Lubricants

9 pages, 7000 KiB

Open AccessArticle

Inhomogeneous Nanoscale Conductivity and Friction on Graphite Terraces Explored via Atomic Force Microscopy

by A. Kutay Ozyurt and Mehmet Z. Baykara

Lubricants 2024, 12(12), 462; https://doi.org/10.3390/lubricants12120462 - 21 Dec 2024

Viewed by 646

The interplay of conductivity and friction in layered materials such as graphite is an open area of investigation. Here, we measure local conductivity and friction on terraces of freshly cleaved highly oriented pyrolytic graphite via atomic force microscopy under ambient conditions. The graphite [...] Read more.

The interplay of conductivity and friction in layered materials such as graphite is an open area of investigation. Here, we measure local conductivity and friction on terraces of freshly cleaved highly oriented pyrolytic graphite via atomic force microscopy under ambient conditions. The graphite surface is found to exhibit a rich electrical landscape, with different terraces exhibiting different levels of conductivity. A peculiar dependency of conductivity on scan direction is observed on some terraces. The terraces that exhibit this dependency are also found to show enhanced friction values. A hypothesis based on tip asymmetry and the puckering effect is proposed to explain the findings. Our results highlight the non-triviality of the electrical and tribological properties of graphite on the nanoscale, as well as their interplay. Full article

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17 pages, 8947 KiB

Open AccessArticle

Exploring the Effect of Interface Contact States on Brush/Ring Current-Carrying Friction

by Chenshi Li, Xinze Zhao, Yaru Lv, Yang Li, Wanting Li and Wei Yang

Lubricants 2024, 12(12), 461; https://doi.org/10.3390/lubricants12120461 - 20 Dec 2024

Viewed by 544

Abstract

A carbon brush/collector ring set will have phenomena such as firing and ablation during operation, which is due to the existence of various abnormal contact modes of the brush/ring during operation, thus changing the carbon brush/collector ring interface state. To analyze the effects [...] Read more.

A carbon brush/collector ring set will have phenomena such as firing and ablation during operation, which is due to the existence of various abnormal contact modes of the brush/ring during operation, thus changing the carbon brush/collector ring interface state. To analyze the effects of different contact modes on the performance of the brush/ring, in this paper, we construct the contact modes of the air gap (loss of contact leads to the existence of a small gap between the two surfaces), direct contact (contact with abrasive particulate media), and surface porosity contact (contact when there is a large pit on the surface of the collector ring due to manufacturing quality defects and abnormal abrasion), and analyze the effects of the various states on the core parameters such as current conduction, ring surface damage, and carbon brush abrasion, which provide a basis for the active suppression of the damage. Full article

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39 pages, 22737 KiB

Open AccessArticle

Comparative Research in the Field of the Parametric Effect of Lubricant Cavitation Initiation and Development on Friction and Wear in Piston Ring and Cylinder Liner Assemblies

by Polychronis Dellis

Lubricants 2024, 12(12), 460; https://doi.org/10.3390/lubricants12120460 - 20 Dec 2024

Viewed by 651

Abstract

This research follows closely previous findings in flow characteristics and phenomena that take place in the piston ring and cylinder liner interface during motoring and firing engine operation, and also compares results between different optical engine set-ups. Cavitation visualisation in a simulating lubrication [...] Read more.

This research follows closely previous findings in flow characteristics and phenomena that take place in the piston ring and cylinder liner interface during motoring and firing engine operation, and also compares results between different optical engine set-ups. Cavitation visualisation in a simulating lubrication single-ring test rig and oil transport and cavitation visualisation in custom made cylinder assemblies of optical engines are the tools used to quantify the transport process under the piston ring and cylinder liner. Simplification of the interface is an essential technique that enhances the researcher’s confidence in results interpretation. Engine complexity and severe oil starvation are impeding the analysis of the experimental results. Visualisation experiments constitute an effective way to test various lubricant types and assess their overall performance characteristics, including their properties and cavitation behaviour. The repeatability of the visualisation method establishes the parametric study effects and offers valuable experimental results. As a further step towards the lubricant composition effect, a link between the lubricant formulation and the operating conditions could be established as the oil performance is assessed with a view to its transport behaviour. Image processing is used to quantify the impact of cavitation on piston ring lubrication in conjunction with varied operating and lubricant parameters. The characteristics of the lubricant and the working environment have an impact on these types of cavities. Viscosity, cavitation, oil film thickness (OFT), lubricant shear-thinning characteristics and friction are all linked. Full article

(This article belongs to the Special Issue Tackling Emissions from the Internal Combustion Engine: Advances in Piston/Bore Tribology)

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14 pages, 11976 KiB

Open AccessArticle

Tribological Characteristics of Biolubricant Obtained by Transesterification of Grape Seed Oil

by Thawan Fonseca Silva, Maria Marliete Fernandes de Melo Neta, Paulo Roberto Campos Flexa Ribeiro Filho, Francisco Murilo Tavares de Luna and Célio Loureiro Cavalcante, Jr.

Lubricants 2024, 12(12), 459; https://doi.org/10.3390/lubricants12120459 - 20 Dec 2024

Viewed by 594

Abstract

Research on and the development of bio-based lubricants as alternatives to mineral-based lubricants have been encouraged worldwide owing to environmental concerns and the possible depletion of oil reserves. This study explored the use of grape seed oil (GSO), a byproduct of wine production, [...] Read more.

Research on and the development of bio-based lubricants as alternatives to mineral-based lubricants have been encouraged worldwide owing to environmental concerns and the possible depletion of oil reserves. This study explored the use of grape seed oil (GSO), a byproduct of wine production, as a raw material for biolubricant synthesis. GSO contains a triglyceride molecule rich in unsaturated fatty acids, which is ideal for obtaining biolubricants. This study addresses the technical challenges of converting GSO into a lubricant by synthesizing methyl esters (FAME) via transesterification with 2-ethylhexanol to produce a biolubricant (BL) sample. The obtained products were characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy to confirm the conversion of the molecules. The density, kinematic viscosity, and viscosity index were determined using the parameters established by ASTM. The tribological characteristics of BL were evaluated using a four-ball tribometer configuration. BL exhibited physicochemical characteristics comparable with those of an ISO VG 10 lubricant, a friction coefficient (FC) 40.82% lower than that of a hydrotreated mineral oil sample, and a smoother wear surface. These results indicate that the polarity of the ester functional group was efficient in producing a protective film on metal surfaces. Full article

(This article belongs to the Special Issue Tribological Properties of Biolubricants)

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19 pages, 15012 KiB

Open AccessArticle

Testing the Effectiveness of Hybrid Milling and Surface Burnishing in Improving the Wear Resistance of Machine Parts Made of Structural Steel

by Joanna Grudzień, Daniel Grochała, Rafał Grzejda and Paweł Kochmański

Lubricants 2024, 12(12), 458; https://doi.org/10.3390/lubricants12120458 - 19 Dec 2024

Viewed by 521

Abstract

Due to the need to form a surface layer with specific operating properties, recent years have seen an increased interest in surface strengthening treatment, which aims to create a surface layer that improves the durability of parts. With a view to the economics [...] Read more.

