TRIBOLOGY SERIES, 6

FRICTION AND WEAR OF POLYMERS GMBARTENEV Institute of Physical Chemistry of the Academy of Science of the U.S.S.R, Moscow, U.S.S.R.

and

VY LAVRENTEV Department of Physics, Second Moscow Medical Institute, Moscow, U.S.S.R.

Translated by D.B. PAYNE

Edited by

LIENG-HUANG LEE

Xerox Corporation, Rochester, New York

and

K.C. LUDEMA University of Michigan, Ann Arbor, Michigan

ELSEVIER SCIENTIFIC PUBLISHING COMPANY

AMSTERDAM - OXFORD - NEW YORK 1981

TABLE OF CONTENTS

EDITOR'S PREFACE

Page

v

PREFACE

FOREWORD BY P. A. REBINDER

NOMENCLATURE

CHAPTER 1 - STRUCTURE AND PHYSICAL PROPERTIES OF POLYMERS 1

1.1 Physical States of Polymers 1 1.2 physical Properties of Macromolecules and

Polymer Structure 2 1.3 Special Characteristics of Thermal Motion in

Polymers 4 1.4 The Rubbery State in Polymers 7 1.5 Relaxation Properties of Polymers 8 1.6 The Principle of Time-Temperature Equivalence 11 1.7 Polymer Glass-Transition Processes 16 1.8 Cold Flow of Polymers 19 1.9 Prolonged Strength (Fatigue) of Polymers 21

References 2 7

CHAPTER 2 - FRICTION OF METALS

2.1 Basic Characteristics of Friction 2.2 The Real Contact Area 2.3 Theories of Solid Friction 2.4 Friction Force and Friction Coefficient

Effect of stationary contact time Effect of sliding velocity Effect of free, normally oriented contact

vibrations Effect of temperature References

30

30 34 38 47 47 49

53 62 63

CHAPTER 3 - POLYMER FRICTION IN THE GLASSY AND CRYSTALLINE STATES 67

3.1 Nature of Rigid-Polymer Friction 67 3.2 Real Area of Contact 74 3.3 Friction Force and Coefficient of Friction 80

Effect of normal load Claw of friction) 80 Effects of contact time, sliding velocity,

and temperature 8 6 Effects of other factors 100

3.4 Selection of Friction Pairs 105 References 108

X V I

P a g e

CHAPTER 4 POLYMER FRICTION IN THE RUBBERY STATE 111 4.1 Nature and Mechanism of Elastomer Friction 113

Molecular-kinetic theory of friction ц з Effect of temperature and sliding velocity 134 Molecular-mechanical theories of friction X38

4.2 Real Area of Contact 145 Effect of contact time and sliding velocity 145 The effect of normal load 150 Effect of temperature 152

4.3 Friction Force 155 Effect of normal load 155 Effect of contact time and the rate of application

of the tangential force 166 Effect of the nature of the polymer and the

characteristics of the surface 175 Effect of internal stress in a polymer 177 Selection of friction pairs 180 References 185

CHAPTER 5 SLIDING AND FRICTION OF POLYMERS IN THE VISCOUS STATE 187

5.1 Mechanisms of Boundary Sliding in Viscous and Dispersed Systems 187

5.2 The Theory of Boundary Sliding 190 5.3 Some Experimental Results and Basic Principles 194

Effect of normal load 194 Effect of sliding velocity 198

5.4 The Significance of the Effect of Boundary Sliding 200

References 201

CHAPTER 6 WEAR OF POLYMERS 202 6.1 Relationship Between Friction and Wear 203 6.2 Fatigue Wear 2 05

Theoretical studies 206 Basic experimental results 213 Effect of pressure 215 Effect of friction coefficient 218 Effect of temperature 221 Effect of sliding velocity 227 Effect of polymer physico-mechanical properties

and composition 229 Effect of surface friction. Transition to

abrasive wear 235 6.3 Abrasive Wear 238

General principles of abrasive wear 239 Effect of external factors 243

6.4 Special Types of Wear for Friction on Smooth Hard Surfaces 248

6.5 Practical Recommendations and Prospects for the Use of Polymers at Friction Contacts 253

References 257

CHAPTER 7 - INSTRUMENTS AND METHODS FOR FRICTION AND WEAR RESEARCH 261

7.1 General Information 261 7.2 Methods for Measuring External Parameters

of Friction 263 Measurement of friction force 264 Measurement of temperature 267 Measurement of sliding velocity 268 Measurement of load 269

7.3 General-Purpose Instruments and Machines 269 Reciprocal-motion instruments 269 Rotary motion instruments 279

7.4 Special-Purpose Instruments and Machines 2 84 Instruments for measuring the area of

real contact 2 85 Instruments for measuring polymer friction

force at high pressure 288 Vacuum tribometers 293 Instruments for special uses 298 References 302

AUTHOR INDEX SUBJECT INDEX

305