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
Advances in Contact Mechanics
Lubricants 2024, 12(5), 179; https://doi.org/10.3390/lubricants12050179 - 16 May 2024
Abstract
Advancements in contact mechanics play an important role in the design of modern mechanical and bio-medical systems, enhancing their efficiency, power density, and reliability [...]
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(This article belongs to the Special Issue Advances in Contact Mechanics)
Open AccessArticle
Investigation of the Tribological Properties of Hybrid Additive-Modified Water-Based Lubricating Fluid
by
Raimondas Kreivaitis, Jolanta Treinytė, Artūras Kupčinskas, Milda Gumbytė and Eglė Sendžikienė
Lubricants 2024, 12(5), 178; https://doi.org/10.3390/lubricants12050178 - 15 May 2024
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Water-based lubricating fluids (WBLFs), known for their significant environmental benefits, are the focus of this study. The properties of WBLFs directly influence lubricated mechanisms’ longevity and operating efficiency. WBLFs are enhanced using additives, which must improve their properties and, at the same time,
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Water-based lubricating fluids (WBLFs), known for their significant environmental benefits, are the focus of this study. The properties of WBLFs directly influence lubricated mechanisms’ longevity and operating efficiency. WBLFs are enhanced using additives, which must improve their properties and, at the same time, remain environmentally friendly. This study combines bis(2-hydroxyethyl) ammonium erucate protic ionic liquid and titanium oxide nanoparticles to formulate the hybrid additive. The lubricity was investigated using Alumina/Bearing steel and WC/Bearing steel friction pairs in a reciprocating ball-on-plate tribo-tester. The results show that protic ionic liquid can significantly improve lubricity and the corrosion-preventing ability of the base fluid. Applying a hybrid additive further improved the wear reduction ability in the WC/Bearing steel friction pair. However, the wear reduction ability was diminished when a hybrid additive was used to lubricate the Alumina/Bearing steel friction pair. The proposed lubricity improvement mechanism is based on forming an adsorption layer of ionic liquid molecules and rolling and tribo-sintering titanium oxide nanoparticles.
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Open AccessArticle
Test Method for Rapid Prediction of Steady-State Temperature of Outer Rings of Bearings under Grease Lubrication Conditions
by
Zhongbing Xia, Fang Yang, Xiqiang Ma, Nan Guo, Xiao Wang, Yunhao Cui and Yuchen Duan
Lubricants 2024, 12(5), 177; https://doi.org/10.3390/lubricants12050177 - 15 May 2024
Abstract
Temperature has a great influence on the stability of bearing performance. For the study of bearing steady-state temperature, this paper proposes a test method to quickly predict the steady-state temperature of the outer ring of a bearing, which solves the problems in traditional
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Temperature has a great influence on the stability of bearing performance. For the study of bearing steady-state temperature, this paper proposes a test method to quickly predict the steady-state temperature of the outer ring of a bearing, which solves the problems in traditional theoretical calculations and simulation analysis methods such as the large number of calculations, complex models, and large errors. Firstly, a mathematical prediction model is established according to the bearing temperature-rise law; then, a bearing steady-state temperature detection device is designed; and finally, the prediction model parameters are solved according to the experimental results, and experimental verification is carried out. It is shown that the prediction model has high accuracy under different load and speed conditions, and the error between the predicted steady-state temperature and the tested steady-state temperature is less than 0.7 °C. This prediction method reduces the single test time of the same speed to 60 min, which greatly improves the efficiency of the temperature detection test. The steady-state temperature model has important theoretical significance in guiding the study of the limiting speed of bearings.
Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
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Open AccessArticle
Tribological Behavior of Polydiethylsiloxane (PDES) in a Si3N4 and M50 System under Low Temperatures from −80 to 25 °C
by
Junhao Han, Yong Tang, Luo Yue, Xianzhen Ma, Hao Jia, Ningxia Liu, Pengpeng Bai, Yonggang Meng and Yu Tian
Lubricants 2024, 12(5), 176; https://doi.org/10.3390/lubricants12050176 - 14 May 2024
Abstract
Lubricants must exhibit good tribological behavior at low temperatures to ensure reliable startups in very cold regions. This study investigates the performance of lubricants, with a specific focus on their capacity for high-temperature lubrication and ensuring reliable low-temperature startup in engines. Experiments were
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Lubricants must exhibit good tribological behavior at low temperatures to ensure reliable startups in very cold regions. This study investigates the performance of lubricants, with a specific focus on their capacity for high-temperature lubrication and ensuring reliable low-temperature startup in engines. Experiments were conducted to assess the friction and wear characteristics of polydiethylsiloxane in conjunction with a Si3N4 ball and M50 (8Cr4Mo4V) steel across a temperature range of −80 °C to 25 °C. The results indicate that the coefficient of friction, as determined through friction and wear tests at various temperatures, remained below 0.1. As temperatures progressively decreased, the system’s friction coefficient increased, and wear volumes recorded at 25 °C and −60 °C were 9749.513 µm³ and 105.006 µm³, respectively, culminating in lubrication failure at −100 °C. This failure is primarily attributed to the increased viscosity and decreased mobility of polydiethylsiloxane at extremely low temperatures. Additionally, the reduced temperature increases the strength of the quenched steel, leading to hard particles or protrusions on the material’s surface, which collide with the Si3N4 ball during friction, causing adhesion and spalling. Despite this, polydiethylsiloxane forms a stable protective oil film on the surface, enhancing the system’s lubrication performance. However, below −80 °C, this oil film begins to tear, leading to diminished lubrication efficacy. This study provides valuable data supporting the field of cryogenic lubrication.
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(This article belongs to the Special Issue Aerospace Tribology)
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Open AccessArticle
AsdinNorm: A Single-Source Domain Generalization Method for the Remaining Useful Life Prediction of Bearings
by
Juan Xu, Bin Ma, Weiwei Chen and Chengwei Shan
Lubricants 2024, 12(5), 175; https://doi.org/10.3390/lubricants12050175 - 14 May 2024
Abstract
The remaining useful life (RUL) of bearings is vital for the manipulation and maintenance of industrial machines. The existing domain adaptive methods have achieved major achievements in predicting RUL to tackle the problem of data distribution discrepancy between training and testing sets. However,
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The remaining useful life (RUL) of bearings is vital for the manipulation and maintenance of industrial machines. The existing domain adaptive methods have achieved major achievements in predicting RUL to tackle the problem of data distribution discrepancy between training and testing sets. However, they are powerless when the target bearing data are not available or unknown for model training. To address this issue, we propose a single-source domain generalization method for RUL prediction of unknown bearings, termed as the adaptive stage division and parallel reversible instance normalization model. First, we develop the instance normalization of the vibration data from bearings to increase data distribution diversity. Then, we propose an adaptive threshold-based degradation point identification method to divide the healthy and degradation stages of the run-to-failure vibration data. Next, the data from degradation stages are selected as training sets to facilitate the RUL prediction of the model. Finally, we combine instance normalization and instance denormalization of the bearing data into a unified GRU-based RUL prediction network for the purpose of leveraging the distribution bias in instance normalization and improving the generalization performance of the model. We use two public datasets to verify the proposed method. The experimental results demonstrate that, in the IEEE PHM Challenge 2012 dataset experiments, the prediction accuracy of our model with the average RMSE value is 1.44, which is 11% superior to that of the suboptimal comparison model (Transformer model). It proves that our model trained on one-bearing data achieves state-of-the-art performance in terms of prediction accuracy on multiple bearings.
Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
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Open AccessArticle
Effect of Nano-CuO and 2-Mercaptobenzothiazole on the Tribological Properties of Ultra-High Molecular Weight Polyethylene
by
Andrey P. Vasilev, Afanasiy A. Dyakonov, Sakhayana N. Danilova, Igor S. Makarov, Anastasia V. Okoneshnikova and Aitalina A. Okhlopkova
Lubricants 2024, 12(5), 174; https://doi.org/10.3390/lubricants12050174 - 12 May 2024
Abstract
In this study, the tribological properties of nanocomposites based on ultra-high molecular weight polyethylene (UHMWPE) filled with nano-CuO and 2-mercaptobenzothiazole (CuO/MBT) in mass ratios of 1:1 and 2:1 were investigated. In the supramolecular structure of UHMWPE nanocomposites, spherulites of several hundred micrometers in
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In this study, the tribological properties of nanocomposites based on ultra-high molecular weight polyethylene (UHMWPE) filled with nano-CuO and 2-mercaptobenzothiazole (CuO/MBT) in mass ratios of 1:1 and 2:1 were investigated. In the supramolecular structure of UHMWPE nanocomposites, spherulites of several hundred micrometers in size are formed. The density of UHMWPE nanocomposites slightly increases relative to the pure polymer, reaching a maximum at 2 wt.% CuO/MBT in both ratios. The Shore D hardness and compressive stress of the UHMWPE nanocomposites showed an improvement of 5–6% and 23–35%, respectively. The wear resistance and coefficient of friction of UHMWPE nanocomposites were tested using a pin-on-disk configuration under dry friction conditions on #45 steel and on P320 sandpaper. It was shown that the wear rate of UHMWPE nanocomposites filled with 2 wt.% CuO/MBT decreased by ~3.2 times compared to the pure polymer, and the coefficient of friction remained at the level of the polymer matrix. Abrasive wear showed an improvement in UHMWPE nanocomposites filled with 1 wt.% CuO/MBT compared to the polymer matrix and other samples. The worn surfaces of the polymer composites after dry friction were examined by scanning electron microscopy and IR spectroscopy. The formation of secondary structures in the form of tribofilms that protect the material from wear was demonstrated. Due to this, the wear mechanism of UHMWPE nanocomposites is transformed from adhesive to fatigue wear. The developed materials, due to improved mechanical and tribological properties, can be used as parts in friction units of machines and equipment.
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(This article belongs to the Special Issue Tribology of Nanocomposites 2024)
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Open AccessArticle
Tribological Behavior of Friction Materials Containing Aluminum Anodizing Waste Obtained by Different Industrial Drying Processes
by
Giovanni Straffelini, Priyadarshini Jayashree, Andrea Barbieri and Roberto Masciocchi
Lubricants 2024, 12(5), 173; https://doi.org/10.3390/lubricants12050173 - 11 May 2024
Abstract
With sustainability dominating the industry, recycling the generated waste from different processes is becoming increasingly important. This study focuses on recycling waste generated during aluminum anodizing waste (AAW) in friction material formulations for automotive braking applications. However, before utilization, the waste needs to
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With sustainability dominating the industry, recycling the generated waste from different processes is becoming increasingly important. This study focuses on recycling waste generated during aluminum anodizing waste (AAW) in friction material formulations for automotive braking applications. However, before utilization, the waste needs to be pre-treated, which mainly involves drying. Hence, four different industrial drying methods were studied to dry the AAW, and the corresponding characteristics were observed by evaluating its residual humidity and crushability index. The waste powders were further characterized using FT-IR and SEM/EDXS to understand their constituents. The initial analysis showed that the waste subjected to the drying process P2 and P1 with the lowest final humidity fetched the most desirable results, with P1 having the simpler drying procedure. The AAW powders were added in a commercial friction material formulation at 6 and 12 wt.% and subjected to friction, wear, and non-exhaust particulate matter analysis. The worn surfaces were analyzed using SEM/EDXS evaluation to understand the extension and composition of the deposited secondary contact plateaus. It was seen that the 12 wt.% addition of waste processed using the P1 technique provided the most satisfactory friction, wear, and emission characteristics, along with expansive secondary contact plateaus with a good contribution of the waste in its formation. This study showed a good relationship between the processing method and a formulation’s tribological and emission characteristics, thereby paving the way for using this drying method for other waste requiring pre-treatment.
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(This article belongs to the Special Issue Emission and Transport of Wear Particles)
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Open AccessArticle
Evaluation of the Degree of Degradation of Brake Pad Friction Surfaces Using Image Processing
by
Teodor Mandziy, Iryna Ivasenko, Olena Berehulyak, Roman Vorobel, Michał Bembenek, Sviatoslav Kryshtopa and Liubomyr Ropyak
Lubricants 2024, 12(5), 172; https://doi.org/10.3390/lubricants12050172 - 11 May 2024
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The improvement of drilling rig systems to ensure a reduction in unproductive time spent on lowering and lifting operations for replacing drilling tools and restoring the performance of drilling equipment units is an important task. At the same time, considerable attention is paid
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The improvement of drilling rig systems to ensure a reduction in unproductive time spent on lowering and lifting operations for replacing drilling tools and restoring the performance of drilling equipment units is an important task. At the same time, considerable attention is paid to the reliable and efficient operation of the braking systems of drilling rig winches. In the process of operation, the polymer pads periodically come into contact with the outer cylindrical surface of the metal pulley during braking, work in extreme conditions and wear out intensively, so they need periodic replacement. Tests were carried out on a modernized stand and in industrial conditions for the brakes of drilling winches. A methodology for evaluating the degradation of the brake pad friction surface during its operation is proposed. The assessment of the degradation degree is carried out based on the image of the brake pad surface using image processing techniques. Geometric transformations of the input image were performed to avoid perspective distortions caused by the concave shape of the brake pads and the spatial angle at which the image is acquired to avoid glares. The crack detection step was implemented based on the scale-space theory, followed by contour detection and skeletonization. The ratios of the area and perimeter of segmented and skeletonized cracks to the total area were chosen as integral characteristics of the degradation degree. With the help of scanning electron microscopy, the character of the destruction of the friction surface and the degradation of the polymer material was investigated. Experimental studies were performed, and the application of the proposed method is illustrated.
