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Surface topography influences friction and transfer layer formation during sliding. In the present investigation, various kinds of surface topography were produced on steel plates. Pins made of metals (pure Al, Cu and Pb) and alloys (Al-4Mg and Al-8Mg) were then slid against prepared steel plates using inclined pin-on-plate sliding tester to understand the role of surface topography of harder surface and load on friction and transfer layer formation under both dry and lubricated conditions. It was observed that the transfer layer formation and coefficient of friction along with its two components, namely adhesion and plowing, are strongly dependent on surface topography and independent of surface roughness (Ra). The plowing component of friction was highest for the surface that promotes plane strain conditions and lowest for the surface that promotes plane stress conditions near the surface.

The frictional performance of a bearing is of significant interest in any mechanical system where there are lubricated surfaces under load and in relative motion. Surface topography plays a major role in determining the coefficient of friction for the bearing because the size of the fluid film and topography are of a comparable order. The problem of optimising topography for such a system is complicated by the separation in scales between the size of the lubricated domain and that of the topography, which is of at least one order of magnitude or more smaller. This paper introduces a multiscale method for optimising the small scale topography for improved frictional performance of the large scale bearing. The approach fully couples the elastohydrodynamic lubrication at both scales between pressure generated in the lubricant and deformation of the bounding surfaces. Homogenised small scale data is used to inform the large scale model and is represented using Moving Least Squares metamodels calibrated by cross validation. An optimal topography for a minimum coefficient of friction for the bearing is identified and comparisons made of local minima in the response, where very different topographies with similar frictional performance are observed. Comparisons of the optimal topography with the smooth surface model demonstrated the complexity of capturing the non-linear effect of topography and the necessity of the multiscale method in capturing this. Deviations from the smooth surface model were quantified by the metamodel coefficients and showed how topographies with a similar frictional performance have very different characteristics. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the influence of the surface topography on the tribological behavior of the wheel/rail contact. Four different groove orientations forming the surface topographies-smooth surface, 0°, 45° and 90°-were manufactured by grinding and compared. All friction tests with different surface topographies were conducted using an alternative tribometer simulating the pure sliding process in the wheel-rail contact. The Hertzian pressure was maintained at 1,000 MPa with two levels of sliding velocity (20 mm/s and 80 mm/s). This study resulted in five main findings. First, the initial surface topographies seemed to have a significant effect on the friction coefficient independently of the speed. Second, the increase of the sliding velocity would decrease the friction coefficient. Third, especially when accompanied with a high sliding velocity, an initial rough surface would have a significant effect on the wear of the wheel. Fourth, the highest wear values were observed at groove orientations of 45° when accompanied with a high sliding velocity. Finally, the break-in duration seemed to depend on the initial surface topographies of the rail and the sliding velocity. [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]

Wear studies of insitu AA5052/ZrB 2 composites show a linear relationship between cumulative wear and sliding distance, whereas, coefficient of friction has fluctuating tendency. Wear rate and coefficient of friction continuously increase with sliding velocity and load showing mild to severe transition at higher values. Amount of ZrB 2 also affects the wear and friction behaviour. The worn surface study and EDS analysis are in agreement with wear and friction results. Morphology and mechanical properties have also been correlated with wear and friction. These composites could be potential candidate in applications like brake drums/rotors, cylinder liners, connecting rods, cylinder blocks and pistons. [ABSTRACT FROM AUTHOR]

One of the main parameters affecting finger friction, friction-induced vibrations in the finger, and consequently tactility is surface topography. Recently Skedung et al. performed finger friction measurements on fine controlled surfaces. These surfaces were sinusoidal with wavelengths from 0.27 to 8.8 µm and amplitudes from 0.007 to 6 µm. Building on those tests an analytical model for the contact was developed to explain the differences in friction coefficient. The contact was modelled as trapezoids in a circular pattern pressed against a sinusoidal plane. Results showed that the calculated contact area and therefore friction coefficient corresponded well with the measurements. This model can be used to see how the different surface parameters influence friction. [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]

