Lubricant Viscosity Research Articles

Friction of lubricated hydrogels: Influence of load, speed and lubricant viscosity

Agarose hydrogels are used to study the tribological response of hydrogel materials. We demonstrate that the dynamic frictional behaviour of agarose hydrogels is influenced by their mechanical properties, lubricant viscosity and applied load. Within the linear viscoelastic regime of the hydrogels, we find the Stribeck-type framework proposed previously for elastomers and other viscoelastic materials describes their tribological behaviour and dependency on lubricant viscosity. However, this breaks down when sufficient stress in the contact is applied so that the hydrogel undergoes yielding (i.e. elastic-plastic deformation). As a result, we find that the friction- normal load relationship differs from the classic trend (F ~ W2/3) observed in elastomers above finite loads. Conventional interpretations of the friction associated with hydrogels should be revised with consideration for the non-linear deformation of the hydrogels. We suggest that theories on viscoelastic lubrication are generally applicable to hydrogels within their linear viscoelastic regime, and propose a conceptual model that considers the effects of bulk mechanical properties and measurement conditions including lubricant viscosity, measuring geometry, speed and load.

Characterization of engine lubricants by fluorescence spectroscopy and chemometrics

In this study, principal component analysis (PCA) and parallel factor analysis (PARAFAC) combined with excitation-emission matrix fluorescence (EEMF) were used to determine the most efficient excitation wavelengths of engine lubricants; identify their fluorophores; classify them and look for correlations between their fluorescence and their physical parameters. EEMF spectra were obtained for the different samples in the range of 260 to 600 nm, and 300 to 700 nm for excitation and emission wavelengths respectively. PCA and PARAFAC showed that the efficient excitation wavelengths for engine lubricants are 300, 350, 400, 450 and 470 nm. These five wavelengths represented the maxima of the PARAFAC recovered excitation profiles, of which two were attributed to fluorene and pyrene. The relative proportions of the PARAFAC retrieved components were used to classify engine lubricants with a satisfactory percentage of classification of 70%. Finally, a good correlation was obtained between some physical parameters (particularly the viscosity) of engine lubricants and their fluorescence.

Mathematical model of a journal bearing with low-melting and porous coating in its structure on different contacting surfaces with incomplete filling of operating clearance

The authors consider the development of a mathematical design model of an infinite journal bearing lubricated with a lubricant with Newtonian rheological properties and a melt of a low-melting metal alloy covering the surface of the bearing bush, as well as a porous coating on the surface of the shaft, taking into consideration the dependence of the viscosity characteristics of the lubricant, the melt and the permeability of the porous coatings on the pressure with incomplete filling of the operating clearance. The authors found asymptotic solution of the system of differential equations with respect to the parameter K due to the melt and the rate of dissipation of mechanical energy and the exact self-similar solution for the zero approximation without regard for the melt and the first approximation taking into consideration the melt. This solution was found according to the equation of motion of a viscous incompressible fluid for a thin layer, the equations of continuity, Darcy equation and the equation determining, taking into account the expression for the rate of dissipation of mechanical energy, the profile of the molten contour of the bearing bush with regard to the dependence of the permeability of the porous coating, the viscosity of the lubricant depending on pressure. As a result, the fields of velocities and pressures in the lubricating and porous layers were determined taking into consideration the dependence of the lubricant viscosity and the permeability of the porous coating on pressure, as well as the function Φ1(θ), reasoned by the melt of the bearing bush surface. In addition, the main performance characteristics were determined: load-bearing capacity and friction force.

Tandem tapered roller bearings no-load torque loss in a rear axle gear transmission

The main no-load power loss source of a rear axle is the pre-loaded pinion tapered roller bearings, as concluded in a previous work. Therefore, the pinion roller bearings torque loss was studied in detail, where the influence of several parameters was considered, such as, the starting torque of the pinion tapered roller bearings, the oil level, the lubricant viscosity and the rotational speed.Due to the nature of the assembly of the pinion shaft assembly, pre-load in the tapered roller bearings is difficult to measure, however the starting torque of this assembly can be easily measured.For this reason, in this work a rolling bearing torque loss empirical equation was developed, where it uses as input parameters the starting torque, the oil dynamic viscosity, operating speed and the rolling bearing mean diameter and width.

