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The functional group in the molecular chain of lubricants is a key factor for a boundary lubricating film, which can further enhance the friction performance by interfacial tribochemistry. In this paper, the tribological behavior of epoxy/graphene (EP/Gra) composites was investigated through varying lubrication conditions, including dry friction, or different lubricants (such as water, hexadecane, oleylamine, and oleic acid). The porosity and Shore hardness (SHD) of the EP composites were significantly improved by the addition of graphene. Results showed that the porosity of the EP/0.75 wt.% Gra composites was reduced by 75.6% and their SHD increased by 5.4 compared with the EP/0.05 wt.% Gra composites. The average coefficient of friction (COF) of the composites was reduced by at least 27.3% under dry friction conditions. For water as lubricant, the EP/0.5 wt.% Gra composite exhibited the lowest COF (0.0455). The EP/0.75 wt.% Gra composite displayed the lowest COF (0.0466) when hexadecane acted as lubricant. By contrast, EP/0.05 wt.% Gra showed the lowest COF (0.0389) with oleylamine as lubricant, and the EP/0.25 wt.% Gra composites gave the lowest COF (0.0433) under oleic acid. The amine group of oleylamine reacted with the EP group to form a hydroxyl group, resulting in a polymer with low friction adhered to the friction interface. Simultaneously, the EP group reacted with the carboxyl group, forming a network of hydrogen bonds with graphene, which reduced the shear stress on the friction interface. Therefore, the functional groups of lubricants have a vital influence on the tribological properties of frictional composites, which may provide a new approach to solving the problem of wear. [ABSTRACT FROM AUTHOR]

Bearings are common components used in the transmission system of tool machinery and linear drive equipment. With increasing demand for higher efficiency and faster production under the required accuracy, the control of bearing temperature rise under high operational speed becomes a critical issue. The improper control of temperature rise can lead to the thermal deformation and life reduction of the machinery. Conventionally, a circulating oil lubrication system is utilized with journal bearings. In this study, a similar lubrication system was adopted for the ball bearing with a retrofit design. Three control factors, i.e., rotational speed, bearing preload, and the viscosity of the lubricant used, were chosen to study their effects on the temperature performance of the proposed lubrication system. Experimental measurements showed that the lubrication system was able to lower the temperature rise of the bearing considerably compared with its unlubricated counterpart, especially at high rotational speeds. Even with the enhanced cooling from the oil circulation system, temperature rise still increased with rotational speed. However, with increased preload, the temperature rise first dropped and then increased owing to the different contact characteristics of the balls and rings of the bearing. A fitted function for the temperature rise of the bearing under different operational conditions was demonstrated to have a prediction accuracy within 3%. Therefore, the retrofitted bearing oil cooling system should be applicable in the design of high-speed machinery for industry. [ABSTRACT FROM AUTHOR]

Introduction: The demand to increase reliability and reduce maintenance costs drives the search for new condition monitoring solutions of machines. Bearings are of special interest in this matter as they are main contributors to machine downtime. Therefore, this article investigates the electric behavior of a hydrodynamic journal bearing using impedance measurement. Methods: For that purpose measurements are taken in boundary lubrication, mixed lubrication and hydrodynamic lubrication of a hydrodynamic journal bearing. In order to interpret the behaviour observed in these measurements, a phenomenological model is developed using the quantitative working space model. The measurement results are also interpreted using analogies to the Stribeck curve as a known tribological model. Additionally, measurements in mixed lubrication are analysed in detail. Results: These measurements show that the electric behaviour of journal bearings changes significantly within the mixed lubrication regime. This change in behaviour shows three distinct states within mixed lubrication which helps to identify destructive operating conditions. Furthermore, the measurements potentially allow the detection of deformation or damage of the bearing in mixed lubrication. Discussion: The quantitative analysis of the electric behaviour of journal bearings is possible in the mixed lubrication regime and can be used in future to extract condition and operating information from a system during operation. [ABSTRACT FROM AUTHOR]

Efficient cooperative lubrication can be achieved via the introduction of core-shell structure lubricant additives with hard core and soft shell, for obtaining the expected anti-wear performance from the structural changes in the friction process. In this study, C@Ag microspheres with a core-shell structure were prepared by the redox method with carbon spheres as the core and Ag nanoparticles as the shell. Their tribological behaviors as base oil (G1830) additive with different concentrations were investigated in detail. Compared with base oil, the addition of C@Ag particles at 0.5 wt% can reduce the coefficient of friction (COF) and wear volume (Wv) up to 15.5% and 88%, respectively. More importantly, C@Ag particles provide superior lubrication performance to single additive (like carbon sphere (CS) and Ag nanoparticle). C@Ag core-shell particles contribute to the formation of tribo-film by melt bonding of flexible Ag and carbon sphere (CS) toward excellent self-repair performance and high-efficiency lubrication. Hence, core-shell structural nanoparticles with hard-core and soft-shell hold bright future for high-performance lubrication application. [ABSTRACT FROM AUTHOR]

