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Lubricants, Volume 10, Issue 4 (April 2022) – 26 articles

Cover Story (view full-size image): The structure and flow of lubricating greases depend on the base oil and the type and concentration of the dissolved thickener. In this study, the linear viscoelastic properties of greases are characterized combining oscillatory shear and squeeze flow. Multiple particle tracking (MPT) microrheology and scanning electron microscopy (SEM) provide further insights into their local viscoelasticity and structure on a submicron length scale. The filamentous lithium thickeners created stronger networks than the roundish aggregates that are formed by magnesium and zinc stearate. Network mesh sizes ranging from 100 to 300 nm were consistently determined through SEM and MPT experiments. MPT also disclosed the existence of gel-like precursors far below the thickener concentrations at which a characteristic grease texture forms. View this paper
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14 pages, 3483 KiB  
Article
On the Stiffness and Damping Characteristics of Line Contacts under Transient Elastohydrodynamic Lubrication
by Congcong Fang, Anyuan Zhu, Wei Zhou, Yongdong Peng and Xianghui Meng
Lubricants 2022, 10(4), 73; https://doi.org/10.3390/lubricants10040073 - 18 Apr 2022
Cited by 8 | Viewed by 3299
Abstract
The elastohydrodynamic lubrication (EHL) oil film between contact interfaces acts as a spring or damper to reduce wear and vibration for frictional pairs. To analyze the dynamic behaviors of friction pairs in mechanical systems both effectively and accurately, the stiffness and damping parameters [...] Read more.
The elastohydrodynamic lubrication (EHL) oil film between contact interfaces acts as a spring or damper to reduce wear and vibration for frictional pairs. To analyze the dynamic behaviors of friction pairs in mechanical systems both effectively and accurately, the stiffness and damping parameters under EHL contact states are essential. The presented work develops a numerical model to investigate the EHL stiffness and damping characteristics based on the transient EHL system and elastic contact theory of line contact, in which the stiffness force is separated according to the relationship with approach distance of the contact body established in the steady process, and then the damping can be obtained. The results show that the stiffness force plays an increasingly important role over the applied load conditions while the damping effects is gradually weakened. EHL stiffness is obviously smaller than dry contact stiffness, but the discrepancy is decreasing with the increasing load. Moreover, the higher entrainment velocity, lubricant viscosity and larger curvature radii leads to smaller stiffness and damping. The elastic modulus generates little effect on dynamic characteristics when the load is light while dominates the maximum level of the contact stiffness. Full article
(This article belongs to the Special Issue Surface Engineering for Wear Protection and Friction Reduction)
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12 pages, 3495 KiB  
Article
Polymeric Coatings for Skutterudite-Based Thermoelectric Materials
by Witold Brostow, IKang Chen and Haley E. Hagg Lobland
Lubricants 2022, 10(4), 72; https://doi.org/10.3390/lubricants10040072 - 18 Apr 2022
Viewed by 2015
Abstract
Thermoelectric (TE) devices have short service lives. These materials undergo thermal degradation at elevated temperatures by processes such as oxidation or sublimation. Our substrates were skutterudite-based TE materials. We covered their surfaces with a liquid high-temperature polymer (HTP)—crosslinked after the deposition, what converted [...] Read more.
Thermoelectric (TE) devices have short service lives. These materials undergo thermal degradation at elevated temperatures by processes such as oxidation or sublimation. Our substrates were skutterudite-based TE materials. We covered their surfaces with a liquid high-temperature polymer (HTP)—crosslinked after the deposition, what converted those surfaces into solid coatings. Sintering was performed at 250 °C for times of up to 48 h on both uncoated (control) and HTP-coated samples. The changes caused by thermal degradation were evaluated by thermogravimetric analysis, electrical resistivity, and energy-dispersive X-ray spectroscopy, and observed by scanning electron microscopy. Significant mitigation of oxidation and sublimation of our TE materials was achieved. Full article
(This article belongs to the Special Issue Tribological Applications of Nano & Submicro Structured Materials)
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20 pages, 7979 KiB  
Article
Accelerated Wear Test Design Based on Dissipation Wear Model Entropy Analysis under Mixed Lubrication
by Hongju Li, Ying Liu, Haoran Liao and Zhurong Liang
Lubricants 2022, 10(4), 71; https://doi.org/10.3390/lubricants10040071 - 16 Apr 2022
Cited by 6 | Viewed by 2451
Abstract
Theoretical life prediction of tribo-pairs such as seals, bearings and gears with the failure form of wear under mixed lubrication depends on quantitative analysis of wear. Correspondingly, the wear life test depends on an accelerated wear test method to save the time and [...] Read more.
Theoretical life prediction of tribo-pairs such as seals, bearings and gears with the failure form of wear under mixed lubrication depends on quantitative analysis of wear. Correspondingly, the wear life test depends on an accelerated wear test method to save the time and financial costs. Therefore, the theoretical basis of accelerated test design is a wear model providing a quantitative relationship between equivalents and accelerated test duration. In this paper, an accelerated wear test design method based on dissipation wear model entropy analysis under mixed lubrication is proposed. Firstly, the dissipation wear model under mixed lubrication is verified by standard experiments as a theoretical basis. Then, an accelerated wear test design method is proposed, taking the entropy increase in the dissipation wear model as an equivalent. The verification test shows that 20 times acceleration could be reached by adjustment of the entropy increase rate. The effect of entropy increase rate gradient of duty parameters is also discussed, revealing the fastest acceleration direction. Finally, the advantages and disadvantages of the proposed method are discussed. The results in this paper are expected to contribute to long life predictions of tribo-pairs. Full article
(This article belongs to the Special Issue Advances in Wear Predictive Models)
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21 pages, 2033 KiB  
Review
Current Status and Future Prospects of Biolubricants: Properties and Applications
by Rakesh Narayana Sarma and Ravikrishnan Vinu
Lubricants 2022, 10(4), 70; https://doi.org/10.3390/lubricants10040070 - 16 Apr 2022
Cited by 25 | Viewed by 11164
Abstract
Biolubricants generated from biomass and other wastes can reduce the carbon footprint of manufacturing processes and power generation. In this paper, the properties and uses of biolubricants have been compared thoroughly with conventional mineral-based lubricants. The biolubricants, which are currently based on vegetable [...] Read more.
