Lubricants, Volume 12, Issue 4 (April 2024) – 38 articles

High-power diesel engine turbochargers predominantly utilize floating ring bearings as their primary supporting components. To further enhance their load capacity, multi-lobe noncircular bearings have been progressively employed. This study focuses on the investigation of noncircular three-lobe SFRBs (semi-floating ring-bearing structures) in marine turbochargers. Employing the half-step center Finite Difference Method (FDM) and the Newton–Raphson iterative procedure, the impact of operational parameters such as the journal speed, external load, oil supply pressure, and oil supply temperature on the static and dynamic characteristics of the inner oil film is analyzed. Subsequently, the accuracy of the theoretical model is validated through a comparative analysis of simulation results obtained from Dyrobes and Fluent. The findings indicate that as the oil supply pressure and temperature increase, the temperature rise and maximum oil film pressure of the three-lobe SFRBs gradually decrease, while the oil film thickness progressively increases, thereby significantly improving the lubrication state. The load capacity of the three-lobe SFRBs is primarily sustained by the bottom tile, where wall friction is most likely to occur. Additionally, within the actual speed range, the stiffness and damping of the three-lobe SFRBs exhibit noticeable nonlinear characteristics. Full article

This study details the mechanical incorporation of graphite particles into the surface of aluminium (Al-1100) to fabricate surface composites using an electrical resistance heating-assisted pressing method. Initially, the aluminium surface is coated with graphite via solution casting. Incorporation is accomplished by locally heating the graphite–aluminium interface with electrical resistance heating and subsequent mechanical pressure application. The magnitude of softening of the aluminium surface can be regulated by process considerations such as the applied current and heating duration. Microstructural assessment of the aluminium–graphite composite was conducted using SEM, TEM, Raman spectroscopy, and XRD. The surface mechanical properties and reduced Young’s modulus were improved by more than 200% and 150%, respectively. A detailed tribological study was conducted, and the study suggested that the wear resistance and COF improved by more than 50%. The progress in wear resistance and COF is corroborated by the microstructural changes in the matrix suggested by the Raman spectroscopy and XRD results. Full article

Structural superlubricity refers to the lubrication state in which the friction between two crystalline surfaces in incommensurate contact is nearly zero; this has become an important branch in recent tribological research. Two-dimensional (2D) materials with structural superlubricity such as graphene, MoS₂, h-BN, and alike, which possess unique layered structures and excellent friction behavior, will bring significant advances in the development of high-performance microelectromechanical systems (MEMS), as well as in space exploration, space transportation, precision manufacturing, and high-end equipment. Herein, the review mainly introduces the tribological properties of structural superlubricity among typical 2D layered materials and summarizes in detail the underlying mechanisms responsible for superlubricity on sliding surfaces and the influencing factors including the size and layer effect, elasticity effect, moiré superlattice, edge effect, and other external factors like normal load, velocity, and temperature, etc. Finally, the difficulties in achieving robust superlubricity from micro to macroscale were focused on, and the prospects and suggestions were discussed. Full article

In order to more accurately characterize the effects of nanoparticles on lubricant viscosity, the effects of copper dialkyl dithiophosphate (HDDP)-modified (CuDDP) nanoparticles on the dynamic viscosity of mineral oils 150N, alkylated naphthalene (AN5), diisooctyl sebacate (DIOS), and polyalphaolefins (PAO4, PAO6, PAO10, PAO40, and PAO100) were investigated at an experimental temperature of 40 °C and additive mass fraction ranging from 0.5% to 2.5%. CuDDP exhibits a viscosity-reducing effect on higher-viscosity base oils, such as PAO40 and PAO100, and a viscosity-increasing effect on lower-viscosity base oils, namely, 150N, AN5, DIOS, PAO4, PAO6, and PAO10. These effects can be attributed to the interfacial slip effect and the shear resistance of the nanoparticles. The experimental dynamic viscosity of the eight base oils containing CuDDP was compared with that calculated by the three classical formulae of nanofluid viscosity, The predicted viscosity values of the formulae deviated greatly from the experimental viscosity values, with the maximum deviation being 7.9%. On this basis, the interface slip effect was introduced into Einstein’s formula, the interface effect was quantified with the aniline point of the base oil, and a new equation was established to reflect the influence of CuDDP nanoparticles on lubricating oil viscosity. It can better reflect the influence of CuDDP on the viscosity of various base oils, and the deviation from the experimental data is less than 1.7%. Full article

