Author: Bo Persson
Publisher: Springer Science & Business Media
Release Date: 2013-03-14
The ability to produce durable low-friction surfaces and lubricant fluids has become an important factor in the miniaturization of moving components in many technological devices, e.g., magnetic storage, recording systems, miniature motors and many aerospace components. This book will be useful to physicists, chemists, materials scientists, and engineers who need to understand sliding friction. This second edition covers several new topics including friction on superconductors, simulations of the layering transition, nanoindentation, wear in combustion engines, rolling and sliding of carbon nanotubes, and the friction dynamics of granular materials.
Author: Bo Persson
Publisher: Springer Science & Business Media
Release Date: 2013-04-17
The study of sliding friction is one of the oldest problems in physics, and certainly one of the most important from a practical point of view. Low-friction surfaces are in increasingly high demand for high-tech components such as computer storage systems, miniature motors, and aerospace devices. It has been estimated that about 5% of the gross national product in the developed countries is "wasted" on friction and the related wear. In spite of this, remarkable little is understood about the fundamental, microscopic processes responsible for friction and wear. The topic of interfacial sliding has experienced a major burst of in terest and activity since 1987, much of which has developed quite independently and spontaneously. This volume contains contributions from leading scientists on fundamental aspects of sliding friction. Some problems considered are: What is the origin of stick-and-slip motion? What is the origin of the rapid processes taking place within a lub at low sliding velocities? On a metallic surface, is the rication layer electronic or phononic friction the dominating energy dissipation pro cess? What is the role (if any) of self-organized criticality in sliding friction? How thick is the water layer during sliding on ice and snow? These and other questions raised in this book are of course only part ly answered: the topic of sliding friction is still in an early state of development.
Solid friction is considered by some to be a fundamental property of two contacting materials, while others consider it to be a property of the larger tribosystem in which the materials are contained. A set of sliding friction experiments were designed to investigate the hypothesis that the unlubricated sliding friction between two materials is indeed a tribosystems-related property and that the relative influence of the materials properties or those of the machine on friction varies from one situation to another. Three tribometers were used: a friction microprobe (FMP), a typical laboratory-scale reciprocating pin-on-flat device, and a heavy-duty commercial wear tester. The slider material was stainless steel (AISI 440C) and the flat specimen material was an ordered alloy of Ni3Al (IC-50). Sphere-on-flat geometry was used at ambient conditions and at normal forces ranging from 0.01 N to 100 N and average sliding velocities of 0.01 to 100.0 mm/s. The nominal, steady-state sliding friction coefficient tended to decrease with increases in normal force for each of the three tribometers, and the steady state value of sliding friction tended to increase as the mass of the machine increased. The variation of the friction force during sliding was also a characteristic of the test system. These studies provide further support to the idea that the friction of both laboratory-scale and engineering tribosystems should be treated as a parameter which may take on a range of characteristic values and not conceived as having a single, unique value for each material pair.
Thermally stimulated electron emission of 40Kh10G10 steel samples subjected to sliding friction at different sliding velocities Nu was studied in a vacuum using a secondary electron multiplier. Also measured were the magnitude of induced wear, intermediate contact electrical resistance, the coefficient of friction, and the emf occurring under friction. As Nu increases from 0.75 to 4.5 m/sec, two maxima appear on the thermally stimulated electron emission curves in the regions 170 and 270 degrees C.A more intense thermally stimulated electron emission is observed after sliding with V equals 4.5 m/sec, and this also produces greater wear.
Interfacial particles (third-bodies), resulting from wear or external contamination, can alter and even dominate the frictional behavior of solid-solid sliding in the absence of effective particle removal processes (e.g., lubricant flow). A unique friction microprobe, developed at Oak Ridge National Laboratory, was used to conduct fine- scale friction studies using 1.0 mm diameter stainless steel spheres sliding on several sizes of loose layers of fine aluminum oxide powders on both aluminum and alumina surfaces. Conventional, pin-on-disk experiments were conducted to compare behavior with the friction microprobe results. The behavior of the relatively thick particle layers was found to be independent of the nature of underlying substrate, substantiating previous work by other investigators. The time-dependent behavior of friction, for a spherical macrocontact starting from rest, could generally be represented by a series of five rather distinct phases involving static compression, slider breakaway, transition to steady state, and dynamic layer instability. A friction model for the steady state condition, which incorporates lamellar powder layer behavior, is described.
Many scientists and engineers do not realize that, under certain conditions, friction can lead to the formation of new structures at the interface, including in situ tribofilms and various patterns. In turn, these structures—usually formed by destabilization of the stationary sliding regime—can lead to the reduction of friction and wear. Friction-Induced Vibrations and Self-Organization: Mechanics and Non-Equilibrium Thermodynamics of Sliding Contact combines the mechanical and thermodynamic methods in tribology, thus extending the field of mechanical friction-induced vibrations to non-mechanical instabilities and self-organization processes at the frictional interface. The book also relates friction-induced self-organization to novel biomimetic materials, such as self-lubricating, self-cleaning, and self-healing materials. Explore Friction from a Different Angle—as a Fundamental Force of Nature The book begins with an exploration of friction as a fundamental force of nature throughout the history of science. It then introduces general concepts related to vibrations, instabilities, and self-organization in the bulk of materials and at the interface. After presenting the principles of non-equilibrium thermodynamics as they apply to the interface, the book formulates the laws of friction and highlights important implications. The authors also analyze wear and lubrication. They then turn their attention to various types of friction-induced vibration, and practical situations and applications where these vibrations are important. The final chapters consider various types of friction-induced self-organization and how these effects can be used for novel self-lubricating, self-cleaning, and self-healing materials. From Frictional Instabilities to Friction-Induced Self-Organization Drawing on the authors’ original research, this book presents a new, twenty-first century perspective on friction and tribology. It shows how friction-induced instabilities and vibrations can lead to self-organized structures, and how understanding the structure–property relationships that lead to self-organization is key to designing "smart" biomimetic materials.
The Quartz Crystal Microbalance (QCM) has been used to record adsorption and sliding friction data for molecularly thin inert gas films, at 77K, on metal surfaces prepared under Ultra High Vacuum (UHV). Adsorption of xenon was studied on nickel, carbonized nickel, copper and lead. Adsorption of krypton was studied on carbonized and clean nickel. Even sub-monolayer quantities of inert gas produce changes in QCM mechanical properties that may be used to estimate coefficients of sliding friction. At 77K, these inert gases are known to adsorb on various surfaces, forming two-dimensional phases analogous to the solid and gas phases exhibited by bulk substances. While previous QCM studies have emphasized the role of two-dimensional solid and liquid phases in damping QCM motion, this work examines the possibility that the two-dimensional gas phase may be the dominant cause of damping at low coverage. QCM data suggest that the sliding motion of the two-dimensional gas phase of inert gases tends to decay within a characteristic time approaching 10 nanoseconds. The 2D solid phase routinely cited as a low friction phase has an order of magnitude higher friction than the 2D gas phase.