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research-article  
Akant Kumar Singh and Siddhartha Vashishtha
J. Tribol   doi: 10.1115/1.4037335
This research work presents a modified mathematical method to estimate the specific wear rate of spur gears for specified service conditions by calculating the coordinates of the point on the involute of gear tooth profile. This work stands apart in a way that an entirely novel manufacturing process developed in-house is used to fabricate functionally graded materials (FGMs) based thermoplastic gears which have never been explored before and the specific wear rate of manufactured gears is estimated using the proposed method. FGM and homogeneous gears are manufactured by means of an especially designed mould and a punch. Polyamide 66 (PA66) filled with 15 wt.% and 30 wt.% glass fibers is used to fabricate FGM and homogeneous gears. Neat PA66 gear is also fabricated for comparative study. Gradation in FGM gears is verified by Scanning electron microscope (SEM) analysis and hardness measurements. Thermal and wear tests of the gears are conducted over a range of rotational speed (500 - 1700 rpm) and torque (0.8 - 3.2 Nm). Thermal and wear behavior of developed gears are successfully analyzed using Taguchi methodology and analysis of variance (ANOVA). The service life of FGM gears is found to be superior as compared to unfilled and homogeneous gear. FGM gear filled with 30 wt% glass fiber exhibited minimum gear tooth surface temperature and specific wear rate among all the fabricated gears.
TOPICS: Wear, Glass fibers, Functionally graded materials, Spur gears, Gears, Gear teeth, Torque, Manufacturing, Service life (Equipment), Temperature, Scanning electron microscopes, Wear testing
research-article  
Deepak Patil and Prof. C. Fred Higgs III
J. Tribol   doi: 10.1115/1.4037212
In multi-particle simulations of industrial granular systems such as hoppers, tumblers, and mixers the particle energy dissipation is governed by an important input parameter called the coefficient of restitution (COR). Oftentimes, the wall thickness in these systems is on the order of a particles diameter or less. However, the COR value implemented in event-driven simulations is either constant or a monotonically decreasing function of the impact velocity. The present work experimentally investigates the effect of wall thickness on the COR through sphere-thin plate elastoplastic impacts and elucidates the underlying impact phenomena. Experiments were performed on 0.635 cm and 0.476 cm diameter (d) spheres of various materials impacting aluminum 6061 plates of different thicknesses (t) with the low impact velocities up to 3.1 m/s. Besides COR, indentation measurements and numerical simulations are performed to gain detailed understanding of the contact process and energy dissipation mechanism. As the 't/d' ratio decreases a considerable amount of energy is dissipated into flexural vibrations leading to a significantly lower COR value. Based on the results, it can be concluded that using a constant COR input value in particle simulations may not always be an appropriate choice, especially, in the case of thin plates. However, these new COR results validate that when the wall thickness is more than twice the sphere diameter (i.e., t/d > 2), a constant COR value obtained for an impact with semi-infinite plate can be reasonably used.
TOPICS: Aluminum, Particulate matter, Computer simulation, Simulation, Energy dissipation, Engineering simulation, Plates (structures), Vibration, Wall thickness
research-article  
Hui Tan, Shuai Wang, Jun Cheng, Shengyu Zhu and Jun Yang
J. Tribol   doi: 10.1115/1.4037213
Aluminum metal matrix composites (Al-MMCs) have been considered as promising materials for aerospace and automotive industries due to their excellent balance of physical, mechanical and tribological properties. In the present work, the Al-Fe-V-Si alloy matrix composites with 0-20 wt.% copper-coated graphite were fabricated by hot pressed sintering. The dry sliding tests were carried out at various temperatures ranging from room temperature (RT) to 350°C. The microstructure, phase, hardness and worn surface of the sintered composites were examined in detail. The effect of copper-coated graphite amount on the properties of the composite was also investigated. The results show that the Al-Fe-V-Si-Graphite composites mainly consists of a-Al, Al8Fe2Si intermetallic and graphite phases. The addition of Cu-coated graphite can decrease the friction coefficient and wear rate from RT to 350 °C. The Al-Fe-V-Si-Graphite composite containing 10 wt.% copper-coated graphite exhibits better wear properties than other composites. The favorable lubricating properties were attributed to the tribolayer with graphite lubricating film formed on the worn surface.