Ionic liquids are getting increased attention due to their potential use as additives or lubricants. One of parameters that influence their performance is anion alkyl chain length. Three chain lengths in imidazolium sulfate ionic liquids were varied in three different types of tests in order to study the friction performance in all lubrication regimes at different shear rates. Results show significant effect of alkyl chain length on friction behaviour and surface topography. The shortest chain length ionic liquid had the poorest friction performance whilst longer alkyl chain lengths performed significantly better, which was evidenced by the electrical contact resistance. Although friction behaviour was not generally reduced with ionic liquid mixtures, clear tribological improvement was observed in high shear conditions depending on alkyl chain length. Atomic force microscopy (AFM) analysis revealed correlation between ionic liquid chemistry and surface topography of samples after the experiments, with significantly increased roughness for short chain ionic liquid mixture. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper the results of experimental tests aimed to determine the friction coefficient in sheet metal forming operations for various sheet metal materials and at different operative conditions are presented. The research has considered the frictional characterization of three kinds of drawing quality steels that are commonly used in automotive industry. These are a drawing quality steel (DQ), a deep drawing quality steel (DDQ), and extra deep drawing quality steel (EDDQ). For measurement of the sheet surface topography, a 3D stylus instrument Alicona InfiniteFocus was used. To determine the friction coefficient three tribological tests, i.e. a strip drawing test, a draw bead test and a pin-on-disc tribometer, have been conducted. The experimental results have ascertained several relationships showing the effect of sheet metal surface roughness, lubricant conditions and sheet orientation on the value of friction coefficient in sheet metal forming processes. The results further showed that the surface topography and sample orientation in the rolling direction of the sheet are significant factors that influence the friction coefficient. It was found that the tested steel sheets, selected from automotive industry applications, exhibit anisotropic resistance to the friction corresponding to the measured orientation in relation to the rolling direction of the sheet. [ABSTRACT FROM AUTHOR]

The correlation between the type of abrasive in the brake friction composite and the braking induced emission was studied. Brake pads with four different abrasives; silicon carbide, alumina, zircon, and magnesia, were evaluated using a reduced scale dynamometer with an airborne particle counter. The results indicated that the particle abrasivity, comprising aspects such as hardness, fracture toughness, and angularity, strongly affected the disc wear and airborne particle emission, whereas the pad wear was more influenced by the strength of the friction film that was changed by the iron moved from the grey iron disc. The fracture toughness of the abrasives had a significant effect on the disc wear rate and mass concentration of airborne wear particles emitted during brake application. In contrast, the number concentration was considerably influenced by the wear mode of the abrasives against the grey iron disc. • Type of abrasives in the friction composite affected wear and brake emission. • Pad wear increased by the iron transferred from the grey iron disc. • Fracture toughness of abrasives strongly affected the brake emission. • Abrasive wear mode causes a discrepancy between number and mass concentrations. [ABSTRACT FROM AUTHOR]

The good physical and chemical properties of CFRPEEK make it advantageous as a friction pair for water hydraulic components. This paper investigated the effects of surface topography and wettability on the tribological properties of CFRPEEK and 316 L under water lubrication, with emphasis on four topographies of hemispherical pit, conical pit, ellipsoidal pit and wedge-shaped pit. From the experimental results, the ellipsoidal pit CFRPEEK samples exhibited the best tribological properties and better wettability. An interesting phenomenon was found that when the contact angle of the CFRPEEK sample is small, the friction coefficient and the wear scar depth are also small. In conclusion, taking the ellipsoidal pit as the surface topography of the CFRPEEK sample is conducive to improving its wettability, and promote the formation of stable water film, thereby improving its performance, reducing wear and increasing its service life. [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]

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]

Tribological properties of acid and alkali solutions on glass surface were studied in aqueous environment using a ball-on-disc reciprocating configuration. Interactions between lubricants and sliding surfaces produce different surface topographies. The lubricating ability of each kind of surface topography was evaluated using the same base oil. Wear tracks which were smooth or with grooves on the surfaces had high coefficient of friction in reciprocating sliding tests. However, surfaces with pits exhibited much lower friction than that the others. Low friction coefficients could be achieved after the running-in process with acidic solutions, accompanied by the formation of a pitted topography on the wear tracks. Especially, the friction coefficient was found to be below 0.01 during the steady sliding period, except at the reversal positions. Such good lubricity could be attributed to the micro-sized pits. [ABSTRACT FROM AUTHOR]

