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.
The rheological properties of a commercial friction-promoting grease (FPG) were investigated using a cone and plane rheometer. Two friction tests were conducted at a low sliding rate (1 mm/s) using a wire rope (designed for mining use) and a commercial friction lining material. One involved dry-friction and the other greased conditions. The corresponding coefficient of friction (COF) in each case was determined and used to evaluate the effect of application of the FPG on the lifting performance of a hoist under normal conditions. In addition, experiments involving high-speed sliding friction between the wire rope and the friction material were also performed (with and without the FPG). Different sliding speeds and applied loads were used. The aim was to obtain the tribological behavior of the friction material in conditions that simulate a severe working environment for the hoist. The experimental results were analyzed and combined with the rheological properties of the FPG. The FPG can substantially protect the friction lining from wear and simultaneously provide an adequate COF (about 0.356) between the friction pair under normal working conditions. When the working conditions are severe, an increase in sliding speed causes a decrease in the COF. However, a larger load does not necessarily result in a smaller COF. Increasing the sliding speed or the load both aggravate the wear of the friction lining.
Friction and wear are important technologically. Tires on wet roads, windshield wipers and human joints are examples where nanometer-thick liquids are confined between flexible-rigid contact interfaces. Fundamental understanding of the structure of these liquids can assist in the design of products such as artificial joints and lubricants for Micro-electromechanical systems [MEMS]. Prior force measurements have suggested an increase in apparent viscosity of confined liquid and sometimes solid-like responses. But, these have not given the state of molecules under confinement. In the present study, we have used a surface sensitive, non-linear optical technique (infrared-visible sum frequency generation spectroscopy [SFG]) to investigate molecular structure at hidden interfaces. SFG can identify chemical groups, concentration and orientation of molecules at an interface. A friction cell was developed to study sliding of a smooth elastomeric lens against a sapphire surface. Experiments were done with dry sliding as well as lubricated sliding in the presence of linear alkane liquids. SFG spectra at the alkane/sapphire interface revealed ordering of the confined alkane molecules. These were more ordered than alkane liquid, but less ordered than alkane crystal. Cooling of the confined alkane below its melting temperature [T(subscript M)] led to molecular orientation that was different from that of bulk crystal next to a sapphire surface. Molecules were oriented with their symmetry axis parallel to the surface normal. In addition, the melting temperature [T(subscript conf)] under confinement for a series of linear alkanes (n=15-27) showed a surprising trend. Intermediate molecular weights showed melting point depression. The T[subscript conf] values suggested that melting started at the alkane/sapphire interface. In another investigation, confinement of water between an elastomeric PDMS lens and sapphire was studied. SFG spectra at the sapphire/water/PDMS interface revealed a heterogeneous morphology. The presence of peaks related to PDMS, as well as water, suggested water puddles in the contact area and the sapphire surface had a layer of bound water. This heterogeneity picture provides insight into high friction and stick-slip behavior found in boundary lubrication. For the first time, a broadband SFG system has been coupled with a friction cell to study dynamics and molecular changes at an interface during sliding; sliding of confined alkane between sapphire and PDMS was investigated. A series of SFG spectra were taken while the confined alkane contact spot moved in and out of the laser beam. Even though the experiments were done 15°C above melting temperature, the spectra showed ordering of alkane molecules, similar to that of the confined crystal at the leading and trailing edge. The results suggest that a large portion of the resistance to sliding may come from ordering of molecules at the lens front.
Qualitative Analysis of Nonsmooth Dynamics: A Simple Discrete System with Unilateral Contact and Coulomb Friction explores the effects of small and large deformations to understand how shocks, sliding, and stick phases affect the trajectories of mechanical systems. By analyzing these non-regularities successively this work explores the set of equilibria and properties of periodic solutions of elementary mechanical systems, where no classical results issued from the theory of ordinary differential equations are readily available, such as stability, continuation or approximation of solutions. The authors focus on unilateral contact in presence of Coulomb friction and show, in particular, how any regularization would greatly simplify the mathematics but lead to unacceptable physical responses. Explores the effects of small and large deformations to understand how shocks, sliding, and stick phases affect the trajectories of mechanical systems Includes theoretical results concerning the full investigation of the behavior under constant or oscillating loadings, even in the case of the simplest mechanical systems Provides a focus on unilateral contact in presence of Coulomb friction Helps you gain an accurate understanding of how the transition occurs to ensure the safe use of any machine involving rotating or sliding mechanisms
Author: Peter J. Blau
Publisher: CRC Press
Release Date: 2008-10-20
Genre: Technology & Engineering
"Should have broad appeal in many kinds of industry, ranging from automotive to computers—basically any organization concerned with products having moving parts!" —David A. Rigney, Materials Science and Engineering Department, Ohio State University, Columbus, USA In-Depth Coverage of Frictional Concepts Friction affects so many aspects of daily life that most take it for granted. Arguably, mankind’s attempt to control friction dates back to the invention of the wheel. Friction Science and Technology: From Concepts to Applications, Second Edition presents a broad, multidisciplinary overview of the constantly moving field of friction, spanning the history of friction studies to the evolution of measurement instruments. It reviews the gamut of friction test methods, ranging from simple inclined plans to sophisticated laboratory tribometers. The book starts with introductory concepts about friction and progressively delves into the more subtle fundamentals of surface contact, use of various lubricants, and specific applications such as brakes, piston rings, and machine components. Includes American Society of Testing and Management (ASTM) Standards This volume covers multiple facets of friction, with numerous interesting and unusual examples of friction-related technologies not found in other tribology books. These include: Friction in winter sports Friction of touch and human skin Friction of footware and biomaterials Friction drilling of metals Friction of tires and road surfaces Describing the tools of the trade for friction research, this edition enables engineers to purchase or build their own devices. It also discusses frictional behavior of a wide range of materials, coatings, and surface treatments, both traditional and advanced, such as thermally oxidized titanium alloys, nanocomposites, ultra-low friction films, laser-dimpled ceramics, and carbon composites. Even after centuries of study, friction continues to conceal its subtle origins, especially in practical engineering situations in which surfaces are exposed to complex and changing environments. Authored by a field specialist with more than 30 years of experience, this one-stop resource discusses all aspects of friction, from its humble beginnings to its broad application for modern engineers.
Friction, wear, and erosion are major issues in mechanical engineering and materials science, resulting in major costs to businesses operating in the automotive, biomedical, petroleum/oil/gas, and structural engineering industries. The good news is, by understanding what friction, wear, or erosion mode predominates in a mechanism or device, you can take action to prevent its costly failure. Seeing Is Believing Containing nearly 300 photos of component failures, macro- and micrographs of surface damage, and schematics on material removal mechanisms collected over 50 years of tribology consulting and research, Friction, Wear, and Erosion Atlas is a must-have quick reference for tribology professionals and laymen alike. Complete with detailed explanations of every friction, wear, and erosion process, the atlas’ catalog of images is supported by a wealth of practical guidance on: Diagnosing the specific causes of part failure Identifying popular modes of wear, including rolling and impact, with a special emphasis on adhesion and abrasion Understanding manifestations of friction, such as force traces from a laboratory test rig for a variety of test couples Recognizing liquid droplet, solid particle, slurry, equal impingement, and cavitation modes of erosion Developing solutions to process-limiting problems Featuring a glossary of tribology terms and definitions, as well as hundreds of visual representations, Friction, Wear, and Erosion Atlas is both user friendly and useful. It not only raises awareness of the importance of tribology, but provides guidance for how designers can proactively mitigate tribology concerns.
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.