Precise control of friction is very important for energy efficiency and sustainability in manufacturing processes. In the present investigation, various surface textures have been employed to vary the frictional conditions. More specifically, textures were varied from unidirectional to criss-cross to unidirectional by grinding the steel surfaces against emery papers for various numbers of cycles. Sliding experiments were conducted using an inclined pin-on-plate apparatus against the prepared steel surfaces under dry and lubricated conditions. In the experiments, it was observed that the coefficient of friction and transfer layer formation on the harder surfaces were controlled by the textures of the harder surfaces under both dry and lubricated conditions. The asperity angle of the harder surface plays a dominant role in controlling the friction and transfer layer at the sliding interface. Thus, by understanding appropriate roughness parameters, the friction and wear performance can be accurately controlled to enhance energy efficiency and the quality of the finished products in manufacturing process.

In self-organized sliding processes, the surfaces align to each other during sliding. This alignment leads to a more ordered contact state and significantly influences the frictional behavior. To understand the self-organization sliding processes, experiments were conducted on a pin-on-plate reciprocating sliding tester for various numbers of cycles. In the experiments, soft magnesium pins were slid against hard steel plates of various surface textures ( undirectional , 8-ground , and random ). Experimental results showed that the transfer layer formation on the steel plates increased with increasing number of cycles for all surfaces textures under both dry and lubricated conditions. The friction also increased with the number of cycles under dry conditions for all of the textures studied. During lubricated conditions, the friction decreased for unidirectional and 8-ground surfaces and increased for random surfaces with the number of cycles. Furthermore, the friction and transfer layer formation depend on the surface textures under both dry and lubricated conditions during the first few sliding cycles. Later on, it is less dependent of surface textures. The variation in the coefficient of friction under both dry and lubrication conditions were attributed to the self-organization process that occurred during repeated sliding.

CVTs are complex tribological systems with high potential concerning increasing efficiency of powertrains. To improve the performance of CVTs it is necessary to deepen the knowledge concerning parameters influencing the system behavior.

Energy and environment are of major concern in internal combustion engine component design. The piston ring-cylinder liner (PRCL) contact plays an essential part in design and is highlighted in this study. In fact, the rings ensure the sealing property, reducing the environmental impact by avoiding lubricant contamination (blow-by) and lubricant consumption. Unfortunately, when sealing, the rings generate between 11 to 24% of the friction losses in an internal combustion engine [1], thus reducing the energy efficiency of the engine. The cylinder liner surface features a special micro-geometry, a classical one is the cross-hatching pattern, obtained by honing. This texturing acts as a micro-bearing, oil reservoir and debris trap. Understanding the influence of texture parameters as groove depth and width or angle, will allow tribological improvements of the PRCL contact. The 2D transient Reynolds equation has to be solved for this kind of surface. The statistical method using the Patir and Cheng [2] flow factors is widely used. This approach lumps the different components of the surface (grooves and plateaux) and does not consider the roughness directionality. Methods decoupling both components, like the homogenization method [3] are also used. Another alternative is to use a deterministic model on measured surfaces, but this is a “hugely” expensive approach. Multigrid methods [4] are used to drastically reduce the calculational cost. The aim of the current study is to facilitate the understanding of measured surface calculations. Hence, analytical surfaces are used. They allow a flexible handling of the cross-hatching parameters. The plateaux are perfectly smooth and the grooves are sinusoidally shaped. The top ring is modelled using a parabolic profile. Periodic boundary conditions are used in the orthoradial direction and zero pressure conditions (Dirichlet) in the axial direction. To investigate the effect of different parameters, various imposed film thicknesses are applied and the mean load carrying capacity (LCC) over time is calculated. When representing the LCC corresponding to each parameter compared to the smooth LCC, as a function of the logarithm of the minimum film thickness, the curves are quite linear for small values of the film thickness and then for larger values they converge to 1.

Effect of surface microtexturing with spherical dimples of 60 μm diameter on friction behaviour of steel 100Cr6/sapphire pairs was studied as function of lubricant viscosity. Tests were run at unidirectional sliding up to 0.30 m/s using a pellet-on-disc geometry with flat contact area and drip lubrication with liquids such as glycerine-water solutions, distilled water and different mineral oils without additives. The texture pattern was produced on the polished sapphire discs by laser ablation processes. Friction force and film thickness of the lubricating liquid were continuously measured during the tests at different sliding velocities. Results showed that effectiveness of microtexturing in reducing friction and increasing load-carrying capacity depended on viscosity of the lubricant, operating conditions such as sliding velocity and applied load as well as texture parameters.

The Navier-Stokes and compressible Reynolds equations are solved for gas lubricated textured parallel slider bearings under hydrodynamic lubrication for a range of realistic texture geometry parameters and operating conditions. The simplifying assumptions inherent in the Reynolds equation are validated by comparing simulation results to the solution of the Navier-Stokes equations. Using the Reynolds equation to describe shear driven gas flow in textured parallel slider bearings is justified for the range of parameters considered.

