Non-Gaussian effects in microcontact

The two parameter Weibull distribution is proposed as a model for asperity heights. Unlike the symmetrical gaussian model usually assumed, it is capable of accounting for skewness, either positive or negative, in the asperity height distribution. The Weibull parameters are shown to be readily determined numerically for a given RMS level and dimensionless skewness of the asperity height distribution. In addition the contact of two Weibull surfaces may be approximated as the contact of an equivalent single Weibull surface and a smooth plane. Using results obtained by simulation it is shown that for the same RMS height the mean asperity pressure can be higher than in the gaussian case by a factor of 1.4 if the skewness is +1 and lower by a factor of 1.7 if the skewness is -1.