Tribological systems are subjected to a steady decrease of friction and wear due to ecological and economical requirements. Ultra-low sliding wear rate, in the order of some nanometres per hour, is desired e.g. for gears of wind turbines, valve and drive train components, or artificial hip joints in order to increase service life time. One way to further decrease the wear rates is to manipulate the run-in behaviour in such way that the steady state phase is reached earlier. Concerning the run-in, the surface topography and surface near material parameters are the important factors. With respect to the surface topography the optimal surfaces are under discussion. Due to the very small wear rates which are achieved within the ultra-mild sliding wear regime, classical investigations of wear like weighting and microstructural analysis are made difficult by the scale and extent of occurring wear appearances. Here localized effects of dissipated friction power e.g. friction energy determine the acting mechanisms and, therefore, the performance of tribosystems during run-in. In this study, wear tests and associated numerical contact calculations will be presented and discussed. Thus carburized martensitic steel is milled and afterwards subjected to boundary lubricated sliding wear. This topography was chosen as model due to its periodical shape and distinct shape of asperities. This allows for microscopical investigations of the nominal contact area as well as for deriving input data of sufficient quality for numerical calculations for the real contact area. Corresponding wear appearances are to be expected to take place at the summits of the machining marks. The numerical contact analyses are carried out using the elastic-half-space model, because the also applied simpler approach by Greenwood–Williamson led to practicable results but does not consider contact pressure distributions. From the in-situ measurements of the friction force and the relative velocity in combination with the corresponding local surface topography the contact simulation of the real contact area allowed for the calculation of the local dissipated friction power per contact area. [ABSTRACT FROM AUTHOR]

This article features a field experiment conducted on existing road pavements to characterise macro- and micro-texture variations at actual road conditions and to substantiate links to friction values. Three-dimensional inspections of the wearing course surface of three asphalt mixes were performed during a short period of 9 months. Several statistical texture indicators, spectral analysis and photo-simulated images of surface height maps were employed to analyse macro/micro-texture evolution and to study the physical phenomena behind it. Fractal and non-fractal parameters, with a focus on Hurst exponent (H), were used in associating texture with friction. The results of texture evolution clearly state that changes in macro/micro-scales occur within full surface profile and not solely from the polishing phenomena of a small percentage of top surface topographies. It was demonstrated that H, as an indicator of full surface profile specification, could not be employed for road texture–friction studies at actual road conditions. [ABSTRACT FROM AUTHOR]

Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding pairs in machinery. [ABSTRACT FROM AUTHOR]

The aim of the present work was to investigate the influence of humidity and corrosion in a high-salinity environment on the friction and wear behaviour of three brake disc materials. Experiments were conducted using a commercially built disc-on-pin machine (SRV4, Optimal Instruments, Germany). Three different disc brake materials were used: cast iron (type FG25), chromium bearing steel (type 100Cr6) and an aluminium-based composite Al MMC (type A359/SiC p ). The pin in all tests was a commercial automotive brake pad material. The results showed that the friction coefficients and the wear rate for all tested materials were sensitive to increasing normal load and the sliding speed. At increased humidity level, a water film formed and behaved as a lubricant. The corrosion due to salt spray had a larger influence on the tribological behaviour of the cast iron and the chromium steel than it did on the Al MMC. The Al MMC A359/SiC p exhibited a better tribological behaviour than the other brake disc materials used in this investigation under the given test conditions. [ABSTRACT FROM AUTHOR]

This article presents the development of a method for manufacturing durable countersurfaces for testing the friction of rubber samples in a laboratory. The surface sample was designed to replicate the surface roughness characteristics of a predefined road surface. Four different types of samples were manufactured: two bitumen bound stone mastic asphalt samples, one concrete bound sample, and one epoxy bound sample. In addition, the surfaces were sandblasted to remove binder from the top of the surface. The similarity in surface roughness between the predefined target road surface and the laboratory surface samples was evaluated using optical 3D surface roughness measurements and surface roughness power spectrums. The durability of the surfaces was investigated by repeated dry rubber sliding friction tests. It was found that out of the studied surface samples the best one to both replicate the surface characteristics of the target surface and to produce a durable surface in terms of wear was the one using epoxy resin as a binder. By replacing bitumen with epoxy, more friction tests could be run without significant changes in the surface topography or rubber friction. In addition a reasonable correlation between the surface roughness power spectrums and the friction results was found, which supports the use of roughness power spectrums as a roughness metric for road surfaces in the context of rubber friction. [ABSTRACT FROM AUTHOR]

A series of experimental tests were carried out using turned and ground mild steel surfaces rubbing against smooth and rough stainless steel 304 (SS304) conterfaces under different operating conditions on a pin-on-disc test rig. During testing, the friction coefficient and wear rate were recorded. The topography of worn surfaces was also observed with optical microscope. The average surface roughness of turned and ground mild steel were measured after friction test. The result displays that normal load, sliding speed and the surface conditions of sliding pairs have a distinct effect on the friction and wear behaviour of turned and ground mild steel rubbing against smooth and rough SS304 conterfaces. During this study, the effects of duration of rubbing on friction coefficient are also observed. Friction coefficient and wear rate of four types of disc-pin combinations such as ground-smooth, turned-smooth, ground-rough and turned-rough are observed under different normal loads and sliding velocities. Experimental results reveal that friction coefficient of mild steel for all types of disc-pin combinations decreases with the increase in normal load and sliding velocity. [ABSTRACT FROM AUTHOR]

