Sliding Friction Behavior Research Articles

Nanoscale sliding friction behavior on Cu/Ag bilayers influenced by water film

Nanoscale sliding friction behavior of nanoparticle o n Cu/Ag bilayers influenced by water film is investigated by molecular dynamics (MD) simulation. The results show that the existence of water film aggravates the subsurface damage and the change of Cu/Ag interface microstructure, but improves the quality of groove surface and decreases the friction coefficient. Under the water-assisted sliding, there is a water-film thickness to minimize subsurface damage and friction coefficient, while make best groove surface quality. The results give an insight into the sliding friction mechanism of nanoparticle on Cu/Ag bilayers during dry and water-assisted sliding. Importantly, a meaningful guidance is provided for the amount of water used when the bilayer materials are subjected to nanoparticle sliding, thereby reducing the subsurface damage, inhibiting the change of interface microstructure, and improving the groove surface quality. The study is beneficial to develop the working performance and engineering application of bilayer materials.

High-Temperature Sliding Friction Behavior of Amorphous Carbon Films: Molecular Dynamics Simulation.

With the development of the aerospace industry, the requirement for mechanical parts, which are serviced under extreme conditions such as high temperature, is more and more severe. Amorphous carbon (a-C) films are widely used in the aviation field as a protective coating because of their excellent antiwear and friction-reduction properties. However, a-C films are vulnerable to failure in a high-temperature environment, and a series of complex changes in the friction process make it a challenge to put forward the friction mechanism. Here, the sliding friction behaviors of amorphous carbon (a-C) films at different simulated temperatures (STs) (300-1300 K) were analyzed by molecular dynamics. The density, average coordination number, and local residual stress as well as the hybridization of sp, sp2, and sp3 of a-C films were analyzed to reveal the high-temperature sliding friction mechanism of a-C films. The results show that the friction coefficient (μ) of a-C films increased with increase in ST. Meanwhile, the friction mechanisms of a-C films are different at an ST lower than 800 K and higher than 1100 K. Compared with those before sliding, the local residual stress of all a-C films is relaxed, which causes transformation of sp3 into sp2. Moreover, when ST is lower than 800 K, the μ increased with increase in sp3%. When ST is higher than 1100 K, the stability of a-C films is broken, which results in the rapid increase in μ.

Dry Sliding Friction of Al Si B 4 C Composites Prepared Through Powder Metallurgy using Taguchi Design

This research paper discuss about the friction behavior of Al-12Si-xB4C composites prepared through powder metallurgy method by varying the weight percentage of reinforcement (x = 2, 4, 6, 8, and 10) content. The samples were prepared by using die and punch assembly and the lubricant used to eject the sample from the die was molybdenum disulfide. The compaction was done by using compression testing machine by applying a pressure of 800MPa. The dry sliding friction behavior of the sample was conducted on Pin-on-Disc machine and the experimental values of friction were calibrated. Taguchi design experiment was done by applying L25 orthogonal array for 3 factors at 5 levels for the response parameter coefficient of friction. Analysis of Variance demonstrated by Mean and S/N ratio table for coefficient of friction was discussed and from the table it can be seen that the reinforcement plays a main role, when the compared with load and sliding distance. The normal probability plot shows that the residuals falls near to the red line, it indicate that the error values were less in the model.

Effects of Porosity and SEBS Fraction on Dry Sliding Friction of EVA Foams for Sports Shoe Sole Applications

Ethylene vinyl acetate (EVA) foam is sometimes used in the outer soles of sport shoes. To improve the slip resistance of EVA foam, this study investigated the effects of porosity and the fraction of styrene–ethylene–butadiene–styrene (SEBS) on the dry sliding friction behavior of EVA foams. Sliding friction tests were performed against a pin specimen with a semicylindrical tip, which was covered with (rough surface) or without abrasive paper (smooth surface). The results revealed that the friction coefficient of the EVA foam increased with porosity when slid against a smooth surface, whereas its friction coefficient increased with porosity and SEBS fraction when slid against a rough surface. The results of this investigation provide insight into how to increase the dry sliding friction of resin foam against smooth and rough surfaces, which will also contribute to improving the slip resistance of shoe soles made from resin foam.

