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The tribological performance of two polymeric friction modifiers, one based on an ester‐based compound and another based on an ethoxylated fatty ester and an organic friction modifier, oleamide, was studied at 50, 90 and 140°C using a Mini Traction Machine equipped with optical interferometry and electrical contact resistance. The ability to form surface film is found to vary among the friction modifiers and with temperature and rubbing duration. Despite a thinner film being formed, polymeric friction modifier (PFMs) exhibited lower friction and wear than oleamide at all the studied temperatures. Further, the PFMs reduced boundary friction more effectively at higher temperature. In accordance with lower boundary friction, a smoother surface topography characterized by low wear was exhibited by PFM lubricated surfaces at higher temperatures. Scanning electron microscopy‐energy dispersive x‐ray analysis and time‐of‐flight secondary ion mass spectrometry provided insights on the tribofilm formation. The improvement in the tribological performance of PFMs is attributed to temperature‐induced conformation transition of adsorbed polymer chains on the surface. The results are corroborated by data obtained from dynamic light scattering and gel permeation chromatography. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study is to experimentally analyze the friction and wear responses of different steels to different surface films generated in oil-lubricated tribological contacts. Design/methodology/approach: Tribological experiments were conducted using a 100Cr6 bearing ball sliding against a V155 carbon steel disk and 316L stainless steel disk, respectively. Lubricants with additives known to form zinc dialkyl-dithiophosphate (ZDDP) or Ca tribofilms were used. Findings: Both of the ZDDP and Ca tribofilms helped stabilize the friction coefficient of the carbon steel and stainless steel. The ZDDP tribofilm could effectively protect the carbon steel from wear, in contrast to the stainless steel, whereas the wear of both carbon steel and stainless steel could be significantly reduced by the Ca tribofilm. In the case of neither ZDDP nor Ca tribofilms formation, the 100Cr6 ball was worn by the V155 disk and generated a special surface topography. A polishing wear mechanism was proposed to explain the wear of the 100Cr6 ball. Originality/value: This study clearly shows the different friction and wear responses of steels to the different surface films and the response is dependent on the tested steel. [ABSTRACT FROM AUTHOR]

AlSi7Mg/SiCp aluminium matrix composites (AMCs) with a high ceramic content (35 vol.%) that were produced by using the field-assisted sintering technique (FAST) were subjected to tribological preconditioning and evaluated as a potential lightweight material to substitute grey cast iron brake discs. However, since an uncontrolled running-in process of the AMC surface can lead to severe wear and thus to failure of the friction system, AMC surfaces cannot be used directly after finishing and have to be preconditioned. A defined generation of a tribologically conditioned surface (tribosurface) is necessary, as was the aim in this study. To simulate tribological conditions in automotive brake systems, the prepared AMC samples were tested in a pin-on-disc configuration against conventional brake lining material under dry sliding conditions. The influence of the surface topography generated by face turning using different indexable inserts and feeds or an additional plasma electrolytic treatment was investigated at varied test pressures and sliding distances. The results showed that the coefficient of friction remained nearly constant when the set pressure was reached, whereas the initial topography of the samples studied by SEM varied substantially. A novel approach based on analysing the material ratio determined by 3D surface measurement was developed in order to obtain quantitative findings for industrial application. [ABSTRACT FROM AUTHOR]

The effect of cylinder liners on engine performance is substantial. Typically, the cylinder surfaces were plateau honed. However, recently additional dimples or grooves were created on them. This work discusses the tribological impacts of textured cylinder liner surfaces based on a review of the literature. The results of the experimental research obtained using test rigs and fired engines were critically reviewed. In addition, the results of the modeling are shown. Circular oil pockets and grooves perpendicular to the sliding direction of piston rings of small depths were typically used. Surface texturing of the cylinder liners governs lubrication between the cylinder liner and the piston ring by an increase in oil film thickness near the reversal points leading to reductions in friction force and wear and in the fired engine to a decrease in fuel consumption and to an increase in power or torque. The correct texturing pattern ensures a decrease in the oil consumption, blow-by, and emissions of the internal combustion engine compared to plateau-honed surfaces. Considerations of future challenges are also addressed. The volume of lubricant reservoir in surface topography, called oil capacity, should be a substantial parameter characterizing textured surfaces. [ABSTRACT FROM AUTHOR]

