Table Of ContentTRlBOLOGY SERIES
Advisory Editor: DOUGLAS SCOTT
Editorial Board
W.J. Bartz (Germany. B.D.R.) I.V. Kragelskii (U.S.S.R.)
C.A. Brockley (Canada) K.C. Ludema (U.S.A.)
E. Capone (Italy) A.J.W. Moore (Australia)
H. Czichos (Germany, B.D.R.) G.W. Rowe (Gt. Britain)
W.A. Glaeser (U.S.A.) T. Sakurai (Japan)
M. Godet (France) J.P. Sharma (India)
H.E. Hintermann (Switzerland)
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Vol. 1 Tribology a systems approach to the science and technology of friction,
lubrication and wear (Czichos)
Vol. 2 Impact Wear of Materials (Engel)
TRIBOLOGY SERIES, 2
IMPACT WEAR
MATERIALS
PETER A. ENGEL
IBM System Products Division, Endicott, N. Y., U.S.A.
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
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AMSTERDAM OXFORD NEW YORK 1978
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
335 Jan van Galenstraat
P.O. Box 211, 1000 AE Amsterdam, The Netherlands
Distributors for the United States and Canada:
ELSEVIERINORTH-HOLLAND INC.
52, Vanderbilt Avenue
New York, N.Y. 10017
First edition 1976
Second impression (with amendments) 1978
230 figures
Librar) of Congress Cataloging in Publication Data
Engel, Peter A
Impact wear of materials.
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Includes biblioara-p hical references and indexes.
1, blaterials--3ynanic testing. 2" Iqact.
I. Title,
~~418.34~5. 621.8'9 76 -44871
ISBN 0-444-41533 -5
ISBN: 0-444-41533-(5V ol. 2)
ISBN: 0-444-41677-(3S eries)
@ Elsevier Scientific Publishing Company, 1978
All rights reserved. No part of this publication may be reproduced, stored in a retrieval
system or transmitted in any form or by any means, electronic, mechanical, photocopy-
ing, recording or otherwise, without the prior written permission of the publisher, Elsevier
Scientific Publishing Company, P.O. Box 330, 1000 AH Amsterdam, The Netherlands
Printed in The Netherlands
PREFACE
The inspiration to write this book essentially grew out of the author's experience
with engineering problems pertaining to impacting machine components. lmpact wear,
i.e. the wear resulting from repetitive impact cycles in machinery, is often a limiting
factor of service life; its importance is accentuated in modern industrial applications
where high-strength materials are called upon to endure a large number of load cycles
under high local (contact) stress. These loads induce wear modes which are character-
istic of the process of contacting, and thus traditional wear tests would not suffice to
evaluate competing designs.
Because impact wear has become a significant factor and prior textbooks hod
traditionally treated sliding and, to an extent, rolling as the main source of mechanical
wear in machinery, this first book devoted to impact wear is hoped to fulfill a vital
mission, Following the conception of this book, the author has continued and widened
his research activities, and diligently studied the literature of tribology; the latter
indicates rapid progress in a field where important discoveries are becoming more
frequent.
In writing this text, the author was concerned to highlight a hitherto neglected
area of wear, and also to give expression to a compact philosophy that considers wear
as a geometric phenomenon dependent an the contact stresses and wear mechanisms.
Wear phenomena due to erosion and percussion are considered under the unified
title of lmpact Wear. Erosion is defined as the action of streams and jets of solid '
particles or liquids, and percussion refers to the impacts of solid bodies of more sub-
stantial size, The unification of erosion and percussion appears justified because the
common features of impact stress analysis are in abundance despite the fact that wear
mechanisms tend to be distinct and characteristic of a particular impact wear process.
The studies, beginning in the 1950'~o~f materials eroded by solid particles and
liquids have followed distinct patterns in their development. An effort has been made
in this text to reconstruct a sense of this historic development within those studies.
lmpact wear caused by percussion is a newer topic and this is the area of the
author's principal research contributions. Consequently, there is an attempt to show
the relationship between the analytical-experimental apparatus used in percussive
impact versus sliding and rolling work.
