Proceedings of SerbiaTrib '13

Figure 4. Diagram of the height and spacing parametersof surface asperitiesIt is evident that in this case there are no limitationson the existence of asperities in various dimensionalranges (both spacing-wise and heightwise).However, in spite of the fact that there is nouniversally substantiated criterion for distinguishingasperities on the basis of scale, at the presenttime there exists the concept of the surface as anensemble of asperities of four dimensional levels:macrodeviations, waviness, roughness, and subroughness[12].4. SURFACE MEASUREMENTIn studying the topography the need arises forthe solution of three basic problems: description ofthe surface, development of representative surfaceevaluation systems and technical realization of themeasurement processes. In spite of the fact that theseproblems are interdependent, the last problem isof special importance, since our theoretical concepts,and therefore our understanding of how anyparticular phenomena may take place on the surface,are based on the quantitative estimates. Thereforeit is evident that roughness measurements areof primary importance in studying the topography.Nowadays a great number of experimental methodsof surface measurement are used. Stylus methodsremain the most widespread; they yield resultsforming the basis for current standards. Opticalmethods involving electromagnetic radiation suchas light section, shadow projection, interferencetechniques etc. have became widely applied. Atomic-forcemicroscopy has found a wide spread in surfacemetrology now. Figure 5 represents some capabilitiesof different methods of roughness measurementand their vertical and lateral resolution. Ascan be seen there is no method for measuring fullrange of asperities deviations.Figure 5. Resolution of various methods of roughnessmeasurementThe foregoing concepts form the basis of therepresentation of a surface in such disciplines asmechanical engineering, machine design, technology,tribology, heattransfer, and so on. On the wholein this representation the surface is examined as therealization of a random field, the characteristics ofwhich are evaluated on the basis of twodimensionalprofilogram samples [12]. In this casethe system of topography estimates is based onanalysis of the histogram characteristics of the asperitiesin some range of their values.A characteristic feature of this approach is thefact that the mutual influence and interrelationshipof the asperities are generally ignored (except forthe fact that the surfaces may be classified as isotropicor anisotropic), i.e., the spatial organizationof the asperities is not taken into account. We canillustrate the ambiguity arising in the surface representationsin this case. Figure 6 a, b shows photographs(obtained on a scanning electron microscope(SEM)) of surfaces having different spatial structure.Table 1 present the results of a comprehensivestudy of their microgeometry.Figure 6. Two types of surface texturesTable 1. Roughness parameters of surfaces on Figure 6.RoghnessparameterSample on Figure 5abRa 3.20.5 2.30.3Rz 19.34.2 15.92.0Rmax 15.03.7 12.21.4S 56.718.6 43.27.6Sm 165.9 4.4 117.78.76 13 th International Conference on Tribology – Serbiatrib’13