J.A. Greenwood

The behaviour of transverse roughness in sliding elastohydrodynamically lubricated contacts

Recent calculations have shown that in a sliding elastohydrodynamically lubricated contact, any initial roughness largely disappears and is replaced by (often large) pressure variations. This paper gives an elementary analysis of the process for transverse roughness which provides the conditions under which it occurs, and allows the magnitude of the pressure ripples to be estimated. If the fluid is non-Newtonian, the behaviour will be very different.

A surface roughness parameter in Hertz contact

Abstract The influence of surface roughness on the accuracy with which the Hertz theory of elastic contact predicts the contact pressure and contact area between a sphere and a plane is examined theoretically and experimentally. Statistical theories of surface contact suggest that the influence of surface roughness is governed primarily by a single non-dimensional parameter α defined by α  σR a 0 2 where σ is the combined roughness of the two surfaces, R is the radius of the sphere and a 0 is the contact radius for smooth surfaces given by the Hertz theory. Experimental measurements of contact area correlate well with this parameter. Provided that the value of α is less than about 0.05, errors in the application of the Hertz theory due to roughness of the surfaces are not likely to exceed about 7%.

An interpolation formula for flash temperatures

Abstract A rule is proposed for estimating the surface temperature rise in a single body due to a moving heat source on its surface, by combining the estimates for slow and fast heat sources. Comparisons with other rules are given.

Surface temperatures in a fretting contact

Abstract A simple analysis for the surface temperature developed in a small-amplitude fretting contact is presented. It is found that the steady temperature is always the major term, and that for low frequencies the maximum temperature rise is equal to that for a unidirectional sliding contact moving at the maximum speed of the fretting contact.