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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 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]

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]

Demand for micro-deep-drawn complex-shaped parts in biomedical, chemical analysis and microsystem technologies has been growing. Micro-deep drawing is a micro-plastic forming used to produce micro-parts from different materials. Researchers have worked upon several aspects of micro-deep drawing (MDD), namely the scaling effects, handling of micro-parts and process intermittency. The present work reviews some of these experimental and numerical studies on the MDD considering the size effects, forming limit diagram, parametric effect, lubrication and coating on punch and die surfaces. The topology modification of the deep drawing tool surface using macro/microstructured coated tool shows substantial potential for the lubricant-free micro-deep drawing. Further, micro-structuring of the blank via laser has emerged as another approach in the MDD process to reduce the effective contact area between tool and sheet and, hence, the friction forces. Finally, challenges and scope for further research in MDD are listed to implement these processes commercially. [ABSTRACT FROM AUTHOR]

Lubricants are usually utilized to decrease wear, reduce friction, and release heat. Although the lubrication approximation originated from thin-film studies, it has limitations because of continuum mechanics assumptions. To overcome these limitations, for the first time, this article employs a hierarchical multiscale approach to study the frictional sliding contact considering elastohydrodynamic lubrication. This multiscale model consists of a molecular model of lubricant and a continuum model of sliding contact components. Specifically, the molecular dynamics method is used at the nanoscale to model the lubricant and analyze the friction coefficient in contacted surfaces. Through MD simulation, the effects of hydrocarbon chain lengths, temperature, and sliding velocity on a constant friction coefficient are studied in this article. The calculated friction coefficients from the molecular model are passed to the continuum model, in which the finite element method is employed to conduct stress and strain analysis of the sliding contact components. Although variations in the frictional sliding response are invariably coupled with the friction coefficients, the molecular-to-continuum hierarchical approach enables us to isolate the relative contributions from the chemical formulation of the lubricant and the temperature. This approach has further potential implications for the evaluation of tribological damage. The results demonstrate that an increase in temperature or the chain length of lubricant hydrocarbon molecules can significantly decrease the friction coefficient and, as a result, reduce contact shear stress, plastic deformation, and pile-up height. [ABSTRACT FROM AUTHOR]

The dynamic behavior of the pump-turbine thrust bearing is important to the safety operation of the unit. This paper analyzed the lubrication and energy dissipation mechanism of pump-turbine thrust bearing during load-rejection based on the thermo-hydrodynamic model. The results show that the variation of the axial force and the maximum pad surface pressure is basically consistent with that of the inclination of the pad surface. The change of the friction loss is consistent with the change of rotational speed, while the change of pad surface temperature is affected by the combination of pad inclination and rotational speed. The chaotic flow in the oil tank is accompanied by different forms of vortices, such as Taylor vortices, vortex pairs, and Karman vortices, and results in a significant asymmetry in the pressure distribution. The flow in the bearing pad groove has an effect on the energy dissipation in the oil film. This paper provides a theoretical basis for the design and optimization of thrust bearings, and provides a reference for solving the problems of wear, oil mist, and other related problems of thrust bearings in engineering. [ABSTRACT FROM AUTHOR]

The long-term wear of the piston/cylinder pair is the main failure reason for axial piston pumps. In this paper, the dynamics of textured films to enhance the lubrication performance of piston/cylinder pairs is investigated systematically. The oil film is divided into three regions: the head region, the texture region, and the tail region. The Reynolds equation is used to predict the dynamics, which includes the carrying capacity and the friction. Influences of the texture geometries and the working conditions are presented in sequence. The results show that the texture enhances the lubrication performance by the collective effect. A shorter head length and a larger area ratio always benefit the lubrication performance, while increasing the texture region length does not always lead to positive effects, and the cell length is found to have negligible influences. The texture effect is found to be enhanced with larger shearing velocities and to be restrained with higher inlet pressures. It is also shown that the texture is effective for small inclination angles. Furthermore, a one-dimensional model is performed to unravel the mathematical mechanism, and an explicit expression is given for the texture region length. [ABSTRACT FROM AUTHOR]

Purpose: Hydro-viscous drive (HVD) clutches are widely used in equipment requiring soft start, such as fans and pumps, to transmit torque and adjust speed by changing the gap distance between friction pairs. This paper aims to propose a novel two-parameter evaluation method for HVD during the mixed lubrication stage. The objective is to develop an effective model that establishes the relationship between these parameters and the actual surface topography. Design/methodology/approach: In the presented methods, the fractal features of the real manufacturing surface are calculated based on the power spectrum function by the ultra-depth three-dimensional microscope. After that, the hybrid friction model of the friction plate is established based on mixed elasto-hydrodynamic lubrication theory, boundary friction model and fractal theory. Then the torque and load bearing characteristics of the clutch are obtained, and the influences of the surface fractal features are investigated and discussed. Finally, the Weierstrass–Mandelbrot function is adopted for the surface topography characterization and evaluation. Findings: The results indicate that the proposed method exhibits good accuracy, while the speed difference between the friction pair exceeds 2,500 rpm. It is concluded that this paper proposed a way to evaluate the torque and loading capacity of HVD considering the real manufacturing surface topography and is helpful for surface optimization. Originality/value: The originality and value of this study lie in its development of a novel torque and load bearing capacity evaluation method for HVD in mixed lubrication stage, considering manufacturing surface topography and describing the real manufacturing surface. [ABSTRACT FROM AUTHOR]

