4. Fuller and Tabor model
dependence of adhesion on surface roughness for elastic solids:
where:
K is the coefficient of reduction in adhesion by asperity deformation forces;
E is the Young's modulus [Pa];
σ is the standard deviation of the asperity height distribution (RMS) [m];
r is the average radius of curvature of individual asperities [m];
Δg is the change in surface energy on contact between the two surfaces [J/m2].
It is assumed that for K < 10 strong adhesion occurs, while for K > 10 asperity deformation forces cause the net adhesion force for elastic materials to be small.

5. Schematic diagram of asperity junction growth under frictional force

6. where:
F is the friction force [N];
W is the normal force (load) [N];
Ar is the real area of contact with tangential force present [m2];
Aro is the real area of contact in the absence of tangential force [m2].

7. Adhesion between gear teeth resulting in scuffing

16. The Delamination theory of Wear