Journal Description
Lubricants
Lubricants
is an international, peer-reviewed, open access journal on tribology 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, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
- Journal Rank: JCR - Q2 (Engineering, Mechanical) / CiteScore - Q2 (Mechanical Engineering)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.8 days after submission; acceptance to publication is undertaken in 3.5 days (median values for papers published in this journal in the second half of 2023).
- 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.
Impact Factor:
3.5 (2022);
5-Year Impact Factor:
3.2 (2022)
Latest Articles
Vibration Analysis of the Double Row Planetary Gear System for an Electromechanical Energy Conversion System
Lubricants 2024, 12(6), 211; https://doi.org/10.3390/lubricants12060211 (registering DOI) - 9 Jun 2024
Abstract
Electromechanical energy conversion systems (EECSs) are widely used in vehicles to combine the double-row planetary gear system (DRPGS) with high transmission efficiency and high-performance motors. The integrated structure of the ring gear and motor rotor have put forward higher demands for the vibration
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Electromechanical energy conversion systems (EECSs) are widely used in vehicles to combine the double-row planetary gear system (DRPGS) with high transmission efficiency and high-performance motors. The integrated structure of the ring gear and motor rotor have put forward higher demands for the vibration performance of the DRPGS. This paper establishes a multibody dynamic model of the DRPGS for an EECS. Based on the kinetic relationship between the gear pairs and bearing components, the dynamic equations of the DRPGS are derived. The DRPGS model is simulated under different operating conditions. The results are compared to reveal the relationships between the system vibration and the operating speed and load torque. The typical conditions are selected to study the effectiveness of the structural parameters in reducing the DRPGS vibrations. The structural parameters, including the bearing clearance, the ball numbers, the gear tooth modification amount, and length, are comprehensively discussed. Several suggestions for the low-vibration design of the DRPGS for the EECS are provided.
Full article
Open AccessArticle
Research on Temperature Rise Characteristics Prediction of Main Shaft Dual-Rotor Rolling Bearings in Aircraft Engines
by
Kai Xu, Hao Hu, Nan Guo, Xiqiang Ma and Xiaoping Li
Lubricants 2024, 12(6), 210; https://doi.org/10.3390/lubricants12060210 (registering DOI) - 9 Jun 2024
Abstract
Traditional aero-engine bearings rotate simultaneously with their inner and outer rings, which makes the temperature rise prediction model computationally large with low accuracy, and it cannot be accurately verified due to the means of testing. This paper presents a method for predicting the
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Traditional aero-engine bearings rotate simultaneously with their inner and outer rings, which makes the temperature rise prediction model computationally large with low accuracy, and it cannot be accurately verified due to the means of testing. This paper presents a method for predicting the temperature rise characteristics of aero-engine bearings under composite load conditions. Firstly, the local method is used to calculate the heat generation from heat sources such as bearing spin, lubricant drag, and the differential sliding of steel ball and collar, respectively, then finite element modelling and steady-state thermal analysis are carried out for aero-engine bearings under the simultaneous action of axial and radial external loads, a double-rotor test setup is designed and the predictive model is validated, and finally, the influences of rotational speed and load on the temperature rise characteristics of the bearings are investigated. The study shows that the aero-engine bearing prediction model proposed in this paper has high accuracy; with the increase in the rotational speed of the inner ring of the bearing, the temperatures of both the inner and outer rings of the bearing increase significantly; the temperatures of the inner and outer rings of the bearing increase with the increase in the axial load, and the effect of the radial load on the temperature of the bearing is not obvious.
Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
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Open AccessArticle
Criteria for Evaluating the Tribological Effectiveness of 3D Roughness on Friction Surfaces
by
Oleksandr Stelmakh, Hongyu Fu, Serhii Kolienov, Vasyl Kanevskii, Hao Zhang, Chenxing Hu and Valerii Grygoruk
Lubricants 2024, 12(6), 209; https://doi.org/10.3390/lubricants12060209 (registering DOI) - 9 Jun 2024
Abstract
A new technique for finishing the surfaces of friction pairs has been proposed, which, in combination with the original test method, has shown a significant influence of the initial roughness configuration (surface texture) on friction and wear. Two types of finishing processing of
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A new technique for finishing the surfaces of friction pairs has been proposed, which, in combination with the original test method, has shown a significant influence of the initial roughness configuration (surface texture) on friction and wear. Two types of finishing processing of the shaft friction surfaces were compared, and it was found that the friction and wear coefficients differ by more than 2–5 and 2–4 times, respectively. Based on a new methodology for analyzing standard roughness parameters, the tribological efficiency criteria (in the sense of reducing friction and wear) are proposed for the initial state of the friction surface of a radial plane sliding bearing shaft relative to the friction direction, which is consistent with its frictional characteristics. Comparison of the laboratory test results with the surface tribological efficiency criteria showed that these criteria are very promising for controlling existing technologies and optimizing new technologies for friction surface finishing in various friction systems.
Full article
(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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Open AccessArticle
Effect of Ultrasonic Rolling on Surface Properties of GCr15 Spherical Joint Bearing
by
Hao Zhang, Xiuli Yang, Xiqiang Ma, Dongliang Jin and Jinyuan You
Lubricants 2024, 12(6), 208; https://doi.org/10.3390/lubricants12060208 (registering DOI) - 8 Jun 2024
Abstract
Ultrasonic surface rolling process (USRP) has the potential to improve the surface mechanical properties of metal components with platelike or cylindrical macrostructure, but its effect on spherical surfaces remains to be studied in depth. In order to investigate the effect of USRP on
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Ultrasonic surface rolling process (USRP) has the potential to improve the surface mechanical properties of metal components with platelike or cylindrical macrostructure, but its effect on spherical surfaces remains to be studied in depth. In order to investigate the effect of USRP on the surface roughness, hardness and wear resistance of a spherical joint bearing made of GCr15 bearing steel, ultrasonic rolling strengthening was carried out on a spherical bearing surface under various conditions. The surface roughness and hardness variations of samples before and after strengthening were investigated. It was found that the USRP strengthening process can effectively enhance the surface properties of GCr15 spherical bearing materials, reduce the surface roughness by more than 45%, and increase the surface hardness by more than 10%. Friction and wear tests were carried out before and after ultrasonic rolling. The results show that the friction coefficient of the bearing surface can be reduced by 28%, and that the wear volume can be reduced by 29%. The variation in the friction coefficient correlated to the variance of wear volume as the reinforcement changes.
Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
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Open AccessArticle
A Novel Methodology for Simulating Skin Injury Risk on Synthetic Playing Surfaces
by
Maxwell MacFarlane, Eric O’Donnell, Eric Harrison, Marc Douglas, Neale Lees and Peter Theobald
Lubricants 2024, 12(6), 207; https://doi.org/10.3390/lubricants12060207 - 6 Jun 2024
Abstract
Artificial turf provides a consistent and durable surface; however, it has historically been associated with a high skin injury risk, or a ‘friction burn’, when a player falls or slides. Second-generation surfaces feature a short carpet pile, whilst third generation (3G) carpet piles
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Artificial turf provides a consistent and durable surface; however, it has historically been associated with a high skin injury risk, or a ‘friction burn’, when a player falls or slides. Second-generation surfaces feature a short carpet pile, whilst third generation (3G) carpet piles are longer, enabling the integration of a performance infill. 3G surfaces provide sufficient energy absorption characteristics to be approved as Rugby Turf; however, such pitches can still cause skin injuries, despite being assessed using a friction-based test. Reducing skin injury risk motivates this study to develop a more sensitive testing methodology. A new test apparatus and impactor are proposed, achieving kinematics representative of an elite male rugby tackle. A commercially available skin simulant is employed to ensure the collection of repeatable and valid data. Photography and thresholding were used to assess surface abrasion and material transfer, whilst a thermal camera captured surface temperature change. Accelerometers quantified the surface resistance during the impact and sliding phases. These metrics were compiled into the Maxwell Tribo Index (MTI), providing a single measure of skin injury risk. The results demonstrated good repeatability and validity when four teams tested four different 3G surfaces. These results compared favourably to an expert panel’s ranked order.
