Accepted Manuscripts

Hui Tan, Jun Cheng, Shuai Wang, Shengyu Zhu, Yuan Yu, Zhuhui Qiao and Jun Yang
J. Tribol   doi: 10.1115/1.4038438
Wear-resistant aluminum alloys have enormous potential applications. In this paper, the Al-20Si-5Fe-2Ni alloy was fabricated by hot pressed sintering, and its dry sliding wear behavior was investigated from 25 to 500 °C sliding against Al2O3 ceramic and AISI 52100 steel. The microstructure, phase, high temperature hardness and worn surface of the sintered alloy were examined. The results indicate that the uniform distribution of Si particles and Al5FeSi intermetallic in Al matrix contribute to its superior tribological properties. Additionally, the correlation of the tribological behavior of the alloy with the sliding testing conditions was studied, and its wear mechanism was discussed.
TOPICS: Alloys, Tribology, Temperature, Wear, Intermetallic compounds, Steel, Ceramics, Particulate matter, Aluminum alloys, Sintering, Testing, High temperature
Eric Djiha Tchaptchet, Germaine Djuidje Kenmoe and Timoléon C. Kofane
J. Tribol   doi: 10.1115/1.4038409
We investigate the effect of the shape potential on the frictional behavior transitions. The Tomlinson parameter for the deformable substrate potential is calculated theoretically and its influence on friction force is studied. Futhermore, effects of temperature and substrate shape on the tip jump probability are presented. We find two critical times which characterize the tip dynamics. The first critical time is the time spent by the tip to reach next potential minimum and the second is the time at which the tip exhibits an equiprobability of forward and backward jump. We show that these critical times depend strongly on the substrate shape as well as on the temperature.
TOPICS: Friction, Probability, Shapes, Temperature, Temperature effects, Dynamics (Mechanics)
Zhijian Wang, Qingtao Yu, Xuejin Shen and Xiaoyang Chen
J. Tribol   doi: 10.1115/1.4038410
This paper developed a point-contact mixed lubrication model, incorporating thermal effect, the asperity elasto-plastic deformation and the boundary film properties, to evaluate the relative severity of contact condition. Then based on the integrity of boundary films and the sharp increase of the friction coefficient, the possibility of the occurrence of scuffing was evaluated. The model was verified with published experimental data. A systematic parametric analysis was made to investigate the influences of surface roughness, contact geometry and the lubricant properties on contact performance. The results suggest that low surface roughness and high-quality boundary film can effectively improve the scuffing resistance under current operating conditions, while high-viscosity oil and large-radius curvature are not as much effective especially when the components work under high-sliding and high-temperature.
TOPICS: Lubrication, Risk assessment, Surface roughness, Temperature effects, Geometry, High temperature, Viscosity, Lubricants, Deformation, Friction
Jian Wang, Qingliang Wang, Xiao Zhang and Dekun Zhang
J. Tribol   doi: 10.1115/1.4038414
The coupled impact and rolling wear behaviors of the medium manganese austenitic steel (Mn8) were studied by comparing with the traditional Hadfield (Mn13) steel. Scanning electron microscopy (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM) were used to analyze the wear and hardening mechanisms. The experimental results show that the impact and rolling wear resistance of hot-rolled medium manganese steel(Mn8) is better than that of high manganese steel(Mn13) under condition of the low impact load. The better work hardening sensitivity effectively improves the wear resistance of medium manganese steel. Not only the coefficient of friction is low, but the weight loss and wear rate of the wear are lower than that of high manganese steel. After impact and rolling wear, a hardened layer with a thickness of about 600µm is formed on the wear surface. The highest micro-hardness of the sub-surface layer for Mn8 is about 594HV and the corresponding Rockwell hardness is about 55HRC, showing the remarkable work hardening effect. The wear-resistant strengthening mechanism of medium manganese steel is the compound strengthening ,including the deformation induced martensitic transformation, dislocation strengthening and twin strengthening. In initial stage of impact and rolling abrasion, the dislocation strengthening plays a major role. When the deformation reaches a certain extent, the deformation induced martensitic transformation and twinning strengthening begins to play a leading role.
