Abstract
An experimental study is presented to evaluate the influence of anisotropically shaped textures on the behaviour of sliding friction and sensitivity to sliding direction. The plate samples were textured with triangular sloped dimples using an ultrafast laser surface texturing technique. Reciprocating cylinder-on-plate tests were conducted with steel sliding pairs using mineral base oil as a lubricant to compare the tribological performance of reference non-textured specimen and dimpled samples. The dimples were designed with varying converging angles in the transverse y–z plane and top-view x–y plane. In this study, no dimple was fully covered in the contact area since the dimples size is much larger than the Hertzian line contact width. Stribeck style dynamic friction curves across boundary, mixed and hydrodynamic lubrication regimes were used to determine the benefit or antagonism of texturing. Observation of the directional friction effect of the anisotropic textures indicated that the converging shapes are beneficial for friction reduction, and the dimpled specimens have a lower friction coefficient particular under prevailing boundary lubrication conditions. It was also found that the real contact length variation rate is a major factor controlling the local friction response. The sloped bottoms of the textures produce effective converging wedge action to generate hydrodynamic pressure and contribute to the overall directional friction effects.
Highlights
Introduction and BackgroundDue to long-term evolution and development, many biological surfaces have unique functions to be energy efficient; such as drag reduction [1], wear resistance [2], superHermann‐von‐Helmholtz‐Platz 1, 76344 Eggenstein‐Leopoldshafen, Germany hydrophobicity [3, 4] and smart adhesives [5]
One of the main concerns is how to use textured surfaces to control the frictional behaviour under various conditions, either to increase or to decrease friction depending on the requirements of a potential application, such as engine cylinder liner to piston ring contacts
The assessment of surface metrology of textured surfaces has shown the possibility of using ultrafast laser surface texturing techniques for the flexible fabrication of complicated texture structures
Summary
Introduction and BackgroundDue to long-term evolution and development, many biological surfaces (including both plants and animals) have unique functions to be energy efficient; such as drag reduction (shark’s skin) [1], wear resistance (beetle’s body) [2], superHermann‐von‐Helmholtz‐Platz 1, 76344 Eggenstein‐Leopoldshafen, Germany hydrophobicity (lotus’ surface) [3, 4] and smart adhesives (gecko’s foot) [5]. Inspired by the multi-functional surface of animals and plants, researchers are producing artificial surfaces with regular asperities to determine the shape, size and distribution to obtain the desired surface and tribological properties. Basic models for various applications, like journal bearings [7], mechanical seals [8], thrust bearings [9] and cylinder liners [10], have been built to find the optimal texture designs. Factors such as oil viscosity, density and temperature, as well as surface deformation were
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