Describing distribution shape: R K and central moment approaches compared

Abstract

An investigation is reported into characterisation techniques for multi-stratum bearing surfaces such as those produced by plateau-honing. Experiments have been undertaken to determine whether the information presented by the recently introduced DIN 4776 R k parameters can be adequately inferred from the existing central moment parameters of the height distribution; R q, R sk and R ku. Measured values of these central moment parameters are used to fit model continuous distribution curves using the Pearson system of distibutions. The bearing ratio representations of these curves are analysed to derive their DIN 4776 R k parameters. These simulated R k parameters are then compared with those obtained by direct measurement from the profile. It is shown that for surfaces with moderate degrees of skewness this modelling procedure allows the R k parameters to be inferred with reasonable accuracy. For highly skewed surfaces, however, the continuous distributions fitted by Pearson techniques cannot adequately model the upper portions of the profile height distribution and so R pk values cannot be estimated at all and the accuracy with which the other DIN 4776 parameters can be inferred is poorer.