Showing papers in "Tribology Transactions in 2017"

Ionic Liquid Lubricants: Basics and Applications

Abstract: Interest in the tribological performance of ionic liquids (ILs) has increased significantly since they were first introduced as lubricants in 2001. The primary advantages of ILs over conventional lubricants lie in their better ability to form tribofilms, higher thermal stability, environmental friendliness, and adaptability to various applications. A remarkable reduction in friction and wear has been observed after the addition of ILs in oil- or water-based media and in grease, suggesting that ILs are promising candidate materials as neat lubricants as well as lubricant additives. Despite the relatively common utilization of ILs as lubricating media, their wider use is limited by their high cost and corrosive properties. This article provides a brief introduction to relevant IL structures and properties, focusing on recent applications of the materials in engineering tribology.

Use of the Roughness Parameters Ssk and Sku to Control Friction—A Method for Designing Surface Texturing

Abstract: The aim of this work was to show that with the use of the surface roughness parameters Ssk and Sku we can predict tribological behavior of contact surfaces and use these parameters to plan surface texturing. This article presents a continuation of our research on virtual texturing and experimental work on surface textures in the form of channels. For this investigation, steel samples were laser surface textured in the shape of dimples with different spacings between the dimples and different dimple depths. The experimental results confirmed that the parameters Ssk and Sku can be used to design the surface texturing, where a higher value of Sku and more negative Ssk lead to lower friction.

Dispersion Stability and Tribological Characteristics of TiO2/SiO2 Nanocomposite-Enriched Biobased Lubricant

Abstract: The stable dispersion of nano-additives is highly desirable for the effective lubrication performance of nanolubricants. The compatibility of base oil with selected nano-additives is required for uniform and stable dispersion. This research evaluated the dispersion stability and tribological characteristics of nano-TiO2/SiO2 (average particle size 50 nm) as an additive in a biobased lubricant. The wear protection and friction reducing characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring–cylinder liner sliding tests. Surface analysis tools, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy, were used to characterize the worn surfaces. Results showed that the nanolubricants demonstrated appreciable dispersion capability in the absence of a surfactant and an improvement in load-carrying capacity, antiwear behavior, and friction reduction capability.

Stress intensity factors evaluation for rolling contact fatigue cracks in rails

Abstract: The stress intensity factors (SIFs) for multiple rolling contact fatigue cracks of a network in the Iran railway under vehicle dynamic load are evaluated in this article. Stress intensity factor evaluation under dynamic loading is simulated in three dimensions using a linear elastic boundary element code. For this purpose, a UIC60 rail with accurate geometry using a boundary element method is studied. A three-dimensional model in Franc3D is provided. Finally, the influence of the friction coefficient between the wheel and rail, crack surface friction, trapped fluid, and initial crack length on SIFs are investigated in detail.

Gas Leakage Prediction of Contact Interface in Fabric Rubber Seal Based on a Rectangle Channel Model

Abstract: In this article, the gas leakage prediction through the contact interfaces between a fabric rubber seal and a metal platen is studied based on numerical simulation. A rectangular channel model based on the contact interface is established. The theoretical prediction about the gas leakage for the initial rectangular channel verifies the result from the computational fluid dynamics (CFD) method. Both the finite element method (FEM) and CFD are used to simulate deformation of the fabric rubber seal and the gas leakage, respectively. The influence of rubber thickness and the modulus of the fabric rubber seal under different loading displacements and different contact stresses is studied. In addition, the rubber thickness does not influence the mass flow rate any more under the same contact stress for the normal rubber seal (h2 ≥ 2,000 μm).

WEC Formation in Rolling Bearings under Mixed Friction: Influences and “Friction Energy Accumulation” as Indicator

Abstract: White etching cracks (WEC) can lead to premature rolling contact fatigue. Possible drivers of WEC can be mixed friction, sliding between rolling elements and raceways, electrical current, critical additives, and water-contaminated lubricant. With respect to WEC failures induced by sliding between rolling elements and raceways under mixed friction, an approach is presented that can explain the experimentally observed failure characteristics of cylindrical roller thrust bearings. Variants of the bearing were tested using a WEC-critical lubricant. The tests showed that not only the contact pressure and sliding between rolling elements and raceways but also the lubrication conditions (specific film thickness) and the frequency of the contact load cycles have an influence on WEC life. These influences are reflected best by a newly introduced characteristic parameter termed friction energy accumulation. As far as WEC failures induced by sliding under mixed friction are concerned the friction energy accu...