Due to the need to form a surface layer with specific operating properties, recent years have seen an increased interest in surface strengthening treatment, which aims to create a surface layer that improves the durability of parts. With a view to the economics of the machining process, it is common to combine shaping milling, characterised by high volumetric efficiency, with finishing burnishing, during which significant forces are applied. In the literature, one of the important limitations of such technological operations is the value of residual stresses, excessive values of which can lead to the flaking and falling off of surface fragments. In the present study, the authors put forward the research hypothesis that, in addition to stresses, the geometry of the machining roughness is also important and may contribute to faster tribological wear than stresses. It has been shown that what is important in hybrid machining is not so much the height of the resulting irregularities and the effectiveness of their levelling by burnishing, but the geometry of the irregularities. After milling, surfaces with small, regular irregularities with smooth peaks and shallow valleys were found to be the best in tribological tests. Such roughness can be plastically levelled out during burnishing. On the basis of the experimental studies carried out, it was shown that a higher burnishing force does not always lead to higher wear resistance. Full article

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14 pages, 2179 KiB

Open AccessReview

Modification of the Surface Layer of Grey Cast Iron by Laser Heat Treatment

by Marta Paczkowska

Lubricants 2024, 12(12), 457; https://doi.org/10.3390/lubricants12120457 - 19 Dec 2024

Viewed by 536

Abstract

This paper presents possible modifications to the properties of grey cast iron by laser heat treatment. These modifications are analyzed especially with regard to wear properties as a result of graphite content, which is a well-known solid lubricant. Examples of applications of grey [...] Read more.

This paper presents possible modifications to the properties of grey cast iron by laser heat treatment. These modifications are analyzed especially with regard to wear properties as a result of graphite content, which is a well-known solid lubricant. Examples of applications of grey cast iron in cases where good wear resistance is required are presented. Laser hardening from the solid state, laser remelting, and laser alloying are characterized. In this study, changes in the surface layer caused by these treatments were analyzed (especially the influence on the microstructure—including graphite content—and wear properties). It was shown that all of these treatments enable the wear resistance of the surface layer to be enhanced, mostly due to the increase in the hardness and microstructure homogeneity. It was also proven that it is possible to retain the graphite phase (at least partially) in the modified surface layer, which is crucial in the case of friction wear resistance. In particular, laser hardening from the solid state does not eliminate graphite. Laser remelting and alloying cause the dilution of carbon from the graphite phase to the melted metal matrix, but, in the case of nodular cast iron, it is possible that not all of the valuable graphite in the surface layer is lost. Full article

(This article belongs to the Special Issue Cast Iron as a Tribological Material)

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12 pages, 4659 KiB

Open AccessArticle

Influence of Nb Reinforcement on the Wear Behavior of Spheroidal Graphite Cast Iron

by Rifat Yakut

Lubricants 2024, 12(12), 456; https://doi.org/10.3390/lubricants12120456 - 19 Dec 2024

Viewed by 454

Abstract

Spheroidal graphite cast iron, which is commonly used in a variety of applications, is subject to sliding wear and tear during operation. This damage can be prevented by increasing its strength value. In this study, 0%, 0.191%, and 0.304% niobium-reinforced spheroidal graphite cast [...] Read more.

Spheroidal graphite cast iron, which is commonly used in a variety of applications, is subject to sliding wear and tear during operation. This damage can be prevented by increasing its strength value. In this study, 0%, 0.191%, and 0.304% niobium-reinforced spheroidal graphite cast irons were produced. Specimens for hardness, compression, and abrasion tests were produced in accordance with the standards for the tests of the sand mold cast specimens. In order to compare the results of the tests, test specimens reinforced with 0.191% and 0.304% niobium, as well as 0% (unreinforced), were also produced. The hardness and compression strength of the niobium-reinforced and unreinforced specimens were tested in accordance with the standards. In addition, wear tests were carried out at 5 N, 10 N, and 15 N loads for 0%, 0.191%, and 0.304% niobium reinforcements, respectively. In the hardness tests, the highest measured value was observed in the sample reinforced with 0.304% niobium, with an average of 272 HB. Since Nb is an element with high hardness, the hardness values of the samples increased with the increase in Nb reinforcement. With an average value of 1411 MPa, the niobium-reinforced sample with 0.191% niobium reinforcement exhibited the highest compression strength. When analyzing the results of the compression tests, an increasing trend was observed with increasing reinforcement ratio, as was the case with the results of the hardness tests. In the wear tests, the changes in wear volume, wear rate, and friction coefficients were examined at loads of 5 N, 10 N, and 15 N. When the test specimens with the same reinforcement ratio were examined, it was found that the wear volume loss values increased with the increase in load. As the wear resistance increases with increasing hardness value, it becomes more difficult to detach the particles from the wear surfaces. The wear volume of the samples, therefore, decreases as the hardness value increases. At the end of the experimental study, a microstructural analysis of the surfaces subjected to sliding wear was carried out. It was observed that wear marks and pits had formed on the surfaces subjected to sliding wear. Full article

(This article belongs to the Special Issue Frictional Behavior and Wear Performance of Cast Irons, 2nd Edition)

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12 pages, 17499 KiB

Open AccessArticle

Comparative Study of the Friction Behavior of Functionalized Graphene Oxide Additives Under Electric Stimulations

by Linghao Zhang, Qiuyu Shi and Xiangyu Ge

Lubricants 2024, 12(12), 455; https://doi.org/10.3390/lubricants12120455 - 19 Dec 2024

Viewed by 498

Abstract

Electro-regulated friction is a widely adopted approach for reducing friction, with graphene oxide (GO) emerging as a promising lubricating additive due to its electro-responsive frictional behaviour. However, with the wide variety of functionalized GO additives available, each exhibiting distinct properties, it remains unclear [...] Read more.

