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Lubricants, Volume 12, Issue 6 (June 2024) – 47 articles

Cover Story (view full-size image): The study of wear particle generation, emission, and transport requires a systematic approach based on the application of various technologies and principles such as tribology, mechanics, heat and mass transfer, aerosol science, and materials chemistry. Our proposed correlation between the wear and emission of brake wear particles on 31 different brake assemblies was experimentally validated using a dynamometer test that measures brake wear particles. The correlation between brake wear, disc wear, and wear particle emissions per particle size was also investigated for elements derived from brake pad materials. This systematic investigation provides a promising approach to reducing wear when focusing on brake wear particle emissions as proposed in the Euro 7 regulation. View this paper
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18 pages, 1647 KiB  
Article
A Graph-Data-Based Monitoring Method of Bearing Lubrication UsingMulti-Sensor
by Xinzhuo Zhang, Xuhua Zhang, Linbo Zhu, Chuang Gao, Bo Ning and Yongsheng Zhu
Lubricants 2024, 12(6), 229; https://doi.org/10.3390/lubricants12060229 - 20 Jun 2024
Viewed by 231
Abstract
Super-precision bearing lubrication condition is essential for equipment’s overall performance. This paper investigates a monitoring method of bearing lubrication using multi-sensors based on graph data. An experiment was designed and carried out, establishing a dataset including vibration, temperature, and acoustic emission signals. Graph [...] Read more.
Super-precision bearing lubrication condition is essential for equipment’s overall performance. This paper investigates a monitoring method of bearing lubrication using multi-sensors based on graph data. An experiment was designed and carried out, establishing a dataset including vibration, temperature, and acoustic emission signals. Graph data were constructed based on a priori knowledge and a graph attention network was employed to conduct a study on monitoring bearing lubrication abnormalities and discuss the influence of a missing sensor on the monitoring. The results show that the designed experiments can effectively respond to the degradation process of bearing lubrication, and the graph data constructed based on a priori knowledge show a good effect in the anomaly monitoring process. In addition, the multi-sensor plays a significant role in monitoring bearing lubrication. This work will be highly beneficial for future monitoring methods of bearing lubrication status. Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
15 pages, 8783 KiB  
Article
A Phenomenological Model for Estimating the Wear of Horizontally Straight Slurry Discharge Pipes: A Case Study
by Xinggao Li, Yidong Guo, Xingchun Li, Hongzhi Liu, Yi Yang and Yingran Fang
Lubricants 2024, 12(6), 228; https://doi.org/10.3390/lubricants12060228 - 19 Jun 2024
Viewed by 240
Abstract
When a slurry TBM advances in pebble and rock strata, large rock particles are carried in pipelines out of a tunnel by moving slurry. To estimate the wear of horizontally straight slurry discharge pipes, a phenomenological model was proposed that was mainly based [...] Read more.
When a slurry TBM advances in pebble and rock strata, large rock particles are carried in pipelines out of a tunnel by moving slurry. To estimate the wear of horizontally straight slurry discharge pipes, a phenomenological model was proposed that was mainly based on knowledge gained by means of direct and indirect in situ observations. The proposed model applies an equation composed of three variables, namely, the wear rate (λ), the central angle (2α), and the excavated tunnel length (L), to estimate the wear distribution along a pipe’s internal surface. The results indicated that wear mainly occurred on the bottoms of pipes. In addition, linear relationships between the maximum pipe wear amount (δmax) and the excavated tunnel length (L) were found for specific pipes and specified types of ground. The observed wear rates of different pipes in different types of ground had varied constants. The wear rates were higher for pipes in rock ground than for those in a pebble layer. For horizontally straight pipes, the observed wear rates were 0.0045 mm/m in a pebble layer and 0.0212 mm/m in rock ground. Lastly, to improve the proposed model, more field monitoring will be necessary to determine the pipe wear rates in different types of ground in the future. Full article
(This article belongs to the Special Issue Modeling and Characterization of Wear)
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12 pages, 7547 KiB  
Article
Effect of CeO2 Content on Microstructure and Wear Resistance of Laser-Cladded Ni-Based Composite Coating
by Bingqing Zhang, Wenqing Shi, Yiming Lin, Longwei Jiang, Lijun Wang and Kuanfang He
Lubricants 2024, 12(6), 227; https://doi.org/10.3390/lubricants12060227 - 19 Jun 2024
Viewed by 392
Abstract
In order to improve the wear resistance of 45 steel, in this study, WC/Ni60 composite coatings with different CeO2 additions (0, 1, 2, and 3 wt%) were prepared on 45 steel by the laser cladding technique; the experimental analysis was carried out [...] Read more.
In order to improve the wear resistance of 45 steel, in this study, WC/Ni60 composite coatings with different CeO2 additions (0, 1, 2, and 3 wt%) were prepared on 45 steel by the laser cladding technique; the experimental analysis was carried out by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), a Vickers hardness tester, and a friction and wear tester. The results show that CeO2 had little effect on the phase composition of the coatings; however, with the increase in CeO2 content, the CeO2 played a key role in refining the grains of the coating, thus reducing the generation of cracks. In addition, CeO2 could effectively strengthen the internal structure of the coating and improve its microhardness and wear resistance. Particularly noteworthy is the observed reduction in both the friction coefficient and mass loss of the coating when the CeO2 addition reached 2%. This suggests an enhancement in the tribological performance of the coating at this concentration. Full article
(This article belongs to the Topic Advanced Manufacturing and Surface Technology)
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17 pages, 1378 KiB  
Article
Prediction of Lubrication Performances of Vegetable Oils by Genetic Functional Approximation Algorithm
by Jianfang Liu, Yaoyun Zhang, Sicheng Yang, Chenglingzi Yi, Ting Liu, Rongrong Zhang, Dan Jia, Shuai Peng and Qing Yang
Lubricants 2024, 12(6), 226; https://doi.org/10.3390/lubricants12060226 - 18 Jun 2024
Viewed by 237
Abstract
Abstract: Vegetable oils, which are considered potential lubricants, are composed of different types and proportions of fatty acids. Because of their diverse types and varying compositions, they exhibit different lubrication performances. The genetic function approximation algorithm was used to model the quantitative structure–property [...] Read more.
