Friction Force Changes Research Articles

Molecular dynamics simulations of atomic-scale tribology between amorphous DLC and Si-DLC films

Silicon-doped diamond-like carbon (Si-DLC) films possess the potential to improve wear performance of DLC films in humid atmospheres and at higher temperatures. But many experimental results of Si-DLC films show that their structures and tribological properties changed greatly with silicon content. Therefore, molecular dynamics (MD) simulations were used to study the sliding friction process between DLC and Si-DLC films on un-lubricated boundary condition. The results show that a part of sp 2 bonding of the Si-DLC films is converted into sp 3 bonding with the addition of silicon atoms, and the sp 3/sp 2 ratio increases with the increase in silicon content. A transfer film between the DLC and Si-DLC films is formed and the friction force changes with the silicon content. Moreover, the simulations have showed that the silicon addition promotes the bonding of interfilms being formed.

Deformation Characteristics of Fine Protrusions Formed by Sputter-Etching of Stainless Steels

Sputter-etching was applied to type 303, 304, 430 and 420 stainless steels to form conical or ring-shaped protrusions on the surface, and the tensile test of the substrate with protrusions, the press and scratch tests of protrusions were carried out. The tensile test shows that the conical protrusion is ductile, and the delamination and dropping out of the protrusions from substrate never occur before fracture of the substrate. The press test of the protrusions reveals that the conical protrusion is so strong to form deep hole on the counter rod of aluminum alloy although the tip of the protrusion is flattened. The scratch test of the surface with conical protrusions shows a large change of friction force with increasing scratch distance, whereas relatively small change of friction force for ring-shaped protrusions due to a smaller height and a narrow space between each ring wall. The maximum scratch force for a typical conical protrusion is about 40mN.

405 摩擦斜面を用いた小型三次元免震装置の研究(免震II,OS-2 耐震・免震・制震,総合テーマ「伝統を,未来へ!」)

This paper deals with research of new compact isolation device with reduction of horizontal relative displacement by using friction force and reduction of vertical response acceleration and relative displacement by using spring and friction force. The isolation device is using a friction surface. The friction surface is subjected to acts on the slope plate. The restoring-force of horizontal direction is given to the isolation device from elastic force of a compression spring attached to the base. In the equation of motion of analytical model, the friction force changes in proportion to displacement. The restoring-force is also proportional to displacement. The restoring-force always works in the direction of a center. The restoring-force of the vertical direction is given to the isolation device from compression springs and draft springs. Condition reducing both response acceleration and displacement effectively is calculated on various conditions using the analysis model. Furthermore, an experiment is conducted using the experimental device. The results the experiment are compared with the results of the analysis. The performance of the isolation device is examined.

Finite Element Modeling and Analysis of Friction Wedge Damping During Suspension Bounce Modes

A two-dimensional finite element model (2D FEM) has been developed to improve the modeling and understanding of the friction damping characteristics of freight bogie suspensions. The specific suspension considered utilizes friction dampers with constant preload force as are widely used in three-piece bogie wagons in Australia. Unlike simpler models commonly used in rail vehicle dynamics, the FE model developed can accommodate distributed normal forces across the wedge surfaces. The model was tested in bounce modes and compared with the normal equations used to model wedge friction forces, which treat the forces on the wedge as a static problem. The simulation results using the 2D FEM model showed that the friction damping force is not constant and changes when the suspension is in motion. It was also shown that the force changes magnitude during the loading and unloading situations. The factors, which affect the change in friction force, are the friction characteristics on wedge contact surfaces, the direction and change in tangent force on wedge angular surface, the elastic deformation of the wedge, the wedge relative movement, and the wedge structure arrangement. The FE model assumptions are investigated and insights on wedge friction and creepage discussed.

