FRICTION,WEAR,

LUBRICATION

A

TEXTBOOK IN TRIBOLOGY

K.C Ludema

Pr

ofessor of Mechanical Engineering
The University of Michigan
Ann Arbor

CRC Press
Boca Raton New York London Tokyo
©1996 CRC Press LLC

The co

ver background is a photograph of a steel surface (light blue) partially covered with streaks
of “protective” film due to sliding in engine oil. The image was created by a polarizing interference
(Françon) microscope objective (25

×

621.8

′

9—dc20 96-12440CIP
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Library of Congress Card Number 96-12440
Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
Printed on acid-free paper
©1996 CRC Press LLC

ABOUT

THE AUTHOR


friction

and

wear

is by

lubrication

, though it is
often not the economical way. These three topics together constitute the broad
area of tribology. Tribology has many entry points because of its great breadth.
The advancement of each of its subtopics requires concentrated effort, and many
people spend a satisfying and useful career in only one of them. By contrast,
product designers and engineers need to be moderately proficient in all related
topics with some understanding of the more specialized topics.

THE ST

ATUS OF TRIBOLOGY

T

ribology as a whole lags behind engineering in general in the development of
equations, formulae, and methods for general use in engineering design. Indeed,
there are some useful methods and equations available, mostly in full film fluid
lubrication and contact stress calculations. The reason for the advanced state of
these topics is that very few variables are needed to characterize adequately the
system under study, namely, fluid properties and geometry in the subject of liquid

the ever-present vendors offer widely different solutions to problems in tribology,
which bewilders managers who would like to believe that tribology is a simple
and straightforward art.
In academic preparation for designing products, most students in mechanical
engineering (the seat of most design instruction) have taken courses in such
topics as:

a.

Fluid mechanics
b. Elasticity (described as solid mechanics)
c. Materials science (survey of atomic structure and the physics of solids)
d. Dynamics (mechanical mostly)
e. Heat transfer
f. Methods of mechanical design.

These are useful tools indeed, b

ut hardly enough to solve a wide range of
problems in friction and wear. Students in materials engineering will have a
different set of tools and will gravitate toward those problems in which their
proficiencies can be applied. But the complete tribologist will have added some
knowledge in the following:

g.

Plasticity
h. Visco-elasticity
i. Contact mechanics
j. The full range of mechanical properties of monolithic materials, composite

The ne

xt four chapters summarize some of the academic topics that may or should
have been a part of the early training of tribologists:

•

Chapter 2

asserts that friction and wear resistance are separate from the usual
mechanical properties of materials and cannot be adequately described in terms
of those properties (though many authors disagree).

•

Chapter 3

discusses atomic structure, atomic energy states, and a few phenom-
ena that are virtually always ignored in the continuum approach to modeling
of the sliding process (and should not be).

•

Chapter 4

shows how real surfaces are made and discusses the inhomogeneous
nature of the final product.

•


cause loss of material from a sliding/rolling interface.

•

Chapter 9

is
on chemical aspects of lubrication, where friction, wear, and
lubrication converge in such problems as scuffing failure and break-in.

The follo

wing three chapters discuss methods of solving problems in friction and
wear:

•

Chapter 10

is
an analysis of design equations in friction and wear, showing
that useful equations require more realistic assumptions than superposition of
individual, steady state mechanisms of wear.


•

Chapter 14

covers bearings and materials, lightly.

A minimum of references has been used in this te

xt since it is not primarily
a review of the literature. In general, each chapter has a list of primary source
books which can be used for historical perspective. Where there is no such book,
detailed reference lists are provided.
There are problems sets for most of the chapters. Readers with training in
mechanics will probably have difficulty with the problems in materials or physics;
materialists will have trouble with mechanics; and scientists may require some
time to fathom engineering methods. Stay with it! Real problems need all of these
disciplines as well as people who are willing to gain experience in solving
problems.
This book is the “final” form of a set of course notes I have used since 1964.
Hundreds of students and practicing engineers have helped me over the years to
gain my present perspective on the complicated and fascinating field of tribology.
I hope you will find this book to be useful.

