Download or read book Theoretical and experimental results on friction for line contacts in mixed and elastohydrodynamic lubrication regimes written by Roberto Bassani and published by . This book was released on 1999 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Elasto Hydrodynamic Lubrication written by D. Dowson and published by Elsevier. This book was released on 2014-07-18 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: Elasto-Hydrodynamic Lubrication deals with the mechanism of elasto-hydrodynamic lubrication, that is, the lubrication regime in operation over the small areas where machine components are in nominal point or line contact. The lubrication of rigid contacts is discussed, along with the effects of high pressure on the lubricant and bounding solids. The governing equations for the solution of elasto-hydrodynamic problems are presented. Comprised of 13 chapters, this volume begins with an overview of elasto-hydrodynamic lubrication and representation of contacts by cylinders, followed by a discussion on equations relevant to lubrication, including the Reynolds equation. The reader is then introduced to lubrication of rigid cylinders; the importance of film thickness in highly loaded rigid contacts; the elasticity of solids in contact; and the theory of elasto-hydrodynamic lubrication. Subsequent chapters focus on apparatus and measurements of film thickness and film shape; friction and viscosity; and lubrication of gears and roller bearings. This book will be of interest to tribologists.

Download or read book Investigation of Dynamic Friction in Lubricated Surfaces written by Hanuman Rachoor and published by . This book was released on 1995 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: The research reported in this dissertation is concerned with the development of friction models for lubricated contacts. A few analytical models have been developed to investigate the friction under dynamic velocity conditions. In this study, two different tribological situations such as conformal and non-conformal contacts have been chosen. Friction modeling covers boundary, mixed and full fluid film friction regions. A new theory based on the elastic properties of the surface materials, and fluid film properties of the lubricant at the contact has been developed to determine the dynamic friction in boundary, mixed and full hydrodynamic lubrication regions. In the full fluid film lubrication region, friction has been determined from the lubrication principles based on the tribological situation, i.e., hydrodynamic lubrication theory for a short journal bearing and elastohydrodynarnic lubrication theory for a line contact. A conformal contact formed by a short journal bearing operating in the region where hydrodynamic lubrication theory is valid has been considered to develop a model. The model is simulated for unidirectional as well as bi-directional sinusoidal velocity oscillations for various frequencies. Simulation resulted in a phase lag in the fiction and hysteresis in ftiction versus velocity (f vs. U) curves. The results obtained for unidirectional velocity oscillations indicate qualitative agreement with experimental work on lubricated line contact by Hess and Soom (1990). Results for bi-directional oscillations also show phase lag in friction and similar hysteresis in f vs U curves. In addition to the hysteresis, results for the bi-directional velocity oscillations show a discontinuity in friction at velocity reversals. These results have been verified experimentally. A special apparatus to measure the friction has been designed and built by using a sleeve bearing. Experiments have been conducted to measure friction under various velocity conditions, and the results have been used to determine the coefficients required to simulate the analytical model. The analytical model has been simulated for the above coefficients and the results have been compared with the friction measurements. The comparison shows similar hysteresis in f vs U curves for uni-directional and bi-directional velocity oscillations. However, the friction behavior of the apparatus during bi-directional oscillations differs in the magnitude of the discontinuity (step function) at velocity reversals. The above analytical friction model developed for the hydrodynamic short journal bearing has been extended to investigate the effect of resisting forces on the dynamic friction behavior at low speed. Resistance forces include sliding friction as well as the presliding friction Dahl effect. The Dahl effect is due to elastic deformation of the compliance in the system before the force reaches the breakaway magnitude when sliding initiates. In this study, stiffness of the asperities as well as elastic support have been considered. Simulation results of the model for uni-directional velocity oscillations are in qualitative agreement with earlier experimental work. Simulation of the model for bi-directional velocity oscillations shows that the discontinuity at velocity reversals has been replaced by a line with slope. This work indicates that the stiffness, of the elastic compliance can play a significant role in replacing the discontinuity. The above concepts of friction modeling has been extended for a non-conformal contact formed with a cylindrical surface sliding over a flat surface operating on elastohydrodynamic lubrication theory. In this model, elastohydrodynamic lubrication theory has been used to determine the friction in full fluid film region. Simulation results of this model for uni-directional as well as bi-directional sinusoidal velocity oscillations indicate a similar phase lag in the friction and hysteresis in f vs. U curves as observed in the earlier models. Results of the present investigation indicate that the instantaneous friction is not only a function of the instantaneous velocity, but it is also a function of previous velocity or velocity history. These models can be improved with the aid of more experimental work. Also, these models can be extended for stick-slip analysis and for friction compensation.