522 小型免震装置の開発

This paper deals with research of new compact isolation device with reduction of horizontal relative displacement by using friction force and reduction of vertical response acceleration and relative displacement by using spring and friction force. The isolation device is using a friction surface. The friction surface is subjected to acts on the slope plate. The restoring-force of horizontal direction is given to the isolation device from elastic force of a compression spring attached to the base. In the equation of motion of analytical model, the friction force changes in proportion to displacement. The restoring-force is also proportional to displacement. The restoring-force always works in the direction of a center. The restoring-force of the vertical direction is given to the isolation device from compression springs and draft springs. Condition reducing both response acceleration and displacement effectively is calculated on various conditions using the analysis model. Furthermore, an experiment is conducted using the experimental device. The results the experiment are compared with the results of the analysis. The performance of the isolation device is examined.

Measurement of Normal Pressures and Friction Forces Acting on Buried Pipes Subjected to Cyclic Axial Displacements in Laboratory Experiments

Abstract The earth pressure acting on buried pipes is decisive for the pipe design. For pipes shifting in the ground, such as district heating pipes, which are subjected to cyclic temperature loading, the mobilizable friction force, which is also dependent on the earth pressure load, is a very important quantity. Friction force changes with cyclic axial displacement of a pipeline in operation. A special testing device was designed to investigate the friction forces and the normal pressures on a pipe buried in sand and how these change during cyclic axial displacement dependent on system and soil parameters. The experimental setup is presented, and in particular the application of the tactile pressure sensor, the special measuring technique used, is described. The dependence of the decrease in friction force on pipe diameter, soil overburden height, and relative density of the soil was investigated in the tests. The results are presented and the findings are discussed.

Friction and wear behavior of engineering materials in a simulated Martian (CO 2) environment, a preliminary study

The friction and wear behavior of materials (primarily metals) is a strong function of operating environment. Ambient conditions provide a natural lubricating oxide on most metals that reduce friction and wear. In vacuum metals have been shown to have friction coefficients exceeding unity with significant adhesive forces. In space applications materials must be designed with adequate solid lubrication to prevent wear and seizure. In between total vacuum and STP lies the surface of Mars with a primarily CO 2 atmosphere at 10–15 Torr (∼1% earth's atm.). Recent exploration missions conducted by NASA involved a wheeled craft navigating the rocky, dusty surface (opportunity and spirit rovers). The materials used in these rovers were tested in dry nitrogen only. This preliminary study measures friction and wear behavior of several materials utilizing an atomic force microscope and a pin on disk wear tester in a controlled environment of air, CO 2 and nitrogen at 760 Torr. The objective was to demonstrate if friction and wear in CO 2 and N 2 are comparable and whether a difference can be measured. Wear surfaces were examined using scanning electron microscopy. Results indicated some change in frictional force and wear in the CO 2 atmosphere.

Study on Isolation Device for Decrease of Displacement by Using Control of Friction

This paper deals with development of new isolation device by using friction force. This isolation device carries out reduction of horizontal relative displacement by using friction force. The isolation device uses a slope plate. The Friction force acts on the slope plate. The restoring-force is given to the isolation device from the compression spring attached to the base. In the equation of motion of analytical model, the friction force changes in proportion to displacement. The restoring-force is also proportional to displacement. The restoring-force always works in the direction of a center. Therefore, the friction force and restoring-force are proportional to displacement. Simulation analysis is calculated on various conditions using the analysis model. Condition reducing both response acceleration and displacement effectively is examined. The reductions of the response acceleration and the relative displacement are shown by the simulation results. The isolation device for the experiment is designed using the analysis model.

Experimental Study on Isolation Device for Decrease of Displacement by Using Control of Friction

This paper deals with development of new isolation device by using friction force. This isolation device carries out reduction of horizontal relative displacement by using friction force. The isolation device uses a slope plate. The Friction force acts on the slope plate. The restoring-force is given to the isolation device from the compression spring attached to the base. In the equation of motion of analytical model, the friction force changes in proportion to displacement. The restoring-force is also proportional to displacement. The restoring-force always works in the direction of a center. Therefore, the friction force and restoring-force are proportional to displacement. Simulation analysis is calculated on various conditions using the analysis model. Condition reducing both response acceleration and displacement effectively is examined. Furthermore, an experiment is conducted using the experimental model. The experimental results are compared with analysis results. The performance of the isolation device is examined. The validity of the performance is shown.

