SEM topographies of the worn surfaces were also studied to evaluate the wear mechanisms. Microstructure observations showed that Widmänstatten ferrite plates were formed in stir zones (SZs) and heat affected zones. As PN increased, these grains were widened due to the increment of the carbon diffusivity and lengthened because of the high heat input and microstructure anisotropy. Besides, increasing the PN causes increasing of the hardness and wear resistance, simultaneously. Specifically, the wear rate in the SZ was reduced from 2.8 × 10-2 mm3 m-1 in base metal to 0.3 × 10-2 mm3 m-1 in sample which was subjected to 4 FSP passes. However, variation in PN had no considerable effect on CoFs. Oxidative wear mechanism was observed on the worn surface of the steel and the FSPed samples while more debris was formed by increasing the PNs.

  15. Friction Mapping as a Tool for Measuring the Elastohydrodynamic Contact Running-in Process

    Science.gov (United States)

    2015-10-01

    friction coefficient of the 2 mating surfaces drops rapidly. The running-in process depends on numerous contact conditions and material properties...state friction coefficient and surface morphology, once the running-in process is complete, does not depend significantly on the ramp direction, nor...Fig. 3 Three-dimensional surface plot of the traction coefficient ( friction coefficient) as a function of entrainment velocity and slip (top) and

  16. Magnetohydrodynamic and thermal radiation effects on the boundary-layer flow due to a moving extensible surface with the velocity slip model: A comparative study of four nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Aly, Emad H., E-mail: efarag@uj.edu.sa [Department of Mathematics, Faculty of Science, University of Jeddah, Jeddah 21589 (Saudi Arabia); Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo 11757 (Egypt); Sayed, Hamed M. [Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo 11757 (Egypt); Department of Mathematics, Faculty of Sciences, Taibah University, Yanbu (Saudi Arabia)

    2017-01-15

    In the current work, we investigated effects of the velocity slip for the flow and heat transfer of four nanofluids over a non-linear stretching sheet taking into account the thermal radiation and magnetic field in presence of the effective electrical conductivity. The governing partial differential equations were transformed into a set of nonlinear ordinary differential equation using similarity transformations before being solved numerically by the Chebyshev pseudospectral differentiation matrix (ChPDM). It was found that the investigated parameters affect remarkably on the nanofluid stream function for the whole investigated nanoparticles. In addition, velocity and skin friction profiles of the four investigated nanofluids decreases and increases, respectively, with the increase of the magnetic parameter, first-order and second-order velocity slips. Further, the flow velocity, surface shear stress and temperature are strongly influenced on applying the velocity slip model, where lower values of the second-order imply higher surface heat flux and thereby making the fluid warmer. - Highlights: • A comparative study for four nanoparticles with MHD and thermal radiation effects was studied. • The effective electrical conductivity is mandatory; otherwise a spurious physical sight will be gained. • The investigated parameters affect remarkably on the nanofluids' flow. • The flow velocity, surface shear stress and temperature are strongly influenced by the slip model. • Lower values of the second-order imply higher surface heat flux and thereby making the fluid warmer.

  17. Friction mechanisms and interfacial slip at fluid-solid interfaces

    CERN Document Server

    Leger, L

    2003-01-01

    We present series of experiments based on near field laser velocimetry, developed to characterize the friction mechanisms at fluid-solid interfaces. For polymers, entangled polymer melts are sheared against smooth solid surfaces, covered by surface attached polymer chains of the same chemical species, having a controlled surface density. Direct measurements of the interfacial velocity and of the shear force allow identification of the molecular mechanisms of friction. Depending on the value of the inverse of the shear rate experienced by the polymer compared to the reptation time, the transition between a regime of high and a regime of low friction observed when increasing the shear rate can be related to disentanglement or to the extraction of the surface chains from the bulk polymer. Surfaces with adjusted friction properties can thus be designed by choosing chain anchored length and surface density. For simple fluids, the direct measurements of the interfacial velocity show that, contrary to the usual hypo...

  18. 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)

  19. Visualization of the impact of water drops on a hot surface: effect of drop velocity and surface inclination

    Energy Technology Data Exchange (ETDEWEB)

    Celata, Gian Piero; Mariani, Andrea; Zummo, Giuseppe [ENEA, Institute of Thermal-Fluid Dynamics, S. Maria di Galeria (Rome) (Italy); Cumo, Maurizio [Universita di Roma ' ' La Sapienza' ' , Rome (Italy)

    2006-08-15

    The behaviour of one drop impinging on a hot surface by varying the surface temperature, the drop velocity and the position of the surface (horizontal and a inclined 45 ) both at a temperature below and above the Leidenfrost temperature has been experimentally evaluated, estimating the temperature at which the drop rebounds. A large influence on the drop velocity has been evidenced. The inclination of the surface decreases the critical value of the temperature above which the surface is not rewetted. (orig.)

  20. Ascent Velocity of Plasmoids Generated by Surface Discharges

    Science.gov (United States)

    Wenzel, Uwe

    The ascent velocity of long-lived plasmoids generated under atmospheric conditions to simulate ball lightning was estimated in [Fussmann et al., Phys. Unserer Zeit 39, 246 (2008) and Jegorov et al., Tech. Phys. 53, 688 (2008): Refs. 1 and 2 in the text, respectively], using a rigid sphere model with poor agreement with the experiment. The plasmoids were, however, deformed. Much better agreement is obtained using the Davies and Taylor formula, which describes the ascent velocity of large spherical-cap bubbles.

  1. Detecting onset of chain scission and crosslinking of γ-ray irradiated elastomer surfaces using frictional force microscopy

    International Nuclear Information System (INIS)

    Banerjee, S; Sinha, N K; Gayathri, N; Ponraju, D; Dash, S; Tyagi, A K; Raj, Baldev

    2007-01-01

    We report here that atomic force microscopy (AFM) in frictional force mode can be used to detect the onset of chain scission and crosslinking in polymeric and macromolecular samples upon irradiation. A systematic investigation to detect chain scission and crosslinking of two elastomers (1) ethylene-propylene-diene monomer rubber and (2) fluorocarbon rubber, upon γ-ray irradiation has been carried out using frictional force microscopy (FFM). From the AFM results we observed that both the elastomers show a systematic smoothening of its surfaces, as the γ-ray dose rate increases. However, the frictional property studied using FFM of the sample surfaces show an initial increase and then a decrease as a function of dose rate. This behaviour of increase in its frictional property has been attributed to the onset of chain scission, and the subsequent decrease in friction has been attributed to the onset of crosslinking of the polymer chains. The evaluated qualitative and semi-quantitative changes observed in the overall frictional property as a function of the γ-ray dose rate for the two elastomers are presented in this paper

  2. 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.

  3. Contact Pressure and Sliding Velocity Maps of the Friction, Wear and Emission from a Low-Metallic/Cast-Iron Disc Brake Contact Pair

    Directory of Open Access Journals (Sweden)

    J. Wahlström

    2017-12-01

    Full Text Available Particulate matter with an aerodynamic diameter less than 10 µm (PM10 from car disc brakes contribute up to 50% of the total non-exhaust emissions from road transport in the EU. These emissions come from the wear of the pad and rotor contact surfaces. Yet few studies have reported contact pressures and offered sliding speed maps of the friction, wear, and particle emission performance of disc brake materials at a material level. Such maps are crucial to understanding material behaviour at different loads and can be used as input data to numerical simulations. A low-metallic pad and grey cast-iron rotor contact pair commonly used today in passenger car disc brakes was studied using a pin-on-disc tribometer at twelve contact pressure and sliding speed combinations. Maps of the coefficient of friction, specific wear rate, particle number, and mass rate are presented and discussed.

  4. Effect of ecological surface treatment method on friction strength properties of nettle (urtica dioica) fibre yarns

    Science.gov (United States)

    Şansal, S.; Mıstık, S. I.; Fettahov, R.; Ovalı, S.; Duman, M.

    2017-10-01

    Over the last few decades, more attention is given to lignocellulose based fibres as reinforcement material in the polymer composites owing to the environmental pollution caused by the extensive usage of synthetic and inorganic fibres. Developing new natural fibre reinforced composites is the focus of many researches nowadays. They are made from renewable resources and they have less environmental effect in comparison to inorganic fibre reinforced composites. The interest of consumers in eco-friendly natural fibres and textiles has increased in recent years. Unlike inorganic fibres, natural fibres present light weight, high strength/density ratio and are readily available, environmentally friendly and biodegradable. Many different types of natural fibres are exploited for the production of biodegradable polymer composites. The nettle (Urtica dioica L.) is a well-known plant growing on rural sites of Europe, Asia, and North America. Nettle plant contains fibre similar to hemp and flax. However, similar to other natural fibres, nettle fibres are poorly compatible with the thermoplastic matrix of composites, due to their hydrophilic character which reduces mechanical properties of nettle fibre reinforced thermoplastics. In order to improve the fibrematrix adhesion of the natural fibre reinforced composites, surface treatment processes are applied to the lignocellulose fibres. In this study nettle (urtica dioica) fibre yarns were treated with NaOH by using conventional, ultrasonic and microwave energy methods. After treatment processes tensile strength, elongation, friction strength and SEM observations of the nettle fibre yarns were investigated. All treatment processes were improved the tensile strength, elongation and friction strength properties of the nettle fibre yarns. Also higher tensile strength, elongation and friction strength properties were obtained from treated nettle fibre yarns which treated by using microwave energy method.

  5. 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

  6. Identification of laboratory techniques to optimize Superpave HMA surface friction characteristics : final report, April 2010.

    Science.gov (United States)

    2010-04-15

    Wet pavement friction is known to be one of the most important roadway safety parameters. In this : research, frictional properties of flexible (asphalt) pavements were investigated. : As a part of this study, a laboratory device to polish asphalt sp...

  7. Development of low-friction and wear-resistant surfaces for low-cost Al hot stamping tools

    OpenAIRE

    Dong Y.; Formosa D.; Fernandez J.; Li X.; Fuentes G.; Zoltan K.; Dong H.

    2015-01-01

    In this study, advanced surfaces and coatings have been developed using plasma thermochemical treatment, PVD coating, electroless Ni-BN plating and duplex surface engineering to produce low-friction and wear-resistant surfaces for cast iron stamping tools. Their microstructural and nano-mechanical properties were systematically analysed and the tribological behaviour of these new surfaces and coatings were evaluated. The experimental results have shown that under dry sliding condition, the tr...

  8. Ultralow Friction of Steel Surfaces Using a 1,3-Diketone Lubricant in the Thin Film Lubrication Regime.

    Science.gov (United States)

    Li, Ke; Amann, Tobias; List, Mathias; Walter, Michael; Moseler, Michael; Kailer, Andreas; Rühe, Jürgen

    2015-10-13

    Ultralow friction (coefficient of friction μ ≈ 0.005) is observed when two steel surfaces are brought into sliding contact in the presence of a particular 1,3-diketone lubricant (1-(4-ethyl phenyl) nonane-1,3-dione). We investigate the friction process of such a system both experimentally and theoretically and show that the superlubricity is caused by a novel, unique mechanism: The formation of iron-1,3-diketonato complexes during frictional contact leads to a self-limiting, tribochemical polishing process while at the same time a self-assembled monolayer of the diketone is formed on the employed steel surfaces. This polishing process reduces the contact pressure and at the same time leads to formation of a boundary lubricant layer. During sliding the system transits from the original boundary lubrication regime toward hydrodynamic lubrication. Conductivity measurements across the friction gap during sliding show that the lubricant layer present in the gap between the two shearing surfaces is a only few 10 nanometers thick, so that the molecules experience under typical sliding conditions shear rates of a few 10(6) s(-1). Simulations show that under such strong shear the molecules become strongly oriented in the friction gap and the effective viscosity in sliding direction is significantly reduced so that the system is in the thin film lubrication regime and superlubricity is observed. The results of the experiments suggest that such diketones are promising lubricants to achieve a decrease of energy loss and frictional damage in steel based mechanical devices.

  9. Measuring surface current velocities in the Agulhas region with ASAR

    CSIR Research Space (South Africa)

    Rouault, MJ

    2010-01-01

    Full Text Available Surface current information collected over the Agulhas Current region and derived from the Doppler centroid anomalies of the Advanced Synthetic Aperture Radar (ASAR) are examined. The sources of errors and potential use of the radar surface...

  10. Evaluation of two transport aircraft and several ground test vehicle friction measurements obtained for various runway surface types and conditions. A summary of test results from joint FAA/NASA Runway Friction Program

    Science.gov (United States)

    Yager, Thomas J.; Vogler, William A.; Baldasare, Paul

    1990-01-01

    Tests with specially instrumented NASA Boeing 737 and 727 aircraft together with several different ground friction measuring devices were conducted for a variety of runway surface types and conditions. These tests are part of joint FAA/NASA Aircraft/Ground Vehicle Runway Friction Program aimed at obtaining a better understanding of aircraft ground handling performance under adverse weather conditions and defining relationships between aircraft and ground vehicle tire friction measurements. Aircraft braking performance on dry, wet, snow and ice-covered runway conditions is discussed as well as ground vehicle friction data obtained under similar runway conditions. For a given contaminated runway surface condition, the correlation between ground vehicles and aircraft friction data is identified. The influence of major test parameters on friction measurements such as speed, test tire characteristics, type and amount of surface contaminant, and ambient temperature are discussed. The effect of surface type on wet friction levels is also evaluated from comparative data collected on grooved and ungrooved concrete and asphalt surfaces.

  11. Development of corrosion resistant surfaces via friction stir processing for bio implant applications

    Science.gov (United States)

    Pal Singh Sodhi, Gurvinder; Singh, Harpreet

    2018-01-01

    Current investigation presents the use of Friction Stir Processing (FSP) to improve the corrosion resistance of pure magnesium for biomedical applications. FSP has been used to incorporate hydroxyapetite (HAP) into Mg-surface so as to modify the chemical composition. FSP was done within a matrix of different parameters and conditions. Influence of various parameters on microstructure was also clearly observed. XRD analysis confirmed the presence of HAP, whereas SEM images revealed a uniform distribution of the imbedded phase. Microhardness and in-vitro corrosion studies were also performed. Influence of grain size on hardness was validated by Hall-Petch relationship. Corrosion behavior was explained on the basis of texture, which indicated better corrosion resistance in comparison to the pure Mg. Therefore, the study reveals that the proposed FSP methodology can be useful tool to improve mechanical and corrosion properties of pure Mg for biomedical applications.

  12. Sliding Friction of Copper

    National Research Council Canada - National Science Library

    Liu, Tung

    1963-01-01

    .... With less clean surfaces, the coefficient of friction obtained was about 0.4. Since the degree of cleanliness cannot be controlled quantitatively, the friction - load curve of sliding copper pairs in air exhibits a bifurcation characteristic...

  13. Near-surface fault detection by migrating back-scattered surface waves with and without velocity profiles

    KAUST Repository

    Yu, Han

    2016-04-26

    We demonstrate that diffraction stack migration can be used to discover the distribution of near-surface faults. The methodology is based on the assumption that near-surface faults generate detectable back-scattered surface waves from impinging surface waves. We first isolate the back-scattered surface waves by muting or FK filtering, and then migrate them by diffraction migration using the surface wave velocity as the migration velocity. Instead of summing events along trial quasi-hyperbolas, surface wave migration sums events along trial quasi-linear trajectories that correspond to the moveout of back-scattered surface waves. We have also proposed a natural migration method that utilizes the intrinsic traveltime property of the direct and the back-scattered waves at faults. For the synthetic data sets and the land data collected in Aqaba, where surface wave velocity has unexpected perturbations, we migrate the back-scattered surface waves with both predicted velocity profiles and natural Green\\'s function without velocity information. Because the latter approach avoids the need for an accurate velocity model in event summation, both the prestack and stacked migration images show competitive quality. Results with both synthetic data and field records validate the feasibility of this method. We believe applying this method to global or passive seismic data can open new opportunities in unveiling tectonic features.

  14. Nanocrystalline nickel films with lotus leaf texture for superhydrophobic and low friction surfaces

    Science.gov (United States)

    Shafiei, Mehdi; Alpas, Ahmet T.

    2009-11-01

    Nanostructured Ni films with high hardness, high hydrophobicity and low coefficient of friction (COF) were fabricated. The surface texture of lotus leaf was replicated using a cellulose acetate film, on which a nanocrystalline (NC) Ni coating with a grain size of 30 ± 4 nm was electrodeposited to obtain a self-sustaining film with a hardness of 4.42 GPa. The surface texture of the NC Ni obtained in this way featured a high density (4 × 10 3 mm -2) of conical protuberances with an average height of 10.0 ± 2.0 μm and a tip radius of 2.5 ± 0.5 μm. This structure increased the water repellency and reduced the COF, compared to smooth NC Ni surfaces. The application of a short-duration (120 s) electrodeposition process that deposited "Ni crowns" with a larger radius of 6.0 ± 0.5 μm on the protuberances, followed by a perfluoropolyether (PFPE) solution treatment succeeded in producing a surface texture consisting of nanotextured protuberances that resulted in a very high water contact angle of 156°, comparable to that of the superhydrophobic lotus leaf. Additionally, the microscale protuberances eliminated the initial high COF peaks observed when smooth NC Ni films were tested, and the PFPE treatment resulted in a 60% reduction in the steady-state COFs.

  15. Simulated studies of wear and friction in total hip prosthesis components with various ball sizes and surface finishes

    Science.gov (United States)

    Swikert, M. A.; Johnson, R. L.

    1976-01-01

    Experiments were conducted on a newly designed total hip joint simulator. The apparatus closely simulates the complex motions and loads of the human hip in normal walking. The wear and friction of presently used appliance configurations and materials were determined. A surface treatment of the metal femoral ball specimens was applied to influence wear. The results of the investigation indicate that wear can be reduced by mechanical treatment of metal femoral ball surfaces. A metallographic examination and surface roughness measurements were made.

  16. Effect of airflow velocity on moisture exchange at surfaces of building materials

    DEFF Research Database (Denmark)

    Mortensen, Lone Hedegaard; Rode, Carsten; Peuhkuri, Ruut Hannele

    2006-01-01

    The moisture transfer between air and construction are affected of the boundary layer conditions close to the surface, which is influenced by the airflow patterns in the room. Therefore an investigation of the relation be-tween the surface resistance and the airflow velocity above a material samp...... resistances decrease for increasing airflow velocity above the boundary layer of the material surface. The measured resistances are somewhat smaller than the ones esti-mated by use of the Lewis relation....

  17. Wetting, adhesion and friction of superhydrophobic and hydrophilic leaves and fabricated micro/nanopatterned surfaces

    Science.gov (United States)

    Bhushan, Bharat; Jung, Yong Chae

    2008-06-01

    Superhydrophobic surfaces have considerable technological potential for various applications due to their extreme water-repellent properties. When two hydrophilic bodies are brought into contact, any liquid present at the interface forms menisci, which increases adhesion/friction and the magnitude is dependent upon the contact angle. Certain plant leaves are known to be superhydrophobic in nature due to their roughness and the presence of a thin wax film on the leaf surface. Various leaf surfaces on the microscale and nanoscale have been characterized in order to separate out the effects of the microbumps and nanobumps and the wax on the hydrophobicity. The next logical step in realizing superhydrophobic surfaces that can be produced is to design surfaces based on understanding of the leaves. The effect of micropatterning and nanopatterning on the hydrophobicity was investigated for two different polymers with micropatterns and nanopatterns. Scale dependence on adhesion was also studied using atomic force microscope tips of various radii. Studies on silicon surfaces patterned with pillars of varying diameter, height and pitch values and deposited with a hydrophobic coating were performed to demonstrate how the contact angles vary with the pitch. The effect of droplet size on contact angle was studied by droplet evaporation and a transition criterion was developed to predict when air pockets cease to exist. Finally, an environmental scanning electron microscope study on the effect of droplet size of about 20 µm radius on the contact angle of patterned surfaces is presented. The importance of hierarchical roughness structure on destabilization of air pockets is discussed.

  18. Diminishing friction of joint surfaces as initiating factor for destabilising permafrost rocks?

    Science.gov (United States)

    Funk, Daniel; Krautblatter, Michael

    2010-05-01

    Degrading alpine permafrost due to changing climate conditions causes instabilities in steep rock slopes. Due to a lack in process understanding, the hazard is still difficult to asses in terms of its timing, location, magnitude and frequency. Current research is focused on ice within joints which is considered to be the key-factor. Monitoring of permafrost-induced rock failure comprises monitoring of temperature and moisture in rock-joints. The effect of low temperatures on the strength of intact rock and its mechanical relevance for shear strength has not been considered yet. But this effect is signifcant since compressive and tensile strength is reduced by up to 50% and more when rock thaws (Mellor, 1973). We hypotheisze, that the thawing of permafrost in rocks reduces the shear strength of joints by facilitating the shearing/damaging of asperities due to the drop of the compressive/tensile strength of rock. We think, that decreasing surface friction, a neglected factor in stability analysis, is crucial for the onset of destabilisation of permafrost rocks. A potential rock slide within the permafrost zone in the Wetterstein Mountains (Zugspitze, Germany) is the basis for the data we use for the empirical joint model of Barton (1973) to estimate the peak shear strength of the shear plane. Parameters are the JRC (joint roughness coefficient), the JCS (joint compressive strength) and the residual friction angle (φr). The surface roughness is measured in the field with a profile gauge to create 2D-profiles of joint surfaces. Samples of rock were taken to the laboratory to measure compressive strength using a high-impact Schmidt-Hammer under air-dry, saturated and frozen conditions on weathered and unweathered surfaces. Plugs where cut out of the rock and sand blasted for shear tests under frozen and unfrozen conditions. Peak shear strength of frozen and unfrozen rocks will be calculated using Barton's model. First results show a mean decrease of compressive

  19. Friction Surface Cladding of AA1050 on AA2024-T351; influence of clad layer thickness and tool rotation rate

    NARCIS (Netherlands)

    Liu, Shaojie; Bor, Teunis Cornelis; Geijselaers, Hubertus J.M.; Akkerman, Remko

    2015-01-01

    Friction Surfacing Cladding (FSC) is a recently developed solid state process to deposit thin metallic clad layers on a substrate. The process employs a rotating tool with a central opening to supply clad material and support the distribution and bonding of the clad material to the substrate. The

  20. The amphoteric effect on friction between the bovine cartilage/cartilage surfaces under slightly sheared hydration lubrication mode.

    Science.gov (United States)

    Pawlak, Zenon; Gadomski, Adam; Sojka, Michal; Urbaniak, Wieslaw; Bełdowski, Piotr

    2016-10-01

    The amphoteric effect on the friction between the bovine cartilage/cartilage contacts has been found to be highly sensitive to the pH of an aqueous solution. The cartilage surface was characterized using a combination of the pH, wettability, as well as the interfacial energy and friction coefficient testing methods to support lamellar-repulsive mechanism of hydration lubrication. It has been confirmed experimentally that phospholipidic multi-bilayers are essentially described as lamellar frictionless lubricants protecting the surface of the joints against wear. At the hydrophilicity limit, the low friction would then be due to (a) lamellar slippage of bilayers and (b) a short-range (nanometer-scale) repulsion between the interfaces of negatively charged (PO4(-)) cartilage surfaces, and in addition, contribution of the extracellular matrix (ECM) collagen fibers, hyaluronate, proteoglycans aggregates (PGs), glycoprotein termed lubricin and finally, lamellar PLs phases. In this paper we demonstrate experimentally that the pH sensitivity of cartilage to friction provides a novel concept in joint lubrication on charged surfaces. Copyright © 2016 Elsevier B.V. All rights reserved.

  1. Control of fingertip forces in young and older adults pressing against fixed low- and high-friction surfaces.

    Directory of Open Access Journals (Sweden)

    Kevin G Keenan

    Full Text Available Mobile computing devices (e.g., smartphones and tablets that have low-friction surfaces require well-directed fingertip forces of sufficient and precise magnitudes for proper use. Although general impairments in manual dexterity are well-documented in older adults, it is unclear how these sensorimotor impairments influence the ability of older adults to dexterously manipulate fixed, low-friction surfaces in particular. 21 young and 18 older (65+ yrs adults produced maximal voluntary contractions (MVCs and steady submaximal forces (2.5 and 10% MVC with the fingertip of the index finger. A Teflon covered custom-molded splint was placed on the fingertip. A three-axis force sensor was covered with either Teflon or sandpaper to create low- and high-friction surfaces, respectively. Maximal downward forces (F(z were similar (p = .135 for young and older adults, and decreased by 15% (p<.001 while pressing on Teflon compared to sandpaper. Fluctuations in F(z during the submaximal force-matching tasks were 2.45× greater (p<.001 for older adults than in young adults, and reached a maximum when older adults pressed against the Teflon surface while receiving visual feedback. These age-associated changes in motor performance are explained, in part, by altered muscle activity from three hand muscles and out-of-plane forces. Quantifying the ability to produce steady fingertip forces against low-friction surfaces may be a better indicator of impairment and disability than the current practice of evaluating maximal forces with pinch meters. These age-associated impairments in dexterity while interacting with low-friction surfaces may limit the use of the current generation of computing interfaces by older adults.

  2. Differences in friction and torsional resistance in athletic shoe-turf surface interfaces.

    Science.gov (United States)

    Heidt, R S; Dormer, S G; Cawley, P W; Scranton, P E; Losse, G; Howard, M

    1996-01-01

    This study evaluated the shoe-surface interaction of 15 football shoes made by 3 manufacturers in both anterior translation and rotation using a specially designed pneumatic testing system. The shoes included traditional cleated football shoes, "court" shoes (basketball-style shoes), molded-cleat shoes, and turf shoes. Under an 11.35-kg (25-pound) axial load, all shoes were tested on synthetic turf under wet and dry conditions and on natural stadium grass. Test-retest reliability, as calculated using the Pearson Product-Moment Correlation test, was 0.85 for force of translation and 0.55 for the moment of rotation. The wet versus dry surface values on translation were significantly different for rotation about the tibial axis. Spatting, which is protective taping of the ankle and heel applied on the outside of the shoe, resulted in a reduction of forces generated in both translation and rotation. No overall difference between shoes on grass versus AstroTurf was noted. However, there were significant differences for cleated and turf shoes. Shoes tested in conditions for which they were not designed exhibited reproducible excessive or extreme minimal friction characteristics that may have safety implications. On the basis of this study, we urge shoe manufacturers to display suggested indications and playing surface conditions for which their shoes are recommended.

  3. A numerical method for predicting Rayleigh surface wave velocity in anisotropic crystals

    Science.gov (United States)

    Cherry, Matthew R.; Sathish, Shamachary; Grandhi, Ramana

    2017-12-01

    A numerical method was developed for calculating the Rayleigh Surface Wave (RSW) velocity in arbitrarily oriented single crystals in 360 degrees of propagation. This method relies on the results from modern analysis of RSW behavior with the Stroh formalism to restrict the domain in which to search for velocities by first calculating the limiting velocity. This extension of existing numerical methods also leads to a natural way of determining both the existence of the RSW as well as the possibility of encountering a pseudo-surface wave. Furthermore, the algorithm is applied to the calculation of elastic properties from measurement of the surface wave velocity in multiple different directions on a single crystal sample. The algorithm was tested with crystal symmetries and single crystal elastic moduli from literature. It was found to be very robust and efficient in calculating RSW velocity curves in all cases.

  4. Modeling of rock friction 1. Experimental results and constitutive equations

    International Nuclear Information System (INIS)

    Dieterich, J.H.

    1979-01-01

    Direct shear experiments on ground surfaces of a granodiorite from Raymond, California, at normal stresses of approx.6 MPa demonstrate that competing time, displacement, and velocity, effects control rock friction. It is proposed that the strength of the population of points of contacts between sliding surfaces determines frictional strength and that the population of contacts changes continuously with displacements. Previous experiments demonstrate that the strength of the contacts increases with the age of the contacts. The present experiments establish that a characteristic displacement, proportional to surface roughness, is required to change the population of contacts. Hence during slip the average age of the points of contact and therefore frictional strength decrease as slip velocity increases. Displacement weakening and consequently the potential for unstable slip occur whenever displacement reduces the average age of the contacts. In addition to this velocity dependency, which arises from displacement dependency and time dependency, the experiments also show a competing but transient increase in friction whenever slip velocity increases. Creep of the sliding surface at stresses below that for steady state slip also observed. Constitutive relationships are developed that permit quantitative simulation of the friction versus displacement data as a function of surface roughness and for different time and velocity histories. Unstable slip in experiments is controlled by these constitutive effects and by the stiffness of the experimental system. It is argued that analogous properties control earthquake instability

  5. Retrieval and assimilation of velocities at the ocean surface

    OpenAIRE

    Isern-Fontanet, Jordi; Ballabrera-Poy, Joaquim; Turiel, Antonio; García-Ladona, Emilio

    2017-01-01

    Ocean currents play a key role in Earth’s climate, they are of major importance for navigation and human activities at sea, and impact almost all processes that take place in the ocean. Nevertheless, their observation and forecasting are still difficult. First, direct measurements of ocean currents are difficult to obtain synoptically at global scale. Consequently, it has been necessary to use Sea Surface Height and Sea Surface Temperature measurements and refer to dynamical frameworks to der...

  6. Modulation of friction dynamics in water by changing the combination of the loop- and graft-type poly(ethylene glycol) surfaces.

    Science.gov (United States)

    Seo, Ji-Hun; Tsutsumi, Yusuke; Kobari, Akinori; Shimojo, Masayuki; Hanawa, Takao; Yui, Nobuhiko

    2015-02-07

    A Velcro-like poly(ethylene glycol) (PEG) interface was prepared in order to control the friction dynamics of material surfaces. Graft- and loop-type PEGs were formed on mirror-polished Ti surfaces using an electrodeposition method with mono- and di-amine functionalized PEGs. The friction dynamics of various combinations of PEG surfaces (i.e., graft-on-graft, loop-on-loop, graft-on-loop, and loop-on-graft) were investigated by friction testing. Here, only the Velcro-like combinations (graft-on-loop and loop-on-graft) exhibited a reversible friction behavior (i.e., resetting the kinetic friction coefficient and the reappearance of the maximum static friction coefficient) during the friction tests. The same tendency was observed when the molecular weights of loop- and graft-type PEGs were tested at 1 k and 10 k, respectively. This indicates that a Velcro-like friction behavior could be induced by simply changing the conformation of PEGs, which suggests a novel concept of altering polymer surfaces for the effective control of friction dynamics.

  7. Fabrication of Al5083/B4C surface composite by friction stir processing and its tribological characterization

    Directory of Open Access Journals (Sweden)

    Narayana Yuvaraj

    2015-10-01

    Full Text Available Improved surface properties with the retainment of bulk properties are necessary for a component for enhanced wear characteristics. Friction stir processing (FSP is used to produce such surface composites. Fabrication of 5083 aluminum alloy with reinforced layers of boron carbide (B4C through FSP was carried out. Micro and nano sized B4C particles were used as reinforcements. The friction processed surface composite layer was analyzed through optical and scanning electron microscopical studies. The number of passes and the size of reinforcement play a vital role in the development of surface composites by FSP. Mechanical properties of the friction stir processed surface composites were evaluated through micro hardness and universal tensile tests. The results were compared with the properties of the base metal. The role of reinforcement and number of passes on properties were also evaluated. Tribological performance of the surface composites is tested through pin on disk test. The surface composite layer resulted in three passes with nano particle reinforcement exhibited better properties in hardness, tensile behavior and wear resistance compared to the behavior of the base metal.

