Showing papers in "Tribology Transactions in 2010"
TL;DR: In this article, a model to predict load-dependent (mechanical) power losses of spur gear pairs is proposed based on an elastohydrodynamic lubrication (EHL) model.
Abstract: A model to predict load-dependent (mechanical) power losses of spur gear pairs is proposed based on an elastohydrodynamic lubrication (EHL) model. The EHL model includes gear-specific time variations of all key contact parameters such as the rolling and sliding velocities, radii of curvature, and normal load such that a single continuous analysis of a tooth contact from its root to tip can be performed under any lubrication condition ranging from full-film to mixed EHL or boundary lubrication conditions. Predicted transient pressure and film thickness distributions are used to determine the instantaneous rolling and sliding shear within the lubricant, from which the gear mesh mechanical power losses are determined. Correction factors are introduced for the power losses to account for the thermal effects. The accuracy of the proposed model is assessed through comparisons to published spur gear efficiency experiments. The contribution of the rolling action to the total power loss is quantified to show that ...
117 citations
TL;DR: In this article, the significance of the microdimples parameters, including dimple diameter, depth, and area ratio, to the frictional performance, were evaluated on chromium-coated specimens by through-mask electrochemical micromachining.
Abstract: Surface texturing has proven to be an effective method to improve tribological performance of sliding surfaces. The pattern of microdimples is the most popular surface texture because it is supposed to obtain additional hydrodynamic pressure easily. In order to evaluate the significance of the dimple parameters, including dimple diameter, depth, and area ratio, to the frictional performance, the dimple patterns with dimple diameter from 50 to 300 μm, dimple depth from 5 to 20 μm, and area ratio from 5 to 20% were manufactured on chromium-coated specimens by through-mask electrochemical micromachining. Experiments were designed using an L 16 (4 5 ) orthogonal array, which contained the above three factors and four levels for each factor. The frictional tests on the above-textured specimens against the specimens of cast iron with oil lubrication were carried out under the contact pressures of 0.2 and 1 MPa and sliding velocities of 0.1 s and 0.5 m/s. The range analysis showed that the optimum dimple pattern...
111 citations
TL;DR: In this article, a three-dimensional hydrodynamic lubrication model of the incompressible Newtonian fluid is proposed on the textured surface with a single spherical cap microdimple based on the full Navier-Stokes equation.
Abstract: Surface texturing has been recognized to be very efficient in modifying the tribological performances of sliding surfaces. In the present article, a three-dimensional hydrodynamic lubrication model of the incompressible Newtonian fluid is proposed on the textured surface with a single spherical cap microdimple based on the full Navier-Stokes equation. The three-dimensional pressure field and velocity field of lubrication film are obtained by employing the finite volume method (FVM). The effects of geometric parameters and Reynolds number on pressure field, load-carrying capacity, friction force, and friction coefficient are investigated. Numerical simulation led the authors to conclude that the load-carrying capacity of the lubrication film is monotonously enhanced with increasing microdimple width and Reynolds number, and a reverse tendency is obtained for friction force and friction coefficient. The dimensionless optimum microdimple depth increases with the increase of the width and decreases with the i...
109 citations
TL;DR: In this paper, the authors used a stacked asperity model to predict the contact area as a function of load, which was first introduced by Archard in the early 1990s.
Abstract: Due to the existence of multiple scales of features on surfaces, during the past two decades models have been developed that employ a fractal description of the rough surface profile. Most of these models use a truncation calculation to predict the contact area. The load corresponding to the truncated area of the fractal surface is then calculated using elastic and elastic–plastic asperity contact models. The current work instead uses a stacked asperity model that was first introduced by Archard to predict contact area as a function of load. From this the elastic contact of multiscale rough surfaces can be solved analytically, providing a closed-form solution for certain cases of surface profiles. The results of the model are then compared to a two-dimensional (2D) deterministic model of rough surface contact. Finally, the analytical relationships are used to create models for three-dimensional (3D) elastic and elastic–plastic contact of fractal/multiscale rough surfaces.
87 citations
TL;DR: Biswas et al. as discussed by the authors described the development of alumina-filled glass fiber-reinforced epoxy matrix composites and compared the experimental results obtained from Taguchi experimental design with the reported theoretical erosion model.