The distribution of lubricant flow field inside the two‐stage transmission reducer is very complicated during splash lubrication, which is difficult to be visually simulated and analysed using traditional finite element methods (FEM). There are many problems in model processing, algorithm selection, mesh division, and computational workload. Through sufficient investigation and experimental validation based on literature, the moving particle semi‐implicit (MPS) method is proposed to study the splash lubrication characteristics of a rail vehicle reducer. Through this method, the visual simulation calculation of multiple working conditions of reducer with complex structure is realised, and the unreasonable structure of the gearbox body is optimised. The model of oil supply demand in the Hertz contact zone of gear transmission is established, and the time‐domain variation law of oil particles number in the contact zone and oil supply state are analysed. It is found that the optimised reducer model can meet the demand of oil supply under the four typical working conditions of the rail vehicle. The higher the initial oil volume is, the more sufficient the oil supply is. Compared with the working temperature conditions of 20 and 80 °C, the lubrication effect is better at 40 and 60 °C. By analysing the power loss proportion of each gear, it is found that the sum of power loss of gear 1 and gear 2 is dominant under different working conditions, reaching 76%–99.5% of the total churning power losses. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to use a machine learning (ML) model for the prediction of traction coefficient and asperity load ratio for different surface topographies of non-conformal rough contacts. Design/methodology/approach: The input data set for the ML model is generated using a mixed-lubrication model. Surface topography parameters (skewness, kurtosis and pattern ratio), rolling speed and hardness are used as input features in the multi-layer perceptron (MLP) model. The hyperparameter tuning and fivefold cross-validation are also performed to minimize the overfitting. Findings: From the results, it is shown that the MLP model shows excellent accuracy (R2 > 90%) on the test data set for making the prediction of mixed lubrication parameters. It is also observed that engineered rough surfaces with high negative skewness, low kurtosis and isotropic surface patterns exhibit a significant low traction coefficient. It is also concluded that the MLP model gives better accuracy in comparison to the random forest regression model based on the training and testing data sets. Originality/value: Mixed lubrication parameters are predicted by developing a regression-based MLP model. The machine learning model is trained using several topography parameters, which are vital in the mixed-EHL regime because of the lack of regression-fit expressions in previous works. The accuracy of MLP with random forest models is also compared. [ABSTRACT FROM AUTHOR]

A series of polyimide (PI)/V2CTx MXene composites was synthesized via polyamide acids (PAA) and two‐dimensional (2D) V2CTx MXene obtained by etching precursor V2AlC. PI/V2CTx MXene composites with different mass ratios were obtained by blending and heating with PAA. The results showed that V2CTx MXene has excellent dispersion in PI. In particular, V2CTx MXene exhibited excellent friction reduction and anti‐wear properties as a solid lubricant additive, and the wear rate (WR) was reduced by 43.2% by incorporating only 0.8 wt% of V2CTx MXene in the pristine PI and 71.9% by incorporating 1.2 wt%. Scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) analyses showed that the continuous transfer film consisting of a high proportion of tribo‐chemical products formed on the contact surface is significant to improve the lubrication performances of the PI composites. This work broadens the application of MXene in the field of tribology and contributes to energy conservation and sustainable development of human society. Highlights: The tribological properties could be tuned by changing the ratio of PI to V2CTx MXene.The WR of PI composites was reduced by 71.9% with incorporating 1.2 wt% of V2CTx MXene.The formation of transfer films on the contact surface is significant for improving anti‐wear of PI. [ABSTRACT FROM AUTHOR]

Porous materials are widely used in friction pairs. The transient squeezing flow of the lubricant significantly affects the lubrication quality. The study found that the lubricant penetrates into the porous matrix in the contact area and exudes upward to the entrance of the contact area. The maximum stress occurs at the subsurface of the contact zone, and the maximum pressure occurs at the contact centre. In the early loading stage, the lubricant exudates, resulting in a higher liquid‐phase load. With the prolongation of the time, the average stress decreases and then increases gradually, whilst the average pressure has the opposite change. In the late loading stage, the load is completely borne by the solid phase. Increasing the load will increases the seepage velocity of the lubricant, which enhance the pumping effect of the friction interface. The findings can help for better understanding of the self‐lubrication mechanism of the porous materials. [ABSTRACT FROM AUTHOR]

In the actual working condition, due to the manufacturing errors, improper installation, load, thermal deformation or other factors can cause the journal surface to produce the form and position errors. The mathematical models are developed that takes into account the form and position errors, the lubrication performance of four‐recess capillary restrictor hybrid journal bearings with different journal tilt angles and cylindricities is studied, and the effect of eccentricity on the oil film lubrication performance is analysed. The results show that the dimensionless oil film pressure and loading capacity increase as the journal tilt angle and eccentricity increase considering journal tilt, and the friction coefficient tends to increase and then decrease. Compared with journal alignment, the oil film thickness distorts, the oil film pressure peak shifts to the edge of bearing, and the horizontal tilt has a greater impact on bearing when the journal is tilted. The oil film pressure distribution has no significant change considering cylindricity errors, while the oil film pressure value increases, the loading capacity increases and the coefficient of friction decreases as the cylindricity and eccentricity increase. The research shows that the presence of a certain cylindricity error contributes to the lubrication performance of four‐recess capillary restrictor hybrid journal bearings. [ABSTRACT FROM AUTHOR]

The artificial joint prosthesis's surface is subjected to wear due to the destruction of the joint lubrication environment after surgery. In this study, an agarose-sodium hyaluronate hydrogel was used as lubricant additive in order to supply and preserve the lubricating fluid of artificial joint prostheses. A ball on disc experiment was conducted using this hydrogel to evaluate the lubrication efficiency and release rate under various frequencies. The results showed that this hydrogel could release lubricant under pressure and then absorb the released fluid after decompression. Furthermore, the agarose-sodium hyaluronate hydrogel acted as an effective transport mechanism to release sodium hyaluronate lubricant into the metal-on-polymer friction interface. Compared with pure water lubrication, the friction coefficient and wear volume were reduced by up to 62.9%, and 86.9% respectively. Moreover, the proposed lubrication method provided a long-term lubrication on artificial hip joints. [ABSTRACT FROM AUTHOR]

