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Reference liquids can be useful in the new quantitative approach to elastohydrodynamic lubrication calculations only if the properties of these liquids are accurately modeled. The pressures in the contact sometimes exceed the pressures of the available viscometer measurements, requiring extrapolation. The previtreous piezoviscous response is always faster-than-exponential with an apparent divergence pressure. Therefore, any model used for extrapolation must possess these characteristics and up to now published work in EHL, where extrapolation of the viscosity of squalane is performed, has not. To date, the only model that has been shown to accurately extrapolate to high pressure is the Hybrid model. This expression was applied to six reference liquids for use in quantitative investigations in EHL. Viscosity measurements for trioctyl trimellitate were extended to 1.1 GPa. The results obtained with high pressure viscometers are preferable over molecular dynamics results if they are different. Molecular dynamics calculations are not currently capable of reliable results for viscosity at very high pressures. [ABSTRACT FROM AUTHOR]

In this paper, the cycloidal pin wheel drive mechanism of the secondary drive component of the rotary vector (RV) reducer is studied. Under the condition of grease lubrication, considering tooth profile modifications and machining errors, we established a three-dimensional load-bearing contact analysis model of a cycloid pinwheel transmission mechanism. We studied the time-varying contact characteristics of the gear teeth and dynamic joint surfaces of the inner and outer races of a crankshaft bearing. Considering the thermal effects, we proposed an analysis model of the lubrication characteristics of cycloid pinwheel transmission mechanisms. We also studied the thermal lubrication properties, such as load de-formation, lubrication film thickness, contact pressure and temperature increase at the lubrication contact area. The accuracy of the model was verified by temperature experiments on the inner raceway of an RV reducer bearing and the evolution law of the dynamic thermal lubrication characteristics of the inner and outer races of the crankshaft bearing, the meshing gear tooth pair and the whole process of single pin tooth meshing were revealed. This study provides an effective method for analyzing the temperature increases of the key joints of RV reducers. [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]

Bending deformation of a hollow cylindrical roller (HCR) was calculated by curve bending theory and slice technology. Furthermore, an elastohydrodynamic lubrication (EHL) model involving hollow rollers was established by coupling the finite line EHL model and bending deformation. Measurements of film thickness for hollow rollers were carried out by using a line-contact optical EHL test rig, and the experimental data and theoretical results agreed well with each other. For a roller with a straight-line profile, the hollow structure could reduce pressure peak at the roller ends, but the edge effect was still present. The film thickness at the ends unfortunately could not be improved by such hollow structures, unless a profile modification for the operating surface is designed. [ABSTRACT FROM AUTHOR]

Determining the film thickness during the bleeding phase of grease lubrication in a bearing is difficult due to the various replenishment and loss mechanisms involved. An additional factor that could influence the film thickness is the amount of grease in the bearing. In this study, film thickness is measured in deep-groove ball bearings using two different greases, each with initial grease filling percentages of 7.5%, 15%, and 30% of the bearing's free volume. Film thickness is measured during the early stage of the bleeding phase at various loads and speeds using the electrical capacitance method. Results show that, after churning, values of temperature and film thickness are similar for the three different filling quantities. This indicates that bulk grease flow or oil bleed from the reservoirs formed in the unswept region does not impact the lubricant film thickness in the early stage of bearing operation. [ABSTRACT FROM AUTHOR]

The key function of lubricants is to reduce the friction, wear, and heat between the parts that are in contact with each other. The main applications of the lubricants are to control temperature, and reduction in wear and corrosion of the machinery. Keeping in mind the importance of lubrication and its applications in varied machines. The goal of this research is to inspect the heat transmission impact in the magnetohydrodynamic flow of Jeffrey liquid near a stagnation point through a lubricated surface. Lubrication is accomplished by a shear-thinning liquid. The velocity, continuity, and shear stress, amalgamated with power-law fluids, are used to develop interfacial conditions. The exclusivity of the anticipated model is the inclusion of variable thermal conductivity and diffusion coefficients in the existence of homogeneous-heterogeneous reactions. Using the Keller–Box finite-difference approximation approach, the numerical results are accomplished. The outcomes are portrayed and tabulated in the form of diagrams and tables, respectively. It is witnessed that a greater magnetic field affects the fluid flow velocity and the drag force coefficient. Moreover, it is also inferred that the heat transfer rate dwindled for the greater thermal conductivity parameter. Authentication of the presented model is also part of this investigation. [ABSTRACT FROM AUTHOR]

In order to analyze the bearing wear in the spindle system considering different speed and load conditions, a four-bearing spindle system was investigated. Two different working conditions, Case I and Case II, are considered. Case I condition has lower spindle speed and higher external loads and preload than Case II condition. Based on Archard model, a new wear depth model of angular contact ball bearing is presented which takes into account the influence of lubrication on bearing wear. The wear depths of inner and outer raceways for angular contact ball bearings are calculated based on the motion parameters and contact parameters of ball elements which are obtained by spindle system model. The effects of spindle speed, angular misalignment, external load and surface roughness on the wear depths of bearings are comparatively studied. Increasing spindle speed at Case I condition can significantly increase bearing wear. Angular misalignment may be beneficial to individual bearing, but overall, no angular misalignment is the most beneficial to spindle system. The change rate of wear depth of bearing raceway with external loads at Case I condition is much greater than that at Case II condition. The surface roughness can significantly affect the bearing wear in the spindle system, especially at Case I condition. [ABSTRACT FROM AUTHOR]