The general intent of this book is an analytical-predictive formulation of various
cases involving impact wear. New results in erosion theory permit the possibility of
quantifying the wear rates that are dependent on a few principal parameters. For per-
cussive impact wear, a generalized engineering theory emerged from the author's
research, and it centers around the master-curve shifting procedure detailed in this
text, An experimental foundation to the analytical results is provided throughout
the work, The following considerations enter into each quantitative application:
(1) Impact analysis, (2) Identification of material behavior and wear mechanisms,
(3) Considerations of the wear geometry, (4) The aspect of surface properties and
behavior.
The emphasis of this book is on conceptual models and a rational treatment, in-
stead of sophisticated mathematical or physico-chemical presentation. It is hoped that
this approach will be of benefit to researchers and engineers, and specifically, to
machine designers, and will stimulate further investigation at colleges, universities,
and research institutions.
When used in university courses, this text corresponds to the level of a senior
undergraduate or first-year graduate course in engineering and the natural sciences.
The organization of the material was designed to enhance an interdisciplinary attitude
to the subject matter by engineers, physicists, and chemists working in various special-
ized fields,, Therefore an appropriate introduction is provided to prepare the reader for
each key aspect of impact wear.
Chapter 1 reviews the basic issues of tribology. Chapter 2 discusses impact (and,
in general, contact) theory; modern computational techniques such as the finite element
method are shown. Chapter 3 is devoted to the various aspects of a single impact on
engineering surfaces; layered surfaces, plastically deformed materials, viscoelasticity
and lubrication are discussed for their role on impact. An introduction to osperity-
models focuses on the "microscopic" elements of contact, the synthesis of which being
the "macroscopic" (apparent, Hertzian) contact. Repetitive impact effects are involved
inasmuch as heat generation is involved.
Ductile cutting and brittle fracture by small erosive particles is described in
Chapter 4. Some successful semi-empirical theories combining wear by the ductile and
brittle aspects of the material are presented. Chapter 5 treats some of the latest in-
vestigations in erosive wear, including the effect of particle fragmentation; single-
/
particle studies have explained several aspects of erosion dependence an velocity,
angle of incidence, etc.
Chapter 6 introduces the experimental techniques and various phenomena arising
in percussive impact wear; some test apparatuses are described, along with test goals.
Chapter 7 is devoted to the initiation of wear and the "zero wear theory" by which it
can be predicted based on an engineering description of the materials and loads involved.
Chapter 8 starts with the optimal wear-path principle, and combining this with the wear
mechanism, laws are derived for the continuous wear process in different geometric
configurations. The master-curve shifting process facilitates a rapid estimation of the
effects of varying the impact- and sliding velocities, surface roughness, lubrication
and other engineering parameters. In Chapter 9, the analytical techniques are extended
to contacts loaded .into the plastic range, after reviewing numerous experimental results.
Percussive wear of metal vs, nonmetal configurations is treated in Chapter 10; the wear
of print-devices and metal vs. polymer pairs is discussed.
The erosion of liquid jets is treated in Chapter 11; impact stress analysis and
damage due to single impacts is followed by fatigue considerations for multiple hits.
The author has been, for many years, principal investigator of impact wear work
in the Materials and EngFneering Analyses Section at the IBM Laboratory in Endicott,
N. Y. He thanks his management for encouraging the research project and the publica-
tion of this work. The thoughtful comments of G. P. Tilly helped shape the final con-
tents of the manuscript. The remarks of E. Sacher and M. B. Peterson are greatly
appreciated. The interest and helpful attitude of many colleagues at IBM and of the
worldwide scientific community are gratefully acknowledged. A special note of admira-
tion is due to the researchers of Cambridge University who pioneered in the study of
erosion. The author also wishes to thank all workers in the field and their publishers,
who consented to lending data and diagrams quoted in this text.
The skeleton of this book was born in courses given at IBM and at the School of
Advanced Technology, State University of New York at Binghamton. Every student is
warmly remembered for his help in crystallizing the material, The author extends his
grateful appreciation to Josie Scanlon for producing an excellent manuscript in the form
of camera-ready copy.
Finally, the author's wife deserves high praise for her patience and cheerful
support during the years of work.
Binghamton, N.Y.
July, 1976
BORROWED ILLUSTRATIONS
The author is grateful for the permission granted by publishers of several books and
journals to reproduce material in this text. The publications that are quoted include
the following:
Technical books published by Edward Arnold, London; Pergamon Press Ltd., Oxford;
Oxford University Press, Oxford; Wiley and Sons, New York.
