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• Dynamic loaded tooth contact analysis (DLTCA) for computing entrainment speed. • Accurate solution to elastohydrodynamic lubrication (EHL) governing equation. • Discrete convolution and fast Fourier transformation (DC-FFT) for flank elastic deformation. • A separation flow method for iteration of EHL governing equation. • Accurate entrainment effect-based EHL forecasting model for hypoid gears. In full consideration of time-varying meshing performance and oil film characteristics, entrainment effect on elastohydrodynamic lubrication (EHL) is developed for establishing accurate forecasting model of the complex hypoid gears. Firstly, dynamic loaded tooth contact analysis (DLTCA) is employed to determine the meshing interface kinematics, load distribution and entrainment speed under dynamic load condition. Then, entrainment speed is introduced into the EHL governing equation and accurate forecasting model is established. With accurate discretization of EHL governing equation, discrete convolution and fast Fourier transformation (DC-FFT) method is employed to compute the flank elastic deformation. Finally, a hypoid gear set in automotive industrial application is exercised to verify entrainment effect on EHL assessment in the proposed model. [ABSTRACT FROM AUTHOR]

• An EHL model considering imperfect transversely isotropic coating was developed. • Imperfect of normal interfacial displacement has a great influence on lubrication. • Coating thickness under cooperative bearing capacity is recommended about 0.03 a to 4 a. Lubricated contact characteristics of transversely isotropic coating considering imperfect interface is of great importance in engineering to provide guidance on tribological design and optimization of tribo-pairs. The current investigation reports an elastohydrodynamic lubrication (EHL) contact model for transversely isotropic coating of imperfect interface. The interface is described by dislocation-like condition, i.e., displacement across it is transmitted discontinuously and such discontinuity is controlled by an imperfect index changing from 0 to 1. Based on this interfacial condition, frequency response functions (FRFs) of elastic field of imperfect transversely isotropic coating were derived, which was further used to establish the EHL contact model combined with the lubrication theory. The proposed model can be reduced to the one without coating, whose calculation results are consistent with those from literatures, providing a good verification. Finally, effects of imperfect index of interfacial displacement, coating thickness on film thickness, surface pressure, stress for transversely isotropic coating were investigated using the proposed model. [ABSTRACT FROM AUTHOR]

To exactly describe lubrication problems modeling micro-scale influence in rough lubricated contact is unavoidable. In this study a novel computational scheme for lubricated problem is presented based on two-scale homogenization method, which facilitates solving the two-scale problem. Homogenization model of mass fluxes is implemented at the micro-scale domain, and represents the influence of surface topography. A linearization method is developed to derive finite derivatives of mass fluxes at the micro-scale domain defined by scale separation. The key strength of the proposed procedure is the finite difference derivative coupling which represents the lubricated problem inclusive of the effect of surface topography. The effectiveness of the proposed multiscale scheme is validated by comparing with the deterministic method. The numerical results show that increasing topography amplitude can improve the performance of journal bearing in terms of load carrying capacity and friction coefficient. [ABSTRACT FROM AUTHOR]

The current study is basically focused on investigating the possible ways to enhance the lubricating oil film performance and hence ship energy efficiency of marine journal bearings in general terms. For the intended purpose, a novel numerical Circumferential Grooved Bearing (CGB) model was developed to assess journal bearing operating conditions based on versatile simulation analyses. Prior to all conducted test trials, the model validation has been confirmed based on the conformity between numerical outcomes and those derived from experimental procedures depending on Universal Journal Bearing Test Rig. CGB performance was evaluated at slow speed variations from 25 rpm up to 125 rpm and different applied loads utilizing the two lubricant oil grades of 5W40 and 0W30. Reducing shaft rotational speed by 80% was found to incur a reduction in the maximum oil film pressure value by 1.17 bar and 0.97 bar for the two aforementioned lubricants respectively. Further, the increase of applied loads from 1079 N up to 1471 N at a constant speed of 75 rpm reduces the maximum oil film pressure ratio by 0.14 and 0.18 for the two oil grades subsequently. [ABSTRACT FROM AUTHOR]

Utilizing universal journal bearing test rig, the performance of a heavy-loaded main journal bearing has been investigated based on tracing operational behavior of oil film temperature and pressure profiles. Test trials were conducted observing the loading program of slow speed diesel engine. Examining the effect of different oil grades, it turned out that oil grade of higher viscosity index enhances journal bearing performance and maintains oil film temperature profile stability at both maximum speeds and heavy loads. Further, medium viscosity grade oil reduces fuel consumption and costs from power production for all operational conditions. Regarding the impact of heavy loads on shaft power performance with medium viscosity oil grade, the differences between optimal and heavy loads get lower as the shaft speed increases. Those were 22 %, 9.7 % and 2.1 % corresponding to the shaft speeds of 43 rpm, 90 rpm and 104 rpm respectively. Additionally, the lower the value of the maximum oil film pressure P max difference between optimal and heavy load, the higher the ability of the lubricant to promote performance and provide enhanced operating condition stability. Yet, at part load operating conditions entailing running journal shaft at slow speeds during ship maneuverability, it cannot be considered as the best selection due to the heavy loads often applied in such critical operating conditions. Finally, the test-trial based experimental outcomes can provide useful guidance regarding the proper selection of a lubricant for enhanced performance, cost saving and prolonged journal bearing working life. [ABSTRACT FROM AUTHOR]

Solid additives can effectively overcome/alleviate the deficiencies of pure liquid lubricants themselves. However, the additive morphology involved in most of the reported solid additive/liquid lubricant systems is mostly irregular. They take more into account species differences and ignore the potential advantages of the sizes of unequal particles for the purpose of superlubricity. Herein, a mixed unequal-diameter sphere additive/ionic liquid analogue (Uneq-SA/ILA) model system is designed from the perspective of asymmetric contact between unequal-diameter spheres. It can easily enter a stable macroscopic superlubricated state (coefficient of friction as low as 0.0046) with negligible wear relative to an equal-diameter sphere additive/ILA system. Such excellent lubrication performance is attributed to the synergy of asymmetric contact between unequal-diameter spheres and low-shear-viscosity ILA; the ILA adsorbed on the sphere additive makes asymmetric slip interface between the spheres mainly concentrated inside the ILA, avoiding direct point-to-surface contact between the spheres. The film thickness of 948 μm implies that unequal-diameter spheres in the ILA have a normal accumulation space during contact, and the lubrication mechanism is dominated by hydrodynamic lubrication. This study deepens the understanding of asymmetric contact function of solid additives and provides new insights for the design of next-generation solid additive/liquid superlubrication systems. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a structural form called double-sided spiral groove gas face seal is considered. Steady-state performances, such as film load-carrying capacity and film stiffness, of gas face seals with single-sided groove on the stator, single-sided groove on the rotor, and double-sided groove are compared. Introducing axial and angular excitations, coupled with gas lubrication, seal rings vibration, contact mechanics, and instantaneous changes in fluid film thickness, the complete dynamic behavior history is obtained. Two dynamic performance indicators, logarithmic decrement and period valley, are defined. The effects of groove depths and equilibrium film thickness on the dynamic performance of gas face seals with three different surface grooving methods are studied. Combined with the transient sealing performance and film dynamic coefficients, the mechanisms of several typical unstable conditions are analyzed. The results show that the double-sided grooving method has both high gas film load-carrying capacity and gas film stiffness when the equilibrium film thickness is relatively large. In addition, double-sided grooving has both advantages of high gas film damping of single-sided grooving on the stator and high gas film stiffness of single-sided grooving on the rotor, which can ensure stable operation under various operation conditions. [ABSTRACT FROM AUTHOR]