  8. Coefficient of Friction of a Brake Disc-Brake Pad Friction Couple

    Directory of Open Access Journals (Sweden)

    Orłowicz A.W.

    2016-12-01

    Full Text Available The paper concerns evaluation of the coefficient of friction characterising a friction couple comprising a commercial brake disc cast of flake graphite grey iron and a typical brake pad for passenger motor car. For the applied interaction conditions, the brake pressure of 0.53 MPa and the linear velocity measured on the pad-disc trace axis equalling 15 km/h, evolution of the friction coefficient μ values were observed. It turned out that after a period of 50 minutes, temperature reached the value 270°C and got stabilised. After this time interval, the friction coefficient value also got stabilised on the level of μ = 0.38. In case of a block in its original state, stabilisation of the friction coefficient value occurred after a stage in the course of which a continuous growth of its value was observed up to the level μ = 0.41 and then a decrease to the value μ = 0.38. It can be assumed that occurrence of this stage was an effect of an initial running-in of the friction couple. In consecutive abrasion tests on the same friction couple, the friction coefficient value stabilisation occurred after the stage of a steady increase of its value. It can be stated that the stage corresponded to a secondary running-in of the friction couple. The observed stages lasted for similar periods of time and ended with reaching the stabile level of temperature of the disc-pad contact surface.

  9. Compressive strength, plastic flow properties, and surface frictional effects of 1100, 3003 and 6061 aluminum alloys

    Energy Technology Data Exchange (ETDEWEB)

    Pinkerton, Gary Wayne [Univ. of Illinois, Urbana-Champaign, IL (United States)

    1993-01-01

    The purpose of this study is to find aluminum alloys that are effective for use as wire vacuum seals in the 800MeV particle accelerator located at the Louis Anderson Meson Physics Facility (LAMPF) in Los Alamos, NM. Three alloys, Al 1100, Al 3003, and Al 6061, are investigated under uniaxial compression to determine stresses for a given height reduction from 0 to 70 percent, and to find plastic flow and surface interaction effects. Right-circular cylindrical specimens are compressed on-end (cylindrically) and radially (for modeling as compressed wire). Aluminum 1100 and 3003 alloys are compared for length to diameter ratios of 1 and 2 for both compression types, and are then compared to results of radial compression of annealed small diameter Al 1100 wire currently used at LAMPE. The specimens are also compressed between three different platen surfaces, polished steel, etched steel, and aluminum 6061-T6, to determine effects of friction. The Al 3003 alloy exhibits 20 to 25% lower stresses at all height reductions than Al 1100 for both cylindrical and radial compression.

  10. Compressive strength, plastic flow properties, and surface frictional effects of 1100, 3003 and 6061 aluminum alloys

    International Nuclear Information System (INIS)

    Pinkerton, G.W.

    1993-01-01

    The purpose of this study is to find aluminum alloys that are effective for use as wire vacuum seals in the 800MeV particle accelerator located at the Louis Anderson Meson Physics Facility (LAMPF) in Los Alamos, NM. Three alloys, Al 1100, Al 3003, and Al 6061, are investigated under uniaxial compression to determine stresses for a given height reduction from 0 to 70 percent, and to find plastic flow and surface interaction effects. Right-circular cylindrical specimens are compressed on-end (cylindrically) and radially (for modeling as compressed wire). Aluminum 1100 and 3003 alloys are compared for length to diameter ratios of 1 and 2 for both compression types, and are then compared to results of radial compression of annealed small diameter Al 1100 wire currently used at LAMPE. The specimens are also compressed between three different platen surfaces, polished steel, etched steel, and aluminum 6061-T6, to determine effects of friction. The Al 3003 alloy exhibits 20 to 25% lower stresses at all height reductions than Al 1100 for both cylindrical and radial compression

  11. Fabrication of Surface Level Cu/Si Cp Nano composites by Friction Stir Processing Route

    International Nuclear Information System (INIS)

    Srinivasan, R. C.; Karunanithi, M.

    2015-01-01

    Friction stir processing (FSP) technique has been successfully employed as low energy consumption route to prepare copper based surface level nano composites reinforced with nano sized silicon carbide particles (Si Cp). The effect of FSP parameters such as tool rotational speed, processing speed, and tool tilt angle on microstructure and microhardness was investigated. Single pass FSP was performed based on Box-Behnken design at three factors in three levels. A cluster of blind holes 2 mm in diameter and 3 mm in depth was used as particulate deposition technique in order to reduce the agglomeration problem during composite fabrication. K-type thermocouples were used to measure temperature histories during FSP. The results suggest that the heat generation during FSP plays a significant role in deciding the microstructure and microhardness of the surface composites. Microstructural observations revealed a uniform dispersion of nano sized Si Cp without any agglomeration problem and well bonded with copper matrix at different process parameter combinations. X-ray diffraction study shows that no intermetallic compound was produced after processing. The microhardness of nano composites was remarkably enhanced and about 95% more than that of copper matrix

  12. Fabrication of Surface Level Cu/SiCp Nanocomposites by Friction Stir Processing Route

    Directory of Open Access Journals (Sweden)

    Cartigueyen Srinivasan

    2015-01-01

    Full Text Available Friction stir processing (FSP technique has been successfully employed as low energy consumption route to prepare copper based surface level nanocomposites reinforced with nanosized silicon carbide particles (SiCp. The effect of FSP parameters such as tool rotational speed, processing speed, and tool tilt angle on microstructure and microhardness was investigated. Single pass FSP was performed based on Box-Behnken design at three factors in three levels. A cluster of blind holes 2 mm in diameter and 3 mm in depth was used as particulate deposition technique in order to reduce the agglomeration problem during composite fabrication. K-type thermocouples were used to measure temperature histories during FSP. The results suggest that the heat generation during FSP plays a significant role in deciding the microstructure and microhardness of the surface composites. Microstructural observations revealed a uniform dispersion of nanosized SiCp without any agglomeration problem and well bonded with copper matrix at different process parameter combinations. X-ray diffraction study shows that no intermetallic compound was produced after processing. The microhardness of nanocomposites was remarkably enhanced and about 95% more than that of copper matrix.

  13. Adhesion and friction of polymer surfaces studied using scanning probe microscopy

    Science.gov (United States)

    Moon, Seung-Ho

    2003-10-01

    Scanning Probe Microscopy has been utilized to investigate the nanomechanical and nanorheological properties at the surface of polymers and polymer blends. To study the surface behavior in detail, it is critical that the SPM instrument have sufficient flexibility. A temperature stage and environmental chamber have been implemented and measurement automation has been achieved using a high-speed data acquisition system controlled by LabView(TM). Finally, new measurement protocols, "X-modulation" and "Force-Distance with X-modulation", have been developed. First measurements using those techniques have been performed for the study of aged model pressure sensitive adhesives. It has been found that the magnitude of the lateral force is so sensitive to adhesion force that X-modulation can identify qualitative differences in the strength of surface stickiness. Variations in surface adhesiveness with humidity are more obvious when the tackifier is present. A large lateral force and strongly reduced stiffness, measured using F-d with X-modulation, have been observed at high humidity for the homogeneous, hydrophilic surface of the adhesive loaded with 60wt% tackifier. These observations are consistent with a model that envisions a tackifier-enriched region near the surface. A large creep effect has also been observed for this sample, and the creep effect is magnified with temperature. These results are consistent with the hypothesis that at a hydrophilic adhesive surface water molecules may strongly alter the surface-tip interactions or modify the mechanical properties of the material nearest the surface. By changing the Z-loading velocity, dynamic adhesion behavior has been investigated. The mechanism of adhesive failure have been elucidated by comparing the velocity dependence of pull-off force and lateral force. Since this dynamic measurement is sensitive to the material composition at the surface, it has been utilized to study the surface segregation of one component at

  14. A Numerical Method for Predicting Rayleigh Surface Wave Velocity in Anisotropic Crystals (Postprint)

    Science.gov (United States)

    2017-09-05

    crystal symmetries and directions of propagation, and the advantages and disadvantages are dis- cussed. An alternative method of finding the RSW velocity...efficient in calculating RSW velocity curves in all cases. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license ...http://creativecommons.org/ licenses /by-nc-nd/4.0/). 1. Introduction Surface acoustic waves (SAW) such as Rayleigh surface waves (RSW) are important in

  15. A nanostructured surface increases friction exponentially at the solid-gas interface

    Science.gov (United States)

    Phani, Arindam; Putkaradze, Vakhtang; Hawk, John E.; Prashanthi, Kovur; Thundat, Thomas

    2016-09-01

    According to Stokes’ law, a moving solid surface experiences viscous drag that is linearly related to its velocity and the viscosity of the medium. The viscous interactions result in dissipation that is known to scale as the square root of the kinematic viscosity times the density of the gas. We observed that when an oscillating surface is modified with nanostructures, the experimentally measured dissipation shows an exponential dependence on kinematic viscosity. The surface nanostructures alter solid-gas interplay greatly, amplifying the dissipation response exponentially for even minute variations in viscosity. Nanostructured resonator thus allows discrimination of otherwise narrow range of gaseous viscosity making dissipation an ideal parameter for analysis of a gaseous media. We attribute the observed exponential enhancement to the stochastic nature of interactions of many coupled nanostructures with the gas media.

  16. Surface-Segregation-Induced Nanopapillae on FDTS-Blended PDMS Film and Implications in Wettability, Adhesion, and Friction Behaviors.

    Science.gov (United States)

    Pan, Zihe; Peng, Ran; Tang, Juntao; Chen, Li; Cheng, Fangqin; Zhao, Boxin

    2018-02-28

    Polymer composites have been extensively used to tune the surface property (e.g., wettability, friction, and adhesion) for its advantages of cost-effectiveness, high efficiency, and ease of fabrication. In this work, different amount of trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FDTS) was added into poly(dimethylsiloxane) elastomer to prepare polymer composite films and were selected as a model to illustrate the effects of surface segregation on surface topology, wettability, friction, and adhesion. The results show that the added FDTS forms aggregations and increasing the content of FDTS leads to the difficulty of air bubble elimination, increase in viscosity, and drop in transparency. Driven by the differences of chemical potential, FDTS aggregations migrate to the air-polymer interface, resulting in surface enrichment and formation of nanopapillae (1-200 nm). This phenomenon becomes more significant with the increment in FDTS. The change in surface composition and structure generates profound effects on wettability, friction, and adhesion. The addition of FDTS makes the surface relatively oleophobic and further increasing the content of FDTS does not helpful in improving the oleophobicity due to the notable aggregation. Friction forces first grow with the increasing content of FDTS and then decline after the maximum point at 1.0 wt % of FDTS, which is attributed to the generated regular larger nanopappillae at high concentration. However, these larger nanopapillae lead to the increase in adhesion because more interactions are formed. The findings demonstrate the behaviors of FDTS in polymer composites and provide important guidance for controlling the formation of nanostructures via aggregation and phase segregation and exploring their implications on surface properties.

  17. Resonant coherent ionization in grazing ion/atom-surface collisions at high velocities

    International Nuclear Information System (INIS)

    Garcia de Abajo, F.J.; Pitarke, J.M.

    1994-01-01

    The resonant coherent interaction of a fast ion/atom with an oriented crystal surface under grazing incidence conditions is shown to contribute significantly to ionize the probe for high enough velocities and motion along a random direction. The dependence of this process on both the distance to the surface and the velocity of the projectile is studied in detail. We focus on the case of hydrogen moving with a velocity above 2 a.u. Comparison with other mechanisms of charge transfer, such as capture from inner shells of the target atoms, permits us to draw some conclusions about the charge state of the outgoing projectiles. (orig.)

  18. The effect of laser surface melting on microstructure and corrosion behavior of friction stir welded aluminum alloy 2219

    Science.gov (United States)

    Ma, Shengchong; Zhao, Yong; Zou, Jiasheng; Yan, Keng; Liu, Chuan

    2017-11-01

    This study aimed to explore the electrochemical properties and microstructure of friction stir welds to understand the correlation between their properties and processing. Friction stir welding is a promising solid-state joining process for high-strength aluminum alloys (AA). Although friction stir welding (FSW) eliminates the problems of fusion welding due to the fact that it is performed below Tm, it causes severe plastic deformation in the material. Some AA welded by FSW exhibit relatively poor corrosion resistance. In this research, the corrosion resistance of such welds was enhanced through laser surface melting. A friction stir weld of AA 2219 was laser melted. The melt depth and microstructure were observed using optical and scanning electron microscopy. The melt zone exhibited epitaxially grown columnar grains. The redistribution of elemental composition was analyzed using energy-dispersive spectroscopy. The anticorrosion properties of both laser-melted and original welds were studied in aqueous 3.5% NaCl solution using cyclic potentiodynamic polarization. The results indicated a noticeable increase in the pitting corrosion resistance after the laser treatment on the surface. The repassivation potential was nobler than the corrosion potential after the laser treatment, confirming that the resistance to pitting growth improved.

  19. Effect of Untampered Plasma Coating and Surface Texturing on Friction and Running-in Behavior of Piston Rings

    Directory of Open Access Journals (Sweden)

    Amirabbas Akbarzadeh

    2018-03-01

    Full Text Available The running-in behavior and the associated transient friction characteristics of a piston ring with different surface treatments are experimentally evaluated using a custom-made engine testing apparatus. Results are reported for a series of running-in and steady-state experiments on piston rings with different combinations of coated and textured surfaces. Comparisons are provided between five different types of piston rings: (1 with no textures; (2 with textures only; (3 with coating only; (4 first textured and then coated; and (5 first coated and then textured. A combination of the texturing and coating showed 12.5% improvement in the frictional behavior and up to 50% improvement in break-in time compared to cases when only one surface treatment was applied.

  20. Friction stir surfacing of cast A356 aluminium–silicon alloy with boron carbide and molybdenum disulphide powders

    Directory of Open Access Journals (Sweden)

    R. Srinivasu

    2015-06-01

    Full Text Available Good castability and high strength properties of Al–Si alloys are useful in defence applications like torpedoes, manufacture of Missile bodies, and parts of automobile such as engine cylinders and pistons. Poor wear resistance of the alloys is major limitation for their use. Friction stir processing (FSP is a recognized surfacing technique as it overcomes the problems of fusion route surface modification methods. Keeping in view of the requirement of improving wear resistance of cast aluminium–silicon alloy, friction stir processing was attempted for surface modification with boron carbide (B4C and molybdenum disulfide (MoS2 powders. Metallography, micro compositional analysis, hardness and pin-on-disc wear testing were used for characterizing the surface composite coating. Microscopic study revealed breaking of coarse silicon needles and uniformly distributed carbides in the A356 alloy matrix after FSP. Improvement and uniformity in hardness was obtained in surface composite layer. Higher wear resistance was achieved in friction stir processed coating with carbide powders. Addition of solid lubricant MoS2 powder was found to improve wear resistance of the base metal significantly.

  1. Development of low-friction and wear-resistant surfaces for low-cost Al hot stamping tools

    Directory of Open Access Journals (Sweden)

    Dong Y.

    2015-01-01

    Full Text Available In this study, advanced surfaces and coatings have been developed using plasma thermochemical treatment, PVD coating, electroless Ni-BN plating and duplex surface engineering to produce low-friction and wear-resistant surfaces for cast iron stamping tools. Their microstructural and nano-mechanical properties were systematically analysed and the tribological behaviour of these new surfaces and coatings were evaluated. The experimental results have shown that under dry sliding condition, the tribological behaviour of aluminium differed great from that of steel regardless of the counterpart material. Highly reactive aluminium had a strong tendency to solder with tool surfaces during dry sliding. However, the lubricity of gray cast irons can be significantly improved by Ni-BN and DLC coatings. The coefficient of friction reduced from about 0.5 for untreated cast irons to about 0.2 sliding against aluminium. Duplex treatment combining plasma nitrocarburising with low-friction coatings showed superior durability than both DLC and Ni-BN coatings.

  2. Indirect measurement of near-surface velocity and pressure fields based on measurement of moving free surface profiles

    International Nuclear Information System (INIS)

    Sibamoto, Yasuteru; Nakamura, Hideo

    2005-01-01

    A non-intrusive technique for measurement of the velocity and pressure fields adjacent to a moving fluid surface is developed. The technique is based on the measurement of fluid surface profile. The velocity and pressure fields are derived with use of the boundary element method (BEM) by seeking for an incompressible flow field that satisfies the kinematic boundary condition imposed by the time-dependent fluid surface profile. The proposed technique is tested by deriving the velocity and pressure fields inversely from the fluid surface profiles obtained by a forward BEM calculation of fluid surface response to externally-imposed pressure. The inverse calculation results show good agreement with the imposed pressure distribution in the forward calculation. (author)

  3. Fabrication of friction-reducing texture surface by selective laser melting of ink-printed (SLM-IP) copper (Cu) nanoparticles(NPs)

    Science.gov (United States)

    Wang, Xinjian; Liu, Junyan; Wang, Yang; Fu, Yanan

    2017-02-01

    This paper reports a process of selective laser melting of ink-printed (SLM-IP) copper (Cu) nanoparticles(NPs) for the fabrication of full dense Cu friction-reducing texture on the metallic surface in ambient condition. This technique synthesizes pure Cu by chemical reduction route using an organic solvent during laser melting in the atmosphere environment, and provides a flexible additive manufacture approach to form complex friction-reduction texture on the metallic surface. Microtextures of ring and disc arrays have been fabricated on the stainless steel surface by SLM-IP Cu NPs. The friction coefficient has been measured under the lubricating condition of the oil. Disc texture surface (DTS) has a relatively low friction coefficient compared with ring texture surface (RTS), Cu film surface (Cu-FS) and the untreated substrate. The study suggests a further research on SLM-IP approach for complex microstructure or texture manufacturing, possibly realizing its advantage of flexibility.

  4. Measurement of friction force between two mica surfaces with multiple beam interferometry

    Directory of Open Access Journals (Sweden)

    Jung J.C.

    2010-06-01

    Full Text Available Friction forces play a crucial role in the tribological behaviour of microcomponents and the application of MEMS products. It is necessary to develop a measurement system to understand and control the material characteristics. In this study, a microscopic measurement system based on multiple beam interferometry is developed to measure the friction force between two mica thin films. Some frictional behaviour between the two mica sheets in contact are reported. The evaluated shear strength of mica agrees well to the existing data. It is possible to use the developed system for micro-tribology study.

  5. Friction Characteristic of Steel Skids Equipped with Skegs on a Lakebed Surface

    Science.gov (United States)

    Sefic, W. J.

    1979-01-01

    The coefficient of friction was determined for steel skids with and without skegs. The addition of a 1.27 centimeter deep skeg caused the coefficient of friction to increase from an average value of .36 to .53, a 47 percent increase over the flat skid. The addition of a .64 centimeter deep skeg increased the friction coefficient from .36 to .46, a 16 percent increase over the flat skid. Comparisons are made with data for similar test conditions obtained during the X-15 program.

  6. Role of Slip Velocity in a Magneto-Micropolar Fluid Flow from a Radiative Surface with Variable Permeability: A Numerical Study

    Directory of Open Access Journals (Sweden)

    Sharma B.K.

    2017-08-01

    Full Text Available An analysis is presented to describe the hydromagnetic mixed convection flow of an electrically conducting micropolar fluid past a vertical plate through a porous medium with radiation and slip flow regime. A uniform magnetic field has been considered in the study which absorbs the micropolar fluid with a varying suction velocity and acts perpendicular to the porous surface of the above plate. The governing non-linear partial differential equations have been transformed into linear partial differential equations, which are solved numerically by applying the explicit finite difference method. The numerical results are presented graphically in the form of velocity, micro-rotation, concentration and temperature profiles, the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall for different material parameters.

  7. Change in Frictional Behavior during Olivine Serpentinization

    Science.gov (United States)

    Xing, T.; Zhu, W.; French, M. E.; Belzer, B.

    2017-12-01

    Hydration of mantle peridotites (serpentinization) is pervasive at plate boundaries. It is widely accepted that serpentinization is intrinsically linked to hydromechanical processes within the sub-seafloor, where the interplay between cracking, fluid supply and chemical reactions is responsible for a spectrum of fault slip, from earthquake swarms at the transform faults, to slow slip events at the subduction zone. Previous studies demonstrate that serpentine minerals can either promote slip or creep depend on many factors that include sliding velocity, temperature, pressure, interstitial fluids, etc. One missing link from the experimental investigation of serpentine to observations of tectonic faults is the extent of alteration necessary for changing the frictional behaviors. We quantify changes in frictional behavior due to serpentinization by conducting experiments after in-situ serpentinization of olivine gouge. In the sample configuration a layer of powder is sandwiched between porous sandstone blocks with 35° saw-cut surface. The starting material of fine-grained (63 120 µm) olivine powder is reacted with deionized water for 72 hours at 150°C before loading starts. Under the conventional triaxial configuration, the sample is stressed until sliding occurs within the gouge. A series of velocity-steps is then performed to measure the response of friction coefficient to variations of sliding velocity from which the rate-and-state parameters are deduced. For comparison, we measured the frictional behavior of unaltered olivine and pure serpentine gouges.Our results confirm that serpentinization causes reduced frictional strength and velocity weakening. In unaltered olivine gouge, an increase in frictional resistance with increasing sliding velocity is observed, whereas the serpentinized olivine and serpentine gouges favor velocity weakening behaviors at the same conditions. Furthermore, we observed that high pore pressures cause velocity weakening in olivine but

  8. A simple measuring technique of surface flow velocity to analyze the behavior of velocity fields in hydraulic engineering applications.

    Science.gov (United States)

    Tellez, Jackson; Gomez, Manuel; Russo, Beniamino; Redondo, Jose M.

    2015-04-01

    An important achievement in hydraulic engineering is the proposal and development of new techniques for the measurement of field velocities in hydraulic problems. The technological advances in digital cameras with high resolution and high speed found in the market, and the advances in digital image processing techniques now provides a tremendous potential to measure and study the behavior of the water surface flows. This technique was applied at the Laboratory of Hydraulics at the Technical University of Catalonia - Barcelona Tech to study the 2D velocity fields in the vicinity of a grate inlet. We used a platform to test grate inlets capacity with dimensions of 5.5 m long and 4 m wide allowing a zone of useful study of 5.5m x 3m, where the width is similar of the urban road lane. The platform allows you to modify the longitudinal slopes from 0% to 10% and transversal slope from 0% to 4%. Flow rates can arrive to 200 l/s. In addition a high resolution camera with 1280 x 1024 pixels resolution with maximum speed of 488 frames per second was used. A novel technique using particle image velocimetry to measure surface flow velocities has been developed and validated with the experimental data from the grate inlets capacity. In this case, the proposed methodology can become a useful tools to understand the velocity fields of the flow approaching the inlet where the traditional measuring equipment have serious problems and limitations. References DigiFlow User Guide. (2012), (June). Russo, B., Gómez, M., & Tellez, J. (2013). Methodology to Estimate the Hydraulic Efficiency of Nontested Continuous Transverse Grates. Journal of Irrigation and Drainage Engineering, 139(10), 864-871. doi:10.1061/(ASCE)IR.1943-4774.0000625 Teresa Vila (1), Jackson Tellez (1), Jesus Maria Sanchez (2), Laura Sotillos (1), Margarita Diez (3, 1), and J., & (1), M. R. (2014). Diffusion in fractal wakes and convective thermoelectric flows. Geophysical Research Abstracts - EGU General Assembly 2014

  9. Reconstruction of Sub-Surface Velocities from Satellite Observations Using Iterative Self-Organizing Maps

    Science.gov (United States)

    Chapman, Christopher; Charantonis, Anastase

    2017-04-01

    A new method based on modified self-organizing maps is presented for the reconstruction of deep ocean current velocities from surface information provided by satellites. This method takes advantage of local correlations in the data-space to improve the accuracy of the reconstructed deep velocities. No assumptions regarding the structure of the water column, nor the underlying dynamics of the flow field, are made. Using satellite observations of surface velocity, sea-surface height and sea-surface temperature, as well as observations of the deep current velocity from autonomous Argo floats to train the map, we are able to reconstruct realistic high-resolution velocity fields at a depth of 1000m. Validation reveals promising results, with a speed root mean squared error of approximately 2.8cm/s, more than a factor of two smaller than competing methods, and direction errors consistently smaller than 30 degrees. The shortcomings of this method will be discussed, as well as recent work to extend the method to produce a fully 3D reconstruction of the interior temperature and velocity fields.

  10. Low Friction and Wear Surface for Application over a Wide Range of Temperature

    National Research Council Canada - National Science Library

    Bhattacharya, Rabi

    1997-01-01

    ...) and Transmission electron microscopy (TEM), both before and after exposure to high temperatures (up to 700 deg C) in air. Friction measurements were performed at temperatures in the range of room temperature to 700 deg C in air...

  11. Dynamic mortar finite element method for modeling of shear rupture on frictional rough surfaces

    Science.gov (United States)

    Tal, Yuval; Hager, Bradford H.

    2017-09-01

    This paper presents a mortar-based finite element formulation for modeling the dynamics of shear rupture on rough interfaces governed by slip-weakening and rate and state (RS) friction laws, focusing on the dynamics of earthquakes. The method utilizes the dual Lagrange multipliers and the primal-dual active set strategy concepts, together with a consistent discretization and linearization of the contact forces and constraints, and the friction laws to obtain a semi-smooth Newton method. The discretization of the RS friction law involves a procedure to condense out the state variables, thus eliminating the addition of another set of unknowns into the system. Several numerical examples of shear rupture on frictional rough interfaces demonstrate the efficiency of the method and examine the effects of the different time discretization schemes on the convergence, energy conservation, and the time evolution of shear traction and slip rate.

  12. Friction and Wear Management Using Solvent Partitioning of Hydrophilic-Surface-Interactive Chemicals Contained in Boundary Layer-Targeted Emulsions

    Science.gov (United States)

    Richmond, Robert Chaffee (Inventor); Schramm, Jr., Harry F. (Inventor); Defalco, Francis G. (Inventor)

    2015-01-01

    Lubrication additives of the current invention require formation of emulsions in base lubricants, created with an aqueous salt solution plus a single-phase compound such that partitioning within the resulting emulsion provides thermodynamically targeted compounds for boundary layer organization thus establishing anti-friction and/or anti-wear. The single-phase compound is termed "boundary layer organizer", abbreviated BLO. These emulsion-contained compounds energetically favor association with tribologic surfaces in accord with the Second Law of Thermodynamics, and will organize boundary layers on those surfaces in ways specific to the chemistry of the salt and BLO additives. In this way friction modifications may be provided by BLOs targeted to boundary layers via emulsions within lubricating fluids, wherein those lubricating fluids may be water-based or oil-based.

  13. Tribological synthesis method for producing low-friction surface film coating

    Science.gov (United States)

    Ajayi, Oyelayo O.; Lorenzo-Martin, Maria De La; Fenske, George R.

    2016-10-25

    An article of method of manufacture of a low friction tribological film on a substrate. The article includes a substrate of a steel or ceramic which has been tribologically processed with a lubricant containing selected additives and the additives, temperature, load and time of processing can be selectively controlled to bias formation of a film on the substrate where the film is an amorphous structure exhibiting highly advantageous low friction properties.

  14. Downward velocity distribution of free surface vortex in a cylindrical vessel

    International Nuclear Information System (INIS)

    Ohguri, Youhei; Monji, Hideaki; Kamide, Hideki

    2008-01-01

    The aim of this study is to reveal the basic flow characteristics, especially downward velocity, of the free surface vortex. The flow field at the vertical cross section in a cylindrical vessel was measured by using PIV. The measurement results showed the inclined vortex center due to the un-axisymmetric structure of the vessel. Therefore, the maximum downward velocity on the cross section was discussed with the depth. The relation between the maximum downward velocity and the depth showed the tendency where the downward velocity increased with the depth non-linearly. By using dye, the downward velocity was also measured but its results showed a little difference from that by PIV. (author)

  15. Influence of Process Parameters in the Friction Surfacing of AA 6082-T6 over AA 2024-T3

    OpenAIRE

    Gandra, J.; Pereira, D.; Miranda, R.M.; Vilaça, P.

    2013-01-01

    VK: T20309 Friction Surfacing is a solid state coating technique with applications in hardfacing, corrosion protection and repair. Since it doesn’t require the fusion of the materials involved, it is suitable to join aluminium alloys while avoiding several of their processing difficulties. The present study addresses the deposition of AA 6082-T6 coatings on AA 2024-T3 substrates, while focusing on the effect of process parameters, such as, axial force, rotation and travel speed. Sound alum...

  16. Effect of friction-induced deformation and oxidation on the structure and microhardness of surface aluminum and silumin layers

    Science.gov (United States)

    Korshunov, L. G.; Chernenko, N. L.; Brodova, I. G.; Shirinkina, I. G.

    2017-11-01

    Metallography, electron microscopy, and X-ray diffraction have been used to investigate structural transformations that take place in a 10-μm-thick surface layer in aluminum and Al-17% Si alloy under conditions of sliding friction and subsequent oxidation at 100 and 200°C for 1 h. Friction-induced deformation has been carried out at room temperature in air and at-196°C in liquid nitrogen by reciprocating sliding of a cylindrical indenter made of cubic boron nitride at a rate of 0.014 m/s and a load of 98 N. It is shown that deformation under these conditions forms nanocrystalline structures in the surface layer in aluminum and Al-17% Si alloy and increases their microhardness by a factor of 1.8-3.5. A high contact deformation and a high affinity of oxygen to aluminum and silicon cause the formation of anomalously supersaturated solid solutions of oxygen in aluminum and silicon in the surface layer of the alloy during friction. Oxidation at 100°C (1 h) of the deformed Al-17% Si alloy increases its microhardness due to the decomposition of anomalously supersaturated solid solutions of oxygen in aluminum and silicon and the formation of their oxides.

  17. Microstructural studies on friction surfaced coatings of Ni-based alloys; Gefuegeuntersuchungen an reibgeschweissten Beschichtungen von Ni-Basislegierungen

    Energy Technology Data Exchange (ETDEWEB)

    Akram, Javed; Puli, Ramesh; Kalvala, Prasad Rao; Misra, Mano [Utah Univ., Salt Lake City, UT (United States). Dept. of Metallurgical Engineering

    2015-07-01

    Inconel 625, Inconel 600, Inconel 800H were friction surfaced on steel and Inconel substrates. The interface between steel and Ni-based alloys showed intermixing of two alloys while the interface between two Ni-based alloys showed no such intermixing. The XRD results confirmed that this intermixed zone consisted of mechanical mix two separate metals and no intermetallics were noticed. Friction surfaced Inconel coatings were metallurgically bonded to steel and Inconel substrates with out any physical defects such as voids or cracks. Friction surfaced coatings showed equiaxed fine grained microstructures (4-18 μm) compared with their consumable rod counterparts (12 - 85 μm). Scanning electron microscope electron backscattered diffraction results showed that the coatings consisted of mainly high angle grain boundaries indicative of dynamic recrystallization mechanism. The temperatures recorded using Infra Red camera showed that the temperature attained at the interface between rod and the substrate is about 1100 C. The grain size of the consumable rod was relatively fine near the coating/substrate interface and relatively coarser away from interface indicating the change in strain and temperature the rod experienced at or away from the interface.

  18. Friction of self-lubricating surfaces by ion beam techniques. Final technical report

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharya, R.S.; Rai, A.K.

