Journal Description
Lubricants
Lubricants
is an international, peer-reviewed, open access journal of tribology. Lubricants is published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), Inspec, and many other databases.
- Journal Rank: CiteScore - Q2 (Mechanical Engineering)
- Rapid Publication: manuscripts are peer-reviewed and a first decision provided to authors approximately 17.3 days after submission; acceptance to publication is undertaken in 3.6 days (median values for papers published in this journal in the first half of 2021).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Latest Articles
Recent Advances in Preparation and Testing Methods of Engine-Based Nanolubricants: A State-of-the-Art Review
Lubricants 2021, 9(9), 85; https://doi.org/10.3390/lubricants9090085 (registering DOI) - 27 Aug 2021
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Reducing power losses in engines is considered a key parameter of their efficiency improvement. Nanotechnology, as an interface technology, is considered one of the most promising strategies for this purpose. As a consumable liquid, researchers have studied nanolubricants through the last decade as
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Reducing power losses in engines is considered a key parameter of their efficiency improvement. Nanotechnology, as an interface technology, is considered one of the most promising strategies for this purpose. As a consumable liquid, researchers have studied nanolubricants through the last decade as potential engine oil. Nanolubricants were shown to cause a considerable reduction in the engine frictional and thermal losses, and fuel consumption as well. Despite that, numerous drawbacks regarding the quality of the processed nanolubricants were discerned. This includes the dispersion stability of these fluids and the lack of actual engine experiments. It has been shown that the selection criteria of nanoparticles to be used as lubricant additives for internal combustion engines is considered a complex process. Many factors have to be considered to investigate and follow up with their characteristics. The selection methodology includes tribological and rheological behaviours, thermal stability, dispersion stability, as well as engine performance. Through the last decade, studies on nanolubricants related to internal combustion engines focused only on one to three of these factors, with little concern towards the other factors that would have a considerable effect on their final behaviour. In this review study, recent works concerning nanolubricants are discussed and summarized. A complete image of the designing parameters for this approach is presented, to afford an effective product as engine lubricant.
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Open AccessArticle
An Evaluation of the Tribological Behavior of Cutting Fluid Additives on Aluminum-Manganese Alloys
Lubricants 2021, 9(8), 84; https://doi.org/10.3390/lubricants9080084 - 21 Aug 2021
Abstract
The introduction of additives enhances the friction and wear reduction properties of cutting fluids (CFs) as well as aids in improving the surface quality of the machined parts. This study examines the tribological behavior of polymer-based and phosphorus-based additives introduced into cutting fluids
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The introduction of additives enhances the friction and wear reduction properties of cutting fluids (CFs) as well as aids in improving the surface quality of the machined parts. This study examines the tribological behavior of polymer-based and phosphorus-based additives introduced into cutting fluids for the machining of Al-Mn alloys. Ball-on-disc tests were used to evaluate the coefficient of friction (COF) and lubrication failure temperature to study the performance of the additives in the cutting fluids. Surface characterization was performed on the sliding tracks induced on the Al-Mn disc surfaces and used to propose the wear and friction reduction mechanisms. The polymer-based additive possessed a higher temperature at which lubrication failure occurred, displayed comparable COF at a lower temperature under certain conditions, and possessed a steadier tribological behavior. However, the phosphorus-based additive was observed to display lower COF and wear damage from 200 °C till failure. The lower COF values for the phosphorus-based additive at 200 °C corresponded with lower surface damage on the Al-Mn surface. The phosphorus-based additive’s performance at 200 °C could be attributed to the forming of a phosphorus-rich boundary layer within the sliding wear track, resulting in less surface damage on the Al-Mn surface and lower material transfer to the counterface steel ball surface.
