Accurately predicting the performance of lubricated rolling elements is critical for certain key bearing applications. A widely employed simulation technique is quasi-static models, which although ...computationally efficient to implement, lack accuracy in predicting the kinematics of bearing components. This problem arises from their construction under kinematic assumptions, instead of solving the kinematic based on real frictional interactions. This paper presents a quasi-static model based on the minimum energy hypothesis for lubricated contacts, which determines the kinematic of the ball considering the effects of the frictional interactions governed by the elastohydrodynamic lubrication mechanism. The influence of kinematic variables on the sliding patterns and power loss distribution of the contact are analysed. The results are compared with other published quasi-static models, revealing substantial differences. The influence of the kinematic hypotheses on power losses are also studied at a bearing component scale. Finally, the effect of the governing lubrication mechanism of the contact is discussed, concluding that the limiting shear stress of the lubricant and the centrifugal forces have a significant effect on the kinematic of the ball.
•Development of a semi-analytical quasi-static model of ball-raceway contacts based on the minimum energy hypothesis.•Analysis of the influence of the pitch angle and pure rolling line locations on the contact kinematics and power losses.•Analysis of the impact of the working conditions on the pitch angle and comparison to literature models.•Study of the governing lubrication mechanism on kinematic and power loss behaviour.•Theoretical demonstration of the transition between inner and outer control raceway hypothesis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Many engineering estimates of the film thickness in the concentrated contacts of real machines have come from extrapolations of measurements of elastohydrodynamic lubrication film thickness performed ...in glass on steel elastohydrodynamic rigs. Such estimates are likely to have large errors due to shear dependence of viscosity. The classical film thickness formulas employed have not been validated except for some Newtonian reference liquids at room temperature because the real pressure-viscosity response measured in viscometers has been ignored. A blend of polyalpha olefin base oils with mild shear-thinning has been employed in a line contact calculation to assess the effects of shear-dependent viscosity on the power-law exponents of the classical film thickness formula. The exponents on the pressure-viscosity coefficient and on the elastic modulus of the solids are not sensitive to the non-Newtonian effect. The exponents on ambient pressure viscosity and velocity are slightly reduced by shear-thinning. The exponents on pressure and scale are substantially increased by the shear dependence. The usual practice of measuring film thickness in an elastohydrodynamic rig to obtain an effective “
α
-value” to use in a classical Newtonian film thickness formula will overstated the film thickness of a liquid which is shear dependent in the elastohydrodynamic lubrication inlet.
The current paper is aimed to investigate the deformability effects of the bearing surface on the lubrication performance of cylindrical journal bearing with finite length under turbulent conditions. ...The bush is coated with a thin resilient layer with a smooth surface, the radial distortions of which are of the same order of magnitude as the film thickness. The elastohydrodynamic problem is studied under elasticity conditions in accordance with the plain strain hypothesis (Winkler model). The modified Reynolds equation is carried out on the base of the turbulent lubrication model of Hirs (bulk flow model). The partial differential equation is solved numerically by successive over-relaxation technique on a finite difference grid, considering different values of coating materials, lubricant viscosity, and journal speed. Results for the performance characteristics of the bearing are given for several selected values of Reynolds number and elasticity parameters of the soft liner on the bush.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Grease lubrication is widely used in rolling element bearing because of its special rheological characteristics. Available studies are mainly based on experiments, while the relevant numerical ...studies of grease are quite limited. The purpose of this article is to establish a mixed elastohydrodynamic lubrication (EHL) model in point contact based on the rheological model of grease, which can calculate film thickness distribution applied to smooth and roughness surface. The obtained result is compared with that of it operated only in base oil. Besides, the impacts of load, surface roughness and rheological parameters on the grease film thickness have been investigated. In addition, the Stribeck curves of four greases covering different base oil viscosity and thickener types were measured on a ball-on-disc device, which can ensure that the contact area was in full film lubrication. From the study, it is concluded that the obtained grease friction behavior agrees well with the variation of grease film thickness calculated by the present mixed EHL model.
•A grease EHL numerical model considering surface roughness was established.•The obtained grease friction behavior agrees well with the variation of grease film thickness calculated by the present mixed EHL model.•Film thickness will be thicker when greases have high base oil viscosity, but thinner when greases take on low base oil viscosity property.•For grease lubrication studied here, the stronger the non-Newtonian characteristics, the smaller film thickness will form.•The contact ratio increases as the surface roughness increases, while the film thickness ratio decreases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In order to investigate the interaction effect between the transient wear behavior and the lubrication characteristics of the main bearing in low-speed diesel engine under the actual working ...condition, a coupling model of mixed elastohydrodynamic transient lubrication and time-varying wear is constructed. The transient lubrication model considering the journal misalignment and elastic-plastic asperity contact is used to consider the lubrication characteristics of the main bearing. The wear mechanism of the main bearing material (Babbitt alloy) is found to be surface fatigue wear mainly by the experiments under the equivalent lubrication state, thus the wear model is based on the fatigue damage theory. Several experiments were conducted to verify the accuracy of the coupled model. It is found that the wear gradually increases with increases with wear time, and meanwhile, the lubrication characteristics also change with the wear status. In addition, the effect of the parameters including radius clearance, rotation speed, journal misalignment and bearing loads on the properties of lubrication and wear were investigated. This work would provide practical support for the investigation of wear and lubrication behavior under actual low-speed diesel engine operation.