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Open AccessArticle
Multi-Objective Optimization of Tribological Characteristics for Aluminum Composite Using Taguchi Grey and TOPSIS Approaches
by
Sandra Gajević, Ana Marković, Saša Milojević, Aleksandar Ašonja, Lozica Ivanović and Blaža Stojanović
Lubricants 2024, 12(5), 171; https://doi.org/10.3390/lubricants12050171 - 10 May 2024
Abstract
In this study, a multi-objective optimization regarding the tribological characteristics of the hybrid composite with a base material of aluminum alloy A356 as a constituent, reinforced with a 10 wt.% of silicon carbide (SiC), size 39 µm, and 1, 3, and 5 wt.%
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In this study, a multi-objective optimization regarding the tribological characteristics of the hybrid composite with a base material of aluminum alloy A356 as a constituent, reinforced with a 10 wt.% of silicon carbide (SiC), size 39 µm, and 1, 3, and 5 wt.% graphite (Gr), size 35 µm, was performed using the Taguchi method, gray relational analysis (GRA), and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) decision-making methods. Tribological tests were carried out on a “block on disc” type tribometer with lubrication. Load, sliding speed, and graphite mass concentration were analyzed as input parameters. As output parameters, wear rate and coefficient of friction were calculated. An analysis of variance (ANOVA) was conducted to identify all parameters that have a significant influence on the output multi-response. It was found that the normal load has the highest influence of 41.86%, followed by sliding speed at 32.48% and graphite addition at 18.47%, on the tribological characteristics of composites. Multi-objective optimization determined that the minimal wear rate and coefficient of friction are obtained when the load is 40 N, the sliding speed is 1 m/s, and the composite contains 3 wt.% Gr. The optimal combination of parameters achieved by GRA was also confirmed by the TOPSIS method, which indicates that both methods can be used with high reliability to optimize the tribological characteristics. The analysis of worn surfaces using scanning electron microscopy revealed adhesive and delamination wear as dominant mechanisms.
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(This article belongs to the Special Issue Tribological and Mechanical Characteristics of Aluminum Metal Matrix Composites and Their Applications)
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Open AccessArticle
Investigation of the Nitriding Effect on the Adhesion and Wear Behavior of CrN-, AlTiN-, and CrN/AlTiN-Coated X45CrMoV5-3-1 Tool Steel Formed Via Cathodic Arc Physical Vapor Deposition
by
Gülşah Aktaş Çelik, Konstantinos Fountas, Şaban Hakan Atapek, Şeyda Polat, Eleni Kamoutsi and Anna D. Zervaki
Lubricants 2024, 12(5), 170; https://doi.org/10.3390/lubricants12050170 - 10 May 2024
Abstract
Monolayer (CrN, AlTiN) and bilayer (CrN/AlTiN) coatings are formed on the surface of conventional heat-treated and gas-nitrided X45CrMoV5-3-1 tool steel via Cathodic Arc Physical Vapor Deposition (CAPVD), and the adhesion characteristics and room- and high-temperature wear behavior of the coatings are compared with
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Monolayer (CrN, AlTiN) and bilayer (CrN/AlTiN) coatings are formed on the surface of conventional heat-treated and gas-nitrided X45CrMoV5-3-1 tool steel via Cathodic Arc Physical Vapor Deposition (CAPVD), and the adhesion characteristics and room- and high-temperature wear behavior of the coatings are compared with those of the un-nitrided ones. Scratch tests on the coatings show that the bilayer coating exhibits better adhesion behavior compared to monolayer ones, and the adhesion is further increased in all coatings due to the high load carrying capacity of the diffusion layer formed by the nitriding process. Dry friction tests performed at room temperature reveal that, among ceramic-based coatings, the coating system with a high adhesion has the lowest specific wear rate (0.06 × 10−6 mm3/N·m), and not only the surface hardness but also the nitriding process is important for reducing this rate. Studies on wear surfaces indicate that the bilayer coating structure has a tendency to remove the surface over a longer period of time. Hot wear tests performed at a temperature (450 °C) corresponding to aluminum extrusion conditions show that high friction coefficient values (>1) are reached due to aluminum transfer from the counterpart material to the surface and failure develops through droplet delamination. Adhesion and tribological tests indicate that the best performance among the systems studied belongs to the steel–CrN/AlTiN system and this performance can be further increased via the nitriding process.