Using cutting fluids has the potential to increase tool life and workpiece quality by reducing loads during cutting. However, cutting fluids lead to additional costs and environmental impacts. To effectively utilise cutting fluids, it is important to gain insights into their working mechanisms, in particular via direct observations of the tribology at the contact surfaces. This paper presents methods to investigate lubrication in cutting, focusing on a new approach for accessing the distribution of cutting fluids at the tool's rake face. This technique of visualising a lubricating film between chip and rake face allows to deeply understand tribological effects. [ABSTRACT FROM AUTHOR]

The lubricating performance of the clearance oil film determines the machining accuracy of the hydrostatic thrust bearing and the stability of the oil film. From the perspective of working parameters and cavity structure, based on tribological principles and lubrication theory, the clearance oil film temperature rise equation, pressure equation, and viscosity-temperature equation are deduced, and the relationship between load-rotating speed-oil film thickness for different cavity shapes is matched. Through the combination of simulation and experiment, the multi-factor coupling influences on the lubricating performance of the clearance oil film are studied. The study found that the degree of influence on the clearance oil film temperature is in order: rotational speed, hydraulic oil viscosity, load, and cavity depth, and the degree of influence on the clearance oil film pressure is in order: load, hydraulic oil viscosity, rotational speed, and cavity depth. This work provides a theoretical basis for the research and optimization of the lubrication performance of hydrostatic thrust bearings, and provides a research direction for the machining accuracy and running stability of high-speed and heavy-duty CNC equipment. • The lubricating performance of the hydrostatic clearance oil film coupled with multiple factors is studied. • The temperature rise equation, pressure equation and viscosity-temperature relationship of different models are deduced. • The coupling relationship of load-rotating speed-oil film thickness under different cavity shapes is matched. • The pressure field and temperature field with different cavity shapes are obtained under the multi-factor coupling. • The optimal suggestions for the lubrication performance of hydrostatic thrust bearings in practical engineering are given. [ABSTRACT FROM AUTHOR]

• A novel time-varying meshing stiffness model incorporating elastic contact, temperature and lubrication is developed. • The engaging process of spur gear system is decomposed and classified and then 5-state meshing behavior are obtained. • A dynamic model of gear-rotor-bearing system with 5-state mesh is established by introducing multiple sub-functions. • Effects of gear temperature and lubrication on the developed time-varying meshing stiffness are clearly acquired. • The bifurcation and evolution law of the 5-state meshing behavior in different two-parameter planes is revealed. Contact behavior of gear teeth plays a key role in modeling and analysis of geared systems. To reasonably evaluate the time-varying contact characteristics of spur gear systems, a new load-dependent time-varying meshing stiffness model incorporating elastic contact stiffness, temperature stiffness and oil film stiffness is developed. Asperity pressure and lubricant pressure are considered for the oil film stiffness. The engagement of the gear pair is decomposed and classified based on the time-varying contact analysis and then five meshing states are obtained. A novel nonlinear dynamic model of the gear-rotor-bearing system with 5-state mesh including time-varying backlash and time-varying meshing stiffness is established by introducing multiple state sub-functions. The effects of gear temperature and load on the meshing stiffness are analyzed. 5-state meshing behavior is identified and characterized by constructing 5 Poincaré maps. The bifurcation and evolution of 5-state meshing behavior are investigated by changing parameters. Distribution of multi-state meshing behavior in two-parameter planes is analyzed to obtain the correlation between multi-parameter and multi-state behavior. The results demonstrate that temperature and load greatly affect the time-varying meshing stiffness, of which the temperature stiffness contributes the most and the oil film stiffness contributes less. The parameters change the system dynamics by affecting the multi-state meshing behavior. The dynamic behavior is highly dependent on the matching and combination of multiple parameters. Diversity of multi-state meshing behavior is clearly revealed. The presented results provide an understanding of the time-varying engaging characteristics and therefore serve as a useful source of reference for engineering in designing and controlling such gear systems. [ABSTRACT FROM AUTHOR]

• Numerical loaded tooth contact analysis (NLTCA) for kinematics analysis. • Time-varying meshing characteristics for complex interface transmission behavior. • Non-Newton fluid Thermal elastohydrodynamic lubrication (TEHL) analysis model. • The rough tooth flank TEHL performance assessment for spiral bevel gears. For time-varying meshing interface geometric and physical state evolution, an innovative rough tooth flank thermal elastohydrodynamic lubrication (TEHL) model is proposed for spiral bevel gears having complex meshing interface behaviors. Firstly, numerical simulation to the actual tooth flank generation is used for macro tooth flank geometry modeling. Then, numerical loaded contact analysis (NLTCA) solution showing a high computational efficiency is applied to output time-varying contact parameters including geometric curvature, entrainment and sliding velocity, load and pressure distribution are determined as the important input to TEHL computation. Moreover, a TEHL analysis model is established by considering non-Newton fluid and entrainment effect. In particular, the measured tooth flank roughness is added into the macro flank to get a new rough tooth flank TEHL analysis model. Some equation simplification and flow coefficient computational strategies are employed to get accurate oil film performance assessment. Finally, a spiral bevel gear set from aerospace engine central transmission system is exercised to show the effect of analysis model on micro flank TEHL performances for spiral bevel gears. [ABSTRACT FROM AUTHOR]

This work presents a high-fidelity lubricated transmission model, coupling Flexible MultiBody (FMB) dynamics with ElastoHydrodynamic Lubrication (EHL). The EHL model is discretised with a coupled finite element approach, in contrast with the more iteration-intensive finite difference approach using relaxation schemes. The finite element method yields nonlinear system matrices, requiring matrix reevaluation in each iteration. To mitigate computational overhead, tensorisation replaces integrals to compute the system matrices with tensor-vector multiplications. Furthermore, this work optimises the use of the discretised EHL model by scaling and reusing it across different contact conditions. Coupling of the contact force resulting from the EHL model with the rigid body displacement resulting from the FMB model enables the computation of steady-state equilibrium for a given torque applied to the gear pair. However, local deformations should be excluded from the FMB model to ensure proper coupling with the EHL model, which exclusively computes local deformation within the contact zone. Newly developed global line contact attachment modes allow the FMB model to exclusively calculate global tooth bending in response to a given contact force. • Elastohydrodynamic lubrication coupled with flexible multibody dynamics. • Finite element method to discretise all physical domains. • Global line contact attachment modes to exclude local deformation from gear pair. • Equivalent finite element model approximating local deformation from gear pair. • Scalable, tensorised finite element model discretising elastohydrodynamic lubrication. [ABSTRACT FROM AUTHOR]