•A coupling analysis model of mixed elastohydrodynamic transient lubrication and time-varying wear of the main bearing under actual dynamic load was established.•The wear mechanism of the main bearing material is found to be surface fatigue wear mainly by the experiments under the equivalent lubrication state of actual condition in low-speed diesel engine.•The verifications of axis orbit, friction coefficient and wear depth indicate the accuracy of the coupling model.•The improvement of bearing lubrication performance after stable wear under actual working conditions was revealed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An approach for mixed elastohydrodynamic lubrication (EHL) analysis of line contact with non-Gaussian rough surface is proposed, and a minimum film thickness formula is derived based on the ...simultaneous solutions. The Patir and Cheng's average flow model and Kogut and Etsion's rough surface contact model is used to obtain hydrodynamic pressure and asperity pressure. The effect of non-Gaussian rough surface on pressure, film thickness and asperity-to-total load ratio are studied. It is observed that the influence of kurtosis on pressure and film thickness is slight. Both skewness and kurtosis have strong effect on asperity-to-total load ratio. Lastly, a minimum film thickness is derived and expresses as a function of dimensionless load, speed, material, standard deviation and skewness.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
7.
Bearings for aerospace applications Rejith, R; Kesavan, D.; Chakravarthy, P ...
Tribology international,
March 2023, 2023-03-00, Volume:
181
Journal Article
Peer reviewed
Rolling element bearings are the most critical parts of any rotary mechanism. One of the challenges in any bearing design is to minimize the friction and maximize life for a particular service ...environment. For critical aerospace systems such as jet/liquid rocket engines, bearings are the key to improving performance benchmarks. Though bearings are a common machine element, literature related to criticality of bearings used in aerospace industries is very limited. The selection of precision class of bearings, surface finish and overall quality of critical contact surfaces in bearings, lubricant selection, lubrication scheme, processing of bearings, integration into mechanisms have been discussed in this review. A glimpse of emerging technologies in active bearing systems and smart bearing solutions has been included.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Dry and lubricated highly deformed contacts appear in engineering, physics, and bio-(fluid)mechanics, with increasingly many applications where the soft materials can exhibit viscoelastic behaviour. ...In this work, the viscoelastic solid lubricated point contact problem has been studied theoretically and experimentally. An efficient visco-elastohydrodynamic lubrication (VEHL) numerical algorithm has been developed by implementing a novel viscoelastic deformation equation. The relevant dimensionless parameters of the VEHL problem are identified and a parameter study is presented showing the effect of solid viscoelasticy on the pressure and film thickness in the conjunction. In addition experimental results are presented for film thickness measurements in configurations of a PMMA ball rolling against a glass disc, and a steel ball rolling against a glass disc using optical interferometry. Finally the scaling of the pressure and film profiles in the inlet and outlet regions to the contact have been studied, investigating self similarity of the pressure and film solution in these regions. The results presented provide a good framework for the understanding and interpretation of viscoelastic solid effects on the film and pressure behavior in highly deformed (soft) lubricated contacts.
•Lubricated soft contact problem is studied theoretically and experimentally.•An efficient visco-elastohydrodynamic lubrication (VEHL) algorithm has been developed.•Soft EHL film thickness is measured using optical interferometry.•Scaling of pressure and film profiles is explored.•Viscoelastic modeling and numerical methods are reviewed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Various methods for calculating the capacitance of unloaded rolling elements are compared to improve the electric characterization of rolling element bearings. Semi-analytical approximations and ...finite element simulations are applied and a closed-form analytical two-dimensional solution is derived for comparison. The results show that the most common semi-analytical approximation, which uses effective radii to express the contact geometry, reproduces the trend from numerical and analytical calculations, but overestimates the results derived from numerical simulations. Another semi-analytical approach is presented that delivers better results for the capacitance of unloaded point contacts.
•Comparison of possible methods to calculate the capacitance of unloaded rolling elements: semi-analytical and numerical methods.•Derivation of an analytic 2D formula for calculating the capacitance per length unit of an unloaded ball-raceway contact.•Comparison of multiple interpretations of the semi-analytical capacitance calculation.•Including the rim area aside of the groove into the capacitance calculation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present paper describes an experimental setup and an associated calculation procedure in order to measure and predict the electric impedance of rolling bearings, in order to use it as a sensor ...model for measuring bearing loads. Based on the state of research, relevant influences on the electric impedance of a rolling bearing are not taken into account in the models known to the author. These influencing factors are added by an approach which takes unloaded rolling elements and the undeflected area of loaded rolling elements into account. A comparison between experimental results and the adapted theory shows that the consideration of unloaded rolling elements in the bearing model improves the predictions made compared to the state of the art. Nevertheless a difference between measurement and calculation remains, which is addressed by pointing out approaches to further reduce this discrepancy.
•Consideration of unloaded rolling elements in the electric model of rolling bearings.•Validation of the improved electric model.•Suitability evaluation as a model for force measurement.•Notes on further influencing factors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
