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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
Discussion  
Adrian Rienäcker and Johann Graf
J. Tribol   doi: 10.1115/1.4040013
Independant validation of algorithm and results
Technical Brief  
Yeong-Jae Lee, Kwang-Hee Lee and Chul-Hee Lee
J. Tribol   doi: 10.1115/1.4039995
In recent years, through the development of 3D printing technology, 3D printed parts have been used in various industries, such as medical equipment and robotics. Various 3D printing methods have been developed. Today, a 3D printer can be used even in precision parts, such as bolts and bearings. In this study, journal bearings are manufactured by a 3D printer to evaluate friction performance and self-lubricating performance. The journal bearings are fabricated using two types of 3D printing method: fused deposition modeling (FDM) and selective laser sintering (SLS). The specimens manufactured by FDM are produced by plastic materials with three-layer thicknesses. Nylon-based materials and aluminum-based materials are used to fabricate the SLS specimen. Micropores are created in the specimens during the printing process. Therefore, the self-lubricating performance can occur by micropores. The experimental setup is designed and constructed to evaluate the friction performance by varying rotational speed and the radial load. Through this study, the self-lubricating performance and friction performance of 3D-printed journal bearings are evaluated, and proper operating conditions for 3D-printed bearings are suggested.
TOPICS: Friction, Journal bearings, Additive manufacturing, Bearings, Medical devices, Modeling, Robotics, Printing, Aluminum, Lasers, Sintering, Stress, Nylon fabrics, Plastics
research-article  
Bhupinder Singh, Sarbjeet Kaushal, Dheeraj Gupta and Hiralal Bhowmick
J. Tribol   doi: 10.1115/1.4039996
In the present experimental study, the application of microwave heating is used to develop the composite clads of Ni based metallic powder (matrix) and Al2O3 powder (reinforcement) on the surface of AISI 304 stainless steel substrate. A domestic microwave oven working at 2.45 GHz frequency and 900 W was used to conduct the experimental trials. The Ni + 10% Al2O3 composite clads were characterized through XRD, SEM, EDS, micro-hardness tests. The pin-on-disk type tribometer was used for analyzing the sliding wear behavior of Ni + 10% Al2O3 clads. The microstructural results revealed the presence of randomly dispersed Al2O3 particles inside Ni matrix. The average microhardness (Vicker’s) of composite clad was enhanced by 3.5 times that of substrate. Craters and groove formation were responsible for wear loss in clad material while plastic deformation caused the failure of AISI 304 substrate.
TOPICS: Wear, Microwaves, Composite materials, Microhardness, Microwave heating, Ovens, Stainless steel, Tribometers, Particulate matter, Disks, Failure, Deformation
research-article  
Rafael B. Obara
J. Tribol   doi: 10.1115/1.4039997
Despite the importance of precise evaluation of wear volume losses from cylinders, several factors make the investigation of large surface areas from cylinder bores a hard issue. Topography analysis has been widely used to quantify wear in cylinders, but no method was found in the literature for the quantification of wear volume losses considering the whole stroke length of cylinder bores. In this work, 3D measurements were taken from a gasoline engine tested in dynamometer for 625 h and wear volume profiles were obtained for all cylinders. The results from the proposed method showed good agreement with both the variation of the core height and the visual analysis from stereo images.
TOPICS: Wear, Cylinders, Gasoline engines, Dynamometers
research-article  
Bifeng Yin, Dashu Gao, Shao Sun, Bo Xu and Hekun Jia
J. Tribol   doi: 10.1115/1.4039957
In this paper, a profile design of surface texture was applied for improving the tribological performance of piston ring-cylinder pair. The design of texture pattern was implemented by numerous textures of different depths in sliding speed direction to imitate the outline of barrel-shaped ring. The thickness and pressure distribution of oil film were obtained through a joint solution of modified Reynolds equation and other governing equations for textured surface. The results indicate that the novel texture pattern has the best overall performance in oil film thickness and friction force compared with normal surface textures, and the average friction power is 10.04% and 16.85% less than normal surface textures and barrel-shaped ring in the whole working cycle. Extra micro-hydrodynamic lubrication can be observed in the middle region of textured piston ring through the pressure distribution of oil film. At last, the experiment was conduct in a motored test rig and exhibited up to 3% reduction in friction power.
