Skip to main content


Refinement of Engine In-Cycle Losses of Parasitic and Errant Dynamic Nature

Home  Research Programme  Surface Tribology  Top Compression Ring  Cylinder Liner  Piston Skirt  Experiments   


 Hierarchical Surface Topography


Surface topography is hierarchical. Thus, boundary friction is a problem of physical scale.


Surface roughness is described by a host of statistical measures according to the roughness pattern.  The surface roughness average height Ra is inappropriate for estimation of friction.

To estimate friction at particular stages of wear other more appropriate topographical parameters are required;  initial stages of friction and wear reduce Rpk (the average height of asperity peaks above the roughness core profile). A good measure for friction during gradual wear is the reduction of the core roughness depth Rk, which for cylinder liners is the average plateau height of a typical cross-hatched and honed finish. Rvk is the average depth of the profile valleys projecting through the roughness core profile, this parameter is used to determine the volume of lubricant oil trapped by the textured surface.

  Monitoring Topography


Surface roughness can be measured according to its physical scale, the type of surface and profilometer tip size. The minimum profilometer tip size is 2 micrometers. The type of analysis is also determined by the measurement resolution required. Friction and wear can be ascertained down to nanoscale or even for a single asperity with an atomic force microscope. This information, together with asperity geometry and distribution, is required by some friction models.