Full article
(This article belongs to the Special Issue Biomechanics and Tribology)
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Open AccessArticle
Brake Wear and Airborne Particle Mass Emissions from Passenger Car Brakes in Dynamometer Experiments Based on the Worldwide Harmonized Light-Duty Vehicle Test Procedure Brake Cycle
by
Hiroyuki Hagino
Lubricants 2024, 12(6), 206; https://doi.org/10.3390/lubricants12060206 - 5 Jun 2024
Abstract
Brake wear particles, as the major component of non-exhaust particulate matter, are known to have different emissions, depending on the type of brake assembly and the specifications of the vehicle. In this study, brake wear and wear particle mass emissions were measured under
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Brake wear particles, as the major component of non-exhaust particulate matter, are known to have different emissions, depending on the type of brake assembly and the specifications of the vehicle. In this study, brake wear and wear particle mass emissions were measured under realistic vehicle driving and full friction braking conditions using current commercial genuine brake assemblies. Although there were no significant differences in either PM10 or PM2.5 emissions between the different cooling air flow rates, brake wear decreased and ultrafine particle (PM0.12) emissions increased with the increase in the cooling air flow rate. Particle mass measurements were collected on filter media, allowing chemical composition analysis to identify the source of brake wear particle mass emissions. The iron concentration in the brake wear particles indicated that the main contribution was derived from disc wear. Using a systematic approach that measured brake wear and wear particle emissions, this study was able to characterize correlations with elemental compositions in brake friction materials, adding to our understanding of the mechanical phenomena of brake wear and wear particle emissions.
Full article
(This article belongs to the Special Issue Emission and Transport of Wear Particles)
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Open AccessReview
Molecular Dynamics Simulation on Polymer Tribology: A Review
by
Tianqiang Yin, Guoqing Wang, Zhiyuan Guo, Yiling Pan, Jingfu Song, Qingjun Ding and Gai Zhao
Lubricants 2024, 12(6), 205; https://doi.org/10.3390/lubricants12060205 - 4 Jun 2024
Abstract
A profound comprehension of friction and wear mechanisms is essential for the design and development of high-performance polymeric materials for tribological application. However, it is difficult to deeply investigate the polymer friction process in situ at the micro/mesoscopic scale by traditional research methods.
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A profound comprehension of friction and wear mechanisms is essential for the design and development of high-performance polymeric materials for tribological application. However, it is difficult to deeply investigate the polymer friction process in situ at the micro/mesoscopic scale by traditional research methods. In recent years, molecular dynamics (MD) simulation, as an emerging research method, has attracted more and more attention in the field of polymer tribology due to its ability to show the physicochemical evolution between the contact interfaces at the atomic scale. Herein, we review the applications of MD in recent studies of polymer tribology and their research focuses (e.g., tribological properties, distribution and conformation of polymer chains, interfacial interaction, frictional heat, and tribochemical reactions) across three perspectives: all-atom MD, reactive MD, and coarse-grained MD. Additionally, we summarize the current challenges encountered by MD simulation in polymer tribology research and present recommendations accordingly, aiming to provide several insights for researchers in related fields.