TOPICS: Design, Internal combustion engines, Piston rings, Surface texture, Texture (Materials), Friction, Pressure, Tribology, Lubrication, Cycles, Cylinders, Film thickness, Pistons
research-article  
Xiaohui Lin, Shuyun Jiang, Chibin Zhang and Xiang Liu
J. Tribol   doi: 10.1115/1.4039959
A thermohydrodynamic (THD) lubrication model of turbulent cavitating flow for high speed spiral groove thrust bearing was developed considering the effects of cavitation, turbulence, inertia, breakage and coalescence of bubbles. Comparing with the classical THD model, this model can predict not only the distributions of pressure and temperature rise but also the distribution of bubble volume and bubble number density. Static characteristics of the water-lubricated spiral groove thrust bearing in the state of turbulent cavitating flow was analyzed, and the influences of multiple effects on the static characteristics of the bearing were researched. The numerical calculation result shows that the bubbles are mainly distributed in inlet and outlet of the spiral groove, the distribution of bubble volume is skewed under the equilibrium state, and small bubbles account for a large proportion of the cavitating flow under high speed condition. Furthermore, the load carrying capacity and the leakage flow of the bearing decrease due to effect of cavitation under high speed. The maximum temperature rise of the bearing decreases due to the effect of cavitation effect.
TOPICS: Flow (Dynamics), Thrust bearings, Water, Thermohydrodynamics, Bubbles, Turbulence, Cavitation, Bearings, Temperature, Leakage flows, Equilibrium (Physics), Load bearing capacity, Lubrication, Density, Inertia (Mechanics), Pressure
research-article  
Umar Azam Muhammad and Abdul Samad Mohammed
J. Tribol   doi: 10.1115/1.4039956
A novel hybrid polymer nanocomposite coating of ultra-high molecular polyethylene (UHMWPE) reinforced with nanoclay (C15A) and carbon nanotubes (CNTs) has been developed to protect metallic mating surfaces in tribological applications. The hybrid nanocomposite coatings were deposited on aluminum substrates using an electrostatic spraying technique. Ball-on-disk wear tests using a 440C stainless steel ball as the counterface were conducted on the coatings under dry conditions to determine the optimum amount of the loadings of the nanofillers and evaluate their tribological performance at different normal loads and linear velocities. Micro-indentation, raman spectroscopy, scanning electron microscopy (SEM) and optical profilometry techniques were used to characterize the coatings in terms of hardness, dispersion of the nanofillers, morphology and wear mechanisms respectively. Results showed that the UHMWPE hybrid nanocomposite coating reinforced with 1.5 wt% of C15A nanoclay and 1.5 wt% of CNTs did not fail even until 100,000 cycles at a normal load of 12 N and a linear speed of 0.1 m/s showing a significant improvement in wear resistance as compared to all other coatings evaluated in this study.
TOPICS: Tribology, Coatings, Nanocomposites, Carbon nanotubes, Nanoclays, Stress, Spraying (Coating processes), Scanning electron microscopy, Disks, Raman spectroscopy, Plasma spraying, Wear, Aluminum, Polymer nanocomposites, Cycles, Stainless steel, Wear resistance, Wear testing
research-article  
Hui Zhang, Mahshid Hafezi, Guangneng Dong and Yang Liu
J. Tribol   doi: 10.1115/1.4039958
This paper aims to improve the tribological performance of journal bearings by optimizing the coverage area of circular micro-textures in divergent region of the sleeve. A numerical model is proposed to calculate the friction coefficient and bearing load of textured journal bearings. The surface of the sleeve is divided into rectangular squares. Textures that located at the center of rectangular grids are assumed to be present or absent, marked as 1 and 0, respectively. Afterwards, different texture coverage area arrangements are evolved and selected based on the Genetic Algorithm. The area of semi-elliptical shape is obtained as the novel and preferable textured coverage area design for journal bearings. Influences of width and eccentricity ratio are discussed, which confirm the semi-major and semi-minor axes of the semi-elliptical shape of texture coverage area equal to one-third of the circumferential length and half of the width of the journal bearing, respectively.