Thin film formation of lubricant plays a key role in supporting lubrication and abating wear. During cold rolling of steel, esters, or film formers in rolling oil play an important role in the mixed lubrication regime. The property of the lubricant holds the key to achieving the mean film thickness during the mixed lubrication regimen. Band formation in cold rolling is often related to inadequate acid pickling. During cold rolling operation, the film formation between asperities plays an important role in controlling friction and coil temperatures. A well formulated lubricant ensures smooth transition of lubrication throughout the range of roll bite temperature and also across the lubrication regimes. A sudden spike in coefficient of friction (CoF) can often lead to increased wear and abnormal increase in coil temperatures resulting in band formation. The study highlights degradation of oil sample leading to the problem and the role of key lubricant properties in esters in mitigating the problem. [ABSTRACT FROM AUTHOR]

Physical vapor deposition (PVD) coatings are vital for enhancing wear resistance. However this technology faces challenges when coating inaccessible surfaces due to its line-of-sight characteristic. A potential remedy is utilizing triboactive CrAlMoN coatings. These form a tribofilm in the contact zone when applied to one contact partner along with a suitable lubricant. This tribofilm can subsequently safeguard inaccessible yet tribologically stressed surfaces. One of the main applications for this method is roller chain drives, whose longevity depends on the joint wear and the resulting chain elongation. Large-scale pin coatings have proven effective in curbing wear and prolonging chain life. However, the inaccessibility of bushes complicates standard PVD coating procedures. Triboactive coatings offer the possibility of forming transfer layers on the bushes, thereby enhancing friction reduction and wear protection. Experimental material studies for chain drives can be costintensive due to complexity and numerous components. This article demonstrates that CrAlN and CrAlMoN coatings in combination with greases with the additives phosphorus and sulfur can reduce friction and wear in chain joints. Furthermore, it is shown that a reasonable selection of tribometer testing can significantly reduce costs. Comparing the results of tests on a pin-on-disk tribometer and component tests show that model tests cannot completely replace component tests. But the combination offers an efficient way to optimize test matrices. Triboactive coatings like CrAlMoN hold promise for addressing the challenge of inaccessible surfaces. Reasonable tribometer test selection can help mitigate the costs of experimental studies, making these coatings a more practical solution. [ABSTRACT FROM AUTHOR]

Falling-film hydrodynamics and heat transfer, a cutting-edge technology, has been widely used in a variety of industrial applications, including desalination and refrigeration. In this study, a two-dimensional and two-phase model was developed to examine the microscopic flow mechanism and transient flow characteristics. Film thickness varies with sprinkle density in the impingement, propagation, and accumulation zones, with the thinnest film appearing between 90° and 140°. In both the unsteady and steady cases, the film thickness over the stabilizing tube is nearly the same. Due to the acquired momentum of the liquid film, the propagation time for the test tube was also shorter than that of the stabilizing tube. Low sprinkle density results in dry regions; high sprinkle density results in mal-distribution, the formation of recirculation zones beneath the tubes, air cavities in the flow field, wavy disturbances in the liquid profile, and fluid waste. Furthermore, as the liquid sprinkle density increases, the developed recirculation zones and air cavities beneath the tubes expand and become modified. A sprinkle density can be set just above the minimum value to achieve steady-state film thickness. The findings can be used to improve flow characteristics and avoid over commitment and insufficient liquid supply. [ABSTRACT FROM AUTHOR]

A comprehensive quasi-static and dynamic ball bearing model is described using many enhanced features, including novel calculations of the contact angle variations and ball–race sliding speeds in two directions, accounting for race curvature, pivoting effects and gyroscopic effects, appropriate lubricant rheology, and sliding forces (driving the balls against miscellaneous braking forces and moments such as, for example, the hydrodynamic rolling force). Ball–cage impact forces and cage-guiding ring forces are also considered, leading to a set of six dynamic differential equations to consider for each ball and three dynamic differential equations for the cage, where movement is assumed to be restricted to one plane. Quasi-static calculations can be undertaken by neglecting the cage and setting the accelerations of each degree of freedom of the ball to zero. New analytical or curve-fitted models are also provided using the mean values of sliding speed and viscosity to calculate sliding forces and moments, avoiding the use of contact slices with some useful relationships derived for calculating the rolling line locations, bearing torque, and dissipated bearing power. Several examples of calculated results are given and compared to available numerical or experimental results published in the literature. Finally, a new tool developed in-house is proposed for predicting many properties, particularly of interest at high speed, including the ball bearing torque, power loss, risk of smearing, and risk of cage failure. [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]