Biolubricants generated from biomass and other wastes can reduce the carbon footprint of manufacturing processes and power generation. In this paper, the properties and uses of biolubricants have been compared thoroughly with conventional mineral-based lubricants. The biolubricants, which are currently based on vegetable oils, are discussed in terms of their physicochemical and thermophysical properties, stability, and biodegradability. This mini-review points out the main features of the existing biolubricants, and puts forward the case of using sustainable biolubricants, which can be generated from agro-residues via thermochemical processes. The properties, applications, and limitations of non-edible oils and waste-derived oils, such as bio-oil from pyrolysis and bio-crude from hydrothermal liquefaction, are discussed in the context of biolubricants. While the existing studies on biolubricants have mostly focused on the use of vegetable oils and some non-edible oils, there is a need to shift to waste-derived oils, which is highlighted in this paper. This perspective compares the key properties of conventional oils with different oils derived from renewable resources and wastes. In the authors’ opinion, the use of waste-derived oils is a potential future option to address the problem of the waste management and supply of biolubricant for various applications including machining, milling applications, biological applications, engine oils, and compressor oils. In order to achieve this, significant research needs to be conducted to evaluate salient properties such as viscosity, flash point, biodegradability, thermo-oxidative and storage stability of the oils, technoeconomics, and sustainability, which are highlighted in this review. Full article
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43 pages, 9488 KiB  
Review
Advances in the Application of Vegetable-Oil-Based Cutting Fluids to Sustainable Machining Operations—A Review
by Rasaq A. Kazeem, David A. Fadare, Omolayo M. Ikumapayi, Adeolu A. Adediran, Samuel J. Aliyu, Stephen A. Akinlabi, Tien-Chien Jen and Esther T. Akinlabi
Lubricants 2022, 10(4), 69; https://doi.org/10.3390/lubricants10040069 - 15 Apr 2022
Cited by 45 | Viewed by 7712
Abstract
Scientists and tribologists are currently exploring sustainable and inexhaustible lubricants as a result of increased awareness of environmental and health-related issues. Vegetable oils are being investigated as a potential form of environmentally friendly cutting fluids due to their excellent renewability, biodegradability, and lubricating [...] Read more.
Scientists and tribologists are currently exploring sustainable and inexhaustible lubricants as a result of increased awareness of environmental and health-related issues. Vegetable oils are being investigated as a potential form of environmentally friendly cutting fluids due to their excellent renewability, biodegradability, and lubricating performance. This report provides an overview of different vegetable oils used as cutting fluids in the machining of engineering materials. The effects of virgin vegetable oils, emulsified vegetable-based oils, and vegetable-oil-based nano-cutting fluids on the cutting force, the surface finish of machined parts, the tool wear, and the temperature of the cutting area were surveyed critically. Compared to mineral-oil-based cutting fluids, studies have demonstrated that vegetable-oil-based cutting fluids meet cleaner manufacturing standards with good or better efficiency. Full article
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3 pages, 173 KiB  
Editorial
Machine Learning in Tribology—More than Buzzwords?
by Stephan Tremmel and Max Marian
Lubricants 2022, 10(4), 68; https://doi.org/10.3390/lubricants10040068 - 15 Apr 2022
Cited by 8 | Viewed by 2896
Abstract
Tribology has been and continues to be one of the most relevant fields, being present in almost all aspects of our lives [...] Full article
(This article belongs to the Special Issue Machine Learning in Tribology)
12 pages, 1799 KiB  
Article
On the Importance of Temporal Information for Remaining Useful Life Prediction of Rolling Bearings Using a Random Forest Regressor
by Christoph Bienefeld, Eckhard Kirchner, Andreas Vogt and Marian Kacmar
Lubricants 2022, 10(4), 67; https://doi.org/10.3390/lubricants10040067 - 14 Apr 2022
Cited by 15 | Viewed by 2867
Abstract
Rolling bearings are frequently subjected to high stresses within modern machines. To prevent bearing failures, the topics of condition monitoring and predictive maintenance have become increasingly relevant. In order to efficiently and reliably maintain rolling bearings in a predictive manner, an estimate of [...] Read more.
Rolling bearings are frequently subjected to high stresses within modern machines. To prevent bearing failures, the topics of condition monitoring and predictive maintenance have become increasingly relevant. In order to efficiently and reliably maintain rolling bearings in a predictive manner, an estimate of the remaining useful life (RUL) is of great interest. The RUL prediction quality achieved when using machine learning depends not only on the selection of the sensor data used for condition monitoring, but also on its preprocessing. In particular, the execution of so-called feature engineering has a major impact on prediction quality. Therefore, in this paper, various methods of feature engineering are presented based on rolling–bearing endurance tests and recorded structure-borne sound signals. The performance of these methods is evaluated in the context of a regression-based RUL model. Furthermore, the way in which the quality of RUL prediction can be significantly improved is demonstrated, by adding further processed, time-considering features. Full article
(This article belongs to the Special Issue Machine Learning in Tribology)
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10 pages, 7220 KiB  
Article
On the Flow Dynamics of Polymer Greases
by Josep Farré-Lladós, Lars G. Westerberg, Jasmina Casals-Terré, Johan Leckner and René Westbroek
Lubricants 2022, 10(4), 66; https://doi.org/10.3390/lubricants10040066 - 13 Apr 2022
Cited by 7 | Viewed by 2767
Abstract
In this paper, the flow dynamics of polymer greases was investigated using micro-particle image velocimetry. Polymer greases have a different thickener structure, compared to widely used lithium-based greases, and they have the well-known ability to release oil. How these properties affect grease deformation [...] Read more.