Electro-regulated friction is a widely adopted approach for reducing friction, with graphene oxide (GO) emerging as a promising lubricating additive due to its electro-responsive frictional behaviour. However, with the wide variety of functionalized GO additives available, each exhibiting distinct properties, it remains unclear which type demonstrates the most effective electro-regulated friction-reducing performance, limiting their broader industrial application. In this study, the frictional behaviour of three functionalized GO additives under electric stimulation was investigated along with an analysis of the corresponding worn surfaces. The findings reveal the role of functional groups in determining the tribological performance of functionalized GO additives and the mechanism of electric stimulation. Notably, the formation of ester groups during the friction process of GO-OH enhances the adsorption of GO additives onto steel surfaces, resulting in superior friction-reducing properties. Under lubrication with GO-OH additives, negative electric stimulation promotes the generation of ester groups and transitions the lubrication regime to mixed lubrication, thereby contributing to friction reduction. This work provides new insights into the tribological performance of functionalized GO additives and the mechanisms underlying their electro-regulated behaviours, laying a foundation for the design of GO additives with superior lubrication performance for practical engineering applications. Full article

(This article belongs to the Special Issue Tribology of 2D Nanomaterials and Active Control of Friction Behavior)

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24 pages, 3564 KiB

Open AccessArticle

Optimizing Femtosecond Texturing Process Parameters Through Advanced Machine Learning Models in Tribological Applications

by Yassmin Seid Ahmed

Lubricants 2024, 12(12), 454; https://doi.org/10.3390/lubricants12120454 - 18 Dec 2024

Viewed by 743

Abstract

Surface texturing plays a vital role in enhancing tribological performance, reducing friction and wear, and improving durability in industrial applications. This study introduces an innovative approach by employing machine learning models—specifically, decision trees, support vector machines, and artificial neural networks—to predict optimal femtosecond [...] Read more.

Surface texturing plays a vital role in enhancing tribological performance, reducing friction and wear, and improving durability in industrial applications. This study introduces an innovative approach by employing machine learning models—specifically, decision trees, support vector machines, and artificial neural networks—to predict optimal femtosecond laser surface texturing parameters for tungsten carbide tested with WS₂ and TiCN coatings. Traditionally, the selection of laser parameters has relied heavily on a trial-and-error method, which is both time-consuming and inefficient. By integrating machine learning, this study advances beyond conventional methods to accurately predict the depth and quality of textured features. The ANN demonstrated superior predictive accuracy among the models tested, outperforming SVM and Decision Trees. This machine learning-based approach not only optimizes the surface texturing process by reducing experimental effort but also enhances the resultant surface performance, making it well-suited for applications in sectors such as automotive and oil and gas. Full article

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Graphical abstract

18 pages, 17988 KiB

Open AccessArticle

Sliding Wear Behavior of WP7V Tool Steel with Different Hardnesses Under Reciprocating Test Rig

by Rogério Breganon, Francisco Arieta and Giuseppe Pintaude

Lubricants 2024, 12(12), 453; https://doi.org/10.3390/lubricants12120453 - 18 Dec 2024

Viewed by 697

Abstract

This study involved the investigation of the mechanical and tribological behaviors of DIN 1.2344 and WP7V tool steels, quenched in a salt bath after austenitization at 1050 °C, followed by triple tempering for 2 h. The selection of tempering temperatures produced two hardness [...] Read more.

This study involved the investigation of the mechanical and tribological behaviors of DIN 1.2344 and WP7V tool steels, quenched in a salt bath after austenitization at 1050 °C, followed by triple tempering for 2 h. The selection of tempering temperatures produced two hardness levels under four metallurgical conditions, with the hardest level found only for WP7V steel (54 and 57 HRC). The mechanical properties were evaluated using Rockwell C, Vickers, and nanoindentation methods, along with unnotched impact tests, according to the SEP 1314 guidelines. Wear tests were conducted in a tribometer configured for a reciprocating setup, with a frequency of 5 Hz, a load of 25 N, and a time of 60 min, at room temperature and at 200 °C. As counterbodies, alumina balls of 5 mm in diameter were used. Wear tracks were evaluated through scanning electron microscopy, EDS, interferometry, and Raman spectroscopy. Friction and wear behaviors were affected by the variation in temperature for softer steels (DIN 1.2344 and WP7V of 48.5 HRC): the higher the temperature, the better the tribological performance. The harder steels were not sensitive to temperature testing. These effects depend on maintaining iron oxide (hematite) at the point of contact. The wear rates determined for the hardest material (57 HRC), considering its impact resistance, make it unsuitable for severe conditions such as hot stamping. Full article

(This article belongs to the Special Issue Recent Advances in Tribological Properties of Machine Tools)

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28 pages, 13746 KiB

Open AccessArticle

A Rolling Bearing Fault Diagnosis Method Combining MSSSA-VMD with the Parallel Network of GASF-CNN and BiLSTM

by Yongzhi Du, Yu Cao, Haochen Wang and Guohua Li

Lubricants 2024, 12(12), 452; https://doi.org/10.3390/lubricants12120452 - 18 Dec 2024

Viewed by 521

Abstract

Once the rolling bearing fails, it will threaten the normal operation of the whole rotating machinery. Therefore, it is very necessary to conduct research on rolling bearing fault diagnosis. This paper proposes a rolling bearing fault diagnosis method combining MSSSA-VMD (variational mode decomposition [...] Read more.

Once the rolling bearing fails, it will threaten the normal operation of the whole rotating machinery. Therefore, it is very necessary to conduct research on rolling bearing fault diagnosis. This paper proposes a rolling bearing fault diagnosis method combining MSSSA-VMD (variational mode decomposition optimized by the improved salp swarm algorithm based on mixed strategy) with the parallel network of GASF-CNN (convolutional neural network based on Gramian angular summation field) and bi-directional long short-term memory (BiLSTM) to solve the problem of poor diagnostic performance for the rolling bearing faults caused by the respective limitations of existing fault diagnosis methods based on signal processing and deep learning. Firstly, MSSSA-VMD is proposed to solve the problem where the decomposition effect of VMD is not ideal due to improper parameter selection. Then, MSSSA-VMD is employed to preprocess and extract characteristics. Finally, the extracted characteristics are input into the parallel network of GASF-CNN and BiLSTM for diagnosis. In one channel of the parallel network, GASF is used to convert the characteristic vectors into a two-dimensional image, which is then fed into CNN for spatial characteristic extraction. In the other channel of the parallel network, the characteristic vectors are directly input into BiLSTM for temporal characteristic extraction. Experimental results demonstrate that the proposed method has good performance in terms of fault diagnosis performance under constant operating conditions, generalization ability under variable operating conditions and noise resistance. Full article

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19 pages, 11868 KiB

Open AccessArticle

Tribological Investigation of Polymer Composite Dynamic Shaft Seals in Extraterrestrial Applications

by Ádám Kalácska, Alexander Coen, Jean Carlos Poletto, Patrick De Baets and Gábor Kalácska

Lubricants 2024, 12(12), 451; https://doi.org/10.3390/lubricants12120451 - 18 Dec 2024

Viewed by 593

Abstract

Polymer seals are utilized in various engineering applications to prevent leakage and contamination. The study investigates the wear and friction behavior of PTFE-based dynamic rotary seals, targeting their usage in space applications. Pin-on-disc dry sliding wear tests were performed with 0.5 MPa contact [...] Read more.

