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
Effect of Acoustic Emission Sensor Location on the Detection of Grinding Wheel Deterioration in Cylindrical Grinding
Lubricants 2024, 12(3), 100; https://doi.org/10.3390/lubricants12030100 - 18 Mar 2024
Abstract
The acoustic emission (AE) technique is an effective method for monitoring grinding wheels, and numerous studies have been published on applying an AE to monitor grinding wheels. However, there are few studies on the effect of the location of the AE sensor in
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The acoustic emission (AE) technique is an effective method for monitoring grinding wheels, and numerous studies have been published on applying an AE to monitor grinding wheels. However, there are few studies on the effect of the location of the AE sensor in stably acquiring the AE signals generated during deterioration in cylindrical grinding wheels. In this study, we propose a stable method for detecting the deterioration of a cubic boron nitride (cBN) grinding wheel during cylindrical grinding using AE. We compared the AE signals acquired during grinding from an AE sensor located on the hydrostatic bearing, which supports the grinding wheel shaft, with those from the tailstock spindle. Although positioning the AE sensor on the hydrostatic bearing was found to reduce the AE signal intensity, the AE signal variations were smaller at the same grinding position, and the effect of the grinding position was less than that for the tailstock spindle. Moreover, positioning an AE sensor on the hydrostatic bearing is considered to provide the characteristics of AE signals specifically focused on the changes in cBN on the grinding wheel surface allowing the surface roughness of the workpiece to be estimated during grinding.
Full article
(This article belongs to the Special Issue Acoustic Emission Techniques in Wear Monitoring II)
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Open AccessArticle
Optimization of Sustainable Production Processes in C45 Steel Machining Using a Confocal Chromatic Sensor
by
Jozef Jurko, Katarína Paľová, Peter Michalík and Martin Kondrát
Lubricants 2024, 12(3), 99; https://doi.org/10.3390/lubricants12030099 - 16 Mar 2024
Abstract
Metal machining production faces a myriad of demands encompassing ecology, automation, product control, and cost reduction. Within this framework, an exploration into employing a direct inspection of the machined area within the work zone of a given machine through a confocal chromatic sensor
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Metal machining production faces a myriad of demands encompassing ecology, automation, product control, and cost reduction. Within this framework, an exploration into employing a direct inspection of the machined area within the work zone of a given machine through a confocal chromatic sensor was undertaken. In the turning process, parameters including cutting speed (A), feed (B), depth of cut (C), workpiece length from clamping (D), and cutting edge radius (E) were designated as input variables. Roundness deviation (Rd) and tool face wear (KM) parameters were identified as output factors for assessing process performance. The experimental phase adhered to the Taguchi Orthogonal Array L27. Confirmatory tests revealed that optimizing process parameters according to the Taguchi method could enhance the turning performance of C45 steel. ANOVA results underscored the significant impact of cutting speed (A), feed (B), depth of cut (C), and workpiece length from clamping (D) on turning performance concerning Rd and KM. Furthermore, initial regression models were formulated to forecast roundness variation and tool face wear. The proposed parameters were found to not only influence the machined surface but also affect confocal sensor measurements. Consequently, we advocate for the adoption of these optimal cutting conditions in product production to bolster turning performance when machining C45 steel.
Full article
(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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Open AccessEditorial
Special Issue on Laser Surface Engineering for Tribology
by
Xiulin Ji and Yong Sun
Lubricants 2024, 12(3), 98; https://doi.org/10.3390/lubricants12030098 - 16 Mar 2024
Abstract
The realm of laser surface engineering has seen continual development, particularly within the realm of tribology, a field dedicated to the examination of friction, wear, and lubrication between interacting surfaces in relative motion [...]