• Main bearing lubrication model considering multi-body motion and asperity contact. • More realistic operation conditions of the main bearings. • Explain the failure of the main bearings from the perspective of lubrication. • The sudden change in the bearing shell profile leads to the rapid failure of the bearing. The lubrication status of crankshaft main bearings significantly affects the stability and reliability of diesel engine operation. This paper primarily investigates the severe failure of main bearings during developing an industrial high-power 6 V diesel engine and analyzes the causes of bearing failure. Main bearings using lemon-shaped bearing shells exhibited failure after a short period of operation. Based on the multi-body dynamics model, average Reynolds equation, and contact model, a lubrication model for the main bearings was established, and the lubrication characteristics of each main bearing were simulated. The research shows that the abrupt peaks of the lemon-shaped bearing shells on the first and second main bearings are located within the area where the bearings suffer from burst pressure, resulting in additional hydrodynamic pressure and asperity contact pressure on the bearing surfaces. This makes the bearing surface prone to wear and high temperature, which are the primary causes of bearing failure. Under the operating conditions, surface damage of the bearings leads to particle abrasion and high temperature. Subsequently, the lubricating oil gradually deteriorates with the combined action of high temperature and wear particles, causing the main bearings to blacken and adhesive wear. [ABSTRACT FROM AUTHOR]

The high-strength, high-density pure tungsten (W) targets were fabricated using hot oscillatory pressing (HOP) sintering. This study examined the influence of sintering temperature, oscillation frequency, amplitude, and median pressure on the relative density, grain size, and bending strength of the tungsten targets. A tungsten target exhibiting a relative density of 99.51%, a grain size of 2.95 μm, a bending strength of 1200.1 MPa, and a purity of 99.95% was synthesized at a sintering temperature of 1600 °C, an oscillation pressure of 60 ± 15 MPa, and a frequency of 1 Hz. Grain rearrangement and plastic deformation (dislocation movement and grain boundary slip) were identified as the primary mechanisms for grain refinement and densification, respectively. The key strengthening mechanism was sub-grain boundary strengthening. The optimal tungsten target was utilized for magnetron sputtering on a reduced activation ferritic/martensitic (RAFM) steel substrate. The effects of sputtering time, power, deposition pressure, and substrate temperature on the crystallinity, roughness, thickness, and bonding force of the tungsten films were investigated. The optimal magnetron sputtering process was achieved by sputtering for 45 min at a power of 60 W, a deposition pressure of 15 Pa, and a substrate temperature of 100 °C. This resulted in dense W films with excellent comprehensive properties, including a roughness of R a = 8.73 nm, R q = 3.34 nm, a thickness of 999.05 nm, and a bonding force of 2.57 N. • High-density and excellent bending strength pure tungsten (W) target can be prepared by hot oscillatory pressing sintering. • Sub-grain boundary strengthening is the primary strengthening mechanism for W target by hot oscillatory pressing sintering. • Suitable substrate temperature can promote the crystallization, density, and bonding force of W films. [ABSTRACT FROM AUTHOR]

Fluid transportation is a critical element in the performance of fluid machinery devices. This paper proposes a ferrofluid linear pump in response to the demand for fluid control without mechanical moving parts inside tubes. The pump includes two rectangular permanent magnets, ferrofluid, tubes, four one-way valves, and a linear actuator. The ferrofluid is bound in the tube by a strong gradient magnetic field generated by two rectangular permanent magnets, forming a liquid plunger. Under the cooperation of four one-way valves on and off, the reciprocating motion of the permanent magnet makes the ferrofluid plunger drive fluid to flow directionally. The maximum backpressure of the ferrofluid plunger under static and dynamic conditions is thoroughly analyzed by theory and experiments. Experiments of the interface profile and backpressure are consistent with the theoretical results in the static condition. The maximum backpressure reaches 8.3kPa in the static condition when the volume of the ferrofluid plunger is 19ul. However, the dynamic test under a reciprocating speed of 10–50 mm/s has a significant backflow phenomenon, and the theory for calculating the backpressure is no longer applicable. The mechanism of the backflow is explored. There is a layer of water film between the ferrofluid plunger and the tube wall. With the increase of the backpressure and reciprocating speed, the thickness of the water film and the velocity gradient may enlarge, which increases the backflow and reduces the volume flow rate. Ultimately, failure occurs when the backpressure exceeds the sealing threshold during the ferrofluid plunger reciprocating process. The critical pressure difference for the pump failure fluctuates around 7.4 kPa. [Display omitted] • The pump consists of two rectangular magnets, a ferrofluid plunger, tubes, four one-way valves, and a linear actuator. • The interface of the ferrofluid plunger basically coincides with the isosurface of the magnetic field strength. • The backflow mainly depends on the volume, the backpressure, and the reciprocating speed of the ferrofluid plunger. [ABSTRACT FROM AUTHOR]

The lubrication properties of food are considered to be closely related to complex sensorial attributes such as creaminess and mouthcoating. In ice cream, these properties can be presumed to be partly linked to the product's melting. It is still unclear how to measure the lubrication properties of ice cream during the melting process and which ice cream characteristics affect lubrication. In this study, a new method was developed to measure the lubrication properties of ice cream both during melting and in a molten state. Different structural elements, including fat content, ice fraction, fat aggregation, viscosity and overrun, were modified to identify the main factors influencing lubrication. Representative tribological parameters were extracted from the tribological curves and were related to ice cream characteristics. Using a tribometer with adjustable probe height, lubrication properties throughout the entire melting process could be measured. The results showed that lubrication behavior of ice cream were mainly positively influenced by the ice fraction and overrun, while the fat content mainly affected the lubrication behavior of molten ice cream. Fat aggregation and serum phase viscosity did not appear to have a significant effect on the lubrication properties during melting. In addition, the penetration distance of the probe into the ice cream samples was measured during the melting process, providing an alternative method to characterize the melting profile of ice cream. This distance was related to changes in the hardness, which were mostly influenced by the ice fraction and overrun. This study indicates that different structural features determine the lubrication properties of ice cream in different melting regimes, and the proposed methodology may provide new possibilities for measuring melting behavior or hardness during the melting process. [Display omitted] • Developed a method to access lubrication behavior of ice cream during melting. • Structural elements showed different effects in different melting regimes. • High ice fraction led to fast friction reduction at the initial melting process. • Overrun and fat content dominated the lubrication at the later stages of melting. • Fat aggregation negatively affects ice cream lubrication in molten state. [ABSTRACT FROM AUTHOR]

Mixed elastohydrodynamic lubrication is the main lubrication style of planetary gear mechanism. In this paper, the dynamic characteristics of planetary gear mechanism under mixed elastohydrodynamic lubrication are investigated using a computational methodology. First, the mathematic model of mixed elastohydrodynamic lubrication is proposed, in which the scaling factors are introduced to depict the balance between the asperities and the oil film. A stiffness formula of the oil film is presented to describe the time varying stiffness of the teeth pair. Then, the stiffness of the oil film and the general stiffness are obtained. Finally, dynamic model of the planetary gear mechanisms is established and the dynamic responses of planetary gear mechanism are analyzed. The influences of operational parameters on stiffnesses and dynamic characteristics of the planetary gear mechanisms are investigated. The simulation results indicate that the nonlinear dynamics characteristics are significantly influenced by the lubrication conditions. [ABSTRACT FROM AUTHOR]