Abstract: This article describes the development of alumina-filled glass fiber–reinforced epoxy matrix composites and compared the experimental results obtained from Taguchi experimental design with the reported theoretical erosion model. An exhaustive literature survey indicated that six control factors, viz. impact velocity, filler content, erodent temperature, impingement angle, stand-off distance, and erodent size, predominantly affect on erosion behavior of polymer composites. This systematic experimentation has led to determination of significant process parameters and material variables that predominantly influence the wear rate of different particulates-filled glass fiber–reinforced composites. The comparative study indicates that although the alumina-filled composites exhibit relatively inferior mechanical properties, their erosion wear performance is better than that of the published literature red mud–filled glass fiber–reinforced composites (S. Biswas and A. Satapathy, Materials and Design, vol. 30, 200...
74 citations
TL;DR: In this paper, a three-dimensional numerical model based on minimization of complementary energy was proposed to analyze elastic-plastic contacts, in which the effect of plastic deformation is included by superimposing the plastic residual displacement on the geometry of contacting surface.
Abstract: Elastic-plastic contacts were analyzed by means of a three-dimensional numerical model based on minimization of complementary energy, in which the effect of plastic deformation is included by superimposing the plastic residual displacement on the geometry of contacting surface. The plastic strain increments are determined through the radial return method and J 2 flow theory, which are integrated with the conjugate gradient method (CGM) algorithm and the fast Fourier transform (FFT) technique for improving numerical efficiency. The results from the present numerical model were compared to those from finite element method (FEM) for three typical contacts—i.e., those of a smooth elastic-plastic ball in contact with a rigid body of different geometry: a smooth plane, a plane superposed with a single asperity, and a sinusoidal wave on the plane—which showed persistent good agreement between our model and FEM. Then, three-dimensional elastic-plastic contacts of real engineering surfaces produced by a grinding p...
65 citations
TL;DR: In this paper, a physical model has been developed to understand the relation between parameters that control oil bleeding in rolling-element bearing applications, and the model relates the pressure gradient, oil viscosity, thickener structure deformations, and permeability to the volumetric oil flow out of the network.
Abstract: One of the criteria in selecting lubricating grease for rolling-element bearing applications is its ability to bleed oil, sometimes called “grease bleeding.” Oil bleeding is assumed to be the dominating mechanism supplying new oil to the rolling track for lubrication. In this study, a physical model has been developed to understand the relation between parameters that control oil bleeding. In the model, lubricating grease is described as a porous network, formed by the thickener fibers, that contains the base oil. This type of structure is confirmed by SEM and AFM images of a lithium complex grease showing a matrix of rigid fibers with random orientation. A relatively simple flow model based on Darcy’s law for viscous flow in porous media and an anisotropic microstructure deformation model was developed. The model relates the pressure gradient, oil viscosity, thickener structure deformations, and permeability to the volumetric oil flow out of the thickener network. The permeability depends strongly on the...
60 citations
TL;DR: In this paper, the impact on wet clutch friction versus sliding speed properties of a range of additive solutions as well as a fully formulated automatic transmission fluid (ATF) was measured using a mini-traction machine.
Abstract: For a wet clutch in an automatic transmission to operate efficiently and smoothly, it is essential that the friction in the clutch contact be high over the whole sliding speed range and also increase with sliding speed. This is achieved by careful design, both of the friction disc material and morphology and of the automatic transmission fluid. This article describes the development and use of a new test rig, based on a mini-traction machine (MTM), to measure the impact on wet clutch friction versus sliding speed properties of a range of additive solutions as well as a fully formulated automatic transmission fluid (ATF). It is found that most organic friction modifiers reduce friction at low sliding speed, whereas succinimide dispersants and some sulfonate detergent additives raise friction over the whole speed range. Overbased and neutral detergents give almost identical friction curves, indicating that, although a calcium carbonate film is deposited on the steel ball when overbased detergent is present,...
58 citations
TL;DR: In this paper, a diamond-like carbon (DLC) coating was applied to a bucket tappet and a motored valve train test was conducted to evaluate its performance in the absence of any lubricants.