Full article
(This article belongs to the Special Issue Laser Surface Engineering for Tribology)
Open AccessArticle
Carrying Capacity of Spherical Hydrostatic Bearings including Elastic Deformation
by
Shengdong Zhang, Dongjiang Yang, Guangming Li, Yongchao Cheng, Guang Chen, Zhiming Zhang and Jichao Li
Lubricants 2024, 12(3), 97; https://doi.org/10.3390/lubricants12030097 - 15 Mar 2024
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This paper presents a theoretical model for calculating the carrying capacity of spherical hydrostatic bearings, including the deduction and solution of differential equations for fluid flow in the oil seal and the generation of bearing characteristic parameters. An example is used to verify
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This paper presents a theoretical model for calculating the carrying capacity of spherical hydrostatic bearings, including the deduction and solution of differential equations for fluid flow in the oil seal and the generation of bearing characteristic parameters. An example is used to verify the accuracy of the proposed calculation model. Additionally, the influence of dynamic pressure on the bearing capacity is investigated under various speed conditions. The results demonstrate that as the minimum width of the oil gap decreases, the maximum dynamic pressure increases non-linearly. Furthermore, the maximum dynamic pressure increases with higher rotational speeds, particularly when the width is smaller.
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Open AccessArticle
Titanium Nitride Coatings on CoCrMo and Ti6Al4V Alloys: Effects on Wear and Ion Release
by
Mohammed AbuAlia, Spencer Fullam, Filippo Cinotti, Noora Manninen and Markus A. Wimmer
Lubricants 2024, 12(3), 96; https://doi.org/10.3390/lubricants12030096 - 15 Mar 2024
Abstract
While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys
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While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys to enhance wear resistance and reduce ion release from prosthetic implants. Three different coating variants were utilized: one variant deposited using arc evaporation (Arc) followed by post-treatment, and two variants deposited using high-power impulse magnetron sputtering (HiPIMS) with or without post-treatment. The coatings’ performance was assessed through standard wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in bovine serum lubricant, and in the presence of abrasive PMMA bone cement particles in the lubricant. The results indicated that Arc and HiPIMS with post-treatment significantly reduced wear and eliminated detectable metal ion release, suggesting that these coatings could extend implant longevity and minimize adverse biological responses. Further long-term simulator and in vivo studies are recommended to validate these promising findings.
Full article
(This article belongs to the Special Issue Advances in Biolubrication and Biomaterials)
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Open AccessArticle
Calculation and Validation of Planet Gear Sliding Bearings for a Three-Stage Wind Turbine Gearbox
by
Huanhuan Ding, Ümit Mermertas, Thomas Hagemann and Hubert Schwarze
Lubricants 2024, 12(3), 95; https://doi.org/10.3390/lubricants12030095 - 15 Mar 2024
Abstract
In recent years, the trend towards larger wind turbines and higher power densities has led to increasing demands on planet gear bearings. The use of sliding bearings instead of rolling bearings in planetary bearings makes it possible to increase the power density with
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In recent years, the trend towards larger wind turbines and higher power densities has led to increasing demands on planet gear bearings. The use of sliding bearings instead of rolling bearings in planetary bearings makes it possible to increase the power density with lower component costs and higher reliability. Therefore, the use of planet gear sliding bearings in wind turbine gearboxes has become more common. However, the flexible structure and complex load conditions from the helical tooth meshes lead to highly complex elastic structure deformation that modifies the lubricant film thickness and pressure distribution and, thus, has to be considered in the calculation of the bearing’s load-carrying capacity. This paper introduces a highly time-efficient calculation procedure that is validated with pressure measurement data from a three-stage planetary gearbox for a multi-megawatt wind energy plant. The investigations focus on three main objectives: (i) analyses of experimental and predicted results for different load cases, (ii) validation of the results of planet gear sliding bearing code, and (iii) discussion on mandatory modeling depths for the different planet stages. Results indicate the necessity of further research in this field of applications, particularly for the third-stage bearings.