Full article
(This article belongs to the Special Issue Advanced Polymeric and Colloidal Lubricants)
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Open AccessArticle
Research on the Milling Performance of Micro-Groove Ball End Mills for Titanium Alloys
by
Shihong Zhang, Hu Shi, Baizhong Wang, Chunlu Ma and Qinghua Li
Lubricants 2024, 12(6), 204; https://doi.org/10.3390/lubricants12060204 - 4 Jun 2024
Abstract
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Titanium alloys are widely used in various fields, but milling titanium alloy materials often leads to problems such as high milling forces, increased milling temperatures, and chip adhesion. Thus, the machinability of titanium alloys faces challenges. To improve the milling performance of titanium
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Titanium alloys are widely used in various fields, but milling titanium alloy materials often leads to problems such as high milling forces, increased milling temperatures, and chip adhesion. Thus, the machinability of titanium alloys faces challenges. To improve the milling performance of titanium alloy materials, this study analyzes the effective working area on the surface of the milling cutter through mathematical calculations. We design micro-grooves in this area to utilize their friction-reducing and wear-resisting properties to alleviate the aforementioned issues. The effective working area of the ball end milling cutter’s cutting edge is calculated based on the amount of milling and the installation position between the milling cutter and the workpiece. By observing the surface structure of seashells, micro-grooves are proposed and designed to be applied in the working area of the milling cutter surface. The impact of the micro-groove area on the milling cutter surface and spindle speed on milling performance is discussed based on milling simulation and experimental tests. Experimental results show that the cutting force, milling temperature, and chip resistance to adhesion produced by micro-groove milling cutters are superior to conventional milling cutters. Milling cutters with three micro-grooves perform best at different spindle speeds. This is because the presence of micro-grooves on the surface of the milling cutter improves the friction state, promoting a reduction in milling force, while the micro-grooves also serve as storage containers for chips, alleviating the phenomenon of chip softening and adhesion to the cutter. When conducting cutting tests with a milling cutter that has three micro-grooves, the milling force is reduced by 10% to 30%, the milling temperature drops by 10% to 20%, and the surface roughness decreases by 8% to 12%.
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Open AccessArticle
Ice-versus-Steel Friction: An Advanced Numerical Approach for Competitive Winter Sports Applications
by
Birthe Grzemba and Roman Pohrt
Lubricants 2024, 12(6), 203; https://doi.org/10.3390/lubricants12060203 - 4 Jun 2024
Abstract
Understanding and predicting the friction between a steel runner and an ice surface is paramount for many winter sports disciplines such as luge, bobsleigh, skeleton, and speed skating. A widely used numerical model for the analysis of the tribological system steel-on-ice is the
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Understanding and predicting the friction between a steel runner and an ice surface is paramount for many winter sports disciplines such as luge, bobsleigh, skeleton, and speed skating. A widely used numerical model for the analysis of the tribological system steel-on-ice is the Friction Algorithm using Skate Thermohydrodynamics (F.A.S.T.), which was originally introduced in 2007 and later extended. It aims to predict the resulting coefficient of friction (COF) from the two contributions of ice plowing and viscous drag. We explore the limitations of the existing F.A.S.T. model and extend the model to improve its applicability to winter sports disciplines. This includes generalizing the geometry of the runner as well as the curvature of the ice surface. The free rotational mechanical mounting of the runner to the moving sports equipment is introduced and implemented. We apply the new model to real-world geometries and kinematics of speed skating blades and bobsleigh runners to determine the resulting COF for a range of parameters, including geometry, temperature, load, and speed. The findings are compared to rule-of-thumb testimonies from athletes, previous numerical approaches, and published experimental results where applicable. While the general trends are reproduced, some discrepancy is found, which we ascribe to the specific assumptions around the formation of the liquid water layer derived from melted ice.
