Lubricants

19 pages, 9952 KiB

Open AccessArticle

Multiple Regression Analysis and Non-Dominated Sorting Genetic Algorithm II Optimization of Machining Carbon-Fiber-Reinforced Polyethylene Terephthalate Glycol Parts Fabricated via Additive Manufacturing Under Dry and Lubricated Conditions

by Anastasios Tzotzis, Nikolaos Efkolidis, Kai Cheng and Panagiotis Kyratsis

Lubricants 2025, 13(2), 63; https://doi.org/10.3390/lubricants13020063 (registering DOI) - 2 Feb 2025

Abstract

The present research deals with the processing of the additively manufactured Carbon-Fiber-Reinforced Polymer (CFRP) under dry and lubricated cutting conditions, focusing on the generated surface roughness. The cutting speed, feed, and depth of cut were selected as the continuous variables. A comparison between [...] Read more.

The present research deals with the processing of the additively manufactured Carbon-Fiber-Reinforced Polymer (CFRP) under dry and lubricated cutting conditions, focusing on the generated surface roughness. The cutting speed, feed, and depth of cut were selected as the continuous variables. A comparison between the generated surface roughness of the dry and the lubricated cuts revealed that the presence of coolant contributed towards reducing surface roughness by more than 20% in most cases. Next, a regression analysis was performed with the obtained measurements, yielding a robust prediction model, with the determination coefficient R² being equal to 94.65%. It was determined that feed and the corresponding interactions contributed more than 45% to the model’s R², followed by the depth of cut and the machining condition. In addition, the cutting speed was the variable with the least effect on the response. The Non-Dominated Sorting Genetic Algorithm 2 (NSGA-II) was employed to identify the front of optimal solutions that consider both minimizing surface roughness and maximizing Material Removal Rate (MRR). Finally, a set of extra experiments proved the validity of the model by exhibiting relative error values, between the measured and predicted roughness, below 10%. Full article

(This article belongs to the Special Issue Tribology in Manufacturing Engineering)

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19 pages, 8080 KiB

Open AccessArticle

Rheological Properties and Lubricating Film Formation Performance of Very Low-Viscosity and Biodegradable Polyalphaolefins

by Yingjun Chen, Zhaorong He, Haiquan Wang, Yueming Li and Hui Wang

Lubricants 2025, 13(2), 62; https://doi.org/10.3390/lubricants13020062 (registering DOI) - 2 Feb 2025

Abstract

Polyalphaolefins (PAOs) are regarded as superior lubricants, but the biodegradability of the very low-viscosity PAO2/PAO4 has been ignored over a long history, despite being inherently biodegradable (PAO2/PAO4 biodegradation rate >20% by OECD guidelines). Previous studies typically concentrated on a single viscosity grade of [...] Read more.

Polyalphaolefins (PAOs) are regarded as superior lubricants, but the biodegradability of the very low-viscosity PAO2/PAO4 has been ignored over a long history, despite being inherently biodegradable (PAO2/PAO4 biodegradation rate >20% by OECD guidelines). Previous studies typically concentrated on a single viscosity grade of PAO with additives, seldom engaging in comparative research efforts involving multiple low-viscosity grades of neat PAO concurrently. This study compares PAO2/PAO4 with non-biodegradable PAO6 regarding rheology and lubricating film formation. PAO2/PAO4 are Newtonian fluids with ≤10% viscosity fluctuation at high shear rates, while PAO6 shows a viscosity fluctuation of ≥15% at high shear rates. Viscosity–temperature equations are derived. An optical interference method measures lubricating film thickness. PAO2/PAO4 films are less sensitive to speed/load changes. PAO2 mainly works in boundary lubrication. Interference images show possible unique EHL characteristics of PAOs. The Hamrock–Dowson formula overestimates PAO6 film thickness at high speeds. Full article

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

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17 pages, 13348 KiB

Open AccessArticle

Structure Modulation and Self-Lubricating Properties of Porous TiN–MoS₂ Composite Coating Under Humidity–Fluctuating Conditions

by Tiancheng Ye, Kai Le, Ganggang Wang, Zhenghao Ren, Yuzhen Liu, Liwei Zheng, Hui Tian and Shusheng Xu

Lubricants 2025, 13(2), 61; https://doi.org/10.3390/lubricants13020061 (registering DOI) - 1 Feb 2025

Abstract

To improve the friction performance and service life of protective coatings in humidity-fluctuating environments, porous hard titanium nitride (TiN)–molybdenum disulfide (MoS₂) composite coatings were prepared by using direct current magnetron sputtering (DCMS) with the mode of oblique angle deposition (OAD) and [...] Read more.