Elastomers are the class of materials that are widely used in a variety of industrial, commercial, and consumer applications due to their unique mechanical properties, including high elasticity, high flexibility, and high resilience. However, there are many challenges in machining of elastomers such as poor surface finish, build up of heat, degradation of elastomers, etc. To overcome these challenges, cryogenic cooling assistance has been introduced as a means of improving the machinability of elastomers. This paper presents a soft computing approach for optimizing the surface roughness and cutting force during turning of elastomers under different lubrication conditions. Three types of elastomers, namely Nitrile Rubber (NBR), Polyurethane Rubber (PU), and Neoprene Rubber (CR), are studied, and a cryogenic fluid delivery system is employed to improve the machining process. Taguchi's L27 array is used to vary the input parameters, and a Back-Propagation Artificial Neural Network (BPANN) model is developed to predict the cutting force and surface roughness. The cutting force and surface roughness are analyzed under different cooling conditions, cutting speeds, feeds, and depths of cut for various elastomers. The results show that changes in cutting conditions significantly affect the cutting force and that the type of lubrication used affects the cutting force by altering the material's physical properties. Cutting force is significantly influenced by cutting conditions, and NBR requires the highest cutting force compared to PU and CR. Further, at a cutting speed of 55 m/min, a feed of 0.11 mm/rev, and a depth of cut of 0.25 mm, the cutting force for NBR (85.1 N), while for PU (75.1 N) and CR (80.3 N), respectively. Finally, with LN2 lubrication conditions, the Cutting Force decreased by 45% and Surface Roughness decreased by 16.9%. This study provides insights into the factors affecting the elastomer machining process, which can be useful for optimizing the machining process parameters and improving machining efficiency. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to prepare ZnFe2O4 nanospheres, sheet MoS2 and three ZnFe2O4@MoS2 core-shell composites with various shell thicknesses, and add them to the base oil 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 lubricant additives were investigated and the effects of shell thickness and sample concentration on the tribological properties of core–shell composite lubricant additives were discussed. Findings: The findings demonstrate that each of the five sample materials can, to varying degrees, enhance the lubricating qualities of the base oil and that the core–shell nanocomposite sample lubricant additive has superior lubricating properties to those of ZnFe2O4 and MoS2 alone, among them ZnFe2O4@MoS2-2 core–shell composites with moderate shell thickness performed most ideally. In addition, the optimal concentration of the ZnFe2O4@MoS2 lubricant additive was 0.5 Wt.%, and a concentration that was too high led to particle deposition and affected the friction effect. Originality/value: In this work, ZnFe2O4@MoS2 core–shell composites were synthesized for the first time using ZnFe2O4 as the carrier and the lubrication mechanism of core–shell composites and single materials were compared and studied, which illustrated the advantages of core–shell composite lubricant additives. At the same time, the influence of different shell thicknesses on the lubricant additives of core–shell composites was studied. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2022-0367/ [ABSTRACT FROM AUTHOR]

[Display omitted] • Non-aqueous lamellar liquid crystal systems DBSA/MEA was constructed. • DBSA/MEA lamellar liquid crystal system has good lubrication and anti-corrosion properties. • Friction chemical reaction film and adsorption film improves the lubrication performance. • The coordination effect of MEA and Fe may be the key to improve corrosion resistance. Since lamellar liquid crystals (LLCS) could be used for lubrication, many LLCS systems have been constructed to improve lubrication performance. However, most studies focused on the LLCS of the water system, and its corrosiveness brought some limitations to its application. Therefore, it is necessary to construct a non-aqueous LLCS system with good lubrication and anti-corrosion properties to improve its applicability. Anionic surfactant dodecyl benzene sulfonic acid (DBSA) was used to construct non-aqueous LLCS in different solvents, including monoethanolamine (MEA) and diethanolamine (DEA). DBSA/H 2 O LLCS system was constructed for comparison. The LLCS was characterized by polarizing microscope (POM), small-angle X-ray scattering (SAXS), and rheology. Its microstructure was discussed. Meanwhile, we evaluated the lubrication and anti-corrosion performance of LLCS. Its lubrication mechanism was explained through tribology tests and X-ray photoelectron spectrometer (XPS) analysis of the wear scar surface. Its anti-corrosion mechanism was investigated by using the weightlessness method, electrochemical test method, and quantum chemical theoretical calculations. The DBSA/MEA non-aqueous LLCS system showed better lubrication performance than DBSA/DEA and DBSA/H 2 O LLCS. It can adsorb on the surface of the friction pair to form a lubrication friction film, which plays a better role in reducing friction and wear. The DBSA/MEA LLCS is less corrosive to metals because it can effectively isolate oxygen and water in the air between friction pairs. Furthermore, the lone pair electrons in the 2p orbital of the N atom in the MEA molecule could coordinate with the 3d empty orbital of the Fe atom, forming a protective film on the metal surface, which plays a good anti-corrosion effect. This work not only enriched the study of non-aqueous LLCS but also expanded its potential applications in the field of lubrication. [ABSTRACT FROM AUTHOR]

Purpose: To understand the service performance of full ceramic ball bearings under extreme working conditions and improve their service life, dynamic characteristic tests of full ceramic ball bearings under ultra-low temperature conditions were carried out by a low-temperature bearing life testing machine, and temperature rise and friction were measured under extreme low-temperature environment. Design/methodology/approach: The heat-flow coupling model of bearing was established by CFD software, and the test results were further analyzed. Findings: The results show that the temperature rise of the bearing is not obvious in the liquid nitrogen environment. With the increase of the chamber temperature, the lubrication state of the bearing changes, resulting in the temperature rise of the outer ring of the bearing. As the temperature of the test chamber increases, the friction force on the bearing increases first and then decreases under the action of multifactor coupling. Research limitations/implications: The research results provide test data and theoretical basis for the application of all-ceramic ball bearings in aerospace and other fields and have important significance for improving the service life of high-end equipment under extreme working conditions. Practical implications: The research results provide test data and theoretical basis for the application of full ceramic ball bearings in aerospace and other fields and have important significance for improving the service life of high-end equipment under extreme working conditions. Social implications: The research results provide test data and theoretical basis for the application of full ceramic ball bearings in aerospace and other fields and have important significance for improving the service life of high-end equipment under extreme working conditions. Originality/value: The research results provide test data and theoretical basis for the application of full ceramic ball bearings in aerospace and other fields and have important significance for improving the service life of high-end equipment under extreme working conditions. [ABSTRACT FROM AUTHOR]