The ocular lubrication, where the eyelid constantly slides on the curved corneal surface, is considered as one of primary lubrication systems in bio-tribology. Under reliable lubrication conditions, sensitive ocular tissues remain intact from fatigue damage during spontaneous blink cycles. The tear film, evenly filled between cornea and conjunctiva, is a biological fluid with dynamic adjustment ability, which provides superior lubrication with the friction coefficient of below 0.01. However, the lubrication failure may result in a variety of uncomfortable symptoms such as inflammatory reactions, tissue damage and neurological abnormalities. Therefore, it is essential to clarify the fundamental mechanism of ocular lubrication, which helps to alleviate and even recover from various ocular symptoms. This review firstly demonstrates that the ocular components, containing lipids and mucins, contribute to maintaining the lubrication stability of tear film. Furthermore, the ocular lubrication state in various physiological environments and the physical effect on tear film dynamics are further discussed. As typical applications, the therapeutic agents of dry eye syndrome and contact lens with superior lubrication effects are introduced and their lubrication mechanisms are clarified. Finally, this review summarizes a series of the latest research inspired by ocular lubrication. Overall, this work will provide a valuable guidance on the theoretical research and extensive applications in the field of biological lubrication. [ABSTRACT FROM AUTHOR]

Sexual problems are highly prevalent in postpartum period. This study aimed to review educational programs and counseling models which had addressed the postpartum sexual health. This narrative review was written based on the SANDRA checklist. A comprehensive search was performed in the international databases (PubMed, Scopus, Embase, WebofScience, ProQuest, Cochrane Library) and Google Scholar, until June-2021. After screening the title and abstract of the observational and interventional articles whose aim was in line with our study(n = 5,758), the texts of 37 articles were fully studied and, finally, 7 articles were selected. Four articles introduced sexual education programs and three articles were about the sexual counseling models (PLISSIT, BETTER, REDI). Sexual education and sexual counseling had 3-7 and 4-6 sessions respectively. They focused on the increasing of sexual knowledge, correction of misconceptions, Kegel exercises, common sexual problems, and appropriate solutions for them. Sex education can improve sexual function by increasing awareness about genital anatomy and sexual response cycle; sexual counseling can also improve sexual function by providing strategies such as the use of lubricants, increased foreplay time, sexual fantasies, and promotion of marital intimacy by expressing sexual feelings and conversations. Present summary of the structure and components of sexual educational/counseling models can empower health care providers in providing postpartum sexual services. Postpartum sexual problems are highly prevalent. Present summary of the components of educational/counseling models can empower health care providers in providing evidence-based postnatal sexual services. They emphasized the increase of sexual knowledge, correction of misconceptions, Kegel exercises, identification of postpartum sexual problems, and provision of solutions for them. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to analyze the dynamic characteristics and the meshing state transition characteristics of spalling defect gears under various lubrication conditions. The time-varying geometric parameters, motion parameters and load distribution of the gears in the state of positive meshing and reverse impact are analyzed. The time-varying meshing stiffness considering the time-varying friction coefficient under elastohydrodynamic lubrication (EHL), mixed lubrication and boundary lubrication are calculated, and the spalling defect is introduced in the stiffness calculation process. The equivalent lubrication model of the gear is established, the switching condition of the lubrication state is derived, and the distribution of the lubrication state in the torque-speed plane is discussed. The multimeshing state dynamic model of the spalling defect gear is established, and the evolution characteristics of the coexistence response and the transition of the meshing state under different lubrication conditions are simulated by using the attraction domain, phase trajectory, meshing force and bifurcation diagram. The results show that the phase trajectory of the gear with the spalling defect is deformed compared with that of the healthy gear. The change of lubrication state has little effect on the phase trajectory and attraction domain of the gear with spalling defect, but has a great influence on the meshing force. At the spalling boundary, the meshing force is changed abruptly, and the worse the lubrication state, the more obvious the mutation. Due to the influence of spalling on tooth stiffness, it will also affect the meshing force in the nonspalling area. [ABSTRACT FROM AUTHOR]

Glass lubricant with a suitable viscosity is essential for producing high‐quality titanium products by the hot extrusion process. In this study, a novel lubricant of B2O3–SiO2–Al2O3–Na2O–TiO2 (BSANT) glass was proposed, where the effects of B2O3/SiO2 molar ratio (B/Si) and B2O3 content on viscosity and structure were investigated. The results showed that the BSANT glass viscosity was gradually decreased, and the viscous activation energy was decreased by 20.24% with an increased B/Si ratio from 0.415 to 0.719. This was attributed to the decreased amounts of Q3, [BO4], [AlO4], and bridging oxygen (BO) in the network structure, which in turn resulted in a decreased network degree of polymerization. When B2O3 content was increased from 18.70 to 33.12 mol.%, the melt viscosity value at 950 ℃ was decreased by 64.51%, and the viscous activation energy was reduced by 15.82%. Boron anomalies were also observed in glass melts with the B2O3 content from 28.28 to 33.12 mol.%. The mechanisms responsible for this phenomenon were thoroughly discussed in the study. Additionally, a comparison and discussion of the applications of glass lubricants in metal hot working were presented. A glass lubricant with a specific composition was recommended for use in hot extrusion process within the temperature range of 950–1100°C due to its relatively stable viscosity properties. A novel lubricant of B2O3–SiO2–Al2O3–Na2O–TiO2 (BSANT) glass was proposed, where the effects of B2O3/SiO2 molar ratio (B/Si) and B2O3 content on viscosity and structure were investigated. A glass lubricant with a specific composition was recommended for use in hot extrusion process within the temperature range of 950–1100°C due to its relatively stable viscosity properties. [ABSTRACT FROM AUTHOR]