In this paper, the flow dynamics of polymer greases was investigated using micro-particle image velocimetry. Polymer greases have a different thickener structure, compared to widely used lithium-based greases, and they have the well-known ability to release oil. How these properties affect grease deformation and its ability to flow is investigated and compared to the corresponding behavior of a lithium complex grease with the same consistency. Two main tests were carried out, where velocity profiles in a straight channel were measured and analyzed, and velocity evolution during the transition period from a no-flow to a fully-established flow was measured, respectively. It was found that the polymer grease flow dynamics is different from that of the lithium grease. This indicates that the internal structure of the grease and the grease ability to bleed oil have a strong influence on the deformation on a global scale, which in turn entails other lubricating abilities for the two grease types. Full article
(This article belongs to the Special Issue Recent Advances in Lubricating Greases II)
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22 pages, 5732 KiB  
Article
Sliding Corrosion Fatigue of Metallic Joint Implants: A Comparative Study of CoCrMo and Ti6Al4V in Simulated Synovial Environments
by Jae Joong Ryu, Edward Cudjoe, Mihir V. Patel and Matt Caputo
Lubricants 2022, 10(4), 65; https://doi.org/10.3390/lubricants10040065 - 13 Apr 2022
Cited by 3 | Viewed by 2212
Abstract
Mechanical contact in a corrosive synovial environment leads to progressive surface damage at the modular interface of the joint implants. The wear debris and corrosion products degrade the synovial fluids and change the lubrication mechanisms at the joints. Consequently, the unstable joint lubrication [...] Read more.
Mechanical contact in a corrosive synovial environment leads to progressive surface damage at the modular interface of the joint implants. The wear debris and corrosion products degrade the synovial fluids and change the lubrication mechanisms at the joints. Consequently, the unstable joint lubrication and corrosion products will further induce the undesirable performance of the joint implants. In this study, the two major joint materials, CoCrMo and Ti6Al4V, were tested during the course of reciprocal sliding contact in simulated synovial liquids. Open circuit potential and coefficient of friction were monitored to describe electrochemical and mechanical responses. Potentiostatic test results illustrated electrochemical damage on both surfaces that modified oxidation chemistry on both surfaces. However, more significant modification of the CoCrMo surface was detected during wear in the simulated joint liquid. Even with a reduced coefficient of friction on the CoCrMo surface in sodium lactate environments, fretting current density drastically increased in corrosive sodium lactate with pH 2. However, the test results from the Ti6Al4V surface presented less coefficient of friction values, and moderate change in fretting current. Therefore, the experimental study concluded that the biocompatibility of Ti6Al4V is superior to that of CoCrMo in the combined effect of mechanical loadings and an electrochemical environment. Full article
(This article belongs to the Special Issue Tribology of Biomaterials for Bone Regeneration)
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9 pages, 1508 KiB  
Article
Increasing Wear Resistance of Heavy-Loaded Friction Pairs by Nanoparticles in Conventional Lubricants: A Proof of Concept
by Valeriy Kosarchuk, Mykola Chausov, Andrii Pylypenko, Volodymyr Tverdomed, Pavlo Maruschak and Vasyl Vasylkiv
Lubricants 2022, 10(4), 64; https://doi.org/10.3390/lubricants10040064 - 11 Apr 2022
Cited by 8 | Viewed by 2018
Abstract
This paper provides experimental data on the effective use of a new lubricating composition, which includes industrial oil of any brand with the addition of a nanometal of the component of a friction pair, which has a lower hardness. It is shown that [...] Read more.
This paper provides experimental data on the effective use of a new lubricating composition, which includes industrial oil of any brand with the addition of a nanometal of the component of a friction pair, which has a lower hardness. It is shown that this composition significantly reduces the wear resistance of the rails and wheels of rolling stock during operation, prevents electrochemical corrosion of the friction pair wheel–rail and, most importantly, stabilizes the coefficient of friction at the optimum level after a relatively short operating time. The experiments were performed on the friction pair, “sample of the bandage material of the railway wheel—a sample of the rail material”, with a ratio of hardness of the bandage material (Rockwell hardness, HRC scale—35.3) to the hardness of the rail material of 1.1. Test results show that in the case of industrial lubricant, the BioRail brand, with the addition of a nanomaterial friction pair with lower wear hardness of the rail metal sample, after three hours in operation the wear was practically not observed. Moreover, the average value of the friction coefficient for three hours of operation was maintained at the level 0.25, which is optimal for the friction pair wheel–rail. Similar experiments using only the same lubricant brand showed much worse results. Full article
(This article belongs to the Special Issue Advances in Novel Lubricant Additives)
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20 pages, 6531 KiB  
Article
Investigation of the Effects of Cooling and Lubricating Strategies on Tribological Characteristics in Machining of Hybrid Composites
by Serhat Şap, Üsame Ali Usca, Mahir Uzun, Mustafa Kuntoğlu, Emin Salur and Danil Yurievich Pimenov
Lubricants 2022, 10(4), 63; https://doi.org/10.3390/lubricants10040063 - 8 Apr 2022
Cited by 38 | Viewed by 3143
Abstract
Engineering materials are expected to contain physical and mechanical properties to meet the requirements and to improve the functionality according to their application area. In this direction, hybrid composites stand as an excellent option to fulfill these requests thanks to their production procedure. [...] Read more.