A Finite Element Approach to Modeling Abrasive Wear Modes

Abstract: Machine components operating in sandy environments will wear because of the abrasive interaction with sand particles. In this work, a method is derived to predict the amount of wear caused by such abrasive action, in order to improve the maintenance concept of the components. A finite element model is used to simulate various tips scratching a smooth surface. The model is verified by comparing the obtained results with a set of experiments performed earlier (M. Woldman, et al., 2013, Wear, 301(1–2), pp 76–81).

Effect of Particle Concentration on Tribological Properties of ZnO Nanofluids

Abstract: In this research, oleic acid surface-modified ZnO nanoparticles were successfully dispersed into 60SN base oil. The distribution of ZnO nanoparticles in the lubricant was tested by transmission electron microscopy. The friction and wear properties of nanofluids were evaluated with a four-ball tester, and the morphologies of wear scars were measured by a scanning electron microscope (SEM) and a surface profiler. Results show that oleic acid can improve the stability of ZnO nanoparticles in the lubricant; oil-based nanofluids with ZnO nanoparticles could remarkably reduce friction and wear. When the amount of oleic acid added was 8 wt% and ZnO nanoparticles was 0.5 wt%, the coefficient of friction and average diameter of the wear scars were minimum and the fluid exhibited better friction-reducing and antiwear properties.

Differences in Mechanisms for Fretting Wear Reduction between Oil and Grease Lubrication

Abstract: The different mechanisms of fretting wear in oil and grease lubrication and methods to reduce fretting wear were examined by means of thrust ball bearings in this study. Tests of fretting wear under oil lubrication were conducted. It was confirmed that high-viscosity oil can reduce fretting wear at high velocity (i.e., high frequency) through oil film formation. In the case of grease lubrication, the influence of velocity on fretting wear was significantly different for low- and high-viscosity greases. Grease with low-viscosity base oils could reduce fretting wear at high velocity. In contrast, grease with high-viscosity base oils could reduce fretting wear at low velocity. Grease thickeners were found to be effective in forming a layer that could prevent fretting wear. These results highlight the large differences in effective fretting wear reduction mechanisms between oil and grease lubrication.

Antiwear, Antifriction, and Extreme Pressure Properties of Motor Bike Engine Oil Dispersed with Molybdenum Disulfide Nanoparticles

Abstract: This work presents studies on the antiwear, antifriction, and extreme pressure properties of motor oil dispersed with MoS2 nanoparticles. Commercial oil (SAE 20W-40 grade) is dispersed with stabilized MoS2 nanoparticles in 0.25, 0.5, 0.75, and 1 wt%. The test oils are tested for antiwear, antifriction, and extreme pressure properties on a four-ball wear tester. The wear and friction offered by nanolubricants has decreased remarkably compared to the commercial base oil. The weld load and load wear index of oils dispersed with nanoparticles were improved substantially compared to the commercial base oil. Metallographic studies conducted on the wear balls from the extreme pressure test show that nanoparticles are deposited on the worn area along with additives in the oil, thereby preventing welding of the surfaces. An optimum weight fraction is arrived at for best performance. A synergy between the additives in the oil and dispersed nanoparticles has been observed, resulting in less dispersion for be...

Analysis of Turbulence and Convective Inertia in a Water-Lubricated Tilting-Pad Journal Bearing Using Conventional and CFD Approaches

Abstract: The influence of turbulence and convective fluid inertia in a water-lubricated journal bearing was investigated using two types of models: a “conventional” solution based on traditional lubrication theory (Reynolds equation) and a more rigorous computational fluid dynamics (CFD) program containing a full Navier-Stokes solution The calculations reveal that turbulence accounts for around 50% of the load capacity in the water-lubricated bearing studied, highlighting the importance of accurate characterization of turbulence in such applications Convective inertia, also referred to as transport inertia because it depends only on the spatial parameters within the film rather than time-dependent journal motions, was found to lower the static film pressures (load capacity) by about 6% compared to an inertialess solutionHydrodynamic pressures calculated by the conventional Reynolds solution were initially about 30% lower than those of the more rigorous CFD model for the water-lubricated bearing operatin

