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The present paper introduces a tire/road friction prediction tool based on modelling the tire/road contact as dynamic, viscoelastic, rough, and lubricated. The tool takes into account a considerable part of influent parameters related to tire, road, contaminant, and contact operating conditions: For the tire, the tool takes into account its geometry and rubber material behaviour. For the road, the texture is taken into account via the surface topography. At the contact interface, dry or wet conditions are taken into account through the lubricant depth, viscosity, and density. The operating conditions are taken into account through the normal load, speed, and slip ratio of the tire. The real novelty of this tool lies in its ability to reproduce the complete curve of the tire/road friction coefficient as a function of the slip rate. The validation of the tool is initially done through parametric studies by analyzing the trends of the results, then by performing braking tests on a passenger car at various speeds on different wet roads with different textures. The tool correctly ranks the peak friction and the sliding friction on these various road surfaces. [ABSTRACT FROM AUTHOR]

Mechanical losses consume about 40% of the total energy developed by a typical automotive engine. The piston–cylinder system accounts for 50% of the engine frictional losses, of which 70% to 80% is attributed to the piston rings. Inadequate lubrication in the parts of the engine reduces the reliability of engines, since high wear, seizure, or catastrophic failure of the components may occur. Moreover, frictional losses adversely affect the economic use of fuel. Therefore, a marginal reduction in frictional losses enables economic fuel consumption and is a significant achievement. Of the various factors, the surface topography of the piston rings and cylinder liner dominates the lubricant flow between them and influences its tribological behaviour. Surface texturing, lubricant formulation, and lubricant additives have undergone significant technological advancements in recent times to satisfy the global requirements of reduced emission and improved fuel economy. One of the emerging technologies for significant improvement in the tribological properties of mechanical components is laser surface texturing. The precise control of the shape and size of the textures (dimples or grooves) and rapid processing rate makes laser surface texturing advantageous. This article reviews the theoretical and numerical methodologies developed to analyse the impact of surface texturing on the friction behaviour of piston ring–cylinder liner contact. In addition, the article presents future directions for the research work on improving the tribological performance of internal combustion engines. The present Part 1 of the article discusses the laser surface texturing process, and Part 2 reviews its use in piston ring–cylinder contact. [ABSTRACT FROM AUTHOR]

Fine particle peening (FPP) is a peening process using fine shots with an average diameter of less than 200 µm. Pairs of twin-disc specimens made of carburized and quenched 18CrNiMo7-6 gear steel were subjected to two different FPP processes and conventional shot peening (CSP) using big shots with an average diameter of 600 µm. Rolling–sliding tribology tests were carried out under oil lubrication, and comparisons of the friction coefficient were made between untreated, FPP-treated, and CSP-treated twin-disc specimens. To characterize the relationship between surface topography and friction coefficient, 3D surface parameters, including root mean square roughness (Sq), skewness (Ssk), kurtosis (Sku), core roughness depth (Sk), reduced peak height (Spk), and reduced valley depth (Svk) were measured before and after tribology tests. A linear regression method was applied to analyze the correlations between the surface parameters and the friction coefficient. It was found that FPP is effective in decreasing the friction coefficient during the lubricated rolling–sliding contact compared to untreated specimens. The friction coefficient has a higher correlation with Ssk and the ratio RSvk, which is defined as the ratio of Svk to the sum of Sk, Spk, and Svk. A lower friction coefficient was obtained when the topography had a more negative Ssk and a higher RSvk in the rolling–sliding condition. However, there was a weak linear correlation between the friction coefficient and surface parameters Sq, Sku, Sk, Spk, and Svk, and the relationship between the trend of friction coefficient and those surface parameters is not obvious. [ABSTRACT FROM AUTHOR]