Vibration signatures in ball bearings as a function of lubricant viscosity ratio κ, under alternating lubrication conditions

This paper analyses the vibrations emitted by a set of grease lubricated ball bearings run under load, when lubrication conditions alternate between good and insufficient. Conditions are varied by adjusting the operational parameters rotational speed and temperature. The dependency of the vibration signature on the lubrication ratio κ is considered. The results show a good correlation between κ and spectral kurtosis for a given frequency band, a: when the bearing is new, and b: when κ is below 0.6.

Modeling on contact fatigue under starved lubrication condition

This study develops a model for the description of surface breaking crack initiation, under starved lubrication condition. Varying from fully flooded to severely starved lubrication condition, impacts of important factors, including surface roughness, contact pressure, and lubricant viscosity, on fatigue life are examined. Surprisingly and interestingly, it is found a lower lubricant viscosity elongates fatigue life when severe starvation occurs, which is opposite to the EHL rule under fully flooded lubrication condition, stating higher viscosity leads to thicker lubrication film and improved fatigue life. However, it is in line with the experimental observation (Cann in Tribol Trans 42(4):867–873, 1999), where film thickness was shown to increase when moving from high viscosity base oil to a lower one under starvation condition.

Recent Trends in Rough Estimation of Lubricant High-Pressure Viscosity by Simple Observation of Its Solidification Pressure

Recent Trends in Rough Estimation of Lubricant High-Pressure Viscosity by Simple Observation of Its Solidification Pressure

Analysis of the Effect of Biodiesel B20 and B100 on the Degradation of Viscosity and Total Base Number of Lubricating Oil in Diesel Engines with Long-Term Operation Using ASTM D2896 and ASTM D445-06 Methods

Based on its characteristics, biodiesel has a higher density, viscosity, and acidity level than diesel fuel, so it has a disadvantages in terms of lubricants especially in the long run. The impact, it can decrease the kinematic viscosity of the lubricant, a decrease in the total base number, and the impact by decreased of the engine performance. This research aims to determine the characteristics of lubricants from the use of biodiesel (B20 and B100) related to the kinematic viscosity of lubricants and Total Base Number (TBN). The testing method were used ASTM D2896-15 and ASTM D445-06 standard. The study used two units Kubota RD 65 DI-NB diesel engines with a cylinder volume of 376 cc. The rotary speed of the machine was keep constant at 2200 rpm and were operated for 300 hours non-stop. Moreover, the sampled was carried out every multiple of 100 hours. Based on the research results, the quality of lubricants with B100 fuel is no better than lubricants with B20 fuel. B100-fueled lubricants have kinematic viscosity values at temperatures of 40 °C and 100 °C and has lower TBN values than B20-fueled lubricants.

Experimental Study on the Flow and Heat Transfer of Graphene-Based Lubricants in a Horizontal Tube

To improve the heat transfer characteristics of lubricant, graphene-based lubricants were prepared by adding graphene particles, due to its advantages of excellent thermal conductivity and two-dimensional sheet structure. In the present study, its physical properties were measured. A flow heat transfer experiment platform was built to study the flow and heat transfer characteristics of the graphene lubricating oil in a horizontal circular tube. The results show that the graphene lubricant prepared using a two-step approach had good stability, and the dispersibility was good without the agglomeration phenomenon, according to measurements undertaken using an electron microscope and centrifuge. The thermal conductivity and viscosity of graphene lubricant increased with the increase of the graphene concentration, and the thermal conductivity of graphene lubricant with the same concentration decreased with the increase of temperature. When the concentration was equal, the convective heat transfer Nusselt number (Nu) of graphene lubricant increased with the increase of Reynolds number (Re). When Re was equal, the convective heat transfer Nu increased with the increase of graphene particle concentration, and the maximum Nu increased by 40%.