K

en Ludema
Ann Arbor, Michigan
January 1996
©1996 CRC Press LLC


Fatigue
Fracture Toughness
Application to Tribology
References
Chapter 3
Adhesion and Cohesion Properties of Solids: Adsorption to Solids
Atomic (Cohesive) Bonding Systems
Adhesion
Atomic Arrangements: Lattice Systems
(See Problem Set question 3 a)
Dislocations, Plastic Flow, and Cleavage
(See Problem Set question 3 b)
Adhesion Energy
Adsorption and Oxidation
Adsorbed Gas Films
(See Problem Set question 3 c)
Introduction
Introduction
©1996 CRC Press LLC
Journals and Periodicals
Books

Chapter 4

Solid Surf

aces
Technological Surface Making
(See Problem Set question 4 a and b)
Residual Stresses in Processed Surfaces

Adhesion of Atoms
Elastic, Plastic, and Visco-elastic Effects in Friction
(See Problem Set question 6 c)
Friction Influenced by Attractive Forces Between Bodies
(See Problem Set question 6 d)
Friction Controlled by Surface Melting and Other Thin Films
Rolling Resistance or Rolling Friction
©1996 CRC Press LLC

Friction of Compliant Materials and Structures, and of Pneumatic

Tires
(See Problem Set question 6 e)
Influence of Some Variables on General Frictional Behavior
Static and Kinetic Friction
Tables of Coefficient of Friction
Vibrations and Friction
Effect of Severe Uncoupled Vibration on Apparent Friction
Tapping and Jiggling to Reduce Friction Effects
Testing
Measuring Systems
(See Problem Set questions 6 f and g)
(See Problem Set questions 6 h, i, and j)
Interaction Between Frictional Behavior and Transducer Response
Electrical and Mechanical Dynamics of Amplifier/Recorders
(See Problem Set question 6 k)
Damping
Analysis of Strip Chart Data
How to Use Test Data
References

Oxidati

ve Wear
Dry Sliding Wear of Polymers
(See Problem Set questions 8 e and f)
Wear of Ceramic Materials
Abrasion, Abrasive Wear, and Polishing
(See Problem Set question 8 g)
Erosion
Fretting
Practical Design
References
Chapter 9
Lubricated Sliding — Chemical and Physical Effects
Friction in Marginal Lubrication
Wear in Marginal Lubrication
Boundary Lubrication
The Mechanical Aspects of Scuffing (without Chemical Considerations)
The

Λ

Ratio
The Plasticity Index
(See Problem Set questions 9 a and b)
Thermal Criteria
Scuffing and Boundary Lubrication
Experimental Work
Further Mechanical Effects of the Boundary Lubricant Layer
Dry Boundary Lubrication

The Search
Analysis of Equations
Results of Applying the Above Criteria to Equations in Erosion
References
Chapter 11
Designing for Wear Life and Frictional Performance:
Wear Testing, Friction Testing, and Simulation
Design Philosophy
Steps in Designing for Wear Life Without Selecting Materials
The Search for Standard Components
In-House Design
Steps in Selecting Materials for Wear Resistance
Restrictions on Material Use
Check of Static Load
Determine Sliding Severity
Determine Whether Break-in is Necessary
Determine Acceptable Modes of Failure
Determine Whether or Not to Conduct Wear Tests
Testing and Simulation
Standard Tests and Test Devices
Necessary Variables to Consider in Wear Testing
Accelerated Tests
Criterion for Adequate Simulation
Measurements of Wear and Wear Coefficients and Test Duration
Material Selection Table
(See Problem Set questions 11 a and b)
Chapter 12
Diagnosing Tribological Problems
Introduction to Problem Diagnosis
Planning