WorldWideScience

Sample records for superelevation side friction

  1. Connecting the dots III: Night side cooling and surface friction affect climates of tidally locked terrestrial planets

    CERN Document Server

    Carone, L; Decin, L

    2016-01-01

    We investigate how night side cooling and surface friction impact surface temperatures and large scale circulation for tidally locked Earth-like planets. For each scenario, we vary the orbital period between $P_{rot}=1-100$~days and capture changes in climate states. We find drastic changes in climate states for different surface friction scenarios. For very efficient surface friction ($t_{s,fric}=$ 0.1 days), the simulations for short rotation periods ($P_{rot} \\leq$ 10 days) show predominantly standing extra tropical Rossby waves. These waves lead to climate states with two high latitude westerly jets and unperturbed meridional direct circulation. In most other scenarios, simulations with short rotation periods exhibit instead dominance by standing tropical Rossby waves. Such climate states have a single equatorial westerly jet, which disrupts direct circulation. Experiments with weak surface friction ($t_{s,fric}=~10 -100$ days) show decoupling between surface temperatures and circulation, which leads to s...

  2. Development of Microstructure and Crystallographic Texture in a Double-Sided Friction Stir Welded Microalloyed Steel

    Science.gov (United States)

    Rahimi, S.; Wynne, B. P.; Baker, T. N.

    2017-01-01

    The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the center of stirred zone reached a temperature between Ac1 and Ac3 during FSW, resulting in a dual-phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool shows the dominance of simple shear components across the whole weld. The austenite texture at Ac1 - Ac3 is dominated by the B { {1bar{1}2} }stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1 { {bar{1}bar{1}2} }weld pass. This is due to continuous dynamic strain-induced recrystallization as a result of simultaneous severe shear deformation and drastic undercooling.

  3. Corrosion Behavior of Top and Bottom Surfaces for Single-Side and Double-Side Friction Stir Welded 7085-T7651 Aluminum Alloy Thick Plate Joints

    Science.gov (United States)

    Xu, Weifeng; Zhang, Wei; Wu, Xiaoli

    2017-03-01

    Thick plate joints of 7085-T7451 aluminum alloy were obtained through both single-side and double-side friction stir welding (SS or DS-FSW). The chloride ions effects on the corrosion behavior of the top and bottom surfaces of the joints were examined by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Results show that the corrosion susceptibility was suppressed significantly in the weld nugget zone, while the base material and heat-affected zone were prone to be corrosion attacked. For the SS-FSWed joint, the top surface showed a higher corrosion resistance than that of the bottom surface, but the larger corrosive heterogeneity was observed between the top and bottom surfaces compared with the two welds of DS-FSWed joint, which was confirmed by the morphology of corrosion attack. A deep insight on the microstructure of the joints indicates that the intermetallic particles played a key role in the corrosion behavior of the FSWed AA7085 aluminum alloy joints in chloride solution.

  4. Corrosion Behavior of Top and Bottom Surfaces for Single-Side and Double-Side Friction Stir Welded 7085-T7651 Aluminum Alloy Thick Plate Joints

    Science.gov (United States)

    Xu, Weifeng; Zhang, Wei; Wu, Xiaoli

    2017-01-01

    Thick plate joints of 7085-T7451 aluminum alloy were obtained through both single-side and double-side friction stir welding (SS or DS-FSW). The chloride ions effects on the corrosion behavior of the top and bottom surfaces of the joints were examined by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Results show that the corrosion susceptibility was suppressed significantly in the weld nugget zone, while the base material and heat-affected zone were prone to be corrosion attacked. For the SS-FSWed joint, the top surface showed a higher corrosion resistance than that of the bottom surface, but the larger corrosive heterogeneity was observed between the top and bottom surfaces compared with the two welds of DS-FSWed joint, which was confirmed by the morphology of corrosion attack. A deep insight on the microstructure of the joints indicates that the intermetallic particles played a key role in the corrosion behavior of the FSWed AA7085 aluminum alloy joints in chloride solution.

  5. THE EFFECT OF THICKNESS OF PILLAR IN THE CHANNEL BEND TO CHANGES THE COEFFICIENT OF SUPERELEVATION

    Directory of Open Access Journals (Sweden)

    ISHAK M. GALIB

    2016-05-01

    Full Text Available The present study discusses phenomena occurred in a natural channel where a bridge is built in a river bend. The present study aims at determining the effect of pillars thickness on water surface slope in transverse direction on channel bend which is defined in superelevation coefficient (Cs. Physical modelling applies 180o channel bend, 0.75 m radius, and 0.5 m width. It was applied in both with pillar and without pillar flows in subcritical-turbulent flow. For the flows with pillar there were pillar interval of 30o and 60o. The results show that the highest value of Cs (7.826 is found in the flows with pillar of the 30o interval in 30o river bend. In the interval of 60 where the pillar thickness is 3cm, the Cs value is greater than when the pillar thickness is 2 cm, on the other hand in the interval of 30o the Cs value is smaller. It is recommended for the next research to apply hydraulic condition with average velocity divided by the critical velocity must be greater than one.

  6. A comparison of laboratory and field observations of superelevation in debris flows

    Science.gov (United States)

    McArdell, Brian W.; Scheidl, Christian; Graf, Christoph; Rickenmann, Dieter

    2017-04-01

    Post-event estimation of debris-flow velocity is a central part of hazard analysis. Estimates of debris-flow velocity are useful for e.g. dimensioning mitigation measures, calibrating or testing debris-flow runout models, constructing intensity-based hazard maps, and designing warning systems. However independent field observations of velocity are rare and it is often necessary to indirectly estimate flow velocity. The difference in mud elevation on either side of a channel through a bend of a constant radius can be used to estimate the flow velocity using a vortex method developed for a Newtonian fluid. In 2015 we reported on the application of the vortex method to calculate the front velocity of debris flows in the laboratory (Scheidl et al., 2015). In the laboratory experiments, we found a statistically significant correction factor k for the application of the vortex equation to debris flows under supercritical flow conditions, with somewhat more scatter for subcritical flows. Nevertheless, it was possible to derive a forced-vortex equation, without a correction factor, after considering active and passive earth pressures within the flow. Herein, we compare the laboratory results with field data from the Illgraben and Schipfenbach torrents in Switzerland. Using video recordings and flow trajectory data for 17 debris flows at the Illgraben debris-flow observation station in Switzerland, we were able to independently test the application of the new forced vortex equation against field data. The general trend observed in the laboratory are confirmed using the field data: the correction factor k decreases with increasing Froude number of the flow. However the field data show a much larger degree of scatter in the vortex-equation correction factor in comparison with the laboratory data. The debris flows in the field differ from the laboratory channel in many ways. Although the observation section at the Illgraben was fairly uniform in terms of the surface width of

  7. Financial Frictions

    DEFF Research Database (Denmark)

    Vestergaard Jensen, Mads

    frictions, a call option should never be exercised early, but only at expiration or just before the underlying stock pays a dividend. Chapter one of this thesis shows that suffciently severe frictions can make early exercise optimal. Short-sale costs especially represent an important driver of early...

  8. A modified debris-flow super-elevation formula with the run-up effect%考虑爬高效应的泥石流弯道超高公式

    Institute of Scientific and Technical Information of China (English)

    赵晋恒; 胡凯衡; 唐金波; 李浦

    2015-01-01

    弯道超高是泥石流运动的显著特征。以往研究认为弯道超高完全是由于泥石流的离心运动造成的,未考虑泥石流在弯道运动时的冲起爬高效应。本文假设弯道超高和爬高分别由泥石流沿弯道的切向和法向速度引起,根据弯道处速度矢量三角形和圆弧三角形的几何相似关系,推导了考虑爬高效应的泥石流弯道超高公式。该公式依赖于弯道的内外曲率半径比、泥石流速度和沟壁倾角,适用于弯道圆心角小于60°和沟道较宽的情形。经云南东川蒋家沟的野外实际调查数据以及其他文献中的数据验证,与实测值误差较小,可用于泥石流弯道爬高的实际计算中。%Debris flow exhibits a noticeable super-elevation when it passes through a meandering stream. Previous studies attributed the super-elevation completely to debris-flow centrifugal motion in bends of the stream and neglected the run-up effect on it. Assuming the super-elevation and run-up caused respectively by tangent and normal velocity components of debris flows along the bends, a new formula for calculating the super-elevation is derived from the combination of the traditional forced vortex equation and the veloci⁃ty head equation by virtue of geometric similar relationship between triangles of velocity vector and the curved channel. The total super-elevation is a function of flow velocity,ratio of internal and external curva⁃ture radiuses, and bank inclination angle. The new formula is applicable to the wide curved channel of which turning angle is less than 60° . The relative error between the calculated and field or experimental measured values is less than 17%,which is acceptable for practical purpose.

  9. The Gulf Stream: Inertia and friction

    OpenAIRE

    ASSAF, GAD

    2011-01-01

    The inertial theory of the Gulf Stream (Charney, 1955) is extended to include vertical friction in the cyclonic shear zone (the western side) of the stream. The vertical friction is assumed to be controlled by local Froude conditions.DOI: 10.1111/j.2153-3490.1977.tb00717.x

  10. 考虑水流路径长度的S型曲线超高段纵坡研究%Longitudinal Slope at Super-Elevation Sections of S Curve Considering Flow Path Length

    Institute of Scientific and Technical Information of China (English)

    张卓; 高建平

    2013-01-01

    雨天公路S型曲线超高缓和路段易形成积水,影响行车安全.以力学为基础,运用有限差分,建立了超高渐变段的水流路径长度与纵坡的关系模型;考虑车辆发生滑水的危险状态,得到水流路径控制长度.以公路单路拱S型曲线为研究对象,对3组不同车道数和7种不同纵坡工况下的±2%超高渐变段的水流路径长度进行分析.结果表明:纵坡由0.5%增加到6%,水流路径长度平均增大2.83倍,纵坡越大,水流路径越长;当纵坡大于4%时,不同车道的水流路径都超过了限定值.以水流路径长度为控制指标,给出了不同车道数S型曲线平缓超高路段最大纵坡建议值.%It is easy to have water at super-elevation section of S curve in rain,which affects the traffic safety.According to the difference of super-elevation gradient direction,the gradient sections are divided into the same change direction and the opposite of cross slope.The calculation models for flow path length of super-elevation section are established by dynamics and FDM.Considering the vehicle in hydroplaning danger state,the control length of flow path is obtained.Taking S curve of highway arch as the research object,flow path length of transition section whose super-elevation value is from-2% to 2% is analyzed,with 3 different types of lane numbers and 7 different types of longitudinal slopes.The results show that when longitudinal slope is increased from 0.5% to 6%,the average flow path length increases 2.83 times; the larger longitudinal slope,the longer of flow path length ; when longitudinal slope is greater than 4%,the prescribed values of different lanes all exceed.Taking the flow path length as the control index,the proposed maximum longitudinal slope values at super-elevation section of S curve with different lanes are put forward.

  11. REDUCED ENGINE FRICTION AND WEAR

    Energy Technology Data Exchange (ETDEWEB)

    Ron Matthews

    2005-05-01

    assembly in an engine. The model appears to produce the correct behavior, but we cannot quantify its strengths or weaknesses until our crank-angle-resolved measurements have been completed. Finally, we proposed and implemented a model for the effects of liner rotation on piston assembly friction. Here, we propose that the rotating liner design is analogous to the shaft-bushing mechanism. Therefore, we used the side-slip rolling friction model to simulate the effects of liner rotation. This model appears to be promising, but final analysis of its strengths and/or weaknesses must await our crank-angle-resolved measurements.

  12. Friction and Wear in Timing Belt Drives

    Directory of Open Access Journals (Sweden)

    B. Stojanovic

    2010-09-01

    Full Text Available Timing belt tooth goes into contact with a drive pulley, stretched to the maximum, because of the previous tension. When the contact begins the peak of the belt tooth makes the contact with the outer surface of the pulley teeth. The process of the teeth entering into the contact zone is accompanied with the relative sliding of their side surfaces and appropriate friction force. The normal force value is changing with the parabolic function, which also leads to the changes of the friction force. The biggest value of the normal force and of the friction force is at the tooth root. Hollow between teeth and the tip of the pulley teeth are also in contact. Occasionally, the face surface of the belt and the flange are also in contact. The friction occurs in those tribomechanical systems, also. Values of these friction forces are lower compared with the friction force, which occurs at the teeth root.

  13. 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

  14. Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.

    2008-01-01

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

  15. Localized Mechanical Properties of Friction Stir Processed Sensitized 5456-H116 Al

    Science.gov (United States)

    2013-04-01

    stir welding (FSW) but it does not create a joint. Friction stir welding is a solid state joining process where the material is softened such that...small randomly distributed porosity. The volumetric defects are representative of those seen in friction stir processing and friction stir welding ...retreating side on the second pass, are typical defects seen in aluminum friction stir processing and friction stir welding

  16. Comparative Frictional Analysis of Automobile Drum and Disc Brakes

    Directory of Open Access Journals (Sweden)

    H.P. Khairnar

    2016-03-01

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

  17. Torsional friction damper optimization

    Science.gov (United States)

    Ye, Shaochun; Williams, Keith A.

    2006-06-01

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

  18. Role of Friction in Cold Ring Rolling

    Institute of Scientific and Technical Information of China (English)

    He YANG; Lianggang GUO; Mei ZHAN

    2005-01-01

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

  19. Friction in orthodontics

    Science.gov (United States)

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

    2015-01-01

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

  20. Iliotibial band friction syndrome.

    Science.gov (United States)

    Lavine, Ronald

    2010-07-20

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

  1. Polymer friction Molecular Dynamics

    DEFF Research Database (Denmark)

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

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

  2. Science 101: What Causes Friction?

    Science.gov (United States)

    Robertson, Bill

    2014-01-01

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

  3. Friction stir welding tool

    Science.gov (United States)

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

    2008-04-15

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

  4. 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

  5. Reflections on Friction in Quantum Mechanics

    Directory of Open Access Journals (Sweden)

    Yair Rezek

    2010-08-01

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

  6. Wet Friction-Elements Boundary Friction Mechanism and Friction Coefficient Prediction

    Directory of Open Access Journals (Sweden)

    WANG Yanzhong

    2012-12-01

    Full Text Available The friction mechanism for the boundary friction course of friction elements engagement was explicitly expressed. The boundary friction model was built up by the surface topography. The model contained the effect of boundary film, adhesion, plough and lubrication. Based on the model, a coefficient for weakening plough for the lubrication was proposed. The modified model could fit for the working condition of wet friction elements. The friction coefficient as a function curve of rotating speed could be finally obtained by the data k and s/sm. The method provides a well interpretation of friction condition and friction coefficient prediction and the agreement between theoretical and experimental friction coefficients is reasonably good.

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

    Directory of Open Access Journals (Sweden)

    S.V. Fedorov

    2015-09-01

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

  8. Characteristics of Deformation Layer for Vermicular Iron under Dry Sliding Friction

    Institute of Scientific and Technical Information of China (English)

    SUN Le-min; SHANG Guan-bao; ZHANG Yong-zhen; CHEN Yue

    2004-01-01

    At room temperature, dry sliding wear tests were carried out using pin-on-disc test rig, in which the pin is made of vermicular iron and the disc is made of 40Cr steel. The microstructures of the frictional surfaces for the pin specimens were investigated. Under the action of both frictional heat and frictional shearing stress, a plastic deformation layer under the frictional surface is formed. The morphology and properties of the plastic deformation layer depend on specimen material, contact pressure and frictional shearing stress. In the plastic deformation layer, the phosphorous mass percent varies at different depth and results in different hardness. On the outer side of surface, the hardness is the biggest and the phosphorous mass percent is the highest. They become gradually small from outer side to inner side of the surface.

  9. Intelligent Flow Friction Estimation

    Directory of Open Access Journals (Sweden)

    Dejan Brkić

    2016-01-01

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

  10. Skin tribology: Science friction?

    NARCIS (Netherlands)

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

    2013-01-01

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

  11. Gravitomagnetic dynamical friction

    CERN Document Server

    Cashen, Benjamin; Kesden, Michael

    2016-01-01

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

  12. Skin friction on a flat perforated acoustic liner

    Science.gov (United States)

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

    1976-01-01

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

  13. Quantum tunneling with friction

    Science.gov (United States)

    Tokieda, M.; Hagino, K.

    2017-05-01

    Using the phenomenological quantum friction models introduced by P. Caldirola [Nuovo Cimento 18, 393 (1941), 10.1007/BF02960144] and E. Kanai [Prog. Theor. Phys. 3, 440 (1948), 10.1143/ptp/3.4.440], M. D. Kostin [J. Chem. Phys. 57, 3589 (1972), 10.1063/1.1678812], and K. Albrecht [Phys. Lett. B 56, 127 (1975), 10.1016/0370-2693(75)90283-X], we study quantum tunneling of a one-dimensional potential in the presence of energy dissipation. To this end, we calculate the tunneling probability using a time-dependent wave-packet method. The friction reduces the tunneling probability. We show that the three models provide similar penetrabilities to each other, among which the Caldirola-Kanai model requires the least numerical effort. We also discuss the effect of energy dissipation on quantum tunneling in terms of barrier distributions.

  14. Friction in rail guns

    Science.gov (United States)

    Kay, P. K.

    1984-01-01

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

  15. High Speed Friction Microscopy and Nanoscale Friction Coefficient Mapping

    OpenAIRE

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

    2014-01-01

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

  16. An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

    Science.gov (United States)

    Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; Shi, Qingyu

    2016-09-01

    For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, the lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. The simulated temperature field is validated by the good agreement to the experimental measurements.

  17. Friction laws for lubricated nanocontacts

    Science.gov (United States)

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

    2006-09-01

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

  18. 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.

  19. Solid friction between soft filaments

    CERN Document Server

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

    2015-01-01

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

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

    NARCIS (Netherlands)

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

    2004-01-01

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

  1. Friction and wear calculation methods

    CERN Document Server

    Kragelsky, I V; Kombalov, V S

    1981-01-01

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

  2. Friction or Closure

    DEFF Research Database (Denmark)

    Lundahl, Mikela

    2014-01-01

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

  3. 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.

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

    Science.gov (United States)

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

    2011-08-01

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

  5. Friction analysis of kinetic schemes : the friction coefficient

    NARCIS (Netherlands)

    Lolkema, Juke S.

    1995-01-01

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

  6. FRICTION ANALYSIS OF KINETIC SCHEMES - THE FRICTION COEFFICIENT

    NARCIS (Netherlands)

    LOLKEMA, JS

    1995-01-01

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

  7. Friction analysis of kinetic schemes : the friction coefficient

    NARCIS (Netherlands)

    Lolkema, Juke S.

    1995-01-01

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

  8. Friction pull plug welding: dual chamfered plate hole

    Science.gov (United States)

    Coletta, Edmond R. (Inventor); Cantrell, Mark A. (Inventor)

    2001-01-01

    Friction Pull Plug Welding (FPPW) is a solid state repair process for defects up to one inch in length, only requiring single sided tooling (OSL) for usage on flight hardware. Early attempts with FPPW followed the matching plug/plate geometry precedence of the successful Friction Push Plug Welding program, however no defect free welds were achieved due to substantial plug necking and plug rotational stalling. The dual chamfered hole has eliminated plug rotational stalling, both upon initial plug/plate contact and during welding. Also, the necking of the heated plug metal under a tensile heating/forging load has been eliminated through the usage of the dual chamfered plate hole.

  9. Slow frictional waves

    Science.gov (United States)

    Viswanathan, Koushik; Sundaram, Narayan; Chandrasekar, Srinivasan

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

  10. Corrosion effects on friction factors

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-03-01

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

  11. Elastic model of dry friction

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-09-15

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

  12. Friction in surface micromachined microengines

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-03-01

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

  13. Tactile friction of topical formulations.

    Science.gov (United States)

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

    2016-02-01

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

  14. Student figures in friction

    DEFF Research Database (Denmark)

    Nielsen, Gritt B.

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

  15. Friction effects on lateral loading behavior of rigid piles

    DEFF Research Database (Denmark)

    Zania, Varvara; Hededal, Ole

    2012-01-01

    The adequacy of the p -y curves used in the current practice for the design of rigid pile foundations with large diameter, like in the case of monopile foundations of offshore wind turbines, has been widely questioned. The current study aims at analyzing the lateral behavior of rigid piles, while...... taking into account the shear frictional resistance along the pile. For this purpose efficient three dimensional finite element models of different diameter have been developed. The increase of the side friction and of the diameter of the pile is shown to alter the failure pattern and increase...... the lateral capacity of the pile. The obtained p - y curves demonstrate the importance of the aforementioned parameters in the design of rigid piles, as the reduction of friction along the interface reduces not only the ultimate load but also the stiffness of the soil-pile response. Read More: http...

  16. Metal Flow During Friction Stir Welding

    Science.gov (United States)

    Guerra, M.; Schmidt, C.; McClure, J. C.; Murr, L. E.; Nunes, A. C.; Munafo, Paul M. (Technical Monitor)

    2001-01-01

    The flow of metal during Friction Stir Welding is clarified using a faying surface tracer and a nib frozen in place during welding. It is shown that material is transported by two processes. The first is a wiping of material from the advancing front side of the nib onto a plug of material that rotates and advances with the nib. The material undergoes a helical motion within the plug that both rotates and advances with the plug and descends in the wash of the threads on the nib and rises on the outer part of the plug. After one or more rotations, this material is sloughed off the plug in its wake, primarily on the advancing side. The second process is an entrainment of material from the front retreating side of the nib that fills in between the sloughed off pieces from the advancing side. These two processes produce material with different mechanical properties and the strength of a weld should depend on the relative importance of the processes.

  17. Frictional properties of confined polymers

    DEFF Research Database (Denmark)

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

    2008-01-01

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

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

    Science.gov (United States)

    Pollak, Eli

    2017-02-01

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

  19. Multimodal Friction Ignition Tester

    Science.gov (United States)

    Davis, Eddie; Howard, Bill; Herald, Stephen

    2009-01-01

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

  20. A Pedagogical Model of Static Friction

    CERN Document Server

    Pickett, Galen T

    2015-01-01

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

  1. Friction Material Composites Materials Perspective

    CERN Document Server

    Sundarkrishnaa, K L

    2012-01-01

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

  2. Kinetic Friction Coefficient of Ice,

    Science.gov (United States)

    1985-03-01

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

  3. Peak mass and dynamical friction

    CERN Document Server

    Del Popolo, A

    1995-01-01

    We show how the results given by several authors relatively to the mass of a density peak are changed when small scale substructure induced by dynamical friction are taken into account. The peak mass obtained is compared to the result of Peacock \\& Heavens (1990) and to the peak mass when dynamical friction is absent to show how these effects conspire to reduce the mass accreted by the peak.

  4. Tire/runway friction interface

    Science.gov (United States)

    Yager, Thomas J.

    1990-01-01

    An overview is given of NASA Langley's tire/runway pavement interface studies. The National Tire Modeling Program, evaluation of new tire and landing gear designs, tire wear and friction tests, and tire hydroplaning studies are examined. The Aircraft Landing Dynamics Facility is described along with some ground friction measuring vehicles. The major goals and scope of several joint FAA/NASA programs are identified together with current status and plans.

  5. Labor Supply and Optimization Frictions

    DEFF Research Database (Denmark)

    Søgaard, Jakob Egholt

    2015-01-01

    In this paper I investigate the nature of optimization frictions by studying the labor market of Danish students. This particular labor market is an interesting case study as it features a range of special institutional settings that affect students’ incentive to earn income and comparing outcomes...... theory. More concretely I find the dominate optimization friction to be individuals’ inattention about their earnings during the year, while real adjustment cost and gradual learning appears to be of less importance....

  6. Intra-articular fibroma of tendon sheath in a knee joint associated with iliotibial band friction syndrome

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Dong Ho; Choi, Sun Seob; Kim, Soo Jin; Lih, Wang [Dong-A University Medical Center, Busan (Korea, Republic of)

    2015-02-15

    Iliotibial band (ITB) friction syndrome is a common overuse injury typically seen in the active athlete population. A nodular lesion on the inner side of the ITB as an etiology or an accompanying lesion from friction syndrome has been rarely reported. A 45-year-old male presented with recurrent pain and a movable nodule at the lateral joint area, diagnosed as ITB friction syndrome. The nodule was confirmed as a rare intra-articular fibroma of the tendon sheath (FTS) on the basis of histopathologic findings. We describe the MRI findings, arthroscopic and pathologic features, in this case of intra-articular FTS presenting with ITB friction syndrome.

  7. Intra-articular fibroma of tendon sheath in a knee joint associated with iliotibial band friction syndrome.

    Science.gov (United States)

    Ha, Dong-Ho; Choi, Sunseob; Kim, Soo-Jin; Lih, Wang

    2015-01-01

    Iliotibial band (ITB) friction syndrome is a common overuse injury typically seen in the active athlete population. A nodular lesion on the inner side of the ITB as an etiology or an accompanying lesion from friction syndrome has been rarely reported. A 45-year-old male presented with recurrent pain and a movable nodule at the lateral joint area, diagnosed as ITB friction syndrome. The nodule was confirmed as a rare intra-articular fibroma of the tendon sheath (FTS) on the basis of histopathologic findings. We describe the MRI findings, arthroscopic and pathologic features, in this case of intra-articular FTS presenting with ITB friction syndrome.

  8. Frictional Effects on Gear Tooth Contact Analysis

    OpenAIRE

    Zheng Li; Ken Mao

    2013-01-01

    The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented us...

  9. Damping of a system of linear oscillators using the generalized dry friction

    OpenAIRE

    Ovseevich, Alexander; Fedorov, Aleksey

    2015-01-01

    The problem of damping a system of linear oscillators is considered. The problem is solved by using a control in the form of dry friction. The motion of the system under the control is governed by a system of differential equations with discontinuous right-hand side. A uniqueness and continuity theorem is proved for the phase flow of this system. Thus, the control in the form of generalized dry friction defines the motion of the system of oscillators uniquely.

  10. Friction stir welding of copper alloys

    Institute of Scientific and Technical Information of China (English)

    Liu Shuhua; Liu Meng; Wang Deqing; Xu Zhenyue

    2007-01-01

    Copper plates,brass plates and copper/brass plates were friction stir welded with various parameters. Experimental results show that the microstructure of the weld is characterized by its much finer grains as contrasted with the coarse grains of parent materials and the heat-affected zones are very narrow. The microhardness of the copper weld is a little higher than that of parent plate. The microhardness of brass weld is about 25% higher than that of parent material. The tensile strength of copper joints increases with increasing welding speed in the test range. The range of parameters to obtain good welds for copper is much wider than that for brass. When different materials were welded, the position of copper plate before welding affected the quality of FSW joints. If the copper plate was put on the advancing side of weld, the good quality of weld could be got under proper parameters.

  11. Metal Flow in Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.

    2006-01-01

    The plastic deformation field in Friction Stir Welding (FSW) is compared to that in metal cutting. A shear surface around the FSW tool analogous to the metal cutting shear plane is identified and comprises the basis of the "rotating plug" flow field model and the "wiping" model of tool interaction with weld metal. Within the context of these models: The FSW shear rate is estimated to be comparable to metal cutting shear rates. The effect of tool geometry on the FSW shear surface is discussed and related to published torque measurements. Various FS W structural features are explained, including a difference in structure of bimetallic welds when alloys on the advancing and retreating sides of the weld seam are exchanged. The joining mechanism and critical parameters of the FSW process are made clear.

  12. Friction anisotropy in boronated graphite

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-01

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

  13. Versatile Friction Stir Welding/Friction Plug Welding System

    Science.gov (United States)

    Carter, Robert

    2006-01-01

    A proposed system of tooling, machinery, and control equipment would be capable of performing any of several friction stir welding (FSW) and friction plug welding (FPW) operations. These operations would include the following: Basic FSW; FSW with automated manipulation of the length of the pin tool in real time [the so-called auto-adjustable pin-tool (APT) capability]; Self-reacting FSW (SRFSW); SR-FSW with APT capability and/or real-time adjustment of the distance between the front and back shoulders; and Friction plug welding (FPW) [more specifically, friction push plug welding] or friction pull plug welding (FPPW) to close out the keyhole of, or to repair, an FSW or SR-FSW weld. Prior FSW and FPW systems have been capable of performing one or two of these operations, but none has thus far been capable of performing all of them. The proposed system would include a common tool that would have APT capability for both basic FSW and SR-FSW. Such a tool was described in Tool for Two Types of Friction Stir Welding (MFS- 31647-1), NASA Tech Briefs, Vol. 30, No. 10 (October 2006), page 70. Going beyond what was reported in the cited previous article, the common tool could be used in conjunction with a plug welding head to perform FPW or FPPW. Alternatively, the plug welding head could be integrated, along with the common tool, into a FSW head that would be capable of all of the aforementioned FSW and FPW operations. Any FSW or FPW operation could be performed under any combination of position and/or force control.

  14. The Reality of Casimir Friction

    Directory of Open Access Journals (Sweden)

    Kimball A. Milton

    2016-04-01

    Full Text Available For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum electromagnetic fluctuations, which break time-reversal symmetry. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Partly because of the lack of contact with observations, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here, we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.

  15. The Reality of Casimir Friction

    CERN Document Server

    Milton, K A; Brevik, I

    2015-01-01

    For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum fluctuations. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Because of the lack of contact with phenomena, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.

  16. The microphysics of phyllosilicate friction

    Science.gov (United States)

    den Hartog, Sabine A. M.; Faulkner, Daniel R.; Spiers, Christopher J.

    2017-04-01

    Phyllosilicate-rich foliations in fault rocks are often thought to reduce overall fault strength and promote fault stability when forming an interconnected network. Indeed, laboratory measurements have shown that the average friction coefficient of dry phyllosilicates of 0.5 is reduced to 0.3 when wet or even 0.1 for smectite. A widely accepted interpretation of these observations is that the strength of phyllosilicates is controlled by breaking of interlayer bonds to form new cleavage surfaces when dry and by the low strength of surface-bound water films when wet. However, the correlation between phyllosilicate shear strength and interlayer bond strength, which formed the basis for this interpretation, was not reproduced in recent experiments (Behnsen and Faulkner, 2012) and is not supported by the latest calculations of the interlayer bond energies (Sakuma and Suehara, 2015). The accepted explanation for phyllosilicate friction also fails to account for the velocity dependence or (a-b) values, which decrease with temperature, reaching a minimum at intermediate temperatures, before increasing again at higher temperatures (Den Hartog et al., 2013, 2014). In this study, we developed a microphysical model for phyllosilicate friction, involving frictional sliding along atomically flat phyllosilicate grain interfaces, with overlapping grain edges forming barriers to sliding. Assuming that the amount of overlap is controlled by crystal plastic bending of grains into pores, together with rate-dependent edge-site cleavage, our model predicts most of the experimentally observed trends in frictional behaviour and provides a basis for extrapolation of laboratory friction data on phyllosilicates to natural conditions.

  17. Low temperature friction force microscopy

    Science.gov (United States)

    Dunckle, Christopher Gregory

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

  18. SURFACE DYNAMIC FRICTION OF POLYMER GELS

    Institute of Scientific and Technical Information of China (English)

    J.P.Gong; G.Kagata; Y.Iwasaki; Y.Osada

    2000-01-01

    The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amonton's law F =μW which well describes the friction of solids. The frictional force and its dependence on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which supported the repulsion-adsorption model proposed by the authors.

  19. The Friction of Saline Ice on Aluminium

    Directory of Open Access Journals (Sweden)

    Christopher Wallen-Russell

    2016-01-01

    Full Text Available The friction of ice on other materials controls loading on offshore structures and vessels in the Arctic. However, ice friction is complicated, because ice in nature exists near to its melting point. Frictional heating can cause local softening and perhaps melting and lubrication, thus affecting the friction and creating a feedback loop. Ice friction is therefore likely to depend on sliding speed and sliding history, as well as bulk temperature. The roughness of the sliding materials may also affect the friction. Here we present results of a series of laboratory experiments, sliding saline ice on aluminium, and controlling for roughness and temperature. We find that the friction of saline ice on aluminium μice-al=0.1 typically, but that this value varies with sliding conditions. We propose physical models which explain the variations in sliding friction.

  20. Modeling of material flow in friction stir welding process

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper presents a 3D numerical model to study the material flow in the friction stir welding process. Results indicate that the material in front of the pin moves upwards due to the extrusion of the pin, and then the upward material rotates with the pin. Behind the rotating tool, the material starts to move downwards and to deposit in the wake. This process is the real cause to make friction stir welding process continuing successfully. The tangent movement of the material takes the main contribution to the flow of the material in friction stir welding process. There exists a swirl on the advancing side and with the increase of the translational velocity the inverse flow of the material on the advancing side becomes faster. The shoulder can increase the velocity of material flow in both radial direction and tangent direction near the top surface. The variations of process parameters do have an effect on the velocity field near the pin, especially in the region in which the material flow is faster.

  1. Coordination Frictions and Job Heterogeneity

    DEFF Research Database (Denmark)

    Kennes, John; le Maire, Christian Daniel

    This paper develops and extends a dynamic, discrete time, job to worker matching model in which jobs are heterogeneous in equilibrium. The key assumptions of this economic environment are (i) matching is directed and (ii) coordination frictions lead to heterogeneous local labor markets. We de- rive...

  2. Frictional heating of tribological contacts

    NARCIS (Netherlands)

    Bos, Johannes

    1995-01-01

    Wherever friction occurs, mechanical energy is transformed into heat. The tem­ perature rise associated with this heating can have an important influence on the tribological behaviour of the contacting components. Apart from determining per­ formance, thermal phenomena affect reliability and may cau

  3. Friction Sensitivity of Primary Explosives

    Science.gov (United States)

    1982-09-01

    potassium dinitrobenzofuroxan none tetrazene 407913 tetrazene 7902454 The mixes which were tested are: NOL 130 (basic lead styphnate , barium nitrate, lead...azide, tetrazene, and antimony sulfide); PA 100 (normal lead styphnate , barium nitrate, tetrazene, lead dioxide, calcium silicide, and antimony...styuhnate, basic lead styphnate , potassium dinitrobenzofuroxan, and tetrazene were tested to determine the- 10% and 50% probability of friction

  4. Friction of atomically stepped surfaces

    Science.gov (United States)

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

    2017-03-01

    The friction behavior of atomically stepped metal surfaces under contact loading is studied using molecular dynamics simulations. While real rough metal surfaces involve roughness at multiple length scales, the focus of this paper is on understanding friction of the smallest scale of roughness: atomic steps. To this end, periodic stepped Al surfaces with different step geometry are brought into contact and sheared at room temperature. Contact stress that continuously tries to build up during loading, is released with fluctuating stress drops during sliding, according to the typical stick-slip behavior. Stress release occurs not only through local slip, but also by means of step motion. The steps move along the contact, concurrently resulting in normal migration of the contact. The direction of migration depends on the sign of the step, i.e., its orientation with respect to the shearing direction. If the steps are of equal sign, there is a net migration of the entire contact accompanied by significant vacancy generation at room temperature. The stick-slip behavior of the stepped contacts is found to have all the characteristic of a self-organized critical state, with statistics dictated by step density. For the studied step geometries, frictional sliding is found to involve significant atomic rearrangement through which the contact roughness is drastically changed. This leads for certain step configurations to a marked transition from jerky sliding motion to smooth sliding, making the final friction stress approximately similar to that of a flat contact.

  5. Rotary Engine Friction Test Rig Development Report

    Science.gov (United States)

    2011-12-01

    5  4.  Friction Rig Development 7  5.  AutoCAD ...Figure 4. Engine friction test rig AutoCAD model. ........................................................................8  Figure 5. Engine...top dead center. 8 5. AutoCAD Model Development A model of the rotary engine friction test rig was developed to determine the optimal

  6. Asbestos free friction composition for brake linings

    Indian Academy of Sciences (India)

    Arnab Ganguly; Raji George

    2008-02-01

    An asbestos free friction material composite for brake linings is synthesized containing fibrous reinforcing constituents, friction imparting and controlling additives, elastomeric additives, fire retarding components and a thermosetting resin. The composite shows exemplary friction characteristics and has great resistance to wear and shows good temperature stability.

  7. Multiscale friction modeling for sheet metal forming

    NARCIS (Netherlands)

    Hol, J.; Cid Alfaro, M.V.; de Rooij, Matthias B.; Meinders, Vincent T.; Felder, Eric; Montmitonnet, Pierre

    2010-01-01

    The most often used friction model for sheet metal forming simulations is the relative simple Coulomb friction model. This paper presents a more advanced friction model for large scale forming simulations based on the surface change on the micro-scale. The surface texture of a material changes when

  8. A thermodynamic model of sliding friction

    Directory of Open Access Journals (Sweden)

    Lasse Makkonen

    2012-03-01

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

  9. Analysis of the moment caused by friction of cardan joint. Cardan joint no friction kishinryoku kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Ono, K.; Yagi, Shida, T. (Atsugi Unisia Corp., Kanagawa (Japan))

    1990-10-01

    Analyzing the vibromotive force, generated by the friction, in generation morphology, level, dynamical characteristics, etc., through measurement of joint unit friction simulation of frictional vibromotive force and on-platform measurement of propeller shaft in vibromotive force, the present report investigated the influence of friction on the vehicle in sound vibration performance. By a vibromotive force measurement system, internally equipped with a piezoelectric type force meter, frictional vibromotive force could be quantitatively grasped. The friction must be appropriately controlled, because the moment, generated by it, is expected to be put in the vehicle by intermediation of a supporting point and adversely influence the sound vibration performance. Apart from the above, elucidation was made of relation between the ordinal number components of rotation of vibromotive force and friction, calculation of reaction force at the supporting point by the frictional measurement, relation between the joint angle and frictional vibromotive force, second couple force due to the friction, etc. 3 refs., 15 figs.