The contact and friction behavior of a medical compression stocking (MCS) under different strains was investigated in friction and compression experiments against a mechanical skin model. In addition, the 3D topography of the MCS surfaces was analyzed in order to study the relationship between macroscopic friction and microscopic surface properties. The load dependence of friction coefficients was found to be in accordance with the adhesion friction model. The surface structure of MCS samples was considerably changed when varying the strain state, while friction coefficients remained comparable, indicating real contact areas independent of strain on the microscopic level. The experimental findings could be confirmed and explained on the basis of the microscopic surface analyses, when interpreting the fabric surfaces to be composed of numerous individual round asperities obeying the Hertz contact model. [ABSTRACT FROM AUTHOR]

For micro/nanoscale devices, surface functionalization is essential to achieve function and performance superior to those that originate from the inherent bulk material properties. As a method of surface functionalization, we dip-coated nanometer-thick liquid lubricant films onto solid surfaces and then patterned the lubricant films with ultraviolet (UV) irradiation through a photomask. Surface topography, adhesion, and friction measurements demonstrated that the patterned films feature a concave–convex thickness distribution with thicker lubricant in the irradiated regions and a functional distribution with lower adhesion and friction in the irradiated convex regions. The pattern linewidth ranged from 100 to as fine as 0.5 μm. The surface functionalization effect of UV-patterning was investigated by measuring the water contact angles, surface energies, friction forces, and depletion of the patterned, as-dipped, and full UV-irradiated lubricant films. The full UV-irradiated lubricant film was hydrophobic with a water contact angle of 102.1°, and had lower surface energy, friction, and depletion than the as-dipped film, which was hydrophilic with a water contact angle of 80.7°. This demonstrates that UV irradiation substantially improves the surface and tribological properties of the nanometer-thick liquid lubricant films. The UV-patterned lubricant films exhibited superior surface and tribological properties than the as-dipped film. The water contact angle increased and the surface energy, friction, and depletion decreased as the pattern linewidth decreased. In particular, the 0.5-μm patterned lubricant film even showed a larger water contact angle and lower friction and depletion than the full UV-irradiated film. These indicate that UV-patterning of nanometer-thick lubricant films with a minimized linewidth has a better surface functionalization effect than full UV irradiation. Enhancement of the surface functionalization effect may be attributed to a transition in the contact state, which was indicated by the different instantaneous friction behavior of the 0.5-μm patterned lubricant film. [ABSTRACT FROM AUTHOR]

In this study, ring compression test was conducted to investigate i) effects of surface topography on friction and lubrication at room temperature with both dry and lubricated conditions, and ii) the effect of die temperature on friction and lubrication by differentiating temperatures of die and ring samples. Findings from experiments and FE results lead to develop a pressure-dependent variable friction model that concurrently changes friction factor during the forming stroke and different contact surface areas. The constant frictional model and this variable friction model were used in FE simulations of ring compression. The prediction results were compared with experimental results in details. The use of variable friction model gave very good correlations of the final ring geometry than other constant friction models in comparison to experiments. This implies that the pressure-dependent variable friction model can better characterize the interfacial friction condition in cold forging applications. In the ring compression with heated dies, the temperature rise was found to degrade the performance of lubricant, which resulted in the tapered shape ring. Therefore, the effect of surface topography and die temperature on interfacial friction condition with lubricant viscosity should be considered for the improved friction model for FE simulations of forging processes with high stroking rates. [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]

[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]

Abstract: Numerical models of surface micro-topography find applications in the development of multiscale models for friction and wear between two interacting surfaces. Although much work has been dedicated to developing such multiscale models, they have been hampered by the strong dependence of surface statistics on the resolution of surface topography measurements. The objective of this study is to develop a systematic approach to reduce this dependence so that the resulting statistical parameters are suitable for developing micro-asperity based continuum friction models. The approach significantly reduces but does not eliminate the dependence of surface statistics on the measurement resolution. It is based on fitting a Gaussian function to numerically calculated autocorrelation functions for randomly selected profiles from a surface. The use of a Gaussian function filters out very small scale asperities that affect the statistical parameters but are not tribologically significant. The distributions of the resulting parameters allow us to calculate the spectral moments using Monte Carlo simulations. The approach is applied to numerically generated surfaces as well as micro-topography measurements of a high density polyethylene (HDPE) surface. Results show that the proposed approach is considerably less sensitive to the measurement resolution, especially in comparison to standard statistical sampling methods. We argue that the Gaussian autocorrelation function used in our work is a better choice compared to other forms for continuum-level applications. [Copyright &y& Elsevier]