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(This article belongs to the Special Issue Metalworking Fluids Technology)
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Open AccessArticle
Impact of the LACKS of Fusion Induced by Additive Manufacturing on the Lubrication of a Gear Flank
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Lubricants 2021, 9(8), 83; https://doi.org/10.3390/lubricants9080083 - 20 Aug 2021
Abstract
Additive Manufacturing (AM) is becoming a more and more widespread technology. Its capability to produce complex geometries opens new design possibilities. Despite the big efforts made by the scientific community for improving the AM processes, this technology still has some limitations, mainly related
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Additive Manufacturing (AM) is becoming a more and more widespread technology. Its capability to produce complex geometries opens new design possibilities. Despite the big efforts made by the scientific community for improving the AM processes, this technology still has some limitations, mainly related to the achievable surface quality. It is known that AM technologies promote the formation of LACKS of fusion inside the material. In some cases, the external surfaces are finished with traditional machining. This is the case of AM-produced gears. While the grinding operation aims to reduce the surface roughness, the presence of porosities just below the surface of the wrought component, could lead, after grinding, to the exposure of those porosities leading to a pitted surface. This phenomenon is surely not beneficial in terms of structural resistance, but can help the lubrication promoting the clinging of the lubricant to the surface. The aim of this paper is to study this effect. Micro-Computer-Tomography (μ-CT) analyses were performed on a 17-4 PH Stainless Steel (SS) produced via Selective Laser Melting (SLM). The real geometry of the pores was reproduced virtually and analyzed by means of multiphase CFD analyses in the presence of centrifugal effects.
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(This article belongs to the Special Issue Laser Technology in Tribology)
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Open AccessTechnical Note
Fundamentals of Physics-Informed Neural Networks Applied to Solve the Reynolds Boundary Value Problem
Lubricants 2021, 9(8), 82; https://doi.org/10.3390/lubricants9080082 - 19 Aug 2021
Abstract
This paper presents a complete derivation and design of a physics-informed neural network (PINN) applicable to solve initial and boundary value problems described by linear ordinary differential equations. The objective with this technical note is not to develop a numerical solution procedure which
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This paper presents a complete derivation and design of a physics-informed neural network (PINN) applicable to solve initial and boundary value problems described by linear ordinary differential equations. The objective with this technical note is not to develop a numerical solution procedure which is more accurate and efficient than standard finite element- or finite difference-based methods, but to give a fully explicit mathematical description of a PINN and to present an application example in the context of hydrodynamic lubrication. It is, however, worth noticing that the PINN developed herein, contrary to FEM and FDM, is a meshless method and that training does not require big data which is typical in machine learning.
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(This article belongs to the Special Issue Machine Learning in Tribology)
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Open AccessArticle
Experimental Study of the Lubrication Mechanism of Micro-Spherical Solid Particles between Flat Surfaces
Lubricants 2021, 9(8), 81; https://doi.org/10.3390/lubricants9080081 - 17 Aug 2021
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In this study, a novel apparatus was designed and constructed to perform micro-sliding friction experiments while simultaneously observing the motion of micro-sized spheres using a visual inspection technique. The apparatus comprises a precision elevation stage that is used to elevate a flat mica
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In this study, a novel apparatus was designed and constructed to perform micro-sliding friction experiments while simultaneously observing the motion of micro-sized spheres using a visual inspection technique. The apparatus comprises a precision elevation stage that is used to elevate a flat mica disk, with the microspheres on top of it, to bring it into contact with a stationary surface and apply low loads on the contact. During micro-sliding experiments, it was found that the velocity of the center of the microsphere was half the velocity of the mica disk; in addition, friction force measurements revealed a very low coefficient of friction (about 0.03), indicating the rolling motion of the microspheres. The main outcome of our study was the verification of the hypothesis that spherical particles can be used to avoid direct contact among flat surfaces and can also introduce rolling motion within the system. The pure rolling motion of the microspheres sandwiched between a stationary and a moving flat surface supports the idea of adding rigid spherical particles to oil lubricants to further reduce friction and wear in the system by performing as micro and nanoscale ball bearings.
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Open AccessArticle
Investigation of Tribological Behavior of Lubricating Greases Composed of Different Bio-Based Polymer Thickeners
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Lubricants 2021, 9(8), 80; https://doi.org/10.3390/lubricants9080080 - 17 Aug 2021
Abstract
One commonly used lubricant in rolling bearings is grease, which consists of base oil, thickener and small amounts of additives. Commercial greases are mostly produced from petrochemical base oil and thickener. Recently, the development of base oils from renewable resources have been significantly
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One commonly used lubricant in rolling bearings is grease, which consists of base oil, thickener and small amounts of additives. Commercial greases are mostly produced from petrochemical base oil and thickener. Recently, the development of base oils from renewable resources have been significantly focused on in the lubricant industry. However, to produce an entirely bio-based grease, the thickener must also be produced from renewable materials. Therefore, this work presents the design and evaluation of three different bio-based polymer thickener systems. Tribological tests are performed to characterize lubrication properties of developed bio-based greases. The effect of thickener type on film thickness and friction behavior of the produced bio-based greases is evaluated on a ball-on-disc tribometer. Moreover, the results are compared to a commercial petrochemical grease chosen as benchmark.