Engineering materials are expected to contain physical and mechanical properties to meet the requirements and to improve the functionality according to their application area. In this direction, hybrid composites stand as an excellent option to fulfill these requests thanks to their production procedure. Despite the powder metallurgy method that allows for manufacturing products with high accuracy, machining operations are still required to obtain a final product. On the other hand, such materials are characterized with uncertainties in the structure and extremely hard reinforcement particles that aggravate the machinability. One of the prominent solutions for better machinability of composites is to use evolutionary cooling and lubricating strategies. This study focuses on the determination of tribological behavior of Cu-based, B-Ti-SiCP reinforced, about 5% wt. hybrid composites under milling of several environments, such as dry, minimum quantity lubrication (MQL)-assisted and cryogenic LN2-assisted. Comprehensive evaluation was carried out by considering tool wear, temperature, energy, surface roughness, surface texture and chips morphology as the machinability characteristics. The findings of this experimental research showed that cryogenic cooling improves the tribological conditions by reducing the cutting temperatures, flank wear tendency and required cutting energy. On the other hand, MQL based lubricating strategy provided the best tool wear index and surface characteristics, i.e., surface roughness and surface topography, which is related to spectacular ability in developing the friction conditions in the deformation zones. Therefore, this paper offers a novel milling strategy for Cu-based hybrid composites with the help of environmentally-friendly techniques. Full article
(This article belongs to the Special Issue Friction and Wear in Machine Design)
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14 pages, 6277 KiB  
Article
Simulation of the Fatigue Crack Initiation in SAE 52100 Martensitic Hardened Bearing Steel during Rolling Contact
by Kiarash Jamali Dogahe, Vinzenz Guski, Marijo Mlikota, Siegfried Schmauder, Walter Holweger, Joshua Spille, Joachim Mayer, Alexander Schwedt, Bernd Görlach and Jürgen Wranik
Lubricants 2022, 10(4), 62; https://doi.org/10.3390/lubricants10040062 - 7 Apr 2022
Cited by 12 | Viewed by 3145
Abstract
An investigation on the White Etching Crack (WEC) phenomenon as a severe damage mode in bearing applications led to the observation that in a latent pre-damage state period, visible alterations appear on the surface of the raceway. A detailed inspection of the microstructure [...] Read more.
An investigation on the White Etching Crack (WEC) phenomenon as a severe damage mode in bearing applications led to the observation that in a latent pre-damage state period, visible alterations appear on the surface of the raceway. A detailed inspection of the microstructure underneath the alterations reveals the existence of plenty of nano-sized pores in a depth range of 80 µm to 200 µm. The depth of the maximum Hertzian stress is calculated to be at 127 µm subsurface. The present study investigates the effect of these nanopores on the fatigue crack initiation in SAE 52100 martensitic hardened bearing steel. In this sense, two micro-models by means of the Finite Element Method (FEM) are developed for both a sample with and a sample without pores. The number of cycles required for the crack initiation for both samples is calculated, using the physical-based Tanaka–Mura model. It is shown that pores reduce the number of cycles in bearing application to come to an earlier transition from microstructural short cracks (MSC) to long crack (LC) propagation significantly. Full article
(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)
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22 pages, 15280 KiB  
Article
CFD Analysis of the Effect of Dimples and Cylinder Liner Honing Groove on the Tribological Characteristics of a Low Displacement Engine
by Sofia Orjuela Abril, Marlen Del Socorro Fonseca-Vigoya and Jhon Pabón-León
Lubricants 2022, 10(4), 61; https://doi.org/10.3390/lubricants10040061 - 7 Apr 2022
Cited by 4 | Viewed by 2504
Abstract
The contact between the piston rings and the cylinder liner is an interface with a strong influence on the tribological behavior and, therefore, directly affects the useful life of the engine components and fuel consumption. Due to this importance, the present investigation carried [...] Read more.
The contact between the piston rings and the cylinder liner is an interface with a strong influence on the tribological behavior and, therefore, directly affects the useful life of the engine components and fuel consumption. Due to this importance, the present investigation carried out an analysis of the effects of dimples and the honing groove in the cylinder liner on the tribological characteristics. A tribological model was developed to study the friction forces, minimum film thickness, and friction coefficient for the present investigation. Similarly, a computational fluid dynamics model was built to determine the dynamic movement of the piston. The validation of the numerical model showed a close similarity with the real behavior of the engine, obtaining an average relative error of 14%. The analysis of the results showed that a 3% increase in dimples’ density leads to a 3.79% increase in the minimum lubricant film and a 2.76% decrease in friction force. Additionally, it was shown that doubling the radius and depth of the dimple produces an increase of 3.86% and 1.91% in the thickness of the lubrication film. The most suitable distribution of the dimples on the surface of the cylinder liner corresponds to a square array. In general, the application of dimples and honing grooves in the cylinder liner are promising alternatives to reduce energy losses and minimize wear of engine components. Full article
(This article belongs to the Special Issue Advances in Tribology and LCA Applied to Thermal Machines)
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17 pages, 38062 KiB  
Article
Study of the Cylinder Deactivation on Tribological Parameters and Emissions in an Internal Combustion Engine
by Sofia Orjuela Abril, Marlen Del Socorro Fonseca-Vigoya and Carlos Pardo García
Lubricants 2022, 10(4), 60; https://doi.org/10.3390/lubricants10040060 - 7 Apr 2022
Cited by 5 | Viewed by 2182
Abstract
In the present investigation, a study is carried out using numerical simulation on the effects of cylinder deactivation on tribological parameters and emissions in an internal combustion engine. For the development of the research, a tribological model was used to predict the characteristics [...] Read more.