This study utilizes molecular dynamics simulations to explore the tribological behavior of rough surfaces across various lubrication regimes—boundary, mixed, and elastohydrodynamic (EHL)—at the nanoscale. The analysis not only highlights the distinct interactions between asperity contacts and lubricant films but also introduces novel insights into how lubricant film thickness and surface roughness interplay to dictate frictional dynamics. The analysis reveals that in dry contact, surface roughness quickly stabilizes despite an initial increase in contact area, indicating a dominant role of asperity interlocking that influences frictional resistance. Transitioning to boundary lubrication, the presence of a lubricant layer modifies the contact mechanics, leading to a slower root mean square (RMS) reduction of surface roughness and a more gradual increase in friction force, emphasizing the lubricant's protective effect against asperity flattening. Nevertheless, under lower loads, this protective effect can lead to increased frictional forces compared to dry contact due to higher final roughness. Mixed lubrication maintains a near-constant contact area after initial contact, with any variations in friction force primarily occurring in the early cycles due to rapid asperity flattening. In the EHL regime, the formation of a complete lubricant film between surfaces results in the lowest friction forces, dominated by viscous shear rather than direct asperity contact. Unique to this study is the quantification of these effects under realistic roughness conditions (RMS of 1.2 nm). These regime-specific behaviors underline the nuanced interplay between RMS, contact area, and friction forces, and enhance our understanding of the fundamental principles guiding the design of lubrication strategies for advanced mechanical systems. [ABSTRACT FROM AUTHOR]

Due to the long-standing use of MAX phase materials since the 1960s and the emergence of MXenes in 2011, both are celebrated for their extraordinary mechano-tribological properties, including layered structures, high mechanical strength, and thermal conductivity. Nevertheless, there remains a crucial research gap in comprehensively comparing their tribological performance under solid lubrication, underscoring the need for an in-depth investigation. To close this research gap, we deposited MAX phase and MXene coatings by spray-coating on stainless-steel substrates. Subsequently, we evaluated their tribological properties, deciphered the underlying mechanisms using linear-reciprocating tribometry and high-resolution material characterizations. Our results demonstrated that the MXene coatings surpass the MAX phase coating in friction reduction by 81.82 %. In terms of wear depth, MXene coating has shown a notably reduced depth compared to both the reference steel sample and the MAX phase coating. Advanced tribochemical analysis indicates that MXenes' superior tribological performance is endorsed by their ability to form a thick, patchy-like transferlayer on the counterbody, which results from their ability to shear and delaminate under acting contact stress. Our study offers a framework for future investigations into utilizing MXene-based materials in tribological applications. [ABSTRACT FROM AUTHOR]

This work explores experimentally the effects of DC electrical currents on lubricant film thickness alteration in lubricated sliding steel contacts in the boundary and mixed regime as measured by ultrasound. The experiments were performed in a two-electrode cell-based pin-on-disk tester instrumented with ultrasonic transducers. Unelectrified and electrified tribological tests were conducted on steel flat-on-flat contacts under various speeds and loads using both a mineral base oil and a gear oil. Film thickness, coefficient of friction (CoF), and electrical contact resistance (ECR) were measured during short experiments (30 s) in unelectrified and electrified (1.5 and 3 A) conditions. The results suggest that film thickness, CoF, and all ECR are altered by passing DC currents through the contact. In particular, film thickness increased and decreased, respectively, by applying electricity at the different speeds and loads tested. These alterations were majorly ascribed to oil viscosity decrease by local heat and surface oxidation caused by electrical discharge and break down at the interface. [ABSTRACT FROM AUTHOR]

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity. [ABSTRACT FROM AUTHOR]

This study is an optimized extension based on the authors' previous research on the tribo-chemical reaction under constant temperature field of two-stroke internal combustion engines (ICEs). It establishes a coupled analysis model that considers the tribo-chemical reactions, dynamic contact, and interface lubrication of the piston ring-cylinder liner (PRCL) system under transient temperature conditions. In this study, for the first time, the prediction of the tribofilm thickness and its influence on the surface micro-topography (the comprehensive roughness) are coupled in the working temperature field of the PRCL system, forming an effective model framework and providing a model basis and analytical basis for subsequent research. This study findings reveal that by incorporating temperature and tribofilm into the simulation model, the average friction deviation throughout the stroke decreases from 8.92% to 0.93% when compared to experimental results. Moreover, the deviation during the combustion regime reduces from 39.56% to 7.34%. The proposed coupled model provides a valuable tool for the evaluation of lubrication performance of the PRCL system and supports the analysis software forward design in two-stroke ICEs. [ABSTRACT FROM AUTHOR]

Inorganic nanoparticles have been proved as powerful lubricant additives at elevated temperature. However, the tribological properties are inevitably impaired due to poor dispersion and insufficient high temperature resistance of organic matter modified nanoparticles. Here, we prepare a self-dispersed molybdenum disulfide quantum dot/graphene crumpled ball (MGCB) comprising molybdenum disulfide quantum dot uniformly interspersed on the wrinkled graphene ball. The crumpled ball composite possesses excellent dispersity in polyalkylene glycol base oil without depending on surface modifiers. Compared with the conventional phosphate esters lubricant, our results indicate MGCB could vastly improve the lubrication performance of polyalkylene glycol with an extremely low concentration (0.05 wt%) at elevated temperature (150 °C), showing a friction reduction of 47% and a wear reduction of 30% compared with the conventional phosphate esters lubricant (tricresyl phosphate, TCP). This is because crumpled ball potentiates synergistic lubrication effect within the boundary lubrication. Overall, we envision our designed self-dispersed MGCB has significant potential in tribological application at elevated temperature. [ABSTRACT FROM AUTHOR]

