Journal Cover Lubricants
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   ISSN (Online) 2075-4442
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  • 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 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)
  • Lubricants, Vol. 5, Pages 1: Surface Film Adsorption and Lubricity of
           Soybean Oil In-Water Emulsion and Triblock Copolymer Aqueous Solution: A
           Comparative Study

    • Authors: Reza Taheri, Buyung Kosasih, Hongtao Zhu, Anh Tieu
      First page: 1
      Abstract: This paper investigates the surface film adsorption and lubricity of two different types of potential environmentally friendly cold metal forming lubricants: soybean vegetable oil in water VO/W emulsions and triblock copolymer aqueous solutions. The lubricants have different visual appearance, surface film adsorption characteristic, lubricity and surface cleaning behaviour. The effects of concentration, temperature and emulsification ultrasonic energy (for VO/W emulsion) are studied. The result shows that the soybean VO/W emulsions have stronger adsorption, superior lubricity and anti-wear property compared to the copolymer solutions. The effect of temperature is investigated at 30 °C and 65 °C which are below and above cloud point of the aqueous copolymer solutions. Both lubricants show improved friction and anti-wear property at 65 °C. However, tenacious residual film remained on the discs surface after surface cleaning indicates lower cleanability of the soybean VO/W emulsions compared to the copolymer solutions, postulating the need for extra post-processing cleaning operations after cold forming process with VO/W emulsion lubricant.
      PubDate: 2016-12-30
      DOI: 10.3390/lubricants5010001
      Issue No: Vol. 5, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 35: Silicon Nitride Bearings for Total Joint

    • Authors: Bryan McEntire, Ramaswamy Lakshminarayanan, Darin Ray, Ian Clarke, Leonardo Puppulin, Giuseppe Pezzotti
      First page: 35
      Abstract: The articulation performance of silicon nitride against conventional and highly cross-linked polyethylene, as well as for self-mated silicon nitride bearings, was examined in a series of standard hip simulation studies. Wear rates for polyethylene liners against silicon nitride femoral heads were consistent with reported literature, although higher than cobalt chromium controls. Excessive protein precipitation was a confounding factor in interpretation of the wear data. Post wear-test Raman spectroscopy of the cross-linked polyethylene liners showed no oxidative degradation. Wear of self-mated silicon nitride was found to be essentially zero and indistinguishable from alumina controls using continuously orbital hip simulation for up to three million cycles. However, introduction of an alternative loading profile from three to five million cycles, including a stop-dwell-start sequence, significantly increased wear for two of six silicon nitride couples. This behavior is associated with formation and disruption of a gelatinous silicic acid tribochemical film, and is consistent with a recurrent transition from fluid-film to boundary lubrication. Overall, these results suggest that silicon nitride articulation against dissimilar counterface surfaces (e.g., highly cross-linked polyethylene) is preferred.
      PubDate: 2016-10-18
      DOI: 10.3390/lubricants4040035
      Issue No: Vol. 4, No. 4 (2016)
  • Lubricants, Vol. 4, Pages 36: Multi-Phase Friction and Wear Reduction by
           Copper Nanopartices

    • Authors: Matthias Scherge, Roman Böttcher, Dominik Kürten, Dominic Linsler
      First page: 36
      Abstract: Finely dispersed copper nanoparticles were added as an additive to fully-formulated engine oils. The copper additive was in colloidal form, with an inner core of Cu2+ atoms covered by surfactants to form stable reverse micelles that are completely dispersible in the base oil. The tribological process to form protective films at the metal surface is comprised of three phases. Phase I can be considered a physical process involving the build-up of polar molecules by absorption to produce a friction modifier film, whereas phases II and III have to be treated as mechanochemical processes comprising a combination of redox reactions and a third body formation. The tribological performance was investigated using atomic force microscopy, a microtribometer, a pin-on-disk tribometer in combination with continuous and high-resolution wear measurements with radionuclide technique, and high pressure stressing in a thrust roller bearing test rig. In addition, the nanostructure of the additive was characterized by atomic force microscopy. Finally, the chemical composition of the metal surface was analyzed using photoelectron spectroscopy.
      PubDate: 2016-10-18
      DOI: 10.3390/lubricants4040036
      Issue No: Vol. 4, No. 4 (2016)
  • Lubricants, Vol. 4, Pages 37: Tribological Stress of Lubricating Greases
           in the Light of System Entropy

    • Authors: Erik Kuhn
      First page: 37
      Abstract: Lubricating greases show a structural degradation due to friction stress. The shear process dissipates energy. This results in a breakdown of the thickener structure, heat and entropy generation. Tribo-systems are energy driven systems. The stressed lubricating grease is modeled as a subsystem and presents an open thermodynamic system. Investigations were made to obtain more information about the correlation of system entropy and structural degradation of a lubricating grease. Experimental studies were done to estimate the role in terms of entropy transport for the open system. The degradation-entropy theorem was applied with the help of an empirical model to describe the correlation between degradation process and entropy production for the special case of a closed and stationary system.
      PubDate: 2016-11-17
      DOI: 10.3390/lubricants4040037
      Issue No: Vol. 4, No. 4 (2016)
  • Lubricants, Vol. 4, Pages 38: Potential Synthetic Biolubricant as an
           Alternative to Bovine Serum