In the present investigation, a study is carried out using numerical simulation on the effects of cylinder deactivation on tribological parameters and emissions in an internal combustion engine. For the development of the research, a tribological model was used to predict the characteristics of the lubrication film, friction conditions, blow-by gas, and deformation of the piston rings. Additionally, the construction of a CFD model was carried out to describe the kinematic movement of the engine piston. The analysis of results allowed for the demonstration of the active cylinders presenting an increase of 21.53% and 7.65% in the pressure and temperature in the cylinder wall. Additionally, the active cylinders present a reduction of 11.33% in the minimum thickness of the lubrication film and an increase in the friction force due to asperities, which implies an increase of 33% in power losses due to friction. The implementation of technologies such as cylinder deactivation causes an increase in combustion gas leaks caused by the increase in pressure of the active cylinders. However, the use of this technology allows reducing 9.09%, 8.26%, and 7.41% in CO, HC, and NO emissions. Although the use of technologies such as cylinder deactivation allows significant fuel savings, it is necessary to consider the negative effects caused by this technology, such as the increase in combustion gas leaks and the increase in power loss by the greatest frictional forces. Full article
(This article belongs to the Special Issue Advances in Tribology and LCA Applied to Thermal Machines)
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15 pages, 5542 KiB  
Article
Investigation of Emission Characteristics and Lubrication Oil Properties in a Dual Diesel–Hydrogen Internal Combustion Engine
by Carlos Pardo-García, Sofia Orjuela-Abril and Jhon Pabón-León
Lubricants 2022, 10(4), 59; https://doi.org/10.3390/lubricants10040059 - 5 Apr 2022
Cited by 7 | Viewed by 3619
Abstract
Hydrogen is considered one of the main gaseous fuels due to its ability to improve thermal performance in diesel engines. However, its influence on the characteristics of lubricating oil is generally ignored. Thus, in the present investigation, an analysis of the effect on [...] Read more.
Hydrogen is considered one of the main gaseous fuels due to its ability to improve thermal performance in diesel engines. However, its influence on the characteristics of lubricating oil is generally ignored. Thus, in the present investigation, an analysis of the effect on the physical and chemical properties of lubricating oil with mixtures of diesel fuel–hydrogen was carried out, and the environmental impacts of this type of mixture were assessed. The development of the research was carried out using a diesel engine under four torque conditions (80 Nm, 120 Nm, 160 Nm and 200 Nm) and three hydrogen gas flow conditions (0.75 lpm, 1.00 lpm and 1.25 lpm). From the results, it was possible to demonstrate that the presence of hydrogen caused decreases of 3.50%, 6.79% and 4.42% in the emissions of CO, HC, and smoke opacity, respectively. However, hydrogen further decreased the viscosity of the lubricating oil by 26%. Additionally, hydrogen gas produced increases of 17.7%, 29.27%, 21.95% and 27.41% in metallic components, such as Fe, Cu, Al and Cr, respectively. In general, hydrogen favors the contamination and oxidation of lubricating oil, which implies a greater wear of the engine components. Due to the significantly negative impact of hydrogen on the lubrication system, it should be considered due to its influence on the economic and environmental cost during the engine’s life cycle. Full article
(This article belongs to the Special Issue Advances in Tribology and LCA Applied to Thermal Machines)
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15 pages, 5969 KiB  
Article
Tribological Properties and Physiochemical Analysis of Polymer-Ceramic Composite Coatings for Bone Regeneration
by Agnieszka Maria Tomala, Dagmara Słota, Wioletta Florkiewicz, Karina Piętak, Mateusz Dyląg and Agnieszka Sobczak-Kupiec
Lubricants 2022, 10(4), 58; https://doi.org/10.3390/lubricants10040058 - 2 Apr 2022
Cited by 6 | Viewed by 2695
Abstract
The biomaterial coatings for bone tissue regeneration described in this study promote bioactivity. The ceramic-polymer composite coatings deposited on polylactide (PLA) plates contain polymers, namely polyvinylpyrrolidone (PVP)/polyethylene glycol (PEG), while the ceramic phase is hydroxyapatite (HA). Additionally, collagen (COL) and glutathione (GSH) are [...] Read more.
The biomaterial coatings for bone tissue regeneration described in this study promote bioactivity. The ceramic-polymer composite coatings deposited on polylactide (PLA) plates contain polymers, namely polyvinylpyrrolidone (PVP)/polyethylene glycol (PEG), while the ceramic phase is hydroxyapatite (HA). Additionally, collagen (COL) and glutathione (GSH) are components of high biological value. Bone tissue materials requires additionally demanding tribological properties, which are thoroughly described in this research. These findings, presented herein for the first time, characterize this type of highly specific composite coating material and their indicate possible application in bone regeneration implants. Implementation of the collagen in the PVP/PEG/HA composite matrix can tailor demanding tribological performance, e.g., anti-wear and friction reduction. The addition of the ceramic phase in too high a content (15%) leads to the decreased swelling ability of materials and slower liquid medium absorption by composite coatings, as well as strong surface roughening and loosening tribological properties. In consequence, small particles of HA from the very rough composite crumble, having a strong abrasive effect on the sample surface. In conclusion, sample C composed of PVP/PEG/GSH/COL/HA (5%) exhibits high bioactivity, strong mechanical and tribological properties, the highest free surface energy, porosity, and accepted roughness to be implemented as a material for bone regeneration. Full article
(This article belongs to the Special Issue Tribology of Biomaterials for Bone Regeneration)
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13 pages, 4734 KiB  
Article
Rheological and Frictional Properties of Lithium Complex Grease with Graphene Additives
by Yanshuang Wang, Xudong Gao, Jianghai Lin and Pu Zhang
Lubricants 2022, 10(4), 57; https://doi.org/10.3390/lubricants10040057 - 1 Apr 2022
Cited by 13 | Viewed by 2713
Abstract
Few-layer graphene (FLG) was added as a nano-additive to lithium complex grease (LCG) to explore the influence of FLG on the microstructure, viscoelasticity, friction and wear properties of LCG. Studies have found that the addition of FLG makes the microstructure of the thickener [...] Read more.