In this paper, External Gear Machine (EGM) torque losses arising from friction at lubricating interfaces are modeled by considering mixed lubrication conditions. A novel contribution of this paper is to consider mixed elastohydrodynamic lubrication contact conditions along with the effect of gear flank surface roughness to determine the meshing losses, which are also the major contributors towards the EGM torque loss. These hydromechanical loss models are integrated in a multibody, multi-physics simulation tool Multics-HYGESim developed at the authors' research center. Experimental activity is performed on two EGM units using different surface finish for gears. Simulated hydromechanical efficiencies match the experimental trends with average deviation of 2.5%. Most importantly, the results capture effects of different gear flank roughness on the torque efficiency. An average increase of 0.9% in the efficiency value is predicted by the simulation model for the EGM with lower teeth roughness, as compared to 1.1% rise obtained via experiments. The proposed torque loss evaluation methodology shows high potential in assisting designers and manufacturers of EGMs to choose the suitable surface finishing for achieving desired hydromechanical performance. • Torque efficiency of external gear machines has been determined via simulation. • Mixed Elasto hydrodynamic lubrication model is used to evaluate meshing frictional loss. • Experimental tests show rise in torque efficiency for lower gear surface roughness. • Computational analysis of lubricating interfaces predicts leakage and friction loss. • Proposed model exhibits potential for virtual prototyping of new gear pump designs. [ABSTRACT FROM AUTHOR]

• A novel modification of spur gear flanks is proposed. • A generating process for the proposed flanks is presented. • The validation of minimizing transmission error is performed. • The effectiveness of enhancing lubrication ability is verified. • A machining process for the proposed flanks is presented. Spur gears are most extensively applied in gearing transmission because of their effortless machinability and high efficiency. However, spur gears still generate substantial noise, vibration, and wear, mainly when operating at high speeds. Therefore, this study introduces a novel modification of spur gear flanks to improve the above inherent weaknesses. Accordingly, its primary objectives encompass diminishing transmission error while augmenting lubrication efficiency. The novel modification adjusts one side of the spur gear flank like the concave side of the curvilinear gear and the other side like a convex surface using double crowning correction. In addition, both gears of the gear pair are modified to ensure the convex surface of one gear will mesh with the concave surface of the other. The modified gear pairs are then modeled and analyzed using KISSsoft software. The effectiveness of this proposed method is verified by significant improvements in the transmission and lubrication characteristics compared to longitudinal or double crowning modification. Furthermore, a complete machining process on a CNC honing machine is also utilized to demonstrate the machinability of the proposed gear flanks. [ABSTRACT FROM AUTHOR]

Herein, the functionalized N-doped carbon nanosheet (N@PCNs) was successfully achieved through pyrolysis of metal−organic framework (MOF) and then surface modification with anti-wear agent. Firstly, the N@PCNs was obtained via carbonization of copper pyridine coordination polymer-based MOFs. Then tannic acid (TA) cross-linked by polyethylenimine (PEI) via Michael addition was grafted on the N@PCNs surfaces. Finally, the anti-wear agent 2,5-dimercaptothiadiazole dimer (DTD) was grafted onto N@PCNs via Michael addition reaction with TA to obtain DTD-N@PCNs. The average COF of 500SN decreases to 0.110 from 0.195, accompanied by 69.3% reduction in wear volume with 1.00 wt% DTD-N@PCNs addition. The lubrication performance is ascribed to the formation of a stable protective film through DTD-N@PCNs facilitating tribochemical reactions, preventing direct contact of the ball-disc pairs. [Display omitted] • The functionalized N@PCNs was prepared through pyrolysis of copper-based MOFs and then surface modification with DTD. • The resultant DTD-N@PCNs exhibits improved anti-wear and friction reducing properties when used as a lubricant additive. • The lubrication performance was attributed to the polishing effect and mending effect of DTD-NN@PCNs, along with formation of a protective film. [ABSTRACT FROM AUTHOR]

The lubrication alignment behaviors of 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystal were investigated. A 60 s-long running-in pre-treatment was first performed using micro-sized diamonds. The ball was then deflected by a certain direction and an alignment agent (Sebacic Acid) was applied on the disc. Results show that the coefficients of friction for GCr15 and Si 3 N 4 self-matching pairs were reduced to 0.036 and 0.017 respectively, 45.5 % and 67.3 % lower than the ones lubricated directly with 5CB. The surface morphology after running-in-deflection was smoother and flatter, with enhanced surface texture characteristics. It is believed that increased the order parameter of 5CB, induced by the synergistic effect of the alignment agent and running-in-deflection, is the reasons for the improvement in lubricating performance. [Display omitted] • The alignment agent and running-in-deflection reduce the COF of 5CB notably. • The reduction of COF is attributed to the liquid crystal molecular orientation. • An appropriate running-in-deflection is beneficial to reduce the COF of 5CB. • The relationship between surface parameters and characteristics has been analyzed. [ABSTRACT FROM AUTHOR]

Lubrication plays an important role in mouthfeel sensation and various tribometers have been developed for in vitro studies. This study introduces a new design to solve artefact of the surface load for a soft tribometer. Reliability of the probe was verified using glycerol as lubricant. Effects of surface load and substrate roughness on the lubrication behaviour were investigated using glass and PDMS probes. It was found that increased surface load lowered friction coefficients in both boundary and mixed lubrication, probably due to the deformation of surface asperity. Increased surface roughness decreased friction coefficient in boundary regime, but rendered a later transition from boundary to mixed lubrication. Hydrophilic contact lowered the friction in boundary and mixed lubrication by promoting full-film lubrication. • A soft tribometer with new probe design has been developed. • The new probe design eliminates surface load artefact in the original design • The new design successfully tested for its reliability with near Newtonian lubricants. • Reliability also tested for both hydrophilic and hydrophobic substrates. [ABSTRACT FROM AUTHOR]

Herein, the internal lubrication of polyether ether ketone (PEEK) with added whiskered carbon nanotubes (Wh-CNTs) was investigated under point-contact dry sliding conditions with various loads and velocities. The wear rate of the composite was reduced by 86.99% at a maximum Hertzian contact pressure of 344.69 MPa, which was attributed to the addition of additives with excellent mechanical properties and high-temperature stability. Wh-CNTs could be uniformly distributed in the PEEK to form a three-dimensional (3D) network structure with load-bearing capacity, thus the load could be effectively borne to prevent crack propagation on the PEEK surface. Besides, the filler was induced to form a micron-sized 3D spherical structure with a ball bearing effect, which promotes lubrication more effectively than the fragment structure. [ABSTRACT FROM AUTHOR]

Most mechanical systems have mating interfaces that require effective lubrication for smooth functioning. Thus, understanding and accurately modeling lubrication regimes is an essential research task. The present work proposes a set of normalized coefficients based on homogenization and stochastic theories to model the partial and full-film lubrication regimes between a smooth and a rough surface. The modified Greenwood and Williamson theory, considering inter-asperity-interactions, was used to model the contact-zones. Subsequently, the film-thickness was evaluated and the homogenized Reynolds equations were solved to compute the normalized coefficients. The estimated coefficients were compared with Patir and Cheng's flow-factors, and the similarities and disagreements between both approaches were discussed. New sets of coefficients for running-in surfaces were proposed for modeling their lubrication regimes. • Normalized homogenization coefficients are evaluated based on stochastic analysis. • Inter-asperity interactions have been considered to model the solid contacts. • New sets of homogenization coefficients for running-in surfaces are proposed. [ABSTRACT FROM AUTHOR]