The initial friction stage between the contacting materials would generate a maximum shear force and an unstable fluctuating time, which had a negative effect on the entire frictional system, especially at low temperature conditions. In order to decrease the occurring shear force and fluctuating time on the onset of friction, two different lubricating oils were applied in this study to investigate the influence of lubricant’s viscosity on these friction behaviors. The frictional experiments were conducted between the steel ball and the 40CrMnMo, and special attention was paid to the relationship between maximum friction force, fluctuating time, frictional vibration and the initial lubricant temperature. The results showed that the friction force first increased to the maximum value and then experienced an oscillation damping period (fluctuating time) before it reached a stable state. And this fluctuating behavior caused corresponding vibrations on the initial contacting. However, compared to the high viscosity lubricating oil (HO), the low viscosity lubricating oil (LO) contributed to more than 50% reductions on max friction force, fluctuating time and vibration at the cold start (0 °C). Moreover, the weakened initial frictional fluctuation was conducive to generating a low and stable friction coefficient (COF) and wear loss of the long-term test. The discrepancy on lubricating performance was that the low viscosity provided high fluidity, which allowed rapid distribution of the lubricant between the contacting surfaces and formed an intact lubricating film. Similarly, the high temperature decreased the viscosity of HO and thus led to satisfactory friction reductions. The knowledge gained herein provides a supporting theory on the design and preparation of a lubricating oil with high performance. Full article

Cold rolling emulsion contains a variety of functional additives, which often exhibit complex interactions with each other. Sodium alkane sulfonate (SAS) is a common corrosion inhibitor used in cold rolling emulsions for temporary rust prevention. In this study, it was found that SAS would deteriorate the tribological properties of the emulsion. Emulsions containing SAS and different friction modifiers were prepared. Tribology tests were carried out on a four-ball friction and wear tester. White light interferometer was used to investigate the 3D morphology of the friction surface and wear volume. Microscopic morphology of friction surfaces was observed using a scanning electron microscope (SEM). The chemical activity and electrostatic potential of the molecules were calculated based on density functional theory (DFT). The adsorption energies of additives on metal surfaces were calculated via molecular dynamics (MD) simulation. The results indicate that the strong electrostatic force gives SAS an advantage in competitive adsorption with ester friction modifiers due to the positive charge on the metal surface. This results in the friction modifier not functioning properly and the tribological properties of the emulsion being significantly reduced. Full article

Pin-on-plate and pin-on-disk wear tests are typically used for assessing the wear behavior of a given material coupling and estimating its wear coefficient using the Archard wear law. This study investigates differences in the Archard law for pin-on-plate and pin-on-disk cases, particularly for flat-ended pins. Both analytical and finite element models of the two tests were developed, assuming a 21 N normal load and a 50π mm sliding distance. In pin-on-disk simulations three different distances between pin and disk axes were considered, i.e., 1.25–2.5–5 times the pin radius (5 mm). For the results, wear volumes, pressure and wear depth maps were compared. Some interesting aspects arose: (i) the rotational effect in pin-on-disk tests causes higher wear volumes (up to 13%) with respect to pin-on-plate tests: the nearer the pin to the disk axis, the higher the wear volume; (ii) a simple quadratic formula is defined to correct the wear volume estimation for pin-on-disk tests; (iii) pressure redistribution occurs with higher values closer to disk axis, opposite to the wear depth trend. Due to the high computational costs, only the running-in phase of wear tests was considered. Numerical strategies are currently under investigation to extend this study to the steady state phase. Full article

