This document discusses the role of tribology in engineering. Tribology comprises the science and technology of interacting surfaces in relative motion, including friction, lubrication, and wear. It is a vast and interdisciplinary field ranging from fundamental physics of surface contact to practical applications. The document emphasizes that tribologists should quantify the profitability of reducing friction and wear, for example through calculating potential cost savings from improved fuel efficiency. Active control of tribological systems using methods like liquid crystal lubricants may also help optimize friction and wear performance. Accuracy of tribological predictions remains limited by various factors.

1. The Role of Tribology in Engineering
Tribology comprises the science and technology of
interacting surfaces in relative motion; that is, friction,
lubrication and wear. Tribology is a vast and
interdisciplinary subject, ranging from the fundamental
physics of surface contact and adhesion to the
application of advanced materials and lubricants to solve
practical industrial friction and wear problems.

3. Motivation:
• Most common forms of metal failure:
– Corrosion
– Fatigue (cyclic loading)
– Wear (surface abrasion due to excessive
friction or lack of lubrication) = TRIBOLOGY

4. What is Friction
• Force tangential to
the interface of two
contacting bodies =
Ff.
– Dynamic and static
– Dynamic produces
heat
NFf µ=
Friction Force
Coefficient of friction
µs and µd
Normal Force
Assumptions: Ff independent of contact area, µ = constant

5. More Complicated Models Exist:
• Contact Mechanics
In actuality, as N
increases,
contact area
increases,
thereby affecting
µ. µ is a non-
linear function of
N. What else
might µ vary
with??

6. More Complicated Models Exist:
F = Fa + Fp + Fs + Fn NFf µ=

7. What about contact
stresses???
Recall: Pitting stress
in gear teeth

8. How to Measure µ???
• Do you want µs or µd???
• For most stress analysis want µs – why??

9. Good for measuring µs.
You should know how
to derive this.
Good for measuring µs
and µd.

10. Typical Friction Force Curves
µs = Fa/N
µd = Fb/N
Stick- Slip – difficult
to get a µ

11. 5.4 Definition of Surface Wear
• Wear - Damage to a solid surface
involving progressive loss of material due
to contact and relative motion with another
surface. 13 types of wear!!
• Erosion – Damage to a solid surface
involving progressive loss of material due
to mechanical interaction between that
surface and a fluid, impinging liquid or
solid particles. 5 kinds of erosion

12. Figure 5.14 – Major Categories of wear and specific types of wear in
each category.

13. Types of Wear:
Figure 5:20 – Adhesion
wear – localized
bonding between
contacting surfaces
Figure 5-21: Galling wear –
severe adhesion actually leads
to material flow up from the
surface.
adhesion
adhesion

14. Figure 5-23:
Fretting wear
of splined
shaft– small
oscillatory
motion
abrades
surface –
looks like rust
– surface
looks pitted.
adhesion

15. F5-24: low stress abrasion wear – bushing sliding
on shaft
abrasion

16. Surface fatigue
F 5-27 – Pitting surface
fatigue – large roller
thrust bearing race –
compressive stress
developed between roller
bearing and race =
pitting. Material actually
fatigued and removed
from surface!!

17. Surface fatigue
F5-28: Impact wear

18. Surface fatigue
F 5-30: Brinelling – brinelling of bearing race due to static overload. Note
brinelling more of a static failure (indentation) versus fatigue or wear failure.

19. F 3-27: Factors that affect wear
at various size levels.
Key: Bonds
between
atoms!
Key:
Dislocation
s
Key: Grain
Size
Key:
Surface
asperities
Key:
Surface
confromanc
e

20. Figure 5-15: Types of Erosion – Note all involve fluids or smoke
(particulates)

21. Fig5– 16: solid
particle erosion
due to fly ash.
Types of Erosion
5-17: Slurry
erosion due to
pumping slurry
mixture of silica
and water
erosion
erosion

22. Stress-Strain Diagram
Strain ( ) (∆L/Lo)
4
1
2
3
5
Stress(F/A)
Elastic
Region
Plastic
Region
Strain
Hardening Fracture
ultimate
tensile
strength
Slope=E
Elastic region
slope =Young’s (elastic) modulus
yield strength
Plastic region
ultimate tensile strength
strain hardening
fracture
necking
yield
strength
UTSσ
yσ
εEσ =
ε
σ
E =
ε
12
y
εε
σ
E
−
=

23. 23
• Resistance to permanently indenting the surface.
• Large hardness means:
--resistance to plastic deformation or cracking in
compression.
--better wear properties.
e.g.,
10mm sphere
apply known force
(1 to 1000g)
measure size
of indent after
removing load
dD
Smaller indents
mean larger
hardness.
increasing hardness
most
plastics
brasses
Al alloys
easy to machine
steels file hard
cutting
tools
nitrided
steels diamond
Hardness