Advanced ball bearing simulations require the use of accurate tribological models, starting with the calculation of the ball-race contact load and pressure in potentially truncated contacts. Ball—cage and cage—guiding ring contact stiffness models are suggested using the Hertzian contact stiffness and/or a structural stiffness. The central ball-race film thickness, a hydrodynamic rolling force, and normal load increase are calculated using relationships respecting miscellaneous lubrication regimes, including iso-viscous-rigid or piezo-viscous-elastic. A drag force acting at the ball center is included, and its magnitude discussed for claiming that the contribution from drag to the final rolling resistance is smaller than the one from hydrodynamic rolling acting at the ball-race contact. The central film thickness and sliding speed are used for defining shear rate, shear stress, and, hence, final sliding force, using a nonlinear visco-elastic-plastic lubricant rheological model including viscosity, elastic lubricant shear modulus, and limiting shear stress, which are all functions of the pressure and temperature. Elastic effects are approximated using a simple nonlinear visco-plastic model with apparent viscosity. The temperature is defined as the sum of the operating temperature and several other sources of temperature increase. It is observed that when adopting Roelands viscosity model and a simple nonlinear visco-plastic model, the final lubricant traction coefficient and its gradient with respect to sliding speed decrease as the rolling speed increases, mostly reducing the need for a lubricant elastic shear modulus. Appropriate experimental results are highlighted to support these analytical models. [ABSTRACT FROM AUTHOR]

As operating under quite high bearing speed with quite narrow clearance, the slip effect generally inevitable exists and closely relates to the performance of Gas Journal Bearing (GJB). However, singly the conventional macroscopic method may not be capable of fully exploring the influence of slip effect and seize tiny details such as slip velocity and flow vortex. In this article, both the Lattice Boltzmann Method (LBM) and the Reynolds equation method are applied to analyze the distributions of lubricant viscous dissipation heat, velocity, slip velocity, pressure, journal position and film thickness versus different operating parameters at multiscale. It shows that the slip effect weakens the squeezing function on lubricant film, reduces the viscous dissipation heat peaks, consumes the maximum pressure peaks, and decreases the bearing capacity, which is more obvious at larger Knudsen number. At higher bearing speed, the high viscous dissipation heat and pressure zone rapidly magnifies, in contrast, under larger bearing load, the high viscous dissipation heat zone concentrates. [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]

We derive an extension of the Maugis-Dugdale-Johnson-Greenwood model for 2D adhesive Hertzian contact to viscoelastic materials. This results in extremely simple approximate results for the maximum amplification of the pull-off due to viscoelastic effects, for arbitrary form of the viscoelastic linear properties. In particular, we assume that the initial loading state is fully relaxed, and unloading occurs at very large pulling speeds. We show that the maximum amplification (of the order of E I / E R 2 / 3 , the ratio between instantaneous and relaxed modulus to the 2/3 power) is only reached for large and soft cylinders, namely, large enough (relaxed) Tabor-Maugis parameters λ of the order of the order of E I / E R , and therefore typically much larger than the Tabor-Maugis parameters to have a "short-range" JKR adhesion regime in quasi-static conditions, which is λ ∼ 1. The results agree well with recent numerical ones by Muser-Persson, but there is an shift factor in the Tabor-Maugis parameter which requires further study and may depend on initial contact area. [ABSTRACT FROM AUTHOR]

Friction drive and wear control is a tough issue for linear standing-wave ultrasonic motors with intermittent contact and impact friction. For the widely recognized reduction of friction/wear, minimum quantity lubrication was adopted to improve the output performances and services for motors through friction regulation. Given different preload and driving voltages, the mechanical characteristics of motors with minimal quantity lubrication were investigated using a homemade test rig. Results show that output performances and driving efficiency under film lubrication differ from those of dry friction. The optimized driving voltage was reduced by 31.5% and the minimum startup voltage was reduced by 41.67% using film lubrication. Additionally, the output speed increased by 26.29%, and thrust decreased by 41.26% under uniform exciting conditions (e.g., 150 V at 39.14 kHz). The existence of film lubrication broadens the effective frictional contact boundary, and effective friction contribution enhances the driving efficiency (the maximum efficiency of motors increased by 14%). Furthermore, the singularity of the effect of preload is significantly improved after lubrication, and the friction interface of the stator/slider becomes more controllable. Suitable lubrication is critical to the improvement of startup performance and prone to realize low-voltage driving, and the combination of lubrication regulation and wear inhibition is conducive to the durability and reliability of motors. This study provides an additional alternative for performance improvement of linear standing-wave motors apart from frictional materials. [ABSTRACT FROM AUTHOR]

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This article investigates the effect of temperature on the lubrication and wear behavior of a grease-lubricated spherical roller bearing (SRB) assuming mixed-elastohydrodynamic lubrication (mixed-EHL) where the contact load is shared between the lubricant film and contact asperities. Temperature effects on internal load distribution and elastic modulus and their subsequent effect on the wear are also analyzed. The effect of temperature is investigated, first on the film thickness and load sharing, and then on the friction and wear. If the temperature rises from ambient to 110 °C, the increase in the contact patch dimensions, due to the decrease of elastic modulus, is only approximately 1% and the decrease in mean contact pressure is approximately 2%. Moreover, the load at ψ = 0 ° decreases by approximately 4%, and the load zone increases by approximately 5%. As the temperature rises from 50 to 110 °C, the asperity portion of the contact load at ψ = 0 ° position is increased by 350%. At 50 °C, only 20% of the total traction is contributed by the contact asperity, which is 80% at 110 °C. For the temperature rise from 50 to 110 °C, the wear volume loss increases by 238% and nonlinearly, due to viscosity reduction and its effect on the reduction of film thickness. The isolated change of internal load distribution and elastic modulus due to temperature rise causes a relatively insignificant change in wear. Hence, the predominant effect of temperature rise on wear is due to a decrease in lubricant film thickness causing the asperity component of the contact load to increase. [ABSTRACT FROM AUTHOR]

