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Lubricants, Volume 11, Issue 12 (December 2023) – 40 articles

Cover Story (view full-size image): Graphene is considered a good lubricant additive. The lubricating properties of graphene lubricant at different concentrations and temperatures were experimentally studied via a four-ball friction and wear-testing machine. The results show that the coefficient of friction (COF) and wear scar diameter (WSD) of the steel ball with 0.035 wt% graphene lubricant decreased by 40.8% and 50.4%, respectively. When the graphene lubricant concentration increases, it will result in an increase in COF. The graphene lubricant with 0.035% concentration has the best lubricating performance for the tested steel-steel friction pairs. With the increase in temperature, the adhesive wear of the worn surface intensifies, and some graphene particles agglomerate around the wear scar. View this paper
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16 pages, 4715 KiB  
Article
Reconstruction and Intelligent Evaluation of Three-Dimensional Texture of Stone Matrix Asphalt-13 Pavement for Skid Resistance
Lubricants 2023, 11(12), 535; https://doi.org/10.3390/lubricants11120535 - 18 Dec 2023
Viewed by 1048
Abstract
To examine the three-dimensional texture structure of SMA-13 asphalt pavement and assess its anti-skid performance, a light gradient-boosting machine evaluation model was developed using non-contact three-dimensional laser-scanning technology. The study focused on collecting three-dimensional texture data from newly laid SMA-13 asphalt pavement. Subsequently, [...] Read more.
To examine the three-dimensional texture structure of SMA-13 asphalt pavement and assess its anti-skid performance, a light gradient-boosting machine evaluation model was developed using non-contact three-dimensional laser-scanning technology. The study focused on collecting three-dimensional texture data from newly laid SMA-13 asphalt pavement. Subsequently, wavelet transform was employed to reconstruct the pavement’s three-dimensional texture, and discrete Fourier transform was utilized to separate macro- and microtextures, enabling the calculation of their characteristics. The macro- and micro-characteristics of the three-dimensional texture and friction coefficient were input into the model. A comparative analysis with linear regression and a random forest model revealed superior accuracy and efficiency in the model. The training set R2 is 0.948, and the testing set R2 is 0.842, effectively enabling the evaluation of pavement anti-skid performance. An analysis of parameter importance indicated that Rku and MPD are still effective indicators for evaluating skid resistance. Furthermore, diverse texture indexes exhibited varying effects on the anti-skid performance. The established asphalt pavement anti-skid evaluation model serves as a theoretical foundation for understanding the actual influence on pavement anti-skid performance. Full article
(This article belongs to the Special Issue Friction Assessment in Pavement Engineering)
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14 pages, 7644 KiB  
Article
Dual Network Co-Crosslinked HNBR Composites with Enhanced Tribological Properties under Water Lubrication
Lubricants 2023, 11(12), 534; https://doi.org/10.3390/lubricants11120534 - 18 Dec 2023
Viewed by 1215
Abstract
Water-lubricated bearings play a critical role in underwater propulsion systems but are often prone to failure due to mechanical wear and vibration, especially under high loads and prolonged friction. In response to this issue, our study introduces a novel approach: a dual network [...] Read more.
Water-lubricated bearings play a critical role in underwater propulsion systems but are often prone to failure due to mechanical wear and vibration, especially under high loads and prolonged friction. In response to this issue, our study introduces a novel approach: a dual network co-crosslinking strategy utilizing hydrogenated nitrile butadiene rubber (HNBR). This strategy connects the rubber network with the epoxy network through epoxidized Eucommia ulmoides gum. A comprehensive analysis was conducted to assess the resulting composite’s damping, tribological, and mechanical properties. The results show that the material has excellent mechanical, damping, and tribological properties relative to pure HNBR, with a 65.9% increase in the damping temperature domain, a 78.5% increase in tensile strength, a low coefficient of friction of 0.022, and a high resistance to abrasion of 3.87 × 10−6 mm3/Nm. The successful synthesis of HNBR-based composites via the dual network co-crosslinking strategy underscores their potential as a practical solution for improving the reliability and prolonging the service life of water-lubricated bearings. Full article
(This article belongs to the Special Issue Water-Lubricated Bearings)
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15 pages, 5680 KiB  
Article
Tribological Synergism of Anodic Aluminum Oxide Surface Containing Micro-Holes and Nanopores under Lubricated Reciprocation
Lubricants 2023, 11(12), 533; https://doi.org/10.3390/lubricants11120533 - 15 Dec 2023
Viewed by 1047
Abstract
Micro-drilled aluminum surfaces containing micro-holes were anodized to produce nanopores over the machined and lapped surfaces. The anodized nanopores had an approximate diameter of 30–40 nm and a depth distribution of 20–30 μm from the surface. The diameter and depth of the machined [...] Read more.
Micro-drilled aluminum surfaces containing micro-holes were anodized to produce nanopores over the machined and lapped surfaces. The anodized nanopores had an approximate diameter of 30–40 nm and a depth distribution of 20–30 μm from the surface. The diameter and depth of the machined micro-holes were 125 μm and 300 μm, respectively. Anodization itself did not change the surface roughness because the nanopores were very small. Ball-on-disk reciprocating tests were performed under lubricated conditions for 2 h using a frequency of 2 Hz, a load of 2 N, and a travel distance of 5 mm. The results showed that both the micro-drilled and anodized surfaces greatly reduced the coefficient of friction compared with the lapped bare surface; however, the coefficient of friction of the hole-textured specimen was not maintained till the end. Contrary to expectations, the lubricant retention capability of the textured structure declined because of hole failure that occurred during oscillation. This gradually increased friction until the end of the reciprocating test. When the micro-drilled surface was anodized, the coefficient of friction decreased again, implying that non-anodized micro-holes alone were ineffective for reducing friction. The surface hardness of Al increased owing to anodization, and thus the micro-holes remained intact. Therefore, it is concluded in this study that a prerequisite for friction reduction in Al is to increase the hardness to minimize the failure of micro-holes, which can be achieved by anodization. The synergistic lubricant retention capability can be maintained by the presence of both nanopores and micro-holes. Full article
(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)
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18 pages, 11343 KiB  
Article
Impact of Gas Foil Bearings, Labyrinth Seals, and Impellers on the Critical Speed of Centrifugal Compressors for Fuel Cell Vehicles: A Comprehensive Investigation
Lubricants 2023, 11(12), 532; https://doi.org/10.3390/lubricants11120532 - 14 Dec 2023
Cited by 1 | Viewed by 984
Abstract
The critical speed is a crucial factor that impacts the stability of high-speed compressors. However, limited research has simultaneously considered the influence of gas foil bearings (GFBs), labyrinth seals, and impellers on critical speed. In this study, we develop a rotordynamic model that [...] Read more.