To improve the friction performance and service life of protective coatings in humidity-fluctuating environments, porous hard titanium nitride (TiN)–molybdenum disulfide (MoS₂) composite coatings were prepared by using direct current magnetron sputtering (DCMS) with the mode of oblique angle deposition (OAD) and chemical vapor deposition (CVD) technologies. The structure and chemical component were characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The tribological properties of these TiN–MoS₂ composite coatings were investigated. The results indicate that the porous TiN–MoS₂ composite coating exhibited outstanding friction performance and long service life under humidity-fluctuating environments. At the initial 20% relative humidity (RH) stage, the MoS₂ on the porous TiN–MoS₂ composite coating surface worked as an effective lubricant; thus, the coating demonstrated excellent lubrication performance, and the friction coefficient (COF) was about 0.05. As the humidity was alternated to 70% RH, the lubrication effect diminished due to the production of molybdenum oxide (MoO₃), and the COF was about 0.2, which was attributed to the degradation of MoS₂ on the wear track and the release of fresh MoS₂ from the porous TiN matrix. After the environmental conditions shifted from 70% to 20% RH, the MoO₃ was removed, and the lubrication effect was restored. In summary, TiN–MoS₂ porous composite coating offers a promising approach for lubrication in humidity-fluctuating environments. Full article

(This article belongs to the Special Issue Coatings and Lubrication in Extreme Environments)

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13 pages, 2288 KiB

Open AccessArticle

Experimental Analysis on the Hysteresis Phenomenon in the Range of Subsynchronous Frequency as a Function of Oil Temperature with Regard to Turbochargers

by Márk Pesthy, Gusztáv Fekete, Máté Boros and Csaba Tóth-Nagy

Lubricants 2025, 13(2), 60; https://doi.org/10.3390/lubricants13020060 - 30 Jan 2025

Abstract

This study presents an experimental analysis of a turbocharger with semi-floating ring bearings, focusing on hysteresis in subsynchronous vibrations. Four automotive oils (SAE 0W-20, SAE 0W-30, SAE 5W-30, SAE 5W-40) were tested across six oil inlet temperatures from 20 °C to 120 °C [...] Read more.

This study presents an experimental analysis of a turbocharger with semi-floating ring bearings, focusing on hysteresis in subsynchronous vibrations. Four automotive oils (SAE 0W-20, SAE 0W-30, SAE 5W-30, SAE 5W-40) were tested across six oil inlet temperatures from 20 °C to 120 °C during ramp-up and ramp-down cycles to examine the effects of lubricant viscosity and temperature on rotor dynamics. Hysteresis and bifurcation points were observed at distinct rotational speeds in both directions, with subsynchronous components providing insights into rotor–lubrication interactions. This study applies the concept of hysteresis loop width for turbocharger rotors, highlighting its nonlinear dependence on oil temperature, an unexpected and unexplained phenomenon. Additionally, the results suggest that vibration sensors could provide real-time feedback on oil supply conditions, offering potential enhancements for turbochargers and other rotating machinery. Full article

(This article belongs to the Special Issue Recent Advances in Automotive Powertrain Lubrication)

22 pages, 16700 KiB

Open AccessArticle

Mechanical Property Degradation of Transmission Wire Rope Caused by Different Wear Evolution

by Xiangdong Chang, Fahui Shi, Xiao Chen, Yuxing Peng, Yu Tang, Wenjie Xiao and Ran Hu

Lubricants 2025, 13(2), 59; https://doi.org/10.3390/lubricants13020059 - 30 Jan 2025

Abstract

Steel wire rope serves as a critical load-bearing and transmission component in the transportation equipment utilized in coal mines. It exhibits various forms of damage during prolonged service, which significantly jeopardizes the safety reliability of the transportation equipment. To investigate the formation process [...] Read more.

Steel wire rope serves as a critical load-bearing and transmission component in the transportation equipment utilized in coal mines. It exhibits various forms of damage during prolonged service, which significantly jeopardizes the safety reliability of the transportation equipment. To investigate the formation process of the surface wear of steel wire rope and its influence on mechanical properties, the tribological evolution and performance degradation of the transmission wire rope under rope–sheave contact and rope–rope contact were studied in this paper. The wire rope’s friction coefficient (COF) is stable between 0.7 and 0.8 under two contact conditions. It is more likely to lead to the accumulation of frictional heat under the condition of rope–sheave contact. The primary wear mechanisms of transmission wire ropes are adhesive wear and fatigue wear. Additionally, the wear evolution leads to the nonlinear degradation of the tensile strength and bending fatigue life of the wire rope, and the wear damage caused by rope–sheave contact is more harmful. As the sliding distance between the wire rope and the sheave increases, the breaking force decreases from approximately 48 kN to 23 kN, and the number of bending fatigues of the wire rope before scrapping is reduced from approximately 6200 times to 200 times. Full article

