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Journal Cover Lubricants
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   ISSN (Online) 2075-4442
   Published by MDPI Homepage  [154 journals]
  • Lubricants, Vol. 5, Pages 20: Wear Characterization of Cemented Carbides
           (WC–CoNi) Processed by Laser Surface Texturing under Abrasive Machining

    • Authors: Shiqi Fang, Luis Llanes, Dirk Bähre
      First page: 20
      Abstract: Cemented carbides are outstanding engineering materials widely used in quite demanding material removal applications. In this study, laser surface texturing is implemented for enhancing, at the surface level, the intrinsic bulk-like tribological performance of these materials. In this regard, hexagonal pyramids patterned on the cutting surface of a tungsten cemented carbide grade (WC–CoNi) have been successfully introduced by means of laser surface texturing. It simulates the surface topography of conventional honing stones for abrasive application. The laser-produced structure has been tested under abrasive machining conditions with full lubrication. Wear of the structure has been characterized and compared, before and after the abrasive machining test, in terms of changes in geometry aspect and surface integrity. It is found that surface roughness of the machined workpiece was improved by the laser-produced structure. Wear characterization shows that laser treatment did not induce any significant damage to the cemented carbide. During the abrasive machining test, the structure exhibited a high wear resistance. Damage features were only discerned at the contacting surface, whereas geometrical shape of pyramids remained unchanged.
      PubDate: 2017-06-22
      DOI: 10.3390/lubricants5030020
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 21: On the Transition from Static to Dynamic
           Boundary Friction of Lubricated PEEK for a Spreading Adhesive Contact by
           Macroscopic Oscillatory Tribometry

    • Authors: Sherif Ahmed Abdel-Wahed, Christof Koplin, Raimund Jaeger, Matthias Scherge
      First page: 21
      Abstract: The tribology of lubricated poly(ether ether ketone) (PEEK)—steel tribosystems was investigated in the static and boundary friction regime. Pentaerythrite ester and trimellitic acid ester were used as lubricants. The lubricants differed in their molecular structure but showed only minor differences in their rheological and cohesive energetic properties. In order to investigate the effect of the lubricants on static and dynamic friction, macroscopic oscillatory tribometry experiments and gliding experiments were carried out. The surface and interfacial energies of PEEK, lubricant, and steel, which can be used to determine e.g. the spreading tendency of the lubricant, were employed to explain the tribological characteristics of the system. The gliding experiments exhibited a velocity dependence of the coefficient of friction which indicates a “rate-and-state” type of friction. Trimellitic acid ester resulted in the lowest static and dynamic friction values due to its high tendency to spread. A different static friction behavior was found for pentaerythrite ester, which indicates a possible lubricant-induced mobilization of the polymer surface chains. This finding was supported by an increased interaction energy measured by contact angle measurements. The macroscopic oscillatory tribometry was shown to be a unique and precise method to investigate the transition from static to dynamic friction and to quantify macroscopic adhesive friction. Both types of experiments used a polished steel surface as a frictional partner, which favors the adhesive component of friction. However, the results for the lubricated contacts of polished steel surfaces in the boundary lubrication regime can give some insight into effects of the polymer transfer to rough steel surfaces in the mixed lubrication regime.
      PubDate: 2017-06-29
      DOI: 10.3390/lubricants5030021
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 22: Tribological Investigation of Layered
           Zirconium Phosphate in Anhydrous Calcium Grease

    • Authors: Yingjing Dai, Wenxing Niu, Xiaosheng Zhang, Hong Xu, Jinxiang Dong
      First page: 22
      Abstract: The tribological properties of α-zirconium phosphate particles as an additive in anhydrous calcium grease were studied by using an Optimol SRV-V oscillating reciprocating tester and a four-ball tester. Fortunately, α-Zr(HPO4)·H2O (α-ZrP) grease exhibits excellent properties in anti-friction and wear-resistant, load-carrying capacity, and extreme pressure properties. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and 3D analysis show that α-ZrP particles appear to form a protective film allowing increased load capacity and operating frequency of the rubbed pairs. Meanwhile, α-ZrP particles can provide low friction coefficient and wear loss during a long-term test.
      PubDate: 2017-06-30
      DOI: 10.3390/lubricants5030022
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 23: Tribological Evaluation of Date Palm Fruit
           Syrup–A Potential Environmental-Friendly Lubricant

    • Authors: Abdul Mohammed
      First page: 23
      Abstract: Date palm is one of the most cultivated palms mostly found in the Middle Eastern regions of the world. The date palm fruits are not only nutritionally rich, but also have a good amount of fatty acids such as oleic acid, palmitic acid, and linoleic acids, which have excellent anti-wear and lubricating properties, making it a potentially good candidate to be used as an environmentally-friendly lubricant. This study is a preliminary effort to explore the lubricating properties of date palm fruit syrup by conducting ball-on-disc wear tests on mild steel samples. Different concentrations (50, 75, and 100 vol %) of the syrup in water were tested at a normal load of 50 N and a sliding linear speed of 0.1 m/s. Scanning electron microscopy and optical profilometry were used to characterize the wear tracks and estimate the wear rates. 100 vol % date syrup with a viscosity of 16.95 mPa·s showed excellent results by reducing the coefficient of friction of steel-on-steel from 0.6 (dry conditions) to a value of ~0.1. The depth of the wear track reduced from ~152 µm (dry conditions) to ~11 µm, signifying a considerable reduction in wear.
      Citation: Lubricants
      PubDate: 2017-07-07
      DOI: 10.3390/lubricants5030023
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 24: Friction and Wear of Self-Lubricating
           Materials for Hydropower Applications under Different Lubricating

