Accepted Manuscripts

Mo Jintao, Gu Chaohua, Pan Xiaohong, Zheng Shuiying and Ying Guangyao
J. Tribol   doi: 10.1115/1.4036835
The transient simulation of the journal bearing temperature in the internal gear pumps is hard due to the complicated shaft motion caused by the complicated loads. In this paper, a thermo-hydrodynamic analysis method, based on dynamic mesh techniques, is presented with the application of the general CFD code Fluent. This method can simulate the complex whirling orbit induced temperature variation in internal gear pumps and has taken into account the conduction in the rotating and orbiting rotor of a hydrodynamic bearing. A test rig has been built according to the structure of an internal gear pump to carry out the validation. The results show that the model is reliable. The relationship between bearing temperature, leakage and axial clearance in the internal gear pump has been studied. It is found that the bearing temperature will decrease slightly while the leakage increases heavily with larger axial clearance. A thermo-hydrodynamic analysis of the self-lubricating bearing in the internal gear pump has been done based on this method. The results show that the pressure profile changes regularly with the whirling motion of the journal while the whirling motion has little effect on the distribution of the temperature. Besides, the increase of the whirling radius will result in the decrease of the pressure profile and the increase of the temperature profile.
TOPICS: Gear pumps, Bearings, Computational fluid dynamics, Thermohydrodynamics, Temperature, Whirls, Leakage, Pressure, Clearances (Engineering), Transients (Dynamics), Heat conduction, Simulation, Stress, Journal bearings, Rotors, Temperature profiles
Ibrahim N. Yildiran, Ilker Temizer and Barbaros Cetin
J. Tribol   doi: 10.1115/1.4036770
The form of the Reynolds-type equation which governs the macroscopic mechanics of hydrodynamic lubrication interfaces with a microscopic texture is well-accepted. The central role of the ratio of the mean film thickness to the texture period in determining the flow factor tensors that appear in this equation had been highlighted in a pioneering theoretical study through a rigorous two-scale derivation (G. Bayada and M. Chambat, J. Tribol. 110:402-407, 1988). However, the resulting homogenization theory still remains to be numerically investigated. For this purpose, after a comprehensive review of the literature, three microscopic regimes of lubrication will be outlined and the transition between these three regimes for different texture types will be extensively demonstrated. In addition to conventional textures, representative re-entrant textures will also be addressed.
TOPICS: Lubrication, Texture (Materials), Tensors, Film thickness, Flow (Dynamics)
Auezhan Amanov, Bakhtiyor Urmanov, Ki-Chol Kim and Young-Sik Pyun
J. Tribol   doi: 10.1115/1.4036721
This paper deals with the improvement in surface properties and micro-scratch resistance of graphites by means of an ultrasonic nanocrystalline surface modification (UNSM) technique. The surface roughness and surface hardness of the untreated and UNSM-treated graphites were investigated using an atomic force microscopy (AFM) and a micro-hardness tester, respectively. The scratch resistance was assessed using a micro-scratch tester at a progressive load. Moreover, a Raman spectroscopy was employed to characterize the microstructure of graphites before and after UNSM treatment. The scratch test results revealed that the resistance to scratch of both UNSM-treated graphites was found to be better in comparison with the untreated graphites. The increase in scratch resistance of both UNSM-treated graphites may be mainly attributed to the reduced surface roughness and increased surface hardness by UNSM treatment. The graphite produced by Poco exhibited a higher resistance to scratch compared to that of the graphite produced by Mersen. The objective of this study is to extend the service life of 3D cover glass moldings made of graphite by the application of UNSM treatment through the understanding the effects of surface roughness and surface hardness on the scratch defect generation behavior during glass molding process.
TOPICS: Molding, Graphite, Surface roughness, Glass, Atomic force microscopy, Raman spectroscopy, Service life (Equipment), Stress, Microhardness, Surface properties
Er-Hui Zhao, Biao Ma and He-yan Li
J. Tribol   doi: 10.1115/1.4036720
This work is devoted to investigate the effects of thermal buckling on the tribological characteristics of a Cu-based wet clutch by artificially modifying friction pairs into different contact ratios. A thermal lubrication model is provided, and corresponding experiments are conducted on the wet clutch comprehensive test bench. The friction results from measurements and simulations for such modified friction pairs are analyzed. The results show that, as the contact ratio reduces, surface temperature rises obviously, and friction coefficient increase dramatically, so local friction torque and total output torque grow significantly. In addition, the vibration of the output torque becomes more severe as the contact ratio reduces. Therefore, the non-uniform contact after thermal buckling exacerbates the friction characteristics of friction pairs severely, and accelerates the failure of wet clutches.