A stochastic uncertain tribodynamic model is established for a spur gear pair for the first time. The stochastic uncertainty of pinion rotation speed propagated to lubrication performance is investigated. The probability density function of the minimum lubricant film thickness hmin evolves over time periodically at interval of an engagement process. Correspondence between abrupt increase in meshing force and amplification of hmin uncertainty is found. Robust and reliable lubrication performance can be achieved by suppressing the hmin uncertainty and decreasing the lubrication failure probability. This can be done by increasing lubricant viscosity, and decreasing input torque and uncertainty level of input rotation speed. This work lays a solid foundation for robust and reliability based optimization for tribodynamic gear system. [ABSTRACT FROM AUTHOR]

Most studies of liquid lubricants were carried out at temperatures below 200 °C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 °C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si3N4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 °C, coefficient of friction (COF) remains at 0.13–0.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.2–0.3. At 200 °C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.16–0.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with the temperature, while the wear rate barely changes at temperatures above 200 °C. The anti-wear mechanism is explained as tribochemical reactions are more likely to occur between CPSO and steel surface with the increased temperature, generating the FeCl2 protective film on the metal surface. Accordingly, FeCl2 tribochemical film improves the lubrication and anti-wear capacity of the system. At high temperatures (200–350 °C), FeCl2 film becomes thicker, and the contact region pressure becomes lower due to the larger wear scar size, so the wear rate growth of M50 steel is much smaller compared with that of low temperatures (22–150 °C). The main findings in this study demonstrate that CPSO lubricant has good anti-wear and lubrication capacity, which is capable of working under temperatures up to 350 °C. [ABSTRACT FROM AUTHOR]

Hydrodynamic linear guides in machine tools offer a high load capacity and excellent damping characteristics, improving stability, precision, and vibration reduction. This study builds on previous research where floating heights were verified with a simulation model limited to measured floating heights. Advancements include incorporating pressure sensors into a fixed steel rail, enabling simultaneous measurement of oil film pressure and floating heights for a comprehensive understanding of lubrication conditions within the lubrication gap. The experimental results explore the effects of different lubrication methods, providing valuable insights into cavitation and lubrication adequacy. The results demonstrate the feasibility of utilizing pressure sensors to measure oil film pressure within the lubrication gap, providing a nuanced understanding of lubrication dynamics. By measuring both floating heights and pressure measurement, distinctions between hydrodynamic lubrication, mixed friction regions, and instances of lubricant deficiency become readily discernible. The variations in real-time oil film pressure and floating heights help to optimize the lubrication cycle for hydrodynamic linear guides, enhancing system performance and longevity. [ABSTRACT FROM AUTHOR]

Within electrical contacts, poor electrical conductivity of lubricants can lead to triboelectric charging, causing electrostatic currents and thermal effects, which accelerate lubrication failure. This study aimed to address these challenges by producing and testing three greases with different base oils: ionic liquid ([Oley][Oleic]), synthetic oil (PAO4), and vegetable oil-based synthetic ester (trimethylolpropane oleate). Each grease was prepared with polytetrafluoroethylene powder as the thickener. The greases were tested using a custom-made tribometer, integrated with a grounded electrical current system, with friction tests conducted with up to a 2 A electrical current flow at a constant voltage supply of 4.5 V. Under triboelectric friction testing, [Oley][Oleic] grease outperformed a commercial perfluoropolyether grease by 27.7% in friction and 16.3% in wear. This grease also showed better performance than formulated lithium grease with extreme pressure additives. The study demonstrates that greases with low interfacial resistance can retain their lubrication capacity under triboelectric conditions. These results indicate that [Oley][Oleic] grease, with its ionic liquid base oil, offers a promising solution for applications involving electrical contacts. This study highlights the potential of using advanced base oils and thickeners to enhance the performance and sustainability of lubricants in demanding environments. [ABSTRACT FROM AUTHOR]

Water‐based lubricants have attractive properties compared to flammable oily lubricants but in high‐temperature environments remain a tricky challenge due to the Leidenfrost effect‐induced poor wettability once contacting sufficiently hot surfaces. Herein, a surfactant‐modified Laponite nanoclay (LNC), as a prototype water‐based lubricant with considerable lubricity, exhibits spontaneous high‐temperature wettability by which the Leidenfrost point (LFP) can be improved above ≈350 °C on crude stainless steels, increasing by ≈140°C compared to pure water. The inter‐particle attractions between LNC nanoplates increase the liquid viscosity, causing viscous force of bulk water near the substrate, allowing in situ deposition of LNC layers on the hot surface to trigger three‐phase contact line (TCL) pinning. As a basis, wettable lubricants are further optimized on their lubricity by intercalating zwitterionic surfactants between LNC nanoplates, thereby reducing friction coefficient to ≈0.1. The LNC lubricants have been demonstrated in a four‐ball tribometer to simulate hot rolling lubrication, providing insights for high‐temperature metal processing, and potential applications in mechanical engineering and the aerospace field. [ABSTRACT FROM AUTHOR]