The critical speed is a crucial factor that impacts the stability of high-speed compressors. However, limited research has simultaneously considered the influence of gas foil bearings (GFBs), labyrinth seals, and impellers on critical speed. In this study, we develop a rotordynamic model that incorporates the aerodynamic forces of GFBs, labyrinth seals, and impellers to explore the effects of each component on the critical speed. To validate the developed model, experimental tests are conducted on a centrifugal compressor test bed, and the results exhibit a high level of agreement with the model calculations. By comparing the model calculations that include different components, we comprehensively analyze the influence of each component on the critical speed. The findings reveal that, for centrifugal compressors used in fuel cell vehicles, the rotordynamic coefficients resulting from GFBs are significantly larger than those resulting from impellers and labyrinth seals. Thus, it is reasonable to disregard the aerodynamic forces caused by impellers and labyrinth seals when calculating the critical speed. Furthermore, substituting rigid gas bearings for GFBs as a means to simplify the calculations has only a very slight impact on the results. This study aims to optimize the design process of centrifugal compressors for fuel cell vehicles and offers valuable insights for designing compressors of similar sizes. Full article
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20 pages, 10917 KiB  
Article
Effects of Erucamide and N-phenyl-α-naphthylamine on the Friction and Torque Behaviors of Grease on Roller Bearings
Lubricants 2023, 11(12), 531; https://doi.org/10.3390/lubricants11120531 - 14 Dec 2023
Viewed by 1130
Abstract
To evaluate the impact of various proportions of erucamide and N-phenyl-α-naphthylamine on grease’s tribological performance for roller bearings, lithium complex grease (LCG) and polyurea grease (PG) were prepared with erucamide and N-phenyl-α-naphthylamine proportions of (0,0), (0,3), (1,2), (2,1), and (3,0). An investigation was [...] Read more.
To evaluate the impact of various proportions of erucamide and N-phenyl-α-naphthylamine on grease’s tribological performance for roller bearings, lithium complex grease (LCG) and polyurea grease (PG) were prepared with erucamide and N-phenyl-α-naphthylamine proportions of (0,0), (0,3), (1,2), (2,1), and (3,0). An investigation was conducted into the microscopic structures of the ten greases and their effects on the friction coefficients and wear scars of GCr15 steel. These findings were validated through bearing friction torque tests. The results indicate that the addition of 2 wt. % erucamide and 1 wt. % N-phenyl-α-naphthylamine to PG/LCG significantly enhances their tribological properties and reduces friction torque, with PG exhibiting superior performance. This enhancement was attributed to the synergistic interaction of erucamide and N-phenyl-α-naphthylamine with the lamellar thickener within PG. Erucamide contributed to friction reduction, while N acted as an antioxidant. Full article
(This article belongs to the Special Issue Friction and Wear of Rolling-Element Bearings)
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24 pages, 10282 KiB  
Article
Research on an Intelligent Classification Algorithm of Ferrography Wear Particles Based on Integrated ResNet50 and SepViT
Lubricants 2023, 11(12), 530; https://doi.org/10.3390/lubricants11120530 - 13 Dec 2023
Viewed by 1069
Abstract
The wear particle classification algorithm proposed is based on an integrated ResNet50 and Vision Transformer, aiming to address the problems of a complex background, overlapping and similar characteristics of wear particles, low classification accuracy, and the difficult identification of small target wear particles [...] Read more.
The wear particle classification algorithm proposed is based on an integrated ResNet50 and Vision Transformer, aiming to address the problems of a complex background, overlapping and similar characteristics of wear particles, low classification accuracy, and the difficult identification of small target wear particles in the region. Firstly, an ESRGAN algorithm is used to improve image resolution, and then the Separable Vision Transformer (SepViT) is introduced to replace ViT. The ResNet50-SepViT model (SV-ERnet) is integrated by combining the ResNet50 network with SepViT through weighted soft voting, enabling the intelligent identification of wear particles through transfer learning. Finally, in order to reveal the action mechanism of SepViT, the different abrasive characteristics extracted by the SepViT model are visually explained using the Grad-CAM visualization method. The experimental results show that the proposed integrated SV-ERnet has a high recognition rate and robustness, with an accuracy of 94.1% on the test set. This accuracy is 1.8%, 6.5%, 4.7%, 4.4%, and 6.8% higher than that of ResNet101, VGG16, MobileNetV2, AlexNet, and EfficientV1, respectively; furthermore, it was found that the optimal weighting factors are 0.5 and 0.5. Full article
(This article belongs to the Special Issue Tribology and Machine Learning: New Perspectives and Challenges)
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17 pages, 34585 KiB  
Article
A Thermal Hydrodynamic Model for Emulsified Oil-Lubricated Tilting-Pad Thrust Bearings
Lubricants 2023, 11(12), 529; https://doi.org/10.3390/lubricants11120529 - 13 Dec 2023
Viewed by 1070
Abstract
On maritime vessels, external factors such as explosions, collisions, and grounding can cause the emulsification of lubricating oil by seawater pollution, which can affect the lubrication of a ship’s thrust bearing. To explore the influence of the mixed emulsification of lubricating oil and [...] Read more.
On maritime vessels, external factors such as explosions, collisions, and grounding can cause the emulsification of lubricating oil by seawater pollution, which can affect the lubrication of a ship’s thrust bearing. To explore the influence of the mixed emulsification of lubricating oil and seawater on the lubrication performance of thrust bearings, this study conducted an emulsification experiment, from which the viscosity equation of the oil–water mixture was obtained. A thermal hydrodynamic model (THD) of bearings considering oil–water mixed emulsification was established, and the Finite Difference Method (FDM) was used for analysis. The results show that according to the characteristics of the manifold, the mixture is divided into water-in-oil (W/O) and oil-in-water (O/W). In the W/O flow with higher viscosity, the film thickness becomes higher, but the power loss increases. In the O/W manifold with low viscosity, the thin film easily causes mixed friction. In the demulsification stage of the mixed liquid, the thickness loss of the film is huge, and the collision between the thrust-bearing pad and the inference plate may cause the pad to be ablated. The influence of specific heat capacity on temperature is greater than the temperature rise caused by viscosity. Full article
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14 pages, 7737 KiB  
Communication
Traction Properties of Aerospace Lubricant under Low-Temperature Micro-Oil Droplet Supply Conditions
Lubricants 2023, 11(12), 528; https://doi.org/10.3390/lubricants11120528 - 13 Dec 2023
Viewed by 959
Abstract
Aerospace bearings need to withstand the low-temperature environment of space, which will cause changes in the internal lubrication state of the bearings. This article aims to assess the traction properties of aerospace lubricants under low-temperature micro-oil droplet (hereinafter referred to as ‘micro-oil’) supply [...] Read more.