TOPICS: Tribology, Friction, Disks, Torque, Buckling, Failure, Lubrication, Temperature, Simulation, Engineering simulation, Vibration
Imran Jamadar and Dipakkumar Vakharia
J. Tribol   doi: 10.1115/1.4036630
This paper presents mathematical expressions to identify the existence of localized surface defects on the raceways of the deep groove ball bearings. For the formulation of the mathematical expressions, matrix method of dimensional analysis based on FLT? system of unis is used. The model is based on the complete set of physical dimensions and operating parameters of the deep groove ball bearing in that the spall size is directly allied with vibration responses. The formulated governing model equations are solved numerically applying a scheme of empirical modeling through multiple factorial regression analysis. Experiments are performed on the laboratory test rig to verify the results obtained from the developed model equations. For the experiments deep groove ball bearings designated as SKF 6307 are used. These bearings are having artificially induced square shaped surface defects of different sizes on the outer and inner races and are analyzed for different operating speeds. A good similarity between the predicted numerical values and the experimental results is noticed. This study showed that the proposed methodology can be successfully used for the characterization of the localized surface defects on the raceways of the deep groove ball bearings.
TOPICS: Ball bearings, Damage, Regression analysis, Dimensions, Dimensional analysis, Bearings, Modeling, Vibration
Anupam Bhattacharya, Jayanta kumar Dutt and R. K. Pandey
J. Tribol   doi: 10.1115/1.4036629
This paper mainly reports stability investigations of rotors supported on fluid film journal bearings possessing multi-locational slip and no-slip zones at the bush-film interface. The coupled solution of governing equations (Reynolds equation, energy equation, heat diffusion equation, lubricant rheological relation and thermal boundary conditions) have been used to find pressure distributions in the lubricating film followed by evaluation of bearing coefficients. These coefficients have been used to determine stability limit speed and robustness of stability for both short (inflexible) and long (flexible) rotors. Numerical simulations show that the pattern of pressure distribution with multiple slip and no slip zones are similar to multilobe bearings; resulting substantial improvement of rotor-bearing stability irrespective of eccentricity ratio. A reduction in friction force (up to Sommerfeld number 1.8), increment in stability limit speed and robustness compared to conventional bearings when used with short rotors. Typically, up to 6 pairs of slip-no-slip zones improve stability limit speed of the rotor-shaft system, and robustness although more pairs deteriorate both these. However, for long rotors, where dynamic rotor forces also act, these bearings provide marginal improvement in stability and robustness only for a small range of slip length.
TOPICS: Journal bearings, Stability, Rotors, Bearings, Robustness, Pressure, Boundary-value problems, Fluid films, Friction, Computer simulation, Lubricants, Rheology, Thermal diffusion
Andreas Lehn, Marcel Mahner and Bernhard Schweizer
J. Tribol   doi: 10.1115/1.4036631
A detailed analysis of the effective thermal resistance for the bump foil of air foil bearings (AFBs) is performed. The presented model puts emphasis on the thermal contact resistances between the bump foil and the top foil as well as between the bump foil and the base plate. It is demonstrated that most of the dissipated heat in the lubricating air film of an air foil bearing is not conducted by micro-contacts in the contact regions. Instead, the air gaps close to the contact area are found to be thin enough in order to effectively conduct the heat from the top foil into the bump foil. On the basis of these findings, an analytical formula is developed for the effective thermal resistance of a half bump arc. The formula accounts for the geometry of the bump foil as well as for the surface roughness of the top foil, the bump foil and the base plate. The predictions of the presented model are shown to be in good agreement with measurements from the literature. In particular, the model predicts the effective thermal resistance to be almost independent of the applied pressure. This is a major characteristic property that has been found by measurements but could not be reproduced by previously published models. The presented formula contributes to an accurate thermohydrodynamic modeling of AFBs.