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(This article belongs to the Special Issue Wear and Corrosion Behaviour of Metals and Alloys)
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Open AccessArticle
Numerical Investigations of Static and Dynamic Characteristics of a Novel Staggered Labyrinth Seal with Semi-Elliptical Structure
by
Shebin Yan, Zhifeng Ye, Dezhao Wang, Huihao Su and Wenjie Zhou
Lubricants 2024, 12(5), 169; https://doi.org/10.3390/lubricants12050169 - 10 May 2024
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In order to optimize sealing performance, a novel labyrinth seal with semi-elliptical teeth (SET) structure is proposed in this paper, which includes semi-elliptical teeth and a series of cavities. The simulation results calculated by the numerical methods are compared with the experimental and
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In order to optimize sealing performance, a novel labyrinth seal with semi-elliptical teeth (SET) structure is proposed in this paper, which includes semi-elliptical teeth and a series of cavities. The simulation results calculated by the numerical methods are compared with the experimental and theoretical results, and static and dynamic characteristics of the novel SET structure are further investigated. The numerical simulations of labyrinth seals with the SET structure demonstrate high accuracy and reliability, with a maximum relative error of less than 6% as compared to experimental results, underscoring the validity of the model. Notably, leakage rates are directly influenced by pressure drop and axial offset, with optimal sealing achieved at zero axial displacement. The direct damping coefficient increases as the pressure drop increases while the other dynamic coefficients decrease. Additionally, the stability results show that the novel SET structure exhibits higher stability for positive axial offsets. The novel model and corresponding results can provide a meaningful reference for the study of sealing structure and coupled vibration in the field of fluid machinery.
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Open AccessEditorial
Recent Advances in Machine Learning in Tribology
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Max Marian and Stephan Tremmel
Lubricants 2024, 12(5), 168; https://doi.org/10.3390/lubricants12050168 - 9 May 2024
Abstract
Tribology, the study of friction, wear, and lubrication, has been a subject of interest for researchers exploring the complexities of materials and surfaces [...]
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(This article belongs to the Special Issue Recent Advances in Machine Learning in Tribology)
Open AccessArticle
Influence of Electrical Stimulation on the Friction Performance of LiPF6-Based Ionic Liquids
by
Xiangyu Ge, Xiaodong Wu, Qiuyu Shi, Yanfei Liu and He Liang
Lubricants 2024, 12(5), 167; https://doi.org/10.3390/lubricants12050167 - 9 May 2024
Abstract
This work studied the influence of the voltage parameters on the friction and superlubricity performances of LiPF6-based ionic liquids (ILs). The results show that the voltage direction and magnitude greatly affected the friction performances of ILs and that macroscale superlubricity can
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This work studied the influence of the voltage parameters on the friction and superlubricity performances of LiPF6-based ionic liquids (ILs). The results show that the voltage direction and magnitude greatly affected the friction performances of ILs and that macroscale superlubricity can be achieved with a stimulation of −0.1 V. The surface analysis and experiment results indicate that the voltage magnitude influences the coefficient of friction (COF) by determining the types of substances in the tribochemical film formed on the ball, while the voltage direction influences the COF by affecting the adsorption behavior of Li(PEG)+ ions on the ball. At −0.1 V, the cation group Li(PEG)+ adsorption film and FeOOH-containing tribochemical film contribute to friction reduction. The formation of FexOy within the tribochemical film results in an increase in friction at −0.8 V. The limited adsorption of Li(PEG)+ ions and the formation of FexOy contribute to the elevated COF at +0.1 V. This work proves that the friction performances of LiPF6-based ILs could be affected by voltage parameters. A lubrication model was proposed hoping to provide a basic understanding of the lubrication mechanisms of ILs in the electric environment.