TOPICS: Temperature, Composite materials, Tribology, Graphite, Copper, Wear, Friction, Aluminum, Intermetallic compounds, Alloys, Sintering, Metal matrix composites, Aerospace industry
research-article  
Hiroyuki Yamada, Hiroo Taura and Satoru Kaneko
J. Tribol   doi: 10.1115/1.4037151
Numerous previous numerical studies have investigated the effect of surface texturing upon the static characteristics of journal bearings, including their load-carrying capacity and friction torque. In general, the dynamic characteristics of journal bearings are also important, since they are essential factors in predicting the vibration behavior of actual rotors supported by journal bearings. However, the effects of surface texture upon these dynamic characteristics have not been investigated through either numerical or experimental analysis. Thus, in the present study, such analyses were conducted to investigate the dynamic characteristics of textured journal bearings, such as their dynamic coefficients of oil film and the stability threshold shaft speed supported by the bearings. Numerical analysis was done using a model that included inertial effects and energy loss; this model agreed well with experimental results concerning static characteristics from our previous study. Dynamic testing based on a sinusoidal-excitation method was also performed using textured journal bearings with uniform square dimples to verify the numerical results, which agreed qualitatively with those of experiment, confirming the validity of the numerical analysis. These results suggest that under the same operating conditions, the main effect of texturing upon the dynamic coefficients is to yield the cross-coupled stiffness coefficients with lower absolute values than the conventional ones with a smooth surface. The linear stability threshold shaft speed of the rotor supported by the textured journal bearings became higher than that of a smooth bearing, mainly due to the reduction of cross-coupled stiffness coefficients. This tendency became more pronounced for high Reynolds number operating conditions and textured bearings with a large number of dimples.
TOPICS: Journal bearings, Bearings, Numerical analysis, Rotors, Stability, Stiffness, Surface texture, Excitation, Torque, Friction, Reynolds number, Energy dissipation, Dynamic testing (Materials), Dynamic testing (Engineering), Load bearing capacity, Vibration, Experimental analysis
research-article  
Shuyun Jiang, Shengye Lin and Chun-dong Xu
J. Tribol   doi: 10.1115/1.4037134
This paper studies the static and dynamic coefficients of an externally pressurized porous gas journal bearing. The finite difference method is used to solve the Reynolds equation of the bearing to obtain the static load capacity. The linear perturbation method is used to derive the perturbation equations considering 4 degrees of freedom, namely, the translational movements in x and in y directions, and the rotational movements around x and around y directions. The effects of various parameters on the dynamic behaviors of the journal bearing are studied. These parameters include the bearing number, the supply pressure, the feeding parameter, the length-to-diameter ratio, the porosity parameter and the eccentricity ratio. Simulated results prove that the proposed method is valid in estimating the static and dynamic characteristics of a porous gas journal bearing with 4 degrees of freedom.
TOPICS: Degrees of freedom, Journal bearings, Bearings, Finite difference methods, Perturbation theory, Porosity, Pressure, Stress
research-article  
Sandip Panda, Mihir Sarangi and S. K. Roy Chowdhury
J. Tribol   doi: 10.1115/1.4037136
This paper proposes a wear model for polymers based on so called mechanistic processes comprising both low cycle fatigue and abrasive wear mechanisms which are prominent in polymer-metal sliding interfaces. Repeated elastic contact causes localized fatigue, whereas abrasive part is an anticipatory outcome of plastic contacts by hard metal asperities on to soft polymer surface. Further, presuming adhesive interactions in elastic-plastic contacts, asperity contact theories with necessary modifications were analyzed to assess load and separation for their subsequent use in elementary wear correlations. Both Gaussian and Weibull distributions of asperity heights were considered to include statistics of surface micro-geometry. Finally, volumetric wear was written in terms of roughness parameters, material properties, and sliding distance. Validation was conducted extensively, and reliability of the formulation was achieved to a large extent. Experimental part of this work included several pin-on-disc tests using PEEK pins and 316L stainless steel discs. Discs with different roughness characteristics generated by polishing, turning and milling were tested. Experimental results agreed well with predictions for the polished surface and with some deviations for other two surfaces. Further, fatigue to abrasive wear ratio was identified as an analytical tool to predict prevailing wear mechanism for polymer-metal tribo-systems. After examining the considered cases, it was both interesting and physically intuitive to observe a complete changeover in wear mechanisms following simply an alteration of roughness characteristics.