    • Authors: Kim Berglund, Yijun Shi
      First page: 24
      Abstract: Self-lubricating bearings in hydropower applications are often lubricated with water under boundary lubricating conditions. Polyhydric alcohols replacing water have shown the potential to reduce both friction and wear. The objective of this work is, therefore, to evaluate the effect of a polyhydric alcohol-based environmentally-acceptable lubricant (EAL) on the friction and wear of self-lubricating materials for conformal contacts under boundary lubricating conditions. The lubricating properties of four commercially-available self-lubricating bearing materials were investigated under three different lubricating conditions: dry, water and a new polyhydric alcohol-based EAL. Bearing materials include one metallic composite and three polymer composites. A reciprocating motion test rig was used to evaluate the wear and friction properties. Surface analysis was performed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and optical profilometry. Results show that the wear rate for the polymer composites is increased when water is present compared to dry operating conditions. The new polyhydric alcohol-based EAL substantially improves both friction and anti-wear performance of all four self-lubricating bearing materials compared to both dry and water conditions. Surface analysis indicates that the material transfer to the counter-surface is limited when the polyhydric alcohol-based EAL is used.
      Citation: Lubricants
      PubDate: 2017-07-15
      DOI: 10.3390/lubricants5030024
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 25: Conventional and Highly Crosslinked
           Polyethylene in Total Knee Arthroplasty—A Design-Independent Wear

    • Authors: Alexander Paulus, Matthias Woicinzski, Volkmar Jansson, Sandra Utzschneider
      First page: 25
      Abstract: Introduction: Improvement of total knee arthroplasty (TKA) materials is one promising approach for extending the lifetime of endoprostheses. The target of this study was to evaluate the sufficiency of TKA-design-independent rolling–sliding screening tests. Additionally, this study attempted to assess the relevance of the design of TKA systems for wear performance by comparison with a simulator study. Materials and Methods: A TKA-design-independent rolling–sliding testing machine was employed at ISO (the International Organization for Standardization) 14243-near conditions and physiologic level unidirectional rolling–sliding. Contact surfaces were generalized into elementary forms at curvatures of real endoprostheses: CoCr-cylinders on flat UHMWPE (ultra-high-molecular-weight-polyethylene) cuboids. Materials varied in resin and crosslinking. One conventional UHMWPE and three highly crosslinked polyethylenes were charged with an axial load of 2.5 kN for 5 million cycles. Wear was determined gravimetrically and the ranking was compared to a simulator study. Results: No statistically significant differences between either material were found. This was inconsistent with the results of a simulator survey. Conclusions: The results of the study indicate that this type of screening test is not able to correctly rank UHMWPE for use in TKA systems. The use of a UHMWPE plate in the test setup with a rolling–sliding cylinder is capable of producing visible wear marks in the bearing area, but the setup followed by a gravimetric measurement does not show reliable results. As the tested materials did not significantly vary in wear performance, it can be concluded that for differences in TKA wear-production, the design of TKR-systems can matter.
      Citation: Lubricants
      PubDate: 2017-07-16
      DOI: 10.3390/lubricants5030025
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 26: Control of Active Magnetic Bearings in
           Turbomolecular Pumps for Rotors with Low Resonance Frequencies of the
           Blade Wheel

    • Authors: Markus Hutterer, Manfred Schrödl
      First page: 26
      Abstract: Rotors with high gyroscopic effects and low resonance frequencies caused by the blade wheel (blade frequencies) can lead to stabilization problems in the application field of turbomolecular pumps. If such a rotor is stabilized by active magnetic bearings, the control structure could be destabilized by the splitting up of the rigid body eigen-frequencies caused by the gyroscopic effect. The control structure of the magnetic bearings can also destabilize the eigen-modes caused by the blade wheel, if the gain of the control structure is too high in the range of the eigen-frequencies of the blade wheel. To deal with the problem of the gyroscopic effect, a decoupling and compensation method was developed based on the inverse dynamics of the rigid body rotor. The gain of the control structure in the range of the blade frequencies is decreased using a Kalman filter. To increase the damping of the system, the predicted states of the linear magnetic bearing model using a Kalman filter are applied instead of the sampled values of the sensors directly. For the decoupled structure, PID controllers are used for stabilization. The functionality of the control structure is verified by a measurement of the current and position signal using the Kalman states and the sensor values. The robustness and performance in the frequency range are verified using the sensitivity and compliance function.
      Citation: Lubricants
      PubDate: 2017-07-25
      DOI: 10.3390/lubricants5030026
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 27: Time-Resolved Characterization of Dynamic
           Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

    • Authors: Roman Nevshupa, Marcello Conte, Silvia Guerra, Elisa Roman
      First page: 27
      Abstract: Dynamic tribochemical processes for dicationic ionic liquid containing a geminal imidazolium cation head group bridged by a poly(ethylene glycol) and a bis(trifluoromethylsulfonyl)imide anion were studied using time-resolved mechanically stimulated gas emission mass-spectrometry (MSGE-MS). In comparison with similar monocationic imidazolium ionic liquids with short alkyl or long polyether side chains, the dicationic ionic liquid had a lower coefficient of friction on Ti6Al4V alloy and smoother behavior. The analysis of volatile decomposition products suggested multiple tribochemical reactions in which both anionic and cationic moieties are involved. The tribochemical degradation of cations was mainly through the detachment of the side and bridging chains from the imidazolium head groups. The absence of volatile products containing nitrogen implies that the imidazole group remained unchanged. Hydrogen and water desorption were attributed to the reactions of hydrogen fluoride being a product of anion degradation with titanium and titanium oxide, respectively.
      Citation: Lubricants
      PubDate: 2017-07-25
      DOI: 10.3390/lubricants5030027
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 28: The Impact of Fatty Acid Diisopropanolamides
           on Marine Gas Oil Lubricity

