Accepted Manuscripts

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
Junho Suh, Alan Palazzolo and Yeon-Sun Choi
J. Tribol   doi: 10.1115/1.4036275
This paper presents a new approach for modeling flexure- pivot journal bearings (FPJB) employing a three-dimensional (3D) elasto-hydro-dynamic (EHD) lubrication model. The finite element (FE) method is adopted for an analysis of the (1) pad-pivot dynamic behavior and the (2) fluid force. The iso-viscosity Reynolds equation is utilized to calculate the fluid force acting on a flexure-pivot pad bearing and spinning journal. Computational efficiency is achieved utilizing modal coordinate transformation for the flexible pad-pivot dynamic analysis. Fluid film thickness plays a critical role in the solution of Reynold’s equation and is evaluated on a node by node basis accounting for the pad and web deflections. The increased fidelity of the novel modeling approach provides rotating machinery designers with a more effective tool to analyze and predict rotor-bearing dynamic behavior.
TOPICS: Computer simulation, Bending (Stress), Bearings, Fluids, Modeling, Rotors, Deflection, Fluid films, Journal bearings, Accounting, Lubrication, Machinery, Viscosity, Spinning (Textile), Spin (Aerodynamics), Dynamic analysis, Finite element analysis
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
Shahid Saleem Sheikh and Mohd Farooq Wani
J. Tribol   doi: 10.1115/1.4036273
Friction and wear studies of Nimonic 80A and 21-4N valve materials against GGG-40 under dry sliding conditions, at temperatures ranging from 50 oC to 500 oC, are presented in this paper. Friction coefficient was found to continuously decrease with time for all tests with prominent running-in behavior seen in the 50 oC and 500 oC tests. Higher friction coefficient and wear was observed at 300 oC, as compared to that at 50 oC and 500 oC. Formation of oxide Fe3O4, at 300 oC, was confirmed by Raman spectroscopy, which resulted in a higher friction coefficient and wear. Raman spectroscopy further revealed the presence of a-Fe2O3, hematite, in most cases, with presence of oxides of Ni-Cr and Ni-Fe as well. EDS results on the samples confirmed the same. Wear at 500 oC was found to be the least for both the valve materials with SEM confirming the formation of well developed glaze layers.
TOPICS: Temperature, Tribology, Valves, Friction, Wear, Raman spectroscopy, Glazes, Magnetite
Zhengfeng Cao and Yanqiu Xia
J. Tribol   doi: 10.1115/1.4036271
Polyaniline (PANI) was doped as lubricating additive to afford grease. The effect of PANI on the physicochemical characteristics, corrosion resistance and tribological performances of lubricating grease were investigated in details, and the tribological action mechanisms of lubricating grease were analyzed in relation to worn surface analyses by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscope (EDS). Results indicate that the PANI-doped grease has superior conductive and thermal properties. And PANI-doped grease has an excellent corrosion resistance, which is attributed to the isolation effect and the compact passivated film generated by reaction of PANI and metal. In the meantime, the PANI-doped grease performs superior friction reduction and wear resistance under different applied loads and frequencies. It is mainly ascribed that the PANI can perform like spacers to avoid direct contact between the contact interfaces and the protective tribofilm is generated by physical adsorption and chemical reaction.
TOPICS: Tribology, Corrosion resistance, Wear resistance, Tribological films, Chemical reactions, Friction, X-rays, Metals, Stress, Thermal properties, Scanning electron microscopy
Mihai Arghir and Antoine Mariot
J. Tribol   doi: 10.1115/1.4036272
The segmented carbon seal is regularly used for sealing bearing chambers of aeronautical turboengines or as part of a buffer seal in space turbopumps. The seal operates with contaminated air or with an inert gas and is made of many identical carbon segments (generally three or six) with reciprocally overlapping ends. The segments are pressed against the rotor by the pressure difference between the upstream and the downstream chambers and by a circumferential (garter) spring. The pressure difference and an axial spring press the segments also against the stator. The inner cylindrical surface of each segment is provided with pads that create an aerodynamic lift proportional to the rotor speed. Following this lift force, the segments of the seal are pushed away from the rotor and the seal opens. The contact between the rotor and the segments is lost and an axial leakage path is thus created. Although it was developed since long, a model for calculating the characteristics of the segmented seal is completely absent from the scientific literature. The goal of the present work is to fill this gap at least for the static characteristics (leakage and torque). The analysis is carried out for a single segment of the seal by supposing that all the segments have the same characteristics. Each segment has a planar motion (i.e. three degrees of freedom) and therefore the film thickness under each pad is not uniform. Given the stationary operating conditions (pressure difference and rotation speed), the present model calculates the equilibrium position of each segment on the bases of the lift and of the friction force acting on the pads, of the friction forces acting on the nose of the seal and of the radial and axial springs. Once found the static equilibrium position, the leakage and the torque of the seal are calculated. A parametric study enlightens the importance of the pad waviness, of the pocket depth and of the spring forces on the characteristics of the segmented seal.