A deep understanding of oil behavior inside roller bearings is important for the precise design of bearing configurations and oil systems in aircraft engines. The numerical method is employed to track oil distribution inside cylindrical roller bearings with under-race lubrication along the circumference and radial direction, respectively. The results demonstrate that oil distribution along the circumference is periodic with the number of under-race nozzles, and higher rotating speed and lower flow rate would reduce the fluctuation amplitude. It is difficult for oil to flow through the gap between the cage pocket and rollers, and higher oil viscosity would worsen it further. In some extreme cases, the oil volume fraction near the outer race may be lower than 0.7%, causing the risk of lubricating and cooling failure. Thus, more attention should be paid to the outer race of the roller bearing with under-race lubrication, especially during the starting stage of the engine and in cold weather. Full article

For future internal combustion engines, driven by regenerative fuels, efficiency is more important than ever. One approach to reduce the losses inside the piston cylinder unit (PCU) is to improve the alignment of the liner and the piston. Therefore, a cylinder liner with a free form was developed at the Institute of Technical Combustion (ITV) of the Leibniz University Hannover which compensates radial and linear deformations along the stroke. The layout is based on a FEM simulation. The liner was manufactured by the Institute of Production Engineering and Machine Tools (IFW) of Leibniz University of Hannover with a novel turn-milling process. The liner was investigated on the heavy-duty Floating-Liner engine of ITV with a displacement of 1991 ccm and a bore diameter of 130 mm. The experimental results show improvement in the friction losses over the whole engine map in the range of 9% and up to 17.3% compared to a serial liner. Sealing efficiency could be improved up to 28.8%, depending on the operational point. Overall, the investigation aims for lower fuel consumption which would in result fewer emissions. Full article

The paper provides a discussion on the results of studies of the effect exerted by combined degradation factors typical of four types of wear: abrasion, impact–abrasion, tribocorrosion, and impact–abrasion–corrosion, conducted for chain wheels made of Ni-Cu alloyed austempered ductile iron. The studies consisted of determining the content of retained austenite in the structure of the cast irons in question, establishing the measures of wear following wear testing, and identifying the basic surface degradation mechanisms observed in the chain wheels tested following multifactorial wear processes. The chain wheels made of ADI were found to have sustained the greatest damage under the impact–abrasion–corrosion (three-factor) wear scenario, while the wear was least advanced in the abrasion (one-factor) wear case. Another observation derived from the studies is that the combined effect of dynamic forces, corrosion, and quartz sand-based abrasives causes increased surface degradation in the cast iron grades taken into consideration compared to processes characterised by a reduced number of degradation factors (i.e., one- or two-factor wear processes). Additional hardness tests and XRD analyses revealed that a distinctive effect attributable to combined degradation factors on the surface hardness increased value and implied that bench testing was followed by phase transition. Full article

A spherical hinge structure is a key swivel bridge element that must be considered when evaluating friction characteristics and lubrication properties to meet the rotation requirement. Polytetrafluoroethylene (PTFE)-based spherical hinge sliders and lubrication coating have been employed for over 20 years, but with the growing tonnage of swivel bridge construction, their capacity to accommodate the required lubrication properties can be exceeded. In this manuscript, the optimal friction coefficient of the spherical hinge is obtained through the finite element analysis method. Four lubrication coatings and four spherical hinge sliders are prepared and tested through a self-developed rotation friction coefficient test, four-ball machine test, dynamic shear rheological test, and compression and shear performance test to evaluate the lubrication and friction properties of the spherical hinge structure. The results of the finite element analysis show that the optimum rotation friction coefficient of the spherical hinge structure is 0.031–1.131. The test results illustrate that the friction coefficient, wear scar diameter, maximum non-seize load, phase transition point, and thixotropic ring area of graphene lubrication coating are 0.065, 0.79 mm, 426 N, 14.6%, and 64,878 Pa/s. The graphene lubrication coating has different degrees of improvement compared with conventional polytetrafluoroethylene lubrication coating, showing more excellent lubrication properties, bearing capacity, thixotropy, and structural strength. Compressive and shear tests demonstrate that polyether ether ketone (PEEK) has good compressive and shear mechanical properties. The maximum compressive stress of PEEK is 87.7% higher than conventional PTFE, and the shear strength of PEEK is 6.07 times higher than that of PTFE. The research results can provide significantly greater wear resistance and a lower friction coefficient of the spherical hinge structure, leading to lower traction energy consumption and ensuring smooth and precise bridge rotation. Full article

