Accepted Manuscripts

Technical Brief  
Jianlin Sun, Shaonan Du, Yanan Meng and Ping Wu
J. Tribol   doi: 10.1115/1.4040512
In this article, triethanolamine modified graphene oxide (TMGO) has been synthesized by filtering and drying the high temperature reaction solution of graphene oxide (GO) and triethanolamine. The tribological performance of TMGO and GO in deionized water (DW) were investigated using a four-ball tribometer. The microscopic morphology of the worn surface was analyzed by optical microscope and scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results showed that the average friction coefficient (AFC) and wear scar diameter (WSD) of 0.1 wt.% TMGO decreased by 21.9% and 6.2% compared with the two values of 0.1 wt.% GO, and no corrosion occurred on metal surface. The minimum of the AFC and WSD occurred at 0.3 wt.% TMGO. This study provides a new reference for the application of graphene oxide in lubrication.
TOPICS: Tribology, Graphene, Water, High temperature, Tribometers, Friction, Wear, Lubrication, Drying, Filtration, Scanning electron microscopes, Spectroscopy, Optical microscopes, Metal surfaces, Corrosion
Ranjan Das, Suhas S. Joshi and harish Barshilia
J. Tribol   doi: 10.1115/1.4040511
In multi-point operations like drilling, cutting velocities and cutting edge geometries vary along cutting lips so is the rate of progression of flank wear. Analytical evaluation of flank wear land width in the case of complex tools has received a limited attention so far. This work evaluates progression of flank wear in orthogonal machining and adopts it to drilling. An abrasive flank wear has been modeled, wherein, cutting speed determines the rate of abrasion, and the feed rate determines the chip load. The model considers stress distribution along rake surfaces, and temperature dependent properties of tool and work materials. Assuming that the flank wear follows a typical wear progression as in a pin-on-disc test, the model evaluates cutting forces and the consequent abrasive wear rate for an orthogonal cutting. To adopt it to drilling, variation in cutting velocity and, dynamic variation in rake, shear and friction angles along the length of the cutting lips have been considered. Knowing the wear rate, the length of the worn out flank (vb) has been evaluated. The model captures progression of flank wear in zones i, ii and iii of a typical tool-life plot. It marginally underestimates the wear in the rapid wear region and marginally overestimates it in the steady-state region.
TOPICS: Drilling, Wear, Cutting, Steady state, Temperature, Machining, Stress, Shear (Mechanics), Stress concentration, Abrasion, Disks, Friction
Cheng Liu, Yanjun Lu, Yongfang Zhang, Sha Li, Jianxiong Kang and Norbert Müller
J. Tribol   doi: 10.1115/1.4040510
The tribological performance of a compression ring-cylinder liner system (CRCL) is numerically studied. A thermal-mixed lubrication model is developed for the lubrication analysis of the CRCL with consideration of the cylinder liner deformation. An oil transport model coupled with a mass conservation cavitation algorithm is employed to predict the oil consumption and the transition between the fully flooded lubrication condition and starved lubrication condition. On this basis, the effects of the oil supply and cylinder liner deformation on the frictional characteristics are investigated under cold and warm engine conditions. The results show that the cylinder liner deformation and oil supply have great influence on the tribological performance of the CRCL. Better tribological performance and lower oil consumption can be obtained by reasonably controlling the oil supply.
TOPICS: Tribology, Lubrication, Cylinders, Deformation, Engines, Cavitation, Algorithms, Compression
Xiaoliang Yan, Yuyan Zhang, Guoxin Xie, Xiaoqiong Du and Fen Qin
J. Tribol   doi: 10.1115/1.4040474
Predicting the mixed thermal lubrication performance and fatigue life of point contact components becomes more and more important with the increasing demand for the load capacity of machinery. To achieve this, a deterministic mixed thermal elastohydrodynamic lubrication (TEHL) model in point contacts considering surface roughness is developed in this study. This model is capable of determining the pressure and temperature under different lubrication regimes from mixed to full-film lubrication. Then, the established model is extended to the subsurface stress and fatigue life predictions. Numerical simulations are conducted to analyze the lubrication characteristics and fatigue life for the three-dimensional sinusoidal surfaces with variable directions. Results show that increasing entraining velocity contributes to the reduction of pressure fluctuation and prolongation of fatigue life. However, the resulting temperature increases with the entraining velocity. As for the influence of lubricant viscosity, increasing it prolongs the fatigue life, especially under mixed TEHL conditions. What's more, the effect of rough surface texture feature on fatigue life has a close relationship with the lubrication regime.