  10. A Brief Introduction to the Theory of Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.

    2008-01-01

    Friction stir welding (FSW) is a solid state welding process invented in 1991 at The Welding Institute in the United Kingdom. A weld is made in the FSW process by translating a rotating pin along a weld seam so as to stir the sides of the seam together. FSW avoids deleterious effects inherent in melting and is already an important welding process for the aerospace industry, where welds of optimal quality are demanded. The structure of welds determines weld properties. The structure of friction stir welds is determined by the flow field in the weld metal in the vicinity of the weld tool. A simple kinematic model of the FSW flow field developed at Marshall Space Flight Center, which enables the basic features of FSW microstructure to be understood and related to weld process parameters and tool design, is explained.

  11. 3D visualization of the material flow in friction stir welding process

    Institute of Scientific and Technical Information of China (English)

    Zhao Yanhua; Lin Sanbao; Shen Jiajie; Wu Lin

    2005-01-01

    The material flow in friction stir welded 2014 Al alloy has been investigated using a marker insert technique (MIT). Results of the flow visualization show that the material flow is asymmetrical during the friction stir welding(FSW)process and there are also significant differences in the flow patterns observed on advancing side and retreating side. On advancing side, some material transport forward and some move backward, but on retreating side, material only transport backward. At the top surface of the weld, significant material traasport forward due to the action of the rotating tool shoulder.Combining the data from all the markers, a three-dimensional flow visualization, similar to the 3D image reconstruction technique, was obtained. The three-dimensional plot gives the tendency chart of material flow in friction stir welding process and from the plot it can be seen that there is a vertical, circular motion around the longitudinal axis of the weld. On the advancing side of the weld, the material is pushed downward but on the retreating side, the material is pushed toward the crown of the weld. The net result of the two relative motions in both side of the advancing and the retreating is that a circular motion comes into being. Comparatively, the material flow around the longitudinal axis is a secondary motion.

  12. Temperature comparison of initial, middle and final point of polypropylene friction stir welded

    Science.gov (United States)

    Kusharjanta, Bambang; Raharjo, Wahyu P.; Triyono

    2016-03-01

    Friction Stir Welding is known as a new solid state joining process. This process is applied in thermoplastic polymers material recently. One of member thermoplastic polymer is polypropylene. Polypropylene sheet 6 mm thick was friction stir welded with a cone cut steel pin. Tool rotation, travelling speed, and plunge depth, as welding parameters were 620 rpm, 7.3 mm/minutes and 0.02 mm respectively. Temperature at the initial, middle, and final point of advance side working piece were measured and compared. Measurement were done by thermocouple and recorded by data acquisition. Based on this research, it is concluded that temperature at the initial, middle and final point of friction stir welding process are different. The highest temperature peak reach at the middle point on the advance side which affects face bending strength.

  13. Mechanical and Microstructural Properties of Friction Welded AISI 304 Stainless Steel to AISI 1060 Steel AISI 1060

    Directory of Open Access Journals (Sweden)

    Ates H.

    2014-10-01

    Full Text Available Rotary Friction welding is one of the most popular methods of joining similar and dissimilar materials. It is widely used with metals and thermoplastics in a wide variety of aviation, transport and aerospace industrial component designs. This study investigates the influence of friction and upsetting pressures on the hardness, tensile properties and microstructure of the welds. The experimental results showed that as the friction and upsetting pressures increased, the hardness and tensile strength values increased, as well. The tensile fracture of welded joint occurred in the AISI 1060 side. The friction processed joints were evaluated for their integrity and quality aspects by optical and scanning electron microscopy. For the perfect interfacial bonding, sufficient upsetting and friction pressures are necessary to reach the optimal temperature and severe plastic deformation to bring these materials within the attraction range.

  14. High temperature skin friction measurement

    Science.gov (United States)

    Tcheng, Ping; Holmes, Harlan K.; Supplee, Frank H., Jr.

    1989-01-01

    Skin friction measurement in the NASA Langley hypersonic propulsion facility is described. The sensor configuration utilized an existing balance, modified to provide thermal isolation and an increased standoff distance. For test run times of about 20 sec and ambient-air cooling of the test section and balance, the modified balance performed satisfactorily, even when it was subjected to acoustic and structural vibration. The balance is an inertially balanced closed-loop servo system where the current to a moving-coil motor needed to restore or null the output from the position sensor is a measure of the force or skin friction tending to displace the moving element. The accuracy of the sensor is directly affected by the position sensor in the feedback loop, in this case a linear-variable differential transformer which has proven to be influenced by temperature gradients.

  15. Self-Reacting Friction Stir Welding for Aluminum Alloy Circumferential Weld Applications

    Science.gov (United States)

    Bjorkman, Gerry; Cantrell, Mark; Carter, Robert

    2003-01-01

    Friction stir welding is an innovative weld process that continues to grow in use, in the commercial, defense, and space sectors. It produces high quality and high strength welds in aluminum alloys. The process consists of a rotating weld pin tool that plasticizes material through friction. The plasticized material is welded by applying a high weld forge force through the weld pin tool against the material during pin tool rotation. The high weld forge force is reacted against an anvil and a stout tool structure. A variation of friction stir welding currently being evaluated is self-reacting friction stir welding. Self-reacting friction stir welding incorporates two opposing shoulders on the crown and root sides of the weld joint. In self-reacting friction stir welding, the weld forge force is reacted against the crown shoulder portion of the weld pin tool by the root shoulder. This eliminates the need for a stout tooling structure to react the high weld forge force required in the typical friction stir weld process. Therefore, the self-reacting feature reduces tooling requirements and, therefore, process implementation costs. This makes the process attractive for aluminum alloy circumferential weld applications. To evaluate the application of self-reacting friction stir welding for aluminum alloy circumferential welding, a feasibility study was performed. The study consisted of performing a fourteen-foot diameter aluminum alloy circumferential demonstration weld using typical fusion weld tooling. To accomplish the demonstration weld, weld and tack weld development were performed and fourteen-foot diameter rings were fabricated. Weld development consisted of weld pin tool selection and the generation of a process map and envelope. Tack weld development evaluated gas tungsten arc welding and friction stir welding for tack welding rings together for circumferential welding. As a result of the study, a successful circumferential demonstration weld was produced leading

  16. Thermodynamic aspects of rock friction

    CERN Document Server

    Mitsui, Noa

    2013-01-01

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

  17. Fault rheology beyond frictional melting.

    Science.gov (United States)

    Lavallée, Yan; Hirose, Takehiro; Kendrick, Jackie E; Hess, Kai-Uwe; Dingwell, Donald B

    2015-07-28

    During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or "pseudotachylytes." It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics.

  18. Friction characteristics of floppy disks

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

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

  19. Side Effects (Management)

    Science.gov (United States)

    ... cancer care is relieving side effects, called symptom management, palliative care, or supportive care. It is important ... treat them. To learn about the symptoms and management of the long-term side effects of cancer ...

  20. Friction stir welding (FSW of aluminium foam sandwich panels

    Directory of Open Access Journals (Sweden)

    M. Bušić

    2016-07-01

    Full Text Available The article focuses on the influence of welding speed and tool tilt angle upon the mechanical properties at the friction stir welding of aluminium foam sandwich panels. Double side welding was used for producing butt welds of aluminium sandwich panels applying insertion of extruded aluminium profile. Such insertion provided lower pressure of the tool upon the aluminium panels, providing also sufficient volume of the material required for the weldment formation. Ultimate tensile strength and flexural strength for three-point bending test have been determined for samples taken from the welded joints. Results have confirmed anticipated effects of independent variables.

  1. 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.

  2. Friction coefficient dependence on electrostatic tribocharging

    Science.gov (United States)

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

    2013-08-01

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

  3. Friction tensor concept for textured surfaces

    Indian Academy of Sciences (India)

    K R Y Simha; Anirudhan Pottirayil; Pradeep L Menezes; Satish V Kailas

    2008-06-01

    Directionality of grinding marks influences the coefficient of friction during sliding. 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 in anisotropic media. This implies that there exists two principal friction coefficients $\\mu_{1,2}$ analogous to the principal conductivities $k_{1,2}$. For symmetrically textured surfaces the principal directions are orthogonal with atleast one plane of symmetry. However, in the case of polished single crystalline solids in relative sliding motion, crystallographic texture controls the friction tensor.

  4. Effects of Applied Load on 6061-T6 Aluminum Joined Employing a Novel Friction Bonding Process

    Science.gov (United States)

    Burkes, Douglas E.; Hallinan, Neil P.; Shropshire, Karen L.; Wells, Peter B.

    2008-12-01

    Friction bonding is under consideration for use in mass production of plate-type nuclear fuels for research reactors. This article discusses the effects of applied load (the most important process parameter for fabrication of these fuels) on temperature distribution, microstructure, and mechanical properties. Friction bonding experiments showed that tool geometry caused temperature gradients across the tool surface. Temperatures at the joint interface suggested the advancing side of the tool produced a majority of the frictional heat, while the retreating side of the tool mainly forged the plasticized material while bonding increased with applied load. The microstructure across the tool surface was also altered and, as a function of applied load, affected the mechanical properties. The 6061 aluminum alloy had mechanical properties close to a T4 temper after processing. Results documented in this article will aid in continual enhancement of friction bonding for nuclear fuel plate fabrication, and will hopefully contribute to continued advancement of friction stir welding (FSW) state of the art.

  5. Rubber friction on (apparently) smooth lubricated surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Mofidi, M; Prakash, B [Division of Machine Elements, Luleaa University of Technology, Luleaa SE-97187 (Sweden); Persson, B N J [IFF, FZ-Juelich, 52425 Juelich (Germany); Albohr, O [Pirelli Deutschland AG, 64733 Hoechst/Odenwald, Postfach 1120 (Germany)

    2008-02-27

    We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving (apparently) smooth surfaces.

  6. Low friction wear resistant graphene films

    Science.gov (United States)

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

    2017-02-07

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

  7. Rubber friction on (apparently) smooth lubricated surfaces

    Science.gov (United States)

    Mofidi, M.; Prakash, B.; Persson, B. N. J.; Albohr, O.

    2008-02-01

    We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving (apparently) smooth surfaces.

  8. Modelling cohesive, frictional and viscoplastic materials

    Science.gov (United States)

    Alehossein, Habib; Qin, Zongyi

    2016-06-01

    Most materials in mining and civil engineering construction are not only viscoplastic, but also cohesive frictional. Fresh concrete, fly ash and mining slurries are all granular-frictional-visco-plastic fluids, although solid concrete is normally considered as a cohesive frictional material. Presented here is both a formulation of the pipe and disc flow rates as a function of pressure and pressure gradient and the CFD application to fresh concrete flow in L-Box tests.

  9. The role of friction in orthodontics

    OpenAIRE

    Mariana Ribeiro Pacheco; Wellington Corrêa Jansen; Dauro Douglas de Oliveira

    2012-01-01

    INTRODUCTION: Sliding mechanics is widely used during orthodontic treatment. One of the disadvantages of this mechanics is the friction generated at the bracket/archwire interface, which may reduce the amount of desired orthodontic movement obtained. Due to the application and great acceptance of this type of mechanics, the role of friction in Orthodontics has been of interest for both clinicians and scientists. OBJECTIVE: Therefore, this article discussed how friction affects orthodontic too...

  10. How to teach friction: Experiments and models

    Science.gov (United States)

    Besson, Ugo; Borghi, Lidia; De Ambrosis, Anna; Mascheretti, Paolo

    2007-12-01

    Students generally have difficulty understanding friction and its associated phenomena. High school and introductory college-level physics courses usually do not give the topic the attention it deserves. We have designed a sequence for teaching about friction between solids based on a didactic reconstruction of the relevant physics, as well as research findings about student conceptions. The sequence begins with demonstrations that illustrate different types of friction. Experiments are subsequently performed to motivate students to obtain quantitative relations in the form of phenomenological laws. To help students understand the mechanisms producing friction, models illustrating the processes taking place on the surface of bodies in contact are proposed.

  11. Noise and vibration in friction systems

    CERN Document Server

    Sergienko, Vladimir P

    2015-01-01

    The book analyzes the basic problems of oscillation processes and theoretical aspects of noise and vibration in friction systems. It presents generalized information available in literature data and results of the authors in vibroacoustics of friction joints, including car brakes and transmissions. The authors consider the main approaches to abatement of noise and vibration in non-stationary friction processes. Special attention is paid to materials science aspects, in particular to advanced composite materials used to improve the vibroacoustic characteristics of tribopairs The book is intended for researchers and technicians, students and post-graduates specializing in mechanical engineering, maintenance of machines and transport means, production certification, problems of friction and vibroacoustics.

  12. Frictional Effects on Gear Tooth Contact Analysis

    Directory of Open Access Journals (Sweden)

    Zheng Li

    2013-01-01

    Full Text Available The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented using finite element method. Nonlinear finite element model for gear tooth contact with rolling/sliding is then developed. The contact zones for multiple tooth pairs are identified and the associated integration situation is derived. The illustrated bending stress and transmission error results with static and dynamic boundary conditions indicate the significant effects due to the sliding friction between the surfaces of contacted gear teeth, and the friction effect can not be ignored. To understand the particular static and dynamic frictional effects on gear tooth contact analysis, some significant phenomena of gained results will also be discussed. The potentially significant contribution of tooth frictional shear stress is presented, particularly in the case of gear tooth contact analysis with both static and dynamic boundary conditions.

  13. Friction Stir Processing of Cast Superalloys Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR effort examines the feasibility of an innovative fabrication technology incorporating sand casting and friction stir processing (FSP) for producing...

  14. Job Heterogeneity and Coordination Frictions

    DEFF Research Database (Denmark)

    Kennes, John; le Maire, Daniel

    the job ladder, how the identification of assortative matching is fundamentally different in directed and undirected search models, how our theory accounts for business cycle facts related to inter-temporal changes in job offer distributions, and how our model could also be used to identify......We develop a new directed search model of a frictional labor market with a continuum of heterogenous workers and firms. We estimate two versions of the model - auction and price posting - using Danish data on wages and productivities. Assuming heterogenous workers with no comparative advantage, we...

  15. Friction of Plastic Rotating Bands

    Science.gov (United States)

    1984-11-01

    for speeds eve ., the rdnge: 10 - 300 cm/s. Overwhelming evidence was presented to support a melt phenomena. Melt depth of: polymer, pins on a glass disk...Polymers," Proc. Roy. Soc., (London),. A291 (1966), p. 186. 24. Rabinowicz , S., et al., "The Effect of Hydrostatic Pressure on the Shear Yield Behavior of...34 Proc. Roy.,Soc., (London), A269. (19620 p. 368. 51. Carignan, F. J., and Rabinowicz , E., "Friction and Wear at ligh Sliding Speeds," ASLE Trans., 24

  16. Fractional trajectories: Decorrelation versus friction

    Science.gov (United States)

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

    2013-11-01

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

  17. Stabilization of Gob-Side Entry with an Artificial Side for Sustaining Mining Work

    Directory of Open Access Journals (Sweden)

    Hong-sheng Wang

    2016-07-01

    Full Text Available A concrete artificial side (AS is introduced to stabilize a gob-side entry (GSE. To evaluate the stability of the AS, a uniaxial compression failure experiment was conducted with large and small-scale specimens. The distribution characteristics of the shear stress were obtained from a numerical simulation. Based on the failure characteristics and the variation of the shear stress, a failure criterion was determined and implemented in the strengthening method for the artificial side. In an experimental test, the distribution pattern of the maximum shear stress showed an X shape, which contributed to the failure shape of the specimen. The shear stress distribution and failure shape are induced by a combination of two sets of shear stresses, which implies that failure of the AS follows the twin shear strength theory. The use of anchor bolts, bolts, and anchor bars enhances the shear strength of the artificial side. When this side is stable, the components can constrain the lateral deformation as well as improve the internal friction angle and cohesion. When the AS is damaged, the components prevent the sliding of broken blocks along the shear failure plane and improve the residual strength of the artificial side. When reinforced with an anchor bar, the AS is still stable even after mining operations for three years.

  18. Comparison of Frictional Heating Models

    Energy Technology Data Exchange (ETDEWEB)

    Davies, Nicholas R [ORNL; Blau, Peter Julian [ORNL

    2013-10-01

    The purpose of this work was to compare the predicted temperature rises using four well-known models for frictional heating under a few selected conditions in which similar variable inputs are provided to each model. Classic papers by Archard, Kuhlmann-Wilsdorf, Lim and Ashby, and Rabinowicz have been examined, and a spreadsheet (Excel ) was developed to facilitate the calculations. This report may be used in conjunction with that spreadsheet. It explains the background, assumptions, and rationale used for the calculations. Calculated flash temperatures for selected material combinations, under a range of applied loads and sliding speeds, are tabulated. The materials include AISI 52100 bearing steel, CDA 932 bronze, NBD 200 silicon nitride, Ti-6Al-4V alloy, and carbon-graphite material. Due to the assumptions made by the different models, and the direct way in which certain assumed quantities, like heat sink distances or asperity dimensions, enter into the calculations, frictional hearing results may differ significantly; however, they can be similar in certain cases in light of certain assumptions that are shared between the models.

  19. Rolling Friction on a Wheeled Laboratory Cart

    Science.gov (United States)

    Mungan, Carl E.

    2012-01-01

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

  20. On the Blasius correlation for friction factors

    CERN Document Server

    Trinh, Khanh Tuoc

    2010-01-01

    The Blasius empirical correlation for turbulent pipe friction factors is derived from first principles and extended to non-Newtonian power law fluids. Two alternative formulations are obtained that both correlate well with the experimental measurements of Dodge, Bogue and Yoo. Key words: Blasius, turbulent friction factor, power law fluids

  1. FACTORS INFLUENCING FRICTION OF PHOSPHATE COATINGS,

    Science.gov (United States)

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

  2. Gimbaled-shoulder friction stir welding tool

    Science.gov (United States)

    Carter, Robert W. (Inventor); Lawless, Kirby G. (Inventor)

    2010-01-01

    A gimbaled-shoulder friction stir welding tool includes a pin and first and second annular shoulders coupled to the pin. At least one of the annular shoulders is coupled to the pin for gimbaled motion with respect thereto as the tool is rotated by a friction stir welding apparatus.

  3. Graphite friction coefficient for various conditions

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

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

  4. Wiping Metal Transfer in Friction Stir Welding

    Science.gov (United States)

    Nunes, Arthur C., Jr.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Much evidence suggests that as the friction stir pin-tool moves along a weld seam the displacement of metal takes place by a wiping action at the surface of a plug of metal that rotates with the tool. The wiping model is explained and some consequences for the friction stir welding process are drawn.

  5. Trial manufacture of rotary friction tester and frictional force measurement of metals

    CERN Document Server

    Abe, T; Kanari, M; Tanzawa, S

    2002-01-01

    In the plasma confinement type fusion reactor, in-vessel structures such as a blanket module slide at the joints each other when plasma disruption occurs, and then frictional heat is generated there. Therefore, for the selection of material and the use as the design data, it is important to understand the frictional characteristics of metals and ceramic films in the vacuum. In the present study, we have manufactured a prototype of rotary friction tester and examined the performances of the tester. The frictional characteristics of metals in the room air was measured using the friction tester, and the results obtained are as follows. A drifting friction force for a constant time and a friction force during the idling were 98 mN and 225 mN, respectively. These values were sufficiently small as compared to pressing load (9.8 - 57.8 N) used in the friction test. In a friction force measurement of stainless steel, dynamic friction force obeyed Amontons' law which indicated that dynamic friction force is not depend...

  6. 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...... cases the frictional shear stress increases monotonically with the sliding velocity. For polymer sliding on polymer [case (b)] the friction is much larger, and the velocity dependence is more complex. For hydrocarbons with molecular lengths from 60 to 140 C-atoms, the number of monolayers of lubricant...... shows no dependence on the sliding velocity, and for the shortest hydrocarbon (20 C-atoms) the frictional shear stress increases nearly linearly with the sliding velocity....

  7. Single-sided NMR

    CERN Document Server

    Casanova, Federico; Blümich, Bernhard

    2011-01-01

    Single-Sided NMR describes the design of the first functioning single-sided tomograph, the related measurement methods, and a number of applications. One of the key advantages to this method is the speed at which the images are obtained.

  8. One-sided arguments

    NARCIS (Netherlands)

    van Laar, J.A.

    2007-01-01

    When is an argument to be called one-sided? When is putting forward such an argument fallacious? How can we develop a model for critical discussion, such that a fallaciously one-sided argument corresponds to a violation of a discussion rule? These issues are dealt with within 'the limits of the dial

  9. FRICTION-BOON OR BANE IN ORTHODONTICS

    Directory of Open Access Journals (Sweden)

    Sameer

    2015-11-01

    Full Text Available OBJECTIVE: Most fixed appliance techniques involve some degree of sliding between brackets and arch wires. A sound knowledge of the various factors affecting the magnitude of friction is of paramount importance to the clinician. The present study was performed to evaluate and compare the frictional resistance and characteristics between self-ligating brackets and pre-adjusted edgewise brackets with different types of ligation. MATERIALS AND METHODS: Tidy's frictional test design was used to simulate retraction of tooth along with artificial saliva to simulate wet conditions in oral cavity. The jig with this assembly was mounted on the Instron machine with the cross head moving upwards at a speed of 5mm/min. The movable bracket was suspended from the load cell of the testing machine, while the jig was mounted on cross head of machine and the load cell readings were recorded on digital display. Following wires are used 0.016 HANT, 0.019X 0.025HANT, 0.019X 0.025 SS, 0.021X 0.025 SS wires are used. The brackets used were 0.022 slot Damon, 0.022 Smart clip and 0.022 slot MBT system. RESULTS: Self ligating brackets were shown to produce lesser friction when compared to the conventional brackets used with modules, and stainless steel ligatures. Damon self-ligating brackets produce a least friction of all the brackets used in the study. Stainless steel ligatures produced the least friction compared to elastomeric. CONCLUSION: Self ligation brackets produce lesser friction than the conventional brackets ligated with elastomeric modules and stainless steel ligature. Damon self-ligating brackets produce a least friction of all the brackets used in the study width of the bracket was also found to be directly proportional to the friction produced 0.0016HANT with elastomeric modules produce more friction due increase in flexibility of wire.

  10. Spectroscopic signatures of quantum friction

    Science.gov (United States)

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

    2016-12-01

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

  11. Friction Stir Welding and Processing

    Energy Technology Data Exchange (ETDEWEB)

    Hovanski, Yuri; Carsley, John; Clarke, Kester D.; Krajewski, Paul E.

    2015-05-01

    With nearly twenty years of international research and collaboration in friction stir welding (FSW) and processing industrial applications have spread into nearly every feasible market. Currently applications exist in aerospace, railway, automotive, personal computers, technology, marine, cutlery, construction, as well as several other markets. Implementation of FSW has demonstrated diverse opportunities ranging from enabling new materials to reducing the production costs of current welding technologies by enabling condensed packaging solutions for traditional fabrication and assembly. TMS has sponsored focused instruction and communication in this technology area for more than fifteen years, with leadership from the Shaping and Forming Committee, which organizes a biannual symposium each odd year at the annual meeting. A focused publication produced from each of these symposia now comprises eight volumes detailing the primary research and development activities in this area over the last two decades. The articles assembled herein focus on both recent developments and technology reviews of several key markets from international experts in this area.

  12. Mapping Instabilities in Polymer Friction

    Science.gov (United States)

    Rand, Charles; Crosby, Alfred

    2005-03-01

    Schallamach waves are instabilities that occur as interfaces between a soft elastomer and rigid surface slide past each other.(1) The presence of Schallamach waves can lead to drastic changes in frictional properties. Although the occurrence of Schallamach waves has been studied for the past several decades, a general map relating fundamental material properties, geometry, and operating conditions (i.e. speed and temperature) has not been established. Using a combinatorial approach, we illustrate the role of modulus, testing velocity and surface energetics of crosslinked poly(dimethyl siloxane) on the generation Schallamach waves. This knowledge will be used with polymer patterning processes to fabricate responsive coatings for applications such as anti-fouling coatings. (1)Schallamach, A.;Wear 1971,17, 301-312.

  13. Dynamical Friction on extended perturbers

    CERN Document Server

    Esquivel, O

    2008-01-01

    Following a wave-mechanical treatment we calculate the drag force exerted by an infinite homogeneous background of stars on a perturber as this makes its way through the system. We recover Chandrasekhar's classical dynamical friction (DF) law with a modified Coulomb logarithm. We take into account a range of models that encompasses all plausible density distributions for satellite galaxies by considering the DF exerted on a Plummer sphere and a perturber having a Hernquist profile. It is shown that the shape of the perturber affects only the exact form of the Coulomb logarithm. The latter converges on small scales, because encounters of the test and field stars with impact parameters less than the size of the massive perturber become inefficient. We confirm this way earlier results based on the impulse approximation of small angle scatterings.

  14. Effects of temperature on internal friction of Graphit-iC graphite-like carbon coatings

    Science.gov (United States)

    Zhu, Zhi-yong; Shi, Wen; Wan, Zi; Yuan, Jun-feng; Li, Xiao

    2013-12-01

    Graphit-iC graphite-like carbon coatings were deposited on SDC90 cold work die steel by using an unbalanced magnetron sputtering technology. Effects of the temperature on microstructure and internal friction of the carbon coatings were characterized by Raman spectroscopy (Raman) and a low-frequency mechanical analyzer (LMA-1) testing system. The results indicate that the internal friction of the two-side deposited carbon coatings is small (2.17×10-4), being higher than one of the substrate (1.63×10-4), and increases with temperature. However, there is an internal friction peak at 250°C accompanied with partial sp3 transferred to sp2 and increasing the intensity ratio ID/IG. There is gradual graphitization tendency of the carbon coatings as temperatures increase from 25°C to 350 °C. This would be progressive transformation from amorphous to crystalline.

  15. Predicting bed form roughness: the influence of lee side angle

    Science.gov (United States)

    Lefebvre, Alice; Winter, Christian

    2016-04-01

    Flow transverse bedforms (ripples and dunes) are ubiquitous in rivers and coastal seas. Local hydrodynamics and transport conditions depend on the size and geometry of these bedforms, as they constitute roughness elements at the bed. Bedform influence on flow energy must be considered for the understanding of flow dynamics, and in the development and application of numerical models. Common estimations or predictors of form roughness (friction factors) are based mostly on data of steep bedforms (with angle-of-repose lee slopes), and described by highly simplified bedform dimensions (heights and lengths). However, natural bedforms often are not steep, and differ in form and hydraulic effect relative to idealised bedforms. Based on systematic numerical model experiments, this study shows how the hydraulic effect of bedforms depends on the flow structure behind bedforms, which is determined by the bedform lee side angle, aspect ratio and relative height. Simulations reveal that flow separation behind bedform crests and, thus, a hydraulic effect is induced at lee side angles steeper than 11 to 18° depending on relative height, and that a fully developed flow separation zone exists only over bedforms with a lee side angle steeper than 24°. Furthermore, the hydraulic effect of bedforms with varying lee side angle is evaluated and a reduction function to common friction factors is proposed. A function is also developed for the Nikuradse roughness (k s), and a new equation is proposed which directly relates k s to bedform relative height, aspect ratio and lee side angle.

  16. Liner surface improvements for low friction piston ring packs

    Science.gov (United States)

    Anderberg, C.; Dimkovski, Z.; Rosén, B.-G.

    2014-01-01

    The development of engine components in the automotive industry is governed by several constraints such as environmental legislation and customer expectations. About a half of the frictional losses in an internal combustion engine come from the interactions between the piston assembly and cylinder liner surface. The tribological considerations in the contact between the piston ring and cylinder liner have attracted much attention over the past few decades. Many non-conventional cylinder liner finishes have been, and are being, developed with the aim to reduce friction losses and oil consumption, but the effects of the surface finish on piston ring pack performance is not well understood. One way of reducing friction in the cylinder system is to reduce the tangential load from the piston ring pack, focusing on the oil control ring. However, the side-effect of this is a disappointingly increased oil consumption. In this study a number of different cylinder liner surface specifications were developed and implemented in test engines with the aim of maintaining the level for oil consumption when decreasing the tangential load for the piston ring pack. To improve our understanding of the result, the same surfaces were evaluated in elastic and elasto-plastic rough contact and hydrodynamic flow simulation models. It is shown that oil consumption is strongly related to surface texture on the cylinder liners and at lower speeds (900-1200 rpm), a ‘rougher surface’ with a high core (e.g. Sk) and valley roughness (e.g. Svk) results in higher oil consumption. At the medium speed range (1200-3600 rpm), oil consumption continues to dominate for the ‘rough’ surfaces but with a visible influence of a lower oil consumption for a decreased roughness within the ‘rough’ surface group. ‘Smooth’ surfaces with a ‘smooth’ core (Sk), irrespective of the valley component (Svk), show similar oil consumption. For engine speeds above 3600 rpms, an increase in plateau

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

    Directory of Open Access Journals (Sweden)

    Mijajlović Miroslav M.

    2016-01-01

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

  18. Thermal activation in boundary lubricated friction

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-05-01

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

  19. Load-Dependent Friction Hysteresis on Graphene.

    Science.gov (United States)

    Ye, Zhijiang; Egberts, Philip; Han, Gang Hee; Johnson, A T Charlie; Carpick, Robert W; Martini, Ashlie

    2016-05-24

    Nanoscale friction often exhibits hysteresis when load is increased (loading) and then decreased (unloading) and is manifested as larger friction measured during unloading compared to loading for a given load. In this work, the origins of load-dependent friction hysteresis were explored through atomic force microscopy (AFM) experiments of a silicon tip sliding on chemical vapor deposited graphene in air, and molecular dynamics simulations of a model AFM tip on graphene, mimicking both vacuum and humid air environmental conditions. It was found that only simulations with water at the tip-graphene contact reproduced the experimentally observed hysteresis. The mechanisms underlying this friction hysteresis were then investigated in the simulations by varying the graphene-water interaction strength. The size of the water-graphene interface exhibited hysteresis trends consistent with the friction, while measures of other previously proposed mechanisms, such as out-of-plane deformation of the graphene film and irreversible reorganization of the water molecules at the shearing interface, were less correlated to the friction hysteresis. The relationship between the size of the sliding interface and friction observed in the simulations was explained in terms of the varying contact angles in front of and behind the sliding tip, which were larger during loading than unloading.

  20. Assessment of semi-active friction dampers

    Science.gov (United States)

    dos Santos, Marcelo Braga; Coelho, Humberto Tronconi; Lepore Neto, Francisco Paulo; Mafhoud, Jarir

    2017-09-01

    The use of friction dampers has been widely proposed for a variety of mechanical systems for which applying viscoelastic materials, fluid based dampers or other viscous dampers is impossible. An important example is the application of friction dampers in aircraft engines to reduce the blades' vibration amplitudes. In most cases, friction dampers have been studied in a passive manner, but significant improvements can be achieved by controlling the normal force in the contact region. The aim of this paper is to present and study five control strategies for friction dampers based on three different hysteresis cycles by using the Harmonic Balance Method (HBM), a numerical and experimental analysis. The first control strategy uses the friction force as a resistance when the system is deviating from its equilibrium position. The second control strategy maximizes the energy removal in each harmonic oscillation cycle by calculating the optimal normal force based on the last displacement peak. The third control strategy combines the first strategy with the homogenous modulation of the friction force. Finally, the last two strategies attempt to predict the system's movement based on its velocity and acceleration and our knowledge of its physical properties. Numerical and experimental studies are performed with these five strategies, which define the performance metrics. The experimental testing rig is fully identified and its parameters are used for numerical simulations. The obtained results show the satisfactory performance of the friction damper and selected strategy and the suitable agreement between the numerical and experimental results.

  1. Effects of friction on forced two-dimensional Navier-Stokes turbulence

    Science.gov (United States)

    Blackbourn, Luke A. K.; Tran, Chuong V.

    2011-10-01

    Large-scale dissipation mechanisms have been routinely employed in numerical simulations of two-dimensional turbulence to absorb energy at large scales, presumably mimicking the quasisteady picture of Kraichnan in an unbounded fluid. Here, “side effects” of such a mechanism—mechanical friction—on the small-scale dynamics of forced two-dimensional Navier-Stokes turbulence are elaborated by both theoretical and numerical analysis. Given a positive friction coefficient α, viscous dissipation of enstrophy has been known to vanish in the inviscid limit ν→0. This effectively renders the scale-neutral friction the only mechanism responsible for enstrophy dissipation in that limit. The resulting dynamical picture is that the classical enstrophy inertial range becomes a dissipation range in which the dissipation of enstrophy by friction mainly occurs. For each α>0, there exists a critical viscosity νc, which depends on physical parameters, separating the regimes of predominant viscous and frictional dissipation of enstrophy. It is found that νc=[η'1/3/(Ckf2)]exp[-η'1/3/(Cα)], where η' is half the enstrophy injection rate, kf is the forcing wave number, and C is a nondimensional constant (the Kraichnan-Batchelor constant). The present results have important theoretical and practical implications. Apparently, mechanical friction is a poor choice in numerical attempts to address fundamental issues concerning the direct enstrophy transfer in two-dimensional Navier-Stokes turbulence. Furthermore, as relatively strong friction naturally occurs on the surfaces and at lateral boundaries of experimental fluids as well as at the interfaces of shallow layers in geophysical fluid models, the frictional effects discussed in this study are crucial in understanding the dynamics of these systems.

  2. Side Effects of Chemotherapy

    Science.gov (United States)

    ... Jacket Fashion Show Contact Us Side Effects of Chemotherapy Each of the chemotherapy drugs available today works in a slightly different ... few rules of thumb when it comes to chemotherapy that should always be kept in mind. Ignore ...

  3. Comparison of frictional resistance of esthetic and semi-esthetic self-ligating brackets

    Directory of Open Access Journals (Sweden)

    M S Kannan

    2015-01-01

    Full Text Available Aim: The frictional resistance encountered during sliding mechanics has been well established in the orthodontic literature, and it consists of complex interactions between the bracket, archwire, and method of ligation the claim of reduced friction with self-ligating brackets is often cited as a primary advantage over conventional brackets. This study was done to compare and evaluate the frictional forces generated between fully esthetic brackets and semi-aesthetic self-ligating brackets, which are of passive form and SEM (scanning electron microscope study of the Brackets after Frictional evaluation. Materials and Methods: Two types of self-ligating esthetic brackets, Damon clear (Ormco made of fully ceramic and Opal (Ultradent Products, USA and, Two types of self-ligating semi-esthetic brackets, Clarity SL (3M Unitek and Damon 3 (Ormco both of which are made of ceramic with metal slot. Arch wires with different dimensions and quality 17 × 25, 19 × 25 Titanium Molybdenum Alloy (TMA and 17 × 25, 19 × 25 stainless steel that came from plain strands of wire were used for frictional comparison test. The brackets used in this study had 0.022 × 0.028 inch slot. Results: The statistical tests showed significantly smaller amount of kinetic frictional forces is generated by Damon 3 (semi-esthetic self-ligating brackets. For each wire used, Damon 3 displayed significantly lower frictional forces (P ≤ 0.05 than any of the self-ligating system, followed by Opal (fully esthetic self-ligating brackets which generated smaller amount of frictional forces but relatively on the higher side when compared with Damon 3. Damon clear (fully esthetic self-ligating brackets generated the maximum amount of kinetic forces with all types of wire dimensions and properties when compared to the other three types of self-ligating system. Clarity SL (semi-esthetic self-ligating brackets generated smaller amount of frictional forces when compared with Damon clear and

  4. Coordinated Water Under Confinement Eases Sliding Friction

    Science.gov (United States)

    Defante, Adrian; Dhopotkar, Nishad; Dhinojwala, Ali

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

  5. An inquiry-based laboratory on friction

    CERN Document Server

    Montalbano, Vera

    2013-01-01

    Sliding friction is usually introduced in high school, but rarely through activities in laboratory. A qualitative introduction to friction is presented by proposing exploration of different kind of materials in order to suggest which aspects can be relevant and which interaction is involved. Different quantitative experiments are proposed for studying Leonardo's laws for friction. The learning path was tested with two high school classes during an instruction trip at department. Students were engaged in the inquiry-based introductory activity and seemed to realize with care the measurements. However, the analysis of their reports shows some learning difficulties.

  6. Methods and Devices used to Measure Friction

    DEFF Research Database (Denmark)

    Jeswiet, Jack; Arentoft, Mogens; Henningsen, Poul

    2004-01-01

    The physical condition at the work-piece/die boundary, in both bulk forming and sheet forming is, arguably, the single most important physical parameter influencing the processing of metals, yet it remains the least understood. Hence the need for basic research into metal-die interface mechanisms....... To gain a good understanding of the mechanisms at the interface and to be able to verify the friction and tribology models that exist, friction sensors are needed. Designing sensors to measure friction-stress in metal working has been pursued by many researchers. This paper surveys methods, which have...