Abstract: Vegetable oils, which are considered potential lubricants, are composed of different types and proportions of fatty acids. Because of their diverse types and varying compositions, they exhibit different lubrication performances. The genetic function approximation algorithm was used to model the quantitative structure–property relationship between fatty acid structure and the wear scar diameter and friction coefficients measured by four-ball friction and wear tests. Based on the models with adjusted R2 greater than 0.9 and fatty acid compositions of vegetable oils, the wear scar diameter and friction coefficients of Xanthoceras sorbifolia bunge oil and Soybean oil as validation oil samples were predicted. The difference between the predicted and experimental values was small, indicating that the models could accurately predict the lubrication performances of vegetable oils. The lubrication performances of 14 kinds of vegetable oils were predicted by GFA-QSPR models, and the primary factors influencing their lubrication properties were studied by cluster analysis. The results show that the content of C18:1 has a positive effect on the lubrication performances of vegetable oils, while the content of C18:3 has a negative effect, and the length of the carbon chain of fatty acids significantly affects their lubrication properties. Full article
30 pages, 8719 KiB  
Review
Fundamental Mechanisms Underlying the Effectiveness of Nanoparticle Additives to Lubricants: 25 Examples Linking Nano- to Macroscale Friction
by Jacqueline Krim and Alex I. Smirnov
Lubricants 2024, 12(6), 225; https://doi.org/10.3390/lubricants12060225 - 18 Jun 2024
Viewed by 271
Abstract
Studies of the fundamental origins of friction have undergone rapid acceleration in recent years by providing valuable information on the nanoscale mechanisms responsible for friction at the macroscopic level. Significant efforts have been directed at developing composite nanofluids and nanoparticle additives to unlock [...] Read more.
Studies of the fundamental origins of friction have undergone rapid acceleration in recent years by providing valuable information on the nanoscale mechanisms responsible for friction at the macroscopic level. Significant efforts have been directed at developing composite nanofluids and nanoparticle additives to unlock new tribological properties unattainable by traditional lubricants. The studies are now further evolving by developing methods to achieve active control over nano- and/or mesoscale friction through the application of magnetic and electric fields external to the contact. These methods constitute an area of rapidly growing interest, and they also illuminate how the performance of conventional lubricants could be enhanced through the synergistic addition of nanoparticles (NPs). This mini review highlights 25 publications that collectively reveal significant progress, as well as important outstanding challenges, to the fundamental understanding of how the addition of NPs impacts lubricant performance. The first two topics focus on how Quartz Crystal Microbalance (QCM) nanotribological response to solid contacts can be linked to macroscale friction coefficients in the boundary lubrication regime and how QCM response upon immersion into a liquid is linked to macroscale lubricity in the mixed and hydrodynamic regimes. The third and fourth topics highlight the pivotal role of nanoparticle charge and surface treatments, while also indicating that the rolling of nanoparticles is ineffective and/or detrimental. The fifth topic focuses on applications that demonstrate the tuning of friction by varying nanoparticle electric charge and/or an external electric potential. The highlighted literature was selected to demonstrate a range of experimental and theoretical research, to provide direct connections between the nanoscale and macroscale tribological attributes, and to emphasize environmentally friendly lubricating materials such as water-based nanofluids. Full article
(This article belongs to the Special Issue Eco-Friendly Lubricating Additives)
20 pages, 6217 KiB  
Article
Research on Design and Optimization of Micro-Hole Aerostatic Bearing in Vacuum Environment
by Guozhen Fan, Youhua Li, Yuehua Li, Libin Zang, Ming Zhao, Zhanxin Li, Hechun Yu, Jialiang Xu, Hongfei Liang, Guoqing Zhang and Weijie Hou
Lubricants 2024, 12(6), 224; https://doi.org/10.3390/lubricants12060224 - 17 Jun 2024
Viewed by 269
Abstract
Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve [...] Read more.
Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve high fidelity of micro-low-gravity simulation tests, in this study, a design and parameter optimization method was proposed for micro-hole aerostatic bearings for a vacuum environment. Firstly, the theoretical analysis was conducted to investigate the impact of various bearing parameters and external conditions on the bearing load capacity and mass flow. Subsequently, a function model describing the variation in bearing load capacity and mass flow with bearing parameters was obtained utilizing a BP neural network. The parameters of aerostatic bearings in a vacuum environment were optimized using the non-dominated sorting genetic algorithm (NSGA-II) with the objectives of maximizing the load capacity and minimizing the mass flow. Subsequently, experimental tests were conducted on the optimized bearings in both atmospheric and vacuum conditions to evaluate their load capacity and mass flow. The results show that in a vacuum environment, the load capacity and mass flow of aerostatic bearings are increased compared to those in standard atmospheric conditions. Furthermore, it has been determined that the optimal solution for the bearing’s load capacity and mass flow occurs when the bearing has an orifice aperture of 0.1 mm, 36 holes, and an orifice distribution diameter of 38.83 mm. The corresponding load capacity and mass flow are 460.644 N and 11.816 L/min, respectively. The experimental and simulated errors are within 10%; thus, the accuracy of the simulation is verified. Full article
(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)
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14 pages, 5569 KiB  
Article
Thermal Stability and High-Temperature Super Low Friction of γ-Fe2O3@SiO2 Nanocomposite Coatings on Steel
by Qunfeng Zeng
Lubricants 2024, 12(6), 223; https://doi.org/10.3390/lubricants12060223 - 17 Jun 2024
Viewed by 220
Abstract
The thermal stability of the γ-Fe2O3@SiO2 nanocomposites and super low friction of the γ-Fe2O3@SiO2 nanocomposite coatings in ambient air at high temperature are investigated in this paper. X-ray diffraction, scanning electron microcopy, transmission [...] Read more.
The thermal stability of the γ-Fe2O3@SiO2 nanocomposites and super low friction of the γ-Fe2O3@SiO2 nanocomposite coatings in ambient air at high temperature are investigated in this paper. X-ray diffraction, scanning electron microcopy, transmission scanning electron microcopy, high-temperature tribometer, thermogravimetric analysis and differential scanning calorimetry were used to investigate the microstructure, surface morphology and high-temperature tribological properties of the γ-Fe2O3@SiO2 nanocomposite coatings, respectively. The results show that the γ-Fe2O3@SiO2 nanocomposite with the core–shell structure has excellent thermal stability because the SiO2 shell inhibits the phase transition of the γ-Fe2O3 phase to the α-Fe2O3 phase in the nanocomposites. The temperature of the phase transition in γ-Fe2O3 can be increased from 460 to 829 °C. The γ-Fe2O3@SiO2 nanocomposite coatings exhibit super low friction (0.05) at 500 °C. A high-temperature super low friction mechanism is attributed to γ-Fe2O3 and the tribochemical reactions during sliding. Full article
(This article belongs to the Collection Rising Stars in Tribological Research)
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16 pages, 3022 KiB  
Article
Wear Characterization of Cold-Sprayed HEA Coatings by Means of Active–Passive Thermography and Tribometer
by Raffaella Sesana, Luca Corsaro, Nazanin Sheibanian, Sedat Özbilen and Rocco Lupoi
Lubricants 2024, 12(6), 222; https://doi.org/10.3390/lubricants12060222 - 17 Jun 2024
Viewed by 244
Abstract
The aim of this work is to verify the applicability of thermography as a non-destructive technique to quantify the wear performance of several high-entropy alloy coatings. Thermal profiles obtained from passive and active thermography were analyzed and the results were correlated with the [...] Read more.