    • Authors: Susan Scholes, Coral Colledge, Andrew Naylor, Mohammed Mahdi, Alan Smith, Thomas Joyce
      First page: 38
      Abstract: It is crucial that orthopaedic implant materials are tested in conditions that replicate the natural body’s environment as closely as possible. Bovine serum is currently recommended for use by the International Organisation for Standardisation (ISO) for the wear testing of these implant materials, however, the rheological properties of bovine serum do not match fully those of the body’s natural lubricant, synovial fluid. This study looks at a potential alternative to bovine serum for the testing of orthopaedic implant materials; 0.5% gellan gum fluid gel. Wear tests using multidirectional motion were conducted on ultra-high molecular weight polyethylene (UHMWPE) pins rubbing against stainless steel plates. Roughness measurements were performed during testing along with particle analysis of the testing lubricant. At two million cycles (equivalent to 121.3 km of sliding), the mean wear factor for the four UHMWPE pins was 0.25 (standard deviation (SD) 0.03) × 10−6 mm3/Nm and there was no evidence of any transfer film on the plate surfaces. The wear factor produced by 0.5% gellan gum fluid gel was lower than that measured in previous studies using bovine serum as the lubricant but greater than the wear factor shown in published work using a similar alternative lubricant (sodium alginate mixed with gellan gum). Work on the development of a suitable alternative lubricant to bovine serum will continue.
      PubDate: 2016-11-18
      DOI: 10.3390/lubricants4040038
      Issue No: Vol. 4, No. 4 (2016)
  • Lubricants, Vol. 4, Pages 23: Synthesis, Characterization and Tribological
           Evaluation of New Generation Materials for Aluminum Cold Rolling Oils

    • Authors: Ponnekanti Nagendramma, Bal Shukla, Dilip Adhikari
      First page: 23
      Abstract: The present concept of being globally “green” puts additional demands on lubricants. They are to be biodegradable and ecofriendly. Therefore, in a search for alternate lubricants meeting the above demands, we have synthesized biodegradable new generation esters using alcohols such as 2,2-dimethyl-1,3-propane diol and 2,2-diethyl-1,3-propane diol and fatty acids like caproic and 2-ethyl caproic in presence of indigenous ion exchange resin catalyst. The synthesized esters were analyzed and characterized for their physico chemical properties. In addition, with a view to finding out the possibility of using these esters as aluminum cold rolling oils, their lubricity characteristics, biodegradability and toxicity were also investigated. The products were found to have good potential for use in biodegradable aluminum cold rolling oils meeting IS: 14385-2002 specification.
      PubDate: 2016-06-28
      DOI: 10.3390/lubricants4030023
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 24: MD Sliding Simulations of Amorphous
           Tribofilms Consisting of either SiO2 or Carbon

    • Authors: Andrey Dmitriev, Anton Nikonov, Werner Österle
      First page: 24
      Abstract: The sliding behaviors of two simplified tribofilms with amorphous structure consisting either of SiO2 molecules or C atoms were simulated by molecular dynamics modeling. The objective was to identify mechanisms explaining the experimentally observed lubricating properties of the two amorphous films. The impacts of layer thickness, normal pressure, temperature and different substrate materials were studied systematically, while the sliding velocity was kept constant at 30 m/s. While the layer thickness was not critical, all the other parameters showed special effects under certain conditions. Normal pressure impeded void formation and could even eliminate voids if applied at high temperature. Stick-slip sliding was changed to smooth sliding at high temperature due to void healing. Considering the carbon film, high friction forces and shearing of the entire film was observed with diamond substrates, whereas interface sliding at low friction forces and an amorphous layer of iron mixed with carbon was observed if the supporting substrates consisted of α-Fe. Both films show a decrease of friction forces and smooth sliding behavior at elevated temperature, corresponding well to the tribological behavior of an advanced nanocomposite sliding against a steel disc under severe stressing conditions when high flash temperatures can be expected.
      PubDate: 2016-06-29
      DOI: 10.3390/lubricants4030024
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 25: A Tribological Assessment of Ultra High
           Molecular Weight Polyethylene Types GUR 1020 and GUR 1050 for Orthopedic

    • Authors: Benjamin Hunt, Thomas Joyce
      First page: 25
      Abstract: The wear properties of biomaterials have been demonstrated to have a high importance within orthopedic bearing surfaces. This study performed a comparison of the wear between the two main grades of Ultra High Molecular Weight Polyethylene types GUR 1020 and GUR 1050 articulating against Cobalt Chromium. Such a high capacity wear comparison has not been reported elsewhere in the scientific literature. Under an identical testing protocol it was found that GUR 1020 had a wear factor of 3.92 ± 0.55 × 10 − 6 ( mm 3 / Nm ) and GUR 1050 had a wear factor of 3.64 ± 0.39 × 10 − 6 ( mm 3 / Nm ) , with a non-statistical significant difference of p = 0.052. These wear factors correlate closely with those observed from other screening wear studies and explant analysis.
      PubDate: 2016-06-30
      DOI: 10.3390/lubricants4030025
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 26: The Friction Reducing Effect of
           Square-Shaped Surface Textures under Lubricated Line-Contacts—An
           Experimental Study