Full article
(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)
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Open AccessArticle
Influence of Polymer Flow on Polypropylene Morphology, Micro-Mechanical, and Tribological Properties of Injected Part
by
Martin Ovsik, Klara Fucikova, Lukas Manas and Michal Stanek
Lubricants 2024, 12(6), 202; https://doi.org/10.3390/lubricants12060202 - 4 Jun 2024
Abstract
This research investigates the micro-mechanical and tribological properties of injection-molded parts made from polypropylene. The tribological properties of polymers are a very interesting area of research. Understanding tribological processes is very crucial. Considering that the mechanical and tribological properties of injected parts are
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This research investigates the micro-mechanical and tribological properties of injection-molded parts made from polypropylene. The tribological properties of polymers are a very interesting area of research. Understanding tribological processes is very crucial. Considering that the mechanical and tribological properties of injected parts are not uniform at various points of the part, this research was conducted to explain the non-homogeneity of properties along the flow path. Non-homogeneity can be influenced by numerous factors, including distance from the gate, mold and melt temperature, injection pressure, crystalline structure, cooling rate, the surface of the mold, and others. The key factor from the micro-mechanical and tribological properties point of view is the polymer morphology (degree of crystallinity and size of the skin and core layers). The morphology is influenced by polymer flow and the injection molding process conditions. Gained results indicate that the indentation method was sufficiently sensitive to capture the changes in polypropylene morphology, which is a key parameter for the resulting micro-mechanical and tribological properties of the part. It was proven that the mechanical and tribological properties are not equal in varying regions of the part. Due to cooling and process parameters, the difference in the indentation modulus in individual measurement points was up to 55%, and the tribological properties, in particular the friction coefficient, showed a difference of up to 20%. The aforementioned results indicate the impact this finding signifies for injection molding technology in technical practice. Tribological properties are a key property of the part surface and, together with micro-mechanical properties, characterize the resistance of the surface to mechanical failure of the plastic part when used in engineering applications. A suitable choice of gate location, finishing method of the cavity surface, and process parameters can ensure the improvement of mechanical and tribological properties in stressed regions of the part. This will increase the stiffness and wear resistance of the surface.
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(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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Open AccessArticle
Tribological Behavior of Hydrocarbons in Rolling Contact
by
Daniel Merk, Thomas Koenig, Janine Fritz and Joerg W. H. Franke
Lubricants 2024, 12(6), 201; https://doi.org/10.3390/lubricants12060201 - 3 Jun 2024
Abstract
In the analysis of tribological contacts, the focus is often on a singular question or result. However, this entails the potential risk that the overall picture and the relationships could be oversimplified or even that wrong conclusions could be drawn. In this article,
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In the analysis of tribological contacts, the focus is often on a singular question or result. However, this entails the potential risk that the overall picture and the relationships could be oversimplified or even that wrong conclusions could be drawn. In this article, a comprehensive consideration of test results including component and lubricant analyses is demonstrated by using the example of rolling contact. For this purpose, thrust cylindrical roller bearings of type 81212 with unadditized base oils were tested in the mixed-friction area. Our study shows that by using an adapted and innovative surface analysis, a deeper dive into the tribo-film is feasible even without highly sophisticated analytical equipment. The characterization of the layers was performed by the three less time-consuming spatially resolved analysis methods of µXRF, ATR FTIR microscopy and Raman spectroscopy adapted by Schaeffler. This represents a bridge between industry and research. The investigations show that especially undocumented and uncontrolled contamination of the test equipment could lead to surprising findings, which would result in the wrong conclusions. Simple substances, like hydrocarbons, are demanding test specimens.
Full article
(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)
Open AccessArticle
Improved Tribological Performance of ta-C/MoSx Coatings Deposited on Laser Micro-Structured Steel Substrates in Both Vacuum and Air
by
Stefan Makowski, Fabian Härtwig, Marcos Soldera, Mahmoud Ojeil, Lars Lorenz, Frank Kaulfuß and Andrés Fabián Lasagni
Lubricants 2024, 12(6), 200; https://doi.org/10.3390/lubricants12060200 - 1 Jun 2024
Abstract
Vacuum and air atmospheres impose very different requirements on tribological-loaded contacts, which usually require different surface materials. While hard tetrahedral amorphous carbon (ta-C) coatings provide good tribological properties in air, soft coatings such as molybdenum disulfide (MoS2) work well in a vacuum. Tribological
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Vacuum and air atmospheres impose very different requirements on tribological-loaded contacts, which usually require different surface materials. While hard tetrahedral amorphous carbon (ta-C) coatings provide good tribological properties in air, soft coatings such as molybdenum disulfide (MoS2) work well in a vacuum. Tribological performance in the respective other environment, however, is poor. In this work, the combination of laser microstructured (direct laser interference patterning) steel substrates and the deposition of ta-C and MoSx coatings with vacuum arc evaporation (LaserArc™) was studied, resulting in steel/DLIP, steel/DLIP/ta-C, steel/DLIP/MoSx, steel/DLIP/ta-C/MoSx, and steel/MoSx surface combinations. The tribological properties were studied using a ball-on-disk tribometer with a steel ball counter body in air and in a vacuum (p < 5 × 10−7 mbar). The type of the topmost coating governed their tribological properties in the respective atmosphere, and no general beneficial influence of the microstructure was found. However, steel/DLIP/ta-C/MoSx performed best in both conditions and endured the highest contact pressure, which is attributed to the mechanical support of the ta-C coating and MoSx reservoir in the remaining structure, as evidenced by Raman spectroscopy. The findings suggest that such combination allows for surfaces bearing a high load capacity that can be applied in both a vacuum and in air, for example, in multi-use space applications.