Transient EHD lubrication, where operating parameters such as speed, load and surface curvature vary over time, occurs in many machine elements such as cams, gears or roller bearings. The effect of transient speed and surface texturing on EHD lubrication films are investigated by the direct observation. For the purposes of the experiment the speed profile of contact point between cam and follower is used. Most critical part of the operation is when the contact surfaces are running in opposite directions. This effect can cause a lubricant film breakdown and in consequence also damage of contact surfaces. For this reason three types of experiments, for the same speed profile, are carried out for polished surface and for contact surfaces with and without surface texturing. It has enabled us to consider if the texture of micro-dents have any significant influence on film thickness especially in critical parts of the operation. To simplify the problem the concept of cam and follower contact was replaced by EHD contact of the flat surface of chromium coated glass disk and a steel ball. Also only transient speed was taken into account. The method used to measured film thickness was thin film colorimetric interferometry. The experimental results show that micro-dents could increase lubrication efficiency under rolling/sliding condition through the lubricant emitted from micro-dents. It was found that the lubricant emitted from micro-dents helps to separate contact surfaces especially in the case where the contact surfaces moves very slowly in the opposite direction.

When frictional sliding is initiated, the coefficient of friction is often high during the initial transient running-in process. After that, the coefficient of friction reaches its stationary value. Running-in is interpreted as friction-induced self-organization stage in that two sliding surfaces adjust to each other due to surface roughness evolution. Shannon entropy was proposed as a surface roughness parameter, and its decrease can be used as a simple test for self-organization. Sliding experiments were conducted on the hard steel plate using a soft Al-Mg alloy pin under both dry and lubricated conditions. Based on the results of the surface profile evolution, obtained by an optical profilometer, during running-in, we discuss change of Shannon entropy for various surface textures. Various textures which are characterized in terms of roughness parameters were produced on the steel plates. We compare how self-organization occurs for different textures during running-in stage.

In the present investigation, various kinds of textures ( undirectional, 8-ground , and r andom ,) were attained on a set of steel plate surfaces. The roughness of the textures was varied using different grits of emery papers or polishing powders. Pins made of pure magnesium were then slid against the steel plates at various numbers of cycles (1, 2, 6, 10 and 20) using an inclined pin-on-plate sliding apparatus. In the experiments, it was observed that the coefficient of friction and the formation of a transfer layer depended on the die surface textures under both dry and lubricated conditions. The coefficient of friction increased with number of cycles under dry conditions for all of the textures studied. Under lubricated conditions, however, the coefficient of friction decreased for unidirectional and 8-ground surfaces and increased for random surfaces with the number of cycles. A stick-slip phenomenon was observed under both dry and lubricated conditions. Occurrence of the stick slip behavior depended on the surface texture, the load and the number of cycles. The variation in the coefficient of friction under both dry and lubrication conditions was attributed to changes in the texture of the surfaces during sliding.

Surface texture influences friction during sliding. In the present investigation, experiments were conducted using an inclined pin-on-plate apparatus to study the tribological response of metals and polymers during sliding against various surface textures. In the experiments, metals (Pb and Sn) and polymers (PP and PVC) were used for the pin and hardened steel was used for the plate. Experiments were conducted under both dry and lubricated conditions in an ambient environment. Two surface parameters of the steel plates — roughness and texture — were varied in the experiments. Using scanning electron microscope images, the surfaces of both the plate and pin materials were examined to determine the transfer layer formation on the plate and the wear of the pins. Based on the experimental results, it was observed that the transfer layer formation and the coefficient of friction were controlled by the surface texture of the plates. Moreover, both polymers and metals exhibited similar frictional responses, but the metals had a significantly larger variation in friction with surface texture.

Highly localized tribological contacts can modify the surface texture of rolling element bearing surfaces. The evolution of the surface texture generates modified subsurface stress fields within the contact and subsequently may alter the bearing rolling contact fatigue (RCF) life. In this present study, relationships between bearing surface topography and subsurface stress states are examined for their effects on bearing RCF life in the limiting case of boundary or dry contact. Results show that seemingly minor changes to surface topography may influence the stress distribution enough to affect RCF life under heavily loaded conditions.

There has recently been much interest in the micro-texturing of slider bearings, where many tiny micro-pockets are incorporated into one of the bearing surfaces. Proponents of this technology have reported that the application of micro-texture to sliding bearing surfaces can result in up to 40% reduction in friction, when the two bearing surfaces have low or zero convergence ratio, i.e. are near parallel [1]. The authors have shown previously, through a series of one dimensional analyses, that the ability of such bearings to generate load support can be explained by a lubrication mechanism termed “Inlet Suction” [2, 3]. In the current paper, these one dimensional analyses are extended to two dimensions with the inclusion of a mass-conserving cavitation algorithm based on Elrod [4]. This allows for a more complete understanding of “Inlet Suction” in real bearing geometries.