This study investigated the frictional properties of HPMC under different load and concentration conditions through friction experiments and surface characterization. The study aimed to explore and reveal the influence of load and concentration on the frictional properties of HPMC, as well as its anti−wear mechanism. The results of the study indicated that under the same solution concentration, the effect of load on the friction coefficient of HPMC was not significant. Specifically, for samples with low concentration (C−0.2), the wear ratio of HPMC under a 4 N load (1.01 × 10⁻¹¹ mm³·N⁻¹·m⁻¹) was significantly lower than the wear ratio under a 2 N load (1.71 × 10⁻¹⁰ mm³·N⁻¹·m⁻¹). The orientation−driven formation of graphite−like carbon nanosheets, initiated by the decomposition of HPMC short chains, created a tribofilm−containing organic−chain mixed nanosheet on the sliding contact surface, which prevented direct contact between the upper and lower friction pairs. This achieved the anti−wear mechanism of two−body wear (tribo−film of an mDLC−coated ball and tribo−film of a GLC−coated Si wafer), ultimately leading to a state of ultra−low wear at the interface. The excellent anti−wear performance of HPMC suggests its potential as a candidate for the next generation of environmentally friendly bio−based solid lubricants. Full article

Typical lubricants behave in a non-Newtonian manner under conditions of high shear and high pressure, as is commonly observed in lubricated rolling/sliding contacts. To optimize and predict the friction therein, knowledge of the high-pressure rheological behaviors of lubricants and limiting shear stress (LSS) is essential. This study developed an approach for determining the LSS of lubricants based on friction mapping of rolling/sliding contacts, using a ball-on-disc traction machine. The main contribution lies in the introduction of a practical approach for the selection of a proper entrainment velocity for determining the LSS, with reduced thermal influences and near isothermal conditions. The proposed approach enables full film lubrication, while keeping the film as thin as possible to prevent excessive shear heating and, thus, thermal effects. The LSS of two lubricants, PAO40 and complex ester, has been measured at pressures ranging from 1.2 GPa to 1.7 GPa. A bilinear model has been used to describe the variation of LSS with pressure. The impact of entrainment velocity selection on the measurement of LSS is also discussed. Full article

In this work, a set of Feed Forward Neural Networks (FNN) for the estimation of the metal ion concentration of diesel fuels is presented. The dataset vector is obtained through in situ measurements from distillate marine diesel fuel storage tanks all over Greece, in order to reduce the selection bias. It has been demonstrated that the most correlated ions among them are Aluminum (Al), Barium (Ba) and Calcium (Ca). Moreover, the FNN models are the most reliable models to be used for the model construction under discussion. The initial L₂ error is relatively small, in the vicinity of 0.3. However, after removing a small dataset that includes 1–2 data points significantly deviating from the model trend, the error is substantially reduced to 0.05, ensuring the reliability and accuracy of the model. If this dataset is cleared, the estimated error is substantially reduced to 0.05, enhancing the reliability and accuracy of the model. The correlation between the sum of the concentrations of the model in relation with the Density and Viscosity are, respectively, 0.15 and 0.29 which are characterized as weak. Full article