Few-layer graphene (FLG) was added as a nano-additive to lithium complex grease (LCG) to explore the influence of FLG on the microstructure, viscoelasticity, friction and wear properties of LCG. Studies have found that the addition of FLG makes the microstructure of the thickener more compact, which in turn leads to an increase in the viscoelasticity of LCG. FLG additives can improve the viscosity-temperature properties of the grease and change the elastic deformation response to temperature changes. Among the temperatures selected in this article, the effect of graphene is more obvious at 70 °C. During the friction process, a proper amount of FLG can quickly form a boundary film and is not easily damaged, thereby optimizing the friction and wear performance of LCG. Full article
(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermal Sciences)
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16 pages, 3776 KiB  
Article
An Empirical Study on the Friction of Reciprocating Rod Seals at Predefined Lubrication Conditions and Shear Rates
by Oliver Feuchtmüller, Lothar Hörl and Frank Bauer
Lubricants 2022, 10(4), 56; https://doi.org/10.3390/lubricants10040056 - 1 Apr 2022
Cited by 4 | Viewed by 2768
Abstract
A key factor influencing the friction of rod seals is a thin oil film, which is dragged into the sealing gap at outstroke and instroke. Accurate determination of oil film thickness in the sealing gap of rod seals is a challenging task since [...] Read more.
A key factor influencing the friction of rod seals is a thin oil film, which is dragged into the sealing gap at outstroke and instroke. Accurate determination of oil film thickness in the sealing gap of rod seals is a challenging task since it is only in the range of a few nanometers. A novel measurement procedure to analyze the friction of common reciprocating sealing systems in direct relation to the shear rate and film thickness is introduced in this paper. Results from a first empirical study with film thicknesses in the range of a few nanometers and shear rates up to γ˙=107 s1 were used to compare the friction of practically relevant polyurethane U-cups. The U-cups differ in their geometry and surface roughness. It is seen that even at such thin films, the measured friction of those seals can be approximated by Newtonian fluid friction (speed, film thickness, viscosity, contact area). In general, the novel measurement procedure is useful in a scientific and technical context, since it offers a new perspective on tribological mechanisms at thin film lubrication conditions. Full article
(This article belongs to the Special Issue Friction and Wear in Machine Design)
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17 pages, 3411 KiB  
Article
Effect of Base Oil and Thickener on Texture and Flow of Lubricating Greases: Insights from Bulk Rheometry, Optical Microrheology and Electron Microscopy
by Annika Hodapp, Andreas Conrad, Bernhard Hochstein, Karl-Heinz Jacob and Norbert Willenbacher
Lubricants 2022, 10(4), 55; https://doi.org/10.3390/lubricants10040055 - 31 Mar 2022
Cited by 7 | Viewed by 3119
Abstract
The structure and flow behavior of lubricating greases depend on the base oil and the type and concentration of the dissolved thickener. In this study, the linear viscoelastic properties of greases were characterized by combining oscillatory shear and squeeze flow covering a broad [...] Read more.
The structure and flow behavior of lubricating greases depend on the base oil and the type and concentration of the dissolved thickener. In this study, the linear viscoelastic properties of greases were characterized by combining oscillatory shear and squeeze flow covering a broad frequency range (0.1–105 rad s−1). Multiple-particle tracking (MPT) microrheology and scanning electron microscopy (SEM) provided further insight into local viscoelastic properties and sample structure on a submicron-length scale. The type and viscosity of the base oil did not affect the absolute value of the complex viscosity and the filament shape formed by a given thickener. High-frequency shear modulus data, however, indicated that the thickener lithium 12-hydroxystearate formed stiffer networks/filaments in poly-α-olefins than in mineral oils. As expected, the viscosity increased with increased thickener concentrations, but microscopy and high-frequency rheometry revealed that the thickness, length, and stiffness of the individual filaments did not change. In mineral oil, the 12-hydroxystearate thickeners yielded higher viscosity than the corresponding stearates with the same metal ion. The filamentous lithium thickeners created stronger networks than the roundish aggregates formed by magnesium and zinc stearate. Network mesh sizes varying between approximately 100 nm and 300 nm were consistently determined from SEM image analysis and MPT experiments. The MPT experiments further disclosed the existence of gel-like precursors of approximately 130 µm at thickener concentrations far below the critical value at which a sample-spanning network resulting in a characteristic grease texture is formed. Full article
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23 pages, 5661 KiB  
Article
Comparative Study of Rheological Effects of Vegetable Oil-Lubricant, TiO2, MWCNTs Nano-Lubricants, and Machining Parameters’ Influence on Cutting Force for Sustainable Metal Cutting Process
by Imhade P. Okokpujie, Lagouge K. Tartibu, Jude E. Sinebe, Adeyinka O. M. Adeoye and Esther T. Akinlabi
Lubricants 2022, 10(4), 54; https://doi.org/10.3390/lubricants10040054 - 31 Mar 2022
Cited by 15 | Viewed by 2499
Abstract
Nano-lubricant machining of Aluminum 8112 alloy is the art of sustainable manufacturing of mechanical components used for defense technology and aerospace application. However, machining aluminum alloys generates excess heat, which tends to increase the cutting force (F.C.), due to the material adhesion of [...] Read more.
Nano-lubricant machining of Aluminum 8112 alloy is the art of sustainable manufacturing of mechanical components used for defense technology and aerospace application. However, machining aluminum alloys generates excess heat, which tends to increase the cutting force (F.C.), due to the material adhesion of the workpiece on the cutting tool. The challenge has drawn researchers’ attention to introducing nano-lubrication processes. This study focused on the comparative assessment of eco-friendly vegetable oil-based-TiO2 and MWCNTs nano-lubricant on cutting force during the machining of the Aluminum 8112 alloy. Nanoparticles were implemented on the base oil using an ultrasonic vibrator and magnetic stirrer before the application in the machining, via the minimum quantity lubrication process. Quadratic central composite designs were employed to carry out the experiment, using five factors at five levels, having experimental runs of 50. The input parameters are helix angle (H.A.), spindle speed (S.S.), axial depth of cut (ADOC), feed rate (F.R.), and length of cut (LOC). The results show that the application of the nanoparticle increases the performance of the vegetable oil on the cutting force. TiO2 nano-lubricant reduces the cutting force by 0.26%, compared with the MWCNTs, and 6% compared with the vegetable oil. Furthermore, the MWCNT nano-lubricant reduces the cutting force by 5% compared with the vegetable oil lubrication environment. Full article
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48 pages, 17565 KiB  
Review
Fretting Fatigue in Mechanical Joints: A Literature Review
by Dario Croccolo, Massimiliano De Agostinis, Stefano Fini, Giorgio Olmi, Francesco Robusto and Chiara Scapecchi
Lubricants 2022, 10(4), 53; https://doi.org/10.3390/lubricants10040053 - 30 Mar 2022
Cited by 19 | Viewed by 7139
Abstract
Fretting fatigue is a fatigue damage process that occurs when two surfaces in contact with each other are subjected to relative micro-slip, causing a reduced fatigue life with respect to the plain fatigue case. Fretting has now been studied deeply for over 50 [...] Read more.