Abstract: Titanium and its alloys generally display poor tribological properties in sliding contacts due to their high chemical activity and strong adhesion to the counter surface. The strong adhesion causes a high tendency to transfer and ultimately galling or build-up edge formation, resulting in severe surface damage. As a result, forming and machining of titanium and its alloys are generally associated with significant problems such as high friction, rapid tool wear and poor surface finish of the formed/machined surface. In the present study, in situ tests in a scanning electron microscope have been performed to increase the understanding of the mechanisms controlling the initial transfer of titanium (Grade 2) in sliding contact with tool surfaces. Tool materials included cover cold work tool steel, cemented carbide, CVD deposited Al2O3 and PVD deposited DLC. In these tests, a relatively sharp tip, representing the titanium work material, slides against a flat surface, representing the tool. The contact conditions result in plastic deformation of the work material against the tool surface, thereby simulating forming or machining. The limited and well-defined contact, along with the possibility to study the sliding in the SEM, makes it possible to correlate local surface variations to transfer of work material and frictional response. Post-test characterization of the contact surfaces was performed by high-resolution SEM, TEM, EDS and EELS. The initial friction was low and stable against all tested materials, but then gradually escalated against all surfaces except the DLC. The friction escalation was associated to increasing levels of transfer, while the DLC stayed virtually free from transfer. From these very initial sliding tests DLC is a promising tool coating in forming and machining of titanium. [Copyright &y& Elsevier]

In this paper distortion of surface topography measurement results by improper selection of the reference plane is taken into consideration. The following types of surfaces from cylindrical elements were analyzed: cylinder liners after plateau honing, cylinder liners with additionally burnished oil pockets and turned piston skirts. Surface topographies of these elements after a low wear process were also studied. In order to obtain areal surface topography parameters, the form was eliminated using cylinders and polynomials of the following degrees: 2, 3, 4, 6, 8, 10 and 12. Parameters of surfaces after form removal were compared. After analysis of results the reference elements for each kind of surface were recommended. A special procedure was proposed in order to select the degree of a polynomial. This method is based on surface topography changes with increase of polynomial degree. The effect of improper form elimination on measuring uncertainty was studied. [ABSTRACT FROM AUTHOR]

Abstract: Effect of water absorption on friction and wear of polyamides, namely monolithic polyamide 66 (PA66) and PA66 composite with 30wt% of short glass fibers, was investigated using a block-on-ring-type tribotester. Monolithic PA66 showed high wear rates after water absorption because of softening by the absorbed water molecules and increased interfacial adhesion on the steel counter surface. Degraded wear characteristics of monolithic PA66 by chain scission of the amide functional group by water molecules were substantially improved by short glass-fiber reinforcement. The improved friction and wear characteristics were attributed to contact plateaus produced during sliding, which were held by condensed glass fibers, suggesting possible applications of PA66 in a humid environment by reinforcing it with short glass fibers. [Copyright &y& Elsevier]

The work reported in this paper aims at understanding sliding friction anisotropy at the nano-, micro-, and macroscales with respect to surface asperity orientation and exploring the mechanisms behind this phenomenon. Experiments were conducted by probing surfaces with grooves parallel or perpendicular to the direction of relative motion. Continuum mechanics analyses with the FEM and a semi-analytical static friction model and the atomic molecular dynamics simulation were performed for the mechanism exploration. Friction anisotropy was understood from the differences in contact area, surface stiffness, stiction length, and energy barrier from the continuum mechanics prospective and from that in the stick-slip phenomena at the atomic level. [ABSTRACT FROM AUTHOR]