TOPICS: Design, Genetic algorithms, Journal bearings, Texture (Materials), Shapes, Bearings, Tribology, Friction, Computer simulation, Stress
research-article  
Kuang Fuming, Zhou Xincong, Huang Jian, Zhou Xiaoran and Wang Jun
J. Tribol   doi: 10.1115/1.4039930
The tribological properties of nitrile rubber(NBR)/ultra-high molecular weight polyethylene (UHMWPE)/nano-molybdenum disulfide (Nano-MoS 2 ) nanocomposites with various contents of Nano-MoS 2 were investigated using a marine stern tube bearing testing apparatus SSB-100V under low-speed and heavy duty conditions with water lubrication. Friction of coefficient (COF), wear rate and surface topographies were compared to anlyse the influence of Nano-MoS 2 and select the optimum Nano-MoS 2 content. The mechanical and physical properties of the rubber-plastic material met the requirements of the Chinese Ship standard CB/T769-2008 and U.S. military standard MIL-DTL-17901C(SH). The results showed that for the nanocomposites with a content of Nano-MoS 2 of 9 phr (parts by weight per hundred parts of rubber materials), exhibited good comprehensive friction and wear properties. It is believed that the knowledge gained from this study can form a theoretical foundation for the modification of rubber-plastic material.
TOPICS: Tribology, Nitrile rubber, Bearings, Water, Rubber, Nanocomposites, Friction, Wear, Lubrication, Testing, Military systems, Molecular weight, molybdenum, Ships, Weight (Mass)
research-article  
Jeremy Moss, Ahmet Kahraman and Carlos H Wink
J. Tribol   doi: 10.1115/1.4039929
An experimental investigation of spur gear behavior was conducted with the aim of quantifying the impact of lubrication methods and conditions on the power losses and contact fatigue lives. Variations of dip and jet-lubrication are defined and these behaviors were observed as a function of the lubrication conditions. Both types of measurements were performed using the same type of back-to-back test machines and the same spur gear test articles such that their evaluations can be correlated. Power loss experiments were performed under both loaded and unloaded conditions to determine both load-independent (spin) and load-dependent (mechanical) losses. Sets of long-cycle contact fatigue experiments were performed under the same lubrication conditions to determined macro-pitting lives in a statistically meaningful manner. Results indicate that the spin power losses are impacted by the lubrication method significantly while the mechanical losses are not influenced. Contact fatigue lives from jet-lubricated tests are comparable to those under dip-lubricated conditions ones as long as jet velocities are sufficient.
TOPICS: Lubrication, Fatigue life, Spur gears, Fatigue, Rotation, Stress, Spin (Aerodynamics), Particle spin, Cycles, Machinery
research-article  
Yazhao Zhang, Alexander Kovalev, Noriyuki Hayashi, Kensuke Nishiura and Yonggang Meng
J. Tribol   doi: 10.1115/1.4039867
A stochastic model for predicting the evolutions of wear profile and surface height probability distribution function of initial line contacts during running-in under mixed lubrication condition is presented. A numerical approach was developed on the basis of stochastic solution of mixed lubrication, which combined the Patir and Cheng’s average flow model for calculation of the hydrodynamic pressure and the Kogut and Etsion’s rough surface contact model for calculation of the asperity contact pressure. The total friction force was assumed to be the sum of the boundary friction at the contact asperities and the integration of viscous shear stress in hydrodynamic region. The wear depth on the contact region was estimated according to the modified Archard’s wear model using the asperity contact pressure. Sugimura’s wear model was modified and used to link the wear particle size distribution and the variation of surface height probability distribution function during wear. In the wear process, the variations of profile and surface height probability distribution function of initial line contacts were calculated step by step in time, and the pressure distribution, friction coefficient and wear rate were updated consequently. Effect of size distribution of wear particles on the wear process was numerically investigated, and the simulation results showed that the lubrication condition in which small wear particles are generated from asperity contact region is beneficial to reduce friction coefficient and wear rate, and leads to a better steady mixed lubrication condition.