    • Authors: George Anastopoulos, Stamatios Kaligeros, Petros Schinas, Ypatia Zannikou, Dimitrios Karonis, Fanourios Zannikos
      First page: 28
      Abstract: In this study, seven mixtures of diisopropanolamides that were synthesized from various vegetable oils (sunflower oil, soybean oil, cotton seed oil, olive oil, tobacco seed oil, coconut oil, used frying oil) were used as lubricating additives in a low-sulfur marine gas oil. All tribological measurements were carried out by using the high-frequency reciprocating ring (HFRR) test procedure, according to EN ISO 12156-1. The obtained wear results showed that all mixtures of diisopropanolamides used provide satisfactory a mean wear scar diameter (WS 1.4) of less than 520 μm, at concentration levels of 60–120 ppm. The concentrations below 60 ppm had no effect on the fuel lubricity. An increase in the concentration of the diisopropanolamide mixtures led to an insignificant increase of the lubrication effectiveness.
      Citation: Lubricants
      PubDate: 2017-08-04
      DOI: 10.3390/lubricants5030028
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 29: Influence of Non-Linear Rotor Dynamics on
           the Bearing Friction of Automotive Turbochargers

    • Authors: Julius Perge, Max Stadermann, Stefan Pischinger, Björn Höpke, Dominik Lückmann, Arthur Back, Tolga Uhlmann
      First page: 29
      Abstract: One of the possibilities to increase the efficiency of an internal combustion engine is to enhance its interaction with the charging system. With the help of new advanced simulation tools, the rotor dynamic behavior and bearing friction losses of turbochargers (TC) can be quantified in the early stage of the development process. This procedure enables virtual bearing development, leading to shortened development times and reduced testing costs. This paper presents a detailed view of the findings in current research; focusing on rotor dynamic simulations with emphasis on the non-linear dynamics (oil whirl; oil whip) and their impact on bearing friction losses. In order to obtain a detailed understanding of these effects; elastic multibody simulations (EMBS) with elastic hydrodynamic bearing (EHD) analysis including a mass-conservative approach are used. Measurement data is obtained using a unique test bench which is designed to quantify the bearing friction losses by means of a drag test. Additionally, hot gas test bench measurements are carried out to assess the non-linear rotor dynamics during steady state operation using shaft motion measurement equipment. In the first step; a multibody simulation model of a common automotive TC is set up; and a model of the friction test bench is mapped into it. The author will show that there is a high agreement between simulated and measured friction losses. In the second step; the TC model is detached from the virtual test bench and a variation of the essential parameters are carried out to identify the influence of the non-linear rotor dynamics on the bearing friction. A final model validation is obtained by comparing the measured shaft orbits for the TC hot gas test bench with the results from the multibody simulation.
      Citation: Lubricants
      PubDate: 2017-08-04
      DOI: 10.3390/lubricants5030029
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 30: Lube Oil Wear Reduction via Organic

    • Authors: Nurul Ismail, Samira Bagheri
      First page: 30
      Abstract: Effective tribofilms are desirable to protect mechanical systems. In the research, the reduction in wear and friction were investigated through the use of organic additives. Graphene-based organic additives were prepared by surface modification of graphene using organic moiety that will provide tribochemical reaction with rubbing metal surface. The role of surface protective additives becomes vital when operating conditions become severe and moving components operate in a boundary lubrication regime. After protecting film is slowly removed by rubbing, it can regenerate through the tribochemical reaction of the additives at the contact. Many researchers demonstrated that organic additives physically or chemically adsorbed on rubbing metal surfaces to form monolayers, with their shear strength deriving primarily from the weak van der Waal interactions between opposing hydrocarbon chains at the interfaces. Experiments were conducted on a base oil where 0.01 wt % of the additive was used. Tribological evaluation was conducted using four-ball tester under room temperature and the morphology of the worn surfaces were characterized using Field emission scanning electron microscopy (FESEM). Experimental results showed a 16% reduction in friction and 30% reduction in wear when compared to the base oil containing no additive.
      Citation: Lubricants
      PubDate: 2017-08-09
      DOI: 10.3390/lubricants5030030
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 31: Ionic Liquids as Grease Base Liquids

    • Authors: Robert Mozes, Peter Cooper, Rob Atkin, Hua Li
      First page: 31
      Abstract: The rheological characteristics of one mineral oil and two ionic liquid (IL) based lubricating greases were explored as a function of thickener concentration. The ILs used are 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14][TFSI]), with polytetra-fluoroethylene (PTFE) particles used as thickeners. Greases with different base liquid concentrations (60–80 wt %) were investigated using small-amplitude oscillatory shear and viscous flow measurements, and contact angle measurements probed adhesion at base liquid–PTFE interfaces. Rheological properties are influenced by base liquid–PTFE adhesion and the chemical structure of the grease base liquids. With the addition of thickener, the greases generally have higher elasticity, strain resistance, and frequency independent properties. Viscometric rheological tests illustrate non-Newtonian shear-thinning behaviour for all greases. [BMIM][TFSI] based greases show the most elastic properties and strain resistance, as well as the highest initial and lowest final viscosities of the greases tested.
      Citation: Lubricants
      PubDate: 2017-08-08
      DOI: 10.3390/lubricants5030031
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 32: Laser Textured Surfaces for Mixed
           Lubrication: Influence of Aspect Ratio, Textured Area and Dimple

    • Authors: Johannes Schneider, Daniel Braun, Christian Greiner
      First page: 32
      Abstract: Unidirectional sliding experiments with polished and laser textured steel surfaces were carried out to investigate the effects of different textured area densities, aspect ratios and dimple arrangements. The system was lubricated with Polyalphaolefin (PAO) at 100 °C and the contact pressure was 3 MPa. For measuring Stribeck curves, the sliding speed was controlled between 40 and 2000 mm/s. The textured area density was varied between 5% and 30%, with the lowest friction values found for 10%. Aspect ratios ranging from 0.02 to 0.2 were investigated and for 0.1 the lowest friction values were measured. The dimple arrangements tested were cubic, hexagonal and a random distribution for a textured area density of 10% and an aspect ratio of 0.1. Our results demonstrate that the dimple arrangement does affect friction values, hinting to the fact that individual texture elements do influence each other. The optimum dimple arrangement was found in a hexagonal packing. This systematic variation of these three key texturing parameters for the morphological texturing of a tribological surface with dimples will allow a strategic choice of texturing parameters. This makes the most of the tremendous potential that laser surface texturing has for reducing friction forces and thereby CO2 emissions.
      Citation: Lubricants
      PubDate: 2017-08-10
      DOI: 10.3390/lubricants5030032
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 33: Albumin Protein Cleavage Affects the Wear
           and Friction of Ultra-High Molecular Weight Polyethylene

