Identifying Key Surface Topography Characteristics Contributing to High Friction

• Applicant: Professor Dr. Christian Greiner
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566243172

The friction force acting between contacting surfaces is a fundamental tribological phenomenon affecting the efficiency and lifetime of mechanical systems. Despite researchers and practitioners being exceptionally familiar with surface topography, particularly roughness, the impact of surface topography on friction remains incomprehensively understood. In many studies, a common method is to quantify a surface’s topography as a scalar, which fails to capture the complexity of the surface. Meanwhile, tiny characteristics on the surfaces might lead to an increase in local friction. Since every surface is unique, this is one of the reasons why it is so very difficult to precisely replicate frictional behavior in tribological experiments. This proposal therefore follows this hypothesis: there are key characteristics of the surface topography that lead to high friction. However, their occurrence is not guaranteed. This is because the oscillations caused by mounting tilt play a crucial role in determining whether key characteristics manifest as high friction, or not. Due to the impact of oscillations and surface topography not being limited to laboratory setups but manifesting in real world tribological interactions, we will use 100Cr6 bearing steel for both contact surfaces to conduct pin-on-disk tests under lubricated conditions. By employing multi-step speeds to generate Stribeck curves, we will identify the key characteristics of disk surface topography and the impact of oscillations on friction forces for boundary, mixed, and hydrodynamic lubrication conditions. These experiments will involve controlling disk surface topographies to have varying waviness, as well as introducing different degrees of oscillations by adjusting the disk mounting tilt. During data analysis, we will examine complex relationships in multidimensional data, including surface topography, friction, oscillation, multi-directional pin acceleration, and wear, aimed at understanding the underlying mechanisms. This process will involve normalizing friction (and surface topography and oscillation if necessary) for comparison. Once we have identified the key characteristics of surface topography and understood the influence of oscillations, we will use this knowledge to strategically achieve a desired, lower friction value. This proposal will pave the way for new strategies for minimizing friction and prolonging the service life of mechanical systems.

• DFG Programme: Research Grants