Experimental Analysis of Dry Sliding Friction and Wear Behavior of OMMT Nanoclay Added EVA/HDPE/MA-g-PE Compatibilized Polymer Blends with Parametric Study of Influencing Factors

Abstract In this study, an attempt has been made to find out the possibility of extending the conventional engineering applications of Maleic Anhydride–grafted Polyethylene (MA-g-PE), compatibilized Ethylene-co-Vinyl Acetate (EVA), and High-Density Polyethylene (HDPE) polymer blends with the addition of Organo-Modified Montmorillonite (OMMT) nanoclay to sliding wear–resistant parts in the automobile, aerospace, and other similar industries. An experimental analysis of dry sliding friction and wear has been investigated for MA-g-PE (2 parts per hundred, i.e., phr) grafted EVA/HDPE (70/30 by weight %) blend with the addition of 0, 1, 2, 3, and 4 phr of OMMT nanoclay. According to ASTM G99, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus, specimens slid against an EN31 steel disk of 60 HRC using a wear and friction tribometer at different forces, sliding distances, and sliding velocities. Effects of forces and sliding distances on sliding friction coefficients and specific wear rates of polymer nanocomposites were evaluated. It was observed that the coefficient of friction decreased with the increase in forces and slightly varied with increments in sliding distance. On the other hand, the specific wear rate increased by increment in forces and decreased with the increase in sliding distance. Wear mechanisms and worn surfaces were analyzed using scanning electron microscopic images. Parametric study of influencing factors (polymer compositions, forces, sliding distances, and sliding velocities) was conducted using the Taguchi design of experiment and ANalysis Of VAriance (ANOVA). Taguchi was used to rank and optimize four influencing factors, viz., composition, force, sliding distance, and sliding velocity. ANOVA determined the statistical significance and percentage contribution of control factors.

Dry Sliding Friction and Wear Behaviour of AA6082-TiB2 in Situ Composites

In this study a composite with AA6082 as the matrix and TiB2 as the reinforcement has been fabricated by in situ method. The effect of TiB2 addition on the mechanical and tribological behaviour has been investigated. The purpose of the study is to improve the friction and wear properties of AA6082 so as to widen the engineering applications of the alloy. The reinforcement varied as (0, 3, 6, 9 wt%). The mechanical characteristics such as hardness and density improved with the addition of the reinforcement particles. The microhardness also shows slight increase in its value with increase in reaction time. The microstructural examination depicted grain refinement of the cast composites with increase in reinforcement. The wear resistance also increases with the addition of the reinforcement. The coefficient of friction exhibited an increasing trend and thereafter it decreased with increasing reinforcement at lower load. However, at higher load, an increase in the coefficient of friction is observed with an increase in reinforcement. SEM and EDS analysis revealed distinct wear mechanisms for different composites and different loads. The present study reveals that with addition of hard TiB2 particles the mechanical and tribological of AA6082 are improved. The results suggest that the developed composite material could be a potential material for various engineering applications.

Effect of Kevlar Hybridization on Dry Sliding Friction and Wear Behaviour of Bamboo/Epoxy Composites

The present work aims to experimentally investigate the effect of Kevlar fiber hybridization on dry sliding friction and wear behaviour of bamboo fiber reinforced laminated epoxy composite. Monolithic bamboo laminated composite and different bamboo/Kevlar inter-ply laminated hybrid composites with variation in number of both the laminas were developed in house by hand layup technique. Pin-on-disc experiment was employed to determine its tribological performance. The wear mass loss, specific wear rate and co-efficient of friction of the developed composites, when slide against a rotating disc, were determined and analyzed. The wear mechanisms were studied from the microstructure. From the results, it is observed that, wear loss and co-efficient of friction values were increased with the increase in number of Kevlar laminas.

Sliding friction of hierarchically micro–micro textured polymer surfaces on ice

The ice friction behavior of various microtextured polymer surfaces was studied with respect to ice temperature and applied load using a customized linear tribometer. Similar micropillar patterns were replicated on polypropylene and two rubber compounds, and when hierarchical micro–micro textures were present, all the materials exhibited superhydrophobicity. Taller protective micropillars were shown to be crucial for protecting the smaller microtextures from abrasive wear. The mechanical properties of the polymers affected the sliding friction of the microtextured surfaces on ice. High loading of hierarchical textures on rigid polypropylene or operation near the ice melting point tended to increase its adhesion tendency or resisting behavior. The sliding performance of the hard and soft rubber compounds was temperature-dependent, and the texture on the soft rubber influenced the sliding friction differently depending on the ice temperature. Consequently, textural modifications of the sliding surface enabled a certain degree of control over the sliding friction behavior on ice.