Aerospace bearings need to withstand the low-temperature environment of space, which will cause changes in the internal lubrication state of the bearings. This article aims to assess the traction properties of aerospace lubricants under low-temperature micro-oil droplet (hereinafter referred to as ‘micro-oil’) supply conditions, and provide a lubrication theoretical basis for studying the motion characteristics of aerospace bearings in a low-temperature environment. An experimental study on the low-temperature micro-oil traction properties of high-speed bearing lubricants was conducted on a specially designed aerospace bearing lubricant traction characteristic tester. A modified Herschel–Bulkley model (modified H–B model) was presented based on test data analysis, and the fitting results were compared with the Tevaarwerk–Johnson model (T–J model). The findings demonstrated that the traction coefficient of this lubricant decreased at a higher load and entrainment velocity, and decreased with a decreasing inlet oil temperature from 0 °C to −50 °C. The modified H–B model accurately fitted the test data and was suitable for the engineering traction coefficient calculation of lubricants and high viscosities at low temperatures. This paper can provide fundamental information for analyzing aerospace bearing friction torque variation. Full article
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27 pages, 6692 KiB  
Review
MoS2 Nanomaterials as Lubricant Additives: A Review
Lubricants 2023, 11(12), 527; https://doi.org/10.3390/lubricants11120527 - 11 Dec 2023
Cited by 1 | Viewed by 1596
Abstract
Improving the lubricating properties of base oils through additives is a crucial objective of tribological research, as it helps to reduce friction and wear of materials. Molybdenum disulfide (MoS2) is a 2D nanomaterial with excellent tribological properties that is often used [...] Read more.
Improving the lubricating properties of base oils through additives is a crucial objective of tribological research, as it helps to reduce friction and wear of materials. Molybdenum disulfide (MoS2) is a 2D nanomaterial with excellent tribological properties that is often used as a lubricant additive. Several studies have been conducted on the preparation and utilization of MoS2 and its nanocomposites as lubricant additives. This paper reviews the research progress on MoS2 nanomaterials as lubricant additives. It firstly introduces various synthesis methods of MoS2 nanomaterials while focusing on the preparation of nano-MoS2 as lubricant additives. It then summarizes the dispersion stability of nano-MoS2 in lubricating oils which has been paid extensive attention. Moreover, this paper reviews and discusses the tribological properties of nano-MoS2 and its various composites as lubricant additives. The possible anti-wear and friction reduction mechanisms of nano-MoS2 and its composites are also discussed. Finally, this paper presents the challenges faced by nano-MoS2 additives in the field of lubrication and the prospects for future research in view of previous studies. Full article
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14 pages, 4805 KiB  
Article
Dynamometric Investigation on Airborne Particulate Matter from Automobile Brake: Impact of Disc Materials on Brake Emission Factor
Lubricants 2023, 11(12), 526; https://doi.org/10.3390/lubricants11120526 - 11 Dec 2023
Viewed by 1131
Abstract
In this work, we evaluated the impact of disc rotors of gray cast iron (GCI), nitrocarburized (NC), and superhard ceramic-coated (SCC) GCI on the brake wear PM emissions of passenger vehicles using dynamometric measurements. The brake emission factor (BEF) of the SCC was [...] Read more.
In this work, we evaluated the impact of disc rotors of gray cast iron (GCI), nitrocarburized (NC), and superhard ceramic-coated (SCC) GCI on the brake wear PM emissions of passenger vehicles using dynamometric measurements. The brake emission factor (BEF) of the SCC was greatly reduced by more than a factor of 1/5 compared with those for the GCI and NC for both low-steel and non-steel friction materials. Surface topological and microstructural analyses confirmed that more severe wear was pronounced for the NC rotor compared with the SCC, as evidenced by large concave pits in the wear tracks. Analysis of the size-classified airborne PM suggests that reduced micron-sized particles, which originated from the GCI disc, were responsible for the lower BEF due to the increased hardness of the SCC. Full article
(This article belongs to the Special Issue Emission and Transport of Wear Particles)
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21 pages, 15394 KiB  
Article
Research on the Relationship between Dynamic Characteristics and Friction Torque Fluctuation of CMGB under the Condition of Time-Varying Moment
Lubricants 2023, 11(12), 525; https://doi.org/10.3390/lubricants11120525 - 11 Dec 2023
Viewed by 983
Abstract
In this paper, a dynamic simulation analysis model was established for CMGB (control moment gyroscope bearing) under the conditions of time-varying moment. The influences of the moment’s response time, axial preload, and working temperature on the dynamic characteristics and friction torque of CMGB [...] Read more.
In this paper, a dynamic simulation analysis model was established for CMGB (control moment gyroscope bearing) under the conditions of time-varying moment. The influences of the moment’s response time, axial preload, and working temperature on the dynamic characteristics and friction torque of CMGB were analyzed, and the relevant verification tests were conducted. The results show that the friction torque fluctuation of CMGB directly corresponds to the dynamic characteristics. The faster the response time of the time-varying moment, the larger the friction torque fluctuation of CMGB. The larger preload minimizes the difference in the ball’s loading state, which is the actual reason for reducing the friction torque fluctuation. Moreover, as the working temperature increases, the friction torque fluctuation of CMGB decreases. Full article
(This article belongs to the Special Issue Condition Monitoring and Simulation Analysis of Bearings)
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15 pages, 12640 KiB  
Article
Preparation and Tribological Behavior of Nitrogen-Doped Willow Catkins/MoS2 Nanocomposites as Lubricant Additives in Liquid Paraffin
Lubricants 2023, 11(12), 524; https://doi.org/10.3390/lubricants11120524 - 10 Dec 2023
Viewed by 1276
Abstract
In this study, willow catkins/MoS2 nanoparticles (denoted as WCMSs) have been prepared using a hydrothermal method. The WCMSs were modified with oleic acid (OA) to improve dispersion in base oil. The friction and wear properties of WCMSs in liquid paraffin (LP) for [...] Read more.