    • Authors: Ping Lu, Robert Wood, Mark Gee, Ling Wang, Wilhelm Pfleging
      First page: 26
      Abstract: Surface texturing has been shown to be an effective modification approach for improving tribological performance. This study examined the friction reduction effect generated by square dimples of different sizes and geometries. Dimples were fabricated on the surface of ASP2023 steel plates using femtosecond laser-assisted surface texturing techniques, and reciprocating sliding line contact tests were carried out on a Plint TE77 tribometer using a smooth 52100 bearing steel roller and textured ASP2023 steel plates. The tribological characterization of the friction properties indicated that the textured samples had significantly lowered the friction coefficient in both boundary (15% improvement) and mixed lubrication regimes (13% improvement). Moreover, the high data sampling rate results indicated that the dimples work as lubricant reservoirs in the boundary lubrication regime.
      PubDate: 2016-07-11
      DOI: 10.3390/lubricants4030026
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 27: Tribofilms Forming in Oil-Lubricated

    • Authors: Matthias Scherge, Angelika Brink, Dominic Linsler
      First page: 27
      Abstract: The subject of the present paper is the characterization of third bodies of run-in systems. By means of continuous friction and wear measurement, lubricated steel-steel and steel-aluminum contacts were evaluated. Microstructure, chemical composition and response of the materials to shear were analyzed by XPS/AES and focused ion beam technique. After a proper running-in, both systems developed a third body. The third body differs significantly from the base materials. In addition to adapted microstructure and near-surface chemistry, the third body exhibited a substructure characterized by a near-surface zone that accommodates shear and a second, deeper region that ensures strengthening.
      PubDate: 2016-07-14
      DOI: 10.3390/lubricants4030027
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 28: Formation of Anti-Wear Tribofilms via α-ZrP
           Nanoplatelet as Lubricant Additives

    • Authors: Wei Dai, Bassem Kheireddin, Hong Gao, Yuwei Kan, Abraham Clearfield, Hong Liang
      First page: 28
      Abstract: Effective tribofilms are desirable to protect mechanical systems. In the present research, we investigated the formation of a tribofilm through the use of α-ZrP (Zr(HPO4)2·H2O) as an additive. Experiments were conducted on a base oil where 0.2 wt% of the additive was used. Experimental results showed a 50% reduction in friction and a 30% reduction in wear when compared to the base oil containing 0.8 wt% ZDDP. Spectroscopic characterization indicated that the tribofilm consists of iron oxide, zirconium oxide, and zirconium phosphates. The worn surface was seen to be smooth which renders it desirable for bearing systems.
      PubDate: 2016-08-05
      DOI: 10.3390/lubricants4030028
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 29: Experimental and Numerical Simulation of the
           Dynamic Frictional Contact between an Aircraft Tire Rubber and a Rough

    • Authors: Iulian Rosu, Hélène Elias-Birembaux, Frédéric Lebon, Hagen Lind, Matthias Wangenheim
      First page: 29
      Abstract: This paper presents a numerical simulation of an aircraft tire in contact with a rough surface using a variable friction coefficient dependent on temperature and contact pressure. A sliding facility was used in order to evaluate this dependence of the friction coefficient. The temperature diffusion throughout the tire cross-section was measured by means of thermocouples. Both frictional heating and temperature diffusion were compared to numerical two- and three- dimensional simulations. An adequate temperature prediction could be obtained. In future simulations, wear should be taken into account in order to have a more accurate simulation especially in the case of high pressures and slipping velocities. A 3D finite element model for a rolling tire at a velocity of 37.79 knots (19.44 m/s) and in a cornering phase was investigated using a variable friction coefficient dependent on temperature and pressure. The numerical simulation tended to predict the temperature of the tire tread after a few seconds of rolling in skidding position, the temperature of the contact zone increases to 140 °C. Further investigations must be carried out in order to obtain the evolution of the temperature observed experimentally. The authors would like to point out that for confidentiality reasons, certain numerical data could not be revealed.
      PubDate: 2016-08-17
      DOI: 10.3390/lubricants4030029
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 30: The Tribological Properties of Multi-Layered
           Graphene as Additives of PAO2 Oil in Steel–Steel Contacts

    • Authors: Yan-Bao Guo, Si-Wei Zhang
      First page: 30
      Abstract: Multi-layered graphene was prepared by supercritical CO2 exfoliation of graphite. As the additives of polyalphaolefin-2 (PAO2) oil, its tribological properties were investigated using four-ball test method. The friction reduction and anti-wear ability of pure lubricant was improved by the addition of graphene. With a favorable concentration, the graphene was dispersive. The PAO2 oil with 0.05 wt % graphene showed better tribological properties than that for the other concentration of graphene additives. It could be used as a good lubricant additive for its excellent tribological characteristics, and the multi-layered graphene can bear the load of the steel ball and prevent direct contact of the mating metal surfaces. However, a higher concentration would cause the agglomeration of graphene and weaken the improvement of tribological properties.
      PubDate: 2016-08-31
      DOI: 10.3390/lubricants4030030
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 31: Synthesis and Tribological Behavior of Ultra
           High Molecular Weight Polyethylene (UHMWPE)-Lignin Composites