TOPICS: Texture (Materials), Elastohydrodynamic lubrication, Fatigue life, Lubrication, Temperature, Surface roughness, Stress, Pressure, Machinery, Viscosity, Computer simulation, Lubricants
Tadeusz Stolarski and Masaaki Miyatake
J. Tribol   doi: 10.1115/1.4040416
The influence of embodiment flexibility on the performance and motion precision of an acoustic journal bearing is presented. Two completely different embodiments of the bearing were investigated using three criteria of performance assessment that is torque at the start-up, amount of separation due to squeeze film pressure and motion stability of the shaft running at speed. The embodiment with built-in flexibility proved to perform far better that the bearing which overall flexibility was much less. However, considerations pertinent to the easy of machining and fatigue endurance mitigate the ranking of performance of the two embodiments investigated.
TOPICS: Acoustics, Geometry, Journal bearings, Bearings, Torque, Pressure, Stability, Fatigue, Separation (Technology), Machining
Aida Nadim, Reza Taghiabadi and Ahmad Razaghian
J. Tribol   doi: 10.1115/1.4040384
The effect of Mn modification on the tribological properties of Al-15Mg2Si-(0.5-2)Fe composites was investigated. The sliding wear tests were conducted under the applied pressures of 0.25, 0.5 and 1.0 MPa at the constant sliding speed of 0.13 m/s. According to the results, the behavior of FeMn-rich intermetallics against the strains induced by sliding wear has an important role in the wear behavior of composites. In low-Fe composites (0.5-1 wt% Fe), Mn promotes the formation of Chinese script ?-Al15(Fe,Mn)3Si2 phases instead of harmful ?-Al5FeSi platelets. The formation of these compounds strengthens the substrate and decreases its microcracking tendency giving rises to a more stable tribolayer and improved wear properties. At the higher Fe contents, Mn modification leads to the formation of primary polyhedral or star-like ?-Al15(Fe,Mn)3Si2 compounds in the microstructure and substantially neutralizes the harmful effect of the primary ?-Fe crystals on the wear behavior. However, when subjected to the friction-induced surface plastic strains, the near-surface ?-FeMn particles fracture and incorporate into the tribolayer making it unstable and less protective. The tribolayer stability in Mn-modified composites decreases the chance of adhesion between contacting surfaces, and, under low applied pressures, lowers the average friction coefficient (AFC) and its fluctuation. At higher applied pressures, however, the non-modified composites exhibit lower AFC which is probably due to the negative impact of ?-Fe fragments on the tribolayer shear strength.
TOPICS: Tribology, Composite materials, Wear, Friction, Ferromanganese, Fracture (Materials), Fracture (Process), Shear strength, Wear testing, Platelets, Stability, Particulate matter, Crystals, Adhesion, Intermetallic compounds
Zhiqian Wang and Xingna Liu
J. Tribol   doi: 10.1115/1.4040385
This paper studies elastic-plastic contact of Greenwood-Williamson (GW) rough surfaces, on which there are many asperities with the same radius whose height obeys Gaussian distribution. The formulas for the load/area-separation relationship of rough surfaces have been presented based on Wang's smooth model of singe-asperity elastic-plastic contact, which improved Kogut-Etsion (KE) empirical model from finite-element-analysis (FEA) data. We find that the load/area-separation relationship can also be described by empirical Gaussian functions. The load-area relationship of rough surfaces is approximately linear. Utilizing Wang's conclusion that Etsion's single-asperity elastic-plastic loading (EPL) index is approximately equal to the ratio of the single-asperity residual plastic contact displacement to the single-asperity total elastic-plastic contact displacement, the formula for Etsion's modified plasticity index (MPI) of elastic-plastic contact of rough surfaces are also presented. We find that the MPI is approximately linear with the separation of rough surfaces for a given GW plasticity index (the standard deviation of the asperity height of rough surfaces ranging from 5 to 30), and an empirical formula has been presented. When the standard deviation is smaller than 5, due to the large proportion of the elastic deformation in the total deformation, the MPI will slightly deviate from linearity.