TOPICS: Wear, Polymers, Disks, Metals, Surface roughness, Fatigue, Polishing, Pins (Engineering), Materials properties, Performance, Adhesives, Reliability, Separation (Technology), Geometry, Low cycle fatigue, Milling, Stainless steel, Weibull distribution, Statistics as topic, Stress
research-article  
Takashi Nogi, Hiroshi Shiomi and Noriko Matsuoka
J. Tribol   doi: 10.1115/1.4037135
Under repeated overrollings, the elastohydrodynamic lubrication (EHL) film thickness can be much less than the fully flooded value due to the ejection of the lubricant from the track. The ejection of the lubricant is caused by the pressure flow in the inlet, and under conditions of negligible reflow, the reduction rate is predicted by the numerical analysis with a uniform inlet film thickness. However, the degree of starvation is determined by the balance of the ejection and reflow. In the previous papers for circular contacts, reflow is taken into account using a non-uniform inlet film thickness obtained based on the Coyne-Elrod boundary condition. In this paper, the model for circular contacts is extended to elliptical contacts, which are of more practical importance in rolling bearings. The model is verified for the inlet distance and the film thickness using a roller on disk optical test device. Numerical results are fitted to an inlet distance formula, which is a function of the initial film thickness, the fully flooded central film thickness, the capillary number and the ellipticity ratio. The inlet distance formula can be applied to the Hamrock-Dowson formulas for the starved film thickness.
TOPICS: Elastohydrodynamic lubrication, Film thickness, Lubricants, Rollers, Rolling bearings, Pressure, Flow (Dynamics), Numerical analysis, Disks, Boundary-value problems
research-article  
Eberhard Abele, Lars Holland and Philipp Hoenig
J. Tribol   doi: 10.1115/1.4037066
Movement analyses of bearings with regard to stable and unstable motion behavior typically investigate the cage whirl. However, some experimental and simulation based studies exist that analyze the movements of the rolling elements. The majority of these investigations focus on lower shaft speeds. This paper presents an image based approach for investigating the rolling element motions under high-speed operation condition. A new evaluation algorithm is presented and its suitability is verified first by generic images and afterwards by experiments on cylindrical roller bearings.
TOPICS: Algorithms, Bearings, Image processing, Whirls, Roller bearings, Simulation
research-article  
Tugce Kasikci, Ming-Chih Wang, Ash Nayak, Turguy Goker and Sinan Muftu
J. Tribol   doi: 10.1115/1.4037067
Traction between a thin tensioned tape and a grooved roller could be significantly affected due to lubrication effects that stem from the air entrainment into the tape-roller interface. An experimental and theoretical investigation was carried out to investigate the tape contact with a grooved roller. The tape-to-roller spacing was measured in a modified tape drive at various operational speed and tension values. The experiments showed that increasing tape tension and tape speed causes the tape-to-land spacing to increase. This unusual result is shown to be due to tape bending laterally into the grooves. The effects of air entrainment on tape deflection and contact with a land is modeled by using shell theory, air lubrication and contact mechanics. A relatively wide range of design parameters (groove width, land width) and device parameters (velocity and tension) were simulated to characterize the traction of a thin tape over a grooved roller. It was shown that air lubrication effects reduce the contact force; however, the underlying effects of tape mechanics are not entirely eliminated. This work shows that in order to characterize the mechanics of thin tape over grooved rollers the tape deflection in the lateral direction should be included in the analysis.
