Asperity (geotechnical engineering)
In geotechnical engineering and contact mechanics the term asperity is used to refer to individual features of unevenness of the surface of a discontinuity, grain, or particle with heights in the range from approximately 0.1 mm to the order of metres. Below the asperity level, surface interactions are normally considered to be a material property, arising from mechanisms of adhesion and repulsion at the atomic scale.
Dilation
An often used definition for asperities in geotechnical engineering:Unevenness of a surface are asperities if these cause dilation if two blocks with in between a discontinuity with matching asperities on the two opposing surfaces move relative to each other, under low stress levels that do not cause breaking of the asperities.