The Performance of PS400 Subjected to Sliding Contact at Temperatures from 260 to 927°C

Abstract: Adequate high-temperature lubrication between loaded surfaces in sliding contact can be one of the most challenging tribological problems confronting today's designers. In an attempt to provide a possible solution a test program was initiated to evaluate PS400, a recently patented, high-temperature solid lubricant coating. Made from nickel–molybdenum–aluminum, chrome oxide, silver, and barium fluoride–calcium fluoride, PS400 is a variant of the earlier coating, PS304, but is formulated for higher density, smoother surface texture, and greater dimensional stability. It was initially developed to minimize the start–stop wear in foil air bearings but is expected to perform well in other high-temperature applications where sliding friction and wear are a concern, such as variable inlet guide vanes and process control valve stems. To better define its operational capabilities, a series of tests was conducted to study the behavior of PS400 under reciprocating sliding contact at temperatures from 260 to ...

Microabrasion Wear Behavior of Fast-Borided Steel Tooth Drill Bits

Abstract: In this study, the surface of steel tooth drill bits (Ni-Cr-Mo based) was subjected to the solid-state boriding treatment with 10- to 50-nm nanoboron powder. Boriding processes were carried out at a constant temperature of 1273 K for 30, 45, 60, 75, 90, and 105 min using a solid-state box boriding technique. Borided drill bit samples were characterized by conventional methods (microstructure, microhardness, X-ray diffraction, and chemical analysis). The wear behavior of borided samples was tested at different loads and sliding speeds by a microabrasion experimental setup. Metallographic studies showed that the boride layers have a sawtooth morphology and consist of FeB and Fe2B. The thickness and hardness of the boride layer were 35.29–202.56 μm and 1300–2333 HV0.1, respectively, depending on the duration. The wear resistance of borided samples increased significantly due to the increase in surface hardness and lubricating effect, both of which were caused by the boriding process. A groove wear me...

Enhancing Weak Defect Features Using Undecimated and Adaptive Wavelet Transform for Estimation of Roller Defect Size in a Bearing

Abstract: Defects in bearings affect the vibration level, resulting in and increase in temperature and decomposition of lubricant. Estimation of roller defect size is a complex task because it revolves as well as rotates during the motion. Signals from a defective roller of a bearing are superimposed by the signal from races, cage, and background noise. In this communication, a signal processing scheme is proposed that makes the signal suitable for estimating the size of the defect in the rolling element of a tapered roller bearing. To achieve this, in the first stage of processing, shift-invariant soft thresholding is applied to denoise the signal. It suppresses the noise without affecting defect-related features. Further, in the second stage of processing, continuous wavelet transform (CWT) using adaptive wavelet is applied. The adaptive wavelet is designed from the impulse extracted from the signal using the least squares fitting method. It results in higher coefficients in the region of impulse produced...

Effect of Heat Treatment Temperature on Microstructure and Mechanical and Tribological Properties of Cold Sprayed Ti-6Al-4V Coatings

Abstract: In this study, Ti-6Al-4V (Ti-64) coatings were prepared on commercial Ti-64 substrates via a high-pressure cold spray process. The coatings were heat treated at different temperatures of 400–1000°C...

Transient Pressure and Temperature Field Measurements in a Lightly Loaded Circumferential Groove Journal Bearing from Startup to Steady-State Thermal Stabilization

Abstract: The fluid film pressure and temperature fields have been measured simultaneously under laboratory conditions at one land of a circumferential groove journal bearing (CGJB), together with friction torque and oil flow rate, during a time span from stand-still startup to the development of a thermally stabilized steady operating regime.A very fine measurement grid—that is, 216 pressure and 180 temperature points spread across the axial and circumferential directions—has been obtained by joining and synchronizing measurements from separate test runs while rigorously re-creating the test conditions.The study confirmed that the pressure field is established faster than the temperature field, that film rupture occurs both from cavitation nuclei downstream the minimum film thickness and through air ingestion from the environment. Furthermore, the high pressures in the convergent zone stabilize relatively quickly, whereas the low pressures in the divergent zone cavitated region require a longer time to sta...