Dry mouth, also known as xerostomia, is a condition in which insufficient or ineffective saliva does not provide sufficient oral lubrication. The severity of this condition can vary from a mild discomfort to a debilitating condition that greatly impairs patients’ lives. Xerostomia arises as a side effect of various medications, diseases, radiation therapy, chemotherapy, or nerve damage. Various aqueous dispersions of macromolecules have been proposed to assist or replace the saliva in these patients. It is vital that these macromolecules have ample lubricity and water retention properties while showing long-lasting efficacy. The emphasis of this review is to provide a general overview on lubricating macromolecules that have been clinically used or reported in the literature as potential replacements for saliva. These include various natural or synthetic polymers, proteins, peptides, and lipids that are used in the form of solutions, gels, emulsions, and colloids. Perspectives into the future of macromolecular oral lubricants in the treatment of xerostomia are also provided. Full article

Rolling mill bearings are prone to wear, erosion, and other damage characteristics due to prolonged exposure to rolling forces. Therefore, regular inspection of rolling mill bearings is necessary. Ultrasonic technology, due to its non-destructive nature, allows for measuring the oil film thickness distribution within the bearing during disassembly. However, during the process of using ultrasonic reflection coefficients to determine the oil film thickness and distribution state of rolling mill bearings, changes in bearing temperature due to prolonged operation can occur. Ultrasonic waves are susceptible to temperature variations, and different temperatures of the measured structure can lead to changes in measurement results, ultimately distorting the results. This paper proposes using density and sound speed compensation methods to address this issue. It simulates and analyzes the oil film reflection coefficients at different temperatures, ultimately confirming the feasibility and effectiveness of this approach. The paper establishes a functional relationship between bearing pressure and reflection coefficients, oil film thickness, and reflection coefficients. This allows for the compensation of reflection coefficients under any pressure conditions, enhancing the accuracy of oil film thickness detection. The proposed method provides technical support for the maintenance of plate rolling processes in the steel industry. Full article

In the ultra-low temperature environment, the material properties of the bearing change, which puts forward higher requirements for the dynamic performance of the bearing cage. The bearings operating in ultra-low temperature environments commonly use solid lubricants. This study first focused on measuring the traction coefficients of molybdenum disulfide (MoS₂) solid lubricant in a nitrogen atmosphere, and the Gupta fitting model is constructed to derive the traction equation. Subsequently, the dynamic differential equation of angular contact ball bearings was established, and the stability of the bearing cage in a nitrogen environment was simulated and analyzed based on the dynamic model. The accuracy of the simulation model was verified through comparison. The results show that less than 10% of errors exist between the experimental data and the traction curve fitted by the Gupta model, and the stability of the cage is closely related to operating parameters and bearing structure parameters. Cage stability increases with axial load but decreases with radial load. The cage stability is optimal when the radial internal clearance of the bearing is approximately 0.06 mm. When other conditions remain unchanged and the ratio of the cage pocket hole gap to the cage guide surface gap is 0.2, the cage stability is the best. The research results will provide a foundation for the design and application of solid-lubricated angular contact ball bearings in ultra-low temperature environments. Full article

An Rtec ball-on-disk tribometer was used to investigate the tribological performance of the synthesised water-based nanolubricants containing hBN/TiO₂ nanocomposite at room temperature. The water-based nanolubricants with different concentrations were prepared by adding glycerol and sodium dodecyl benzene sulfonate (SDBS) under ultrasonication. These as-prepared nanolubricants demonstrated exceptional dispersion stability for 7 days without distinct sedimentation. The results indicate that the water-based nanolubricants with an overall concentration of 1.0 wt% at different ratios (hBN: TiO₂ = (1:0), (0.7:0.3), (0.5:0.5), (0.3:0.7), (0:1)) can effectively reduce the coefficient of friction (COF) and the wear of the ball and disk. In particular, the water-based nanolubricant containing 0.5 wt% hBN and 0.5 wt% TiO₂ exhibited the best tribological performance, leading to a significant reduction in COF up to 70%, and decreased the wear area of the ball and disk by up to 79.57% and 60.40%, respectively, compared to those obtained using distilled water. The lubrication mechanisms were mainly attributed to the formation of a protective film, and the mending, polishing, rolling, and synergistic effects of the hBN nanosheets and TiO₂ nanoparticles. Full article