    • Authors: Yasha Dwivedi, Michel Laurent, Shravan Sarvepalli, Thomas Schmid, Markus Wimmer
      First page: 33
      Abstract: It is well established that the total protein concentration and albumin-to-globulin ratio influence the wear of ultra-high molecular polyethylene (UHMWPE, “polyethylene”) in joint prostheses. A factor on wear not yet studied, but of possible clinical relevance, is protein cleavage. Such cleavage is expected in the presence of an inflammatory response and as a result of wear processes at the articular interface. The aim of this study was to compare the tribological behavior of polyethylene articulated against an orthopedic wrought CoCrMo alloy for three lubricants: cleaved albumin, uncleaved albumin, and newborn calf serum (control). We hypothesized that the cleavage of albumin will increase the friction and wear rate of polyethylene, with a concomitant roughening of the polymer surface and the generation of larger wear debris particles. Cleavage of the bovine albumin into five fragments was performed by digestion with cyanogen bromide. In pin-on-flat (POF) wear tests of polyethylene pins made of Ticona GUR® 1020/1050 against CoCrMo alloy discs, the cleaved albumin led to the lowest polyethylene wear and highest friction coefficients, whereas albumin led to the highest wear rates. In knee simulator tests, the albumin lubricant also led to a 2.7-fold increase in the tibial insert wear rate compared to the regular bovine serum lubricant (a wear rate for the cleaved albumin could not be obtained). The generated polyethylene wear particles were of increasing size and fibrillar shape in going from serum to albumin to cleaved albumin, although only the shape achieved statistical significance. Unlike bovine serum, cleaved albumin led to wear scars for both the POF and simulator wear tests that closely emulated the morphological features observed on explanted polyethylene tibial inserts from total knee replacements. We posit that the smaller protein fragments can more efficiently adsorb on the surfaces of both the polyethylene and the metal, thus offering protection against wear, while at the same time leading to an increase in friction, particle size, and particle elongation, as the protein fragment films interact adhesively during sliding. The results of this study have implications for pre-clinical wear testing methodology as they suggest that albumin concentration may be more pertinent than total protein concentration for wear testing polyethylene.
      Citation: Lubricants
      PubDate: 2017-08-17
      DOI: 10.3390/lubricants5030033
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 34: Film Thickness and Friction Relationship in
           Grease Lubricated Rough Contacts

    • Authors: David Gonçalves, António Vieira, António Carneiro, Armando Campos, Jorge Seabra
      First page: 34
      Abstract: The relationship between the film generation and the coefficient of friction in grease lubricated contacts was investigated. Ball-on-disc tests were performed under different operating conditions: entrainment speed, lubricant temperature and surface roughness. The tests were performed with fully formulated greases and their base oils. The greases were formulated with different thickener types and also different base oils natures and viscosities. Film thickness measurements were performed in ball-on-glass disc tests, and Stribeck curves were measured in ball-on-steel disc tests with discs of different roughness. The role of the thickener and the base oil nature/viscosity on the film thickness and coefficient of friction was addressed and the greases’ performance was compared based on their formulation.
      Citation: Lubricants
      PubDate: 2017-08-17
      DOI: 10.3390/lubricants5030034
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 35: Low Friction and High Solid-Solid Contact
           Ratio—A Contradiction for Laser-Patterned Surfaces'

    • Authors: Simon Bettscheider, Philipp Grützmacher, Andreas Rosenkranz
      First page: 35
      Abstract: Recording of Stribeck-like curves is a common way to study the effect of laser-patterned surfaces on the frictional efficiency. However, solely relying on the coefficient of friction when identifying the lubrication regime and the underlying working principles can be misleading. Consequently, a ball-on-disc tribometer was combined with an electrical resistivity circuit to simultaneously measure Stribeck-like curves and solid-solid contact ratios for polished and laser-patterned samples. Line-like surface patterns with different periodicities were produced by direct laser interference patterning on steel substrates (AISI304). The reference shows a Stribeck-like behavior well correlating with the contact ratios. The behavior deviates for high sliding velocities (high contact ratios) due to a loss of lubricant induced by centrifugal forces pulling the lubricant out of the contact zone. In contrast, the solid–solid contact ratio of the laser-patterned samples is around 80% for all sliding velocities. Those values can be explained by higher contact pressures and the structural depth induced by the surface topography which make a full separation of the surfaces unlikely. Despite those high values for the contact ratio, laser-patterning significantly reduces friction, which can be traced back to a reduced real contact area and the ability to store oil in the contact zone.
      Citation: Lubricants
      PubDate: 2017-08-26
      DOI: 10.3390/lubricants5030035
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 36: Water Pool Behaviors of Water Lubricating
           for Glass/Steel Point Contact

    • Authors: Hang Zhang, Shu-Hai Liu, Hua-Ping Xiao
      First page: 36
      Abstract: The behavior of pools of water for lubrication under a point of contact between a glass disk and a steel ball is studied here, employing a home-built apparatus. A deformed water pool is found to form around the contact region under different rolling speeds. To investigate the effect of rolling speed on the water pool, two parameters (advancing angle and receding angle) are introduced to describe the shape of the water pool. Two distinct glass surfaces, namely a smooth surface and a microgrooved surface, are observed. In the case of the smooth surface, the advancing/receding angle of the water pool significantly decreases with increasing rolling speed before the rolling speed reaches a critical value (80 mm/s). At speeds higher than 80 mm/s, the water pool is in a stable state and the advancing/receding angle remains steady. In the case of the microgrooved surface, the influence of the microgroove on water lubricating flow disappears when the rolling speed reaches a critical value (1030 mm/s).
      Citation: Lubricants
      PubDate: 2017-09-03
      DOI: 10.3390/lubricants5030036
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 37: Current Insights Regarding Metal-on-Metal
           Bearings for Hip Arthroplasty