Effects of Nano-TiO2 Additive in Oil-in-Water Lubricant on Contact Angle and Antiscratch Behavior

Abstract: Contact angle and scratch tests have been conducted to investigate the effects of nano-TiO2 additive in oil-in-water (O/W) lubricant. The results show that the contact angle between high-speed steel with oxide scale and 1% (oil concentration) O/W lubricant decreases first and then increases as the concentration of nano-TiO2 particle in the O/W lubricant increases. The smallest contact angle is obtained after an addition of 4% nano-TiO2 additive to the O/W lubricant. This is because the nano-TiO2 can enhance the surface excess of the oil when the nano-TiO2 particles distribute throughout the surface of the oil droplets, and after saturation they can distribute throughout the water and also improve the surface excess of the water in the O/W lubricant. The scratch and hot rolling tests show that the nano-TiO2 particles in the O/W lubricant can also reduce friction, improve scratch resistance, and reduce rolling force. A method for measuring the adhesion force of the oxide scale is proposed and the ef...

Fretting Wear Behavior and Mechanism of Inconel 690 Alloy Related to the Displacement Amplitude

Abstract: Fretting wear tests on Inconel 690 alloy were carried out at different displacement amplitudes. The results indicated that with an increase in displacement amplitude, the ratio of tangential force to normal load and wear volume increased. The fretting mode gradually transformed from mostly stick, mixed stick–slip, to full sliding, showing the competition of fretting-induced fatigue cracking and fretting-induced wear. There was a gradient plastic strain created by fretting, which resulted in the formation of a nanocrystalline tribologically transformed structure (TTS) and plastic deformation layers. The plastic strain in the plastic deformation layer gradually increased with an increase in displacement amplitude.

An Analysis of the Multiscale Structure of Surfaces with Various Finishes

Abstract: Even with the various surface finishing techniques, all surfaces are rough with different structures and geometric characteristics over multiple scales. In this work, a profilometer is utilized to measure the profiles of different rough surfaces, and the profiles are characterized using a variety of statistical, spectral, and fractal methodologies. Three different methods are implemented in calculating the fractal dimension, D, and these three methods are then compared. The relationship between the fractal dimension and the fractal scaling constant, G, is investigated as well. The measured rough profiles are also compared with Weierstrass-Mandelbrot (W-M) function–generated rough profiles using the characterization results of the measured profiles. After comparing a series of statistical and fractal parameters, which are calculated based on the surface profile data of the original and regenerated profiles, it can be found that the W-M function does not always appear to be very suitable for represe...

Dry Sliding Wear Behavior of Palmyra Shell Ash–Reinforced Aluminum Matrix (AlSi10Mg) Composites

Abstract: High strength, light weight, ease of fabrication, excellent castability, and good wear resistance make aluminum alloy composites suitable for commercial applications. In this work, a silica-rich ash particle (palmyra shell ash) was reinforced with aluminum alloy (AlSi10Mg) composites and its mechanical and tribological properties were studied. The aluminum alloy was reinforced with 3, 6, and 9 wt% of palmyra shell ash particles, and its dry sliding wear behavior was studied using a pin-on-disc machine under different loading conditions. The result shows that the dry sliding wear resistance of Al–palmyra shell ash composites was almost similar to that of fly ash– and rice husk ash–reinforced Al-alloy composites and these composites exhibit better wear resistance compared to unreinforced alloy. The palmyra shell ash particle weight fraction significantly affects the wear and friction properties of the composites. Scanning electron microscopic examination of the worn surface reveals that at various l...

Morphological Feature Extraction Based on Multiview Images for Wear Debris Analysis in On-line Fluid Monitoring

Abstract: Wear state is an important indicator of machinery operation condition that reveals whether faults have developed and maintenance should be scheduled. Among the available techniques, vision-based on-line monitoring of wear particles in the lubricant circuit is preferred, where three-dimensional particle characterizations can be obtained for wear mode analysis. This article presents the application of an imaging system that captures wear particles in lubricant flow and the development of image processing procedures for multiview feature extraction. In particular, a framework including background subtraction, object segmentation, and debris tracking was adopted. Particle features were then used in a comprehensive morphological description of wear debris. Experiments showed that the system is able to produce a feasible and reliable indication of wear debris characteristics for machine condition monitoring.