21 pages, 2371 KiB

Open AccessArticle

Dynamic Response Analysis of Ballastless Tracks Considering the Temperature-Dependent Viscoelasticity of Cement-Emulsified Asphalt Mortar Based on a Vehicle–Track–Subgrade Coupled Model

by Yunqing Chen, Bing Wu, Linquan Yao and Xianglong Su

Lubricants 2025, 13(2), 58; https://doi.org/10.3390/lubricants13020058 - 30 Jan 2025

Abstract

This study aims to explore the dynamic response of ballastless tracks under various temperatures of the cement-emulsified asphalt (CA) mortar layer and other environmental factors. CA mortar is the key material in the ballastless track structure, exhibiting notably temperature-dependent viscoelastic properties. It can [...] Read more.

This study aims to explore the dynamic response of ballastless tracks under various temperatures of the cement-emulsified asphalt (CA) mortar layer and other environmental factors. CA mortar is the key material in the ballastless track structure, exhibiting notably temperature-dependent viscoelastic properties. It can be damaged or even fail due to the continuous loads from trains. However, the dynamic behaviors of ballastless tracks considering the temperature-dependent viscoelasticity of CA mortar have been insufficiently studied. This paper captures the temperature-dependent viscoelastic characteristics of CA mortar by employing the fractional Maxwell model and applying it to finite element simulations through a Prony series. A vehicle–track–subgrade (VTS) coupled CRTS I ballastless track model, encompassing Hertz nonlinear contact and track irregularity, is established. The model is constrained symmetrically on both of the longitudinal sides, and the bottom is fixed on the infinite element boundary, which can reduce the effects of reflected waves. After the simulation outcomes in this study are validated, variations in the dynamic responses under different environmental factors are analyzed, offering a theoretical foundation for maintaining the ballastless tracks. The results show that the responses in the track subsystem will undergo significant changes as the temperature rises; a notable effect is caused by the increase in speed and fastener stiffness on the entire system; the CA mortar layer experiences the maximum stress at its edge, which makes it highly susceptible to damage in this area. The original contribution of this work is the establishment of a temperature-dependent vehicle–track–subgrade coupled model that incorporates the viscoelasticity of the CA mortar, enabling the investigation of dynamic responses in ballastless tracks. Full article

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

25 pages, 8306 KiB

Open AccessArticle

Investigation of the Contact Characteristics of a Single-Nut Ball Screw Considering Geometric Errors

by Jun Liu, Huaxi Zhou, Xiaoyi Wang and Changguang Zhou

Lubricants 2025, 13(2), 57; https://doi.org/10.3390/lubricants13020057 - 29 Jan 2025

Abstract

As the critical performance index of ball screws, the contact characteristics have a significant influence on the lubricant properties, tribological properties, and wear properties of ball screws, which further directly affect the service life of ball screws. The non-uniform load distribution induced by [...] Read more.

As the critical performance index of ball screws, the contact characteristics have a significant influence on the lubricant properties, tribological properties, and wear properties of ball screws, which further directly affect the service life of ball screws. The non-uniform load distribution induced by geometric errors results in imbalances among balls along the nut, negatively impacting the service life of ball screws. This study focuses on the load distribution of single-nut ball screws under low-speed working conditions. This paper proposes a self-adjustable model of load distribution that considers the flexibility of the screw and nut with respect to the determination of the non-bearing ball. A refined model for axial stiffness is proposed to systematically analyze the influence of geometric errors on stiffness variations under various loading conditions. The results confirm the ability of the proposed model to reveal the static load distribution in view of geometric errors. The greatest discrepancy observed between the theoretical predictions and the experimental data was 9.22%. The numerical simulations demonstrate variation trends in the normal contact load, the loaded-ball number, and the axial deformation of a nut with geometric errors. Furthermore, the relationship between the axial stiffness of a single-nut ball screw and the geometric error is obtained. The self-adjustable model of load distribution is helpful for studying the carrying capacity of a single-nut ball screw. The findings of the study provide a definite reference for optimization of structural design and wear life prediction. Full article

(This article belongs to the Special Issue High Performance Machining and Surface Tribology)

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38 pages, 11631 KiB

Open AccessReview

Synthesis, Stability, and Tribological Performance of TiO₂ Nanomaterials for Advanced Applications

by Kai Zeng, Liang Cheng, Wenjing Hu and Jiusheng Li

Lubricants 2025, 13(2), 56; https://doi.org/10.3390/lubricants13020056 - 29 Jan 2025

Abstract

The enhancement of tribological properties represents a pivotal strategy for achieving energy efficiency and environmental protection. Titanium dioxide (TiO₂) nanomaterials have been garnering significant attention due to their exemplary tribological properties and due to the abundance of titanium reserves. The present [...] Read more.