Journal articles:
ASLE Transactions Amer. Soc. of Lubrication Engineers,
Park Ridge, ll linois
ASME Transactions Amer. Soc. of Mechanical Engineers,
Journal of Applied Mechanics New York, N.Y.
Journal of Basic Engineering
Journal of Engineering for Industry
Journal of Lubrication Technology
Comptes Rendus de I'Academie des Sciences Centrale des Revues Dunod-Gauthier-
Vil lars, Paris
Experimental Mechanics Society of Experimental Stress Analysis,
Bridgeport, Connecticut
IBM Journal of Research and Development IBM Corporation, Armonk, N. Y.
International Journal of Mechanics and Pergamon Press Ltd., Oxford
Physics of Sol ids
International Journal of Solids and Structures Pergamon Press Ltd., Oxford
International Journal of Numerical Wiley and Sons, New York
Methods in Engineering
Journal of Applied Physics Amer. lnsti tute of Physics, New York
Journal of Macromolecular Science, Marcel Dekker Journals, New York
Reviews in Macromolecular Chemistry
Journal of Materials Amer. Soc. of Testing Materials,
Philadelphia, Pa.
Journal of Research of the National U. S. Department of Commerce,
Bureau of Standards Washington, D.C.
Metals Engineering Quarter1y Amer. Soc. for Metals, Metals Park, Ohio
Proceedings and Philosophical Oxford University Press, Oxford
Transactions of the Royal Society of London
Wear Elsevier Sequoia, Lausanne
NOMENCLATURE
Symbols which are only used locally are not listed here.
A Area
A, Real area of contact
a Contact radius for spherical contact; major axis of contact ellipse
aT(T) Viscoelastic shift factor
B Bulkmodulus
b Half-length of cor\tact, for cylindrical contact; minor axis of contact ellipse
C Constraint factor; stress severity factor
C Specific heat
c Velocity exponent in erosion; sound velocity; clearance
c Phase velocity
D Ductility; contact diameter; erosion resistance; damage
d Indenter diameter; distance; particle size (diameter); jet diameter
E Modulus of elasticity
E, Reduced modulus of elasticity, [ ((1 - vl2 )/"El) + ((1 - v22 )/rE 2)1 -1
E* Complex modulus
e Coefficient of restitution
F Friction force
f Slip factor, vibration frequency
G Shear modulus
H Oil film thickness; layer thickness; hardness
h Depth of wear
I Moment of inertia; erosion intensity
J Impulse
J1,2,3 Invariants of the stress deviator tensor
K Wear constant; stiffness matrix; thermal conductivity
k Spring constant
L Span length
M Bending moment; mass
m Mass
N Impulse; number of cycles
n Impact repetition rate
Normal contact force
Linear normal force per unit width
Flow pressure; hardness; fluid pressure
Heat; volume; failure parameter
Contact pressure
Volumetric heat generation
Radius of curvature; roundness
Reynolds number
Sliding pass-length; sheor force; shape factor; impact strength
Radius of wear crater; percentage of weight undersize for erosive particle sample
Temperature; modulus of toughness; tension
Time
Contact time (duration)
Slipping time during impact
Energy
Velocity; radial surface displacement
Impact velocity
Tangential (sliding) velocity
Volume (or mass) of wear
(Elastic) displacement; width of cylindrical indenter
SI ip
Sliding distance
In subscript, denotes yield
Contact approach; pressure-viscosity constant; angle of attack
Combined curvature; surface damage contribution factor; rake angle
Y Wear factor
A Logarithmic decrement
6 Peak-t~-~eosku rface finish
tan 6 Viscoelastic dissipation factor
Strain; deformation wear factor; energy
Nondimensional curvature parameter
Viscosity; asperity density
Angle; rotation
Thermal diffusivity
Nondimensional curvature parameter for wearing plane
Coefficient of friction
Poisson's ratio
Mass density; nondimensional curvature parameter for wearing round body
Normal stress; contact pressure; standard deviation of asperity heights
Shear stress
impact frequency; cutting Weor factor ; primary erosion factor
Probability distribution
Contact force ratio, P/F; optical reflection coefficient
Angle between principal planes of contacting bodies; plasticity index;
secondary erosion factor
Angular speed