Polymer seals are utilized in various engineering applications to prevent leakage and contamination. The study investigates the wear and friction behavior of PTFE-based dynamic rotary seals, targeting their usage in space applications. Pin-on-disc dry sliding wear tests were performed with 0.5 MPa contact pressure and 0.2 m/s sliding velocity combining different lip seal (PTFE, PTFE+GF+MoS₂), packing (PTFE, PTFE+Aramid fiber+solid lubricant) and shaft materials (34CrNiMo6, PEEK) involving third-body lunar (LHS-1) and Martian regolith (MGS-1) simulants. To understand the different influences of extraterrestrial regolith simulants compared to commonly encountered abrasives on Earth, quartz sand was selected as a reference. Quartz soil resulted in lower wear rates but a similar coefficient of friction to other regoliths. In the case of lip seals, testing with LHS-1 on PEEK and testing with MGS-1 on steel resulted in the most severe wear. Post-mortem surface analysis revealed the effect of external abrasive particles on the wear process and the transfer layer formation. The surface analysis confirmed that both lunar and Martian regolith simulants resulted in significant embedded particles. Based on the wear performance results, the lip seals performed better, but installation with an external packing could further aid the tribosystem. Full article

(This article belongs to the Special Issue Modeling and Characterization of Wear)

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16 pages, 15131 KiB

Open AccessArticle

Friction and Wear Properties of AgCuNi Alloy/Au-Electroplated Layer Sliding Electrical Contact Material

by Hongjian Wu, Yanan Zhang, Hui Cao, Han Li, Qingjian Jia and Ming Ma

Lubricants 2024, 12(12), 450; https://doi.org/10.3390/lubricants12120450 - 16 Dec 2024

Viewed by 629

Abstract

Understanding the tribological properties of alloy-based sliding electrical contacts is crucial for both fundamental research and practical applications. Here, to explore the friction, wear, and contact resistance of a AgCuNi alloy/Au-electroplated layer during sliding, a ball-on-disk tribometer was coupled with a source meter. [...] Read more.

Understanding the tribological properties of alloy-based sliding electrical contacts is crucial for both fundamental research and practical applications. Here, to explore the friction, wear, and contact resistance of a AgCuNi alloy/Au-electroplated layer during sliding, a ball-on-disk tribometer was coupled with a source meter. The experiments were conducted under various conditions including a current ranging from 0 to 1.0 A, a normal load ranging from 0.5 to 3.0 N, and a sliding speed of 40 mm/s. The results indicate that the wear of the friction pair is aggravated by both the current and the increase in the normal load. When the current was 0.5 A, the wear loss reached its lowest point. However, as the current increased from 0.5 A to 1.0 A, there was an intensification in Ag transfer from the alloy ball to the Au-electroplated layer, resulting in an increase in wear loss. Both the normal load and current have significant effects on both friction coefficient and contact resistance. The variation in contact resistance over time follows a similar pattern to that of the friction coefficient over time. The formation of a transfer film plays a crucial role in determining contact resistance, wear resistance, and friction coefficient. The experiment demonstrates that optimizing the normal load and current can adjust both the contact resistance and friction coefficient, thereby prolonging service life and ensuring the stability of contacts. Full article

(This article belongs to the Special Issue Space Tribology)

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15 pages, 2430 KiB

Open AccessArticle

Impact of Brake Wear Particles on Eukaryotic Cell Viability and Associated Oxidative Stress Responses

by Lina Trečiokaitė, Yurii Tsybrii, Oleksii Nosko and Lina Ragelienė

Lubricants 2024, 12(12), 449; https://doi.org/10.3390/lubricants12120449 - 16 Dec 2024

Viewed by 674

Abstract

In this study, the cytotoxic effects of brake wear particles (≥250 nm ceramic/ceramic wear particles (CCWPs) and ≤100 nm ceramic/steel wear particles (CSWPs)) and 100 nm iron (III) oxide ultrafine particles (IOUFPs) on human lung carcinoma (A549) and Chinese hamster ovary (CHO) cells [...] Read more.

In this study, the cytotoxic effects of brake wear particles (≥250 nm ceramic/ceramic wear particles (CCWPs) and ≤100 nm ceramic/steel wear particles (CSWPs)) and 100 nm iron (III) oxide ultrafine particles (IOUFPs) on human lung carcinoma (A549) and Chinese hamster ovary (CHO) cells were investigated. Cell viability was determined using the MTT and Calcein AM methods. Oxidative stress was assessed by measuring reactive oxygen species (ROS), intracellular reduced glutathione (GSH), and malondialdehyde (MDA) concentrations under exposure to the above particles in the concentration range of 10–80 µg/mL. The initial assessments of CCWPs and CSWPs on the cell viability were performed after a 4-h exposure but later extended to 24 h to investigate the time-dependent of the cell viability and oxidative stress. MTT and Calcein AM assays indicated that the A549 cells are less susceptible to CCWPs and CSWPs than the CHO cells when exposed for both 4 h and 24 h. This study highlights that oxidative stress induced by CCWPs, CSWPs, and IOUFPs is cell-specific. While CCWPs did not affect glutathione (GSH) levels in the CHO cells, it significantly reduced GSH levels in A549 cells, with the exception of 80 µg/mL. Both CCWPs and CSWPs increased the lipid peroxidation in both cell types; however, the A549 cells demonstrated lower sensitivity to these treatments. Full article

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15 pages, 13259 KiB

Open AccessArticle

Carbon Nanotubes Decorated with Nickel or Copper as Anti-Wear and Extreme-Pressure Additives for Greases

by Magdalena Skrzypek, Łukasz Wojciechowski, Jarosław Kałużny, Sławomir Boncel, Adam A. Marek, Tomasz Runka, Marek Nowicki, Rafał Jędrysiak, Szymon Ruczka and Paulina Błaszkiewicz

Lubricants 2024, 12(12), 448; https://doi.org/10.3390/lubricants12120448 - 16 Dec 2024

Cited by 1 | Viewed by 803

Abstract

To increase the anti-wear (AW) and anti-scuffing possibilities of commercially available lithium grease, this paper proposed enriching the original composition with functionalised carbon nanotubes (CNTs) at a concentration of 0.1% (w/w). The CNTs were modified by decorating them with [...] Read more.

To increase the anti-wear (AW) and anti-scuffing possibilities of commercially available lithium grease, this paper proposed enriching the original composition with functionalised carbon nanotubes (CNTs) at a concentration of 0.1% (w/w). The CNTs were modified by decorating them with nanoparticles of two metals with established tribological potential: copper and nickel. The AW and extreme-pressure properties were determined using the customised ISO-20623 test on a four-ball apparatus. The AW properties were determined using the standardised parameter MWSD (mean wear scar diameter) and the anti-scuffing properties using the last non-seizing load. The greases enriched with nanoadditives showed better AW properties compared to the reference grease at higher loads (1–1.2 kN). Particularly favourable results were observed for grease with the addition of Cu-decorated CNTs, for which the MWSD values were more than 50% lower than the reference. Optical microscopy, SEM and TEM microscopy with EDS analysis, and Raman spectroscopy were used to identify the wear mechanisms and characterise the role of nanoadditives in the lubrication process. Full article

(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)

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17 pages, 29213 KiB

Open AccessArticle

Lubrication-Enhanced Mechanisms of Bentonite Grease Using 2D MoS₂ with Narrow Lateral Size and Thickness Distributions

by Shaoyicheng Zhu, Shuo Xiang, Xue Yang, Xin Yang, Hebin Bao, Hao He, Xin Du, Qinhui Zhang, Junjie Zhang, Kai Ma, Yi Cao, Yuehao Liu, Liangyi Peng, Zhitao Li and Yunhong Fan

Lubricants 2024, 12(12), 447; https://doi.org/10.3390/lubricants12120447 - 16 Dec 2024

Viewed by 634

Abstract

2D MoS₂ with narrow lateral size and thickness distributions was introduced to promote the anti-friction and anti-wear properties of the bentonite grease (BG) in a state of boundary lubrication. Optical microscopy (OM), and 3D optical profilers (3D OP), Raman spectrometry (Raman), scanning [...] Read more.

