Materials for engineering, 3rd Edition - (Malestrom)

130
Materials for engineering
Wear rate
10
10 –6
10 –3
1
10 –4
0.1
Resistance
10 –5
0.01
1 10 100 1000
Load (N)
3.36 Wear rate and electrical contact resistance for a leaded α/β brass
pin sliding against a hard stellite ring as a function of normal load.
(After Hirst and Lancaster.)
Wear rate (mm 3 m 1 )
10 –2
Lubricants are employed to reduce both wear and the frictional force between
surfaces. They act by introducing between the sliding surfaces a material with
a lower shear strength than the surfaces themselves. In hydrodynamic lubrication,
the surfaces are separated by a fluid film, whereas, in boundary lubrication, the
surfaces are separated by adsorbed molecular films.
At the end of this chapter, there is a guide to further reading on the subject
of tribology, the study of friction, wear and lubrication, where the detailed
mechanisms of these processes are fully discussed.
Contact resistance (Ω)
3.4.5 Fretting corrosion and fretting fatigue
Fretting may be defined as the damage occurring at the interface of two