TOPICS: Seals, Carbon, Theoretical analysis, Springs, Rotors, Leakage, Pressure, Torque, Friction, Lift (Fluid dynamics), Equilibrium (Physics), Degrees of freedom, Bearings, Film thickness, Stators, Sealing (Process), Polishing equipment, Rotation
Nithesh R, Radhika N and Shiam Sunder S
J. Tribol   doi: 10.1115/1.4036185
The modern technology developments have seeded for the necessity of composite materials that are incorporated with high hardness, high tensile strength and better wear properties. Cu-Sn-Ni alloy as well as the composites of varying wt% of Si3N4 (5, 10 and 15) are fabricated by liquid metallurgy technique. The alloy and composites are tested for their tensile strength and hardness on Universal Testing Machine and Vickers microhardness tester respectively. Based on the tests, Cu-Sn-Ni/ 10 wt% of Si3N4 is found to have optimum mechanical properties. The scuff type adhesive wear behaviour is studied through pin-on-disc tribometer under dry sliding conditions for Cu-Sn-Ni/ 10 wt% of Si3N4 composite. Taguchi's Design of Experiments technique based on L27 orthogonal array model is used for analyses of process parameters in three levels such as applied load (10, 20 and 30 N), sliding distance (500,1000 and 1500 m) and sliding velocity (1, 2 and 3 m/s). The parameters are ranked based on Signal-to-Noise ratio and Analysis of Variance approach. Based on wear results, applied load is found to have highest stature on influencing wear rate followed by sliding distance and sliding velocity. A generalized wear rate equation is obtained based on the linear regression model and its feasibility is checked. Scanning Electron Microscope analyses revealed severe delamination occurred on maximum load condition. The development of this copper composite can have the possibility of replacing aluminium bearings.
TOPICS: Wear, Composite materials, Adhesives, Silicon nitride ceramics, Tin, Mechanical properties, Stress, Alloys, Tensile strength, Delamination, Tribometers, Bearings, Testing, Signal to noise ratio, Disks, Experimental design, Microhardness, Regression models, Technology development, Scanning electron microscopes, Metallurgy, Copper, Aluminum, Machinery
Hiroyuki Ohta, Tatsuya Tsuruoka, Yukitoshi Fujinami and Soichiro Kato
J. Tribol   doi: 10.1115/1.4036176
This article is errata to "Effects of Grease Characteristics on Sound and Vibration of a Linear-Guideway Type Recirculating Ball Bearing" [Journal of Tribology, 2016, 138, p.021101].
TOPICS: Vibration, Ball bearings, Tribology
Niraj Kumar and Punit Kumar
J. Tribol   doi: 10.1115/1.4036167
Transient thermal EHL line contact simulations are carried out to study the traction behavior during accelerated motion considering realistic shear-thinning and surface roughness effects. Using three lubricants with different inlet viscosity and shear-thinning parameters, the application of present analysis for lubricant selection is demonstrated. Owing to squeeze film action, the film evolution is delayed and start-up traction is found to increase much above the designed value. This effect increases with decreasing roughness wavelength especially at high amplitudes. The most shear-thinning test oil considered here yields the lowest traction coefficient with minimum variation in its value desirable for smooth and vibration-free operation.
TOPICS: Lubricants, Traction, Shear (Mechanics), Surface roughness, Transients (Dynamics), Engineering simulation, Vibration, Simulation, Wavelength, Viscosity
G. X. Chen and Xiaolu Cui
J. Tribol   doi: 10.1115/1.4036168
Recently, one of the present authors proposed a new model to explain the generation mechanism of brake squeal based on the time delay between a varying applied normal force and the resulting friction force. The present work conducts a series of experimental tests examining the behavior of this time delay using a special test apparatus. The test apparatus suppresses the effect of interference in the time delay owing to the excitation normal force to the greatest extent possible. Several calibration tests of the test apparatus are conducted to ensure the validity of the normal force and friction force measurements. The varying friction force is extracted from the overall friction force signal without phase distortion using a zero-phase filter. The test results demonstrate a time delay between the varying normal force and the resulting friction force under various testing parameters. The time delay is found to increase with increasing excitation frequency. The generation mechanism of the time delay is also discussed.