Numerical investigation of sliding friction behaviour and mechanism of engineering surfaces

PurposeThis study aims to investigate the sliding friction behaviour and mechanism of engineering surfaces.Design/methodology/approachA new numerical approach is proposed. This approach derives the macroscale friction coefficient from microscale asperity interactions. By applying this approach, the sliding friction behaviour under different operating conditions were investigated in terms of molecular and mechanical components.FindingsNumerical results demonstrate an independent relationship between normal load and friction coefficient, which is governed by the saturated plastic ratio. Numerical results also demonstrate that under very small load, an increase in load increases the friction coefficient. In addition, numerical results confirm the existence of optimal surface roughness where the friction coefficient is the lowest. For the surface profiles used in the current calculation, an optimal surface roughness value is obtained as Rq = 0.125 μm.Originality/valueThis new approach characterizes the deterministic relationship between macroscale friction coefficient and microscale asperity molecular/mechanical interactions. Numerical results facilitate the understanding of sliding friction mechanism.

Adhesive friction and wear of micro-pillared polymers in dry contact

Elastomers are currently used intensively in various industrial applications. However, their deployment in dry tribological contact is normally inhibited by their poor dry sliding friction behaviour due to their intrinsically high adhesive characteristics. This problem is normally addressed in the industry by using various fluid (greases or oils) or solid (coatings or lacks) lubricants. Alternatives to the use of lubricants for tribosystems involving elastomers exist in the form of modifications of the elastomer composition or by reducing their effective nominal contact area by using surface texturing. The latter approach of reducing the adhesive nature of elastomers by surface structuring is the main focus of the present study.Two different micro-sized structures (consisting of micro-pits) were produced on thin Al inlays using a microscopically scaled punching process. These inlays were thereafter glued onto laboratory-scale injection moulds. These micro-pitted moulds were subsequently used to produce injection moulded micro-pillared Liquid Silicone Rubber (LSR) pads.The present study was focused on three different aspects: 1. Determination of the degree of replication of microstructures from injection moulds to the surface of LSR pads; 2. Evaluation of any possible friction reduction induced by a decrease of the nominal contact area through micro-texturing of LSR pads in dry tribological tests; and 3. Evaluation of the wear resistance of micro-pillared LSR pads under dry conditions.The results have shown that successful production and relatively accurate replication of micro-pitted structures from injection moulds onto LSR pad surfaces in the form of micro-pillars may be achieved. Furthermore, it was shown that a decrease of the effective nominal contact area through micro-pillars may enable a reduction of friction in comparison to the benchmark (unstructured LSR pads), but only for low normal loads where the adhesive component of friction is playing a determining role. Finally, wear tests have shown that the wear resistance of both micro-pillared structures produced on LSR pads under dry conditions against Al or PA6.6-GF30 was relatively poor. Both structures exhibited extensively worn regions after a testing distance of 11 m: structure 1 showed a larger worn area ratio than structure 2 (ratio worn area/total area ~45%–60% for structure 1 and ~30% for structure 2).

Tribo‐Induced Structural Transformation and Lubricant Dissociation at Amorphous Carbon–Alpha Olefin Interface

AbstractAmorphous carbon (a‐C) combined with a fluid lubricant is capable of providing an ultra‐low friction state and thus achieving long lifetime and reliable operation. However, the understanding of the atomistic process occurring at the sliding friction interfaces, especially the interfacial structure transformation and lubricant dissociation at different contact states, is still not well understood. Here, using reactive molecular dynamics simulation, the friction behavior of a self‐mated a‐C system composited with different alpha olefins (AOs) as lubricants is comparatively investigated, and the results present that due to the co‐existence of tribo‐induced thermal and shearing effects, AOs exhibit different physicochemical behaviors at the a‐C–a‐C interface compared to that at the a‐C surface. Although introducing AOs into a self‐mated a‐C system reduces the friction coefficient, its efficiency strongly relies on the AO variety and contact pressure. The pressure‐driven dissociation of AOs passivates the friction interface, resulting in the evolution of the primary friction mechanism from hydrodynamic lubrication to interfacial passivation that is not accessible by experimental characterization. The corresponding scission sites of different AOs are demonstrated, which enriches the fundamental understanding on sliding friction behavior and offers a comprehensive design criterion for lubricants (viscosity, chain length, and bond saturated states) and a‐C to achieve nearly frictionless sliding interface.