Wax is a prevalent lubrication material extensively employed in various engineering applications. Understanding the degradation characteristics of the waxy lubrication layer under diverse stress variables and levels is crucial for ensuring system security and reliability. Due to the unclear mechanism governing the degradation of the waxy lubrication layer under different stress variables, existing degradation models are unsuitable for modeling waxy lubrication layer degradation data. To address this challenge, we propose a functional data‐driven method leveraging dense observations of waxy degradation. Through extensive simulations and a case study, we demonstrate the superior performance and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In this work, we prepared nitrile butadiene rubber (NBR) composites with fluorographene (FG) and carbon nanotubes (CNTs) as hybrid fillers by a solution‐blending method. The resulting composites xFG/yCNTs‐NBR, where x and y represent the loading of FG and CNTs respectively, show significantly improved physical and mechanical properties. The hybrid fillers can form a filler network in the rubber matrix, leading to efficient energy dissipation. As a result, when the mass ratio of FG to CNTs is 1:1 and the total filler loading is 20 phr, the tensile strength of 10FG/10CNTs‐NBR is as high as 12.1 MPa. Furthermore, due to inherent lubricating and oil‐repelling effects of FG, 10FG/10CNTs‐NBR shows an abrasion resistance index (ARI) of 187% and a volume change of 2.38% after 72 h of soaking in aviation oil, which are 24% higher and 48% lower than the corresponding values of unfilled NBR composites, respectively. These results indicate that the hybrid fillers can effectively enhance the mechanical, wear and oil resistant properties of the elastomer composites, which is conductive for application of the NBR‐based composites. [ABSTRACT FROM AUTHOR]

Osteoarthritis is a common degenerative disease characterized by continuous detachment of lubrication factors from damaged cartilage matrix. This study proposes a paradigm that combines natural polyanionic polysaccharides (hyaluronic acid, HA) with dopamine (DA) to design a synovial lubrication factors‐recruiting biomimetic polyphenolized lubrication system. The biomimetic lubricants can use DA's polarity and hydrophilic groups as specific binding sites of type II collagen's polarity and hydrophilic groups to stably bind cartilage surface, and further utilize molecular specific interaction to recruit detached, joint endogenous or chondrocytes expressed synovial lubrication factors, continuously forming supramolecular lubrication complex onto cartilage matrix to induce joint lubrication. Simultaneously, the biolubricants can also utilize catechol groups to eliminate anionic free radicals and resist reactive oxygen species invasion in the early stages of joint lubrication failure. The prepared biolubricants exhibit low coefficient of friction (µ < 0.08), which is attributed to fluid and hydration lubrication provided by HA and DA side chains through fluid dynamic effect and interfacial hydration adsorption. Cell and animal experiments also demonstrate polyphenolic biolubricants have good biocompatibility and promote cartilage regeneration. Therefore, the developed synovial lubricants‐recruiting biomimetic polyphenolized biolubricants have potential for treating osteoarthritis, and also provide a theoretical basis for other biological tissues with lubrication problems. [ABSTRACT FROM AUTHOR]

In this manuscript, the impact of a permanent magnetic field on the intensity of external lubricant/gaseous metal cutting environments in the turning process is studied. Tool life and wear resistance of solid High-Speed Steel (HSS) metal cutting tool was researched in diverse cutting modes and environments in turning steel 40X [analog: AISI 5135] and steel 25 [analog: AISI 1025] to study the effect of permanent magnetic field on the ferromagnetic tool. Experiments were conducted creating machine oil, oxygen, and argon conditions as an exterior machining environment in the process. The ferromagnetic HSS cutting tool is magnetically treated and used in diverse external machining conditions to analyze the intensity of affecting the lubricant/gaseous environment in the metal machining process. Furthermore, the influence of cutting speed and feed on the efficiency of magnetic field impact in lubricating and gaseous environment in the machining process is also researched. According to the experimental study, it is found that tool life and wear resistance of ferromagnetic HSS cutting tool is increased after the tool is magnetically treated with 10,000 ÷ 20,000 Oe of magnetic field strength in machining. However, the magnetic field effect on the HSS cutting tool showed subsidence while the cutting speed was increased in all external environments. Also, it is found that supplying oxygen and argon gases in metal cutting areas has a noticeably positive effect on tool wear and life, especially, since the influence of the gaseous environments has intensified results while the tool is used after magnetic treatment. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to prepare thymol-based deep eutectic solvents (DESs) and use them as lubricates for friction and wear tests to simulate the wear conditions of hybrid bearings. Design/methodology/approach: Through the characterization and analysis of the morphology of wear scars and the elemental composition of friction films, the tribological behavior and wear mechanism of sample materials as lubricants were investigated and the anti-wear mechanism of thymol-based DESs was discussed. Findings: The findings demonstrate that because of the formation of a fluid lubrication film and excellent kinematic viscosity, the lubrication effect of the prepared DES is improved by about 50% compared to the base lubricating oil. The prepared [Ch]Cl-thymol DES has a better anti-friction and lubrication effect than citric-thymol, EG-thymol and urea-thymol DESs, with an average friction coefficient of about 0.04. Originality/value: In this work, the friction reduction properties of thymol-based DESs were studied as lubricants for the first time, and the lubrication mechanism of sample materials was investigated. [ABSTRACT FROM AUTHOR]