Thrust bearing finds application as a key element for heavy duty machines such as hydro-power plants (vertical shaft), submarines, steam engines, cement plant-ball mills (horizontal shaft) etc. Bearing temperature is a primary factor that affects the performance of hydrodynamic thrust bearings. Thermal deformation, misalignment, reduction in minimum oil film thickness and subsequent drop in load carrying capacity, are some of the manifestations related to high bearing temperatures. The present study attempts to decrease the bearing temperature by utilizing novel hybrid bearing set up. It involves the integration of water-cooled pads coupled with nanoparticle-infused lubricant films. This approach represents a convergence of two key technologies aimed at addressing the thermal effects linked with elevated temperatures generated during the operation of bearings. This study utilizes computational simulations to evaluate the effect of integrated thrust pad design on performance characteristics like pressure, temperature, and thermal deformation of a thrust bearing. The simulation results of new integrated design confirm (i) enhancement in pressure values e.g. maximum pressure increases from 5.6 MPa to 6.5 MPa (ii) reduction of pad temperature values e.g. maximum pad temperature value reduces from 85 ℃ to 70 ℃ (iii) reduction of pad thermal deformation values e.g. maximum pad thermal deformation value reduces from 36.5 µm to 22.3 µm. By leveraging the direct cooling effect of embedded cooling circuitry and the enhanced thermophysical properties of nanoparticles, this novel configuration promises to unlock new levels of efficiency and reliability in thrust bearing operation. [ABSTRACT FROM AUTHOR]

A radial shaft seal (RSS) model is established to reveal mixed thermal lubrication (MTL) and wear performance at speeds ranging from 3000 r/min to 7000 r/min. The model takes into account the initial temperatures of the oil medium and the running time of the RSS to investigate the transition limit of lubrication. Then a thermal fluid-solid method was developed to simulate the lubrication performance of RSS, which shows lubrication transition boundaries through rough micro convex bodies for wear deformation. The RSS deforms wedge-shaped during the wear process and a localized fluid pressure is created on the convex bodies. Considering the wear deformation of the convex bodies due to the wedge effect, the micro performance of the RSS can fully describe the mechanism of the leakage rate. As the dynamic pressure decreases and the leakage rate increases with the temperature of the medium, the RSS lubrication gradually transitions from MTL to EHL. Thus, the initial medium temperature should be considered to maintain the RSS under the mixed lubrication regime with low friction. [ABSTRACT FROM AUTHOR]

Estimating the film thickness in a grease lubricated bearing in the post-churning phase is complex because of the prevalent starved lubrication conditions. In our earlier work, we showed that the relative film thickness ( h g / h f f ) in an axially loaded 6209 deep groove ball bearing (DGBB) depends on the product of viscosity, load and linear speed (η b u). In this article, we present the results of experiments performed using bearings of different sizes – 6204, 6206, 6209 – and show that the relative film thickness maintains a power-law relationship with η b u , independent of the bearing size. • Level of starvation in grease-lubricated DGBBs correlate well with η b u. • The η b u concept is independent of bearing size. • Lubricant replenishment is a local phenomenon. • Starvation reduces film thickness dependency on speed. • Starvation increases film thickness dependency on load. [ABSTRACT FROM AUTHOR]

• The real-time coupled tribo-dynamics calculation of piston-cylinder liner and piston ring-cylinder liner is realized. • Modeling is based on unified global coordinates, making the coupling and solution between lubrication and dynamics more efficient. • The influencing mechanism of piston deformation on the ring tribo-dynamics properties is given. • The effect of the assembly position on the ring tribo-dynamics properties is revealed, and the worst assembly position is discovered. Research on the tribo-dynamics of the piston-cylinder liner (PCL) and piston ring-cylinder liner (PRCL) is vital due to their role in generating over 50 % of total engine friction loss and the impact on carbon emissions. Traditional studies, hindered by the structural and functional differences between pistons and rings, required separate simulation models, often overlooking crucial coupling characteristics. A unified tribo-dynamics modeling method for the piston-ring-liner (PRL) system is proposed in this paper, integrating the ring pack and piston into one multi-body system. This article models with global coordinates, unifying the form of governing, film thickness, and load equations of discontinuous lubrication domains for more efficient dynamics-lubrication coupling. The described method is applied to a marine engine, and the new tribology characteristics discovered after calculations are exhibited. It shows how piston deformation impacts ring tribology, indicating that increased profile height reduces the squeezing effect by allowing more ring movement. Additionally, ring assembly position significantly affects tribology parameters' circumferential distribution. Installing the ring with the end gap facing the piston pin side should be avoided, as it maximizes the negative impact of elastic force and secondary motion, deteriorating lubrication. [Display omitted] [ABSTRACT FROM AUTHOR]

Enhancing friction force in lubricated, compliant contacts is of particular interest due to its wide application in various engineering and biological systems. In this study, we have developed bioinspired surfaces featuring film-terminated ridges, which exhibit a significant increase in lubricated friction force compared to flat samples. We propose that the enhanced sliding friction can be attributed to the energy dissipation at the lubricated interface caused by elastic hysteresis resulting from cyclic terminal film deformation. Furthermore, increasing inter-ridge spacing or reducing terminal film thickness are favorable design criteria for achieving high friction performance. These findings contribute to our understanding of controlling lubricated friction and provide valuable insights into surface design strategies for novel functional devices. • Bioinspired film-terminated ridges enhance lubricated friction on elastomers. • System energy dissipates at the lubricated interface due to elastic hysteresis. • Thin films and wide ridge spacing boost friction enhancement. [ABSTRACT FROM AUTHOR]

[Display omitted] • A line-contact mixed EHL model is established based on the ellipsoidal asperity elastoplastic contact model. • The effect of surface morphology-lubrication coupling, residual stress, and hardness on gear contact fatigue is investigated. • The proposed contact fatigue model is validated through gear contact fatigue experiments under various operating torque. • The proposed model offers novel methodologies for selecting surface manufacturing processes and designing surface roughness. A three-dimensional(3D) line-contact mixed lubrication model and contact fatigue life prediction model for gears are established, considering the elastoplastic contact of ellipsoidal asperities and their interactions. The localized lubrication states across the actual 3D rough surfaces are visually depicted. The direct asperity contact pressures calculation exhibits greater accuracy and universality. The proposed mixed lubrication model can be applied accurately and efficiently to heavy-load conditions. The synergistic mechanisms of multi-scale surface integrity parameters, such as surface morphology-lubrication coupling, hardness gradient, and residual stress, on gear contact fatigue has been revealed. The results reveal that surface roughness significantly affects the competitive failure mechanism between surface-initiated micropitting and subsurface-initiated macropitting. The increase in surface compressive residual stress is more sensitive to the enhancement of near-surface and subsurface fatigue lives, compared to the increase of peak residual stress and the depth of peak residual stress. The proposed physics-based gear contact fatigue life prediction model has been validated through gear contact fatigue experiments under various operating conditions. The maximum deviation between the predicted and experimental fatigue lives is within 10%. This paper presents theoretical methodologies and data-driven support for optimizing the design and manufacturing processes of gears, specifically focusing on enhancing anti-fatigue properties. [ABSTRACT FROM AUTHOR]