TOPICS: Delays, Friction, Excitation, Testing, Calibration, Filters, Force measurement, Signals, Brakes
Jianlin Xu, Shuhua Yang, Lei Niu, Xiaoqi Liu and Jinqiang Zhao
J. Tribol   doi: 10.1115/1.4036172
Antimony nanoparticles, which surfaces were modified by alkyl phenol polyoxyethylene ether, were used as a kind of lubricating additives in liquid paraffin. The tribological properties of antimony nanoparticles as lubricating additives were evaluated and compared with those of pure liquid paraffin on a four-ball test machine. The morphology and chemical composition of worn surface were investigated and analyzed by using SEM and EDS. The results show that the additives can obviously improve the anti-wear and friction reducing properties of liquid paraffin, which are better under high friction load. The double-layer crystal structure of antimony can be separated and glided along cleavage plane by friction-shear force and normal load, respectively. The separating and gliding of antimony can form a physical adsorption film, which can separate friction surface to avoid direct contact of friction surface and play an important role in improving the anti-wear and friction reducing properties.
TOPICS: Tribology, Paraffin wax, Nanoparticles, Friction, Wear, Stress, Shear (Mechanics), Crystal structure, Ethers (Class of compounds), Machinery
Esteban Correa, Juan Felipe Mejía, Juan Guillermo Castaño, Félix Echeverría and Maryory Gómez
J. Tribol   doi: 10.1115/1.4036169
Ni-B coatings have been deposited directly on commercial purity magnesium and evaluated by means of sliding wear and friction testing. The nickel and boron are distributed throughout the whole thickness of the coating. Parametric optimization has been carried out using design of experiment based on Taguchi analysis. The friction coefficients of the coatings vary between 0.01-0.3, depending of the evaluated conditions. The lowest wear rate of the coating was 0.19 × 10-5 mm3 N-1 m-1. Wear and friction coefficient maps of Ni-B electroless coatings formed on magnesium surfaces are reported. Nanoparticles present in the lubricating fluid acts as a third wear body increasing the wear of the electroless coating.
TOPICS: Tribology, Coatings, Magnesium (Metal), Wear, Friction, Fluids, Nanoparticles, Design, Optimization, Testing, Boron, Nickel
Fanming Meng, Ling Zhang and Tao Long
J. Tribol   doi: 10.1115/1.4036170
Operation parameter influences on the behavior of the gaseous bubbles in the lubricant for a groove textured journal bearing is studied under the consideration of the thermal effect of the bearing-shaft system. The influence is analyzed by simultaneously solving Rayleigh-Plesset (RP), energy and Reynolds equations. The computer code for the analyzing the bubble behavior is validated. Numerical results show that appropriately increasing the width-diameter ratio of the bearing and rotational speed of the shaft, or decreasing the applied load and inlet temperature of the lubricant, can decrease the maximum radius, collapse pressure and temperature of the bubble.
TOPICS: Lubricants, Bubbles, Journal bearings, Bearings, Temperature, Pressure, Stress, Computers, Collapse, Temperature effects
Chenglong Lian, Kwang-Hee Lee and Chul-Hee Lee
J. Tribol   doi: 10.1115/1.4036173
Magnetorheological elastomers (MREs) are smart materials that have been studied widely for their material properties. The elasticity modulus or hardness of an MRE can be changed when an external magnetic field is applied. In this study, a study of MREs applied to rolling friction control under various external magnetic strengths is conducted. To accomplish this, the rolling friction property of an elastomer on a rigid plate is analyzed. Then, MREs are prepared, and a rolling friction tester is designed to evaluate the changes in the rolling friction coefficient. The results show that the rolling friction coefficient can be changed with different magnetic field strengths. The rolling friction coefficient of the MRE can be controlled by the applied magnetic field, which can be applied to control the slip rate and be adapted to achieve the optimal friction effect in the future.
TOPICS: Elastomers, Rolling friction, Magnetic fields, Friction, Smart materials, Materials properties, Elastic moduli
Nicolás S Fochesatto, Fernando S Buezas, M.B. Rosales and Walter R. Tuckart
J. Tribol   doi: 10.1115/1.4036181
In this work, the influence of different crack arrangements in the stress distribution of hard chromium coatings was determined. Three parameters for position and length of the cracks for two different types of coatings were probabilistically modelled based on measured scanning electron microscopy (SEM) images. Probability density functions for those parameters were obtained to characterise each kind of coating. A 2D finite element model of the coating in contact with a rigid disc was developed, modelling cracks with elliptical shapes. A Monte Carlo method was used to simulate different crack distributions for each kind of coating, and values of stress and strains in the domain were obtained. Both the J-integral and the stress intensity factors were taken as comparative parameters of the results. Coatings which statistically present larger quantities of shorter cracks have lower values of J-integral and stress intensity factors, and, therefore, distribute stresses better than those with low density of longer cracks.