In this study, willow catkins/MoS2 nanoparticles (denoted as WCMSs) have been prepared using a hydrothermal method. The WCMSs were modified with oleic acid (OA) to improve dispersion in base oil. The friction and wear properties of WCMSs in liquid paraffin (LP) for steel balls were investigated using a four-ball wear tester. The results have shown that at a high reaction temperature, willow catkins (being used as a template) and urea (being used as a nitrogen resource) can effectively decrease the wear scar diameters (WSDs) and coefficients of friction (COFs). At a concentration of 0.5 wt.%, the WSD and COF of steel balls, when lubricated using LP containing modified WCMS with urea, decreased from 0.65 mm and 0.175 of pure LP to 0.46 mm and 0.09, respectively. The addition of urea and hydroxylated catkins can generate a significant number of loose nano-sheets and even graphene-like sheets. The weak van der Waals forces, decreasing the shear forces that the steel balls must overcome, provide effective lubrication during rotation. On the other hand, the tribo-films containing MoS2, FeS, azide, metal oxides and other compounds play important roles in reducing friction and facilitating anti-wear properties. Full article
(This article belongs to the Special Issue Functional Lubricating Materials)
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20 pages, 7674 KiB  
Article
Dry and Minimum Quantity Lubrication Machining of Additively Manufactured IN718 Produced via Laser Metal Deposition
Lubricants 2023, 11(12), 523; https://doi.org/10.3390/lubricants11120523 - 10 Dec 2023
Viewed by 1268
Abstract
Inconel 718 (IN718), a Ni-based superalloy, is immensely popular in the aerospace, nuclear, and chemical industries. In these industrial fields, IN718 parts fabricated using conventional and additive manufacturing routes require subsequent machining to meet the dimensional accuracy and surface quality requirements of practical [...] Read more.
Inconel 718 (IN718), a Ni-based superalloy, is immensely popular in the aerospace, nuclear, and chemical industries. In these industrial fields, IN718 parts fabricated using conventional and additive manufacturing routes require subsequent machining to meet the dimensional accuracy and surface quality requirements of practical applications. The machining of IN718 has been a prominent research topic for conventionally cast, wrought, and forged parts. However, very little attention has been given to the machinability of IN718 additively manufactured using laser metal deposition (LMD). This lack of research can lead to numerous issues derived from the assumption that the machining behavior corresponds to conventionally fabricated parts. To address this, our study comprehensively assesses the machinability of LMDed IN718 in dry and minimum quantity lubrication (MQL) cutting environments. Our main goal is to understand how LMD process variables and the cutting environment affect cutting forces, tool wear, surface quality, and energy consumption when working with LMDed IN718 walls. To achieve this, we deposited IN718 on SS309L substrates while varying the following LMD process parameters: laser power, powder feed rate, and scanning speed. The results unveil that machining the deposited wall closer to the substrate is significantly more difficult than away from the substrate, owing to the variance in hardness along the build direction. MQL greatly improves machining across all processing parameters regardless of the machining location along the build direction. Laser power is identified as the most influential parameter, along with the recommendation for a specific combination of power feed rate and scanning speed, providing practical guidelines for optimizing the machining process. While MQL positively impacts machinability, hourly energy consumption remains comparable to dry cutting. This work offers practical guidance for improving the machinability of LMDed IN718 walls and the successful adoption of LMD and the additive–subtractive machining chain. The outcomes of this work provide a significant and critical understanding of location-dependent machinability that can help develop targeted approaches to overcome machining difficulties associated with specific areas of the LMDed structure. The finding that MQL significantly improves machining across all processing parameters, particularly in the challenging bottom region, offers practical guidance for selecting optimal cutting conditions. The potential economic benefits of MQL in terms of tool longevity without a substantial increase in energy costs is also highlighted, which has implications for incorporating MQL in several advanced manufacturing processes. Full article
(This article belongs to the Special Issue Laser Surface Engineering for Tribology)
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18 pages, 13365 KiB  
Article
Sources and Destinations of Oil Leakage through TPOCR Based on 2D-LIF Observation and Modeling Analysis
by and
Lubricants 2023, 11(12), 522; https://doi.org/10.3390/lubricants11120522 - 09 Dec 2023
Viewed by 1171
Abstract
The Three-Piece Oil Control Ring (TPOCR) is becoming a viable option for heavy duty gas and hydrogen engines due to the low particle concentration in these engines. Although direct oil leakage from the gap is not likely to happen with the misalignment of [...] Read more.
The Three-Piece Oil Control Ring (TPOCR) is becoming a viable option for heavy duty gas and hydrogen engines due to the low particle concentration in these engines. Although direct oil leakage from the gap is not likely to happen with the misalignment of the upper and lower rail gaps, there exist other less-apparent oil leaking mechanisms through the TPOCR. This work is targeted at understanding the oil leakage’s source and destination through the rail and liner interfaces across the whole cycle. The 2D Laser Induced Fluorescence technique was applied on an optical engine to study the oil transport behavior. Combined with a TPOCR model for dynamics and lubrication, the mechanisms that cause rail twist and oil scraping by the upper rail were analyzed. It was found that the symmetrical rail can scrape the oil up in the up-strokes. The scraped oil first accumulates in the clearance between the upper rail and groove, as well as at the upper corner of the rail Outer Diameter before being transferred to both the third land and liner when the piston changes direction at Top Dead Center. Rails with an asymmetrical profile can reduce or enhance these effects depending the orientation of the rails. This study provides findings that could help design the engine to better control Lubricate Oil Consumption and properly lubricate the Top Dead Center’s dry region at the same time. Full article
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17 pages, 9819 KiB  
Article
Study on the Lubricating Characteristics of the Oil Film of the Slipper Pair in a Large Displacement Piston Pump
Lubricants 2023, 11(12), 521; https://doi.org/10.3390/lubricants11120521 - 08 Dec 2023
Viewed by 1015
Abstract
Due to the large size of the bottom surface, the slipper pair of the large displacement piston pump (LDPP) will form a larger linear speed difference in the inner and outer positions of the slipper relative to the center of the swash plate [...] Read more.