The aim of this work is to verify the applicability of thermography as a non-destructive technique to quantify the wear performance of several high-entropy alloy coatings. Thermal profiles obtained from passive and active thermography were analyzed and the results were correlated with the classical tribological approaches defined in standards. HEA coatings made of several chemical compositions (AlxCoCrCuFeNi and MnCoCrCuFeNi) and realized by using different cold spray temperatures (650 °C, 750 °C, and 850 °C) were tested in a pin-on-disk configuration, with a dedicated pin developed for the wear tests. Then, the wear performances of each sample were analyzed with the hardness and wear parameter results. The thermal profiles of passive and active thermography allowed a complete characterization of the wear resistance and performance analysis of the coatings analyzed. The results are also compared with those presented in the literature. Full article
(This article belongs to the Special Issue Wear-Resistant Coatings and Film Materials)
17 pages, 3036 KiB  
Article
Heat and Mass Transformation of Casson Hybrid Nanofluid (MoS2 + ZnO) Based on Engine Oil over a Stretched Wall with Chemical Reaction and Thermo-Diffusion Effect
by Shreedevi Madiwal and Neminath B. Naduvinamani
Lubricants 2024, 12(6), 221; https://doi.org/10.3390/lubricants12060221 - 16 Jun 2024
Viewed by 268
Abstract
This study investigates the potential of a hybrid nanofluid composed of MoS2 and ZnO nanoparticles dispersed in engine oil, aiming to enhance the properties of a lubricant’s chemical reaction with the Soret effect on a stretching sheet under the influence of an [...] Read more.
This study investigates the potential of a hybrid nanofluid composed of MoS2 and ZnO nanoparticles dispersed in engine oil, aiming to enhance the properties of a lubricant’s chemical reaction with the Soret effect on a stretching sheet under the influence of an applied magnetic field. With the growing demand for efficient lubrication systems in various industrial applications, including automotive engines, the development of novel nanofluid-based lubricants presents a promising avenue for improving engine performance and longevity. However, the synergistic effects of hybrid nanoparticles in engine oil remain relatively unexplored. The present research addresses this gap by examining the thermal conductivity, viscosity, and wear resistance of the hybrid nanofluid, shedding light on its potential as an advanced lubrication solution. Overall, the objectives of studying the hybrid nanolubricant MoS2 + ZnO with engine oil aim to advance the development of more efficient and durable lubrication solutions for automotive engines, contributing to improved reliability, fuel efficiency, and environmental sustainability. In the present study, the heat and mass transformation of a Casson hybrid nanofluid (MoS2 + ZnO) based on engine oil over a stretched wall with chemical reaction and thermo-diffusion effect is analyzed. The governing nonlinear partial differential equations are simplified as ordinary differential equations (ODEs) by utilizing the relevant similarity variables. The MATLAB Bvp4c technique is used to solve the obtained linear ODE equations. The results are presented through graphs and tables for various parameters, namely, M, Q, β, Pr, Ec, Sc, Sr, Kp, Kr, and ϕ2* (hybrid nanolubricant parameters) and various state variables. A comparative survey of all the graphs is presented for the nanofluid (MoS2/engine oil) and the hybrid nanofluid (MoS2 + ZnO/engine oil). The results reveal that the velocity profile diminished against the values of M, Kp, and β, and the temperature profile rises with Ec and Q, whereas Pr decreases. The concentration profile is incremented (decremented) with the value of Sr (Sc and Kr). A comparison of the nanofluid and hybrid nanofluid suggests that the velocity f′ (η) becomes slower with the augmentation of ϕ2* whereas the temperature increases when ϕ2* = 0.6 become slower. Full article
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11 pages, 2893 KiB  
Article
Driving Water through Sub-2-Nanometer Carbon Nanotubes
by Jian Liu and Wei Cao
Lubricants 2024, 12(6), 220; https://doi.org/10.3390/lubricants12060220 - 16 Jun 2024
Viewed by 250
Abstract
The ultra-low friction observed between water and carbon nanotubes has been extensively reported recently. In this study, we delve into the factors influencing the liquid–solid friction, including surface properties such as surface wettability and roughness of carbon nanotubes, as well as the driving [...] Read more.
The ultra-low friction observed between water and carbon nanotubes has been extensively reported recently. In this study, we delve into the factors influencing the liquid–solid friction, including surface properties such as surface wettability and roughness of carbon nanotubes, as well as the driving forces involving temperature gradient and pressure drop. Utilizing non-equilibrium molecular dynamics simulations on carbon nanotube models with a diameter of ~1 nm, we observe a significant increase in water flux within a specific range of wettability, independent of roughness. This range is expected to shift to smaller values with increased pressure drop and temperature gradient. Both the mechanical transport coefficient and the thermo-osmosis coefficient exhibit a negative correlation with wettability, and roughness further decreases these coefficients. Through this work, we provide insights into the effects of surface properties on fluid transport through nanopores, contributing valuable information for the optimization of high-performance membrane processes. Full article
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15 pages, 18401 KiB  
Article
Laser-Induced Graphene/h-BN Laminated Structure to Enhance the Self-Lubricating Property of Si3N4 Composite Ceramic
by Wei Li, Jinzhi Dong, Dalong Xu, Yifan Dong, Sikandar Iqbal, Jingwei Li, Ting Luo and Bingqiang Cao
Lubricants 2024, 12(6), 219; https://doi.org/10.3390/lubricants12060219 - 15 Jun 2024
Viewed by 331
Abstract
Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated [...] Read more.
Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated laser-induced reduced graphene oxide/hexagonal boron nitride (L-rGO/h-BN) was introduced as an additive into a silicon nitride matrix, then a silicon nitride/reduced graphene oxide/hexagonal boron nitride (Si3N4/L-rGO/h-BN) ceramic composite was successfully synthesized using Spark Plasma Sintering technology. This approach led to enhancements in both the mechanical and self-lubricating properties of silicon nitride ceramics. This is due to the good monodispersity of the incorporating graphene in the silicon nitride matrix. The flexural strength and fracture toughness of the ceramic composite experienced notable increases of 30.4% and 34.4%, respectively. Tribological experiments demonstrate a significant enhancement in the self-lubricating performance of ceramic composites upon the incorporation of L-rGO/h-BN. The coefficient of friction and wear spot diameter experienced reductions of 26.6% and 21%, respectively. These improvements extend the potential industrial applications of Si3N4/L-rGO/h-BN ceramic composites. Throughout the friction process, the evenly exposed rGO and h-BN demonstrate an effective self-lubricating effect on the wear surface. This research paves the way for a novel approach to fabricating high-performance self-lubricating structural ceramics. Full article
(This article belongs to the Special Issue 2D Materials in Tribology)
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26 pages, 7889 KiB  
Article
Emergence of Coated Piston Ring Scuffing Behavior on an Application-Oriented Tribological Model Test System
by Thomas Markut, Florian Summer, Michael Pusterhofer and Florian Grün
Lubricants 2024, 12(6), 218; https://doi.org/10.3390/lubricants12060218 - 14 Jun 2024
Viewed by 281
Abstract
A major problem in lubricated piston ring/cylinder liner contact sliding systems is the tribological failure mechanisms known as scuffing. In order to evaluate and better understand this damage phenomenon in these tribological systems, a tilted linear tribometer (TE77) for application-oriented reciprocating model tests [...] Read more.
