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Researchers have not reached an agreement on which biomimetic shape has the best lubrication performance. This paper aims to study the influence of microtexture size, shape and direction on bearing capacity, end leakage, friction coefficient and wear of oil film.

Different oil film thickness equations considering the microtexture of bearing surface are gained. The two-dimensional finite difference equation and the calculation equation of wear are established.

The theoretical research shows that the wear value and the wear ratio when long side is perpendicular to the axial direction of the bearing are generally lower than when the long axis is parallel to the axial direction of bearing. The theoretical and experimental results show that the appropriate microtexture shape, such as circular dimple, crescent-shaped dimple, triangular dimple and fish-shaped dimple can improve effectively the lubrication performance of journal bearing and reduce the friction coefficient.

The research has great significance to reduce friction and improve the wear resistance of equipment.

This research aims to present the characteristics of dimple structure which was fabricated using a turning machine, where the characteristics include sizes, shapes, area ratio and aspect ratio. This research aims at filling the gap in the machining parameters of previous research in producing dimple by using turning process with the aid of dynamic assisted tooling for turning (DATT). In producing dimple, a carbide insert grade H1 was used on a hypereutectic aluminium silicon alloy (A390) material. Dimple has many advantages such as for reducing friction coefficient, load-carrying capacity and trap wear debris for sliding mechanical components.

There are seven machining parameters (cutting speed, feed rate, depth of cut, frequency, amplitude, rake angle, relief angle and nose radius) which have an influence on dimple produced. Taguchi method (orthogonal arrays L8) was used to conduct the experiment systematically and efficiently for these seven parameters. A carbide insert grade H1 was used as a cutting tool on a turning machine with the aid of DATT. The dimple structure was fabricated on a cylindrical rod hypereutectic aluminium silicon alloy (A390). A profilometer 3D Alicona infinite focus and an optical microscope equipped with Vis software were used to analyse the fabricated dimple structure.

Various shapes and sizes of ellipse dimples were produced in this research, including short and long drops with lengths in the range of 517.03–3,927.61 µm, widths of 565.15–1,039.19 µm, depths of 14.46–124.87 µm, area ratios of 5.05–25.65% and aspect ratios of 0.007%–0.111%. There were four experiments within the optimal area ratio range of 10%–20%, i.e. the second, third, seventh and eighth experiments. The width of these dimples was 895.95, 961.39, 787.27 and 829.22 µm, length was 826.26, 3163.13, 885.98 and 1026.65 µm, depth was 83.67, 84.19, 87.05 and 110.70 µm and area ratio was 15.12%, 13.14%, 14.79% and 12.70%. The surface roughness of textured surface was below 1 µm. In this research, the results obtained were similar with that of previous researchers on dimple structure related to tribology performance.

There exists machining parameters, namely, cutting speed and frequency, that were not used by previous research in producing dimple. These machining parameters (cutting speed and frequency) were used in this research to produce dimple via turning process with the aid of DATT using carbide insert grade H1. The turning process is an environmentally friendly process which is suitable for mass production for fabricating dimple structure as compared to most of the current methods which are widely used in fabricating dimple structure.

The purpose of this paper is to produce dimple structure on a cylindrical surface for Aluminium-Silicon (Al-Si) alloy piston (A390) using turning process. The process selection is based on factors such as the capability of machining process, low cost process, minimum set up time and green working environment.

Three main machining parameters that greatly influenced the dimple structure fabrication were identified from previous researches (cutting parameters, vibration and cutting tool geometry). To facilitate dimple structure fabrication using turning process, a dynamic assisted tooling (DATT) was developed. Experiments were conducted on Al-Si A390 material for future application of automotive piston. A three-dimensional surface profiler (Alicona) was used for geometry measurement and analysis of dimple structure. The Taguchi method, with an L8 orthogonal array, was used to accommodate seven parameters used in the fabrication of dimpled structures using turning process. Signal-to-noise (S/N) ratio and observation on the shape of dimple structure array were used to determine the optimum machining condition.