In many technical applications, understanding the behavior of tribological contacts is pivotal for enhancing efficiency and lifetime. Traditional experimental investigations into tribology are often both costly and time-consuming. A more profound insight can be achieved through elastohydrodynamic lubrication (EHL) simulation models, such as the ifas-DDS, which determines precise friction calculations in reciprocating pneumatic seals. Similar to other distributed parameter simulations, EHL simulations require a labor-intensive resolution process. Physics-informed neural networks (PINNs) offer an innovative method to expedite the computation of such complex simulations by incorporating the underlying physical equations into the neural network’s parameter optimization process. A hydrodynamic PINN framework has been developed and validated for a variant of the Reynolds equation. This paper elucidates the framework’s capacity to handle multi-case scenarios—utilizing one PINN for various simulations—and its ability to extrapolate solutions beyond a limited training domain. The outcomes demonstrate that PINNs can overcome the typical limitation of neural networks in extrapolating the solution space, showcasing a significant advancement in computational efficiency and model adaptability. Full article

The modification of surface geometries to reduce friction is an omnipresent topic of research. In nature, different low-friction surfaces, such as fish skins, exist. To transfer this knowledge to technical applications, for example, to journal or plain bearings, many numerical and experimental studies of textured surfaces have been performed. In this work, the influence of the geometric parameters (texture length $l$, width $b$, angle $\alpha$ and start position $x_{start})$ of a wedge-shaped texture on three different convergent oil film gaps was analyzed in full-film lubrication and compared with untextured oil film gaps. With the aid of a CFD (computational fluid dynamics) model, a comprehensive variation study was conducted, and the best-performing wedge-shaped texture was determined. The results show that an open texture at the inlet provides the largest improvement. Furthermore, it can be observed that the optimal relative texture width and absolute inlet height for the three investigated oil film gaps are similar. In contrast to the volume flow of the untextured geometry, the volume flow of the textured one is significantly higher, especially that perpendicular to the movement direction. Full article

The outstanding lubrication of articular cartilage in the major synovial joints such as hips and knees, essential for the joint well-being, has been attributed to boundary layers of lipids at the outer cartilage surfaces, which have very low friction mediated by the hydration lubrication mechanism at their highly hydrated exposed headgroups. However, the role of spontaneously present lipid splays—lipids with an acyl tail in each of the opposing bilayers—in modulating the frictional force between lipid bilayers has not, to date, been considered. In this study, we perform all-atom molecular dynamics simulations to quantitatively assess the significance of splayed molecules within the framework of lubricating lipid bilayers. We demonstrate that, although transient, splayed molecules significantly increase the inter-membrane friction until their retraction back into the lamellar phase, with this effect more steadily occurring at lower sliding velocities that are comparable to the physiological velocities of sliding articular cartilage. Full article

Lip seals are components subjected to high mechanical stress and they are responsible for many out-of-service in pneumatic cylinders. The aim of this work is the development of an experimental methodology to evaluate lifetime duration and analyse failures and damages of rod lip seals for pneumatic cylinders. A dedicated test bench was designed and manufactured which reproduces actual working conditions of the seals i.e., compressed air action (seal pressurisation) and relative linear reciprocating motion. Three types of seals made of two elastomers (NBR and polyurethane) were tested; dry condition was considered to speed up the tests. The influence of geometric parameters like seal seat dimension and seal axis misalignment with respect to the rod axis, was analysed by multiple experimental tests. Results in terms of seal life duration and failure modes are presented which allow comparison of seals performance and provide a helpful tool to end-users in a proper selection of seals geometry, material and key working parameters. Full article

Titanium alloy material has physical properties such as low thermal conductivity, high hardness, and surface resilience, which are prone to problems such as large milling force, low machining efficiency, and poor surface quality in processed products during dry milling. This document details our process of isolating micro-textures from biological structures, applying them to cutting tool surfaces to create micro-texture milling cutters, and employing this micro-texture technique to reduce friction and prevent wear on these cutters. According to the milling dosage and the installation position between the tool and the workpiece, the effective working area of the cutting edge of the ball-end milling cutter is calculated. At the same time, a self-lubricating cutter was constructed by using a laser to process micro-textures and filling solid lubricant inside the micro-textures. An analysis was conducted to compare the milling efficiency of bionic microtextured cutters in both dry and micro-lubricated environments. It was found that the self-lubricating tool promoted a 3% to 5% decrease in milling force, a reduction in the coefficient of friction, a high surface finish of the machined workpiece, and an alleviation of chip sticking at the edge area. Full article