In the rotating parts of large mechanical equipment, the existence of friction and wear will inevitably cause energy consumption and loss. Coating a layer of solid lubricating material on the surface of mechanical equipment is an effective means to reduce friction and wear. In this study, for the first time, a composite film with high mechanical and lubricating properties was prepared by hot-pressing the mixture of graphene oxide (GO), polyethylene glycol (PEG), and polyvinyl alcohol (PVA). Its structure and properties were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy (Raman), and thermogravimetric analysis (TGA). The lubrication and tribological properties of GO-PEG-PVA composite film and other single films under different lubrication conditions were analyzed. The lubrication characteristics of GO-PEG-PVA composite film under oil lubrication were discussed in detail. The results show that the surface coating with GO-PEG-PVA can ensure a lower friction coefficient, especially in the condition of oil lubrication, the friction coefficient is 82% lower than that without oil film. The hot pressing process ensures that the surface morphology will not produce large shear deformation. The lubrication mechanism and lubrication model were discussed in detail, and the concept of improving surface lubrication performance by co-lubrication was put forward. [ABSTRACT FROM AUTHOR]

To improve the tool lubrication performance and reduce the use of cutting fluid as much as possible, a new type of tool with continuous lubrication on the tool-chip contact interface has been fabricated. The atomized cutting fluid can be directly delivered to the tool-chip contact interface through the inner microchannel. Experiments were conducted on the new lubrication method, dry cutting, and traditional MQL cutting of 45 steel. The three-dimensional cutting forces and the cutting temperatures were measured. The wear surface of the rake face was analyzed through SEM micromorphology and EDS element detection. The results showed that the main cutting force of the tool with continuous lubrication at the tool-chip interface decreased by 14.5% and 5.9% compared with the conventional tools of dry cutting and MQL cutting. Moreover, the friction coefficient decreased by 14.2% and 9.8%, the length of the tool-chip contact interface decreased by 35.4% and 19.1%, and the amount of cutting fluid was only 1/10 of that in MQL cutting. The new lubrication method had better cutting fluid penetration and lubrication film formation performance than the traditional MQL method on the tool-chip interface. Furthermore, the surface wear of the new lubrication method was significantly reduced, and the main wear form of the new lubrication method was adhesive wear. [ABSTRACT FROM AUTHOR]

In recent years, there has been a challenge: how to meet the requirements of cutting lubrication and use the least cutting fluid for environmental protection simultaneously. To resolve this problem, novel cutting tools with micro textures on the rake face for lubrication were proposed, which can directly transport the cutting fluid to the tool-chip contact interface by using a micro-pipe. Cutting tests were performed on AISI 1045 steel. Then, the cutting force, friction coefficient, tool-chip contact length as well as wear of tools were investigated. The results show that the novel tools with micro textures have better cutting performance than other tools, by using much less cutting fluid than traditional flood lubricating cutting. Especially for the TVT tool, it has the best comprehensive performance. The main lubricating mechanism is that the cutting fluids can be more widely distributed on the tool rake face by the micro textures. This leads to better lubrication and less adhesion of the rake face. [ABSTRACT FROM AUTHOR]

Functionally graded materials (FGMs) are a promising engineering material, which is highly desirable in extreme environments of aerospace, nuclear, and bio-implants. Although the surface accuracy and quality of 3D-printed Ni–Fe FGMs can meet most application scenarios, it still requires post-cutting treatment especially in nuclear industry. The FGMs, with the gradient of mechanical property, are a new type of difficult-to-cut material. However, no ready-made post milling process can be referred. The poor-machined surface quality induced by excessive tool wear still cannot be handled even with textured tool under minimum quantity lubrication (MQL). In this paper, the mechanical properties and machinability of the Ni–Fe FGMs as well as its 5 isotropic component 304LxIN625y were firstly studied and correlated. Then, two milling parameter selection strategies were proposed by minimum milling force and by minimum surface roughness, corresponding to strategy I and strategy II. The results show that tool breakage occurs in bottom cutting edge when strategy I is adopted. On the contrary, strategy II can reduce tool major flank wear 40.1% by forming an elastohydrodynamic lubrication between bottom cutting edge and the machined surface, which is a prospective method to solve the tool failure during milling of 3D-printed Ni–Fe FGMs. [ABSTRACT FROM AUTHOR]

The tooth form is the most influential factor on the bearing capacity and operation performance of a gear drive. Tooth profiles of spur gears can be designed based on control of relative curvature of conjugate profiles, but how to conceive appropriate control strategies and appraise gear pairs accurately needs to be investigated in depth. This paper presents the control strategies through analysis of the effect mechanisms of relative curvature on the bearing capacity and lubrication performance. Evaluation approaches of the gear pairs are then proposed by establishing the analytical models (AMs). In case studies, gear pairs with optimal comprehensive performance are designed through five control strategies. The AMs for contact and bending capacity are validated with the finite element models. The effects of the control strategies are discussed through comparative analysis. Results reveal that the control strategies lead to remarkable enhancement of bearing capacity and lubrication performance. [ABSTRACT FROM AUTHOR]