  7. Quantized friction across ionic liquid thin films

    Science.gov (United States)

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

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

  8. Forming of aluminium alloy friction stir welds

    Science.gov (United States)

    Bruni, Carlo

    2016-10-01

    The present paper aims at investigating, through analytical models, numerical models and experiments, the effect of the warm deformation phase, realised with an in temperature upsetting, on the weld previously performed by friction stir lap welding on aluminium alloy blanks. The investigation allows to show the deformation zones after upsetting that determine the homogenisation of the weld section. The analytical model allows to relate the friction factor with the upsetting load. The presence on the weld of not elevated friction factor values determines the deformation and localisation levels very useful for the weld. Such methodology allows to improve the weld itself with the forming phase.

  9. Study on the Friction Coefficient in Grinding

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

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

  10. Quantized friction across ionic liquid thin films.

    Science.gov (United States)

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

    2013-10-07

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

  11. Heat transfer and friction factors in the ribbed square convergent and divergent channels

    Science.gov (United States)

    Lee, M. S.; Ahn, S. W.

    2016-06-01

    Heat transfer and friction factors are reported for the measurements of turbulent flows in the convergent and divergent square channels with one-sided ribbed wall as well as two opposite in-line ribbed walls. The study covers three different hydraulic diameter ratios between inlet and exit at the test section such as Dho/Dhi = 0.75, 1.0, and 1.33 and Reynolds numbers in the range of 25,000-79,000. The channels, composing of ten isolated copper sections in the length of test section of 1 m, have the hydraulic diameter of 87.5 mm for the straight channel (Dho/Dhi = 1.0); the rib height-to-hydraulic diameter is 0.114; the rib pitch-to-height ratio equals 10. On the contrary to public opinion that the friction factor depends on the portion of the ribbed area, the total friction factor in the two opposite ribbed walls are lower than in the one-sided ribbed wall in the divergent channel of Dho/Dhi = 1.33 because the total pressure, summing positive dynamic and negative static pressures, is acted. The results show that the two opposite ribbed divergent channel of Dho/Dhi = 1.33 provides the best heat transfer enhancement and the two opposite ribbed convergent channel of Dho/Dhi = 0.75 provides the worst friction factor enhancement, and the ribbed divergent channels are generally recommended.

  12. Multiple pass and multiple layer friction stir welding and material enhancement processes

    Science.gov (United States)

    Feng, Zhili [Knoxville, TN; David, Stan A [Knoxville, TN; Frederick, David Alan [Harriman, TN

    2010-07-27

    Processes for friction stir welding, typically for comparatively thick plate materials using multiple passes and multiple layers of a friction stir welding tool. In some embodiments a first portion of a fabrication preform and a second portion of the fabrication preform are placed adjacent to each other to form a joint, and there may be a groove adjacent the joint. The joint is welded and then, where a groove exists, a filler may be disposed in the groove, and the seams between the filler and the first and second portions of the fabrication preform may be friction stir welded. In some embodiments two portions of a fabrication preform are abutted to form a joint, where the joint may, for example, be a lap joint, a bevel joint or a butt joint. In some embodiments a plurality of passes of a friction stir welding tool may be used, with some passes welding from one side of a fabrication preform and other passes welding from the other side of the fabrication preform.

  13. High friction and low wear properties of laser-textured ceramic surface under dry friction

    Science.gov (United States)

    Xing, Youqiang; Deng, Jianxin; Wu, Ze; Wu, Fengfang

    2017-08-01

    Two kinds of grooved textures with different spacing were fabricated on Al2O3/TiC ceramic surface by an Nd:YAG laser. The dry tribological properties of the textured samples were investigated by carrying out unidirectional rotary sliding friction and wear tests using a ball-on-disk tribometer. Results show that the laser textured samples exhibit higher friction coefficient and excellent wear resistance compared with the smooth sample under dry friction conditions. Furthermore, the texture morphology and spacing have a significant influence on the tribological properties. The sample with small texture spacing may be beneficial to increasing the friction coefficient, and the wavy-grooved sample exhibits the highest friction coefficient and shallowest wear depth. The increasing friction coefficient and anti-wear properties are attributed to the combined effects of the increased surface roughness, reduced real contact area, micro-cutting effect by the texture edges and entrapment of wear debris.

  14. Frictional torque numbers for ball cup and journal bearings

    OpenAIRE

    Ligterink, D.J.

    1982-01-01

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

  15. [Psychoanalysis and Side Effect].

    Science.gov (United States)

    Shirahase, Joichiro

    2015-01-01

    A study of psychoanalysis from the perspective of side effects reveals that its history was a succession of measures to deal with its own side effects. This, however, does not merely suggest that, as a treatment method, psychoanalysis is incomplete and weak: rather, its history is a record of the growth and development of psychoanalysis that discovered therapeutic significance from phenomena that were initially regarded as side effects, made use of these discoveries, and elaborated them as a treatment method. The approach of research seen during the course of these developments is linked to the basic therapeutic approach of psychoanalysis. A therapist therefore does not draw conclusions about a patient's words and behaviors from a single aspect, but continues to make efforts to actively discover a variety of meanings and values from them, and to make the patient's life richer and more productive. This therapeutic approach is undoubtedly one of the unique aspects of psychoanalysis. I discuss the issue of psychoanalysis and side effects with the aim of clarifying this unique characteristic of psychoanalysis. The phenomenon called resistance inevitably emerges during the process of psychoanalytic treatment. Resistance can not only obstruct the progress of therapy; it also carries the risk of causing a variety of disadvantages to the patient. It can therefore be seen as an adverse effect. However, if we re-examine this phenomenon from the perspective of transference, we find that resistance is in fact a crucial tool in psychoanalysis, and included in its main effect, rather than a side effect. From the perspective of minimizing the character of resistance as a side effect and maximizing its character as a main effect, I have reviewed logical organization, dynamic evaluation, the structuring of treatment, the therapist's attitudes, and the training of therapists. I conclude by stating that psychoanalysis has aspects that do not match the perspective known as a side

  16. Surface defects and temperature on atomic friction

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-09-07

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

  17. Shell Galaxies, Dynamical Friction, and Dwarf Disruption

    CERN Document Server

    Ebrova, Ivana; Canalizo, Gabriela; Bennert, Nicola; Jilkova, Lucie

    2009-01-01

    Using N-body simulations of shell galaxies created in nearly radial minor mergers, we investigate the error of collision dating, resulting from the neglect of dynamical friction and of gradual disruption of the cannibalized dwarf.

  18. Frictional Sliding without Geometrical Reflection Symmetry

    Science.gov (United States)

    Aldam, Michael; Bar-Sinai, Yohai; Svetlizky, Ilya; Brener, Efim A.; Fineberg, Jay; Bouchbinder, Eran

    2016-10-01

    The dynamics of frictional interfaces plays an important role in many physical systems spanning a broad range of scales. It is well known that frictional interfaces separating two dissimilar materials couple interfacial slip and normal stress variations, a coupling that has major implications on their stability, failure mechanism, and rupture directionality. In contrast, it is traditionally assumed that interfaces separating identical materials do not feature such a coupling because of symmetry considerations. We show, combining theory and experiments, that interfaces that separate bodies made of macroscopically identical materials but lack geometrical reflection symmetry generically feature such a coupling. We discuss two applications of this novel feature. First, we show that it accounts for a distinct, and previously unexplained, experimentally observed weakening effect in frictional cracks. Second, we demonstrate that it can destabilize frictional sliding, which is otherwise stable. The emerging framework is expected to find applications in a broad range of systems.

  19. Frictional sliding with geometrically broken reflection symmetry

    CERN Document Server

    Aldam, Michael; Svetlizky, Ilya; Brener, Efim A; Fineberg, Jay; Bouchbinder, Eran

    2016-01-01

    The dynamics of frictional interfaces play an important role in many physical systems spanning a broad range of scales. It is well-known that frictional interfaces separating two dissimilar materials couple interfacial slip and normal stress variations, a coupling that has major implications on their stability, failure mechanism and rupture directionality. In contrast, interfaces separating identical materials are traditionally assumed not to feature such a coupling due to symmetry considerations. We show, combining theory and experiments, that interfaces which separate bodies made of identical materials, but lack geometric reflection symmetry, generically feature such a coupling. We discuss two applications of this novel feature. First, we show that it accounts for a distinct and previously unexplained weakening effect in frictional cracks observed experimentally. Second, we demonstrate that it can destabilize frictional sliding which is otherwise stable. The emerging framework is expected to find applicatio...

  20. Permeability equipment for porous friction surfaces

    Science.gov (United States)

    Standiford, D. L.; Graul, R. A.; Lenke, L. R.

    1985-04-01

    Hydroplaning is the loss of traction between tires and pavement due to the presence of a layer of water. This loss of traction can result in loss of vehicle control. A porous friction surface (PFS) applied over an existing pavement permits the water to drain laterally and vertically away from the tire path, effectively lowering hydroplaning potential. Equipment used to measure pavement drainage (permeability) is discussed with respect to usage on porous friction surface. Background information on hydroplaning, flow theory, and PFS field performance as they are affected by permeability are also presented. Two dynamic test devices and four static devices are considered for measuring PFS permeability. Permeability tests are recommended to measure PFS permeability for maintenance purposes and construction control. Dynamic devices cited could possibly estimate hydroplaning potential; further research must be done to determine this. Permeability devices cannot be used to accurately estimate friction of a pavement surface, however, decreased permeability of a pavement infers a decrease in friction.

  1. Torque Control of Friction Stir Welding Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Longhurst Engineering, PLC and Vanderbilt University propose the innovation of torque control of friction stir welding (FSW) as a replacement to force control of...

  2. Transient effects in friction fractal asperity creep

    CERN Document Server

    Goedecke, Andreas

    2013-01-01

    Transient friction effects determine the behavior of a wide class of mechatronic systems. Classic examples are squealing brakes, stiction in robotic arms, or stick-slip in linear drives. To properly design and understand mechatronic systems of this type, good quantitative models of transient friction effects are of primary interest. The theory developed in this book approaches this problem bottom-up, by deriving the behavior of macroscopic friction surfaces from the microscopic surface physics. The model is based on two assumptions: First, rough surfaces are inherently fractal, exhibiting roughness on a wide range of scales. Second, transient friction effects are caused by creep enlargement of the real area of contact between two bodies. This work demonstrates the results of extensive Finite Element analyses of the creep behavior of surface asperities, and proposes a generalized multi-scale area iteration for calculating the time-dependent real contact between two bodies. The toolset is then demonstrated both...

  3. Friction Stir Processing of Cast Superalloys Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR Phase I effort examines the feasibility of an innovative fabrication technology incorporating sand casting and friction stir processing (FSP) for producing...

  4. Composites materials for friction and braking application

    Science.gov (United States)

    Crăciun, A. L.; Pinca-Bretotean, C.; Birtok-Băneasă, C.; Josan, A.

    2017-05-01

    The brake pads are an important component in the braking system of automotive. Materials used for brake pads should have stable and reliable frictional and wear properties under varying conditions of load, velocity, temperature and high durability. These factors must be satisfied simultaneously which makes it difficult to select effective brake pads material. The paper presents the results of the study for characterisation of the friction product used for automotive brake pads. In the study it was developed four frictional composites by using different percentages of coconut fibres (0%, 5%, 10%, 15%) reinforcement in aluminium matrix. The new composites tested in the laboratory, modelling appropriate percentage ratio between matrix and reinforcement volume and can be obtained with low density, high hardness properties, good thermal stability, higher ability to hold the compressive force and have a stable friction coefficient. These characteristics make them useful in automotive industry.

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

    Science.gov (United States)

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

    1974-01-01

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

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

    CERN Document Server

    Yastrebov, Vladislav A

    2015-01-01

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

  7. A review of dynamics modelling of friction wedge suspensions

    Science.gov (United States)

    Wu, Qing; Cole, Colin; Spiryagin, Maksym; Sun, Yan Quan

    2014-11-01

    Three-piece bogies with friction wedge suspensions are the most widely used bogies in heavy haul trains. Fiction wedge suspensions play a key role in these wagon systems. This article reviews current techniques in dynamic modelling of friction wedge suspension with various motivations: to improve dynamic models of friction wedge suspensions so as to improve general wagon dynamics simulations; to seek better friction wedge suspension models for wagon stability assessments in complex train systems; to improve the modelling of other friction devices, such as friction draft gear. Relevant theories and friction wedge suspension models developed by using commercial simulation packages and in-house simulation packages are reviewed.

  8. Thermo-mechanical Modeling for Residual Stresses of Friction Stir Welding of Dissimilar Alloys

    Directory of Open Access Journals (Sweden)

    ABDUL ARIF

    2013-06-01

    Full Text Available Friction stir welding is an advanced joining process that has been used for high production since 1996. FSW produces a weld that is strong than the base material because melting does not occur and joining takes place below the melting temperature of the material. FSW produces no fumes and can join aluminum alloys, magnesium, steels, copper and titanium. In this study, a thermo-mechanical model with improved potential is developed to study the formation of residual stress field in dissimilar materials. The model predictions were confirmed with experimental data obtained by Jamshidi et al. on dissimilar aluminum alloys AA6061 to AA5086. A commercial finite element software ANSYS® is used for simulation of friction stir welding. Longitudinal and transverse residual stresses are obtained when AA5086-O on the advancing side and AA6061- T6 on the retreating side after 15sec.

  9. Process of friction-stir welding high-strength aluminum alloy and mechanical properties of joint

    Institute of Scientific and Technical Information of China (English)

    王大勇; 冯吉才; 郭德伦; 孙成彬; 栾国红; 郭和平

    2004-01-01

    The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters in order to improve a range of material properties. The results showed that the joint strength and elongation arrived at their parameters changing, joint tensile strength and elongation had similar development. Hardness measurement indicated that the weld was softened. However, there was considerable difference in softening degree for different joint zone. The weld top had lower hardness and wider softening zone than other zone of the weld. And softening zone at advancing side was wider than that at retreating side.

  10. Flexible Friction Stir Joining Technology

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Zhili [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lim, Yong Chae [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Mahoney, Murray [MegaStir Technologies LLC, Orem, UT (United States); Sanderson, Samuel [MegaStir Technologies LLC, Orem, UT (United States); Larsen, Steve [MegaStir Technologies LLC, Orem, UT (United States); Steel, Russel [MegaStir Technologies LLC, Orem, UT (United States); Fleck, Dale [MegaStir Technologies LLC, Orem, UT (United States); Fairchild, Doug P [ExxonMobil, Upstream Research Company (URC), Houston, TX (United States); Wasson, Andrew J [ExxonMobil, Upstream Research Company (URC), Houston, TX (United States); Babb, Jon [MegaStir Technologies LLC, Orem, UT (United States); Higgins, Paul [MegaStir Technologies LLC, Orem, UT (United States)

    2015-07-23

    Reported herein is the final report on a U.S. Department of Energy (DOE) Advanced Manufacturing Office (AMO) project with industry cost-share that was jointly carried out by Oak Ridge National Laboratory (ORNL), ExxonMobil Upstream Research Company (ExxonMobil), and MegaStir Technologies (MegaStir). The project was aimed to advance the state of the art of friction stir welding (FSW) technology, a highly energy-efficient solid-state joining process, for field deployable, on-site fabrications of large, complex and thick-sectioned structures of high-performance and high-temperature materials. The technology innovations developed herein attempted to address two fundamental shortcomings of FSW: 1) the inability for on-site welding and 2) the inability to weld thick section steels, both of which have impeded widespread use of FSW in manufacturing. Through this work, major advance has been made toward transforming FSW technology from a “specialty” process to a mainstream materials joining technology to realize its pervasive energy, environmental, and economic benefits across industry.

  11. Linearization of friction effects in vibration of two rotating blades

    Directory of Open Access Journals (Sweden)

    Hajžman M.

    2013-06-01

    Full Text Available This paper is aimed at modelling of friction effects in blade shrouding which are realized by means of friction elements placed between blades. In order to develop a methodology of modelling, two blades with one friction element in between are considered only. Flexible blades fixed to a rotating disc are discretized by FEM using 1D Rayleigh beam elements derived in rotating space as well as the friction element modelled as a rigid body. The blades and the friction element are connected through two concurrent friction planes, where the friction forces arise on the basis of centrifugal force acting on the friction element. The linearization of friction is performed using the harmonic balance method to determine equivalent damping coefficients in dependence on the amplitudes of relative slip motion between the blades and the friction element. The methodology is applied to a model of two real blades and will be extended for the whole bladed disc with shrouding.

  12. Comparisons of friction models in bulk metal forming

    DEFF Research Database (Denmark)

    Tan, Xincai

    2002-01-01

    A friction model is one of the key input boundary conditions in finite element simulations. It is said that the friction model plays an important role in controlling the accuracy of necessary output results predicted. Among the various friction models, which one is of higher accuracy is still...... unknown and controversial. In this paper, finite element analyses applying five different friction models to experiments of upsetting of AA 6082 lubricated with four lubricants are presented. Frictional parameter values are determined by fitness of data of friction area ratio from finite element analysis...... to experimental results. It is found that calibration curves of the friction area ratio for all of the five chosen friction models used in the finite element simulation do fit the experimental results. Usually, calbration curves of the friction area ratio are more sensitive to friction at the tool...

  13. Comparing numerically exact and modelled static friction

    Directory of Open Access Journals (Sweden)

    Krengel Dominik

    2017-01-01

    Full Text Available Currently there exists no mechanically consistent “numerically exact” implementation of static and dynamic Coulomb friction for general soft particle simulations with arbitrary contact situations in two or three dimension, but only along one dimension. We outline a differential-algebraic equation approach for a “numerically exact” computation of friction in two dimensions and compare its application to the Cundall-Strack model in some test cases.

  14. THE FRICTION OF QUARTZ IN HIGH VACUUM

    Science.gov (United States)

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

  15. Network-Configurations of Dynamic Friction Patterns

    CERN Document Server

    Ghaffari, H O

    2012-01-01

    The complex configurations of dynamic friction patterns-regarding real time contact areas- are transformed into appropriate networks. With this transformation of a system to network space, many properties can be inferred about the structure and dynamics of the system. Here, we analyze the dynamics of static friction, i.e. nucleation processes, with respect to "friction networks". We show that networks can successfully capture the crack-like shear ruptures and possible corresponding acoustic features. We found that the fraction of triangles remarkably scales with the detachment fronts. There is a universal power law between nodes' degree and motifs frequency (for triangles, it reads T(k)\\proptok{\\beta} ({\\beta} \\approx2\\pm0.4)). We confirmed the obtained universality in aperture-based friction networks. Based on the achieved results, we extracted a possible friction law in terms of network parameters and compared it with the rate and state friction laws. In particular, the evolutions of loops are scaled with p...

  16. Methods and devices used to measure friction in rolling

    DEFF Research Database (Denmark)

    Jeswiet, J.; Arentoft, Mogens; Henningsen, Poul

    2006-01-01

    a good understanding of the mechanisms at the interface and to be able to verify the friction and tribology models that exist, friction sensors are needed. Designing sensors to measure frictional stress in metal working has been pursued by many researchers. This paper surveys methods that have been used...... to measure friction in rolling in the past and discusses some of the recent sensor designs that can now be used to measure friction both in production situations and for research purposes....

  17. Numerical implementation of a state variable model for friction

    Energy Technology Data Exchange (ETDEWEB)

    Korzekwa, D.A. [Los Alamos National Lab., NM (United States); Boyce, D.E. [Cornell Univ., Ithaca, NY (United States)

    1995-03-01

    A general state variable model for friction has been incorporated into a finite element code for viscoplasticity. A contact area evolution model is used in a finite element model of a sheet forming friction test. The results show that a state variable model can be used to capture complex friction behavior in metal forming simulations. It is proposed that simulations can play an important role in the analysis of friction experiments and the development of friction models.

  18. Nano-Sized Grain Refinement Using Friction Stir Processing

    Science.gov (United States)

    2013-03-01

    friction stir weld is a very fine grain microstructure produced as a result of dynamic recrystallization. The friction stir ... Friction Stir Processing, Magnesium, Nano-size grains Abstract A key characteristic of a friction stir weld is a very fine grain microstructure...state process developed on the basis of the friction stir welding (FSW) technique invented by The Welding Institute (TWI) in 1991 [2]. During

  19. A coupled thermo-mechanical model of friction stir welding

    Directory of Open Access Journals (Sweden)

    Veljić Darko M.

    2012-01-01

    Full Text Available A coupled thermo-mechanical model was developed to study the temperature fields, the plunge force and the plastic deformations of Al alloy 2024-T351 under different rotating speed: 350, 400 and 450 rpm, during the friction stir welding (FSW process. Three-dimensional FE model has been developed in ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and the Coulomb’s Law of friction. Numerical results indicate that the maximum temperature in the FSW process is lower than the melting point of the welding material. The temperature filed is approximately symmetrical along the welding line. A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface. With increasing rotation speed, the low plastic strain region is reduced. When the rotational speed is increased, the plunge force can be reduced. Regions with high equivalent plastic strains are observed which correspond to the nugget and the flow arm.

  20. Working the Dark Side

    DEFF Research Database (Denmark)

    Bjering, Jens Christian Borrebye

    A few days after the terror attacks of 9/11, then Vice President Dick Cheney appeared on television with a call for “working the dark side.” While still unclear what this expression entailed at the time, Cheney's comment appears in retrospect to almost have been prophetic for the years to come....... By analyzing official reports and testimonies from soldiers partaking in the War On Terror, the dissertation's second part—dark arts—focuses on the transformation of the dark side into a productive space in which “information” and the hunt for said information overshadowed all legal, ethical, or political...

  1. Working the Dark Side

    DEFF Research Database (Denmark)

    Bjering, Jens Christian Borrebye

    half—dark side—documents the making and nature of the dark side by analyzing a series of legal memos from the Department of Justice's Office of Legal Council and from the White House and concludes by relating its findings to traditional ideas about emergency action, national security, and torture....... By analyzing official reports and testimonies from soldiers partaking in the War On Terror, the dissertation's second part—dark arts—focuses on the transformation of the dark side into a productive space in which “information” and the hunt for said information overshadowed all legal, ethical, or political...

  2. Friction Stir Processing for Efficient Manufacturing

    Energy Technology Data Exchange (ETDEWEB)

    Mr. Christopher B. Smith; Dr. Oyelayo Ajayi

    2012-01-31

    Friction at contacting surfaces in relative motion is a major source of parasitic energy loss in machine systems and manufacturing processes. Consequently, friction reduction usually translates to efficiency gain and reduction in energy consumption. Furthermore, friction at surfaces eventually leads to wear and failure of the components thereby compromising reliability and durability. In order to reduce friction and wear in tribological components, material surfaces are often hardened by a variety of methods, including conventional heat treatment, laser surface hardening, and thin-film coatings. While these surface treatments are effective when used in conjunction with lubrication to prevent failure, they are all energy intensive and could potentially add significant cost. A new concept for surface hardening of metallic materials and components is Friction Stir Processing (FSP). Compared to the current surface hardening technologies, FSP is more energy efficient has no emission or waste by products and may result in better tribological performance. FSP involves plunging a rotating tool to a predetermined depth (case layer thickness) and translating the FSP tool along the area to be processed. This action of the tool produces heating and severe plastic deformation of the processed area. For steel the temperature is high enough to cause phase transformation, ultimately forming hard martensitic phase. Indeed, FSP has been used for surface modification of several metals and alloys so as to homogenize the microstructure and refine the grain size, both of which led to improved fatigue and corrosion resistance. Based on the effect of FSP on near-surface layer material, it was expected to have beneficial effects on friction and wear performance of metallic materials. However, little or no knowledge existed on the impact of FSP concerning friction and wear performance the subject of the this project and final report. Specifically for steel, which is the most dominant

  3. Frictional Fluid Dynamics and Plug Formation in Multiphase Millifluidic Flow

    Science.gov (United States)

    Dumazer, Guillaume; Sandnes, Bjørnar; Ayaz, Monem; Mâløy, Knut Jørgen; Flekkøy, Eirik Grude

    2016-07-01

    We study experimentally the flow and patterning of a granular suspension displaced by air inside a narrow tube. The invading air-liquid interface accumulates a plug of granular material that clogs the tube due to friction with the confining walls. The gas percolates through the static plug once the gas pressure exceeds the pore capillary entry pressure of the packed grains, and a moving accumulation front is reestablished at the far side of the plug. The process repeats, such that the advancing interface leaves a trail of plugs in its wake. Further, we show that the system undergoes a fluidization transition—and complete evacuation of the granular suspension—when the liquid withdrawal rate increases beyond a critical value. An analytical model of the stability condition for the granular accumulation predicts the flow regime.

  4. Four Sided Seal Tester

    Science.gov (United States)

    2009-07-01

    The Center for Advanced Food Technology School of Enviromental and Biological Sciences New Brunswick, NJ 08903 FTR 216 Defense Logistics Agency...specification for four sided seal tester as function of confinement plate distance” The following modifications were issued :  Jul 18, 2007 0013/01

  5. Colorectal cancers choosing sides

    NARCIS (Netherlands)

    Albuquerque, Cristina; Bakker, Elvira R. M.; van Veelen, Wendy; Smits, Ron

    2011-01-01

    In contrast to the majority of sporadic colorectal cancer which predominantly occur in the distal colon, most mismatch repair deficient tumours arise at the proximal side. At present, these regional preferences have not been explained properly. Recently, we have screened colorectal tumours for mutat

  6. Side effects of ergotamine

    NARCIS (Netherlands)

    Meyler, WJ

    1996-01-01

    Ergotamine has been used for many years in the treatment of migraine, although there is Little formal clinical evidence that it is significantly more efficacious than placebo. A number of side effects associated with ergotamine have been reported in the literature, including myocardial infarction, i

  7. Frictional transfer and the self-organization phenomenon in the friction

    Science.gov (United States)

    Kolesnikov, I. V.; Manturov, D. S.

    2017-05-01

    The paper is devoted to the investigation of the mechanism and kinetics of the surface structures formation in the process of metal-polymer frictional contact. IR spectroscopy methods have showed that the formation kinetics of a frictionally transferred film is determined by the adhesion of the composite components and the direction of the electric field at the contact.

  8. Frictional stability-permeability relationships for fractures in shales: Friction-Permeability Relationships

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Yi [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Elsworth, Derek [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Department of Geosciences, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Wang, Chaoyi [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Ishibashi, Takuya [Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, Pennsylvania State University, University Park Pennsylvania USA; Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology, Koriyama Japan; Fitts, Jeffrey P. [Department of Civil and Environmental Engineering, Princeton University, Princeton New Jersey USA

    2017-01-01

    There is wide concern that fluid injection in the subsurface, such as for the stimulation of shale reservoirs or for geological CO2 sequestration (GCS), has the potential to induce seismicity that may change reservoir permeability due to fault slip. However, the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation (e.g., stable versus unstable). As seismicity is controlled by the frictional response of fractures, we explore friction-stability-permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in Green River shale (GRS) and Opalinus shale (OPS). We observe that carbonate-rich GRS shows higher frictional strength but weak neutral frictional stability. The GRS fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline. By comparison, the phyllosilicate-rich OPS has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction. Hence, we conclude that the friction-stability-permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration.

  9. Ultralow Friction in a Superconducting Magnetic Bearing

    Science.gov (United States)

    Bornemann, Hans J.; Siegel, Michael; Zaitsev, Oleg; Bareiss, Martin; Laschuetza, Helmut

    1996-01-01

    Passive levitation by superconducting magnetic bearings can be utilized in flywheels for energy storage. Basic design criteria of such a bearing are high levitation force, sufficient vertical and horizontal stability and low friction. A test facility was built for the measurement and evaluation of friction in a superconducting magnetic bearing as a function of operating temperature and pressure in the vacuum vessel. The bearing consists of a commercial disk shaped magnet levitated above single grain, melt-textured YBCO high-temperature superconductor material. The superconductor was conduction cooled by an integrated AEG tactical cryocooler. The temperature could be varied from 50 K to 80 K. The pressure in the vacuum chamber was varied from 1 bar to 10(exp -5) mbar. At the lowest pressure setting, the drag torque shows a linear frequency dependence over the entire range investigated (0 less than f less than 40 Hz). Magnetic friction, the frequency independent contribution, is very low. The frequency dependent drag torque is generated by molecular friction from molecule-surface collisions and by eddy currents. Given the specific geometry of the set-up and gas pressure, the molecular drag torque can be estimated. At a speed of 40 Hz, the coefficient of friction (drag-to-lift ratio) was measured to be mu = 1.6 x 10(exp -7) at 10(exp -5) mbar and T = 60 K. This is equivalent to a drag torque of 7.6 x 10(exp -10) Nm. Magnetic friction causes approx. 1% of the total losses. Molecular friction accounts for about 13% of the frequency dependent drag torque, the remaining 87% being due to eddy currents and losses from rotor unbalance. The specific energy loss is only 0.3% per hour.

  10. Gimballed Shoulders for Friction Stir Welding

    Science.gov (United States)

    Carter, Robert; Lawless, Kirby

    2008-01-01

    In a proposed improvement of tooling for friction stir welding, gimballed shoulders would supplant shoulders that, heretofore, have been fixedly aligned with pins. The proposal is especially relevant to self-reacting friction stir welding. Some definitions of terms, recapitulated from related prior NASA Tech Briefs articles, are prerequisite to a meaningful description of the proposed improvement. In friction stir welding, one uses a tool that includes (1) a rotating shoulder on top (or front) of the workpiece and (2) a pin that rotates with the shoulder and protrudes from the shoulder into the depth of the workpiece. In conventional friction stir welding, the main axial force exerted by the tool on the workpiece is reacted through a ridged backing anvil under (behind) the workpiece. When conventional friction stir welding is augmented with an auto-adjustable pin-tool (APT) capability, the depth of penetration of the pin into the workpiece is varied in real time by a position- or forcecontrol system that extends or retracts the pin as needed to obtain the desired effect. In self-reacting (also known as self-reacted) friction stir welding as practiced heretofore, there are two shoulders: one on top (or front) and one on the bottom (or back) of the workpiece. In this case, a threaded shaft protrudes from the tip of the pin to beyond the back surface of the workpiece. The back shoulder is held axially in place against tension by a nut on the threaded shaft. Both shoulders rotate with the pin and remain aligned coaxially with the pin. The main axial force exerted on the workpiece by the tool and front shoulder is reacted through the back shoulder and the threaded shaft into the friction-stir-welding machine head, so that a backing anvil is no longer needed. A key transmits torque between the bottom shoulder and the threaded shaft, so that the bottom shoulder rotates with the shaft. This concludes the prerequisite definitions of terms.

  11. Study of Simulated Temperature of Butt Joint during Friction Stir Welding Of Aluminium Alloy by Using Hyperworks

    Directory of Open Access Journals (Sweden)

    Mohd Anees Siddiqui

    2015-01-01

    Full Text Available Friction stir welding (FSW is one of the latest welding technology that utilizes a special tool for generation of frictional heat in the work piece by its rotation due to which joining occurs without melting of metal. For this reason friction stir welding lies under the category of solid state joining. A part from experimental work, there is large space to work on simulation of FSW by using simulation tools. In the present paper, simulation of friction stir welding of aluminium alloy AA-6061 is done by using HyperWeld module of Altair HyperWorks. The virtual experiment of friction stir welding is conducted for variable tool rotational speeds with constant travelling speed and study of simulation results of variation in temperature distribution along the weld line of butt joint is done. The results of simulation shows that the temperature is symmetrically distributed along the weld line. It is observed that the maximum temperature along the weld line increases with the increase in rotational speed. It is also observed that the temperature at advancing side is greater that retreating side.

  12. New design and the manufacturing techniques of the main friction pair of frictional dampers

    Directory of Open Access Journals (Sweden)

    Aleksander GOLUBENKO

    2007-01-01

    Full Text Available The design of the main friction pair of the frictional oscillations damper of passenger car axle box stage suspension and its manufacturing techniques are described. The difference of the design of the main friction pair consists in replacement of a conicalcontact surface of the shpinton sleeve by a pyramidal surface as well as a cylindrical surface of the frictional slide block by a flat surface of the rectangular form. Technological ways of increase of strength and wear resistance were developed that allowed quantitatively to estimate a reserve of increase of strength and thermal wear resistance by methods of plastic deforming. With the purpose of increase of wear resistance and resource saving the new technology of producing the shpinton sleeve blank is offered by a method of cold die forging, and a frictional slide block – by hot dieforging.

  13. Torsional Vibrations of a Cantilever with Lateral Friction in a Resonance Friction Microscope

    Institute of Scientific and Technical Information of China (English)

    CHEN Jian-Song; GE Yun; ZHANG Hui

    2012-01-01

    A model of fundamental torsional vibration of a cantilever with lateral friction is presented by using the harmonic balance method. The model demonstrates that the torsional vibration has close relations with the lateral friction threshold, the lateral contact stiffness and the torsional vibration amplitude of the cantilever. When the threshold is larger than a product of the stiffness and the vibration amplitude, the lateral friction is a linear force with the amplitude. If the lateral friction threshold is less than the product, the motions of the tip on the sample can be stick-slip or slip motions. The results are useful to optimize and to manipulate the fundamental flexural vibration of the piezo-cantilever, and give an insight into the tribological characterization of the interface in a resonance friction microscope.%A model of fundamental torsional vibration of a cantilever with lateral friction is presented by using the harmonic balance method.The model demonstrates that the torsional vibration has close relations with the lateral friction threshold,the lateral contact stiffness and the torsional vibration amplitude of the cantilever.When the threshold is larger than a product of the stiffness and the vibration amplitude,the lateral friction is a linear force with the amplitude.If the lateral friction threshold is less than the product,the motions of the tip on the sample can be stick-slip or slip motions.The results are useful to optimize and to manipulate the fundamental flexural vibration of the piezo-cantilever,and give an insight into the tribological characterization of the interface in a resonance friction microscope.

  14. Time dependent friction in a free gas

    Science.gov (United States)

    Fanelli, Cristiano; Sisti, Francesco; Stagno, Gabriele V.

    2016-03-01

    We consider a body moving in a perfect gas, described by the mean-field approximation and interacting elastically with the body, we study the friction exerted by the gas on the body fixed at constant velocities. The time evolution of the body in this setting was studied in Caprino et al. [Math. Phys. 264, 167-189 (2006)], Caprino et al. [Math. Models Methods Appl. Sci. 17, 1369-1403 (2007)], and Cavallaro [Rend. Mat. Appl. 27, 123-145 (2007)] for object with simple shape; the first study where a simple kind of concavity was considered was in Sisti and Ricciuti [SIAM J. Math. Anal. 46, 3759-3611 (2014)], showing new features in the dynamic but not in the friction term. The case of more general shape of the body was left out for further difficulties, and we believe indeed that there are actually non-trivial issues to be faced for these more general cases. To show this and in the spirit of getting a more realistic perspective in the study of friction problems, in this paper, we focused our attention on the friction term itself, studying its behavior on a body with a more general kind of concavity and fixed at constant velocities. We derive the expression of the friction term for constant velocities, we show how it is time dependent, and we give its exact estimate in time. Finally, we use this result to show the absence of a constant velocity in the actual dynamic of such a body.

  15. 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...... 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...... cases the frictional shear stress increases monotonically with the sliding velocity. For polymer sliding on polymer (case b) the friction is much larger, and the velocity dependence is more complex. For hydrocarbons with molecular lengths from 60 to 140 C atoms, the number of monolayers of lubricant...

  16. Friction characteristics of trocars in laparoscopic surgery.

    Science.gov (United States)

    Alazmani, Ali; Roshan, Rupesh; Jayne, David G; Neville, Anne; Culmer, Peter

    2015-04-01

    This article investigates the friction characteristics of the instrument-trocar interface in laparoscopic surgery for varying linear instrument velocities, trocar seal design and material, and trocar tilt. Furthermore, the effect of applying lubrication at the instrument-trocar seal interface on friction was studied. A friction testing apparatus was designed and built to characterise the resistance force at the instrument-trocar interface as a function of the instrument's linear movement in the 12-mm trocar (at constant velocity) for different design, seal material, and angle of tilt. The resistance force depended on the trocar seal design and material properties, specifically surface roughness, elasticity, hardness, the direction of movement, and the instrument linear velocity, and varied between 0.25 and 8 N. Lubricating the shaft with silicone oil reduced the peak resistance force by 75% for all trocars and eliminated the stick-slip phenomenon evident in non-lubricated cases. The magnitude of fluctuation in resistance force depends on the trocar design and is attributed to stick-slip of the sealing mechanism and is generally higher during retraction in comparison to insertion. Trocars that have an inlet seal made of rubber/polyurethane showed higher resistance forces during retraction. Use of a lubricant significantly reduced frictional effects. Comparisons of the investigated trocars indicate that a low friction port, providing the surgeon with improved haptic feedback, can be designed by improving the tribological properties of the trocar seal interface.

  17. Assessing the clarity of friction ridge impressions.

    Science.gov (United States)

    Hicklin, R Austin; Buscaglia, JoAnn; Roberts, Maria Antonia

    2013-03-10

    The ability of friction ridge examiners to correctly discern and make use of the ridges and associated features in finger or palm impressions is limited by clarity. The clarity of an impression relates to the examiner's confidence that the presence, absence, and attributes of features can be correctly discerned. Despite the importance of clarity in the examination process, there have not previously been standard methods for assessing clarity in friction ridge impressions. We introduce a process for annotation, analysis, and interchange of friction ridge clarity information that can be applied to latent or exemplar impressions. This paper: (1) describes a method for evaluating the clarity of friction ridge impressions by using color-coded annotations that can be used by examiners or automated systems; (2) discusses algorithms for overall clarity metrics based on manual or automated clarity annotation; and (3) defines a method of quantifying the correspondence of clarity when comparing a pair of friction ridge images, based on clarity annotation and resulting metrics. Different uses of this approach include examiner interchange of data, quality assurance, metrics, and as an aid in automated fingerprint matching.