Abstract: The friction and wear characteristics of thin diamond-like carbon (DLC) coatings have been investigated extensively in recent years mostly in laboratory bench tests. These coatings are known to provide significant friction reduction in the absence of lubricants. In the presence of lubricants, the friction benefits of these coatings are not clearly demonstrated. The current investigation is focused on exploring the friction reduction potential of a DLC coating obtained from a supplier in laboratory bench tests and in a motored valve train test. The DLC coating was deposited on the bucket tappet. In laboratory bench tests, results showed significant friction reduction in the absence of any lubricant but not in the presence of engine oil. In motored valve train tests a significant reduction in friction torque was observed when compared against a slightly rougher uncoated bucket, but no reduction was observed when compared against uncoated bucket tappet with comparable surface finish. Under boundary lubricati...
54 citations
TL;DR: In this article, a model is presented that makes it possible to predict temperature distributions in high-speed thrust ball bearings, and the predicted temperature distributions appear as very sensitive to the relative importance given to hydrodynamic rolling tractions or drag losses.
Abstract: In high-speed rolling element bearings (REB), the lubricant is used to separate the mating surfaces but also to cool down the parts while the system is in operation. In the context of optimizing oil circuits, a clear understanding of the lubricant cooling mechanisms is therefore required in order to reach a compromise between a good cooling capacity and the constraints on mass, size, and power. In this article, a model is presented that makes it possible to predict temperature distributions in high-speed thrust ball bearings. It is found that the prediction or measurement of global power loss cannot discriminate between several combinations of traction and drag forces. On the other hand, the predicted temperature distributions appear as very sensitive to the relative importance given to hydrodynamic rolling tractions or drag losses. Based on these findings, a methodology is suggested in order to define the most realistic power loss models to be used in high-speed REB simulations.
51 citations
TL;DR: In this article, an optical interferometric technique has been used to investigate fluid film thickness in sliding, isoviscous elastohydrodynamic contacts (I-EHL).
Abstract: An optical interferometric technique has been used to investigate fluid film thickness in sliding, isoviscous elastohydrodynamic contacts (I-EHL). Monochromatic two-beam interferometry has been employed to map lubricant film thickness across a range of applied loads and entrainment speeds. The contact was formed between an elastomer sphere and plain glass disc, illuminated under red light, λ= 630 nm. Experimental work has employed sunflower oil and glycerol/water solutions as the test lubricants, due to their similar refractive indices and varying viscosity. A black-and-white-image-intensified camera has been employed to capture interference images and a computer processing technique used to analyse these images, pixel by pixel, and create film thickness maps based on their gray-scale intensity representations. Comparison of film thickness results to theoretical models shows reasonable qualitative agreement. Experimental results show both a reduced horseshoe, which is limited to the rear of the contact, a...
TL;DR: In this paper, the authors provided some relevant statistical parameters for mechanical seal faces and presented some methods of modelling them in order to study mixed lubrication, including surface roughness and waviness.
Abstract: The aim of this article is to provide some relevant statistical parameters for mechanical seal faces and to present some methods of modelling them in order to study mixed lubrication. Three mechanical seals with faces of three different material combinations were analyzed at three operating times (unused, run-in, and worn). Surface roughness and waviness were analyzed. Generally speaking, the amplitude of the waves tends to increase with time, whereas roughness height shows the opposite trend, except in the case of the hard faces combination. The seal surfaces are extremely skewed, this phenomenon being enhanced by wear. The surfaces are nearly isotropic with a slightly higher correlation length in the sliding direction. Two models with two different autocorrelation functions (ACFs) were used to simulate surfaces. These models, based on the Patir approach (Patir (1)), used the Johnson translation curves to impose non-Gaussian height distribution. Even if the models are able to reproduce experimental tende...
TL;DR: In this paper, a simplified fluid mechanics-based model is proposed to predict windage power loss of a spur gear pair operating under jet lubrication conditions, which is defined as the sum of the losses associated with the interactions of individual gears with the air or air-oil mixture and the losses due to pocketing/squeezing of the same medium at the gear mesh interface.
Abstract: This article proposes a simplified fluid mechanics–based model to predict the windage power loss of a spur gear pair operating under jet lubrication conditions. In this model, the total windage power loss is defined as the sum of (a) the losses associated with the interactions of individual gears with the air or air–oil mixture and (b) the losses due to pocketing/squeezing of the same medium at the gear mesh interface. The first group of losses is modeled through a formulation for air drag forces induced on each rotating gear body along its faces and periphery (circumference). The pocketing power loss is modeled analytically through a compressible fluid flow formulation. The windage power loss model predictions are compared to published gear pair windage experiments and empirical formulae to assess their accuracy. Results of a parametric study are also presented to quantify the impact of key system parameters as well as individual contributions of each component to the total windage power loss.