The seawater hydraulic variable ballast system (SHVBS) is critical equipment for underwater operations. Reciprocating seals play a vital role in the efficiency and safety of seawater hydraulic components working in SHVBS. However, the sealing performance and friction behavior of reciprocating seals remain unknown under high isostatic and water-lubricating conditions. In this work, an innovative mixed lubrication model for reciprocating water hydraulic rod seals is developed based on the elastohydrodynamic lubrication (EHL) theory. An elastic deformation method is introduced to update the film thickness rapidly. The characteristics of the reciprocating seal are studied in a full-ocean-depth pressure range. With the rod speed of 500 mm/s, for sealed pressure of 0.1 MPa and 120 MPa, the maximum friction force increases 10-fold, from about 30 N to 300 N. A test rig is designed to measure friction force under high pressure. The numerical and experimental results have the same variation pattern, and the relative error is less than 15%. [ABSTRACT FROM AUTHOR]

This article studies the tribological behavior of the lubricant film when the Q1-224 hydrostatic turntable is operated at constant cutting speed. First, the rotational speed equation of the worktable under the constraint of constant cutting speed is derived. Based on the lubrication mechanism of hydrostatic turntables, the flow-rate equation of the oil film, the temperature-rise equation of the oil film, and the bearing-capacity equation of the double rectangular cavity are deduced. Furthermore, the prediction model of the lubrication performance of hydrostatic turntable operating at constant cutting speed is established. Meanwhile the quasi-steady-state analysis is carried out by numerical simulation to obtain the change law for the lubricating oil film temperature, pressure, and other performance indicators with time under the different loads. Finally, these laws are verified by designed experiments. It is found that the load has a large effect on the change of oil film performance; it affects the temperature rise of the oil film by influencing the dissipation capacity, and there is a nonlinear relationship between the increase of the load and the average temperature rise of the oil film. [ABSTRACT FROM AUTHOR]

Based on mixed thermal-elastohydrodynamic lubrication, the dynamic contact of ball bearings with worn band is investigated, and the film thickness, pressure, profile and interfacial temperature are analyzed. The temperature-pressure-viscoelastic equation of lubricant is constructed. The surface roughness, the elastic deformation and the worn band are included in the film thickness. The discretization method and compound iteration method are combined to solve the problem. Through numerical examples, the distribution and contour of film thickness, pressure and temperature with consideration of surface roughness and worn band are discussed, and the point contact with lower entrainment speed is found. [ABSTRACT FROM AUTHOR]

We develop a lubrication-type model of contact line motion on a surface patterned by an array of square patches of decreased wettability. The model accounts for evaporation of the liquid due to surface heating, as well as effects of surface tension and disjoining pressure. Stick-slip motion and strong interface deformations are found from the simulations. The height of the capillary ridge becomes spatially nonuniform when the stable contact line travels over the region of decreased wettability. Coupling between the surface pattern and intrinsic contact line instability is investigated. For the weak evaporation limit, the model predictions are compared to previous studies of contact line dynamics under isothermal conditions. [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]

Previous lubrication and wear analysis for the planetary roller screw mechanism (PRSM) has mainly concentrated on the isothermal conditions without considering temperature rise. However, the PRSMs applied in aviation and aerospace always operate in intensely varying thermal conditions with intricate thermal convection and thermal radiation environments. For this purpose, a modified Archard wear model is established by incorporating the entraining speed of threads and the load distribution, considering axial thermal errors. The variation of bulk temperature is characterized by the thermal network model (TNM). The modified Weierstrass–Mandelbrot (W-M) function is used to evaluate the lubrication conditions of the machined surfaces. Meanwhile, the contact flash temperature, wear depth, and precision loss rate are investigated in dry contact and lubricated phrase for mixed thermal elastohydrodynamic lubrication (TEHL) point contact. The results reveal that the temperature rise has a more pronounced influence on the precision maintenance capability compared to the uneven load sharing. The wear results are also compared to previous experimental simulation obtained using a rolling-sliding tribometer that utilize a rolling wheel on a rotating disk with similar patterns. It indicates that the wear life span of PRSMs can be improved by reasonable machining trajectory, thermal management, and lubrication parameters. [ABSTRACT FROM AUTHOR]