Fretting fatigue is a fatigue damage process that occurs when two surfaces in contact with each other are subjected to relative micro-slip, causing a reduced fatigue life with respect to the plain fatigue case. Fretting has now been studied deeply for over 50 years, but still no univocal design approach has been universally accepted. This review presents a literature study that involves the three main types of mechanical joint affected by fretting fatigue (press-fitted shaft hub joints, dovetail joints, and bolted joints) aiming at giving insight into the progress made in terms of design guidelines for engineers. Full article
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24 pages, 3190 KiB  
Article
Evaluation of Mango Kernel Seed (Mangifera indica) Oil as Cutting Fluid in Turning of AISI 1525 Steel Using the Taguchi-Grey Relation Analysis Approach
by Rasaq A. Kazeem, David A. Fadare, Omolayo M. Ikumapayi, Stephen A. Akinlabi and Esther T. Akinlabi
Lubricants 2022, 10(4), 52; https://doi.org/10.3390/lubricants10040052 - 29 Mar 2022
Cited by 9 | Viewed by 4325
Abstract
The hunt for environmentally friendly cutting fluids is underway as the problems of conventional cutting fluids become more evident. To achieve environmentally conscious machining, the current study examines the use of Mango Kernel Seed Oil (MKSO) as a cutting fluid during the turning [...] Read more.
The hunt for environmentally friendly cutting fluids is underway as the problems of conventional cutting fluids become more evident. To achieve environmentally conscious machining, the current study examines the use of Mango Kernel Seed Oil (MKSO) as a cutting fluid during the turning of AISI 1525 steel. According to the 24 complete factorial techniques, the vegetable-oil-based cutting was produced by dissolving four different additives in mango kernel seed oil: emulsifying, antimicrobial, anti-corrosive, and antifoam substances. Afterward, the formulated vegetable oil was characterized both physically and chemically to determine its capability. The developed MKSO was mechanically evaluated using a Taguchi L9 orthogonal array. Spindle speed, depth of cut, and feed rate served as the input parameters, while surface roughness, cutting temperature, machine sound level, and machine vibration rate were the responses. Taguchi-based Grey Relational Analysis was used to perform multi-objective optimization. It was used to determine the best machining conditions. The best parameters for mango kernel seed oil are a spindle speed of 0.683 rev/min, feed of 0.617 mm/rev, and depth of cut of 0.620 mm, while the optimum parameter for Mineral-Oil-based Cutting Fluid (MOCF) is 0.7898 rev/min spindle speed, 0.6483 mm/rev feed, and a 0.6373 mm depth of cut. This research revealed that, when compared to the feed rate and the depth of cut, the spindle speed has the highest influence on multi-responses in turning operations with both cutting fluids. Generally, MOCF outperformed mango kernel seed cutting fluid in most machining conditions. Full article
(This article belongs to the Special Issue Tribology in Manufacturing and Design)
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8 pages, 4748 KiB  
Article
Wear Study of Cubic Boron Nitride (cBN) Cutting Tool for Machining of Compacted Graphite Iron (CGI) with Different Metalworking Fluids
by Long Zhu, Robert Evans, Yan Zhou and Fei Ren
Lubricants 2022, 10(4), 51; https://doi.org/10.3390/lubricants10040051 - 26 Mar 2022
Cited by 3 | Viewed by 2334
Abstract
Due to its desirable mechanical properties, compacted graphite iron (CGI) has been used to replace conventional gray cast iron (CI) in various applications, such as automotive engine blocks and cylinder heads. However, the poor machinability of CGI can lead to excessive tool wear [...] Read more.
Due to its desirable mechanical properties, compacted graphite iron (CGI) has been used to replace conventional gray cast iron (CI) in various applications, such as automotive engine blocks and cylinder heads. However, the poor machinability of CGI can lead to excessive tool wear and consequently high manufacturing costs. Various strategies have been developed to improve the machinability of CGI, including optimizing machining parameters and the development of novel metalworking fluids. In this study, machining of CGI was conducted using cubic boron nitride (cBN) tools under different cutting speeds, with both soluble and full-synthetic water-based metalworking fluids at different levels of sulfur addition and water dilution. The effects of the metalworking fluids on the tool wear behavior were examined. Results showed that at 200 m/min cutting speed, the soluble metalworking fluid at 4% dilution and 0.3% sulfur compound exhibited the best performance, with a cutting distance reaching 23.8 km. In contrast, the least effective soluble metalworking fluid at 9% dilution and 0.3% sulfur compound resulted in a 28.6% decrease in the cutting distance (17.0 km) compared to the best one. At a higher speed (300 m/min), the cutting distance for all metalworking fluids dropped to less than 6.0 km, with the full-synthetic metalworking fluid showing the shortest cutting distance of 4.8 km. Full article
(This article belongs to the Special Issue Metalworking Fluids Technology)
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14 pages, 5989 KiB  
Article
Friction-Excited Oscillation of Air Conditioner Rotary Compressors: Measurements and Numerical Simulations
by Yusheng Hu, Rongting Zhang, Jinquan Zhang, Qifeng Song and Guangxiong Chen
Lubricants 2022, 10(4), 50; https://doi.org/10.3390/lubricants10040050 - 25 Mar 2022
Cited by 1 | Viewed by 4460
Abstract
The oscillation of a rotary compressor was measured and analyzed in the frequency and time domains. The harmonic wavelet transform was used to dissolve the oscillation signal into a series of single-frequency components. A power spectrum analysis of the single-frequency components shows that [...] Read more.
