Effect of Sampling Interval on Dependence Between Hybrid Parameters of Machined Surface Textures

Surface topography affects the functional properties of machined surfaces. To assess these effects, special parameters were developed. Among them, the hybrid parameters rms. slope Sdq and the developed interfacial areal ratio Sdr are of high significance. However, these parameters are interrelated. Sdr can be estimated from Sdq using the special formula. The connections between these parameters were studied in this work depending on the sampling interval. Sixty-four surface topographies, after various machining treatments, were measured by white light interferometer Talysurf CCI Lite and analysed. The same measurement condition was performed for all surfaces. The application of the formula that interrelated the hybrid parameters was tested for different sampling intervals. It was found that the Sdq parameter was strongly linearly correlated with the Sdr parameter, independent of the sampling interval. The dependence between hybrid parameters had a nonlinear character. The estimation of the Sdr parameter based on the values of the Sdq parameter yielded very accurate results for smooth surfaces, independent of the sampling interval. Relative errors in estimating Sdq based on Sdr decreased as the sampling interval increased. High errors corresponded to surfaces with high roughness amplitude. A proposal was presented for sampling interval selection. Because hybrid parameters are interrelated, one parameter should be selected for the description of the areal surface texture. The Sdq parameter is recommended because of its lower sensitivity to measurement errors than the Sdr parameter.