Global Three‐dimensional Flow of a Neutron Superfluid in a Spherical Shell in a Neutron Star

We integrate for the first time the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov equations of motion of a 1S0-paired neutron superfluid in a rotating spherical shell, using a pseudo-spectral collocation algorithm coupled with a time-split fractional scheme. Numerical instabilities are smoothed by spectral filtering. Three numerical experiments are conducted, with the following results. (1) When the inner and outer spheres are put into steady differential rotation, the viscous torque exerted on the spheres oscillates quasi-periodically and persistently (after an initial transient). The fractional oscillation amplitude (~10-2) increases with the angular shear and decreases with the gap width. (2) When the outer sphere is accelerated impulsively after an interval of steady differential rotation, the torque increases suddenly, relaxes exponentially, then oscillates persistently as in (1). The relaxation timescale is determined principally by the angular velocity jump, whereas the oscillation amplitude is determined principally by the gap width. (3) When the mutual friction force changes suddenly from Hall-Vinen to Gorter-Mellink form, as happens when a rectilinear array of quantized Feynman-Onsager vortices is destabilized by a counterflow to form a reconnecting vortex tangle, the relaxation timescale is reduced by a factor of ~3 compared to (2), and the system reaches a stationary state in which the torque oscillates with fractional amplitude ~10-3 about a constant mean value. Preliminary scalings are computed for observable quantities such as angular velocity and acceleration as functions of the Reynolds number, angular shear, and gap width. The results are applied to the timing irregularities (e.g., glitches and timing noise) observed in radio pulsars.

Characteristic Sliding Frictional Behavior on the Surface of Nanocomposite Hydrogels Consisting of Organic‐Inorganic Network Structure

AbstractSummary: Sliding frictional behavior on the surface of novel nanocomposite hydrogels (NC gels), composed of poly(N‐isopropylacrylamide) and exfoliated clay, was investigated and compared with that of conventional chemically‐crosslinked hydrogels (OR gels). Since OR gels are so weak, the sliding test, in general, could not be carried out on their surfaces except when wet. On the contrary, NC gels can withstand sliding friction under high loading and it was found that the frictional forces are sensitive to the environmental surroundings (wet or in‐air), the gel composition (water, clay contents), and loading. In air, NC gels exhibit a characteristic force profile with a maximum static frictional force (max‐SFF) and subsequent constant dynamic frictional force. In contrast, NC gels exhibit very low frictional forces under wet conditions. The change in frictional force with surroundings was very distinctive for NC gels, particularly for those with low clay contents. Max‐SFF for NC1 gel decreased more than 100‐fold by changing the environment from in‐air to wet. The characteristic sliding frictional behaviors are explained on the basis of a unique organic/inorganic network structure of NC gels.The model of sliding process on NC gel and effects of clay content of NC gels on the sliding frictional behavior.magnified imageThe model of sliding process on NC gel and effects of clay content of NC gels on the sliding frictional behavior.

Demonstration of topography modification by friction processes and vice versa

Contact formation and development are the basis of friction and wear modelling and understanding. Unanimously topography formation and development in friction contacts are regarded of highest importance for understanding and modelling friction processes. The frequently found running in behaviour of sliding contacts is—aside from the build up of reaction and transfer layers-at least partly caused by the topography development due to friction processes until a stable equilibrium state is reached. Experimental results of friction and topography measurements are presented which demonstrate the mutual modification of friction and contact topography. A special experimental set up with an AFM allowed to correlate the measured friction forces with the contact position and the topography at this point. In this way, friction force transitions and changes can be assigned to topography changes due to abrasion, adhesion and wear particle agglomeration. Contact surfaces with artificial regular structures have been prepared to avoid problems with topography and friction correlation due to the statistical nature of roughness on technical contact surfaces. The friction effects of roughness were simulated by etched ditches of defined width, depth and distance on silicon or metal surfaces. This allowed to explain the mutual influences of topography and friction. The effect of a single ‘asperity’ and of the ‘roughness structures’ could be demonstrated. Topography measurements with an AFM correlated with the friction force could help to understand friction changes without changing any parameter.