As an important precision transmission functional component in industrial fields such as large mechanical equipment, high-speed CNC machining center, and aerospace, the service life of the ball screw are directly related to the life of high-end equipment. Fatigue failure is the main failure mode of the ball screw in the transmission application where the transmission accuracy is not high. Therefore, the fatigue life of the ball screw is studied from the perspective of fatigue. The load distribution form of the double-nut ball screw under axial load is analyzed. Based on the ball load distribution, a mixed lubrication model of the ball screw considering non-Newtonian effect of lubricant is established, and a fatigue life prediction method of the ball screw based on maximum secondary surface stress is proposed. The lubrication performance of the ball screw under maximum contact load is compared with that under equal load distribution, and the effects of ball load distribution, curvature ratio, and temperature rise on fatigue life are analyzed. Two kinds of ball screw including BT GD8020 and NSK DFD8020 are used for running test of fatigue life, and the fatigue life calculation method based on the maximum secondary surface stress is verified. The hardness distribution of the transition zone between ball and raceway is analyzed, and the fatigue failure modes of two ball screws are explored. [ABSTRACT FROM AUTHOR]

In high-speed sawing, the penetration of cutting fluid is limited due to the narrow kerf and large cutting depth. To improve the machining performance of high-speed sawing and the lubrication and cooling efficiency of cutting fluid, a technology named electrostatic minimum quantity lubrication (EMQL) high-speed sawing with water-based nanofluid as cutting fluids was developed. The adsorption and motion characteristics of droplets on the solid surface under airflow were studied. Furthermore, the machinability of EMQL in high-speed sawing was explored. The results show that the charged droplet's surface tension, static contact angle, and velocity under tangential airflow are lower than those of the uncharged droplet, while the dynamic contact angle hysteresis is higher. This indicates that the adsorbability of charged droplets on solid surface is enhanced. In high-speed sawing processing, the principal sawing force is reduced by 19% when the fluid is charged at − 4 kV. The reason may be that charging reduces the drag force of the droplet and increases the capillary force generated by the deformation of the contact line between the droplet and the solid surface, which enhances the adsorption capacity of the charged droplets on the sawtooth surfaces and improves the lubrication performance of the sawing area. [ABSTRACT FROM AUTHOR]

In mechanical industry, most mechanical systems contain lubrication clearance joints. Consequently, to analyze the dynamic response errors and accuracy reliability for mechanisms with lubrication clearance joints is very necessary. So far majority studies have focused on kinematic accuracy reliability for mechanism, but few on dynamic response errors and accuracy reliability. Moreover, the only studies on dynamic accuracy reliability mainly focus on mechanisms with dry contact clearance joint, while the studies on dynamic accuracy reliability for mechanisms with lubrication clearance joint are very few. This paper presents an analysis method of dynamic response errors and accuracy reliability for mechanism with lubrication clearance joints. Firstly, the lubrication clearance joint model and dry contact clearance joint model are established, respectively. The dynamic model of nine-bar mechanism with multiple lubrication clearance joints is developed according to Lagrangian multiplier method. And then, the dynamic accuracy reliability model for mechanism is derived by first-order second-moment method. Finally, the influences of lubrication clearance and dry contact clearance on dynamic response errors and accuracy reliability for mechanism are compared and analyzed at different driving speeds. And the influences of dynamic viscosity and clearance values on dynamic response errors and accuracy reliability for mechanism with lubrication clearance joints are researched. This research offers the theory foundation for design of reliability for mechanism. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to study the influence of dimple textures on the friction and wear properties of tapered roller bearings (TRBs) with many pattern parameters, e.g. diameter, depth and area density under starved lubrication. Design/methodology/approach: The pattern parameters include the dimple diameter (D; 60, 100 and 200 µm), dimple depth (H; 5, 10 and 20 µm) and area density (S; 6%, 12% and 24%). Dimples were fabricated on the outer ring (OR) of TRBs using a laser marking machine. The tribological properties of dimple-textured TRBs under starved lubrication were studied on a vertical universal friction wear tester with special friction pairs. The effect mechanisms of dimple textures on the tribological properties of TRBs are presented and summarized through experiments and discussions. Findings: When dimple-textured TRBs revolve under starved lubrication, the average coefficients of friction (ACOF) and wear losses are markedly lower than those of non-textured bearings. S has the greatest influence on the COF curve. When D is 100 µm and S is 24%, the ACOF and wear losses are both lowest, i.e. 0.00426 and 0.51 mg, respectively. Under the same test conditions, compared with the non-textured group, its COF and wear loss decreased by 35.6% and 62.5%, respectively. Originality/value: This work provides a useful reference for the research on the raceways of textured TRBs. [ABSTRACT FROM AUTHOR]

Attempts have been made to use air-vortex cotton-blended spun yarn of 30s and 40s count as sewing thread by using 2.9% and 5.9% concentrations of lubricant. No systematic study has been conducted as of now for vortex because all the sewing threads used in the garment industry are produced from ring yarn. Yarn strength, elongation, hairiness, dry heat shrinkage, yarn abrasion, snarling of yarn after heat setting, loop strength, and knot strength of air-vortex-spun sewing threads have been studied. It is observed that the sewing thread made with 5.9% concentration of lubricant performs better in comparison to that made with a 2.9% lubrication level. Seam strength and efficiency of different types of seams made by air-vortex sewing threads have also been studied. Flat and lapped seams are found to produce higher seam strength and seam efficiency. Seam strength and efficiency improve with an increase in the concentration of lubricant in both 30S and 40S yarn. [ABSTRACT FROM AUTHOR]