This review presents a series of studies which have demonstrated that the diffusion characteristics of rarefied mobile lubricant films used in modern magnetic disks can be evaluated by a novel diffusion theory based on continuum mechanics, and that the meniscus force of the rarefied film is the major interaction force at the head-disk interface. The limitations of the conventional diffusion and disjoining pressure equations are first shown, and diffusion and disjoining pressure equations for rarefied liquid films are proposed, showing that the diffusion coefficient is in good agreement with the experiment. The experiment, in which glass spheres with radii of 1 and 2 mm collided with magnetic disks of different film thicknesses, showed that attraction similar to the pull-off forces of a static meniscus was measured only at the separation. Furthermore, mathematical analysis of the elastic meniscus contact between a sphere and a plane with a submonolayer liquid film showed that the maximum adhesion force is equal to the meniscus pull-off force and that the contact characteristics become similar to those of the JKR theory as the liquid film thickness decreases. A basic physical model of submonolayer liquid film is also proposed to justify the continuum mathematical equations. Full article

In practical engineering applications, high temperatures and water ingress seriously affect the service life of hydrocarbon lubricants. In this study, the deterioration process of hydrocarbon lubricants under high temperatures and humid environments was investigated, and a new health state prediction model was proposed. Simulation of hydrocarbon lubricant Polyalpha−olefin (PAO) molecules used the ReaxFF force field to analyse the high temperature thermal oxidation process of lubricants. The rheological properties of oil−water emulsions were determined by observing the morphology of oil−water two−phase mixtures with different water contents. A multiparameter fusion viscosity prediction model was proposed using a linear model of the viscosity of aqueous fluids, as affected by temperature and water content, and was fitted with the Andrade viscosity−temperature equation to predict lubricant viscosity changes under multiple parameters. Online validation tests were carried out on a compound planetary transmission system, and the surface topographical parameters of the transmission components were further discussed. Experimental results show that the linear correlation with the improved lubricant viscosity prediction model is 0.966, and the surface wear of transmission components is consistent with the trend of lubricant quality change. These findings provide a fundamental basis for the assessment of lubricant service life in high temperatures and humid environments. Full article

Lubricating oils play an important role in friction-reducing and anti-wear, as well as enhancing mechanical efficiency. To improve the oxidation stability and service life of lubricating oils, the composition and structure of antioxidants should be strategically designed, and these parameters have significantly affected the performance of antioxidants in lubricating oils. Antioxidants are classified into two types based on the substrates they act on: peroxide decomposers and radical scavengers. In this review, the effects of peroxide decomposers (including sulfur compounds, phosphorus compounds, sulfur–phosphorus compounds, and sulfur–nitrogen compounds) and radical scavengers, such as hindered phenols and aromatic amines, have been discussed as additives in the antioxidant properties of lubricating oils. The results indicate that peroxide decomposers have excellent performances in lubricating oils, but high pollution of S and P is not conducive to their widespread use. On the contrary, radical scavengers also have superior antioxidant properties and no pollution, possessing the potential to replace traditional antioxidants. In addition, molecular structures with (multiple) synergistic antioxidant properties have been extensively designed and reported. This review serves as a reference for researchers to design and develop high-end new antioxidants. Full article