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(This article belongs to the Special Issue Advances in Dry and Lubricated Electrical Contacts)
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Open AccessSystematic Review
Nanotechnology in Lubricants: A Systematic Review of the Use of Nanoparticles to Reduce the Friction Coefficient
by
Milton Garcia Tobar, Rafael Wilmer Contreras Urgiles, Bryan Jimenez Cordero and Julio Guillen Matute
Lubricants 2024, 12(5), 166; https://doi.org/10.3390/lubricants12050166 - 9 May 2024
Abstract
The study of lubricating oil is paramount for the optimal functioning of modern engines, and it has generated intensive research in the automotive industry. The aim is to improve the tribological properties of lubricants by including nanomaterials as additives in base oils. This
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The study of lubricating oil is paramount for the optimal functioning of modern engines, and it has generated intensive research in the automotive industry. The aim is to improve the tribological properties of lubricants by including nanomaterials as additives in base oils. This article presents an exhaustive bibliographic review of the experiments carried out to optimize the tribological properties of nano-lubricants in order to identify the nanoparticles and experimental processes used and analyze the results obtained. The methodology adopted combines inductive and deductive elements. It begins with the formulation of a general theory on the application of nanoparticles in lubricants, followed by the collection of specific data on the conceptualization and preparation of nano-lubricants. A total of 176 articles focused on the application of nanoparticles in lubricants, especially to reduce the coefficient of friction, are reviewed. These works, with impact levels Q1 and Q2, delve into the application and are analyzed to review the obtained results. Most researchers worked with a nanoparticle concentration range of 0% to 1% by volume.
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(This article belongs to the Special Issue Thermophysical and Tribological Characterization of Additivated Lubricants with Nanoparticles)
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Open AccessArticle
Synergistic Effect of Acrylate of Dialkyl Dithiophosphoric Acid Combined with Molybdenum Dialkyl Dithiocarbamate as Additives in Gear Oil
by
Minghao Ding, Yimin Mo, Hong Zhang and Qingchun Liu
Lubricants 2024, 12(5), 165; https://doi.org/10.3390/lubricants12050165 - 9 May 2024
Abstract
With the aim of improving the tribological properties of low-viscosity gear oil for automobiles, an acrylate of dialkyl dithiophosphoric acid (ADDP) with strong polar groups was synthesized. The tribological behavior of ADDP combined with molybdenum dialkyl dithiocarbamate (MoDTC) in gear oil was systematically
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With the aim of improving the tribological properties of low-viscosity gear oil for automobiles, an acrylate of dialkyl dithiophosphoric acid (ADDP) with strong polar groups was synthesized. The tribological behavior of ADDP combined with molybdenum dialkyl dithiocarbamate (MoDTC) in gear oil was systematically studied. Tribological performances of gear oil containing different additives were assessed using a four-ball friction and wear tester. The obtained tribological characteristics reveal that ADDP and MoDTC can significantly improve the antiwear and antifriction performance of low-viscosity gear oil. Moreover, compared with using MoDTC or ADDP alone, the average friction coefficient and wear scar diameter of ADDP combined with MoDTC further decreased by 2.41–19.15% and 5.00–18.19%, respectively. Analysis of the worn surface showed that the structural characteristics and physical synergistic lubricating actions of the ADDP with MoDTC additives during the friction process can contribute to the exceptional tribological properties of the hybrid additives.