TL;DR: In this article, the friction and wear properties of PTFE/PEEK composites filled with potassium titanate whisker (PTW) or short carbon fiber (CF) at elevated temperatures (160, 180, 200, 220, and 240°C), different loads (100 and 200 N), and various sliding velocities (0.7 and 1.4 m/s) were investigated.
Abstract: The friction and wear properties of PTFE/PEEK composites filled with potassium titanate whisker (PTW) or short carbon fiber (CF) at elevated temperatures (160, 180, 200, 220, and 240°C), different loads (100 and 200 N), and various sliding velocities (0.7 and 1.4 m/s) were investigated in this article. The results show that the friction coefficient of PTW/PTFE/PEEK composites is more stable and 30% lower than that of CF/PTFE/PEEK composites at various sliding conditions. Moreover, it is found that the wear rate of PTW-filled PTFE/PEEK composites is only 10 to 40% that of CF/PTFE/PEEK composites. The wear rate of PTW/PTFE/PEEK composites is only 20% of CF/PTFE/PEEK composites at 200 N, 1.4 m/s, and 240°C. Scanning electron microscopy (SEM) study reveals that PTW can reduce the adhesive wear of PTFE/PEEK composites.
TL;DR: In this paper, the efficacy of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles as engine oil friction modifier additive was investigated using a high-stroke reciprocating piston ring-cylinder bore bench test system.
Abstract: The efficacy of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles as engine oil friction modifier additive was investigated using a high-stroke reciprocating piston ring–cylinder bore bench test system. Frictional characteristics of various IF-WS2 nanoparticle concentrations in mineral oil were experimentally analyzed in simulated engine conditions controlling oil temperature, speed, and normal load. Though the effect of IF-WS2 nanoparticles on piston ring and cylinder bore friction was minor in low concentrations, after a running period in a mixed lubrication regime with 10% additive, a considerable reduction in friction coefficient was observed when the IF-WS2 formulated oil was used. This reduction remains to some extent with reference mineral oil after solvent cleaning of the mating components. The results show that a thin tribofilm gradually forms on the piston ring and the cylinder bore surfaces, reducing the friction coefficient in a mixed lubrication regime. However, in order to...
TL;DR: In this article, a plane contact tribometer was used to study powder lubrication and four kinds of powders (polytetrafluoroethylene (PTFE), graphite, MoS2, and ball-like copper) were used during the experiments.
Abstract: Powder lubrication has been studied using a plane contact tribometer. Four kinds of powders—polytetrafluoroethylene (PTFE), graphite, MoS2, and ball-like copper—were used during the experiments. The results show that powder can be introduced into frictional clearance without any special treatment. The powder's physical properties significantly influence the tribological characteristics in the powder lubrication. The friction coefficient and wear are obviously decreased when the powders are PTFE, graphite, and MoS2, which are excellent solid lubricants. At lower load capacity, powder lubrication using ball-like copper had certain antifriction effects, but it rapidly became worse with increasing load capacity. Observation with optical microscopy showed that the lubricant film is dynamically formed on the rubbing surfaces in most experiments.
TL;DR: In this paper, the wear behavior of aluminum silicon alloy and its composites reinforced with graphite particulates (3 wt. %) fabricated using a stir casting route were examined.
Abstract: In the present investigation, wear behavior of aluminum silicon alloy and its composites reinforced with graphite particulates (3 wt. %) fabricated using a stir casting route were examined. In order to improve the wettability of graphite with matrix alloy, graphite particulates were separately ball milled with 2% Cu and 2% Ni by weight percentage, preheated to 400°C, and incorporated into the molten metal. The uniform distribution of graphite particulates was observed in the microstructural investigation of developed composites, which resulted in more wear resistance than that of the matrix alloy. Scanning electron microscopic analysis of wear surface and wear debris supported the wear behavior of both the matrix alloy and the composites.