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(This article belongs to the Special Issue Grease)
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Open AccessArticle
Improvements of the MQL Cooling-Lubrication Condition by the Addition of Multilayer Graphene Platelets in Peripheral Grinding of SAE 52100 Steel
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, , , , , , and
Lubricants 2021, 9(8), 79; https://doi.org/10.3390/lubricants9080079 - 16 Aug 2021
Abstract
In most grinding processes, the use of cutting fluid is required, and research has been carried out to reduce the amount of fluid used due to costs and environmental impacts. However, such a reduction of fluid can result in thermal damage to the
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In most grinding processes, the use of cutting fluid is required, and research has been carried out to reduce the amount of fluid used due to costs and environmental impacts. However, such a reduction of fluid can result in thermal damage to the machined component because the amount of cutting fluid may not be sufficient to lubricate and cool the system. One way of improving the cutting fluid properties is to add micro or nanoparticles of solid lubricants. This paper aims to evaluate the performance of multilayer graphene platelets dispersed in cutting fluid and applied through the technique of minimum quantity of lubrication (MQL) during the peripheral surface grinding of SAE 52100 hardened steel. In this sense, the influence of these solid particles with respect to the surface and sub-surface integrity of the machined components was analyzed, performing the roughness and microhardness measurement and analyzing the ground surfaces. The results showed that the cooling–lubrication conditions employing graphene could obtain smaller roughness values and decreases of microhardness in relation to the reference value and components with better surface texture compared to the conventional MQL technique without solid particles.
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(This article belongs to the Special Issue Application of Solid Lubricants in Metal Processing)
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Open AccessArticle
Tungsten Disulfide Inorganic Nanotubes Functionalized by PTFE for Friction Application
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, , , , , and
Lubricants 2021, 9(8), 78; https://doi.org/10.3390/lubricants9080078 - 11 Aug 2021
Abstract
Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfoliate at the contact interface and facilitate tribofilm formation. While the tribological properties are greatly improved by exfoliated NPs that shed easily, they may be diminished by agglomeration in
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Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfoliate at the contact interface and facilitate tribofilm formation. While the tribological properties are greatly improved by exfoliated NPs that shed easily, they may be diminished by agglomeration in oil. Therefore, surface functionalization is employed to improve dispersion in oil-based suspensions. Here, WS2 INTs were functionalized by polytetrafluoroethylene (PTFE) in a simple and cost-effective bath sonication method. WS2-INTs with two concentrations of added PTFE were characterized by scanning and transmission electron microscopy, micro-Raman spectroscopy, and thermogravimetric analysis. Superior distribution of WS2 was observed before and during friction experiments. Chemical analysis showed a significantly greater amount of PTFE-coated INTs on rubbed surfaces, in accordance with the improved friction and wear properties.
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(This article belongs to the Special Issue Carbon Nano-materials for Controlling Friction and Wear)
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An Approach for the Transfer of Real Surfaces in Finite Element Simulations
Lubricants 2021, 9(8), 77; https://doi.org/10.3390/lubricants9080077 - 05 Aug 2021
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Virtual simulations are a relevant element in product engineering processes and facilitate engineers to test different concepts during early phases of the development. However, in tribological product engineering, simulations are hardly used because input data such as material behavior are often missing. Besides
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Virtual simulations are a relevant element in product engineering processes and facilitate engineers to test different concepts during early phases of the development. However, in tribological product engineering, simulations are hardly used because input data such as material behavior are often missing. Besides the material behavior, the surface roughness of the contacting elements is relevant for tribological systems. To expand the capabilities of the virtual engineering of tribological components such as bearings or brakes, the hereby presented approach allows for the depiction of real rough surfaces in finite element simulations. Rough surfaces are scanned by a white-light interferometer (WLI) and further processed by removing the outliers and replacing non-measured samples. Next, a spline generation creates a solid body, which is imported to CAD software and afterwards meshed with triangle and quadrilateral elements in different sizes. The results comprise the evaluation of six differently manufactured (turned, coated, and pressed) real surfaces. The surfaces are compared by the deviations of the roughness values after measuring with the WLI and after meshing them. Furthermore, the elements’ aspect ratios and skewness describe the mesh quality. The results show that the transfer is dependent upon deep cliffs and large Sz values in comparison to the lateral expansion.
