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Lubricants
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Dynamic Morphology of Tribological Interfaces in Theory, Simulation and Experiment
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Dynamic Morphology of Tribological Interfaces in Theory, Simulation and Experiment

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (31 October 2018) | Viewed by 20008

Special Issue Editors

Prof. Dr. Michael Müller

E-Mail Website
Guest Editor
Institute of Dynamics and Vibrations, Braunschweig University of Technology, Schleinitzstraße 20, 38106 Braunschweig, Germany
Interests: mechanical contacts under the presence of interface media; partially filled gaps and starved lubrication
Prof. Dr. habil. Georg-Peter Ostermeyer

E-Mail Website
Guest Editor
Institute of Dynamics and Vibrations, Braunschweig University of Technology, Schleinitzstraße 20, 38106 Braunschweig, Germany
Interests: dynamics of friction and wear; evolution and self organization effects in tribological interfaces

Special Issue Information

Dear Colleagues,

Macroscopic parameters of frictional contacts are often governed by highly dynamic processes in the tribological boundary layer. Elements of these processes are heat, wear, tribochemical reactions, and in particular, energy and material transport phenomena. These transport phenomena often form complex local meta-structures whose associated dissipation mechanisms give rise to a friction coefficient that depends on both time and load history.

This Special Issue addresses all scientists working in the field of interface dynamics of tribological contacts, concerning the dynamics of tribofilms, tribocoatings, patches, lubricant accumulations, etc. Contributions on all lubrication regimes are equally welcome, from dry friction to solid lubrication, starved lubrication, and full EHD. This also includes papers on optimizations and modifications of interfaces with respect to coatings, textures, wear debris channels and lubricant reservoirs. The focus is not limited to a particular length scale—so the range from nanoscopic to macroscopic studies by theoretical and/or experimental considerations is of interest. Although at first glance essentially dissimilar, it is expected that the processes at various length scales and lubrication regimes have significant similarities that are correlated with the dynamics of the associated meta-structures.

It is the purpose of this Special Issue to bring together the diverse tribological disciplines towards an improved understanding of the role of the interfaces.  

Prof. Dr. Michael Müller
Prof. Dr. Georg-Peter Ostermeyer
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Friction Interface
  • Lubrication Regimes
  • Material Transport
  • Energy Transport
  • Multi-Scale Problems
  • Surface Optimization
  • Heat and Wear
  • Load History Dependence

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Published Papers (4 papers)

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Research

24 pages, 11671 KiB  
Article
Experimental Studies of Lubricant Flow and Friction in Partially Filled Gaps
by Michael Müller, Lukas Stahl and Georg-Peter Ostermeyer
Lubricants 2018, 6(4), 110; https://doi.org/10.3390/lubricants6040110 - 18 Dec 2018
Cited by 13 | Viewed by 5120
Abstract
Starved lubrication is an important strategy for minimizing the amount of lubricant needed, and also inevitably occurs during idling and fail-safe lubrication. In this regime, however, the flow of the lubricant and the related friction coefficients are yet to be fully understood. This [...] Read more.
Starved lubrication is an important strategy for minimizing the amount of lubricant needed, and also inevitably occurs during idling and fail-safe lubrication. In this regime, however, the flow of the lubricant and the related friction coefficients are yet to be fully understood. This research aims to make fundamental contributions to the understanding of contact mechanics of partially lubricated contacts. Recent experiments with a pin-on-disk tribometer examined the microscopic behavior of partially filled gaps. Using a new experimental setup on a macroscale, new insights into partially filled gaps with rough surfaces were gained. This work presents the systematic analyses of the lubricant flow, friction coefficients, and other variables over a wide range of friction parameters. Distinct friction behaviors were observed, and similar effects occur on both the micro and macroscale. The experimental results show that a typical Stribeck characteristic is visible regarding not only the relative velocity, but also regarding the lubricant filling level in the gap. The fluid exhibits a variety of flow patterns for various velocities and viscosities. The patterns relate to different friction regimes, such as dry friction and mixed lubrication. It is concluded that the filling level is a valid parameter for regulating the transition from dry friction to hydrodynamic lubrication. These findings are quantified regarding the filling level and it is shown that for the identification of the friction regimes the filling level is an independent parameter in addition to the established parameters like speed, viscosity and pressure. Full article
(This article belongs to the Special Issue Dynamic Morphology of Tribological Interfaces in Theory, Simulation and Experiment)
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15 pages, 1212 KiB  
Article
Influence of Copper/Graphite Properties on the Tribological and Electrical Behavior of Copper-Graphite Third Body Layer
by Eric Chapteuil, Mathieu Renouf, Chaoqun Zeng and Yves Berthier
Lubricants 2018, 6(4), 109; https://doi.org/10.3390/lubricants6040109 - 14 Dec 2018
Cited by 7 | Viewed by 3334
Abstract
The understanding of rail braking is irrevocably dependent on the tribological analysis of contacts such as the wheel/rail contact or the wheel/brake disc contact. Because it is very complex to experimentally analyze the inside of a contact, a numerical approach based on discrete [...] Read more.
The understanding of rail braking is irrevocably dependent on the tribological analysis of contacts such as the wheel/rail contact or the wheel/brake disc contact. Because it is very complex to experimentally analyze the inside of a contact, a numerical approach based on discrete element modeling was used to model a third body composed of copper and graphite, the main elements present in sintered brake materials. Simulations were analyzed by measuring several global quantities as a function of the proportion of copper and the local properties of the material to determine the extent to which local parameters influence the electrical and tribological properties of the third body. Among the results noted was the fact that a certain proportion of mixture makes it possible to achieve a balance between electrical and tribological properties. Full article
(This article belongs to the Special Issue Dynamic Morphology of Tribological Interfaces in Theory, Simulation and Experiment)
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Graphical abstract