Effect of sliding conditions on the macroscale lubricity of multilayer graphene coatings grown on nickel by CVD

A multilayer graphene (MLG) coating was grown on a nickel substrate by atmospheric chemical vapor deposition (CVD). The macroscale dry sliding friction behavior of the coated specimens against a stainless steel counterface was investigated under various contact loads ranging from 1 N to 5 N and at various rotational speeds from 30 rpm to 240 rpm. After the tests, the sliding surfaces were characterized by optical and scanning electron microscopes and Raman spectroscopy. The results show that contact load and sliding speed had significant effects on the lubricity of the MLG coatings under dry sliding conditions. At relatively low contact loads (1–3 N) and sliding speeds (30–120 rpm), the MLG coating exhibited good lubricity with coefficient of friction (COF) below 0.06 and lasted a long period of sliding time for >3600 cycles. With increasing contact loads and speeds, the COF of the MLG coating was gradually increased and the coating suffered from sudden breakdown after limited sliding cycles, losing its lubricity. Detailed examination and analysis revealed that material transfer occurred at the early stage of the sliding process, where MLG was transferred from the coating surface to the counterface. This graphene transfer was responsible for the lubricity of the sliding pair and the sustainability of the transferred material on the counterface determined the lifetime of the lubricity regime. High contact loads and high speeds favored severe plastic deformation and mechanical damages of the substrate, which limited the lifetime of the transferred material and thus the lifetime of the lubricity regime. Sliding induced defects in the MLG both on the coating and on the counterface were confirmed by Raman spectroscopy.

The Sliding Wear and Friction Behavior of M50-Graphene Self-Lubricating Composites Prepared by Laser Additive Manufacturing at Elevated Temperature

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si3N4 ball from 25 to 550 °C at 18 N–0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10−7 mm3 N−1 m−1. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10−7mm3 N−1 m−1). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer.

Effect of Axial Vibration on Sliding Frictional Force between Shale and 45 Steel

Activating drill string vibration is an effective means to mitigate the excessive drag encountered during drilling complex‐structure wells. However, the Coulomb model cannot describe the sliding friction behavior between drill string and borehole rock with imposed axial vibrations. To solve this problem, a specially designed experimental setup was utilized to investigate the characteristics of axial vibrating‐sliding coupling friction. The results indicate that when vibration velocity is greater than sliding velocity, axial vibration can significantly reduce friction force between contact surfaces. Its friction reduction mechanism embodies not only the changes of instantaneous friction force, but also friction coefficient. Meanwhile, a friction coupling model was established based on the Hertz contact theory and Dahl model. The corresponding computational program was developed in Matlab/Simulink environment. The calculation results are in good agreement with the experimental results, verifying the validity of the present method. Furthermore, to overcome the shortcoming of Dahl model, a dynamic friction coefficient model was proposed to evaluate the friction‐reducing effect of axial vibration using dimensional analysis method. The model parameters under different lubrication conditions were retrieved through inverse calculation with experimental data. This method provides a new solution for evaluating the friction‐reducing effect of hydraulic oscillator and optimizing its placement.

Chemical effects on the sliding friction of Ag and Au(111)

We have investigated the sliding friction behavior of metallic couples with different enthalpy of mixing or reaction by friction force microscopy. Comparing the friction behavior of miscible and immiscible couples we find that in the first case friction is governed by adhesion while the shear strength is low (τ = 3–6 MPa). In the latter case of immiscible couples, adhesion is found to be low and the shear strength is large (τ ≈ 70 MPa). Statistical analysis of atomic stick-slip images recorded on an Au(111) surface with tips of different affinities with gold allows for a deeper understanding of our results. The periodicity of atomic stick-slip images corresponds to the interatomic distance of gold for immiscible counter-bodies. In contrast, for a reactive couple the periodicity of atomic stick-slip significantly differs from the gold interatomic distance and may correspond to the structural length of an ordered intermediate phase at the tip-surface interface.

Influences of temperature and load on the dry friction behaviour of tire tread compounds in contact with rough granite

The temperature and load dependence of the sliding friction behaviour of a racing tire tread compound on coarse and fine rough granite substrates is analysed by experimental and theoretical techniques. Based on dry friction measurements at different temperatures, friction master curves are constructed by shifting the data horizontally on the velocity axis using the same shifting factors as found from viscoelastic master curves. The obtained isothermal friction curves increase rapidly with increasing sliding velocities and show a more or less pronounced plateau over a broad velocity range, which decreases with increasing load. For analysing this behaviour, the Klüppel and Heinrich theory of rubber friction and contact mechanics is applied, which considers the multi-scale contacts and excitations of the rubber sliding on rough surfaces in the frame of a linear viscoelastic approach. The extension of this theory to more realistic surfaces with two or more scaling ranges is described in some detail. It takes adhesion and hysteresis contributions into account referring to the viscoelastic response of the rubber on different frequency scales. The theory predicts that under isothermal conditions the coefficient of friction decreases with load, which is more pronounced for the adhesion than for the hysteresis contribution. This result is found to be in fair agreement with the measure friction curves confirming the contact mechanical approach of the theory.