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Open AccessArticle
A New Computational Tool for the Development of Advanced Exergy Analysis and LCA on Single Effect LiBr–H2O Solar Absorption Refrigeration System
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, , , and
Lubricants 2021, 9(8), 76; https://doi.org/10.3390/lubricants9080076 - 05 Aug 2021
Abstract
A single effect LiBr–H2O absorption refrigeration system coupled with a solar collector and a storage tank was studied to develop an assessment tool using the built-in App Designer in MATLAB®. The model is developed using balances of mass, energy,
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A single effect LiBr–H2O absorption refrigeration system coupled with a solar collector and a storage tank was studied to develop an assessment tool using the built-in App Designer in MATLAB®. The model is developed using balances of mass, energy, and species conservation in the components of the absorption cooling system, taking into account the effect of external streams through temperature and pressure drop. The whole system, coupled with the solar energy harvesting arrangement, is modeled for 24 h of operation with changes on an hourly basis based on ambient temperature, cooling system load demand, and hourly solar irradiation, which is measured and recorded by national weather institutes sources. Test through simulations and validation procedures are carried out with acknowledged scientific articles. These show 2.65% of maximum relative error on the energy analysis with respect to cited authors. The environmental conditions used in the study were evaluated in Barranquilla, Colombia, with datasets of the Institute of Hydrology, Meteorology and Environmental Studies (IDEAM), considering multiannual average hourly basis solar irradiation. This allowed the authors to obtain the behavior of the surface temperature of the water in the tank, COP, and exergy efficiency of the system. The simulations also stated the generator as the biggest source of irreversibility with around 45.53% of total exergy destruction in the inner cycle without considering the solar array, in which case the solar array would present the most exergy destruction.
Full article
(This article belongs to the Special Issue Advances in Tribology and LCA Applied to Thermal Machines)
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A Study on the Flow Resistance of Fluids Flowing in the Engine Oil-Cooler Chosen
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Lubricants 2021, 9(8), 75; https://doi.org/10.3390/lubricants9080075 - 29 Jul 2021
Abstract
Oil-coolers are necessary components in high performance diesel engines. The heat removed by the cooler is a component in the total heat rejection via the engine coolant. Oil-cooler absorbs the heat rejected during the piston cooling and engine rubbing friction power loss. During
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Oil-coolers are necessary components in high performance diesel engines. The heat removed by the cooler is a component in the total heat rejection via the engine coolant. Oil-cooler absorbs the heat rejected during the piston cooling and engine rubbing friction power loss. During flows of both coolant and engine oil via the oil-cooler, some flow resistances occur. The aim of the study is to determine values of the flow resistance coefficient for oil going through the cooler at various temperatures. The test stand was developed to determine time needed to empty tanks from liquids flowing through oil-cooler. The flow model was elaborated to study the mentioned flow resistance coefficient with respect to changing liquid temperature. The 20 °C increase in liquid temperature resulted in a flow resistance coefficient decrease of 30% for coolant and of the much more for engine oil. It was found that better results would be achieved with flows forced by means of pumps instead of using gravitational forces on the test stand.
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(This article belongs to the Special Issue Automotive Tribology II)
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Open AccessCommunication
Low Friction Powertrains: Current Advances in Lubricants and Coatings
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Lubricants 2021, 9(8), 74; https://doi.org/10.3390/lubricants9080074 - 27 Jul 2021
Abstract
Improving fuel economy and reducing emissions is nowadays more important than ever. Apart from powertrain electrification, automotive manufacturers have constantly been seeking to improve the efficiency of the internal combustion engine. Downsizing and boosting have become common practice in the internal combustion engine
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Improving fuel economy and reducing emissions is nowadays more important than ever. Apart from powertrain electrification, automotive manufacturers have constantly been seeking to improve the efficiency of the internal combustion engine. Downsizing and boosting have become common practice in the internal combustion engine (ICE) design. Increased power density and torque output of modern boosted engines, in combination with the introduction of automatic stop-start systems and ultralow viscosity lubricants tends to stress the engine beyond the limits foreseen in the classical design. This leads to wear problems. Each engine component comes with a unique landscape of competing manufacturing technologies, among which advanced surface finishing and coating methods play an important role. This presentation provides an overview of different industrial trends related thereto. The role of lubricant on the engine tribology is studied for different engine designs. The importance of in-design “pairing” of low-viscosity motor oils with the engine characteristics is highlighted filling the gap in the understanding of complex interactions between the crankcase lubricant and engine mechanics.