Evaluation of the influence of compositional variables on the viscosity of industrial lubricants

Evaluation of the influence of compositional variables on the viscosity of industrial lubricants

Experiment Study on the Influence of Lubricant Viscosity and Solid Additives on Irregular Cavitation Noise in the Oscillatory Squeeze Film

Experiment Study on the Influence of Lubricant Viscosity and Solid Additives on Irregular Cavitation Noise in the Oscillatory Squeeze Film

Dynamic contact angle measurements on lubricant infused surfaces

HypothesisEven though lubricant-infused surfaces (LISs) are known to affect the mobility of working fluid depending on the infused lubricant, previous studies have not yet quantified their slippery property. This study proposes the slippery nature of the LIS can be assessed by dynamic contact angles of the working fluid on the LIS and its scaling model. ExperimentsWe measured the apparent dynamic advancing and receding contact angles on a LIS using a modified Wilhelmy plate technique for the first time. Lubricant having different viscosities was infused into the sanded polytetrafluoroethylene surface to fabricate the LIS. The surface was immersed into or withdrawn from an aqueous glycerol-water solution by varying the capillary number and the lubricant viscosity. FindingsThe dynamic contact angles on LIS was found to be sensitive to changes in both the lubricant viscosity and the capillary number. The cube of the dynamic contact angles on the LIS was proportional to θD3~Ca1, which follows a conventional hydrodynamic theory. In addition, the decreasing lubricant viscosity shifted the cube of the dynamic contact angles to high capillary numbers. Our dynamic contact angle data coincided with the prediction from a scaling law derived in this study.

Transient elastohydrodynamic analysis of finite line contact under load impulse

Numerical analysis is performed to study the transient behavior of EHL finite line contact of a cylindrical roller and flat plane under load impulse. In the present work, effect of pressure on the density and viscosity of lubricant is considered. Finite difference method is used to discretize the governing equations. Multilevel Multi-integration method is used to calculate the elastic deformation. Moreover, Multigrid method is implemented to accelerate the convergence process. Uniqueness of this finite line contact analysis is that it provides an ability to determine the transient behavior of lubricated contact even at the edges of roller. Results show that the load impulse causes squeezing and separation movement within the contact that develops film dimple and pressure ripples at the inlet region, which propagate towards the exit region due to the entrainment motion. It is noticed that the time taken by oil film [Formula: see text] to travel the Hertzian contact width and the time period [Formula: see text] of load impulse decides the behavior of lubricated contacts. Firstly, under a relatively heavy load when the contact width is large enough so that [Formula: see text], then a significant rise in central film thickness (CFT), central minimum film thickness (CMFT) and minimum film thickness (MFT) occurs after the execution of load impulse. Further, under the light load generating a relatively small contact width such that [Formula: see text], then comparatively a small rise in CFT occurs right during the load impulse. Lastly, for a given load if the time period of impulse [Formula: see text] is large enough satisfying the condition [Formula: see text], then a considerable reduction in CFT, CMFT and MFT takes place during the application of load impulse. Moreover, as compare to other cases, for [Formula: see text] the steady state condition is reestablished after a relatively more number of time cycles. It is observed that the maximum pressure and MFT occurs at the contact edges of roller which can be controlled by a proper choice of the radius of end profile [Formula: see text].