TOPICS: Wear, Hardening, Steel, Deformation, Martensitic transformations, Dislocations, Wear resistance, Work hardening, Weight (Mass), Microhardness, Twinning, Electron microscopes, Stress, Abrasion, Scanning electron microscopy, Friction, X-rays
Joseph Polly, David Talbot, Ahmet Kahraman, Avinash Singh and Hai Xu
J. Tribol   doi: 10.1115/1.4038412
In this study, load-independent (spin) power losses of a gearbox operating under dip-lubrication conditions are investigated experimentally using a final-drive helical gear pair from an automotive transmission as the example system. A dedicated gearbox is developed to operate a single gear or a gear pair under given speed and temperature conditions. A test matrix that consists of sets of tests with (i) a single spur, helical gears, or disks with no teeth, and (ii) helical gear pairs is executed at various temperatures, immersion depths and pinion positions relative to its mating gear. Power losses from single gear and gear pair at identical operating conditions are compared to quantify the components of the total spin loss in the form of losses due to gear drag, gear mesh pocketing, and bearings and seals.
TOPICS: Mechanical drives, Gears, Helical gears, Temperature, Spin (Aerodynamics), Particle spin, Rotation, Lubrication, Drag (Fluid dynamics), Stress, Bearings, Disks, Automotive transmissions
Ning Yang, Zhihui Xia and Xingjun Wang
J. Tribol   doi: 10.1115/1.4038407
Lapping is still an efficient and economical way in diamond shaping process, which is important in both industrial and scientific applications. It has known that the material removal originates from the phase change or amorphization of diamond crystal carbon atoms which is chemically activated by stress and forming a topmost layer of amorphous carbon atoms. In this paper, the phase change of amorphous carbon atoms undergoing nano cutting of amorphous layer during diamond lapping process is studied by molecular dynamics(MD) simulation. Two regions, the debris layer and cutting surface underneath, are focused. In the debris layer, change of sp2 carbon atoms is directly affected by impact, while underneath the cutting surface the changes of carbon atoms are almost not affected; the change speed of amorphous carbon atoms is higher than that of pristine crystal ones; main phase change is transformation of sp3 into sp2; cutting depth to different extent affects the phase changes of sp3 and sp2 carbon atoms. Our study expands the understanding of diamond lapping process.
TOPICS: Atoms, Grinding, Carbon, Cutting, Diamonds, Crystals, Simulation, Stress, Molecular dynamics, Phase transitions
Bhushan Nandre and Girish Desale
J. Tribol   doi: 10.1115/1.4038355
The present experimental study investigates the effect of constant kinetic energy on erosion wear of Aluminium alloy 6063. Three different natural erodents (quartz, silicon carbide and alumina) with different particle sizes are used to impact at 45° and 90° impact angles. For calculating the number of particles in the slurry pot, it is assumed that the solid particles are of spherical shape. The total numbers of impacting solid particles were kept constant by adjusting the solid concentration, velocity and test duration. The SEM images of the three erodents show that the alumina particles have sharp edges with more angularity, silicon carbide particles have sub angular nature while quartz particles are blocky in shape. The mass loss per particle at 45° impact angle is observed higher than at normal impact angle. It may be due to the change in material removal mechanism with changing the impact angle. It is also found that the mass loss per particle from the target material having different particle size with constant kinetic energy remains constant for respective erodents. This indicates that the velocity exponent of impacting particles is around 2. The SEM images of eroded surfaces reveal the different mechanisms of material removal at 45° impact angle and at normal impact angle.
TOPICS: Kinetic energy, Erosion, Slurries, Wear, Particulate matter, Quartz, Shapes, Silicon, Aluminum alloys, Particle size
Fanming Meng and Wei Zhang
J. Tribol   doi: 10.1115/1.4038353
The noise of a journal bearing with the compound groove texture is studied based on computation fluid dynamic (CFD) theory and broadband noise source mode. In doing so, the acoustic power levels of the noise for the journal bearing with the compound groove textures and simple ones are separately solved at the varied geometry sizes and positions of the groove texture, and varied lubricant parameters using CFD method. Numerical results show that the compound groove texture can more effectively lower the acoustic power level of the journal bearing, compared with the simple groove texture. This reduction depends on the groove size and its position, and density and viscosity of the lubricant.
TOPICS: Noise (Sound), Texture (Materials), Journal bearings, Computational fluid dynamics, Acoustics, Lubricants, Density, Fluids, Viscosity, Computation, Geometry
Micheal McKee and Faramarz Gordaninejad
J. Tribol   doi: 10.1115/1.4038354
This study reviews the work performed in the field of reciprocating shaft seals from the advent of the scientific topic in the 1940s. Concepts of leakage, film layers, friction, wear, and other concerns with shaft seals are discussed. The importance of shaft seals as it pertains to liquid springs is brought to light along with issues requiring a need for these seals to withstand high temperatures and high pressures. Issues resulting from a seal exposure to high temperatures, such as thermosetting and embrittlement are discussed in conjunction with materials and properties that allow seals to operate in high-temperature environments. High-pressure sealing challenges are identified along with the techniques currently employed to overcome these issues, such as fiber reinforcement and backup rings. Sealing solutions have been implemented independently for both high-pressure and high-temperature applications, however, the combination of high pressures coupled with high temperatures is still a challenge today.