A Ni–Cr–MoS 2 coating with trivalent Cr was prepared on the surface of the cylinder liner by the composite co-deposition method to modify its tribology performance. The effects of MoS 2 concentration on the properties of the coatings and tribological properties of cylinder liners were studied by surface detection methods and reciprocating wear tests. The results show that Ni–Cr–MoS 2 coating has a smaller grain size, higher micro-hardness, and greater coating thickness, compared with Ni–Cr coating. Doping by MoS 2 effectively reduces the friction coefficient of Ni–Cr coating from 0.142 to 0.107, the wear amount of coating decreases from 7.9 mg to 7.1 mg, and the scuffing time increases from 19 min to 56 min. It is found that the doping of MoS 2 provided more nucleation sites and promoted the deposition of ions, which resulted in the refined grain and thicker coating. The formation of solid lubrication film by MoS 2 during the wear process and more coating thickness are mainly responsible for the modification of the tribology performance of cylinder liners. This research provides a practical approach to prolong the service life of friction pairs. • The inclusion of MoS 2 significantly increased the Ni–Cr coating thickness. • The doping of MoS 2 increased nucleation sites and changed the coating structure. • The friction and scuffing properties of cylinder liner were significantly improved. • A solid lubrication film produced on the surface of composite coating by MoS 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • The calculation method of pad lubrication characteristics with different defects is presented. • The critical failure condition of defect pad of thrust bearing is proposed. • A CFD calculating method and influence rules for predicting pad failure are put forward. • A scaled test bench is designed and set up to verify the reliability of the calculation method. Thrust bearing surface defects directly affect the safe use of the nuclear main pump. Based on the actual defective pads of nuclear power plant, the Fluid-solid iteration (FSI) technique is used to analyze thermal-hydrodynamic (THD) lubrication of thrust bearings. The influence of defect area and depth on the lubrication characteristics of thrust bearings is illustrated based on Computational Fluid Dynamics (CFD) dynamic mesh, and a set of critical conditions for the failure of pads are obtained according to the minimum allowable oil film thickness and the maximum allowable temperature of the pad. A test system for scale thrust bearing is designed, where the oil film pressure and temperature distribution of defective pads are measured and verified under different conditions. The temperature distribution is a gradient rise at the inlet and the outlet side of the pad, and the bearing area with small area has greater pressure value. The influence on the lubrication characteristics of tilting pad is investigated to predict the failure performance of defective pad, which have guiding significance for the safe use of thrust bearings in nuclear main pumps. [ABSTRACT FROM AUTHOR]

[Display omitted] • Boundaryand elastohydrodynamic lubrication models with additives under sinusoidal load were studied by NEMD. • The additive's solidification degree reflects the interlacing strength, thus relative motion less occurs in the BL regime. • The liquefaction degree and the velocity difference of base oil and additive regions, affect friction in the EHL regime. The evolution of lubricating oil containing additives under dynamic conditions is very significant, since its oil film structure, velocity distribution, and adsorption characteristic have an obvious impact on friction and wear. In this work, a boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) models under sinusoidal load were carried out by nonequilibrium molecular dynamics (NEMD), using iron oxide as the substrate, hexadecane, and stearic acid molecules as lubricants. It was discovered that the friction in the BL regime is positively correlated with the degree of additive's solidification. The greater the solidification degree of additive layers, the less the interlacing between them, making the relative motion between them easier and reducing compression oscillation within them, thus diminishing friction in the BL regime. The degree of liquefaction of base oil and additive regions, as well as the velocity difference within their interlacing zones, are connected to the friction force in the EHL regime. At high frequencies as well as large amplitudes, the oil film has a very high degree of liquefaction, which facilitates internal shear in it, and there is essentially no relative motion between the base oil and additives, resulting in low friction. [ABSTRACT FROM AUTHOR]

A method for calculating time-varying mesh stiffness (TVMS) is proposed by developing a stiffness model for elastohydrodynamic lubrication (EHL) contact and integrating it into three-dimensional loaded tooth contact analysis (3D-LTCA). To enhance the accuracy and efficiency of the calculation, three projects have been implemented: Firstly, the contact deformation is modified, and the average slope is employed for calculating contact stiffness. Secondly, the lubricant film and EHL contact deformation are introduced into the deformation compatibility equations. Finally, the polynomial chaos expansion (PCE) surrogate model is employed to enhance computational efficiency. The proposed method is used to calculate TVMS of the planetary gear set, and the influence of speed, torque, and rough surface are analyzed. The results show that the previous method underestimating the TVMS of planet-ring gear pair in double-teeth meshing area under fluid lubrication, while the proposed method effectively addresses the issue. The different effects of the torque and speed on TVMS under mixed and fluid lubrication also have been revealed, emphasizing the significance of surface topography in gear meshing characteristics. [ABSTRACT FROM AUTHOR]

An analytical EHL model suitable for highly loaded point contacts operating in mixed and boundary regimes of lubrication is presented. The results are compared and validated with the experimental measurements of friction coefficient from an MTM tribometer. Measurements are carried out upon a PAO40 oil at medium to high temperatures. In general, a good agreement in trend and magnitude over a wide range of operating conditions is observed. Both the experimental findings and the model predictions show an inverse relationship between friction and contact load in mixed and boundary regimes of lubrication, an effect not hitherto reported in literature. [ABSTRACT FROM AUTHOR]

Accurately predicting the performance of lubricated rolling elements is critical for certain key bearing applications. A widely employed simulation technique is quasi-static models, which although computationally efficient to implement, lack accuracy in predicting the kinematics of bearing components. This problem arises from their construction under kinematic assumptions, instead of solving the kinematic based on real frictional interactions. This paper presents a quasi-static model based on the minimum energy hypothesis for lubricated contacts, which determines the kinematic of the ball considering the effects of the frictional interactions governed by the elastohydrodynamic lubrication mechanism. The influence of kinematic variables on the sliding patterns and power loss distribution of the contact are analysed. The results are compared with other published quasi-static models, revealing substantial differences. The influence of the kinematic hypotheses on power losses are also studied at a bearing component scale. Finally, the effect of the governing lubrication mechanism of the contact is discussed, concluding that the limiting shear stress of the lubricant and the centrifugal forces have a significant effect on the kinematic of the ball. • Development of a semi-analytical quasi-static model of ball-raceway contacts based on the minimum energy hypothesis. • Analysis of the influence of the pitch angle and pure rolling line locations on the contact kinematics and power losses. • Analysis of the impact of the working conditions on the pitch angle and comparison to literature models. • Study of the governing lubrication mechanism on kinematic and power loss behaviour. • Theoretical demonstration of the transition between inner and outer control raceway hypothesis. [ABSTRACT FROM AUTHOR]

Misalignment of roller bearings is a characteristic defect mode, which is accompanied by variations in thermal, mechanical, and lubrication performances. Regarding this aspect, a novel model considering the thermal-fluid-solid coupled effect is proposed to evaluate the performance evolution of lubricated cylindrical roller bearings (CRB) under misalignment states. The proposed model regards structural parameters, contact characteristics, and lubrication status as time-varying variables. By integrating the quasi-static model of CRB with a thermal network model, the influence of internal contact shape and stress on the thermal characteristics of misaligned bearings is reasonably considered. The accuracy of the proposed model is validated through the thermal performance experimental platform. In addition, the influence of thermal and misalignment on time-varying mechanical properties such as contact load, radial stiffness, and clearance loss is assessed. Eventually, the deterioration of the lubrication performance over operational time is quantitatively characterized by the time-varying film thickness at the load region. [Display omitted] • A novel model of misaligned bearings with the thermal-fluid-solid coupled effect is developed. • A transient thermal contact resistance evaluation method for spindle shape is presented. • The influence of thermal and misalignment on time-varying mechanical properties is investigated. • The degradation level of the lubricant is characterized through the time-varying film thickness. [ABSTRACT FROM AUTHOR]

