This paper discusses rough surfaces contact phenomena and in particular examines surfaces machined with abrasive instruments. The nature of surface roughness obtained as a result of this type of mechanical treatment can be described by the random field of two variables. Attention is paid to three-dimensional surface roughness parameters whose statistical characteristics are determined by the simple rough surface model: for an anisotropic random field obtained by mathematical stretching of an isotropic random field. Consideration is given to surface contacts: rough and smooth surface interaction and the contact of two rough surfaces. Two types of asperities contact are examined: plastic and elastic. The criteria for contact type have been developed. Contact theory is used for the calculation of contact resistance in welding and of wear intensity. The equations obtained reveal that all of them contain one surface roughness height parameter and two spacing parameters.

The authors of the research have analysed spacing parameters of anisotropic 3D surface roughness crosswise to machining (friction) traces RSm 1 and lengthwise to machining (friction) traces RSm 2 . The main issue arises from the RSm 2 values being limited by values of sampling length l in the measuring devices; however, on many occasions RSm 2 values can exceed l values. Therefore, the mean spacing values of profile irregularities in the longitudinal direction in many cases are not reliable and they should be determined by another method. Theoretically, it is proved that anisotropic surface roughness anisotropy coefficient c=RSm 1 /RSm 2 equals texture aspect ratio Str, which is determined by surface texture standard EN ISO 25178-2. This allows using parameter Str to determine mean spacing of profile irregularities and estimate roughness anisotropy.

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This technical brief clarifies origins of the piston ring conformability bounds presented by Dunaevsky (1990, Tribol. Trans. 33(1), pp. 33–40) and provides their correct expression. The subject has strong practical significance in the field of piston engines and compressors, and it is currently getting additional prominence due to stringent emission regulations. The bounds stem from an earlier version, developed by the authors using a semi-empirical approach, and published in the 1970s in Russian technical journals. A semi-empirical background of the bounds was inadvertently missed in the aforementioned Tribology Transactions’ publication. This fact, and the virtual inaccessibility of Russian sources to the English reader, interfere with the proper use of the bounds and cloud their authorship. In this technical brief, the correct expression of these conformability bounds, the development process, and uses are highlighted.