In this study, the effects of surface roughness and thermal on slider bearings with turbulent fluid film were examined using the Streamline Upwind Petrov–Galerkin (SUPG)-Finite Element Method. Using the assumption that roughness is stochastic and has a Gaussian random distribution, one-dimensional transverse and longitudinal surface roughness models were taken into consideration. The texture of the surface's irregularity is changed into a regular domain for computational efficiency. To derive the modified Reynolds equation for turbulent lubrication, the Ng-Pan turbulent model is used. For all local Reynolds values, the pressure distribution of the combined effect is less than the thermal and surface roughness influences of the one-dimensional longitudinal surface roughness, which is a reduction of 16% in load-carrying capacity performance and 3% decrease in friction force, for non-parallel (w = 0.4) between the surface roughness effect and the combined effect condition, respectively. However, the pressure distribution of the thermal effect is smaller than the combined and surface roughness effects in the transverse, one-dimensional roughness model for all local Reynolds values, which is a reduction of 33% in load–carrying capacity performance and 13% decrease in friction force, for non-parallel (w = 0.4) between the surface roughness effect and the thermal effect condition, respectively. Moreover, the combined effects at various temperatures are examined. As a result, the load-carrying capacity performance is better in the case where the pad temperature is lower than the slider in both longitudinal and transverse models. The performance of a slider bearing will generally be improved by taking surface roughness and the coefficients of turbulent lubrication equations into account. Tables and figures were used to present the results. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to understand how axial cylinder distortions influence the tribological performance of piston ring. The current model contains the effects of axial distortions and ring conformability under mixed to hydrodynamic regimes of lubrication through computational fluid dynamics predictions. The axial cylinder profiles were modelled using series of sinusoidal waves. The effect of axial distortions on ring wear rate was determined using the Archard's model. The ring friction and minimum lubricant film were predicted for low and high combustion pressures near to top dead centre. The study shows that, when the maximum combustion pressure rises, the different wear identities affect the operation of the ring friction much more limited, while the number of sine waves are more pronounced. Finally, it is proved that, even the increase of oil film thickness, it does not presuppose the reduction of friction when it comes to shaping the surface of the cylinder liner. [ABSTRACT FROM AUTHOR]

The effect of electric potential on the lubrication of a non-halogenated phosphonium orthoborate ionic liquid used as an additive in a biodegradable oil was studied. An in-house tribotronic system was built around an instrument designed to measure lubricant film thickness between a rolling steel ball and a rotating silica-coated glass disc. The application of an electric field between the steel ball and a set of customized counter-electrodes clearly induced changes in the thickness of the lubricant film: a marked decrease at negative potentials and an increase at positive potentials. Complementary neutron reflectivity studies demonstrated the intrinsic electroresponsivity of the adsorbate: this was performed on a gold-coated silicon block and made possible in the same lubricant system by deuterating the oil. The results indicate that the anions, acting as anchors for the adsorbed film on the steel surface, are instrumental in the formation of thick and robust lubricating ionic boundary films. The application of a high positive potential, outside the electrochemical window, resulted in an enormous boost to film thickness, implicating the formation of ionic multi-layers and demonstrating the plausibility of remote control of failing contacts in inaccessible machinery, such as offshore wind and wave power installations. [ABSTRACT FROM AUTHOR]

Lubricating oil is usually injected in the gap between mechanical interfaces to reduce the friction and wear and improve the normal bearing capacity of the interface. The state of the mixed lubrication is induced from the inadequate lubrication. However, in the investigation of this state, the irregular oil pits of rough surfaces are usually simplified to be the cylindrical or conical in traditional contact models, which is disagreed with the actual contact situations and makes errors in the contact analysis when it is used to reveal the contact performance of the mixed lubrication. To investigate the normal and tangential contact performances for the real mixed lubrication, the normal and tangential contact models reproducing the effects of both the surface roughness and the lubrication viscosity on the normal contact force as well as the tangential fraction force are proposed in this work. Based on the statistical theory, the total area of oil pits is presented to describe irregular oil pits of rough surfaces. Then, the contact performance between the solid and liquid parts involved in the mixed lubrication is analyzed referring to the elastic–plastic theory and the hydrodynamics theory. Finally, several key influencing factors (including the surface roughness, the film thickness, and the lubrication oil viscosity) on the normal and tangential contact performances of mechanical interface are revealed. The main contribution of this work is providing some guidance on the improvement of the normal and tangential contact performances of the mechanical interface by adjusting the normal pressure, the surface roughness, the relative movement speed, and the viscosity of the lubricating medium. [ABSTRACT FROM AUTHOR]