Per- and polyfluoroalkyl substances (PFAS), also known as forever chemicals, exhibit exceptional chemical stability and resistance to environmental degradation thanks to their strong C-F bonds and nonpolar nature. However, their widespread use and persistence have a devastating impact on the environment. This review examines the roles of PFAS in tribological applications, specifically in lubricants and lubricating systems. This article focuses on conventional and advanced lubricants, including ionic liquids (ILs) and their use in modern automotive vehicles. The objective of this paper is to provide a comprehensive overview of the adverse impacts of PFAS whilst acknowledging their outstanding performance in surface coatings, composite materials, and as additives in oils and greases. The pathways through which PFAS are introduced into the environment via lubricating systems such as in seals and O-rings are identified, alongside their subsequent dispersion routes and the interfaces across which they interact. Furthermore, we examine the toxicological implications of PFAS exposure on terrestrial and aquatic life forms, including plants, animals, and humans, along with the ecological consequences of bioaccumulation and biomagnification across trophic levels and ecosystems. This article ends with potential remediation strategies for PFAS use, including advanced treatment technologies, biodegradation, recovery and recycling methods, and the search for more environmentally benign alternatives. Full article

The working device of an excavator in construction machinery is prone to damage and wear under ordinary working conditions. Based on a model of an excavator under typical working conditions, the dynamic load-bearing situation of the three main joint friction subsets of the working device is simulated by using the virtual prototype technology; the location of the functional device with high stress is identified based on finite element analysis, and the correctness of the simulation results is verified by designing strain gauges. Based on this, the dynamic contact stress variation law of the contact surface of the end-face friction subsets was explored, and the end-face wear depth was calculated by combining Archard wear theory and finite element wear simulation technology; the specimens were worn on the end-face wear tester, and the surface wear was observed under the scanning electron microscope to summarize the wear mechanism and analyze the element content changes of the worn surface. The results show that the three main joints of the working device produce large dynamic fluctuations and are prone to wear, and the destructive degree is more prominent; the wear process is accompanied by higher temperatures, fatigue wear, and abrasive wear on the wear surface, and the wear depth value of the right end face is significantly larger than that of the left end face. This method has a significant reference value for reliability analysis and optimization improvement when using construction machinery’s main joint friction pairs. Full article

Electric vehicle (EV) transmissions operate at high speeds. High-speed operation puts higher demands on bearings, seals, and gears. Bearings in EV transmissions are prone to electrically induced bearing damage and may exhibit signs of pitting and fluting. Surface-initiated rolling contact fatigue is another common problem gaining increased attention lately. Most EV transmissions require a coupling between an oil-lubricated gearbox to an electrical motor that runs with minimal lubrication at very high rpm. The high mechanical and thermal stresses the seals are exposed to under starved lubrication conditions have a detrimental impact on their service life. Hence, proper lubrication is critical. In general, EV transmission fluids call for a somewhat different spectrum of properties compared to conventional ATFs. Gear tribology simulations open new ways to the design and optimization of lubrication for EV transmissions. Additionally, such simulations can also provide valuable insights into the effects of different oil properties on cooling and lubrication efficiencies, thereby helping in matching the lubricant and hardware characteristics for optimal performance. In the present communication, we demonstrate the effects of different lubricants and surface finishing technologies on the tribology of high-speed gears using tribological tests and advanced thermal elastohydrodynamic (TEHD) simulations. The important roles of lubricity additives and surface finish optimization are highlighted in conjunction with a move towards ultralow viscosity EV transmission fluids. Full article

Aiming to improve the comprehensive performance of the journal bearing system, this paper presents a multi-objective adaptive scale texture optimization design approach. A mixed lubrication model for the textured journal bearing system is established by considering the effects of cavitation and roughness. The geometrical parameters of the textures were co-optimized using a multi-objective grey wolf optimizer to obtain the optimal texture schemes that are suitable for different operating conditions. Through this approach, the influences of different texture schemes under transient operating conditions can be investigated. According to the results, it was found that different texture schemes result in different friction reduction effects. Proper surface texture is beneficial in increasing the minimum oil film thickness and reducing the possibility of asperity contact. The adaptive scale texture exhibits strong adaptability and achieves significant hydrodynamic effects. Therefore, the developed approach provides valuable insights for the optimization design of journal bearing systems. Full article