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(This article belongs to the Special Issue Tribology in Mobility)
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Open AccessReview
Water-Based Lubricants: Development, Properties, and Performances
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, , , , , , and
Lubricants 2021, 9(8), 73; https://doi.org/10.3390/lubricants9080073 - 23 Jul 2021
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Water-based lubricants (WBLs) have been at the forefront of recent research, due to the abundant availability of water at a low cost. However, in metallic tribo-systems, WBLs often exhibit poor performance compared to petroleum-based lubricants. Research and development indicate that nano-additives improve the
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Water-based lubricants (WBLs) have been at the forefront of recent research, due to the abundant availability of water at a low cost. However, in metallic tribo-systems, WBLs often exhibit poor performance compared to petroleum-based lubricants. Research and development indicate that nano-additives improve the lubrication performance of water. Some of these additives could be categorized as solid nanoparticles, ionic liquids, and bio-based oils. These additives improve the tribological properties and help to reduce friction, wear, and corrosion. This review explored different water-based lubricant additives and summarized their properties and performances. Viscosity, density, wettability, and solubility are discussed to determine the viability of using water-based nano-lubricants compared to petroleum-based lubricants for reducing friction and wear in machining. Water-based liquid lubricants also have environmental benefits over petroleum-based lubricants. Further research is needed to understand and optimize water-based lubrication for tribological systems completely.
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(This article belongs to the Special Issue Advances in Water-Based Nanolubricants)
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Open AccessCommunication
Cold Welding in Hold Down Points of Space Mechanisms Due to Fretting When Omitting Grease
Lubricants 2021, 9(8), 72; https://doi.org/10.3390/lubricants9080072 - 21 Jul 2021
Abstract
Cold welding refers to an effect related to space (vacuum). The heavy vibrations during a launch subject interfaces (hold down points) to oscillating motions which may lead to formation of a kind of “friction weld”. If so, these mechanisms may get stuck, and
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Cold welding refers to an effect related to space (vacuum). The heavy vibrations during a launch subject interfaces (hold down points) to oscillating motions which may lead to formation of a kind of “friction weld”. If so, these mechanisms may get stuck, and deployment will be hindered. This may endanger the functionality of the mission (instruments) or even the whole spacecraft (if solar panels do not open). Several studies have been done to characterize material combinations (including coatings) for their ability to cold welding in space. Meanwhile, also during launch grease free contacts are demanded. If grease hat to be omitted, the risk of cold welding under fretting was found to increase (when testing in high vacuum). To rate this risk under launch conditions, the test method was recently extended for testing under launch conditions. The new tests procedure consists of fretting applied in the sequence in air, low vacuum and high vacuum. The paper shall present first results gained with this new method of testing in launch conditions and compare them to previous studies done in vacuum. Following the need of space industry on mechanisms for launch and in-orbit life, a first set of combinations of materials and coatings were selected for this new test sequence where fretting is now applied in a sequence of air, low vacuum and high vacuum. Under this sequence, the measured levels of adhesion and it’s evolvement was found to differ strongly from tests done formerly. The paper outlines these first results and compares them to existing data.
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(This article belongs to the Special Issue Tribology of Space Mechanisms)
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Open AccessArticle
Impacts of a Profile Failure of the Cycloidal Drive of a Planetary Gear on Transmission Gear
Lubricants 2021, 9(7), 71; https://doi.org/10.3390/lubricants9070071 - 20 Jul 2021
Abstract
Recently, cycloidal drives have been increasingly used due to their beneficial features, such as the implementation of a large transmission, efficiency, and high performance density. Production accuracy is inevitable in order to ensure the dynamically proper and smooth operation of the drive. Smaller
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Recently, cycloidal drives have been increasingly used due to their beneficial features, such as the implementation of a large transmission, efficiency, and high performance density. Production accuracy is inevitable in order to ensure the dynamically proper and smooth operation of the drive. Smaller backlash and minimal transmission fluctuations can only be achieved by improving the production accuracy, reducing the number of production failures, and shrinking the tolerance zone. This research primarily focuses on the investigation of the tolerable production accuracy of small-series and individually manufactured drives. The analysis of load distribution was calculated on the cogs of a planetary gear made with a wire EDM machine. On the other hand, we investigate how production failures affect transmission fluctuations and the backlash of a drive. The novelty of this research is based on the determined analytical equations, which can help engineers to find the right tolerances to a given gear ratio fluctuation.
