Tribology Flashcards
Tribology=
The science of wear, friction and lubrication
No surface is … so 2 surfaces are in contact where…….. so
Perfectly flat
In contact where asperities meet
Real contact area less than measured contact area
Coefficient of friction =
Sliding force/ normal force
3 laws of friction
2 reasons for the laws
Friction force proportional to normal load
F independent of apparent area of contact
F independent of sliding speed
Because:
Contact occurs over small area
Shear stress to break junctions proportional to area
Oxide coated junctions(rust) slide …
More easily than clean ones
Wear=
Damage/erosion by friction/use
Adhesive wear=
E.g
Adhesion at the work hardened junctions causes shear off of materials when surfaces slide
E.g chalk
Abrasive wear=
Asperities of the harder materials or embedded hard particles plough through the softer ones, grinding off wear particles
Wear equation
W= load/ hardness
Archard wear equation
X= ka* (Fn/An)* distance slid
(Distance worn)= archard constant *(normal force/nominal area) * distance slid
Wear rate is dependent on
Surface toughness, load and hardness
Boundary layer=
when the contacts between 2 layers are very close so there is some asperities contact between surfaces
Hydrodynamic lubrication=
Contact separated by thicker, continuos, unbroken film/ layer of lubrication
Boundary layer lubrication allows for
Easy shear between surfaces
