How to determine the number of asperity peaks, their radii and their heights for engineering surfaces: a critical appraisal

A. Pogačnik, M. Kalin

Wear 300 (2013) 143-154.


Asperity-peak criteria are necessary in order to identify the relevant, load-carrying asperity peaks in the contacts between rough surfaces. Once these load-carrying asperity peaks are identified, the real contact area can be calculated using deterministic contact models. This work focuses on the effect that different asperity-peak identification criteria have on the identified asperity-peak properties (number, radii and heights) for rough surfaces. Different criteria, which take into account the number of required neighbouring points (i.e., 3, 5 and 7 points), and also the peak-threshold value (z-direction), were applied in this study and analysed for five different real surface roughnesses in the broad engineering range from Ra = 0.003 µm to Ra = 0.70 µm. In addition, the effect of the data resolution in the x-direction on the asperity-peak properties is also evaluated.

The results show that criteria with three neighbouring points result in much more trustworthy asperity-peak properties than those with five and seven neighbouring-points criteria. The results also show that the x-direction data resolution has an important influence on the number of asperity peaks and their radii, but has little effect on the peak heights; the x-direction data resolution values of Δx below 1 µm should be used. Peak threshold value (z-direction criteria) has very diverse effect for rough and smooth surfaces and lacks clear guidelines for its use. It seems from the results that the criteria with only three neighbouring points (3PP) should be used for asperity-peak identification, especially if the data resolution in the x-direction could be correlated with different surface roughnesses.

Keywords: Surface topography, Roughness, Asperity peak, Real contact area, Identification criteria

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