    • Authors: Surojit Gupta, M. Riyad, Yun Ji
      First page: 31
      Abstract: In this paper, we report the synthesis and characterization of ultra-high molecular weight polyethylene (UHMWPE)-lignin composites. During this study four different compositions, namely UHMWPE, UHMWPE-13 wt. % lignin, UHMWPE-25 wt. % lignin and UHMWPE-42.5 wt. % lignin were fabricated by hot pressing. Detailed microstructural studies by scanning electron microscopy (SEM) showed that UHMWPE and UHMWPE-13 wt. % lignin had a uniform microstructure, whereas UHMWPE-25 wt. % lignin and UHMWPE-42.5 wt. % lignin samples were riddled with pores. UHMWPE and UHMWPE-13% lignin showed comparable flexural strengths of ~32.2 MPa and ~32.4 MPa, respectively. However, the flexural strength dropped drastically in UHMWPE-25 wt. % lignin and UHMWPE-42.5 wt. % samples to ~13 MPa and ~8 MPa, respectively. The tribology of UHMWPE-lignin composites is governed by the tribofilm formation. All the compositions showed similar µmean values and the specific wear rates (WR) decreased gradually as the concentration of lignin in UHMWPE was increased.
      PubDate: 2016-08-31
      DOI: 10.3390/lubricants4030031
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 32: Tribological Performance of MoS2 Coatings in
           Various Environments

    • Authors: Thomas Gradt, Thomas Schneider
      First page: 32
      Abstract: Molybdenum disulfide (MoS2) is a well-known solid lubricant for tribosystems running in vacuum or dry gases. Problems arise due to its sensitivity to humidity, which is a drawback for its application under ambient conditions. However, by using a physical vapor deposition (PVD) process, deposition parameters can be optimized not only to gain a coatings structure with favorable frictional properties but also to minimize the sensitivity to attack by water molecules. Therefore, an improved tribological behavior even under moist conditions can be achieved. MoS2 coatings are also candidates for being applied at cryogenic temperatures. They already have proven their suitability, e.g., for sliding support elements between superconducting magnets of the nuclear fusion-experiment Wendelstein 7-X. However, these coatings were exclusively produced for this particular application and the utilization for more common tribosystems may be precluded due to cost considerations. In view of a wider range of applications, pure and Cr containing PVD-MoS2 coatings with an optimized structure were tested under varying environments including hydrogen gas and cryogenic temperatures. Results of the most promising variant are presented in this paper.
      PubDate: 2016-09-07
      DOI: 10.3390/lubricants4030032
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 33: Towards Accurate Prediction of Unbalance
           Response, Oil Whirl and Oil Whip of Flexible Rotors Supported by
           Hydrodynamic Bearings

    • Authors: Rob Eling, Mathys te Wierik, Ron van Ostayen, Daniel Rixen
      First page: 33
      Abstract: Journal bearings are used to support rotors in a wide range of applications. In order to ensure reliable operation, accurate analyses of these rotor-bearing systems are crucial. Coupled analysis of the rotor and the journal bearing is essential in the case that the rotor is flexible. The accuracy of prediction of the model at hand depends on its comprehensiveness. In this study, we construct three bearing models of increasing modeling comprehensiveness and use these to predict the response of two different rotor-bearing systems. The main goal is to evaluate the correlation with measurement data as a function of modeling comprehensiveness: 1D versus 2D pressure prediction, distributed versus lumped thermal model, Newtonian versus non-Newtonian fluid description and non-mass-conservative versus mass-conservative cavitation description. We conclude that all three models predict the existence of critical speeds and whirl for both rotor-bearing systems. However, the two more comprehensive models in general show better correlation with measurement data in terms of frequency and amplitude. Furthermore, we conclude that a thermal network model comprising temperature predictions of the bearing surroundings is essential to obtain accurate predictions. The results of this study aid in developing accurate and computationally-efficient models of flexible rotors supported by plain journal bearings.
      PubDate: 2016-09-08
      DOI: 10.3390/lubricants4030033
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 34: On Monitoring Physical and Chemical
           Degradation and Life Estimation Models for Lubricating Greases

    • Authors: Asghar Rezasoltani, M. Khonsari
      First page: 34
      Abstract: Degradation mechanisms for lubricating grease are categorized and described. An extensive survey of the available empirical and analytical grease life estimation models including degradation monitoring standards and methods are presented. A summary of the important contributions on grease degradation is presented.
      PubDate: 2016-09-13
      DOI: 10.3390/lubricants4030034
      Issue No: Vol. 4, No. 3 (2016)
  • Lubricants, Vol. 4, Pages 10: Influence of Workpiece Material on Tool Wear
           Performance and Tribofilm Formation in Machining Hardened Steel