Resource and energy efficiency are of high importance in gearbox applications. To reduce friction and wear, an external lubricant supply like dip or injection lubrication is used to lubricate tribosystems in machine elements. This leads to the need for large lubricant volumes and elaborate sealing requirements. One potential method of minimizing the amount of lubricant and simplifying sealing in gearboxes is the self-lubrication of tribosystems using oil-impregnation of porous materials. Although well established in low-loaded journal bearings, self-lubrication of rolling-sliding contacts in gears is poorly understood. This study presents the self-lubrication method using oil-impregnated porous sinter material variants. For this, the tribosystem of gear contacts is transferred to model contacts, which are analyzed for friction and temperature behavior using a twin-disk tribometer. High-resolution surface images are used to record the surface changes. The test results show a significant increase in self-lubrication functionality of tribosystems by oil-impregnated porous sinter material and a tribo-performance comparable to injection-lubricated tribosystems of a sinter material with additionally solid lubricant added to the sinter material powder before sintering. Furthermore, the analyses highlight a significant influence of the surface finish, and in particular the surface porosity, on the overall tribosystem behavior through significantly improved friction and wear behavior transferable to gear applications. [ABSTRACT FROM AUTHOR]

The study explored the viability of using waste plastic oil (PO) as an alternative lubricant to petroleum-based lubricants in industrial settings. To enhance the lubrication performance of the PO, this study incorporated cost-efficient, oleic acid-modified, graphene nano platelets [GNP (f)] and hexagonal boron nitride [hBN (f)] nano solid lubricant additives into the PO in various concentrations, forming functionalized nano lubricants. The PO and its functionalized nano lubricant's rheological, dispersion stability, thermal degradation, friction, and wear performance were investigated. Results manifest that incorporating GNP (f) and hBN (f) into the PO significantly enhanced the viscosity and dispersion stability. In addition, it was seen that GNP (f) and hBN (f) nano lubricants lowered the coefficient of friction (COF) by 53% and 63.63% respectively, compared to the PO. However, the GNP (f) and hBN (f) nano lubricants demonstrated a 3.16% decrease and a 50.08% increase in wear volume relative to the PO. Overall, the GNP (f) and hBN (f) nano lubricants displayed a synergistic friction behavior, while they exhibited an antagonistic behavior pertaining to the wear volume. The study elucidated the mechanisms underlying friction and wear performance of the nano lubricants. [ABSTRACT FROM AUTHOR]

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Lubrication by hydrogels is an emerging area in surface science. Although oil‐driven friction reduction is predominant in literature, emulsion gel‐based lubrication has attracted very little attention to date. We hypothesize that an interplay of viscoelasticity and oil volume fraction may modulate the lubricity of emulsion‐filled gels. Herein, phase‐change gelatin‐based emulsion‐filled gels with different sugar alcohols and oil droplet concentrations (0–30 wt%) are tested for their lubrication performance. The rheological and tribological tests are analyzed in conjunction with spectroscopic and structural characterizations to reveal structure–function relationship. Structural characterizations demonstrate that hydrogen bonding is enhanced in pure gelatin gels with the increase of sugar alcohol (glycerol)‐replacement time, which enhance the storage modulus (G′) of the gel networks. Emulsified droplets serve as active fillers further strengthening the G′ and strikingly the presence of glycerol reduced the thermoresponsiveness of the emulsion‐filled gels. Emulsion‐filled gels containing sugar alcohols, irrespective of their type, can greatly reduce the friction coefficients (μ) between hydrophobic surfaces in the boundary and mixed regimes versus the systems without sugar alcohols. In the hydrodynamic regime, the friction coefficient of the system is proportional to the second plateau shear viscosity, regulated by the oil content. [ABSTRACT FROM AUTHOR]

Seizure is a severe accident that can abruptly stop or even damage running equipment. Improving the anti-seizure properties of friction pair materials is also crucial as lubricating and wear resistance. While the tribological performances of molybdenum disilicide (MoSi2) and ferrophosphorus (FemPn) particle-doped copper-tin-bismuth (Cu-Sn-Bi) composites have been investigated in previous studies, the specific effects of MoSi2 and FemPn particles on the anti-seizure property of Cu-Sn-Bi materials remain unclear. This study explores the seizure resistance of Cu-Sn-Bi composites containing MoSi2 and/or FemPn under conformal and nonconformal contact conditions. The materials were prepared using powder sintering technology, and the metallographic structures of four types of self-lubricating copper composites were observed. Seizure resistance under starved lubrication conditions was investigated, and the worn surfaces under different contact types were discussed and analyzed. The results indicate that the addition of MoSi2 and/or FemPn particles effectively refines the grain size, and these particles exhibit different distribution trends after powder sintering. The MoSi2 and FemPn particles improved the maximum seizure load of copper-based composite samples by 66.67% and 84.62%, respectively. The seizure forms under different contact types were also discussed. [ABSTRACT FROM AUTHOR]

We numerically investigate the pressure drop reduction (PDR) performance of microchannels equipped with liquid-infused surfaces, along with determining the shape of the interface between the working fluid and lubricant within the microgrooves. The effects of different parameters, such as the Reynolds number of working fluid, density and viscosity ratios between the lubricant and working fluid, the ratio of the thickness of the lubricant layer over the ridges to the depth of the groove, and the Ohnesorge number as a representative of the interfacial tension, on the PDR and interfacial meniscus within the microgrooves are comprehensively studied. The results reveal that the density ratio and Ohnesorge number do not significantly affect the PDR. On the other hand, the viscosity ratio considerably affects the PDR, and a maximum PDR of 62% compared to a smooth non-lubricated microchannel is achieved for a viscosity ratio of 0.01. Interestingly, the higher the Reynolds number of the working fluid, the higher the PDR. The meniscus shape within the microgrooves is strongly affected by the Reynolds number of the working fluid. Despite the insignificant effect of interfacial tension on the PDR, the interface shape within the microgrooves is appreciably influenced by this parameter. [ABSTRACT FROM AUTHOR]