A major problem in lubricated piston ring/cylinder liner contact sliding systems is the tribological failure mechanisms known as scuffing. In order to evaluate and better understand this damage phenomenon in these tribological systems, a tilted linear tribometer (TE77) for application-oriented reciprocating model tests was developed and validated with scuffed field engine parts. With precise oil lubrication, original engine parts, such as CKS-coated piston rings (chromium-based coating with included aluminum oxides), original liners and fully formulated lubrications, were tested under conditions similar to the most critical part of the internal combustion engines (ICEs), known as fired top dead center (FTDC). Various in situ measurements during the tests allowed for a detailed investigation of the damage processes (crack transformation) on the tribological components. For the coated piston ring, vertical cracks were attributed to residual stresses, while horizontal cracks resulted from shear stresses. The crack transformation and wear results from other studies were confirmed for the liner. The results from FIB (Focused Ion Beam) cuts, along with EDS and SEM analyses, revealed that Fe (deriving from material transfer) acts as a catalyst on the CKS layer for the tribopads and that zinc sulfides are not present everywhere. Full article
23 pages, 6785 KiB  
Article
Influence of Natural Gas Composition and Operating Conditions on the Steady-State Performance of Dry Gas Seals for Pipeline Compressors
by Fan Wu, Jinbo Jiang, Xudong Peng, Liming Teng, Xiangkai Meng and Jiyun Li
Lubricants 2024, 12(6), 217; https://doi.org/10.3390/lubricants12060217 - 14 Jun 2024
Viewed by 355
Abstract
A dry gas seal (DGS) is one of the key basic components of natural gas transmission pipeline compressors, and the sealing performance of a DGS dealing with complex multi-component pipeline natural gas is different from that dealing with conventional nitrogen medium. In this [...] Read more.
A dry gas seal (DGS) is one of the key basic components of natural gas transmission pipeline compressors, and the sealing performance of a DGS dealing with complex multi-component pipeline natural gas is different from that dealing with conventional nitrogen medium. In this paper, a spiral groove DGS of the compressor in natural gas transmission pipeline systems is taken as the research object. The thermal hydrodynamic lubrication model of the DGS is established considering turbulence effect and choking effect. Based on the finite difference method, the temperature and pressure distributions and the steady-state performance of the DGS are obtained by simulating. The influence of unitary impurity compositions such as light hydrocarbon, heavy hydrocarbon, non-hydrocarbon, and their contents on the steady-state performance of the DGS is analyzed. The steady-state performance of the DGS dealing with multi-impurity natural gas such as in the West-East gas transmission is investigated under different operating conditions. The results show that turbulence had a significant effect on the DGS, while choking had a weak effect. Increasing the content of light hydrocarbon such as C2H6 and heavy hydrocarbon such as C5H10 resulted in an increase in the gas film stiffness, leakage rate, and the temperature difference between the inlet and outlet, while non-hydrocarbon, such as N2, reduced the temperature difference between the inlet and outlet. The greatest impact on seal performance was produced by the heavy hydrocarbon, followed by the light hydrocarbon, and the least was produced by the non-hydrocarbon. Full article
(This article belongs to the Special Issue Gas Lubrication and Dry Gas Seal)
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16 pages, 16144 KiB  
Article
Effect of Substrate Preheating Temperature on the Microstructure and Properties of Laser Cladding Fe/TiC Composite Coating
by Wenqing Shi, Cai Cheng, Bingqing Zhang, Fenju An, Kaiyue Li, Zhaoting Xiong, Yuping Xie and Kuanfang He
Lubricants 2024, 12(6), 216; https://doi.org/10.3390/lubricants12060216 - 14 Jun 2024
Viewed by 357
Abstract
In this study, Fe/TiC composite coating was fabricated on the surface of 65Mn steel using substrate preheating combined with laser cladding technology. In order to characterize the impact of various preheating temperatures, four coatings were fabricated on a 65Mn substrate using laser cladding [...] Read more.
In this study, Fe/TiC composite coating was fabricated on the surface of 65Mn steel using substrate preheating combined with laser cladding technology. In order to characterize the impact of various preheating temperatures, four coatings were fabricated on a 65Mn substrate using laser cladding at different temperatures (ambient temperature, 100 °C, 200 °C, and 300 °C). The microstructures and properties of four Fe/TiC composite coatings were investigated using SEM, XRD, EDS, a Vickers microhardness meter, a wear tester, and an electrochemical workstation. The research results show that the cladding angle of the Fe/TiC composite coating initially increases and then decreases as the substrate preheating temperature rises. The solidification characteristics of the Fe/TiC composite coating structure are not obviously changed at substrate preheating temperatures ranging from room temperature to 300 °C. However, the elemental distribution within the cladding layer was significantly influenced by the preheating temperature. An increase in the preheating temperature led to a more uniform elemental distribution. Regarding the comprehensive properties, including hardness, wear characteristics, and corrosion resistance, the optimum substrate preheating temperature for the cladding layer was found to be 300 °C. Full article
(This article belongs to the Special Issue Wear and Corrosion Behaviour of Metals and Alloys)
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23 pages, 38250 KiB  
Article
Enhancing Wear Resistance and Mechanical Behaviors of AA7020 Alloys Using Hybrid Fe3O4-GNP Reinforcement
by Ufuk Taşcı, Taha Alper Yılmaz, Halil Karakoç and Şener Karabulut
Lubricants 2024, 12(6), 215; https://doi.org/10.3390/lubricants12060215 - 13 Jun 2024
Viewed by 283
Abstract
This study investigates the effect of graphene nanoplatelets (GNPs) and milling duration on the microstructure, mechanical properties, and wear resistance of the AA7020 alloy reinforced with Fe3O4 and GNP. The composites were prepared with a fixed 10 wt.% Fe3 [...] Read more.