The enhancement of tribological properties represents a pivotal strategy for achieving energy efficiency and environmental protection. Titanium dioxide (TiO₂) nanomaterials have been garnering significant attention due to their exemplary tribological properties and due to the abundance of titanium reserves. The present review is concerned with the study of TiO₂ nanomaterials in lubricants. The properties and various synthesis methods of TiO₂ nanomaterials are presented. The dispersion stability of these TiO₂ nanomaterials in lubricating oils is discussed in depth, as well as strategies to improve their dispersion stability, such as enhancing compatibility with base oils, reducing the dynamic light scattering (DLS) particle size, modulating the zeta potential, and optimizing the drying step. Aggregation and dispersion instability remain key challenges for TiO₂ nanomaterials, especially bare TiO₂ nanoparticles (NPs). In contrast, in situ surface-modified TiO₂ NPs show improved stability and tribological performance, offering promise for further research. The tribological performance of lubricants has been demonstrated to be enhanced by TiO₂ nanomaterials, with the observed enhancement attributed to the synergistic effect of multiple mechanisms, including rolling, patching, polishing, and the formation of a protective film. Furthermore, future research suggestions are proposed to provide a reference for the design and synthesis of high-performance TiO₂ nano-lubricants and promote their wide application. Full article

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14 pages, 4258 KiB

Open AccessArticle

Synergistic Tribological Performance of Phosphorus- and Sulfur-Based Extreme Pressure and Anti-Wear Additives

by Jingyu Wang, Jinhua Zheng, Jun Wang, Xiao Yao, Xing Xiong and Haipeng Huang

Lubricants 2025, 13(2), 55; https://doi.org/10.3390/lubricants13020055 - 28 Jan 2025

Abstract

Higher demands on extreme pressure lubrication performance are posed by stringent working conditions. In this study, the synergistic tribological properties of phosphate ammonium salt in combination with active sulfurized olefin (S1) and non-active sulfurized fatty acids (S2) were investigated to meet the needs [...] Read more.

Higher demands on extreme pressure lubrication performance are posed by stringent working conditions. In this study, the synergistic tribological properties of phosphate ammonium salt in combination with active sulfurized olefin (S1) and non-active sulfurized fatty acids (S2) were investigated to meet the needs under stringent working conditions. The anti-wear mechanisms were further explored using scanning electron microscopy (SEM) with EDS, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), and focused ion beam microscopy. The experimental results indicate that P-S2 demonstrates superior friction reduction and wear resistance under low loads, potentially attributable to its higher polarity, whereas P-S1 exhibits better wear resistance under high loads. P-S1 also shows superior extreme pressure performance attributed to its higher active sulfur content and stronger film-forming ability, evidenced by a thicker friction film (82.62 nm vs. 24.28 nm for P-S2). The study highlights that the variations in the synergistic tribological performance of phosphorus- and sulfur-based additives may link to differences in molecular structure, active sulfur content, polarity, and corrosiveness, with P-S1 demonstrating enhanced extreme pressure performance possibly through the formation of a multi-layered friction film of polyphosphate, sulfide, oligophosphate, and sulfate layers. Full article

(This article belongs to the Special Issue Friction and Wear Mechanism Under Extreme Environments)

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25 pages, 7162 KiB

Open AccessArticle

Intelligent Analysis and Optimization of Lubrication Status Factor Based on Dynamically Loaded Roll Gap in Cold Strip Rolling

by Shuren Jin, Xu Li, Pengfei Wang, Feng Luan, Fangsheng Chen, Dianhua Zhang and Haidong Zhang

Lubricants 2025, 13(2), 54; https://doi.org/10.3390/lubricants13020054 - 28 Jan 2025

Abstract

Lubrication is a critical process in cold strip rolling, and the accurate characterization of lubrication characteristics is an essential factor affecting the strip quality. The roll bending and tilting roll in the flatness actuators change the loaded roll gap profile and affect the [...] Read more.