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(This article belongs to the Special Issue Tribology of Textured Surfaces)
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Open AccessEditorial
Tribology of 2D Nanomaterials
by
Yanfei Liu and Xiangyu Ge
Lubricants 2024, 12(6), 199; https://doi.org/10.3390/lubricants12060199 - 1 Jun 2024
Abstract
Tribology is the science and engineering of interacting surfaces in relative motion [...]
Full article
(This article belongs to the Special Issue Tribology of 2D Nanomaterials)
Open AccessArticle
Comparison of Friction Properties of GI Steel Plates with Various Surface Treatments
by
Miroslav Tomáš, Stanislav Németh, Emil Evin, František Hollý, Vladimír Kundracik, Juliy Martyn Kulya and Marek Buber
Lubricants 2024, 12(6), 198; https://doi.org/10.3390/lubricants12060198 - 31 May 2024
Abstract
This article presents the improved properties of GI (hot-dip galvanized) steel plates in combination with a special permanent surface treatment. The substrate used was hot-dip galvanized deep-drawn steel sheets of grade DX56D + Z. Subsequently, various surface treatments were applied to their surface.
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This article presents the improved properties of GI (hot-dip galvanized) steel plates in combination with a special permanent surface treatment. The substrate used was hot-dip galvanized deep-drawn steel sheets of grade DX56D + Z. Subsequently, various surface treatments were applied to their surface. The coefficient of friction of the metal sheets without surface treatment, with a temporary surface treatment called passivation, and a thin organic coating (TOC) based on hydroxyl resins dissolved in water, Ti and Cr3+ were determined by a cup test. The surface quality and corrosion resistance of all tested samples were also determined by exposing them for up to 288 h in an atmosphere of neutral salt spray. The surface microgeometry parameters Ra, RPc and Rz(I), which have a significant influence on the pressing process itself, were also determined. The TOC deposited on the Zn substrate was the only one to exhibit excellent lubrication and anticorrosion properties, resulting in the lowest surface microgeometry values owing to the uniform and continuous layer of the thin organic coating compared to the GI substrate and passivation surface treatment, respectively.
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(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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Open AccessArticle
Lubricating Greases from Fried Vegetable Oil—Preparation and Characterization
by
Olga V. Săpunaru, Ancaelena E. Sterpu, Cyrille A. Vodounon, Jack Nasr, Cristina Duşescu-Vasile, Sibel Osman and Claudia I. Koncsag
Lubricants 2024, 12(6), 197; https://doi.org/10.3390/lubricants12060197 - 30 May 2024
Abstract
Biobased greases are derived from renewable resources, are considered more environmentally friendly, and offer comparable performance to petroleum-based greases. In this study, lubricating greases from frying cooking oils were prepared, thus valorizing waste in order to obtain sustainable and environmentally friendly products. Twelve
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Biobased greases are derived from renewable resources, are considered more environmentally friendly, and offer comparable performance to petroleum-based greases. In this study, lubricating greases from frying cooking oils were prepared, thus valorizing waste in order to obtain sustainable and environmentally friendly products. Twelve batches (500 g each) were produced from sunflower and palm frying oils, with 20% by weight calcium/lithium stearate soaps prepared in situ and filled with 15 wt.% cellulose or lignin sulfate. The greases were rheologically characterized. Their consistency was assessed by the penetration test performed before and after working the greases. Dropping point determinations offered information about the stability at higher temperatures, and oil bleeding tests were performed. The average values of the friction coefficient (COF), the contact resistance, and the wear scar diameter were measured through mechanical tests. The greases prove to be comparable to those obtained from mineral oils, with good rheological properties, soft consistency, and good antiwearing behavior, e.g., in open or total-loss lubricating systems, like in open gears and certain food processing machinery; they are thermally stable andprone touse in low-loading working mechanisms.