TOPICS: Stress concentration, Fracture (Materials), Modeling, Coatings, Stress, Density, Scanning electron microscopy, Disks, Finite element model, Monte Carlo methods, Probability, Shapes
Scott Bair, Wassim Habchi, Mark Baker and David M. Pallister
J. Tribol   doi: 10.1115/1.4036171
The first calculations of film thickness for an oil/refrigerant system using quantitative elastohydrodynamics are reported in this work. It is demonstrated that primary measurements of the properties of the oil/refrigerant system can be employed to accurately predict film thickness in concentrated contacts. An unusual response to lubricant inlet temperature is revealed wherein the film thickness may increase with temperature as a result of decreasing refrigerant solubility in oil when the inlet pressure is high. There is competition between the reduction in viscosity of the oil and the reduction of refrigerant concentration with increased temperature. For high inlet pressure, the dilution effect is dominant, whereas for low inlet pressure, the temperature dependence of the viscosity of the solution dominates over the range of inlet temperatures considered. It seems that only central film thicknesses have been experimentally measured for oil/refrigerant systems leaving these calculations as the only means of assessing the minimum.
TOPICS: Refrigerants, Film thickness, Temperature, Pressure, Viscosity, Lubricants, Temperature effects, Elastohydrodynamic lubrication
Ahmet D. Usta, Sohan Shinde and Melih Eriten
J. Tribol   doi: 10.1115/1.4036183
Interfacial damping in assembled structures is difficult to predict and control since it depends on numerous system parameters such as elastic mismatch, roughness, contact geometry and loading profiles. Most recently, phase difference between normal and tangential force oscillations has been shown to have a significant effect on interfacial damping. In this study, we conduct microscale (asperity-scale) experiments to investigate the influence of magnitude and phase difference of normal and tangential force oscillations on the energy dissipation in presliding spherical contacts. Our results show that energy dissipation increases with increasing normal preload fluctuations and phase difference. This increase is more prominent for higher tangential force fluctuations thanks to larger frictional slip along the contact interface. We also show that the energy dissipation and tangential fluctuations are related through a power-law. The power exponents we identify from the experiments reveal that contacts deliver a nonlinear damping for all normal preload fluctuation amplitudes and phase differences investigated. This is in line with the damping uncertainties and nonlinearities observed in structural dynamics community.
TOPICS: Energy dissipation, Tangential loading, Damping, Fluctuations (Physics), Oscillations, Surface roughness, Structural dynamics, Microscale devices, Geometry, Uncertainty
Kyosuke Ono
J. Tribol   doi: 10.1115/1.4036174
The vibration characteristics of a thermal fly-height control (TFC) head slider in the proximity and asperity contact regimes attract much attention, because the head–disk spacing must be less than 1 nm in order to increase the recording density in hard disk drives. This paper presents a numerical analysis of the microwaviness (MW)-excited vibrations in the flying head slider during the touchdown process. We first formulate the total force applied to the TFC head slider as a function of the head–disk spacing, based on the rough-surface adhesion contact models and the air-bearing force model. Then, the MW-excited vibrations of a single–degree-of-freedom slider model at touchdown are simulated by the Runge–Kutta method. It is found that, when the MW amplitude is less than the spacing range of static instability in the total force, the slider jumps to a contact state from a near-contact or mobile-lubricant–contact state. It then jumps to a flying state even when the head surface is protruded further by increasing the TFC power. When the MW amplitude is relatively large, a drastically large spacing variation, whose spectrum contains a wide range of frequency components below 100 kHz, appears in the static unstable region. These calculated results can clarify the mechanisms behind a few peculiar experimental phenomena reported in the past.
TOPICS: Vibration, Disks, Runge-Kutta methods, Air bearings, Density, Adhesion, Lubricants, Surface roughness, Degrees of freedom, Numerical analysis
Xingliang Li, Wen Yue, Chengbiao Wang, Jiajun Liu and Guolong Li
J. Tribol   doi: 10.1115/1.4036175
W, Mo and W-Mo alloy films are prepared on 316L stainless steel by means of ion beam assisted deposition (IBAD). Tribological behaviors of the treated surfaces are investigated under lubrication with MoDTC on a MS-T3000 friction and wear tester. The micromorphologies and chemical characteristics of the tribofilms generated on the worn surfaces are analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS), respectively. The results showed that the obvious synergistic effects of better friction reduction and wear resistance between W-Mo film and MoDTC are attributed to the hard surface and the high decomposition rate of additives on the worn W-Mo surface.
TOPICS: Lubrication, Tribology, Friction, Wear, Alloys, Scanning electron microscopy, Stainless steel, Wear resistance, Tribological films, Atomic, molecular, and chemical characteristics

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