    • Authors: Junfeng Yuan, Jeremy Boyd, Danielle Covelli, Taib Arif, German Fox-Rabinovich, Stephen Veldhuis
      First page: 10
      Abstract: In addition to the bulk properties of a workpiece material, characteristics of the tribofilms formed as a result of workpiece material mass transfer to the friction surface play a significant role in friction control. This is especially true in cutting of hardened materials, where it is very difficult to use liquid based lubricants. To better understand wear performance and the formation of beneficial tribofilms, this study presents an assessment of uncoated mixed alumina ceramic tools (Al2O3+TiC) in the turning of two grades of steel, AISI T1 and AISI D2. Both workpiece materials were hardened to 59 HRC then machined under identical cutting conditions. Comprehensive characterization of the resulting wear patterns and the tribofilms formed at the tool/workpiece interface were made using X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy. Metallographic studies on the workpiece material were performed before the machining process and the surface integrity of the machined part was investigated after machining. Tool life was 23% higher when turning D2 than T1. This improvement in cutting tool life and wear behaviour was attributed to a difference in: (1) tribofilm generation on the friction surface and (2) the amount and distribution of carbide phases in the workpiece materials. The results show that wear performance depends both on properties of the workpiece material and characteristics of the tribofilms formed on the friction surface.
      PubDate: 2016-04-19
      DOI: 10.3390/lubricants4020010
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 11: Tribo-Mechanisms of Carbon Nanotubes:
           Friction and Wear Behavior of CNT-Reinforced Nickel Matrix Composites and
           CNT-Coated Bulk Nickel

    • Authors: Leander Reinert, Sebastian Suárez, Andreas Rosenkranz
      First page: 11
      Abstract: In this study, nickel matrix composites reinforced by carbon nanotubes (CNTs) are compared to unreinforced CNT-coated (by drop-casting) bulk nickel samples in terms of their friction and wear behavior, thus gaining significant knowledge regarding the tribological influence of CNTs and the underlying tribo-mechanism. It has been shown that the frictional behavior is mainly influenced by the CNTs present in the contact zone, as just minor differences in the coefficient of friction between the examined samples can be observed during run-in. Consequently, the known effect of a refined microstructure, thus leading to an increased hardness of the CNT reinforced samples, seems to play a minor role in friction reduction compared to the solid lubrication effect induced by the CNTs. Additionally, a continuous supply of CNTs to the tribo-contact can be considered isolated for the reinforced composites, which provides a long-term friction reduction compared to the CNT-coated sample. Finally, it can be stated that CNTs can withstand the accumulated stress retaining to some extent their structural state for the given strain. A comprehensive study performed by complementary analytical methods is employed, including Raman spectroscopy and scanning electron microscopy to understand the involved friction and wear mechanisms.
      PubDate: 2016-04-19
      DOI: 10.3390/lubricants4020011
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 12: Tribological Properties of the Lubricant
           Containing Titanium Dioxide Nanoparticles as an Additive

    • Authors: Filip Ilie, Cristina Covaliu
      First page: 12
      Abstract: To improve the oil-solubility of nanoparticles, a new technology was used to prepare a kind of lubricant containing titanium dioxide (TiO2) nanoparticles. The microstructures of the prepared nanoparticles were characterized via transmission electron microscope (TEM) and infrared spectroscopy (IR). Tribological properties of TiO2 nanoparticles used as an additive in base oil were evaluated using four-ball tribometer and ball-on-disk tribometer. In addition, the worn surface of the steel ball was investigated via polarized microscopy (PM) and X-ray photoelectron spectroscopy (XPS). The TiO2 nanoparticles can be completely well-dispersed in the base oil under a new process (NP), which has no significantly negative effect on the anti-oxidation property. The results of the tribological tests show that TiO2 nanoparticles under the NP show a better anti-wear property and friction-reducing property in base oil compared to TiO2 nanoparticles under the tradition process (TP). The main aim of this paper lies in solving with the oil-solubility problem through the combination effect of surface modification and special blend process of lubricating oil. This method was first used to prepare lubricant containing TiO2 nanoparticles and then used as additives in engine oil, gear oil, and other industrial lubricants. At the same time, tribological properties of TiO2 nanoparticles in base oil as a lubricating additive were also studied.
      PubDate: 2016-04-21
      DOI: 10.3390/lubricants4020012
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 13: The Study of Mechanical and Tribological
           Performance of Fulleroid Materials Filled PA 6 Composites

    • Authors: Dmitry Pikhurov, Vjacheslav Zuev
      First page: 13
      Abstract: The effect of fulleroid materials (fullerene С60 and fullerene soot which is used for fullerene production) and carbon fibers on the mechanical and tribological properties of polymer nanocomposites based on polyamide 6 (PA6) was investigated. Composites were synthesized by in situ polymerization and direct mixing in an extruder. It was found that addition of these fillers during in situ polymerization was more effective at improving the mechanical and tribological properties of the composites. The use of the nanoparticles was an effective way to decrease the friction coefficient of the polymer composites because the fillers were the same size as the segments of the surrounding polymer chains. The steady state coefficients of friction with the addition of fulleroid fillers were lower than that of unfilled PA6. The lowest coefficient of friction was observed for PA6 filled with 1 wt. % fullerene soot.
      PubDate: 2016-04-28
      DOI: 10.3390/lubricants4020013
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 14: The Lubrication Ability of Ionic Liquids as
           Additives for Wind Turbine Gearboxes Oils