Tribological thin film coatings can enhance performance in mechanical components such as bearings and gears. Although lubricant is present in most applications, the interactions of the lubricant with coated surfaces are not always well understood. In the present study, Stribeck curves (i.e., traction coefficient vs. dimensionless film thickness Λ) were generated for lubricated rolling contact between coated and uncoated surfaces. Chromium nitride, tungsten carbide reinforced amorphous hydrocarbon, and silicon-incorporated diamond-like carbon coatings are evaluated. A ball-on-flat test configuration is used in a 100% slide-to-roll condition. The test lubricant was a polyalphaolefin containing rust and oxidation inhibitor additives only. Differences in traction performance are observed for different coating types. The traction coefficient decreases at high Λ with increasing hydrocarbon content in the coating. The combination of coating micro-texture and composition are believed to influence traction as A becomes small.

In the present investigation, basic studies were conducted using Inclined pin-on-plate sliding Tester to understand the role of surface texture of hard material against soft materials during sliding. Soft materials such as Al-Mg alloy, pure Al and pure Mg were used as pins and 080 M40 steel was used as plate in the tests. Two surface parameters of steel plates — roughness and texture — were varied in tests. It was observed that the transfer layer formation and the coefficient of friction which has two components, namely adhesion and plowing component, are controlled by the surface texture of harder material. For the case of Al-Mg alloy, stick-slip phenomenon was absent under both dry and lubricated conditions. However, for the case of Al, it was observed only under lubricated conditions while for the case of Mg, it was observed under both dry and lubricated conditions. Further, it was observed that the amplitude of stick-slip motion primarily depends on plowing component of friction. The plowing component of friction was highest for the surface that promotes plane strain conditions near the surface and was lowest for the surface that promotes plane stress conditions near the surface.

A numerical model is developed to study the effect of texture on air bearing sliders at large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.

It is well established that roughness or texture on bearing surfaces may generate hydrodynamic pressures exceeding those generated by smooth surfaces of the same nominal macro-geometry. The effect is often attributed to the local positive pressure excursions being larger than the negative ones. It is shown that this interpretation is erroneous, and that the effect of cavitation plays a very minor role. Similarly, solutions based on the Navier-Stokes equations indicate that asymmetric pressure profiles that may be generated at very steep edges of surface micro-profile excursions, usually have little effect. It is concluded that the increased pressure is essentially caused by the changes in flow impedance.

Surface texturing has been shown to have friction reducing / load capacity increasing effects in parallel sliders, as well as in cylinder-liner contacts and in hydrodynamic seals. However, if texture is to be regarded as the sole mean of hydrodynamic lift in parallel sliders, or as a way of improving hydrodynamic performance in slider, thrust and journal bearings, several issues have to be addressed, such as optimal texturing parameters and corresponding performance gains. This paper deals with these issues in the case of a plane inclined textured slider. Parametric studies are conducted to determine optimal texturing extents, dimple depth and texturing density, as well as the influence of the operating conditions on these optimal texturing parameters.

The design of a head-disk interface for an ultra-low flying height was studied from the viewpoint of contact vibration. It is known that a super-smooth disk is necessary for a slider to fly at an ultra-low flying height; however, such a disk increases the friction force, which potentially increases the vibration of the slider. To solve this problem, the head-disk interface must be optimized to reduce this increased vibration. We found that the use of micro-texture on the air bearing surface can prevent contact vibration. Combining trimming with the use of a micro-texture was most effective in reducing contact vibration. A frequency-shift-damping slider was also found to damp vibration effectively.

In this paper, from the viewpoint of lubricant spreading, we investigate the effect of lube textures which mean a nonuniform distribution of bonding strength between lubricant molecules and the disk surface. Lube textures were formed by irradiating ultraviolet rays through a stripe-patterned mask onto a magnetic disk surface which was partially coated with one-monolayer film of perfluoropolyether. Surface characteristics of the lube textures were evaluated by surface energies ascertained from contact angle measurements. Spreading of the lubricant film was measured by scanning microellipsometry on the striped lube textures in the directions parallel and perpendicular to the stripes. The thickness-dependent diffusion coefficients extracted from the spreading profiles show that lubricant spreading in the regime of film thickness less than 0.2 nm is faster along the stripes, indicating the possibility of controlling the behavior of a lubricant film with lube textures.

This study is focused on characterization of microstructural changes linked to deformation and crack formation mechanisms in duplex Ti-6Al-4V specimens used in displacement controlled fretting only experiments. In particular, the effect of slip displacement amplitude and number of fretting cycles on the evolution of grain morphology, grain orientation, misorientation distribution, composition, and microhardness is investigated using electron backscatter diffraction (EBSD), energy dispersive X-ray analysis (EDX) and nanoindentation. A strong basal microtexture and significant oxygen diffusion were observed in the Ti-6Al-4V specimen that exhibited the most significant cracking. A critical slip amplitude threshold may exist for which a combination of mechanisms such as plastic deformation, grain reorientation, and oxygen diffusion occur during fretting that make conditions ideal for crack formation. The results provide insights for development and validation of computational crystal plasticity models with application to fretting and sliding contact problems. New fretting damage assessment measures have also been identified and have application for components that suffer from fretting wear and/or fatigue related failures.