TOPICS: Modeling, Thermal resistance, Foil bearings, Heat, Surface roughness, Geometry, Pressure, Thermohydrodynamics
Fatma zouch, Zied Antar, Amir Bahri, Khaled Elleuch and Mustafa Urgen
J. Tribol   doi: 10.1115/1.4036628
Ternary iron-tungsten-phosphorus (Fe-W-P) coatings were electrodeposited with different sodium tungstate (NaWO4.2H2O) concentration on stainless steel 316 L substrate. These coatings were characterized by Energy Dispersive X-ray spectrometer (EDX), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD). The friction and wear behavior of these coatings were investigated using pin-on-disc tribometer under dry conditions. This study reveals an amorphous and nodular structure with nanometric grain size of the deposited alloy. The maximum level of incorporation of tungsten (W) is about 37.17 at. %. It was obtained with 0.5 M of sodium tungstate concentration and it increases the microhardness of the coatings. Moreover, it was found that Fe-W-P coatings had significantly improved the tribological properties of the substrate due to their higher wear resistance and lower friction coefficient.
TOPICS: Coatings, Tribology, Stainless steel, Tungsten, Friction, Sodium, Wear, X-rays, Wear resistance, Tribometers, Alloys, Scanning electron microscopes, X-ray diffraction, Disks, Grain size, Iron, Microhardness
Hansjörg Schultheiss, Thomas Tobie and Karsten Stahl
J. Tribol   doi: 10.1115/1.4036493
The wear behavior of grease lubricated gears is significantly affected by a number of factors besides the composition of the grease that is used for lubrication. A main influence factor on the wear behavior of grease lubricated gears is the lubrication supply mechanism (“circulating” or “channeling”), which is, among other things, strongly affected by the rotational speed of the gears. Especially at higher rotational speed, the dominant grease lubrication supply mechanism for grease lubricated gears tends to be “channeling”, which generally promotes increased wear on account of limited lubricant availability in the mesh as well as limited heat dissipation from the mesh. Experimental investigations conducted herein have shown that the gear wear behavior, especially at higher rotational speed, can be influenced by the internal geometry of the gear casing as well as by the direction of rotation of the gears. Additional investigations that were conducted focus on the effect of the material pairing and heat treatment on the wear behavior of grease lubricated gears in comparison to a case-carburized reference gear set. Furthermore, the effect of the gear size on the lubrication supply mechanism and thus on the wear behavior was investigated. For both gear sizes investigated (mn = 1.0 mm and mn = 0.6 mm), circulating was observed at low rotational speeds. At high rotational speeds, channeling effects were dominant.
TOPICS: Wear, Gears, Lubrication, Heat, Lubricants, Heat treating (Metalworking), Energy dissipation, Geometry, Rotation
A. Neurouth, C. Changenet, F. Ville, M. Octrue and E. Tinguy
J. Tribol   doi: 10.1115/1.4036447
In order to use electric motors which run up to 40,000 rpm in future automotive applications, this study aims to experimentally investigate if splash lubrication technique is worth considering for high-speed gears, i.e., for tangential gear speed up to 60 m/s. To this end, a specific test rig has been used to operate a single spur or helical gear in various operating conditions (lubricant, oil sump volume, temperature). Churning loss is measured and, as the fraction of air in the lubricant (namely, oil aeration) can be influential on this source of dissipation, a specific sensor is also employed for on-line monitoring of oil sump aeration. By inserting some moveable walls in the gearbox, it is demonstrated that churning losses and oil aeration can be significantly reduced by mounting these flanges at an appropriate distance to the gear lateral faces. Based on dimensional analysis, an engineering criterion is proposed to properly choose the clearance between the tested gear and the flanges.