This study investigates the effect of graphene nanoplatelets (GNPs) and milling duration on the microstructure, mechanical properties, and wear resistance of the AA7020 alloy reinforced with Fe3O4 and GNP. The composites were prepared with a fixed 10 wt.% Fe3O4 and varying GNP contents (0.5 and 1 wt.%) using high-energy ball milling for 4 and 8 h, followed by hot pressing. The aim was to enhance the performance of the AA7020 alloy for potential use in defense, automotive, aviation, and space applications, where superior mechanical properties and wear resistance are required. The results showed that the incorporation of 0.5 wt.% GNP and optimized milling significantly improved the composite’s performance. The AA7020 + 10 wt.% Fe3O4 + 0.5 wt.% GNP composite achieved the highest density (99.70%) when milled for 4 h. Its hardness increased with both the inclusion of GNP and extended milling duration, with the composite milled for 8 h exhibiting the highest hardness value (149 HBN). The tensile strength also improved, with the composite milled for 4 h showing a 28% increase (292 MPa) compared with the unreinforced alloy. Additionally, the friction coefficient decreased with GNP content and milling duration, with the composite milled for 8 h showing a 26% reduction. Wear resistance was notably enhanced, with the composite milled for 8 h exhibiting the lowest specific wear rate (7.86 × 10−7 mm3/Nm). Full article
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27 pages, 6366 KiB  
Review
Electric Potential Controlled Ionic Lubrication
by Zhongnan Wang, Hui Guo, Sudesh Singh, Vahid Adibnia, Hongjiang He, Fang Kang, Ye Yang, Chenxu Liu, Tianyi Han and Chenhui Zhang
Lubricants 2024, 12(6), 214; https://doi.org/10.3390/lubricants12060214 - 12 Jun 2024
Viewed by 300
Abstract
Electric potential controlled lubrication, also known as triboelectrochemistry or electrotunable tribology, is an emerging field to regulate the friction, wear, and lubrication performance under charge distribution on the solid–liquid interfaces through an applied electric potential, allowing to achieve superlubrication. Electric potential controlled lubrication [...] Read more.
Electric potential controlled lubrication, also known as triboelectrochemistry or electrotunable tribology, is an emerging field to regulate the friction, wear, and lubrication performance under charge distribution on the solid–liquid interfaces through an applied electric potential, allowing to achieve superlubrication. Electric potential controlled lubrication is of great significance for smart tunable lubrication, micro-electro-mechanical systems (MEMS), and key components in high-end mechanical equipment such as gears and bearings, etc. However, there needs to be a more theoretical understanding of the electric potential controlled lubrication between micro- and macro-scale conditions. For example, the synergistic contribution of the adsorption/desorption process and the electrochemical reaction process has not been well understood, and there exists a significant gap between the theoretical research and applications of electric potential controlled lubrication. Here, we provide an overview of this emerging field, from introducing its theoretical background to the advantages and characteristics of different experimental configurations (including universal mechanical tribometers, atomic force microscopes, and surface force apparatus/balances) for electric potential controlled lubrication. Next, we review the main experimental achievements in the performance and mechanisms of electrotunable lubrication, especially using ionic lubricants, including electrolyte solutions, ionic liquids, and surfactants. This review aims to survey the literature on electric potential controlled lubrication and provide insights into the design of superlubricants and intelligent lubrication systems for various applications. Full article
(This article belongs to the Special Issue Advanced Polymeric and Colloidal Lubricants)
17 pages, 8341 KiB  
Article
Synergistic Effect of B4C and Multi-Walled CNT on Enhancing the Tribological Performance of Aluminum A383 Hybrid Composites
by Priyaranjan Samal, Himanshu Raj, Arabinda Meher, B. Surekha, Pandu R. Vundavilli and Priyaranjan Sharma
Lubricants 2024, 12(6), 213; https://doi.org/10.3390/lubricants12060213 - 11 Jun 2024
Viewed by 415
Abstract
The requirement for high-performance and energy-saving materials motivated the researchers to develop novel composite materials. This investigation focuses on utilizing aluminum alloy (A383) as the matrix material to produce hybrid metal matrix composites (HMMCs) incorporating boron carbide (B4C) and multi-walled carbon [...] Read more.
The requirement for high-performance and energy-saving materials motivated the researchers to develop novel composite materials. This investigation focuses on utilizing aluminum alloy (A383) as the matrix material to produce hybrid metal matrix composites (HMMCs) incorporating boron carbide (B4C) and multi-walled carbon nanotube (MWCNT) through a cost-effective stir casting technique. The synthesis of HMMCs involved varying the weight fractions of B4C (2%, 4%, and 6%) and MWCNT (0.5%, 1%, and 1.5%). The metallographic study was carried out by field emission scanning electron microscopy (FESEM) mapped with EDS analysis. The results indicated a uniform dispersion and robust interfacial interaction between aluminum and the reinforced particles, significantly enhancing the mechanical properties. Micro-hardness and wear characteristics of the fabricated HMMCs were investigated using Vickers microhardness testing and the pin-on-disc tribometer setup. The disc is made of hardened chromium alloy EN 31 steel of hardness 62 HRC. The applied load was varied as 10N, 20N, 30N with a constant sliding speed of 1.5 m/s for different sliding distances. The micro-hardness value of composites reinforced with 1.5 wt% MWCNT and 6 wt% B4C improved by 61% compared to the base alloy. Additionally, the wear resistance of the composite material improved with increasing reinforcement content. Incorporating 1.5% CNT and 6% B4C as reinforcements results in the composite experiencing about a 40% reduction in wear loss compared to the unreinforced aluminum alloy matrix. Furthermore, the volumetric wear loss of the HMMCs was critically analyzed with respect to different applied loads and sliding distances. This research underscores the positive impact of varying the reinforcement content on the mechanical and wear properties of aluminum alloy-based hybrid metal matrix composites. Full article
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17 pages, 5948 KiB  
Article
Thermo-Fluid–Structural Coupled Analysis of a Mechanical Seal in Extended Loss of AC Power of a Reactor Coolant Pump
by Youngjun Park, Gwanghee Hong, Sanghyun Jun, Jeongmook Choi, Taegyu Kim, Minsoo Kang and Gunhee Jang
Lubricants 2024, 12(6), 212; https://doi.org/10.3390/lubricants12060212 - 10 Jun 2024
Viewed by 333
Abstract
We proposed a numerical method to investigate the thermo-fluid–structural coupled characteristics of a mechanical seal of a reactor coolant pump (RCP), especially during extended loss of AC power (ELAP) operation. We developed a finite element program for the general Reynolds equation, including the [...] Read more.
We proposed a numerical method to investigate the thermo-fluid–structural coupled characteristics of a mechanical seal of a reactor coolant pump (RCP), especially during extended loss of AC power (ELAP) operation. We developed a finite element program for the general Reynolds equation, including the turbulence effect to calculate the pressure, opening force, and leakage rate of fluid lubricant and the two-dimensional energy equation to calculate the temperature distribution of the fluid lubricant. We verified the accuracy of the developed program by comparing the simulated temperature distribution and leakage rate of this study with those of previous research. Heat conduction and elastic deformation due to pressure and temperature changes at the seal structure were analyzed using an ANSYS program. The results showed that temperature more significantly affected the elastic deformation of the seal structure near clearance than pressure both under normal and ELAP operating conditions. High temperature and pressure of the coolant under ELAP operating conditions deform the seal structure, resulting in a much smaller clearance of the fluid film than normal operating condition. However, even with a small clearance under ELAP operation, the leakage rate slightly increases due to the high internal pressure of the coolant. This research will contribute to the development of robust mechanical seals for RCPs by accurately predicting the characteristics of mechanical seals, especially when the RCP is operating under ELAP. Full article
(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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14 pages, 5811 KiB  
Article
Vibration Analysis of the Double Row Planetary Gear System for an Electromechanical Energy Conversion System
by Xinyong Li, Yajun Xu, Jing Liu and Wei Wu
Lubricants 2024, 12(6), 211; https://doi.org/10.3390/lubricants12060211 - 9 Jun 2024
Viewed by 325
Abstract
Electromechanical energy conversion systems (EECSs) are widely used in vehicles to combine the double-row planetary gear system (DRPGS) with high transmission efficiency and high-performance motors. The integrated structure of the ring gear and motor rotor have put forward higher demands for the vibration [...] Read more.