    1992-05-01

    UES, Inc. conducted a research and development program designed to establish conditions for ion implantation/mixing of suitable additives into the surfaces of bulk ceramics and metals for obtaining self-lubricating low friction and wear characteristics. The substrates considered were ZrO{sub 2}, Al{sub 2}O{sub 3}, Si{sub 3}N{sub 4}, steel and Ni-base superalloy. The lubricant additives chosen were BaF{sub 2}/CaF{sub 2}Ag, MoS{sub 2}, WS{sub 2}and B{sub 2}O{sub 3}. The initial tasks of the program were to synthesis these lubricant compounds by co-implantation of constituent elements if sufficient beams of desired elements were obtained. The final tasks were to investigate high energy (MeV) ion mixing of deposited coatings as well as to investigate ion beam assisted deposition using low energy ion beams. It was shown that MoS{sub 2} can be synthesized by co-implantation of Mo{sup +} and S{sup +} in ceramic materials with appropriate choice of energies to obtain nearly overlapping depth profiles. The sliding life of DC magnetron sputtered MoS{sub 2} films of thicknesses {approximately}7500{Angstrom} on ceramic materials such as sapphire, Si{sub 3}N{sub 4} and ZrO{sub 3} were improved by ten to thousand fold after 2 Mev Ag{sup +} ion mixing. Ion beam assisted deposition (IBAD) and ion beam mixing were utilized to fabricate self-lubricating coatings of CaF{sub 2}/Ag and BaF/CaF{sub 2}/Ag composites.

  19. Slope-velocity equilibrium and evolution of surface roughness on a stony hillslope

    Science.gov (United States)

    Nearing, Mark A.; Polyakov, Viktor O.; Nichols, Mary H.; Hernandez, Mariano; Li, Li; Zhao, Ying; Armendariz, Gerardo

    2017-06-01

    Slope-velocity equilibrium is hypothesized as a state that evolves naturally over time due to the interaction between overland flow and surface morphology, wherein steeper areas develop a relative increase in physical and hydraulic roughness such that flow velocity is a unique function of overland flow rate independent of slope gradient. This study tests this hypothesis under controlled conditions. Artificial rainfall was applied to 2 m by 6 m plots at 5, 12, and 20 % slope gradients. A series of simulations were made with two replications for each treatment with measurements of runoff rate, velocity, rock cover, and surface roughness. Velocities measured at the end of each experiment were a unique function of discharge rates, independent of slope gradient or rainfall intensity. Physical surface roughness was greater at steeper slopes. The data clearly showed that there was no unique hydraulic coefficient for a given slope, surface condition, or rainfall rate, with hydraulic roughness greater at steeper slopes and lower intensities. This study supports the hypothesis of slope-velocity equilibrium, implying that use of hydraulic equations, such as Chezy and Manning, in hillslope-scale runoff models is problematic because the coefficients vary with both slope and rainfall intensity.

  20. Friction enhancement via micro-patterned wet elastomer adhesives on small intestinal surfaces

    Science.gov (United States)

    Kwon, Jiwoon; Cheung, Eugene; Park, Sukho; Sitti, Metin

    2006-12-01

    A micro-pillar-based silicone rubber adhesive coated with a thin silicone oil layer is investigated in this paper for developing friction-based clamping mechanisms for robotic endoscopic microcapsules. These adhesives are shown to enhance the frictional force between the capsule and the intestinal wall by a factor of about seven over a non-patterned flat elastomer material. In this study, tests performed on fresh samples of pig small intestine are used to optimize the diameter of the micro-pillars to maximize the frictional forces. In addition, the effects of other factors such as the oil viscosity and applied normal forces are investigated. It is demonstrated that the proposed micro-pillar pattern based elastomer adhesive exhibits a maximal frictional force when the pillar diameter is 140 µm and coated silicon oil has a very high viscosity (10 000 cSt). It is also found that the frictional force of the micro-patterned adhesive increases nonlinearly in proportion to the applied normal force. These adhesives would be used as a robust attachment material for developing robotic capsule endoscopes inside intestines with clamping capability.

  1. Features of static and dynamic friction profiles in one and two dimensions on polymer and atomically flat surfaces using atomic force microscopy

    International Nuclear Information System (INIS)

    Watson, G S; Watson, J A

    2008-01-01

    In this paper we correlate the Atomic Force Microscope probe movement with surface location while scanning in the imaging and Force versus distance modes. Static and dynamic stick-slip processes are described on a scale of nanometres to microns on a range of samples. We demonstrate the limits and range of the tip apex being fixed laterally in the force versus distance mode and static friction slope dependence on probe parameters. Micron scale static and dynamic friction can be used to purposefully manipulate soft surfaces to produce well defined frictional gradients

  2. Pitting corrosion resistance and bond strength of stainless steel overlay by friction surfacing on high strength low alloy steel

    Directory of Open Access Journals (Sweden)

    Amit Kumar Singh

    2015-09-01

    Full Text Available Surface modification is essential for improving the service properties of components. Cladding is one of the most widely employed methods of surface modification. Friction surfacing is a candidate process for depositing the corrosion resistant coatings. Being a solid state process, it offers several advantages over conventional fusion based surfacing process. The aim of this work is to identify the relationship between the input variables and the process response and develop the predictive models that can be used in the design of new friction surfacing applications. In the current work, austenitic stainless steel AISI 304 was friction surfaced on high strength low alloy steel substrate. Friction surfacing parameters, such as mechtrode rotational speed, feed rate of substrate and axial force on mechtrode, play a major role in determining the pitting corrosion resistance and bond strength of friction surfaced coatings. Friction surfaced coating and base metal were tested for pitting corrosion by potentio-dynamic polarization technique. Coating microstructure was characterized using optical microscopy, scanning electron microscopy and X-ray diffraction. Coatings in the as deposited condition exhibited strain-induced martensite in austenitic matrix. Pitting resistance of surfaced coatings was found to be much lower than that of mechtrode material and superior to that of substrate. A central composite design with three factors (mechtrode rotational speed, substrate traverse speed, axial load on mechtrode and five levels was chosen to minimize the number of experimental conditions. Response surface methodology was used to develop the model. In the present work, an attempt has been made to develop a mathematical model to predict the pitting corrosion resistance and bond strength by incorporating the friction surfacing process parameters.

  3. Effect of Surface States on Joining Mechanisms and Mechanical Properties of Aluminum Alloy (A5052) and Polyethylene Terephthalate (PET) by Dissimilar Friction Spot Welding

    OpenAIRE

    Farazila Yusof; Mohd Ridha bin Muhamad; Raza Moshwan; Mohd Fadzil bin Jamaludin; Yukio Miyashita

    2016-01-01

    In this research, polyethylene terephthalate (PET), as a high-density thermoplastic sheet, and Aluminum A5052, as a metal with seven distinct surface roughnesses, were joined by friction spot welding (FSW). The effect of A5052’s various surface states on the welding joining mechanism and mechanical properties were investigated. Friction spot welding was successfully applied for the dissimilar joining of PET thermoplastics and aluminum alloy A5052. During FSW, the PET near the joining interfac...

  4. Nanoscale adhesion, friction and wear studies of biomolecules on silane polymer-coated silica and alumina-based surfaces

    Science.gov (United States)

    Bhushan, Bharat; Kwak, Kwang Joo; Gupta, Samit; Lee, Stephen C

    2009-01-01

    Proteins on biomicroelectromechanical systems (BioMEMS) confer specific molecular functionalities. In planar FET sensors (field-effect transistors, a class of devices whose protein-sensing capabilities we demonstrated in physiological buffers), interfacial proteins are analyte receptors, determining sensor molecular recognition specificity. Receptors are bound to the FET through a polymeric interface, and gross disruption of interfaces that removes a large percentage of receptors or inactivates large fractions of them diminishes sensor sensitivity. Sensitivity is also determined by the distance between the bound analyte and the semiconductor. Consequently, differential properties of surface polymers are design parameters for FET sensors. We compare thickness, surface roughness, adhesion, friction and wear properties of silane polymer layers bound to oxides (SiO2 and Al2O3, as on AlGaN HFETs). We compare those properties of the film–substrate pairs after an additional deposition of biotin and streptavidin. Adhesion between protein and device and interfacial friction properties affect FET reliability because these parameters affect wear resistance of interfaces to abrasive insult in vivo. Adhesion/friction determines the extent of stickage between the interface and tissue and interfacial resistance to mechanical damage. We document systematic, consistent differences in thickness and wear resistance of silane films that can be correlated with film chemistry and deposition procedures, providing guidance for rational interfacial design for planar AlGaN HFET sensors. PMID:18986962

  5. Upper-Mantle Shear Velocities beneath Southern California Determined from Long-Period Surface Waves

    OpenAIRE

    Polet, J.; Kanamori, H.

    1997-01-01

    We used long-period surface waves from teleseismic earthquakes recorded by the TERRAscope network to determine phase velocity dispersion of Rayleigh waves up to periods of about 170 sec and of Love waves up to about 150 sec. This enabled us to investigate the upper-mantle velocity structure beneath southern California to a depth of about 250 km. Ten and five earthquakes were used for Rayleigh and Love waves, respectively. The observed surface-wave dispersion shows a clear Love/Rayleigh-wave d...

  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. Shear wave velocity structure in North America from large-scale waveform inversions of surface waves

    Science.gov (United States)

    Alsina, D.; Woodward, R.L.; Snieder, R.K.

    1996-01-01

    A two-step nonlinear and linear inversion is carried out to map the lateral heterogeneity beneath North America using surface wave data. The lateral resolution for most areas of the model is of the order of several hundred kilometers. The most obvious feature in the tomographic images is the rapid transition between low velocities in the technically active region west of the Rocky Mountains and high velocities in the stable central and eastern shield of North America. The model also reveals smaller-scale heterogeneous velocity structures. A high-velocity anomaly is imaged beneath the state of Washington that could be explained as the subducting Juan de Fuca plate beneath the Cascades. A large low-velocity structure extends along the coast from the Mendocino to the Rivera triple junction and to the continental interior across the southwestern United States and northwestern Mexico. Its shape changes notably with depth. This anomaly largely coincides with the part of the margin where no lithosphere is consumed since the subduction has been replaced by a transform fault. Evidence for a discontinuous subduction of the Cocos plate along the Middle American Trench is found. In central Mexico a transition is visible from low velocities across the Trans-Mexican Volcanic Belt (TMVB) to high velocities beneath the Yucatan Peninsula. Two elongated low-velocity anomalies beneath the Yellowstone Plateau and the eastern Snake River Plain volcanic system and beneath central Mexico and the TMVB seem to be associated with magmatism and partial melting. Another low-velocity feature is seen at depths of approximately 200 km beneath Florida and the Atlantic Coastal Plain. The inversion technique used is based on a linear surface wave scattering theory, which gives tomographic images of the relative phase velocity perturbations in four period bands ranging from 40 to 150 s. In order to find a smooth reference model a nonlinear inversion based on ray theory is first performed. After

  8. Quantification of glacial and ground surface velocities from repeat terrestrial LiDAR scans

    Science.gov (United States)

    Shahzad, F.; Ehlers, T. A.

    2012-04-01

    Repeat terrestrial LiDAR scans of moving surfaces (e.g. around faults, glaciers, mass movements, etc.) collected at different times offer the opportunity to quantify surface velocities in high resolution. This study presents a new approach for quantifying surface velocities from remote sensing data. Emphasis is placed on the interpretation of terrestrial LiDAR grid point cloud (GPC) data, but the technique presented is also applicable to other (RASTER) remote sensing datasets. The method used consists of investigating two or more temporally variable GPCs referred as a raw and displaced/deformed scans. A user-defined grid is defined on the raw and deformed scans and the center point of each grid is identified. A search window size is determined for comparison between the two scans. Elevations in both scans are then converted to a reference elevation and a normalized cross correlation is applied between the images for pattern recognition. The focal points of the raw image and correlated deformed location are used to prepare an affine transformation for that grid. This procedure is applied on all the grids to prepare the spatial distribution of the affine transformation. Finally, the affine transformation is extended to calculate the horizontal components of surface deformation. These components are used to prepare the spatial distribution of the displacement distance and angle between each grid on each scan. The routine was applied to a series of synthetic (test) datasets and to repeat LiDAR scans (ILRIS-LR) of the Rhone glacier, Switzerland collected in August 2011. Results from the synthetic tests indicate the approach provides a robust reconstruction of spatially non-uniform velocity fields on scans with different surface characteristics. For the Rhone glacier data both temporal and spatial variations in surface velocities were recovered across a large portion of the glacier at centimeter scale. Temporal variations in the glacier surface velocity were resolved

  9. Resolution potential of surface wave phase velocity measurements at small arrays

    Science.gov (United States)

    Bodin, Thomas; Maupin, Valérie

    2008-02-01

    The deployment of temporary arrays of broadband seismological stations over dedicated targets is common practice. Measurement of surface wave phase velocity across a small array and its depth-inversion gives us information about the structure below the array which is complementary to the information obtained from body-wave analysis. The question is however: what do we actually measure when the array is much smaller than the wave length, and how does the measured phase velocity relates to the real structure below the array? We quantify this relationship by performing a series of numerical simulations of surface wave propagation in 3-D structures and by measuring the apparent phase velocity across the array on the synthetics. A principal conclusion is that heterogeneities located outside the array can map in a complex way onto the phase velocities measured by the array. In order to minimize this effect, it is necessary to have a large number of events and to average measurements from events well-distributed in backazimuth. A second observation is that the period of the wave has a remarkably small influence on the lateral resolution of the measurement, which is dominantly controlled by the size of the array. We analyse if the artefacts created by heterogeneities can be mistaken for azimuthal variations caused by anisotropy. We also show that if the amplitude of the surface waves can be measured precisely enough, phase velocities can be corrected and the artefacts which occur due to reflections and diffractions in 3-D structures greatly reduced.

  10. Effect of soil surface conditions on runoff velocity and sediment mean aggregate diameter

    Science.gov (United States)

    César Ramos, Júlio; Bertol, Ildegardis; Paz González, Antonio; de Souza Werner, Romeu; Marioti, Juliana; Henrique Bandeira, Douglas; Andrighetti Leolatto, Lidiane

    2013-04-01

    Soil cover and soil management are the factors that most influence soil erosion by water, because they directly affect soil surface roughness and surface cover. The main effect of soil cover by crop residues consists in dissipation of kinetic energy of raindrops and also partly kinetic energy of runoff, so that the soil disaggregation is considerably reduced but, in addition, soil cover captures detached soil particles, retains water on its surface and decreases runoff volume and velocity. In turn, soil surface roughness, influences soil surface water storage and infiltration and also runoff volume and velocity, sediment retention and subsequently water and sediment losses. Based on the above rationale, we performed a field experiment to assess the influence of soil cover and soil surface roughness on decay of runoff velocity as well as on mean diameter of transported sediments (D50 index). The following treatments were evaluated: SRR) residues of Italian ryegrass (Lolium multiflorum) on a smooth soil surfcace, SRV) residues of common vetch (Vicia sativa) on a smooth soil surface, SSR) scarification after cultivation of Italian ryegrass resulting in a rough surface, SSV) scarification after cultivation of common vetch resulting in a rough surface, and SBS) scarified bare soil with high roughness as a control. The field experiments was performed on an Inceptisol in South Brazil under simulated rainfall conditions during 2012. Experimental plots were 11 m long and 3.5 m wide with an area of 38.5 m2. Six successive simulated rainfall tests were applied using a rotating-boom rain simulator. During each test, rain intensity was 60 mmhr-1, whereas rain duration was 90 minutes. Runoff velocity showed no significant differences between cultivated treatments. However, when compared to bare soil treatment, SBS (0.178 m s-1) and irrespective of the presence of surface crop residues or scarification operations, cultivated soil treatments significantly reduced runoff velocity

  11. Enhanced Locomotion Efficiency of a Bio-inspired Walking Robot using Contact Surfaces with Frictional Anisotropy

    DEFF Research Database (Denmark)

    Manoonpong, Poramate; Petersen, Dennis; Kovalev, Alexander

    2016-01-01

    stability. It shows high frictional anisotropy due to an array of sloped denticles. The orientation of the denticles to the underlying collagenous material also strongly influences their mechanical interlocking with the substrate. This study not only opens up a new way of achieving energy-efficient legged...

  12. Using squeeze-film effect to reduce surface friction in electrostatic actuators

    DEFF Research Database (Denmark)

    Zsurzsan, Tiberiu-Gabriel; Yamamoto, Akio; Zhang, Zhe

    2015-01-01

    This paper presents a method of reducing load friction in two degrees-of-freedom (2-DOF) transparent electrostatic induction actuator by using vibration-induced squeeze film effect. An experimental set-up was built to prove the concept. An overall 70% reduction in required driving voltage was obt...

  13. Retrieval of sea surface velocities using sequential Ocean Colour Monitor (OCM) data

    Digital Repository Service at National Institute of Oceanography (India)

    Prasad, J.S.; Rajawat, A; Pradhan, Y.; Chauhan, O.S.; Nayak, S.R.

    . Sequential data of IRS-P4 OCM has been analysed over parts of both east and west coast of India and a methodology to retrieve sea surface current velocities has been applied. The method is based on matching sus- pended sediment dispersion patterns...

  14. On measuring surface wave phase velocity from station–station cross-correlation of ambient signal

    DEFF Research Database (Denmark)

    Boschi, Lapo; Weemstra, Cornelis; Verbeke, Julie

    2012-01-01

    We apply two different algorithms to measure surface wave phase velocity, as a function of frequency, from seismic ambient noise recorded at pairs of stations from a large European network. The two methods are based on consistent theoretical formulations, but differ in the implementation: one met...

  15. Surface ice flow velocity and tide retrieval of the amery ice shelf using precise point positioning

    DEFF Research Database (Denmark)

    Zhang, X.H.; Andersen, Ole Baltazar

    2006-01-01

    Five days of continuous GPS observation data were collected in the frontal zone of the Amery ice shelf and subsequently post-processed using precise point position (PPP) technology based on precise orbit and clock products from the International GNSS service. The surface ice flow velocity...

  16. Short-period surface-wave phase velocities across the conterminous United States

    Science.gov (United States)

    Ekström, G.

    2017-09-01

    Surface-wave phase-velocity maps for the full footprint of the USArray Transportable Array (TA) across the conterminous United States are developed and tested. Three-component, long-period continuous seismograms recorded on more than 1800 seismometers, most of which were deployed for 18 months or longer, are processed using a noise cross-correlation technique to derive inter-station Love and Rayleigh dispersion curves at periods between 5 and 40 s. The phase-velocity measurements are quality controlled using an automated algorithm and then used in inversions for Love and Rayleigh phase-velocity models at discrete periods on a 0.25°-by-0.25° pixel grid. The robustness of the results is examined using comparisons of maps derived from subsets of the data. A winter-summer division of the cross-correlation data results in small model differences, indicating relatively minor sensitivity of the results to seasonal variations in the distribution of noise sources. Division of the dispersion data based on inter-station azimuth does not result in geographically coherent model differences, suggesting that azimuthal anisotropy at the regional scale is weak compared with variations in isotropic velocities and does not substantially influence the results for isotropic velocities. The phase-velocity maps and dispersion measurements are documented and made available as data products of the 10-year-long USArray TA deployment.

  17. Near Surface Seismic Hazard Characterization in the Presence of High Velocity Contrasts

    Science.gov (United States)

    Gribler, G.; Mikesell, D.; Liberty, L. M.

    2017-12-01

    We present new multicomponent surface wave processing techniques that provide accurate characterization of near-surface conditions in the presence of large lateral or vertical shear wave velocity boundaries. A common problem with vertical component Rayleigh wave analysis in the presence of high contrast subsurface conditions is Rayleigh wave propagation mode misidentification due to an overlap of frequency-phase velocity domain dispersion, leading to an overestimate of shear wave velocities. By using the vertical and horizontal inline component signals, we isolate retrograde and prograde particle motions to separate fundamental and higher mode signals, leading to more accurate and confident dispersion curve picks and shear wave velocity estimates. Shallow, high impedance scenarios, such as the case with shallow bedrock, are poorly constrained when using surface wave dispersion information alone. By using a joint inversion of dispersion and horizontal-to-vertical (H/V) curves within active source frequency ranges (down to 3 Hz), we can accurately estimate the depth to high impedance boundaries, a significant improvement compared to the estimates based on dispersion information alone. We compare our approach to body wave results that show comparable estimates of bedrock topography. For lateral velocity contrasts, we observe horizontal polarization of Rayleigh waves identified by an increase in amplitude and broadening of the horizontal spectra with little variation in the vertical component spectra. The horizontal spectra offer a means to identify and map near surface faults where there is no topographic or clear body wave expression. With these new multicomponent active source seismic data processing and inversion techniques, we better constrain a variety of near surface conditions critical to the estimation of local site response and seismic hazards.

  18. Direct ambient noise tomography for 3-D near surface shear velocity structure: methodology and applications

    Science.gov (United States)

    Yao, H.; Fang, H.; Li, C.; Liu, Y.; Zhang, H.; van der Hilst, R. D.; Huang, Y. C.

    2014-12-01

    Ambient noise tomography has provided essential constraints on crustal and uppermost mantle shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for imaging near surface or shallow crustal shear velocity structures. This approach provides important information for strong ground motion prediction in seismically active area and overburden structure characterization in oil and gas fields. Here we propose a new tomographic method to invert all surface wave dispersion data for 3-D variations of shear wavespeed without the intermediate step of phase or group velocity maps.The method uses frequency-dependent propagation paths and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. The wavelet coefficients of the velocity model are estimated with an iteratively reweighted least squares (IRLS) algorithm, and upon iterations the surface wave ray paths and the data sensitivity matrix are updated from the newly obtained velocity model. We apply this new method to determine the 3-D near surface wavespeed variations in the Taipei basin of Taiwan, Hefei urban area and a shale and gas production field in China using the high-frequency interstation Rayleigh wave dispersion data extracted from ambient noisecross-correlation. The results reveal strong effects of off-great-circle propagation of high-frequency surface waves in these regions with above 30% shear wavespeed variations. The proposed approach is more efficient and robust than the traditional two-step surface wave tomography for imaging complex

  19. 3D Simulation of a Loss of Vacuum Accident (LOVA in ITER (International Thermonuclear Experimental Reactor: Evaluation of Static Pressure, Mach Number, and Friction Velocity

    Directory of Open Access Journals (Sweden)

    Jean-François Ciparisse

    2018-04-01

    Full Text Available ITER (International Thermonuclear Experimental Reactor is a magnetically confined plasma nuclear reactor. Inside it, due to plasma disruptions, the formation of neutron-activated powders, which are essentially made out of tungsten and beryllium, occurs. As many windows for diagnostics are present on the reactor, which operates at very low pressure, a LOVA (Loss of Vacuum Accident could be possible and may lead to dust mobilisation and a toxic and radioactive fallout inside the plant. This study is aimed at reproducing numerically the first seconds of a LOVA in ITER, in order to get information about the dust resuspension risk. This work has been carried out by means of a CFD (Computational Fluid Dynamics simulation of the beginning of the pressurisation transient inside the whole Tokamak. It has been found that the pressurization transient is extremely slow, and that the friction speed on the walls is very high, and therefore a high mobilization risk of the dust is expected on the entire internal surface of the reactor. It has been observed that a LOVA in a real-scale reactor is more severe than the one reproduced in reduced-scale facilities, as STARDUST-U, because the speeds are higher, and the dust resuspension capacity of the flow is greater.

  20. Reduction in Friction and Wear of Alumina Surfaces as Assisted with Surface-Adsorbing Polymers in Aqueous Solutions

    DEFF Research Database (Denmark)

    Røn, Troels; Lee, Seunghwan

    2016-01-01

    electrostatic attraction and form a protective layer. For example, polyacrylic acid (PAA) showed a reduction in coefficient of friction by ca. 28% and wear rate by 50% at a concentration of 10 mg/mL in PBS solution compared to polymer-free buffer solution. This effect was comparable to reported lubricating...

  1. Finishing of sliding surfaces with geometrically defined cutting edges: Presentation held at "Friction, Wear and Wear Protection", Symposium "TriboMan-Session", 26.- 28. Oct 2011, Karlsruhe

    OpenAIRE

    Schubert, Andreas; Schmidt, Torsten; Schneider, Jörg

    2011-01-01

    The rising importance of friction reduction of parts and components, especially in the power train, leads to increasing demands on the finishing of sliding surfaces. In order to meet these new requirements, new methods have to be applied. A new approach for the surface finishing is, to generate an approximated run-in condition to the surface by the finishing process in order to obtain lower initial friction and a shorter run-in period. This requires specific surface properties to ensure the p...

  2. Laser Peening and Shot Peening Effects on Fatigue Life and Surface Roughness of Friction Stir Welded 7075-T7351 Aluminum

    Science.gov (United States)

    Hatamleh, Omar; Lyons, Jed; Forman, Royce

    2006-01-01

    The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening conditions with different intensities, durations, and peening order were tested to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using laser peening compared to shot peened versus their native welded specimens.

  3. Near surface velocity and Q S structure of the Quaternary sediment in Bohai basin, China

    Science.gov (United States)

    Chong, Jiajun; Ni, Sidao

    2009-10-01

    Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation ( Q P and Q S) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1-10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0-500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 M W4.9 Wen’an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average ν P and ν S of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high ν P/ ν S ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain Q S and the near surface velocity structure. Our modeling indicates that Q S is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (˜10), but consistent with Q S modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0-50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation.

  4. 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.

  5. Combining DLC, Shot blasting, chemical dip and nano fullerene surface treatments to reduce wear and friction when used with bio-lubricants in automotive contacts

    OpenAIRE

    Carrell, J.; Slatter, T.; Little, U.; Lewis, R.

    2017-01-01

    The interaction of three bio-lubricant base oil candidates with seventeen combinations of surface treatment was studied, comparing wear scar volumes and coefficient of friction results. Substrates were initially ground, then a combination of superfinished, Dymon-iC™ DLC, an impact technique of ultra-fine shot blasting method doped with Tin and Molybdenum Disulfide, a calcium based chemical dip containing calcium sulfate and nano fullerene, were used.DLC is well reported to reduce friction. So...

  6. Surface Modification of Orthodontic Bracket Models via Ion Implantation: Effect on Coefficients of Friction

    Science.gov (United States)

    1989-01-01

    was accomplished and tested against the four major orthodontic alloy groups, [stainless steel (S.S.), cobalt-chromium (Co-Cr), nickel-titanium ( NiTi ...premolar extraction case measured friction values as a bracket slid over an arch wire. To deliver a constant ligature force, a coil spring maintained...accomplished and tested against the four major orthodontic alloy groups, [stainless steel (S.S.), cobalt-chromium (Co-Cr), nickel-titanium ( NiTi

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

    Science.gov (United States)

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

    2013-03-06

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

  8. Test data on electrical contacts at high surface velocities and high current densities for homopolar generators

    International Nuclear Information System (INIS)

    Brennan, M.; Tolk, K.M.; Weldon, W.F.; Rylander, H.G.; Woodson, H.H.

    1977-01-01

    Test data is presented for one grade of copper graphite brush material, Morganite CMlS, over a wide range of surface velocities, atmospheres, and current densities that are expected for fast discharge (<100 ms) homopolar generators. The brushes were run on a copper coated 7075-T6 aluminum disk at surface speeds up to 277 m/sec. One electroplated copper and three flame sprayed copper coatings were used during the tests. Significant differences in contact voltage drops and surface mechanical properties of the copper coatings were observed

  9. Friction and Wear of Unlubricated NiTiHf with Nitriding Surface Treatments

    Science.gov (United States)

    Stanford, Malcolm K.

    2018-01-01

    The unlubricated friction and wear properties of the superelastic materials NiTi and NiTiHf, treated by either gas nitriding or plasma nitriding, have been investigated. Pin on disk testing of the studied materials was performed at sliding speeds from 0.01 to 1m/s at normal loads of 1, 5 or 10N. For all of the studied friction pairs (NiTiHf pins vs. NiTi and NiTiHf disks) over the given parameters, the steady-state coefficients of friction varied from 0.22 to 1.6. Pin wear factors ranged from approximately 1E-6 against the NiTiHf and plasma nitrided disks to approximately 1E-4 for the gas nitrided disks. The plasma nitrided disks provided wear protection in several cases and tended to wear by adhesion. The gas nitrided treatment generated the most pin wear but had essentially no disk wear except at the most severe of the studied conditions (1N load and 1m/s sliding speed). The results of this study are expected to provide guidance for design of components such as gears and fasteners.

  10. Wear Behavior of AZ31/Al2O3 Magnesium Matrix Surface Nanocomposite Fabricated via Friction Stir Processing

    Science.gov (United States)

    Azizieh, Mahdi; Larki, Arsham Norouzi; Tahmasebi, Mehdi; Bavi, Mehdi; Alizadeh, Ehsan; Kim, Hyoung Seop

    2018-03-01

    The aim of this study was to produce magnesium-based surface nanocomposites via friction stir processing and to investigate the effect of tool rotational speed on the microstructure, hardness and wear behavior. The surface of the nanocomposites was characterized using optical and scanning electron microscopes, as well as through microhardness and wear tests. The results indicated that with the increase in rotational speed, the grain size of the surface nanocomposites increased, but its hardness decreased despite the improved distribution of Al2O3 nanoparticles. It was also found that the wear resistance has a direct relation to the distribution of the Al2O3 nanoparticles. Furthermore, the addition of nano-Al2O3 changed the wear mechanism from the adhesive mode in the as-received AZ31 to the abrasive mode in the nanocomposite specimens. The rotational speed of 1400 rpm was an optimum parameter to achieve a suitable composite layer with the highest wear resistance.

  11. Velocity gradients in the Earth's upper mantle: insights from higher mode surface waves

    Science.gov (United States)

    Fishwick, Stewart; Maupin, Valerie; Afonso, Juan Carlos

    2016-04-01

    The majority of seismic tomographic models of the uppermost mantle beneath Precambrian regions show a positive velocity gradient from the Moho to depths of around 100 km. It is becoming increasingly well recognised that this gradient is not readily compatible with simple models of a craton with constant composition and a steady-state geotherm and more complex compositional variations are invoked to explain this feature. At these depths most of the models are dominated by data from fundamental mode surface waves, and the combination of the sensitivity kernels alongside the choice of model parameterisation means that the velocity gradient could be an artefact of the particular inversion. Indeed, recent work using thermodynamically consistent velocity models suggests that in some cases there is not a requirement of this style of gradient. We investigate this aspect of the mantle structure further by returning to the Sa phase. This phase can be considered as the build up of a wave packet due to the overlapping group velocities of higher modes at periods of around 8 - 30 s. Using the Australian shield as a test-case we compare waveforms built from three different styles of velocity model. Firstly, the 1D model AU3 (Gaherty & Jordan, 1995) which did incorporate the Sa phase as part of the waveform in their modelling. Secondly, recent tomographic models of the Australian continent are used, which include no a priori information from the phase. Thirdly, a thermodynamically consistent velocity model that fits the broad dispersion characteristics of the tomography is tested. Finally, these synthetic waveforms are compared to real data crossing the Australian shield. The results illustrate small, but clear, variations in waveform dependent on the velocity structure. Complicating factors in any analysis involve the importance of having good knowledge of the crustal structure and a very accurate source depth (particularly if this is similar to the average crustal thickness).