TOPICS: Lubrication, Gears, Flanges, Clearances (Engineering), Automotive industry, Lubricating oils, Helical gears, Temperature, Electric motors, Mechanical drives, Sensors, Dimensional analysis, Lubricants, Energy dissipation
Khalida Akhtar, Hina Khalid, Ikram Ul Haq, Naila Zubair, Zia Ullah Khan and Abid Hussain
J. Tribol   doi: 10.1115/1.4036450
Uniform nanoparticles of cobalt oxide precursors were prepared by the chemical precipitation in which the headspace vapors of ammonium hydroxide solution of known concentration was allowed to bubble through the aqueous solutions of cobalt sulfate, containing appropriate amount of the nonionic surfactant, octylphenoxy poly ethoxy ethanol. SEM images showed that uniformity in particle size was dependent upon the applied precipitation conditions. Extensive optimization was therefore performed for the attainment of uniformity in particle size and shape. The amorphous precursor was transformed into crystalline Co3O4 as confirmed by X-ray diffractometry. These particles, with isoelectric point at pH~ 8.4, were then employed as reinforcement additive for strengthening the electrodeposited nickel matrix. Effect of various parameters, i.e. stirring rate, applied current density, and temperature was studied on the amount of the codeposited Co3O4 particles in the nanocomposite coatings (Ni-Co3O4) during the electrodeposition process. pH of the coating mixtures was kept below IEP value of Co3O4 so that the latter particles carried net positive surface charge. The coated surfaces were subjected to various tests, i.e. microhardness, wear / friction, and corrosion. Results revealed that irrespective of the amount of the embedded Co3O4 particles, nanocomposite coatings demonstrated superior performance as compared to pure nickel coatings.
TOPICS: Coatings, Steel, Tribology, Nanocomposites, Particulate matter, Particle size, Precipitation, Cobalt, Nickel, Shapes, Surfactants, Friction, Wear, Temperature, X-rays, Vapors, Electrodeposition, Bubbles, Nanoparticles, Corrosion, Optimization, Current density, Ethanol, Microhardness
Vesa Saikko
J. Tribol   doi: 10.1115/1.4036448
Circular translation pin-on-disk (CTPOD) tests were performed for ultrahigh molecular weight polyethylene (UHMWPE) with a view to reproducing wear mechanisms that prevail in total hip prostheses. The contact surface diameter varied from 3.0 mm to 30 mm while the slide track diameter was fixed, 10 mm. The counterface was polished CoCr and the lubricant was diluted alpha calf serum. Either the nominal contact pressure (1.1 MPa) or the load (126 N) was kept constant. With a constant contact pressure, the wear factor decreased steeply when the contact diameter exceeded the slide track diameter, apparently because the wear debris was not readily conveyed away from the contact. With constant load, both the wear factor and coefficient of friction increased linearly with increasing contact area. This trend was in agreement with clinical observations that the wear rate of UHMWPE acetabular cups increase with increasing femoral head size. With nominal contact pressures approaching 10 MPa however, the bearing surface topography markedly differed from clinical observations. This was probably due to overheating of the contact and plastic deformation that resulted in the formation of protuberances not seen clinically. The present study emphasized the importance of test parameters in the pin-on-disk wear screening of prosthetic joint materials. It appeared that the contact surface diameter of the flat-on-flat test should be below the slide track diameter and that the nominal contact pressure should be of the order of 1 MPa.
TOPICS: Friction, Wear, Disks, Pressure, Stress, Polishing, Bearings, Deformation, Lubricants, Artificial limbs, Molecular weight, Hip joint prostheses
Wei Dai, Kyungjun Lee, Alexander M. Sinyukov and Hong Liang
J. Tribol   doi: 10.1115/1.4036449
In this research, rheological and tribological performance of additive V2O5 nanoparticles in a light mineral oil has been investigated. For rheological performance, the addition of 0.2 wt% V2O5 could reduce the viscosity of the base oil for 6%. Considering the overall friction reduction in boundary, mixed, and hydrodynamic lubrication regimes, that with 0.1 wt% V2O5 exhibited the best effect. Friction coefficient of a base oil could be reduced by 33%. In terms of wear, the addition of 0.2 wt% V2O5 showed the lowest wear rate, which is 44% reduction compared to base oil. Through Raman spectrum and EDS analysis, it was found that V2O5 involved tribochemical reaction during rubbing. Vanadium intermetallic alloy (V-Fe-Cr) was found to enhance the antiwear performance. This research revealed that V2O5 nanoparticles could be an effective additive to improve tribological performance.