In this study, the influence of the in-situ tribo-oxide-layer on non-lubricated tribological behaviours of LM27/SiCp composites was studied at different applied loads. For this purpose, LM27/SiCp composites were manufactured by stir casting route with reinforcement of different amounts (3–12 wt.%) and different sizes (fine: 1–20 µm and coarse: 106–125 µm) of SiCp. A comprehensive characterization of the friction and wear mechanisms ranging from mild to severe wear for oxidative and delamination at a contact pressure of 0.125–0.624 MPa was discussed. Results indicate that the friction and wear behaviour is strongly influenced by the morphology and the nature of the oxide scale on the wear track. In-situ formation of oxide layers on the contact region of the specimen supports the self-lubrication which supports better wear performance of LM27/SiCp composites. However, these study portraits that composite with 12wt. % fine size SiCp exhibits better wear performance in comparison to the other developed composites. [ABSTRACT FROM AUTHOR]

This paper investigates the strong coupling between friction power losses and film thickness that prevent from clearly identifying the mechanism of scuffing through classical test procedures. As the film thickness appears of great influence on the phenomena, a new test method is presented, allowing scuffing initiation study with the film thickness as a key parameter. This new test method allows film thickness variation with minimal friction losses and bulk temperature variations. This procedure has been developed with nitrided steels and a synthetic base oil on a twin disks test rig. Even though asperity contact is considered necessary in literature for scuffing, the test result shows that it can be reached in full film lubrication, potentially through the collapse of the oil film. Different test methods allowing triggering scuffing through different parameters are identified, which shows that a variety of parameters is able to influence scuffing. [ABSTRACT FROM AUTHOR]

This work quantifies the high-pressure rheological performance of two jet engine turbine oils and three helicopter transmission oils. The jet engine oils are qualified for both the MIL-PRF-23699 high thermal stability and AS5780 high performance classifications, and the helicopter oils are classified against DOD-PRF-85734. Rheological properties include relative volume, low shear, and high shear viscosity. Relative volume measurements are presented for temperatures ranging from 20 to 100 °C and up to 300 MPa. Low shear viscosity measurements range from 20 to 100 °C and up to 1 GPa. Apparent shear or high shear viscosity measurements varied pressure up to 550 MPa and shear stresses up to 5 MPa. The non-Newtonian limit for each lubricant was observed. Rheological models obtained from the measurements include the Tait and Murnaghan relative volume models, the Williams-Landel-Ferry (WLF) modified Yasutomi low shear viscosity model, and both the modified Carreau-Yasuda and double modified Carreau-Yasuda shear viscosity models. The regressed models highlight shortcomings of classical elastohydrodynamic lubrication (EHL) expressions in describing the measured lubricants' rheological response. These property models support the development of modern EHL calculations as they relate to high-performance aerospace applications. [ABSTRACT FROM AUTHOR]

Presented in this article is a new method to measure the film thickness in a rolling bearing running under starved conditions, such as in grease-lubricated bearings, using the electrical capacitance method. The method was used to study the impact of speed on film thickness. Results show that fully flooded conditions prevail at lower speeds where the film thickness increases with increasing speed. At higher speeds, where grease-lubricated bearings run under starved lubrication conditions, this increase is less pronounced. At even higher speeds, the film thickness becomes almost independent of the speed. [ABSTRACT FROM AUTHOR]

Skid-resistance performance of a runway greatly influences aircraft landing safety. A wet runway significantly increases the incidence rates of aircraft overrun. To study the influence of the skid-resistance performance of a runway on aircraft landing, a co-simulation method is proposed. First, a finite element (FE) model of the local tire-water film-runway simulation is established to obtain the combination coefficient-slip ratio curve of a tire on a wet runway. Second, a global model of an Airbus A320 virtual prototype (VP) is created. Then, on the basis of fuzzy control theory, a two-dimensional (2D) fuzzy controller of the aircraft AB is established. The friction coefficient-slip ratio curve of the tire on the wet runway obtained in the local simulation is introduced into the full-scale hydroplaning simulation model of the aircraft. Finally, the global-local multiscale simulation method is used to analyze the skid-resistance behaviour of the aircraft on three types of runways. It is found that the increase of water film thickness of the pavement and the increase of the grounding speed cause the attenuation of the friction coefficient of a runway, finally causing the reduction of the deceleration rate of the aircraft and the increase of the braking distance. [ABSTRACT FROM AUTHOR]

Micro-cantilever beam are now widely used in modern micro and nano devices. This device includes micro-switches and microscopes which are operated by atomic force. The dynamic analysis of cantilever beams is of critical prior to manufacturing of the beams. Dynamic analysis is carried out using an energy technique based on Galerkin method and pull-in parameters are to be found out for prismatic cantilever. In squeeze film damping the air present between movable beam and fixed beam behave as squeezed fluid and producing the damping effect which lead to reducing in displacement. In case of fringing field the line of action of electrostatic force do not remain perpendicular at the boundaries. The effect of damping due to Squeeze film and fringing field on dynamic performance of beam is studied and found out the pull-in factors and matched with the published outcomes. This area opens novel opportunities for structural optimization of electrostatic micro-beams. [ABSTRACT FROM AUTHOR]