TOPICS: Wear, Lubrication, Surface roughness, Pressure, Friction, Statistical distributions, Particulate matter, Flow (Dynamics), Shear stress, Particle size, Simulation results
Discussion  
Stephen Boedo and John F. Booker
J. Tribol   doi: 10.1115/1.4039797
None
research-article  
Fanming Meng, Zhongtao Cui, Zhitao Cheng and Huali Han
J. Tribol   doi: 10.1115/1.4039796
The graphite-MoS2 coated on GCr15 bearing steel is prepared through air spraying and its tribological performances are investigated experimentally. Then its coefficient of friction (COF) and wear scar width (WSW) are investigated through the MFT-5000 multi-function tribometer and other test equipments. The experimental results show that the addition of the graphite can effectively decrease the COF and narrow the WSW of the MoS2. There exists a critical applied load for wearing out the surface with the graphite-MoS2 coating. Moreover, there exists an optimal rotational speed of 500 rpm to decrease the COF and WSW of the GCr15 steel.
TOPICS: Coating processes, Coatings, Tribology, Graphite, Tribometers, Friction, Wear, Steel, Plasma spraying, Bearing steel, Stress, Spraying (Coating processes)
Closure  
Noel Brunetiere and Jeremy Cochain
J. Tribol   doi: 10.1115/1.4039798
This paper presents a general formulation of the Reynolds equation for gas and liquid lubricants, including cavitation. A finite element solution of this equation is also given. The model is compared to those obtained in the previous literature on liquid and gas lubrication. One of the advantages of the model is the continuous description of cavitation in liquid lubrication. It is possible to deal with all lubricants by adjusting the amount of gas in the fluid.
TOPICS: Lubrication, Cavitation, Lubricants, Finite element analysis, Fluids
research-article  
Zilong Zhao, Kai Feng, Xueyuan Zhao and Wanhui Liu
J. Tribol   doi: 10.1115/1.4039721
The stability of oil-free high-speed turbo-machinery can be effectively improved by increasing the damping characteristic of the gas foil bearing (GFB). Novel hybrid bump-metal mesh foil bearings (HB-MFBs) have been previously developed. Prior experimental results show that the parallel combination of bump structure and metal mesh not only can improve the structure stiffness but also provide better damping property compared with the bump-type foil structure. To investigate the dynamic behavior of floating HB-MFBs and promote its application, this study measured the dynamic force coefficients of HB-MFBs on a rotating test rig. The vibrations of HB-MFBs with different mesh densities (40%, 32.5%, and 25%) and a generation ? bump-type foil bearing (BFB) with similar size are measured under static and impact loads to estimate the bearing characteristics. Static load tests results show that the linear stiffness decreases when the air film is generated (from 0 rpm to 20 krpm) but increases gradually with speed (from 20 krpm to 30 krpm and 40krpm). Moreover, the dynamic force coefficients of HB-MFBs indicate the significant influence of metal mesh density on bearing dynamic characteristics. The growth in block density increases the dynamic stiffness and damping coefficients of bearing. The comparison of HB-MFB (32.5% and 40%) and BFB emphasizes the good damping characteristics of HB-MFB.
TOPICS: Metals, Foil bearings, Damping, Stiffness, Bearings, Stress, Density, Stability, Turbomachinery, Vibration
research-article  
M.K.A. Ali, Hou Xianjun, F.A. Essa, Mohamed A. Abdelkareem, Ahmed Elagouz and S.W. Sharshir
J. Tribol   doi: 10.1115/1.4039720
This study aims to reveal the roles and mechanisms of Al2O3/TiO2 hybrid nanoparticles into the lube oils which could reinforce engine components durability via reducing either the friction, wear or fuel economy in automotive engines. The tribological tests were carried out under different sliding speed from 0.21 to 1.75 m/s and loads from 30 to 250 N using a reciprocating tribometer to simulate the ring/liner interface in the engine according to ASTM G181. The tribological results using hybrid nanolubricants suggested that the friction coefficient and wear rate of the ring decreased in the ranges 39-53% and 25-33%, respectively, compared to nanoparticles-free lube oil. The combined evidence of FE-SEM and EDS confirmed that the key mechanisms in anti-friction and anti-wear are a combination of the nanoparticles rolling mechanism and the replenishment mechanism of tribofilms on the sliding contact interfaces. In addition, a tribofilm formed on the rubbing surfaces is not only from the nanoparticles but also from Fe which is formed as result of iron debris particles and oil additive package such as P and S originating from zinc dialkyldithiophosphate (ZDDP).