Effect of Normal Load and Velocity on Continuous Sliding Friction and Wear Behavior of Woven Glass Fiber Reinforced Epoxy Composite

The tribological performance of glass epoxy composite under different conditions has been examined. In this study, the effect of normal loads and sliding velocities on the friction and wear behavior of glass fiber reinforced epoxy composite sliding against a steel disc in dry condition is investigated experimentally using a pin on disc type wear and friction monitor. The composite with 60 wt% of woven E glass fiber reinforcement is fabricated in hand lay up technique followed by compression moulding process. The fiber orientation of the composite has been kept perpendicular to the sliding direction. Tests are conducted at normal loads of 5, 10, 20, 30, 40, and 50 N and the sliding velocities of 0.5, 1, 2, and 3 m/s. Friction and wear are influenced by the duration of sliding, normal load, and sliding velocity. The variation of friction coefficient with the change of sliding duration under different conditions has been considered in detail. In general, friction coefficient decreases with the increase of normal load and it increases with the increase of the sliding velocity for all sliding velocities and normal loads respectively. Wear loss increases in respect of increase in normal loads and sliding velocities for all the conditions.

Dry Sliding Friction and Wear Behaviour of Reinforced Hybrid Composites of Uniaxial Glass Fiber with Silicon Carbide, Aluminium Oxide and Graphite

In recent years, both industrial and academic world are focussing their attention towards the development of sustainable composites, reinforced with fibres. In particular, among the fibres that can be used as reinforcement, the uniaxial glass fiber ones represent the most interesting for their properties. The aim of this work is to illustrate the results of friction and wear behaviour of uniaxial glass fibers with silicon carbide, aluminium oxide and graphite as the fillers. Moreover, its main manufacturing technologies have been described. The major component of these hybrid composite is uniaxial glass fibre with Epoxy LY556 (Resin). Hardener HY951 is used for hardening and support. Resin + Hardener are mixed in the ratio 10:1 and the mixture made up is called Matrix. Test materials of glass Fibre with varying compositions of 15% Al2O3 + SiC and glass fibre with varying compositions of 15% Graphite + SiC have been prepared by applying the matrix on glass cloth which is wrapped around the mandrel. The samples were tested in a pin-on-disc machine to determine the friction and wear losses. Further, the samples were tested on a pin-on-disc machine and frictional characteristics were monitored by varying speed and loads. Thus, the friction and wear characteristics have also been found out for the two specimens. From the experimental test results, it is observed that Al2O3 +Sic exihibits lower wear loss than SiC + Graphite under dry sliding conditions. Based on the observations, this hybrid composite are recommended to the manufacturing of the aircraft structures.

Study of the Sliding Wear and Friction Behavior of WC + NiCrBSi Laser Cladding Coatings as a Function of Actual Concentration of WC Reinforcement Particles in Ball-on-Disk Test

This work studies the effects that different percentages of WC reinforcement particles produce on the wear of a NiCrBSi coatings obtained by laser cladding. The density of the WC particles, which is higher than those of the matrix, makes it necessary to control the volume provided from each material to maintain the height of the coating. In addition, said difference of density promotes the precipitation of the WC particles inside the Ni matrix, causing a non-homogeneous distribution of the particles in the cross section of the coating. Unlike other studies in which the adjusted concentration of WC in the feeder is considered (wt% WCfeeder concentration), this work studies the dry wear behavior of coatings, using a ball-on-disk configuration tests, as a function of the actual WC% by weight present on the surface tested for wear (wt% WCactual concentration), this being determined by image processing software. Wear decreases exponentially with the increase in WC concentration, to a limit of 27 wt% WCactual. At this limit, an increase in reinforcement particles does not generate a significant decrease in wear. The predominant wear mechanism varies depending on the wt% WCactual, passing from the adhesive and oxidative types to abrasive when WC percentage increases.

Crystallographic aspects on cyclic sliding friction behavior of a single crystal Ni-base superalloy

Crystallographic aspects on cyclic sliding friction behavior of a single crystal Ni-base superalloy