    • Authors: Miguel Gutierrez, Michael Haselkorn, Patricia Iglesias
      First page: 14
      Abstract: The amount of energy that can be gained from the wind is unlimited, unlike current energy sources such as fossil and coal. While there is an important push in the use of wind energy, gears and bearing components of the turbines often fail due to contact fatigue, causing costly repairs and downtime. The objective of this work is to investigate the potential tribological benefits of two phosphonium-based ionic liquids (ILs) as additives to a synthetic lubricant without additives and to a fully formulated and commercially available wind turbine oil. In this work, AISI 52100 steel disks were tested in a ball-on-flat reciprocating tribometer against AISI 440C steel balls. Surface finish also affects the tribological properties of gear surfaces. In order to understand the combined effect of using the ILs with surface finish, two surface finishes were also used in this study. Adding ILs to the commercial available or synthetic lubricant reduced the wear scar diameter for both surface finishes. This decrease was particularly important for trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) amide, where a wear reduction of the steel disk around 20% and 23% is reached when 5 wt % of this IL is added to the commercially available lubricant and to the synthetic lubricant without additives, respectively.
      PubDate: 2016-05-05
      DOI: 10.3390/lubricants4020014
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 15: Pleural Lubrication

    • Authors: Cristina Porta, Chiara Sironi, Francesca Bodega, Emilio Agostoni
      First page: 15
      Abstract: During breathing, the pleural surfaces slide against each other continuously without damage. Pleural liquid and lubricating molecules should provide the lubrication of the sliding surfaces, thus protecting the mesothelium from shear-induced abrasion. D’Angelo et al. (Respir. Physiol. Neurobiol. 2004) measured the coefficient of kinetic friction (μ) of rabbit parietal pleura sliding against visceral pleura in vitro at physiological velocities and under physiological loads; it was ~0.02 and did not change with sliding velocity, consistent with boundary lubrication. μ in boundary lubrication can be influenced by surface molecules like hyaluronan, sialomucin or surface active phospholipidis. Hyaluronan or sialomucin is able to restore good boundary lubrication in damaged mesothelium. Nevertheless, hyaluronidase and neuraminidase treatment of the mesothelium does not increase μ, though neuraminidase cleaves sialic acid from the mesothelium. Short pronase or phospholipase treatment, so as to affect only the mesothelial glycocalyx, increases μ, and this increase is removed by hyaluronan or sialomucin. On the other hand, addition of phospholipids after phospholipase treatment produces a small effect relative to that of hyaluronan or sialomucin, and this effect is similar with unsaturated or saturated phospholipids. In damaged mesothelium, the lubrication regimen becomes mixed, but addition of hyaluronan or sialomucin restores boundary lubrication.
      PubDate: 2016-05-19
      DOI: 10.3390/lubricants4020015
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 16: Theoretical and Experimental Study of the
           Friction Behavior of Halogen-Free Ionic Liquids in Elastohydrodynamic

    • Authors: Karthik Janardhanan, Patricia Iglesias
      First page: 16
      Abstract: Ionic Liquids have emerged as effective lubricants and additives to lubricants, in the last decade. Halogen-free ionic liquids have recently been considered as more environmentally stable than their halogenated counterparts, which tend to form highly toxic and corrosive acids when exposed to moisture. Most of the studies using ionic liquids as lubricants or additives of lubricants have been done experimentally. Due to the complex nature of the lubrication mechanism of these ordered fluids, the development of a theoretical model that predicts the ionic liquid lubrication ability is currently one of the biggest challenges in tribology. In this study, a suitable and existing friction model to describe lubricating ability of ionic liquids in the elastohydrodynamic lubrication regime is identified and compared to experimental results. Two phosphonium-based, halogen-free ionic liquids are studied as additives to a Polyalphaolefin base oil in steel–steel contacts using a ball-on-flat reciprocating tribometer. Experimental conditions (speed, load and roughness) are selected to ensure that operations are carried out in the elastohydrodynamic regime. Wear volume was also calculated for tests at high speed. A good agreement was found between the model and the experimental results when [THTDP][Phos] was used as an additive to the base oil, but some divergence was noticed when [THTDP][DCN] was added, particularly at the highest speed studied. A significant decrease in the steel disks wear volume is observed when 2.5 wt. % of the two ionic liquids were added to the base lubricant.
      PubDate: 2016-05-19
      DOI: 10.3390/lubricants4020016
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 17: Assessing Boundary Film Forming Behavior of
           Phosphonium Ionic Liquids as Engine Lubricant Additives

    • Authors: Mayank Anand, Mark Hadfield, Jose-Luis Viesca, Ben Thomas, Ruben González, Rob Cantrill, Antolin Hernández Battez
      First page: 17
      Abstract: The reduction of friction and wear losses in boundary lubrication regime of a piston ring-cylinder liner tribo-system has always been a challenge for engine and lubricant manufacturers. One way is to use lubricant additives, which can form boundary film quickly and reduce the direct contact between asperities. This article focuses on the assessment of boundary film forming behavior of two phosphonium-based ionic liquids (ILs) as additives in engine-aged lubricant to further improve its film forming capabilities and hence reduce friction and wear of contacting surfaces. A reciprocating piston ring segment-on-flat coupon under fully flooded lubrication conditions at room temperature (approx. 25 °C) was employed. The trihexyltetradecyl phosphonium bis(2-ethylhexyl) phosphate and trihexyltetradecyl phosphonium bis(2,4,4-tri-methylpentyl) phosphinate ionic liquids were used as additives in 6 vol. % quantity. Benchmark tests were conducted using fully formulated new lubricant of same grade (with and without ILs). Results revealed that the addition of phosphonium ILs to engine-aged lubricant led to quicker initiation of boundary film forming process. In addition, friction and wear performance of engine-aged lubricant improved by the addition of both ILs and these mixtures outperformed the fresh fully formulated oil. Chemical analysis showed higher concentration of phosphorus element on the worn surface indicating presence of ILs in the formed tribofilms.
      PubDate: 2016-05-30
      DOI: 10.3390/lubricants4020017
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 18: The Role of Counter-Face Roughness on the
           Tribological Performance of a Clutch System Tested with a Pin-On-Disc