Electromechanical energy conversion systems (EECSs) are widely used in vehicles to combine the double-row planetary gear system (DRPGS) with high transmission efficiency and high-performance motors. The integrated structure of the ring gear and motor rotor have put forward higher demands for the vibration performance of the DRPGS. This paper establishes a multibody dynamic model of the DRPGS for an EECS. Based on the kinetic relationship between the gear pairs and bearing components, the dynamic equations of the DRPGS are derived. The DRPGS model is simulated under different operating conditions. The results are compared to reveal the relationships between the system vibration and the operating speed and load torque. The typical conditions are selected to study the effectiveness of the structural parameters in reducing the DRPGS vibrations. The structural parameters, including the bearing clearance, the ball numbers, the gear tooth modification amount, and length, are comprehensively discussed. Several suggestions for the low-vibration design of the DRPGS for the EECS are provided. Full article
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15 pages, 4151 KiB  
Article
Research on Temperature Rise Characteristics Prediction of Main Shaft Dual-Rotor Rolling Bearings in Aircraft Engines
by Kai Xu, Hao Hu, Nan Guo, Xiqiang Ma and Xiaoping Li
Lubricants 2024, 12(6), 210; https://doi.org/10.3390/lubricants12060210 - 9 Jun 2024
Viewed by 446
Abstract
Traditional aero-engine bearings rotate simultaneously with their inner and outer rings, which makes the temperature rise prediction model computationally large with low accuracy, and it cannot be accurately verified due to the means of testing. This paper presents a method for predicting the [...] Read more.
Traditional aero-engine bearings rotate simultaneously with their inner and outer rings, which makes the temperature rise prediction model computationally large with low accuracy, and it cannot be accurately verified due to the means of testing. This paper presents a method for predicting the temperature rise characteristics of aero-engine bearings under composite load conditions. Firstly, the local method is used to calculate the heat generation from heat sources such as bearing spin, lubricant drag, and the differential sliding of steel ball and collar, respectively, then finite element modelling and steady-state thermal analysis are carried out for aero-engine bearings under the simultaneous action of axial and radial external loads, a double-rotor test setup is designed and the predictive model is validated, and finally, the influences of rotational speed and load on the temperature rise characteristics of the bearings are investigated. The study shows that the aero-engine bearing prediction model proposed in this paper has high accuracy; with the increase in the rotational speed of the inner ring of the bearing, the temperatures of both the inner and outer rings of the bearing increase significantly; the temperatures of the inner and outer rings of the bearing increase with the increase in the axial load, and the effect of the radial load on the temperature of the bearing is not obvious. Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
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18 pages, 5305 KiB  
Article
Criteria for Evaluating the Tribological Effectiveness of 3D Roughness on Friction Surfaces
by Oleksandr Stelmakh, Hongyu Fu, Serhii Kolienov, Vasyl Kanevskii, Hao Zhang, Chenxing Hu and Valerii Grygoruk
Lubricants 2024, 12(6), 209; https://doi.org/10.3390/lubricants12060209 - 9 Jun 2024
Viewed by 342
Abstract
A new technique for finishing the surfaces of friction pairs has been proposed, which, in combination with the original test method, has shown a significant influence of the initial roughness configuration (surface texture) on friction and wear. Two types of finishing processing of [...] Read more.
A new technique for finishing the surfaces of friction pairs has been proposed, which, in combination with the original test method, has shown a significant influence of the initial roughness configuration (surface texture) on friction and wear. Two types of finishing processing of the shaft friction surfaces were compared, and it was found that the friction and wear coefficients differ by more than 2–5 and 2–4 times, respectively. Based on a new methodology for analyzing standard roughness parameters, the tribological efficiency criteria (in the sense of reducing friction and wear) are proposed for the initial state of the friction surface of a radial plane sliding bearing shaft relative to the friction direction, which is consistent with its frictional characteristics. Comparison of the laboratory test results with the surface tribological efficiency criteria showed that these criteria are very promising for controlling existing technologies and optimizing new technologies for friction surface finishing in various friction systems. Full article
(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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12 pages, 7583 KiB  
Article
Effect of Ultrasonic Rolling on Surface Properties of GCr15 Spherical Joint Bearing
by Hao Zhang, Xiuli Yang, Xiqiang Ma, Dongliang Jin and Jinyuan You
Lubricants 2024, 12(6), 208; https://doi.org/10.3390/lubricants12060208 - 8 Jun 2024
Viewed by 307
Abstract
Ultrasonic surface rolling process (USRP) has the potential to improve the surface mechanical properties of metal components with platelike or cylindrical macrostructure, but its effect on spherical surfaces remains to be studied in depth. In order to investigate the effect of USRP on [...] Read more.
Ultrasonic surface rolling process (USRP) has the potential to improve the surface mechanical properties of metal components with platelike or cylindrical macrostructure, but its effect on spherical surfaces remains to be studied in depth. In order to investigate the effect of USRP on the surface roughness, hardness and wear resistance of a spherical joint bearing made of GCr15 bearing steel, ultrasonic rolling strengthening was carried out on a spherical bearing surface under various conditions. The surface roughness and hardness variations of samples before and after strengthening were investigated. It was found that the USRP strengthening process can effectively enhance the surface properties of GCr15 spherical bearing materials, reduce the surface roughness by more than 45%, and increase the surface hardness by more than 10%. Friction and wear tests were carried out before and after ultrasonic rolling. The results show that the friction coefficient of the bearing surface can be reduced by 28%, and that the wear volume can be reduced by 29%. The variation in the friction coefficient correlated to the variance of wear volume as the reinforcement changes. Full article
(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)
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14 pages, 3210 KiB  
Article
A Novel Methodology for Simulating Skin Injury Risk on Synthetic Playing Surfaces
by Maxwell MacFarlane, Eric O’Donnell, Eric Harrison, Marc Douglas, Neale Lees and Peter Theobald
Lubricants 2024, 12(6), 207; https://doi.org/10.3390/lubricants12060207 - 6 Jun 2024
Viewed by 469
Abstract
Artificial turf provides a consistent and durable surface; however, it has historically been associated with a high skin injury risk, or a ‘friction burn’, when a player falls or slides. Second-generation surfaces feature a short carpet pile, whilst third generation (3G) carpet piles [...] Read more.