In this study, the influence of the in-situ tribo-oxide-layer on non-lubricated tribological behaviours of LM27/SiCp composites was studied at different applied loads. For this purpose, LM27/SiCp composites were manufactured by stir casting route with reinforcement of different amounts (3–12 wt.%) and different sizes (fine: 1–20 µm and coarse: 106–125 µm) of SiCp. A comprehensive characterization of the friction and wear mechanisms ranging from mild to severe wear for oxidative and delamination at a contact pressure of 0.125–0.624 MPa was discussed. Results indicate that the friction and wear behaviour is strongly influenced by the morphology and the nature of the oxide scale on the wear track. In-situ formation of oxide layers on the contact region of the specimen supports the self-lubrication which supports better wear performance of LM27/SiCp composites. However, these study portraits that composite with 12wt. % fine size SiCp exhibits better wear performance in comparison to the other developed composites. [ABSTRACT FROM AUTHOR]

Laser surface texturing (LST) is widely explored for modifying the surface topography of various materials. In this study, a detailed investigation of laser textured surfaces produced on austenitic stainless steel (AISI 304) was carried out. Three different textures (square, parallel, perpendicular) were produced by a Ti sapphire laser. The processed surfaces were characterized by surface morphology, phase structure, microhardness, surface roughness, and wettability. A ball-on-disk tribometer was used to study the tribological performance of both untextured and textured samples. The experimental observations demonstrate that LST improves both surface wettability and surface roughness. Average surface roughness (Ra) was increased by 350% and the contact angle was reduced from 43° to 22°. The textured surfaces show a lower coefficient of friction and better wear resistance than the untextured surface. Out of the investigated patterns, the square textures exhibited a maximum reduction of 68% in the friction coefficient and a 50% lower wear rate. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the effect of engineered micro-structures on the tribological properties of metal-polyetheretherketone (PEEK) surface. Design/methodology/approach: Circular dimples with diameters of 25 and 50 µm were designed and manufactured on PEEK plate specimens using picosecond laser. Reciprocating friction and wear tests on a ball-on-flat configuration were performed to evaluate the tribological properties of the designed micro-structures in dry contacts. The loading forces of 0.9 and 3 N were applied. Findings: As a result, obvious fluctuations of coefficient of friction curve were observed in tribosystems consisting of non-textured and textured PEEK with circular dimples of 25 µm in diameter. GCr15 ball/textured PEEK plate specimens with circular dimples of 50 µm in diameter revealed a superior friction and wear property. Originality/value: Different to the existing studies in which the tribopairs consist of hard bearing couples, this study investigated the tribological properties of the engineered micro-structures on the hard-on-soft bearing couples. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to investigate the influence of different finish processes on the surface integrity and tribological behaviour of cylinder running surfaces for internal combustion engines.Design/methodology/approach The cutting force during finishing and the resulting surface topography was measured for a variety of cylinder running surfaces made of EN-GJL-250, EN-GJV-400 and thermal sprayed aluminium alloy. A separate conditioning tool was developed and tested. Different analysis methods (SEM, EDX, SIMS and FIB) for the characterisation of the boundary conditions were used. By an oscillating friction wear test and a single cylinder floating liner engine, the running-in and frictional behaviour was rated.Findings It was shown that honing with low cutting forces and silicon carbide cutting material decreases the friction in operation. The characteristics of the boundary layers after running-in depend on the finish machining process. A preconditioning with a separate tool can adjust the boundary layer and running-in behaviour. Based on the experimental results, a multi-body and computational fluid dynamics simulation was developed for the floating liner engine.Originality/value The results demonstrate the potential of finishing with low process forces to reduce friction and the need for a complete consideration of the tribological system piston ring/cylinder liner surface. [ABSTRACT FROM AUTHOR]