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(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)
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Open AccessArticle
Comparing Bio-Ester and Mineral-Oil Emulsions on Tool Wear and Surface Integrity in Finish Turning a Ni-Based Superalloy
by
Paul Wood, Fathi Boud, Andrew Mantle, Wayne Carter, Syed Hossain, Urvashi Gunputh, Marzena Pawlik, Yiling Lu, José Díaz-Álvarez and María Henar Miguélez
Lubricants 2024, 12(5), 164; https://doi.org/10.3390/lubricants12050164 - 8 May 2024
Abstract
The paper compares the performance of two bio-ester and two mineral-oil emulsion metalworking fluids (MWFs) in finish turning an Inconel 718 alloy bar with a high hardness (HB 397 – 418). In this study, a coolant with a lean concentrate diluted at 6.5%
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The paper compares the performance of two bio-ester and two mineral-oil emulsion metalworking fluids (MWFs) in finish turning an Inconel 718 alloy bar with a high hardness (HB 397 – 418). In this study, a coolant with a lean concentrate diluted at 6.5% to create an emulsion with stabilised water hardness was used to prepare each MWF. The finish-turning method used a small tool nose radius (0.4 mm) and small depth of cut (0.25 mm) to turn down 52.2 mm diameter bars in multiple passes to reach a maximum tool flank wear of 200 µm. In each MWF turning test, the tool flank wear, cutting forces, and surface roughness were measured against cut time. Chips from each MWF turning test were also collected at the same cut time instances. The surface and subsurface integrity on a workpiece obtained from each MWF turning test were compared by using a new unworn tool. Overall, for the machining parameters studied, the findings suggest the bio-esters were capable of equivalent machining performance as the mineral-oil emulsions, apart from one bio-ester that displayed improved surface roughness. Common to all MWF turning tests was a change in the chip form at low flank wear, which is discussed. Further findings discussed include the sensitivity of the concentration of the MWF diluted in the emulsion and the effect of the workpiece hardness within the batch used, with useful recommendations to improve the finish-turning method for the assessment of MWFs.
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(This article belongs to the Special Issue Friction and Wear of Alloys)
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Open AccessArticle
Preparation and Tribological Performance of Multi-Layer van der Waals Heterostructure WS2/h-BN
by
Yunqi Fang, Yang Sun, Fengqin Shang, Jing Zhang, Jiayu Yao, Zihan Yan and Hangyan Shen
Lubricants 2024, 12(5), 163; https://doi.org/10.3390/lubricants12050163 - 7 May 2024
Abstract
Van der Waals heterostructures with incommensurate contact interfaces show excellent tribological performance, which provides solutions for the development of new solid lubricants. In this paper, a facile electrostatic layer-by-layer self-assembly (LBL) technique was proposed to prepare multi-layer van der Waals heterostructures tungsten disulfide/hexagonal
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Van der Waals heterostructures with incommensurate contact interfaces show excellent tribological performance, which provides solutions for the development of new solid lubricants. In this paper, a facile electrostatic layer-by-layer self-assembly (LBL) technique was proposed to prepare multi-layer van der Waals heterostructures tungsten disulfide/hexagonal boron nitride (vdWH WS2/h-BN). The h-BN and WS2 were modified with poly (diallyldimethylammonium chloride) (PDDA) and sodium dodecyl benzene sulfonate (SDBS) to obtain the positively charged PDDA@h-BN and the negatively charged SDBS@WS2, respectively. When the mass ratio of PDDA to h-BN and SDBS to WS2 were both 1:1 and the pH was 3, the zeta potential of PDDA@h-BN and SDBS@WS2 were 60.0 mV and −50.1 mV, respectively. Under the electrostatic interaction, the PDDA@h-BN and SDBS@WS2 attracted each other and stacked alternately along the (002) crystal plane forming the multi-layer (four-layer) vdWH WS2/h-BN. The addition of the multi-layer vdWH WS2/h-BN (1.0 wt%) to the base oil resulted in a significant reduction of 33.8% in the friction coefficient (0.104) and 16.8% in the wear rate (4.43 × 10−5 mm3/(N·m)). The excellent tribological property of the multi-layer vdWH WS2/h-BN arose from the lattice mismatch (26.0%), a 15-fold higher interlayer slip possibility, and the formation of transfer film at the contact interface. This study provided an easily accessible method for the multi-layer vdWH with excellent tribological properties.