  12. EFFECTS OF A SAND RUNNING SURFACE ON THE KINEMATICS OF SPRINTING AT MAXIMUM VELOCITY

    Directory of Open Access Journals (Sweden)

    P E Alcaraz

    2011-05-01

    Full Text Available Performing sprints on a sand surface is a common training method for improving sprint-specific strength. For maximum specificity of training the athlete’s movement patterns during the training exercise should closely resemble those used when performing the sport. The aim of this study was to compare the kinematics of sprinting at maximum velocity on a dry sand surface to the kinematics of sprinting on an athletics track. Five men and five women participated in the study, and flying sprints over 30 m were recorded by video and digitized using biomechanical analysis software. We found that sprinting on a sand surface was substantially different to sprinting on an athletics track. When sprinting on sand the athletes tended to ‘sit’ during the ground contact phase of the stride. This action was characterized by a lower centre of mass, a greater forward lean in the trunk, and an incomplete extension of the hip joint at take-off. We conclude that sprinting on a dry sand surface may not be an appropriate method for training the maximum velocity phase in sprinting. Although this training method exerts a substantial overload on the athlete, as indicated by reductions in running velocity and stride length, it also induces detrimental changes to the athlete’s running technique which may transfer to competition sprinting.

  13. CONSTRAINING THE NFW POTENTIAL WITH OBSERVATIONS AND MODELING OF LOW SURFACE BRIGHTNESS GALAXY VELOCITY FIELDS

    International Nuclear Information System (INIS)

    Kuzio de Naray, Rachel; McGaugh, Stacy S.; Mihos, J. Christopher

    2009-01-01

    We model the Navarro-Frenk-White (NFW) potential to determine if, and under what conditions, the NFW halo appears consistent with the observed velocity fields of low surface brightness (LSB) galaxies. We present mock DensePak Integral Field Unit (IFU) velocity fields and rotation curves of axisymmetric and nonaxisymmetric potentials that are well matched to the spatial resolution and velocity range of our sample galaxies. We find that the DensePak IFU can accurately reconstruct the velocity field produced by an axisymmetric NFW potential and that a tilted-ring fitting program can successfully recover the corresponding NFW rotation curve. We also find that nonaxisymmetric potentials with fixed axis ratios change only the normalization of the mock velocity fields and rotation curves and not their shape. The shape of the modeled NFW rotation curves does not reproduce the data: these potentials are unable to simultaneously bring the mock data at both small and large radii into agreement with observations. Indeed, to match the slow rise of LSB galaxy rotation curves, a specific viewing angle of the nonaxisymmetric potential is required. For each of the simulated LSB galaxies, the observer's line of sight must be along the minor axis of the potential, an arrangement that is inconsistent with a random distribution of halo orientations on the sky.

  14. Flow of nanofluid by nonlinear stretching velocity

    Science.gov (United States)

    Hayat, Tasawar; Rashid, Madiha; Alsaedi, Ahmed; Ahmad, Bashir

    2018-03-01

    Main objective in this article is to model and analyze the nanofluid flow induced by curved surface with nonlinear stretching velocity. Nanofluid comprises water and silver. Governing problem is solved by using homotopy analysis method (HAM). Induced magnetic field for low magnetic Reynolds number is not entertained. Development of convergent series solutions for velocity and skin friction coefficient is successfully made. Pressure in the boundary layer flow by curved stretching surface cannot be ignored. It is found that magnitude of power-law index parameter increases for pressure distibutions. Magnitude of radius of curvature reduces for pressure field while opposite trend can be observed for velocity.

  15. Use of Textured Surfaces to Mitigate Sliding Friction and Wear of Lubricated and Non-Lubricated Contacts

    Energy Technology Data Exchange (ETDEWEB)

    Blau, Peter Julian [ORNL

    2012-03-01

    If properly employed, the placement of three-dimensional feature patterns, also referred to as textures, on relatively-moving, load-bearing surfaces can be beneficial to their friction and wear characteristics. For example, geometric patterns can function as lubricant supply channels or depressions in which to trap debris. They can also alter lubricant flow in a manner that produces thicker load-bearing films locally. Considering the area occupied by solid areas and spaces, textures also change the load distribution on surfaces. At least ten different attributes of textures can be specified, and their combinations offer wide latitude in surface engineering. By employing directional machining and grinding procedures, texturing has been used on bearings and seals for well over a half century, and the size scales of texturing vary widely. This report summarizes past work on the texturing of load-bearing surfaces, including past research on laser surface dimpling of ceramics done at ORNL. Textured surfaces generally show most pronounced effects when they are used in conformal or nearly conformal contacts, like that in face seals. Combining textures with other forms of surface modification and lubrication methods can offer additional benefits in surface engineering for tribology. As the literature and past work at ORNL shows, texturing does not always provide benefits. Rather, the selected pattern and arrangement of features must be matched to characteristics of the proposed application, bearing materials, and lubricants.

  16. Bio-inspired low frictional surfaces having micro-dimple arrays prepared with honeycomb patterned porous films as wet etching masks.

    Science.gov (United States)

    Saito, Y; Yabu, H

    2015-01-27

    Some kinds of snakes have micro-dimple arrays on their skins and show low frictional properties. Cost-effective and simple preparation methods of surfaces having micro-dimple arrays without burrs have been required. In this study, micro-dimple arrays were successfully prepared on aluminum plates and pipes by using honeycomb patterned porous films as wet etching masks. Resulting surfaces having 5 and 8 μm dimple diameters show low frictional coefficients compared with polished surfaces at a fluid lubrication regime.

  17. Simulations of atomic-scale sliding friction

    DEFF Research Database (Denmark)

    Sørensen, Mads Reinholdt; Jacobsen, Karsten Wedel; Stoltze, Per

    1996-01-01

    Simulation studies of atomic-scale sliding friction have been performed for a number of tip-surface and surface-surface contacts consisting of copper atoms. Both geometrically very simple tip-surface structures and more realistic interface necks formed by simulated annealing have been studied....... Kinetic friction is observed to be caused by atomic-scale Stick and slip which occurs by nucleation and subsequent motion of dislocations preferably between close-packed {111} planes. Stick and slip seems ro occur in different situations. For single crystalline contacts without grain boundaries...... at the interface the stick and slip process is clearly observed for a large number of contact areas, normal loads, and sliding velocities. If the tip and substrate crystal orientations are different so that a mismatch exists in the interface, the stick and slip process is more fragile. It is then caused by local...

  18. Nanoscale processes on insulating surfaces

    National Research Council Canada - National Science Library

    Gnecco, Enrico; Szymoński, Marek

    2009-01-01

    ... the group of Prof. Ernst Meyer in Basel, where he investigated friction processes on alkali halide surfaces in ultra high vacuum (UHV). The main result was the observation of a logarithmic velocity dependence of atomic friction, which was interpreted within a combination of the classical Tomlinson and Eyring models. After his Ph.D. he joined the ...

  19. Impact of Assimilating Surface Velocity Observations on the Model Sea Surface Height Using the NCOM-4DVAR

    Science.gov (United States)

    2016-09-26

    surface velocity observations available in 15-min intervals for each drifter. The observations are given an error standard deviation value of 0.02m s21... Standard Form 298 (Rev. 8/98) REPORT DOCUMENTATION PAGE Prescribed by ANSI Std. Z39.18 Form Approved OMB No. 0704-0188 The public reporting... statistical analysis is done by not only examining the SSH forecast error across the entire do- main, but also by concentrating on the areamost densely covered

  20. Remote measurement of surface-water velocity using infrared videography and PIV: a proof-of-concept for Alaskan rivers

    Science.gov (United States)

    Kinzel, Paul J.; Legleiter, Carl; Nelson, Jonathan M.; Conaway, Jeffrey S.

    2017-01-01

    Thermal cameras with high sensitivity to medium and long wavelengths can resolve features at the surface of flowing water arising from turbulent mixing. Images acquired by these cameras can be processed with particle image velocimetry (PIV) to compute surface velocities based on the displacement of thermal features as they advect with the flow. We conducted a series of field measurements to test this methodology for remote sensing of surface velocities in rivers. We positioned an infrared video camera at multiple stations across bridges that spanned five rivers in Alaska. Simultaneous non-contact measurements of surface velocity were collected with a radar gun. In situ velocity profiles were collected with Acoustic Doppler Current Profilers (ADCP). Infrared image time series were collected at a frequency of 10Hz for a one-minute duration at a number of stations spaced across each bridge. Commercial PIV software used a cross-correlation algorithm to calculate pixel displacements between successive frames, which were then scaled to produce surface velocities. A blanking distance below the ADCP prevents a direct measurement of the surface velocity. However, we estimated surface velocity from the ADCP measurements using a program that normalizes each ADCP transect and combines those normalized transects to compute a mean measurement profile. The program can fit a power law to the profile and in so doing provides a velocity index, the ratio between the depth-averaged and surface velocity. For the rivers in this study, the velocity index ranged from 0.82 – 0.92. Average radar and extrapolated ADCP surface velocities were in good agreement with average infrared PIV calculations.

  1. Isotopic study of the wear of sliding bearings with plastic friction surface

    International Nuclear Information System (INIS)

    Pandur, J.; Varkonyi, A.

    1978-01-01

    A new complex device has been elaborated for the investigation of the duration of bearings in the Institute of Isotopes of the Hungarian Academy of Sciences. The simultaneous determination of wear by an isotopic method the coefficient of friction by means of a Wheatstone bridge and the bearing temperature by means of a thermoresistor is described. Dynamic loading and variable revolution per minute are applied to produce a forced wear of the bearings. The isotopically labelled wear products are removed by oil and the collected sample is measured by a scintillation detector. Wear of a steel axle in plastic housing and plastic coated axle in cast iron housing was determined. (V.N.)

  2. Quantum Friction in Different Regimes

    Science.gov (United States)

    Klatt, Juliane; Buhmann, Stefan

    2015-03-01

    Quantum friction is the velocity-dependent force between two polarizable objects in relative motion, resulting from field-fluctuation mediated transfer of energy and momentum between them. Due to its short-ranged nature it has proven difficult to observe experimentally. Theoretical attempts to determine the precise velocity-dependence of the quantum drag experienced by a polarizable atom moving parallel to a surface arrive at contradicting results. Scheel and Barton predict a force linear in relative velocity v - the former using the quantum regression theorem and the latter employing time-dependent perturbation theory. Intravaia, however, predicts a v3 power-law starting from a non-equilibrium fluctuation-dissipation theorem. In order to learn where exactly the above approaches part, we set out to perform all three calculations within one and the same framework: macroscopic QED. In addition, we include contributions to quantum friction from Doppler shift and Röntgen interaction, which play a role for perpendicular motion and retarded distances, respectively, and consider non-stationary states of atom and field. DFG Emmy-Noether Program.

  3. Subnanometer Resolution and Enhanced Friction Contrast at the Surface of Perylene Diimide PDI8-CN2 Thin Films in Ambient Conditions.

    Science.gov (United States)

    Buzio, Renato; Gerbi, Andrea; Barra, Mario; Chiarella, Fabio; Gnecco, Enrico; Cassinese, Antonio

    2018-03-13

    We report high-resolution surface morphology and friction force maps of polycrystalline organic thin films derived by deposition of the n-type perylene diimide semiconductor PDI8-CN 2 . We show that the in-plane molecular arrangement into ordered, cofacial slip-stacked rows results in a largely anisotropic surface structure, with a characteristic sawtooth corrugation of a few Ångstroms wavelength and height. Load-controlled experiments reveal different types of friction contrast between the alternating sloped and stepped regions, with transitions from atomic-scale dissipative stick-slip to smooth sliding with ultralow friction within the surface unit cell. Notably, such a rich phenomenology is captured under ambient conditions. We demonstrate that friction contrast is well reproduced by numerical simulations assuming a reduced corrugation of the tip-molecule potential nearby the step edges. We propose that the side alkyl chains pack into a compact low-surface-energy overlayer, and friction modulation reflects periodic heterogeneity of chains bending properties and subsurface anchoring to the perylene cores.

  4. 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

  5. The boundary condition for vertical velocity and its interdependence with surface gas exchange

    Directory of Open Access Journals (Sweden)

    A. S. Kowalski

    2017-07-01

    Full Text Available The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E/ρ. This is true even right down at the surface where the boundary condition is w|0 = E/ρ|0 (where w|0 and ρ|0 represent the vertical velocity and density of air at the surface. This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, for example but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux–gradient relationships (eddy diffusivities requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube – with vapour transport into an overlying, horizontal airstream – was described long ago in classical mechanics and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterisations of ecosystem and plant functioning.

  6. The boundary condition for vertical velocity and its interdependence with surface gas exchange

    Science.gov (United States)

    Kowalski, Andrew S.

    2017-07-01

    The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w) in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E) and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E/ρ. This is true even right down at the surface where the boundary condition is w|0 = E/ρ|0 (where w|0 and ρ|0 represent the vertical velocity and density of air at the surface). This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, for example) but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux-gradient relationships (eddy diffusivities) requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube - with vapour transport into an overlying, horizontal airstream - was described long ago in classical mechanics and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterisations of ecosystem and plant functioning.

  7. Improved measurements of mean sea surface velocity in the Nordic Seas from synthetic aperture radar

    Science.gov (United States)

    Wergeland Hansen, Morten; Johnsen, Harald; Engen, Geir; Øie Nilsen, Jan Even

    2017-04-01

    The warm and saline surface Atlantic Water (AW) flowing into the Nordic Seas across the Greenland-Scotland ridge transports heat into the Arctic, maintaining the ice-free oceans and regulating sea-ice extent. The AW influences the region's relatively mild climate and is the northern branch of the global thermohaline overturning circulation. Heat loss in the Norwegian Sea is key for both heat transport and deep water formation. In general, the ocean currents in the Nordic Seas and the North Atlantic Ocean is a complex system of topographically steered barotropic and baroclinic currents of which the wind stress and its variability is a driver of major importance. The synthetic aperture radar (SAR) Doppler centroid shift has been demonstrated to contain geophysical information about sea surface wind, waves and current at an accuracy of 5 Hz and pixel spacing of 3.5 - 9 × 8 km2. This corresponds to a horizontal surface velocity of about 20 cm/s at 35° incidence angle. The ESA Prodex ISAR project aims to implement new and improved SAR Doppler shift processing routines to enable reprocessing of the wide swath acquisitions available from the Envisat ASAR archive (2002-2012) at higher resolution and better accuracy than previously obtained, allowing combined use with Sentinel-1 and Radarsat-2 retrievals to build timeseries of the sea surface velocity in the Nordic Seas. Estimation of the geophysical Doppler shift from new SAR Doppler centroid shift retrievals will be demonstrated, addressing key issues relating to geometric (satellite orbit and attitude) and electronic (antenna mis-pointing) contributions and corrections. Geophysical Doppler shift retrievals from one month of data in January 2010 and the inverted surface velocity in the Nordic Seas are then addressed and compared to other direct and indirect estimates of the upper ocean current, in particular those obtained in the ESA GlobCurrent project.

  8. Pitting corrosion resistance and bond strength of stainless steel overlay by friction surfacing on high strength low alloy steel

    OpenAIRE

    Amit Kumar Singh; G. Madhusudhan Reddy; K. Srinivas Rao

    2015-01-01

    Surface modification is essential for improving the service properties of components. Cladding is one of the most widely employed methods of surface modification. Friction surfacing is a candidate process for depositing the corrosion resistant coatings. Being a solid state process, it offers several advantages over conventional fusion based surfacing process. The aim of this work is to identify the relationship between the input variables and the process response and develop the predictive mo...

  9. Near-surface shear-wave velocity measurements in unlithified sediment

    Science.gov (United States)

    Richards, B.T.; Steeples, D.; Miller, R.; Ivanov, J.; Peterie, S.; Sloan, S.D.; McKenna, J.R.

    2011-01-01

    S-wave velocity can be directly correlated to material stiffness and lithology making it a valuable physical property that has found uses in construction, engineering, and environmental projects. This study compares different methods for measuring S-wave velocities, investigating and identifying the differences among the methods' results, and prioritizing the different methods for optimal S-wave use at the U. S. Army's Yuma Proving Grounds YPG. Multichannel Analysis of Surface Waves MASW and S-wave tomography were used to generate S-wave velocity profiles. Each method has advantages and disadvantages. A strong signal-to-noise ratio at the study site gives the MASW method promising resolution. S-wave first arrivals are picked on impulsive sledgehammer data which were then used for the tomography process. Three-component downhole seismic data were collected in-line with a locking geophone, providing ground truth to compare the data and to draw conclusions about the validity of each data set. Results from these S-wave measurement techniques are compared with borehole seismic data and with lithology data from continuous samples to help ascertain the accuracy, and therefore applicability, of each method. This study helps to select the best methods for obtaining S-wave velocities for media much like those found in unconsolidated sediments at YPG. ?? 2011 Society of Exploration Geophysicists.

  10. Effect of Tip Shape of Frictional Stir Burnishing Tool on Processed Layer’s Hardness, Residual Stress and Surface Roughness

    Directory of Open Access Journals (Sweden)

    Yoshimasa Takada

    2018-01-01

    Full Text Available Friction stir burnishing (FSB is a surface-enhancement method used after machining, without the need for an additional device. The FSB process is applied on a machine that uses rotation tools (e.g., machining center or multi-tasking machine. Therefore, the FSB process can be applied immediately after the cutting process using the same machine tool. Here, we apply the FSB to the shaft materials of 0.45% C steel using a multi-tasking machine. In the FSB process, the burnishing tool rotates at a high-revolution speed. The thin surface layer is rubbed and stirred as the temperature is increased and decreased. With the FSB process, high hardness or compressive residual stress can be obtained on the surface layer. However, when we applied the FSB process using a 3 mm diameter sphere tip shape tool, the surface roughness increased substantially (Ra = 20 µm. We therefore used four types of tip shape tools to examine the effect of burnishing tool tip radius on surface roughness, hardness, residual stress in the FSB process. Results indicated that the surface roughness was lowest (Ra = 10 µm when the tip radius tool diameter was large (30 mm.

  11. The Role of Friction Stir Processing (FSP Parameters on TiC Reinforced Surface Al7075-T651 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Felipe García-Vázquez

    Full Text Available Abstract: Aluminum alloys are very promising for structural applications in aerospace, military and transportation industries due to their light weight, high strength-to-weight ratio and excellent resistance to corrosion. In comparison to unreinforced aluminum alloys, aluminum/aluminum alloy matrix composites reinforced with ceramic phases exhibit higher strength and hardness, improved tribological characteristics. A novel surface modifying technique, friction stir processing (FSP, has been developed for fabrication of surface composite with an improved performance. The effect of FSP parameters such as number of passes, direction of each pass, sealed or unsealed groove on microstructure was investigated. In this work, nano-particles of TiC (2% in weight were added to aluminum alloy AA7075-T651 to produce a functional surface. Fixed parameters for this AA7075 alloy were used; rotation speed of 1000 rpm, travel speed of 300 mm/min and pin penetration of 2.8 mm. Optical microscopy (OM, scanning electron microscopy (SEM and atomic force microscopy (AFM were employed to study the microstructure of the fabricated surface composites. The results indicated that the selected FSP parameters influenced the area of surface composite, distribution of TiC particles and micro-hardness of the surface composites. Finally, in order to evaluate rate wear the pin on disk test was carried out.

  12. Microstructural Characterization and Wear Behavior of Nano-Boride Dispersed Coating on AISI 304 Stainless Steel by Hybrid High Velocity Oxy-Fuel Spraying Laser Surface Melting

    Science.gov (United States)

    Sharma, Prashant; Majumdar, Jyotsna Dutta

    2015-07-01

    The current study concerns the detailed microstructural characterization and investigation of wear behavior of nano-boride dispersed coating developed on AISI 304 stainless steel by high velocity oxy-fuel spray deposition of nickel-based alloy and subsequent laser melting. There is a significant refinement and homogenization of microstructure with improvement in microhardness due to laser surface melting (1200 VHN as compared to 945 VHN of as-sprayed and 250 VHN of as-received substrate). The high temperature phase stability of the as-coated and laser melted surface has been studied by differential scanning calorimeter followed by detailed phase analysis at room and elevated temperature. There is a significant improvement in wear resistance of laser melted surface as compared to as-sprayed and the as-received one due to increased hardness and reduced coefficient of friction. The mechanism of wear has been investigated in details. Corrosion resistance of the coating in a 3.56 wt pct NaCl solution is significantly improved (4.43 E-2 mm/year as compared to 5 E-1 mm/year of as-sprayed and 1.66 mm/year of as-received substrate) due to laser surface melting as compared to as-sprayed surface.

  13. Fabrication of AZ31/MWCNTs Surface Metal Matrix Composites by Friction Stir Processing: Investigation of Microstructure and Mechanical Properties

    Science.gov (United States)

    Arab, Seyed Mohammad; Zebarjad, Seyed Mojtaba; Jahromi, Seyed Ahmad Jenabali

    2017-11-01

    The surface metal matrix composites of AZ31 Mg alloy reinforced with multiwall carbon nanotubes (MWCNTs) have been fabricated through the friction stir processing by a conventional and two stepped tools. The microstructure and mechanical properties of fabricated composites were studied by optical and electron microscopy, microhardness and tensile tests, respectively. The processing has developed a fine-grain structure along with good distribution of reinforcements. The hardness and tensile strength of fabricated MWCNT/AZ31 composites are generally higher than as-received and FSPed samples. The accumulative effect of grain refinement and reinforcing nanotubes is assumed to be the reason for increasing the ductility after friction stir processing. The hardness is nearly doubled for FSPed samples and some more for nanocomposites compared with the as-received sample. The elongation of nanocomposites is about two times greater than that of the as-rolled sample. The speed ratio, pass number and CNT amount are three important factors influencing the resulting microstructure and mechanical properties. The stepped tools also give a more uniform distribution of reinforcement and higher grain refinement.

  14. Measurement of surface recombination velocity for silicon solar cells using a scanning electron microscope with pulsed beam

    Science.gov (United States)

    Daud, T.; Cheng, L. J.

    1981-01-01

    The role of surface recombination velocity in the design and fabrication of silicon solar cells is discussed. A scanning electron microscope with pulsed electron beam was used to measure this parameter of silicon surfaces. It is shown that the surface recombination velocity, s, increases by an order of magnitude when an etched surface degrades, probably as a result of environmental reaction. A textured front-surface-field cell with a high-low junction near the surface shows the effect of minority carrier reflection and an apparent reduction of s, whereas a tandem-junction cell shows an increasing s value. Electric fields at junction interfaces in front-surface-field and tandem-junction cells acting as minority carrier reflectors or sinks tend to alter the value of effective surface recombination velocity for different beam penetration depths. A range of values of s was calculated for different surfaces.

  15. Burning velocity and flame surface area in high Karlovitz number flames

    Science.gov (United States)

    Lapointe, Simon; Cheng, Lionel; Blanquart, Guillaume

    2017-11-01

    Accurate knowledge of the burning velocity of turbulent flames is of importance for many combustion devices. For low Karlovitz number flames, Damkohler proposed that the ratio of turbulent to laminar flame speed is proportional to the ratio of turbulent to laminar flame surface area. In recent DNS studies, it has been observed that Damkolher's scaling for low Karlovitz number flames still holds for high Karlovitz number flames. However, recent experimental studies have reported notable differences between global burning velocities and flame surface area measurements. In this work, the numerical and experimental results are further analyzed to explain the apparent contradiction. Emphasis is placed on identifying and quantifying potential experimental limitations at high Karlovitz numbers. More specifically, experimental flame surface measurements typically use binarized PLIF images. These images are two-dimensional and their resolution is limited by that of the PLIF system. The implications of using a two-dimensional iso-contour and the effects of the image resolution are assessed through post-processing of DNS datasets. Furthermore, the effects of integral length scale, Karlovitz number, and differential diffusion on the flame surface area are considered separately.

  16. Fabrication of Al5083 surface composites reinforced by CNTs and cerium oxide nano particles via friction stir processing

    Energy Technology Data Exchange (ETDEWEB)

    Hosseini, S.A. [Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz (Iran, Islamic Republic of); Ranjbar, Khalil, E-mail: k_ranjbar@scu.ac.ir [Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz (Iran, Islamic Republic of); Dehmolaei, R. [Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz (Iran, Islamic Republic of); Amirani, A.R. [12th Ghaem Street, Bld. Hashemzadeh, Shahrak Golestan, Tehran (Iran, Islamic Republic of)

    2015-02-15

    Highlights: • Using friction stir processing, an effect of CNTs and CeO{sub 2} reinforcements on mechanical and corrosion properties of Al5083 alloy is reported. • The strength of Al5083 was increased by 42%, its matrix grain size reduced five times, and hardness was doubled by the incorporation of CNTs-CeO{sub 2} mixture in the volume ratio of 75-25 respectively. • Unlike the CNTs, incorporation of nanosized CeO{sub 2} particles resulted in remarkable increase in pitting resistance of the alloy. - Abstract: In the present investigation, friction stir processing (FSP) was utilized to incorporate Multi Walled Carbon Nano Tubes (MWCNT) and nanosized cerium oxide particles into the matrix of Al5083 alloy to form surface reinforced composites. The effect of these nanosized reinforcements either separately or in the combined form, on microstructural modification, mechanical properties and corrosion resistance of FSPed Al5083 surface composites was studied. A threaded cylindrical hardened steel tool was used with the rotation speeds of 600 and 800 rpm and travel speeds of 35 and 45 mm/min and a tilt angle of 5°. Mechanical properties and corrosion resistance of FSPed samples were evaluated and compared with the base alloy. The maximum tensile strength and hardness value were achieved for the hybrid composite containing a mixture of CNTs and cerium oxide in the volume ratio of 75-25, respectively, whereas a significant increase in pitting resistance of the base alloy was obtained when cerium oxide alone was incorporated. The corrosion behavior of the samples was investigated by potentiodynamic polarization tests and assessed in term of pitting potential and passivation range. Microstructural analysis carried out by using optical and electron microscopes showed that reinforcements are well dispersed inside the nugget zone (NZ), and remarkable grain refinement is gained. The study was aimed to fabricate surface composites with improved mechanical properties and

  17. Northern Korean Peninsula 1-D velocity model from surface wave dispersion and full-waveform data

    Science.gov (United States)

    Lee, S. J.; Rhie, J.; Kim, S.; Kang, T. S.; Cho, C.

    2016-12-01

    Monitoring seismic activities in the northern Korean Peninsula is important not only for understanding the characteristics of earthquakes but also for watching nuclear tests. To better monitor those natural and man-made seismic activities, reliable seismic velocity models are required. However, the seismic velocity structure of the region is not known well due to the lack of available seismic data directly measured in the region. This study presents 1-D velocity models of the region using two different datasets comprised of two-year-long continuous waveform and the 2013 North Korea nuclear test event waveform recorded at stations surrounding the region. Two reference 1-D models for the inland and offshore areas (Western East Sea) were estimated by 1-D inversion of surface wave dispersion measurements from ambient noise cross-correlations of the continuous waveform. To investigate the variations in the velocity models, many 1-D models for the paths between the 2013 nuclear test site and stations in China and South Korea were constructed by forward waveform modeling. The velocity variations are not significant for both models representing the inland and offshore paths, respectively. The 1-D models for the inland paths are similar to the models constructed for the southern Korean Peninsula. Interestingly, waveforms sampling through the offshore paths are not well explained by simple 1-D isotropic models. The preliminary result indicates that there exists radial anisotropy with SH being faster than SV by 3-5% in the upper mantle beneath the offshore northern Korean Peninsula, although further studies are necessary to explain the origin of anisotropy. A proper characterization of propagation effects along the offshore paths would be useful for monitoring future nuclear tests because many seismic stations in the eastern South Korea record waveforms sampling the offshore region from the nuclear test site to those stations.

  18. Friction Testing of Thermoplastic Composites

    NARCIS (Netherlands)

    Sachs, Ulrich; Haanappel, Sebastiaan; Rietman, Bert; Akkerman, Remko; Erath, Mark A.

    2011-01-01

    Friction phenomena play a major role in thermoplastic composite forming processes. In order to make use of the large potential these materials have, accurate CAE tools are needed that as a consequence incorporate temperature, pressure and velocity dependent friction behavior. To obtain a sound

  19. Frictional properties of silicic to calcareous ooze on the Cocos Plate entering the Costa Rica Subduction Zone

    Science.gov (United States)

    Tsutsumi, A.; Kameda, J.; Ujiie, K.

    2012-12-01

    Here we report experimental results on the frictional properties of the cover sediments on the Cocos plate incoming into the erosive Costa Rica subduction zone. Mechanical properties of the incoming sediments to subduction plate boundaries are essential to constrain subduction-related faulting processes. However, knowledge of the frictional properties of sediments composed of abundant biogenic component, such as spicules, diatoms, and radiolarians are limited. Experimental samples were silicic to calcareous ooze collected at a reference site (Site U1381) off shore Osa Peninsula during IODP Expedition 334 (Vannucchi et al., 2012). To be used in the experiments, the discrete samples was disaggregated, oven dried at 60 degrees centigrade for 24 hours. The experimental fault is composed of a 24.9 mm diameter cylinder of gabbro cut perpendicularly to the cylinder axis in two halves that are ground to obtain rough wall surfaces, and re-assembled with an intervening thin layer (~1.0 mm) disaggregated sample. Frictional experiments have been performed using a rotary-shear friction testing machine, at normal stresses up to 5 MPa, over a range of slip velocities from 0.0026 mm/s to 1.3 m/s, with more than ~150 mm of displacements for water saturated condition. Experimental results reveal that friction values at slow slip velocities (v ~30 mm/s), steady state friction decreases dramatically. For example, at a velocity of 260 mm/s, the friction coefficient for samples U1381A-9R and -10R show a gradual decrease with a large weakening displacement toward the establishment of a nearly constant level of friction at ~0.1. The velocity weakening behavior at slow velocities could provide a condition to initiate unstable fault motion at shallow depths along the subduction channel if the input sediments are incorporated into faulting. On the contrary, neutral to velocity strengthening behavior observed for intermediate velocities could stabilize the propagation process of earthquake

  20. Regional velocity structure in northern California from inversion of scattered seismic surface waves

    Science.gov (United States)

    Pollitz, Fred F.

    1999-07-01

    Seismic surface waves recorded by the Berkeley Digital Seismic Network have been analyzed in order to constrain three-dimensional lateral heterogeneity of the upper mantle under northern California. A total of 2164 seismograms from 173 teleseismic events were windowed for the fundamental mode Rayleigh wave, followed by estimation of complex amplitude spectra over the period range 16 to 100 s using a multiple-taper method. Since Rayleigh waves at shorter periods, particularly below 35 s, suffer from serious multipathing or "non-plane" wave arrivals, these amplitude spectra have been interpreted as the product of wavefront distortion along the teleseismic propagation path and seismic structure beneath the network. The amplitude spectra are first modeled in terms of non-plane incoming wavefields and structural phase velocity perturbations period by period. After corrections for Moho and surface topography, the phase velocity maps are inverted for three-dimensional shear velocity perturbations δνs down to a depth of 200 km. The δνs maps are in good agreement with the results of body studies over a broad spatial scale. The dominant signals are associated with the thermal effects of the active Gorda and fossil Farallon subducted slab stretching from Mount Shasta through the western Sierran foothills to the southern Great Valley and asthenospheric upwelling beneath the northern Coast Ranges. The southern Sierra Nevada Range is characterized by fast δνs down to ˜50 km and slow velocities between ˜60 and 120 km depth, in agreement with independent inferences of a cold crust and warm upper mantle, which may provide the buoyancy forces necessary to support the elevation of the range.

  1. Inversion of Surface Wave Phase Velocities for Radial Anisotropy to an Depth of 1200 km

    Science.gov (United States)

    Xing, Z.; Beghein, C.; Yuan, K.