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(This article belongs to the Special Issue Automotive Tribology II)
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Open AccessArticle
Effect of Graphene Addition in Cutting Fluids Applied by MQL in End Milling of AISI 1045 Steel
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Lubricants 2021, 9(7), 70; https://doi.org/10.3390/lubricants9070070 - 19 Jul 2021
Abstract
The cutting fluids applied to the machining processes by the MQL process aim to reduce the machining temperatures and tool wear as well as improve the surface and dimensional finishing of the parts. To increase the efficiency of these fluids, graphene lubricating platelets
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The cutting fluids applied to the machining processes by the MQL process aim to reduce the machining temperatures and tool wear as well as improve the surface and dimensional finishing of the parts. To increase the efficiency of these fluids, graphene lubricating platelets are added. This work investigated the performance of three different cutting fluids with graphene sheets added and applied via MQL, considering the tool life, wear, and wear mechanisms acting on TiAlN-coated cemented carbide cutting tools in the end milling of AISI 1045 steel. We evaluated two vegetable- (MQL15 and LB1000) and one mineral-based (MQL14) neat oils and the same fluids with the addition of 0.05 and 0.1%wt graphene nanoplatelets. Dry cuts were also performed and investigated for comparison. The experiments were conducted under fixed cutting conditions (vc = 250 m/min, fz = 0.14 mm/tooth, ap = 1 mm, and ae = 20 mm). The end-of-tool-life criterion followed the guidelines of ISO 8688-1 (1989). To analyze the results, ANOVA and Tukey’s test were applied. The addition of graphene sheets in the vegetable-based cutting fluids effectively increased the lubricating properties, partially reducing the wear mechanisms acting on the tools. In addition, there was a predominance of thermal fatigue cracks and mechanical cracks as well as adhesive and abrasive wear mechanisms on the tools used in the cutting with the MQL15 and MQL14 fluids, indicating greater cyclical fluctuations in temperature and surface stresses.
Full article
(This article belongs to the Special Issue Application of Solid Lubricants in Metal Processing)
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Open AccessArticle
The Influence of Mechanical Deformations on Surface Force Measurements
Lubricants 2021, 9(7), 69; https://doi.org/10.3390/lubricants9070069 - 13 Jul 2021
Abstract
Surface Force Balance (SFB) experiments have been performed in a dry atmosphere and across an ionic liquid, combining the analysis of surface interactions and deformations, and illustrate that the mechanical deformations of the surfaces have important consequences for the force measurements. First, we
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Surface Force Balance (SFB) experiments have been performed in a dry atmosphere and across an ionic liquid, combining the analysis of surface interactions and deformations, and illustrate that the mechanical deformations of the surfaces have important consequences for the force measurements. First, we find that the variation of the contact radius with the force across the ionic liquid is well described only by the Derjaguin–Muller–Toporov (DMT) model, in contrast with the usual consideration that SFB experiments are always in the Johnson–Kendall–Roberts (JKR) regime. Secondly, we observe that mica does not only bend but can also experience a compression, of order with mica. We present a modified procedure to calibrate the mica thickness in a dry atmosphere, and we show that the structural forces measured across the ionic liquid cannot be described by the usual exponentially decaying harmonic oscillation, but should be considered as a convolution of the surface forces across the liquid and the mechanical response of the confining solids. The measured structural force profile is fitted with a heuristic formulation supposing that mica compression is dominant over liquid compression, and a scaling criterion is proposed to distinguish situations where the solid deformation is negligible or dominant.
