Contact Mechanics

There is a huge difference between the apparent area of contact and the real area of contact which is related to the contact of individual asperities (from each surface) at the micrometre and sub-micrometre scale.

Before we deal with multiasperity contacts, it is useful to consider an individual asperity summit contact (an asperity pair, one asperity from each material surface). This can be complex but can be approximated by the contact of two spheres with (generally) different radii of curvature and mechanical properties.

This simplified case reflects better the geometry of an AFM tip interacting with the asperities of a nominally flat surface.