Skating on ice is possible due to the low friction coefficient between ice and steel, which is thought to result from a lubricating water film formed through frictional melting. Although the phenomenon has been studied through various models and experiments, few studies report direct observations of the wear tracks on the ice surface. Here we use white light interferometry to accurately measure the surface topography on multiple length scales immediately after an ice skate slides over it. We find signs of surface melting only on short length scales as refrozen meltwater droplets, but no evidence of a global melt layer. Repeatedly sweeping over the same ice track results in an increasing friction coefficient, which we link to an increase in the contact area. We also consider the effect that the surface profile of the ice skate blade has on friction by using two different blades. [ABSTRACT FROM AUTHOR]

Despite environmental concerns, the automotive, aerospace and other manufacturing industries still extensively use hard-chrome coatings. This is mainly due to the coatings' ability to combine unmatched aesthetics with high hardness, excellent wear resistance, low friction and good corrosion protection in aggressive environments. However, the performance of hard-chrome coatings is dependent on the micro cracks developed during the deposition process. These cracks alter the surface topography, which has a major influence on the tribological performance of the contact, especially under mixed lubricated conditions. The aim of this study was to investigate the effect of a coating's crack density and a post-polishing process on the friction and wear performance of hard-chrome coatings. Three different crack densities combined with a post-polishing process were tested using the ball-on-disc configuration in a poly-alpha-olefin oil (PAO) lubricated point contact. The results clearly show that for hard-chrome coatings and random, non-uniform crack-type textures the size and density of the crack pattern determine the friction and wear performance of the contact. For the investigated contact conditions the best performance, i.e., low friction, fast running-in and minimum wear, was obtained when combining medium-density cracks of ∼3% and the post-polishing. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of surface topography and lubrication on the tribological behavior of AA5083 alloy for wide range of average roughness, R a . Reciprocating sliding tests were conducted under lubricated and dry regimes over different pre-textured surfaces using AISI-52100 steel ball under two contact pressures. Scanning Electron Microscope (SEM) and profilometer were employed for characterizing wear land and type. Particularly, the effect of the mean absolute profile slope Δ a of AA5083 plates on friction and wear was investigated within an early repetitive sliding stage. Experimental results show that a close correlation was found between the tribological behavior and the mean absolute slope, Δ a , contrary to the average roughness, R a , which shows a partial link. From SEM inspections, dry sliding correlates with the generation of ploughing over aluminum topographies, and with the formation of Built-Up Layer (BUL) due to adhesion over steel ball. However, lubrication, transforms material removal process over the ball from adhesion to abrasion which affects inevitably the initial topography. The evolution of crater area S  −  reflects high sensitivity to Δ a . In order to predict the wear evolution, a mathematical model taking into account the impact of Δ a and the number of sliding cycles ( N ) was developed using Response Surface Method (RSM). [ABSTRACT FROM AUTHOR]