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(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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Open AccessArticle
Determination of the Natural Frequency of the Model Spindle System with Active Regulation of the Initial Tension of the Bearings
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Lubricants 2021, 9(7), 68; https://doi.org/10.3390/lubricants9070068 - 13 Jul 2021
Abstract
This article presents a test stand with a model high-speed spindle equipped with a system of active control of the preload of the bearings. This preload was changed by means of three piezo actuators. The work presents the results of tests during which
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This article presents a test stand with a model high-speed spindle equipped with a system of active control of the preload of the bearings. This preload was changed by means of three piezo actuators. The work presents the results of tests during which the commercial Abacus measuring equipment from Data Physics was used. Its application has shown that the spindle system with angular contact ball bearings is responsive to changes in the preload value of these bearings. The change preload resulted in a change in the value of the resonant frequency of the system and its amplitude. This article presents the dependence between the variable value of the preload of the bearings and the corresponding values of the resonance frequency and amplitude of the spindle system. The use of the Abacus measuring equipment for testing allowed for the preparation of a model showing the dynamic behavior of the spindle. The system was forced by a signal with known parameters, and the response to this excitation was recorded at eleven points located on the surface of the entire spindle.
Full article
(This article belongs to the Special Issue Research Trends in Hydrodynamic Journal and Thrust Bearings)
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Open AccessArticle
Geometrical Optimization of the EHL Roller Face/Rib Contact for Energy Efficiency in Tapered Roller Bearings
Lubricants 2021, 9(7), 67; https://doi.org/10.3390/lubricants9070067 - 22 Jun 2021
Abstract
In the context of targeted improvements in energy efficiency, secondary rolling bearing contacts are gaining relevance. As such, the elastohydrodynamically lubricated (EHL) roller face/rib contact of tapered roller bearings significantly affects power losses. Consequently, this contribution aimed at numerical optimization of the pairing’s
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In the context of targeted improvements in energy efficiency, secondary rolling bearing contacts are gaining relevance. As such, the elastohydrodynamically lubricated (EHL) roller face/rib contact of tapered roller bearings significantly affects power losses. Consequently, this contribution aimed at numerical optimization of the pairing’s macro-geometric parameters. The latter were sampled by a statistical design of experiments (DoE) and the tribological behavior was predicted by means of EHL contact simulations. For each of the geometric pairings considered, a database was generated. Key target variables such as pressure, lubricant gap and friction were approximated by a meta-model of optimal prognosis (MOP) and optimization was carried out using an evolutionary algorithm (EA). It was shown that the tribological behavior was mainly determined by the basic geometric pairing and the radii while eccentricity was of subordinate role. Furthermore, there was a trade-off between high load carrying capacity and low frictional losses. Thereby, spherical or toroidal geometries on the roller end face featuring a large radius paired with a tapered rib geometry were found to be advantageous in terms of low friction. For larger lubricant film heights and load carrying capacity, spherical or toroidal roller on toroidal rib geometries with medium radii were favorable.
Full article
(This article belongs to the Special Issue Design for Tribology: Theoretical and Practical Assessment in Modern Mechanical Components)
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Open AccessReview
Energy Efficiency, Emissions, Tribological Challenges and Fluid Requirements of Electrified Passenger Car Vehicles
Lubricants 2021, 9(7), 66; https://doi.org/10.3390/lubricants9070066 - 22 Jun 2021
Abstract
The motivations for the move to electrified vehicles are discussed with reference to their improved energy efficiency, their potential for lower CO2 emissions (if the electricity system is decarbonized), their lower (or zero) NOx/particulate matter (PM) tailpipe emissions, and the
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The motivations for the move to electrified vehicles are discussed with reference to their improved energy efficiency, their potential for lower CO2 emissions (if the electricity system is decarbonized), their lower (or zero) NOx/particulate matter (PM) tailpipe emissions, and the lower overall costs for owners. Some of the assumptions made in life-cycle CO2 emissions calculations are discussed and the effect of these assumptions on the CO2 benefits of electric vehicles are made clear. A number of new tribological challenges have emerged, particularly for hybrid vehicles that have both a conventional internal combustion engine and a battery, such as the need to protect against the much greater number of stop-starts that the engine will have during its lifetime. In addition, new lubricants are required for electric vehicle transmissions systems. Although full battery electric vehicles (BEVs) will not require engine oils (as there is no engine), they will require a system to cool the batteries—alternative cooling systems are discussed, and where these are fluid-based, the specific fluid requirements are outlined.
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(This article belongs to the Special Issue Tribology in Mobility)
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