Optimum parameters obtained using S/N ratio analysis were cutting speed of 9 m/min, depth of cut of 0.01 mm, amplitude displacement of 1 mm, nose radius of 0.4 mm and frequency of (25 Hertz). Whereas feed rate, rake and relief angles were not significant to the size, shape and dimple array; therefore, their selected values depend on requirement of the application. Based on the S/N ratio and uniformity of the array of dimple structure as the main reference, the sixth and eighth experiment conditions almost achieved the optimum condition which are able to produce the width of dimple structure of 396.82 and 560.43 μm, respectively, dimple length of 3,261.6 and 2,422.7 μm, respectively, dimple depth of 63.43 and 65.97 μm, respectively, area ratio of 10 and 10.39 per cent, respectively, and surface roughness of 3.0023 and 3.0054 μm, respectively. These results are within the range of dimple structure obtained by the previous researchers for sliding mechanical components application.

The optimum condition of machining parameters in producing uniform dimple structure led to the compilation of data base in dimple structure research via turning process. Dimple structure produced is similarly obtained with other processes like laser, burnishing, photochemical, etc. DATT developed has the ability to produce repeatable vibration frequency, stable and consistent amplitude displacement using a simple crank concept and structure that can be mounted on all types of lathe machine either conventional or computer numerical control.

This paper aims to research the effect of the different structures of dimpled textures on the rod bearing surfaces on improving the engine’s lubrication efficiency and friction power loss (LE-FPL).

Based on the hydrodynamic model of the rod bearing, the effect of different structures of dimpled surfaces including circular dimples (CD), square dimples (SD), wedge-shaped dimples (WSD), circular-square dimples (CSD) and square-wedge-shaped dimples (SWSD) on ameliorating the LE-FPL is analyzed under the different operating conditions of the engine. The oil film pressure (p), asperity contact force (W_ac), friction force (F_f) and coefficient of friction (COF) of the rod bearing are chosen to evaluate the LE-FPL.

The SD’s performance on improving the LE-FPL is better than all other structures of the CD, WSD, CSD and SWSD. Particularly, the average values of W_ac, F_f and COF with the SD is significantly reduced by 14.5%, 28.5% and 33.3% compared to the optimal dimensions of the rod bearing; and by 26.4%, 34.5% and 43.7% compared to the optimal CD (n = m = 6).

The generated friction between surfaces of rod bearings of the engine not only reduces the engine power but also affects the durability of the structures. Thus, the optimal design of the SD to further improve the LE-FPL is very necessary.

This study aims to present the discrepancy in oil film distribution in reciprocating motion experimentally with zero entraining velocity (ZEV) on a conventional ball-disk test rig with oil lubrication.

Driven independently by two individual servomotors, a steel ball and a sapphire disc move at equal speed but in opposite directions in a triangle wave. The oil film images between the ball and the disc were recorded by a camera. After the experiments, the mid-section film thickness was evaluated by using a dichromatic interference intensity modulation approach.

The dimpled oil film in transient condition is shallower than that at steady state with the same load and velocities, and the transient dimple depth decreases with the decrease of time. The increase of the applied load offers a beneficial effect on lubrication. Boundary slippage happens in ZEV reciprocating motion. The slippage at the interface is related to the transient effect and applied load.

This study reveals the significant difference of the oil film variation in ZEV reciprocating motion, especially the complex boundary slippage at the interface of the oil and the sapphire disc.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0021

This study aims to obtain a design scheme of the surface texture on mechanical seal with lower friction and leakage by comparing two common texture types: dimples and grooves.

An optimal free-form shape and an optimal circular shape were chosen by multi-objective optimization, and two types of grooves with different directions were chosen by a series of experiments. Then, the optimal free-form dimple, the optimal circular dimple, the groove perpendicular to the direction of movement (hereafter called groove-1) and the groove angled at 60° to the direction of movement (hereafter called groove-2) were compared by experiments under different loads.

The optimal free-form dimple shows a better performance in terms of a lower coefficient of friction (COF) and a lower leakage than the other shapes, especially for the high speed and low load conditions. The reduction rate of COF is up to 37.5%, and the leakage rate is reduced by about 12.5%. The dimples have a lower leakage than the grooves. The groove angled at 60° to the direction of movement is easier to pump the oil into the interface of the sealing face, leading to a lower friction but a higher leakage.

This study provides a feasible surface texture design scheme for improving the combination performance of mechanical seals.