Artificial turf provides a consistent and durable surface; however, it has historically been associated with a high skin injury risk, or a ‘friction burn’, when a player falls or slides. Second-generation surfaces feature a short carpet pile, whilst third generation (3G) carpet piles are longer, enabling the integration of a performance infill. 3G surfaces provide sufficient energy absorption characteristics to be approved as Rugby Turf; however, such pitches can still cause skin injuries, despite being assessed using a friction-based test. Reducing skin injury risk motivates this study to develop a more sensitive testing methodology. A new test apparatus and impactor are proposed, achieving kinematics representative of an elite male rugby tackle. A commercially available skin simulant is employed to ensure the collection of repeatable and valid data. Photography and thresholding were used to assess surface abrasion and material transfer, whilst a thermal camera captured surface temperature change. Accelerometers quantified the surface resistance during the impact and sliding phases. These metrics were compiled into the Maxwell Tribo Index (MTI), providing a single measure of skin injury risk. The results demonstrated good repeatability and validity when four teams tested four different 3G surfaces. These results compared favourably to an expert panel’s ranked order. Full article
(This article belongs to the Special Issue Biomechanics and Tribology)
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32 pages, 26330 KiB  
Article
Brake Wear and Airborne Particle Mass Emissions from Passenger Car Brakes in Dynamometer Experiments Based on the Worldwide Harmonized Light-Duty Vehicle Test Procedure Brake Cycle
by Hiroyuki Hagino
Lubricants 2024, 12(6), 206; https://doi.org/10.3390/lubricants12060206 - 5 Jun 2024
Viewed by 334
Abstract
Brake wear particles, as the major component of non-exhaust particulate matter, are known to have different emissions, depending on the type of brake assembly and the specifications of the vehicle. In this study, brake wear and wear particle mass emissions were measured under [...] Read more.
Brake wear particles, as the major component of non-exhaust particulate matter, are known to have different emissions, depending on the type of brake assembly and the specifications of the vehicle. In this study, brake wear and wear particle mass emissions were measured under realistic vehicle driving and full friction braking conditions using current commercial genuine brake assemblies. Although there were no significant differences in either PM10 or PM2.5 emissions between the different cooling air flow rates, brake wear decreased and ultrafine particle (PM0.12) emissions increased with the increase in the cooling air flow rate. Particle mass measurements were collected on filter media, allowing chemical composition analysis to identify the source of brake wear particle mass emissions. The iron concentration in the brake wear particles indicated that the main contribution was derived from disc wear. Using a systematic approach that measured brake wear and wear particle emissions, this study was able to characterize correlations with elemental compositions in brake friction materials, adding to our understanding of the mechanical phenomena of brake wear and wear particle emissions. Full article
(This article belongs to the Special Issue Emission and Transport of Wear Particles)
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22 pages, 32696 KiB  
Review
Molecular Dynamics Simulation on Polymer Tribology: A Review
by Tianqiang Yin, Guoqing Wang, Zhiyuan Guo, Yiling Pan, Jingfu Song, Qingjun Ding and Gai Zhao
Lubricants 2024, 12(6), 205; https://doi.org/10.3390/lubricants12060205 - 4 Jun 2024
Viewed by 423
Abstract
A profound comprehension of friction and wear mechanisms is essential for the design and development of high-performance polymeric materials for tribological application. However, it is difficult to deeply investigate the polymer friction process in situ at the micro/mesoscopic scale by traditional research methods. [...] Read more.
A profound comprehension of friction and wear mechanisms is essential for the design and development of high-performance polymeric materials for tribological application. However, it is difficult to deeply investigate the polymer friction process in situ at the micro/mesoscopic scale by traditional research methods. In recent years, molecular dynamics (MD) simulation, as an emerging research method, has attracted more and more attention in the field of polymer tribology due to its ability to show the physicochemical evolution between the contact interfaces at the atomic scale. Herein, we review the applications of MD in recent studies of polymer tribology and their research focuses (e.g., tribological properties, distribution and conformation of polymer chains, interfacial interaction, frictional heat, and tribochemical reactions) across three perspectives: all-atom MD, reactive MD, and coarse-grained MD. Additionally, we summarize the current challenges encountered by MD simulation in polymer tribology research and present recommendations accordingly, aiming to provide several insights for researchers in related fields. Full article
(This article belongs to the Special Issue Advanced Polymeric and Colloidal Lubricants)
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20 pages, 15368 KiB  
Article
Research on the Milling Performance of Micro-Groove Ball End Mills for Titanium Alloys
by Shihong Zhang, Hu Shi, Baizhong Wang, Chunlu Ma and Qinghua Li
Lubricants 2024, 12(6), 204; https://doi.org/10.3390/lubricants12060204 - 4 Jun 2024
Viewed by 299
Abstract
Titanium alloys are widely used in various fields, but milling titanium alloy materials often leads to problems such as high milling forces, increased milling temperatures, and chip adhesion. Thus, the machinability of titanium alloys faces challenges. To improve the milling performance of titanium [...] Read more.
Titanium alloys are widely used in various fields, but milling titanium alloy materials often leads to problems such as high milling forces, increased milling temperatures, and chip adhesion. Thus, the machinability of titanium alloys faces challenges. To improve the milling performance of titanium alloy materials, this study analyzes the effective working area on the surface of the milling cutter through mathematical calculations. We design micro-grooves in this area to utilize their friction-reducing and wear-resisting properties to alleviate the aforementioned issues. The effective working area of the ball end milling cutter’s cutting edge is calculated based on the amount of milling and the installation position between the milling cutter and the workpiece. By observing the surface structure of seashells, micro-grooves are proposed and designed to be applied in the working area of the milling cutter surface. The impact of the micro-groove area on the milling cutter surface and spindle speed on milling performance is discussed based on milling simulation and experimental tests. Experimental results show that the cutting force, milling temperature, and chip resistance to adhesion produced by micro-groove milling cutters are superior to conventional milling cutters. Milling cutters with three micro-grooves perform best at different spindle speeds. This is because the presence of micro-grooves on the surface of the milling cutter improves the friction state, promoting a reduction in milling force, while the micro-grooves also serve as storage containers for chips, alleviating the phenomenon of chip softening and adhesion to the cutter. When conducting cutting tests with a milling cutter that has three micro-grooves, the milling force is reduced by 10% to 30%, the milling temperature drops by 10% to 20%, and the surface roughness decreases by 8% to 12%. Full article
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18 pages, 13638 KiB  
Article
Ice-versus-Steel Friction: An Advanced Numerical Approach for Competitive Winter Sports Applications
by Birthe Grzemba and Roman Pohrt
Lubricants 2024, 12(6), 203; https://doi.org/10.3390/lubricants12060203 - 4 Jun 2024
Viewed by 374
Abstract
Understanding and predicting the friction between a steel runner and an ice surface is paramount for many winter sports disciplines such as luge, bobsleigh, skeleton, and speed skating. A widely used numerical model for the analysis of the tribological system steel-on-ice is the [...] Read more.
