Narrow Results

The friction and wear problem of the electrical contact system (ECS) is common in various electrical equipment. Once the electrical contact fails due to wear, the electrical system may not work normally, which brings serious safety risks. Surface texture has been shown to have a good potential to improve interface wear under no-current conditions, while few studies have been performed to study the relationship between surface texture and current-carrying tribological performance. In addition, graphene is also receiving attention in the field of electrical contact due to its high electrical conductivity. However, the wear consumption of graphene during the friction process limits its long-term role. Therefore, combining the ability of surface texture to reduce wear and the ability of graphene in conducting and lubrication, a texture-graphene composite surface (TS-G surface) is constructed. The effects of TS-G surfaces on the tribological properties of electrical contact surfaces are studied by comparing them with smooth surfaces (SS surfaces), textured surfaces (TS surfaces) and smooth-graphene surfaces (SS-G surfaces). The results show that TS-G can effectively reduce the friction coefficient (COF), and the COF stays at about 0.15 during the whole current-carrying friction process, and no visible fluctuation can be observed from the COF curve. In addition, the TS-G surface can effectively suppress the interface friction-induced vibration. More importantly, the TS-G surface has a good effect on the electrical contact stability. The surface topography analysis shows that the wear degree of the TS-G surface is quite slight, and the width of the wear track is only 30$\mu$m. The texture is found to be able to store graphene and continue to play the role of surface conduction and lubrication. The results of this study provide potential means for surface design to improve the stability of electrical contact.

Recently, synchronization in the Burridge–Knopoff model has been found to depend on the initial conditions. Here we report the existence of three modes of oscillations of the system of three blocks. In one of the modes, two lateral blocks are synchronized. In the second mode, the central block moves with almost constant velocity, i.e., it does not stick. Two lateral blocks do stick and they move in opposite phases. In the third mode, the blocks oscillate with aperiodic amplitude. The lateral blocks move in opposite phases and their frequency is lower than the one for the central block. The mode selected by the system depends on the initial conditions. Numerical results indicate that there is no modes in the phase space.

A computational study of sliding blocks on inclined surfaces is presented. Assuming that the friction coefficient μ is a function of position, the probability P(λ) for the block to slide down over a length λ is numerically calculated. Our results are consistent with recent experimental data suggesting a power-law distribution of events over a wide range of displacements when the chute angle is close to the critical one, and suggest that the variation of μ along the surface is responsible for this.

We study the statical indeterminacy of contact forces in 2D random frictional packings of perfectly rigid disks. Based on contact dynamics simulations we perform a random walk in the force space in order to explore the equilibrium force-states for a fixed packing structure. Our measurement is in agreement with the isostaticity of frictionless hard particles, in that case forces are fully determined. For non-zero friction coefficient the problem gets undetermined, the possible force fluctuations are growing with increasing friction up to a maximum at friction coefficient around 0.1. Further increase of friction reduces the force fluctuations on the average.

Tribological experiments were conducted on a ball-on-disk, unlubricated, with a speed of V≈ 140mm/s, V≈ 70mm/s, with an applied load between 20 and 100N, and with different combinations of ceramic materials. A wear test was conducted on disk material zirconia with regard to various ceramic ball materials (zirconia, alumina, silicon carbide and silicon nitride). The results show that the properties of the counter materials cause a difference in friction and wear characteristics.

The mechanical response of spherical indentation of superelastic shape memory alloys (SMAs) was theoretically studied in this paper. Firstly, the friction effect was examined. It was found that the friction influence is negligibly small. Secondly, the influence of the elasticity of the indenter was investigated. Numerical results indicate that this influence can not be neglected as long as the indentation depth is not very small. After that, this paper focused on the effect of transformation volume contraction. Our results show that the transformation volume contraction due to forward martensitic transformation can reduce the maximum indentation force and the spherical indentation hardness. These research results enhance our understanding of the spherical indentation responses, including the hardness of the smart material SMAs.

The service life of industrial components is limited predominantly by Chemical corrosion/mechanical wear. The project is concerned with the investigation of the capability of Ti(Al,O)/Al₂O₃ coatings to improve the service life of tool steel (H13) used for dies in aluminium high pressure die casting.

This paper gives a general review on the research work conducted at the University of Waikato on producing and evaluating the titanium/alumina based composite coatings. The powder feedstocks for making the composite coatings were produced by high energy mechanical milling of a mixture of Al and TiO₂ powders in two different molar ratios followed by a thermal reaction process. The feedstocks were then thermally sprayed using a high velocity air-fuel (HVAF) technique on H13 steel substrates to produce a Ti(Al,O)/Al₂O₃ composite coatings. The performance of the coating was assessed in terms of thermal shock resistance and reaction kinetics with molten aluminium. The composite powders and coatings were characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD).

