Friction and wear - Orthopaedic Biomaterials in Research and Practice - page 263

Boundary
lubrication

Mixed lubrication Hydrodynamic

or
fluid film lubrication

0.25
0.2
0.15
0.1
0.05
0

λ < 1 1< λ < 3 λ < 3

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Lubricating film thickness (µm)

FIGUre 11.4 (See color insert.) mechanisms of lubrication as depen-
dent on film thickness and friction. (adapted from stewart, t.d.,
Orthop Trauma 26: 435- 440, 2010.)

Displacement perpendicular to the interface of as little as h min as possible
in lateralization or microseperation can disrupt the lubricating film and
introduce impact and fatigue wear, replacing the normal mechanisms of
lubrication (discussed in the next section).

Mechanisms of
lubrication

There are four principal lubrication mechanisms or regimes that depend
on the nature of the relative motion and on the type of the lubricant used
(Figure 11.5).

Hydrodynamic or Fluid Film . This is the lubrication mechanism
present in most engineering applications, such as rotating bear-
ings in electric motors, internal combustion engines, and turbines.
As motion of the surfaces occurs, sufficient pressure results in the
lubricant that the surfaces are completely isolated from each other
and all shear deformation occurs in the film between them. If inter-
mediate viscosity lubricants are used with very smooth (lapped, etc.)
surfaces, the dynamic coefficient of friction and the wear rate are both

Hydrodynamic

Elasto-
hydrodynamic

Mixed

Boundary

FIGUre 11.5 (See color insert.) Principal mechanisms of lubrication.