Due to the large size of the bottom surface, the slipper pair of the large displacement piston pump (LDPP) will form a larger linear speed difference in the inner and outer positions of the slipper relative to the center of the swash plate during high-speed rotation. It is more likely to lead to the slipper overturning, which makes the slipper partially worn. To make improvements, the comprehensive performance of the slipper pair of the LDPP, the motion law of the slipper pair of the LDPP was explored. Firstly, a mathematical model of the oil film thickness of the slipper pair of the LDPP under the state of residual compression force is established, based on the consideration of the linear velocity difference formed by the high-speed rotation of the large bottom surface slipper and the theory of dynamics and thermodynamics. Secondly, the impact of rotational speed, piston chamber pressure and oil temperature on the oil film thickness of the slipper pair was simulated and analyzed. Finally, to measure the oil film thickness of the slipper pair, oil film thickness measuring equipment was created, and the accuracy of the mathematical model was verified. The study revealed the changing rules of the oil film thickness and tilt angle of the bottom surface of the slipper pair under various working conditions. The consistency of the simulation and test findings demonstrates that the mathematical model can accurately describe influencing elements and changing rules of the LDPP slipper pair’s oil film lubrication characteristics. Full article
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19 pages, 9267 KiB  
Article
Research on Splash Lubrication Characteristics of a Spiral Bevel Gearbox Based on the MPS Method
Lubricants 2023, 11(12), 520; https://doi.org/10.3390/lubricants11120520 - 08 Dec 2023
Viewed by 1047
Abstract
In order to accurately and efficiently analyze the distribution law and motion status of lubricating oil in the spiral bevel gearbox of the electric multiple unit (EMU), a high-fidelity 3D CFD model of the spiral bevel gearbox of the EMU was established for [...] Read more.
In order to accurately and efficiently analyze the distribution law and motion status of lubricating oil in the spiral bevel gearbox of the electric multiple unit (EMU), a high-fidelity 3D CFD model of the spiral bevel gearbox of the EMU was established for the first time. The moving particle semi-implicit method was used to visualize the lubricating-oil flow field distribution characteristics of the gearbox. The distribution characteristics of lubricating oil in the gearbox with varying gear rotation speeds, initial lubricating-oil volume levels and oil temperatures were analyzed. It was found that the initial lubricating-oil volume is the factor with the largest influence, while the influences of gear rotation speed and oil temperature are relatively small. By analyzing the churning loss under various simulation conditions, it was found that the churning loss is positively correlated with the gear rotation speed and initial oil volume, and is more affected by the initial oil volume. The churning loss is negatively correlated with the oil temperature, and both are nonlinear relationships. The proportion of churning loss related to the driven gear is higher compared to that of the driving gear. These results can provide a theoretical basis for the subsequent optimization of the gearbox. Full article
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35 pages, 4714 KiB  
Review
Unveiling the Effect of Particle Incorporation in PEO Coatings on the Corrosion and Wear Performance of Magnesium Implants
Lubricants 2023, 11(12), 519; https://doi.org/10.3390/lubricants11120519 - 08 Dec 2023
Viewed by 1309
Abstract
Magnesium has been a focal point of significant exploration in the biomedical engineering domain for many years due to its exceptional attributes, encompassing impressive specific strength, low density, excellent damping abilities, biodegradability, and the sought-after quality of biocompatibility. The primary drawback associated with [...] Read more.
Magnesium has been a focal point of significant exploration in the biomedical engineering domain for many years due to its exceptional attributes, encompassing impressive specific strength, low density, excellent damping abilities, biodegradability, and the sought-after quality of biocompatibility. The primary drawback associated with magnesium-based implants is their susceptibility to corrosion and wear in physiological environments, which represents a significant limitation. Research findings have established that plasma electrolytic oxidation (PEO) induces substantial modifications in the surface characteristics and corrosion behavior of magnesium and its alloy counterparts. By subjecting the surface to high voltages, a porous ceramic coating is formed, resulting in not only altered surface properties and corrosion resistance, but also enhanced wear resistance. However, a drawback of the PEO process is that excessive pore formation and porosity within the shell could potentially undermine the coating’s corrosion and wear resistances. Altering the electrolyte conditions by introducing micro- and nano-particles can serve as a valuable approach to decrease coating porosity and enhance their ultimate characteristics. This paper evaluates the particle adhesion, composition, corrosion, and wear performances of particle-incorporated coatings applied to magnesium alloys through the PEO method. Full article
(This article belongs to the Special Issue Plasma Surface Treatments for Wear and Corrosion Protection)
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18 pages, 11426 KiB  
Article
Static and Dynamic Performances of Novel Aerostatic Bearings with Primary and Secondary Orifice Restrictors
Lubricants 2023, 11(12), 518; https://doi.org/10.3390/lubricants11120518 - 08 Dec 2023
Cited by 1 | Viewed by 1079
Abstract
Aerostatic bearings are crucial support components in ultra−precision manufacturing equipment. However, improvements in the load−carrying capability (LCC) of aerostatic bearings often lead to higher intensity nano−vibrations. This paper introduces a novel primary and secondary orifice restrictor (PSOR) designed to simultaneously enhance the LCC [...] Read more.
Aerostatic bearings are crucial support components in ultra−precision manufacturing equipment. However, improvements in the load−carrying capability (LCC) of aerostatic bearings often lead to higher intensity nano−vibrations. This paper introduces a novel primary and secondary orifice restrictor (PSOR) designed to simultaneously enhance the LCC and mitigate nano−vibrations in aerostatic bearings. The static performance of complex turbulent flows occurring within the chamber of aerostatic bearings with PSORs was investigated. The dynamic performance of the turbulent flows was analyzed through 3D transient numerical simulation using the large eddy simulation method. The LCC and nano−vibration acceleration were measured experimentally, and the results indicated that the design of the secondary orifice diameter could enhance LCC and mitigate nano−vibrations, consistent with theoretical predictions. The accuracy of the proposed model was validated, confirming the effectiveness of PSOR. In the experiments, an aerostatic bearing with a secondary orifice diameter of 0.1 mm exhibited the lowest LCC and largest nano−vibration. Conversely, an aerostatic bearing with a secondary orifice diameter of 0.26 mm exhibited the highest LCC and weakest nano−vibration. This study provides insights into the formation mechanism of turbulent vortex and interaction mechanism among the primary orifice and secondary orifices in aerostatic bearings with a PSOR. Full article
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16 pages, 7959 KiB  
Article
Study on the Influence of the MoS2 Addition Method on the Tribological and Corrosion Properties of Greases
Lubricants 2023, 11(12), 517; https://doi.org/10.3390/lubricants11120517 - 08 Dec 2023
Viewed by 1137
Abstract
MoS2 lithium-based grease is suitable for lubrication protection between bearings at high temperatures and loads due to its excellent tribological properties. However, there is little research on the influence of different addition methods of MoS2 additive on its tribology and corrosion [...] Read more.
