A microscopic high point on a real engineering surface. Even a ground finish of 0.2 micron Ra is a field of peaks and valleys under magnification, and when two parts touch only the asperity tips carry the load, so the true contact area is a small fraction of the apparent area. Asperity contact drives friction, heat and wear whenever the film thins, and running-in exists largely to flatten the tallest ones.
Under the scope you can see the asperity tips on the tooth flank have all been polished flat.
Also heard as
- surface peak
- roughness peak
Related terms
Lambda ratio
Oil film thickness divided by the combined roughness of the two surfaces, used to judge the lubrication regime.
Running-in
Early period when new contacting surfaces wear and smooth each other until they settle into a stable state.
Boundary lubrication
Regime where surfaces touch through the oil and protection comes from chemical surface films, not fluid pressure.
Adhesive wear
Wear where touching asperities weld together and tear, moving metal from one surface to the other.