TL;DR: In this article, a mathematical optimization method for logarithmic profiles in roller bearing applications is proposed, and rolling contact fatigue life tests are carried out to make a comparison among log-arithmically crowned, standard partially crowned, and modified partially crowned rollers.
Abstract: A logarithmic profile is essentially an optimal geometry for rolling machine elements such as bearing rollers and raceways. Under most conditions of loading, it yields lower stresses to give longer endurance. Lundberg first suggested the basic profile, and some researchers followed him by modifying it to satisfy engineering requirements. In this article, the authors propose a mathematical optimization method for logarithmic profiles in roller bearing applications. Moreover, rolling contact fatigue life tests are carried out to make a comparison among logarithmically crowned, standard partially crowned, and modified partially crowned rollers. Results show that the logarithmically crowned rollers are beyond the modified partially crowned rollers in fatigue life, especially in poor lubrication conditions, although the logarithmic rollers require less workload to process the crowning.
TL;DR: In this article, the rolling contact fatigue (RCF) performance of vibro-mechanical textured surfaces in a point elastohydrodynamic lubrication (EHL) condition is investigated.
Abstract: The rolling contact fatigue (RCF) performance of vibro-mechanical textured surfaces in a point elastohydrodynamic lubrication (EHL) condition is investigated. Two dimple designs, small (100 μ m × 100 μ m) and large (240 μ m × 100 μ m), are compared with a nontextured sample. Experimental RCF tests show that the textured surfaces exhibit a significantly reduced number of cycles to failure compared with the nontextured sample for the high load, pure rolling conditions evaluated. In order to understand these results, numerical models are used to calculate the lubrication and contact pressure conditions and the subsurface stress distribution. The fatigue failure trends observed experimentally are compared with the simulation results with good agreement. It is determined that RCF performance is related to the presence and size of the generated dimple.
TL;DR: In this paper, the authors introduced TiO2 and SiO2 nanoparticles into hybrid polytetrafluoroethylene (PTFE)/Kevlar fabric/phenolic composites.
Abstract: TiO2 and SiO2 nanoparticles were introduced into hybrid polytetrafluoroethylene (PTFE)/Kevlar fabric/phenolic composites. The results showed the incorporation of TiO2 nanoparticles can reduce the wear rate of the fabric/phenolic composite at elevated temperatures, although the wear of hybrid PTFE/Kevlar fabric/phenolic composite did not change much when TiO2 or SiO2 nanoparticles were used as filler. The wear behavior was explained in terms of morphology of transfer films and worn surfaces. There was a good correlation between the morphology of transfer film and wear results.
TL;DR: In this paper, laser surface texturing and surface molybdenizing duplex treatment was performed on Ni-base alloy in order to improve its wear resistance at high temperature.
Abstract: Laser surface texturing (LST) and surface molybdenizing duplex-treatment was performed on Ni-base alloy in order to improve its wear resistance at high temperature. Surface molybdenizing was performed on the laser surface textured Ni-base alloy by a double glow plasma surface alloying technology. The friction and wear properties of the duplex-treated, the single-treated, and the untreated alloys were tested on a ball-on-disk tribometer by rubbing against an alumina ceramic ball from room temperature to 600°C. The topography of the laser surface textured dimples was measured by a white light interferometer and optical microscope. The dimples are 150-200 μ m in diameter and 45-50 μ m in depth. The distance between the dimples is 500 μ m. The molybdenized layer is approximately 20 μ m in thickness. The elastic modulus of Ni-base alloy is improved by molybdenizing. After texturing and the molybdenizing duplex treatment, the friction coefficient of the Ni-base alloy decreases from 0.38 to 0.26 at room temperat...
TL;DR: In this paper, the tribological behavior of superelastic TiNi alloy was studied and compared to Ni, Ti, and AISI 304 stainless steel using dry sliding wear and friction tests.
Abstract: It has been established that the superelastic effect of TiNi alloy is related to a reversible martensitic transformation; that is, stress-induced transformation. The high elastic recovery of TiNi alloy has made it a potential candidate for high wear resistance applications. In the present study the tribological behavior of superelastic TiNi alloy was studied and compared to Ni, Ti, and AISI 304 stainless steel using dry sliding wear and friction tests. The effect of normal load and testing temperature on superelasticity has been investigated. It has been found that although AISI 304 stainless steel and superelastic TiNi alloy have similar hardness, TiNi exhibits superior wear resistance. The wear rate of AISI 304 stainless steel is over four times higher than TiNi. The superior wear resistance of TiNi and the effect of load and temperature on wear were discussed and related to the reversible martensitic phase transformation, as well as self-accommodation and stabilization of martensite.