TOPICS: Friction, Wear, Nanoparticles, Tribology, Rheology, Mineral oil, Tribochemistry, Lubrication, Intermetallic compounds, Alloys, Viscosity
Takashi Nogi, Kazuaki Maniwa and Noriko Matsuoka
J. Tribol   doi: 10.1115/1.4036451
Cage motions in ball bearings are investigated using a dynamic analysis program. Increases in the cage friction coefficient induce unstable motions of the cage. The instability is more likely to occur under high load and low speed conditions due to less ball-race sliding. A simple theory of cage instability is developed, and a critical cage friction coefficient formula is proposed, which is a function of the cage mass, ball-race traction, ball-cage contact stiffness, cage rotational speed and number of balls. The prediction of this formula agrees with the results of the dynamic analysis. With a nonuniform separation between the balls, a high speed whirl is superimposed on the normal whirl with the ball group speed. The direction of the high speed whirl is the same as the cage rotational direction in inner race rotation, but they are opposite in outer race rotation. These results agree with some experimental results in the literature and validate the dynamic analysis.
TOPICS: Dynamic analysis, Ball bearings, Whirls, Rotation, Friction, Separation (Technology), Stress, Stiffness, Traction
Philip Varney and Itzhak Green
J. Tribol   doi: 10.1115/1.4036380
Mechanical face seals are constitutive components of a much larger turbomachine. The interplay between the seal and the turbomachine is complicated by the trend of increasing turbomachine efficiency by reducing seal clearances, increasing rotor shaft speeds, and making rotors lighter and more flexible. These methods for increasing efficiency heighten the importance of incorporating the coupled rotordynamics into the seal dynamics. The principal objective of this work is to, for the first time, determine how the rotor affects the seal performance. Thresholds can then be established beyond which the rotor influences the seal performance but not vice-versa. A general model of a flexibly-mounted stator (FMS) face seal is provided including the coupled dynamics of the flexible shaft and seal seat. The model accounts for rotor and FMS axial and angular deflections. Specifically, a lumped-parameter model is used to simulate the rotordynamics (if required, a more complicated model is certainly permissible). Static and dynamic rotor angular misalignments are considered. For expediency, the EOMs are linearized in the non-contacting regime and solved analytically at steady-state to investigate rotor inertia ratio, shaft speed, and angular misalignment. Importantly, results reveal that in some operating regimes, neglecting the rotordynamics implies healthy seal operation when instead contact exists between the seal faces. The effect of rotor-stator inertia ratio is investigated, demonstrating that when the rotor inertia is much larger than the seal’s, the rotordynamics can be solved separately and sent to the seal model as an external input.
TOPICS: Rotors, Stators, Steady state, Rotordynamics, Turbomachinery, Inertia (Mechanics), Dynamics (Mechanics), Flexible manufacturing systems, Deflection
Lijun Cao, Farshid Sadeghi and Lars-Erik Stacke
J. Tribol   doi: 10.1115/1.4036378
In this paper, a model was developed to study the effects of rotor and support flexibilities on the performance of rotor-bearing-housing system. The system is composed of a flexible rotor and two supporting deep-groove ball bearings mounted in flexible bearing housings. The dynamics of the ball bearings were simulated using an existing dynamic bearing model, which was developed using the discrete element method (DEM). The explicit finite element method (EFEM) was used to model the flexibilities of the rotor and bearing support. In order to combine the dynamic bearing model with finite element rotor and support system, new contact algorithms were developed for the interactions between the various components in the system. The Total Lagrangian formulation approach was applied to decrease the computational effort needed for modeling the rotor-bearing-housing system. The combined model was then used to investigate the effects of bearing clearances and housing clearances. And it was found that, as the rotor is deformed due to external loading, the clearances have a significant impact on the bearing varying compliance motion and reaction moments. Results also show that deformation of the flexible housing depends on the total force and moment generated within the bearing due to rotor deformation. The first critical speed of rotor was simulated to investigate the unbalance response of the rotor-bearing system. It was demonstrated that rotor critical speed has a significant effect on inner race displacement and reaction moment generated at bearing location.