Full article
(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)
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Open AccessArticle
Erosive Wear of Structured Carbon-Fibre-Reinforced Textile Polymer Composites under Sands Blasting
by
Tong Deng, Vivek Garg and Michael S.A. Bradley
Lubricants 2024, 12(3), 94; https://doi.org/10.3390/lubricants12030094 - 15 Mar 2024
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Textile polymer composite is made of structured fibre matrix using textile technologies in fabrication, and gains benefits from strong mechanical properties with extra light weight. However, erosion behaviours and associated wear mechanisms of the composites may be influenced by the fibre structures due
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Textile polymer composite is made of structured fibre matrix using textile technologies in fabrication, and gains benefits from strong mechanical properties with extra light weight. However, erosion behaviours and associated wear mechanisms of the composites may be influenced by the fibre structures due to heterogeneous composition and complex architectural topologies. Understanding the erosive mechanisms of the structured composites can be important, not only for preventing surface damage and loss of mechanical strength but also for improving design and fabrication of the composites. This paper presents an experimental study of erosive wear under sand blasting on 3D woven carbon-fibre-reinforced textile composites with epoxy. The architectural topology methods of the composites include non-crimped bidirectional, tufted bidirectional, 3D layer-to-layer and 3D orthogonal textile methods. The erosion tests were conducted on four impact angles (20°, 30°, 45° and 90°) under one impact velocity at 40 m/s. The study results show that the erosive mechanism of the textile composites is different from that of the neat substrate material. The observations from this study also reveal the different erosive behaviours between the composites with different fibre structures. It concludes that architectural structures can influence the erosion of a textile composite but will not result in significant differences in the wear resistance of the composites (<20%).
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Open AccessArticle
Examining Wear Mechanisms in Railway Wheel Steels: Experimental Insights and Predictive Mapping
by
Nicola Zani, Angelo Mazzù, Luigi Solazzi and Candida Petrogalli
Lubricants 2024, 12(3), 93; https://doi.org/10.3390/lubricants12030093 - 14 Mar 2024
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Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were
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Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were conducted using a high-performance bi-disc apparatus, evaluating a range of materials, contact pressures, and lubrication conditions. Shakedown maps were employed to assess ratcheting behaviour, while the wear rate was analysed as a function of the fatigue index (FI). The results reveal the intricate interplay of contact pressure, slip ratio, material properties, and lubrication in determining wear and ratcheting behaviour. Oxidative and mild wear mechanisms were identified, and wear debris composition and morphology were characterised. The outcomes from this research clarify the pivotal role that wear processes play within railway systems and the far-reaching environmental repercussions they entail. This exploration contributes to the ongoing optimisation of railway operations, offering valuable insights aimed at mitigating unavoidable pollution sources and strengthening sustainability efforts. By delving into the intricate dynamics of wear phenomena within wheel–rail material, this research paves the way for innovative solutions that not only enhance operational efficiency but also minimise the ecological footprint of railway transportation.
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Open AccessArticle
Machine Learning-Based Predictive Model to Assess Rheological Dynamics of Eco-Friendly Oils as Biolubricants Enriched with SiO2 Nanoparticles
by
Girish Hariharan, Meghana Kundala Navada, Jeevan Brahmavar and Ganesha Aroor
Lubricants 2024, 12(3), 92; https://doi.org/10.3390/lubricants12030092 - 14 Mar 2024
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Efficient machinery operation relies on the performance of high-quality lubricants. Currently, mineral oils of different grades are widely employed for lubricating machine components, but their environmental impact is a concern. Biolubricants are potential alternatives to mineral oils due to environmental factors. The present
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Efficient machinery operation relies on the performance of high-quality lubricants. Currently, mineral oils of different grades are widely employed for lubricating machine components, but their environmental impact is a concern. Biolubricants are potential alternatives to mineral oils due to environmental factors. The present study focuses on assessing the rheological characteristics of SiO2 nanoparticle (NP)-enhanced ecofriendly biolubricants for near zero and high-temperature conditions. Pure neem oil, pure castor oil and a 50:50 blend of both oils were considered as the base oils. Nanobiolubricants with enhanced dispersion stability were prepared for varied concentrations of NPs using an ultrasonification method. Viscosity analysis was conducted using an MCR-92 rheometer, employing the Herschel Bulkley model to precisely characterize the viscosity behavior of bio-oils. Due to the fluid–solid interaction between SiO2 NPs and bio-oils, a crossover trend was observed in the flow curves generated for different base oils enriched with SiO2 NPs. For neem oil, a significant increase in viscosity was noted for 0.2 wt% of NPs. Using the multilayer perceptron (MLP) algorithm, an artificial neural network (ANN) model was developed to accurately predict the viscosity variations in nanobiolubricants. The accuracy of the predicted values was affirmed through experimental investigations at the considered nanoSiO2 weight concentrations.