Download or read book Lubrication at the Frontier The Role of the Interface and Surface Layers in the Thin Film and Boundary Regime written by M. Priest and published by Elsevier. This book was released on 1999-07-01 with total page 911 pages. Available in PDF, EPUB and Kindle. Book excerpt: The 25th Leeds-Lyon Symposium on Tribology was held at the Institut des Sciences Appliquées de Lyon, from 8-11th September, 1998. Its central theme was, "Lubrication at the frontier: the role of the interface and surface layers in the thin film and boundary regime". This topic was chosen because it represents an important evolution of the research field.The Symposium opened with a keynote address entitled "Role of surface-anchored polymer chains in polymer friction" which described the processes taking place at the interface between "solid" and "liquid". The keynote address was followed by two invited lectures. Firstly, "Fuel efficient engine oils, additive interactions, boundary friction and wear" presented the industrial point of view on lubricant formulation and engine testing and its evolution. The second lecture was entitled "For establishment of a new EHL theory" and stressed the need to extend the current EHL theory.Beginning in 1974, The Leeds-Lyon Symposia have now covered a wide range of topics. The essential aim each year is to select a topic of current interest to tribologists and to contribute to further the advance of knowledge in selected fields.

Download or read book Friction at a Lubricated Line Contact Operating at Oscillating Sliding Velocities written by D. P. Hess and published by . This book was released on 1989 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although many contacts operate under unsteady loading and sliding conditions, friction behavior under such conditions is still not well understood. In this paper we report on a series of experiments that were run to examine friction-velocity characteristics of line contacts operating under unsteady sliding velocities in the mixed, elastohydrodynamic and hydrodynamic lubrication regimes. A periodic, time-varying velocity component was superimposed on a steady sliding speed in such a way that all three lubrication regimes could be covered in a cycle. It was found that as the frequency of oscillation was increased, a multi-valued friction coefficient appeared as a loop about the average (steady state) friction-velocity relation. It is shown that this behavior can be modeled by a characteristic time lag between a changing velocity and the corresponding steady state friction. The latter is described by a single equation that was matched to measured average friction data. In the mixed lubrication regime, which is where this lag most significantly affects friction behavior, the lag time increases with normal load and lubricant viscosity. It is shown that the time shift is not associated with a fixed characteristic distance. The observed delay arises due to entrainment and normal approach, which includes squeeze-films combined with rough surface contact deformations.

Download or read book Encyclopedia of Tribology written by Q. Jane Wang and published by Springer. This book was released on 2013-09-26 with total page 4139 pages. Available in PDF, EPUB and Kindle. Book excerpt: TRIBOLOGY – the study of friction, wear and lubrication – impacts almost every aspect of our daily lives. The Springer Encyclopedia of Tribology is an authoritative and comprehensive reference covering all major aspects of the science and engineering of tribology that are relevant to researchers across all engineering industries and related scientific disciplines. This is the first major reference that brings together the science, engineering and technological aspects of tribology of this breadth and scope in a single work. Developed and written by leading experts in the field, the Springer Encyclopedia of Tribology covers the fundamentals as well as advanced applications across material types, different length and time scales, and encompassing various engineering applications and technologies. Exciting new areas such as nanotribology, tribochemistry and biotribology have also been included. As a six-volume set, the Springer Encyclopedia of Tribology comprises 1630 entries written by authoritative experts in each subject area, under the guidance of an international panel of key researchers from academia, national laboratories and industry. With alphabetically-arranged entries, concept diagrams and cross-linking features, this comprehensive work provides easy access to essential information for both researchers and practicing engineers in the fields of engineering (aerospace, automotive, biomedical, chemical, electrical, and mechanical) as well as materials science, physics, and chemistry.