    2012-12-01

    This study aims to evaluate three dimensional radial anisotropy to an depth of 1200 km. Radial anisotropy describes the difference in velocity between horizontally polarized Rayleigh waves and vertically polarized Love waves. Its presence in the uppermost 200 km mantle has well been documented by different groups, and has been regarded as an indicator of mantle convection which aligns the intrinsically anisotropic minerals, largely olivine, to form large scale anisotropy. However, there is no global agreement on whether anisotropy exists in the region below 200 km. Recent models also associate a fast vertically polarized shear wave with vertical upwelling mantle flow. The data used in this study is the globally isotropic phase velocity models of fundamental and higher mode Love and Rayleigh waves (Visser, 2008). The inclusion of higher mode surface wave phase velocity provides sensitivities to structure at depth that extends to below the transition zone. While the data is the same as used by Visser (2008), a quite different parameterization is applied. All the six parameters - five elastic parameters A, C, F, L, N and density - are now regarded as independent, which rules out possible biased conclusions induced by scaling relation method used in several previous studies to reduce the number of parameters partly due to limited computing resources. The data need to be modified by crustal corrections (Crust2.0) as we want to look at the mantle structure only. We do this by eliminating the perturbation in surface wave phase velocity caused by the difference in crustal structure with respect to the referent model PREM. Sambridge's Neighborhood Algorithm is used to search the parameter space. The introduction of such a direct search technique pales the traditional inversion method, which requires regularization or some unnecessary priori restriction on the model space. On the contrary, the new method will search the full model space, providing probability density

  2. The influence of surface on the running velocities of elite and amateur orienteer athletes.

    Science.gov (United States)

    Hébert-Losier, K; Jensen, K; Mourot, L; Holmberg, H-C

    2014-12-01

    We compared the reduction in running velocities from road to off-road terrain in eight elite and eight amateur male orienteer athletes to investigate whether this factor differentiates elite from amateur athletes. On two separate days, each subject ran three 2-km time trials and three 20-m sprints "all-out" on a road, on a path, and in a forest. On a third day, the running economy and maximal aerobic power of individuals were assessed on a treadmill. The elite orienteer ran faster than the amateur on all three surfaces and at both distances, in line with their better running economy and aerobic power. In the forest, the elites ran at a slightly higher percentage of their 2-km (∼3%) and 20-m (∼4%) road velocities. Although these differences did not exhibit traditional statistical significance, magnitude-based inferences suggested likely meaningful differences, particularly during 20-m sprinting. Of course, cognitive, mental, and physical attributes other than the ability to run on different surfaces are required for excellence in orienteering (e.g., a high aerobic power). However, we suggest that athlete-specific assessment of running performance on various surfaces and distances might assist in tailoring training and identifying individual strengths and/or weaknesses in an orienteer. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  3. Effects of surface friction treatment on the in vitro release of constituent metals from the biomedical Co–29Cr–6Mo–0.16N alloy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaoyu [Graduate School of Engineering, Tohoku University, Sendai 980-8577 (Japan); Li, Yunping, E-mail: lyping@csu.edu.cn [State Key Lab for Powder Metallurgy, Central South University, Changsha 410083 (China); School of Materials Science and Engineering, Central South University, Changsha (China); Hou, Yuhang [Graduate School of Engineering, Tohoku University, Sendai 980-8577 (Japan); Bian, Huakang; Koizumi, Yuichiro; Chiba, Akihiko [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

    2016-07-01

    Due to the ignorance by many researchers on the influence of starting microstructure on the metal release of biomedical materials in human body after implant, in this study, the effect of surface friction treatment on the in vitro release of the constituent elements of the biomedical Co–29Cr–6Mo–0.16N (CCM) alloy is investigated for the first time by immersion test in lactic acid solution combined with electron backscatter diffraction, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP-EOS). The results indicate that friction treatment on the as-annealed CCM alloy sample surface leads to a planar strain-induced martensitic transformation (SIMT) on sample surface; this greatly accelerates the release of all the constituent elements and, in particular, that of Co as indicated by the ICP-EOS analysis. This increase can be ascribed to a localized deformation that occurred over the entire sample surface, with the dislocation density being high within the SIMTed phase and low in the alloy matrix. - Highlights: • Immersion test of biomedical CCM alloy in lactic acid solution was conducted. • Surface friction on CCM alloy leads to martensitic transformation. • The friction treatment accelerated the release of all the elements especially Co. • Localized deformation accounts for the accelerated release of elements.

  4. Calculation of acoustic field based on laser-measured vibration velocities on ultrasonic transducer surface

    Science.gov (United States)

    Hu, Liang; Zhao, Nannan; Gao, Zhijian; Mao, Kai; Chen, Wenyu; Fu, Xin

    2018-05-01

    Determination of the distribution of a generated acoustic field is valuable for studying ultrasonic transducers, including providing the guidance for transducer design and the basis for analyzing their performance, etc. A method calculating the acoustic field based on laser-measured vibration velocities on the ultrasonic transducer surface is proposed in this paper. Without knowing the inner structure of the transducer, the acoustic field outside it can be calculated by solving the governing partial differential equation (PDE) of the field based on the specified boundary conditions (BCs). In our study, the BC on the transducer surface, i.e. the distribution of the vibration velocity on the surface, is accurately determined by laser scanning measurement of discrete points and follows a data fitting computation. In addition, to ensure the calculation accuracy for the whole field even in an inhomogeneous medium, a finite element method is used to solve the governing PDE based on the mixed BCs, including the discretely measured velocity data and other specified BCs. The method is firstly validated on numerical piezoelectric transducer models. The acoustic pressure distributions generated by a transducer operating in an homogeneous and inhomogeneous medium, respectively, are both calculated by the proposed method and compared with the results from other existing methods. Then, the method is further experimentally validated with two actual ultrasonic transducers used for flow measurement in our lab. The amplitude change of the output voltage signal from the receiver transducer due to changing the relative position of the two transducers is calculated by the proposed method and compared with the experimental data. This method can also provide the basis for complex multi-physical coupling computations where the effect of the acoustic field should be taken into account.

  5. Sensitivities of surface wave velocities to the medium parameters in a radially anisotropic spherical Earth and inversion strategies

    Directory of Open Access Journals (Sweden)

    Sankar N. Bhattacharya

    2015-11-01

    Full Text Available Sensitivity kernels or partial derivatives of phase velocity (c and group velocity (U with respect to medium parameters are useful to interpret a given set of observed surface wave velocity data. In addition to phase velocities, group velocities are also being observed to find the radial anisotropy of the crust and mantle. However, sensitivities of group velocity for a radially anisotropic Earth have rarely been studied. Here we show sensitivities of group velocity along with those of phase velocity to the medium parameters VSV, VSH , VPV, VPH , h and density in a radially anisotropic spherical Earth. The peak sensitivities for U are generally twice of those for c; thus U is more efficient than c to explore anisotropic nature of the medium. Love waves mainly depends on VSH while Rayleigh waves is nearly independent of VSH . The sensitivities show that there are trade-offs among these parameters during inversion and there is a need to reduce the number of parameters to be evaluated independently. It is suggested to use a nonlinear inversion jointly for Rayleigh and Love waves; in such a nonlinear inversion best solutions are obtained among the model parameters within prescribed limits for each parameter. We first choose VSH, VSV and VPH within their corresponding limits; VPV and h can be evaluated from empirical relations among the parameters. The density has small effect on surface wave velocities and it can be considered from other studies or from empirical relation of density to average P-wave velocity.

  6. Viscosity, granular-temperature, and stress calculations for shearing assemblies of inelastic, frictional disks

    International Nuclear Information System (INIS)

    Walton, O.R.; Braun, R.L.

    1986-01-01

    Employing nonequilibrium molecular-dynamics methods the effects of two energy loss mechanisms on viscosity, stress, and granular-temperature in assemblies of nearly rigid, inelastic frictional disks undergoing steady-state shearing are calculated. Energy introduced into the system through forced shearing is dissipated by inelastic normal forces or through frictional sliding during collisions resulting in a natural steady-state kinetic energy density (granular-temperature) that depends on the density and shear rate of the assembly and on the friction and inelasticity properties of the disks. The calculations show that both the mean deviatoric particle velocity and the effective viscosity of a system of particles with fixed friction and restitution coefficients increase almost linearly with strain rate. Particles with a velocity-dependent coefficient of restitution show a less rapid increase in both deviatoric velocity and viscosity as strain rate increases. Particles with highly dissipative interactions result in anisotropic pressure and velocity distributions in the assembly, particularly at low densities. At very high densities the pressure also becomes anisotropic due to high contact forces perpendicular to the shearing direction. The mean rotational velocity of the frictional disks is nearly equal to one-half the shear rate. The calculated ratio of shear stress to normal stress varies significantly with density while the ratio of shear stress to total pressure shows much less variation. The inclusion of surface friction (and thus particle rotation) decreases shear stress at low density but increases shear stress under steady shearing at higher densities

  7. Interplay of nonlocal response, damping, and low group velocity in surface-plasmon polaritons

    DEFF Research Database (Denmark)

    Raza, Søren; Mortensen, N. Asger

    2016-01-01

    The miniaturization of metal structures down to the nanoscale has been accompanied with several recent studies demonstrating plasmonic effects not explainable by classical electromagnetic theory. Describing the optical properties of materials solely through the bulk dielectric function has been...... augmented with quantum mechanical corrections, such as the electron spill-out effect and nonlocal response. Here, we discuss the latter and its implications on the waveguiding characteristics, such as dispersion and group velocity, of the surface-plasmon polariton mode supported at a metal-air interface....

  8. Interplay of nonlocal response, damping, and low group velocity in surface-plasmon polaritons

    Science.gov (United States)

    Raza, Søren; Mortensen, N. Asger

    2016-03-01

    The miniaturization of metal structures down to the nanoscale has been accompanied with several recent studies demonstrating plasmonic effects not explainable by classical electromagnetic theory. Describing the optical properties of materials solely through the bulk dielectric function has been augmented with quantum mechanical corrections, such as the electron spill-out effect and nonlocal response. Here, we discuss the latter and its implications on the waveguiding characteristics, such as dispersion and group velocity, of the surface-plasmon polariton mode supported at a metal-air interface.

  9. The North Atlantic Oscillation, Surface Current Velocities, and SST Changes in the Subpolar North Atlantic.

    Science.gov (United States)

    Flatau, Maria K.; Talley, Lynne; Niiler, Pearn P.

    2003-07-01

    Changes in surface circulation in the subpolar North Atlantic are documented for the recent interannual switch in the North Atlantic Oscillation (NAO) index from positive values in the early 1990s to negative values in 1995/96. Data from Lagrangian drifters, which were deployed in the North Atlantic from 1992 to 1998, were used to compute the mean and varying surface currents. NCEP winds were used to calculate the Ekman component, allowing isolation of the geostrophic currents. The mean Ekman velocities are considerably smaller than the mean total velocities that resemble historical analyses. The northeastward flow of the North Atlantic Current is organized into three strong cores associated with topography: along the eastern boundary in Rockall Trough, in the Iceland Basin (the subpolar front), and on the western flank of the Reykjanes Ridge (Irminger Current). The last is isolated in this Eulerian mean from the rest of the North Atlantic Current by a region of weak velocities on the east side of the Reykjanes Ridge.The drifter results during the two different NAO periods are compared with geostrophic flow changes calculated from the NASA/Pathfinder monthly gridded sea surface height (SSH) variability products and the Advanced Very High Resolution Radiometer (AVHRR) SST data. During the positive NAO years the northeastward flow in the North Atlantic Current appeared stronger and the circulation in the cyclonic gyre in the Irminger Basin became more intense. This was consistent with the geostrophic velocities calculated from altimetry data and surface temperature changes from AVHRR SST data, which show that during the positive NAO years, with stronger westerlies, the subpolar front was sharper and located farther east. SST gradients intensified in the North Atlantic Current, Irminger Basin, and east of the Shetland Islands during the positive NAO phase, associated with stronger currents. SST differences between positive and negative NAO years were consistent with

  10. Understanding and Observing Subglacial Friction Using Seismology

    Science.gov (United States)

    Tsai, V. C.

    2017-12-01

    Glaciology began with a focus on understanding basic mechanical processes and producing physical models that could explain the principal observations. Recently, however, more attention has been paid to the wealth of recent observations, with many modeling efforts relying on data assimilation and empirical scalings, rather than being based on first-principles physics. Notably, ice sheet models commonly assume that subglacial friction is characterized by a "slipperiness" coefficient that is determined by inverting surface velocity observations. Predictions are usually then made by assuming these slipperiness coefficients are spatially and temporally fixed. However, this is only valid if slipperiness is an unchanging material property of the bed and, despite decades of work on subglacial friction, it has remained unclear how to best account for such subglacial physics in ice sheet models. Here, we describe how basic seismological concepts and observations can be used to improve our understanding and determination of subglacial friction. First, we discuss how standard models of granular friction can and should be used in basal friction laws for marine ice sheets, where very low effective pressures exist. We show that under realistic West Antarctic Ice Sheet conditions, standard Coulomb friction should apply in a relatively narrow zone near the grounding line and that this should transition abruptly as one moves inland to a different, perhaps Weertman-style, dependence of subglacial stress on velocity. We show that this subglacial friction law predicts significantly different ice sheet behavior even as compared with other friction laws that include effective pressure. Secondly, we explain how seismological observations of water flow noise and basal icequakes constrain subglacial physics in important ways. Seismically observed water flow noise can provide constraints on water pressures and channel sizes and geometry, leading to important data on subglacial friction

  11. Friction control using ultrasonic oscillation for rolling-element linear-motion guide

    International Nuclear Information System (INIS)

    Oiwa, Takaaki

    2006-01-01

    This article reports a friction-control method for rolling-element linear-motion guides used for precision positioning. In general, static friction greater than dynamic friction generates stick-slip motion and diminishes the positioning accuracy. Two ultrasonic actuators excite both the rail and the carriage of the guide to give relative displacements to bearing surfaces. In order to effectively propagate the vibration over the entire rail without damping, the actuator drives at that frequency with a half wavelength corresponding to the distances between the rail mounting bolts. This also minimizes undesirable vibration of the machine structure. Moreover, the bearing surfaces of the carriage are resonated by a second ultrasonic actuator. The experiments using a force sensor showed that the static and dynamic friction forces were reduced by approximately 25% at any place on the 600-mm-long rail. Moreover, excitation only at very low velocity decreased the static friction peak

  12. Collisional Processing Of Comet And Asteroid Surfaces: Velocity Effects On Absorption Spectra

    Science.gov (United States)

    Jensen, Elizabeth; Lederer, S. M.; Wooden, D. H.; Lindsay, S. S.; Nakamura-Messenger, K.; Keller, L. P.; Cintala, M. J.; Zolensky, M. E.

    2012-10-01

    A new paradigm has emerged where 3.9 Gyr ago, a violent reshuffling reshaped the placement of small bodies in the solar system (the Nice model). Surface properties of these objects may have been affected by collisions caused by this event, and by collisions with other small bodies since their emplacement. These impacts affect the spectroscopic observations of these bodies today. Shock effects (e.g., planar dislocations) manifest in minerals allowing astronomers to better understand geophysical impact processing that has occurred on small bodies. At the Experimental Impact Laboratory at NASA Johnson Space Center, we have impacted forsterite and enstatite across a range of velocities. We find that the amount of spectral variation, absorption wavelength, and full width half maximum of the absorbance peaks vary non-linearly with the velocity of the impact. We also find that the spectral variation increases with decreasing crystal size (single solid rock versus granular). Future analyses include quantification of the spectral changes with different impactor densities, temperature, and additional impact velocities. Results on diopside, fayalite, and magnesite can be found in Lederer et al., this meeting. Funding was provided by the NASA PG&G grant 09-PGG09-0115, NSF grant AST-1010012, and a Cottrell College Scholarship through the Research Corporation.

  13. Improved Near-surface Velocity Models from Waveform Tomography Applied to Vibroseis MCS Reflection Data

    Science.gov (United States)

    Smithyman, B.; Clowes, R. M.

    2009-12-01

    Multichannel vibroseis reflection surveys are prevalent in the land exploration seismic industry because of benefits in speed and cost, along with reduced environmental impact when compared to explosive sources. Since the downgoing energy must travel through the shallow subsurface, an improved model of near-surface velocity can in theory substantially improve the resolution of deeper reflections. We describe techniques aimed at allowing the use of vibroseis data for long-offset refraction processing of first-arrival traveltimes and waveforms. Refraction processing of surface vibroseis data is typically limited to near-offset refraction statics. Velocity models of the shallow subsurface can be built to facilitate CDP stacking and migration, but these models are typically coarse and of limited use for interpretation. Waveform tomography combines inversion of first-arrival traveltime data with full waveform inversion of densely-sampled refracted arrivals. Since inversion of the waveform amplitude and phase is not limited by the ray-theory approximation, identification of low-velocity zones and small scattering targets is possible. Incorporating a wide range of offsets is critical for a more complete characterization of the near-surface. Because of the use of a non-linear frequency-domain approach to the solution of this inverse problem, low data frequencies are important in comparison with conventional reflection processing. Through the use of waveform tomography, we plan to build useful, detailed near-surface velocity models for both the reflection work flow and direct interpretation. Several difficulties exist in first-arrival analysis and waveform inversion of vibroseis data. The mixed-phase vibroseis source signature exhibits variations in phase with offset that are difficult to quantify without detailed a priori knowledge of the near-surface. This causes difficulties with picking and initial model building, which is critical for non-linear waveform inversion. A

  14. Effects of surface coating on reducing friction and wear of orthopaedic implants

    Science.gov (United States)

    Ching, Hee Ay; Choudhury, Dipankar; Julker Nine, Md; Azuan Abu Osman, Noor

    2014-02-01

    Coatings such as diamond-like carbon (DLC) and titanium nitride (TiN) are employed in joint implants due to their excellent tribological properties. Recently, graphite-like carbon (GLC) and tantalum (Ta) have been proven to have good potential as coating as they possess mechanical properties similar to bones—high hardness and high flexibility. The purpose of this systematic literature review is to summarize the coating techniques of these four materials in order to compare their mechanical properties and tribological outcomes. Eighteen studies published between January 2000 and February 2013 have met the inclusion criteria for this review. Details of their fabrication parameters, material and mechanical properties along with the tribological outcomes, such as friction and wear rate, were identified and are presented in a systematic way. Although experiment conditions varied, we conclude that Ta has the lowest wear rate compared to DLC, GLC and TiN because it has a lower wear rate with high contact pressure as well as higher hardness to elasticity ratio. However, a further tribology test is needed in an environment which replicates artificial joints to confirm the acceptability of these findings.

  15. Effects of surface coating on reducing friction and wear of orthopaedic implants

    Science.gov (United States)

    Ching, Hee Ay; Choudhury, Dipankar; Nine, Md Julker; Abu Osman, Noor Azuan

    2014-01-01

    Coatings such as diamond-like carbon (DLC) and titanium nitride (TiN) are employed in joint implants due to their excellent tribological properties. Recently, graphite-like carbon (GLC) and tantalum (Ta) have been proven to have good potential as coating as they possess mechanical properties similar to bones—high hardness and high flexibility. The purpose of this systematic literature review is to summarize the coating techniques of these four materials in order to compare their mechanical properties and tribological outcomes. Eighteen studies published between January 2000 and February 2013 have met the inclusion criteria for this review. Details of their fabrication parameters, material and mechanical properties along with the tribological outcomes, such as friction and wear rate, were identified and are presented in a systematic way. Although experiment conditions varied, we conclude that Ta has the lowest wear rate compared to DLC, GLC and TiN because it has a lower wear rate with high contact pressure as well as higher hardness to elasticity ratio. However, a further tribology test is needed in an environment which replicates artificial joints to confirm the acceptability of these findings. PMID:27877638

  16. Effects of surface coating on reducing friction and wear of orthopaedic implants.

    Science.gov (United States)

    Ching, Hee Ay; Choudhury, Dipankar; Nine, Md Julker; Abu Osman, Noor Azuan

    2014-02-01

    Coatings such as diamond-like carbon (DLC) and titanium nitride (TiN) are employed in joint implants due to their excellent tribological properties. Recently, graphite-like carbon (GLC) and tantalum (Ta) have been proven to have good potential as coating as they possess mechanical properties similar to bones-high hardness and high flexibility. The purpose of this systematic literature review is to summarize the coating techniques of these four materials in order to compare their mechanical properties and tribological outcomes. Eighteen studies published between January 2000 and February 2013 have met the inclusion criteria for this review. Details of their fabrication parameters, material and mechanical properties along with the tribological outcomes, such as friction and wear rate, were identified and are presented in a systematic way. Although experiment conditions varied, we conclude that Ta has the lowest wear rate compared to DLC, GLC and TiN because it has a lower wear rate with high contact pressure as well as higher hardness to elasticity ratio. However, a further tribology test is needed in an environment which replicates artificial joints to confirm the acceptability of these findings.

  17. Effects of surface coating on reducing friction and wear of orthopaedic implants

    Directory of Open Access Journals (Sweden)

    Hee Ay Ching

    2014-01-01

    Full Text Available Coatings such as diamond-like carbon (DLC and titanium nitride (TiN are employed in joint implants due to their excellent tribological properties. Recently, graphite-like carbon (GLC and tantalum (Ta have been proven to have good potential as coating as they possess mechanical properties similar to bones—high hardness and high flexibility. The purpose of this systematic literature review is to summarize the coating techniques of these four materials in order to compare their mechanical properties and tribological outcomes. Eighteen studies published between January 2000 and February 2013 have met the inclusion criteria for this review. Details of their fabrication parameters, material and mechanical properties along with the tribological outcomes, such as friction and wear rate, were identified and are presented in a systematic way. Although experiment conditions varied, we conclude that Ta has the lowest wear rate compared to DLC, GLC and TiN because it has a lower wear rate with high contact pressure as well as higher hardness to elasticity ratio. However, a further tribology test is needed in an environment which replicates artificial joints to confirm the acceptability of these findings.

  18. 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…

  19. Ice Velocity Mapping of Ross Ice Shelf, Antarctica by Matching Surface Undulations Measured by Icesat Laser Altimetry

    Science.gov (United States)

    Lee, Choon-Ki; Han, Shin-Chan; Yu, Jaehyung; Scambos, Ted A.; Seo, Ki-Weon

    2012-01-01

    We present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetrydata from the Ice Cloud and land Elevation Satellite (ICESat; 20032009). The method matches undulations measured at crossover points between successive campaigns.

  20. Expressions to Rayleigh circumferential phase velocity and dispersion relation for a cylindrical surface under mechanical pressure

    Science.gov (United States)

    Sebold, Jean Eduardo; de Lacerda, Luiz Alkimin

    2018-04-01

    This paper describes a substantiated mathematical theory for Rayleigh waves propagated on some types of metal cylinders. More specifically, it presents not only a new way to express the dispersion relation of Rayleigh waves propagated on the cylindrical surface, but also how it can be used to construct a mathematical equation showing that the applied static mechanical pressure affects the shear modulus of the metal cylinder. All steps, required to conclude the process, consider the equation of motion as a function of radial and circumferential coordinates only, while the axial component can be overlooked without causing any problems. Some numerical experiments are done to illustrate the changes in the Rayleigh circumferential phase velocity in a metal cylindrical section due to static mechanical pressure around its external surface.

  1. Surface Wave Multipathing and its Influence on Phase Velocities Measured by Small Networks

    Science.gov (United States)

    Maupin, V.

    2011-12-01

    Networks of temporary broadband seismological stations are commonly deployed over dedicated targets. Measurement of surface wave phase velocity across the network and its depth-inversion gives us information about the structure below the network which is complementary to the information obtained from body-wave analysis. For small networks, we face however the fundamental problem that the dimensions of the heterogeneities to image are not large compared to the wavelengths of the surface waves used to image them. In addition, multipathing is very common is teleseismic surface waves at moderate frequencies and the complexity of the incoming wavefield has to be taken into account during the tomographic process. We perform a series of numerical simulations of surface wave propagation in 3-D structures using complex incoming wavefields in order to analyse how the nature of the incoming wavefield plays together with the 3-D structure to determine phases and amplitudes at the different stations of a network. We analyse how different tomographic methods cope with the complex wavefield, the consequences on the resolution of the resulting tomographic models and we try to provide recommendations for data selection. The numerical simulations are done using a multiple-scattering mode coupling scheme. The amount of multipathing is taken from a recent study using teleseismic surface waves recorded on a temporary network in Southern Norway. The period range of 20 to 200s and the 450km x 600km dimension of the network is also taken form the same study.

  2. Motor unit action potential conduction velocity estimated from surface electromyographic signals using image processing techniques.

    Science.gov (United States)

    Soares, Fabiano Araujo; Carvalho, João Luiz Azevedo; Miosso, Cristiano Jacques; de Andrade, Marcelino Monteiro; da Rocha, Adson Ferreira

    2015-09-17

    In surface electromyography (surface EMG, or S-EMG), conduction velocity (CV) refers to the velocity at which the motor unit action potentials (MUAPs) propagate along the muscle fibers, during contractions. The CV is related to the type and diameter of the muscle fibers, ion concentration, pH, and firing rate of the motor units (MUs). The CV can be used in the evaluation of contractile properties of MUs, and of muscle fatigue. The most popular methods for CV estimation are those based on maximum likelihood estimation (MLE). This work proposes an algorithm for estimating CV from S-EMG signals, using digital image processing techniques. The proposed approach is demonstrated and evaluated, using both simulated and experimentally-acquired multichannel S-EMG signals. We show that the proposed algorithm is as precise and accurate as the MLE method in typical conditions of noise and CV. The proposed method is not susceptible to errors associated with MUAP propagation direction or inadequate initialization parameters, which are common with the MLE algorithm. Image processing -based approaches may be useful in S-EMG analysis to extract different physiological parameters from multichannel S-EMG signals. Other new methods based on image processing could also be developed to help solving other tasks in EMG analysis, such as estimation of the CV for individual MUs, localization and tracking of innervation zones, and study of MU recruitment strategies.

  3. Reduction of Friction of Metals Using Laser-Induced Periodic Surface Nanostructures

    OpenAIRE

    Zhuo Wang; Quanzhong Zhao; Chengwei Wang

    2015-01-01

    We report on the effect of femtosecond-laser-induced periodic surface structures (LIPSS) on the tribological properties of stainless steel. Uniform periodic nanostructures were produced on AISI 304L (American Iron and Steel Institute steel grade) steel surfaces using an 800-nm femtosecond laser. The spatial periods of LIPSS measured by field emission scanning electron microscopy ranged from 530 to 570 nm. The tribological properties of smooth and textured surfaces with periodic nanostructures...

  4. Research and Development on Investigation of Galling and Friction Characteristics of Metallic Materials and Surface Treated Materials

    Science.gov (United States)

    1956-07-01

    strain gauge ring measures the tangential load or frictional force. A dash pot is added to the system to prevent oscillations of the loading arm. The new...consisting of the slider and normal loading apparatus pivots on bearings in a plane paralleý to the plate against a strain ring which measures the...3TIMATING ITIERFACH TEMPE’RATURE Ff014 FRICTION M~EASUREMNENTS The theory Xor estimating interface temperature from friction measurements is given

  5. Characterization of Aluminum-Based-Surface Matrix Composites with Iron and Iron Oxide Fabricated by Friction Stir Processing

    Science.gov (United States)

    Mahmoud, Essam R. I.; Tash, Mahmoud M.

    2016-01-01

    Surface composite layers were successfully fabricated on an A 1050-H24 aluminum plate by dispersed iron (Fe) and magnetite (Fe3O4) particles through friction stir processing (FSP). Fe and Fe3O4 powders were packed into a groove of 3 mm in width and 1.5 mm in depth, cut on the aluminum plate, and covered with an aluminum sheet that was 2-mm thick. A friction stir processing (FSP) tool of square probe shape, rotated at a rate of 1000–2000 rpm, was plunged into the plate through the cover sheet and the groove, and moved along the groove at a travelling speed of 1.66 mm/s. Double and triple passes were applied. As a result, it is found that the Fe particles were homogenously distributed in the whole nugget zone at a rotation speed of 1000 rpm after triple FSP passes. Limited interfacial reactions occurred between the Fe particles and the aluminum matrix. On the other hand, the lower rotation speed (1000 rpm) was not enough to form a sound nugget when the dispersed particles were changed to the larger Fe3O4. The Fe3O4 particles were dispersed homogenously in a sound nugget zone when the rotation speed was increased to 1500 rpm. No reaction products could be detected between the Fe3O4 particles and the aluminum matrix. The saturation magnetization (Ms) of the Fe-dispersed nugget zone was higher than that of the Fe3O4-dispersed nugget zone. Moreover, there were good agreement between the obtained saturation magnetization values relative to that of pure Fe and Fe3O4 materials and the volume content of the dispersed particles in the nugget zone. PMID:28773629

  6. 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 ...

  7. Effect of chlorhexidine-containing prophylactic agent on the surface characterization and frictional resistance between orthodontic brackets and archwires: an in vitro study

    Science.gov (United States)

    2013-01-01

    Background The purpose of this study was to assess the surface characterization and frictional resistance between stainless steel brackets and two types of orthodontic wires made of stainless steel and nickel-titanium alloys after immersion in a chlorhexidine-containing prophylactic agent. Methods Stainless steel orthodontic brackets with either stainless steel (SS) or heat-activated nickel-titanium (Ni-Ti) wires were immersed in a 0.2% chlorhexidine and an artificial saliva environment for 1.5 h. The frictional force was measured on a universal testing machine with a crosshead speed of 10 mm/min over a 5-mm of archwire. The surface morphology of bracket slots and surface roughness of archwires after immersion in chlorhexidine were also characterized using a scanning electron microscope (SEM) and an atomic force microscope (AFM), respectively. Results There was no significant difference in the frictional resistance values between SS and Ni-Ti wires immersed in either chlorhexidine or artificial saliva. The frictional resistance values for the SS and Ni-Ti wires immersed in 0.2% chlorhexidine solution were not significantly different from that inartificial saliva. No significant difference in the average surface roughness for both wires before (as-received) and after immersion in either chlorhexidine or artificial saliva was observed. Conclusions One-and-half-hour immersion in 0.2% chlorhexidine mouthrinse did not have significant influence on the archwires surface roughness or the frictional resistance between stainless steel orthodontic brackets and archwires made of SS and Ni-Ti. Based on these results, chlorhexidine-containing mouthrinses may be prescribed as non-destructive prophylactic agents on materials evaluated in the present study for orthodontic patients. PMID:24325758

  8. General predictive model of friction behavior regimes for metal contacts based on the formation stability and evolution of nanocrystalline surface films.

    Energy Technology Data Exchange (ETDEWEB)

    Argibay, Nicolas [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Cheng, Shengfeng [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Sawyer, W. G. [Univ. of Florida, Gainesville, FL (United States); Michael, Joseph R. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Chandross, Michael E. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2015-09-01

    The prediction of macro-scale friction and wear behavior based on first principles and material properties has remained an elusive but highly desirable target for tribologists and material scientists alike. Stochastic processes (e.g. wear), statistically described parameters (e.g. surface topography) and their evolution tend to defeat attempts to establish practical general correlations between fundamental nanoscale processes and macro-scale behaviors. We present a model based on microstructural stability and evolution for the prediction of metal friction regimes, founded on recently established microstructural deformation mechanisms of nanocrystalline metals, that relies exclusively on material properties and contact stress models. We show through complementary experimental and simulation results that this model overcomes longstanding practical challenges and successfully makes accurate and consistent predictions of friction transitions for a wide range of contact conditions. This framework not only challenges the assumptions of conventional causal relationships between hardness and friction, and between friction and wear, but also suggests a pathway for the design of higher performance metal alloys.