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Open AccessArticle
Tribofilm Formation and Friction Reduction Performance on Laser-Textured Surface with Micro-Grooved Structures
by
Qianru Li, Renguo Lu, Hiroshi Tani, Shohei Kawada, Shinji Koganezawa, Xujun Liu and Peihong Cong
Lubricants 2024, 12(3), 91; https://doi.org/10.3390/lubricants12030091 - 13 Mar 2024
Abstract
Tribofilms, resulting from tribochemical reactions involving lubricants, additives, and metal surfaces, are pivotal in reducing friction, preventing adhesion, and minimizing wear. This study investigates the tribological characteristics of textured surfaces in boundary lubrication, emphasizing the impact of surface texturing on tribofilm formation. Untextured
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Tribofilms, resulting from tribochemical reactions involving lubricants, additives, and metal surfaces, are pivotal in reducing friction, preventing adhesion, and minimizing wear. This study investigates the tribological characteristics of textured surfaces in boundary lubrication, emphasizing the impact of surface texturing on tribofilm formation. Untextured surfaces manifest high friction coefficients and low wear owing to the development of thick tribofilms. However, debris accumulation impedes further tribochemical reactions, necessitating more energy for sliding and resulting in higher friction coefficients. Additionally, molybdenum dialkyl dithiocarbamate-derived MoS2 oxidation diminishes the expected lubrication effect. Textured surfaces exhibit lower friction coefficients and higher wear because the structure aids debris removal, promoting the formation of thinner tribofilms. Despite increased wear from solid-to-solid contact, textured surfaces facilitate an early fluid lubrication transition and enhance cavitation capacity, leading to reduced friction coefficients. We also consider the impact of sliding direction angles on friction coefficients, revealing that lower angles parallel to the grooves heighten friction, whereas higher angles enhance cavitation capacity. Unexpectedly, a 90° sliding direction angle increases the friction coefficients, attributed to MoS2 distribution in the tribofilms. These results provide crucial insights for optimizing lubrication strategies and enhancing wear resistance in boundary lubrication scenarios.
Full article
(This article belongs to the Special Issue Advances in Surface Engineering and Tribology)
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Open AccessArticle
The Performance of Carbon-Based Nanomaterials in Different Base Oils and an Oil Blend
by
Jack Nasr and Diana-Luciana Cursaru
Lubricants 2024, 12(3), 90; https://doi.org/10.3390/lubricants12030090 - 13 Mar 2024
Abstract
Different carbon-based nanomaterials (fullerenes, graphene, SWCNTs, and SWCNT-COOH) were tested as additives in a base mineral oil, SN150; rapeseed oil (RSO); and a 50/50 by volume blend of the two using an HFRR (high-frequency reciprocating rig) tester for coefficient of friction (COF) and
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Different carbon-based nanomaterials (fullerenes, graphene, SWCNTs, and SWCNT-COOH) were tested as additives in a base mineral oil, SN150; rapeseed oil (RSO); and a 50/50 by volume blend of the two using an HFRR (high-frequency reciprocating rig) tester for coefficient of friction (COF) and wear scar diameter (WSD) determinations and a four-ball tester for welding point determinations. The concentrations considered for the HFRR tests were 0.1, 0.5, 1, and 2 wt.%, while the concentration considered for the welding point tests was 0.5 wt.%. The results of the welding point tests showed that the addition of different nanoparticles made it so that welding occurred at much lower pressures compared to the pure oils. This is due to the hardness of the nanoparticles, which increases the local temperature and pressure at the contact points between them and the surfaces, causing welding to occur much sooner. The results of the HFRR tests showed a possible synergistic effect between the fullerenes and SWCNT-COOH and the oil blend, which may be attributed to possible interactions that occurred at a molecular level between the nanoparticles and the different molecules of the oil blend.