Tribological Analysis of a Hydrodynamic Journal Bearing under the Influence of Synthetic and Biolubricants

Abstract: This study investigated the tribological characteristics of journal bearings exclusively for automotive applications under the influence of a synthetic lubricant (SAE20W40) and chemically modified rapeseed oil (CMRO) as a biolubricant, dispersed with TiO2, WS2, and CuO nanoparticles used as antiwear additive. The effects of synthetic and nanobased biolubricants on the tribological behavior of the hydrodynamic journal bearing were examined using a journal bearing test rig by measuring the coefficient of friction, oil film thickness, and wear under a load of 10 kN and a speed of 3,000 rpm. The test results show that CuO nanoadditives that are added to the biolubricant exhibit outstanding wear and friction reduction behavior, better than that with synthetic lubricants as well as other nanobased biolubricants. The inclusion of CuO nanoparticles in the biolubricant decreased the coefficient of friction by 27% and wear by about 47% compared to a synthetic lubricant. Additionally, investigations were per...

Effects of Loading and Sliding Speed on the Dry Sliding Wear Behavior of Mg-3Al-0.4Si Magnesium Alloy

Abstract: The friction and wear properties of Mg-3Al-0.4Si alloy were investigated using a pin-on-disc tester. Morphologies and compositions of worn surfaces were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) for identification of the wear mechanisms. Microstructural evolution and hardness change in subsurfaces were analyzed by confocal scanning laser microscopy and hardness testing. The results revealed that the wear behavior of Mg-3Al-0.4Si alloy was classified into two types of wear regimes; that is, mild and severe. In the mild wear regime, wear rates increased at a low slope with increasing load; the corresponding wear mechanisms were oxidation, abrasion, and delamination. In the severe wear regime, wear rates increased rapidly at a high slope with load; the wear mechanisms were severe plastic deformation and surface melting. Analysis of microstructural evolution on the subsurface identified the reason for the transition from mild to severe wear; tha...

Analysis of Tribological Properties of Palm Biodiesel and Oxidized Biodiesel Blends

Abstract: Biodiesel has become an increasingly significant alternative fuel to replace conventional diesel completely or partially. Although biodiesel has several advantages, such as environmental friendliness, renewability, and reduced emissions, it also has major drawbacks. Tribology is one of the major concerns for biodiesel usage, in which biodiesel lubricity deteriorates by usage and/or by storage because of its oxidative nature. The present study aims to investigate the lubrication behavior of oxidized and pure palm biodiesel blends by using a four-ball tribotester machine. Tests were carried out in diesel, pure biodiesel (B100), their blends (B10 [10% biodiesel in diesel], B20, B30, and B50), and oxidized biodiesel (Oxd B100) and its blends (Oxd B10, Oxd B20, Oxd B30, and Oxd B50). Tests were conducted at room temperature under a normal load of 40 kg for 1 h at 1,200 rpm. Surface analyses were carried out by scanning electron microscopy, energy-dispersive spectrometry, and optical microscopy, and fue...

Nonlinear Dynamic Response of Cylindrical Roller Bearing–Rotor System with 9 Degree of Freedom Model Having a Combined Localized Defect at Inner–Outer Races of Bearing

Abstract: This article presents a nonlinear dynamic model for a cylindrical roller bearing–rotor system with interaction forces between the inner race, outer race, and roller. Roller–race contacts are modeled predicting nonlinear stiffness (Hertz contact theory) and nonlinear damping for a rotor–cylindrical roller bearing system. Here a shaft–rotor bearing system is modeled with 9 degrees of freedom with one defect on the inner race and one defect on the outer race for a case of combined localized defects. In the mathematical formulation, contacts between rolling elements and inner and outer races are considered as nonlinear springs and nonlinear damping is taken into consideration. Contact force calculations with nonlinearity are solved using the Newton-Raphson method for n unknown nonlinear simultaneous equation. The Newmark-β implicit integration technique coupled with the Newton-Raphson method is used to solve the differential equations. The results are obtained in the form of a time domain plot, freque...