  18. Friction and wear in polymer-based materials

    CERN Document Server

    Bely, V A; Petrokovets, M I

    1982-01-01

    Friction and Wear in Polymer-Based Materials discusses friction and wear problems in polymer-based materials. The book is organized into three parts. The chapters in Part I cover the basic laws of friction and wear in polymer-based materials. Topics covered include frictional interaction during metal-polymer contact and the influence of operating conditions on wear in polymers. The chapters in Part II discuss the structure and frictional properties of polymer-based materials; the mechanism of frictional transfer when a polymer comes into contact with polymers, metals, and other materials; and

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

    DEFF Research Database (Denmark)

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

    2012-01-01

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

  20. Direct friction measurement in draw bead testing

    DEFF Research Database (Denmark)

    Olsson, David Dam; Bay, Niels; Andreasen, Jan Lasson

    2005-01-01

    The application of draw beads in sheet metal stamping ensures controlled drawing-in of flange parts. Lubrication conditions in draw beads are severe due to sliding under simultaneous bending. Based on the original draw bead test design by Nine [1] comprehensive studies of friction in draw beads...... have been reported in literature. A major drawback in all these studies is that friction is not directly measured, but requires repeated measurements of the drawing force with and without relative sliding between the draw beads and the sheet material. This implies two tests with a fixed draw bead tool...... and a freely rotating tool respectively, an approach, which inevitably implies large uncertainties due to scatter in the experimental conditions. In order to avoid this problem a new draw bead test is proposed by the authors measuring the friction force acting on the tool radius directly by a build...

  1. Hyperstaticity and loops in frictional granular packings

    Science.gov (United States)

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

    2009-06-01

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

  2. CAM/LIFTER forces and friction

    Science.gov (United States)

    Gabbey, D. J.; Lee, J.; Patterson, D. J.

    1992-02-01

    This report details the procedures used to measure the cam/lifter forces and friction. The present effort employed a Cummins LTA-10, and focuses on measurements and dynamic modeling of the injector train. The program was sponsored by the US Department of Energy in support of advanced diesel engine technology. The injector train was instrumented to record the instantaneous roller speed, roller pin friction torque, pushrod force, injector link force, and cam speed. These measurements, together with lift profiles for pushrod and injector link displacement, enabled the friction work loss in the injector train to be determined. Other significant design criteria such as camshaft roller follower slippage and maximum loads on components were also determined. Future efforts will concentrate on the dynamic model, with tests run as required for correlation.

  3. Physics of Friction in Disposable Plastic Syringes

    Science.gov (United States)

    Liebmann-Vinson, A.; Vogler, E. A.; Martin, D. A.; Montgomery, D. B.; Sugg, H. W.; Monahan, L. A.

    1997-03-01

    Nosocomial applications of disposable plastic syringes demand excellent frictional behavior with no stick-slip over a broad velocity range and, simultaneously, a tight seal between stopper and barrel. However, when used in syringe pumps at slow injection speeds, stick-slip motion is frequently observed and high "break-out" forces are often necessary to initiate plunger movement after extended storage times. We have traced this frictional behavior to a velocity-dependent interaction between the elastomeric stopper and the plastic syringe barrel mediated by the syringe lubricant, almost universally a polydimethyl siloxane fluid. Lubricant properties were altered by crosslinking the surface of the silicone oil in an oxygen plasma. Changes in surface chemistry and morphology of the crosslinked oil were correlated with changes in frictional performance.

  4. Direct friction measurement in draw bead testing

    DEFF Research Database (Denmark)

    Olsson, David Dam; Bay, Niels; Andreasen, Jan Lasson

    2005-01-01

    have been reported in literature. A major drawback in all these studies is that friction is not directly measured, but requires repeated measurements of the drawing force with and without relative sliding between the draw beads and the sheet material. This implies two tests with a fixed draw bead tool...... and a freely rotating tool respectively, an approach, which inevitably implies large uncertainties due to scatter in the experimental conditions. In order to avoid this problem a new draw bead test is proposed by the authors measuring the friction force acting on the tool radius directly by a build......-in piezoelectric torque transducer. This technique results in a very sensitive measurement of friction, which furthermore enables recording of lubricant film breakdown as function of drawing distance. The proposed test is validated in an experimental investigation of the influence of lubricant viscosity...

  5. Sensitivity to friction for primary explosives.

    Science.gov (United States)

    Matyáš, Robert; Šelešovský, Jakub; Musil, Tomáš

    2012-04-30

    The sensitivity to friction for a selection of primary explosives has been studied using a small BAM friction apparatus. The probit analysis was used for the construction of a sensitivity curve for each primary explosive tested. Two groups of primary explosives were chosen for measurement (a) the most commonly used industrially produced primary explosives (e.g. lead azide, tetrazene, dinol, lead styphnate) and (b) the most produced improvised primary explosives (e.g. triacetone triperoxide, hexamethylenetriperoxide diamine, mercury fulminate, acetylides of heavy metals). A knowledge of friction sensitivity is very important for determining manipulation safety for primary explosives. All the primary explosives tested were carefully characterised (synthesis procedure, shape and size of crystals). The sensitivity curves obtained represent a unique set of data, which cannot be found anywhere else in the available literature. Copyright © 2012 Elsevier B.V. All rights reserved.

  6. Friction enhancement in concertina locomotion of snakes.

    Science.gov (United States)

    Marvi, Hamidreza; Hu, David L

    2012-11-07

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

  7. Friction enhancement in concertina locomotion of snakes

    Science.gov (United States)

    Marvi, Hamidreza; Hu, David L.

    2012-01-01

    Narrow crevices are challenging terrain for most organisms and biomimetic robots. Snakes move through crevices using sequential folding and unfolding of their bodies in the manner of an accordion or concertina. In this combined experimental and theoretical investigation, we elucidate this effective means of moving through channels. We measure the frictional properties of corn snakes, their body kinematics and the transverse forces they apply to channels of varying width and inclination. To climb channels inclined at 60°, we find snakes use a combination of ingenious friction-enhancing techniques, including digging their ventral scales to double their frictional coefficient and pushing channel walls transversely with up to nine times body weight. Theoretical modelling of a one-dimensional n-linked crawler is used to calculate the transverse force factor of safety: we find snakes push up to four times more than required to prevent sliding backwards, presumably trading metabolic energy for an assurance of wall stability. PMID:22728386

  8. 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.

  9. Adhesion and friction of thin metal films

    Science.gov (United States)

    Buckley, D. H.

    1976-01-01

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

  10. Friction Reduction of Chrome-Coated Surface with Micro-Dimple Arrays Generated by Electrochemical Micromachining

    Science.gov (United States)

    Chen, Xiaolei; Qu, Ningsong; Hou, Zhibao; Wang, Xiaolei; Zhu, Di

    2017-02-01

    Surface coating and surface texture play a significant role in enhancing the tribological properties of mechanical components. In this study, to further improve the tribological properties of a chrome-coated surface, arrays of circular- and square-shaped micro-dimples were generated on chrome-coated surfaces via electrochemical machining. Through-mask electrochemical micromachining (TMEMM) is a popular electrochemical micromachining method for generating micro-dimple arrays. However, photolithography is a necessary process in conventional TMEMM before electrochemical micromachining, which is time-consuming and expensive when used in mass production. A reusable polydimethylsiloxane mask was introduced to prepare the micro-dimples. Circular micro-dimples of 120 μm diameter and square micro-dimples of 106 μm side length were fabricated on a chrome-coated surface. The results of friction tests indicated that at a load of 220 N, 10 μm deep micro-dimples reduced the coefficient of friction (CoF) significantly compared to an untextured surface. At a load of 320 and 420 N, the CoF continually decreased when the depth of the micro-dimples was increased from 0 to 20 μm. In addition, the results showed that, compared to circular micro-dimples, square micro-dimples contributed to a higher friction reduction ratio under the same conditions. The best friction reduction ratio was found for square dimples with a depth of 20 μm.

  11. A temperature dependent slip factor based thermal model for friction stir welding of stainless steel

    Indian Academy of Sciences (India)

    M Selvaraj

    2013-12-01

    This paper proposes a new slip factor based three-dimensional thermal model to predict the temperature distribution during friction stir welding of 304L stainless steel plates. The proposed model employs temperature and radius dependent heat source to study the thermal cycle, temperature distribution, power required, the effect of process parameters on heat generation per mm length of the weld and peak temperature during the friction stir welding process. Simulations of friction stir welding process were carried out on 304L stainless steel workpieces for various rotational and welding speeds. The predicted thermal cycle, power required and temperature distributions were found to be in good agreement with the experimental results. The heat generation per mm length of weld and peak temperature were found to be directly proportional to rotational speed and inversely proportional to welding speed. The rate of increase in heat generation per mm length of the weld and peak temperature are found to be higher at lower rotational speeds and lower at higher rotational speed. The heat generation during friction stir welding was found to be 80.8 % at shoulder, 16.1 % at pin side and 3.1 % at the bottom of the pin.

  12. Mechanical properties and structure of friction stir welds of rolled Zr-modified AA5083 alloy

    Science.gov (United States)

    Malopheyev, S.; Mironov, S.; Kaibyshev, R.

    2016-11-01

    Microstructure and mechanical properties of friction stir welds of Zr-modified AA5083 aluminum sheets were studied. The sheets were produced by cold or hot rolling with a total reduction of 80%. In both rolled conditions, the average high angle boundary spacing was 17-18 µm. The density of free dislocations was ˜5.6 × 1013 and ˜3.5 × 1014 m-2 in hot rolled and cold rolled conditions, respectively. The volume fraction of incoherent Al6Mn dispersoids with an average diameter of ˜25 nm was measured to be ˜0.076%. Defect-free welds were produced by double-side friction stir welding (FSW). Friction stir welding led to the formation of fully recrystallized microstructures with the average grain size about 2.5 µm and low dislocation density in the stir zone in both conditions. The average size and volume fraction of Al6Mn particles increased to ˜25 nm and ˜0.1%, respectively. The joint efficiency of the friction stir welds for ultimate tensile strength was found to be 74 and 94% in the cold-rolled and hot-rolled preprocessed material conditions. The relatively low weld strength was attributed to the elimination of dislocation substructure strengthening during FSW.

  13. Determination of the Mechanical Properties of Friction Welded Tube Yoke and Tube Joint

    Directory of Open Access Journals (Sweden)

    Efe Işık

    2016-01-01

    Full Text Available This paper deals with the friction welding of the tube yoke and the tube of the drive shaft used in light commercial vehicles. Tube yoke made from hot forged microalloyed steel and the tube made from cold drawn steel, with a ratio (thickness/outside diameter ratio of less than 0.1, were successfully welded by friction welding method. Hardness distributions on both sides of the welded joint across the welding interface were determined and the microstructure of the joint was investigated. Furthermore, joint strength was tested under tensile, static torsional, and torsional fatigue loadings. The tested data were analyzed by Weibull distribution. The maximum hardness value along the welded joint was detected as 553 Hv1. The lowest detected tensile strength of the joint was 13% less than the base materials’ tensile strength. The torsional load carrying capacity of the friction welded thin walled tubular joint without any damage was obtained as 4.252,5 Nm in 95% confidence interval. After conducting fully reversed torsional fatigue tests, the fatigue life of friction welded tubular joints was detected as 220.066,3 cycles.

  14. Protecting the radiation-damaged skin from friction: a mini review

    Energy Technology Data Exchange (ETDEWEB)

    Herst, Patries M [Department of Radiation Therapy, University of Otago, Wellington (New Zealand)

    2014-06-15

    Radiation-induced skin reactions are an unavoidable side effect of external beam radiation therapy, particularly in areas prone to friction and excess moisture such as the axilla, head and neck region, perineum and skin folds. Clinical studies investigating interventions for preventing or managing these reactions have largely focussed on formulations with moisturising, anti-inflammatory, anti-microbial and wound healing properties. However, none of these interventions has emerged as a consistent candidate for best practice. Much less emphasis has been placed on evaluating ways to protect the radiation-damaged skin from friction and excess moisture. This mini review analyses the clinical evidence for barrier products that form a protective layer by adhering very closely to the skin folds and do not cause further trauma to the radiation-damaged skin upon removal. A database search identified only two types of barrier products that fitted these criteria and these were tested in two case series and six controlled clinical trials. Friction protection was most effective when the interventions were used from the start of treatment and continued for several weeks after completion of treatment. Soft silicone dressings (Mepilex Lite and Mepitel Film) and Cavilon No Sting Barrier Film, but not Cavilon Moisturizing Barrier Cream, decreased skin reaction severity, most likely due to differences in formulation and skin build-up properties. It seems that prophylactic use of friction protection of areas at risk could be a worthwhile addition to routine care of radiation-damaged skin.

  15. High fidelity frictional models for MEMS.

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-10-01

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

  16. Friction stir welding of single crystal aluminium

    DEFF Research Database (Denmark)

    Fonda, Richard Warren; Wert, John A.; Reynolds, A.P.

    2007-01-01

    Friction stir welds were prepared in different orientations in an aluminium single crystal. The welds were quenched to preserve the microstructure surrounding the tool and then electron backscattered diffraction was used to reveal the generation of grain boundaries and the evolution of crystallog......Friction stir welds were prepared in different orientations in an aluminium single crystal. The welds were quenched to preserve the microstructure surrounding the tool and then electron backscattered diffraction was used to reveal the generation of grain boundaries and the evolution...

  17. Ratchet device with broken friction symmetry

    DEFF Research Database (Denmark)

    Norden, Bengt; Zolotaryuk, Yaroslav; Christiansen, Peter Leth

    2002-01-01

    An experimental setup (gadget) has been made for demonstration of a ratchet mechanism induced by broken symmetry of a dependence of dry friction on external forcing. This gadget converts longitudinal oscillating or fluctuating motion into a unidirectional rotation, the direction of which is in ac......An experimental setup (gadget) has been made for demonstration of a ratchet mechanism induced by broken symmetry of a dependence of dry friction on external forcing. This gadget converts longitudinal oscillating or fluctuating motion into a unidirectional rotation, the direction of which...

  18. Analysis of nonlinear channel friction inverse problem

    Institute of Scientific and Technical Information of China (English)

    CHENG Weiping; LIU Guohua

    2007-01-01

    Based on the Backus-Gilbert inverse theory, the singular value decomposition (SVD) for general inverse matrices and the optimization algorithm are used to solve the channel friction inverse problem. The resolution and covari- ance friction inverse model in matrix form is developed to examine the reliability of solutions. Theoretical analyses demonstrate that the convergence rate of the general Newton optimization algorithm is in the second-order. The Wiggins method is also incorporated into the algorithm. Using the method, noise can be suppressed effectively, and the results are close to accurate solutions with proper control parameters. Also, the numerical stability can be improved.

  19. Design of Piston Ring Friction Tester Apparatus

    DEFF Research Database (Denmark)

    Klit, Peder

    2006-01-01

    the frictional behavior of a piston ring correctly is knowledge about the amount of lubricant present. For piston rings the external load may be established by measuring the pressure distribution, i.e. the pressure drop in the piston ring package. Speed and temperature may also be established. The amount...... and forces on piston rod. Since the frictional forces are small compared to the rest of the acting forces the main design idea is to fix the piston, while the cylinder liner moves. This approach makes it simple to measure the parameters mentioned above by putting the instrumentation in the piston....

  20. Frictional coupling between sliding and spinning motion

    CERN Document Server

    Farkas, Z; Unger, T; Wolf, D E; Farkas, Zeno; Bartels, Guido; Unger, Tamas; Wolf, Dietrich E.

    2002-01-01

    We show that the friction force and torque, acting at a dry contact of two objects moving and rotating relative to each other, are inherently coupled. As a simple test system, a sliding and spinning disk on a horizontal flat surface is considered. We calculate, and also measure, how the disk is slowing down, and find that it always stops its sliding and spinning motion at the same moment. We discuss the impact of this coupling between friction force and torque on the physics of granular materials.

  1. Monomeric Friction Coefficient of Metalnanodispersible Polymeric Systems

    Directory of Open Access Journals (Sweden)

    B.B. Kolupayev

    2016-12-01

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

  2. Bifurcations in Systems with Friction : Basic Models and Methods

    NARCIS (Netherlands)

    Ivanov, A. P.

    2009-01-01

    Examples of irregular behavior of dynamical systems with dry friction are discussed. A classification of frictional contacts with respect to their dimensionality, associativity, and the possibility of interruptions is proposed and basic models showing typical features are stated. In particular,

  3. Micromechanisms of friction and wear introduction to relativistic tribology

    CERN Document Server

    Lyubimov, Dmitrij; Pinchuk, Leonid

    2013-01-01

    The modern vision of the micromechanism of friction and wear is explored, from the examination of ideal and real crystal structure and adhesion properties to the dynamics of solid frictional interaction. The fundamental quantum-mechanical and relativity principles of particle interaction are considered as basis of friction micro-process examination. The changes in solid structure originated from the influence of different kinds of force fields are considered. The principal possibility of relativity effect manifestation by friction is explained. The critical state of friction – triboplasma – was studied. Structural peculiarities of triboplasma, the kinetics of its transformation during frictional interaction as well as the influence of plasma and postplasma processes on tribojunction friction characteristics and complex formation by friction were examined. The book addresses to tribology researchers.

  4. Assessing slipperiness in fast-food restaurants in the USA using friction variation, friction level and perception rating.

    Science.gov (United States)

    Chang, Wen-Ruey; Huang, Yueng-Hsiang; Way Li, Kai; Filiaggi, Alfred; Courtney, Theodore K

    2008-05-01

    Although friction variation is speculated to be a significant contributor to slip and fall incidents, it has not been related to a measurement of slipperiness in the literature. This field study investigated the relationship among multiple friction variations, friction levels and the perception ratings of slipperiness in six major working areas of 10 fast-food restaurants in the USA. The mean perception rating score for each working area was correlated with various friction reduction variables across all the restaurants in comparison with its correlation with the mean friction coefficient of each working area. The results indicated that the absolute and relative reductions in friction over the whole working area, among 12 friction reduction variables evaluated, could have a slightly better correlation with the perception rating score (r=0.34 and 0.37, respectively) than the mean friction coefficient of each working area (0.33). However, in friction measurements, more effort and time are needed to quantify friction variations than to obtain the mean friction coefficient. The results of the multiple regression model on the perception rating indicated that adding friction reduction variables into the regression model, in addition to the mean friction coefficient, did not make a significant impact on the outcomes. The results further indicated a statistically significant correlation between the mean friction coefficient and the maximum relative friction reduction over the whole area in each working area across all the restaurants evaluated (r=0.80). Despite a slightly lower correlation with perception rating than the friction variation, the mean friction coefficient of an area is still a reasonably good indicator of slipperiness.

  5. Peak Stir Zone Temperatures during Friction Stir Processing

    Science.gov (United States)

    Swaminathan, Srinivasan; Oh-Ishi, Keiichiro; Zhilyaev, Alexander P.; Fuller, Christian B.; London, Blair; Mahoney, Murray W.; McNelley, Terry R.

    2010-03-01

    The stir zone (SZ) temperature cycle was measured during the friction stir processing (FSP) of NiAl bronze plates. The FSP was conducted using a tool design with a smooth concave shoulder and a 12.7-mm step-spiral pin. Temperature sensing was accomplished using sheathed thermocouples embedded in the tool path within the plates, while simultaneous optical pyrometry measurements of surface temperatures were also obtained. Peak SZ temperatures were 990 °C to 1015 °C (0.90 to 0.97 T Melt) and were not affected by preheating to 400 °C, although the dwell time above 900 °C was increased by the preheating. Thermocouple data suggested little variation in peak temperature across the SZ, although thermocouples initially located on the advancing sides and at the centerlines of the tool traverses were displaced to the retreating sides, precluding direct assessment of the temperature variation across the SZ. Microstructure-based estimates of local peak SZ temperatures have been made on these and on other similarly processed materials. Altogether, the peak-temperature determinations from these different measurement techniques are in close agreement.

  6. Deciphering viscous flow of frictional melts with the mini-AMS method

    Science.gov (United States)

    Ferré, Eric C.; Chou, Yu-Min; Kuo, Ruo Lin; Yeh, En-Chao; Leibovitz, Natalie R.; Meado, Andrea L.; Campbell, Lucy; Geissman, John W.

    2016-09-01

    The anisotropy of magnetic susceptibility (AMS) is widely used to analyze magmatic flow in intrusive igneous bodies including plutons, sills and dikes. This method, owing its success to the rapid nature of measurements, provides a proxy for the orientation of markers with shape anisotropy that flow and align in a viscous medium. AMS specimens typically are 25 mm diameter right cylinders or 20 mm on-a-side cubes, representing a volume deemed statistically representative. Here, we present new AMS results, based on significantly smaller cubic specimens, which are 3.5 mm on a side, hence∼250 times volumetrically smaller than conventional specimens. We show that, in the case of frictional melts, which inherently have an extremely small grain size, this small volume is in most cases sufficient to characterize the pseudotachylyte fabric, particularly when magnetite is present. Further, we demonstrate that the mini-AMS method provides new opportunities to investigate the details of frictional melt flow in these coseismic miniature melt bodies. This new method offers significant potential to investigate frictional melt flow in pseudotachylyte veins including contributions to the lubrication of faults at shallow to moderate depths.

  7. Putting the Side first

    Energy Technology Data Exchange (ETDEWEB)

    1994-02-01

    SIDE Minerals is a relative newcomer to the South African mining industry. It combines coal and anthracite mining and has base and precious metal interests. Side Minerals has offices in Boksburg from where its mining operations in Delmas, Witbank and Carolina in the Eastern Transvaal, and Newcastle in Natal are controlled. Lakeside Colliery at Witbank -a mine with a life expectancy of 15 years - is both an underground and opencast operation with an annual production capacity of 1,2 Mt of high, medium and low grade coal. Opencast extraction there is by the strip mining method. This is done on contract by Concor Mining Opencast Division, a member of the Concor Holding Group. A high wall face provides entry to the underground operations. Eastside Colliery at Carolina, which has the capacity to produce 480 000 tons of coal a year, is currently an opencast operation with underground mining scheduled to begin during 1994. Westside Colliery near Delmas is on a care and maintenance basis, but it has the capacity to produce 600 000 tons of low grade phosphorous coal which is required by the ferro-alloy and steel industries. 2 figs.

  8. An empirical model for friction in cold forging

    DEFF Research Database (Denmark)

    Bay, Niels; Eriksen, Morten; Tan, Xincai

    2002-01-01

    With a system of simulative tribology tests for cold forging the friction stress for aluminum, steel and stainless steel provided with typical lubricants for cold forging has been determined for varying normal pressure, surface expansion, sliding length and tool/work piece interface temperature...... of normal pressure and tool/work piece interface temperature. The model is verified by process testing measuring friction at varying reductions in cold forward rod extrusion. KEY WORDS: empirical friction model, cold forging, simulative friction tests....

  9. Low-impact friction materials for brake pads

    OpenAIRE

    2016-01-01

    State-of-the-art friction materials for applications in disc brake systems are constituted by composite materials, specifically formulated to ensure proper friction and wear performances, under the sliding contact conditions of braking events. The bases of typical friction compound formulations usually include 10 to 30 different components bonded with a polymeric binder cross-linked in situ. Main requests to be fulfilled during braking are an adequate friction efficiency and enough mechanical...

  10. Interfacial Friction and Adhesion of Polymer Brushes

    KAUST Repository

    Landherr, Lucas J. T.

    2011-08-02

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

  11. Multiscaling behavior of atomic-scale friction

    Science.gov (United States)

    Jannesar, M.; Jamali, T.; Sadeghi, A.; Movahed, S. M. S.; Fesler, G.; Meyer, E.; Khoshnevisan, B.; Jafari, G. R.

    2017-06-01

    The scaling behavior of friction between rough surfaces is a well-known phenomenon. It might be asked whether such a scaling feature also exists for friction at an atomic scale despite the absence of roughness on atomically flat surfaces. Indeed, other types of fluctuations, e.g., thermal and instrumental fluctuations, become appreciable at this length scale and can lead to scaling behavior of the measured atomic-scale friction. We investigate this using the lateral force exerted on the tip of an atomic force microscope (AFM) when the tip is dragged over the clean NaCl (001) surface in ultra-high vacuum at room temperature. Here the focus is on the fluctuations of the lateral force profile rather than its saw-tooth trend; we first eliminate the trend using the singular value decomposition technique and then explore the scaling behavior of the detrended data, which contains only fluctuations, using the multifractal detrended fluctuation analysis. The results demonstrate a scaling behavior for the friction data ranging from 0.2 to 2 nm with the Hurst exponent H =0.61 ±0.02 at a 1 σ confidence interval. Moreover, the dependence of the generalized Hurst exponent, h (q ) , on the index variable q confirms the multifractal or multiscaling behavior of the nanofriction data. These results prove that fluctuation of nanofriction empirical data has a multifractal behavior which deviates from white noise.

  12. Modelling and Testing of Friction in Forging

    DEFF Research Database (Denmark)

    Bay, Niels

    2007-01-01

    Knowledge about friction is still limited in forging. The theoretical models applied presently for process analysis are not satisfactory compared to the advanced and detailed studies possible to carry out by plastic FEM analyses and more refined models have to be based on experimental testing...

  13. [Penis friction edema: not a venereal disease

    NARCIS (Netherlands)

    Erceg, A.; Verlind, J.; Berretty, P.J.

    2003-01-01

    A 35-year-old man presented with a local swelling of the penis, which increased until the entire penis was thick and swollen. After infectious and obstructive causes had been eliminated, a diagnosis of 'penis friction oedema' was made. The swelling disappeared during several weeks of abstinence from

  14. Friction welding thermal and metallurgical characteristics

    CERN Document Server

    Yilbas, Bekir Sami

    2014-01-01

    This book provides insight into the thermal analysis of friction welding incorporating welding parameters such as external, duration, breaking load, and material properties. The morphological and metallurgical changes associated with the resulting weld sites are analysed using characterization methods such as electron scanning microscope, energy dispersive spectroscopy, X-ray Diffraction, and Nuclear reaction analysis.

  15. Ratchet due to broken friction symmetry

    DEFF Research Database (Denmark)

    Norden, Bengt; Zolotaryuk, Yaroslav; Christiansen, Peter Leth

    2002-01-01

    A ratchet mechanism that occurs due to asymmetric dependence of the friction of a moving system on its velocity or a driving force is reported. For this kind of ratchet, instead of a particle moving in a periodic potential, the dynamics of which have broken space-time symmetry, the system must...

  16. Sensitivity to friction for primary explosives

    Energy Technology Data Exchange (ETDEWEB)

    Matyas, Robert, E-mail: robert.matyas@upce.cz [Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, Pardubice 532 10 (Czech Republic); Selesovsky, Jakub; Musil, Tomas [Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, Pardubice 532 10 (Czech Republic)

    2012-04-30

    Highlights: Black-Right-Pointing-Pointer The friction sensitivity of 14 samples of primary explosives was determined. Black-Right-Pointing-Pointer The same apparatus (small scale BAM) and the same method (probit analysis) was used. Black-Right-Pointing-Pointer The crystal shapes and sizes were documented with microscopy. Black-Right-Pointing-Pointer Almost all samples are less sensitive than lead azide, which is commercially used. Black-Right-Pointing-Pointer The organic peroxides (TATP, DADP, HMTD) are not as sensitive as often reported. - Abstract: The sensitivity to friction for a selection of primary explosives has been studied using a small BAM friction apparatus. The probit analysis was used for the construction of a sensitivity curve for each primary explosive tested. Two groups of primary explosives were chosen for measurement (a) the most commonly used industrially produced primary explosives (e.g. lead azide, tetrazene, dinol, lead styphnate) and (b) the most produced improvised primary explosives (e.g. triacetone triperoxide, hexamethylenetriperoxide diamine, mercury fulminate, acetylides of heavy metals). A knowledge of friction sensitivity is very important for determining manipulation safety for primary explosives. All the primary explosives tested were carefully characterised (synthesis procedure, shape and size of crystals). The sensitivity curves obtained represent a unique set of data, which cannot be found anywhere else in the available literature.

  17. On the superradiance-tidal friction correspondence

    CERN Document Server

    Glampedakis, K; Kennefick, D

    2013-01-01

    Since the work of Hartle in the 1970s, and the subsequent development of the the Membrane Paradigm approach to black hole physics it has been widely accepted that superradiant scattering of gravitational waves bears strong similarities with the phenomenon of ``tidal friction'' (well-known from Newtonian gravity) operating in binary systems of viscous material bodies. In this paper we revisit the superradiance-tidal friction analogy within the context of ultracompact relativistic bodies. We advocate that as long as these bodies have non-zero viscosity they should undergo tidal friction that can be construed as a kind of superradiant scattering from the point of view of the dynamics of an orbiting test-body. In addition we consider the presence of anisotropic matter, which is required for at least some ultracompact bodies, if they are to sustain a radius very close to the gravitational radius. We find that the tidal friction/superradiance output is enhanced with increasing anisotropy and that strongly anisotrop...

  18. Rolling Friction on a Wheeled Laboratory Cart

    Science.gov (United States)

    2012-01-01

    by gravity, and a vehicle (such as a car or bicycle ) accelerating along a level road is driven by a motor or by pedalling. In such cases, static...continuously roll. Consider a cart of mass m that is free rolling up an incline, as sketched in figure 1. The total frictional force f on the cart

  19. Friction Stir Welding of Aluminum Alloys

    Institute of Scientific and Technical Information of China (English)

    FU Zhi-hong; HE Di-qiu; WANG Hong

    2004-01-01

    Friction stir welding(FSW), a new solid-state welding technology invited in the early 1990s,enables us weld aluminum alloys and titanium alloys etc. The processing of FSW, the microstructure in FSW alloysand the factors influencing weld quality are introduced. The complex factors affecting the properties are researched.

  20. Frictional Dermatosis in a Courier Driver

    Directory of Open Access Journals (Sweden)

    Uwe Wollina

    2017-07-01

    Full Text Available Frictional hypermelanosis is an uncommon finding in Caucasians. We report the unusual case of 56-year-old male courier driver who developed linear and patchy hypermelanosis of the back caused by the driver's seat. Histology has included other pathologies. Treatment of the asymptomatic hyper pigmentation was not warranted.

  1. Validation of measured friction by process tests

    DEFF Research Database (Denmark)

    Eriksen, Morten; Henningsen, Poul; Tan, Xincai;

    The objective of sub-task 3.3 is to evaluate under actual process conditions the friction formulations determined by simulative testing. As regards task 3.3 the following tests have been used according to the original project plan: 1. standard ring test and 2. double cup extrusion test. The task ...

  2. Frictional Torque on a Rotating Disc

    Science.gov (United States)

    Mungan, Carl E.

    2012-01-01

    Resistance to motion often includes a dry frictional term independent of the speed of an object and a fluid drag term varying linearly with speed in the viscous limit. (At higher speeds, quadratic drag can also occur.) Here, measurements are performed for an aluminium disc mounted on bearings that is given an initial twist and allowed to spin…

  3. Friction Force: From Mechanics to Thermodynamics

    Science.gov (United States)

    Ferrari, Christian; Gruber, Christian

    2010-01-01

    We study some mechanical problems in which a friction force is acting on a system. Using the fundamental concepts of state, time evolution and energy conservation, we explain how to extend Newtonian mechanics to thermodynamics. We arrive at the two laws of thermodynamics and then apply them to investigate the time evolution and heat transfer of…

  4. Tribology: Friction, lubrication, and wear technology

    Science.gov (United States)

    Blau, Peter J.

    1993-01-01

    The topics are presented in viewgraph form and include the following: introduction and definitions of terms; friction concepts; lubrication technology concepts; wear technology concepts; and tribological transitions. This document is designed for educators who seek to teach these concepts to their students.

  5. [Penis friction edema: not a venereal disease

    NARCIS (Netherlands)

    Erceg, A.; Verlind, J.; Berretty, P.J.

    2003-01-01

    A 35-year-old man presented with a local swelling of the penis, which increased until the entire penis was thick and swollen. After infectious and obstructive causes had been eliminated, a diagnosis of 'penis friction oedema' was made. The swelling disappeared during several weeks of abstinence from

  6. Fibre Distribution in Friction-spun Yarns

    Institute of Scientific and Technical Information of China (English)

    Eric Oyondi Nganyi; YU Chong-wen

    2006-01-01

    According to the yarn forming characteristics in friction spinning, the arrangement of fed sliver is designed, to get the desired fiber distribution in the resultant yarn. On the base of that, the relation between the theoretical fibre distribution and the actual fibre distribution is analyzed by use of electron microscope.

  7. 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. Ki...

  8. 30 CFR 57.19008 - Friction hoist synchronizing mechanisms.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist synchronizing mechanisms. 57... MINES Personnel Hoisting Hoists § 57.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with...

  9. 30 CFR 56.19008 - Friction hoist synchronizing mechanisms.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist synchronizing mechanisms. 56... Personnel Hoisting Hoists § 56.19008 Friction hoist synchronizing mechanisms. Where creep or slip may alter the effective position of safety devices, friction hoists shall be equipped with synchronizing...

  10. 30 CFR 56.19014 - Friction hoist overtravel protection.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist overtravel protection. 56.19014 Section 56.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 56.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  11. 30 CFR 57.19014 - Friction hoist overtravel protection.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Friction hoist overtravel protection. 57.19014 Section 57.19014 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Hoisting Hoists § 57.19014 Friction hoist overtravel protection. In a friction hoist installation, tapered...

  12. Atomic-scale friction : thermal effects and capillary condensation

    NARCIS (Netherlands)

    Jinesh, Kochupurackal Balakrishna Pillai

    2006-01-01

    This work entitled as "Atomic-scale friction: thermal effects and capillary condensation" is a study on the fundamental aspects of the origin of friction from the atomic-scale. We study two realistic aspects of atomic-scale friction, namely the effect of temperature and the effect of relative humidi

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

    NARCIS (Netherlands)

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

    2015-01-01

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

  14. 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...

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

    NARCIS (Netherlands)

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

    2015-01-01

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

  16. Frictional torque numbers for ball cup and journal bearings

    NARCIS (Netherlands)

    Ligterink, D.J.

    1982-01-01

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

  17. Observing the Forces Involved in Static Friction under Static Situations

    Science.gov (United States)

    Kaplan, Daniel

    2013-01-01

    Static friction is an important concept in introductory physics. Later in the year students apply their understanding of static friction under more complex conditions of static equilibrium. Traditional lab demonstrations in this case involve exceeding of the maximum level of static friction, resulting in the "onset of motion." (Contains…

  18. Microstructure and mechanical properties of hard zone in friction stir welded X80 pipeline steel relative to different heat input

    Energy Technology Data Exchange (ETDEWEB)

    Aydin, Hakan, E-mail: hakanay@uludag.edu.tr [Engineering and Architecture Faculty, Mechanical Engineering Department, Uludag University, 16059 Gorukle-Bursa (Turkey); Nelson, Tracy W. [Mechanical Engineering Department, Brigham Young University, 435 CTB, Provo, UT 84602 (United States)

    2013-12-01

    The study was conducted to investigate the microstructure and mechanical properties of the hard zone in friction stir welded X80 pipeline steel at different heat inputs. Microstructural analysis of the welds was carried out using optical microscopy, transmission electron microscopy, and microhardness. Heat input during friction stir welding process had a significant influence on the microstructure and mechanical properties in the hard zone along the advancing side of the weld nugget. Based on the results, the linear relationships between heat input and post-weld microstructures and mechanical properties in the hard zone of friction stir welded X80 steels were established. It can be concluded that with decrease in heat input the bainitic structure in the hard zone becomes finer and so hard zone strength increases.

  19. A Microphysical Model for Phyllosilicate Friction

    Science.gov (United States)

    Den Hartog, S. A. M.; Faulkner, D.; Spiers, C. J.

    2016-12-01

    Phyllosilicate-rich foliations in fault rocks are often thought to reduce overall fault strength and promote fault stability when forming an interconnected network. Indeed, laboratory measurements have shown that the average friction coefficient of dry phyllosilicates of 0.5 is reduced to 0.3 when wet or even 0.1 for smectite. A widely accepted interpretation of these observations is that the strength of phyllosilicates is controlled by breaking of interlayer bonds to form new cleavage surfaces when dry and by the low strength of surface-bound water films when wet. However, the correlation between phyllosilicate shear strength and interlayer bond strength, which formed the basis for this interpretation, was not reproduced in recent experiments (Behnsen and Faulkner, 2012) and is not supported by the latest calculations of the interlayer bond energies (Sakuma and Suehara, 2015). The accepted explanation for phyllosilicate friction also fails to account for the velocity dependence or (a-b) values, which decrease with temperature, reaching a minimum at intermediate temperatures, before increasing again at higher temperatures (Den Hartog et al., 2013, 2014). In this study, we developed a microphysical model for phyllosilicate friction, involving frictional sliding along atomically flat phyllosilicate grain interfaces, with overlapping grain edges forming barriers to sliding. Assuming that the amount of overlap is controlled by crystal plastic bending of grains into pores, together with rate-dependent edge-site cleavage, our model predicts the experimentally observed temperature dependence of (a-b) and provides a basis for extrapolation of laboratory friction data on phyllosilicates to natural conditions.