TL;DR: In this paper, the authors used microparticle image velocimetry to study the behavior close to the boundary where wall slip effects are shown to be present, where three greases with different consistencies (NLGI00, NLGI1, and NLGI2) and three wall materials (steel, brass, and polyamide) with different surface roughness were used.
Abstract: The grease flow in a rectangular channel is investigated using microparticle image velocimetry. Of certain interest is to study the behavior close to the boundary where wall slip effects are shown to be present. Three greases with different consistencies (NLGI00, NLGI1, and NLGI2) have been used, together with three wall materials (steel, brass, and polyamide) with different surface roughness. The pressure drop is also varied. It is shown that the velocity profile is strongly dependent on the consistency, having a dominating plug flow structure for a stiff grease. Furthermore, it is shown that wall slip effects occur in a thin shear layer close to the boundary where a very large velocity gradient is present. An analytical solution for the velocity across the channel is described using a Herschel-Bulkley rheology model. The model fits well with the measured velocity profile for all three above-mentioned greases.
TL;DR: In this paper, the authors conducted fatigue tests in hydrogen and air at a contact pressure of below 42 GPa, corresponding to the basic static load capacity in rolling contact bearing using the four-ball tester.
Abstract: Rolling contact fatigue tests were conducted in hydrogen and air at a contact pressure of 41 GPa, below 42 GPa, corresponding to the basic static load capacity in rolling contact bearing using the four-ball tester The lubricating conditions employed were partial and full elastohydrodynamic lubrication (EHL) The results were compared with those at 56 GPa above the basic static load capacity in a previous paper (Endo, et al (1)) Rolling fatigue occurred in hydrogen but did not occur in air regardless of lubricating conditions In hydrogen, a crack was initiated in the subsurface under partial EHL conditions and at or in the vicinity of the surface under full EHL conditions On the other hand, at 56 GPa, a crack was initiated at the surface under partial EHL conditions and in the subsurface under full EHL conditions In a hydrogen environment, the fatigue life in a rolling contact was confirmed to be significantly shortened compared with that in air The decrease in fatigue life and the difference in
TL;DR: In this article, an ANN model based on data obtained from experiments performs self-learning by updating weightings and repeated learning epochs to predict the solid particle erosion wear response of a new class of metal-ceramic coatings.
Abstract: This article proposes the application of an artificial neural network (ANN) to a Taguchi orthogonal experiment to develop a robust and efficient method of analyzing and predicting the solid particle erosion wear response of a new class of metal–ceramic coatings. An ANN model based on data obtained from experiments performs self-learning by updating weightings and repeated learning epochs. In this work, plasma-sprayed coatings of fly ash premixed with aluminum powder in different weight proportions are deposited on aluminum substrates at various input power levels of the plasma torch. Erosion wear characteristics of these coatings are investigated following a plan of experiments based on the Taguchi technique, which is used to acquire the erosion test data in a controlled way. The study reveals that the impact velocity is the most significant among various factors influencing the wear rate of these coatings. An ANN approach is then implemented taking into account training and test procedure to predict the ...
TL;DR: In this paper, the wear behavior of metal-impregnated carbon materials (MIC) and carbon-carbon composites (C-C) was investigated using a self-made current-carrying wear tester producing an electrical current of 40-160 A and a contact speed of 10-50 m/s.
Abstract: In this article, the wear behavior of metal-impregnated carbon materials (MIC) and carbon–carbon composites(C-C) was investigated using a self-made current-carrying wear tester producing an electrical current of 40–160 A and a contact speed of 10–50 m/s. The worn surfaces were observed by means of scanning electron microscopy (SEM), and a new parameter for current-carrying stability that describes the stability of the current as a function of wear was proposed. The results indicate that the wear rate of both materials tested increased with either an increase in electrical current or contact sliding speed. Compared to the metal-impregnated carbon material, the C-C composite material not only displayed superior wear resistance but superior current-carrying stability as well. With increasing electrical current, the current-carrying stability of the two materials changed within a narrow range at a speed of 20 m/s and decreased at a speed of 50 m/s. Wear failure was mainly due to electrical erosion occurring a...