TOPICS: High pressure (Physics), High temperature, Sealing (Process), Friction, Wear, Fibers, Embrittlement, Springs, Leakage
Wang Yunlong, Wang Wenzhong, Li Yulong and Zhao Ziqiang
J. Tribol   doi: 10.1115/1.4038356
Lubrication analysis of rolling bearing is often conducted with assumed operating conditions, which doesn't consider the effect of internal dynamics of rolling bearing. In this paper, the effects of the applied load and bearing rotational speed on the lubrication performance in an angular contact ball bearing are conducted which combines the bearing dynamic analysis and thermo-elastohydrodynamic lubrication (TEHL) analysis. Firstly, the internal motions and contact forces are obtained from the developed bearing dynamic model, and then it was integrated into the TEHL model to investigate the lubrication performance of the bearing. The results show that the rotational speed and external load has significant effects on film thickness, temperature and power loss; if the improper axial load is applied for certain bearing speed, the lubrication performance will deteriorate and thermal failure may occur; there exists critical load or speed to keep good lubrication performance and avoid thermal failure; the skidding contributes to the thermal failure and bad lubrication performance.
TOPICS: Lubrication, Failure mechanisms, Ball bearings, Bearings, Stress, Failure, Rolling bearings, Dynamic models, Dynamic analysis, Film thickness, Dynamics (Mechanics), Temperature
Jinwoo Lim, Kwang-Hee Lee and Chul-Hee Lee
J. Tribol   doi: 10.1115/1.4038352
In recent studies, many mathematical models have been introduced to describe the shear deformation characteristics of a magnetorheological elastomer (MRE). Owing to its beneficial elastomeric characteristics, an MRE can be adopted in novel controllable devices such as friction dampers and brakes. In this study, mathematical models are introduced to identify the frictional behavior of an MRE under different magnetic field conditions. Specifically, the improved LuGre model and the strain-stiffening model are compared using a system identification method. To identify the model that best describes the stick/slip behavior of an MRE, a harmonic frictional force was exerted on its surface with magnetic fields of varying strength. The improved LuGre model showed a precise correlation with the experimental results, and the strain-stiffening model was shown to have a simple structure for describing the frictional phenomenon. The system output error of the I-LuGre model remained within smaller errors than that of the strain-stiffening model. The parameter variations of each model that can be utilized to construct a control strategy are provided herein.
TOPICS: Magnetic fields, Elastomers, Stick-slip, Errors, Shear deformation, Dampers, Brakes, Friction
Janith Samarasinghe, Wyatt Culler, Bryan D. Quay, Domenic Santavicca and Jacqueline O'Connor
J. Tribol   doi: 10.1115/1.4037461
Fuel staging is a commonly used strategy in the operation of gas turbine engines. In multi-nozzle combustor configurations, this is achieved by varying fuel flow rate to different nozzles. The effect of fuel staging on flame structure and self-excited instabilities is investigated in a research can combustor employing five swirl-stabilized, lean-premixed nozzles. At an operating condition where all nozzles are fueled equally and the combustor undergoes a self-excited instability, fuel staging successfully suppresses the instability: both when overall equivalence ratio is increased by staging as well as when overall equivalence ratio is kept constant while staging. Increased fuel staging changes the distribution of time-averaged heat release rate in the regions where adjacent flames interact and reduces the amplitudes of heat release rate fluctuations in those regions. Increased fuel staging also causes a breakup in the monotonic phase behavior that is characteristic of convective disturbances that travel along a flame. In particular, heat release rate fluctuations in the middle flame and flame-flame interaction region are out-of-phase with those in the outer flames, resulting in a cancellation of the global heat release rate oscillations. The Rayleigh integral distribution within the combustor shows that during a self-excited instability, the regions of highest heat release rate fluctuation are in phase-with the combustor pressure fluctuation. When staging fuel is introduced, these regions fluctuate out-of-phase with the pressure fluctuation, further illustrating that fuel staging suppresses instabilities through a phase cancellation mechanism.
TOPICS: Fuels, Combustion chambers, Nozzles, Flames, Heat, Pressure, Fluctuations (Physics), Gas turbines, Flow (Dynamics), Oscillations

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