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(This article belongs to the Special Issue Advances in Tribochemistry)
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Open AccessArticle
Preparation and Tribological Behaviors of Sulfur- and Phosphorus-Free Organic Friction Modifier of Amide–Ester Type
by
Xiaomei Xu, Fan Yang, Hongmei Yang, Yanan Zhao, Xiuli Sun and Yong Tang
Lubricants 2024, 12(6), 196; https://doi.org/10.3390/lubricants12060196 - 30 May 2024
Abstract
With the increasingly demanding engine conditions and the implementation of “double carbon” policies, the demand for high-quality lubricants that are cost-effective and environmentally friendly is increasing. Additives, especially high-performance friction modifiers, play an important role in boosting lubricant efficiency and fuel economy, so
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With the increasingly demanding engine conditions and the implementation of “double carbon” policies, the demand for high-quality lubricants that are cost-effective and environmentally friendly is increasing. Additives, especially high-performance friction modifiers, play an important role in boosting lubricant efficiency and fuel economy, so their developments are at the forefront of lubrication technologies. In this study, 1,3-dioleoamide-2-propyloleate (DOAPO), which incorporates polar amide, ester, and nonpolar alkyl chains, was synthesized from 1,3-diamino-2-propanol to give an eco-friendly organic friction modifier. Nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HR-MS), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to characterize the structure and thermal stability of DOAPO. Meanwhile, the storage stability and tribological behaviors of DOAPO in synthetic base oil were studied and compared with a commercial oleamide. The results show that DOAPO has better thermal stability and better storage stability in synthetic base oil. Additionally, 0.5 wt.% of DOAPO could shorten the running-in period and reduce the average friction coefficient (ave. COF) and wear scar diameter (ave. WSD) by 8.2% and 16.2%, respectively. The worn surface analysis and theoretical calculation results show that the ester bond in DOAPO breaks preferentially during friction, which can reduce the interfacial shear force and easily react with metal surfaces to form iron oxide films, thus demonstrating a better friction-reducing and anti-wear performance.
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(This article belongs to the Special Issue Functional Lubricating Materials)
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Open AccessArticle
Braking Friction Coefficient Prediction Using PSO–GRU Algorithm Based on Braking Dynamometer Testing
by
Shuwen Wang, Yang Yu, Shuangxia Liu and David Barton
Lubricants 2024, 12(6), 195; https://doi.org/10.3390/lubricants12060195 - 29 May 2024
Abstract
The coefficients of friction (COFs) is one of the most important parameters used to evaluate the braking performance of a friction brake. Many indicators that affect the safety and comfort of automobiles are associated with brake COFs. The manufacturers of friction brakes and
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The coefficients of friction (COFs) is one of the most important parameters used to evaluate the braking performance of a friction brake. Many indicators that affect the safety and comfort of automobiles are associated with brake COFs. The manufacturers of friction brakes and their components are required to spend huge amounts of time and money to carry out experimental tests to ensure the COFs of a newly developed braking system meet the required standards. In order to save time and costs for the development of new friction brake applications, the GRU (Gate Recurrent Unit) algorithm optimized by the improved PSO (particle swarm optimization) global optimization method is employed in this work to predict brake COFs based on existing experimental data obtained from friction braking dynamometer tests. Compared with the LSTM (Long Short-Term Memory) method, the GRU algorithm optimized by PSO avoids the accuracy reduction problem caused by gradient descent in the training process and hence reduces the prediction error and computational cost. The combined PSO–GRU algorithm increases the coefficient of determination (R2) of the prediction by 4.7%, reduces the MAE (mean absolute error) by 14.3%, and increases the prediction speed by 40.1% compared with the standalone GRU method. The prediction method based on machine learning proposed in this study can not only be applied to the prediction of automobile braking COFs but also for other frictional system problems, such as the prediction of braking noise and the friction of various bearing transmission components.