Full article
(This article belongs to the Special Issue Additives for Lubricating Oil and Grease: Mechanism, Properties and Applications)
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Open AccessCommentary
Behavior of Lubricated Bearings in Electric Circuits
by
Eckhard Kirchner, Marcel Bartz and Florian Becker-Dombrowsky
Lubricants 2024, 12(3), 89; https://doi.org/10.3390/lubricants12030089 - 11 Mar 2024
Abstract
In recent years, electrical damage phenomena in rolling and plain bearings have become increasingly important due to the growing electrification of individual mobility and renewable energy technologies [...]
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Open AccessArticle
Green-Emitting Carbon Quantum Dots: Highly Sensitive Temperature Sensing Probe in Nanocomposite and Lubrication System
by
Jiannan Sun, Ke Yan, Pan Zhang, Aizhao Pan, Xuehang Chen and Xinyi Shi
Lubricants 2024, 12(3), 88; https://doi.org/10.3390/lubricants12030088 - 11 Mar 2024
Abstract
Carbon quantum dots (CQDs) have already demonstrated their utility as lubricant additives, and non-contact temperature sensing based on CQDs offers considerable potential for condition monitoring in mechanical, electrical, and other fields, as well as lubrication-temperature multifunctional applications in lubricants. In this paper, we
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Carbon quantum dots (CQDs) have already demonstrated their utility as lubricant additives, and non-contact temperature sensing based on CQDs offers considerable potential for condition monitoring in mechanical, electrical, and other fields, as well as lubrication-temperature multifunctional applications in lubricants. In this paper, we have successfully synthesized and designed high-brightness carbon quantum dots/polyvinyl alcohol (PVA) temperature sensor thin film and dispersions of CQDs in a liquid paraffin lubrication system. Based on fluorescence intensity and the fluorescence intensity ratio, the carbon quantum dot/PVA film exhibited exponential temperature-dependent properties with a wide applicability range, a high goodness of fit (R2 > 0.99), and high relative thermal sensitivity (relative sensitivities of 1.74% K−1 and 1.39% K−1 for fluorescence intensity and fluorescence intensity ratio, respectively). In addition, based on the fluorescence intensity, the CQDs exhibited a wide temperature range (20–90 °C), a high goodness of fit (R2 > 0.99), and higher sensitivity (2.84% K−1) in a liquid paraffin lubrication system, which reflects the temperature responsive properties of carbon quantum dots as additives in lubrication systems. These findings provide convenient and effective possibilities for the sensing and monitoring of carbon quantum dots and their multifunctional applications under lubrication systems.
Full article
(This article belongs to the Special Issue Current and Future Trends in Tribological Research: Fundamentals and Applications–The 10th Anniversary of Lubricants)
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Open AccessArticle
Tribological Improvement of Low-Viscosity Nanolubricants: MoO3, MoS2, WS2 and WC Nanoparticles as Additives
by
José M. Liñeira del Río, Carlos M. C. G. Fernandes and Jorge H. O. Seabra
Lubricants 2024, 12(3), 87; https://doi.org/10.3390/lubricants12030087 - 10 Mar 2024
Abstract
The aim of this research is studying the tribological performance of MoO3, MoS2, WS2 and WC nanoparticles as additives of PAO4. Pure sliding tribological tests were performed at 120 °C, finding outstanding friction and wear reductions in comparison
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The aim of this research is studying the tribological performance of MoO3, MoS2, WS2 and WC nanoparticles as additives of PAO4. Pure sliding tribological tests were performed at 120 °C, finding outstanding friction and wear reductions in comparison with the PAO4, with maximum friction reductions of 64% for the 0.1 wt% MoS2 nanolubricant and greatest wear decreases for 0.1 wt% MoS2 nanolubricant: a width reduction of 62% and a worn area decrease of 97%. Raman mapping and a roughness evaluation of the worn pins confirmed the tribofilm formation and mending as tribological mechanisms. Rolling–sliding tests were conducted with best nanolubricants performance in pure sliding, observing excellent antifriction capabilities of MoS2 nanoparticles at low speeds, indicating that the use of nanoparticles is vital in boundary lubrication.