SUMMARY A triangular wedge, composed of a frictional material such as sand, and accreting additional material at its front, is the classical prototype for accretionary wedges and fold-and-thrust belts. A simplified method is proposed to capture the internal deformation of this structure resulting from a large number of faulting events during compression. The method combines the application of the kinematic approach of limit analysis to predict the optimum thrust-fold and a set of geometrical rules to update the geometry accordingly, at each increment of shortening. It is shown that the structure topography remains approximately planar with a slope predicted by the critical Coulomb wedge theory. Failure by faulting occurs anywhere within the wedge at criticality, and its exact position is sensitive to topographic perturbations resulting from the deformation history. The convergence analysis in terms of the shortening increments and of the topography discretization reveals that the timing and the position of a single faulting event cannot be predicted. The convergence is achieved nevertheless in terms of the statistics of the distribution of the faulting events throughout the structure and during the entire deformation history. It is these two convergence properties that are presented to justify the claim that these compressed frictional wedges are imperfection sensitive, chaotic systems. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In any attempt to theoretically calculate the real contact area for 3D engineering surfaces, a criterion is needed to identify the relevant asperity-peaks that carry the load in tribological contacts. In our recent work, we investigated how different, available 2D criteria affect the properties of the theoretically determined asperity-peaks in 2D surfaces. In this work, however, we focused on a 3D surface characterisation. The effect of different asperity-peak identification criteria on the properties of the asperity-peaks (numbers, radii and heights) is studied in the 3D domain. Several different criteria that take into account the number of neighbouring points, the distances between them (lateral resolution) and their heights were evaluated for real measured surfaces with five different surface roughnesses in the broad engineering range of arithmetic surface roughness from S a =0.005µm to S a =0.529µm. From the results it follows that all three chosen asperity-peak identification criteria (5PP-3D, 9PP-3D and 9PP-R-3D) result in reliable asperity-peak properties, and none of them can be favoured based on a theoretical evaluation only. There are, however, important differences between them. The data resolution in the x and y directions has a very important influence on the numbers, radii and heights of the asperity-peaks, and the results suggest that the data's lateral resolution, below 1µm, should be used for the relevant asperity-peak identification. [ABSTRACT FROM AUTHOR]

Abstract: Despite favourable gravitational instability and ridge-push, elastic and frictional forces prevent subduction initiation from arising spontaneously at passive margins. Here, we argue that forces arising from large continental topographic gradients are required to initiate subduction at passive margins. In order to test this hypothesis, we use 2D numerical models to assess the influence of the Andean Plateau on stress magnitudes and deformation patterns at the Brazilian passive margin. The numerical results indicate that “plateau-push” in this region is a necessary additional force to initiate subduction. As the SE Brazilian margin currently shows no signs of self-sustained subduction, we examined geological and geophysical data to determine if the margin is in the preliminary stages of subduction initiation. The compiled data indicate that the margin is presently undergoing tectonic inversion, which we infer as part of the continental–oceanic overthrusting stage of subduction initiation. We refer to this early subduction stage as the “Brazilian Stage”, which is characterized by >10km deep reverse fault seismicity at the margin, recent topographic uplift on the continental side, thick continental crust at the margin, and bulging on the oceanic side due to loading by the overthrusting continent. The combined results of the numerical simulations and passive margin analysis indicate that the SE Brazilian margin is a prototype candidate for subduction initiation. [Copyright &y& Elsevier]

Background: When scanning surfaces, humans perceive some of their physical attributes. These percepts are frequently accompanied by a sensation of (un)pleasantness. We therefore hypothesized that aspects of the mechanical activity induced by scanning surfaces with fingertips could be objectively associated with a pleasantness sensation. Previously, we developed a unidimensional measure of pleasantness, the Pleasant Touch Scale, quantifying the pleasantness level of 37 different materials. Findings of this study suggested that the sensation of pleasantness was influenced by the average magnitude of the frictional forces brought about by sliding the finger on the surface, and by the surface topography. In the present study, we correlated (i) characteristics of the fluctuations of frictional forces resulting from the interaction between the finger and the surface asperities as well as (ii) the average friction with the sensation of pleasantness. Results: Eight blindfolded participants tactually explored twelve materials of the Pleasant Touch Scale through lateral sliding movements of their index fingertip. During exploration, the normal and tangential interaction force components, fN and fT, as well as the fingertip trajectory were measured. The effect of the frictional force on pleasantness sensation was investigated through the analysis of the ratio fT to fN, i.e. the net coefficient of kinetic friction, μ. The influence of the surface topographies was investigated through analysis of rapid fT fluctuations in the spatial frequency domain. Results showed that high values of μ were anticorrelated with pleasantness. Furthermore, surfaces associated with fluctuations of fT having higher amplitudes in the low frequency range than in the high one were judged to be less pleasant than the surfaces yielding evenly distributed amplitudes throughout the whole spatial frequency domain. Conclusion: Characteristics of the frictional force fluctuations and of the net friction taking place during scanning can reliably be correlated with the pleasantness sensation of surfaces. [ABSTRACT FROM AUTHOR]