    • Authors: Catherine Van Der Straeten
      First page: 37
      Abstract: Modern small diameter metal-on-metal (MoM) bearings for total hip arthroplasty (THA) have been developed in the nineteen-eighties to address the problem of polyethylene wear related osteolysis. Subsequently large diameter MoM hip resurfacings (HRA) were designed for young and active patients to preserve bone and avoid dislocation. Large diameter MoM THA were originally meant as an easy femoral component-only revision solution for femoral neck fractures in HRA, but were then advocated for primary THA as well. In the last decade however, increasing numbers of revisions for adverse local tissues reactions (ALTR) to metal debris have been reported. These ALTR are due to excessive wear of the MoM bearings, usually related to malpositioning of the components leading to edge loading, or in rare cases to metal sensitivity. Besides the immunological reactions, metal particles and ions have a potential local and systemic toxicity. Wear and tribocorrosion at the taper-trunnion connections of MoM THA but also THA with polyethylene and ceramic bearings have also been recognized as a cause of ALTR with extensive tissue destruction. Despite the fact that the long-term survivorship and functional results of certain MoM HRA are excellent and better than THA in the young and active patients group, MoM bearings have become very unpopular and are likely to be replaced by bearing couples of other materials.
      Citation: Lubricants
      PubDate: 2017-09-11
      DOI: 10.3390/lubricants5030037
      Issue No: Vol. 5, No. 3 (2017)
  • Lubricants, Vol. 5, Pages 9: Friction Reduction Tested for a Downsized
           Diesel Engine with Low-Viscosity Lubricants Including a Novel Polyalkylene

    • Authors: David Sander, Christoph Knauder, Hannes Allmaier, Slavitsa Damjanović-Le Baleur, Philippe Mallet
      First page: 9
      Abstract: With the increasing pressure to reduce emissions, friction reduction is always an up-to-date topic in the automotive industry. Among the various possibilities to reduce mechanical friction, the usage of a low-viscosity lubricant in the engine is one of the most effective and most economic options. Therefore, lubricants of continuously lower viscosity are being developed and offered on the market that promise to reduce engine friction while avoiding deleterious mixed lubrication and wear. In this work, a 1.6 L downsized Diesel engine is used on a highly accurate engine friction test-rig to determine the potential for friction reduction using low viscosity lubricants under realistic operating conditions including high engine loads. In particular, two hydrocarbon-based lubricants, 0W30 and 0W20, are investigated as well as a novel experimental lubricant, which is based on a polyalkylene glycol base stock. Total engine friction is measured for all three lubricants, which show a general 5% advantage for the 0W20 in comparison to the 0W30 lubricant. The polyalkylene glycol-based lubricant, however, shows strongly reduced friction losses, which are about 25% smaller than for the 0W20 lubricant. As the 0W20 and the polyalkylene glycol-based lubricant have the same HTHS-viscosity , the findings contradict the common understanding that the HTHS-viscosity is the dominant driver related to the friction losses.
      PubDate: 2017-04-07
      DOI: 10.3390/lubricants5020009
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 10: Specific Features of Aerodynamic Journal
           Bearings with Elastically Supported Pads

    • Authors: Jiří Šimek
      First page: 10
      Abstract: Aerodynamic bearings with elastically supported tilting pads have operational properties comparable with widely-used foil journal bearings. They combine the excellent stability of tilting pad bearings, as a result of very small cross-coupling stiffness terms, with the positive properties of foil bearings, namely their ability to adapt to changing operating conditions and presence of additional damping due to friction between elastic members and bearing casings. Air cycle machines (ACMs) are used in the environmental control systems of aircrafts to manage the pressurization of the cabin. An ACM with the abovementioned type of bearings and an operational speed of 60,000 rpm was designed and successfully tested, even under conditions of strong external excitation. Some problems with rotor stability in certain operation regimes were encountered. Rotor relative vibrations measured at both bearing locations increased substantially when excitation frequency was close to the lowest rotor eigenvalues. In spite of that and the 1000 start/stop cycles passed by the end of the test, any traces of wear on the bearing sliding surfaces were negligible. When the bearing distance had to be shortened in order to insert the machine into the defined space, the rotor quickly became unstable at relatively low speeds. Although rotor stability reserve was reduced only slightly, the rotor had to be redesigned in order to achieve stability. Operation characteristics of aerodynamic bearings with elastically supported tilting pads are presented together with rotor dynamic analysis and validated with measured results.
      PubDate: 2017-04-11
      DOI: 10.3390/lubricants5020010
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 11: Chemical/Structural Modification of Canola
           Oil and Canola Biodiesel: Kinetic Studies and Biodegradability of the

    • Authors: Venu Borugadda, Asish Somidi, Ajay Dalai
      First page: 11
      Abstract: Canola oil and canola biodiesel derived alkoxides are prepared in the present investigation through a series of structural modifications. Epoxidation of canola oil and canola biodiesel were carried out by hydrogen peroxide using IR-120 as an acidic catalyst. The alkoxylation of epoxidized feedstocks was promoted using 2-propanol and tert-Butyl alcohol in the presence of montmorillonite catalyst and optimum reaction conditions were obtained for complete epoxide conversion to alkoxylated products as follows: reaction temperature of 90 °C, epoxide to alcohol molar ratio of 1:6, and reaction time between 6 and 8 h. The products were identified with one- and two-dimensional Nuclear Magnetic Resonance (NMR) techniques, and the kinetic and thermodynamic parameters of the alkoxylation reactions were also investigated. The thermo-oxidative stability, rheology, biodegradability and lubricity properties of the prepared alkoxides were determined using American Society for Testing and Materials (ASTM) and American Oil Chemists Society (AOCS) standard methods. Structural modification of the feedstocks enhanced the significant properties for lubrication and exhibited their potential application as gear and engine oils.
      PubDate: 2017-04-28
      DOI: 10.3390/lubricants5020011
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 12: The Reduction of Static Friction of Rubber
           Contact under Sea Water Droplet Lubrication