TL;DR: In this article, the contact between a steel ball and a glass disc over an entrainment speed ranging from 0.05 m s−1 to 20 m s −1 was studied.
Abstract: At very high speeds, elastohydrodynamic (EHD) films may be considerably thinner than is predicted by classical isothermal regression equations such as that due to Dowson and Hamrock. This may arise because of viscous dissipation, shear thinning, frictional heating or starvation. In this article, the contact between a steel ball and a glass disc over an entrainment speed ranging from 0.05 m s−1 to 20 m s−1 was studied. Two sets of tests were performed. In the preliminary testing, the disc was driven at speeds of up to 20 m s−1 and the ball was driven by tractive rolling against the disc, its speed being determined using a magnetic method. After all possible explanations for the reduction in film thickness at high speeds were considered, it was shown that the results, which fall well below classical predictions, are consistent with inlet shear heating at the observed sliding speeds. Another set of tests was then performed, with both disc and ball driven separately, so that the accuracy of the shear heating ...
TL;DR: In this paper, the effect of both static and dynamic deformations of the bearing liner on the dynamic performance characteristics and stability of a water-lubricated, rubber-lined journal bearing operating under small harmonic vibrations is theoretically investigated.
Abstract: In this article, the effect of both static and dynamic deformations of the bearing liner on the dynamic performance characteristics and stability of a water-lubricated, rubber-lined journal bearing operating under small harmonic vibrations is theoretically investigated. To take into account the dynamic deformations of the bearing liner, the first-order perturbation technique is used to determine the eight dynamic coefficients for a given excitation frequency value. The static and dynamic deformation of the fluid/bearing-liner interface is assumed to be proportional to the steady-state and dynamic fluid-film pressures. It was found that the dynamic properties and stability of the compliant finite-length journal bearing are affected by surface coatings from soft materials. It was also shown that when dynamic deformations are considered in the calculations, the dynamic coefficients depend on the excitation frequency, especially for higher values of this parameter. Moreover, the two cross-damping coefficients...
TL;DR: In this paper, the authors present the phenomenon of micro-sliding within the ball bearing contact zone, the parameters that impact its generation, and the extent and the impact of micro sliding on bearing life.
Abstract: Micro-sliding within the contact ellipse of high-speed ball bearings is a tribological phenomenon that occurs in large, high-speed aircraft turbine engine ball bearings that should be taken into consideration in the design of high-speed ball bearings. This article presents the phenomenon of micro-sliding within the ball bearing contact zone, the parameters that impact its generation, and the extent and the impact of micro-sliding on bearing life. Micro-sliding, especially under poor lubrication conditions, superimposes shear stresses into the contact area surface, which move the depth of maximum stress toward the surface. Whenever there is micro-sliding rather than rolling, there is superimposed frictional heating within the contact ellipse. This localized heating can degrade or break down the oil film, which leads to even more local friction and more local heat generation. The effects from the increased local stressing near the surface combined with the local degradation of the material fatigue strength ...
TL;DR: In this paper, the authors investigated the unlubricated tribological behavior of silicon nitride-boron nitride (Si 3 N 4 -hBN) composites with two test modes in air by using a pin-on-disc tribometer.
Abstract: Unlubricated tribological behaviors of silicon nitride–boron nitride (Si 3 N 4 -hBN) composites were investigated with two test modes in air by using a pin-on-disc tribometer. Under upper-disc-on-bottom-pin test mode, the addition of hBN to Si 3 N 4 resulted in a significant decrease of the friction coefficient, from 0.54 for Si 3 N 4 against Si 3 N 4 to 0.19 for Si 3 N 4 -20% hBN against Si 3 N 4 . The surface analysis indicated that a tribochemical film consisting of SiO2 and H 3 BO 3 was formed on the wear surfaces. The formation of tribochemical film might be attributed to the embedment of wear debris into the spalling pits on the wear surfaces of Si 3 N 4 -hBN specimen. The wear debris reacted with moisture in air, and the resultant tribochemical film lubricated the wear surfaces. Under upper-pin-on-bottom-disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. A slight decrease of the friction coefficient, from 0.85 for...