17 pages, 6865 KiB  
Article
Experimental Evaluation of Brake Pad Material Propensity to Stick-Slip and Groan Noise Emission
by Alessandro Lazzari, Davide Tonazzi, Giovanni Conidi, Cristian Malmassari, Andrea Cerutti and Francesco Massi
Lubricants 2018, 6(4), 107; https://doi.org/10.3390/lubricants6040107 - 11 Dec 2018
Cited by 21 | Viewed by 5176
Abstract
Frictional and dynamic responses of brake pad materials, when sliding on brake disc counterfaces, are at the origin of noise, vibration and harshness (NVH) issues such as brake noise emissions. In more detail, groan is a low frequency noise emission often associated to [...] Read more.
Frictional and dynamic responses of brake pad materials, when sliding on brake disc counterfaces, are at the origin of noise, vibration and harshness (NVH) issues such as brake noise emissions. In more detail, groan is a low frequency noise emission often associated to the stick-slip frictional response of the brake system. The instability of such contact is the result of the coupling between the system dynamics and the frictional response of the materials in contact. In this work, an experimental approach is proposed for measuring the frictional response and the propensity to generate stick-slip of different lining materials, coming from commercial brake pads, when sliding on a worn surface of a brake disc, under the same controlled boundary conditions. The proposed methodology allowed for comparing the propensity of the tested pad materials to stick-slip vibrations, which is in agreement with feedback from automotive industry on groan emission. Full article
(This article belongs to the Special Issue Dynamic Morphology of Tribological Interfaces in Theory, Simulation and Experiment)
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16 pages, 7965 KiB  
Article
Theoretical and Experimental Investigations on Transient Run-Up Procedures of Journal Bearings Including Mixed Friction Conditions
by Maximilian Prölß, Hubert Schwarze, Thomas Hagemann, Philipp Zemella and Philipp Winking
Lubricants 2018, 6(4), 105; https://doi.org/10.3390/lubricants6040105 - 1 Dec 2018
Cited by 13 | Viewed by 5945
Abstract
This paper focuses on the operating behavior of journal bearings for industrial machinery application during run-ups. For this purpose, a numerical simulation code that is based on a two-dimensional extended and generalized Reynolds equation and a full three-dimensional energy equation, was advanced by [...] Read more.
This paper focuses on the operating behavior of journal bearings for industrial machinery application during run-ups. For this purpose, a numerical simulation code that is based on a two-dimensional extended and generalized Reynolds equation and a full three-dimensional energy equation, was advanced by a theoretical model considering the effects of mixed friction and warming of journal components during start-up. The mixed friction routine contained the elastic half-spaces model proposed by Boussinesq, which considers the influence of rough surfaces by implementing flow factors and calculates additional stiffness and dissipation in areas with solid interactions. Furthermore, a transient term was added in the energy equation to consider the thermal inertia of journal, and bearing to ensure a realistic heating during run-ups. Results of the prediction were compared to experimental data taken from a special test rig built up for validation procedures. Besides the conventional sensors for temperature, oil flow, and relative motion between shaft and stator, a contact voltage measurement was installed to determine the intensity of mixed friction. The evaluation of experimental data by Stribeck curves, based on a shaft torsion measurement, indicated a significant influence of run-up time on frictional moment. The friction coefficient of the rotor bearing system was strongly influenced by the run-up time. A short run-up time reduced the frictional coefficient in the mixed lubrication regime while the opposite behavior was observed in the hydrodynamic lubrication regime. The numerical code predicted these tendencies in good agreement with experimental data, however, only if the transient energy model was applied. Full article
(This article belongs to the Special Issue Dynamic Morphology of Tribological Interfaces in Theory, Simulation and Experiment)
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