The effects of surface roughness and topographical orientation on surface stresses influencing wear have been investigated for diamond like carbon (DLC) coated steel surfaces with three levels of surface roughness in the range of 0.004–0.11 μm R a values, and with topographical groove orientations of 0°, 45° and 90°. A novel multiscale numerical finite element method (FEM) model was developed to integrate the layered and microstructural material features with the grooved topography. Fractal geometry and a surface voxelisation based approach were utilised to derive 3D surface topography. The surface texture representation includes: fractal signatures, which are sets of fractal dimensions calculated at individual scales in different directions, texture aspect ratio describing surface anisotropy, and texture direction signatures calculated by the variance orientation transform (VOT) method. The simulations show details of the main topographical orientation effects on local stresses affecting wear as they appear at a single scratch test with a spherical diamond ball and in a self-mated sliding situation of two rough surfaces. The 45° sliding direction in relation to grooves resulted in a mixed state of surface loading in the scratch test contact. In the complex state of stress-strain within the roughness peaks the overall tensile stress decreased, leading to greater surface resistance to cracking as compared to 0° and 90° directions. Model based calculations showed that the surface structure was about four times more rigid in the direction of grooves as compared to the more flexible behaviour in the perpendicular direction. This behaviour was empirically confirmed. The numerical calculations of rough vs rough sliding surface include real surface topographical features at various scales, material microstructural features down to nano-scale and topographical-microstructural interaction features. This approximation is thus more comprehensive than the classical approach. The real area of contact was 15–30% of the apparent contact area. The macro-topography dominated the tendency for surface cracking and plastic deformation, which is influencing on both wear and friction, while the micro-topographical features contributed to cracking and deformation by less than 40%. [ABSTRACT FROM AUTHOR]

Wear tests were conducted using a ball-on-disc tester. In the experiment, a 42CrMo4 steel disc with a hardness of 40HRC was placed in contact with a 100Cr6 steel ball with a diameter of 6.35 mm. The hardness of the ball was set to 62HRC. Disc samples were prepared to obtain surfaces in range to the Sq parameter but of less than 0.5 μm. Dry tests were carried out. During the tests, the friction force was monitored as a function of time. Disc and ball wear was measured after the tests using a white light interferometer Talysurf CCI Lite. To decrease variations in the experimental results, during the tests, wear debris was continuously removed from the disc surfaces. It was found that the initial surface topography has a significant influence on friction and wear levels under dry sliding conditions. It was also identified the correlation between several surface topography parameters and friction and wear. [ABSTRACT FROM AUTHOR]

The frictional capacity of rubber-tired metros decreases over time under the action of metro traffic. It is well known that the texture of rolling tracks contributes to evacuate water from the tire/track interface and generate friction forces. There is then a need to understand the evolution under traffic of the texture of rolling tracks to optimize their maintenance in terms of surface texturing. This paper investigates the friction and wear of steel rolling tracks subjected to laboratory polishing tests. Specimens are extracted from real metro tracks. Different initial textures obtained from different initial treatments of the surfaces are studied. Polishing and friction measurements are performed. During the polishing process, the surface topographies are measured at different polishing states and functional volumes and texture descriptors evaluated. Results show that the surface asperity's height and sharpness decrease with the number of polishing cycles. Also, the wear characterized by the difference in terms of material volumes between the initial and polished states, increases with the polishing duration. This evolution is composed of two phases corresponding respectively to transient and stationary wear. The evolution of wear volume during the stationary phase is in agreement with Archard's wear law. Tight correlation is found between friction and wear volume. [ABSTRACT FROM AUTHOR]

Purpose During running-in, the change in the honed cylinder liner surface alters the performance and efficiency of the piston ring-pack system. The present paper, thus, aims to investigate the surface topography and wear and friction evolution of a cylinder liner surface during the running-in tests on a reciprocating ring–liner tribometer under a mixed lubrication regime. After an initial period of rapid wear termed “running-in wear”, a relatively long-term steady-state surface topography can emerge. A numerical model is developed to predict the frictional performance of a piston ring-pack system at the initial and steady-state stages.Design/methodology/approach The liner surfaces are produced by slide honing (SH) and plateau honing (PH). The bearing area parameter (Rk family), commonly used in the automotive industry, is used to quantitatively characterize the surface topography change during the running-in process. A wear volume-sensitive surface roughness parameter, Rktot, is used to show the wear evolution.Findings The experimental results show that a slide-honed surface leads to reduced wear, and it reduces the costly running-in period compared to the plateau-honed surface. The simulation results show that running-in is a beneficial wear process that leads to a reduced friction mean effective pressure at the steady-state.Originality/value To simulate the mixed lubrication performance of a ring–liner system with non-Gaussian roughness, a one-dimensional homogenized mixed lubrication model was established. The real surface topography instead of its statistical properties is taken into account. [ABSTRACT FROM AUTHOR]