  9. Toe clearance and velocity profiles of young and elderly during walking on sloped surfaces

    Directory of Open Access Journals (Sweden)

    Begg Rezaul K

    2010-04-01

    Full Text Available Abstract Background Most falls in older adults are reported during locomotion and tripping has been identified as a major cause of falls. Challenging environments (e.g., walking on slopes are potential interventions for maintaining balance and gait skills. The aims of this study were: 1 to investigate whether or not distributions of two important gait variables [minimum toe clearance (MTC and foot velocity at MTC (VelMTC] and locomotor control strategies are altered during walking on sloped surfaces, and 2 if altered, are they maintained at two groups (young and elderly female groups. Methods MTC and VelMTC data during walking on a treadmill at sloped surfaces (+3°, 0° and -3° were analysed for 9 young (Y and 8 elderly (E female subjects. Results MTC distributions were found to be positively skewed whereas VelMTC distributions were negatively skewed for both groups on all slopes. Median MTC values increased (Y = 33%, E = 7% at negative slope but decreased (Y = 25%, E = 15% while walking on the positive slope surface compared to their MTC values at the flat surface (0°. Analysis of VelMTC distributions also indicated significantly (p th percentile (Q1 values in the elderly at all slopes. Conclusion The young displayed a strong positive correlation between MTC median changes and IQR (interquartile range changes due to walking on both slopes; however, such correlation was weak in the older adults suggesting differences in control strategies being employed to minimize the risk of tripping.

  10. Quantification of displacement and velocity noise in vibrometer measurements on transversely moving or rotating surfaces

    Science.gov (United States)

    Dräbenstedt, Alexander

    2007-06-01

    The heterodyne interferometer (vibrometer) is a well established technique for measuring all kinds of mechanical vibrations in a broad range of applications. The non-contact measurement principle relies upon the Doppler (or phase-) shift that laser light experiences when it is reflected by the vibrating surface. The speckle nature of the reflected light imposes problems and creates additional measurement noise if the object is moving transversely through the laser spot or is rotating around an axis perpendicular to the laser direction. Another implication that can arise is cross coupling from in-plane vibrations into the out-of-plane measurement direction when small in-plane vibrations are present. A model is presented in this paper that describes the origin of these disturbances. Using this model it is possible to quantify the amplitude spectrum of the noise in displacement and velocity measurements. This enables the user to calculate the limits of resolvable vibration amplitudes when transverse motion is present. The results of the model have been confirmed well by measurements. In addition, the influence of the surface roughness and beam inclination on the out-of-plane vibration measurements at a tilted surface is investigated. The conditions for the measurability of the profile of a transversely moving surface are derived in this work. It is discussed that the R q-roughness parameter has to be less than λ/4 to obtain the slope information in the speckle-perturbed interferometer signal.

  11. Friction Drag Reduction Using Superhydrophobic Surface in High Reynolds Number Turbulent Flow

    Science.gov (United States)

    2017-12-25

    at Princeton using the water channel. SLIPS-coated bodies (prepared according to the instructions provided by Aizenberg) were tested...ASME), 2016 (Smits). 3. Technology Transfer A Switchable Liquid Repellent and Active Fog Harvesting Surface (2016). US Patent Pending

  12. Limitations on Inferring 3D Architecture and Dynamics From Surface Velocities in the India-Eurasia Collision Zone

    Science.gov (United States)

    Flesch, L.; Bendick, R.; Bischoff, S.

    2018-02-01

    Surface velocities derived from Global Positioning System observations and Quaternary fault slip rates measured throughout an extended region of high topography in South Asia vary smoothly over thousands of kilometers and are broadly symmetrical, with components of both north-south shortening and east-west extension relative to stable Eurasia. The observed velocity field does not contain discontinuities or steep gradients attributable to along-strike differences in collision architecture, despite the well-documented presence of a lithospheric slab beneath the Pamir but not the Tibetan Plateau. We use a modified Akaike information criterion (AICc) to show that surface velocities do not efficiently constrain 3D rheology, geometry, or force balance. Therefore, although other geophysical and geological observations may indicate the presence of mechanical or dynamic heterogeneities within the Indian-Asian collision, the surface Global Positioning System velocities contain little or no usable information about them.

  13. Crustal structure of northern Egypt from joint inversion of receiver functions and surface wave dispersion velocities

    Science.gov (United States)

    Badawy, Ahmed; Hegazi, Mona; Gaber, Hanan; Korrat, Ibrahim

    2018-01-01

    In this study, we used a combined inversion of body wave receiver functions and surface wave dispersion measurements to provide constraints on the crustal structure of northern Egypt. The two techniques are complementary to each other: receiver functions (RFs) are sensitive to shear-wave velocity contrasts, while surface wave dispersion (SWD) measurements are sensitive to finite variations of shear-wave velocity with depth. A database of 122 teleseismic events digitally recorded by the Egyptian National Seismological Network (ENSN) stations has been used as well. To enhance the resulting RFs at each ENSN station, the H-k stacking method was applied. A joint inversion process between the resulting receiver functions and the surface wave dispersion curves was applied as well. We have produced three averaged velocity structure models for distinct geographic and tectonic provinces namely Sinai, eastern desert, and western desert from east to the west respectively. These models will deeply help in estimation the epicenter distance of earthquake, focal mechanism solutions, and earthquake hazard analysis in northern Egypt. An obvious image of the subsurface structure has been determined which shows that generally the crustal structure of northern Egypt consists of three layers covered with a sequence of sediments that differs in thickness from across the region except in the Sharm area where the sedimentary cover is absent. The obtained results indicate that crustal thickness differs from east to west and reaches its maximum value of about 36 km at Siwa station (SWA) in the western desert and its minimum value of about 28 km at Sharm station (SHR) of the southern tip of the Sinai Peninsula. The Vp/Vs ratio varies between 1.71 and 2.07 in northern Egypt. Generally, the high values (1.93) of (Vp/Vs) at SWA station may reflect the well-known rich aquifer with fully saturated sediments of the Swia Oasis in the Western Desert. Moreover, the highest value (2.07) of (Vp/Vs) at

  14. Finger pad friction and tactile perception of laser treated, stamped and cold rolled micro-structured stainless steel sheet surfaces

    NARCIS (Netherlands)

    Zhang, Sheng; Zeng, X.; Matthews, D.T.A.; Igartua, A.; Rodriguez Vidal, E.; Contreras Fortes, J.; Van Der Heide, E.

    2017-01-01

    Tactile perception is a complex system, which depends on frictional interactions between skin and counter-body. The contact mechanics of tactile friction is governed by many factors such as the state and properties of skin and counter-body. In order to discover the connection between perception and

  15. Finger pad friction and tactile perception of laser treated, stamped and cold rolled micro-structured stainless steel sheet surfaces

    NARCIS (Netherlands)

    Zhang, S.; Zeng, X.; Matthews, D. T A; Igartua, A.; Rodriguez-Vidal, E.; Contreras Fortes, J.; van der Heide, E.

    2017-01-01

    Tactile perception is a complex system, which depends on frictional interactions between skin and counter-body. The contact mechanics of tactile friction is governed by many factors such as the state and properties of skin and counter-body. In order to discover the connection between perception

  16. Synchronous Surface Pressure and Velocity Measurements of standard model in hypersonic flow

    Directory of Open Access Journals (Sweden)

    Zhijun Sun

    2018-01-01

    Full Text Available Experiments in the Hypersonic Wind tunnel of NUAA(NHW present synchronous measurements of bow shockwave and surface pressure of a standard blunt rotary model (AGARD HB-2, which was carried out in order to measure the Mach-5-flow above a blunt body by PIV (Particle Image Velocimetry as well as unsteady pressure around the rotary body. Titanium dioxide (Al2O3 Nano particles were seeded into the flow by a tailor-made container. With meticulous care designed optical path, the laser was guided into the vacuum experimental section. The transient pressure was obtained around model by using fast-responding pressure-sensitive paint (PSPsprayed on the model. All the experimental facilities were controlled by Series Pulse Generator to ensure that the data was time related. The PIV measurements of velocities in front of the detached bow shock agreed very well with the calculated value, with less than 3% difference compared to Pitot-pressure recordings. The velocity gradient contour described in accord with the detached bow shock that showed on schlieren. The PSP results presented good agreement with the reference data from previous studies. Our work involving studies of synchronous shock-wave and pressure measurements proved to be encouraging.

  17. Near-surface wave velocity structure of Faial (Azores - Portugal) Island for site effect studies

    Science.gov (United States)

    Borges, José; Neves, Samuel; Caldeira, Bento; Bezzeghoud, Mourad; Carvalho, João; Carvalho, Alexandra

    2015-04-01

    Throughout history, the life of the Azorean people has been marked by earthquakes that have had different effects depending on their proximity and magnitude. This seismic activity, which may have volcanic or tectonic origins, has affected the population of these islands by destroying infrastructure and claiming lives. The social and economic impacts of these phenomena are enormous. The last significant event affecting the Azores (Portugal) was the July 1998 Mw=6.2 earthquake causing major destruction affecting more than 5000 people, causing 8 deaths, 150 persons injured and 1500 homeless. Ground motion simulations are mainly based on source characteristics and are heavily dependent on the medium, which is still poorly understood. Subsurface soil condition can amplify the seismic waves, so, for seismic response analysis, it is necessary to know the shallow soil properties and its spatial variability. For this purpose, we applied P and S-wave refraction, Multichannel Analysis of Surface Waves (MASW) to characterize shear wave velocity at different sites in the Faial Island, in particular, in sites where already occurred amplification. Ambient vibrations can also be used to estimate physical properties of the shallower geological formations. With this goal, the obtained velocity models were confirmed by comparison between real H/V curves with synthetic ones. We concluded that the anomalous intensities observed in some sites are strongly related to thick layers of soft sediments of pyroclastic deposits produced by old volcanic eruptions occurred in the Faial Island.

  18. Skin tribology: Science friction?

    OpenAIRE

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

    2013-01-01

    The application of tribological knowledge is not just restricted to optimizing mechanical and chemical engineering problems. In fact, effective solutions to friction and wear related questions can be found in our everyday life. An important part is related to skin tribology, as the human skin is frequently one of the interacting surfaces in relative motion. People seem to solve these problems related to skin friction based upon a trial-and-error strategy and based upon on our sense for touch....

  19. Effects of surface friction and turbulent mixing on long-term changes in the near-surface wind speed over the Eastern China Plain from 1981 to 2010

    Science.gov (United States)

    Wu, Jian; Zha, Jinlin; Zhao, Deming; Yang, Qidong

    2017-11-01

    A significant slowdown in the near-surface wind speed (SWS) due to combined effects of the driving and drag forces of the atmosphere has been demonstrated in different regions in the globe. The drag force includes two sources: the friction force between the underlying surface and the bottom of the atmosphere, which is the external friction force (EFF), and the vertical exchange of the horizontal momentum induced by turbulent mixing, which is the turbulent friction force (TFF). In this paper, we propose a diagnostic method to separate the effects of the EFF and the TFF on long-term changes in the SWS over the Eastern China Plain (ECP) region from 1981 to 2010. The results show that the TFF could have caused an increase of 0.5 ± 0.2 m s- 1 in the SWS over the ECP region in the past 30 years and the TFF showed an increasing influence of 0.17 m s- 1 decade- 1. In contrast, the EFF distinctly decreased the SWS by an average of - 1.1 ± 0.4 m s- 1 and presented a significant decreasing trend of - 0.36 m s- 1 decade- 1. The effect of EFF is the main inducer of the observed regional long-term decrease of the SWS, which is in accordance with the distinct land use and cover change (LUCC) occurring in the ECP region in recent decades. Furthermore, the effects of the EFF and TFF on the changes in the SWS are more significant in large cities than those in small cities. The TFF effect can accelerate the SWS, with means of 0.5 ± 0.2 and 0.4 ± 0.2 m s- 1 in large and small cities, respectively. The EFF effect can decelerate the SWS, with means of - 1.2 ± 0.4 and - 0.7 ± 0.4 m s- 1 in large and small cities, respectively.

  20. Muscle conduction velocity, surface electromyography variables, and echo intensity during concentric and eccentric fatigue.

    Science.gov (United States)

    Gonzalez-Izal, Miriam; Lusa Cadore, Eduardo; Izquierdo, Mikel

    2014-03-01

    Concentric (CON) and eccentric (ECC) contractions may involve different mechanisms related to changes in sarcolemma status and the consequent alteration of action potential transmission along muscle fibers. Muscle conduction velocity (CV), surface electromyography signal (sEMG), muscle quality, and blood lactate concentrations were analyzed during CON and ECC actions. Compared with ECC, the CON protocol resulted in greater muscle force losses, blood lactate concentrations, and changes in sEMG parameters. Similar reductions in CV were detected in both protocols. Higher echo intensity values were observed 2 days after ECC due to greater muscle damage. The effects of the muscle damage produced by ECC exercise on the transmission of action potentials along muscle fibers (measured as the CV) may be comparable with the effects of hydrogen accumulation produced by CON exercise (related to greater lactate concentrations), which causes greater force loss and change in other sEMG variables during CON than during ECC actions.

  1. Aero-servo-viscoelasticity theory: Lifting surfaces, plates, velocity transients, flutter, and instability

    Science.gov (United States)

    Merrett, Craig G.

    -partial differential equations. The spatial component of the governing equations is eliminated using a series expansion of basis functions and by applying Galerkin's method. The number of terms in the series expansion affects the convergence of the spatial component, and convergence is best determined by the von Koch rules that previously appeared for column buckling problems. After elimination of the spatial component, an ordinary integral-differential equation in time remains. The dynamic stability of elastic and viscoelastic problems is assessed using the determinant of the governing system of equations and the time component of the solution in the form exp (lambda t). The determinant is in terms of lambda where the values of lambda are the latent roots of the aero-servo-viscoelastic system. The real component of lambda dictates the stability of the system. If all the real components are negative, the system is stable. If at least one real component is zero and all others are negative, the system is neutrally stable. If one or more real components are positive, the system is unstable. In aero-servo-viscoelasticity, the neutrally stable condition is termed flutter. For an aero-servo-viscoelastic lifting surface, the unstable condition is historically termed torsional divergence. The more general aero-servo-viscoelastic theory has produced a number of important results, enumerated in the following list: 1. Subsonic panel flutter can occur before panel instability. This result overturned a long held assumption in aeroelasticity, and was produced by the novel application of the von Koch rules for convergence. Further, experimental results from the 1950s by the Air Force were retrieved to provide additional proof. 2. An expanded definition for flutter of a lifting surface. The legacy definition is that flutter is the first occurrence of simple harmonic motion of a structure, and the flight velocity at which this motion occurs is taken as the flutter speed. The expanded definition

  2. 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 ...

  3. S-wave velocity measurements along levees in New Orleans using passive surface wave methods

    Science.gov (United States)

    Hayashi, K.; Lorenzo, J. M.; Craig, M. S.; Gostic, A.

    2017-12-01

    In order to develop non-invasive methods for levee inspection, geophysical investigations were carried out at four sites along levees in the New Orleans area: 17th Street Canal, London Avenue Canal, Marrero Levee, and Industrial Canal. Three of the four sites sustained damage from Hurricane Katrina in 2005 and have since been rebuilt. The geophysical methods used include active and passive surface wave methods, and capacitively coupled resistivity. This paper summarizes the acquisition and analysis of the 1D and 2D passive surface wave data. Twelve wireless seismic data acquisition units with 2 Hz vertical component geophones were used to record data. Each unit includes a GPS receiver so that all units can be synchronized over any distance without cables. The 1D passive method used L shaped arrays of three different sizes with geophone spacing ranging from 5 to 340 m. Ten minutes to one hour of ambient noise was recorded with each array, and total data acquisition took approximately two hours at each site. The 2D method used a linear array with a geophone spacing of 5m. Four geophones were moved forward every 10 minutes along 400 1000 m length lines. Data acquisition took several hours for each line. Recorded ambient noise was processed using the spatial autocorrelation method and clear dispersion curves were obtained at all sites (Figure 1a). Minimum frequencies ranged from 0.4 to 0.7 Hz and maximum frequencies ranged from 10 to 30 Hz depending on the site. Non-linear inversion was performed and 1D and 2D S-wave velocity models were obtained. The 1D method penetrated to depths ranging from 200 to 500 m depending on the site (Figure 1b). The 2D method penetrated to a depth of 40 60 m and provided 400 1000 m cross sections along the levees (Figure 2). The interpretation focused on identifying zones beneath the levees or canal walls having low S-wave velocities corresponding to saturated, unconsolidated sands, or low-rigidity clays. Resultant S-wave velocity profiles

  4. Effect of fluorocarbon self-assembled monolayer films on sidewall adhesion and friction of surface micromachines with impacting and sliding contact interfaces

    International Nuclear Information System (INIS)

    Xiang, H.; Komvopoulos, K.

    2013-01-01

    A self-assembled monolayer film consisting of fluoro-octyltrichlorosilane (FOTS) was vapor-phase deposited on Si(100) substrates and polycrystalline silicon (polysilicon) surface micromachines. The hydrophobic behavior and structural composition of the FOTS film deposited on Si(100) were investigated by goniometry and X-ray photoelectron spectroscopy, respectively. The effects of contact pressure, relative humidity, temperature, and impact/sliding cycles on the adhesive and friction behavior of uncoated and FOTS-coated polysilicon micromachines (referred to as the Si and FOTS/Si micromachines, respectively) were investigated under controlled loading and environmental conditions. FOTS/Si micromachines demonstrated much lower and stable adhesion than Si micromachines due to the highly hydrophobic and conformal FOTS film. Contrary to Si micromachines, sidewall adhesion of FOTS/Si micromachines demonstrated a weak dependence on relative humidity, temperature, and impact cycles. In addition, FOTS/Si micromachines showed low and stable adhesion and low static friction for significantly more sliding cycles than Si micromachines. The adhesive and static friction characteristics of Si and FOTS/Si micromachines are interpreted in the context of physicochemical surface changes, resulting in the increase of the real area of contact and a hydrophobic-to-hydrophilic transition of the surface chemical characteristics caused by nanoscale surface smoothening and the removal of the organic residue (Si micromachines) or the FOTS film (FOTS/Si micromachines) during repetitive impact and oscillatory sliding of the sidewall surfaces.

  5. Seismic velocity site characterization of 10 Arizona strong-motion recording stations by spectral analysis of surface wave dispersion

    Science.gov (United States)

    Kayen, Robert E.; Carkin, Brad A.; Corbett, Skye C.

    2017-10-19

    Vertical one-dimensional shear wave velocity (VS) profiles are presented for strong-motion sites in Arizona for a suite of stations surrounding the Palo Verde Nuclear Generating Station. The purpose of the study is to determine the detailed site velocity profile, the average velocity in the upper 30 meters of the profile (VS30), the average velocity for the entire profile (VSZ), and the National Earthquake Hazards Reduction Program (NEHRP) site classification. The VS profiles are estimated using a non-invasive continuous-sine-wave method for gathering the dispersion characteristics of surface waves. Shear wave velocity profiles were inverted from the averaged dispersion curves using three independent methods for comparison, and the root-mean-square combined coefficient of variation (COV) of the dispersion and inversion calculations are estimated for each site.

  6. An Experimental Investigation of Skin Friction on Smooth Surfaces Supporting Air Bearing Channels.

    Science.gov (United States)

    1986-07-01

    existing knowledge. LABORATORY TECHNICAL REPORTS (LTR): Information receiving limited distribution because of preliminary data, security classification...LISSES PORTEUSES DE CANAUX ANTI-FROTTEMENT by/par M. Khalid National Aeronautical Establishment AERONAUTICAL NOTE OTTAWA NAE-AN-39 JULY 1986 NRC NO...installant sur la surface des canaux qui agissent comme des valiers d’air. Les mesures ont &t prises A l’aide d’une balance de mesure du frottement

  7. Advective surface velocity in the north west Pacific derived from NOAA AVHRR images

    Digital Repository Service at National Institute of Oceanography (India)

    Pankajakshan, T.; Akiyama, M.; Okada, Y.; Sugimori, Y.

    Using sequential AVHRR images in November 1983, nearsurface advective velocities are derived in the region Kuroshio south of Japan. For deriving the velocities two methods are used. One is the Method of Cross Correlation (MCC), using image pair...

  8. Influence of process parameters on physical dimensions of AA6063 aluminium alloy coating on mild steel in friction surfacing

    Directory of Open Access Journals (Sweden)

    B. Vijaya Kumar

    2015-09-01

    Full Text Available An attempt is made in the present study to obtain the relationships among process parameters and physical dimensions of AA6063 aluminium alloy coating on IS2062 mild steel obtained through friction surfacing and their impact on strength and ductility of the coating. Factorial experimental design technique was used to investigate and select the parameter combination to achieve a coating with adequate strength and ductility. Spindle speed, axial force and table traverse speed were observed to be the most significant factors on physical dimensions. It was observed that the thickness of the coating decreased as the coating width increased. In addition, the width and thickness of the coatings are higher at low and high torques. At intermediate torque values, when the force is high, the width of the coating is high, and its thickness is thin; and when the force is low, the width and thickness are low. The interaction effect between axial force (F – table traverse speed (Vx and spindle speed (N – table traverse speed (Vx produced an increasing effect on coating width and thickness, but other interactions exhibited decreasing influence. It has also been observed that sound coatings could be obtained in a narrow set of parameter range as the substrate-coating materials are metallurgically incompatible and have a propensity to form brittle intermetallics.

  9. Workflow for near-surface velocity automatic estimation: Source-domain full-traveltime inversion followed by waveform inversion

    KAUST Repository

    Liu, Lu

    2017-08-17

    This paper presents a workflow for near-surface velocity automatic estimation using the early arrivals of seismic data. This workflow comprises two methods, source-domain full traveltime inversion (FTI) and early-arrival waveform inversion. Source-domain FTI is capable of automatically generating a background velocity that can kinematically match the reconstructed plane-wave sources of early arrivals with true plane-wave sources. This method does not require picking first arrivals for inversion, which is one of the most challenging aspects of ray-based first-arrival tomographic inversion. Moreover, compared with conventional Born-based methods, source-domain FTI can distinguish between slower or faster initial model errors via providing the correct sign of the model gradient. In addition, this method does not need estimation of the source wavelet, which is a requirement for receiver-domain wave-equation velocity inversion. The model derived from source-domain FTI is then used as input to early-arrival waveform inversion to obtain the short-wavelength velocity components. We have tested the workflow on synthetic and field seismic data sets. The results show source-domain FTI can generate reasonable background velocities for early-arrival waveform inversion even when subsurface velocity reversals are present and the workflow can produce a high-resolution near-surface velocity model.

  10. Frictional Performance and Temperature Rise of a Mining Nonasbestos Brake Material during Emergency Braking

    Directory of Open Access Journals (Sweden)

    Jiusheng Bao

    2015-01-01

    Full Text Available By simulating emergency braking conditions of mine hoisters, tribological experiments of a mining nonasbestos brake material sliding on E355CC steel friction disc investigated a pad-on-disc friction tester. It is shown that, under combined influence of braking velocity and pressure, the lubricating film and micro-convex-apices on wear surface would have complex physicochemical reactions which make the instant friction coefficient rise gradually while the instant surface temperature rises first and then falls. With the antifriction effect from lubricating film and the desquamating of composite materials, the mean friction coefficient decreases first, then rises, and decreases again with the increasing of initial braking velocity. And with the existence of micro-convex-apices and variation from increment ratio of load and actual contacting area, it rises first and then falls with the increasing of braking pressure. However, the mean surface temperature rises obviously with the increasing of both initial braking velocity and braking pressure for growth of transformed kinetic energy. It is considered that the friction coefficient cannot be considered as a constant when designing brake devices for mine hoisters. And special attention should be paid to the serious influence of surface temperature on tribological performance of brake material during emergency braking.

  11. Evaluation of Effect of Air Abrasion on Friction and Surface Micromorphology of Passive Stainless Steel Self-Ligated Brackets: An In Vitro Study

    Directory of Open Access Journals (Sweden)

    Yasir Sate Mizhir

    2018-03-01

    Full Text Available The friction that occur between arch wire and the brackets during arch wire sliding in fixed orthodontic appliance will affect negatively on the outcome of the orthodontic treatment in addition to the treatment time. The process of friction is a critical issue and should be understood properly by the orthodontist in order to provide the optimum treatment result in a short period of time. Aim: The aim of our study was to compare the effect of calcium carbonate air abrasive on static friction and micromorphology of bracket slot surface for two different stainless steel self-ligated brackets. Methods: 120 passive stainless steel self-ligated brackets from two different commercial brands where involved in the study (discovery® sl2.0, Dentaurum co. and Damon®, Ormco co.. The samples were divided randomly into 8 groups, and every group with 5 samples, the criteria for classification of these groups depend on bracket types and air abrasion periods. Round (18 inches NITI arch wire was used to slide through 3 brackets with the middle one 1 mm higher than the others, the distance of sliding through the brackets was 10 mm, the machine used for measurement included the (instron universal testing machine, the roughness of the bracket slot surface was analyzed be the machine of (scanning electron microscope. Results: The effect of air abrasive agent calcium carbonate on the both types of metal self-ligated brackets result in elevation the amount of static friction for (discovery® l2.0 by 35.157%, Damon® by 36.652%. Viewing the slot of the brackets under microscope by using (SEM device reveal great modification in surface of the slot with uneven and rougher surface when compared to the brackets of control group that appear with polished and smooth surface.

  12. Friction and wear behaviour of plasma sprayed Cr2O3-TiO2 coating

    Science.gov (United States)

    Bagde, Pranay; Sapate, S. G.; Khatirkar, R. K.; Vashishtha, Nitesh; Tailor, Satish

    2018-02-01

    Cr2O3-25TiO2 coating was deposited by atmospheric plasma spray (APS) coating technique. Effect of load (5–30 N) and sliding velocity (0.25, 0.75 m s‑1) on friction coefficient and abrasive wear behaviour of the Cr2O3-25TiO2 coating was studied. Mechanical and microstructural characterization of the Cr2O3-25TiO2 coating was carried out. With an increase in sliding velocity, abrasive wear rate and friction coefficient (COF) decreased while wear rate and friction coefficient showed an increasing trend with the load. The worn out surfaces were analyzed by SEM, EDS and XRD. At lower sliding velocity, XRD analysis revealed peaks of Ti2O3, Ti3O5, CrO2 and CrO3. In addition, peak of Ti4O7 was also detected at higher sliding velocity and at 30 N load. At higher sliding velocity medium to severe tribo oxidation was observed. XPS analysis of worn surfaces at both the sliding velocities, showed surface film of oxides of titanium and chromium along with Cr(OH)3. Magneli phase titanium oxides with sub stoichiometric composition, along with surface films of chromium oxides and hydroxides altered the friction and wear behaviour of the coating. The decrease in friction coefficient with an increase in sliding velocity was attributed to tribo oxides and tribochemical reaction films having lower shear strength with good lubricating properties. The mechanism of material removal involved plastic deformation at lower load whereas inter-granular and trans-granular fracture, delamination cracking and splat fracture was observed with an increase load from 10 N to 30 N.

  13. Probing into frictional contact dynamics by ultrasound and electrical simulations

    Directory of Open Access Journals (Sweden)

    Changshan Jin

    2014-12-01

    Full Text Available Friction arises in the interface of friction pair, and therefore, it is difficult to detect it. Ultrasonic means, as a NDT, is the correct alternative. This paper introduces a means of detecting dynamic contact and an interpretation of behaviors of dry friction. It has been determined that frictional surfaces have a specific property of dynamic response hardening (DRH. Dynamic response forces and oscillation arise during static–kinetic transition process. While the contact zone of sliding surfaces appears “hard” in motion, it appears “soft” at rest. Consequently, a separation of the surfaces occurs and the real area of contact is decreased as sliding velocity increases. This is the cause of F–v descent phenomenon. When the friction comes to a rest, the remaining process of DRH and micro-oscillation do not disappear instantaneously, instead they gradually return to their original static position. The contact area, therefore, is increased by rest period (F–T ascent characteristics. Based on analogies between a solid unit (η–m–k and an R-L-C circuit, the DRH is demonstrated by electrical simulations.

  14. Measurement of sliding velocity and induction time of a single micro-bubble under an inclined collector surface

    Energy Technology Data Exchange (ETDEWEB)

    Najafi, A.S.; Xu, Z.; Masliyah, J. [Alberta Univ., Edmonton, AB (Canada). Dept. of Chemical and Materials Engineering

    2008-12-15

    Flotation is a major process by which bitumens are recovered from oil sands slurries, and air bubble-bitumen attachment is necessary for the effective separation of aerated bitumen. This study investigated the interactions between a gas bubble and a solid, flat surface. Various physical and chemical conditions were studied in order to determine their impact on the sliding velocity and induction times of the micro-bubble as it slid underneath an inclined solid surface. The bubble's trajectory was monitored by a high-speed video imaging system. Tests were conducted using de-aerated process water in order to study the effect of dissolved gases on bubble sliding velocity. Simulated process water was also used to study the role of the natural surfactants contained in recycle process water. The study showed that terminal and sliding velocities of the bubbles were functions of temperature. Sliding velocities increased with increases in liquid temperature. Increases in liquid temperature also reduced the induction time used to quantify bubble-solid attachment. Induction times were also reduced with increases in surface hydrophobicity. Induction times measured for CO{sub 2} bubbles were shorter than those observed with air, oxygen, and hydrogen bubbles. It was concluded that the use of natural surface active agents in process water reduced bubble terminal rising velocity and increased the induction times of bubble-solid attachment. 36 refs., 2 tabs., 15 figs.

  15. Comparative study on the lateral run-out of friction surfaces measurement of brake discs using a brake roller tester and a dial gauge

    OpenAIRE

    Toma Marius; Andreescu Cristian; Micu Dan

    2017-01-01

    Brake system diagnosis is one of the most common and necessary technical operations applied to the car, regardless of its type and operating phases. Measuring the diagnostic parameters on a roller brake tester is a fast operation with no disassembly necessary. Measuring the run-out of friction surfaces of brake discs with a dial gauge is an action that requires more extensive preparatory operations but it offers a high accuracy of the results. The paper aims to analyze the correlation between...

  16. Mitigation of defocusing by statics and near-surface velocity errors by interferometric least-squares migration

    KAUST Repository

    Sinha, Mrinal

    2015-08-19

    We propose an interferometric least-squares migration method that can significantly reduce migration artifacts due to statics and errors in the near-surface velocity model. We first choose a reference reflector whose topography is well known from the, e.g., well logs. Reflections from this reference layer are correlated with the traces associated with reflections from deeper interfaces to get crosscorrelograms. These crosscorrelograms are then migrated using interferometric least-squares migration (ILSM). In this way statics and velocity errors at the near surface are largely eliminated for the examples in our paper.

  17. 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.

  18. Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces.