The purpose of this paper is to investigate and discuss the effect of multi-shape laser surface texturing (LST) steel surfaces on tribological performance.

The textured surface with some specific formula arrays was fabricated by laser ablation process by combining patterns of circles and triangles, circles and squares and circles and ellipses. The tribological test was performed by a flat-on-flat tribometer under dry and lubrication conditions, and results were compared with that of untextured surface.

The results showed that the textured surface had better friction coefficient performance than the untextured surface due to hydrodynamic lubrication effect. Through an increase in sliding speed, the beneficial effect of LST performance was achieved under dry and lubrication conditions.

This paper develops multi-shape LST steel surfaces for improving the friction and wear performance under dry and lubrication conditions.

The study aims to compare tribological properties between laser dimple textured surface and drilled dimple textured surface, and to analyze the influence of dimple hardened edges and ability of trapping wear debris on wear properties of dimple textured surfaces.

Circular textured dimples were produced on AISI 1,045 specimen surfaces using laser surface texturing (LST) and drilled surface texturing (DST) methods. Tribological behaviors of LST, DST and non-textured specimens were studied using ball-on-disc tribo-tester. Metallographic structures, dimples and worn surface morphologies were observed using a three-dimensional digital microscope. Hardnesses of substrate and dimple edges were measured.

There was no obvious difference in wear and friction coefficients between LST and DST specimens. Hardnesses of laser dimple edges were much higher than that of drilled dimple edges and specimen substrate. The hardened materials of laser dimple edge included recast zone and heat affect zone. Laser dimple was cone-shaped and drilled dimple was cylinder-shaped. Drilled dimple had a better ability of trapping wear debris than laser dimple. Non-uniform wear phenomenon occurred on worn surfaces of LST dimple specimens.

The ability of textured dimples to trap wear debris is affected by single dimple volume. Hardened edges of dimples cause non-uniform wear on worn surfaces of LST specimens.

The purpose of this paper is to study the effect of liner surface texture on journal bearing performance. Modeling the profile curvature of the dimples or grooves is planned for different cases of texture surface under thermo-hydrodynamic condition (THD). The aim of this paper is to determine the effect the texture surface on the performance of journal bearing and specify the optimum shape for texture dimples.

The paper was opted for an exploratory study by applying finite difference method to solve the energy equation, the heat conduction equations and the Reynolds equation numerically. The lubricant film thickness is divided to a mesh of 640,000 points. The equations were solved for each point of the mesh by using a MATLAB code. For texture shape optimization, 24 cases of different texture shapes were selected which includes elliptical, triangle and square curvature shape.

The paper provides theoretical insights about the effect of texture shape on journal bearing performance. It was concluded that to get a high load-carrying capacity, the direction of curvature is preferably to be perpendicular to the sliding direction. The convex texture has higher load carrying capacity than concave texture. Finally, the surface with textures in channel form yields better overall performance than the surface with several dimples.

This paper fulfils an identified need to study how texture surface affects the performance of journal bearing under thermo-hydrodynamic conditions.

The purpose of this paper is to investigate the optimal geometry parameters in a dimple/protrusion-pin finned channel with high thermal performance.

The BSL turbulence model is used to calculate the flow structure and heat transfer in a dimple/protrusion-pin finned channel. The optimization algorithm is set as Non-dominated Sorting Genetic Algorithm II (NSGA-II). The high Nusselt number and low friction factor are chosen as the optimization objectives. The pin fin diameter, dimple/protrusion diameter, dimple/protrusion location and dimple/protrusion depth are applied as the optimization variables. An in-house code is used to generate the geometry model and mesh. The commercial software Isight is used to perform the optimization process.

The results show that the Nusselt number and friction factor are sensitive to the geometry parameters. In a pin finned channel with a dimple, the Nusselt number is high at the rear part of the dimple, while it is low at the upstream of the dimple. A high dissipative function is found near the pin fin. In the protrusion channel, the Nusselt number is high at the leading edge of the protrusion. In addition, the protrusion induces a high pressure drop compared to the dimpled channel.

The originality of this paper is to optimize the geometry parameters in a pin finned channel with dimple/protrusion. This is good application for the heat transfer enhancement at the trailing side for the gas turbine.