nghu Ji

Influence of Geometric Shapes on the Hydrodynamic Lubrication of a Partially Textured Slider With Micro-Grooves

The effect of partial surface texturing in the form of parabolic grooves, rectangular grooves, and triangular grooves on the hydrodynamic pressure is investigated in the present work. The dimensionless hydrodynamic pressure generated by the partial surface texturing is obtained by the multigrid method. The effect of the texturing parameters on the dimensionless average pressure is analyzed for a given set of operating parameters. The results indicate that the geometric shape, area density, groove depth, and orientation of the grooves have an obvious influence on the hydrodynamic pressure. However, the groove width has little effect on the dimensionless average pressure. The results of the present work demonstrate that surface texturing design is very important to generate additional hydrodynamic pressure according to the operating parameters of the mechanical components. [DOI: 10.1115/1.4027633]

The Influence of Partially Textured Slider with Oriented Parabolic Grooves on the Behavior of Hydrodynamic Lubrication

An analytical model is developed to investigate a partially textured slider of infinite width with orientation parabolic grooves. The generating mechanism for hydrodynamic lubrication of the partial surface texturing in the sliding surface is similar to that of a step slider. By using the multigrid method, the hydrodynamic pressure generated by the partial surface texturing is obtained. The surface texturing parameters are numerically optimized to obtain maximum hydrodynamic effect in terms of the dimensionless average pressure for a given set of operating parameters. The results indicate that parameters such as groove orientation angle, depth, area density, and textured fraction have an obvious influence on the hydrodynamic pressure for partial surface texturing. However, the groove width has little or no effect on the dimensionless average pressure. The results of the study show that the hydrodynamic lubrication performance can be ameliorated by optimizing the surface texturing according to the operating parameters of the mechanical components.

The influence of partially textured slider with orientation ellipse dimples on the behavior of hydrodynamic lubrication

Purpose – The purpose of this paper is to investigate a partially textured slider of infinite width with orientation ellipse dimples in liquid application. Design/methodology/approach – In this paper, the pressure distribution of lubrication between a partially textured slider and a smooth sliding slider is calculated by the multi-grid method. For the same dimple area, the influence of the ellipse dimple with geometric parameters, and distribution and orientation on the hydrodynamic lubrication is evaluated in terms of the dimensionless average pressure for a given set of operating parameters. Findings – In the present work, the magnitude of the dimensionless average pressure seems proportional to the slender ratio. Consequently, the slender ratio may be chosen as large as possible based on fabrication techniques. The longer axes of ellipse dimples placed parallel to the direction of sliding always show the better hydrodynamic effect. Furthermore, the results show that the ellipse dimples can greatly impr...

Hydrodynamic Lubrication of Conformal Contacting Surfaces With Parabolic Grooves

The effect of surface texturing in the form of parabolic grooves on the hydrodynamic lubrication properties is investigated in this paper. Numerical simulation of the pressure distribution of lubricant between a textured slider and a smooth, moving slider has been performed. The evaluation criterion of hydrodynamic effect of dimensionless average pressure is calculated and presented with the variation of minimum film thickness, groove width, groove depth, spacing and orientation angle. Optimum values of geometrical parameters such as the dimensionless groove depth, spacing and orientation angle are obtained which correspond to maximum average pressure. It is also noted that the average pressure increases monotonically with increasing groove width. The results show that the hydrodynamic effect can be improved by employing optimized surface texturing design.

Tribological Properties of Laser Microtextured Surface Bonded With Composite Solid Lubricant at High Temperature

A combination technology of the solid lubricant and the laser surface texturing (LST) can significantly improve the tribological properties of friction pairs. The plate sample was textured by fiber laser and composite lubricant of polyimide (PI) and molybdenum disulfide (MoS2) powders were filled in the microdimples. Sliding friction performances of micron-sized composite lubricant and nano-sized composite lubricant were investigated by ring-plate tribometer at temperatures ranging from room temperature (RT) to 400 °C. On the one hand, the results of the micron-sized composite lubricant show that the friction coefficient of the textured surface filled with composite lubricant (TS) exhibits the lowest level and the highest stability compared to a textured surface without solid lubrication, smooth surface without lubrication, smooth surface burnished with a layer of composite solid lubricant. The better dimple density range is 35-46%. The friction coefficients of the sample surface filled with micron-composite solid lubricant with the texture density of 35% are maintained at a low level (about 0.1) at temperatures ranging from RT to 300 °C. On the other hand, the results of the nano-sized composite lubricant show that these friction properties are better than those of MoS2-PI micron-sized composite. The friction coefficients of MoS2-PI-CNTs nano-sized composite solid lubricant are lower than those of the MoS2-PI composite lubricant at temperatures ranging from RT to 400 °C. In addition, the possible mechanisms involving the synergetic effect of the surface texture and the solid lubricant are discussed in the present work.

