A Strategy for Obtaining Topographically Comparable Tracks Reveals Shifts in Stribeck Curve

Surface topography plays a critical role in the tribological behavior of interacting surfaces. In experimental studies, a controlled variable strategy commonly relies on a limited number of parameters to characterize the state of a surface. However, this approach is intrinsically limited because it reduces multiscale surface morphology to a few descriptors and assumes that the remaining topographic features can be kept comparable. In practice, preparing surfaces that are similar across all length scales is highly challenging. In this study, we established a customized radial grinding strategy to produce circumferential tracks with closely comparable surface topographies at different radial positions on the same 100Cr6 steel disk. The topographic comparability of these tracks was verified across multiple length scales with both roughness parameters and power spectral density (PSD). Lubricated ball-on-disk tests were then performed using 10 mm 100Cr6 steel balls, FVA 1 base oil, a normal load of 2 N, and a multistep sliding speed protocol ranging from 50 mm/s to 600 mm/s. Angle-resolved friction analysis showed that the main spatial distribution of friction was largely preserved among the different radii, although the mean friction level between radii varied systematically with sliding speed. Despite the verified topographic comparability and the similar spatial friction distribution, the resulting Stribeck type curves did not collapse under identical linear sliding speeds. This deviation may arise from differences in angular velocity and/or from multiscale effects of surface topography that are not fully captured by conventional statistical parameters.