Tribology | 1. Introduction and Need of Tribology

Introduction to Tribology

 Tribology is derived from
the Greek word “Tribos”. Meaning of Tribos is

 Tribology is a science
that deals with friction, lubrication and wear in all
contacting pairs

 Tribological knowledge
helps to improve service life, safety and reliability
of interacting machine components; and yields
substantial economic benefits.

Few Examples :

1) Example 1:

Pitting of cam surface
Fig.1 Pitting of cam

Example 1 is related pitting wear on the
cam surface(as shown in Fig. 1). Cams are used to
transmit rotary motion in reciprocating motion. These
components are subjected to jerks in sliding distance,
which leads to form some pits on the cam surface.
Creation of pits on cam surface increases noise
pollution and reduces mechanical performance.
Understanding the mechanism of pit formation helps to
estimate the life of component and find methods to
reduce such pitting failures.

2) Example 2 : Journal

Abrasive wear and rubbing wear
Fig 2  Abrasive wear and
 Fig 3  Rubbing wear

The following figures(Fig. 2 and Fig. 3)
are examples of two journal bearing. Left hand side is
photograph of centrally grooved engine journal bearing.
It appears that bearing is worn out due to foreign
particles. Right hand side is a photograph of an
aluminum bearing subjected to heavy load, which causes
shaft surface to run over bearing inner surface. In
these examples of journal bearing, wear increases the
clearance between shaft and bearing and leads to
reduction in load support capacity of the bearing.
Often such failures occur in absence of sufficient
lubricant hydrodynamic film thickness due to relatively
low speed. Learning tribology cultivates an
understanding that at low speeds, the main purpose of
oil is the lubrication and high viscosity oil will be
preferred to low viscosity oil, while at high speeds
the major purpose of oil is to act as a coolant and low
viscosity lubricants are preferred to carry away
frictional heat of operation. Here lubrication is a
secondary consideration.

3) Example 3: Gear

Gear teeth removed from gear.
Fig 4. Gear teeth removed from

A pit on the surface of gear tooth is shown in Fig.
4. The pit generally occurs due to excessive contact
stress. Understanding the effect of contact stress
helps in developing an equation for estimation of
perspective gear life.

Pits on gear teeth.
Fig 5. Pits on gear

Studies of fluid film bearings, rolling element
bearings, seals, gears, cams, and brakes are some of
the applications in which tribology is required.

Basic knowledge gained by Tribology
course is very useful for industries related to
power, steel, cement, oil etc. Practicing such
knowledge in problems ranging from house hold
appliances to large size ships earns great economic
benefits. Therefore tribology course is often named
as : “Industrial Tribology”, “Applied

Need of Tribology as subject

Friction, wear and lubrication have
been taught in many science and engineering classes
at a rudimentary level. It means empirically derived
trends (friction force is proportional to loading
force, static friction is greater than kinetic
friction, viscous friction in a fluid is proportional
to the normal contact force, etc.) are often used as
the only predictive tools available. These approaches
have the drawbacks of being predictive only over a
limited range of parameters. Since the under-laying
physical mechanisms are not well understood, often
one does not even know which are the important
parameters or over what range the observed trends are
valid. This poor predictive power has led the field
of tribology being perceived in many scientific

• Most
tribological phenomena are inherently complicated and
interconnected, making it necessary to understand the
concepts of TRIBOLOGY in details.

Integration of knowledge from multifaceted
disciplines(solid mechanics, fluid mechanics,
material science, chemistry etc) is essential and
therefore a separate subject is

Solid Mechanics: Focus is on
expressions of contact stresses/deformations and
surface temperatures due to

Material science and chemistry.
Fig 6. Material science and

Fluid Mechanics:
Study of lubricant film formed between various
geometric shapes of rolling/sliding

Material Science: Focus is on atomic and
micro scales mechanisms whereby solid surface
degradation or alteration occurs during relative

Chemistry: Deals with reactivity between
lubricants and solid surfaces.

Thermodynamics: Heat and mass transfer in
fluids and bounding solids.

See Also :