Characterisation of group behaviour surface texturing with multi-layers fitting method

Abstract Surface texturing was widely applied in improving the tribological properties of mechanical components, but study of measurement of this technology was still insufficient. This study proposed the multi-layers fitting (MLF) method to characterise the dimples array texture surface. Based on the synergistic effect among the dimples, the 3D morphology of texture surface was rebuilt by 2D stylus profiler in the MLF method. The feasible regions of texture patterns and sensitive parameters were confirmed by non-linear programming, and the processing software of MLF method was developed based on the Matlab®. The characterisation parameters system of dimples was defined mathematically, and the accuracy of MLF method was investigated by comparison experiment. The surface texture specimens were made by laser surface texturing technology, in which high consistency of dimples’ size and distribution was achieved. Then, 2D profiles of different dimples were captured by employing Hommel-T1000 stylus profiler, and the data were further processed by MLF software to rebuild 3D morphology of single dimple. The experiment results indicated that the MLF characterisation results were similar to those of Wyko T1100, the white light interference microscope. It was also found that the stability of MLF characterisation results highly depended on the number of captured cross-sections.

Effect of Elliptical Dimples on Hydrodynamic Lubrication

This paper develops an analytical model to investigate the effect of elliptical dimples on hydrodynamic lubrication of surface contact. The hydrodynamic pressure generated by elliptical dimples is solved by the multi-grid method. The evaluation criterion of hydrodynamic effect of dimensionless average pressure is calculated and presented with the variation of elliptical dimple depth, area density, slender ratio and inclination angle. The results indicate that geometrical parameters of elliptical dimples have an obvious influence on the hydrodynamic pressure. The hydrodynamic lubrication performance can be ameliorated by optimizing the geometrical parameters of elliptical dimples according to the operating parameters of the mechanical components.

Lubrication adaptability to the variations of combustion modes by texturing cylinder liner in engines

The application of different combustion modes in engines has placed greater demands on the lubrication of cylinder liners and piston rings. In this study, a mixed lubrication model was built to investigate the tribological properties of a liner textured with micro-dimples. The simulation results indicate that surface texturing can improve the lubrication and friction properties of the ring/liner pair and adapt to different combustion modes in an engine. Due to the significant differences in external loads around top dead center of the compression stroke under pre-mixed charge combustion ignition, conventional combustion and retarded injection modes, when the liner remains untextured, the lubrication performance of the friction pair appears to be unstable in a mixed lubrication region. For the textured liner, micro-dimples enhance the hydrodynamic effects between the ring and liner, increasing the oil film thickness and its bearing capacity. As a result, the mixed lubrication interval shrinks and the micro asperity contact is reduced, thus improving the tribological properties of the friction pair. The numerical fluctuation ranges of parameters, the maximum asperity pressure, the average friction force and the frictional loss, are narrowed by 21.6%, 27.8% and 24.5%, respectively, under the three different combustion modes around top dead center of the compression stroke.

Tribological performance and self-lubricating mechanism of the laser-textured surface filled with solid lubricant in rolling friction pair

Purpose This paper aims to find out the tribological performance and self-lubricating mechanism of the laser-textured surface filled with solid lubricant in rolling friction pair. Design/methodology/approach The textures on the surfaces of GCr15 bearing steel were produced by acousto-optic Q diode-pumped yttrium aluminum garnet laser with the technology of “single pulse one time, repeating at intervals” and filled with composite solid lubricant. The tribology tests were conducted on the MMW-1A universal friction and wear testing machine. Findings It was found that the solid-lubricated micro-textured surface can reduce the friction coefficient effectively. The MoS2/PI composite solid lubricant works better than the single MoS2 solid lubricant, and the ratio of PI/MoS2 + PI at 20 per cent is the best recipe. The friction coefficient of the sample surfaces decreases first and then increases with the increase in texture densities, and a texture density of 19.6 per cent has the best effect on friction reduction. The friction coefficient of the textured surfaces gradually decreases with the increase in both rational speed and load. For the same texture density, the friction coefficient of textured surfaces decreases slightly with the increase in diameter. Furthermore, the mechanism of “rolling-extrusion-accumulation” occurred on the textured surface can collect the solid lubricant, thereby, improve the effect of lubricating and anti-friction. Originality/value The results of the experimental studies demonstrated the application prospect of laser surfaces texturing combined with solid lubricant in rolling friction pair.

Influence of short grooves on hydrodynamic lubrication of textured infinitely long sliders

The influence of geometrical parameters of the short grooves on the hydrodynamic lubrication is studied in this article. Based on Reynolds equation and Jakobsson–Floberg–Olsson cavitation theory, an analytical model is developed to investigate the hydrodynamic lubrication of the short grooves. The study employs a multigrid method to calculate the distribution of hydrodynamic pressure and the average pressure of textured surfaces. The results indicate that the interactions between neighboring short micro-grooves and the end effect on the hydrodynamic pressure should be considered in the process of numerical simulation. There exist the optimum values of horizontal spacing and short micro-groove depth to maximize the hydrodynamic pressure. The average film pressure decreases with the increase in the vertical spacing, but it increases alongside the short groove width. The increase rate of the average pressure declines gradually as the short groove length grows. Therefore, hydrodynamic lubrication performance can be improved by optimizing the geometrical parameters of the short grooves according to operating conditions.