Full article
(This article belongs to the Special Issue Advances in Tribochemistry)
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Open AccessArticle
Magnetorheological Polishing Based on Honing Vertical Mechanism for Inner Surface of Titanium Alloy Pipes
by
Wanli Song, Zhen Yang, Dezhi Meng, Na Wang and Seung-Bok Choi
Lubricants 2024, 12(3), 86; https://doi.org/10.3390/lubricants12030086 - 08 Mar 2024
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Recently, high internal surfaces for titanium alloy pipes have been required due to the increment of various applications such as aerospace components. In this work, vertical magnetorheological polishing (VMRP) is carried out to achieve high polishing performance on the internal surface of the
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Recently, high internal surfaces for titanium alloy pipes have been required due to the increment of various applications such as aerospace components. In this work, vertical magnetorheological polishing (VMRP) is carried out to achieve high polishing performance on the internal surface of the titanium alloy pipe. A series of comparative experiments were conducted to investigate the polishing mechanism of magnetorheological polishing (MRP) fluid and enhance the polishing performance. It is shown from the experimental results that the VMRP method under the opposite polarity arrangement improves the surface roughness from 47.85% to 83.34% by reducing unwanted vibration and noise during operation. This provides nanoscale surface polishing quality, while such a precision cannot be achieved from the previous horizontal MR polishing apparatus method. It is found that under a 2700 cycle polishing time, a polishing process combining a rough and fine polishing approach with a combination of different particle diameters results in an axial surface roughness of 0.05 μm and circumferential surface roughness of 0.038 μm, respectively. It is also identified that the axial surface roughness of 0.04 μm–0.041 μm is achieved through the combination of high- and low-speed polishing process after 1602 cycles.
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Open AccessArticle
Calculation and Analysis of Equilibrium Position of Aerostatic Bearings Based on Bivariate Interpolation Method
by
Shuai Li, Yafu Huang, Hechun Yu, Wenbo Wang, Guoqing Zhang, Xinjun Kou, Suxiang Zhang and Youhua Li
Lubricants 2024, 12(3), 85; https://doi.org/10.3390/lubricants12030085 - 07 Mar 2024
Abstract
The solution of equilibrium positions is a critical component in the calculation of the dynamic characteristic coefficients of aerostatic bearings. The movement of the rotor in one direction leads to bidirectional variations in the air film force, resulting in low efficiency when using
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The solution of equilibrium positions is a critical component in the calculation of the dynamic characteristic coefficients of aerostatic bearings. The movement of the rotor in one direction leads to bidirectional variations in the air film force, resulting in low efficiency when using conventional calculation methods. It can even lead to iterative divergence if the initial value is improperly selected. This study concentrates on the orifice throttling aerostatic bearings and proposes a novel method called the bivariate interpolation method (BIM) to calculate the equilibrium position. The equilibrium equation for the rotor under the combined influence of air film forces, gravity, and external loads is established. A calculation program based on the finite difference method is developed to determine the equilibrium position. The process of solving the equilibrium position and the convergence is compared with the secant method and the search method. Furthermore, the variation trend of the equilibrium position and stiffness when the external loads changes are studied based on the BIM. Finally, the correctness of the BIM to solve the equilibrium position is proved by comparing it with the experiment results. The calculation results indicate that the BIM successfully resolves the problem of initial value selection and exhibits superior computational efficiency and accuracy. The equilibrium position initially moves away from the direction of the external load as the load increases, and then this gradually approaches the load direction. The main stiffness increases with increases in the external load, while the variation in cross stiffness depends on the direction of the external load.