MoS2 lithium-based grease is suitable for lubrication protection between bearings at high temperatures and loads due to its excellent tribological properties. However, there is little research on the influence of different addition methods of MoS2 additive on its tribology and corrosion properties. In this work, eco-friendly vegetable oil was selected as the base oil, with MoS2 powder as the additive to synthesize lithium-based grease. The effects of different adding modes of MoS2 on the tribology and corrosion properties of the grease were studied. The experimental results showed that adding 0.01 wt% MoS2 before thickening (Method D) was more conducive to improving the tribological properties of lithium grease. The average friction coefficient was reduced by 26.1%, and the average wear scar diameter was reduced by 0.16 mm. After grinding and adding (Method B) 0.01 wt% MoS2, the corrosion inhibition efficiency of the steel sheet was as high as 96.97%. The reason was that the tribochemical reaction of MoS2 evenly distributed throughout the grease during friction, forming a thin friction film, reducing friction and wear. The protective film formed by MoS2 and GCr15-bearing steel improved the corrosion inhibition performance of the grease. Full article
(This article belongs to the Special Issue Functional Lubricating Materials)
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18 pages, 27252 KiB  
Article
High-Temperature Friction and Wear Behavior of Nickel-Alloy Matrix Composites with the Addition of Molybdate
Lubricants 2023, 11(12), 516; https://doi.org/10.3390/lubricants11120516 - 07 Dec 2023
Viewed by 1069
Abstract
To improve the tribological characteristics of materials employed in spatial mechanisms, there is a significant requirement to develop solid lubricating composites with superior performance. This study investigates the tribological characteristics of composites consisting of a nickel matrix combined with silver molybdate and barium [...] Read more.
To improve the tribological characteristics of materials employed in spatial mechanisms, there is a significant requirement to develop solid lubricating composites with superior performance. This study investigates the tribological characteristics of composites consisting of a nickel matrix combined with silver molybdate and barium molybdate. The experimental analysis focuses on evaluating the tribological behaviors of these composites from 25 °C to 800 °C. The findings indicate that the combined application of silver molybdate and barium molybdate resulted in enhanced self-lubricating properties of the composites, particularly at temperatures over 400 °C. The inclusion of both silver molybdate and barium molybdate in the composite resulted in the achievement of a low friction coefficient (0.34–0.5), as well as a wear rate ranging from 0.47 to 1.25 × 10−4 mm3 N−1m−1, within the temperature range of 400 to 800 °C. Furthermore, an analysis was conducted to examine the wear processes of the composites at various sliding temperatures. This analysis was based on the evaluation of the chemical composition and morphologies of the sliding surfaces, which were verified by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Full article
(This article belongs to the Special Issue Recent Advances in High Temperature Tribology)
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30 pages, 13786 KiB  
Article
A Study on the Influence of Nonlinear Vibration on Fretting Damage of Involute Spline Pairs in Aero-Engines
Lubricants 2023, 11(12), 515; https://doi.org/10.3390/lubricants11120515 - 06 Dec 2023
Viewed by 1023
Abstract
To meticulously examine the repercussions of nonlinear vibrations on fretting damage within aero-engine involute spline pairs, a dynamic model was constructed rooted in well-established theories and methodologies. MATLAB was engaged to resolve the model, where the vibration displacement function was treated under Fourier [...] Read more.
To meticulously examine the repercussions of nonlinear vibrations on fretting damage within aero-engine involute spline pairs, a dynamic model was constructed rooted in well-established theories and methodologies. MATLAB was engaged to resolve the model, where the vibration displacement function was treated under Fourier transformation. The emergent sub-model was then integrated into finite element analysis software to scrutinize the distribution curves of fretting damage over the external spline tooth surface. The analysis included a comprehensive comparison of the axial and radial distributions, in addition to scenarios with and without vibration interferences. Further, an empirical platform was devised to authenticate the outcomes harvested through finite element simulation. The results indicate that the principal mode of fretting damage failure in aero-engine involute spline pairs fundamentally comprises fretting wear. This wear occurs throughout the rotational period of the fretting cycle and reciprocally interacts with fretting fatigue phenomena. Significantly, it was ascertained that acute nonlinear vibrations escalate the magnitude of fretting damage and the quantity of worn teeth within aero-engine spline pairs. Beyond that, angular misalignment was recognized as an aggravating factor that compounds fretting damage in the secondary bond teeth of involute spline pairs. These newfound insights are of paramount significance for the strategic design of involute splines to combat wear. Full article
(This article belongs to the Special Issue Wear Prediction in Aeroengine Rotor System)
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20 pages, 10260 KiB  
Article
Predicting Wear under Boundary Lubrication: A Decisive Statistical Study
Lubricants 2023, 11(12), 514; https://doi.org/10.3390/lubricants11120514 - 04 Dec 2023
Viewed by 1211
Abstract
The forthcoming revolution in mobility and the use of lubricants to ensure ecological friendliness intensifies the pressure on tribology for predictors in new life cycles, mainly addressing wear. The current paper aims to obtain such predictors by studying how the wear processes that [...] Read more.
The forthcoming revolution in mobility and the use of lubricants to ensure ecological friendliness intensifies the pressure on tribology for predictors in new life cycles, mainly addressing wear. The current paper aims to obtain such predictors by studying how the wear processes that occur in a standard FE8 bearing test rig under thin film lubrication are conducted by the properties of the lubricant rather than simple viscosity parameters. Assuming that the activity of a lubricant with respect to the temperature, surface, and chemicals is a matter of its chemical potential, the results show that the nature of the base oil is a key parameter, apart from the chemical structure of the additives. Moreover, it becomes clear that chemical predictors are changing by altering the conditions they are exposed to. As an important result, the lubricant is effective in the prevention of wear if it has the capacity to uptake and transmit electrical charges due to its polarisability during a wear process. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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15 pages, 9055 KiB  
Article
Numerical Simulation and Wear Resistance Property of Ni-Based Alloy Coating on the Surface of Ti-6Al-4V Substrate
Lubricants 2023, 11(12), 513; https://doi.org/10.3390/lubricants11120513 - 03 Dec 2023
Viewed by 1080
Abstract
Laser cladding is a new technology to improve the wear resistance or corrosion resistance properties of metal parts. A finite element model of laser cladding coating was established by numerical simulation technology. The temperature field distribution was studied and analyzed during the laser [...] Read more.