Cooperativity Between Zirconium Dioxide Nanoparticles and Extreme Pressure Additives in Forming Protective Tribofilms: Toward Enabling Low Viscosity Lubricants

Realizing the efficiency benefits of low viscosity lubricants requires novel strategies to avoid failures resulting from increased boundary contact. Zirconium dioxide (ZrO2) nanoparticles (NPs) form protective tribofilms through tribosintering at lubricated contacts in pure hydrocarbon base oils, suggesting they hold promise for reducing boundary contact-induced failures. However, their tribological behavior alongside co-additives found in fully formulated oils has not been examined in depth. Here, the macroscopic tribological performance of dispersed ZrO2 NPs (1 wt% loading; 5 nm diameter nearly spherical ZrO2 tetragonal phase NPs with organic capping ligands for oil solubility) with and without the presence of co-additives found in fully formulated commercial gear oils was studied using a mini-traction machine (MTM). The results show that ZrO2 NPs reproducibly develop surface-bound ~ 100 nm thick tribofilms on both contacting surfaces under a wide range of rolling-sliding contact conditions, from 0 to 100% slide-to-roll ratio. Steady-state traction coefficient values of ZrO2 tribofilms formed alongside co-additives (0.10–0.11) do not substantially differ from ZrO2 tribofilms formed in neat polyalphaolefin base oils (0.10–0.13). However, there is improvement in the tribological performance of the contact, with at least a twofold reduction of wear of the steel. This behavior is proposed to be a result of cooperating mechanisms, where the extreme pressure additives adsorbed on the steel surfaces protect them against early adhesive wear, during the time that a protective ZrO2 tribofilm incorporating the co-additives forms on the steel surfaces, preventing further wear.

Tire/road friction prediction: introduction a simplified numerical tool based on contact modelling

The present paper introduces a tire/road friction prediction tool based on modelling the tire/road contact as dynamic, viscoelastic, rough, and lubricated. The tool takes into account a considerable part of influent parameters related to tire, road, contaminant, and contact operating conditions: For the tire, the tool takes into account its geometry and rubber material behaviour. For the road, the texture is taken into account via the surface topography. At the contact interface, dry or wet conditions are taken into account through the lubricant depth, viscosity, and density. The operating conditions are taken into account through the normal load, speed, and slip ratio of the tire. The real novelty of this tool lies in its ability to reproduce the complete curve of the tire/road friction coefficient as a function of the slip rate. The validation of the tool is initially done through parametric studies by analyzing the trends of the results, then by performing braking tests on a passenger car at various speeds on different wet roads with different textures. The tool correctly ranks the peak friction and the sliding friction on these various road surfaces.

A New Progress in Random Hydrodynamic Lubrication for Movable Non-Rotational Curvilinear Biosurfaces with Phospholipid Bilayers

This paper aims to highlight the result of a new progression of mathematical estimation methods of stochastic bio-hydrodynamic lubrication parameters for arbitrary, curvilinear, non-rotational, co-operating, living biological surfaces coated with phospholipid bi-layers. Movable, non-rotational, co-operating surfaces occur in various biological friction nods like the collar bone, the blade bone, the jump joint, and the wrist joint. Specifically, the author presents a synthetic and comprehensive estimation of stochastic bio-hydrodynamic lubrication parameters for co-operating, rotational cartilage bio-surfaces with phospholipid bi-layers occurring in human spherical hip joints and cylindrical elbow joints. The method of research discussed in this paper focuses on a review of stochastic analytical considerations performed by the author. This research is based on the measurements of the gap height between two movable, non-rotational bio-surfaces. The gap is restricted between two co-operating biological surfaces. After several experiments, it could be inferred that there are symmetric as well as asymmetric random increments and decrements in the gap height. Such changes are applicable to the hydrodynamic pressure, load-carrying capacity, friction forces, and wear of the co-operating biological surfaces in human friction nods and contacts. The prime purpose of this paper is to demonstrate the influence of variations in the expected values and standard deviation of the gap height on the hydrodynamic lubrication parameters that occur during the friction process. It can thus be concluded that the apparent dynamic viscosity of biological lubricant varies in the ultra-thin gap height direction, depending on the susceptibility of the superficial layer of the lubricated bio-surface. The results presented in this paper are obtained considering the 3D variations in the dynamic viscosity of the biological fluid, particularly the random variations crosswise the film thickness in non-Newtonian biological fluid properties.