2D MoS₂ with narrow lateral size and thickness distributions was introduced to promote the anti-friction and anti-wear properties of the bentonite grease (BG) in a state of boundary lubrication. Optical microscopy (OM), and 3D optical profilers (3D OP), Raman spectrometry (Raman), scanning electron microscope, energy dispersion spectrum (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) were applied to characterize the wear surface of the GCr15 bearing steel/GCr15 bearing steel contact. It is found that the average friction coefficient (AFC), wear scar diameter (WSD), surface roughness and average wear scar depth of BG + 1.2 wt.% 2D MoS₂ were effectively reduced by approximately 22.15%, 23.14%, 55.15%, and 21.1%, respectilvely, compared with BG under the working condition of 392N, 75 °C, 1 h, and 1200 rpm. Raman, EDS and XPS results jointly demonstrated that a stable adsorbed film and a robust tribochemical film composed of Fe₂O₃, FeSO₄, Fe₂(SO₄)₃, FeSO₃, FeS, FeO and MoO₃, which further contributes to the enhancement of lubrication performance. Full article

(This article belongs to the Special Issue Wear-Resistant Coatings and Film Materials)

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15 pages, 1332 KiB

Open AccessArticle

Synthesis and Evaluation of Bio-Lubricants from Renewable Raw Materials

by Dimosthenis Filon, George Anastopoulos and Dimitrios Karonis

Lubricants 2024, 12(12), 446; https://doi.org/10.3390/lubricants12120446 - 16 Dec 2024

Viewed by 684

Abstract

The objective of this study was the evaluation of the production of base oils for lubricants of biological origin using vegetable and used frying oils as feedstock. The production method was based on a two-stage transesterification process. Initially, fatty acid methyl esters were [...] Read more.

The objective of this study was the evaluation of the production of base oils for lubricants of biological origin using vegetable and used frying oils as feedstock. The production method was based on a two-stage transesterification process. Initially, fatty acid methyl esters were obtained via methanolysis (first stage), and they were used as feedstock for bio-lubricants production by a second-stage transesterification process with the proper long-chain polyols. The produced oleochemical esters were evaluated based on their flow properties and their oxidation stability, as well as their capability of being renewable substitutes for conventional base oils, such as SN-150 and SN-500 mineral oils. The evaluation showed the remarkable physicochemical properties of these bio-lubricants, such as the viscosity, the viscosity index, and the pour, cloud and flash points, which, in combination with their high biodegradability and non-corrosive behavior, make these bio-lubricants ideal for use in special applications of non-recoverable lubrication or of high risk but low heat load and oxidative potential. This is because the oxidation stability of these bio-lubricants is not comparable to that shown by the used mineral oils and therefore they cannot totally substitute for these mineral oils. The reduced oxidation stability can be overcome by blending the bio-lubricants with mineral base oils at proper blending ratios. Full article

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19 pages, 13111 KiB

Open AccessArticle

Study on Performance of Compliant Foil Gas Film Seal Based on Different Texture Bottom Designs

by Zhenpeng He, Yuchen Zou, Jiaxin Si, Ziyi Lei, Ning Li and Yuhang Guo

Lubricants 2024, 12(12), 445; https://doi.org/10.3390/lubricants12120445 (registering DOI) - 12 Dec 2024

Viewed by 533

Abstract

To investigate how texture affects the sealing performance of compliant foil, a systematic analysis was conducted on the impact of various bottom shapes of rectangular textures on the gas film sealing performance of the foil. The Reynolds equation for the compliant foil seal [...] Read more.

To investigate how texture affects the sealing performance of compliant foil, a systematic analysis was conducted on the impact of various bottom shapes of rectangular textures on the gas film sealing performance of the foil. The Reynolds equation for the compliant foil seal is solved using the finite difference method., and the average gas film pressure, bearing capacity, leakage, and friction performance parameters of the compliant foil gas film seal are obtained. The results indicate that the convergent right triangle bottom shape texture provides the best sealing performance, with the average gas film pressure reaching 1.457. This is 0.10% higher than the non-textured case and 0.55% higher than the horizontal bottom shape texture. For the same texture area ratio, increasing the texture length in the axial direction improves the dynamic pressure effect. When the aspect ratio is 2/1, the gas film pressure reaches its maximum, and leakage is minimized. With an area ratio of 0.25 and a depth of 5 μm, the compliant foil gas film seal achieves the highest pressure and the lowest leakage. Compared with the average pressure without texture, the average pressure can be increased by 0.83%, and the leakage can be reduced by 6.61%. Full article

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology, 2nd Edition)

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25 pages, 4129 KiB

Open AccessArticle

Response Modeling and Optimization of Process Parameters in Turning Medium Carbon Steel Under Minimum Quantity Lubrication (MQL) with Vegetable Oil and Oil Blends

by Indranil Das and Prianka Binte Zaman

Lubricants 2024, 12(12), 444; https://doi.org/10.3390/lubricants12120444 - 12 Dec 2024

Viewed by 972

Abstract

Machining is an important aspect of manufacturing. The application of cutting fluid in the field of engineering manufacturing has a history of hundreds of years, and it plays a vital role in the processing efficiency and surface quality of parts. The use of [...] Read more.