TOPICS: Bearings, Rotors, Dynamic models, Ball bearings, Deformation, Finite element methods, Algorithms, Finite element analysis, Modeling, Displacement, Discrete element methods, Dynamics (Mechanics)
Shubrajit Bhaumik, Shubhabrata Dutta and Sateesh Pathak
J. Tribol   doi: 10.1115/1.4036379
The present work investigates the tribological properties of castor oil with various carbonaceous friction modifiers (nano and micro size additives) assessed using four ball tester as per ASTM D 4172 and ASTM D 2783. Castor oil has been chosen because of its high viscosity and ease of availability. Graphite (GRT), multi-walled carbon nanotube (MWCNT) and multi layered graphene (GRPHN) are used as friction modifiers in castor oil on weight percentage basis. Significant enhancements of tribological properties with a certain level of concentration of friction modifiers have been observed. The surface features of the tested balls were also analyzed using a three-dimensional non-contact type profilometer, scanning electron microscope (SEM) and energy dispersive system (EDS). Decrease in surface roughness indicated better anti-wear properties in case of friction modifiers based castor oil as compared to micro (GRT) based and neat castor oil. The formation of tribo film and mending effect as detected by SEM and EDS are most likely mechanisms for enhancing the tribological properties. In order to assess the suitability of castor oil as a replacement for mineral oil, the results of castor oil samples are also compared with commercially available mineral oil. The tribological properties of castor oil are found to be competitive and generally superior to the mineral gear oil. The data generated are used to develop a neural network model to map the input-output correlation.
TOPICS: Tribology, Friction, Mineral oil, ASTM International, Multi-walled carbon nanotubes, Weight (Mass), Wear, Scanning electron microscopes, Viscosity, Surface roughness, Graphene, Graphite, Neural network models
J. S. Rudas, L. M. Gomez, A. Toro, J. M. Gutiérrez and A. Corz
J. Tribol   doi: 10.1115/1.4036321
The potential of applying thermodynamics to study the tribological response of a tribological system is addressed in this article. In order to do so, a model was developed to obtain the entropy flow generated by three different dissipative processes present in dry sliding, namely thermal gradient, heat conduction and abrasion. The flash and bulk temperatures at the contact interface were obtained with the aid of the finite element method and Pin-on-Disk tests were performed by using titanium alloy (Ti6Al4V) disks and Tungsten Carbide (WC/10Co) pins. Then, the wear rate obtained from the tribological tests was correlated with the calculated entropy flow and a degradation coefficient was associated to the sliding process. A linear dependence of the wear rate and the degradation coefficient was observed regardless of the variation of the points of operation of the system, so it is proposed that the coefficient of degradation used is inherent to the tribological system.
TOPICS: Wear, Entropy, Tribology, Flow (Dynamics), Disks, Tungsten, Temperature gradient, Finite element methods, Pins (Engineering), Abrasion, Thermodynamics, Temperature, Heat conduction, Titanium alloys
Eberhard Abele and Lars Holland
J. Tribol   doi: 10.1115/1.4036320
Movement analyses of bearings focusing on cage motion behavior are often conducted by simulations, typically by investigating the cage whirl. Some experimental studies exist in which a metal cage or a modified one is analysed with sensors. This paper presents an image based approach for investigating the cage motion of an injection moulded, window-type cage under operation condition. Besides analyses at constant rotational speed the cage center movement behavior for different accelerations is investigated.
TOPICS: Bearings, Roller bearings, Engineering simulation, Whirls, Metals, Sensors, Simulation
Wenhu Zhang, Sier Deng, Guo-Ding Chen and Yongcun Cui
J. Tribol   doi: 10.1115/1.4036274
In this paper, the formulas of elastohydrodynamic traction coefficients of four Chinese aviation lubricating oils, namely 4109, 4106, 4050 and 4010, were obtained by a great number of elastohydrodynamic traction tests. The nonlinear dynamics differential equations of high-speed cylindrical roller bearing were built on the basis of dynamic theory of rolling bearings and solved by HHT(Hilber-Hughes-Taylor) integer algorithm with variable step. The influence of lubricant traction coefficient on cage's nonlinear dynamic behavior was investigated, and Poincaré map was used to analyze the influence of four types of aviation lubricating oils on the nonlinear dynamic response of cage's mass center. The period of nonlinear dynamic response of cage's mass center was used to assess cage's stability. The results of this paper provide the theoretical basis for selection of aviation lubricating oil.
TOPICS: Lubricants, Traction, Roller bearings, Aviation, Lubricating oils, Dynamic response, Stability, Algorithms, Differential equations, Poincaré maps, Rolling bearings, Nonlinear dynamics

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