  20. Productive friction: how difficult business partnerships can accelerate innovation.

    Science.gov (United States)

    Hagel, John; Brown, John Seely

    2005-02-01

    Companies are becoming more dependent on business partners, but coordinating with outsiders takes its toll. Negotiating terms, monitoring performance, and, if needs are not being met, switching from one partner to another require time and money. Such transaction costs, Ronald Coase explained in his 1937 essay "The Nature of the Firm," drove many organizations to bring their activities in-house. But what if Coase placed too much emphasis on these costs? What if friction between companies can be productive? Indeed, as John Hagel and John Seely Brown point out, interactions between organizations can yield benefits beyond the goods or services contracted for. Companies get better at what they do--and improve faster than their competitors--by working with outsiders whose specialized capabilities complement their own. Different enterprises bring different perspectives and competencies. When these enterprises tackle a problem together, they dramatically increase the chances for innovative solutions. Of course, misunderstandings often arise when people with different backgrounds and skill sets try to collaborate. Opposing sides may focus on the distance that separates them rather than the common challenges they face. How can companies harness friction so that it builds capabilities? Start by articulating performance goals that everyone buys into. Then make sure people are using tangible prototypes to wrangle over. Finally, assemble teams with committed people who bring different perspectives to the table. As individual problems are being addressed, take care that the underpinnings of shared meaning and trust are also being woven between the companies. Neither can be dictated--but they can be cultivated. Without them, the performance fabric quickly unravels, and business partnerships disintegrate into rivalrous competition.

  1. Trade Friction, Upgrading Path and Development of Chinese Textile and Apparel Industry

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jun-li

    2008-01-01

    China is the largest producer and exporter in textiles in the world now, but most Chinese textile and apparel enterprises operate in the low stream of global value chain-processing and assembling. A combination of domestic supply side constrains of high wages and external pressures of appreciation of RMB and trade friction make it difficult for Chinese textile and apparel industry to maintain the low-wage manufacturing. The paper analyzes by stakeholder map for trade friction. It may be more effective that China deals with the trade issues based on the analysis of different stakeholders. The political agreement is only a temporary resolution; the more important way is try to upgrade the operations in developed regions. According to industrial organization theory and global value chain theory, it is suggested product development and marketing are upgrading paths for Chinese enterprises.

  2. Probiotics: Safety and Side Effects

    Science.gov (United States)

    ... of this page please turn JavaScript on. Feature: Probiotics Safety and Side Effects Past Issues / Winter 2016 ... Says About the Safety and Side Effects of Probiotics Whether probiotics are likely to be safe for ...

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

    Directory of Open Access Journals (Sweden)

    Yuri V. Konovalov

    2012-09-01

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

  4. Measurement of friction coefficient in aluminum sheet warm forming

    Institute of Scientific and Technical Information of China (English)

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

    2005-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2008-01-01

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

  6. 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...

  7. Friction Effects in Pedestrian Headform Impacts with Engine Hoods

    Institute of Scientific and Technical Information of China (English)

    LIU Qi; XIA Yong; ZHOU Qing

    2009-01-01

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

  8. Ferrous friction stir weld physical simulation

    Science.gov (United States)

    Norton, Seth Jason

    2006-04-01

    Traditional fusion welding processes have several drawbacks associated with the melting and solidification of metal. Weld defects associated with the solidification of molten metal may act as initiation sites for cracks. Segregation of alloying elements during solidification may cause local changes in resistance to corrosion. The high amount of heat required to produce the molten metal in the weld can produce distortion from the intended position on cooling. The heat from the electric arc commonly used to melt metal in fusion welds may also produce metal fumes which are a potential health hazard. Friction stir welding is one application which has the potential to make full thickness welds in a single pass, while eliminating fume, reducing distortion, and eliminating solidification defects. Currently the friction stir welding process is used in the aerospace industry on aluminum alloys. Interest in the process by industries which rely on iron and its alloys for structural material is increasing. While friction stir welding has been shown to be feasible with iron alloys, the understanding of friction stir welding process effects on these materials is in its infancy. This project was aimed to better that understanding by developing a procedure for physical simulation of friction stir welding. Friction stir weld material tracer experiments utilizing stainless steel markers were conducted with plates of ingot iron and HSLA-65. Markers of 0.0625" diameter 308 stainless steel worked well for tracing the end position of material moved by the friction stir welding tool. The markers did not produce measurable increases in the loading of the tool in the direction of travel. Markers composed of 0.25" diameter 304 stainless steel did not perform as well as the smaller markers and produced increased loads on the friction stir welding tool. The smaller markers showed that material is moved in a curved path around the tool and deposited behind the tool. Material near the surface

  9. HIV Medicines and Side Effects

    Science.gov (United States)

    Side Effects of HIV Medicines HIV Medicines and Side Effects (Last updated 1/17/2017; last reviewed 1/17/2017) Key Points HIV medicines help people with ... will depend on a person’s individual needs. Can HIV medicines cause side effects? HIV medicines help people ...

  10. Efficacy of 15% trichloroacetic Acid and 50% glycolic Acid peel in the treatment of frictional melanosis: a comparative study.

    Science.gov (United States)

    Sacchidanand, S; Shetty, Ashvith B; Leelavathy, B

    2015-01-01

    Frictional dermal melanosis is aesthetically displeasing. Various modalities ranging from depigmenting agents to lasers have been tried but it continues to be a difficult problem to treat. To study and compare the efficacy of 15% trichloroacetic acid (TCA) and 50% glycolic acid in the treatment of frictional melanosis of the forearm. 40 patients of frictional melanosis of the forearm were included in the study. Patients were randomly divided into two equal groups A and B. Pre-peel priming was carried out with 12% glycolic acid and sunscreen for 2 weeks. Group A was treated with trichloroacetic acid (TCA-15%) peel and Group B with glycolic acid (GA-50%) peel. Four peels were done one every 15 days. Clinical photographs were taken to assess the response. Response to therapy was evaluated by both objective and subjective methods. The patients were followed up for 3 months after the last peel to note any relapse. Both TCA and glycolic acid peels were effective in frictional melanosis. TCA showed better response compared to glycolic acid at the end of the treatment, both by subjective and objective methods. However, this difference was not statistically significant (P > 0.05). No permanent side effects were seen in any of the treated patients and the improvement was sustained without any relapse at 3 months. Chemical peeling with both tricholoroacetic acid (15%) and glycolic acid (50%) is safe and effective for the treatment of frictional dermal melanosis. Tricholoroacetic acid was found to be marginally superior to glycolic acid.

  11. Investigation of the effect of wall friction on the flow rate in 2D and 3D Granular Flow

    Science.gov (United States)

    Carballo-Ramirez, Brenda; Pleau, Mollie; Easwar, Nalini; Birwa, Sumit; Shah, Neil; Tewari, Shubha

    We have measured the mass flow rate of spherical steel spheres under gravity in vertical, straight-walled 2 and 3-dimensional hoppers, where the flow velocity is controlled by the opening size. Our measurements focus on the role of friction and its placement along the walls of the hopper. In the 2D case, an increase in the coefficient of static friction from μ = 0.2 to 0.6 is seen to decrease the flow rate significantly. We have changed the placement of frictional boundaries/regions from the front and back walls of the 2D hopper to the side walls and floor to investigate the relative importance of the different regions in determining the flow rate. Fits to the Beverloo equation show significant departure from the expected exponent of 1.5 in the case of 2D flow. In contrast, 3D flow rates do not show much dependence on wall friction and its placement. We compare the experimental data to numerical simulations of gravity driven hopper granular flow with varying frictional walls constructed using LAMMPS*. *http://lammps.sandia.gov Supported by NSF MRSEC DMR 0820506.

  12. Friction Reduction for Microhole CT Drilling

    Energy Technology Data Exchange (ETDEWEB)

    Ken Newman; Patrick Kelleher; Edward Smalley

    2007-03-31

    The objective of this 24 month project focused on improving microhole coiled tubing drilling bottom hole assembly (BHA) reliability and performance, while reducing the drilling cost and complexity associated with inclined/horizontal well sections. This was to be accomplished by eliminating the need for a downhole drilling tractor or other downhole coiled tubing (CT) friction mitigation techniques when drilling long (>2,000 ft.) of inclined/horizontal wellbore. The technical solution to be developed and evaluated in this project was based on vibrating the coiled tubing at surface to reduce the friction along the length of the downhole CT drillstring. The Phase 1 objective of this project centered on determining the optimum surface-applied vibration system design for downhole CT friction mitigation. Design of the system would be based on numerical modeling and laboratory testing of the CT friction mitigation achieved with various types of surface-applied vibration. A numerical model was developed to predict how far downhole the surface-applied vibration would travel. A vibration test fixture, simulating microhole CT drilling in a horizontal wellbore, was constructed and used to refine and validate the numerical model. Numerous tests, with varying surface-applied vibration parameters were evaluated in the vibration test fixture. The data indicated that as long as the axial force on the CT was less than the helical buckling load, axial vibration of the CT was effective at mitigating friction. However, surface-applied vibration only provided a small amount of friction mitigation as the helical buckling load on the CT was reached or exceeded. Since it would be impractical to assume that routine field operations be conducted at less than the helical buckling load of the CT, it was determined that this technical approach did not warrant the additional cost and maintenance issues that would be associated with the surface vibration equipment. As such, the project was

  13. Fault Wear and Friction Evolution: Experimental Analysis

    Science.gov (United States)

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

    2011-12-01

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

  14. Microhardness and Strain Field Characterization of Self-Reacting Friction Stir and Plug Welds of Dissimilar Aluminum Alloys

    Science.gov (United States)

    Horton, Karla Renee

    2011-01-01

    Friction stir welding (FSW) is a solid state welding process with potential advantages for aerospace and automotive industries dealing with light alloys. Self-reacting friction stir welding (SR-FSW) is one variation of the FSW process being developed at the National Aeronautics and Space Administration (NASA) for use in the fabrication of propellant tanks. Friction plug welding is used to seal the exit hole that remains in a circumferential SR-FSW. This work reports on material properties and strain patterns developed in a SR-FSW with a friction plug weld. Specifically, this study examines the behavior of a SR-FSW formed between an AA 2014-T6 plate on the advancing side and an AA 2219-T87 plate on the retreating side and a SR-FSW (AA 2014-T6 to AA 2219-T87) with a 2219-T87 plug weld. This study presents the results of a characterization of the micro-hardness, joint strength, and strain field characterization of SR-FSW and FPW joints tested at room temperature and cryogenic temperatures.

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

    CERN Document Server

    Abdel-Aal, Hisham A

    2012-01-01

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

  16. Friction material composites copper-metal-free material design perspective

    CERN Document Server

    Sundarkrishnaa, K L

    2015-01-01

    This book examines material composites used in connection with brake friction, their design and safety. To aid in understanding, the essentials of friction are explained. This second edition was extended to include friction material composites without copper, as they offer an environmentally friendlier option. The second edition is intended to support beginners by offering insights into the essentials of friction material composites, helping them to develop a broader understanding of brake friction materials. Friction materials find wide-ranging applications in household and industrial appliances, brake pads for automotive applications, rail brake friction pads and composition brake blocks. This second edition is an introductory volume to a set of related books, and is based on the author’s experience and expertise with various material manufacturers, brake manufacturers, vehicle manufacturers, researchers and testing labs around the world with which the author has been associated for the past 28 years.

  17. Device for Measuring Sliding Friction on Highloft Nonwovens

    Directory of Open Access Journals (Sweden)

    Stephen Michielsen

    2006-08-01

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

  18. Formation and rupture of capillary bridges in atomic scale friction

    Science.gov (United States)

    Barel, Itay; Filippov, Aleksander E.; Urbakh, M.

    2012-10-01

    While formation of capillary bridges significantly contributes to the adhesion and friction at micro- and nanoscales, many key aspects of dynamics of capillary condensation and its effect on friction forces are still not well understood. Here, by analytical model and numerical simulations, we address the origin of reduction of friction force with velocity and increase of friction with temperature, which have been experimentally observed under humid ambient conditions. These observations differ significantly from the results of friction experiments carried out under ultrahigh vacuum, and disagree with predictions of thermal Prandtl-Tomlinson model of friction. Our calculations demonstrate what information on the kinetics of capillary condensation can be extracted from measurements of friction forces and suggest optimal conditions for obtaining this information.

  19. Friction drive of an SAW motor. Part II: analyses.

    Science.gov (United States)

    Shigematsu, Takashi; Kurosawa, Minoru Kuribayashi

    2008-09-01

    The mechanics of the friction drive of a surface acoustic wave motor were investigated by means of contact mechanics theory. As a means to control the contact condition, the motor's slider had projections on its frictional surface. Assuming the projection was a rigid circular punch and the slider body was an elastic half-space allowed application of contact mechanics formulae to the analyses of the friction drive. Because the projection contacted the Rayleigh wave vibration, the projection's responses were considered dynamic; thus, the dynamics were also analyzed in the same framework of contact mechanics formulae. Moreover, the analyses were applied to measurements of the projection's displacement to examine the detailed mechanics during the friction drive. We calculated the contact/frictional forces based on the measurement and indicated the necessity of further investigation of the surface acoustic wave motor's friction drive, because the usual friction law was unable to explain the measurement.

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

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

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

  1. Superhydrophobic surfaces of the water bug Notonecta glauca: a model for friction reduction and air retention

    Directory of Open Access Journals (Sweden)

    Petra Ditsche-Kuru

    2011-03-01

    Full Text Available Superhydrophobic surfaces of plants and animals are of great interest for biomimetic applications. Whereas the self-cleaning properties of superhydrophobic surfaces have been extensively investigated, their ability to retain an air film while submerged under water has not, in the past, received much attention. Nevertheless, air retaining surfaces are of great economic and ecological interest because an air film can reduce friction of solid bodies sliding through the water. This opens perspectives for biomimetic applications such as low friction fluid transport or friction reduction on ship hulls. For such applications the durability of the air film is most important. While the air film on most superhydrophobic surfaces usually lasts no longer than a few days, a few semi-aquatic plants and insects are able to hold an air film over a longer time period. Currently, we found high air film persistence under hydrostatic conditions for the elytra of the backswimmer Notonecta glauca which we therefore have chosen for further investigations. In this study, we compare the micro- and nanostructure of selected body parts (sternites, upper side of elytra, underside of elytra in reference to their air retaining properties. Our investigations demonstrate outstanding air film persistence of the upper side of the elytra of Notonecta glauca under hydrostatic and hydrodynamic conditions. This hierarchically structured surface was able to hold a complete air film under hydrostatic conditions for longer than 130 days while on other body parts with simple structures the air film showed gaps (underside of elytra or even vanished completely after a few days (sternites. Moreover, the upper side of the elytra was able to keep an air film up to flow velocities of 5 m/s. Obviously the complex surface structure with tiny dense microtrichia and two types of larger specially shaped setae is relevant for this outstanding ability. Besides high air film persistence, the

  2. Control of friction at the nanoscale

    Science.gov (United States)

    Barhen, Jacob; Braiman, Yehuda Y.; Protopopescu, Vladimir

    2010-04-06

    Methods and apparatus are described for control of friction at the nanoscale. A method of controlling frictional dynamics of a plurality of particles using non-Lipschitzian control includes determining an attribute of the plurality of particles; calculating an attribute deviation by subtracting the attribute of the plurality of particles from a target attribute; calculating a non-Lipschitzian feedback control term by raising the attribute deviation to a fractionary power .xi.=(2m+1)/(2n+1) where n=1, 2, 3 . . . and m=0, 1, 2, 3 . . . , with m strictly less than n and then multiplying by a control amplitude; and imposing the non-Lipschitzian feedback control term globally on each of the plurality of particles; imposing causes a subsequent magnitude of the attribute deviation to be reduced.

  3. Frictional Impact Modeling of a Cereal Thresher

    Directory of Open Access Journals (Sweden)

    Christian O. Osueke

    2011-01-01

    Full Text Available Problem statement: There is no point producing cereal threshing models that cannot replicate its performance on the field. The frictional impact that occurs between the crop surface and threshing cylinder has been often neglected by most researchers in cereal threshing. Approach: Study proffers a solution to this issue by developing a model for threshing which in-cooperate friction. This was done by analyzing the crop/threshing cylinder behavior, hence establishing mathematical sub-models to characterize the performance of this model. Results: The model was further packaged with computer aided software based on visual basic programming language and finally applied. Conclusion: Upon application, it was discovered that at a moisture content of 15% v = 9 m sec-1, Q = 0.18 kg sec-1 the model yielded performance characteristics as Eff = 88.22%, TNL = 11.78% and CAPTH = 211.52 kg h-1.

  4. Mars - Wind friction speeds for particle movement

    Science.gov (United States)

    Greeley, R.; Leach, R.; White, B.; Iversen, J.; Pollack, J.

    1976-01-01

    Wind friction threshold speeds for particle movement were determined in a low pressure boundary layer wind tunnel at an atmospheric pressure of 5.3 mb. The results imply that for comparable pressures on Mars, the minimum wind friction threshold speed is about 2.5 m/sec, which would require free-stream winds of 50 to 135 m/sec, depending on the character of the surface and the atmospheric conditions. The corresponding wind speeds at the height of the Viking lander meteorology instrument would be about a factor of two less than the free-stream wind speed. The particle size most easily moved by winds on Mars is about 160 microns; particles both larger and smaller than this (at least down to about 5 microns) require stronger winds to initiate movement.

  5. Friction Experiments for Dynamical Coefficient Measurement

    Directory of Open Access Journals (Sweden)

    J. J. Arnoux

    2011-01-01

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

  6. Network Theory, Cracking and Frictional Sliding

    CERN Document Server

    Ghaffari, H O

    2012-01-01

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

  7. Frictional Coulomb drag in strong magnetic fields

    DEFF Research Database (Denmark)

    Bønsager, Martin Christian; Flensberg, Karsten; Hu, Ben Yu-Kuang;

    1997-01-01

    A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21) is eval......A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21......) is evaluated using diagrammatic techniques. The transresistivity is given by an integral over energy and momentum transfer weighted by the product of the screened interlayer interaction and the phase space for scattering events. We demonstrate, by a numerical analysis of the transresistivity, that for well...

  8. Friction boosted by spontaneous epitaxial rotations

    Science.gov (United States)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2015-03-01

    It is well known in surface science that incommensurate adsorbed monolayers undergo a spontaneous, energy-lowering epitaxial rotation from aligned to misaligned relative to a periodic substrate. We show first of all that a model 2D colloidal monolayer in an optical lattice, of recent importance as a frictional model, also develops in full equilibrium a small rotation angle, easy to detect in the Moiré pattern. The colloidal monolayer misalignment is then shown by extensive sliding simulations to increase the dynamic friction by a considerable factor over the aligned case. More generally, this example suggests that spontaneous rotations are rather ubiquitous and should not be ignored in all tribological phenomena between mismatched lattices. This work was mainly supported by the ERC Advanced Grant No. 320796-MODPHYSFRICT, and partly by SINERGIA contract CRSII2 136287, by PRIN/COFIN Contract 2010LLKJBX 004, by COST Action MP1303.

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

    Science.gov (United States)

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

    2012-04-01

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

  10. Effect of welding speed on the material flow patterns in friction stir welding of AZ31 magnesium alloy

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hua; Wu Huiqiang; Huang Jihua; LIN Sanbao; WU Lin

    2007-01-01

    The clear zigzag-line pattern on transverse cross sections can be used to explain the formation mechanism of the weld nugget when friction stir welded AZ31 magnesium alloy without any other insert material is used as mark. It provides a simple and useful method to research the joining mechanism of friction stir welding. The rotation speed is kept at 1000 r/min and the welding speed changes from 120 mm/min to 600 mm/min. The macrostructure on the transverse cross section was divided into several parts by faying surface. The results show that the shape and formation procedure of the weld nugget change with the welding speed. There are two main material flows in the weld nugget: one is from the advancing side and the other is from the retreating side. A simple model on the weld nugget formation of FSW is presented in this article.

  11. Fundamental Mechanisms Affecting Friction Welding under Vacuum

    Science.gov (United States)

    1991-06-01

    z Professor Koichi Masubuchi Ocean Engineering Dept., Thesis Supervisor ~Certified by - CProfessor Ltmest Rabinowicz Mechanical Engineering Dept...welding and oxide layer affects. 60 REFERENCES 1. Rabinowicz ,E., "Friction and Wear of Materials", Wiley, 1964 2. SmithM., "Effect of Vacuum on the...Professor ELnest Rabinowicz Mechanical Engineering Dept., Thesis Reader Accepted by- 14,~/G 1, ~ Z a- ’A. Douglas Carn-chtir,-hirman Departmental Graduate

  12. Aftershocks in a frictional earthquake model.

    Science.gov (United States)

    Braun, O M; Tosatti, Erio

    2014-09-01

    Inspired by spring-block models, we elaborate a "minimal" physical model of earthquakes which reproduces two main empirical seismological laws, the Gutenberg-Richter law and the Omori aftershock law. Our point is to demonstrate that the simultaneous incorporation of aging of contacts in the sliding interface and of elasticity of the sliding plates constitutes the minimal ingredients to account for both laws within the same frictional model.

  13. Thermal modelling of friction stir welding

    DEFF Research Database (Denmark)

    Schmidt, Henrik Nikolaj Blicher; Hattel, Jesper Henri

    2008-01-01

    The objective of the present work is to present the basic elements of the thermal modelling of friction stir welding as well as to clarify some of the uncertainties in the literature regarding the different contributions to the heat generation. Some results from a new thermal pseudomechanical model...... in which the temperature-dependent yield stress of the weld material controls the heat generation are also presented....

  14. Biotribology :articular cartilage friction, wear, and lubrication

    OpenAIRE

    Schroeder, Matthew O

    1995-01-01

    This study developed, explored, and refined techniques for the in vitro study of cartilage-on-cartilage friction, deformation, and wear. Preliminary results of in vitro cartilage-on- cartilage experiments with emphasis on wear and biochemistry are presented. Cartilage-bone specimens were obtained from the stifle joints of steers from a separate controlled study. The load, sliding speed, and traverse of the lower specimens were held constant as lubricant and test length were varied. Lubric...

  15. Frictional cooling of positively charged particles

    Directory of Open Access Journals (Sweden)

    Daniel Greenwald

    2012-02-01

    Full Text Available One of the focuses of research and development towards the construction of a muon collider is muon beam preparation. Simulation of frictional cooling shows that it can achieve the desired emittance reduction to produce high-luminosity muon beams. We show that for positively charged particles, charge-exchange interactions necessitate significant changes to schemes previously developed for negatively charged particles. We also demonstrate that foil-based schemes are not viable for positive particles.

  16. Managing Friction Blisters of the Feet.

    Science.gov (United States)

    Ramsey, M L

    1992-01-01

    In brief Active people often develop friction blisters on their feet. Although such blisters rarely create significant medical problems, they can be quite painful and can hinder athletic performance. People can decrease the chance of blister formation by wearing properly fitting shoes, doubling up on socks, and applying dressings or lubricants. If lesions do develop, conservative treatment will speed healing and lessen pain and disability.

  17. Simulating frictional contact in smoothed particle hydrodynamics

    Institute of Scientific and Technical Information of China (English)

    WANG; Jian; WU; Hao; GU; ChongShi; HUA; Hui

    2013-01-01

    Smoothed Particle Hydrodynamics (SPH) is a powerful tool for large deformation computation of soil flow. However, the method to simulate frictional contact in the framework of SPH is still absent and needs to be developed. This paper presents an algorithm to simulate frictional contact between soil and rigid or deformable structure in the framework of SPH. In this algo-rithm, the computational domain is divided into several sub-domains according to the existing contact boundaries, and contact forces are used as bridges of these sub-domains to fulfill problem solving. In the process of the SPH discretization for govern-ing equation of each sub-domain, the inherent problem of boundary deficiency of SPH is handled properly. Therefore, the par-ticles located at contact boundary can have precise acceleration, which is critical for contact detection. Then, based on the as-sumption that the SPH particle of soil can slightly penetrate into the structure, the contact forces along normal and tangential directions of the contact surface are computed by momentum principle, and the frictional force is modified if sliding occurs.Compared with previous methods, in which only particle-to-particle contact is considered or frictional sliding is just ignored,the method proposed in this study is more efficient and accurate, and is suitable for simulating interaction between soft materi-als and rigid or deformable structures, which are very common in geotechnical engineering. A number of numerical tests have been carried out to verify the accuracy and stability of the proposed algorithm, and the results have been compared with ana-lytical solutions or FEM results. The consistency obtained from these comparisons indicates that the algorithm is robust and can enhance the computing capability of SPH.

  18. Welding defects at friction stir welding

    Directory of Open Access Journals (Sweden)

    P. Podržaj

    2015-04-01

    Full Text Available The paper presents an overview of different types of defects at friction stir welding. In order to explain the reasons for their occurrence a short theoretical background of the process is given first. The main emphasis is on the parameters that influence the process. An energy supply based division of defects into three disjoint groups was used. The occurring defects are demonstrated on various materials.

  19. Ramsey monetary policy with labour market frictions

    OpenAIRE

    Faia, Ester

    2007-01-01

    This paper studies the design of optimal monetary policy (in terms of unconstrained Ramsey allocation) in a framework with sticky prices and matching frictions. Furthermore I consider the role of real wage rigidities. Optimal policy features significant deviations from price stability in response to various shocks. This is so since search externalities generate an unemployment/inflation trade-off. In response to productivity shocks optimal policy is pro-cyclical when the worker’s bargaining p...

  20. Microstructure and Mechanical Properties of Friction Stir Welded 5083 and 7075 Aluminum Alloys

    Science.gov (United States)

    Kalemba-Rec, I.; Hamilton, C.; Kopyściański, M.; Miara, D.; Krasnowski, K.

    2017-02-01

    Through microscopy, mechanical testing, and numerical modeling, the microstructure and mechanical performance of friction stir welded aluminum alloys 7075-T651 and 5083-H111 were characterized. In particular, the influence of the weld configuration, i.e., the locations of the 7075 and 5083 alloys alternately on the advancing and retreating sides, on material flow, microstructure, and mechanical properties was considered. Thermographic data in conjunction with a process simulation demonstrated that the weld configuration significantly impacts heat generation during friction stir welding. The microstructure in the stir zone was a clear visualization of the material flow and was characterized by a vortex-like structure with alternating bands of the alloys being joined. These bands differed in elemental content and grain size. The microstructure became more complex when greater heat generation (higher temperatures) occurred. The weld configuration strongly influenced the material flow, but did not impact the tensile properties (such as yield strength, tensile strength, and elongation). The configuration of 5083 on the advancing side and 7075 on the retreating side produced the most uniform material flow. The joint efficiencies of all tested welds were above 100%.

  1. Partial squeeze film levitation modulates fingertip friction.

    Science.gov (United States)

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

    2016-08-16

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

  2. Friction and wear of human hair fibres

    Science.gov (United States)

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

    2016-06-01

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

  3. Controlling vortex motion and vortex kinetic friction

    Science.gov (United States)

    Nori, Franco; Savel'ev, Sergey

    2006-05-01

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

  4. Theory of friction based on brittle fracture

    Science.gov (United States)

    Byerlee, J.D.

    1967-01-01

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

  5. Friction and Wear Behaviors of Nanostructured Metals

    Institute of Scientific and Technical Information of China (English)

    Zhong HAN; Yusheng ZHANG; Ke LU

    2008-01-01

    Nanostructured (ns) materials, i.e., polycrystalline materials with grain sizes in the nanometer regime (typically below 100 nm), have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained (cg) counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained (ufg) materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.

  6. Friction, force chains, and falling fruit

    Science.gov (United States)

    Krim, Jacqueline; Behringer, Robert

    2010-03-01

    Friction is of great concern from both a national security and quality-of-life point of view, and the economic impact of energy efficiency, wear, and manufacturing cannot be underestimated. Theorists have always believed that friction plays a great role in avalanche-like collapse of a granular piles, but the predictions have proven difficult to test. We devised an experimentally controlled way to prove it, accessible to all who dare try, and report on it here [1,2]. With the aid of a middle school assistant, we studied and filmed piles of apples, oranges, and onions as one or more pieces of fruit were removed. Among other things, we discovered that increasing the friction of the onions (by peeling them) vastly decreased the likelihood of collapse. Our work includes videos written by, produced, and starring our seventh grade assistant, some of which are posted on the Physics Today YouTube channel [1] and featured in the Sept. 2009 issue of Physics Today [2]. [4pt] [1] Youtube.com, keywords ``unpeeled onions'', with full set at www.dukefruit.info. [0pt] [2] J. Krim and R.P. Berhinger, Physics Today (Sept., 2009) volume 62, pp.66-67

  7. Friction Modeling in Concentric Tube Robots.

    Science.gov (United States)

    Lock, Jesse; Dupont, Pierre E

    2011-01-01

    Concentric tube robots are a novel class of continuum robots that are constructed by combining pre-curved elastic tubes such that the overall shape of the robot is a function of the relative rotations and translations of the constituent tubes. Frictionless kinematic and quasistatic force models for this class of robots have been developed that incorporate bending and twisting of the tubes. Experimental evaluation of these models has revealed, however, a directional dependence of tube rotation on robot shape that is not predicted by these models. To explain this behavior, this paper models the contributions of friction arising from two sources: the distributed forces of contact between the tubes along their length and the concentrated bending moments generated at discontinuities in curvature and at the boundaries. It is shown that while friction due to distributed forces is insufficient to explain the experimentally observed tube twisting, a simple model of frictional torque arising from concentrated moments provides a good match with the experimental data.

  8. Markov state modeling of sliding friction

    Science.gov (United States)

    Pellegrini, F.; Landes, François P.; Laio, A.; Prestipino, S.; Tosatti, E.

    2016-11-01

    Markov state modeling (MSM) has recently emerged as one of the key techniques for the discovery of collective variables and the analysis of rare events in molecular simulations. In particular in biochemistry this approach is successfully exploited to find the metastable states of complex systems and their evolution in thermal equilibrium, including rare events, such as a protein undergoing folding. The physics of sliding friction and its atomistic simulations under external forces constitute a nonequilibrium field where relevant variables are in principle unknown and where a proper theory describing violent and rare events such as stick slip is still lacking. Here we show that MSM can be extended to the study of nonequilibrium phenomena and in particular friction. The approach is benchmarked on the Frenkel-Kontorova model, used here as a test system whose properties are well established. We demonstrate that the method allows the least prejudiced identification of a minimal basis of natural microscopic variables necessary for the description of the forced dynamics of sliding, through their probabilistic evolution. The steps necessary for the application to realistic frictional systems are highlighted.

  9. Dry friction avalanches: Experiment and theory

    Science.gov (United States)

    Buldyrev, Sergey V.; Ferrante, John; Zypman, Fredy R.

    2006-12-01

    Experimental evidence and theoretical models are presented supporting the conjecture that dry friction stick-slip is described by self-organized criticality. We use the data, obtained with a pin-on-disk tribometer set to measure lateral force, to examine the variation of the friction force as a function of time. We study nominally flat surfaces of matching aluminum and steel. The probability distribution of force drops follows a negative power law with exponents μ in the range 3.2-3.5. The frequency power spectrum follows a 1/fα pattern with α in the range 1-1.8. We first compare these experimental results with the well-known Robin Hood model of self-organized criticality. We find good agreement between theory and experiment for the force-drop distribution but not for the power spectrum. We explain this on a physical basis and propose a model which takes explicitly into account the stiffness and inertia of the tribometer. Specifically, we numerically solve the equation of motion of a block on a friction surface pulled by a spring and show that for certain spring constants the motion is characterized by the same power law spectrum as in experiments. We propose a physical picture relating the fluctuations of the force drops to the microscopic geometry of the surface.

  10. 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.

  11. Structure-property relationships of dissimilar friction stir welded aluminum alloys

    Science.gov (United States)

    Quinones, Rogie Irwin Rodriguez

    In this work, the relationship between microstructure and mechanical properties of dissimilar friction stir welded AA6061-to-AA7050 aluminum alloys were evaluated. Experimental results from this study revealed that static strength increased with the tool rotational speed and was correlated with the material intermixing. Fully-reversed low cycle fatigue experimental results showed an increase in the strain hardening properties as well as the number of cycles-to-failure as the tool rotational speed was increased. Furthermore, under both static and cyclic loading, fracture of the joint was dominated by the AA6061 alloy side of the weld. In addition, inspection of the fatigue surfaces revealed that cracks initiated from intermetallic particles located near the surface. In order to determine the corrosion resistance of the dissimilar joint, corrosion defects were produced on the crown surface of the weld by static immersion in 3.5% NaCl for various exposure times. Results revealed localized corrosion damage in the thermo-mechanically affected and heat affected zones. Results demonstrated a decrease in the fatigue life, with evidence of crack initiation at the corrosion defects; however, the fatigue life was nearly independent of the exposure time. This can be attributed to total fatigue life dominated by incubation time. Furthermore, two types of failure were observed: fatigue crack initiation in the AA6061 side at high strain amplitudes (>0.3%); and fatigue crack initiation in the AA7050 side at low strain amplitudes (friction stir welded joints in order to capture the crack initiation and propagation in as-welded and pre-corroded conditions. Good correlation between experimental fatigue results and the model was achieved based on the variation in the initial defect size, microstructure, and mechanical properties of the dissimilar friction stir welded AA6061-to-AA7050 aluminum alloys.

  12. Boils at Frictional Locations in a Patient with Hidradenitis Suppurativa.

    Science.gov (United States)

    Boer, Jurr; Mihajlovic, Dalibor

    2016-12-01

    Dear Editor, Hidradenitis suppurativa (HS) is a chronic, recurrent, inflammatory skin disease. The primary clinical presentation are painful inflamed nodules or boils of inverse areas, i.e. the axillary and anogenito-crural regions, but it can also involve the infra- and inter-mammary regions (1,2). The etiology of HS is not clearly defined. Obesity, smoking, and genetic factors are considered important risk factors. In addition, it has also been suggested that friction may contribute to the development of HS, especially in the obese, but this is based on highly anecdotal reports (3-5). We describe a case with classic HS, obesity, and HS-like lesions at the position of the bra strap, suggesting that mechanical stress was an external pathogenic factor for HS development. A 33-year old woman presented with an 18-year history of chronic, recurrent, inflammatory nodules in the axillae, the groin, the pubic region, and to a lesser extent the abdomen and buttocks. She was obese with as result of 33.2 kg/m-2 of 33.2, had a positive family history of two first grade family members with HS, and was a smoker (19 Pack years). There were no other known comorbidities. The inflamed lesions had been treated with several courses of oral antibiotics (minocycline, erythromycin, and combination therapy of clindamycin and rifampicine) and surgical treatments: lancing, deroofing, and excisions (2,6). On examination, there were nodules, folliculitis, cysts, and depressed scars in the axillae and groins, including the inner thighs (Figure 1). On the chest, corresponding to where the lower edge of the patient's bra was usually located, a superficial nodule and follicular papules were observed, exactly coinciding with the red stripe caused by mechanical stress (friction and pressure) of the bra edge. There was no skin fold present on the location of the HS lesions, and there were no lesions observed in the intermammary region or on the side of the breasts in contact with the skin of the

  13. Microstructural Evolution and Fracture Behavior of Friction-Stir-Welded Al-Cu Laminated Composites

    Science.gov (United States)

    Beygi, R.; Kazeminezhad, Mohsen; Kokabi, A. H.

    2014-01-01

    In this study, we attempt to characterize the microstructural evolution during friction stir butt welding of Al-Cu-laminated composites and its effect on the fracture behavior of the joint. Emphasis is on the material flow and particle distribution in the stir zone. For this purpose, optical microscopy and scanning electron microscopy (SEM) images, energy-dispersive spectroscopy EDS and XRD analyses, hardness measurements, and tensile tests are carried out on the joints. It is shown that intermetallic compounds exist in lamellas of banding structure formed in the advancing side of the welds. In samples welded from the Cu side, the banding structure in the advancing side and the hook formation in the retreating side determine the fracture behavior of the joint. In samples welded from the Al side, a defect is formed in the advancing side of the weld, which is attributed to insufficient material flow. It is concluded that the contact surface of the laminate (Al or Cu) with the shoulder of the FSW tool influences the material flow and microstructure of welds.

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

    Science.gov (United States)

    Weber, F.; Boston, C.

    2010-04-01

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

  15. General Friction Model Extended by the Effect of Strain Hardening

    DEFF Research Database (Denmark)

    Nielsen, Chris V.; Martins, Paulo A.F.; Bay, Niels

    2016-01-01

    An extension to the general friction model proposed by Wanheim and Bay [1] to include the effect of strain hardening is proposed. The friction model relates the friction stress to the fraction of real contact area by a friction factor under steady state sliding. The original model for the real co...... of friction in metal forming, where the material generally strain hardens. The extension of the model to cover strain hardening materials is validated by comparison to previously published experimental data.......An extension to the general friction model proposed by Wanheim and Bay [1] to include the effect of strain hardening is proposed. The friction model relates the friction stress to the fraction of real contact area by a friction factor under steady state sliding. The original model for the real......-ideally plastic material, and secondly, to extend the solution by the influence of material strain hardening. This corresponds to adding a new variable and, therefore, a new axis to the general friction model. The resulting model is presented in a combined function suitable for e.g. finite element modeling...

