Detailed Program of the 22nd ISC 2024
Influence of surface topography on stick-slip-effects – an experimental and numerical study
Summary
Lubricated sealing systems, such as in automotive brake master cylinders or other hydraulic systems, tend to have undesirable stick-slip-effects under certain service conditions. These stick-slip-effects are clearly driven by the complex frictional behavior in the mixed lubrication regime. A significant factor in this tribological system is the surface topography. Thus, it is necessary to investigate and describe the lubrication effects on a micromechanical level.
In the presented study, SRV-tribometer tests are performed in order to study stick-slip-effects and significant parameters, such as the surface topography. In these tests, a cylindrical EPDM specimen is moved over a ground steel surface in a sinusoidal manner. The steel surface is wetted with brake fluid, so that conditions close to a hydraulic cylinder sealing system are achieved. The test results then show: If the EPDM specimen is moved perpendicular to the grinding direction of the steel sample, the stick-slip effect does not occur with any of the tested fluids. However, if the steel sample is rotated by 90°, so that the EPDM specimen is moved in the direction of grinding, it is possible to provoke a stick-slip-effect. This clearly proves that the surface topography has a strong influence on the stick-slip-effect.
Corresponding numerical contact- and CFD-simulations, based on the measured surface topography are performed and consider the surface roughness on a micro-scale. These numerical studies allow to motivate the influence of the surface topography on the fluid dynamics in the lubrication gap. The data from these micromechanical models is then used in a transient finite element computation of a reciprocating sealing system, considering the fluid film dynamics. Finally, these numerical investigations enable a deeper understanding of the stick-slip mechanisms in lubricated sealing contacts and point out the influence of surface topology.