In mixed elastohydrodynamic lubrication (EHL), the load distribution between the gear meshing surfaces is shared by the oil film and the asperities of the gear's rough surface. Based on the load‐sharing concept, this paper proposes a time‐varying meshing stiffness (TVMS) model for gears with mixed EHL. The initial step involves the utilization of the Greenwood‐Williamson model to calculate the contact stiffness of surface asperities, while the lubricating film is assessed using a curve‐fitting formula to investigate the influence of gear surface morphology on TVMS. Subsequently, the incorporation of gear fillet foundation deformation and friction enables accurate TVMS determination. The proposed method is employed to examine the meshing stiffness of the gear pair under both dry lubrication and EHL conditions. Comparative analysis reveals favorable agreement between the proposed model and experimental results obtained under dry lubrication, thereby highlighting the superior performance of the proposed approach. Moreover, the time‐varying friction coefficient under EHL is computed, and the impacts of gear surface morphology parameters, temperature, speed, and load on lubrication conditions and TVMS are investigated. The findings presented in this paper contribute significantly to advancements in gear design and performance. [ABSTRACT FROM AUTHOR]

This study introduces a novel organosilicon-modified polysaccharide (Si-AP) synthesized via grafting and comprehensively evaluates its performance in water-based drilling fluids (WBDFs). The molecular structure of Si-AP was characterized using Fourier-transform infrared spectroscopy (FTIR) and 1H-NMR experiments. Thermalgravimetric analysis (TGA) confirmed the good thermal stability of Si-AP up to 235 °C. Si-AP significantly improves the rheological properties and fluid loss performance of WBDFs. With increasing Si-AP concentration, system viscosity increases, API filtration rate decreases, clay expansion is inhibited, and drilling cuttings hydration dispersion is suppressed, especially under high-temperature conditions. Additionally, mechanistic analysis indicates that the introduction of siloxane groups can effectively inhibit the thermal degradation of AP chains and enhance their high-temperature resistance. Si-AP can form a lubricating film by adsorbing on the surface of clay particles, improving mud cake quality, reducing the friction coefficient, and significantly enhancing the lubricating performance of WBDFs. Overall, Si-AP exhibits a higher temperature-resistance limit compared to AP and more effectively optimizes the lubrication, inhibition, and control of the filtration rate of WBDFs under high-temperature conditions. While meeting the requirements of drilling fluid systems under high temperatures, Si-AP also addresses environmental concerns and holds promise as an efficient solution for the exploitation of deep-seated oil and gas resources. [ABSTRACT FROM AUTHOR]

The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double‐rectangular‐cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range. [ABSTRACT FROM AUTHOR]

In the present scenario, human safety is one of the most important parameters in design and manufacturing of a vehicle, which is the reason every organization is very keen in ensuring durability and reliability of automobile components. One such critical component in the vehicle is the suspension system consisting of leaf springs whose primary role is to absorb and store strain energy, which can be further released slowly during operation. This plays a vital role in ensuring both human safety and ride comfort. Also, it acts as a structural member to establish linkage between chassis frame and axle. In this paper, we would like to review the previous work done by researchers in the field of leaf spring design, FEM analysis, manufacturing process optimisation, durability testing and failure analysis, alternate material selection (both steel and composite) for weight and cost optimization. Detailed failure mode investigation on modes of failure and its causative factors like improper heat treatment, surface decarburization, hydrogen embrittlement, fretting fatigue and corrosion pitting is discussed. This review provides the improvement scope in current design and manufacturing processes, which will enhance the durability and avoid premature failure of leaf springs. The paper discusses about the additional life enhancement manufacturing processes such as shot peening, ausforming during heat treatment, lubrication improvement and corrosion prevention by using solid lubricants. These processes are proposed to be considered at design stage itself to optimise the size and weight of suspension by reducing number of leaves for the same vehicle application. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to explore the operating characteristics of gallium-based liquid metals (GLMs) by directly adding them as lubricants in real mechanical equipment. Design/methodology/approach: This paper conducts an analysis of the rotor-bearing system under GLM lubrication using a constructed test rig, focusing on vibration signals, surface characteristics of the friction pair, contact resistance and temperature rise features. Findings: The study reveals that GLM can effectively improve the lubrication condition of the tribo-pair, leading to a more stable vibration signal in the system. Surface analysis demonstrates that GLM can protect the sample surface from wear, and phase separation occurs during the experimental process. Test results of contact resistance indicate that, in addition to enhancing the interfacial conductivity, GLM also generates a fluid dynamic pressure effect. The high thermal conductivity and anti-wear effects of GLM can reduce the temperature rise of the tribo-pair, but precautions should be taken to prevent oxidation and the loss of its fluidity. Originality/value: The overall operating characteristics of the rotor-bearing system under GLM lubrication were investigated to provide new ideas for the lubrication of the rotor-bearing system. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0067/ [ABSTRACT FROM AUTHOR]

Semi‐solid lubricant in the leg joints of insects is represented by tiny cylindrical fragments. The dynamics of lubricant behavior between contact surfaces at the joint scale are investigated using numerical simulation. Results of modeling show that lubricant fragments tend to stick together and form clots of varying shapes and sizes under the influence of shear motion. Formation of such clots, accompanied by constant loss and reproduction of the lubricant, allows maintaining of fluctuating clearance between contact surfaces and helps to reduce friction. Foreign contaminant particles penetrating an open insect joint are removed by the lubricant, to which they stick, reducing abrasive wear. [ABSTRACT FROM AUTHOR]