Download or read book Fundamentals of Fluid Film Lubrication written by Bernard J. Hamrock and published by CRC Press. This book was released on 2004-03-15 with total page 794 pages. Available in PDF, EPUB and Kindle. Book excerpt: Specifically focusing on fluid film, hydrodynamic, and elastohydrodynamic lubrication, this edition studies the most important principles of fluid film lubrication for the correct design of bearings, gears, and rolling operations, and for the prevention of friction and wear in engineering designs. It explains various theories, procedures, and equations for improved solutions to machining challenges. Providing more than 1120 display equations and an introductory section in each chapter, Fundamentals of Fluid Film Lubrication, Second Edition facilitates the analysis of any machine element that uses fluid film lubrication and strengthens understanding of critical design concepts.

Download or read book Rheological Effects on Friction in Elastohydrodynamic Lubrication written by Edward G. Trachman and published by . This book was released on 1973 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytical and experimental investigation is presented of the friction in a rolling and sliding elastohydrodynamic lubricated contact. The rheological behavior of the lubricant is described in terms of two viscoelastic models. These models represent the separate effects of non-Newtonian behavior and the transient response of the fluid. A unified description of the non-Newtonian shear rate dependence of the viscosity is presented as a new hyperbolic liquid model. The transient response of viscosity, following the rapid pressure rise encountered in the contact, is described by a compressional viscoelastic model of the volume response of a liquid to an applied pressure step. The resulting momentum and energy equations are solved by an iterative numerical technique, and a friction coefficient is calculated. The experimental study was performed, with two synthetic paraffinic lubricants, to verify the friction predictions of the analysis. The values of friction coefficient from theory and experiment are in close agreement.

Download or read book Interdisciplinary Approach to the Lubrication of Concentrated Contacts written by P. M.. Ku and published by . This book was released on 1970 with total page 616 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Elastohydrodynamic Lubrication written by Institution of Mechanical Engineers (Great Britain). Lubrication and Wear Group and published by . This book was released on 1966 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rheology and Elastohydrodynamic Lubrication written by B.O. Jacobson and published by Elsevier. This book was released on 1991-07-24 with total page 399 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book gives a thorough overview on recent developments in lubricant rheology, elastohydrodynamic lubrication and the effects of surface roughness and particulate contamination in the lubricant on the overall behaviour of a heavily loaded lubricated contact. One of the aims of the book is to make clear to the reader that a Newtonian model for the lubricant behaviour does not have enough degrees of freedom to be able to describe the friction - traction behaviour of heavily loaded lubricated contacts or the oil film build-up and collapse under surface asperities for rough surfaces. The book contains quite a lot of experimental data of lubricants at high pressures, both solidification pressures, compressibilities and shear strength increase coefficients, which make it possible to estimate the friction and power loss in heavily loaded lubricated contacts for different pressures, temperatures, sliding speeds, and lubricant types. This is the first time that data of this type has been included in a textbook and it is hoped that the questions highlighted will serve to initiate and guide future research in this field.

Download or read book Boundary and Mixed Lubrication Science and Applications written by D. Dowson and published by . This book was released on 2002-07-10 with total page 694 pages. Available in PDF, EPUB and Kindle. Book excerpt: Session headings. Keynote address and invited paper. Boundary lubrication 1. Boundary lubrication 2. Mixed lubrication. Lubricants 1. Lubricants 2. Nano-boundary lubrication and molecular dynamics. Coatings. Dry wear. Lubricated wear. Bio-tribology- total replacement hip joints. Elastohydrodynamic lubrication. Friction 1. Bearings. Friction 2. Mechanical systems.