TOPICS: Surface roughness, Stress, Separation (Technology), Plasticity, Deformation, Finite element analysis, Displacement, Gaussian distribution
Itzhak Green
J. Tribol   doi: 10.1115/1.4040386
TOPICS: Lubrication, Cavitation
Hoa Ngan Nguyen and philippe Bocher
J. Tribol   doi: 10.1115/1.4040305
The objective of this research is to conduct a finite element analysis to better understand the effects of induction hardening on rolling contact fatigue (RCF). The finite element analysis was developed in 3D to estimate the maximal loading and the positions of the crack nucleation sites in the case of cylinder contact rolling. Rolling contact with or without surface compressive residual stress were studied and compared. The residual stress profile was chosen to simulate the effects of an induction hardening treatment on a 48HRC tempered AISI4340 steel component. As this hardening process not only generates a residual stress gradient in the treated component, but also a hardness gradient (called over-tempered region), both types of gradients were introduced in the present model. Residual stresses in compression were generated in the hard case (about 60HRC), tension values were introduced in the over-tempered region, where hardness as low as 38HRC were set. In order to estimate the maximal allowable loadings in the rotating cylinders to target a life of 106 cycles, a multiaxial Dang Van criterion and a shear stress fatigue limit were used in the positive and negative hydrostatic conditions, respectively. With the proposed approach, the induction hardened component was found to have a maximal allowable loading significantly higher than that obtained with a non-treated one, and it was observed that the residual tensile stress peak found in the over-tempered region could become a limiting factor for fatigue rolling contact life.
TOPICS: Fatigue, Electromagnetic induction, Rolling contact, Hardening, Simulation, Finite element analysis, Stress, Cylinders, Tension, Fatigue limit, Shear stress, Compression, Cycles, Nucleation (Physics), Fracture (Materials), Steel, Residual stresses, Hydrostatics
Dara Childs
J. Tribol   doi: 10.1115/1.4038867
New models are developed for flexibly-mounted stator (FMS) and flexibly-mounted rotor (FMR) mechanical seals that incorporate the radial reaction force components produced by supporting O-rings due to relative squeezing motion across the O-rings. Supporting data come from tests done in relation to O-ring supports for ball bearing races. The reaction-force model is linear but a nonlinear function of excitation frequency. The model accounts for the axial displacement doz of the O-ring from the mass center of the seal stator (FMS configuration) or seal rotor (FMR configuration), which couples the radial and pitch-yaw motion of the model's stiffness and damping matrices. Greens' coned-face-seal model is used to define the reaction moment arising across the seal faces via stiffness and damping matrices. The damping matrix does not not coincide with Green's. His is constant; the matrix developed here contains terms that are harmonic at twice the precession-frequency. When averaged over one precession cycle, the new average damping matrix coincides with Green's result. When the averaged damping matrix is used, the resultant model is linear. However, because of the viscoelastic reaction-force and reaction-moment models used for the O-ring coefficients, most of the stiffness and damping matrices are strong functions of the assumed precession frequency. The new FMR model contains a skew-symmetric stiffness matrix due to the O-ring damping terms. In rotordynamics, skew symmetric stiffness matrices due to internal damping in the rotor can lead to rotordynamic instabilitities.
TOPICS: Seals, Structural dynamics, Pumps, Vibration analysis, Damping, Stiffness, Rotors, Flexible manufacturing systems, Stators, Excitation, Yaw, Rotordynamics, Ball bearings, Cycles, Displacement
Mamoun Fellah and Linda Aissani
J. Tribol   doi: 10.1115/1.4038103
The aim of the present research was focused on the study of the effect of replacing vanadium by niobium and iron on the tribological behavior of Hot Isostatic Pressed (HIPed) titanium alloy (Ti-6Al-4V) biomaterial, using a ball-on-disk type Oscillating tribometer, under wet conditions using physiological solution conditions (Ringer solution) in accordance with the ASTMG 99, ISO 7148-1:2012, and ASTM G 133–95 standards. The tests were carried out under a normal load of 6 N, with an AISI 52100 grade steel ball as a counter face. The morphological changes and structural evolution of the nanoparticle powders using different milling times (2, 6, 12 and 18 h) were studied. The morphological characterization indicated that the particle and crystallite size continuously decreases with increasing milling time to reach the lowest value of 4 nm at 18 hours milling. The friction coefficient and wear rate were lower in the samples milled at 18 h (0.226, 0.297 and 0.423) and (0.66 x10-2, 0.87x10-2 and 1.51x10-2 µm3.N-1.µm-1) for Ti-6Al-4Fe, Ti-6Al-4Nb and Ti-6Al-4V, respectively. This improvement in friction and wear resistance is attributed to the grain refinement at 18 hour milling. The Ti-6Al-4Fe samples showed good tribological performance for all milling times
TOPICS: Wear, Titanium alloys, Milling, Sliding friction, Biomedicine, Tribology, Friction, ASTM International, Tribometers, Wear resistance, Physiology, Stress, Nanoparticles, Disks, Iron, Steel, Particulate matter, Biomaterials

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