Machining is an important aspect of manufacturing. The application of cutting fluid in the field of engineering manufacturing has a history of hundreds of years, and it plays a vital role in the processing efficiency and surface quality of parts. The use of vegetable oil in machining operations is receiving attention currently for sustainable alternatives to mineral-based cutting oil. If the vegetable oil is applied through the minimum quantity lubrication (MQL) technique, it becomes more cost effective, eco-friendly, and sustainable. This study aims to investigate the effects (cutting force and temperature) of coconut oil, a coconut–rice bran oil blend, and a coconut–olive oil blend, and compare them with VG 68 oil using MQL. A magnetic stirrer was employed for mixing oils (coconut–rice bran oil and coconut–olive oil), performed at 40 °C and 250 rpm. The response parameter values were evaluated at different combinations of speed (78, 113.5, and 149 mm/min), feed (0.1, 0.13, and 0.16 mm/rev), and depth of cut (0.5, 0.75, and 0.1 mm). The design of the experiment (DOE) was created using the value of input parameters using response surface methodology (RSM). Percentage (%) reduction was calculated to compare the reduction in cutting force and temperature by using coconut oil, a coconut–rice bran oil blend, and a coconut–olive oil blend concerning mineral oil. Empirical models were developed for cutting force and temperature by RSM for the four cutting environments. The ANOVA result shows that the model performed satisfactorily for both temperature and force analysis. RSM-based optimization was carried out and the optimal solution was found at the cutting speed of 80.15 m/min, feed rate of 0.10 mm/min, and 0.5 mm depth of cut for the coconut–olive oil blend. Also, the model performed better in the reduction in force than temperature. Full article

(This article belongs to the Special Issue Recent Advances in Green Lubricants)

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25 pages, 10155 KiB

Open AccessArticle

Effect of Surface Roughness on the Friction Moment in a Lubricated Deep Groove Ball Bearing

by Harsh Kumar, Vaibhav Gupta, Velamala Bharath, Mayank Tiwari, Surajit Kumar Paul, Lokesh Agrawal, Arendra Pal Singh and Ayush Jain

Lubricants 2024, 12(12), 443; https://doi.org/10.3390/lubricants12120443 - 11 Dec 2024

Viewed by 1010

Abstract

Deep groove ball bearings (DGBBs) are extensively utilized in industrial machinery, mechanical systems, and household appliances due to their simple design, low maintenance, and ability to operate at high speeds. A critical issue in the performance of these bearings is the power loss [...] Read more.

Deep groove ball bearings (DGBBs) are extensively utilized in industrial machinery, mechanical systems, and household appliances due to their simple design, low maintenance, and ability to operate at high speeds. A critical issue in the performance of these bearings is the power loss by internal friction torque, which adversely affects system efficiency, longevity, and reliability, particularly in demanding applications such as aviation and marine systems. The friction torque in DGBBs is influenced by factors such as load, speed, surface roughness, and lubricant viscosity, making the precise understanding of these elements essential for optimizing system efficiency. Despite its significance, the effect of surface roughness on friction torque in DGBBs remains underexplored. This paper presents an analytical model to evaluate the frictional moments resulting from interactions between the ball–race and ball–cage in lubricated, low-speed DGBBs. This model employs a mixed elastohydrodynamic lubrication approach to determine the friction coefficient at the contact interfaces. This study explores how surface roughness and speed affect both ball–race and ball–cage friction torque, offering a comprehensive analysis of their influence on overall frictional torque. Additionally, the effect of surface roughness on ball–cage contact forces is investigated, enhancing the understanding of its contribution to friction torque. These insights aim to improve DGBB design and operation, maximizing performance and energy efficiency. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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21 pages, 6166 KiB

Open AccessArticle

Sealing Performance Analysis of Lip Seal Ring for High-Speed Micro Bearing

by Hengdi Wang, Yulu Yue, Yongcun Cui, Xiaobiao Qiu and Chang Li

Lubricants 2024, 12(12), 442; https://doi.org/10.3390/lubricants12120442 - 11 Dec 2024

Viewed by 649

Abstract

This article focuses on the problem of sealing failure in high-speed micro bearings. Based on a thermal-stress coupled finite element model, the distribution of equivalent stress and contact pressure of the sealing ring and the influence of various factors on the sealing performance [...] Read more.

This article focuses on the problem of sealing failure in high-speed micro bearings. Based on a thermal-stress coupled finite element model, the distribution of equivalent stress and contact pressure of the sealing ring and the influence of various factors on the sealing performance are analyzed. Based on this, the Latin Hypercube sampling method, Kriging surrogate model and genetic algorithm are used to find the optimal combination of sealing performance. Finally, the accuracy of the model and method is verified through orthogonal experiments. Research has found that the maximum equivalent stress of the seal ring is 0.59234 MPa, and it increases first and then decreases with the increase in lip inclination angle, friction coefficient and radial interference amount, increases with the increase in lubricant temperature, and decreases with the increase in bearing rotation speed. The maximum contact pressure is 0.20433 MPa, and it decreases with the increase in the lip inclination angle, increases first and then decreases with the increase in the friction coefficient, and decreases first and then increases with the increase in the lubricant temperature, bearing rotation speed and radial interference amount. The most significant factor affecting the equivalent stress of the seal ring is the lubricant temperature, and the most significant factor affecting the contact stress is the interference fit amount. When the seal lip inclination angle is 43.99°, the friction coefficient is 0.01 mm, the lubricant temperature is 111.5 °C, the bearing rotation speed is 28,853 rpm and the radial interference amount is 0.04 mm, the sealing performance of the sealing ring is optimal. Full article

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23 pages, 5711 KiB

Open AccessArticle

Modeling and Dynamic Analysis of Double-Row Angular Contact Ball Bearing–Rotor–Disk System

by Haibiao Zhang, Zhen Li, Haijian Liu, Tao Liu and Qingshan Wang

Lubricants 2024, 12(12), 441; https://doi.org/10.3390/lubricants12120441 - 10 Dec 2024

Viewed by 645

Abstract

This article presents a general numerical method to establish a mathematical model of a bearing–rotor–disk system. This mathematical model consists of two double-row angular contact ball bearings (DRACBBs), a rotor and a rigid disk. The mathematical model of the DRACBB is built on [...] Read more.

This article presents a general numerical method to establish a mathematical model of a bearing–rotor–disk system. This mathematical model consists of two double-row angular contact ball bearings (DRACBBs), a rotor and a rigid disk. The mathematical model of the DRACBB is built on the basis of elastic Hertz contact by adopting the Newton Raphson iteration method, and three different structure forms are taken into account. The rotor is modeled by employing a finite element method in conjunction with Timoshenko beam theory, and the rigid disk is modeled by applying the lumped parameter method. The mathematical model of the bearing–rotor–disk system is constructed by the coupling of the bearing, rotor and disk, and the dynamic response of the bearing–rotor–disk system can be solved by employing the Newmark-β method. The validation of the above mathematical model is demonstrated by comparing the proposed results with the results from the existing literature and finite element software. The dynamic characteristics of the DRACBBs and the dynamic response of the bearing–rotor–disk system are investigated by parametric study. A dynamic characteristic analysis of the DRACBB is conducted to ensure the optimal structure form of the DRACBB under complex external loads, and it can provide a reference for the selection of the structural forms of DRACBBs. Full article

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17 pages, 45748 KiB

Open AccessFeature PaperArticle

Utilization of Magnetic Fraction Isolated from Steel Furnace Slag as a Mild Abrasive in Formulation of Cu-Free Friction Composites

by Vlastimil Matějka, Priyadarshini Jayashree, Kryštof Foniok, Jozef Vlček, Petra Matějková and Giovanni Straffelini

Lubricants 2024, 12(12), 440; https://doi.org/10.3390/lubricants12120440 - 10 Dec 2024

Viewed by 672

Abstract

Magnetic fraction isolated from steel furnace slag was tested as a component of Cu-free friction composites. The friction–wear performance and production of wear particles during their testing using a pin-on-disc tester against a cast iron disc were evaluated. To compare the effect of [...] Read more.