Download or read book Elastohydrodynamic Lubrication for Line and Point Contacts written by Ilya I. Kudish and published by CRC Press. This book was released on 2013-06-17 with total page 703 pages. Available in PDF, EPUB and Kindle. Book excerpt: Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches describes a coherent asymptotic approach to the analysis of lubrication problems for heavily loaded line and point contacts. This approach leads to unified asymptotic equations for line and point contacts as well as stable numerical algorithms for the so

Download or read book Interdisciplinary Approach to the Lubrication of Concentrated Contacts written by Pei Moo Ku and published by . This book was released on 1971 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Pressure Rheology for Quantitative Elastohydrodynamics written by Scott S. Bair and published by Elsevier. This book was released on 2007-03-06 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational elastohydrodynamics, a part of tribology, has existed happily enough for about fifty years without the use of accurate models for the rheology of the liquids used as lubricants. For low molecular weight liquids, such as low viscosity mineral oils, it has been possible to calculate, with precision, the film thickness in a concentrated contact provided that the pressure and temperature are relatively low, even when the pressure variation of viscosity is not accurately modelled in detail. Other successes have been more qualitative in nature, using effective properties which come from the fitting of parameters used in calculations to experimental measurements of the contact behaviour, friction or film thickness. High Pressure Rheology for Quantitative Elastohydrodynamics is intended to provide a sufficiently accurate framework for the rheology of liquids at elevated pressure that it may be possible for computational elastohydrodynamics to discover the relationships between the behaviour of a lubricated concentrated contact and the measurable properties of the liquid lubricant. The required high-pressure measurement techniques are revealed in detail and data are presented for chemically well-defined liquids that may be used as quantitative reference materials.* Presents the property relations required for a quantitative calculation of the tribological behaviour of lubricated concentrated contacts.* Details of high-pressure experimental techniques.* Complete description of the pressure and temperature dependence of viscosity for high pressures.* Some little-known limitations on EHL modelling.

Download or read book On Lubrication and Friction in Soft Rough Conformal Sliding Contacts written by Bengt Wennehorst and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Soft micro-elastohydrodynamic lubrication, mixed lubrication, friction in lubricated elastomeric contacts, elastomeric radial lip seal, fluid-structure interaction. - Weiche mikro-elastohydrodynamische Schmierung, Mischreibung, Reibung in geschmierten Elastomerkontakten, elastomerer Radialwellendichtring, Fluid-Struktur-Interaktion

Download or read book Fundamentals Of Tribology Third Edition written by Ramsey Gohar and published by World Scientific. This book was released on 2018-07-17 with total page 519 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamentals of Tribology deals with the fundamentals of lubrication, friction and wear, as well as mechanics of contacting surfaces and their topography. It begins by introducing the reader to the importance of tribology in everyday life and offers a brief history of the subject. It then describes the nature of rough surfaces and the mechanics of contacting elastic solids and their deformation under load and friction in their relative motion. The book goes on to discuss the importance of lubricant rheology with respect to viscosity and density. Then, the principles of hydrodynamic lubrication are covered with derivations of the governing Reynolds and energy equations. Applications of hydrodynamic lubrication in various forms of bearings — journal bearings, thrust bearings and externally pressurised bearings — are outlined. The important and still evolving subject of elastohydrodynamic lubrication is treated in some detail, both at its fundamentals and its applications in thin shell or overlay bearings, cam-followers and internal combustion engine pistons.The fundamentals of biotribology are also covered, particularly its applications to endo-articular mammalian joints such as hip and knee joints and their arthroplasty. In addition, there is a treatment of the rapidly emerging knowledge of tribological phenomena in lightly loaded vanishing conjunctions (nanotribology), in natural systems and very small devices, such as MEMS and high density data storage media. There is also a new chapter on the rapidly emerging subject of surface texturing to promote retention of microreservoirs of lubricant, acting as microbearings and improving lubrication of otherwise poorly lubricated conjunctions.This book targets the undergraduate and postgraduate body as well as engineering professionals in industry, where often a quick solution or understanding of certain tribological fundamentals is sought. The book can also form an initial basis for those interested in research into certain aspects of tribology.