Full article
(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)
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Open AccessArticle
Dynamic Effect Analysis of Cryogenic Solid-Lubricated Ball Bearings with Geometrical-Frictional Defects
by
Yuhao Zhao, Zhenyi Chen, Yanyang Zi, Mingquan Zhang and Tao Tang
Lubricants 2024, 12(3), 84; https://doi.org/10.3390/lubricants12030084 - 06 Mar 2024
Abstract
The traction behavior in cryogenic solid-lubricated ball bearings (CSLBBs) of liquid rocket engines (LREs) has a significant effect on the dynamic response of the bearing–rotor system. To reveal the fault mechanism of CSLBBs, a tribo-dynamic model is proposed in this paper that considers
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The traction behavior in cryogenic solid-lubricated ball bearings (CSLBBs) of liquid rocket engines (LREs) has a significant effect on the dynamic response of the bearing–rotor system. To reveal the fault mechanism of CSLBBs, a tribo-dynamic model is proposed in this paper that considers the solid-lubricated traction, six-DOF motion of the ball and contact collisions between the ball and the cage. The modified traction model uses fan-shaped and arched sections to discretize the contact area to eliminate the meshing error. The newly developed fault model, called ‘geometrical-frictional defects’, can more realistically represent solid-lubrication coating defects. The results show that the frictional excitation can significantly increase bearing vibration by increasing the traction force on the raceway. The change in the amplitude of the bearing vibration and its derivative can be used as a reference to determine the depth of defects. The width of the defect can be diagnosed by monitoring the double-pulse time interval and spectrum of the bearing vibration signal. This research may provide some theoretical guidance for the design and condition monitoring of CSLBBs.
Full article
(This article belongs to the Special Issue Selected Papers from the 8th Conference on Lubrication, Maintenance and Tribotechnology (LUBMAT))
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Open AccessFeature PaperArticle
A New Plasticity Index including Size-Effects in the Contact of Rough Surfaces
by
M. Ciavarella
Lubricants 2024, 12(3), 83; https://doi.org/10.3390/lubricants12030083 - 06 Mar 2024
Abstract
It is known that contact of rough surfaces occurs over an area much smaller than the nominal contact area, and at asperity scale, increased hardness results in experimentally observed asperity “persistence”, namely that it is hard to flatten asperities. Here, we consider Persson’s
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It is known that contact of rough surfaces occurs over an area much smaller than the nominal contact area, and at asperity scale, increased hardness results in experimentally observed asperity “persistence”, namely that it is hard to flatten asperities. Here, we consider Persson’s elasto-plastic solution for rough contact together with an hardness equation proposed by Swadener, George and Pharr for spherical indentation, including size effects depending on sphere radius, in particular to define a new plasticity index that defines the tendency to plastic deformation. While the classical plasticity index shows that at sufficiently small scales, there will be plastic deformations unless surfaces are extremely smooth, and with size effects, the small roughness scales the content of spectrum matter in defining the real state of asperities. In particular, what may appear as plastic at a bulk scale returns to an elastic behaviour at a small scale, as suggested by the “asperity persistence” experimental observation. Some illustrative examples are shown, but clearly, our index and elasto-plastic solution are mainly qualitative, as a realistic investigation is much more complex and still computationally too demanding.