High-speed machining of austenitic stainless steel normally causes significant tool damage and generates reduced tool life. In this paper, five AlTiN PVD coatings with different Al/Ti atomic ratios (50/50, 60/40, 67/33, 70/30 and 73/27) which deposited on cemented carbide inserts were used to conduct high-speed of 370 m/min finish turning tests. The experiments were carried out under different cooling conditions (dry and wet) on SS304 to study the tribological behavior of the AlTiN coatings with different Al/Ti ratios and the effect of the coolant under such aggressive cutting conditions. During the experiments, tool life, cutting force, wear mechanism, friction condition and surface integrity of machined workpiece were investigated. Crater wear was found to be the predominant wear mode during the cutting test, while the complex combination of oxidation, abrasion/attrition, adhesion, and chipping contributed to the tool failure. Given the machining conditions proposed in this study, the results revealed that all coated inserts possessed an improved friction behavior in the wet cutting condition. Compared to the dry machining, all five coatings had exhibited 2–3 times longer tool life. The AlTiN coated insert (Al/Ti = 60/40), in particular, exhibited a cutting length of almost 7000 m, compared to 1000 m for the AlTiN coated insert (Al/Ti = 73/27). • Novel dry and wet high-speed turning (370 m/min) of austenitic stainless steel 304. • Wear performance and tribological characteristics of five different Al/Ti ratios in AlTiN PVD coating. • Chip cross-section characteristics including micro-hardness and microstructure topography. • Surface integrity of machined workpiece provides evidence of machinability of stainless steel 304. [ABSTRACT FROM AUTHOR]

In this study, molybdenum dithiocarbamate (MoDTC) coatings were fabricated on 304 stainless steel substrates via an electrodynamic spraying process with the aim to clearly understand the evolutionary process from MoDTC to MoS 2 during contact sliding. Experiments were performed using an in-situ tribo-tester equipped with Raman spectroscopy to continuously monitor the chemical state of the wear track. The tribochemical reaction and removal process of MoDTC were assessed, and the evolution process of MoDTC was determined systematically. Additionally, it was determined that the tribological performance of the MoDTC coating was dominated by a tribochemical reaction at the microscale and by surface topography at the macroscale. • The tribochemical mechanism of MoDTC as a solid lubricant was first revealed. • Chemical evolution was monitored by an in-situ tribo-tester. • Tribochemical reaction affected by temperature and substrate roughness was studied. • Tribological performance of the MoDTC coating was highly dependent on scale. • The MoDTC coating exhibited low COF of 0.07 under severe conditions. [ABSTRACT FROM AUTHOR]

Numerical simulation of sheet metal forming processes has become indispensable in the last decades. Although the complexity of the frictional behaviour is identified as a key factor for the prediction accuracy, the industry commonly considers a constant friction coefficient for the whole tool. Furthermore, the influence of roughness distribution of the tool in the friction behaviour has not yet been addressed. In this study the influence of the die local roughness in an advanced friction model has been evaluated in three industrial automotive components. The newly implemented advanced friction model (TriboZone) is suggested for advance or mature process verifications. • An industrial mass study surface topography at multiple tools has been carried out. • The radii present the lowest roughness followed by the flat areas. • Constant friction model is the most conservative. • The model with local roughness leads to higher draw-in. • The advance model efficiency is worth it for mature models. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an investigation on the correlation between surface topography and its mechanical properties measured by a novel multi-function tribological probe microscope (TPM) at the micro/nanometre level. Four surface functions of topography, friction, nano-hardness and Young's modulus are measured over a range of materials, on a point-by-point basis using the TPM. The capability of multi-function mapping of the TPM allows the cross correlation to be carried out, in order to investigate the influence of one function on another, especially the surface topography's effect on its mechanical properties. A general negative correlation between surface topography and hardness/Young's modulus has been found for most homogeneous surfaces, which indicates a modulation effect of surface geometrical features on its mechanical properties. [Copyright &y& Elsevier]

Abstract: Composites forming processes involve mechanical interactions on the ply, tow, and filament level. 0The deformations that occur during forming processes are governed by friction between tows and tooling material on the mesoscopic level and consequently between filaments and a counterface on the microscopic level. A thorough understanding of the frictional properties on the level of individual filaments is important to understand and predict the macroscopic deformations of a fabric during forming. The contact mechanics based friction model in this work confirms an experimentally observed decrease of frictional forces with an increasing roughness of the counterface. The developed model provides a qualitative understanding of the frictional behaviour of filaments on a cylindrical metal counterface. [Copyright &y& Elsevier]