TOPICS: Stress, Friction, Wear, Nanoparticles, Engines, Tribological films, Tribology, ASTM International, Tribometers, Corporate average fuel economy, Particulate matter, Durability, Iron, Oils, Petroleum, Automotive engines, Fuel efficiency
research-article  
Zhefeng Lei, Xiaodong Zhu, Yanhuai Li, Zhongxiao Song, Haiping Liu and Yong Qing Fu
J. Tribol   doi: 10.1115/1.4039723
Effects of partial pressure of methane on deposition rate, hardness, bonding strength and friction coefficient of TiAlN/TiAlC0.37N0.63 multilayer coating were investigated. The TiAlN coating was deposited at a N2 flow rate of 70 sccm, and TiAlC0.37N0.63 coating were deposited at a N2 flow rate of 35 sccm and a CH4 flow rate of 35 sccm. TiAlN/TiAlC0.37N0.63 multilayer coatings with different modulation periods but the same total thickness of 3.56 µm were deposited on high speed steel substrates using multi-arc ion plating technology. Microhardness and tribological measurement showed that the multilayer coating with a modulating ratio of 1:1 and a modulation period of 68 nm had a hardness of 2793.9 HV0.10, an excellent bonding strength of 52N and the minimum friction coefficient of 0.46 and low wear rate.
TOPICS: Tribology, Coatings, Flow (Dynamics), Friction, Bonding, Methane, Microhardness, Plating, Tool steel, Wear, Pressure
research-article  
Arnaud Duchosal, Damien Joly, René Leroy and Roger Serra
J. Tribol   doi: 10.1115/1.4039722
In this paper the effect of compacted graphite iron (CGI) microstructure have been investigated in tribological strategy. From industrial context two coatings have been chosen: a single layer coating (PVD) and a multilayer coating (CVD). Pin-on-disk tests have been done to analyze wear mechanisms and to directly obtain the coefficient of friction. Rotation speed of the disk have been adjusted to get the same linear velocity on different disk radii to get up to 150 m.min-1 similar to machining condition. Three-dimensional profilometer, scanning electron microscopy and nano-identation were used to observe the track profiles, the pin and the disk wears and to measure the hardness of microstructure components respectively. Results showed that PVD coating was more abrasive and had more volume of sticking materials. CVD coating which could be the most appropriate for machining CGI, has a real anti-sticking property and has less friction coefficient than PVD coating. But the presence of small TiCN precipitates in CGI material have a proven negative effects in CVD coating lifetime.
TOPICS: Tribology, Cast iron, Coatings, Disks, Chemical vapor deposition, Friction, Machining, Rotation, Wear, Scanning electron microscopy
research-article  
Ehsan Fatourehchi, Hamed Shahmohamadi, Mahdi Mohammadpour, Ramin Rahmani, Stephanos Theodossiades and Homer Rahnejat
J. Tribol   doi: 10.1115/1.4039567
Improved fuel efficiency and reduced emissions are key drivers for modern drivetrain systems. Therefore, in recent years, dry sumps with air-oil mist lubrication have been used for efficient transmission design in order to reduce the churning losses. With dry sumps appropriate cooling measures should be implemented to dissipate the generated contact heat in an efficient manner. This paper integrates a tribological model with three- dimensional thermofluid analysis in order to predict the heat generated in the lubricated meshing gear contacts and its dissipation rate by an impinging oil jet in air-oil mist environment. Such an approach has not hitherto been reported in literature. The results show that the generated heat under realistic conditions cannot be entirely dissipated by the impinging oil jet in the air-oil mist transmission casing. Numerical results are used to derive extrapolated regressed equations for heat transfer purposes for time-efficient analysis. These conform well with the detailed numerical results.
TOPICS: Gears, Thermal analysis, Heat, Heat transfer, Cooling, Energy dissipation, Design, Thermofluids, Fuel efficiency, Emissions, Tribology, Lubrication

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