The effect of surface topography on lubricated systems plays a crucial role in terms of friction performance, because surface micro-irregularities can improve the load-carrying capacity of mechanical parts in lubricated conformal and nonconformal contacts. Sintered materials, which can be applied to manufacturing several mechanical components such as gears, axial thrust bearings, and disc brake pads, are interesting candidates, because they present pores that could be somewhat compared to microcavities produced by surface texturing techniques. This work aims at studying the influence of surface pores originated from the sintering process on the frictional performance of lubricated contacts under different lubrication regimes and slide-to-roll ratios (SRR). The research contributes to understanding how random micro-irregularities could change lubrication conditions and promote effects similar to those of more expensive and precise surface features produced by texturing techniques. The experimental results showed that a decrease in porosity led to a reduction in the coefficient of friction. Furthermore, less porous samples promoted friction reduction compared to nonporous materials due to the probable additional load support caused by small-scale surface pores. Therefore, in addition to the traditional appeal of the use of sintered materials to reduce production costs, the present contribution reveals that this type of material could also be used to reduce friction in contacting mechanical components operating under certain tribological conditions. [ABSTRACT FROM AUTHOR]

The modern trend toward miniaturization has provided an innovative push toward the creation of micro-fabrication parts. Micro-extrusion is one such emerging process. It finds its various industrial applications in mechanical, electronic and micro-fabrication parts. Micro-punches are the main part of the micro-extrusion process. In the extrusion process, high contact forces are generated due to the sliding between the punch and billet. These high contact forces are governed by the surface topography of the punch. When the punches are finely finished, lesser contact forces are generated. To fulfill this requirement, the rotating rectangular core magnetorheological finishing process is used. On the basis of the applications, four industrial micro-punches are used for the present investigation. After MR finishing, surface roughness values of the micro-punches of the initial ground surface 0.210, 0.230, 0.250 and 0.200 µm are reduced to 0.02, 0.02, 0.03, and 0.01 µm. The operative functionality of the magnetorheological finished micro-punch is examined for its improved performance in the micro-extrusion process. The decrease in the roughness value reduces the frictional force between the micro-punch surface and the billet. Improvement in surface topography of the magnetorheological finished micro-punches enhances the quality of the product outcome and more uniform deformation of billet material. [ABSTRACT FROM AUTHOR]

Carbon fabric (CF) was pretreated by air-plasma bombardment and then further modified by deposition of polydopamine on the surface of the pretreated CF. Epoxy resin composites reinforced by unmodified or surface-modified carbon fabric were fabricated. The friction and wear behaviors of the resulting composites were evaluated in a ring-on-block contact mode. The flexural strength and Rockwell hardness of the composites were also evaluated. The morphologies of the worn surfaces of the unmodified and modified composites were analyzed by scanning electron microscopy. The surface treatment increased the surface roughness and changed the surface topography of the CF, which contributed to enhancing the interfacial adhesion of the composites and thus improved the mechanical properties and tribo-performance. The friction and wear properties of both the unfilled and filled composites were highly dependent on the load and sliding velocity. Moreover, the results were supplemented with scanning electron micrographs to help understand the possible wear mechanisms. [ABSTRACT FROM AUTHOR]

The change in surface topography caused by friction and wear influences the wear properties and service life of mechanical seal. To investigate the wear properties of mechanical seals and obtain the variation in surface topography, it is practical to carry out accelerating experiments by increasing the load, speed, or temperature of the medium than safe life tests in the field device. Based on the assumption that the same fractal roughness corresponds to the same wear properties, the pi theorem was introduced to derive the relationship of wear under experimental and actual conditions. By providing detailed values of constants in the pi theorem through accelerating experiments, a fractal model was established to predict the life expectancy of mechanical seals. Under the state of mixed friction, measured values of surface topography for experimental stationary rings and data on a mechanical seal ring's service life in the field device were in accordance with those of the model. The establishment of the fractal model provides conditions for the performance study of long-period operating mechanical seals. [ABSTRACT FROM PUBLISHER]

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]