Aim: To evaluate the changes in surface roughness and frictional features of 'ion-implanted nickel titanium (NiTi) and titanium molybdenum alloy (TMA) arch wires' from its conventional types in an in-vitro laboratory set up. Materials and Methods: 'Ion-implanted NiTi and low friction TMA arch wires' were assessed for surface roughness with scanning electron microscopy (SEM) and 3 dimensional (3D) optical profilometry. Frictional forces were studied in a universal testing machine. Surface roughness of arch wires were determined as Root Mean Square (RMS) values in nanometers and Frictional Forces (FF) in grams. Statistical Analysis Used: Mean values of RMS and FF were compared by Student's 't' test and one way analysis of variance (ANOVA). Results: SEM images showed a smooth topography for ion-implanted versions. 3D optical profilometry demonstrated reduction of RMS values by 58.43% for ion-implanted NiTi (795.95 to 330.87 nm) and 48.90% for TMA groups (463.28 to 236.35 nm) from controls. Nonetheless, the corresponding decrease in FF was only 29.18% for NiTi and 22.04% for TMA, suggesting partial correction of surface roughness and disproportionate reduction in frictional forces with ion-implantation. Though the reductions were highly significant at P < 0.001, relations between surface roughness and frictional forces remained non conclusive even after ion-implantation. Conclusion: The study proved that ion-implantation can significantly reduce the surface roughness of NiTi and TMA wires but could not make a similar reduction in frictional forces. This can be attributed to the inherent differences in stiffness and surface reactivity of NiTi and TMA wires when used in combination with stainless steel brackets, which needs further investigations. [ABSTRACT FROM AUTHOR]

The article discusses an atomic force microscope (AFM)-based method for characterizing a nanoscale friction mechanism. The AFM-based method measures friction and adhesion forces. According to the authors, this method allows for the detection of a friction mechanism they call desorption stick. The role of surface topography in friction behavior is explained. The authors note that the characterization of desorption stick is likely to guide the development of low-friction surface coatings.

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]

Friction between articulating surfaces cause temperature rise in the acetabular cup and femoral head. This heating may influence the rate of wear, fatigue, creep and oxidative degradation of bearing materials. The objective of this study is to determine the effect of surface patterning on frictional temperature rise of the articulating surfaces of vitamin E blended ultra-high molecular weight polyethylene acetabular component paired with a cobalt–chromium (CoCrMo) femoral component. For this reason concave dimples were formed on inner surface of the acetabular cup with 0.5mm diameter and 0.5mm depth. Temperature rise between the bearing surfaces was measured under different loading conditions. Frictional measurements of the joints were carried out on a custom made hip joint friction experimental set up. The prostheses were of 28mm diameter. Applied static loads were changed from 200N to 1500N. In the flexion–extension plane, a simple harmonic oscillatory motion between ±24° was applied to the ultra high molecular weight polyethylene acetabular component. The frequency of motion was 1Hz and the tests were run up to 11,000 cycles. Temperature rise in acetabular and femoral component was recorded with embedded thermocouples. Lower temperature rise in patterned sample pairs were measured than unpatterned samples. So it can be said that the surface patterning contributes to reduction of frictional heating of sliding surfaces. [ABSTRACT FROM AUTHOR]

Abstract: One way of controlling friction and associated energy losses is to engineer a deterministic structural pattern on the surface of the rubbing parts (i.e., texture engineering). Custom texturing enhances the quality of lubrication, reduces friction, and allows the use of lubricants of lower viscosity. To date, a standardized procedure to generate deterministic texture constructs is virtually non-existent. Many engineers, therefore, study natural species to explore surface construction and to probe the role that surface topography assumes in friction control. Snakes offer rich examples of surfaces where topological features allow the optimization and control of frictional behavior. In this paper, we investigate the frictional behavior of a constrictor type reptile, Python regius. The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional response of snakeskin. The coefficient of friction depends on the direction of sliding: the value in forward motion is lower than that in the converse direction. Detailed analysis of the surface metrological feature reveals that tuning frictional response in snakes originates from the hierarchical nature of surface topology combined to the profile asymmetry of the surface micro-features, and the variation of the curvature of the contacting scales at different body regions. Such a combination affords the reptile the ability to optimize the frictional response. [Copyright &y& Elsevier]

Thefriction anisotropy of human hair has been investigated asa function of angle using AFM fiber probe measurements to evaluatethe role of cuticle alignment. It is found that friction hysteresis,the difference in friction coefficients between sliding with or againstthe cuticle direction, is essentially nonexistent for native humanhair. For damaged human hair, however, a clear friction hysteresisis observed, which appears to be a periodic function of the anglebetween the fibers. The implication is that antiparallel sliding isnot in itself sufficient for friction isotropy but that lifting ofthe cuticle edges is required. A methodology to perform friction analysisindependently for trace and retrace was therefore developed, whichis applicable to any type of AFM lateral force measurement. It explicitlyaccounts for roll, noncircular cross section, and off-axis alignmentas well as baseline drift, which allows real anisotropy in the frictioncoefficient to be deconvoluted from these artifacts. [ABSTRACT FROM AUTHOR]