Purpose: To solve the problem of oil film thinning when hydrostatic thrust bearings are overloaded or rotating at high speed, the dynamic pressure formed by tiny oil wedges is used to compensate, and the optimum height of oil wedges is determined by the compensation rate to improve the bearing capacity of hydrostatic thrust bearings. Design/methodology/approach: This research method is aimed at the new type of double rectangular cavity static bearing with microbevel surface of q1-205. The wedge parameters of oil film were defined. The oil film lubrication performance of the bearing with the wedge parameters of 0, 0.02, 0.04, 0.06, 0.08 and 0.10 mm was simulated by the finite volume method, the comprehensive influence law of the wedge-shaped parameters on the vorticity and flow rate of the oil cavity pressure fluid was revealed. Finally, the oil cavity pressure changes of oil films with different wedge parameters under certain load and speed were tested by design experiments, and the theoretical analysis and simulation were verified. Findings: This study found that the oil film wedge shape can well compensate the static pressure loss caused by the high-speed or heavy-duty operation of the bearing, but the dynamic pressure effect of the wedge shape does not always increase with the increase of the wedge height. The oil film exhibits superior lubrication performance in the range of 0.06–0.08 mm. Originality/value: The original hydrostatic oil pad was designed as a microinclined plane, and the dynamic pressure caused by the microwedge of the oil pad was used to compensate the static pressure loss of the bearing. The lubrication performance of the oil film under the condition of varying viscosity was obtained by using the simulation method. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to put forward the lubrication model of oil bearing and enrich the design theory under the condition of mixed lubrication. Design/methodology/approach: A mixed lubrication model of bilayer porous bearing is established. The effects of the working conditions on the lubrication performance and seepage behavior were analyzed. Findings: Results show that the oil film pressure mainly occurs in the bearing convergence zone and contact pressure mainly occurs near the minimum film thickness. The oil infiltrates into the porous matrix in the contact area and precipitates out to the friction surface at the inlet of the contact area. The oil seepage velocity and dynamic pressure effect at the friction interface can be improved by reasonably matching the load and speed. With the decrease of the external load or increase of the rotating speed, the lubrication performance becomes well. Originality/value: This study provides a reference for the design and application of oil bearing under harsh working conditions. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the performance improvement of journal bearing by applying the arc-shaped textures on various regions of bearing expressly full, second half and pressure increasing regions operating with and without nanoparticles in the lubricant. Design/methodology/approach: The Reynolds equation is solved numerically by using the finite element method to obtain static performance parameters such as load-carrying capacity (LCC) and coefficient of friction (COF), which are then compared with untextured bearing at eccentricity ratios of 0.2 to 0.8. Aluminum oxide (Al2O3) and copper oxide (CuO) nanoparticles additives are used, and viscosity variation due to the addition of additives in the base lubricant is computed for considering the range of temperatures 50 to 90°C at a weight fraction of 0.1 to 0.5% by using an experimentally validated regression model. Findings: The results indicate that the maximum LCC and the lower COF are found in the pressure-increasing region. A maximum increase of 34.42% is observed in the pressure-increasing region without nanoparticles, and furthermore, with the addition of Al2O3 and CuO nanoparticles in lubricants in the same region, the LCC increased to 21 and 24%, respectively. Originality/value: Designers should use optimal parameters from the present work to achieve high bearing performance. [ABSTRACT FROM AUTHOR]

Using pure water in comparison to water-based lubricant containing 4% TiO2 nanoparticles (NPs), the hot rolling tests of 304 stainless steel were carried out at a rolling temperature of 1050 °C under varying rolling reductions and speeds. The effects of lubrication on rolling force, torque, power and contact friction were systematically investigated. The coefficient of friction (COF) during steady-state hot steel rolling was inversely calculated using a developed flow stress model. The COF models including the effects of rolling reduction and speed were proposed via multiple linear regression. The results indicated that the use of the nanolubricant enabled a reduction of rolling force up to 6.1% and decreases in rolling torque and power up to 21.6%, compared to that of water condition. The results obtained from the linear regression agreed well with those from the inverse calculation, suggesting the developed COF models had high accuracy. The lubrication mechanisms were derived from a boundary lubrication regime, owing to ball bearing and mending effects of TiO2 NPs, and formation of thin lubricant film under high rolling pressure. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to report the tribological behavior of dimples textured rolling element bearings (REBs) under variable load and starved lubrication. Design/methodology/approach: The pattern parameters include line-diameter of dimples (200 µm, 250 µm, 300 µm), depth of dimples (10 µm, 20 µm, 30 µm). Dimple patterns were prepared on the raceways of the shaft washers of cylindrical roller thrust bearings (CRTBs). A vertical wear test rig was used to obtain their coefficients of friction (COFs) under stepped load (1200–6000 N, with a manually increase of 1200 N every 3600 s) and starved lubrication. The wear losses and worn surfaces were characterized. The tribological performance between stepped load and fixed load (4000 N) was compared. The influence mechanism of dimples on the friction and wear properties of CRTBs under stepped load and starved lubrication was also discussed. Findings: Compared with the data of smooth ones, the average COFs of the dimples textured bearings are almost all reduced under stepped load and starved lubrication, while their mass losses almost all get higher. The depth−diameter ratio and the effective volume coefficient of dimples are the important factors. In this work, compared with the smooth group, when the line-diameter of dimple is 250 µm and the depth is 20 µm, i.e. the depth−diameter ratio is 0.08, its average COF is reduced by 46.8% and its mass loss is reduced by about 7%, showing wonderful friction-reducing effect and good wear resistance. Originality/value: This work can provide a reference for the raceway design of REBs. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to compare the spherical protruded and dimple textured journal bearings performance characteristics with the untextured bearing. Design/methodology/approach: The governing Reynolds equation considering the mass conserving (JFO) boundary conditions is solved using the computationally efficient progressive mesh densification (PMD) method. The central difference scheme is used for the discretization of the governing Reynolds equation. The numerical code developed is validated with the experimental results available in the literature. Findings: From this numerical study, it has been observed that the protruded textured journal bearing gives better performance compared to the dimple textured and untextured journal bearing for friction variable, whereas dimple textured journal bearing provides better performance compared to the protruded textured and untextured journal bearing for load carrying capacity and flow coefficient. For better performance, dimple and protruded textured bearings must be textured in second-half textured region configuration. Practical implications: The results shown here would be quite useful for the researchers generally and the bearing designers particularly. Originality/value: The load carrying capacity should be maximum whereas, the friction coefficient should be minimum and also the adequate flow of lubricant is necessary to maintain hydrodynamic lubrication and to remove the heat generated within the bearing due to friction, which impacts the bearing performance and life. Thus, this study would be significant in effective bearing design aspect. [ABSTRACT FROM AUTHOR]