    • Authors: Graciliano Fernandes, Paulo Zanotto, Amilton Sinatora
      First page: 18
      Abstract: This study was a continuous investigation of the roles played by the tribofilm on dry automotive clutch system performance. Tribological experiments were performed by the addition of wear debris at the beginning of tribometer tests and by reducing the surface roughness of a cast iron counter-face. The initial surface conditions of cast discs were 0.2 and 1.2 µm. The pin-on-disc tests were carried out at three different PV levels: 3.08, 7.88, and 10.09 MPa·ms−1, and the current results were correlated to those previously obtained in the standard tribometer procedure. When the wear debris was added into the tribosystem, the friction coefficient level dropped drastically while the assembly wear rate rose. In contrast, the modified cast discs provided a reduced wear rate of assembly and a higher and more stable friction coefficient level. These improvements were obtained in a severe condition where higher temperature levels were reached. For the tests with added debris, SEM observations revealed a more intense tribofilm development over the worn surfaces of the clutch friction material. The smoothest cast disc did not damage the developed tribofilms and maintained them more stably due to a reduction in contact area stresses at the highest tribometer test.
      PubDate: 2016-05-31
      DOI: 10.3390/lubricants4020018
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 19: Microstructural and Chemical
           Characterization of the Tribolayer Formation in Highly Loaded Cylindrical
           Roller Thrust Bearings

    • Authors: Carsten Gachot, ChiaJui Hsu, Sebastián Suárez, Philipp Grützmacher, Andreas Rosenkranz, Andreas Stratmann, Georg Jacobs
      First page: 19
      Abstract: Zinc dithiophosphates (ZDDP) have been widely applied in automobile industry for over 70 years as a lubricant additive for wear protection. Tribolayers have been described as blue- and brown-colored layers on surfaces observed by microscopical observation or even bare eye presumably as a consequence of layer thickness or chemical composition. However, the reaction pathways of ZDDP tribolayers are still not yet fully understood. In the present study, the difference between the blue- and brown-colored tribolayers has been revealed by high resolution methods in cylindrical roller thrust bearings at relatively high contact pressures of around 1.92 GPa. After running a FE8 standard bearing test with a normal load of 80 kN and a temperature of 60 °C, said tribolayers could be identified on the bearing surfaces. By using Raman spectroscopy, it could be shown that the blue-colored layers are enriched by FeS and ZnS whereas the brown-colored layers show a significant amount of Fe3O4. This is an interesting finding as it clearly shows a correlation between the color appearance of the films and the chemical composition besides potential film thickness variations. Finally, transmission electron microscopy verified the amorphous nature of the formed tribolayer which is in a good agreement with literature.
      PubDate: 2016-06-08
      DOI: 10.3390/lubricants4020019
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 20: Tribology of Graphite-Filled Polystyrene

    • Authors: Raffaele Gilardi
      First page: 20
      Abstract: Self-lubricating polymer compounds are currently used for a wide range of applications such as bearings, gears, and water meters. Under severe conditions such as high pressure, high velocity, and/or high temperatures, the material fails (PV limit). In this study, we investigated the effect of graphite on the tribological properties of polystyrene (PS) with “ball-on-three-plates” tests. Graphite-filled PS plates were produced via an internal mixer and compression molding. Unhardened steel (1.4401) and nylon (PA66) balls were used for the tribological tests. Our results indicate that graphite loading, graphite type, and particle size have a big influence on the friction coefficient, the wear resistance, and the PV limit of PS both against steel and PA66. In particular, primary synthetic graphite performs better than secondary synthetic graphite due to the higher degree of crystallinity.
      PubDate: 2016-06-09
      DOI: 10.3390/lubricants4020020
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 21: On the Growth Rate of Tribomaterial in
           Bovine Serum Lubricated Sliding Contacts

    • Authors: Alfons Fischer, Daniel Stickel, Christian Schoss, Rob Bosman, Markus Wimmer
      First page: 21
      Abstract: Considering total hip arthroplasty, so-called tribolayers (aka tribomaterial), consist of carbonaceous material from the periprosthetic joint fluid or bovine serum mixed with nanometer size metal and oxide wear particles. Currently, its growth sequence and rate are unknown. Thus, smooth surfaces of low-Carbon (LC-) vs. high-Carbon (HC-)CoCrMo (Cobalt-Chromium-Molybdenum) alloys have been worn in a conforming contact under bovine serum lubrication by means of a pin-on-ball wear tester. These tests were interrupted at certain numbers of cycles in order to weigh the specimens, characterize the topography, and investigate the wear appearances. In addition, after cleaning in ethanol and anionic detergent, before-and-after comparison rendered the weight of the tribomaterial. This revealed that, during run-in, the specimens gained weight by generating tribomaterial. Afterwards the loss of material surpassed the generation of new tribomaterial and a steady weight-loss was measured. Topography measurements were used as input data for contact mechanics calculations. Apparently the incipient, locally high contact stresses accelerated tribochemical reactions. After run-in, the contact situation changes and leads to a much smaller generation rate. This paper provides information about the growth sequence and rate of such tribomaterial formation. It further highlights the significance of highly localized contact stress as an important factor for tribomaterial generation.
      PubDate: 2016-06-21
      DOI: 10.3390/lubricants4020021
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 22: Towards Phosphorus Free Ionic Liquid
           Anti-Wear Lubricant Additives