Al-2.26% Mg alloy reinforced with Al 3 Zr particles was synthesised by Direct Melt Reaction in situ technique. Wear rate, wear rate/vol% Al 3 Zr (normalised with respect to amount of Al 3 Zr), normalised wear, and wear coefficient have been evaluated. At different combinations of normal load and sliding velocity two modes of wear i.e. mild/oxidative and severe/oxidative-metallic modes are observed. With increase in the amount of high hardness Al 3 Zr particles, composites can be used even at higher load and sliding velocity while still being in mild wear regime. Coefficient of friction (COF) has fluctuating tendency with sliding distance. COF shows a decreasing trend with load, whereas, with sliding velocity and composition trend is reversed. Low wear and high COF indicates its suitability in brake materials. [ABSTRACT FROM AUTHOR]

Coulomb friction model is modified with considering the preliminary distance of rigid bristles and shear stiffness of the contact surface. The degeneration in friction drive and wear behavior induced by nonlinear contact (i.e., impact, intermittent, and fretting) is outlined. Wear tests of LUSMs with V-shape transducers are conducted by a homemade reciprocating apparatus. Results show that chemical inertness, thermotolerance, elasticity as well as surface topography are critical for the contact interface of LUSMs A systematic approach involving, for instance, dynamic contact, friction model, and wear behavior provides new perspectives in improving service performances and promoting practical applications. [ABSTRACT FROM AUTHOR]

This study is aimed at investigating the influence of counter surfaces׳ topography on tribological behavior of several carbon-filled polyphenylene sulfide (PPS) composites in water lubricated contacts. The results of this study showed significant increase in wear rate of pure, graphite and/or multi-walled carbon nanotubes filled PPS composites with increase in mean slope of profile along the sliding direction (Δ α y ). This is while SCF filled PPS composites exhibited 1–3 orders of magnitude lower wear rate with little dependence on counter surface roughness characteristics. Among the roughness parameters studied, R pk and lay orientation played a more significant role in friction, and R pk and Δ α y were found to correlate best with the wear rate of the composites not containing SCF in their matrices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adopting micro-bulge textures to inhibit stick–slip behavior. • Investing stick–slip behavior in the sight of motion, friction, and wear. • Comparison of anti-stick–slip effect between micro-dimple and micro-bulge textures. • Micro-bulge textures exhibit better anti-stick–slip effect compared with others. Stick-slip behavior, a common problem of contact under severe lubrication, is closely related with surface topography. To investigate the influence of surface topography types on stick–slip behavior, micro-dimple and micro-bulge textures, typical concave and convex topographies, were fabricated by pulse picosecond laser and CW fiber, respectively. A gyroscope sensor was mounted on the pin-on-disc modular of multifunctional tribometer to conduct friction dynamics tests. The intensity of stick–slip behavior is characterized by the amplitude and duration of stick–slip behavior. The results show that, under the same starved lubrication, the micro-bulge textured disc showed the lowest intensity while the untextured one showed the highest intensity. In comparison with micro-dimple and micro-bulge textured disc exhibits higher efficiency in inhibiting stick–slip behavior as well as starting stable sliding. The mechanism of inhibiting stick–slip behavior for micro-dimple textures is generated by trapping wear debris and forming effective oil film. However, the cause of micro-bulge textures is the reduced contact area, which result in the reduction of the propensity of secondary plateaus, plastic flow, and adhesive junctions between asperities. [ABSTRACT FROM AUTHOR]