Laser cladding is a new technology to improve the wear resistance or corrosion resistance properties of metal parts. A finite element model of laser cladding coating was established by numerical simulation technology. The temperature field distribution was studied and analyzed during the laser cladding process at three different scanning speeds and three different laser powers. A Ni-based coating was also fabricated on the substrate by a CO2 laser. The optimum parameters of the laser cladding were selected and compared with the melt pool depth and width of the Ni-based coating. Then, the cooling rate, temperature gradient, temperature and stress fields were calculated and analyzed. The growth mechanism of the crystal structure was analyzed by scanning electron microscope (SEM). The wear resistance of the Ni-based coating was measured by a friction and wear testing machine. The results showed that the optimal parameters were laser power 1600 W and scanning speed 3 mm/s. The temperature trends at different locations were similar. The calculated maximum residual stress was 0.157 GPa. The stress concentration appeared near the surface and both sides of the cladding layer. From the coating’s microstructure, it could be seen that it contained a large number of columnar dendrites, and the crystal size gradually decreased with the increase of cooling rate. The wear rates of the Ti-6Al-4V (TC4) substrate and the Ni-based coating were 6.98 mm3/(N·m) and 3.45 mm3/(N·m), respectively. The Ni-based layer had a low wear rate and good wear resistance, which is helpful to obtain good friction and wear resistance of TC4 substrates. Full article
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14 pages, 5339 KiB  
Article
Effect of Oil Dispersion on Lubricating Film Thickness Generation under Oil Droplet Supply Conditions
Lubricants 2023, 11(12), 512; https://doi.org/10.3390/lubricants11120512 - 03 Dec 2023
Viewed by 1256
Abstract
Oil–air lubrication has proven to be very effective for high-speed bearings because the oil supply in the form of droplets can be precisely controlled. This work uses optical interferometry to study the mechanism of lubricating film formation in rolling point contact with oil [...] Read more.
Oil–air lubrication has proven to be very effective for high-speed bearings because the oil supply in the form of droplets can be precisely controlled. This work uses optical interferometry to study the mechanism of lubricating film formation in rolling point contact with oil droplet lubrication. The effect of a double oil drop pair, where two oil droplets are positioned in mirror images about the central axis of the lubricated track, is examined. The process by which pairs of oil droplets approach and lubricate a bearing contact is analysed. This study also covers the effect of multiple oil droplets supplied in a tailored or a random dispersion pattern. Additionally, the effects of oil viscosity, entrainment velocity, and droplet distribution on starvation are also investigated. Full article
(This article belongs to the Special Issue Friction and Wear of Rolling-Element Bearings)
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17 pages, 6560 KiB  
Article
Self-Lubricating Properties of Polyether-Ether-Ketone Composites Filled with CNTs@RC2540 Nano-Capsules
Lubricants 2023, 11(12), 511; https://doi.org/10.3390/lubricants11120511 - 01 Dec 2023
Viewed by 1358
Abstract
Polyether-ether-ketone (PEEK) exhibits great potential in being a replacement for metal components across various applications relying on the mechanical and tribological properties. However, there is still much to be done to improve its properties. The main motivation of this paper is to improve [...] Read more.
Polyether-ether-ketone (PEEK) exhibits great potential in being a replacement for metal components across various applications relying on the mechanical and tribological properties. However, there is still much to be done to improve its properties. The main motivation of this paper is to improve the tribological and mechanical properties of PEEK simultaneously for more severe working environment. Therefore, dialkyl pentasulfide (RC2540) was proposed to fill into the cavity of CNTs to prepare nano-capsules, which were then filled into PEEK to prepare PEEK/nano-capsules composites. The existence of nano-capsules in PEEK was analyzed, and the friction and wear properties exhibited by PEEK composites against GCr15 steel were examined using pin-disk friction pairs, and the self-lubricating mechanism of PEEK composites in friction was revealed. Findings of this study indicated that when the mass fraction of nano-capsules was less than 5%, the filling of nano-capsules could improve the tensile strength of PEEK and reduced the friction coefficient and specific wear rate of PEEK by filling nano-capsules. During the friction process, RC2540 in the nano-capsules can be released as PEEK wears so that a self-lubricating layer can be formed for reducing PEEK composites’ friction and wear. Full article
(This article belongs to the Special Issue Tribology of Polymer-Based Composites)
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16 pages, 12729 KiB  
Article
Experimental Study of Piezoelectric Control for Changing Tilting Pad Journal Bearing Circumferential Angle and Radial Displacement
Lubricants 2023, 11(12), 510; https://doi.org/10.3390/lubricants11120510 - 01 Dec 2023
Viewed by 1072
Abstract
In order to improve the vibration performance of the oil-lubricated tilting pad bearing system, an experimental approach using a piezoelectric actuator to control two new flexible tilting pads is proposed. The performance test bench of the bearing–rotor system based on a tilting pad [...] Read more.
In order to improve the vibration performance of the oil-lubricated tilting pad bearing system, an experimental approach using a piezoelectric actuator to control two new flexible tilting pads is proposed. The performance test bench of the bearing–rotor system based on a tilting pad bearing with a flexible support is established. The different circumferential angles of the angle bearing tilting pad and the radial displacement of the displacement bearing are tested by a piezoelectric actuator. At the same time, the trajectory of the rotor center under actual operating conditions is analyzed. The experimental results show that the amplitude of the rotor journal can be significantly reduced by controlling the control variables related to the circumferential angle and radial displacement of the bearing bush. Therefore, this control improvement can improve the vibration performance of two new flexible tilting pad bearing–rotor systems. The technical means are provided for the active control of an oil-lubricated tilting pad bearing. Full article
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18 pages, 5357 KiB  
Article
A Fractal Prediction Method for Contact Stiffness of Helical Gear Considering Asperity Lateral Contact and Interaction
Lubricants 2023, 11(12), 509; https://doi.org/10.3390/lubricants11120509 - 30 Nov 2023
Viewed by 961
Abstract
The normal contact stiffness (NCS) on rough surfaces has a significant impact on the dynamic characteristics of helical gear. Aiming at the problem of inaccurate calculation of the NCS model under the traditional Hertz theory of smooth surfaces, a fractal prediction model of [...] Read more.