    Science.gov (United States)

    Endlein, Thomas; Ji, Aihong; Samuel, Diana; Yao, Ning; Wang, Zhongyuan; Barnes, W Jon P; Federle, Walter; Kappl, Michael; Dai, Zhendong

    2013-03-06

    To live and clamber about in an arboreal habitat, tree frogs have evolved adhesive pads on their toes. In addition, they often have long and slender legs to facilitate not only long jumps, but also to bridge gaps between leaves when climbing. Both adhesive pads and long limbs are used in conjunction, as we will show in this study. Previous research has shown that tree frogs change from a crouched posture (where the limbs are close to the body) to a sprawled posture with extended limbs when clinging on to steeper inclines such as vertical or overhanging slopes. We investigated this change in posture in White's tree frogs (Litoria caerulea) by challenging the frogs to cling onto a tiltable platform. The platform consisted of an array of 24 three-dimensional force transducers, which allowed us to measure the ground reaction forces of the frogs during a tilt. Starting from a crouched resting position, the normal forces on the forelimbs changed sign and became increasingly negative with increasing slope angle of the platform. At about 106° ± 12°, tilt of the platform the frogs reacted by extending one or two of their limbs outwards. At a steeper angle (131° ± 11°), the frogs spread out all their limbs sideways, with the hindlimbs stretched out to their maximum reach. Although the extension was strongest in the lateral direction, limbs were significantly extended in the fore-aft direction as well. With the extension of the limbs, the lateral forces increased relative to the normal forces. The large contribution of the in-plane forces helped to keep the angle between the force vector and the platform small. The Kendall theory for the peeling of adhesive tape predicts that smaller peel angles lead to higher attachment forces. We compare our data with the predictions of the Kendall model and discuss possible implications of the sliding of the pads on the surface. The forces were indeed much larger for smaller angles and thus can be explained by peeling theory.

  19. Earthquake friction

    Science.gov (United States)

    Mulargia, Francesco; Bizzarri, Andrea

    2016-12-01

    Laboratory friction slip experiments on rocks provide firm evidence that the static friction coefficient μ has values ∼0.7. This would imply large amounts of heat produced by seismically active faults, but no heat flow anomaly is observed, and mineralogic evidence of frictional heating is virtually absent. This stands for lower μ values ∼0.2, as also required by the observed orientation of faults with respect to the maximum compressive stress. We show that accounting for the thermal and mechanical energy balance of the system removes this inconsistence, implying a multi-stage strain release process. The first stage consists of a small and slow aseismic slip at high friction on pre-existent stress concentrators within the fault volume but angled with the main fault as Riedel cracks. This introduces a second stage dominated by frictional temperature increase inducing local pressurization of pore fluids around the slip patches, which is in turn followed by a third stage in which thermal diffusion extends the frictionally heated zones making them coalesce into a connected pressurized region oriented as the fault plane. Then, the system enters a state of equivalent low static friction in which it can undergo the fast elastic radiation slip prescribed by dislocation earthquake models.

  20. Arbitrary Lagrangian-Eulerian finite element analysis of free surface flow using a velocity-vorticity formulation

    International Nuclear Information System (INIS)

    Lo, D.C.; Young, D.L.

    2004-01-01

    This paper describes the application of velocity-vorticity formulation of the Navier-Stokes equations for two-dimensional free surface flow using an arbitrary Lagrangian-Eulerian method. The velocity Poisson equations and the vorticity transport equations are solved using a finite element method to obtain the velocity and the vorticity fields in the interior region of the computational domain. The boundary-fitted coordinates system is adopted to solve the boundary equations for kinematic and dynamic conditions at the free surface using a finite difference method. The numerical model for the velocity-vorticity formulation is validated for a square cavity flow at Re=400 and 1000. The solitary wave reflected from a vertical wall is chosen as a test case for comparison and validation of the free surface flow model. Then the proposed numerical model is used to obtain flow results for the following free surface flow cases: (i) interaction between two opposite solitary waves, (ii) seiche phenomenon in a rectangular reservoir, and (iii) solitary wave through a submerged rectangular structure in a viscous fluid. The efficiency of the present numerical model for numerical treatment of free surface flows is discussed. Furthermore the advantage of this formulation with respect to primitive variables formulation is addressed from the computational point of view

  1. Impulse excitation scanning acoustic microscopy for local quantification of Rayleigh surface wave velocity using B-scan analysis.

    Science.gov (United States)

    Cherry, M; Dierken, J; Boehnlein, T; Pilchak, A; Sathish, S; Grandhi, R

    2018-01-01

    A new technique for performing quantitative scanning acoustic microscopy imaging of Rayleigh surface wave (RSW) velocity was developed based on b-scan processing. In this technique, the focused acoustic beam is moved through many defocus distances over the sample and excited with an impulse excitation, and advanced algorithms based on frequency filtering and the Hilbert transform are used to post-process the b-scans to estimate the Rayleigh surface wave velocity. The new method was used to estimate the RSW velocity on an optically flat E6 glass sample, and the velocity was measured at ±2 m/s and the scanning time per point was on the order of 1.0 s, which are both improvement from the previous two-point defocus method. The new method was also applied to the analysis of two titanium samples, and the velocity was estimated with very low standard deviation in certain large grains on the sample. A new behavior was observed with the b-scan analysis technique where the amplitude of the surface wave decayed dramatically on certain crystallographic orientations. The new technique was also compared with previous results, and the new technique has been found to be much more reliable and to have higher contrast than previously possible with impulse excitation.

  2. Impulse excitation scanning acoustic microscopy for local quantification of Rayleigh surface wave velocity using B-scan analysis

    Science.gov (United States)

    Cherry, M.; Dierken, J.; Boehnlein, T.; Pilchak, A.; Sathish, S.; Grandhi, R.

    2018-01-01

    A new technique for performing quantitative scanning acoustic microscopy imaging of Rayleigh surface wave (RSW) velocity was developed based on b-scan processing. In this technique, the focused acoustic beam is moved through many defocus distances over the sample and excited with an impulse excitation, and advanced algorithms based on frequency filtering and the Hilbert transform are used to post-process the b-scans to estimate the Rayleigh surface wave velocity. The new method was used to estimate the RSW velocity on an optically flat E6 glass sample, and the velocity was measured at ±2 m/s and the scanning time per point was on the order of 1.0 s, which are both improvement from the previous two-point defocus method. The new method was also applied to the analysis of two titanium samples, and the velocity was estimated with very low standard deviation in certain large grains on the sample. A new behavior was observed with the b-scan analysis technique where the amplitude of the surface wave decayed dramatically on certain crystallographic orientations. The new technique was also compared with previous results, and the new technique has been found to be much more reliable and to have higher contrast than previously possible with impulse excitation.

  3. Stress State at the Vertex of a Composite Wedge, One Side of Which Slides Without Friction Along a Rigid Surface

    Directory of Open Access Journals (Sweden)

    V. Pestrenin

    Full Text Available Abstract For studying the stress-strain state at singular points and their neighborhoods new concept is proposed. A singular point is identified with an elementary volume that has a characteristic size of the real body representative volume. This makes it possible to set and study the restrictions at that point. It is shown that problems with singular points turn out to be ambiguous, their formulation depends on the combination of the material and geometric parameters of the investigated body. Number of constraints in a singular point is redundant compared to the usual point of the boundary (it makes singular point unique, exclusive. This circumstance determines the non-classical problem formulation for bodies containing singular points. The formulation of a non-classical problem is given, the uniqueness of its solution is proved (under the condition of existence, the algorithm of the iterative-analytical decision method is described. Restrictions on the state parameters at the composite wedge vertex, one generatrix of which is in non-friction contact with a rigid surface are studied under temperature and strength loading. The proposed approach allows to identify critical combinations of material and geometric parameters that define the singularity of stress and strain fields close to singular representative volumes. The constraints on load components needed to solution existence are established. An example of a numerical analysis of the state parameters at the wedge vertex and its neighborhood is considered. Solutions built on the basis of a new concept, directly in a singular point, and its small neighborhood differ significantly from the solutions made with asymptotic methods. Beyond a small neighborhood of a singular point the solutions obtained on the basis of different concepts coincide.

  4. Seismic Velocity Structure and Depth-Dependence of Anisotropy in the Red Sea and Arabian Shield from Surface Wave Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, S; Gaherty, J; Schwartz, S; Rodgers, A; Al-Amri, A

    2007-07-25

    We investigate the lithospheric and upper mantle structure as well as the depth-dependence of anisotropy along the Red Sea and beneath the Arabian Peninsula using receiver function constraints and phase velocities of surface waves traversing two transects of stations from the Saudi Arabian National Digital Seismic Network. Frequency-dependent phase delays of fundamental-mode Love and Rayleigh waves, measured using a cross-correlation procedure, require very slow shear velocities and the presence of anisotropy throughout the upper mantle. Linearized inversion of these data produce path-averaged 1D radially anisotropic models with about 4% anisotropy in the lithosphere, increasing to about 4.8% anisotropy across the lithosphere-asthenosphere boundary (LAB). Models with reasonable crustal velocities in which the mantle lithosphere is isotropic cannot satisfy the data. The lithospheric lid, which ranges in thickness from about 70 km near the Red Sea coast to about 90 km beneath the Arabian Shield, is underlain by a pronounced low-velocity zone with shear velocities as low as 4.1 km/s. Forward models, which are constructed from previously determined shear-wave splitting estimates, can reconcile surface and body wave observations of anisotropy. The low shear velocity values are similar to many other continental rift and oceanic ridge environments. These low velocities combined with the sharp velocity contrast across the LAB may indicate the presence of partial melt beneath Arabia. The anisotropic signature primarily reflects a combination of plate- and density-driven flow associated with active rifting processes in the Red Sea.

  5. Rubber friction: comparison of theory with experiment.

    Science.gov (United States)

    Lorenz, B; Persson, B N J; Dieluweit, S; Tada, T

    2011-12-01

    We have measured the friction force acting on a rubber block slid on a concrete surface. We used both unfilled and filled (with carbon black) styrene butadiene (SB) rubber and have varied the temperature from -10 °C to 100 °C and the sliding velocity from 1 μm/s to 1000 μm/s. We find that the experimental data at different temperatures can be shifted into a smooth master-curve, using the temperature-frequency shifting factors obtained from measurements of the bulk viscoelastic modulus. The experimental data has been analyzed using a theory which takes into account the contributions to the friction from both the substrate asperity-induced viscoelastic deformations of the rubber, and from shearing the area of real contact. For filled SB rubber the frictional shear stress σ(f) in the area of real contact results mainly from the energy dissipation at the opening crack on the exit side of the rubber-asperity contact regions. For unfilled rubber we instead attribute σ(f) to shearing of a thin rubber smear film, which is deposited on the concrete surface during run in. We observe very different rubber wear processes for filled and unfilled SB rubber, which is consistent with the different frictional processes. Thus, the wear of filled SB rubber results in micrometer-sized rubber particles which accumulate as dry dust, which is easily removed by blowing air on the concrete surface. This wear process seams to occur at a steady rate. For unfilled rubber a smear film forms on the concrete surface, which cannot be removed even using a high-pressure air stream. In this case the wear rate appears to slow down after some run in time period.

  6. Topographic imaging and velocity measurements of surface expansion during laser ablation of a metal layer on glass

    Science.gov (United States)

    Rodriguez, G.; Valenzuela, A. R.; Clarke, S. A.; Thomas, K. A.

    2006-05-01

    We report on the development of novel high-speed techniques to measure the surface topography and instantaneous velocity of ablatively launched thin metal layers with sub-nanosecond temporal resolution. Applications for laser detonator technology require the understanding of laser fiber optical energy deposition and ablative launch of a thin metal layer into an explosive. Characterization of the ablation process requires a time-resolved diagnosis of the ejected material state (topography, velocity, density, pressure, etc.). A pulsed Nd:YAG fibercoupled laser is used to ablate a 250 nm layer of titanium deposited on a 500 μm thick fused silica substrate at fluences below 10 J/cm2. Time-resolved imaging of the free expansion of the metal surface is accomplished with Fourier plane imaging using a Shack-Hartmann lenticular array coupled to a fast framing camera. The imager performs topographical surface measurements by detecting changes in the optical wavefront of a reflected picosecond probe laser beam off the expanding surface. Consequently, single-event sub-nanosecond time-resolved "movies" of surface motion dynamics are captured. Crosscheck of the Shack-Hartmann imager is done using advanced velocimetry. A 1550 nm heterodyne laser-based Photonic Doppler Velocimeter is used to measure surface velocity. Using a 1550 nm single mode fiber laser, 10 GHz InGaAs detectors and telecom hardware, we directly record the resulting beat signal produced by the accelerated surface onto a fast digitizer. Free surface velocities as high as 6.5 μm/ns are recorded. Comparisons between the dynamic topography, surface velocimetry and laser hydrocode simulations are presented.

  7. Measurement of Normal and Friction Forces in a Rolling Process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    by the fric-tion conditions. To achieve this important informa-tion, measurements of the normal pressure and friction stresses in the deformation zone are re-quested. The direction of the friction stresses is changing during the rolling gap. At the entrance of the de-formation zone, the peripherical velocity...... of the roll is higher than for the incoming material, which causes frictional stresses at the material acting in the rolling direction. At the outlet of the rolling gap, the velocity of the deformed material exceeds the velocity of the roll, generating frictional stresses contrary to the direction of rolling...

  8. Frictional response of simulated faults to normal stresses perturbations probed with ultrasonic waves

    Science.gov (United States)

    Shreedharan, S.; Riviere, J.; Marone, C.

    2017-12-01

    We report on a suite of laboratory friction experiments conducted on saw-cut Westerly Granite surfaces to probe frictional response to step changes in normal stress and loading rate. The experiments are conducted to illuminate the fundamental processes that yield friction rate and state dependence. We quantify the microphysical frictional response of the simulated fault surfaces to normal stress steps, in the range of 1% - 600% step increases and decreases from a nominal baseline normal stress. We measure directly the fault slip rate and account for changes in slip rate with changes in normal stress and complement mechanical data acquisition by continuously probing the faults with ultrasonic pulses. We conduct the experiments at room temperature and humidity conditions in a servo controlled biaxial testing apparatus in the double direct shear configuration. The samples are sheared over a range of velocities, from 0.02 - 100 μm/s. We report observations of a transient shear stress and friction evolution with step increases and decreases in normal stress. Specifically, we show that, at low shear velocities and small increases in normal stress ( 5% increases), the shear stress evolves immediately with normal stress. We show that the excursions in slip rate resulting from the changes in normal stress must be accounted for in order to predict fault strength evolution. Ultrasonic wave amplitudes which first increase immediately in response to normal stress steps, then decrease approximately linearly to a new steady state value, in part due to changes in fault slip rate. Previous descriptions of frictional state evolution during normal stress perturbations have not adequately accounted for the effect of large slip velocity excursions. Here, we attempt to do so by using the measured ultrasonic amplitudes as a proxy for frictional state during transient shear stress evolution. Our work aims to improve understanding of induced and triggered seismicity with focus on

  9. Comparison of frictional forces on graphene and graphite

    International Nuclear Information System (INIS)

    Lee, Hyunsoo; Lee, Naesung; Seo, Yongho; Eom, Jonghwa; Lee, SangWook

    2009-01-01

    We report on the frictional force between an SiN tip and graphene/graphite surfaces using lateral force microscopy. The cantilever we have used was made of an SiN membrane and has a low stiffness of 0.006 N m -1 . We prepared graphene flakes on a Si wafer covered with silicon oxides. The frictional force on graphene was smaller than that on the Si oxide and larger than that on graphite (multilayer of graphene). Force spectroscopy was also employed to study the van der Waals force between the graphene and the tip. Judging that the van der Waals force was also in graphite-graphene-silicon oxide order, the friction is suspected to be related to the van der Waals interactions. As the normal force acting on the surface was much weaker than the attractive force, such as the van der Waals force, the friction was independent of the normal force strength. The velocity dependency of the friction showed a logarithmic behavior which was attributed to the thermally activated stick-slip effect.

  10. Slope-Velocity-Equilibrium and evolution of surface roughness on a stony hillslope

    Science.gov (United States)

    Slope-velocity equilibrium is hypothesized as a state that evolves naturally over time due to the interaction between overland flow and bed morphology, wherein steeper areas develop a relative increase in physical and hydraulic roughness such that flow velocity is a unique function of overland flow ...

  11. Rubber friction and force transmission during the shearing process of actively-driven vacuum grippers on rough surfaces; Elastomerreibung und Kraftuebertragung beim Abscheren von aktiv betriebenen Vakuumgreifern auf rauen Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Kern, Patrick

    2016-12-21

    Nowadays, vacuum grippers come in many different shapes and sizes. Their stability is guaranteed through specially manufactured metal fittings. These fittings are non-positively and positively connected to the elastic part of the vacuum gripper. The design of the elastic part may vary, though. Elastomer components are used to ensure tightness for the negative pressure in the active cave chamber of the vacuum gripper, as well as for the transfer of shearing forces, which acting parallel to the surface. Some vacuum grippers feature one elastomer for both the sealing function and the transfer of shear forces; other gripper types are equipped with various elastomers for those applications. The vacuum grippers described in this work are equipped with structured rubber friction pads, their tightness being ensured by sealing lips made of a flexible foam rubber. A restraint system consisting of one or several vacuum grippers must be sized prior to its actual practical use. For the transmission of shearing forces, which acting parallel to the surface, it is necessary to take the tribological system, consisting of the suction element's elastomer and the base material, into account since these loads put shearing stress on the vacuum gripper. In practice, however, a standardized value is given for the coefficient of friction μ; i.e. the ratio of transmissible frictional force to the normal force. This does neither include a detailed description of the elastomer used nor of the roughness of the base material. The standardized friction coefficients cannot be applied to the practical design of restraint systems. The present work includes the analysis of the load transmission and the modeling of the friction coefficients μ on rough surfaces during the shearing process of actively-driven vacuum grippers. Based on current theories, the phenomenon of elastomeric friction can be attributed to the two main components of hysteresis and adhesion friction. Both components are

  12. An Ice Track Equipped with Optical Sensors for Determining the Influence of Experimental Conditions on the Sliding Velocity

    Science.gov (United States)

    Lungevics, J.; Jansons, E.; Gross, K. A.

    2018-02-01

    The ability to slide on ice has previously focused on the measurement of friction coefficient rather than the actual sliding velocity that is affected by it. The performance can only be directly measured by the sliding velocity, and therefore the objective was to design and setup a facility to measure velo-city, and determine how experimental conditions affect it. Optical sensors were placed on an angled ice track to provide sliding velocity measurements along three sections and the velocity for the total sliding distance. Experimental conditions included the surface roughness, ambient temperature and load. The effect of roughness was best reported with a Criterion of Contact that showed a similar sliding velocity for metal blocks abraded with sand paper smoother than 600 grit. Searching for the effect of temperature, the highest sliding velocity coincided with the previously reported lowest coefficient of ice friction. Load showed the greatest velocity increase at temperatures closer to the ice melting point suggesting that in such conditions metal block overcame friction forces more easily than in solid friction. Further research needs to be conducted on a longer ice track, with larger metal surfaces, heavier loads and higher velocities to determine how laboratory experiments can predict real-life situations.

  13. An Ice Track Equipped with Optical Sensors for Determining the Influence of Experimental Conditions on the Sliding Velocity

    Directory of Open Access Journals (Sweden)

    Lungevics J.

    2018-02-01

    Full Text Available The ability to slide on ice has previously focused on the measurement of friction coefficient rather than the actual sliding velocity that is affected by it. The performance can only be directly measured by the sliding velocity, and therefore the objective was to design and setup a facility to measure velo-city, and determine how experimental conditions affect it. Optical sensors were placed on an angled ice track to provide sliding velocity measurements along three sections and the velocity for the total sliding distance. Experimental conditions included the surface roughness, ambient temperature and load. The effect of roughness was best reported with a Criterion of Contact that showed a similar sliding velocity for metal blocks abraded with sand paper smoother than 600 grit. Searching for the effect of temperature, the highest sliding velocity coincided with the previously reported lowest coefficient of ice friction. Load showed the greatest velocity increase at temperatures closer to the ice melting point suggesting that in such conditions metal block overcame friction forces more easily than in solid friction. Further research needs to be conducted on a longer ice track, with larger metal surfaces, heavier loads and higher velocities to determine how laboratory experiments can predict real-life situations.

  14. General theory of frictional heating with application to rubber friction

    Science.gov (United States)

    Fortunato, G.; Ciaravola, V.; Furno, A.; Lorenz, B.; Persson, B. N. J.

    2015-05-01

    The energy dissipation in the contact regions between solids in sliding contact can result in high local temperatures which may strongly effect friction and wear. This is the case for rubber sliding on road surfaces at speeds above 1 mm s-1. We derive equations which describe the frictional heating for solids with arbitrary thermal properties. The theory is applied to rubber friction on road surfaces and we take into account that the frictional energy is partly produced inside the rubber due to the internal friction of rubber and in a thin (nanometer) interfacial layer at the rubber-road contact region. The heat transfer between the rubber and the road surface is described by a heat transfer coefficient which depends on the sliding speed. Numerical results are presented and compared to experimental data. We find that frictional heating results in a kinetic friction force which depends on the orientation of the sliding block, thus violating one of the two basic Leonardo da Vinci ‘laws’ of friction.

  15. Feasibility of surface-coated friction stir welding tools to join AISI 304 grade austenitic stainless steel

    Directory of Open Access Journals (Sweden)

    A.K. Lakshminarayanan

    2014-12-01

    Full Text Available An attempt is made to develop the tools that are capable enough to withstand the shear, impact and thermal forces that occur during friction stir welding of stainless steels. The atmospheric plasma spray and plasma transferred arc hardfacing processes are employed to deposit refractory ceramic based composite coatings on the Inconel 738 alloy. Five different combinations of self-fluxing alloy powder and 60% ceramic reinforcement particulate mixtures are used for coating. The best friction stir welding tool selected based on tool wear analysis is used to fabricate the austenitic stainless steel joints.

  16. [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

  17. Strong Velocity-Weakening of Nanograins at High Slip-Rates

    Science.gov (United States)

    Han, R.; Hirose, T.; Ando, J.

    2008-12-01

    It has been observed that slip localization zones in some experimental and natural faults consist of crystalline or amorphous nanograins of different minerals. Prolonged grinding of silicate rocks (e.g., quartz rock and granite) is known to produce amorphous silica nanograins and mechanical properties of the material (especially under wet condition) have been attributed to a mechanism of fault weakening. Also, recent high- velocity friction tests on carbonate rocks showed that faults can be weakened by thermal decomposition of calcite into nanograins of lime and carbon dioxide and the lubrication effect of the nanograins would be critical for the fault weakening. However, mechanical behavior(s) and friction mechanism(s) of fault slip zones with nanograins, especially at high slip-rates, are still poorly understood, despite their potential importance to the understanding of seismic faulting. In this contribution, we show you our experimental results indicating velocity-weakening of nanograins (probably caused by still unknown mechanical behaviors of nanograins) rather than by temperature-related weakening behavior. In our high-velocity friction tests on Carrara marble at seismic slip-rates, we have tried to "cool" the simulated fault with liquid nitrogen and compressed air during frictional sliding, and found, in the simulated fault coated with nanopowders of lime (CaO) formed by thermal decomposition, no correlation between friction and temperature measured with thermocouples (i.e., no temperature-related weakening behavior), although strong "velocity-weakening" behavior appeared. The observation was confirmed by another experiment: from (1) the calculated "maximum" sliding surface temperature [Carslaw and Jaeger, 1959] using the mechanical data, with an assumption of strong slip localization into a very thin layer, and (2) the measured temperature with thermocouples at a place just below the sliding surface and close to the periphery of the specimen, it was found

  18. 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

  19. An atlas of monthly mean distributions of SSMI surface wind speed, AVHRR/2 sea surface temperature, AMI surface wind velocity, TOPEX/POSEIDON sea surface height, and ECMWF surface wind velocity during 1993

    Science.gov (United States)

    Halpern, D.; Fu, L.; Knauss, W.; Pihos, G.; Brown, O.; Freilich, M.; Wentz, F.

    1995-01-01

    The following monthly mean global distributions for 1993 are presented with a common color scale and geographical map: 10-m height wind speed estimated from the Special Sensor Microwave Imager (SSMI) on a United States (U.S.) Air Force Defense Meteorological Satellite Program (DMSP) spacecraft; sea surface temperature estimated from the Advanced Very High Resolution Radiometer (AVHRR/2) on a U.S. National Oceanic and Atmospheric Administration (NOAA) satellite; 10-m height wind speed and direction estimated from the Active Microwave Instrument (AMI) on the European Space Agency (ESA) European Remote Sensing (ERS-1) satellite; sea surface height estimated from the joint U.S.-France Topography Experiment (TOPEX)/POSEIDON spacecraft; and 10-m height wind speed and direction produced by the European Center for Medium-Range Weather Forecasting (ECMWF). Charts of annual mean, monthly mean, and sampling distributions are displayed.

  20. The influence of flow velocity on electrochemical reaction of metal surface

    Science.gov (United States)

    Li, Zhen; Zhang, Jiding

    2017-12-01

    In order to find out the effect of fluid flow velocity on electrochemical reaction, the electrochemical parameters of super 13Cr stainless steel in 3.5% NaCl aqueous solution were measured by a jet flow system at different flow velocities. The electrochemical characters such as open-circuit potential and polarization curve were monitored online using a three-electrode electrochemical system. The results show that the increase of wall shear stress caused by the high flow velocity leads to the rupture of passive films and the exposure of fresh metal in the corrosive media, which causes the increase of corrosion rate. Meanwhile, the corrosion rate shows a significant growth when the flow velocity is less than 0∼10.0 m/s. But it gradually decreases after reaching a maximum value.

  1. Retrieval of sea surface velocities using sequential ocean colour monitor (OCM) data

    Digital Repository Service at National Institute of Oceanography (India)

    Prasad, J.S.; Rajawat, A.S.; Pradhan, Y.; Chauhan, O.S.; Nayak, S.R.

    patterns in successive images. The technique provides actual flow during a specified period by integrating both tidal and wind influences. The current velocities retrieved were compared with synchronous data collected along east coast during GSI cruise ST...

  2. Crustal velocity structure of the Deccan Volcanic Province, Indian Peninsula, from observed surface wave dispersion

    Directory of Open Access Journals (Sweden)

    Gaddale Suresh

    2014-08-01

    Full Text Available Through inversion of fundamental mode group velocities of Love and Rayleigh waves, we study the crustal and subcrustal structure across the central Deccan Volcanic Province (DVP, which is one of the world’s largest terrestrial flood basalts. Our analysis is based on broadband seismograms recorded at seismological station Bhopal (BHPL in the central India from earthquakes located near west coast of India, with an average epicentral distance about 768 km. The recording station and epicentral zone are situated respectively on the northern and southern edges of DVP with wave paths across central DVP. The period of group velocity data ranges from 5 to 60 s for Rayleigh waves and 5 to 45 s for Love waves. Using the genetic algorithm, the observed data have been inverted to obtain the crust and subcrustal velocity structure along the wavepaths. Using this procedure, a similar velocity structure was also obtained earlier for the northwestern DVP, which is in the west of the present study region. Comparison of results show that the crustal thickness decreases westward from central DVP (39.6 km to northwestern DVP (37.8 km along with the decrease of thickness of upper crust; while the thickness of lower crust remains nearly same. From east to west S-wave velocity in the upper crust decreases by 2 to 3 per cent, while P-wave velocity in the whole crust and subcrust decreases by 3 to 6 per cent. The P- and S-wave velocities are positively correlated with crustal thickness and negatively correlated with earth’s heat flow. It appears that the elevated crustal and subcrustal temperature in the western side is the main factor for low velocities on this side.

  3. HF Radar Bistatic Measurement of Surface Current Velocities: Drifter Comparisons and Radar Consistency Checks

    OpenAIRE

    Lipa, Belinda; Whelan, Chad; Rector, Bill; Nyden, Bruce

    2009-01-01

    We describe the operation of a bistatic HF radar network and outline analysis methods for the derivation of the elliptical velocity components from the radar echo spectra. Bistatic operation is illustrated by application to a bistatic pair: Both remote systems receive backscattered echo, with one remote system in addition receiving bistatic echoes transmitted by the other. The pair produces elliptical velocity components in addition to two sets of radials. Results are compared with drifter me...

  4. A prototype of radar-drone system for measuring the surface flow velocity at river sites and discharge estimation

    Science.gov (United States)

    Moramarco, Tommaso; Alimenti, Federico; Zucco, Graziano; Barbetta, Silvia; Tarpanelli, Angelica; Brocca, Luca; Mezzanotte, Paolo; Rosselli, Luca; Orecchini, Giulia; Virili, Marco; Valigi, Paolo; Ciarfuglia, Thomas; Pagnottelli, Stefano

    2015-04-01

    Discharge estimation at a river site depends on local hydraulic conditions identified by recording water levels. In fact, stage monitoring is straightforward and relatively inexpensive compared with the cost necessary to carry out flow velocity measurements which are, however, limited to low flows and constrained by the accessibility of the site. In this context the mean flow velocity is hard to estimate for high flow, affecting de-facto the reliability of discharge assessment for extreme events. On the other hand, the surface flow velocity can be easily monitored by using radar sensors allowing to achieve a good estimate of discharge by exploiting the entropy theory applied to rivers hydraulic (Chiu,1987). Recently, a growing interest towards the use of Unmanned Aerial Vehicle (UVA), henceforth drone, for topographic applications is observed and considering their capability drones may be of a considerable interest for the hydrological monitoring and in particular for streamflow measurements. With this aim, for the first time, a miniaturized Doppler radar sensor, operating at 24 GHz, will be mounted on a drone to measure the surface flow velocity in rivers. The sensor is constituted by a single-board circuit (i.e. is a fully planar circuits - no waveguides) with the antenna on one side and the front-end electronic on the other side (Alimenti et al., 2007). The antenna has a half-power beam width of less than 10 degrees in the elevation plane and a gain of 13 dBi. The radar is equipped with a monolithic oscillator and transmits a power of about 4 mW at 24 GHz. The sensor is mounted with an inclination of 45 degrees with respect to the drone flying plane and such an angle is considered in recovering the surface speed of the water. The drone is a quadricopter that has more than 30 min, flying time before recharging the battery. Furthermore its flying plan can be scheduled with a suitable software and is executed thanks to the on-board sensors (GPS, accelerometers

  5. Water erosion in surface soil conditions: runoff velocity, concentration and D50 index of sediments in runoff

    Directory of Open Access Journals (Sweden)

    Júlio César Ramos

    2016-06-01

    Full Text Available ABSTRACT Water erosion and contamination of water resources are influenced by concentration and diameter of sediments in runoff. This study aimed to quantify runoff velocity and concentration and the D50 index of sediments in runoff under different soil surface managements, in the following treatments: i cropped systems: no-tilled soil covered by ryegrass (Lolium multiflorum Lam. residue, with high soil cover and minimal roughness (HCR; no tilled soil covered by vetch (Vicia sativa L. residue, with high soil cover and minimal roughness (HCV; chiseled soil after ryegrass crop removing the above-ground residues and keeping only the root system, with high roughness (HRR; chiseled soil after vetch crop removing the above-ground residues and keeping only the root system, with high roughness (HRV; ii bare and chiseled soil, with high roughness (BHR. The research was conducted on a Humic Dystrupept under simulated rainfall. The design was completely randomized and each treatment was replicated twice. Eight rainfall events of controlled intensity (65 mm h−1 were applied to each treatment for 90 minutes. The D50 index, runoff velocity and sediment concentration were influenced by crop and soil management. Runoff velocity was more intensely reduced by cover crop residues than by surface roughness. Regardless of surface condition, the D50 index and concentration of sediment in runoff were lower under ryegrass than vetch crop. Runoff velocity and the D50 index were exponentially and inversely correlated with soil cover by residues and with surface roughness, while the D50 index was positively and exponentially correlated with runoff velocity.

  6. A new theory for the static contact between rough, unmated surfaces in non-elastically deforming rock and its implications for rock friction

    Science.gov (United States)

    Stesky, R. M.; Hannan, S. S.