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(This article belongs to the Special Issue Tribology of 2D Nanomaterials)
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Open AccessArticle
Elastic and Elastoplastic Contact Mechanics of Concentrated Coated Contacts
by
Patricia M. Johns-Rahnejat, Nader Dolatabadi and Homer Rahnejat
Lubricants 2024, 12(5), 162; https://doi.org/10.3390/lubricants12050162 - 7 May 2024
Abstract
Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam–follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been
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Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam–follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been predicted using classical Hertzian contact mechanics. However, the theory is only applicable when the contact between a pair of ellipsoidal solids of revolution may be considered as a rigid indenter penetrating a semi-infinite elastic half-space. Many coatings act as thin bonded elastic layers that undergo considerably higher pressures than those predicted by the classical theory. Furthermore, inelastic deformation of bonded solids can cause plastic flow, work-hardening, and elastoplastic behaviour. This paper presents a comprehensive, integrated contact mechanics analysis that includes induced sub-surface stresses in concentrated counterformal finite line contacts for all the aforementioned cases. Generated pressures and deformation are predicted for hard coated surfaces, for which there is a dearth of relevant analysis. The contact characteristics, which are of particular practical significance, of many hard, wear-resistant advanced coatings are also studied. The paper clearly demonstrates the importance of using efficient semi-analytical, detailed holistic contact mechanics rather than the classical idealised methods or empirical numerical ones such as FEA. The novel approach presented for the finite line contact of thin-layered bonded solids has not hitherto been reported in the open literature.
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(This article belongs to the Special Issue Selected Papers from the 8th Conference on Lubrication, Maintenance and Tribotechnology (LUBMAT))
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Open AccessArticle
Research on Sudden Unbalance Response of Rigid-Elastic-Oil Coupled Ball Bearings
by
Yan Li, Yongcun Cui and Sier Deng
Lubricants 2024, 12(5), 161; https://doi.org/10.3390/lubricants12050161 - 6 May 2024
Abstract
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(1) Background: To better understand the dynamic characteristics of a ball bearing with an elastic ring squeeze film damper (ERSFD) under sudden unbalance, a novel dynamic model was established by fully considering the coupling between the ERSFD, bearing outer ring (the journal), rotor,
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(1) Background: To better understand the dynamic characteristics of a ball bearing with an elastic ring squeeze film damper (ERSFD) under sudden unbalance, a novel dynamic model was established by fully considering the coupling between the ERSFD, bearing outer ring (the journal), rotor, and disc (loading bearing); (2) Methods: An improved secant method was developed to determine the initial eccentricity values of the bearing’s outer ring and the disc. The dynamic response of the outer ring under different speed ratios, damping ratios, and mass ratios was solved using the variable-step Runge–Kutta method; (3) Results: In comparison, a low-speed ratio, high damping ratio, and low mass ratio were more conducive to suppressing the bearing vibration. When the imbalance was suddenly introduced, the displacement amplitude of the eccentricity, transmissibility, amplitude–frequency response, and the radius of the outer ring center locus increased; (4) Conclusions: This work provides a reference for further studying the nonlinear vibration of rolling bearings coupled with an ERSFD.
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Influence of Nanoparticles in Lubricant on Sliding Contact of Atomic Rough Surfaces—A Molecular Dynamics Study
by
Xuan Zheng, Lihong Su and Guanyu Deng
Lubricants 2024, 12(5), 160; https://doi.org/10.3390/lubricants12050160 - 6 May 2024
Abstract
In this work, large-scale molecular dynamics (MD) computational simulations were performed in order to explore the sliding contact responses of rough surfaces with hexadecane lubricant and added nanoparticles. Simulation results revealed that the frictional state was dependent on the fluid, nanoparticle, and surface
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In this work, large-scale molecular dynamics (MD) computational simulations were performed in order to explore the sliding contact responses of rough surfaces with hexadecane lubricant and added nanoparticles. Simulation results revealed that the frictional state was dependent on the fluid, nanoparticle, and surface roughness. Three lubricating conditions were compared based on considerations of different amounts of fluid molecules. The lubricant was not able to separate the frictional contact surfaces if the quantity of lubricant molecules was insufficient. Particularly, there were no lubricating contributions when the amount of lubricant was too low, and the lubricant therefore only filled the pits in the surface roughness. Thus, the normal load was primarily supported by the contact between the two surfaces and nanoparticles, leading to significant surface morphology changes. In contrast, the frictional contact surfaces were able to be completely separated by the lubricant when there was a sufficient amount of fluid, and a very good lubricating effect could thus be achieved, resulting in a smaller friction force. In addition, the changes in surface morphology, contact area, and RMS are discussed in this paper, in order to reveal the dynamic frictional process.
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(This article belongs to the Special Issue Frictional and Wear Behaviors of Sliding Interfaces across Scales)
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