Lubrication is a critical process in cold strip rolling, and the accurate characterization of lubrication characteristics is an essential factor affecting the strip quality. The roll bending and tilting roll in the flatness actuators change the loaded roll gap profile and affect the lubrication characteristics by flatness dynamic correction, thus the mismatch between the actual and setting values of the lubrication status factor. Firstly, the flatness deviation correction model of roll bending and tilting roll based on the key information of the rolling process is established according to the high-order flatness target. Secondly, the characterization of the instantaneous oil film thickness in the work zone based on the loaded roll gap profile is derived from Reynolds’ equation. Finally, the explicit characterization method of the lubrication status factor in the rolling force model of the final stand is established with the work roll bending, tilting roll, and instantaneous oil film thickness of the work zone as variables, relying on the UCM five-stand, six-roll tandem cold rolling mill. The statistical evaluation and application results show that the mentioned optimization method can improve the setting accuracy of the rolling force by about 60% and the after-rolling gauge accuracy by about 50%. Full article

(This article belongs to the Special Issue Intelligent Rolling Dynamics: Enhancing Friction and Lubrication in Plate and Strip Mills)

11 pages, 2457 KiB

Open AccessArticle

Low-Foaming/Aeration and Low-Traction Electric Drivetrain Fluid (EDF) Solutions for High-Speed E-Mobility

by Philip Ma, Donna Mosher and Chad Steele

Lubricants 2025, 13(2), 53; https://doi.org/10.3390/lubricants13020053 - 28 Jan 2025

Abstract

The use of electrically driven drivetrains is increasing for passenger cars and light-, medium-, and heavy-duty trucks. Off-the-shelf automatic transmission fluids (ATFs) are still being used as electric drivetrain fluids (EDFs). EDFs are trending toward lower viscosity for better energy efficiency and better [...] Read more.

The use of electrically driven drivetrains is increasing for passenger cars and light-, medium-, and heavy-duty trucks. Off-the-shelf automatic transmission fluids (ATFs) are still being used as electric drivetrain fluids (EDFs). EDFs are trending toward lower viscosity for better energy efficiency and better heat transfer capacity, while satisfying all the other challenging requirements, such as gear/bearing scuffing/wear protection, oxidative stability, copper corrosion, and coating/seal material compatibility. In this paper, we will highlight the importance of low foaming, low aeration, and low traction coefficient which are critical for the performance of the EDF during high-speed applications, measured using metrics such as energy efficiency, heat transfer capacity, and longer oil drain interval. Full article

(This article belongs to the Special Issue Tribology of Electric Vehicles)

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11 pages, 5586 KiB

Open AccessArticle

The Tribological Reduction Mechanism of the Rubber Hexagonal Surface Texture of the Screw Pump Stator

by Zhongxian Hao, Songbo Wei, Deli Jia, Qinghai Yang, Xinglong Niu, Gang Zheng, Shijia Zhu and Xinfu Liu

Lubricants 2025, 13(2), 52; https://doi.org/10.3390/lubricants13020052 - 27 Jan 2025

Abstract

This paper develops a composite weaving structure, combining hexagonal micro-bumps and hexagonal grooves, in the design of the rubber surface of the screw pump. This allows us to solve the problem of high torque and fast wear of the rubber stator during the [...] Read more.

This paper develops a composite weaving structure, combining hexagonal micro-bumps and hexagonal grooves, in the design of the rubber surface of the screw pump. This allows us to solve the problem of high torque and fast wear of the rubber stator during the operation of screw pump lifting oil recovery, based on the bionic hexagonal surface structure, traditional surface damping principle, and fluid dynamic pressure lubrication theory. Finite element analysis is first conducted to quantitatively analyze the impacts of the parallel side distance, groove width, and groove depth on the surface flow field and wall pressure field of the composite hexagonal structure. Based on the simulation law, the rubber surface laser structure is then designed and prepared by nanosecond laser processing. Afterward, tribological experiments are conducted under the condition of long-term immersion in the actual extraction fluid of shale oil wells. This aims at simulating the actual downhole oil production conditions and quantitatively studying the impact of the size of the composite hexagonal structure on the lubrication characteristics of the friction part of the stationary rotor, as well as the effect of abrasion reduction. The results show that, within the simulation range, the smaller the parallel side distance, the higher the load-carrying capacity. In addition, the hexagonal weave with a parallel side distance of 3 mm has a higher wall load carrying capacity than that with distances of 4 mm and 5 mm. When the groove width is equal to 0.4 mm, the oil film load carrying capacity is higher than that in the case of 0.2 mm. When the groove depth increases, the oil film pressure first increases and then stabilizes or decreases after reaching 0.3 mm. In the hexagonal weave, the friction ratio of the rotor is equal to 0.4 mm. In the tribological experiment of hexagonal weave, the smaller the parallel side distance, the smaller the friction coefficient, and the 0.5 mm weave has the highest performance. Full article

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18 pages, 8358 KiB

Open AccessArticle

Research on Rotor Dynamic Characteristics of High Speed Aviation Piston Pump

by Lijun Chen, Rushen Deng, Jun Zha, Jianning Gu, Tianxiang Xia and Runlin Chen

Lubricants 2025, 13(2), 51; https://doi.org/10.3390/lubricants13020051 - 25 Jan 2025

Abstract

The high-speed aviation piston pump plays a vital role in hydraulic systems in the aviation field. Extremely complex force situations happen during running operations due to the coupling between multiple components, as a result of the overall dynamic characteristics being complex and changeable, [...] Read more.