Full article
(This article belongs to the Special Issue Current and Future Trends in Tribological Research: Fundamentals and Applications–The 10th Anniversary of Lubricants)
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Open AccessArticle
Experimental and Numerical Analysis of Torsional—Lateral Vibrations in Drive Lines Supported by Hydrodynamic Journal Bearings
by
Fabrizio Antonio Stefani, Carlo Alberto Niccolini Marmont Du Haut Champ, Paolo Silvestri and Aristide Fausto Massardo
Lubricants 2024, 12(3), 82; https://doi.org/10.3390/lubricants12030082 - 06 Mar 2024
Abstract
The driving and resistance torques of some rotating machinery for industrial applications are nonstationary and affect system dynamics. Under such operating conditions, coupling between torsional and lateral vibrations may become significant for drive lines supported by hydrodynamic bearings in particular design configurations. Indeed,
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The driving and resistance torques of some rotating machinery for industrial applications are nonstationary and affect system dynamics. Under such operating conditions, coupling between torsional and lateral vibrations may become significant for drive lines supported by hydrodynamic bearings in particular design configurations. Indeed, the occurrence of fluid–structure interactions causes a reduction in the stability threshold of the journal bearings. A hypothesis based on Hopf bifurcation theory (HBT), which justifies how the coupling phenomenon develops, is validated by means of overall experimental observations and a suitable numerical model. When the pulsating driving torque induces significant angular speed oscillation, the rotor-bearing system lateral operating response becomes more complex, and bearing instability onset is detected. Such observation proves the influence of bearings in converting torsional oscillations to lateral vibrations. Particularly, during run-up and run-down tests, localized hysteresis is observed in trends of fundamental order contents. The numerical model of the hydrodynamic bearings solves the Reynolds equation in unsteady conditions to quantify the lateral vibrations amplitude in the presence of both angular speed oscillation and dynamic perturbation. The proposed approach proves the onset of torsional–lateral vibration coupling due to hydrodynamic bearings, to a certain extent. The detected hysteresis phenomena can also be explained by the onset of journal bearing instability.
Full article
(This article belongs to the Special Issue Applied Tribology: Rotordynamics)
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Open AccessArticle
Tribological Properties of Al2O3/Graphite-Al2O3 Laminated Composites under Water Lubrication Conditions
by
Zhengxian Di, Zhijia Wang, Xiaoyu Zhang, Jiaxin Si, Junjie Song, Hengzhong Fan, Yunfeng Su, Litian Hu and Yongsheng Zhang
Lubricants 2024, 12(3), 81; https://doi.org/10.3390/lubricants12030081 - 05 Mar 2024
Abstract
High-performance Al2O3/graphite-Al2O3 laminated composites exhibit an excellent self-lubricating ability for moving components, such as sliding shaft sleeves and dynamic seals. The tribological behaviors of Al2O3/graphite-Al2O3 laminated composites should be
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High-performance Al2O3/graphite-Al2O3 laminated composites exhibit an excellent self-lubricating ability for moving components, such as sliding shaft sleeves and dynamic seals. The tribological behaviors of Al2O3/graphite-Al2O3 laminated composites should be studied extensively under water working conditions. Here, we attempted to explore the practicability of the Al2O3/graphite-Al2O3 laminated composite as a sealing material from a tribological point of view under water lubrication conditions. The tribological properties and mechanism of friction and wear of laminated composite ceramics were investigated under dry sliding friction, water environment, and suspended particle working conditions. It was found that the Al2O3/graphite-Al2O3 laminated composite has a better friction performance under water lubrication compared to dry sliding because of the separation effects formed by a water molecule film and a transfer film. Meanwhile, the wear rate under dry contact was found to be approximately six times that under water lubrication conditions. Under the water lubrication conditions, the formation of graphite films and water-adsorbed layers improved the anti-wear properties of the laminated materials, and the friction coefficient and the wear rate were as low as 0.16 and 1.76 × 10−6 mm3/Nm, respectively. Under the suspended particle working condition, the solid particles destroyed the graphite lubricating film and abrasive wear dominated the wear mode. The Al2O3/graphite-Al2O3 laminated composite demonstrates a potential for application in dynamic sealing and sliding components.
Full article
(This article belongs to the Special Issue Advances in Ceramic-Based Lubricants)
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