Theoretical Analysis of Experimentally Observed Perplexing Calibration Characteristics of Ball-in-Vortex Flow-Meter

This investigation analyzes the calibration nonlinearity of the ball-in-vortex flow-meter, designed to work on the principle of a rotating sphere in and due to a vortex flow. The comparison of this flow-meter reading with the standard flow-meter indicates the existence of different calibration regimes, bifurcated by a sharp change in slope of the calibration curve. Based on the governing mechanics of this flow-meter, this paper explains this nonlinearity, and proposes its mathematical form. In particular, the bifurcation in calibration characteristics is attributed to the change in the surface contact frictional force, due to translation of the ball. The mathematical model captures the various calibration regimes associated with this translation, from one plane of rotation in the flow-meter to another, or from one periphery to another. Thus, calibration nonlinearity of this flow-meter can be fully comprehended through its governing mechanics, and harnessed for flow measurement.

Effect of water on the surface molecular mobility of poly(lactide) thin films: an atomic force microscopy study.

Physical properties associated with molecular mobility on the surface of thin films with 300 nm thickness for poly(lactide)s (PLAs) were studied under vacuum conditions as well as under aqueous conditions by using friction force mode atomic force microscopy (AFM). Two types of PLAs were applied for the experimental samples as uncrystallizable PLA (uc-PLA) and crystallizable PLA (c-PLA). The friction force on the surface of thin films was measured as a function of temperature to assess the surface molecular mobility both under vacuum and under aqueous conditions. A lower glass-transition temperature of the uc-PLA surface in water was detected than that under vacuum conditions. In the case of the c-PLA thin film, change in friction force was detected at a lower temperature under aqueous conditions than in vacuo. A morphological change was observed in the c-PLA thin film during heating process from room temperature to 100 degrees C by temperature-controlled AFM. The surface of the c-PLA thin film became rough due to the cold crystallization, and the crystallization of c-PLA molecules in water took place at a lower temperature than in vacuo. These friction force measurements and AFM observations suggest that molecular motion on the surface of the both uc- and c-PLA thin films is enhanced in the presence of water molecules. In addition, in situ AFM observation of the enzymatic degradation process for the c-PLA thin film crystallized at 160 degrees C was carried out in buffer solution containing proteinase K at room temperature. The amorphous region around the hexagonal crystal was eroded within 15 min. It has been suggested that the adsorption of water molecules on the PLA film surface enhances the surface molecular mobility of the glassy amorphous region of PLA and induces the enzymatic hydrolysis by proteinase K.

ゴルフスウィングにおけるグリップ圧力と摩擦力の測定(ゴルフ(1))

In this paper, we investigate the gripping force in golf swing, which is considered to have close relationship with performance and feeling of the club. The sensor grip using the force sensor chip was developed which can detect the gripping force in radial direction (Fz), tangential direction (Fx). and axial direction (Fy). The sensor grip was attached on the shaft of the test club and the dynamic: gripping force on some part of finger and palm in swing action was examined. Some remarkable results of change in radial and frictional force were obtained as follows. (1) Using a parallel structure plates, we were able to manufacture the reliable sensor chip. Which detects forces in radial direction, tangential direction, and axial direction. (2) In golf swing, the force changes in five periods at swing start, down swing, rist release, impact, and after impact. (3) On the left hand, large axial force is applied as a drawing force for the swing. In the right hand, large tangential force appeared as a force to control of the head face direction. (4) Near the impact, the reduction of the axial force in the left little appeared which may cause the head move straight.

The reduction of stick-slip friction in hydraulic actuators

The stick-slip friction phenomenon is observed near zero relative velocity, during the transition from static to dynamic friction, when static friction is greater than dynamic friction. This nonlinear change in friction force over a small change in velocity results in difficulties in achieving accurate and repeatable position control. In some cases, the actuator position controller reaches a limit cycle (hunting effect). Friction compensation at low speeds has traditionally been approached through various control techniques. This paper proposes an alternative solution, namely, friction avoidance. By rotating the piston and rod, the Stribeck region of the friction-velocity curve is avoided and the axial friction opposing the piston movement is approximately linearized. Simulation and experimental results are presented to validate this approach.