[Display omitted] • Graphene oxide (GO) nanosheets are used on steel surfaces to realize macroscopic superlubricity with electric stimulation. • GO adsorption film's morphology on the intermittent contact surface is the main factor affecting lubricating performances. • This study lays a foundation for superlubricity applications in electrical environments in engineering contexts. Achieving macroscopic superlubricity in electric environments on steel surfaces remains a challenge. This study achieved macroscopic superlubricity on steel surfaces by employing graphene oxide (GO) nanosheet additives with electric stimulation. Multiple factors were studied regarding the effect on lubrication performances. The morphology of the GO adsorption film on the intermittent contact surface (disc) is the main factor affecting the COF, as the continuous contact surface (ball) is required to overcome the peaks of GO film during sliding. The mechanism underlying the friction reduction is concluded as follows: when the intermittent contact surface (disc) was the positive pole, negatively charged GO migrated towards it, forming an adsorption film on its surface. The surface layer orientation of the GO film is relatively smooth, attributed to its contact with the negative pole (ball), resulting in friction reduction. This study illustrates the feasibility of achieving macroscopic superlubricity on steel interfaces through electric stimulation, thereby laying the groundwork for practical applications of superlubricity in engineering contexts, particularly in electric environments. [ABSTRACT FROM AUTHOR]

In this work, we propose a functionalised bi-viscous lubrication model to study the material properties of concentrated non-Brownian suspensions and explore the possible confinement-induced non-Newtonian effects of the lubricant in the rheological response of this type of suspensions. From tribological studies, it is well-known that even macroscopically Newtonian liquids under strong confinement might exhibit properties which deviate significantly from their bulk behaviour. When two surfaces separated by an extremely small gap (still large compared to the molecular size) are sheared, strong shear-thinning of the lubricant viscosity at low shear-rates is observed, in spite of its Newtonian-like bulk response. This is connected to a significant increase of the zero-shear-rate viscosity under extreme confinement. We start from an effective lubrication algorithm recently proposed and develop a new gap-size-dependent interparticle bi-viscous lubrication model, able to capture qualitatively the main phenomenology of confined lubricants. We solve the lubrication interaction between particles iteratively via a semi-implicit splitting scheme. Since the handling of lubrication is made implicitly here, the method copes efficiently with large increases of the inter-particle effective viscosities, which would otherwise lead to simulation blow-up or the use of vanishing time-steps in standard explicit schemes. We analyse the rheological response of the suspension systematically in terms of model parameters. In contrast to pure Newtonian lubrication interactions, distinct shear-thinning and shear-thickening regimes in the relative suspension viscosity are observed, which are discussed in terms of particle microstructure coupled with the complex rheology of the confined lubricant. In addition, normal-stress response is negative in both N 1 and N 2 , which is difficult to achieve with standard contact frictional models. • A Functionalised Bi-Viscous model is proposed to consider augmented viscosity effects due to confinement. • FBV model considers an extreme viscosity rise with decreasing interparticle gaps. • DST features are predicted with the FBV model considering normal lubrication-forces. • An alternative mechanism leading to DST phenomenon is proposed. [ABSTRACT FROM AUTHOR]

Laser surface texturing is an effective method to enhance gear lubrication by improving lipophilic properties, thereby increasing transmission performance and longevity. This study investigated the effects of laser parameters on lipophilicity using a grid texture and found that a scanning speed of 100 mm/s maximized diffusion and climbing. The textured specimens showed higher wetting hysteresis and adsorption, forming a thicker oil film for better lubrication. Wear tests indicated that the textured specimen had reduced friction, wear quality, and depth by 49.2% and 66.34% compared to unprocessed specimens. Gear efficiency is effectively increased, and gear oil temperature is significantly reduced. This research offers insights into lipophilic characterization and gear lubrication enhancement, potentially decreasing surface failures like pitting, adhesion, and wear. • A method for characterizing the lipophilicity of material surfaces is proposed. • Maximum wettability and adsorption force increased by 49.2% and 66.34% over US. • Minimum wear quality and depth decreased by 29.65% and 45.33% compared to US. • Textured gears increase efficiency > 3.67%, reduce oil temp > 7.45% vs. untextured. [ABSTRACT FROM AUTHOR]

Surface micro-texturing involves creating microscopic pits or textures, serving as lubricant reservoirs to enhance lubrication distribution, potentially reducing friction and wear. This study specifically delves into the influence of varied depth patterns of pits on the operational performance of textured rolling bearings under severe lubrication conditions. Five distinct patterns with a fixed pit diameter (250 µm) and different depth variations (concave, decreasing, increasing, convex, and horizontal) were introduced on the shaft rings of cylindrical roller thrust bearings using the laser marking method. Wear tests were conducted under starved lubrication condition. Wear loss and signal analysis highlight the profound effect of depth variations, whereby bearings with shallow pits near the outer side of their working surfaces exhibit longer lubrication times, improved tribological performance, and enhanced vibration characteristics. Notably, the convex pattern stands out for providing comprehensive and favorable tribological and vibration properties. This research contributes valuable insights for the optimal design of micro-textures for rolling bearings, paving the way for enhanced efficiency and reliability in mechanical systems. [ABSTRACT FROM AUTHOR]

The journal-thrust coupled bearing (abbreviated as JTC bearing) works at the end of the crankshaft in diesel engine, with the function of carrying radial load and prevent axial movement of the crankshaft. The journal part and the thrust part of this special bearing both form the oil film lubrication when subjected to the time-varying loads in axial and radial directions during the working condition. In this work, the JTC bearing in marine diesel engines was analyzed using a transient thermal elastohydrodynamic (TEHD) lubrication model. The thermal and pressure (thermal-pressure) coupled effects were taken into consideration based on the flow, pressure, and thermal continuity conditions between the journal and thrust parts. Moreover, the transient time-varying load was considered in the lubrication analysis to explore the coupled effect under the actual operating conditions. A test rig was built to validate the established transient TEHD lubrication model for the JTC bearing. The thermal-pressure coupled effect between the journal and thrust parts was found to significantly affect the transient lubrication behaviors of the JTC bearing, which cannot be ignored. Also, different boundary conditions were investigated for the influence of the coupled effect on transient lubrication characteristics, including axial clearances, radial clearances, waveforms of radial load, incline angles and inlet oil temperatures. This work could theoretically support the lubrication design of the JTC bearings used in the diesel engine crankshafts. [ABSTRACT FROM AUTHOR]