  16. PREFACE: The International Conference on Science of Friction

    Science.gov (United States)

    Miura, Kouji; Matsukawa, Hiroshi

    2007-07-01

    The first international conference on the science of friction in Japan was held at Irago, Aichi on 9-13 September 2007. The conference focused on the elementary process of friction phenomena from the atomic and molecular scale view. Topics covered in the conference are shown below.: Superlubricity and friction Electronic and phononic contributions to friction Friction on the atomic and molecular scales van der Waals friction and Casimir force Molecular motor and friction Friction and adhesion in soft matter systems Wear and crack on the nanoscale Theoretical studies on the atomic scale friction and energy dissipation Friction and chaos Mechanical properties of nanoscale contacts Friction of powder The number of participants in the conference was approximately 100, registered from 11 countries. 48 oral and 29 poster talks were presented at the conference. This volume of Journal of Physics: Conference Series includes 23 papers devoted to the above topics of friction. The successful organization of the conference was made possible by the contribution of the members of the Organizing Committee and International Advisory Committee. The conference was made possible thanks to the financial support from Aichi University of Education and the Taihokogyo Tribology Research Foundation (TTRF), and moreover thanks to the approval societies of The Physical Society of Japan, The Surface Science Society of Japan, The Japanese Society of Tribologists and Toyota Physical and Chemical Research Institute. The details of the conference are available at http://www.science-of-friction.com . Finally we want to thank the speakers for the high quality of their talks and all participants for coming to Irago, Japan and actively contributing to the conference. Kouji Miura and Hiroshi Matsukawa Editors

  17. Effect of weld line shape on material flow during friction stir welding of aluminum and steel

    Science.gov (United States)

    Yasui, Toshiaki; Ando, Naoyuki; Morinaka, Shinpei; Mizushima, Hiroki; Fukumoto, Masahiro

    2014-08-01

    The effect of weld line shape on material flow during the friction stir welding of aluminum and steel was investigated. The material flow velocity was evaluated with simulated experiments using plasticine as the simulant material. The validity of the simulated experiments was verified by the marker material experiments on aluminum. The circumferential velocity of material around the probe increased with the depth from the weld surface. The effect is significant in cases where the advancing side is located on the outside of curve and those with higher curvature. Thus, there is an influence of weld line shape on material flow.

  18. TMD FRICTION - a company profile; TMD FRICTION - ein Unternehmen stellt sich vor

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, E.

    2000-07-01

    TMD FRICTION came into existence in August 2000 by separation of the friction material sector from BBA PLC. This transaction was supported by HSBC PE, the private equity branch of HSBC, the third largest bank world-wide. This report shall give some market background, the current position of the company and information about the strategic orientation of the new group regarding R and D and production - especially against the background of our customers' global activities. (orig.) [German] TMD FRICTION entstand im August 2000 durch Ausgliederung des Reibbelag-Bereichs aus der BBA PLC. Diese Transaktion wurde unterstuetzt durch HSBC, PE, dem Private Equity-Zweig von HSBC, der drittgroessten Bank weltweit. Der Bericht erlaeutert Markthintergruende, die aktuelle Positionierung des Unternehmens und gibt Hinweise auf die strategische Ausrichtung der neuen Gruppierung im Bereich Entwicklung und Produktion - insbesondere vor dem Hintergrund der globalen Ausrichtung unserer Kunden. (orig.)

  19. Dynamic friction of self-affine surfaces

    Science.gov (United States)

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

    1994-02-01

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

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

    Directory of Open Access Journals (Sweden)

    P. Raveendiran

    2015-06-01

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

  1. Three sided complex adaptative systems

    CERN Document Server

    D'Hulst, R

    1999-01-01

    We introduce two three sided adaptative systems as toy models to mimic the exchange of commodities between buyers and sellers. These models are simple extensions of the minority game, exhibiting similar behaviour as well as some new features. The main difference between our two models is that in the first the three sides are equivalent while in the second, one choice appears as a compromise between the two other sides. Both models are investigated numerically and compared with the original minority game.

  2. Atomic-Scale Friction and Microfriction of Graphite and Diamond Using Friction Force Microscopy

    Science.gov (United States)

    1993-10-07

    19), 2642-2645 (1991). 21 [12] R. M. Overney, E. Meyer, J. Frommer , D. Brodbeck, R. Luithi, L. Howald, H. -J. GUntherodt, M. Fuji.,La, H. Takano, and Y...Meyer, R. Overney, D. Brodbeck, L. Howard, R. Luithi, J. Frommer , and H. -J. Guntherodt, "Friction and Wear of Langmuir-Blodgett Films Observed by...Friction Force Microscopy", Phys. Rev. Lett., Vol. 69(12), 1777-1780 (1992). [14] E. Meyer, R. Overney, R. Luthi, D. Brodbeck, L. Howald, J. Frommer , H

  3. 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...... may depend linearly on ln (v/v0), as usually observed experimentally, rather than non-linearly [−ln (v/v0)]2/3 as predicted by a simple theory of activated processes. We also discuss the role of elasticity at stop and start. We show that for "simple" rubber (at low start velocity), the static friction...

  4. Analysis and Comparison of Friction Stir Welding and Laser Assisted Friction Stir Welding of Aluminum Alloy

    OpenAIRE

    Sabina Luisa Campanelli; Giuseppe Casalino; Caterina Casavola; Vincenzo Moramarco

    2013-01-01

    Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. Laser Assisted Friction Stir Welding (LAFSW) is a combination in which the FSW is the dominant welding process and the laser pre-heats the we...

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

    Institute of Scientific and Technical Information of China (English)

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

    2013-01-01

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

  6. Material Flow and Oxide Particle Distributions in Friction-Stir Welded F/M-ODS Sheets

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Suk Hoon; Noh, Sanghoon; Jin, Hyun Ju; Kim, Tae Kyu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-05-15

    It is well known that uniform nano-oxide dispersoids act as pinning points to obstruct dislocation and grain boundary motion in ODS(Oxide dispersion strengthened) steel. However, these advantages will disappear while the material is subjected to the high temperature of conventional fusion welding. There is only limited literature available on the joining of ODS steels. Friction stir welding (FSW) is considered to be the best welding technique for welding ODS steels as the technique helps in retaining the homogeneous nano-oxide particles distributions in matrix. FSW is a solid.state, hot.shear joining process in which a rotating tool with a shoulder and terminating in a threaded pin, moves along the butting surfaces of two rigidly clamped plates placed on a backing plate. Heat generated by friction at the shoulder and to a lesser extent at the pin surface, softens the material being welded. Severe plastic deformation and flow of this plasticised metal occurs as the tool is translated along the welding direction. Material is transported from the front of the tool to the trailing edge where it is forged into a joint. Friction stir welding appears to be a very promising technique for the welding of FMS and ODS steels. This study found that, during FSW, the forward movement of the tool pin results in loose contact between the tool pin and the receding material on the advancing side.

  7. Velocity tuning of friction with two trapped atoms

    CERN Document Server

    Gangloff, Dorian; Counts, Ian; Jhe, Wonho; Vuletić, Vladan

    2015-01-01

    Friction is the basic, ubiquitous mechanical interaction between two surfaces that results in resistance to motion and energy dissipation. In spite of its technological and economic significance, our ability to control friction remains modest, and our understanding of the microscopic processes incomplete. At the atomic scale, mismatch between the two contacting crystal lattices can lead to a reduction of stick-slip friction (structural lubricity), while thermally activated atomic motion can give rise to a complex velocity dependence, and nearly vanishing friction at sufficiently low velocities (thermal lubricity). Atomic force microscopy has provided a wealth of experimental results, but limitations in the dynamic range, time resolution, and control at the single-atom level have hampered a full quantitative description from first principles. Here, using an ion-crystal friction emulator with single-atom, single substrate-site spatial resolution and single-slip temporal resolution, we measure the friction force...

  8. Friction laws from dimensional-analysis point of view

    CERN Document Server

    Hatano, Takahiro

    2015-01-01

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

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

    Science.gov (United States)

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

    2013-12-01

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

  10. Anomalous friction of graphene nanoribbons on waved graphenes

    Directory of Open Access Journals (Sweden)

    Jun Fang

    2015-11-01

    Full Text Available Friction plays a critical role in the function and maintenance of small-scale structures, where the conventional Coulomb friction law often fails. To probe the friction at small scales, here we present a molecular dynamics study on the process of dragging graphene nanoribbons on waved graphene substrates. The simulation shows that the induced friction on graphene with zero waviness is ultra-low and closely related to the surface energy barrier. On waved graphenes, the friction generally increases with the amplitude of the wave at a fixed period, but anomalously increases and then decreases with the period at a fixed amplitude. These findings provide insights into the ultra-low friction at small scales, as well as some guidelines into the fabrication of graphene-based nano-composites with high performance.

  11. Friction related size-effect in microforming – a review

    Directory of Open Access Journals (Sweden)

    Wang Chunju

    2014-01-01

    Full Text Available This paper presents a thorough literature review of the size effects of friction in microforming. During miniaturization, the size effects of friction occur clearly. The paper first introduces experimental research progress on size effects of friction in both micro bulk and sheet forming. The effects of several parameters are discussed. Based on the experimental results, several approaches have been performed to develop a model or functions to analyse the mechanism of size effects of friction, and simulate the micro deep drawing process by integrating them into an FE program. Following this, surface modification, e.g. a DLC film and a micro structure/textured surface, as a method to reduce friction are presented. Finally, the outlook for the size effect of friction in the future is assessed, based on the understanding of the current research progress.

  12. Friction Model for FEM Simulation of Sheet Metal Forming Operations

    Science.gov (United States)

    Keum, Y. T.; Wagoner, R. H.; Lee, J. K.

    2004-06-01

    In order to find the effect of frictional characteristics, lubricant viscosity, tool geometry, and forming speed on the sheet metal forming, a friction tester was designed and manufactured. Friction tests were performed using drawing oils, various tool radii and forming speeds for aluminum alloy sheets, galvanized steels sheets and cold rolled steel sheets. From the experimental observation, the mathematical friction model considering lubricant viscosity, sheet surface roughness and hardness, punch corner radii, and punch speed is developed. By comparing the punch load found by FEM using the proposed friction model with that of experimental measurement when the steel sheets are formed in 2-D geometry in dry and lubricating conditions, the validity and accuracy of the mathematical friction model are demonstrated.

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

    DEFF Research Database (Denmark)

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

    2013-01-01

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

  14. The Frictional Coefficient of Bovine Knee Articular Cartilage

    Institute of Scientific and Technical Information of China (English)

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

    2006-01-01

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

  15. Paradoxical stabilization of forced oscillations by strong nonlinear friction

    Science.gov (United States)

    Esirkepov, Timur Zh.; Bulanov, Sergei V.

    2017-08-01

    In a dissipative dynamic system driven by an oscillating force, a strong nonlinear highly oscillatory friction force can create a quasi-steady tug, which is always directed opposite to the ponderomotive force induced due to a spatial inhomogeneity of oscillations. When the friction-induced tug exceeds the ponderomotive force, the friction stabilizes the system oscillations near the maxima of the oscillation spatial amplitude of the driving force.

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

    Directory of Open Access Journals (Sweden)

    Iosif S. Gershman

    2015-12-01

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

  17. Friction Buttering: A New Technique for Dissimilar Welding

    Science.gov (United States)

    Karthik, G. M.; Mastanaiah, P.; Janaki Ram, G. D.; Kottada, Ravi Sankar

    2017-02-01

    This work offers a fresh perspective on buttering, a technique often considered for fusion welding of dissimilar metals. For the first time, buttering was attempted in solid state using friction deposition. Using this new "friction buttering" technique, fusion welding of two different dissimilar metal pairs (austenitic stainless steel/borated stainless steel and Al-Cu-Mg/Al-Zn-Mg-Cu) was successfully demonstrated. The results show that friction buttering can simplify a tough dissimilar welding problem into a routine fusion welding task.

  18. PROGRAM-PATTERN MULTIPOLE BOUNDARY ELEMENT METHOD FOR FRICTIONAL CONTACT

    Institute of Scientific and Technical Information of China (English)

    Yu Chunxiao; Shen Guangxian; Liu Deyi

    2005-01-01

    A mathematical program is proposed for the highly nonlinear problem involving frictional contact. A program-pattern using the fast multipole boundary element method (FMBEM) is given for 3-D elastic contact with friction to replace the Monte Carlo method. A new optimized generalized minimal residual (GMRES) algorithm is presented. Numerical examples demonstrate the validity of the program-pattern optimization model for node-to-surface contact with friction. The GMRES algorithm greatly improves the computational efficiency.

  19. Mathematical Programming Solution for the Frictional Contact Multipole BEM

    Institute of Scientific and Technical Information of China (English)

    YU Chunxiao; SHEN Guangxian; LIU Deyi

    2005-01-01

    This paper presents a new mathematical model for the highly nonlinear problem of frictional contact. A programming model, multipole boundary element method (BEM), was developed for 3-D elastic contact with friction to replace the Monte Carlo method. A numerical example shows that the optimization programming model for the point-to-surface contact with friction and the fast optimization generalized minimal residual algorithm (GMRES(m)) significantly improve the analysis of such problems relative to the conventional BEM.

  20. The Dark Side of Creativity

    Science.gov (United States)

    Cropley, David H., Ed.; Cropley, Arthur J., Ed.; Kaufman, James C., Ed.; Runco, Mark A., Ed.

    2010-01-01

    With few exceptions, scholarship on creativity has focused on its positive aspects while largely ignoring its dark side. This includes not only creativity deliberately aimed at hurting others, such as crime or terrorism, or at gaining unfair advantages, but also the accidental negative side effects of well-intentioned acts. This book brings…

  1. Managing Chemotherapy Side Effects: Diarrhea

    Science.gov (United States)

    ... such as Pedialyte ® ••Tea (without caffeine) ••Water ••Applesauce ••Bananas ••Crackers ••Cream of wheat or rice cereal ••Eggs •• ... has a series of 18 Chemotherapy Side Effects Sheets at: www.cancer.gov/chemo-side-effects

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

    Science.gov (United States)

    Svetlizky, Ilya; Fineberg, Jay

    2014-05-08

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

  3. Friction Joint Between Basalt-Reinforced Composite and Aluminum

    DEFF Research Database (Denmark)

    Costache, Andrei; Glejbøl, Kristian; Sivebæk, Ion Marius

    2015-01-01

    The purpose of this study was to anchor basalt-reinforced polymers in an aluminum grip using dry friction. Dry friction clamping is considered the optimal solution for post-mounting of load-bearing terminations on composite structures. A new test method is presented for characterizing the frictio......The purpose of this study was to anchor basalt-reinforced polymers in an aluminum grip using dry friction. Dry friction clamping is considered the optimal solution for post-mounting of load-bearing terminations on composite structures. A new test method is presented for characterizing...

  4. Microstructure analysis in friction welding of copper and aluminum

    Science.gov (United States)

    Wibowo, A. G. Wahyu; Ismail, Rifky; Jamari, J.

    2016-04-01

    The Friction welding is a welding method with utilizing heat generated due to friction. Surfaces of two materials to be joined, one rotates the other being idle, is contacted by a pressure force. Friction on the second contact surface is done continuously so that the heat generated by the continuous friction will continue to rise. With the heat and the pressure force on the second surface to the second meeting of the material reaches its melting temperature then there is the process of welding. This paper examines the influence of the pressure force, rotational speed and contact time on friction welding of Aluminum (Al) and Copper (Cu) to the quality of welded joints. Friction welding process is performed on a friction welding machine that is equipped with the loading mechanism. The parameters used are the pressure force, rotational speed and friction time. Determination of the quality of welding is done by testing the tensile strength, hardness, and micro structure on the weld joint areas. The results showed that the friction welding quality is very good, this is evidenced by the results of a tensile strength test where the fault occurs outside the weld joint and increased violence in the weld joint. On the results visually cuts the welding area did not reveal any porosity so that it can be concluded that each metal contacts have melted perfectly and produce a connection with good quality.

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

    Directory of Open Access Journals (Sweden)

    Simona Grigaliūnienė

    2015-03-01

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

  6. Friction Compensation in the Upsetting of Cylindrical Test Specimens

    DEFF Research Database (Denmark)

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

    2016-01-01

    This manuscript presents a combined numerical andexperimental methodology for determining the stress-straincurve of metallic materials from the measurements of forceand displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens...... model or combined friction models are utilized .Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction...... Appendix is provided for those readers interested in utilizing the associated numerical algorithm for determining the stress straincurves of metallic materials....

  7. MODIFICATION OF FLAKE REINFORCED FRICTION BRAKE COMPOSITE MATERIAL

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

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

  8. Methods and devices used to measure friction in rolling

    DEFF Research Database (Denmark)

    Jeswiet, J.; Arentoft, Mogens; Henningsen, Poul

    2006-01-01

    Friction at the workpiece-die boundary, in both bulk forming and sheet forming is, arguably, the single most important physical parameter influencing the processing of metals; yet it remains the least understood. Hence there is a need for basic research into metal-die interface mechanisms. To gain...... a good understanding of the mechanisms at the interface and to be able to verify the friction and tribology models that exist, friction sensors are needed. Designing sensors to measure frictional stress in metal working has been pursued by many researchers. This paper surveys methods that have been used...

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

    Science.gov (United States)

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

    2007-01-01

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

  10. Skin friction related behaviour of artificial turf systems.

    Science.gov (United States)

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

    2017-08-01

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

  11. Tool For Friction Stir Tack Welding of Aluminum Alloys

    Science.gov (United States)

    Bjorkman, Gerald W.; Dingler, Johnny W.; Loftus, Zachary

    2003-01-01

    A small friction-stir-welding tool has been developed for use in tack welding of aluminum-alloy workpieces. It is necessary to tack-weld the workpieces in order to hold them together during friction stir welding because (1) in operation, a full-size friction-stir-welding tool exerts a large force that tends to separate the workpieces and (2) clamping the workpieces is not sufficient to resist this force. It is possible to tack the pieces together by gas tungsten arc welding, but the process can be awkward and time-consuming and can cause sufficient damage to necessitate rework. Friction stir tack welding does not entail these disadvantages. In addition, friction stir tack welding can be accomplished by use of the same automated equipment (except for the welding tool) used in subsequent full friction stir welding. The tool for friction stir tack welding resembles the tool for full friction stir welding, but has a narrower shoulder and a shorter pin. The shorter pin generates a smaller workpiece-separating force so that clamping suffices to keep the workpieces together. This tool produces a continuous or intermittent partial-penetration tack weld. The tack weld is subsequently consumed by action of the larger tool used in full friction stir welding tool.

  12. Experimental investigation of friction coefficient in tube hydroforming

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

  13. Progress and development in thermodynamic theory of friction and wear

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Tribology theory lags well behind engineering needs because of those complex and multi-dimensional characteristics associated with friction and wear. The mechanism of friction is reviewed and discussed from a static thermodynamics perspective; research methods on the process of friction and wear and thermodynamic studies within the field of tribology are also reviewed. We propose that entropy can be a critical parameter in describing the evolution of friction and wear, and the entropy balance equation could be considered as a fundamental cornerstone for a systematic tribology theory. Applications of irreversible thermodynamic theory of tribology to various fields are reviewed.

  14. Progress and development in thermodynamic theory of friction and wear

    Institute of Scientific and Technical Information of China (English)

    DAI ZhenDong; XUE QunJi

    2009-01-01

    Tribology theory lags well behind engineering needs because of those complex and multi-dimensional characteristics associated with friction and wear. The mechanism of friction is reviewed end discussed from a static thermodynamics perspective; research methods on the process of friction and wear and thermodynamic studies within the field of tribology are also reviewed. We propose that entropy can be a critical parameter in describing the evolution of friction and wear, and the entropy balance equation could be considered as a fundamental cornerstone for a systematic tribology theory. Applications of irreversible thermodynamic theory of tribology to various fields are reviewed.

  15. Electrochemical Studies of Passive Film Formation and Corrosion of Friction Stir Processed Nickel Aluminum Bronze

    Science.gov (United States)

    2011-06-01

    friction stir welding (FSW) but is used for the purpose of refining...mechanical properties [11]. C. FRICTION STIR WELDING AND PROCESSING Friction Stir Processing (FSP) is derived from Friction Stir Welding (FSW) which was...Temple-Smith, and C. Dawes, Friction - stir butt welding , GB Patent No. 9125978.8, International patent application No. PCT/GB92/02203, 1991. [4

  16. Measuring Search Frictions Using Japanese Microdata

    DEFF Research Database (Denmark)

    Sasaki, Masaru; Kohara, Miki; Machikita, Tomohiro

    2013-01-01

    This paper estimates individual-level matching functions to measure search frictions in the Japanese labour market and presents the determinants of search duration. We employ administrative microdata that track the job search process of job seekers who left or lost their job in August 2005...... and subsequently registered at their local public employment service. Our finding is that the matching function exhibits decreasing rather than constant returns-to-scale for job seekers and vacancies. We also find that after controlling for the benefits period, job seekers who lost their job involuntarily were...

  17. Measuring Search Frictions Using Japanese Microdata

    DEFF Research Database (Denmark)

    Sasaki, Masaru; Kohara, Miki; Machikita, Tomohiro

    This paper estimates matching functions to measure search frictions in the Japanese labor market and presents determinants of search duration to explain the effect of unemployment benefits on a job seeker’s behavior. We employ administrative micro data that track the job search process...... unemployment benefits lengthen (shorten) the duration of job search for job seekers who voluntarily (involuntarily) leave employment....... of individuals who left or lost their job in August 2005 and subsequently registered at their local public employment service. Our finding is that the matching function would exhibit decreasing returns-to-scale for job seekers and vacancies, rather than constant return-to-scale. We also find that generous...

  18. Inverse Faraday Effect driven by Radiation Friction

    CERN Document Server

    Liseykina, T V; Macchi, A

    2015-01-01

    In the interaction of extremely intense ($>10^{23}~\\mbox{W cm}^{-2}$), circularly polarized laser pulses with thick targets, theory and simulations show that a major fraction of the laser energy is converted into incoherent radiation because of collective electron motion during the "hole boring" dynamics. The effective dissipation due to radiative losses allows the absorption of electromagnetic angular momentum, which in turn leads to the generation of an axial magnetic field of tens of gigagauss value. This peculiar "inverse Faraday effect" is demonstrated in three-dimensional simulations including radiation friction.

  19. Bioeconomy, Moral Friction and Symbolic Law

    DEFF Research Database (Denmark)

    Hoeyer, Klaus

    2016-01-01

    ‘symbolic’, treaties aimed at protecting the body are symbols with great impact. Similarly, the material preparation of body parts as tradable grafts involves symbolic work and this symbolism is an essential part of making a ‘market’. I argue that instances of ‘symbolic law’ can reflect situations in which...... several competing agendas are at play and to understand the effects, we therefore need to investigate empirically what emerges through this friction between competing governmental ambitions. My discussion is based on studies of tissue exchange in Europe and seeks to integrate theories of symbolic law...

  20. Frictional behavior of carbon fiber tows: a contact mechanics model of tow–tow friction

    NARCIS (Netherlands)

    Cornelissen, Bo; Rooij, de Matthijn B.; Rietman, Bert; Akkerman, Remko

    2014-01-01

    Composite-forming processes involve mechanical interactions at the ply, tow, and filament level. The deformations that occur during forming processes are governed by friction between the contacting tows on the mesoscopic level and consequently between filaments on the microscopic level. A thorough u

  1. Effect of Traverse/Rotational Speed on Material Deformations and Temperature Distributions in Friction Stir Welding

    Institute of Scientific and Technical Information of China (English)

    Zhao ZHANG; Jun BIE; Yali LIU; Hongwu ZHANG

    2008-01-01

    A fully coupled thermo-mechanical model was developed to study the temperature fields and the plastic deformations of alloy AL6061-T6 under different process parameters during the friction stir welding (FSW) process.Three-dimensional results under different process parameters were presented.Results indicate that the maximum temperature is lower than the melting point of the welding material.The higher temperature gradient occurs in the leading side of the workpiece.The calculated temperature field can be fitted well with the one from the experimental test.A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface,which is formed by the specific material flow patterns in FSW.The maximum temperature can be increased with increasing the welding speed and the angular velocity in the current numerical modelling.

  2. Optimizing Powder Distribution in Production of Surface Nano-Composite via Friction Stir Processing

    Science.gov (United States)

    Heydarian, Arash; Dehghani, Kamran; Slamkish, Taymor

    2014-06-01

    Notwithstanding the extensive interest in using friction stir processing (FSP) for producing metal matrix composite (MMC), more uniform powder distribution along the composite zone is still needed. In most studies, one groove is machined out of the specimen, filled with powder, and then processed by identical passes. In this investigation, an innovative technique was used that involved machining out of three gradient grooves with increasing depth from the advancing side to the retreating side instead of using a conventional sample with just a groove. Macro, optical, and scanning electron microscopy (SEM) images and microhardness test were used to evaluate the powder distribution. The images indicated that the most uniform distribution of SiC particles in the whole composite zone was related to a three-gradient grooves sample. Microohardness measurement of a three-gradient grooves sample, carried out along the cross section and perpendicular to the traverse direction of FSP, experiences less fluctuation in hardness compared with other techniques.

  3. Natural Aging Behavior Of Friction Stir Welded Al-Zn-Mg-Cu Aluminum Alloys

    Directory of Open Access Journals (Sweden)

    Kalemba I.

    2015-06-01

    Full Text Available The long term natural aging behavior of friction stir welded aluminum 7136-T76 and 7042 T6 extrusions was investigated. The microstructural characteristics and mechanical properties in the as-welded and six years naturally aged conditions were studied and correlated to a coupled thermal/material flow model of the joining process. Hardness profiles for the 7136 alloy taken along the mid-plane thickness of the workpiece displayed the characteristic W-shape. With natural aging, hardness recovery occurred on both sides of the weld, but the position of the hardness minima, particularly on the advancing side, shifted away from the weld centerline. The hardness profile for the 7042 alloy displayed U-shape in the as-welded condition and W-shape after natural aging. The hardness behavior upon natural aging correlated to the temperature profile developed during welding and the degree to which phase dissolution occurred in the regions adjacent to the stir zone.

  4. Blind loop perforation after side-to-side ileocolonic anastomosis

    Institute of Scientific and Technical Information of China (English)

    Raffaele; Dalla; Valle; Roberto; Zinicola; Maurizio; Iaria

    2014-01-01

    Blind loop syndrome after side-to-side ileocolonic anas-tomosis is a well-recognized entity even though its in-cidence and complication rates are not clearly defined. The inevitable dilation of the ileal cul-de-sac leads to stasis and bacterial overgrowth which eventually leads to mucosal ulceration and even full-thickness perfora-tion. Blind loop syndrome may be an underestimated complication in the setting of digestive surgery. It should always be taken into account in cases of acute abdomen in patients who previously underwent right hemicolectomy. We herein report 3 patients who were diagnosed with perforative blind loop syndrome a few years after standard right hemicolectomy followed by a side-to-side ileocolonic anastomosis.

  5. Blind loop perforation after side-to-side ileocolonic anastomosis.

    Science.gov (United States)

    Valle, Raffaele Dalla; Zinicola, Roberto; Iaria, Maurizio

    2014-08-27

    Blind loop syndrome after side-to-side ileocolonic anastomosis is a well-recognized entity even though its incidence and complication rates are not clearly defined. The inevitable dilation of the ileal cul-de-sac leads to stasis and bacterial overgrowth which eventually leads to mucosal ulceration and even full-thickness perforation. Blind loop syndrome may be an underestimated complication in the setting of digestive surgery. It should always be taken into account in cases of acute abdomen in patients who previously underwent right hemicolectomy. We herein report 3 patients who were diagnosed with perforative blind loop syndrome a few years after standard right hemicolectomy followed by a side-to-side ileocolonic anastomosis.

  6. Scale dependence of rock friction at high work rate.

    Science.gov (United States)

    Yamashita, Futoshi; Fukuyama, Eiichi; Mizoguchi, Kazuo; Takizawa, Shigeru; Xu, Shiqing; Kawakata, Hironori

    2015-12-10

    Determination of the frictional properties of rocks is crucial for an understanding of earthquake mechanics, because most earthquakes are caused by frictional sliding along faults. Prior studies using rotary shear apparatus revealed a marked decrease in frictional strength, which can cause a large stress drop and strong shaking, with increasing slip rate and increasing work rate. (The mechanical work rate per unit area equals the product of the shear stress and the slip rate.) However, those important findings were obtained in experiments using rock specimens with dimensions of only several centimetres, which are much smaller than the dimensions of a natural fault (of the order of 1,000 metres). Here we use a large-scale biaxial friction apparatus with metre-sized rock specimens to investigate scale-dependent rock friction. The experiments show that rock friction in metre-sized rock specimens starts to decrease at a work rate that is one order of magnitude smaller than that in centimetre-sized rock specimens. Mechanical, visual and material observations suggest that slip-evolved stress heterogeneity on the fault accounts for the difference. On the basis of these observations, we propose that stress-concentrated areas exist in which frictional slip produces more wear materials (gouge) than in areas outside, resulting in further stress concentrations at these areas. Shear stress on the fault is primarily sustained by stress-concentrated areas that undergo a high work rate, so those areas should weaken rapidly and cause the macroscopic frictional strength to decrease abruptly. To verify this idea, we conducted numerical simulations assuming that local friction follows the frictional properties observed on centimetre-sized rock specimens. The simulations reproduced the macroscopic frictional properties observed on the metre-sized rock specimens. Given that localized stress concentrations commonly occur naturally, our results suggest that a natural fault may lose its

  7. Two-Sided Tests and One-Sided Confidence Bounds

    OpenAIRE

    1994-01-01

    Based on the duality between tests and confidence sets we introduce a new method to derive one-sided confidence bounds following the rejection of a null hypothesis with two-sided alternatives. This method imputes that the experimenter is only interested in confidence bounds if the null hypothesis is rejected. Furthermore, we suppose that he is only interested in the direction and a lower confidence bound concerning the distance of the true parameter value to the parameter values in the null h...

  8. Science friction: data, metadata, and collaboration.

    Science.gov (United States)

    Edwards, Paul N; Mayernik, Matthew S; Batcheller, Archer L; Bowker, Geoffrey C; Borgman, Christine L

    2011-10-01

    When scientists from two or more disciplines work together on related problems, they often face what we call 'science friction'. As science becomes more data-driven, collaborative, and interdisciplinary, demand increases for interoperability among data, tools, and services. Metadata--usually viewed simply as 'data about data', describing objects such as books, journal articles, or datasets--serve key roles in interoperability. Yet we find that metadata may be a source of friction between scientific collaborators, impeding data sharing. We propose an alternative view of metadata, focusing on its role in an ephemeral process of scientific communication, rather than as an enduring outcome or product. We report examples of highly useful, yet ad hoc, incomplete, loosely structured, and mutable, descriptions of data found in our ethnographic studies of several large projects in the environmental sciences. Based on this evidence, we argue that while metadata products can be powerful resources, usually they must be supplemented with metadata processes. Metadata-as-process suggests the very large role of the ad hoc, the incomplete, and the unfinished in everyday scientific work.

  9. Molecular friction in an actomyosin molecular machine.

    Science.gov (United States)

    Suda, H

    1990-10-07

    In muscle contraction, it has been widely recognized that a binding state exists between myosin and actin in the presence of Mg-ATP. To estimate the magnitude of binding strength, I introduce a concept of frictional phenomena which occurs between two sliding bodies in contact each other. In such cases, the sliding speed can be formulated as a function of the actin-myosin bond strength. In order to validate this, the present theory is applied for the two movement assay systems with no external load; one movement assay of Phalloidin Rhodamine bound F-actin on a myosin coated hydrophobic cover glass and another assay of myosin coated beads along actin cables of Nitella. If a coefficient of 0.005 is applied to the kinetic friction, 1pN for the sliding force per cross-bridge and 10 microns sec-1 for the sliding speed, it is found that the bond strength between actin and one myosin head is about 200 pN in the contracting state.

  10. Slip versus Friction : Modifying the Navier condition

    Science.gov (United States)

    Kotsalis, Evangelos; Walther, Jens; Koumoutsakos, Petros

    2006-03-01

    The modeling of fluid-solid interfaces remains one of the key challenges in fluid mechanics. The prevailing model, attributed to Navier, defines the fluid ``slip'' velocity as proportional to the wall shear and a parameter defined as the slip length. Several works have in turn proposed models for this slip length but no universal model for the slip velocity has been accepted. We present results from large scale molecular dynamics simulations of canonical flow problems, indicating, that the inadequacy of this classic model, stems from not properly accounting for the pressure field. We propose and validate a new model, based on the fundamental observation that the finite ``slip'' velocity is a result of an imbalance between fluid and solid intermolecular forces. An excess force on the fluid elements will lead to their acceleration which in turn may result in a slip velocity at the interface. We formulate the slip velocity in terms of fluid-solid friction Ff and propose a generalized boundary condition: Ff= Fs+ Fp= λuus+ λpp where p denotes the pressure, and λuand λp the viscous and static friction coefficients, for which universal constants are presented. We demonstrate that the present model can overcome difficulties encountered by the classical slip model in canonical flow configurations.

  11. A frictional sliding algorithm for liquid droplets

    Science.gov (United States)

    Sauer, Roger A.

    2016-12-01

    This work presents a new frictional sliding algorithm for liquid menisci in contact with solid substrates. In contrast to solid-solid contact, the liquid-solid contact behavior is governed by the contact line, where a contact angle forms and undergoes hysteresis. The new algorithm admits arbitrary meniscus shapes and arbitrary substrate roughness, heterogeneity and compliance. It is discussed and analyzed in the context of droplet contact, but it also applies to liquid films and solids with surface tension. The droplet is modeled as a stabilized membrane enclosing an incompressible medium. The contact formulation is considered rate-independent such that hydrostatic conditions apply. Three distinct contact algorithms are needed to describe the cases of frictionless surface contact, frictionless line contact and frictional line contact. For the latter, a predictor-corrector algorithm is proposed in order to enforce the contact conditions at the contact line and thus distinguish between the cases of advancing, pinning and receding. The algorithms are discretized within a monolithic finite element formulation. Several numerical examples are presented to illustrate the numerical and physical behavior of sliding droplets.

  12. Origins of Shear Jamming for Frictional Grains

    Science.gov (United States)

    Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert

    2016-11-01

    Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.

  13. Thermomechanical Modelling of Friction Stir Welding

    DEFF Research Database (Denmark)

    Hattel, Jesper Henri; Schmidt, Henrik Nikolaj Blicher; Tutum, Cem Celal

    2009-01-01

    Friction Stir Welding (FSW) is a fully coupled thermomechanical process and should in general be modelled as such. Basically, there are two major application areas of thermomechanical models in the investigation of the FSW process: i) Analysis of the thermomechanical conditions such as e.g. heat ...... together with selected modelling results including prediction of material flow during welding, prediction of heat generation with the thermal-pseudo mechanical model as well as residual stress and deformation analysis combined with in-service loads.......Friction Stir Welding (FSW) is a fully coupled thermomechanical process and should in general be modelled as such. Basically, there are two major application areas of thermomechanical models in the investigation of the FSW process: i) Analysis of the thermomechanical conditions such as e.g. heat......, typically on a local scale, the latter will very often be based on a semi-coupled, global procedure where the transient temperatures drive the stresses but not vice-versa. However, in the latter, prior knowledge about the heat generation must be obtained somehow, and if experimental data are not available...

  14. Numerical simulation of friction stir welding

    Directory of Open Access Journals (Sweden)

    Mijajlović Miroslav

    2014-01-01

    Full Text Available Friction stir welding is a solid-state welding technique that utilizes thermo-mechanical influence of the rotating welding tool on parent material resulting with monolith joint-weld. On the contact of welding tool and parent material, significant stirring and deformation of parent material appears, and during this process mechanical energy is partially transformed into heat. The paper describes the software for the numerical simulation of friction stir welding developed at Mechanical Engineering Faculty, University of Nis. Numerical solution for estimation of welding plates temperature is estimated using finite difference method-explicit scheme with adaptive grid, considering influence of temperature on material's conductivity, contact conditions between welding tool and parent material, material flow around welding tool etc. The calculated results are in good agreement with the experimental results. [Projekat Ministarstva nauke Republike Srbije, br. TR35034: The research of modern non-conventional technologies application in manufacturing companies with the aim of increase efficiency of use, product quality, reduce of costs and save energy and materials

  15. On Heels and Toes: How Ants Climb with Adhesive Pads and Tarsal Friction Hair Arrays.

    Science.gov (United States)

    Endlein, Thomas; Federle, Walter

    2015-01-01

    Ants are able to climb effortlessly on vertical and inverted smooth surfaces. When climbing, their feet touch the substrate not only with their pretarsal adhesive pads but also with dense arrays of fine hairs on the ventral side of the 3rd and 4th tarsal segments. To understand what role these different attachment structures play during locomotion, we analysed leg kinematics and recorded single-leg ground reaction forces in Weaver ants (Oecophylla smaragdina) climbing vertically on a smooth glass substrate. We found that the ants engaged different attachment structures depending on whether their feet were above or below their Centre of Mass (CoM). Legs above the CoM pulled and engaged the arolia ('toes'), whereas legs below the CoM pushed with the 3rd and 4th tarsomeres ('heels') in surface contact. Legs above the CoM carried a significantly larger proportion of the body weight than legs below the CoM. Force measurements on individual ant tarsi showed that friction increased with normal load as a result of the bending and increasing side contact of the tarsal hairs. On a rough sandpaper substrate, the tarsal hairs generated higher friction forces in the pushing than in the pulling direction, whereas the reverse effect was found on the smooth substrate. When the tarsal hairs were pushed, buckling was observed for forces exceeding the shear forces found in climbing ants. Adhesion forces were small but not negligible, and higher on the smooth substrate. Our results indicate that the dense tarsal hair arrays produce friction forces when pressed against the substrate, and help the ants to push outwards during horizontal and vertical walking.