24. TH130
Impact Device D integrated for general use
Easy handling
Optional Printer
Memory up to 99 data
TH132
Impact Device C integrated for thin work piece
Optional Printer
Memory up to 99 data
TH134
Impact Device DL integrated for narrow space and holes
Optional Printer
Memory up to 99 data

25. 25
Conversion of
Hardness
Scales
Also see: ASTM E140 - 07
Volume 03.01
Standard Hardness Conversion
Tables for Metals Relationship
Among Brinell Hardness, Vickers
Hardness, Rockwell Hardness,
Superficial Hardness, Knoop
Hardness, and Scleroscope
Hardness

26. 18-26
Symbols Used to Identify Surface
Finishes and Characteristics

27. SURFACE ROUGHNESS TESTER

28. Mechanical Seals
Haward Technology Middle East 28Section 1

33. Section 8 Haward Technology Middle East 33
Electromechanical Maintenance

35. Haward Technology Middle East 35
Tribology of the machine
Section 1

36. Viscosity Index
Figure 4.11 Graphical explanation of viscosity
index where L = low VI oil, x = unknown oil, and
H=high VI oil.)

37. Haward Technology Middle East 37
Lube Oil System, Design & Troubleshooting
Section 3
Properties of Lube Oils
Note: The numbers in parentheses are unitless
numbers that show the difference between viscosity at
40°C and 100° C.

61. TRIBOLOGY ，
Its
Possibility and
Impossibility

62. ・ Heavy industry
to IT-related Industry
・ Restructuring in Industry
Recent Changes
in Social Conditions
Around TRIBOLOGY
→ Micro-, Nano-scale Tribology
→ Decrease in the Number of
Tribologists

63. What is Expected of
TRIBOLOGY and
What Can We Do
in the Future?
・ Predictability
・ Controllability
・ Profitability

64. Accuracy of Prediction in
Hydrodynamic Lubrication
Depends upon ……
Factors to be included in analyses
• Elastic deformation
• Temperature / Pressure effects
• Transition phenomena, etc.
Limitation on computation
• Models expecting increase in
computation speed

65. Factors Impairing Accuracy
of Prediction During
Boundary/Dry Sliding
・ Form and dimensional errors
・ Surface irregularities
・ Surface contamination
・ Material contamination
・ Changes in these with operation

66. Controllability
-Changes
in the requirement for Tribology
・ Reduction of friction alone
・ Prevention of surface damage
→ Maintaining friction
in certain ranges
→ Maintaining wear rates
in certain ranges??

67. Control of Friction
-Control of normal load
or friction coefficient
Passive control
Active control
・ Selecting Lubricants
・ Mechanical Design
・ Materials
・ Using active feedback
elements or ……

68. Possibility of Active Control
With Liquid Crystal Lubricant
By applying electric field ……
・ Change in apparent viscosity
・ Change in friction in boundary
lubrication
→ Control of friction in hydro-
dynamic lubrication

69. Another Important Issue
- Control of Deterioration
・ Changes in form and dimension,
micro-geometry, surface films,
subsurface layers; contamination
of lubricant, depletion of additives,
additives, etc.
・ Sensing and preventing, or
compensating for, those changes

70. -Tribologists should show profitability
of tribology, quantitatively
and explicitly.
Profitability
・ How much cost can be cut
by lowering friction
coefficient by 0.01?
Example : Fuel saving by
friction reduction at piston-
cylinder wall

71. No. of cars in use 71×106
No. of gas cars in use 57×106
Gasoline sales 57×106
kl
Total gasoline cost $57×109
Statistics (Japan, 1998)

72. Fuel Energy Consumption
in a Car ： EPA Mode
62% ： Thermal
6% ： Air pumping
3% ： Piston-Cylnder
4% ： Engine/Others
13% ： Others
12% ：
Wheels
100
80
60
40
20
0
%

73. Power Loss Analysis Between
Piston and Cylinder Wall
Friction coefficient
•0.05 for Piston rings
•0.03 for Piston skirt
Distribution of Mechanical loss
•60% for Piston rings
•40% for Piston skirt
•0.042 between Piston and
Cylinder Wall

74. Possible Friction Reduction
・ 0.01 of Decrease of
Friction Coefficient
・ 445×103
kL of Fuel
or $445×106
Cost Saving
30% ： coating on rings
20% ： barrel-shaped piston skirts
→26% Reduction
of Average Friction Coefficient