    The closure behavior of fractures in marble and alabaster is markedly different from that in quartzite. The aperture decreases considerably more under normal stress and remains permanently reduced, for the same ratio of normal stress to unconfined compressive strength. Also, a larger permanent relative contact area develops between the surfaces of marble and alabaster than it does between surfaces of quartzite. The permanent contact area increases at an increasing rate with normal stress in marble and alabaster, unlike the nearly linear increase in quartzite. The failure of surface asperities of calcite and gypsum during closure accounts for these differences. We modeled this process by considering the surfaces to consist of paraboloids lying on a flat plane and having a range of initial heights. Closure occurs by pressing a plane rigid surface against the 'hills', flattening their peaks, keeping the base area of the hills constant. To allow for a changing resistance to deformation, the contact stress is assumed to vary linearly with the shortening strain, to a first approximation. This model was tested against measurements of fracture closure and contact area of rough surfaces of calcite marble with a known initial height distribution of surface peaks. The fit to the data is quite good. In all cases, the model shows that closure is accompanied by a decrease in contact strength of deforming asperities, suggested also by the cataclastic deformation observed petrographically. The number of contact spots and the total length of contact seen in profile are also reasonably well modeled. These results have important implications for our understanding of frictional strength of fractures. The overall resistance to shear along rough surfaces depends upon the product of the shear strength and true area of the contacts, both of which are affected by normal stress. Application of this model approach shows that the initial frictional resistance of some fractures in ductile

  7. Molecular dynamics simulation study of friction force and torque on a rough spherical particle.

    Science.gov (United States)

    Kohale, Swapnil C; Khare, Rajesh

    2010-06-21

    Recent developments in techniques of micro- and nanofluidics have led to an increased interest in nanoscale hydrodynamics in confined geometries. In our previous study [S. C. Kohale and R. Khare, J. Chem. Phys. 129, 164706 (2008)], we analyzed the friction force experienced by a smooth spherical particle that is translating in a fluid confined between parallel plates. The magnitude of three effects--velocity slip at particle surface, the presence of confining surfaces, and the cooperative hydrodynamic interactions between periodic images of the moving particle--that determine the friction force was quantified in that work using molecular dynamics simulations. In this work, we have studied the motion of a rough spherical particle in a confined geometry. Specifically, the friction force experienced by a translating particle and the torque experienced by a rotating particle are studied using molecular dynamics simulations. Our results demonstrate that the surface roughness of the particle significantly reduces the slip at the particle surface, thus leading to higher values of the friction force and hence a better agreement with the continuum predictions. The particle size dependence of the friction force and the torque values is shown to be consistent with the expectations from the continuum theory. As was observed for the smooth sphere, the cooperative hydrodynamic interactions between the images of the sphere have a significant effect on the value of the friction force experienced by the translating sphere. On the other hand, the torque experienced by a spherical particle that is rotating at the channel center is insensitive to this effect.

  8. Influence of Al2O3 particles on the microstructure and mechanical properties of copper surface composites fabricated by friction stir processing

    Directory of Open Access Journals (Sweden)

    L. Suvarna Raju

    2014-12-01

    Full Text Available The influence of three factors, such as volume percentage of reinforcement particles (i.e. Al2O3, tool tilt angle and concave angle of shoulder, on the mechanical properties of Cu–Al2O3 surface composites fabricated via friction stir processing was studied. Taguchi method was used to optimize these factors for maximizing the mechanical properties of surface composites. The fabricated surface composites were examined by optical microscope for dispersion of reinforcement particles. It was found that Al2O3 particles are uniformly dispersed in the stir zone. The tensile properties of the surface composites increased with the increase in the volume percentage of the Al2O3 reinforcement particles. This is due to the addition of the reinforcement particles which increases the temperature of recrystallization by pinning the grain boundaries of the copper matrix and blocking the movement of the dislocations. The observed mechanical properties are correlated with microstructure and fracture features.

  9. A novel facility for reduced-gravity testing: A setup for studying low-velocity collisions into granular surfaces

    Science.gov (United States)

    Sunday, C.; Murdoch, N.; Cherrier, O.; Morales Serrano, S.; Valeria Nardi, C.; Janin, T.; Avila Martinez, I.; Gourinat, Y.; Mimoun, D.

    2016-08-01

    This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ˜0.1 to 1.0 m/s2. Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. Data from calibration tests verify the efficiency of the experiment's deceleration system and provide a quantitative understanding of the performance of the Atwood system.

  10. A novel facility for reduced-gravity testing: A setup for studying low-velocity collisions into granular surfaces.

    Science.gov (United States)

    Sunday, C; Murdoch, N; Cherrier, O; Morales Serrano, S; Valeria Nardi, C; Janin, T; Avila Martinez, I; Gourinat, Y; Mimoun, D

    2016-08-01

    This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ∼0.1 to 1.0 m/s(2). Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. Data from calibration tests verify the efficiency of the experiment's deceleration system and provide a quantitative understanding of the performance of the Atwood system.

  11. A Mobile System for Measuring Water Surface Velocities Using Unmanned Aerial Vehicle and Large-Scale Particle Image Velocimetry

    Science.gov (United States)

    Chen, Y. L.

    2015-12-01

    Measurement technologies for velocity of river flow are divided into intrusive and nonintrusive methods. Intrusive method requires infield operations. The measuring process of intrusive methods are time consuming, and likely to cause damages of operator and instrument. Nonintrusive methods require fewer operators and can reduce instrument damages from directly attaching to the flow. Nonintrusive measurements may use radar or image velocimetry to measure the velocities at the surface of water flow. The image velocimetry, such as large scale particle image velocimetry (LSPIV) accesses not only the point velocity but the flow velocities in an area simultaneously. Flow properties of an area hold the promise of providing spatially information of flow fields. This study attempts to construct a mobile system UAV-LSPIV by using an unmanned aerial vehicle (UAV) with LSPIV to measure flows in fields. The mobile system consists of a six-rotor UAV helicopter, a Sony nex5T camera, a gimbal, an image transfer device, a ground station and a remote control device. The activate gimbal helps maintain the camera lens orthogonal to the water surface and reduce the extent of images being distorted. The image transfer device can monitor the captured image instantly. The operator controls the UAV by remote control device through ground station and can achieve the flying data such as flying height and GPS coordinate of UAV. The mobile system was then applied to field experiments. The deviation of velocities measured by UAV-LSPIV of field experiments and handhold Acoustic Doppler Velocimeter (ADV) is under 8%. The results of the field experiments suggests that the application of UAV-LSPIV can be effectively applied to surface flow studies.

  12. Micro-PIV and CFD characterization of flows in a microchannel: Velocity profiles, surface roughness and Poiseuille numbers

    International Nuclear Information System (INIS)

    Silva, Goncalo; Leal, Nuno; Semiao, Viriato

    2008-01-01

    Microfluidics is a promising technology, although the governing physical mechanisms are still not quite understood due to the difficulties arising in measuring at such small scales. This work intends to bring some insight on the influence of surface phenomena in microscale flows by proposing a different method to quantify such influence. In this new method, detailed velocity measurements are performed to evaluate the influence on the flow of the surface phenomena instead of using measured bulk flow properties. For that micro-Particle Image Velocimetry (micro-PIV) is used to characterize the flow kinematics inside a DantecDynamics microchannel (with hydraulic diameter of 637 μm) that possesses rather rough walls (relative roughness of 1.6%) and a very irregular cross-section shape. Two-dimensional velocity profiles were measured in 61 horizontal planes to define the three-dimensional laminar flows (Re ≤ 50). Integration of the velocity profiles yielded volumetric flow rates with a maximum deviation of 3% from the measured volume of fluid discharged as function of time, which gives the magnitude of the bias error of the experimental technique. Effects of walls roughness were quantified by comparing Poiseuille numbers obtained from experimental velocity profiles against those obtained from CFD predictions for the same operating conditions but with hydrodynamically smooth walls, according to the new method proposed herein. Those Poiseuille numbers differed 11% demonstrating the need to account for wall roughness in microflows

  13. Friction and wear of stainless steel, titanium and aluminium with various surface treatments, ion implantation and overlay hard coatings

    International Nuclear Information System (INIS)

    Bunshah, R.F.

    1979-01-01

    This paper deals with the evaluation of the wear properties of 304 stainless steel, commercial grade titanium and commercial grade aluminium without and with different surface treatments, i.e., ion implantation of boron and nitrogen, and overlay coating of superhard materials, titanium carbide and nitride by the Biased Activated Reactive Evaporation (BARE) process. Wear properties were evaluated in adhesive, erosive and abrasive modes of wear. In the case of adhesive wear, ion implantation resulted in an improved wear behaviour in lubricated conditions but had no beneficial effect in dry wear conditions. Overlay coatings on the other hand resulted in improved wear behaviour for both the dry and lubricating conditions. In the case of erosive wear with SiC particles at high velocities, overlay coatings showed higher erosion rates (typical of brittle materials in normal impingement) whereas ion implanted materials behaved similarly as untreated materials; i.e., a lower wear rate than the specimens with overlay coatings. In the case of abrasive wear, it was again observed that the wear rates of overlay coatings is far lower than the wear rates of untreated or ion implanted materials. (author)

  14. Comparative study on the lateral run-out of friction surfaces measurement of brake discs using a brake roller tester and a dial gauge

    Directory of Open Access Journals (Sweden)

    Toma Marius

    2017-01-01

    Full Text Available Brake system diagnosis is one of the most common and necessary technical operations applied to the car, regardless of its type and operating phases. Measuring the diagnostic parameters on a roller brake tester is a fast operation with no disassembly necessary. Measuring the run-out of friction surfaces of brake discs with a dial gauge is an action that requires more extensive preparatory operations but it offers a high accuracy of the results. The paper aims to analyze the correlation between the dial gauge measured values and the diagnostic obtained using the brake roller tester.

  15. Theoretical Analysis of Unit Friction Force Working on the Metal Contact Surface with the Roll Change during Feedstock with Non-Uniform Temperature Distribution Rolling Process

    Directory of Open Access Journals (Sweden)

    Sygut P.

    2016-06-01

    Full Text Available The paper presents the results of theoretical studies influence of non-uniform temperature distribution along the feedstock length to the unit friction force working on the metal contact surface with the roll change during the round bars 70 mm in diameter continuous rolling process. This value is one of the major factors affecting the grooves wear during the rolling process. The studies were carried out based on the actual engineering data for 160 × 160 mm square cross-section feedstock of steel S355J0. Numerical modelling of the rolling process was performed using Forge2008®, a finite-element based computer program.

  16. Evolution of wear and friction along experimental faults

    Science.gov (United States)

    Boneh, Yeval; Chang, Jefferson C.; Lockner, David A.; Reches, Zeev

    2014-01-01

    We investigate the evolution of wear and friction along experimental faults composed of solid rock blocks. This evolution is analyzed through shear experiments along five rock types, and the experiments were conducted in a rotary apparatus at slip velocities of 0.002–0.97 m/s, slip distances from a few millimeters to tens of meters, and normal stress of 0.25–6.9 MPa. The wear and friction measurements and fault surface observations revealed three evolution phases: A) An initial stage (slip distances surface; B) a running-in stage of slip distances of 1–3 m with intense wear-rate, failure of many asperities, and simultaneous reduction of the friction coefficient and wear-rate; and C) a steady-state stage that initiates when the fault surface is covered by a gouge layer, and during which both wear-rate and friction coefficient maintain quasi-constant, low levels. While these evolution stages are clearly recognizable for experimental faults made from bare rock blocks, our analysis suggests that natural faults “bypass” the first two stages and slip at gouge-controlled steady-state conditions.

  17. Dependence of Pin Surface Roughness for Friction Forces of Ultrathin Perfluoropolyether Lubricant Film on Magnetic Disks by Pin-on-Disk Test

    Directory of Open Access Journals (Sweden)

    H. Tani

    2012-01-01

    Full Text Available We fabricated supersmooth probes for use in pin-on-disk sliding tests by applying gas cluster ion beam irradiation to glass convex lenses. In the fabrication process, various changes were made to the irradiation conditions; these included one-step irradiation of Ar clusters or two-step irradiation of Ar and N2 clusters, with or without Ar cluster-assisted tough carbon deposition prior to N2 irradiation, and the application of various ion doses onto the surface. We successfully obtained probes with a centerline averaged surface roughness that ranged widely from 1.08 to 4.30 nm. Using these probes, we measured the friction forces exerted on magnetic disks coated with a molecularly thin lubricant film. Perfluoropolyether lubricant films with different numbers of hydroxyl end groups were compared, and our results indicated that the friction force increases as the surface roughness of the pin decreases and that increases as the number of hydroxyl end groups increases.

  18. Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

    Science.gov (United States)

    d'Alessio, M. A.; Williams, C.F.; Burgmann, R.

    2006-01-01

    Heat flow measurements along much of the San Andreas fault (SAF) constrain the apparent coefficient of friction (??app) of the fault to 0.2 should be detectable even with the sparse existing observations, implying that ??app for the creeping section is as low as the surrounding SAF. Because the creeping section does not slip in large earthquakes, the mechanism controlling its weakness is not related to dynamic processes resulting from high slip rate earthquake ruptures. Copyright 2006 by the American Geophysical Union.

  19. Velocity and stage data collected in a laboratory flume for water-surface slope determination using a pipe manometer

    Science.gov (United States)

    Lee, Jonathan K.; Visser, H.M.; Jenter, H.L.; Duff, M.P.

    2000-01-01

    U.S. Geological Survey (USGS) hydrologists and ecologist are conducting studies to quantify vegetative flow resistance in order to improve numerical models of surface-water flow in the Florida Everglades. Water-surface slope is perhaps the most difficult of the flow resistance parameters to measure in the Everglades due to the very low gradients of the topography and flow. In an effort to measure these very small slopes, a unique pipe manometer was developed for the local measurement of water-surface slopes on the order of 1 centimeter per kilometer (cm/km). According to theory, a very precise measurement of centerline velocity obtained inside the pipe manometer should serve as a unique proxy for water-surface slope in the direction of the pipe axis. In order to confirm this theoretical relationship and calibrate the pipe manometer, water-surface elevation and pipe centerline velocity data were simultaneously measured in a set of experiments carried out in the tilting flume at the USGS Hydraulic Laboratory Facility at Stennis Space Center, Mississippi. A description of the instrumentation and methods used to evaluate this technique for measuring water-surface slope as well as a summary of the entire data set is presented.

  20. Seismic Technology Adapted to Analyzing and Developing Geothermal Systems Below Surface-Exposed High-Velocity Rocks Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Hardage, Bob A. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; DeAngelo, Michael V. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Ermolaeva, Elena [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Hardage, Bob A. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Remington, Randy [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Sava, Diana [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Wagner, Donald [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Wei, Shuijion [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology

    2013-02-01

    The objective of our research was to develop and demonstrate seismic data-acquisition and data-processing technologies that allow geothermal prospects below high-velocity rock outcrops to be evaluated. To do this, we acquired a 3-component seismic test line across an area of exposed high-velocity rocks in Brewster County, Texas, where there is high heat flow and surface conditions mimic those found at numerous geothermal prospects. Seismic contractors have not succeeded in creating good-quality seismic data in this area for companies who have acquired data for oil and gas exploitation purposes. Our test profile traversed an area where high-velocity rocks and low-velocity sediment were exposed on the surface in alternating patterns that repeated along the test line. We verified that these surface conditions cause non-ending reverberations of Love waves, Rayleigh waves, and shallow critical refractions to travel across the earth surface between the boundaries of the fast-velocity and slow-velocity material exposed on the surface. These reverberating surface waves form the high level of noise in this area that does not allow reflections from deep interfaces to be seen and utilized. Our data-acquisition method of deploying a box array of closely spaced geophones allowed us to recognize and evaluate these surface-wave noise modes regardless of the azimuth direction to the surface anomaly that backscattered the waves and caused them to return to the test-line profile. With this knowledge of the surface-wave noise, we were able to process these test-line data to create P-P and SH-SH images that were superior to those produced by a skilled seismic data-processing contractor. Compared to the P-P data acquired along the test line, the SH-SH data provided a better detection of faults and could be used to trace these faults upward to the boundaries of exposed surface rocks. We expanded our comparison of the relative value of S-wave and P-wave seismic data for geothermal

  1. Application and evaluation of LS-PIV technique for the monitoring of river surface velocities in high flow conditions

    OpenAIRE

    Jodeau , M.; Hauet , A.; Paquier , A.; Le Coz , J.; Dramais , G.

    2008-01-01

    Large Scale Particle Image Velocimetry (LS-PIV) is used to measure the surface flow velocities in a mountain stream during high flow conditions due to a reservoir release. A complete installation including video acquisition from a mobile elevated viewpoint and artificial flow seeding has been developed and implemented. The LS-PIV method was adapted in order to take into account the specific constraints of these high flow conditions. Using a usual LS-PIV data processing, significant variations...

  2. Parametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil moisture for arid and semi-arid areas

    Directory of Open Access Journals (Sweden)

    F. Fécan

    1999-01-01

    Full Text Available Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account for the influence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w' (depending on the soil texture, these capillary forces are considered as not strong enough to significantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w' is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coefficients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w' and soil clay content has been established. The erosion threshold ratios simulated for different soil textures were found to be in good agreement with the experimental data.Key words. Atmospheric composition and structure (Aerosols and particles · Hydrology (soil moisture

  3. Parametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil moisture for arid and semi-arid areas

    Energy Technology Data Exchange (ETDEWEB)

    Fecan, F.; Marticorena, B.; Bergametti, G. [Paris-7 Univ. (France). Lab. Interuniversitaire des Systemes Atmospheriques

    1999-01-01

    Large-scale simulation of the soil-derived dust emission in semiarid regions needs to account for the influence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension) are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w` (depending on the soil texture), these capillary forces are considered as not strong enough to significantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w` is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coefficients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w` and soil clay content has been established. The erosion threshold ratios simulated for different soil textures were found to be in good agreement with the experimental data. (orig.) 24 refs.

  4. Parametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil moisture for arid and semi-arid areas

    Directory of Open Access Journals (Sweden)

    F. Fécan

    Full Text Available Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account for the influence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w' (depending on the soil texture, these capillary forces are considered as not strong enough to significantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w' is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coefficients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w' and soil clay content has been established. The erosion threshold ratios simulated for different soil textures were found to be in good agreement with the experimental data.

    Key words. Atmospheric composition and structure (Aerosols and particles · Hydrology (soil moisture

  5. Surface wave waveform inversions for local shear-wave velocities under eastern Australia

    NARCIS (Netherlands)

    Passier, M.L.; Hilst, R.D. van der; Snieder, R.K.

    1997-01-01

    The waveform inversion method developed by Kushnir et al. [1989] and expanded by Passier and Snieder [1995b] yields estimates of structure along short interstation paths and of average velocity gradients. In contrast, 3D tomographic inversions yield local estimates of the earth structure by

  6. High resolution 3-D shear wave velocity structure in South China from surface wave tomography

    Science.gov (United States)

    Ning, S.; Guo, Z.; Chen, Y. J.

    2017-12-01

    Using continuous data from a total of 638 seismic stations, including 484 from CEArray between 2008 and 2013 and 154 from SINOPROBE between 2014 and 2015, we perform both ambient noise and earthquake Rayleigh wave tomography across South China. Combining Rayleigh wave phase velocity between 6and 40s periods from ambient noise tomography and Rayleigh wave phase velocity between 20and 140s from teleseismic two-plane-wave tomography, we obtain phase velocity maps between 6 and140 s periods. We then invert Rayleigh wave phase velocity to construct a 3-D shear wave velocity structure of South China by Markov Chain Monte Carlo method. Similar to other inversion results, our results correspond topography well. Moreover, our results also reveal that velocity structure of the eastern South China in mantle depth is similar to eastern North China, the core of the western South China, Sichuan Block (SB),still exists thick lithosphere. However, owing to much more data employed and some data quality control techniques in this research, our results reveal more detailed structures. Along Qinling-Dabie Orogenic Belt (QDOB), North-South Gravity Lineament (NSGL) and the Sichuan-Yunnan Rhombic Block (SYRB), there are obvious high speed anomalies in depths of 10-20 km, which possibly imply ancient intrusions. Moreover, it seems that Tancheng-Lujiang Fault Zone (TLFZ) has already cut through QDOB, forming a deep fracture cutting through the crust of the whole China continent. Although SB still exists thick lithosphere, there are indications for thermal erosion. At the same time, the lithosphere of the central SYRB seems to be experiencing delamination process, obviously forming a barrier to prevent the hot Tibetan Plateau (TP) mantle material from flowing further southeast. Upwelling hot mantle material possibly triggered by this delamination process might be the cause of the Emeishan Large Igneous Province. There exists an intercontinental low velocity layer in the crust of the TP

  7. The mechanism and universal scaling law of the contact line friction for the Cassie-state droplets on nanostructured ultrahydrophobic surfaces.

    Science.gov (United States)

    Zhao, Lei; Cheng, Jiangtao

    2018-04-05

    Besides the Wenzel state, liquid droplets on micro/nanostructured surfaces can stay in the Cassie state and consequently exhibit intriguing characteristics such as a large contact angle, small contact angle hysteresis and exceptional mobility. Here we report molecular dynamics (MD) simulations of the wetting dynamics of Cassie-state water droplets on nanostructured ultrahydrophobic surfaces with an emphasis on the genesis of the contact line friction (CLF). From an ab initio perspective, CLF can be ascribed to the collective effect of solid-liquid retarding and viscous damping. Solid-liquid retarding is related to the work of adhesion, whereas viscous damping arises from the viscous force exerted on the liquid molecules within the three-phase (liquid/vapor/solid) contact zone. In this work, a universal scaling law is derived to generalize the CLF on nanostructured ultrahydrophobic surfaces. With the decreasing fraction of solid-liquid contact (i.e., the solid fraction), CLF for a Cassie-state droplet gets enhanced due to the fact that viscous damping is counter-intuitively intensified while solid-liquid retarding remains unchanged. Nevertheless, the overall friction between a Cassie-state droplet and the structured surface is indeed reduced since the air cushion formed in the interstices of the surface roughness underneath the Cassie-state droplet applies negligible resistance to the contact line. Our results have revealed the genesis of CLF from an ab initio perspective, demonstrated the effects of surface structures on a moving contact line and justified the critical role of CLF in the analysis of wetting-related situations.

  8. Effect of friction on the motion of plasma filaments

    DEFF Research Database (Denmark)

    Garcia, Odd Erik; Madsen, Jens; Naulin, Volker

    is influenced by the collisional friction with the neutral gas fluid. In magnetically confined plasmas, the motion of filamentary structures in the edge region can be influenced by parallel dynamics in a manner that resembles an effective friction. In the presence of strong ballooning, such a frictional...... an effective friction, is investigated. In the inertial regime the radial filament velocity scales as the square root of its size. In the limit of strong friction regime the velocity scales as the inverse of the structure size. A discussion of these results will be given in the context of irregularities...

  9. Collets and friction

    Science.gov (United States)

    McIlraith, A. H.

    2005-07-01

    Conical sleeves, known as collets, have long been used for clamping sliding bodies to cylindrical columns in any desired position. Quantitative expressions for their properties are presented. Of particular interest is the ability of a collet to hold a shaft stationary against axial forces in either direction, and yet be able to release its grip with a minimum of additional force. This treatment relates the firmness of grip, the ease of release and the interface stresses to the cone angle, the coefficients of friction and the applied axial forces. The central part played by hysteresis is revealed. Experiments employing a test model give good support to the theoretical conclusions. They show that, up to the interface pressures reached, about 250 MPa, the friction between lubricated hardened steel and mild steel surfaces is independent of pressure. The strong dependence of friction on surface roughness is demonstrated. The possible adaptation of the collet test equipment to the measurement of friction at high interface pressures is touched upon. It could be a complementary alternative to the more flexible pin-on-disc method. With much larger working areas, it should have the advantages of better defined areas of contact, reduced ploughing effects and less leakage of lubricant.

  10. Symmetric-Galerkin BEM simulation of fracture with frictional contact

    CSIR Research Space (South Africa)

    Phan, AV

    2003-06-14

    Full Text Available A symmetric-Galerkin boundary element framework for fracture analysis with frictional contact (crack friction) on the crack surfaces is presented. The algorithm employs a continuous interpolation on the crack surface (utilizing quadratic boundary...

  11. Friction management on Kansas Department of Transportation highways.

    Science.gov (United States)

    2017-04-01

    The Federal Highway Administration (FHWA) estimates that about 70% of wet pavement crashes can be : prevented or minimized by improving pavement friction. High Friction Surface Treatment (HFST), a speciallydesigned : thin surface application of hard ...

  12. Friction and wear characteristics of carbon steels in vacuum

    Science.gov (United States)

    Verkin, B. I.; Lyubarskiy, I. M.; Udovenko, V. F.; Guslyakov, A. A.

    1974-01-01

    The nature of carbon steel friction and wear under vacuum conditions is described within the framework of general friction and wear theory. Friction is considered a dynamic process and wear is considered to be the result of a continuous sequence of transitions of the friction surface material from one state into another.

  13. Corrosion effects on friction factors

    International Nuclear Information System (INIS)

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

    1996-01-01

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

  14. A nonlinear rheological model for the ultrasonically induced squeeze film effect in variable friction haptic displays

    Science.gov (United States)

    Son, Kwon Joong

    2017-08-01

    A squeeze film induced by ultrasonic vibration between two solid surfaces in contact can dramatically reduce the friction between them. This phenomenon, so-called the squeeze film effect, has been utilized in variable friction tactile displays for texture rendering purposes. Such tactile displays can provoke a haptic sensation to a finger pad in a controllable way. A real-time adjustment of the coefficient of lateral friction between the human finger pad and the tactile display can be accomplished by modulating the vibration amplitude of the tactile panel. Therefore, driving a reliable friction model is a key step towards designing and controlling tactile displays utilizing the squeeze film effect. This paper derives a modified Herschel- Bulkley rheological model to express the lateral friction exerted on a human fingertip via an air squeeze film as a function of the operating parameters such as the driving voltage amplitude, the finger sliding speed, and the contact pressure. In contrast to the conventional Coulomb friction model, such a rheology model can account for the sliding velocity dependence. This modeling work may contribute to the optimal control of the ultrasonic variable friction tactile displays.

  15. Calculation of the Arc Velocity Along the Polluted Surface of Short Glass Plates Considering the Air Effect

    Directory of Open Access Journals (Sweden)

    Tao Yuan

    2012-03-01

    Full Text Available To investigate the microphysics mechanism and the factors that influence arc development along a polluted surface, the arc was considered as a plasma fluid. Based on the image method and the collision ionization theory, the electric field of the arc needed to maintain movement with different degrees of pollution was calculated. According to the force of the charged particle in an arc plasma stressed under an electric field, a calculation model of arc velocity, which is dependent on the electric field of the arc head that incorporated the effects of airflow around the electrode and air resistance is presented. An experiment was carried out to measure the arc velocity, which was then compared with the calculated value. The results of the experiment indicated that the lighter the pollution is, the larger the electric field of the arc head and arc velocity is; when the pollution is heavy, the effect of thermal buoyancy that hinders arc movement increases, which greatly reduces the arc velocity.

  16. Nonexponential decay of velocity correlations in surface diffusion: The role of interactions and ordering

    DEFF Research Database (Denmark)

    Vattulainen, Ilpo Tapio; Hjelt, T.; Ala-Nissila, T.

    2000-01-01

    We study the diffusive dynamics of adparticles in two model systems with strong interactions by considering the decay of the single-particle velocity correlation function phi (t). In accordance with previous studies, we find phi (t) to decay nonexponentially and follow a power-law phi (t)similar ......We study the diffusive dynamics of adparticles in two model systems with strong interactions by considering the decay of the single-particle velocity correlation function phi (t). In accordance with previous studies, we find phi (t) to decay nonexponentially and follow a power-law phi (t...... be rationalized in terms of interaction effects. Namely, x is typically larger than two in cases where repulsive adparticle-adparticle interactions dominate, while attractive interactions lead to x...

  17. Investigating Near Surface S-Wave Velocity Properties Using Ambient Noise in Southwestern Taiwan

    Directory of Open Access Journals (Sweden)

    Chun-Hsiang Kuo

    2015-01-01

    Full Text Available Ambient noise is typically used to estimate seismic site effects and velocity profiles instead of earthquake recordings, especially in areas with limited seismic data. The dominant Horizontal to Vertical Spectral Ratio (HVSR frequency of ambient noise is correlated to Vs30, which is the average S-wave velocity in the top 30 m. Vs30 is a widely used parameter for defining seismic amplification in earthquake engineering. HVSR can detect the vertical discontinuity of velocities, that is, the interfaces between hard bedrock and soft sediments. In southwestern Taiwan most strong motion stations are located in the plains and show a dominant frequency lower than 3 Hz. Several stations near the coast have low dominant frequencies of less than 1 Hz. The dominant frequencies are higher than 4 Hz at piedmont stations. The stations in the mountains with dominant frequencies over 8 Hz are typically located on very hard sites. This study analyzed the HVSR characteristics under different seismic site conditions considering the Vs30 from previous study (Kuo et al. 2012. The result implies that HVSRs are a better tool than Vs30 to classify the sites where bedrock is deeper than 30 m. Furthermore, we found a linear correlation between Vs30 and dominant HVSR frequency which could be used as a proxy of Vs30. The Vs30 map in this area was derived using the Engineering Geological Database for Taiwan Strong Motion Instrumentation Program (EGDT. The comparable distribution pattern between the dominant frequency and Vs30 demonstrate that HVSR can recognize S-wave velocity properties at the shallow subsurface.

  18. Eliminating friction with friction: 2D Janssen effect in a friction-driven system.

    Science.gov (United States)

    Karim, M Yasinul; Corwin, Eric I

    2014-05-09

    The Janssen effect is a unique property of confined granular materials experiencing gravitational compaction in which the pressure at the bottom saturates with an increasing filling height due to frictional interactions with side walls. In this Letter, we replace gravitational compaction with frictional compaction. We study friction-compacted 2D granular materials confined within fixed boundaries on a horizontal conveyor belt. We find that even with high-friction side walls the Janssen effect completely vanishes. Our results demonstrate that gravity-compacted granular systems are inherently different from friction-compacted systems in at least one important way: vibrations induced by sliding friction with the driving surface relax away tangential forces on the walls. Remarkably, we find that the Janssen effect can be recovered by replacing the straight side walls with a sawtooth pattern. The mechanical force introduced by varying the sawtooth angle θ can be viewed as equivalent to a tunable friction force. By construction, this mechanical friction force cannot be relaxed away by vibrations in the system.

  19. 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.

  20. High Speed Ice Friction

    Science.gov (United States)

    Seymour-Pierce, Alexandra; Sammonds, Peter; Lishman, Ben

    2014-05-01

    Many different tribological experiments have been run to determine the frictional behaviour of ice at high speeds, ostensibly with the intention of applying results to everyday fields such as winter tyres and sports. However, experiments have only been conducted up to linear speeds of several metres a second, with few additional subject specific studies reaching speeds comparable to these applications. Experiments were conducted in the cold rooms of the Rock and Ice Physics Laboratory, UCL, on a custom built rotational tribometer based on previous literature designs. Preliminary results from experiments run at 2m/s for ice temperatures of 271 and 263K indicate that colder ice has a higher coefficient of friction, in accordance with the literature. These results will be presented, along with data from further experiments conducted at temperatures between 259-273K (in order to cover a wide range of the temperature dependent behaviour of ice) and speeds of 2-15m/s to produce a temperature-velocity-friction map for ice. The effect of temperature, speed and slider geometry on the deformation of ice will also be investigated. These speeds are approaching those exhibited by sports such as the luge (where athletes slide downhill on an icy track), placing the tribological work in context.