TOPICS: Contact mechanics, Rollers, Tension, Lubrication, Deflection, Traction, Air entrainment, Shells, Design
research-article  
Mohsen Pezeshkian, Iman Ebrahimzadeh and Farhad Gharavi
J. Tribol   doi: 10.1115/1.4037069
In the present investigation, Friction stir processing (FSP) was used to integrate Ni particles into the surface of copper in order to fabricate a surface composite. Determining an optimized percentage of Ni particles, different dimensions of grooves were machined into the Cu plates. Optical microscope (OM) and scanning electron microscope (SEM) were used to evaluate the microstructure. Pin-on-disk test was performed using pins manufactured from the FSPed zone. Using FSP parameters, rotation and transverse speed of 800 rpm and 50 mm/min, respectively, the results show that the best properties is obtained using 2×2 mm groove on the copper plate. In this situation, hardness and wear properties were improved as 40% and 60% compared to the substrate, respectively.
TOPICS: Tribology, Friction, Composite materials, Particulate matter, Manufacturing, Copper, Rotation, Wear, Dimensions, Scanning electron microscopes, Optical microscopes, Pins (Engineering), Plates (structures), Disks
research-article  
H. K. Pant, D. Debnath, S. chakraborty, Mohd Farooq Wani and P.K. Das
J. Tribol   doi: 10.1115/1.4037068
SiC-TiB2 (10 wt.%) and SiC-TiB2 (10 wt.%)-TaC (5 wt.%) composites are consolidated using spark plasma sintering technique at different sintering temperatures (2000oC and 2100oC) for 15 min soaking time under 35 MPa pressure. The effects of sintering temperature on densification and mechanical properties of composites have been investigated in detail. SiC-TiB2 and SiC-TiB2-TaC composites sintered at 2100°C showed high Vickers hardness value i.e. 27.20±1.23 GPa and 26.40±0.80 GPa, respectively under 1 kgf (9.81 N) load. Poor fracture toughness {2.28 MPa(m)1/2 at 1 kgf (9.81 N) load} of monolithic SiC sintered at 2100°C is improved with addition of TiB2 and TaC as secondary phases. Scratch resistance of SiC-TiB2 and SiC-TiB2-TaC composites show coefficient of friction value below 0.40 and 0.50 under 5 N and 10 N loads, respectively. SiC-TiB2 and SiC-TiB2-TaC composites show constant thermal conductivity response above 810°C and 603°C in the range of 48.70-47.15 W/m?K and 60.35-60.41 W/m?K, respectively.
TOPICS: Temperature, Composite materials, Sintering, Plasmas (Ionized gases), Tribology, Stress, Mechanical properties, Thermal conductivity, Fracture toughness, Vickers hardness testing, Friction, Pressure
research-article  
Yanming Wang, Peng Cai, Tingmei Wang and Qihua Wang
J. Tribol   doi: 10.1115/1.4036935
Tribological and mechanical properties of aramid fiber (AF), graphite (Gr), hexagonal boron nitride (h-BN) hybrid polyimide composites were investigated under room and high temperature. Results show that, Gr in composite reinforced with AF and h-BN can reduce coefficient of friction (COF) and improve anti-wear property of composites under room temperature. Gr can accelerate the formation of transfer film under high temperature without sacrifice the wear resistant of composites. Transfer film of composites reinforced with Gr and h-BN simultaneously present more smooth and uniform compared with that of composites reinforced with only AF and h-BN. However, under higher temperature, composite reinforced with pure Gr present higher COFs and WRs compared with composites filled with h-BN and Gr simultaneously. Comprehensively, composite filled with 10% AF, 3% h-BN and 4% Gr is the optimum composition.