Effect of C60 molecular rotation on nanotribology.

The effect of C60 molecular rotation on the nanotribological properties of C60 single crystal surfaces has been studied by atomic/frictional force microscopy. The orientational order-disorder phase transition, in which the high temperature C60 free rotation is reduced to a low temperature hindered rotation, is shown to give rise to an abrupt change in friction and adhesion. This change in frictional force is quantitatively consistent with the observed change in adhesion. The similar slopes of the friction versus load curves in both phases indicate that the friction coefficient in the two phases remains about the same. Hence the C60 rotation does not provide an additional energy dissipation channel in the friction process.

19S ゴルフスイングにおけるグリップ力の測定

In this paper, we investigate the gripping force of golf which is considered to have close relationship with performance and feeling of the club. The force sensor cell composed by bridge structure featured small light and strain gages was newly designed in order to detect the gripping force in golf swing. The sensor grip using the force sensor cell was developed which can detect the gripping force in radial direction (Fz), tangential direction (Fx) and thrust direction (Fy). The sensor grip was attached on the shaft of the test club and the dynamic gripping force on some part of finger and palm in swing action was examined. Some remarkable results of change in radial and frictional force were obtained as follows. (1) The gripping forces of three direction show the tendency to change rapidly at around the impact point. (2) The force of frictional direction (Fx, Fy) in swing were large on the all measured points. (3) The force of radial direction on the palm of left hand was detected steadily. (4) The force of tangential direction on the palm of left hand and the middle finger of right hand were detected markably at back swing and impact. (5) The thrust direction force on the thumb of right hand was detected stably in down swing. It is considered that these results will offer the many useful data in order to develop the advanced sports gear which have funtional design and appropriate specification for each player.

Studies on friction and wear characteristics of cam and follower: influences of soot contamination in engine oil

In order to clarify the friction and wear mechanism of the contact between cam and follower in the valve train incorporated in an EGR system, an experimental investigation was performed with a cam-follower test rig. A fresh CD-class SAE10W-30 multigrade oil and its deteriorated versions with different contaminants were tested. Changes in friction force and amount of wear were measured during the course of the tests. The influence of the soot in the deteriorated oil was examined by mixing the exhaust gas soot blended with the dispersant, ZnDTP and MoDTC additives. Results are summarized as follows. (1) The friction fluctuated and gradually increased with the lapse of time in case of contaminated oils with the soot. (2) Under the coexistence of ZnDTP and MoDTC, however, the friction gradually decreased in spite of existence of soot. (3) The soot dispersed in the oil increased wear rate and reduced the anti-wear effect of the ZnDTP. (4) The smallest wear rate was observed because the anti-wear effect was maintained owing to the MoDTC.

Effects of recycling on the mechanical properties and the surface topography of nickel-titanium alloy wires.

The purpose of this study was to investigate the changes in mechanical properties, surface topography, and frictional forces of various nickel-titanium wires after recycling. Three types of nickel-titanium wires were separated into 3 groups: as-received condition (T0, control group), treated in artificial saliva for 4 weeks (T1), and treated in artificial saliva and autoclaved (T2). Strength changes were observed by tensile testing, and surface topography was assessed by scanning electron microscope and 3-D profilogram. Frictional coefficients were tested by friction test, and fatigue by bending fatigue test. Our findings showed that there were no statistically significant differences between the wires in maximum tensile strength, elongation rate, modulus of elasticity, and bending fatigue. Two wires demonstrated increased pitting and corrosion after recycling. The same 2 wires also demonstrated significantly greater surface roughness and maximum frictional coefficients compared with the control wires (P <.05), but the third wire showed no significant difference. However, surface roughness and frictional coefficient of the 2 wires after recycling were not greater than those of the third wire before treatment. Recycling increased the surface roughness and friction coefficients, but these seemed to have limited clinical significance.