  16. The DarkSide project

    Energy Technology Data Exchange (ETDEWEB)

    Agnes, P.; Agostino, L.; Albuquerque, Ivone Freire Da Mota; Alexander, Thomas R.; Alton, A.; Arisaka, K.; Back, Henning O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Bottino, Bianca; Brigatti, A.; Brodsky, J.; Budano, F.; Bussino, Severino; Cadeddu, Matteo; Cadonati, L.; Cadoni, M.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Carlini, Macro; Catalanotti, Sergio; Cavalcante, P.; Chepurnov, A.; Cocco, A. G.; Covone, G.; Crippa, L.; D' Angelo, D.; D' Incecco, M.; Davini, S.; De Cecco, Sandro; De Deo, M.; De Vincenzi, Mario; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, Giuseppe; Edkins, E.; Empl, Anton; Fan, A.; Fiorillo, G.; Fomenko, K.; Forster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Giganti, C.; Goretti, A.; Granato, Francesco; Grandi, L.; Gromov, M.; Guan, M. Y.; Guardincerri, Y.; Hackett, B.; Herner, K.; Hungerford, Edward; Ianni, Al.; Ianni, An.; James, I.; Jollet, C.; Keeter, K.; Kendziora, C.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kubankin, Alexander; Li, X.; Lissia, M.; Lombardi, P.; Luitz, S.; Ma, Y. Q.; Machulin, I.; Mandarano, A.; Mari, S. M.; Maricic, J.; Marini, L.; Martoff, J.; Meregaglia, A.; Meyers, P. D.; Miletic, T.; Milincic, R.; Montanari, D.; Monte, Alissa; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B.; Muratova, V.; Musico, P.; Napolitano, James; Nelson, A.; Odrowski, S.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, Marco; Pantic, E.; Parmeggiano, S.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D.; Qian, H.; Randle, K.; Ranucci, Gioacchino; Razeto, A.; Reinhold, B.; Renshaw, Andrew; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, Samuele; Savarese, Claudio; Segreto, E.; Semenov, D.; Shields, E.; Singh, Parth; Skorokhvatov, Mikhail; Smirnov, Oleg; Sotnikov, Albert; Stanford, Chris; Suvorov, Yura; Tartaglia, Roberto; Tatarowicz, John; Testera, Gemma; Tonazzo, Alessandra; Trinchese, P.; Unzhakov, Eugenii; Vishneva, Alina; Vogelaar, R. B.; Wada, Masayuki; Walker, Susan E.; Wang, H.; Wang, Y.; Watson, A. W.; Westerdale, S.; Wilhelmi, James; Wojcik, M.; Xiang, Xin; Xu, Jingke; Yang, C. G.; Yoo, J.; Zavatarelli, Sandra; Zec, Adam; Zhong, W. L.; Zhu, Chengliang; Zuzel, G.

    2016-02-01

    DarkSide is a graded experimental project based on radiopure argon, and is now, and will be, used in direct dark matter searches. The present DarkSide-50 detector, operating at the Gran Sasso National Laboratory, is a dual-phase, 50 kg, liquid argon time-projection-chamber surrounded by an active liquid scintillator veto. It is designed to be background free in 3 years of operation. DS-50 performances, when filled with atmospheric argon, are reported. However DS-50 filled with underground argon, shows impressive reduction of the 39Ar isotope. The application of this powerful technology in a future generation of the DarkSide program is discussed.

  17. Inertia Friction Welding Dissimilar Nickel-Based Superalloys Alloy 720Li to IN718

    Science.gov (United States)

    Huang, Z. W.; Li, H. Y.; Preuss, M.; Karadge, M.; Bowen, P.; Bray, S.; Baxter, G.

    2007-07-01

    This article describes a comprehensive microstructural characterization of an inertia friction welded joint between nickel-based superalloys 720Li and IN718. The investigation has been carried out on both as-welded and postweld heat-treated conditions. The detailed metallographic analysis has enabled the relation of hardness profiles across inertia-welded alloy 720Li to IN718 and morphological changes of the precipitates present. The work demonstrates that inertia friction welding (IFW) 720Li to IN718 results in a weld free of micropores and microcracks and no significant chemical migration across the weld line. However, substantial differences in terms of grain structure and precipitation phase distribution variations are observed on each side of the dissimilar weld. The high γ‧ volume fraction alloy 720Li exhibits a wider heat-affected zone than the mainly γ‧‧ strengthened IN718. Alloy 720Li displays only a small hardness trough near the weld line in the as-welded condition due to the depletion of γ‧, while γ″-strengthened IN718 shows a soft precipitation-free weld region. Postweld heat treatment (PWHT) of the dissimilar weld at 760 °C, a typical annealing temperature for alloy 720Li, results in an overmatch of the heat-affected zone in both sides of the weld. The comparison of the as-welded and postweld heat-treated condition also reveals that IN718 is in an overaged condition after the stress relief treatment.

  18. Analysis of pile load-transfer under pile-side softening

    Institute of Scientific and Technical Information of China (English)

    刘杰; 张可能

    2003-01-01

    A set of analytical equations for the variation of the axial force along depth and the pile-top load-settle-ment curve were established, using tri-linear softening model to pile-side soil and bilinear hardening model to pile-end soil . Influences of the pile-side and pile-end soil behavior on the load-settlement curve were discussed, indica-ting that the lowering reason for the variation step degree of the axial force along depth is the softening of the pile-side soil to result in the side friction lowering when the pile-top load is increased. To verify the reliability of thismethod, the parameters used in calculation are obtained from the test in Zhuzhou area. The obtained results are thencompared with the tested results. Contrast shows that the calculated results and the tested values are very close,which illustrates that the proposed method is reliable.

  19. Microstructure and Fatigue Behavior of Friction Stir-welded Noncombustive Mg-9Al-Zn-Ca Magnesium Alloy

    Science.gov (United States)

    Zhou, L.; Li, Z. Y.; Nakata, K.; Feng, J. C.; Huang, Y. X.; Liao, J. S.

    2016-06-01

    Microstructure and fatigue behavior of friction stir-welded noncombustive Mg-9Al-Zn-Ca magnesium alloy were investigated. The as-received hot-extruded material consisted of equiaxed α-Mg grains with β-Mg17Al12 and Al2Ca compounds distributed along the grain boundaries. Friction stir welding produced much refined α-Mg grains accompanied by the dissolution of the eutectic β-Mg17Al12 phase, while Al2Ca phase was dispersed homogenously into the Mg matrix. Friction stir welding produced slightly increased hardness and tensile strength in the defect-free welds compared with the base material due to microstructural refinement and uniform distribution of intermetallic compounds. The load-controlled uniaxial tensile high-cycle fatigue tests indicated that fatigue strength of 90 MPa was obtained for the friction stir-welded joint with fatigue crack initiated basically near the specimen's surface and at the retreating side of the joint. Crack propagation was characterized by cleavage and fatigue striations.

  20. Design and manufacture of intelligent Cu-based wet friction materials

    Institute of Scientific and Technical Information of China (English)

    丁华东; 韩文政; 傅苏黎; 杜建华; 遇元宏

    2004-01-01

    The friction sheets working process was analyzed. It is found that its characteristic is microregion instantaneous high temperature and the current cooling method, making the sheets cooled by the lubricating oil flowing through the friction surface, is not very efficient. Then, intelligent materials concept was introduced, the component and microstructure of intelligent Cu-based friction materials were designed, and the intelligent Cu-based wet friction materials as well as sheets were manufactured. And the intelligent friction materials working principle, i.e. the materials cooling the friction microregion in real time or the friction sheets cutting the peak value of microregion instantaneous high temperature during friction process, was given depending on the characteristics of the materials' and friction sheets' working process. Finally, it is indicated that the intelligent friction sheets excell the currently used friction sheets in properties, including anti-heating property, anti-wearing property as well as friction characteristic.

  1. 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.

  2. Friction at seismic slip rates: testing thermal weakening models experimentally

    Science.gov (United States)

    Nielsen, S. B.; Spagnuolo, E.; Violay, M.; Di Toro, G.

    2013-12-01

    Recent experiments systematically explore rock friction under crustal earthquake conditions (fast slip rate 1desing an efficient and accurate wavenumber approximation for a solution of the temperature evolution on the fault. Finally, we propose a compact and paractical model based on a small number of memory variables for the implementation of thermal weakening friction in seismic fault simulations.

  3. Biomechanics of iliotibial band friction syndrome in runners.

    Science.gov (United States)

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

    1996-01-01

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

  4. Microstructure Evolution during Friction Stir Spot Welding of TRIP Steel

    DEFF Research Database (Denmark)

    Lomholt, Trine Colding; Pantleon, Karen; Somers, Marcel A. J.

    2010-01-01

    In this study, the feasibility of friction stir spot welding of TRIP steel is investigated. In addition to manufacturing successful welds, the present study aims at a fundamental understanding of the mechanisms occurring at the (sub)micron scale during friction stir spot welding. As one of the main...

  5. Scale effects in metal-forming friction and lubrication

    DEFF Research Database (Denmark)

    Nielsen, Peter Søe; Paldan, Nikolas Aulin; Calaon, Matteo

    2011-01-01

    equipment is developed for studies of the size effect in metal-forming friction in the range from macro-to microscale. Investigations confirm a significant friction increase when downscaling. Visual inspection of the workpieces shows this to be explained by the amount of open and closed lubricant pockets....

  6. Associated computational plasticity schemes for nonassociated frictional materials

    DEFF Research Database (Denmark)

    Krabbenhoft, K.; Karim, M. R.; Lyamin, A. V.;

    2012-01-01

    A new methodology for computational plasticity of nonassociated frictional materials is presented. The new approach is inspired by the micromechanical origins of friction and results in a set of governing equations similar to those of standard associated plasticity. As such, procedures previously...

  7. Apparatus Measures Friction In Vacuum Or Pressurized Gas

    Science.gov (United States)

    Trevathan, Joseph R.

    1996-01-01

    Friction-testing apparatus in small test chamber contains special atmosphere, which could include vacuum or pressurized gas. Provides readings indicative of friction between pin specimen and plate specimen sliding under pin in reciprocating linear motion. Pin and plate specimens made of same or different material.

  8. The role of friction in perceived oral texture

    NARCIS (Netherlands)

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

    2005-01-01

    Instrumentally measured in vitro friction in semi-solid foods was related to oral texture sensations. Increased fat content resulted in lower sensations of roughness, higher sensations of creaminess, and lower friction, suggesting that lubrication is the mechanism by which fat affects oral texture

  9. Measurements of Normal and Friction Forces in a Rolling Process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    To improve the quality of frictional data and to validate the simulations in rolling, a load transducer for measuring normal and friction stresses in the deformation zone has been developed. The transducer consists of a strain gauge equipped insert embedded in the surface of the roll. The length ...

  10. Statistical analysis of friction sleeve length effects on soil classification

    Science.gov (United States)

    Saussus, D. R.; Frost, J. D.; Dejong, J. T.

    2004-10-01

    The cone penetration test (CPT) provides profiles of the tip resistance, sleeve friction, and pore water pressure encountered while penetrating the subsurface. These parameters are used either directly or indirectly to classify the soil types present and to obtain geotechnical design parameters. However, fundamental discrepancies exist in the manner by which these parameters are measured. This paper describes the results of a study that shows the sleeve friction measurement introduces unnecessary redundancy due to the length of the standard friction sleeve compared to the measurement increment. Further, the high sleeve length to measurement increment ratio results in filtering and smoothing of the friction data, thereby causing the variability of the friction between the soil and the cone sleeve to be underestimated. The importance of understanding the role of the sleeve length on measurements is demonstrated using synthetically generated friction profiles and estimating the profiles that would be measured using sleeves of different lengths. Differences in how the soils are classified as a function of the sleeve length used to obtain each profile are illustrated. Solutions are presented to validate the synthetic sleeve friction profiles, to demonstrate the filtering and smoothing effects of the friction sleeve on the data, and to explain the implications of the sleeve length on soil classification. Copyright

  11. Friction and stick-slip in a telescope construction

    NARCIS (Netherlands)

    Hammerschlag, R.H.

    1986-01-01

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

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

    NARCIS (Netherlands)

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

    2013-01-01

    In the past decades, skin friction research has focused on determining which variables are important to affect the frictional behaviour of in vivo human skin. Until now, there is still limited knowledge on these variables. This study has used a large dataset to identify the effect of variables on t

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

    NARCIS (Netherlands)

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

    2013-01-01

    In the past decades, skin friction research has focused on determining which variables are important to affect the frictional behaviour of in vivo human skin. Until now, there is still limited knowledge on these variables.This study has used a large dataset to identify the effect of variables on the

  14. Synovial sarcoma presenting as iliotibial band friction syndrome.

    Science.gov (United States)

    Mesiha, Mena; Bauer, Thomas; Andrish, Jack

    2009-10-01

    Iliotibial band friction syndrome is a common entity that is often quickly diagnosed in orthopedic clinics. However, synovial sarcoma is an elusive clinical entity that appears around many joints with variable presentations. This case report is an example of a patient with a classic presentation of iliotibial band friction syndrome that was diagnosed as a synovial sarcoma on further investigation.

  15. Shearing Nanometer-Thick Confined Hydrocarbon Films: Friction and Adhesion

    DEFF Research Database (Denmark)

    Sivebæk, I. M.; Persson, B. N. J.

    2016-01-01

    We present molecular dynamics (MD) friction and adhesion calculations for nanometer-thick confined hydrocarbon films with molecular lengths 20, 100 and 1400 carbon atoms. We study the dependency of the frictional shear stress on the confining pressure and sliding speed. We present results...

  16. A lubrication approach to friction in thermoplastic composites forming processes

    NARCIS (Netherlands)

    Thije, ten R.H.W.; Akkerman, R.; Ubbink, M.P.; Meer, van der L.

    2011-01-01

    Friction is an important phenomenon that can dominate the resulting product geometry of thermoplastic composites upon forming. A model was developed that predicts the friction between a thermoplastic laminate and a rigid tool. The model is based on the Reynolds equation for thin film lubrication and

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

    CERN Document Server

    Alben, Silas

    2013-01-01

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

  18. Influence of Friction Condition on Cold Upsetting of Tube Flange

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    FEM is used to analyze the influence of interface friction on the material flow and the cause of forming defect in the cold upsetting of tube flange. Based on the FEM simulation results, the relationships between flange width and the extreme friction factors are established. The concept of forming limit diagram for cold upsetting of tube flange is presented.

  19. Numerical simulation and experimental observations of initial friction transients

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, D.A.; Weingarten, L.I.; Dawson, D.B.

    1995-07-01

    Experiments were performed to better understand the sliding frictional behavior between metals under relatively high shear and normal forces. Microstructural analyses were done to estimate local near-surface stress and strain gradients. The numerical simulation of the observed frictional behavior was based on a constitutive model that uses a state variable approach.

  20. The role of friction in perceived oral texture

    NARCIS (Netherlands)

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

    2005-01-01

    Instrumentally measured in vitro friction in semi-solid foods was related to oral texture sensations. Increased fat content resulted in lower sensations of roughness, higher sensations of creaminess, and lower friction, suggesting that lubrication is the mechanism by which fat affects oral texture i

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

    Science.gov (United States)

    Wu, Y Q; Huang, F L

    2010-11-15

    The frictional properties of single crystals of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) secondary explosives are examined using a sensitive friction machine. The explosive crystals used for the measurements are at least 3.5 mm wide. The friction coefficients between crystals of the same explosive (i.e., HMX on HMX, etc.), crystals of different explosives (i.e., HMX on RDX, etc.), and each explosive and a well-polished gauge steel surface are determined. The frictional surfaces are also studied under an environmental scanning electron microscope (ESEM) to analyze surface microstructural changes under increasing loading forces. The friction coefficients vary considerably with increasing normal loading forces and are particularly sensitive to slider shapes, crystal roughness and the mechanical properties of both the slider and the sample. With increasing loading forces, most friction experiments show surface damage, consisting of grooves, debris, and nano-particles, on both the slider and sample. In some cases, a strong evidence of a localized molten state is found in the central region of the friction track. Possible mechanisms that affect the friction coefficient are discussed based on microscopic observations. Copyright © 2010 Elsevier B.V. All rights reserved.

  2. Effect of energetic dissipation processes on the friction unit tribological

    Directory of Open Access Journals (Sweden)

    Moving V. V.

    2007-01-01

    Full Text Available In article presented temperature influence on reological and fric-tion unit coefficients cast iron elements. It has been found that surface layer formed in the temperature friction has good rub off resistance. The surface layer structural hardening and capacity stress relaxation make up.

  3. Friction Stir Welding Technology: Adapting NASA's Retractable Pin Tool

    OpenAIRE

    ECT Team, Purdue

    2007-01-01

    In late 1991, The Welding Institute (TWI), a British research and technology organization, invented and patented a welding process named Friction Stir Welding (FSW). Friction Stir Welding is a highly significant advancement in aluminum welding technology that can produce stronger, lighter, and more efficient welds than any previous process.

  4. Cladding of Advanced Al Alloys Employing Friction Stir Welding

    NARCIS (Netherlands)

    Stelt, van der A.A.; Bor, T.C.; Geijselaers, H.J.M.; Akkerman, R.; Boogaard, van den A.H.

    2013-01-01

    In this paper an advanced solid state cladding process, based on Friction Stir Welding, is presented. The Friction Surface Cladding (FSC) technology enables the deposition of a solid-state coating using filler material on a substrate with good metallurgical bonding. A relatively soft AA1050 filler m

  5. Damage Tolerance Behavior of Friction Stir Welds in Aluminum Alloys

    Science.gov (United States)

    McGill, Preston; Burkholder, Jonathan

    2012-01-01

    Friction stir welding is a solid state welding process used in the fabrication of various aerospace structures. Self-reacting and conventional friction stir welding are variations of the friction stir weld process employed in the fabrication of cryogenic propellant tanks which are classified as pressurized structure in many spaceflight vehicle architectures. In order to address damage tolerance behavior associated with friction stir welds in these safety critical structures, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size. Test data describing fracture behavior, residual strength capability, and cyclic mission life capability of friction stir welds at ambient and cryogenic temperatures have been generated and will be presented in this paper. Fracture behavior will include fracture toughness and tearing (R-curve) response of the friction stir welds. Residual strength behavior will include an evaluation of the effects of lack of penetration on conventional friction stir welds, the effects of internal defects (wormholes) on self-reacting friction stir welds, and an evaluation of the effects of fatigue cycled surface cracks on both conventional and selfreacting welds. Cyclic mission life capability will demonstrate the effects of surface crack defects on service load cycle capability. The fracture data will be used to evaluate nondestructive inspection and proof test requirements for the welds.

  6. Damage Tolerance Assessment of Friction Pull Plug Welds

    Science.gov (United States)

    McGill, Preston; Burkholder, Jonathan

    2012-01-01

    Friction stir welding is a solid state welding process developed and patented by The Welding Institute in Cambridge, England. Friction stir welding has been implemented in the aerospace industry in the fabrication of longitudinal welds in pressurized cryogenic propellant tanks. As the industry looks to implement friction stir welding in circumferential welds in pressurized cryogenic propellant tanks, techniques to close out the termination hole associated with retracting the pin tool are being evaluated. Friction pull plug welding is under development as a one means of closing out the termination hole. A friction pull plug weld placed in a friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite, plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size in the test or service environments. Test data relating residual strength capability to flaw size in two aluminum alloy friction plug weld configurations is presented.

  7. Frictional characteristics of the newer orthodontic elastomeric ligatures

    Directory of Open Access Journals (Sweden)

    A V Arun

    2011-01-01

    Full Text Available Introduction: Elastomeric ligatures reduce chairside time but increase friction. Polymeric coatings and 45° angulations have been introduced to the ligature modules to combat its disadvantages and reduce friction. This in vitro study compared the frictional characteristics of six different types of the most commonly used elastomeric modules. Materials and Methods: Thecoefficient of friction for six ligation methods: the non-coated Mini Stix† and coated Super Slick Mini Stix™ (TP Orthodontics, 45° angulated but non-coated Alastik Easy-To-Tie™ (3M Unitek elastomerics and non-angulated non-coated Alastik QuiK-StiK FNx01 , 0.110′- and 0.120′-diameter elastomerics™ (Reliance Orthodontics were measured in dry conditions utilizing a jig according to the protocol of Tidy. Results: A significant difference was observed between the various types of elastomeric ligatures (P<.01. Among the six types of elastomeric ligatures, the 45° angulated elastomeric ligatures produced the least friction, followed by the coated Super Slick† elastomers. No difference in the friction was noted when the diameter of the elastomeric ligatures was varied. Conclusions: Polymeric surface coatings and introduction of angulations into elastomeric ligatures reduce the friction during sliding; however, the diameter of the ligature made no difference to sliding friction.

  8. Static friction in elastic adhesive MEMS contacts, models and experiment

    NARCIS (Netherlands)

    Tas, Niels Roelof; Gui, C.; Elwenspoek, Michael Curt

    2000-01-01

    Static friction in shearing mode can be expressed as the product of the shear strength of the interface and the real contact area. The influence of roughness on friction in elastic adhesive contact is analyzed. Special attention is paid to low loading conditions, in which the number of contact

  9. Bifurcations in Systems with Friction : Basic Models and Methods

    NARCIS (Netherlands)

    Ivanov, A. P.

    2009-01-01

    Examples of irregular behavior of dynamical systems with dry friction are discussed. A classification of frictional contacts with respect to their dimensionality, associativity, and the possibility of interruptions is proposed and basic models showing typical features are stated. In particular, bifu

  10. Frictional Forces Required for unrestrained locomotion in dairy cattle

    NARCIS (Netherlands)

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

    2005-01-01

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

  11. The Static Ladder Problem with Two Sources of Friction

    Science.gov (United States)

    Bennett, Jonathan; Mauney, Alex

    2011-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

  13. Measurements of normal and frictional forces in a rolling process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2006-01-01

    To improve the quality of frictional data and to validate the simulations in rolling, a load transducer for measuring normal and frictional stresses in the deformation zone has been developed. The transducer consists of a strain-gauge-equipped insert embedded in the surface of the roll. The length...

  14. Contact mechanics, friction and adhesion with application to quasicrystals

    DEFF Research Database (Denmark)

    Persson, Bo; Carbone, Giuseppe; Samoilov, Vladimir N.;

    2015-01-01

    We discuss the origin of friction and adhesion between hard solids such as quasicrystals. We emphasize the fundamental role of surface roughness in many contact mechanics problems, in particular for friction and adhesion between solid bodies. The most important property of rough surfaces is the s...

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

    DEFF Research Database (Denmark)

    Fidlin, A.; Thomsen, Jon Juel

    2001-01-01

    A mathematical model is set up to quantify vibration-induced motions of a slider, sandwiched between friction layers with different coefficients of friction, and equipped with an imbedded resonator that oscillates at high frequency and small amplitude. This model is highly nonlinear, involving non...

  16. The Static Ladder Problem with Two Sources of Friction

    Science.gov (United States)

    Bennett, Jonathan; Mauney, Alex

    2011-01-01

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

  17. A lubrication approach to friction in thermoplastic composites forming processes

    NARCIS (Netherlands)

    ten Thije, R.H.W.; Akkerman, Remko; Ubbink, M.P.; van der Meer, L.

    2011-01-01

    Friction is an important phenomenon that can dominate the resulting product geometry of thermoplastic composites upon forming. A model was developed that predicts the friction between a thermoplastic laminate and a rigid tool. The model is based on the Reynolds equation for thin film lubrication and

  18. Certification of a weld produced by friction stir welding

    Science.gov (United States)

    Obaditch, Chris; Grant, Glenn J

    2013-10-01

    Methods, devices, and systems for providing certification of friction stir welds are disclosed. A sensor is used to collect information related to a friction stir weld. Data from the sensor is compared to threshold values provided by an extrinsic standard setting organizations using a certification engine. The certification engine subsequently produces a report on the certification status of the weld.

  19. Coping – Late Side Effects

    Science.gov (United States)

    Cancer treatment can cause late side effects that may not show up for months or years after treatment. These late effects may include heart and lung problems, bone loss, eye and hearing changes, lymphedema, and other problems

  20. Managing Chemotherapy Side Effects: Constipation

    Science.gov (United States)

    N ational C ancer I nstitute Managing Chemotherapy Side Effects Constipation Take these steps: Eat high-fiber foods such as: ● ● Whole-grain breads and cereals ● ● Fruits and vegetables ● ● Nuts and seeds ...

  1. Novel side branch ostial stent.

    Science.gov (United States)

    Chen, Shao-Liang; Lv, Shu-Zheng; Kwan, Tak W

    2009-04-01

    Bifurcation lesions are technically challenging and plagued by a high incidence of restenosis, especially at the side branch orifice, which results in a more frequent need for revascularization during the follow-up period. This report discusses two clinical experiences with a novel side branch ostial stent, the BIGUARD stent, designed for the treatment of bifurcation lesions; procedural success with no in-hospital complications was observed in types IVb and Ia lesions.

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

    DEFF Research Database (Denmark)

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

    1997-01-01

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

  3. Weldability of AISI 304 to copper by friction welding

    Energy Technology Data Exchange (ETDEWEB)

    Kirik, Ihsan [Batman Univ. (Turkey); Balalan, Zulkuf [Firat Univ., Elazig (Turkey)

    2013-06-01

    Friction welding is a solid-state welding method, which can join different materials smoothly and is excessively used in manufacturing industry. Friction welding method is commonly used in welding applications of especially cylindrical components, pipes and materials with different properties, for which other welding methods remain incapable. AISI 304 stainless steel and a copper alloy of 99.6 % purity were used in this study. This couple was welded in the friction welding machine. After the welding process, samples were analyzed macroscopically and microscopically, and their microhardness was measured. Tensile test was used to determine the bond strength of materials that were joined using the friction welding method. At the end of the study, it was observed that AISI 304 stainless steel and copper could be welded smoothly using the friction welding method and the bond strength is close to the tensile strength of copper. (orig.)

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

    Indian Academy of Sciences (India)

    T N Singh; A K Verma; Tanmay Kumar; Avi Dutt

    2011-02-01

    Understanding the fundamental issues related with the effect of shear velocity on frictional characteristics at the interface of rock surfaces is an important issue. In this paper, strain-rate dependence on friction is investigated in relation to sliding behaviour under normal load. The phenomenon of stick-slip of granite and shaly sandstone with a tribometer at constant rate of strain under normal loads was observed. 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 for shaly sandstone may be attributed to the fact that its surface had a greater number of pronounced asperities. Rubbing between the surfaces does not mean that surface becomes smoother. This is because of variation of friction between surfaces.

  5. Method for Investigation of Frictional Properties at Impact Loading

    Science.gov (United States)

    Sundin, K. G.; Åhrström, B. O.

    1999-05-01

    In the assessment of lubricant performance and also in various other contact applications it is of importance to know the frictional qualities of a surface. Under quasi-static conditions, normal and frictional forces are measured using force transducers but the task is more difficult when loads are transient. The experimental method presented in this paper is based on the analysis of propagating waves in a beam, due to an impact on the end surface. The impact is oblique and therefore a transverse as well as a normal force is generated. The normal force history is measured from the axial non-dispersive wave using strain gauges. Transverse force and bending moment both generate dispersive flexural waves. From the FFT of two transverse acceleration histories, the frictional force at the end of the rod is evaluated using beam theory. The relation between normal and frictional force histories displays the frictional properties at the impact. Preliminary results are presented.

  6. Friction Modelling In Connection With Cold Forming Processes

    DEFF Research Database (Denmark)

    Tan, Xincai

    soap or molybdenum disulphide. As processes testing friction sensitive flow, the ring-compression tests and the double cup extrusion tests are carried out. An absolute constant friction model has been proposed to separate the influence of strain hardening from friction. This model has been applied...... in the FEM analyses of the process tests. In the simulative testing, the compression-twist tests in open die and closed die are carried out to measure friction stress directly at varying normal pressure, surface expansion, sliding length and tool temperature etc. It is found that normal pressure...... differences in the results. New empirical friction models have therefore been developed, based on the results of the simulative tests. Applying these models in the FEM simulations shows that they are acceptable for direct applications. In direct process testing, the forward rod extrusion test is investigated...

  7. A review of dynamics modelling of friction draft gear

    Science.gov (United States)

    Wu, Qing; Cole, Colin; Luo, Shihui; Spiryagin, Maksym

    2014-06-01

    Longer and heavier trains mean larger in-train forces and more complicated force patterns. Practical experience indicates that the development of fatigue failure of coupling systems in long heavy trains may differ from conventional understanding. The friction-type draft gears are the most widely used draft gears. The ever developing heavy haul transport environment requires further or new understanding of friction draft gear behaviour and its implications for train dynamics as well as fatigue damage of rolling stock. However, modelling of friction draft gears is a highly nonlinear question. Especially the poor predictability, repeatability and the discontinuity of friction make this task more challenging. This article reviews current techniques in dynamics modelling of friction draft gears to provide a starting point that can be used to improve existing or develop new models to achieve more accurate force amplitude and pattern predictions.

  8. On Sliding Friction of PEEK Based Composite Coatings

    Institute of Scientific and Technical Information of China (English)

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

    2004-01-01

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

  9. On Sliding Friction of PEEK Based Composite Coatings

    Institute of Scientific and Technical Information of China (English)

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

    2004-01-01

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

  10. Measurement of Normal and Friction Forces in a Rolling Process

    DEFF Research Database (Denmark)

    Henningsen, Poul; Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    For the rolling process, knowledge about interface conditions is important since it directly influences the maximum reduction ratio and thereby the num-ber of steps required for a given reduction. The mechanical properties of the produced sheet and the surface quality of it are also influenced...... 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...

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

    Institute of Scientific and Technical Information of China (English)

    周细应; 李培耀; 罗军明; 钱士强; 童建华

    2004-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

    CHEN Shao-Hua; MI Chun-Hui

    2009-01-01

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

  13. 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...... response may take place in both the electrostatic and the electromagnetic regimes. Results are presented from two-dimensional numerical simulations of an isolated blob structure in a non-uniform magnetic field [1,2]. The effect of a linear damping term in the vorticity equation, which describes...... 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...

  14. Friction Compensation in the Upsetting of Cylindrical Test Specimens

    DEFF Research Database (Denmark)

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

    2016-01-01

    This manuscript presents a combined numerical andexperimental methodology for determining the stress-straincurve of metallic materials from the measurements of forceand displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens...... model or combined friction models are utilized .Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction...... in the determination of the material flow curve. Comparison with the flow curves determined without friction compensation shows the viability of the proposed methodology. The proposed methodology is a simple and effective alternative to other solutions available in the literature and the pseudo-code supplied inthe...

  15. Friction measurement in MEMS using a new test structure

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-12-09

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

  16. Friction Coefficient of UHMWPE During Dry Reciprocating Sliding

    Directory of Open Access Journals (Sweden)

    F. Zivic

    2014-09-01

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

  17. The behaviour of molybdenum dialkyldithiocarbamate friction modifier additives

    CERN Document Server

    Graham, J C H

    2001-01-01

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

  18. Static and kinetic friction characteristics of nanowire on different substrates

    Science.gov (United States)

    Kim, Hyun-Joon; Nguyen, Gia Hau; Ky, Dinh Le Cao; Tran, Da Khoa; Jeon, Ki-Joon; Chung, Koo-Hyun

    2016-08-01

    Friction characteristics of nanowires (NWs), which may be used as building blocks for nano-devices, are crucial, especially for cases where contact sliding occurs during the device operation. In this work, the static and kinetic friction characteristics of oxidized Si NWs deposited on thermally grown SiO2 and chemical vapor-deposited single layer graphene were investigated using an atomic force microscope (AFM). Kinetic friction between the oxidized Si NWs and the substrates was directly measured by the AFM. Static friction was also obtained from the most bent state of the NWs using the individually determined elastic moduli of the NWs from kinetic friction experiments based on elastic beam theory. Furthermore, the shear stress between the oxidized Si NWs and the substrates was estimated based on adhesive contact theory. It was found that both static and kinetic friction increased as the radius of the NWs increased. The friction of the oxidized Si NWs on the graphene substrate was found to be smaller than that on the SiO2 substrate, which suggests that chemical vapor-deposited graphene can be used as a lubricant or as a protective layer in nano-devices to reduce friction. The shear stress estimated from the kinetic friction data between the oxidized Si NWs and the SiO2 substrate ranged from 7.5 to 12.3 MPa while that between the oxidized Si NWs and the graphene substrate ranged from 4.7 to 7.0 MPa. The result also indicated that the dependence of shear stress on the radius of the NWs was not significant. These findings may provide insight into the friction characteristics of NWs.

  19. Experimental Investigation of Gas-Side Performance of a Compact Finned-Tube Heat Exchanger

    Science.gov (United States)

    Gedeon, Louis

    1959-01-01

    Heat-transfer and pressure-drop data were obtained experimentally for the gas side of a liquid-metal to air, compact finned-tube heat exchanger. The heat exchanger was fabricated from 0.185-inch Inconel tubing in an inline array. The fins were made of 310 stainless-steel- clad copper with a total thickness of 0.010 inch, and the fin pitch was 15.3 fins per inch. The liquid used as the heating medium was sodium. The heat-exchanger inlet gas temperature was varied from 5100 to 1260 R by burning JP fuel for airflow rates of 0.4 to 10.5 pounds per second corresponding to an approximate Reynolds number range of 300 to 9000. The sodium inlet temperature was held at 1400 R with the exception of a few runs taken at 1700 and 1960 R. The maximum ratio of surface temperature to air bulk temperature was 1.45. Friction-factor data with heat transfer were best represented by a single line when the density and viscosity of Reynolds number were evaluated at the average film temperature. At the lower Reynolds numbers reported, the friction data with heat transfer plotted slightly above the friction data without heat transfer. The density of the friction factor was calculated at the average bulk temperature. Heat-transfer results of this investigation were correlated by evaluating the physical properties of air (specific heat, viscosity, and thermal conductivity) at the film temperature.

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

    Directory of Open Access Journals (Sweden)

    Deepu Leander

    2011-01-01

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

  1. The Moon's near side megabasin and far side bulge

    CERN Document Server

    Byrne, Charles

    2013-01-01

    Since Luna and Lunar Orbiter photographed the far side of the Moon, the mysterious dichotomy between the face of the Moon as we see it from Earth and the side of the Moon that is hidden has puzzled lunar scientists. As we learned more from the Apollo sample return missions and later robotic satellites, the puzzle literally deepened, showing asymmetry of the crust and mantle, all the way to the core of the Moon. This book summarizes the author’s successful search for an ancient impact feature, the Near Side Megabasin of the Moon and the extensions to impact theory needed to find it. The implications of this ancient event are developed to answer many of the questions about the history of the Moon.

  2. Creep motion of a model frictional system

    CERN Document Server

    Blanc, Baptiste; Géminard, Jean-Christophe

    2011-01-01

    We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the springs we observe a reptation of the chain. We account for the average reptation velocity theoretically. The velocity of small systems exhibits a series of plateaus as a function of the incline angle. Due to elastic e ects, there exists a critical amplitude below which the reptation is expected to cease. However, rather than a full stop of the creep, we observe in numerical simulations a transition between a continuous-creep and an irregular-creep regime when the critical amplitude is approached. The latter transition is reminiscent of the transition between the continuous and the irregular compaction of granular matter submitted to periodic temperature changes.

  3. Frictional granular mechanics: A variational approach

    Energy Technology Data Exchange (ETDEWEB)

    Holtzman, R.; Silin, D.B.; Patzek, T.W.

    2009-10-16

    The mechanical properties of a cohesionless granular material are evaluated from grain-scale simulations. Intergranular interactions, including friction and sliding, are modeled by a set of contact rules based on the theories of Hertz, Mindlin, and Deresiewicz. A computer generated, three-dimensional, irregular pack of spherical grains is loaded by incremental displacement of its boundaries. Deformation is described by a sequence of static equilibrium configurations of the pack. A variational approach is employed to find the equilibrium configurations by minimizing the total work against the intergranular loads. Effective elastic moduli are evaluated from the intergranular forces and the deformation of the pack. Good agreement between the computed and measured moduli, achieved with no adjustment of material parameters, establishes the physical soundness of the proposed model.

  4. Frictionally decaying frontal warm-core eddies

    CERN Document Server

    Rubino, Angelo

    2016-01-01

    The dynamics of nonstationary, nonlinear, axisymmetric, warm-core geophysical surface frontal vortices affected by Rayleigh friction is investigated semi-analytically using the nonlinear, nonstationary reduced-gravity shallow-water equations. In this frame, it is found that vortices characterized by linear distributions of their radial velocity and arbitrary structures of their section and azimuthal velocity can be described exactly by a set of nonstationary, nonlinear coupled ordinary differential equations. The first-order problem (i.e., that describing vortices characterized by a linear azimuthal velocity field and a quadratic section) consists of a system of 4 differential equations, and each further order introduces in the system three additional ordinary differential equations and two algebraic equations. In order to illustrate the behavior of the nonstationary decaying vortices, the system's solution for the first-order and for the second-order problem is then obtained numerically using a Runge-Kutta m...

  5. Friction welding; Magnesium; Finite element; Shear test.

    Directory of Open Access Journals (Sweden)

    Leonardo Contri Campanelli

    2013-06-01

    Full Text Available Friction spot welding (FSpW is one of the most recently developed solid state joining technologies. In this work, based on former publications, a computer aided draft and engineering resource is used to model a FSpW joint on AZ31 magnesium alloy sheets and subsequently submit the assembly to a typical shear test loading, using a linear elastic model, in order to conceive mechanical tests results. Finite element analysis shows that the plastic flow is concentrated on the welded zone periphery where yield strength is reached. It is supposed that “through the weld” and “circumferential pull-out” variants should be the main failure behaviors, although mechanical testing may provide other types of fracture due to metallurgical features.