Rolling contact fatigue properties of ultrasonic surface rolling treated 25CrNi2MoV steel under different lubricant viscosities

Ultrasonic surface rolling (USR) treatment was subjected to the 25CrNi2MoV shaft steel surface. The rolling contact fatigue (RCF) properties of treated samples under different lubricant viscosities were investigated. Results showed that the USR treatment significantly refined the surface grains, improved the surface hardness and generated a compressive residual stress (CRS) field in the subsurface layer. Reduced surface roughness changed the lubrication regime between contact pairs and relieved the local surface stress concentration. USR treatment is an effective way to improve the RCF life under high lubricant viscosity. Moreover, the dominant failure mode of USR treated sample was delamination.

Effect of die pressure on the lubricating regimes achieved in wire drawing

An experimental campaign of wire drawing was carried out under different conditions of average die pressure. Experiments were carried out measuring the drawing force and the temperature at the exit of the deformation zone with the use of a thermocouple closely located to the wire-die interface. Dies of three different semi-angles (6°, 7° and 9°), were employed to obtain different values of die pressure, while different lubrication regimes were achieved varying the drawing speed in the range 1–22 m/s. It was demonstrated that lubricating regimes of lower friction coefficient are achieved at smaller values of the drawing speed with increasing the die pressure. Likewise, the hydrodynamic regime arises at lower drawing speeds by increasing the die semi-angle. For example, it was observed that the hydrodynamic regimes developed at 19 m/s for the 6° die but at 15 m/s for the 9° die. This behaviour was correlated to the response of the lubricant viscosity to the die pressure by means of the Hersey analysis. The consequences of this finding on the problem of optimizing the die angle with the objective to reduce the drawing stress are discussed. On this basis, it is shown that the optimum die angle decreases as the drawing speed increases, other things being equal.

Tilting Pad Journal Bearing Misalignment Effect on Thermally Induced Synchronous Instability (Morton Effect)

Abstract This paper investigates the influence of misaligned journal bearing effects on the thermally induced rotor instability (Morton effect “ME”) problem. The Morton effect is caused by uneven viscous heating of the journal in a fluid film bearing, which causes thermal bending, especially in rotors with an overhung disc or coupling weight. The thermally induced bending in the shaft may cause a vibration instability, which results in an excessive level of synchronous vibration. Previous research focused on parametric studies of the rotor and bearing design parameters, including overhung mass, bearing radial clearance, and lubricant viscosity. The present study investigates the influence of journal misalignment on the Morton effect. A coupled fluid-thermal-structural, three-dimensional finite element model (FEM) is developed to simulate fluid film pressures and temperatures, and shaft temperatures and vibrations. Simulations were conducted with different ratios of journal misalignment, and different pad-pivot types to determine their effect on the phenomenon. The simulation results indicate that the amplitude of the misalignment angle affects the instability speed range (ISR) caused by the Morton effect under certain conditions.

Impact factors on lubricant performance of stern bearing with misalignment angle induced by transverse vibration of shaft

The reliability of marine propulsion system is seriously affect by abnormal vibrations of propeller shaft on the lubricated stern bearings. An applicable numerical model regarding the lubricant performance of misalignment bearing induced by the transverse vibration of shaft is proposed. Comparisons with results presented in the literature is conducted to verify the accuracy of present results and demonstrate the applicability of proposed method. The hydrodynamic lubrication including fluid pressure, film thickness, load capacity and its attitude angle, misalignment moment and its attitude angle, end leakage flow rate and frictional coefficient are numerically calculated by solving the Reynolds equation with centered finite difference method. The impact factors of misalignment angle, eccentricity ratio, shaft rotational speed, lubricant viscosity and center-line eccentricity angle on the lubricant performance are investigated with different model parameters. To capture the nature of shaft-bearing interaction, the misalignment angle induced by rotational speed is experimentally obtained. This interaction is simultaneously considered in proposed model to discuss the nonlinear response of the lubricant performance. Therefore, an optimized design for the interaction of marine propeller shaft and oil lubricated stern bearing is realized.