MoS 2 and WS 2 nano-objects have been studied in tribological applications and increasingly in other applications where nano-objects come into sliding contact with each other. Fundamental friction studies on a single nano-object are of interest. In this research atomic force/friction force microscopy (AFM/FFM) studies have been conducted on MoS 2 and WS 2 nanotubes to study scale effects and analyze the contributions of surface topography and orientation effects on friction. Variations in friction force due to topography were determined to be as a result of the ratchet mechanism and “collision” effect. There were no orientation effects on coefficient of friction on either of the nanotubes. [ABSTRACT FROM AUTHOR]

Clutch actuators in the automotive industry are used to convert the force applied by the driver to the clutch. A typical pneumatic actuator consists of an anodised aluminium cylinder in which a piston, with a rubber lip seal and a PTFE guiding ring, slides. The system is silicone grease lubricated. The aluminium cylinder is most often cast, e.g. permanent mould, sand, or high pressure die cast. An interesting alternative is extrusion. After anodising the cylinders display different surface topography due to, amongst other things, the fabrication method. In this study, the friction behaviour of the anodised surfaces from the four mentioned methods are investigated in a reciprocating sliding test. Two test setups were used, one simulating the real contact situation, and one using a simpler sphere on flat geometry. The extruded surface oxide cracked during testing, resulting in very fluctuating friction behaviour. The high pressure die cast surface showed rather good results, but never the best. However, it is considered not suitable for the application due to its poor oxide properties. The permanent mould cast surface displayed the lowest friction coefficient, while the sand cast surface often showed the highest friction. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigate the running-in behavior of brass (i.e. 95% Copper and 5% Zinc) sliding against 100Cr6 under lubricated conditions. Prior to the tribological tests, the materials are characterized using microindention, nanoindentation, Focused Ion Beam analysis (FIB), X-Ray Photoelectron Spectroscopy (XPS), and White Light Interferometry (WLI) in order to quantify the mechanical properties, grain sizes, chemistry, and topography. The sliding experiments are performed using “real time” tribometry with a pin on plate tribometer with varying contact pressures (1–4MPa) and sliding velocities (10–20mm/s). We found that a significant reduction in friction during running-in occurs only at a small range of pressure (2.4–2.9MPa). We suggest that two main mechanisms are favorable for running-in. The first mechanism is the presence of ZnO in the near-surface region of the wear track, which acts as lubrication and reduces the friction. The second mechanism is the presence of C/CH X within the first 200nm of the pin which acts as a passivation layer and thus keeps the transfer film thin and stable. [Copyright &y& Elsevier]

Abstract: Gold and silver nanoparticles in polyelectrolyte multilayers film can be prepared by alternate immersion of a substrate in poly(diallyldimethylammonium) chloride (PDDA)–AuCl4 − complexes solution and poly(acrylic acid) (PAA)–Ag+ complexes solution followed by reduction of the metal cations (Au3+, Ag+) through immersion of NaBH4 solution. UV–vis spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectra (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to confirm the successful construction of the polyelectrolyte multilayers film and the formation of gold and silver nanoparticles. The coefficient of friction as a function of sliding velocity and normal load also has been studied. The nanoparticles composite polyelectrolyte multilayers exhibited increased wear resistance compared with the pure polyelectrolyte multilayers. [Copyright &y& Elsevier]

Abstract: The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. 60SiCr7 spring steel samples were austempered in a salt bath maintained at 250, 300 and 350°C respectively for 1h. Rolling with 5% sliding wear tests were performed using self mated discs for three different test cycles, namely 6000, 18,000 and 30,000 cycles. The aim was to study the wear performance of the 60SiCr7 steel with a carbide-free microstructure containing different amounts of retained austenite. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analysed by scanning electron microscopy and X-ray diffraction. Microhardness profiles were also obtained in order to analyse strain-hardening effects beneath the contact surfaces. The results indicate that the material with highest hardness—the one austempered at 250°C—exhibited the lowest wear rate in every case. It was also observed that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles. Finally, the results appear to indicate that the initial roughness of the samples has no major effect in the wear rate of the samples above 2500 cycles. The higher wear performance of the sample austempered at 250°C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples undergo the TRIP phenomenon since, after wear; no retained austenite could be detected by XRD. [Copyright &y& Elsevier]