  6. Thermomechanical Modelling of Friction Stir Welding

    DEFF Research Database (Denmark)

    Hattel, Jesper Henri; Schmidt, Henrik Nikolaj Blicher; Tutum, Cem Celal

    2009-01-01

    Friction Stir Welding (FSW) is a fully coupled thermomechanical process and should in general be modelled as such. Basically, there are two major application areas of thermomechanical models in the investigation of the FSW process: i) Analysis of the thermomechanical conditions such as e.g. heat...... generation and local material deformation (often referred to as flow) during the welding process itself. ii) Prediction of the residual stresses that will be present in the joint structure post to welding. While the former in general will call for a fully-coupled thermomechanical procedure, however...... for the FSW process at hand, the heat generation must either be prescribed analytically or based on a fully coupled analysis of the welding process itself. Along this line, a recently proposed thermal-pseudo-mechanical model is presented in which the temperature dependent yield stress of the weld material...

  7. The Friction Theory for Viscosity Modeling

    DEFF Research Database (Denmark)

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

    2001-01-01

    In this work the one-parameter friction theory (f-theory) general models have been extended to the viscosity prediction and modeling of characterized oils. It is demonstrated that these simple models, which take advantage of the repulsive and attractive pressure terms of cubic equations of state...... such as the SRK, PR and PRSV, can provide accurate viscosity prediction and modeling of characterized oils. In the case of light reservoir oils, whose properties are close to those of normal alkanes, the one-parameter f-theory general models can predict the viscosity of these fluids with good accuracy. Yet......, in the case when experimental information is available a more accurate modeling can be obtained by means of a simple tuning procedure. A tuned f-theory general model can deliver highly accurate viscosity modeling above the saturation pressure and good prediction of the liquid-phase viscosity at pressures...

  8. Advanced adhesion and friction measurement system

    Science.gov (United States)

    Li, Meng; Huang, Wei; Wang, Xiaolei

    2017-03-01

    An advanced micro-force tester for investigating the micromechanical behavior of various patterned surfaces in dry and wet conditions is presented in this paper. The parallel slice-beam configuration of the tester not only eliminates the large load-dependent slope and tangential displacement at the free end that is found in a single beam system, but also performs a trans-scale deflection with high sensitivity and linearity for force sensing. Meanwhile, the simple structure is characterized by low cost, high efficiency, and ease of fabrication. An integrated nano- and micro-stage comprise the mobile table to produce a large stroke with high resolution, which is specifically required in wet adhesion testing because of the formation of a long liquid bridge. Preliminary experiments of adhesion and friction conducted using PDMS pillars with a plano-convex lens validated the feasibility of this setup.

  9. Some Hamiltonian Models of Friction II

    CERN Document Server

    Egli, Daniel

    2011-01-01

    In the present paper we consider the motion of a very heavy tracer particle in a medium of a very dense, non-interacting Bose gas. We prove that, in a certain mean-field limit, the tracer particle will be decelerated and come to rest somewhere in the medium. Friction is caused by emission of Cerenkov radiation of gapless modes into the gas. Mathematically, a system of semilinear integro-differential equations, introduced in [FSSG10], describing a tracer particle in a dispersive medium is investigated, and decay properties of the solution are proven. This work is an extension of [FGS10]; it is an extension because no weak coupling limit for the interaction between tracer particle and medium is assumed. The technical methods used are dispersive estimates and a contraction principle.

  10. Tool Forces Developed During Friction Stir Welding

    Science.gov (United States)

    Melendez, M.; Tang, W.; Schmidt, C.; McClure, J. C.; Nunes, A. C.; Murr, L. E.

    2003-01-01

    This paper will describe a technique for measuring the various forces and the torque that exist on the Friction Stir Welding pin tool. Results for various plunge depths, weld speeds, rotational speed, and tool configurations will be presented. Welds made on 6061 aluminum with typical welding conditions require a downward force of 2800 lbs. (12.5 kN) a longitudinal force in the direction of motion of 300 lbs (1.33 kN), a transverse force in the omega x v direction of 30 lbs (135 N). Aluminum 2195 under typical weld conditions requires a downward force of 3100 lbs. (1.38 kN), a longitudinal force of 920 lbs. (4.1 kN), and a transverse force of 45 lbs. (200 N) in the omega x v direction.

  11. Dynamical friction force exerted on spherical bodies

    CERN Document Server

    Esquivel, O

    2007-01-01

    We present a rigorous calculation of the dynamical friction force exerted on a spherical massive perturber moving through an infinite homogenous system of field stars. By calculating the shape and mass of the polarization cloud induced by the perturber in the background system, which decelerates the motion of the perturber, we recover Chandrasekhar's drag force law with a modified Coulomb logarithm. As concrete examples we calculate the drag force exerted on a Plummer sphere or a sphere with the density distribution of a Hernquist profile. It is shown that the shape of the perturber affects only the exact form of the Coulomb logarithm. The latter converges on small scales, because encounters of the test and field stars with impact parameters less than the size of the massive perturber become inefficient. We confirm this way earlier results based on the impulse approximation of small angle scatterings.

  12. Friction stir processing on carbon steel

    Energy Technology Data Exchange (ETDEWEB)

    Tarasov, Sergei Yu., E-mail: tsy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055, Russia and National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Melnikov, Alexander G., E-mail: melnikov-ag@tpu.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Rubtsov, Valery E., E-mail: rvy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2014-11-14

    Friction stir processing of medium carbon steel samples has been carried out using a milling machine and tools made of cemented tungsten carbide. Samples have been machined from 40 and 40X steels. The tools have been made in the shape of 5×5×1.5 mm and 3×3×1.5 mm tetrahedrons. The microstructure of stirred zone has been obtained using the smaller tool and consists of fine recrystallized 2-3 μm grains, whereas the larger tool has produced the 'onion-like' structures comprising hard quenched 'white' 500-600 MPa layers with 300-350 MPa interlayers of bainite needles. The mean values of wear intensity obtained after measuring the wear scar width were 0.02 mm/m and 0.001 mm/m for non-processed and processed samples, respectively.

  13. Frictional granular mechanics: A variational approach

    Energy Technology Data Exchange (ETDEWEB)

    Holtzman, R.; Silin, D.B.; Patzek, T.W.

    2009-10-16

    The mechanical properties of a cohesionless granular material are evaluated from grain-scale simulations. Intergranular interactions, including friction and sliding, are modeled by a set of contact rules based on the theories of Hertz, Mindlin, and Deresiewicz. A computer generated, three-dimensional, irregular pack of spherical grains is loaded by incremental displacement of its boundaries. Deformation is described by a sequence of static equilibrium configurations of the pack. A variational approach is employed to find the equilibrium configurations by minimizing the total work against the intergranular loads. Effective elastic moduli are evaluated from the intergranular forces and the deformation of the pack. Good agreement between the computed and measured moduli, achieved with no adjustment of material parameters, establishes the physical soundness of the proposed model.

  14. Wake flow behind two side-by-side square cylinders

    Energy Technology Data Exchange (ETDEWEB)

    Yen, Shun C., E-mail: scyen@mail.ntou.edu.t [Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, Keelung 202, Taiwan (China); Liu, Jung H. [Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, Keelung 202, Taiwan (China)

    2011-02-15

    This study investigates the flow structures, form drag coefficients and vortex-shedding characteristics behind a single-square cylinder and two side-by-side cylinders in an open-loop wind tunnel. The Reynolds number (Re) and gap ratio (g*) are 2262 < Re < 28,000 and 0 {<=} g* {<=} 12, respectively. The flow patterns around the square cylinders are determined using the smoke-wire scheme. Experimental results indicate that the flow structures behind two side-by-side square cylinders are classified into three modes -single mode, gap-flow mode and couple vortex-shedding. The gap-flow mode displays anti-phase vortex shedding induced from the interference between the two square cylinders. However, the couple vortex-shedding mode exhibits in-phase vortex shedding that is caused by the independent flow behavior behind each square cylinder. The surface-pressure profile, form drag coefficient for each square cylinder (C{sub D}-bar) and vortex-shedding frequency were measured and calculated using a pressure transducer and a hot-wire anemometer. For two side-by-side cylinder configurations, the maximum C{sub D}-bar of 2.24 occurs in the single mode, while the minimum C{sub D}-bar of 1.68 occurs in the gap-flow mode. Additionally, the C{sub D}-bar in the coupled vortex-shedding mode is intermediate and approximately equal to that of a single (isolated) square cylinder. Moreover, the single mode has the highest Strouhal number (St) and the gap-flow mode has the lowest St.

  15. Effect of friction time on the properties of friction welded YSZ‐alumina composite and 6061 aluminium alloy

    Directory of Open Access Journals (Sweden)

    Uday M. Basheer

    2012-03-01

    Full Text Available The aim of this work was to study the effect of friction time on the microstructure and mechanical properties of alumina 0, 25, 50 wt% yttria stabilized zirconia (YSZ composite and 6061 aluminium alloy joints formed by friction welding. The alumina-YSZ composites were prepared through slip casting in plaster of Paris molds (POP and subsequently sintered at 1600°C, while the aluminium rods were machined down using a lathe machine to the dimension required. The welding process was carried out under different rotational speeds and friction times, while friction force (0.5 ton-force was kept constant. Scanning electron microscopy was used to characterize the interface of the joints structure. The experimental results showed that the friction time has a significant effect on joint structure and mechanical properties.

  16. Friction Stir Welding of very thin plates

    Directory of Open Access Journals (Sweden)

    Ivan Galvão

    2012-03-01

    Full Text Available The results obtained in present research, relative to friction stir welding of 1 mm thick plates of aluminium, copper, copper-zinc and zinc alloys, prove that the application of the process in the joining of very thin plates is feasible and desirable. In fact, independently of the base material, the welds produced presented very good morphological characteristics and significant grain refinement in the nugget. Tensile and hardness tests proved that all the welds were at least in even-match relative to the base material properties. Based on the AA 5182 aluminium alloy results it was also possible to conclude that augmenting the welding speed, which improves process productivity, increases grain refinement in the nugget, improving the mechanical properties of the welds.Os resultados obtidos no presente estudo, referentes a friction stir welding de chapas de alumínio, cobre, cobre-zinco e zinco com 1 mm de espessura, provam que a aplicação desta tecnologia para a ligação de chapas muito finas é possível e desejável. De fato, independentemente do material de base, as soldas produzidas apresentaram características morfológicas muito boas e um significativo refinamento do grão na zona do nugget. Ensaios de dureza e tração provaram que todas as soldas apresentavam, no mínimo, propriedades mecânicas semelhantes às dos materiais de base. Com base nos resultados da liga de alumínio AA 5182 foi também possível concluir que ao aumentar a velocidade de soldagem, o que melhora a produtividade do processo, aumenta-se o refinamento do grão no nugget, melhorando as propriedades mecânicas das soldas.

  17. Brushless machine having ferromagnetic side plates and side magnets

    Science.gov (United States)

    Hsu, John S

    2012-10-23

    An apparatus is provided having a cylindrical stator and a rotor that is spaced from a stator to define an annular primary air gap that receives AC flux from the stator. The rotor has a plurality of longitudinal pole portions disposed parallel to the axis of rotation and alternating in polarity around a circumference of the rotor. Each longitudinal pole portion includes portions of permanent magnet (PM) material and at least one of the longitudinal pole portions has a first end and an opposing second end and a side magnet is disposed adjacent the first end and a side pole is disposed adjacent the second end.

  18. Static and kinetic friction characteristics of nanowire on different substrates

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyun-Joon [Department of Precision Mechanical Engineering, Kyungpook National University, Sangju 37224 (Korea, Republic of); Nguyen, Gia Hau; Ky, Dinh Le Cao; Tran, Da Khoa [School of Mechanical Engineering, University of Ulsan, Ulsan 44610 (Korea, Republic of); Jeon, Ki-Joon [Department of Environmental Engineering, Inha University, Incheon 22212 (Korea, Republic of); Chung, Koo-Hyun, E-mail: khchung@ulsan.ac.kr [School of Mechanical Engineering, University of Ulsan, Ulsan 44610 (Korea, Republic of)

    2016-08-30

    Highlights: • Direct measurement of kinetic friction of oxidized Si NW using AFM. • Determination of static friction of oxidized Si NW from most bent state. • Friction characteristics of oxidized Si NW on SiO{sub 2} and graphene. • Estimation of shear stress between cylindrical NW and flat substrate. • No significant dependence of shear stress on NW radius. - Abstract: Friction characteristics of nanowires (NWs), which may be used as building blocks for nano-devices, are crucial, especially for cases where contact sliding occurs during the device operation. In this work, the static and kinetic friction characteristics of oxidized Si NWs deposited on thermally grown SiO{sub 2} and chemical vapor-deposited single layer graphene were investigated using an atomic force microscope (AFM). Kinetic friction between the oxidized Si NWs and the substrates was directly measured by the AFM. Static friction was also obtained from the most bent state of the NWs using the individually determined elastic moduli of the NWs from kinetic friction experiments based on elastic beam theory. Furthermore, the shear stress between the oxidized Si NWs and the substrates was estimated based on adhesive contact theory. It was found that both static and kinetic friction increased as the radius of the NWs increased. The friction of the oxidized Si NWs on the graphene substrate was found to be smaller than that on the SiO{sub 2} substrate, which suggests that chemical vapor-deposited graphene can be used as a lubricant or as a protective layer in nano-devices to reduce friction. The shear stress estimated from the kinetic friction data between the oxidized Si NWs and the SiO{sub 2} substrate ranged from 7.5 to 12.3 MPa while that between the oxidized Si NWs and the graphene substrate ranged from 4.7 to 7.0 MPa. The result also indicated that the dependence of shear stress on the radius of the NWs was not significant. These findings may provide insight into the friction characteristics

  19. Processing and Optimization of Dissimilar Friction Stir Welding of AA 2219 and AA 7039 Alloys

    Science.gov (United States)

    Venkateswarlu, D.; Nageswara rao, P.; Mahapatra, M. M.; Harsha, S. P.; Mandal, N. R.

    2015-12-01

    The present paper discusses the optimization of dissimilar friction stir welding of AA 2219 and AA 7039 alloys with respect to tool design issues including microstructural study of weld. The optimized ultimate tensile strength was ~280 MPa, and % elongation was ~11.5. It was observed that the extent of tool shoulder flat surface and tool rotational speed influenced the weld quality significantly. A mathematical model was also developed using response surface regression analysis to predict the effects of tool geometry and process variables on dissimilar AA 2219 and AA 7039 alloys welds. The microstructure evolution and mechanical properties were investigated by employing electron backscatter diffraction technique, Vickers microhardness, and tensile testing, respectively. The microstructural observations indicated that the grain size obtained at advancing side (AA 2219 alloy side) was much finer compared to the retreating side (AA 7039 alloy side). Hardness distribution in the stir zone was inhomogeneous, which might be due to inadequate mixing of weld zone material. The hardness values observed at the weld zone were lower than that in the base materials.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-15

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

  1. Friction compensation design based on state observer and adaptive law for high-accuracy positioning system

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Friction is one of the main factors that affect the positioning accuracy of motion system. Friction compensation based on friction model is usually adopted to eliminate the nonlinear effect of friction. This paper presents a proportional-plus-derivative (PD) feedback controller with a friction compensator based on LuGre friction model. We also design a state observer to observe the unknown state of LuGre friction model, and adopt a parameter adaptive law and off-line approximation to estimate the parameters of LuGre friction model. Comparative experiments are carried out among our proposed controller, PD controller with friction compensation based on classical friction model, and PD controller without friction compensation. Experimental results demonstrate that our proposed controller can achieve better performance, especially higher positioning accuracy.

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

    Science.gov (United States)

    Sang, Yi; Dubé, Martin; Grant, Martin

    2008-03-01

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

  3. Giant and Tunable Anisotropy of Nanoscale Friction in Graphene

    Science.gov (United States)

    Almeida, Clara M.; Prioli, Rodrigo; Fragneaud, Benjamin; Cançado, Luiz Gustavo; Paupitz, Ricardo; Galvão, Douglas S.; de Cicco, Marcelo; Menezes, Marcos G.; Achete, Carlos A.; Capaz, Rodrigo B.

    2016-08-01

    The nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction forces in graphene are highly dependent on the scanning direction: under some conditions, the energy dissipated along the armchair direction can be 80% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations.

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

    Science.gov (United States)

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

    2015-05-01

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

  5. Gaseous Dynamical Friction in Presence of Black Hole Radiative Feedback

    Science.gov (United States)

    Park, KwangHo; Bogdanović, Tamara

    2017-04-01

    Dynamical friction is thought to be a principal mechanism responsible for orbital evolution of massive black holes (MBHs) in the aftermath of galactic mergers and an important channel for formation of gravitationally bound MBH binaries. We use 2D radiative hydrodynamic simulations to investigate the efficiency of dynamical friction in the presence of radiative feedback from an MBH moving through a uniform density gas. We find that ionizing radiation that emerges from the innermost parts of the MBH’s accretion flow strongly affects the dynamical friction wake and renders dynamical friction inefficient for a range of physical scenarios. MBHs in this regime tend to experience positive net acceleration, meaning that they speed up, contrary to the expectations for gaseous dynamical friction in absence of radiative feedback. The magnitude of this acceleration is however negligibly small and should not significantly alter the velocity of MBHs over relevant physical timescales. Our results suggest that suppression of dynamical friction is more severe at the lower mass end of the MBH spectrum which, compounded with inefficiency of the gas drag for lower mass objects in general, implies that <107 {M}ȯ MBHs have fewer means to reach the centers of merged galaxies. These findings provide formulation for a sub-resolution model of dynamical friction in presence of MBH radiative feedback that can be easily implemented in large scale simulations.

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

    Science.gov (United States)

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

    1996-04-01

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

  7. Influence of rolling friction on single spout fluidized bed simulation

    Institute of Scientific and Technical Information of China (English)

    Christoph Goniva; Christoph Kloss; Niels G. Deen; Johannes A. M. Kuipers; Stefan Pirker

    2012-01-01

    In this paper we study the effect of rolling friction on the dynamics in a single spout fluidized bed using Discrete Element Method (DEM) coupled to Computational Fluid Dynamics (CFD).In a first step we neglect rolling friction and show that the results delivered by the open source CFD-DEM framework applied in this study agree with previous simulations documented in literature.In a second step we include a rolling friction sub-model in order to investigate the effect of particle non-sphericity.The influence of particle-particle as well as particle-wall rolling friction on the flow in single spout fluidized bed is studied separately.Adequate rolling friction model parameters are obtained using first principle DEM simulations and data from literature.Finally,we demonstrate the importance of correct modelling of rolling friction for coupled CFD-DEM simulations of spout fluidized beds.We show that simulation results can be improved significantly when applying a rolling friction model,and that experimental data from literature obtained with Positron Emission Particle Tracking (PEPT) technique can be satisfactorily reproduced.

  8. In-process discontinuity detection during friction stir welding

    Science.gov (United States)

    Shrivastava, Amber

    The objective of this work is to develop a method for detecting the creation of discontinuities (e.g., voids) during friction stir welding. Friction stir welding is inherently cost-effective, however, the need for significant weld inspection can make the process cost-prohibitive. A new approach to weld inspection is required -- where an in-situ characterization of weld quality can be obtained, reducing the need for post-process inspection. Friction stir welds with discontinuity and without discontinuity were created. In this work, discontinuities are generated by reducing the friction stir tool rotation frequency and increasing the tool traverse speed in order to create "colder" welds. During the welds, forces are measured. Discontinuity sizes for welds are measured by computerized tomography. The relationship between the force transients and the discontinuity sizes indicate that the force measurement during friction stir welding can be effectively used for detecting discontinuities in friction stir welds. The normalized force transient data and normalized discontinuity size are correlated to develop a criterion for discontinuity detection. Additional welds are performed to validate the discontinuity detection method. The discontinuity sizes estimated by the force measurement based method are in good agreement with the discontinuity sizes measured by computerized tomography. These results show that the force measurement based discontinuity detection model method can be effectively used to detect discontinuities during friction stir welding.

  9. Friction and Wear Behaviors of Nano-Silicates in Water

    Institute of Scientific and Technical Information of China (English)

    Chen Boshui; Lou Fang; Fang Jianhua; Wang Jiu; Li Jia

    2009-01-01

    Nano-metric magnesium silicate and zinc silicate with particle size of about 50--70nm were prepared in water by the method of chemical deposition. The antiwear and friction reducing abilities of the nano-silicates, as well as their compos-ites with oleie acid tri-ethanolamine (OATEA), were evaluated on a four-ball friction tester. The topographies and tribochemical features of the worn surfaces were analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). Results show that nano-silicates alone provide poor antiwear and friction reducing abilities in water, but exhibits excellent synergism with OATEA in reducing friction and wear. The synergism in reducing friction and wear between naao-silicates and OATEA does exist almost regardless of particle sizes and species, and may be attributed, on one hand, to the formation of an adsorption film of OATEA, and, on the other hand, to the formation oftdbochemical species of silicon dioxide and iron oxides on the friction surfaces. Tribo-reactions and tribo-adsorptions of nano-silicates and OATEA would produce hereby an effective composite boondary lubrication film, which could efficiently enhance the anti-wear and friction-reducing abilities of water.

  10. Social identity performance : Extending the strategic side of SIDE

    NARCIS (Netherlands)

    Klein, Olivier; Spears, Russell; Reicher, Stephen

    This article extends the social identity model of deindividuation effects (SIDE) by considering the various ways in which relations of visibility to an audience can affect the public expression of identity-relevant norms (identity performance). It is suggested that social identity performance can

  11. Side Effects of Side Effects Information in Drug Information Leaflets.

    Science.gov (United States)

    Maat, H. Pander; Klaassen, R.

    1994-01-01

    Describes a study in which drug information leaflets given to patients were improved in two ways, first by adding a short introductory paragraph on the nature of side effects generally, and second by adjusting frequency descriptors to more accurately reflect pretesting of the drug. Explains that participants in the study were less likely to…

  12. Running away from side effects

    DEFF Research Database (Denmark)

    Casla, S; Hojman, P; Márquez-Rodas, I

    2015-01-01

    be an integrative complementary intervention to improve physiological, physical and psychological factors that affect survival and quality of life of these patients. For that reason, the main objective of this review is to provide a general overview of exercise benefits in breast cancer patients and recommendations......The number of breast cancer survivors increases every year, thanks to the development of new treatments and screening techniques. However, patients present with numerous side effects that may affect their quality of life. Exercise has been demonstrated to reduce some of these side effects......, but in spite of this, few breast cancer patients know and follow the exercise recommendations needed to remain healthy. In this review, we describe the different breast cancer treatments and the related side effects and implications of exercise in relation to these. We propose that exercise could...

  13. Efficacy of 15% trichloroacetic acid and 50% glycolic acid peel in the treatment of frictional melanosis: A comparative study

    Directory of Open Access Journals (Sweden)

    S Sacchidanand

    2015-01-01

    Full Text Available Background: Frictional dermal melanosis is aesthetically displeasing. Various modalities ranging from depigmenting agents to lasers have been tried but it continues to be a difficult problem to treat. Objective: To study and compare the efficacy of 15% trichloroacetic acid (TCA and 50% glycolic acid in the treatment of frictional melanosis of the forearm. Materials and Methods: 40 patients of frictional melanosis of the forearm were included in the study. Patients were randomly divided into two equal groups A and B. Pre-peel priming was carried out with 12% glycolic acid and sunscreen for 2 weeks. Group A was treated with trichloroacetic acid (TCA-15% peel and Group B with glycolic acid (GA-50% peel. Four peels were done one every 15 days. Clinical photographs were taken to assess the response. Response to therapy was evaluated by both objective and subjective methods. The patients were followed up for 3 months after the last peel to note any relapse. Results: Both TCA and glycolic acid peels were effective in frictional melanosis. TCA showed better response compared to glycolic acid at the end of the treatment, both by subjective and objective methods. However, this difference was not statistically significant (P > 0.05. No permanent side effects were seen in any of the treated patients and the improvement was sustained without any relapse at 3 months. Conclusion: Chemical peeling with both tricholoroacetic acid (15% and glycolic acid (50% is safe and effective for the treatment of frictional dermal melanosis. Tricholoroacetic acid was found to be marginally superior to glycolic acid.

  14. Microstructural characterization in dissimilar friction stir welding between 304 stainless steel and st37 steel

    Energy Technology Data Exchange (ETDEWEB)

    Jafarzadegan, M. [Department of Materials Eng., Tarbiat Modares University, P.O. Box: 14115-143, Tehran (Iran, Islamic Republic of); State Key Laboratory of Advanced Welding Production Technology, School of Materials Science and Eng., Harbin Institute of Technology, P.O. Box: 150001, Harbin (China); Feng, A.H. [State Key Laboratory of Advanced Welding Production Technology, School of Materials Science and Eng., Harbin Institute of Technology, P.O. Box: 150001, Harbin (China); Abdollah-zadeh, A., E-mail: zadeh@modares.ac.ir [Department of Materials Eng., Tarbiat Modares University, P.O. Box: 14115-143, Tehran (Iran, Islamic Republic of); Saeid, T. [Advanced Materials Research Center, Sahand University of Technology, P.O. Box: 51335-1996, Tabriz (Iran, Islamic Republic of); Shen, J. [State Key Laboratory of Advanced Welding Production Technology, School of Materials Science and Eng., Harbin Institute of Technology, P.O. Box: 150001, Harbin (China); Assadi, H. [Department of Materials Eng., Tarbiat Modares University, P.O. Box: 14115-143, Tehran (Iran, Islamic Republic of)

    2012-12-15

    In the present study, 3 mm-thick plates of 304 stainless steel and st37 steel were welded together by friction stir welding at a welding speed of 50 mm/min and tool rotational speed of 400 and 800 rpm. X-ray diffraction test was carried out to study the phases which might be formed in the welds. Metallographic examinations, and tensile and microhardness tests were used to analyze the microstructure and mechanical properties of the joint. Four different zones were found in the weld area except the base metals. In the stir zone of the 304 stainless steel, a refined grain structure with some features of dynamic recrystallization was evidenced. A thermomechanically-affected zone was characterized on the 304 steel side with features of dynamic recovery. In the other side of the stir zone, the hot deformation of the st37 steel in the austenite region produced small austenite grains and these grains transformed to fine ferrite and pearlite and some products of displacive transformations such as Widmanstatten ferrite and martensite by cooling the material after friction stir welding. The heat-affected zone in the st37 steel side showed partially and fully refined microstructures like fusion welding processes. The recrystallization in the 304 steel and the transformations in the st37 steel enhanced the hardness of the weld area and therefore, improved the tensile properties of the joint. - Highlights: Black-Right-Pointing-Pointer FSW produced sound welds between st37 low carbon steel and 304 stainless steel. Black-Right-Pointing-Pointer The SZ of the st37 steel contained some products of allotropic transformation. Black-Right-Pointing-Pointer The material in the SZ of the 304 steel showed features of dynamic recrystallization. Black-Right-Pointing-Pointer The finer microstructure in the SZ increased the hardness and tensile strength.

  15. Scale effects in sliding friction: An experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Blau, P.J.

    1991-07-24

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

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

    Science.gov (United States)

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

    2013-01-01

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

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

    Science.gov (United States)

    Jang, Bo-An

    2016-04-01

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

  18. A Typology of Multi-sided Platforms

    DEFF Research Database (Denmark)

    Staykova, Kalina Stefanova; Damsgaard, Jan

    2015-01-01

    which evolved several steps into being multi-sided (Facebook). Our analysis shows a structural difference between one-sided, two-sided and multi-sided platforms and that platforms consist of a core and potentially also a periphery. The sides of a platform and the ties which connect them can be arranged...

  19. Dark Side of the Universe

    CERN Document Server

    2016-01-01

    The Dark Side of the Universe (DSU) workshops bring together a wide range of theorists and experimentalists to discuss current ideas on models of the dark side, and relate them to current and future experiments. This year's DSU will take place in the colorful Norwegian city of Bergen. Topics include dark matter, dark energy, cosmology, and physics beyond the standard model. One of the goals of the workshop is to expose in particular students and young researchers to the fascinating topics of dark matter and dark energy, and to provide them with the opportunity to meet some of the best researchers in these areas .

  20. The Dark Side of Management

    DEFF Research Database (Denmark)

    Hanlon, Gerard; Dunne, Stephen; Johnsen, Christian Garmann

    2017-01-01

    Towards the end of 2015, the ephemera collective organised, chaired and participated within two separate Q+A panels celebrating the launch of Gerard Hanlon’s The dark side of management: A secret history of management theory. The events took place in The University of Leicester’s School of Manage......Towards the end of 2015, the ephemera collective organised, chaired and participated within two separate Q+A panels celebrating the launch of Gerard Hanlon’s The dark side of management: A secret history of management theory. The events took place in The University of Leicester’s School...

  1. A new Friction and Lubrication Test for Cold Forging

    DEFF Research Database (Denmark)

    Bay, Niels; Wibom, Ole; Aalborg Nielsen, J

    1995-01-01

    This paper presents a new friction and lubrication test for cold forging. The test allows controlled variation of the surface expansion in the range 0-2000%, the tool temperature in the range 20-270°C and the sliding length between 0 and infinite. Friction is decreasing with increasing temperature...... in the range 30-150°C. Above this temperature range friction increases. As regards lubricant performance Lubrication Limit Curves (LLC) are plotted in a sliding length-surface enlargement diagram with the tool temperature as a parameter. Larger tool temperature implies lower acceptable surface expansion...

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

    Science.gov (United States)

    1992-11-01

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

  3. Data-driven algorithm to estimate friction in automobile engine

    DEFF Research Database (Denmark)

    Stotsky, Alexander A.

    2010-01-01

    Algorithms based on the oscillations of the engine angular rotational speed under fuel cutoff and no-load were proposed for estimation of the engine friction torque. The recursive algorithm to restore the periodic signal is used to calculate the amplitude of the engine speed signal at fuel cutoff....... The values of the friction torque in the corresponding table entries are updated at acquiring new measurements of the friction moment. A new, data-driven algorithm for table adaptation on the basis of stepwise regression was developed and verified using the six-cylinder Volvo engine....

  4. Viscosity Prediction of Natural Gas Using the Friction Theory

    DEFF Research Database (Denmark)

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

    2002-01-01

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

  5. On the origin of Amonton’s friction law

    DEFF Research Database (Denmark)

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

    2008-01-01

    Amonton's law states that the sliding friction force increases linearly with the load. We show that this result is expected for stiff enough solids, even when the adhesional interaction between the solids is included in the analysis. As a function of the magnitude of the elastic modulus E, one can...... on the load and is non-vanishing at zero load. In this last case a finite pull-off force is necessary in order to separate the solids. Based on molecular dynamics calculations, we also discuss the pressure dependence of the frictional shear stress for polymers. We show that the frictional shear stress...

  6. Friction Stir Spot Welding of Advanced High Strength Steels

    Energy Technology Data Exchange (ETDEWEB)

    Hovanski, Yuri; Grant, Glenn J.; Santella, M. L.

    2009-11-13

    Friction stir spot welding techniques were developed to successfully join several advanced high strength steels. Two distinct tool materials were evaluated to determine the effect of tool materials on the process parameters and joint properties. Welds were characterized primarily via lap shear, microhardness, and optical microscopy. Friction stir spot welds were compared to the resistance spot welds in similar strength alloys by using the AWS standard for resistance spot welding high strength steels. As further comparison, a primitive cost comparison between the two joining processes was developed, which included an evaluation of the future cost prospects of friction stir spot welding in advanced high strength steels.

  7. Semi-Active Friction Damping of Large Space Truss Structures

    Directory of Open Access Journals (Sweden)

    L. Gaul

    2004-01-01

    Full Text Available The present approach for vibration suppression of flexible structures is based on friction damping in semi-active joints. At optimal locations conventional rigid connections of a large truss structure are replaced by semi-active friction joints. Two different concepts for the control of the normal forces in the friction interfaces are implemented. In the first approach each semi-active joint has its own local feedback controller, whereas the second concept uses a global, clipped-optimal controller. Simulation results of a 10-bay truss structure show the potential of the proposed semi-active concept.

  8. Applications of Friction Stir Processing during Engraving of Soft Materials

    Directory of Open Access Journals (Sweden)

    V. Kočović

    2015-12-01

    Full Text Available Friction stir processing has extensive application in many technological operations. Application area of friction stir processing can be extended to the processing of non-metallic materials, such as wood. The paper examines the friction stir processing contact between a specially designed hard and temperature-resistant rotating tool and workpiece which is made of wood. Interval of speed slip and temperature level under which the combustion occurs and carbonization layer of soft material was determined. The results of the research can be applied in technological process of wood engraving operations which may have significant technological and aesthetic effects.

  9. Electronic contribution to friction on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Applied Science and Technology Graduate Group, UC Berkeley; Dept. of Materials Sciences and Engineering, UC Berkeley; Salmeron, Miquel; Qi, Yabing; Park, J.Y.; Hendriksen, B.L.M.; Ogletree, D.F.; Salmeron, Miquel

    2008-04-15

    The electronic contribution to friction at semiconductor surfaces was investigated by using a Pt-coated tip with 50nm radius in an atomic force microscope sliding against an n-type GaAs(100) substrate. The GaAs surface was covered by an approximately 1 nm thick oxide layer. Charge accumulation or depletion was induced by the application of forward or reverse bias voltages. We observed a substantial increase in friction force in accumulation (forward bias) with respect to depletion (reverse bias). We propose a model based on the force exerted by the trapped charges that quantitatively explains the experimental observations of excess friction.

  10. Physically representative atomistic modeling of atomic-scale friction

    Science.gov (United States)

    Dong, Yalin

    Nanotribology is a research field to study friction, adhesion, wear and lubrication occurred between two sliding interfaces at nano scale. This study is motivated by the demanding need of miniaturization mechanical components in Micro Electro Mechanical Systems (MEMS), improvement of durability in magnetic storage system, and other industrial applications. Overcoming tribological failure and finding ways to control friction at small scale have become keys to commercialize MEMS with sliding components as well as to stimulate the technological innovation associated with the development of MEMS. In addition to the industrial applications, such research is also scientifically fascinating because it opens a door to understand macroscopic friction from the most bottom atomic level, and therefore serves as a bridge between science and engineering. This thesis focuses on solid/solid atomic friction and its associated energy dissipation through theoretical analysis, atomistic simulation, transition state theory, and close collaboration with experimentalists. Reduced-order models have many advantages for its simplification and capacity to simulating long-time event. We will apply Prandtl-Tomlinson models and their extensions to interpret dry atomic-scale friction. We begin with the fundamental equations and build on them step-by-step from the simple quasistatic one-spring, one-mass model for predicting transitions between friction regimes to the two-dimensional and multi-atom models for describing the effect of contact area. Theoretical analysis, numerical implementation, and predicted physical phenomena are all discussed. In the process, we demonstrate the significant potential for this approach to yield new fundamental understanding of atomic-scale friction. Atomistic modeling can never be overemphasized in the investigation of atomic friction, in which each single atom could play a significant role, but is hard to be captured experimentally. In atomic friction, the

  11. Side-View Face Recognition

    NARCIS (Netherlands)

    Santemiz, Pinar; Spreeuwers, Luuk J.; Veldhuis, Raymond N.J.; Biggelaar , van den Olivier

    2011-01-01

    As a widely used biometrics, face recognition has many advantages such as being non-intrusive, natural and passive. On the other hand, in real-life scenarios with uncontrolled environment, pose variation up to side-view positions makes face recognition a challenging work. In this paper we discuss th

  12. The DarkSide Program

    Directory of Open Access Journals (Sweden)

    Rossi B.

    2016-01-01

    Full Text Available DarkSide-50 at Gran Sasso underground laboratory (LNGS, Italy, is a direct dark matter search experiment based on a liquid argon TPC. DS-50 has completed its first dark matter run using atmospheric argon as target. The detector performances and the results of the first physics run are presented in this proceeding.

  13. The Human Side of Libraries.

    Science.gov (United States)

    Surace, Cecily J.

    This paper discusses current trends in personnel management, with emphasis on performance standards and employee evaluation. Advances in personnel management from the scientific management theory to the application of the "human side of enterprise" approach should be reflected in how library managers review personnel and operate their libraries.…

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

    Science.gov (United States)

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

    2010-06-01

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

  15. Modeling of the voltage-controlled friction effect

    Institute of Scientific and Technical Information of China (English)

    孟永钢; 蒋洪军; 常秋英; 黄柏林

    2002-01-01

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

  16. Ultrahigh interlayer friction in multiwalled boron nitride nanotubes.

    Science.gov (United States)

    Niguès, A; Siria, A; Vincent, P; Poncharal, P; Bocquet, L

    2014-07-01

    Friction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons-Coulomb. Here, by using a 'Christmas cracker'-type of system in which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF-AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing surfaces.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-05-15

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

  18. Talc as friction reducing additive to lubricating oil

    Science.gov (United States)

    Rudenko, Pavlo; Bandyopadhyay, Amit

    2013-07-01

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

  19. 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...

  20. In-Space Friction Stir Welding Machine Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Longhurst Engineering, PLC, and Vanderbilt University propose an in-space friction stir welding (FSW) machine for joining complex structural aluminum components. The...