    • Authors: Yong-Jie Zhou, De-Guo Wang, Yan-Bao Guo
      First page: 12
      Abstract: In this work, a series of experimental tests is carried out in laboratory conditions which set the rubber compound (soft and stiff), the normal load, and the direction of propagation of sea water droplets into the interface of rubber–steel pipe contact as variables. The results show that the maximum static frictions (F) of rubber–pipe contacts increase as the normal load increases in both dry and lubricating conditions, and the values of F for the softer rubber are higher than that for the stiffer rubber. However, significant reduction in static friction is found due to the lubrication of sea water droplets. The influence of lubrication is stronger when the droplets propagate into the contact interfaces at the tail edge than that at the front edge. Capture sequences of the contact region facilitate the lubrication of seawater droplets by accelerating the progress of separation in the contact interfaces, thus reducing the static friction force. This investigation improves our understanding of the lubrication of sea water droplets during pipe-laying operation, and it will help us to conduct further research on the accuracy and safety of offshore engineering.
      PubDate: 2017-05-12
      DOI: 10.3390/lubricants5020012
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 13: The Tribological Performance of CrMoN/MoS2
           Solid Lubrication Coating on a Piston Ring

    • Authors: Yuelan Di, Zhihai Cai, Ping Zhang
      First page: 13
      Abstract: In order to improve the tribological properties of an engine piston ring and enhance its service life, magnetron sputtering technology and low temperature ion sulphurizing treatment technology were used to prepare CrMoN/MoS2 solid lubricant coating on the surface of an engine piston ring. The morphologies and compositions of the surface and cross-section of the sulfuration layer were analyzed by field emission scanning electron microscopy (FESEM), and wear property under high load, high speed and high temperature conditions were tested by a SRV®4 friction and wear testing machine. The results show that the CrMoN/MoS2 composite coatings appear as a dense grain structure, and the coating is an ideal solid lubrication layer that possesses an excellent high temperature wear resistance, reducing the engine operating temperature abrasion effectively and prolonging the service life of the engine.
      PubDate: 2017-05-23
      DOI: 10.3390/lubricants5020013
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 14: Ionanocarbon Lubricants. The Combination of
           Ionic Liquids and Carbon Nanophases in Tribology

    • Authors: María-Dolores Avilés, Noelia Saurín, José Sanes, Francisco-José Carrión, María-Dolores Bermúdez
      First page: 14
      Abstract: The present overview will focus on the tribological applications of what we have called ionanocarbon lubricants, that is, the combination of carbon nanophases (graphene, carbon nanotubes, nanodiamonds, carbon nanodots) and room-temperature ionic liquids in new dispersions, blends, or modified nanostructures and their use in tribology, lubrication, and surface engineering as friction-reducing, antiwear, and surface-protecting agents in thin films and composite materials. Further research lines and factors that limit the practical applications of the outstanding research results are also highlighted. The very recent results in these lines of research make this a necessary brief review.
      PubDate: 2017-05-23
      DOI: 10.3390/lubricants5020014
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 15: Chemical-Mechanical Impact of Nanoparticles
           and pH Effect of the Slurry on the CMP of the Selective Layer Surfaces

    • Authors: Filip Ilie, George Ipate
      First page: 15
      Abstract: This paper provides a tribochemical study of the selective layer surface by chemical mechanical planarization (CMP). CMP is used to remove excess material obtained in the process of selective transfer. The paper aims at a better understanding of the planarization (polishing) and micromachining. The planarization becomes effective if the material removal rate (MRR) is optimal and the surface defects are minimal. The pH of the slurry plays a very important role in removing the selective layer by CMP, and hydrogen peroxide (H2O2) is the most common oxidizer used in CMP slurry. The purpose of this paper is the analysis of the pH effect on the etching rate (ER) and on the behavior of selective layer polishing by a constant concentration of H2O2 and the influence of nanoparticles size and concentration on selective layer surface CMP. The nanoparticle size used is 250 nm. The MRR results through CMP and ER have been shown to be influenced by the presence of oxides on the selective layer surface and have been found to vary with the slurry pH at constant H2O2 concentrations. The CMP slurry plays an important role in the CMP process performance and should be monitored for optimum results and minimal surface defects. The paper analyzes the impact of chemical-mechanical, inter-nanoparticle, and pad-nanoparticle-substrate interactions on CMP performance, taking into account the state of friction at the interface, by measuring the friction force. Selective layer CMP optimization studies were required to control the chemical and mechanical interactions at the interface between the slurry and the selective layer, the slurry chemistry, the properties, and the stability of the suspended abrasive nanoparticles.
      PubDate: 2017-05-23
      DOI: 10.3390/lubricants5020015
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 16: Nonlinear Transient Modeling and Design of
           Turbocharger Rotor/Semi-Floating Bush Bearing System

    • Authors: Jianming Cao, Saeid Dousti, Paul Allaire, Tim Dimond
      First page: 16
      Abstract: This work presents the bearing design and analysis of radial semi-floating bush oil lubricated bearings for a typical industrial turbocharger configuration. Initially, the stability analysis for a linear rotor/bearing system is evaluated through eigenvalues and eigenvectors. The stiffness and damping coefficients of the inner oil film are obtained for the linear modeling process. The operating speed range of the turbocharger is high enough, at 21,000 to 24,000 rpm, to be unstable, indicating that the analysis should be and is carried out with nonlinear transient modeling. The nonlinear transient analysis evaluates the rotor and bush limit cycle orbits, rotor dynamics, the forces acting on the rotor and semi-floating bush surfaces, the oil flow through the bearing, the oil temperatures, and the power loss of the two oil films. The optimum design of a set of semi-floating bush bearings for this application depends strongly upon the clearances of the bush and squeeze film damper, usually expressed as the non-dimensional clearance to radius ratio. A typical clearance is evaluated to determine the bearing performance in terms of orbit size, forces acting on the bush and squeeze damper surfaces, oil flow through the bearing, power loss, and thermal heating. The nonlinear transient orbit values are evaluated for frequency content using the FFT to determine which orbits show both the synchronous and sub-synchronous vibration components and the associated rotor modes excited. These results are compared to the linear analysis over the operating speed range. The oil flow through the bearing component is much larger than the squeeze film damper. The forces acting on the bush and squeeze damper surfaces are related to the fatigue life of the bearing.
      PubDate: 2017-06-12
      DOI: 10.3390/lubricants5020016
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 17: Full Dynamic Ball Bearing Model with Elastic
           Outer Ring for High Speed Applications

