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 0 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 Investigation of Solid Film Lubricants and Sliding Contacts at Temperatures Above 1000 degrees F written by Marshall B. Peterson and published by . This book was released on 1960 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 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 NASA Reference Publication written by and published by . This book was released on 1977 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 728 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 Friction and Heat Generation in Rolling sliding Contacts in the Elastohydrodynamic Lubrication Regime written by Salem Almail and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fundamentals of Fluid Film Lubrication written by Bernard J. Hamrock and published by NASA Office of Management Scientific a. This book was released on 1991 with total page 680 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tribological Design of Machine Elements written by D. Berthe and published by Elsevier. This book was released on 1989-10-03 with total page 535 pages. Available in PDF, EPUB and Kindle. Book excerpt: On previous occasions each Symposium has focused attention on a current and significant research topic, usually reflecting the interests of the Leeds or Lyon research groups, however this time the main focus was on the vitally important subject of technology transfer, providing the 154 delegates from 21 countries with the rare opportunity to discuss the impact of their studies on machine design.

Download or read book Use of Textured Surfaces to Mitigate Sliding Friction and Wear of Lubricated and Non Lubricated Contacts written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: If properly employed, the placement of three-dimensional feature patterns, also referred to as textures, on relatively-moving, load-bearing surfaces can be beneficial to their friction and wear characteristics. For example, geometric patterns can function as lubricant supply channels or depressions in which to trap debris. They can also alter lubricant flow in a manner that produces thicker load-bearing films locally. Considering the area occupied by solid areas and spaces, textures also change the load distribution on surfaces. At least ten different attributes of textures can be specified, and their combinations offer wide latitude in surface engineering. By employing directional machining and grinding procedures, texturing has been used on bearings and seals for well over a half century, and the size scales of texturing vary widely. This report summarizes past work on the texturing of load-bearing surfaces, including past research on laser surface dimpling of ceramics done at ORNL. Textured surfaces generally show most pronounced effects when they are used in conformal or nearly conformal contacts, like that in face seals. Combining textures with other forms of surface modification and lubrication methods can offer additional benefits in surface engineering for tribology. As the literature and past work at ORNL shows, texturing does not always provide benefits. Rather, the selected pattern and arrangement of features must be matched to characteristics of the proposed application, bearing materials, and lubricants.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1989 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Understanding Contact Mechanics and Friction on Rough Surfaces written by Siddhesh Narayan Dalvi and published by . This book was released on 2020 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the mechanism of adhesion and friction in soft materials is critical to the fields of transportation (tires, wiper blades, seals etc.), prosthetics and soft robotics. Most surfaces are inherently rough and the interfacial area between two contacting bodies depends largely on the material properties and surface topography of the contacting bodies. Johnson, Kendall and Roberts (JKR) derived an equilibrium energy balance for the behavior of smooth elastic spherical bodies in adhesive contact that predicts a thermodynamic work of adhesion for two surfaces in contact. The JKR equation gives a reversible work of adhesion value during approach and retraction. However, viscoelastic dissipation, surface roughness and chemical bonding result in different work of adhesion values for approach and retraction. This discrepancy is termed adhesion hysteresis. Roughness is undermined as a cause of hysteresis in adhesion studies. Recently, a continuum mechanics model has been developed that predicts the work of adhesion on rough surfaces with known roughness in the form of power spectral density (PSD) function. To test the above mentioned theoretical model, we have conducted JKR experiments between highly cross-linked smooth polydimethylsiloxane (PDMS) of four different elastic moduli and diamond surfaces of four different crystal sizes and roughness.The rough diamond surfaces are characterized for topography using stylus profilometry, atomic force microscopy and in-situ transmission electron microscopy combined to give a comprehensive PSD. Results suggest that the observed work of adhesion during approach is equivalent to energy required to stretch the PDMS network at the surface and in the bulk to form the real rough contact area. However, in retraction work of adhesion is found to be proportional to the ratio of excess energy spent in the loading-unloading cycle and the true contact area obtained from topography indicating conformal contact matching fracture mechanics behavior. Thus, the study resolves adhesion hysteresis discrepancy on rough surfaces.It is known that adhesion hysteresis increases interfacial friction on rough surfaces. However, an experimentally proven quantitative model is still missing. Previous studies on smooth surfaces have shown that shear stress increases with velocity initially, reaching a maximum and then either plateaus out or decreases depending upon the modulus of the sliding elastomer. We have performed shear measurements with velocities ranging from nm/sec to cm/sec between PDMS elastomers and diamond surfaces. Data suggests higher shear stresses at lower velocities for rough surfaces and thus a shift for the peak previously observed on smooth surfaces. Additionally, there are states such as steady-state sliding, stick-slip and detachment waves with increasing stress in the same order. These states are found to occur at a critical stress and their onset is linearly proportional to the elastic modulus of the sliding rubber. The stress predictions using existing theories do not decouple adhesion and deformation energy losses during friction observed ex- perimentally on rough surfaces and further investigation is required in order to obtain a better friction model.

Download or read book Friction in low speed lubricated rolling and sliding contacts written by Kenneth Holmberg and published by . This book was released on 1984 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Fundamentals of Machine Elements written by Steven R. Schmid and published by CRC Press. This book was released on 2014-07-18 with total page 627 pages. Available in PDF, EPUB and Kindle. Book excerpt: New and Improved SI Edition-Uses SI Units Exclusively in the TextAdapting to the changing nature of the engineering profession, this third edition of Fundamentals of Machine Elements aggressively delves into the fundamentals and design of machine elements with an SI version. This latest edition includes a plethora of pedagogy, providing a greater u

Download or read book Micro elastohydrodynamic Lubrication in Concentrated Sliding Contacts written by Jan Willem Sloetjes and published by . This book was released on 2006 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: