G. Barber, H. Gao and M. Shillor,
ASME Journal of Tribology.

The engagement of a wet clutch with skewed surface roughness was investigated.
A Weibull asperity height distribution rather than a Gaussian one was utilized in the
asperity contact pressure model. The combined effects of surface roughness and
skewness on the friction coefficient were studied for new, run-in and glazed wet
friction materials. The results show that the engagement time predicted by the Weibull
distribution is greater than that obtained using the Gaussian distribution. A torque
spike at the beginning of engagement occurs using the Weibull distribution by taking
the skewness into account. A positively sloped curve of friction coefficient versus
velocity can reduce the torque increase near the end of the engagement. The strain
value at the end of engagement obtained by including the skewness is lower than that
predicted by excluding it. The surface topography and the friction characteristics
change with the engagement wear and thermal glazing. The torque response and the
phase plane are presented for the run-in and the glazed wet friction materials as a
function of surface roughness, skewness and friction characteristic.