We report the fabrication of graphene oxide (GO) and polymer composite coatings on a copper substrate using electrophoretic deposition (EPD) by varying the deposition times from 5 to 15 min. This study deals with the erosion wear and corrosion behaviour of the GO and poly(2-vinylpyridine) (P) composite coating after being treated with polymethyl hydro siloxane (p) at 140°C for 2 h. Taguchi's experimental design was adopted to optimize erosion parameters, i.e., stand-off distance, powder feed rate, impact velocity and impingement angle. The lowest erosion rate, i.e., 50 mg kg−1 was achieved for the 10-min GOPp composite-coating sample treated at an impact velocity of 30 m s−1, a stand-off distance of 30 mm, a powder feed rate of 6 g min−1, and an impingement angle of 60°. The reduction in the erosion rate for the 10-min GOPp composite coating might be attributed to lubrication and improved densification of the composite coating. Along with that, it is observed that the GOPp composite coating provides self-lubrication with the solid lubricant feature of GO, reducing friction in the contact area. Apart from erosion resistance, the composite coating offers improved corrosion resistance as well. [ABSTRACT FROM AUTHOR]

Super-precision bearing lubrication condition is essential for equipment's overall performance. This paper investigates a monitoring method of bearing lubrication using multi-sensors based on graph data. An experiment was designed and carried out, establishing a dataset including vibration, temperature, and acoustic emission signals. Graph data were constructed based on a priori knowledge and a graph attention network was employed to conduct a study on monitoring bearing lubrication abnormalities and discuss the influence of a missing sensor on the monitoring. The results show that the designed experiments can effectively respond to the degradation process of bearing lubrication, and the graph data constructed based on a priori knowledge show a good effect in the anomaly monitoring process. In addition, the multi-sensor plays a significant role in monitoring bearing lubrication. This work will be highly beneficial for future monitoring methods of bearing lubrication status. [ABSTRACT FROM AUTHOR]

This study investigates the potential of a hybrid nanofluid composed of MoS2 and ZnO nanoparticles dispersed in engine oil, aiming to enhance the properties of a lubricant's chemical reaction with the Soret effect on a stretching sheet under the influence of an applied magnetic field. With the growing demand for efficient lubrication systems in various industrial applications, including automotive engines, the development of novel nanofluid-based lubricants presents a promising avenue for improving engine performance and longevity. However, the synergistic effects of hybrid nanoparticles in engine oil remain relatively unexplored. The present research addresses this gap by examining the thermal conductivity, viscosity, and wear resistance of the hybrid nanofluid, shedding light on its potential as an advanced lubrication solution. Overall, the objectives of studying the hybrid nanolubricant MoS2 + ZnO with engine oil aim to advance the development of more efficient and durable lubrication solutions for automotive engines, contributing to improved reliability, fuel efficiency, and environmental sustainability. In the present study, the heat and mass transformation of a Casson hybrid nanofluid (MoS2 + ZnO) based on engine oil over a stretched wall with chemical reaction and thermo-diffusion effect is analyzed. The governing nonlinear partial differential equations are simplified as ordinary differential equations (ODEs) by utilizing the relevant similarity variables. The MATLAB Bvp4c technique is used to solve the obtained linear ODE equations. The results are presented through graphs and tables for various parameters, namely, M, Q, β, Pr, Ec, Sc, Sr, Kp, Kr, and ϕ 2 * (hybrid nanolubricant parameters) and various state variables. A comparative survey of all the graphs is presented for the nanofluid (MoS2/engine oil) and the hybrid nanofluid (MoS2 + ZnO/engine oil). The results reveal that the velocity profile diminished against the values of M, Kp, and β, and the temperature profile rises with Ec and Q, whereas Pr decreases. The concentration profile is incremented (decremented) with the value of Sr (Sc and Kr). A comparison of the nanofluid and hybrid nanofluid suggests that the velocity f′ (η) becomes slower with the augmentation of ϕ 2 * whereas the temperature increases when ϕ 2 * = 0.6 become slower. [ABSTRACT FROM AUTHOR]

Electric potential controlled lubrication, also known as triboelectrochemistry or electrotunable tribology, is an emerging field to regulate the friction, wear, and lubrication performance under charge distribution on the solid–liquid interfaces through an applied electric potential, allowing to achieve superlubrication. Electric potential controlled lubrication is of great significance for smart tunable lubrication, micro-electro-mechanical systems (MEMS), and key components in high-end mechanical equipment such as gears and bearings, etc. However, there needs to be a more theoretical understanding of the electric potential controlled lubrication between micro- and macro-scale conditions. For example, the synergistic contribution of the adsorption/desorption process and the electrochemical reaction process has not been well understood, and there exists a significant gap between the theoretical research and applications of electric potential controlled lubrication. Here, we provide an overview of this emerging field, from introducing its theoretical background to the advantages and characteristics of different experimental configurations (including universal mechanical tribometers, atomic force microscopes, and surface force apparatus/balances) for electric potential controlled lubrication. Next, we review the main experimental achievements in the performance and mechanisms of electrotunable lubrication, especially using ionic lubricants, including electrolyte solutions, ionic liquids, and surfactants. This review aims to survey the literature on electric potential controlled lubrication and provide insights into the design of superlubricants and intelligent lubrication systems for various applications. [ABSTRACT FROM AUTHOR]