The high-speed aviation piston pump plays a vital role in hydraulic systems in the aviation field. Extremely complex force situations happen during running operations due to the coupling between multiple components, as a result of the overall dynamic characteristics being complex and changeable, which brings great difficulties and challenges to its performance optimization. Taking the high-speed aviation piston pump as the research object, a mechanical balance equation of the piston based on the dynamic balance method was proposed. The reaction force of the swashplate and the influence of rotational speed and outlet pressure on it were modeled. Through the balance of the system and the component subsystem, the load of the support bearing of the piston pump under different working conditions is analyzed, as well as the influence of the rotational speed and the outlet pressure on the bearing stiffness by the quasi-static method. In addition, the discrete model of the piston pump spindle and the discrete model of the rotor system are established. The accuracy of the model is verified by the finite element method. The maximum error of the spindle discrete model is 6.13%, and the maximum error of the rotor system discrete model is 15.28%. The transfer matrix analysis shows that the working condition parameters have little effect on the critical speed of the spindle and rotor system, and the outlet pressure has a more significant effect than the speed. The research results provide a theoretical basis and analysis method for the dynamic analysis and structural optimization of the high-speed aviation piston pump. Full article

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22 pages, 6133 KiB

Open AccessArticle

Targeted Minimum Quantity Fluid Application in Machining

by Chandra Sekhar Rakurty, Patricio Ivan Varela and Alagar Krishnan Balaji

Lubricants 2025, 13(2), 50; https://doi.org/10.3390/lubricants13020050 - 25 Jan 2025

Abstract

The surface integrity of a machined component is crucial for its service life part. One of the main final specifications that a machined part is inspected for is the surface integrity metrics, including surface residual stresses, surface microhardness, surface roughness, and microstructure. In [...] Read more.

The surface integrity of a machined component is crucial for its service life part. One of the main final specifications that a machined part is inspected for is the surface integrity metrics, including surface residual stresses, surface microhardness, surface roughness, and microstructure. In this paper, the cutting fluid is strategically targeted to utilize heat energy effectively in the primary, secondary, and tertiary shear zones to positively affect the surface integrity metrics and machining mechanics. In this study, a lower quantity of the cutting fluids is targeted at the high-temperature zones to reduce the machining temperatures, thereby effectively simulating the effect of a ‘flood coolant’. The cutting fluid is applied simultaneously as a targeted Minimum Quantity Fluid (MQF) on the cutting tool’s flank and rake faces to improve the surface integrity metrics and chip formation. Also, this study analyzes the effect of the cutting fluid composition, the type of cutting fluid, and the amount of fluid quantities. The machining-induced surface integrity metrics are analyzed to understand the effects of targeted minimum quantity fluid application. The impact of the targeted application of cutting fluid on machining mechanics metrics, such as cutting forces and chip formation, is analyzed. Applying a targeted MQF application at the flank face of the cutting tool leads to higher compressive subsurface principal residual stresses. The results indicate that using MQF on both the flank and rake faces simultaneously enhances the surface integrity. The effect of a cutting fluid jet on the flank face is modeled to highlight the thermophysical properties that are crucial for selecting the appropriate cutting fluid to lower the machining-induced temperatures. With targeted MQF application, the fluid jet acts as a dynamic and external chip control mechanism. Overall, effectively managing temperatures in machining could enhance subsurface residual stresses and surface roughness using various cutting fluid combinations. Also, this paper presents a targeted cutting fluid application that improves the microstructural formation, enhancing chip control and producing machined surfaces and components with better surface integrity. Full article

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

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18 pages, 3930 KiB

Open AccessArticle

Lubricant Viscosity Impact in Fuel Economy: Experimental Uncertainties Compensation

by Fernando Fusco Rovai and Eduardo Tomanik

Lubricants 2025, 13(2), 49; https://doi.org/10.3390/lubricants13020049 - 24 Jan 2025

Abstract

Climate constraints impose greenhouse gas emissions mitigation, and passenger cars have considerable contributions to contribute to this. To improve the engine efficiency of vehicles equipped with conventional powertrains, many technologies are available but with limited individual contribution. The experimental assessment of some technology [...] Read more.