Under mixed lubrication, when there is direct rough contact between two contact surfaces, surface wear occurs, altering surface morphology, which in turn changes their lubrication state. The tribological performance of materials can be improved with in-depth understanding of the coupling mechanism linking surface wear and lubrication. A numerical model was established to predict the lubrication state and wear characteristics of the surface wear process based on non-Gaussian surface reconstruction technology and a mixed elastohydrodynamic lubrication sliding wear model. The evolution of wear characteristics in Gaussian and non-Gaussian rough surfaces was investigated, and the effect of surface skewness and kurtosis on lubrication and wear characteristics was discussed. The results indicated that as the wear cycle increases, the contact area and contact load ratios of the rough surfaces decrease before gradually stabilizing, while the coefficient of friction and maximum flash temperature rise and then gradually decrease. Increasing surface skewness and kurtosis increases the probability of wear, leading to increased accumulated wear, friction coefficient, and maximum flash temperature rise. [ABSTRACT FROM AUTHOR]

Lubrication is essential in metal cold rolling operation to regulate friction at the metal–roll interface, reduce energy loss and improve the product surface finish. A novel non-intrusive pitch-catch technique, based on the reflection of ultrasound, was employed on a pilot mill to evaluate oil-film thickness at the metal–roll interface during the metal cold rolling operation. During the metal rolling process, oil-film thickness was measured under varying rolling load and rolling speed. The oil-film thickness increases as the roll speed increases and reduces as the rolling load increases. The values of oil-film thickness obtained from this non-intrusive ultrasonic technique agree with theoretical values. This study is a proof of concept and has shown promising results. If further developed, the technique could be employed for in situ monitoring of lubricant during rolling operation in metal rolling industries. [ABSTRACT FROM AUTHOR]

This article describes the finite element modeling of a spherical hybrid thrust bearing (SHTB), taking into account the influence of three-dimensional surface irregularities and magnetorheological (MR) lubricant behavior. The rheological behavior of MR lubricant was described using the Herschel–Bulkley model, and the yield shear stress relationship of MR fluid was expressed using the asymmetrical sigmoidal function. The finite-element method (FEM) is used to solve the governing Reynolds equation for an irregular surfaced SHTB configuration along with the orifice restrictor equation. The findings of the study indicate that the performance of the SHTB is improved by considering the three-dimensional (3-D) surface irregularities and operating with MR fluid at the expense of power loss due viscous friction. The percentage increase in the value of dynamic coefficients ( S ¯ ) and ( C ¯ ) due to the coupled effect of MR fluid and three-dimensional surface irregularity ( h ¯ a = 0.125) on the spherical hybrid thrust bearing is of the order of 52.37% and 71.22%, respectively, at ε y = 0 and I = 2 A. [ABSTRACT FROM AUTHOR]

The paper presents the numerical solution of line contact thermal elastohydrodynamic lubrication (EHL) with bio-based lubricant. The model comprises Reynolds equation, film thickness, load balance and energy equations with appropriate boundary conditions by incorporating viscosity–pressure–temperature and density–pressure–temperature relations. Second-order finite difference scheme is used for the discretised form and their equation. The multigrid method with full approximation scheme is used to solve the Reynolds equation along with multilevel multi-integration method for film thickness equation. The pressure, film thickness and temperature distributions for two rolling velocities and various loads with a bio-based lubricant are presented in detail. The present findings yield a reduction in the minimum film thickness for high speed. Details of pressure spike as a function of relevant parameters are given. The results are compared with earlier findings based on different methods. [ABSTRACT FROM AUTHOR]

Lubricated contact performance can be improved by using a textured surface as well as a hydrophobic surface. A procedure to obtain the optimal partially textured journal bearing combined with the hydrophobic coating is presented through the computational fluid dynamics (CFD) codes. In this study, lubricated hydrophobic textured contacts with and without cavitation modeling are discussed. The cavitation phenomena in the lubricant is modeled using a multiphase model of “mixture” to obtain a realistic condition. The effect of dimple depth, as well as the eccentricity ratio, on the tribological performance, is of particular interest. It is found that the tribological performance is greatly influenced by the multiphase flow cavitation scheme. When cavitation modeling is taken into account, higher load support is noted. Furthermore, the simulation results show that a hydrophobic textured surface with a shallow depth (d/hmin<1) seems to be better for enhancing the tribological performance. Meanwhile, for the case of the low eccentricity ratio, there is an optimal dimple depth giving the highest load support. The findings explored in this work can be considered as a theoretical basis to increase the performance of hydrophobic textured journal bearing. [ABSTRACT FROM AUTHOR]

The research work presents the study of a heterostructured surface acoustic wave (SAW) resonator consisting of an interdigital transducer (IDT), lithium niobate (LN), and silicon (Si) substrate. In the proposed structure, Silicon is the base substrate, above it layer of LN is placed then IDT is designed on it. The presented analysis includes the variation of the quality factor and electromechanical coupling coefficient with the change in the width of the piezoelectric layer. The electromechanical coupling coefficient (K2), quality factor (Q-factor), velocity, resonance, admittance, and anti-resonance frequency have been studied for the thickness of the different layers of LN film. The higher quality factor of one port SAW devices reduces the energy loss and the K2 of the devices indicates faster energy conversion. The Q-factor and K2 are found to be depending on the thickness of LN, resonance, and anti-resonance frequency. [ABSTRACT FROM AUTHOR]