The friction and wear of silicon nitride (Si₃N₄) against silicon nitride (Si₃N₄) and zirconia (Y–TZP) and chilled cast iron and Alumina sliding under dry friction at room temperature conditions were investigated with pin-on-disk tribometer at sliding speed of 0.56ms^-1 and normal load of 50N, 80N, respectively. Based on the variety regulation of the wear maps, the wear mechanisms of the two couples were analyzed. Get the result of friction coefficient and maps of wear Rate of the Pin and the Disk. The results of comparing this couple is Si₃N₄/ chilled cast iron < Si₃N₄/ ZrO₂< Si₃N₄/ Si₃N₄< Si₃N₄/ Al₂O₃.

Different treatment time and bias voltage with RF Ar plasma were used to improve tribological properties of NBR (Nitrile Butadiene Rubber). Chemical structure analyses of NBR by Attenuated Total Reflectance (ATR) were performed to clarify the functionality modification after the plasma treatment. In addition, wetting experiments were carried out by measuring the contact angle of distilled water drops on the NBR surface. ATR analysis revealed that the number of -C=O, -C-O, O-H functional groups increased after the argon plasma treatment. The functional groups led to changes in the contact angle from 100 to 50 degrees. The results showed that form-like nanostructures on the NBR was observed at the bias voltage of -400 V. The friction test showed that coefficient of friction after modified NBR in lubricated condition decreased from 0.25 to 0.15 with the increasing bias voltage due to the surface structure formations and better bonding with grease lubricant.

Fluorinated diamond-like carbon (DLC) films have good biocompatibility and bloodcompatibility. When they are used in cardiac valve prosthesis, the wear resistance has to be investigated in more detail. In this paper, the tribological behavior of fluorinated DLC films under different loads and sliding speeds in bull serum albumin (BSA) solutions were investigated by ball-on-disc friction tests. The results show that the proteins in BSA solutions promoted the DLC film adhesion failure because of the increased friction coefficients and accelerated corrosion rate. The fluorine doping can lower the corrosion rate of DLC film, thereby improving the adhesion stability and wear resistance of DLC in BSA solutions.

The automatic tool changer (ATC) in computerized numerical control (CNC) milling machine often uses pneumatic dynamic sources. Friction in the pneumatic cylinder affects the ATC’s stopping position; this friction depends on many factors, including the air environment’s relative humidity and temperature. This paper presents the results of research on the effects of relative humidity (RH) and air temperature (T) on the stopping position of an ATC using a pneumatic cylinder. Studies were conducted at temperatures of $15^{\circ }$C, $32^{\circ }$C and $49^{\circ }$C and relative humidity values of 51%, 75% and 99% for different speeds of the pneumatic cylinder (30, 50 and 100 mm/s). The results show that when the humidity increases from 51% to 99% and the temperature increases from $15^{\circ }$C to $49^{\circ }$C, the friction force decreases. The friction force is related to the relative humidity and temperature of the air. Thus, the deviation of the ATC’s stopping position depends on the relative humidity and temperature of the area under investigation.

The microscopic origin of friction is an important topic in science and technology. To date, noteworthy aspects of it remain unsolved. In an effort to shed some light on the possible mechanisms that could give rise to the macroscopic emergence of friction, a very simple 1D system of two particles is considered, one of them is free but moving with an initial velocity, and the other confined by a harmonic potential. The two particles interact via a repulsive Gaussian potential. While it represents in a straightforward manner a tip substrate system in the real world, no analytic solutions can be found for its motion. Because of the interaction, the free particle (tip) may overcome the bound particle (substrate) losing part of its kinetic energy. We solve Newton’s equations of the two particles numerically and calculate the net exchange of energy in the asymptotic state in terms of the relevant parameters of the problem. The effective dissipation that emerges from this simple, classical model with no ad hoc terms shows, surprisingly, a range of rich, nontrivial, behavior. We give theoretical reasoning which provides a satisfactory qualitative description. The essential ingredient of that reasoning is that the transfer of energy from the incoming particle to the confined one can be regarded as the source of the emergent dissipation force the friction experienced by the incoming particle.

This paper develops an efficient three-dimensional numerical procedure to predict incompressible flow in long microchannels. The major advantage of the present numerical procedure is its fast speed due to the parabolic character of the governing equations.