Climate constraints impose greenhouse gas emissions mitigation, and passenger cars have considerable contributions to contribute to this. To improve the engine efficiency of vehicles equipped with conventional powertrains, many technologies are available but with limited individual contribution. The experimental assessment of some technology regarding fuel economy measurement results is sometimes lower than test uncertainties. This study proposes a methodology to compensate the fuel economy for two test uncertainties: vehicle speed variations and battery recharging. The proposed method can be applied when investigating the effects of different vehicle design changes, including engine power cell design. In this work, the proposed method is demonstrated on the test of two oils: one 5W40, the other 5W20, both without FM. Applying the proposed methodology to experimental results, the expected higher influence of oil viscosity on urban conditions could be observed, and the experimental results presented a much better correlation with the vehicle numerical simulation. Applying the proposed compensation, fuel savings of using the 5W20 in comparison to the 5W40 oil was 3.5% under urban conditions and 2.0% on highways. 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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23 pages, 3482 KiB

Open AccessArticle

Comparative Study of Squalane Products as Sustainable Alternative to Polyalphaolefin: Oxidation Degradation Products and Impact on Physicochemical Properties

by Jessica Pichler, Adam Agocs, Lucia Pisarova, Ichiro Minami, Marcella Frauscher and Nicole Dörr

Lubricants 2025, 13(2), 48; https://doi.org/10.3390/lubricants13020048 - 24 Jan 2025

Abstract

The growing demand for sustainable lubricant solutions is driving the exploration of bio-based materials that deliver comparable performance to conventional, primarily fossil-based lubricant chemistries. This study focuses on squalane as a sustainable base oil, which can be derived from different renewable sources. A [...] Read more.

The growing demand for sustainable lubricant solutions is driving the exploration of bio-based materials that deliver comparable performance to conventional, primarily fossil-based lubricant chemistries. This study focuses on squalane as a sustainable base oil, which can be derived from different renewable sources. A total of two squalane products were evaluated for thermal-oxidative stability and benchmarked against a polyalphaolefin, PAO 4, of the same total carbon number. Oils artificially altered in a closed reactor were sampled and subjected to conventional lubricant analyses, including infrared spectroscopy, to determine the changes due to autoxidation over time. For in-depth information, direct-infusion high-resolution mass spectrometry and gas chromatography coupled with triple quadrupole mass spectrometry were employed to identify degradation products from thermo-oxidative stress. The results revealed substantial variability in the stability of squalane products, suggesting that differences in raw materials and production processes have a major impact on their performance, including rheological properties. The degradation products of polyalphaolefin and squalane, identified through detailed mass spectrometry, were analyzed to understand their impact on conventional physicochemical properties. While polyalphaolefin predominantly generated carboxylic acids with short to medium chain lengths as degradation products, squalane oxidation produced carboxylic acids with medium to long chain lengths as well as several alcohols and ketones. Despite these differences, squalane demonstrates its potential as a non-fossil hydrocarbon base oil, as squalane products matched and even exceeded PAO 4 stability. Full article

(This article belongs to the Special Issue Progress and Challenges in Lubrication: Green Tribology)

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19 pages, 10767 KiB

Open AccessArticle

Surface Integrity and Machining Mechanism of Al 7050 Induced by Multi-Physical Field Coupling in High-Speed Machining

by Wei Lu, Chenbing Ni, Youqiang Wang, Chengguo Zong, Dejian Liu and Xingbao Huang

Lubricants 2025, 13(2), 47; https://doi.org/10.3390/lubricants13020047 - 22 Jan 2025

Abstract

Improving the surface quality and controlling the microstructure evolution of difficult-to-cut materials are always challenges in high-speed machining (HSM). In this paper, surface topography, defects and roughness are assessed to characterize the surface features of 7050 aluminum alloy (Al 7050) under HSM conditions [...] Read more.

Improving the surface quality and controlling the microstructure evolution of difficult-to-cut materials are always challenges in high-speed machining (HSM). In this paper, surface topography, defects and roughness are assessed to characterize the surface features of 7050 aluminum alloy (Al 7050) under HSM conditions characterized by high temperature, strain and strain rate. Based on multi-physical field coupling, the mechanism of microstructure evolution of Al 7050 is investigated in HSM. The results indicate that the surface morphology and roughness of Al7050 during HSM are optimal at f_z = 0.025 mm/z, and the formation of surface defects (adherent chips, cavities, microcracks, material compression and tearing) in HSM is mainly affected by thermo-mechanical coupling. Significant differences are observed in the microstructure of different machined subsurfaces by electron backscatter diffraction (EBSD) technology, and high cutting speeds and high feed rates contributed to recrystallization. The crystallographic texture types on machined subsurface are mainly {110}<112> Brass texture, {001}<100> Cube texture, {123}<634> S texture and {124}<112> R texture, and the crystallographic texture type and intensity are significantly affected by multi-physical field coupling. The elastic–plastic deformation and microstructural evolution of Al7050 alloy during the HSM process are mainly influenced by the coupling effects of multiple physical fields (stress–strain field and thermo-mechanical coupling field). This study reveals the internal mechanism of multi-physical field coupling in HSM and provides valuable enlightenment for the control of microstructure evolution of difficult-to-cut materials in HSM. Full article