The ring–liner interface of an internal combustion engine is a very important interface because its behavior directly affects fuel efficiency of an automobile and the engine life. The liner surface is complicated, with honing features on top of the primary roughness. Moreover, liner surfaces considered here also contain pores that are random in terms of their shape and distribution. The work reported in this article systematically models the tribological performance of such surfaces in a ring–liner interface. A microscopic single-pore computational fluid dynamics analysis is conducted on the representative pore shape obtained from liner–surface characterization to quantify the effect of pores on friction. A pore influence zone is suggested, and a friction reduction factor is defined for pores. A macroscopic ring–liner interface model is developed in parallel to solve the average Reynolds equation for a representative section with the consideration of the starvation and cavitation effects. The two models are then combined to predict friction at the ring–liner interface for the liner surfaces with pores. Excellent agreement is observed between our modeling and experimental results. The effects of random pores of varying densities in the range of 2–10% on the ring–liner interface performance are studied under flooded and starved conditions. The results indicate that surface pores increase friction when the ring–liner set is operated under flooded conditions. However, when starvation occurs, surface pores help reduce friction. [ABSTRACT FROM AUTHOR]

Due to increasingly stringent environmental regulations, leakage-free shaft seals with minimal friction are growing ever more important. The trend toward higher operating speed (e.g., in the field of e-mobility) additionally aggravates the sealing task. Reliable, leakage-free shaft seals—such as gas-lubricated mechanical seals—are difficult to manufacture and thus expensive. Therefore, there is still significant interest in an efficient and easy-to-manufacture shaft seal design. This study discusses the development of sleeve-type lip seals made of fluoroelastomer with an innovative, sickle-shaped back-structure design. The novel lip seals are capable of operating at near-zero friction. Compared to state-of-the-art, gas-lubricated mechanical seals, near-frictionless sliding on an air film is achieved with a simple, robust, and easy-to-manufacture sealing-lip design. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to investigate the dynamic mixed elastohydrodynamic lubrication (DMEHL) behavior of the water-lubricated bearing with unbalanced rotor during start-up. To achieve this, a DMEHL model that couples the rotor dynamic model considering the unbalanced load with the transient mixed lubrication model is established. The validity of the calculation procedure is verified by comparisons with published experimental and numerical results. Using numerical studies, the optimal accelerating mode for reducing the transient asperity contact during start-up is identified. Numerical results indicate that during start-up, the rotor dynamic characteristic and hydrodynamic force are more sensitive to the unbalanced load than the transient contact force, and the rotor imbalance eccentricity will affect the transient contact behaviors if the surface roughness is relatively large. In addition, the DMEHL responses are affected by the unbalanced load only when the accelerating time is small. Finally, the DMEHL responses during start-up using three different water-lubricated materials, namely, polymer, Thordon, and ceramic, are compared. It is found that DMEHL performance at the start-up stage highly depends on the elastic modulus and hardness of the water-lubricated material. [ABSTRACT FROM AUTHOR]

The instability of oil film stiffness in mixed elastohydrodynamic lubrication (EHL) is a prominent cause of the fretting wear of continuously variable transmission pulley–metal sheet friction pairs. In severe cases, it can induce dynamic system failure. In this study, an oil film normal stiffness model equivalent to a massless spring element is established using linear contact mixed EHL theory. The effects of microscopic parameters (roughness amplitude) and macroscopic operating parameters (torque ratio) on the oil film stiffness in the pulley–sheet contact area are studied. The film stiffness increases initially and then decreases with an increase in roughness amplitude. In addition, it increases continuously and then stabilizes with an increase in torque ratio. The effects of macro- and microparameters are considered and a safety threshold model of oil film stiffness is established. Results show that oil film stiffness exhibits the highest safety stability when the roughness amplitude is 0.10 μm and the torque ratio is 0.8. The influence of roughness amplitude on the safety threshold of oil film stiffness is greater than that of torque ratio. [ABSTRACT FROM AUTHOR]

To investigate the effects of the oil film between deformed discs on the dynamic torque behavior of hydroviscous drive (HVD), a mathematical model incorporating film lubrication, asperity contact, and translational and rotational motion from a friction system is developed based on four kinds of representative film gap cases. The main analytical solutions including squeeze velocity, angular velocity of the driven disc, hydrodynamic torque, and total torque are obtained. Soft-start experimental tests are conducted to verify the feasibility of the theoretical model. The results show that both peak value of total torque and hydrodynamic torque increase with an increase in the divergent angle or the convergent angle. Due to the increase in squeeze velocity, surface asperity contact begins to dominate the dynamic torque behavior in the mixed and boundary lubrication regimes, which inevitably caused the soft-start process to become nonstationary. For all of the film gap effects, consideration should be given to both the dynamic torque response and improvement of the soft-start characteristics. Moreover, some key parameters including convergent angle, divergent angle, and location of the minimum or maximum initial film thickness have a great influence on the dynamic torque behavior. Based on the comparison with experimental results, the performance of the theoretical model is satisfactory. [ABSTRACT FROM AUTHOR]

