Avoiding Starvation in Tribocontact Through Active Lubricant Transport in Laser Textured Surfaces

Tobias Stark,Holger Marschall,Andrés Fabián Lasagni,Thomas Kiedrowski

doi:10.3390/lubricants7060054

Abstract

Laser texturing is a viable tool to enhance the tribological performance of surfaces. Especially textures created with Direct Laser Interference Patterning (DLIP) show outstanding improvement in terms of reduction of coefficient of friction (COF) as well as the extension of oil film lifetime. However, since DLIP textures have a limited depth, they can be quickly damaged, especially within the tribocontact area, where wear occurs. This study aims at elucidating the fluid dynamical behavior of the lubricant in the surroundings of the tribocontact where channel-like surface textures are left after the abrasion wear inside the tribocontact area. In a first step, numerical investigations of lubricant wetting phenomena are performed applying OpenFOAM®. The results show that narrow channels (width of 10 μ m ) allow higher spreading than wide channels (width of 30 μ m ). In a second step, fluid transport inside DLIP textures is investigated experimentally. The results show an anisotropic spreading with the spreading velocity dependent on the period and depth of the laser textures. A mechanism is introduced for how lubricant can be transported out of the channels into the tribocontact. The main conclusion of this study is that active lubricant transport in laser textured surfaces can avoid starvation in the tribocontact.

Highlights

Tribology is a wide-spread field with various application fields including the automobile industry.For instance, in passenger cars, friction occurs in the engine, transmission, tires and brakes
This study aims at elucidating the fluid dynamical behavior of the lubricant in the surroundings of the tribocontact where channel-like surface textures are left after the abrasion wear inside the tribocontact area
The comparison of the Stribeck curves for the different Direct Laser Interference Patterning (DLIP) textures S1–S4 introduced in this study show no difference in terms of coefficient of friction

Summary

Introduction

Tribology is a wide-spread field with various application fields including the automobile industry. In passenger cars, friction occurs in the engine, transmission, tires and brakes. According to Holmberg et al [1], the direct frictional losses, with braking friction excluded, represent 28% of the fuel energy. 21.5% of the fuel energy is used to move the car. There is an enormous potential to reduce the global energy consumption by enhancing the tribological performance of engine parts. There are other fields of application, e.g., bionic engineering where, for example, the sandfish’s skin, which is structured in a way that friction is reduced, serves as a model [2]

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Conclusion