Traditional methods of evaluating the performance of journal bearings, for example thermal-elastic-hydrodynamic- lubrication theory, are limited to simplified conditions that often fail to accurately model real-world components. Numerical models that include additional phenomena such as cavitation and fully coupled effects like deformation, temperature, pressure and viscosity can be more accurate but require a large amount of computational overhead, making analysis slower and more costly. To address this limitation, a novel machine learning-driven approach is developed to predict the 2D distribution of surface deformation, film thickness, temperature, and pressure across the bearing surface as a function of design variables such as load and speed. The training dataset, generated using a fully coupled Reynolds' Equation solver implemented in OpenFOAM, contains a significantly extended range of conditions than in previous studies with approximately 39 000 000 points encompassing 4925 different test cases. Modelled bearing speeds range from 2000 to 10 000 rpm, while load values are varied between 1 and 30 kN. Predicting surface deformation, film thickness, temperature and pressure across the bearing surface results in a mean absolute percentage error below 0.4 % or better. The work also demonstrates that the trained models have a strong ability to generalise the prediction beyond the original training data range with only a 1 % error at up to 200 % of the highest trained speed. This work also demonstrates that machine learning-based processes are a practical alternative to physics-based numerical modelling, especially in cases where rapid performance evaluation is desired as real-time calculation is possible with significantly reduced computational cost. This has the potential to enable development of rapid design optimisation tools and real-time performance monitoring at high resolution and with low latency. Using consumer hardware, it is found that the neural network-based approach is faster than the existing numerical modelling technique by a factor of over 10 000, enabling real-time predictions of lubrication systems. • A neural network approach is demonstrated, using independent models to predict each variable. • Neural network models trained using an OpenFOAM numerical model display a mean error of < 0.4%. • Once trained, the neural network models are ∼ 10 000 x faster than traditional numerical models. [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]

The main idea of this study was to utilize the pressure and heat produced in the friction process to make Mo nanoparticles mixed in lubrication oil into the multi-layered tribo-film. An in-house developed reciprocating wear rig was used for the tribo-film deposition and associated tribological tests. By design of experiment, the optimal deposition parameter was obtained. Results indicate that the multi-layered film consists of a Mo-based concrete structure layer and a carbon-based film. The carbon-based film was produced by the dehydrogenation and carbonization of the lubricating oil catalyzed with Mo nanoparticles. The consumption and deposition of the carbon-based film was dynamically balanced during the wear process, resulting in the outstanding tribological performance. [Display omitted] • A great amount of Mo nanoparticles were ultrasonically mixed in the base oil. • Film fabricated by utilizing the heat and pressure produced in friction process. • The film consists of Mo-based film mixed with amorphous carbide. • Realize carbon film formation and restoration in lubrication. [ABSTRACT FROM AUTHOR]

Protecting bearings from electrical environments is crucial as modern industry evolves. With increasing exposure to electrical conditions, the risk of bearing failure due to electric erosion becomes a significant concern. To better understand how lubrication interacts with electric discharge in rolling bearings, an optical ball-on-disc tribometer was modified to measure film thickness under elastohydrodynamic lubrication (EHL) with electric discharge. The results of the study revealed that an electrical potential difference between the surfaces separated by the lubrication film leads to a reduction in film thickness, which can be attributed to the generation of Joule heating. As the electrical potential difference increases, the film thickness decreases even further, ultimately resulting in destructive electric discharge. Interestingly, sporadic discharge was observed in the region of minimum film thickness as the entrainment velocities increased prior to the occurrence of destructive discharge. In addition, the study also investigated the use of grease with a conductive additive, a double trifluoro-sulfonate ionic liquid. It was found that incorporating this ionic liquid into the grease can decrease the energy during discharge, thereby mitigating bearing electric erosion. [Display omitted] • An optical ball-on-disc tribometer was revised to measure film thickness under an applied electric field. • The electric potential difference across oil film reduced film thickness, lessened friction due to Joule heating by current. • Two forms of electric discharge were identified in the contact area: sporadic discharge and destructive discharge. • With double trifluoro-sulfonate ionic liquid added as the additive it was shown that the electric discharge becomes weak. [ABSTRACT FROM AUTHOR]

Genetic algorithms and machine learning methods can accurately anticipate hybrid nanofluids' complicated rheology. Scientists and engineers can understand hybrid materials by using genetic algorithms to optimize and machine learning to discover complicated relationships between input variables and rheological responses. As a continuation of the author's previous research on the rheological properties of a nano-lubricant based on engine oil and hybrid nanoparticles, this study uses machine learning and genetic algorithms to theoretically assess the dynamic viscosity of the MWCNT-MgO/oil SAE 50 hybrid nanofluid and identify optimal properties. MLR, D-Tree, Ridge, PLR, SVM, Lasso, ECR, GPR, and MPR are used for regression analysis. Best multi-objective issue solutions are represented by the Pareto front. The NSGA-II algorithm determines the Pareto front. The MPR and NSGA-II algorithms provide a Pareto front with the most precise optimal spot boundaries. The Weighted Sum Method (WSM) simplifies multi-objective problems into single-objective problems, making optimal solutions easier to find. The results show that the maximum margin of deviation for μ nf and τ is − 2.5615 and − 5.239, respectively. According to the Taylor chart, the best μ nf mode for R, RMSE and STD is equal to 0.9983, 7.6639, 130.0056. Also, these values for τ are equal to 0.9996, 15.4515, and 516.0219. • Rheological behavior of the MWCNT-MgO/SAE 50 hybrid nanofluid was studied. • use of meta-heuristic algorithm NSGA-Ⅱ to find the most optimal point that satisfies μ nf and τ. • Optimal solution is represented by a set of points known as the Pareto front. • The best algorithm in terms of the Taylor diagram for μ nf output is the MPR algorithm, and the worst is the Lasso algorithm. [ABSTRACT FROM AUTHOR]

This study explores the influence of fluid viscoelasticity in soft lubrication, in which elastohydrodynamic lubrication (EHL) plays an important role. Our findings reveal that introducing polymers can significantly reduce the friction coefficient, particularly for high Deborah numbers, i.e., the ratio between the polymer relaxation time and the flow residence time, due mainly to an increased minimum film height. This augmented film thickness reduces the Newtonian pressure contributions, lowering friction. The study highlights the non-linear relationship between Deborah numbers, load, and viscoelasticity effects, as well as the complex interplay between these factors in the Pipkin space analysis. These insights provide a comprehensive understanding of the fluid viscoelasticity in soft lubricated contacts. [ABSTRACT FROM AUTHOR]