Understanding and predicting the friction between a steel runner and an ice surface is paramount for many winter sports disciplines such as luge, bobsleigh, skeleton, and speed skating. A widely used numerical model for the analysis of the tribological system steel-on-ice is the Friction Algorithm using Skate Thermohydrodynamics (F.A.S.T.), which was originally introduced in 2007 and later extended. It aims to predict the resulting coefficient of friction (COF) from the two contributions of ice plowing and viscous drag. We explore the limitations of the existing F.A.S.T. model and extend the model to improve its applicability to winter sports disciplines. This includes generalizing the geometry of the runner as well as the curvature of the ice surface. The free rotational mechanical mounting of the runner to the moving sports equipment is introduced and implemented. We apply the new model to real-world geometries and kinematics of speed skating blades and bobsleigh runners to determine the resulting COF for a range of parameters, including geometry, temperature, load, and speed. The findings are compared to rule-of-thumb testimonies from athletes, previous numerical approaches, and published experimental results where applicable. While the general trends are reproduced, some discrepancy is found, which we ascribe to the specific assumptions around the formation of the liquid water layer derived from melted ice. Full article
(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)
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25 pages, 11409 KiB  
Article
Influence of Polymer Flow on Polypropylene Morphology, Micro-Mechanical, and Tribological Properties of Injected Part
by Martin Ovsik, Klara Fucikova, Lukas Manas and Michal Stanek
Lubricants 2024, 12(6), 202; https://doi.org/10.3390/lubricants12060202 - 4 Jun 2024
Viewed by 242
Abstract
This research investigates the micro-mechanical and tribological properties of injection-molded parts made from polypropylene. The tribological properties of polymers are a very interesting area of research. Understanding tribological processes is very crucial. Considering that the mechanical and tribological properties of injected parts are [...] Read more.
This research investigates the micro-mechanical and tribological properties of injection-molded parts made from polypropylene. The tribological properties of polymers are a very interesting area of research. Understanding tribological processes is very crucial. Considering that the mechanical and tribological properties of injected parts are not uniform at various points of the part, this research was conducted to explain the non-homogeneity of properties along the flow path. Non-homogeneity can be influenced by numerous factors, including distance from the gate, mold and melt temperature, injection pressure, crystalline structure, cooling rate, the surface of the mold, and others. The key factor from the micro-mechanical and tribological properties point of view is the polymer morphology (degree of crystallinity and size of the skin and core layers). The morphology is influenced by polymer flow and the injection molding process conditions. Gained results indicate that the indentation method was sufficiently sensitive to capture the changes in polypropylene morphology, which is a key parameter for the resulting micro-mechanical and tribological properties of the part. It was proven that the mechanical and tribological properties are not equal in varying regions of the part. Due to cooling and process parameters, the difference in the indentation modulus in individual measurement points was up to 55%, and the tribological properties, in particular the friction coefficient, showed a difference of up to 20%. The aforementioned results indicate the impact this finding signifies for injection molding technology in technical practice. Tribological properties are a key property of the part surface and, together with micro-mechanical properties, characterize the resistance of the surface to mechanical failure of the plastic part when used in engineering applications. A suitable choice of gate location, finishing method of the cavity surface, and process parameters can ensure the improvement of mechanical and tribological properties in stressed regions of the part. This will increase the stiffness and wear resistance of the surface. Full article
(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)
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15 pages, 2039 KiB  
Article
Tribological Behavior of Hydrocarbons in Rolling Contact
by Daniel Merk, Thomas Koenig, Janine Fritz and Joerg W. H. Franke
Lubricants 2024, 12(6), 201; https://doi.org/10.3390/lubricants12060201 - 3 Jun 2024
Viewed by 228
Abstract
In the analysis of tribological contacts, the focus is often on a singular question or result. However, this entails the potential risk that the overall picture and the relationships could be oversimplified or even that wrong conclusions could be drawn. In this article, [...] Read more.
In the analysis of tribological contacts, the focus is often on a singular question or result. However, this entails the potential risk that the overall picture and the relationships could be oversimplified or even that wrong conclusions could be drawn. In this article, a comprehensive consideration of test results including component and lubricant analyses is demonstrated by using the example of rolling contact. For this purpose, thrust cylindrical roller bearings of type 81212 with unadditized base oils were tested in the mixed-friction area. Our study shows that by using an adapted and innovative surface analysis, a deeper dive into the tribo-film is feasible even without highly sophisticated analytical equipment. The characterization of the layers was performed by the three less time-consuming spatially resolved analysis methods of µXRF, ATR FTIR microscopy and Raman spectroscopy adapted by Schaeffler. This represents a bridge between industry and research. The investigations show that especially undocumented and uncontrolled contamination of the test equipment could lead to surprising findings, which would result in the wrong conclusions. Simple substances, like hydrocarbons, are demanding test specimens. Full article
(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)
14 pages, 5096 KiB  
Article
Improved Tribological Performance of ta-C/MoSx Coatings Deposited on Laser Micro-Structured Steel Substrates in Both Vacuum and Air
by Stefan Makowski, Fabian Härtwig, Marcos Soldera, Mahmoud Ojeil, Lars Lorenz, Frank Kaulfuß and Andrés Fabián Lasagni
Lubricants 2024, 12(6), 200; https://doi.org/10.3390/lubricants12060200 - 1 Jun 2024
Viewed by 226
Abstract
Vacuum and air atmospheres impose very different requirements on tribological-loaded contacts, which usually require different surface materials. While hard tetrahedral amorphous carbon (ta-C) coatings provide good tribological properties in air, soft coatings such as molybdenum disulfide (MoS2) work well in a vacuum. Tribological [...] Read more.
Vacuum and air atmospheres impose very different requirements on tribological-loaded contacts, which usually require different surface materials. While hard tetrahedral amorphous carbon (ta-C) coatings provide good tribological properties in air, soft coatings such as molybdenum disulfide (MoS2) work well in a vacuum. Tribological performance in the respective other environment, however, is poor. In this work, the combination of laser microstructured (direct laser interference patterning) steel substrates and the deposition of ta-C and MoSx coatings with vacuum arc evaporation (LaserArc™) was studied, resulting in steel/DLIP, steel/DLIP/ta-C, steel/DLIP/MoSx, steel/DLIP/ta-C/MoSx, and steel/MoSx surface combinations. The tribological properties were studied using a ball-on-disk tribometer with a steel ball counter body in air and in a vacuum (p < 5 × 10−7 mbar). The type of the topmost coating governed their tribological properties in the respective atmosphere, and no general beneficial influence of the microstructure was found. However, steel/DLIP/ta-C/MoSx performed best in both conditions and endured the highest contact pressure, which is attributed to the mechanical support of the ta-C coating and MoSx reservoir in the remaining structure, as evidenced by Raman spectroscopy. The findings suggest that such combination allows for surfaces bearing a high load capacity that can be applied in both a vacuum and in air, for example, in multi-use space applications. Full article
(This article belongs to the Special Issue Tribology of Textured Surfaces)
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