Abstract: The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength Boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength Boron steel. Reducing the wear of rails and wheels and controlling the frictional behavior in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic, etc. Therefore, the aim of this work has been to investigate and compare the tribological properties of Boron steel and UIC 1100 rail steel in contact with Blue Light wheel steel (AAR Class C (69-JDG-8)) under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro-hardness indenter, light microscope and SEM/EDS were used to analyze the results. Results from the experiments show that the friction coefficient in tests with Boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the Boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased. [Copyright &y& Elsevier]

Abstract: Introducing specific textures on a tribological surface can contribute to friction reduction in sliding contacts. In the present paper, a pulsed Nd:YAG laser emitting at 1064nm, was used against 100Cr6 steel samples in order to produce well-defined surface micro-pores, which can act as lubricant reservoirs, micro-hydrodynamic bearings as well as traps for wear debris. Due to the high flexibility of the laser system, structural features such as shape, size, density and depth can be varied easily by changing the laser parameters. To optimize the parameters of the laser surface texturing process, an investigation was performed using different pulse numbers, various pulse energies and two different modes (single- and multi-mode). The microtextures were characterized with optical microscopy, scanning electron microscopy (SEM) and by topography techniques. The relationship between the laser processing parameters and qualitative and quantitative profile of the micro-pores was studied. Tribological testing of laser textured surfaces was performed in a low frequency–long displacement reciprocating sliding wear tester under boundary lubrication and results compared to un-textured case. Tribological comparison of textured, textured and lapped, and untextured surfaces shows only minimal influence of texturing for contact conditions investigated. [Copyright &y& Elsevier]

Abstract: This work aims to study and understand the influence of the surface topography on wear of grey cast iron used for heavy duty diesel engine cylinder liners. A micro-alloyed grey cast iron was tested with different surface topographies. These were polished surfaces, honed surfaces (with two different honing parameters) and three model surfaces with well defined grooves on a polished specimen. Reciprocating friction tests using a steel ball rubbing against a flat or a cylindrical sample (extracted from a cylinder liner) were carried out on a Cameron Plint test rig. A commercial synthetic oil for diesel engine was used as the lubricant. The friction coefficient and the electrical contact resistance were measured during the tests. The wear volume of the cylinder liner part was also measured at the end of the test. The influence of the surface topography on the tribochemical film formation and on the wear behaviour of cast iron was established. Surfaces exhibiting lots of surface asperities had the highest wear, mainly due to delayed formation of protective tribochemical film. In our test conditions, the spacing between the grooves on model specimens had no influence on the wear behaviour of the cast iron specimens. [Copyright &y& Elsevier]

Abstract: Friction and wear are constant problems encountered in camshaft development. Among a wide amount of factors, surface topography is an important feature to improve in this complex system. Four parts of different shapes can be differentiated on an injection cam profile. Therefore the machining of such component is quite particular. Considering the complex shape of an injection cam, this paper is divided in two studies: 1. Variations of surface topography around freshly produced cams in order to emphasize the particular profile of cams which leads to a complex machining. 2. Evolution of surfaces during run-in in order to discover the effects of wear process on a group of roughness parameters. The results show a variation of density of peaks along the freshly produced cam surface and highlight also the importance of roller type on the evolution of topography. Further results show that summits of the surface are rounded off during run-in. Concerning the future, results of the study are encouraging to investigate more deeply the tribological behaviour (contact mechanic, oil film thickness) of the surfaces. [Copyright &y& Elsevier]