    • Authors: Christian Wagner, Andreas Krinner, Thomas Thümmel, Daniel Rixen
      First page: 17
      Abstract: Ball bearings are commonly used in high speed turbomachinery and have a critical influence on the rotordynamic behavior. Therefore, a simulation model of the bearing to predict the dynamic influence is essential. The presented model is a further step to develop an accurate and efficient characterization of the ball bearing’s rotor dynamic parameters such as stiffness and deflections as well as vibrational excitations induced by the discrete rolling elements. To make it applicable to high speed turbomachinery, the model considers centrifugal forces, gyroscopic effects and ball spinning. The consideration of an elastic outer ring makes the bearing model suitable for integrated lightweight bearing constructions used in modern aircraft turbines. In order to include transient rotordynamic behavior, the model is built as a full dynamic multibody simulation with time integration. To investigate the influence of the elasticity of the outer ring, a comparison with a rigid formulation for several rotational speeds and loads is presented.
      PubDate: 2017-06-12
      DOI: 10.3390/lubricants5020017
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 18: Lubricity Assessment, Wear and Friction of
           CNT-Based Structures in Nanoscale

    • Authors: Elias Koumoulos, Costas Charitidis
      First page: 18
      Abstract: In this work, three case studies are reported, namely carbon nanotube/polyvinyl butyral composites, MWCNTs/polydimethylsiloxane-based coatings and vertically aligned CNT forest array, of which the friction and resistance to wear/deformation were assessed through nanoindentation/nanoscratch. Additional deformation parameters and findings are also addressed and discussed; namely, material deformation upwards (pile-up) or downwards (sink-in) with respect to the indented surface plane, hardness to modulus ratio (index of resistance to wear) and coefficient of friction. The enhancement of the scratch resistance due to the incorporation of CNTs in a polymer matrix is investigated. For the case of the forest structure, sliding between neighboring nanotubes is identified, while, through ploughing of the tip, local deformation and the extent of plasticity are also addressed.
      PubDate: 2017-06-16
      DOI: 10.3390/lubricants5020018
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 19: Tribological Properties of Porous PEEK
           Composites Containing Ionic Liquid under Dry Friction Condition

    • Authors: Xianzhu Huang, Jian Wu, Xiaohua Lu, Xin Feng, Yijun Shi
      First page: 19
      Abstract: NaCl particles were added into Polyetheretherketone (PEEK) and its composites to produce porous PEEK-based materials by washing NaCl away after the high-temperature compression molding process. After that, an ionic liquid was added into the porous materials under vacuum condition. Carbon fibers (CF), as reinforcement, and PTFE, as an internal solid lubricant, were employed to prepare PEEK composites. Tribological properties under dry friction condition were studied on a ring-on-disc tribo-meter. The influence of CF and PTFE on tribological properties was carefully investigated. The results indicated that, in comparison with traditional PEEK composites (CF/PTFE/PEEK), the porous PEEK composites containing ionic liquid showed much better tribological properties. It is found that CF can help PEEK form effective pores to suck in the ionic liquid resulting in a better tribological performance. CF reinforced porous PEEK containing ionic liquid (p-CF/PEEK + IL) demonstrated the lowest friction coefficient (27% of CF/PTFE/PEEK) and the lowest wear loss (only 0.9% of CF/PTFE/PEEK). Long time tribological test revealed that the wear mass loss comes from the running-in period, while its wear is negligible after this period. It is also found that the addition of PTFE has a negative influence on the tribological behaviors, especially under high sliding velocity and applied load.
      PubDate: 2017-06-17
      DOI: 10.3390/lubricants5020019
      Issue No: Vol. 5, No. 2 (2017)
  • Lubricants, Vol. 5, Pages 2: Acknowledgement to Reviewers of Lubricants in

    • Authors: Lubricants Editorial Office
      First page: 2
      Abstract: The editors of Lubricants would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...]
      PubDate: 2017-01-10
      DOI: 10.3390/lubricants5010002
      Issue No: Vol. 5, No. 1 (2017)
  • Lubricants, Vol. 5, Pages 3: The Influence of Tool Texture on Friction and
           Lubrication in Strip Reduction Testing

    • Authors: Mohd Sulaiman, Peter Christiansen, Niels Bay
      First page: 3
      Abstract: While texturing of workpiece surfaces to promote lubrication in metal forming has been applied for several decades, tool surface texturing is rather new. In the present paper, tool texturing is studied as a method to prevent galling. A strip reduction test was conducted with tools provided with shallow, longitudinal pockets oriented perpendicular to the sliding direction. The pockets had small angles to the workpiece surface and the distance between them were varied. The experiments reveal that the distance between pockets should be larger than the pocket width, thereby creating a topography similar to flat table mountains to avoid mechanical interlocking in the valleys; otherwise, an increase in drawing load and pick-up on the tools are observed. The textured tool surface lowers friction and improves lubrication performance, provided that the distance between pockets is 2–4 times larger than the pocket width. Larger drawing speed facilitates escape of the entrapped lubricant in the pockets. Testing with low-to-medium viscosity oils leads to a low sheet roughness on the plateaus, but also local workpiece material pick-up on the tool plateaus. Large lubricant viscosity results in higher sheet plateau roughness, but also prevents pick-up and galling.
      PubDate: 2017-01-17
      DOI: 10.3390/lubricants5010003
      Issue No: Vol. 5, No. 1 (2017)
  • Lubricants, Vol. 5, Pages 4: Editorial: Friction and Lubricants Related to
           Human Bodies