Magnetic fraction isolated from steel furnace slag was tested as a component of Cu-free friction composites. The friction–wear performance and production of wear particles during their testing using a pin-on-disc tester against a cast iron disc were evaluated. To compare the effect of the magnetic fraction on the parameters studied, the composite with alumina and the composite with original steel furnace slag were also prepared and tested. All composites showed a comparable friction coefficient. The composite with original steel furnace slag, and the composite with a magnetic fraction showed higher wear resistance compared to the composite containing alumina. The positive effect of the magnetic fraction on the extent of the emission of wear particles was observed and explained by the decreased aggressiveness of this composite to the cast iron disc. The influence of the phase composition of the steel furnace slag and the magnetic fraction on the friction film formation was also indicated, and its effect on the production of wear particles was proposed. Full article

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17 pages, 16276 KiB

Open AccessArticle

Effect of Counterbody Material on the Boundary Lubrication Behavior of Commercially Pure Titanium in a Motor Oil

by Yizhao Liu, Mohammed Al-Shan, Richard Bailey and Yong Sun

Lubricants 2024, 12(12), 439; https://doi.org/10.3390/lubricants12120439 - 10 Dec 2024

Viewed by 860

Abstract

Titanium possesses many useful properties and is a technologically important material in engineering. However, lubrication of titanium has long been a problem that has prevented titanium from being more widely used. This is due to its poor tribological properties, deriving from its high [...] Read more.

Titanium possesses many useful properties and is a technologically important material in engineering. However, lubrication of titanium has long been a problem that has prevented titanium from being more widely used. This is due to its poor tribological properties, deriving from its high tendency towards adhesive wear, material transfer, and abrasive wear. Lubrication is a system engineering which involves material combinations, material surfaces, lubricants, and operating conditions as a system. In this work, the boundary lubrication behavior of commercially pure titanium (CP-Ti) sliding against various counterbody materials in a motor oil (0W-30) was investigated under ball-on-plate reciprocating sliding conditions. The counterbody materials (balls) include CP-Ti, ceramic (Al₂O₃), steel (AISI 52100), and polymer (nylon). The results show that depending on material combination, the lubricating behavior can be divided into three categories, i.e., (1) lubrication failure (Ti-Ti), (2) improved lubrication but with friction instability (Ti-Al₂O₃), and (3) effective lubrication (Ti–steel and Ti–nylon). Lubrication failure of the Ti-Ti pair leads to high and unstable friction and severe wear from both the plate and ball, while friction instability of the Ti-Al₂O₃ pair leads to friction spikes and high wear rates. Effective lubrication of the Ti–steel pair results in low and smooth friction and much-reduced wear rates of the Ti plate by nearly 10,000 times. However, there is a load-dependence of the lubrication effectiveness of the Ti–steel pair. Although the Ti–nylon pair is effectively lubricated in terms of much-reduced friction, the nylon ball suffers from severe wear. The friction and wear mechanisms of the various sliding pairs are discussed in this paper. Full article

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11 pages, 3788 KiB

Open AccessArticle

Ceramic–Ceramic Hip Implants: Investigation of Various Factors Associated with Squeaking

by Stefan Schroeder, Luisa Gaedeke, Mustafa Hariri, Therese Bormann, Maurice Weiss, Jan Philippe Kretzer and Maximilian Uhler

Lubricants 2024, 12(12), 438; https://doi.org/10.3390/lubricants12120438 - 9 Dec 2024

Viewed by 632

Abstract

Despite the low wear rate of ceramic–ceramic hip implants, hard-on-soft bearings remain the most commonly used bearings in North America and Western Europe. A major concern with ceramic–ceramic hip implants is the occurrence of squeaking phenomena, which are still not fully understood. Various [...] Read more.

Despite the low wear rate of ceramic–ceramic hip implants, hard-on-soft bearings remain the most commonly used bearings in North America and Western Europe. A major concern with ceramic–ceramic hip implants is the occurrence of squeaking phenomena, which are still not fully understood. Various factors are mentioned in the literature, but currently, studies mostly focus on only one specific parameter. The goal of this study was to systematically analyze four different factors (cup orientation, protein concentration of the test fluid, contact pressure and head roughness) that may influence the squeaking behavior of this bearing type. An in vitro simulation according to ISO 14242-1 was performed using an AMTI Vivo simulator, and acoustic signals were recorded. No squeaking occurred for any of the four parameters when bovine serum or water was used as the test fluid. Squeaking was observed only under dry conditions with the ceramic–ceramic bearing. Under dry conditions, the maximum resulting torque increased steadily, and squeaking occurred after approximately 300 cycles at a resulting torque of more than 22 Nm. Thus, the resulting torque might be one factor leading to squeaking and should be kept low to reduce the risk of squeaking. Full article

(This article belongs to the Special Issue Biomechanics and Tribology)

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24 pages, 6499 KiB

Open AccessArticle

Sliding Contact Fatigue Damage of Metallic Implants in a Simulated Body Fluid Environment

by Mihir V. Patel, Edward Cudjoe and Jae Joong Ryu

Lubricants 2024, 12(12), 437; https://doi.org/10.3390/lubricants12120437 - 8 Dec 2024

Viewed by 760

Abstract

At the modular interface of the joint implants, repeated contact stresses in a corrosive synovial environment cause surface degradation that worsens over time. The lubricating mechanisms at the joints are altered by the deteriorated synovial fluid by the wear debris and corrosion products. [...] Read more.

At the modular interface of the joint implants, repeated contact stresses in a corrosive synovial environment cause surface degradation that worsens over time. The lubricating mechanisms at the joints are altered by the deteriorated synovial fluid by the wear debris and corrosion products. As a result, the joint implants’ unsatisfactory performance will be exacerbated by the synergistic combination of wear and corrosion. In this work, reciprocal sliding contact tests in simulated synovial fluid were conducted on the two main metallic implant materials, CoCrMo and Ti6Al4V. The mechanical and electrochemical reactions were described by monitoring the open-circuit potential (OCP) and coefficient of friction (COF). The electrochemical damage that altered the oxidation chemistry on both surfaces was illustrated by the potentiostatic test findings. The surface damage process of CoCrMo under all contact loads presented unstable chemomechanical responses. On the other hand, the Ti6Al4V results revealed a moderate decrease in fretting current and stable changes in the coefficient of friction. Consequently, the experimental investigation determined that, when mechanical loadings and electrochemical stimulus are combined, Ti6Al4V’s biocompatibility would be superior to CoCrMo’s. Full article

(This article belongs to the Special Issue Biomechanics and Tribology)

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17 pages, 5396 KiB

Open AccessArticle

Fumed Silica in Coconut Oil Based Nanofluids for Cooling and Lubrication in Drilling Applications

by Jesús J. Jiménez-Galea and Ana Isabel Gómez-Merino

Lubricants 2024, 12(12), 436; https://doi.org/10.3390/lubricants12120436 - 8 Dec 2024

Viewed by 659

Abstract

Virgin coconut oil (VCO) is an edible vegetable oil that is eco-friendly, biodegradable, and sustainable, with high thermal and chemical stability as a phase change material (PCM). In this work, VCO filled with fumed silica A200 nanoparticles was tested as a cutting fluid [...] Read more.