TOPICS: Temperature, Composite materials, Tribology, Graphite, High temperature, Wear, Boron, Friction, Aramid fibers, Mechanical properties
research-article  
Michele Ciavarella
J. Tribol   doi: 10.1115/1.4036917
We show the full multiscale Persson’s theory for rubber friction due to viscoelastic losses can be approximated extremely closely to simpler models, like that suggested by Persson in 1998 and similarly by Popov in his 2010 book (but notice that we do not make any use of the so-called "Method of Dimensionality Reduction"), so it is essentially a single scale model at the so called large wavevector cutoff. The dependence on the entire spectrum of roughness is therefore only confusing, at least for range of fractal dimensions of interest D ? 2.2, and we confirm this with actual exact calculations and reference to recent Lorenz et al data. Moreover, we discuss the critical assumption of the choice of the "free parameter" best fit truncation cutoff.
TOPICS: Friction, Rubber, Dimensions, Surface roughness, Fractals
research-article  
Sergej Mozgovoy, Jens Hardell, Liang Deng, Mats Oldenburg and Braham Prakash
J. Tribol   doi: 10.1115/1.4036924
Press hardening is employed in the automotive industry to produce advanced high-strength steel components for safety and structural applications. This hot forming process depends on friction as it controls the deformation of the sheet. However, friction is also associated with wear of the forming tools. Tool wear is a critical issue when it comes to the dimensional accuracy of the produced components and it reduces the service life of the tool. It is therefore desirable to enhance the durability of the tools by studying the influence of high contact pressures, cyclic thermal loading and repetitive mechanical loading on tool wear. This is difficult to achieve in conventional tribological testing devices. Therefore, the tribological behaviour of tool-workpiece material pairs at elevated temperatures was studied in a newly developed experimental set-up simulating the conditions prevalent during interaction of the hot sheet with the tool surface. Uncoated 22MnB5 steel and aluminium-silicon (Al-Si) coated 22MnB5 steel were tested at 750 ° and 920 °, respectively. It was found that higher loads led to lower and more stable friction coefficients independent of sliding velocity or surface material. The influence of sliding velocity on the coefficient of friction was only marginal. In the case of Al-Si coated 22MnB5, the friction coefficient was generally higher and unstable due to transfer of Al-Si coating material to the tool. Adhesion was the main wear mechanism in the case of uncoated 22MnB5.
TOPICS: Tribology, Tool steel, Hardening, Friction, Wear, Steel, Safety, High strength steel, Service life (Equipment), Stress, Automotive industry, Durability, Testing, Silicon, Temperature, Adhesion, Aluminum, Coating processes, Coatings, Deformation
research-article  
Yang Xu and Robert L. Jackson
J. Tribol   doi: 10.1115/1.4036920
In this study, the concept of the fracture mechanics is used to solve the (i) frictionless purely normal contact and (ii) the similar material contact under the mutual actions of the normal and tangential load. Consider the contact region is simply connected, the out-of-contact regions can be treated as periodic collinear cracks. Through evaluating the stress intensity factor(SIF), we are able to obtain the size and location of the contact/out-of-contact region. Then, the normal traction, shear traction and interfacial gap can be directly determined by the Green’s function of the periodic collinear crack. In the case of frictionless purely normal contact, the new approach is applied to two classic problems, namely, the Wester-gaard problem (sinusoidal waviness punch) and the periodic flat-end punch problem. Then, the sinusoidal waviness contact pair in the full stick and the partial slip conditions under the mutual actions of the normal and tangential loads are solved by the newly developed approach.
TOPICS: Elasticity, Fracture mechanics, Contact mechanics, Tangential loading, Traction, Fracture (Materials), Stress, Shear (Mechanics)
Errata  
Stephen Boedo and John F. Booker
J. Tribol   doi: 10.1115/1.4036925
Paper No: TRIB-15-1270; DOI: 10.1115/1.4031753; Journal of Tribology, 2016, 138 (3), p. 034502.
TOPICS: Tribology, Mechanical admittance

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