The normal contact stiffness (NCS) on rough surfaces has a significant impact on the dynamic characteristics of helical gear. Aiming at the problem of inaccurate calculation of the NCS model under the traditional Hertz theory of smooth surfaces, a fractal prediction model of helical gear contact stiffness considering asperity lateral contact and interaction between asperities is proposed in this paper. The variation formula of asperity and the correction coefficient of a tooth contact surface under asperity lateral contact and interaction are derived, and the influence of micro-elements on normal load and NCS is qualitatively analyzed. The results show that the NCS of considering the interaction and lateral contact of asperity is closer to the experimental results; the contact surface correction coefficient increases with the increase of curvature radius and load. The NCS of a tooth surface increases with the increase in fractal dimension D or the decrease in roughness amplitude G. The influence of asperity lateral contact and interaction decreases with the increase in D and the decrease in G. The NCS of the helical gear decreases under the lateral contact and interaction of the asperity, which is critical for exact estimation of the NCS of contact surfaces in gear. Full article
(This article belongs to the Special Issue Advances in Gear Tribology)
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17 pages, 8699 KiB  
Article
Analysis, Modeling and Experimental Study of the Normal Contact Stiffness of Rough Surfaces in Grinding
Lubricants 2023, 11(12), 508; https://doi.org/10.3390/lubricants11120508 - 30 Nov 2023
Viewed by 1008
Abstract
Grinding is the most important method in machining, which belongs to the category of precision machining processes. Many mechanical bonding surfaces are grinding surfaces. Therefore, the contact mechanism of grinding a joint surface is of great significance for predicting the loading process and [...] Read more.
Grinding is the most important method in machining, which belongs to the category of precision machining processes. Many mechanical bonding surfaces are grinding surfaces. Therefore, the contact mechanism of grinding a joint surface is of great significance for predicting the loading process and dynamic characteristics of precision mechanical products. In this paper, based on the collected grinding surface roughness data, the profile parameters and topography characteristics of the asperity were analyzed, the rough surface data were fitted, the asperity profile was reconstructed, and the parabola y = nx2 + mx + l of the cylindrical asperity model was established. After analyzing the rough surface data of the grinding process, the asperity distribution height was fitted with a Gaussian distribution function, which proved that asperity follows the Gaussian distribution law. The validity of this model was confirmed by the non-dimensional processing of the assumed model and the fitting of six plasticity indices. When the pressure is the same, the normal stiffness increases with the decrease in the roughness value of the joint surface. The experimental stiffness values are basically consistent with the fitting stiffness values of the newly established model, which verifies the reliability and effectiveness of the new model established for the grinding surface. In this paper, a new model for grinding joint surface is established, and an experimental platform is set up to verify the validity of the model. Full article
(This article belongs to the Topic Advanced Manufacturing and Surface Technology)
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16 pages, 3962 KiB  
Article
A Comprehensive Investigation of BN and VC Reinforcements on the Properties of FSP AA6061 Composites
Lubricants 2023, 11(12), 507; https://doi.org/10.3390/lubricants11120507 - 30 Nov 2023
Viewed by 1027
Abstract
This present study investigated the impact of incorporating boron nitride (BN) and vanadium carbide (VC) reinforcements on various properties of friction stir processed (FSP) AA6061 alloy composites, focusing specifically on grain structure, thermal conductivity, electrical conductivity, and compressive strength. The findings indicate that [...] Read more.
This present study investigated the impact of incorporating boron nitride (BN) and vanadium carbide (VC) reinforcements on various properties of friction stir processed (FSP) AA6061 alloy composites, focusing specifically on grain structure, thermal conductivity, electrical conductivity, and compressive strength. The findings indicate that VC more effectively refines the grain structure of the AA6061 alloy during FSP compared to BN. The inclusion of BN particles in the metal matrix composites resulted in a decrease in both thermal and electrical conductivity. In contrast, the addition of VC particles led to an increase in both thermal and electrical conductivity. The AA6061/VC composite material exhibited the highest thermal conductivity among all composites tested. The electrical conductivity of the hybrid-composite AA6061/30%BN+70%VC showed a slight reduction, measuring only 2.8% lower than the base alloy AA6061. The mono-composite AA6061/VC exhibited a marginal decrease in thermal conductivity, with a measured value only 7.5% lower than the conventional alloy AA6061. However, the mono-composite AA6061/BN displayed a more significant decline, exhibiting a loss of 14.7% and 13.9% in electrical and thermal conductivity, respectively. The composite material comprising 30% BN and 70% VC reinforcement demonstrated the highest compressive strength compared to all other tested composites. The observed percentage enhancement in the mechanical properties of mono and hybrid composites, compared to the parent AA6061 alloy, ranged from 17.1% to 31.5%. Full article
(This article belongs to the Special Issue Friction Stir Processing of Structural Metallic Materials)
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15 pages, 5471 KiB  
Article
Study on the Lubricating Characteristics of Graphene Lubricants
Lubricants 2023, 11(12), 506; https://doi.org/10.3390/lubricants11120506 - 30 Nov 2023
Viewed by 1211
Abstract
Graphene is considered a good lubricant additive. The lubricating properties of graphene lubricant at different concentrations and temperatures are studied via a four-ball friction and wear-testing machine. The results show that the coefficient of friction (COF) and wear scar diameter (WSD) of the [...] Read more.
Graphene is considered a good lubricant additive. The lubricating properties of graphene lubricant at different concentrations and temperatures are studied via a four-ball friction and wear-testing machine. The results show that the coefficient of friction (COF) and wear scar diameter (WSD) of the steel ball with 0.035 wt% graphene lubricant decreased by 40.8% and 50.4%, respectively. Finally, through surface analysis, the following lubrication mechanism is proposed: as the added graphene particles can easily fill and cover the pores of the friction surface, the contact pressure of the rough peak is reduced, resulting in a lower COF and smoother surface. Although the COF increases with temperature, graphene lubricants still exhibit good lubrication effects. Full article
(This article belongs to the Special Issue Tribology of 2D Nanomaterials)
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