Virgin coconut oil (VCO) is an edible vegetable oil that is eco-friendly, biodegradable, and sustainable, with high thermal and chemical stability as a phase change material (PCM). In this work, VCO filled with fumed silica A200 nanoparticles was tested as a cutting fluid in drilling processes. Silica concentrations ranging from 1 to 4 vol% were analyzed. Thermal properties were evaluated by differential scanning calorimetry (DSC) and thermal conductivity measurements at different temperatures and concentrations. Thermal conductivity showed an enhancement with the addition of silica powder and reduced with increasing temperature. Based on thermal and flow properties, VCO-3A200 was found to be the optimal concentration. The thermal images of this nanofluid taken after 60 s of drilling exhibited a reduction of 12 °C with respect to the dry process. The friction coefficient versus shear rate was also measured. With 8% VCO, a reduction in the friction coefficient of 8% compared to the dry test was achieved. The addition of 3 vol% of silica to the base oil reduced the friction coefficient by 16% compared to the dry test. The use of fumed silica dispersed in VCO has proven to be a sustainable, recyclable, and environmentally friendly refrigerant and lubricant cutting fluid. Full article

(This article belongs to the Special Issue Advances in Sustainable Cooling/Lubrication Techniques for Improving the Tribological Characteristics and Machining Performance)

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15 pages, 97256 KiB

Open AccessArticle

In Situ Operando Indicator of Dry Friction Squeal

by Maël Thévenot, Jean-François Brunel, Florent Brunel, Maxence Bigerelle, Merten Stender, Norbert Hoffmann and Philippe Dufrénoy

Lubricants 2024, 12(12), 435; https://doi.org/10.3390/lubricants12120435 - 8 Dec 2024

Viewed by 696

Abstract

In various applications, dry friction could induce vibrations. A well-known example is frictional braking systems in ground transportation vehicles involving a sliding contact between a rotating and a stationary part. In such scenarios, the emission of high-intensity noise, commonly known as squeal, can [...] Read more.

In various applications, dry friction could induce vibrations. A well-known example is frictional braking systems in ground transportation vehicles involving a sliding contact between a rotating and a stationary part. In such scenarios, the emission of high-intensity noise, commonly known as squeal, can present human health risks based on the noise’s intensity, frequency, and occurrences. Despite the importance of squeal in the context of advancing urbanization, the parameters determining its occurrence remain uncertain due to the complexity of the involved phenomena. This study aims to identify a relevant operando indicator for predicting squeal occurrences. To this end, a pin-on-disc test rig was developed to replicate various contact conditions found in road profiles and investigate resulting squealing. Each test involves a multimodal instrumentation, complemented by surface observations. It is illustrated that the enhanced thermal indicator identified is relevant because it is sensitive to the thermomechanical and tribological phenomena involved in squealing. Full article

(This article belongs to the Special Issue Tribology in Vehicles)

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10 pages, 2799 KiB

Open AccessArticle

The Temperature Dependence of Divergence Pressure

by Scott Bair

Lubricants 2024, 12(12), 434; https://doi.org/10.3390/lubricants12120434 - 6 Dec 2024

Viewed by 592

Abstract

The so-called controversy in elastohydrodynamic lubrication (EHL) regarding the nature of the shear dependence of viscosity, Eyring versus Carreau, is truly a controversy regarding the pressure and temperature dependence of low-shear viscosity. Roelands removed data that contradicted his claims of accuracy for his [...] Read more.

The so-called controversy in elastohydrodynamic lubrication (EHL) regarding the nature of the shear dependence of viscosity, Eyring versus Carreau, is truly a controversy regarding the pressure and temperature dependence of low-shear viscosity. Roelands removed data that contradicted his claims of accuracy for his correlation. The Roelands hoax became acceptable in EHL because ignoring the universal previtreous piezoviscous response made the traction calculated with the Eyring assumption appear to be reasonable. Traction and minimum film thickness calculations sometimes require the description of viscosity at pressures up to the glass transition pressure. There have been few measurements of viscosity at pressures up to glass pressure. Therefore, a need exists for a piezoviscous model that extrapolates accurately, and the Hybrid model fills that need. Here, an improved relation for the temperature dependence of divergence pressure is offered and extrapolation is demonstrated for a polyalphaolefin and propylene carbonate. A linear dependence of divergence pressure with temperature is more useful than previous versions. An improvement in the capability of high-pressure viscometry is suggested based upon the fractional Stokes Einstein Debye relation and the relatively simple measurements of DC conductivity. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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14 pages, 8524 KiB

Open AccessArticle

Levitation Performance of Radial Film Riding Seals for Gas Turbine Engines

by Syed Muntazir Mehdi, Young Cheol Kim and Eojin Kim

Lubricants 2024, 12(12), 433; https://doi.org/10.3390/lubricants12120433 - 5 Dec 2024

Viewed by 671

Abstract

Turbomachinery in gas turbines uses seals to control the leakage between regions of high and low pressure, consequently enhancing engine efficiency and performance. A film riding seal hybridizes the advantages of contact and non-contact seals, i.e., low leakage and low friction and wear. [...] Read more.

Turbomachinery in gas turbines uses seals to control the leakage between regions of high and low pressure, consequently enhancing engine efficiency and performance. A film riding seal hybridizes the advantages of contact and non-contact seals, i.e., low leakage and low friction and wear. The literature focuses on the leakage performance of these seals; however, one of their fundamental characteristics, i.e., the gap between the rotor and seal surface, is scarcely presented. The seal pad levitates due to the deflection of the springs at its back under the influence of hydrodynamic forces. This study develops a test rig to measure the levitation of film riding seals. A high-speed motor rotates the rotor and gap sensors measure the levitation of the seal pads. Measurements are also compared with the predictions from a Reynolds equation-based theoretical model. Tests performed for the increasing rotor speed indicated that, initially, until a certain rotor speed, the pads adjust their position, then rub against the rotor until another rotor speed is reached, before finally starting levitating with further increased rotor speeds. Moreover, both the measured and predicted results show that pads levitated the most when located 90° clockwise from the positive horizontal axis (bottom of seal housing) compared to other circumferential positions. Full article

(This article belongs to the Special Issue Thermal Hydrodynamic Lubrication)

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