In recent years, porous bearings have been increasingly used in various industrial applications because they are less noisy, have good precision, and are relatively maintenance free. In this article, the numerical analysis of a conical porous hybrid journal bearing system (CPHJBS) has been carried out. The interactive effects of permeability parameter, semi cone angle, and pseudoplastic (shear thinning) lubricant behavior on the performance of CPHJBS have been theoretically investigated. The governing Reynolds equation for a non-Newtonian lubricant in the bearing clearance space of CPHJBS is solved using a finite element model. Findings of this study indicate that the CPHJBS operating with a pseudoplastic lubricant offers a higher value of stability threshold speed margin ( ω ¯ t h ) for the lower value of semi cone angle (γ = 10 0 ) and lower value of permeability parameter (Ψ = 0.005). [ABSTRACT FROM AUTHOR]

A mixture model suitable for studying the thermal effect on elastohydrodynamic lubrication (EHL) of emulsions is proposed. The maximum temperature rise occurs at the emulsion layer because sliding occurs mainly in the emulsion layer to generate shear heating, and it increases with increasing oil concentration, slide-to-roll ratio, mean speed, and load. The rise in surface temperature of the rollers decreases with the increase in the adsorbed layer's thickness at the entrance. This result indicates that the adsorbed layers insulate the heat flux across the film, so that the surface temperature becomes cooler with a greater thickness of the adsorbed layer. [ABSTRACT FROM AUTHOR]

A solid contact model with high accuracy is required for mixed lubrication calculation to predict friction loss and wear in sliding parts by computer-aided engineering; however, existing models have numerous limitations. A new asperity contact model was constructed to determine contact states using the roughness parameters of pairs of surfaces. Although the contact states differed greatly depending on differences in skewness and kurtosis, the calculated results of the proposed model agreed well with the results of direct calculation between various pairs of surfaces. Furthermore, even when the pairs of rough surfaces had the same composite roughness, skewness, and kurtosis, the trend of the increase in the contact force was different when the individual skewness and kurtosis of the surfaces were different. Therefore, we determined that it is necessary to carry out detailed asperity contact calculations when the two rough surfaces differ greatly. We plan to further investigate the influence of skewness and kurtosis on the contact tendency for the elastoplastic deformation by the extended model considering the contact stress distribution of asperities. [ABSTRACT FROM AUTHOR]

The elastohydrodynamic (EHD) lubrication straight line contact conjunction is studied to evaluate the mixed lubrication heat generation experimentally over bordering operating conditions in a disc-on-disc machine. An experimental investigation is carried out using an accessory device that collects and measures the outlet lubricant temperature. The experimental results show the typical transition from mixed to elastohydrodynamic lubrication, tracking the difference of outlet lubricant temperature and the total average full-film EHD temperature. A new variable coupling flash temperature was introduced as an in situ approach to demonstrate the lubricant capacity of removing heat from asperity interaction in mixed lubrication contacts. It was possible to estimate the metal–metal contact area in mixed lubrication by coupling flash temperature as a direct correlation to the true flash temperature in relation to correspondence to final surface roughness characterizations. [ABSTRACT FROM AUTHOR]

During their lifetime, gears may undergo starved lubrication operating conditions. Starvation has an impact on friction between gears and leads to modified gearbox efficiency. In this article, lubricant starvation tests on an FZG test rig adapted to this condition are presented. Gears were equipped with an embedded thermocouple sensor to measure their operating bulk temperature. An experimental method to isolate the test box power loss of the FZG machine is proposed. A thermal model of this test rig draws up the power loss distribution into the test box for a nominal condition of lubrication. A numerical method based on experimental results is proposed to estimate gear power loss variation during lubricant starvation. [ABSTRACT FROM AUTHOR]

The commonly used quasi-static model for angular contact bearings is enhanced by coupling contact mechanics and bearing kinematic analyses with traction or friction behavior in ball–race contacts. The points of pure rolling in the contacts, which constitute the primary inputs in the kinematic equations, are determined by minimizing the frictional dissipation based on a prescribed elastohydrodynamic traction model. Such an intricate coupling between contact mechanics, bearing kinematics, and lubricant behavior provides significant enhancement of simple quasi-static model for greatly improved prediction of traction behavior and heat generation in ball bearing contacts. The predictions are in close agreement with those obtained by much more sophisticated dynamic analysis based on integration of classical differential equations of motion of bearing elements. The enhanced quasi-static model can therefore be effectively used as a design tool for optimizing thermal dissipation in ball–race contacts in ball bearings. To facilitate immediate evaluation and implementation of the model to practical problems, a standalone software, containing the enhanced quasi-static model, is made freely available at . [ABSTRACT FROM AUTHOR]

The paper presents steady isothermal elastohydrodynamic lubrication (EHL) of elliptical contact with Roelands pressure–viscosity model over varying rotational speed. The governing Reynolds and film-thickness equation for elliptical contact in roller bearings are analysed by using multigrid method with full approximation scheme. The non-dimensional pressure distribution and film-thickness for elliptical contacts are obtained. The distinct friction models appropriate to lubricants in contact regions are predicted. The result shows that rolling contact weariness does not occur on the surfaces with longitudinal roughness and wear or scraping exists in circular EHL contacts with entrainment along major axis to that of minor axis. The computation predicts that minimum film thickness, central film thickness and elastic deformation increase as the rotational speed increases. The computed results are compared with earlier finding which are in good agreement. [ABSTRACT FROM AUTHOR]