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 aim of the present work is to determine the influence of boron surface layers on the friction parameters in sliding pairs under lubricated friction conditions. Tribological evaluation included pack boronizing, laser boronizing, and TiB2 coating deposited on 46Cr2 steel (AISI 5045). The pack-borided surface layer had a characteristic denticular structure with a hardness of 2,000 HV and thickness of up to 40 μm. The laser-borided surface layer had a maximum hardness of 1,800 HV and the melting depth of 25 μm. The TiB2 coating was characterized by a hardness of about 3,000 HV and thickness reaching about 3 μm. Modified surface layers of ring specimens were matched under test conditions with a counterpart made from SAE-783 bearing alloy. Tested sliding pairs were lubricated with LOTOS 5W/40 synthetic engine oil. The modification technologies applied to the surface layer of steel allowed obtaining construction materials with predetermined tribological characteristics required for the elements of sliding pairs in lubricated contacts. The results showed differences in the wear of the bearing alloy due to the interaction between the cooperating surface layers and the physiochemical changes of their surfaces induced by external forces. The pack-borided surface layer reduced the friction coefficient, the moment during the start-up of the frictional pair, and the wear of the bearing material. Analysis of the surface layer indicated that the content of aluminum on pack-borided ring specimens reached 21%, and on the TiB2 coating it exceeded 8%. [ABSTRACT FROM AUTHOR]

This paper analyses the influence of surface roughness on adhesive bond strength. Numerical simulations were performed to evaluate the influence of geometry on the performance of structural adhesive joints. The objective is to create a model to describe the behaviour of the interphase of adhesive joints according to its geometry. Two-dimensional simulations with theoretical geometries were performed considering parameters of roughness, stress distribution, and contact area to verify the qualitative influence of substrate topography on the adhesion of a joint. Numerical analyses were done to verify the effect of the interpenetration of materials on the mechanical properties of the interphase. [ABSTRACT FROM AUTHOR]

In recent years, continuous slip torque converter clutches (CSTCCs) have been widely used in automatic transmissions, mainly to improve fuel efficiency. With the adoption of these devices the problem of shudder vibration has arisen. To help alleviate this problem, better anti-shudder characteristics are desired for automatic transmission fluids (ATFs). Positive µ-v curves are well recognized to correlate to the avoidance of shudder. A variable-speed friction tester (VSFT), which combines a low-velocity friction apparatus (LVFA)-type test with the ability to age an oil in situ, was used to determine friction characteristics of four model ATF formulations in a wet clutch tribosystem. The linear-defined multiple parameter spider chart ATF evaluation (LSAE) method was applied to present the ATF's overall friction results including anti-shudder performance and durability (Zhao, et al. (1)). One modified SAE No. 2 test was also used to test the four oils' friction behavior, to compare with the VSFT results. Similar performance rankings have been obtained from those two tests. Both test results and evaluation parameters will be discussed in this article and the response will be linked to the physical parameters defining the posttest surface. The oil absorption ability of post test friction material is shown to be important to the overall friction performance. The environmental scanning electron microscope (ESEM) images and 3D profiling results showed that some surface topographical parameters, such as Vvc (void volume of the core) and Vvv (void volume of valleys), can be linked with the friction modifying mechanisms in the ATF tests. [ABSTRACT FROM AUTHOR]

Laser surface texturing (LST) and surface molybdenizing duplex-treatment was performed on Ni-base alloy in order to improve its wear resistance at high temperature. Surface molybdenizing was performed on the laser surface textured Ni-base alloy by a double glow plasma surface alloying technology. The friction and wear properties of the duplex-treated, the single-treated, and the untreated alloys were tested on a ballon-disk tribometer by rubbing against an alumina ceramic ball from room temperature to 600.C. The topography of the laser surface textured dimples wasmeasured by a white light interferometer and optical microscope. The dimples are 150-200 ƒÊm in diameter and 45-50 ƒÊm in depth. The distance between the dimples is 500 ƒÊm. The molybdenized layer is approximately 20 ƒÊm in thickness. The elastic modulus of Ni-base alloy is improved by molybdenizing. After texturing and the molybdenizing duplex treatment, the friction coefficient of the Ni-base alloy decreases from 0.38 to 0.26 at room temperature and from 0.42 to 0.34 at 600.C. The wear rate of the duplex-treated alloy is much lower than that of the pristine alloy at 600.C due to the textured dimples storing lubricious oxides. [ABSTRACT FROM AUTHOR]