Diamond films are often applied in places where there is intense friction. The use of lasers to fabricate textured arrays on diamond films can effectively reduce the friction coefficient. In this paper, we use a UV nanosecond laser to produce periodic linear and pit micro-textures over the areas of $14\ast 7{\mathrm{\text{mm}}}^2$. Laser irradiation was below the single-pulse ablation threshold corresponding to the conditions of surface graphitization during the multi-pulse irradiation. Irradiated graphitization can be detected by Raman spectroscopy, and at the same time, lattice distortion and crack initiation that accompany graphitization can be obtained by XRD and SEM, respectively. The shape of the texture also has a great influence on the residual stress. Grooved texture released the residual stress, but pit texture gave rise to uneven stress, as shown in the test result. SEM was used for observing morphological change at the edge of texture and the mechanism of internal stress changes is analyzed. Detection of texture antifriction performance by reciprocating friction and wear tester. After rubbing, the layered shedding marks of the edge of the texture were observed, and the influence of the superposition of residual stress and external stress on the texture damage was proved based on this.

This study aims to examine the frictional behavior of staple carbon fiber composites (sCFCs). The staple carbon fiber reinforced polycarbonate (PC) composites were prepared by film stacking for two different impregnation levels. Mechanical properties such as tensile and flexural strengths and moduli and static/dynamic friction coefficient (COF) were determined. The COF and temperature as a function of wearing cycles for sCFCs subjected to different applied pressures were also determined by a disk-on-disk sliding wear test machine. The less impregnated sample exhibited superior tribological performance owing to its rough surface and low frictional heat generation.

High strength low alloy steel has excellent heat resistance and high strength. As it is commonly used as gun barrel material, a long service life and superior wear resistance are necessary for steel components. Here we investigated the wear characteristics of high strength low alloy steel surfaces under various environmental conditions, using a pin-on-disk wear test. Oxidation and wear debris effects on the coefficient of friction (COF) of the alloy steel were examined under air and argon (Ar) gas flow at atmospheric conditions.

Two-degree-of-freedom autonomous system with friction is analyzed numerically. The friction coefficient has been smoothened using arc tan function. The standard, but slightly modified chaos identification tools have been applied for the analyzed discontinuous system. Some interesting examples of stick-slip regular and chaotic dynamics have been illustrated and discussed.

The paper studies the dynamics of a stop-belt friction oscillator (SBO). The system consists of a visco-elastic oscillator which is dragged by a rough support moving with constant driving velocity and can collide with a rigid obstacle. The peculiarity of this system is that, in the phase space, it exhibits two different discontinuity boundaries. Nonsmooth responses are consequently observed with nonstandard attracting properties. The evolution of steady state limit sets as the position of the obstacle is varied is described. The nonsmoothness sets of the system and, in particular, the presence of discontinuity boundaries caused by friction and impacts, lead to nonstandard bifurcations which are studied here by means of analytical and numerical tools.

This work is devoted to modeling and the analytical/numerical analysis of tribological processes occurring on the contact surface of shields of a mechanical friction clutch. Although the considered problems have been already studied earlier, however, simplified mathematical models have been used and applied. Unlike previous works, our work takes into account elasticity and wear properties of material of shields rubbing themselves. A general nonlinear differential model of wear is considered, as well as a wear model in the integral form taking into account gradual decrease of speed of wear of shields as a result of abrasive adapting to each other in the process of the exploitation. Equations modeling contact pressure on the contact surface of shields are derived and they yield the contact pressure and the wear of the shields. An analytical/numerical analysis is carried out with the qualitative and quantitative theories of differential and integral equations, including Laplace transformation. Many interesting results are obtained, illustrated and discussed. The presented results can be widened and used in other disciplines of the science, for instance, in physics of solids or biomechanics of various human joints.

Dry-friction contacts in mechanical oscillators can be modeled using nonsmooth differential equations, and recent advances in dynamical theory are providing new insights into the stability and uniqueness of such oscillators. A classic model is that of spring-coupled masses undergoing stick-slip motion on a rough surface. Here, we present a phenomenon in which multiple masses transition from stick to slip almost simultaneously, but suffer a brief loss of determinacy in the process. The system evolution becomes many-valued, but quickly collapses back down to an infinitesimal set of outcomes, a sort of “micro-indeterminacy”. Though fleeting, the loss of determinacy means masses may each undergo different microscopic sequences of slipping events, before all masses ultimately slip. The microscopic loss of determinacy is visible in local changes in friction forces, and in creating a bistability of global stick-slip oscillations. If friction forces are coupled between the oscillators then the effect is more severe, as solutions are compressed instead onto two (or more) macroscopically different outcomes.