(This article belongs to the Special Issue Friction and Wear of Alloys)

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14 pages, 15081 KiB

Open AccessArticle

CFD-Based Investigation of Static and Dynamic Pressure Effect in Aerostatic Bearings with Annular Grooves at High Speed

by Wentao Song, Minggui Li, Peng Cheng, Decheng Wang, Chenxi Shao and Junying Zhou

Lubricants 2025, 13(2), 46; https://doi.org/10.3390/lubricants13020046 - 22 Jan 2025

Abstract

Based on the SST k-ω turbulence model, this study investigated the flow fields of annular groove and non-groove small-hole throttling aerostatic bearings (AGSTABs and STABs). It examined the formation mechanisms of static and dynamic pressure effects in both flow fields at high speed, [...] Read more.

Based on the SST k-ω turbulence model, this study investigated the flow fields of annular groove and non-groove small-hole throttling aerostatic bearings (AGSTABs and STABs). It examined the formation mechanisms of static and dynamic pressure effects in both flow fields at high speed, evaluating how parameters such as eccentricity, groove width ratio, and depth ratio influence the average load capacity and static and dynamic pressure effects. The findings show that STABs combine static and dynamic pressure effects at high speeds, while AGSTABs decouple them to enhance load capacity, simultaneously reducing vortex and backflow intensity. At low eccentricities, AGSTABs exhibit superior performance over STABs, achieving 20% higher average load capacity at 0.1 eccentricity. Additionally, increasing eccentricity enhances static and dynamic pressure effects in both bearings. A larger groove width ratio decreases the throttling efficiency and dynamic pressure, with pressure dropping from 3.5 MPa (static) to 1.6 MPa, and 6.3 MPa (dynamic) to 1.7 MPa respectively, at 30,000 RPM. In contrast, the depth ratio of annular groove has only a minor impact on static and dynamic pressure effects. Full article

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14 pages, 4236 KiB

Open AccessCommunication

Catalytic and Tribological Performances of a Novel Bi-Functional Ionic Liquid in Lubricating Ester Oil

by Yanan Wang, Huaigang Su, Jun Yin, Cheng Jiang, Qilong Zhao, Wenjing Lou and Qian Jia

Lubricants 2025, 13(2), 45; https://doi.org/10.3390/lubricants13020045 - 22 Jan 2025

Abstract

To address the detrimental effects of the residue of catalysts on the tribological performances of ester lubricants, a novel and efficient bi-functional ionic liquid 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methylimidazole di(2-ethylhexyl) phosphate ([(BHT-1)MIM][DEHP]) was prepared. The catalyst not only facilitates the synthesis of pentaerythritol tetra-hexanoate (PETH) through the [...] Read more.

To address the detrimental effects of the residue of catalysts on the tribological performances of ester lubricants, a novel and efficient bi-functional ionic liquid 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methylimidazole di(2-ethylhexyl) phosphate ([(BHT-1)MIM][DEHP]) was prepared. The catalyst not only facilitates the synthesis of pentaerythritol tetra-hexanoate (PETH) through the catalytic esterification reaction—achieving up to 96% conversion with a 94% yield—but also enhances the tribological performance of ester oil PETH when used as a lubricant additive. The tribological property has been improved remarkably: the mean friction coefficient for PETH + [(BHT-1)MIM][DEHP] is notably lower, at 0.110, compared to the PETH, which has a coefficient of 0.180. Meanwhile, the wear scar diameter of the steel ball, when lubricated with PETH + [(BHT-1)MIM][DEHP], is notably smaller than that of a steel ball lubricated solely with PETH. Especially, the reduction in the wear volume at 100 °C is up to 81.46% compared with the base oil PETH. [(BHT-1)MIM][DEHP], PETH + [(BHT-1)MIM][DEHP], and the worn track of the upper running ball and lower disc were systematically characterized by using Nuclear Magnetic Resonance (NMR) spectra, a Fourier Transform Infrared Spectrometer (FT-IR), a field emission scanning electron microscope (FESEM), Thermal gravity analysis (TG), X-ray photoelectron spectroscopy (XPS), and an optical microscope (OM). The wear mechanism of the tailored lubricant oil was discussed in terms of the chemical composition of the worn surface. Full article

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