Lubricant Additives Based on Carbon Nanotubes Produced from Carbon-Rich Fly Ash

Abstract: Carbon-rich fly ash has been reported to be a suitable precursor and catalyst for carbon nanotube (CNT) growth. In this work, CNTs grown from carbon-rich fly ash were evaluated as a lubricant oil additive to reduce the friction coefficient of metallic surfaces using a ball-on-disk tribometer. Different concentrations of the as-grown CNTs in the range 0.005–0.5 wt% were dispersed in a base sunflower oil. The value of the friction coefficient was also investigated as a function of load. Excellent results were obtained for the value of the friction coefficient, where it drastically decreased to around 58% of its original value without additives. This was achieved at a very low concentration of CNTs; that is, 0.1 wt%. The obtained result was compared with that of a commercial multiwalled CNT at the same concentration and found to be superior. This superiority of CNTs produced from fly ash could be attributed to the existence of active radical sites on their side wall. Moreover, the friction coefficien...

Numerical Calculation of Rotation Effects on Hybrid Air Journal Bearings

Abstract: Hybrid air journal bearings are of great importance in the precision engineering. Despite much progress, the influence of the aerostatic effect and the aerodynamic effect on the bearings is still not clear. Numerical calculation is a useful technique to evaluate bearing performance. Many theoretical problems related to Reynolds equation have been figured out by numerical simulation. The present study analyzes the effects of rotational speed—that is, the bearing speed number—on the performance of hybrid bearings. The behaviors of the pure aerostatic bearing and the pure aerodynamic bearing are investigated for comparison. The second-order finite difference method (FDM) and an iterative procedure are proposed to solve the Reynolds equation and derive the air film pressure distribution. The bearing characteristics such as load capacity, stiffness, friction coefficient, attitude angle, and mass inflow rate are taken into consideration. The research reveals the very dependence of the hybrid bearing's p...

Tribological Behavior of Electrodeposited Ni-Fe Multilayer Coating

Abstract: In the present study, the sliding wear behavior of pulse-electrodeposited multilayer Ni-Fe coatings as a function of pulse parameters including frequency and duty cycle has been studied using pin-on-disc tests against an Al2O3 counterbody. Sliding wear was investigated with respect to the coefficient of friction (COF), worn surfaces, wear rate, and wear debris. The results of COF with sliding distance revealed a two-region state. At the start of the test the COF was higher, which was due to high stress at the contact region and the occurrence of delamination wear. Then the COF was collapsed as a result of pin penetration and decreased stress at the contact region. The intensity of delamination is decreased at the later stage. The wear resistance of multilayer coatings is increased with increasing frequency and decreasing duty cycles as a consequence of grain refinement and hardness enhancement.

Tribological Performance and Surface Analysis of a Borate Calcium as Additive in Lithium and Polyurea Greases

Abstract: In this work, a borate calcium additive was added to lithium and polyurea greases to investigate the tribological performance. Friction and wear tests were conducted on a four-ball machine under higher load and a reciprocating tribometer under lower load. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analyses were performed on the worn surface after the tests. It was found that the tribological performance affected the boundary layers formed by the additive and the soap fibers. The boundary films in lithium grease mainly consist of ferrum hydroxide, and more oxide can be found in polyurea-based films. SEM analyses of soap fibers show that the soap fibers in polyurea-based grease were more separated than those in lithium-based grease. Compared to the base grease, the soap shows smaller and shorter fibers.

Third Particle Ejection Effects on Wear with Quenched and Tempered Steel Fretting Contact

Abstract: The design and life prediction of fretting wear-sensitive mechanical components remain a challenge. In the present work, the role of wear particle movements under conditions of axisymmetric loading of an annular flat-on-flat contact were investigated using self-mated quenched and tempered steel specimens. Total fretting wear significantly increased when loose wear particles were periodically removed from the interface, and this effect increased as a function of the sliding amplitude. Additionally, increased wear was measured when grooves perpendicular to the sliding direction were added to the interface. Increasing the rate of wear debris ejection leads to increased wear rate because naturally occurring entrapped third-body particles significantly reduce the wear. The shape of fretting loops and values of the average and maximum coefficient of friction remained unaffected by the removal of entrapped wear debris and by the introduction of the grooves.