Adjacent segment degenerative diseases are a major clinical concern for anterior cervical corpectomy with fusion surgery. In this study, a hybrid motion-preserving cervical prosthesis consists of two articulating joints and one porous fusion body is designed to provide motion ability and reduce the occurrence of degenerative diseases. The hybrid design is fabricated from Ti–6Al–4V (TC4) alloy using selective laser melting (SLM) technology. After carburization pretreatment, two types of bearing couple SLM-TC4 self-mating and SLM-TC4/UHMWPE were studied in terms of lubrication regime, contact mechanics and wear performance. According to the ISO 18192-1 standard, five million cycles (Mc) of in vitro spine simulator wear tests were conducted in bovine serum lubricated condition. Hamrock-Dawson minimum lubrication film thickness analysis stated that both bearing was likely under boundary lubrication only, with extensive surface asperities contact. And, the contact stress encountered during in vitro condition was not enough to cause surface fatigue failure of any bearing couple. In term of wear performance, the obtained steady state wear rates were 0.160 ± 0.004 mm3/Mc for SLM-TC4 self-mating and 8.57 ± 0.06 mm3/Mc for SLM-TC4/UHMWPE bearing couples, respectively. According to these outcomes, SLM-TC4 self-mating couple was more promising for the articulating joint bearing design. For SLM-TC4 self-mating couple, the initial wear mechanism was abrasion with potential third-body abrasion wear. As the wear cycle proceeding, the TiC cermet layer was gradually damaged and exposed the local bare metal. Under this circumstance, material loss was consisted of abrasion wear, adhesion wear, and tribo-corrosion. In comparison, the wear mechanism of SLM-TC4/UHMWPE bearing was always abrasion-adhesion of UHMWPE. The surface of UHMWPE socket was severely plowed by the hard micro bulge of the TiC layer, and material loss and plastic deformation occurred only on the UHMWPE socket. In conclusion, carburization pre-treatment causes a hard TiC cermet layer formation on the SLM-TC4, which enhance its hardness and protect underling material from corrosion damage. The thickness and quality of the TiC layer directly affect the longevity of the joint prosthesis in vivo. [ABSTRACT FROM AUTHOR]

The selection of appropriate geometrical characteristics of enclosure has salient influence on performance of different thermal engineering processes and devices like microelectronics, heat exchangers, power engines, boilers, solar collectors, nuclear reactors and so forth. Specifically, the triangular cavity of different aspect ratios are used to obtain multi-objective optimization and gaining excellence in thermal performance of micro channels. Subsequently, the installation of cold cylinder in a triangular enclosure are extensively used to remove high energy dissipation in micro heat sinks and heat exchangers. So, the purpose of current effort is to probe thermal characteristics of power-law liquid describing features of shear thinning and thickening materials containing applications in lubrication and polymer industry. Heat transfer is generated by the consideration of natural convection process generated due to consideration of cold walls and cylinder with provision of non-uniform heating at base wall. No-slip velocity conditions are supposed at all walls of isosceles triangle cavity. Solution of attained differential system is simulated by capitalizing finite element based COMSOL Multiphysics software (Version 5.6). Domain discretization by distributing into triangular and rectangular elements is conceded and equations at element levels are discretized by executing weak formulation. The validation of adopted numerical procedure is established by making agreement with formerly available works in both statistical and graphical approaches. Streamlines and isotherms are plotted and discussed against various parametric regimes. This study reveals noticeable influence of involved physical parameters on average and local heat flux coefficients, kinetic energy and cutlines against involved physical parameters are also evaluated. It is inferred thorough the analysis that with uplift in Rayleigh number (R a) produces enrichment in kinetic energy and local heat transfer coefficients whereas reverse pattern is depicted against power-law index. (n). [ABSTRACT FROM AUTHOR]

[Display omitted] • Five precision machining tests of form grinding, vibratory finishing, barrel finishing, honing, and abrasive flow machining were conducted on spur gears. • A solid–liquid-thermal multi-physics field coupling interface lubrication contact analysis model for gear transmission was established. • The surface integrity parameters and lubrication performance parameters were compared and analyzed under various finishing processes. • The developed program offers theoretical guidance and data support for the selection and optimization design of gear surface finishing processes. Surface integrity is crucial for the load-bearing capacity, transmission performance, and service life of gears. Finishing processes can effectively improve surface quality and are widely used in gear manufacturing processes to enhance surface integrity and improve the service performance of gears. Five precision machining tests of form grinding, vibratory finishing, barrel finishing, honing, and abrasive flow machining were conducted on spur gears. High-precision surface integrity characterization methods were used to analyze the surface integrity parameters of the finished gear surfaces, including surface roughness, surface microtopography, residual stress, texture aspect ratio, roughness peak curvature radius. The finishing processes uniformity and effectiveness of the tooth profile surface were also evaluated. By using the finished rough surfaces as inputs and considering the impact of thermal elasto hydrodynamic lubrication on the gear surface, a multi-field coupling contact analysis model encompassing solid, liquid, and thermal fields at the gear meshing interface was established. Lubrication performance parameters such as oil film pressure, oil film thickness, oil film temperature rise, and friction coefficient under various finishing surfaces were compared and analyzed. Experimental results indicate that barrel finishing can simultaneously improve various parameters, such as surface roughness, texture aspect ratio, and compressive residual stress. Finishing processes can effectively reduce surface roughness, improve lubrication performance and reduce the risk of scuffing failure. This approach provided an effective method for the comprehensive evaluation of the effects of various finishing processes. The developed program offers theoretical guidance and data support for the selection and optimization design of gear surface finishing processes. [ABSTRACT FROM AUTHOR]

When modeling bearings in the context of entire transmissions or drivetrains, there are practical limits to the calculation resources available to calculate single bearings or even contacts. In settings such as these, curve-fitting methods have historically been deployed to estimate the elastohydrodynamic lubrication conditions. Machine learning methods have the potential to enable more sophisticated physical modeling in the context of larger computation environments, as the evaluation time of a trained model is typically negligible. We present a neural network that accurately evaluates the locally variable elastohydrodynamic film pressure and film thickness distributions and explore its application to (e.g.) cylindrical roller bearings. Employing a neural network for the EHL film thickness calculations rather than the curve-fitted, simplified methods that are today's standard can enable a more physically precise modeling strategy at almost no additional computational cost. • A neural network for EHL film pressure and thickness is presented and evaluated. • This network enables efficient use of fully coupled EHL equations in modeling. • Advantages of the neural network for practical EHL over current models are shown. [ABSTRACT FROM AUTHOR]

To prevent severe friction between water-lubricated bearings (WLBs) and stern shafts under harsh conditions, a method is introduced that uses a lubrication pump to supply a small amount of secondary lubricant into the bearing for a short period of time. The effect of the secondary lubricant viscosity on friction-reducing performance is investigated by a modified block-on-ring friction and wear tester. The transfer process of the secondary lubricant within the bearing is observed with a self-designed visualization experimental platform. A flow model for capturing the diffusion of the secondary lubricant is developed, and the flow velocity equations are used as a "bridge" to link the mixed lubrication model and Volume-of-Fluid (VOF) model. The results indicate that injecting the secondary lubricant in the mixed lubrication state has the effect of rapidly reducing the friction coefficient, while supplying the lubricant in the elastohydrodynamic lubrication state tends to increase the friction coefficient. The backflow zones are primarily located at the bearing inner surface and the upper half of the fluid. The high-viscosity secondary lubricant separates into "free lubricant" and "adhesive lubricant" during the transfer process. The "oil-free zone" appears in the lubricating film due to the obstruction of lubricant diffusion by the "backflow effect". The area of the "oil-free zone" decreases with increasing lubricant viscosity and decreasing load. This study provides a reference for friction-reducing technologies of friction pairs under water-lubrication conditions. • Secondary lubricant can rapidly reduce friction coefficient in the ML state. • High-viscosity lubricant separates into two types of lubricant during diffusion. • The area of the "oil-free zone" decreases with increased lubricant viscosity. [ABSTRACT FROM AUTHOR]