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(This article belongs to the Special Issue Tribology in Vehicles)
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Open AccessArticle
Practical Evaluation of Ionic Liquids for Application as Lubricants in Cleanrooms and under Vacuum Conditions
by
Andreas Keller, Knud-Ole Karlson, Markus Grebe, Fabian Schüler, Christian Goehringer and Alexander Epp
Lubricants 2024, 12(6), 194; https://doi.org/10.3390/lubricants12060194 - 28 May 2024
Abstract
As part of a publicly funded cooperation project, novel high-performance lubricants (oils, greases, assembly pastes) based on ionic liquids and with the addition of specific micro- or nanoparticles are to be developed, which are adapted in their formulation for use in applications where
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As part of a publicly funded cooperation project, novel high-performance lubricants (oils, greases, assembly pastes) based on ionic liquids and with the addition of specific micro- or nanoparticles are to be developed, which are adapted in their formulation for use in applications where their negligible vapor pressure plays an important role. These lubricants are urgently needed for applications in cleanrooms and high vacuum (e.g., pharmaceuticals, aerospace, chip manufacturing), especially when the frequently used perfluoropolyethers (PFPE) are no longer available due to a potential restriction of per- and polyfluoroalkyl substances (PFAS) due to European chemical legislation. Until now, there has been a lack of suitable laboratory testing technology to develop such innovative lubricants for extreme niche applications economically. There is a large gap in the tribological test chain between model testing, for example in the so-called spiral orbit tribometer (SOT) or ball-on-disk test in a high-frequency, linear-oscillation test machine (SRV-Tribometer from German “Schwing-Reib-Verschleiß-Tribometer”), and overall component testing at major space agencies (ESA—European Space Agency, NASA—National Aeronautics and Space Administration) or their service providers like the European Space Tribology Laboratory (ESTL) in Manchester. A further aim of the project was therefore to develop an application-orientated and economical testing methodology and testing technology for the scientifically precise evaluation and verifiability of the effect of ionic liquids on tribological systems in cleanrooms and under high vacuum conditions. The newly developed test rig is the focus of this publication. It forms the basis for all further investigations.
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(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)
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Open AccessFeature PaperArticle
Viscoelastic Hertzian Impact
by
Ivan Argatov
Lubricants 2024, 12(6), 193; https://doi.org/10.3390/lubricants12060193 - 28 May 2024
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The problem of normal impact of a rigid sphere on a Maxwell viscoelastic solid half-space is considered. The first-order asymptotic solution is constructed in the framework of Hunter’s model of viscoelastic impact. In particular, simple analytical approximations have been derived for the maximum
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The problem of normal impact of a rigid sphere on a Maxwell viscoelastic solid half-space is considered. The first-order asymptotic solution is constructed in the framework of Hunter’s model of viscoelastic impact. In particular, simple analytical approximations have been derived for the maximum contact force and the time to achieve it. A linear regression method is suggested for evaluating the instantaneous elastic modulus and the mean relaxation time from a set of experimental data collected for different spherical impactors and impact velocities.
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Open AccessEditorial
Friction and Wear of Cutting Tools and Cutting Tool Materials
by
Guoliang Liu, Chuanzhen Huang, Xiangyu Wang, Bin Zhao and Min Ji
Lubricants 2024, 12(6), 192; https://doi.org/10.3390/lubricants12060192 - 28 May 2024
Abstract
The friction between cutting tools and the workpiece/chip can significantly affect the tool wear, cutting force, cutting temperature, machined surface integrity, and machined parts’ service performance. [...]
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(This article belongs to the Special Issue Friction and Wear of Cutting Tools and Cutting Tool Materials)
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