    • Authors: Ille Gebeshuber, George van Aken
      First page: 4
      Abstract: n/a
      PubDate: 2017-02-13
      DOI: 10.3390/lubricants5010004
      Issue No: Vol. 5, No. 1 (2017)
  • Lubricants, Vol. 5, Pages 5: Progress in Tribological Properties of
           Nano-Composite Hard Coatings under Water Lubrication

    • Authors: Qianzhi Wang, Fei Zhou
      First page: 5
      Abstract: The tribological properties, under water-lubricated conditions, of three major nano-composite coatings, i.e., diamond-like carbon (DLC or a-C), amorphous carbon nitride (a-CNx) and transition metallic nitride-based (TiN-based, CrN-based), coatings are reviewed. The influences of microstructure (composition and architecture) and test conditions (counterparts and friction parameters) on their friction and wear behavior under water lubrication are systematically elucidated. In general, DLC and a-CNx coatings exhibit superior tribological performance under water lubrication due to the formation of the hydrophilic group and the lubricating layer with low shear strength, respectively. In contrast, TiN-based and CrN-based coatings present relatively poor tribological performance in pure water, but are expected to present promising applications in sea water because of their good corrosion resistance. No matter what kind of coatings, an appropriate selection of counterpart materials would make their water-lubricated tribological properties more prominent. Currently, Si-based materials are deemed as beneficial counterparts under water lubrication due to the formation of silica gel originating from the hydration of Si. In the meantime, the tribological properties of nano-composite coatings in water could be enhanced at appropriate normal load and sliding velocity due to mixed or hydrodynamic lubrication. At the end of this article, the main research that is now being developed concerning the development of nano-composite coatings under water lubrication is described synthetically.
      PubDate: 2017-02-17
      DOI: 10.3390/lubricants5010005
      Issue No: Vol. 5, No. 1 (2017)
  • Lubricants, Vol. 5, Pages 6: The Effect of Non-Circular Bearing Shapes in
           Hydrodynamic Journal Bearings on the Vibration Behavior of Turbocharger

    • Authors: Lukas Bernhauser, Martin Heinisch, Markus Schörgenhumer, Manfred Nader
      First page: 6
      Abstract: Increasing quality demands of combustion engines require, amongst others, improvements of the engine’s acoustics and all (sub)components mounted to the latter. A significant impact to the audible tonal noise spectrum results from the vibratory motions of fast-rotating turbocharger rotor systems in multiple hydrodynamic bearings such as floating bearing rings. Particularly, the study of self-excited non-linear vibrations of the rotor-bearing systems is crucial for the understanding, prevention or reduction of the noise and, consequently, for a sustainable engine acoustics development. This work presents an efficient modeling approach for the investigation, optimization, and design improvement of complex turbocharger rotors in hydrodynamic journal bearings, including floating bearing rings with circular and non-circular bearing geometries. The capability of tonal non-synchronous vibration prevention using non-circular bearing shapes is demonstrated with dynamic run-up simulations of the presented model. These findings and the performance of our model are compared and validated with results of a classical Laval/Jeffcott rotor-bearing model and a specific turbocharger model found in the literature. It is shown that the presented simulation method yields fast and accurate results and furthermore, that non-circular bearing shapes are an effective measure to reduce or even prevent self-excited tonal noise.
      PubDate: 2017-03-03
      DOI: 10.3390/lubricants5010006
      Issue No: Vol. 5, No. 1 (2017)
  • Lubricants, Vol. 5, Pages 7: Rotordynamic and Friction Loss Measurements
           on a High Speed Laval Rotor Supported by Floating Ring Bearings

    • Authors: Rob Eling, Mathys te Wierik, Ron van Ostayen, Daniel Rixen
      First page: 7
      Abstract: Floating ring bearings are the commonly used type of bearing for automotive turbochargers. The automotive industry continuously investigates how to reduce the bearing friction losses and how to create silent turbochargers. Many of these studies involve creating a numerical model of the rotor-bearing system and performing validation on a test bench on which a turbocharger is driven by hot gases. This approach, however, involves many uncertainties which diminish the validity of the measurement results. In this study, we present a test setup in which these uncertainties are minimized. The measurement results show the behavior of the floating ring bearing as a function of oil feed pressure, oil feed temperature, rotor unbalance and bearing clearances. Next to an increased validity, the test setup provides measurement data with good repeatability and can therefore represent a case study which can be used for validation of rotor-bearing models.
      PubDate: 2017-03-15
      DOI: 10.3390/lubricants5010007
      Issue No: Vol. 5, No. 1 (2017)
  • Lubricants, Vol. 5, Pages 8: Influence of Organo-Sulfur Compounds with
           Overbased Calcium Compounds on Lubrication in Cold Forming

    • Authors: Tomohiro Takaki, Kazuhiro Yagishita, Teppei Tsujimoto, Toshiaki Wakabayashi
      First page: 8
      Abstract: The authors analyzed the structures of sulfurized olefins using NMR spectroscopy and studied the effects of sulfur chain length and alkyl structure on the ironing performance. They found that branched chain olefins, which contain branched alkyl groups, show superior ironing performance to straight chain olefins, provided that their carbon numbers are relatively low. When the sulfurized olefins were used in combination with overbased detergents (calcium sulfonate or salicylate), they showed a higher performance in ironing than with sulfurized olefins alone. It was also found that lubricating films consisting of both iron sulfide and calcium carbonate seem to improve ironing performance.
      PubDate: 2017-03-16
      DOI: 10.3390/lubricants5010008
      Issue No: Vol. 5, No. 1 (2017)
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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