Abstract: Brake noise is an example of noise caused by vibrations induced by friction forces. During brake operation, the friction between the pad and the disc can induce a dynamic instability in the system. Brake squeal can occur in the frequency range between 1 and 20kHz, and more. Approaches to this problem are usually confined to the analysis of the system dynamics or to the tribological studies (analysis of the contact surfaces). In a previous dynamic analysis, the squeal events treated in this paper were identified to be dynamic instabilities of the brake system. This paper presents an experimental tribological analysis performed in parallel to the dynamic one and aimed to highlight the role of the contact problems in the squeal phenomena. The topography of the contact surface after braking phase with and without squeal is presented. The features of the third body and the surface topography were found to be completely different in the two cases. After squeal events the topography of the surface and the internal structure of the pad material close to the contact show several cracks and material exfoliations; on the contrary, after braking without squeal the contact surfaces were found to be smooth and compact. The analysis of the system vibrations during squeal and the numerical analysis of the contact stresses allow to relate these features to the fatigue excitation due to the local oscillation of the contact stresses at the contact surface at the squeal frequencies. The surface topography after squeal, by revealing several fatigue evidences, points out a further problem, i.e., the possible increasing of wear rates that are consequent to the squeal vibrations. [Copyright &y& Elsevier]

Abstract: Development of surface topography of two solids in a frictional contact is studied with the method of movable cellular automata. After the running-in process, the bodies are separated and the surface power spectra of both bodies are determined. The power spectra show a dependence on the wave vector, which is typical for fractal surfaces. It is shown, that roughness parameters of friction surface depend on relative velocity of sliding and external pressure. [Copyright &y& Elsevier]

Abstract: In brake systems the surface topography of the brake pad is characterized by an equilibrium of flow of hard patches, which are built up and destroyed, depending on the load history. Since these patches carry the main friction power, the friction coefficient itself depends on the load history, too. So the friction coefficient has to be described by differential equations instead of algebraic equations, connecting intimately the friction- and wear process. With these dynamic dependencies we are able to build up a new model, using the technique of Cellular Automata, which gives a dynamic and detailed insight into the brake pad''s surface topography during the friction process. [Copyright &y& Elsevier]

• The physicochemical properties of modified desert date oil were improved. • Copper nanoparticles addition shows improvement in the tribological performance. • Excessive amount of nanoparticles results in more friction and wear behaviour. • Modified desert date oil with nanoparticles addition are a suitable alternate to the mineral oil. Based on the environmental concerns related to the pollution caused by the vehicles and the demand for an alternative to the conventional lubricant resulted in the studies to be conducted that are environmental-friendly. In this study, friction and wear behavior of the surfaces in contact was conducted to observe their tendency during the application of an alternative lubricant to the mineral oil. Desert date oil was having the potential of an alternative to the mineral oil and they were available in abundant amount. During the initial stage, desert date oil was transesterified using the two-step transesterification process and further it was added to the trimethylolpropane. After this process, nanoparticles were added in different amounts to the modified desert date oil. The friction and wear behavior of the modified desert date oil was tested using four-ball tester under different conditions. For the surface topography analysis, SEM and EDS analysis were conducted. The concentration of the nanoparticles added to the biolubricant was considered based on the previous work conducted. The input parameters which were considered during the test consists of normal load, sliding speed, variation in the addition of the nanoparticles to the biolubricant (0.3–1.6% with a gap of 0.3%). Based on the study conducted, 0.9% concentration of the copper nanoparticles showed a significant improvement in term of reducing COF, wear rate, mean wear scar diameter and improved worn surface morphology was obtained with comparison to the mineral oil. The maximum increment in the properties relative to the tribological analysis was shown when the concentration of the copper nanoparticles to the modified desert date oil increases beyond 0.9% copper nanoparticles during the addition in the amount of 1.3% and 1.6%. Conclusively, the performance of the modified desert date oil with 0.9% copper nanoparticles addition has the potential impact as a lubricant with comparison to the mineral oil and other samples. The modified desert date oil with an application of 0.9% copper nanoparticles could be considered as a suitable alternative to the mineral oil while considering environmental concern and energy saving. [ABSTRACT FROM AUTHOR]