The oscillation of a rotary compressor was measured and analyzed in the frequency and time domains. The harmonic wavelet transform was used to dissolve the oscillation signal into a series of single-frequency components. A power spectrum analysis of the single-frequency components shows that there are many vibration components whose frequencies are one, double, triple, quadruple, and even tens of times the rotating frequency. An envelope spectrum analysis shows that some single-frequency components originate from the friction-excited oscillation of the compressor. A full-size mode-coupling model of the rotary compressor was established to forecast the friction-excited oscillation of the compressor using the transient dynamics method and the complex eigenvalue method. The measurement results are consistent with the predictive results. A sensitivity analysis of the main parameters shows that the coefficient of friction has a major impact on the development tendency of the friction-excited oscillation of rotary compressors. Full article
(This article belongs to the Special Issue Tribology in Manufacturing and Design)
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16 pages, 87678 KiB  
Article
Performance of MQL and Nano-MQL Lubrication in Machining ER7 Steel for Train Wheel Applications
by Kerem Yavuz Çamlı, Recep Demirsöz, Mehmet Boy, Mehmet Erdi Korkmaz, Nafiz Yaşar, Khaled Giasin and Danil Yurievich Pimenov
Lubricants 2022, 10(4), 48; https://doi.org/10.3390/lubricants10040048 - 23 Mar 2022
Cited by 35 | Viewed by 3387
Abstract
In the rail industry, there are four types of steel grades used for monoblock wheels, namely ER6, ER7, ER8 and ER9. ER7 steel is manufactured in accordance with the EN13262 standard and is utilized in European railway lines. These train wheels are formed [...] Read more.
In the rail industry, there are four types of steel grades used for monoblock wheels, namely ER6, ER7, ER8 and ER9. ER7 steel is manufactured in accordance with the EN13262 standard and is utilized in European railway lines. These train wheels are formed by pressing and rolling after which they are machined using turning process to achieve their final dimensions. However, machining ER7 steels can be challenging due to their high mechanical properties, which can facilitate rapid tool wear and thermal cracking. Therefore, while the use of coolants is critical to improving their machinability, using conventional flood coolants adds extra operational costs, energy and waste. An alternative is to use minimum quantity lubrication (MQL) cooling technology, which applies small amounts of coolant mixed with air to the cutting zone, leaving a near-dry machined surface. In the current study, preliminary tests were undertaken under dry conditions and using coated carbide inserts to determine the optimal cutting parameters for machining ER7 steel. The impact of the cutting speed and feed rate on surface roughness (Ra), energy consumption and cutting temperature were investigated and used as a benchmark to determine the optimal cutting parameters. Next, additional machining tests were conducted using MQL and nano-MQL cooling technologies to determine their impact on the aforementioned machining outputs. According to preliminary tests, and within the tested range of the cutting parameters, using a cutting speed of 300 m/min and a feed rate of 0.15 mm/rev resulted in minimal surface roughness. As a result, using these optimal cutting parameters with MQL and Nano-MQL (NMQL) cooling technologies, the surface roughness was further reduced by 24% and 34%, respectively, in comparison to dry conditions. Additionally, tool wear was reduced by 34.1% and 37.6%, respectively. The overall results from this study demonstrated the feasibility of using MQL coolants as a sustainable machining alternative for steel parts for rail wheel applications. In addition, the current study highlight the enhanced performance of MQL cooling technology with the addition of nano additives. Full article
(This article belongs to the Special Issue Application of Solid Lubricants in Metal Processing)
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20 pages, 6965 KiB  
Article
Thrust-Bearing Layout Design of a Large-Sized Hydrostatic Rotary Table to Withstand Eccentric Loads for Horizontal Boring Machine Applications
by Hua-Chih Huang and Shen-Hen Yang
Lubricants 2022, 10(4), 49; https://doi.org/10.3390/lubricants10040049 - 22 Mar 2022
Cited by 7 | Viewed by 2778
Abstract
There is an increasing demand for large-sized hydrostatic rotary tables due to the industrial need for the precision machining of large workpieces for wind generation, aerospace, shipbuilding, and national defense applications. As a consequence, under eccentric loads, the deformation of the large-sized hydrostatic [...] Read more.
There is an increasing demand for large-sized hydrostatic rotary tables due to the industrial need for the precision machining of large workpieces for wind generation, aerospace, shipbuilding, and national defense applications. As a consequence, under eccentric loads, the deformation of the large-sized hydrostatic rotary table of a horizontal boring machine would negatively affect machining precision. Indeed, the hydrostatic thrust-bearing recess layout design is the main factor that affects the rotary table’s resistance against deformations caused by eccentric loads. This study focused on the capillary-compensated constant-pressure large-sized hydrostatic rotary table for a horizontal boring machine. ANSYS software was used to simulate the thermal and structural deformation of the worktable under eccentric loads. In addition to the original layout of the hydrostatic thrust bearing, three other bearing recess layouts, which involved two different recess diameters, were designed in order to examine the deformation of the worktable under eccentric loads. The results showed that, in terms of a single-ring hydrostatic thrust-bearing layout, a larger recess diameter resulted in a smaller worktable deformation compared to a smaller recess diameter; in terms of a dual-ring hydrostatic thrust bearing layout, the worktable deformation was smaller than that of the single-ring layout with a larger recess diameter. Under the spatial and geometric constraints of the worktable, adopting a hydrostatic thrust bearing with a dual-ring recess layout would minimize the worktable deformation under eccentric loads. For thermal deformation in a single-ring hydrostatic bearing pad layout, however, a larger recess diameter resulted in a larger worktable thermal deformation compared to a smaller recess diameter. Full article
(This article belongs to the Special Issue Friction and Lubrication of Sliding Bearings, Volume II)
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