    • Authors: Anthony Somers, Ruhamah Yunis, Michel Armand, Jennifer Pringle, Douglas MacFarlane, Maria Forsyth
      First page: 22
      Abstract: The development of improved anti-wear additives would enable the use of lower viscosity oils that would lead to improved efficiency. Ionic liquids have the potential to be this type of new anti-wear additive. However, currently the best performing ionic liquids that are miscible in non-polar base oils, the phosphonium phosphates, contain phosphorus on both the cation and anion. Manufacturers are seeking to reduce the presence of phosphorus in oils. Here, as a first step towards phosphorus-free anti-wear additives, we have investigated ionic liquids similar to the phosphonium phosphates but having either a phosphorus-free cation or anion. Two quaternary ammonium phosphates (N6,6,6,14)(BEHP) and (N8,8,8,8)(BEHP) and a phosphonium silyl-sulfonate (P6,6,6,14)(SSi) were compared to a phosphonium phosphate (P6,6,6,14)(BEHP) and a traditional zinc dithiophosphate (ZDDP) as anti-wear additives in mineral oil. The change from a phosphonium to a quaternary ammonium cation drastically reduced the miscibility of the Ionic liquid (IL) in the oil, while the change to a smaller silicon containing anion also resulted in limited miscibility. For the pin-on-disk wear test conditions used here none of the ionic liquids outperformed the ZDDP except the (P6,6,6,14)(BEHP) at a relatively high loading of 0.10 mol·kg−1 (approximately 8 wt%). At a more moderate loading of 0.025 mol·kg−1 the (P6,6,6,14)(SSi) was the best performing ionic liquid by a significant amount, reducing the wear to 44% of the neat mineral oil, while the ZDDP reduced the wear to 25% of the mineral oil value. Electron microscopy and energy dispersive X-ray spectroscopy showed that the presence of a silicon containing tribofilm was responsible for this protective behaviour, suggesting that silicon containing ionic liquids should be further investigated as anti-wear additives for oils.
      PubDate: 2016-06-22
      DOI: 10.3390/lubricants4020022
      Issue No: Vol. 4, No. 2 (2016)
  • Lubricants, Vol. 4, Pages 1: Acknowledgement to Reviewers of Lubricants in

    • Authors: Lubricants Editorial Office
      First page: 1
      Abstract: The editors of Lubricants would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...]
      PubDate: 2016-01-27
      DOI: 10.3390/lubricants4010001
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 2: Direct Laser Interference Patterning:
           Tailoring of Contact Area for Frictional and Antibacterial Properties

    • Authors: Andreas Rosenkranz, Michael Hans, Carsten Gachot, Adrian Thome, Simon Bonk, Frank Mücklich
      First page: 2
      Abstract: Surface functionalization by topographic micro- and nano-structures in order to achieve unique properties, like super-hydrophobicity or ultrahigh light absorption, is a common strategy in nature. In this paper, direct laser interference patterning (DLIP) is presented as a promising tool allowing for the generation of such surface patterns on technical surfaces in order to mimic these biological surfaces and effects. Friction optimization and antibacterial effects by DLIP are exemplarily described. Topographic surface patterns on the micro- and nano-scale demonstrated a significant reduction in the coefficient of friction and bacterial adhesion. It was shown that in both cases, the control of the contact area between surfaces or between surface and bacteria is of utmost importance.
      PubDate: 2016-01-27
      DOI: 10.3390/lubricants4010002
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 3: Quantitative Analysis of Retrieved Glenoid

    • Authors: Katelyn Childs, Lynn Crosby, Tarun Goswami
      First page: 3
      Abstract: Revision of orthopedic surgeries is often expensive and involves higher risk from complications. Since most total joint replacement devices use a polyethylene bearing, which serves as a weak link, the assessment of damage to the liner due to in vivo exposure is very important. The failures often are due to excessive polyethylene wear. The glenoid liners are complex and hemispherical in shape and present challenges while assessing the damage. Therefore, the study on the analysis of glenoid liners retrieved from revision surgery may lend insight into common wear patterns and improve future product designs. The purpose of this pilot study is to further develop the methods of segmenting a liner into four quadrants to quantify the damage in the liner. Different damage modes are identified and statistically analyzed. Multiple analysts were recruited to conduct the damage assessments. In this paper, four analysts evaluated nine glenoid liners, retrieved from revision surgery, two of whom had an engineering background and two of whom had a non-engineering background. Associated human factor mechanisms are reported in this paper. The wear patterns were quantified using the Hood/Gunther, Wasielewski, Brandt, and Lombardi methods. The quantitative assessments made by several observers were analyzed. A new, composite damage parameter was developed and applied to assess damage. Inter-observer reliability was assessed using a paired t-test. Data reported by four analysts showed a high standard deviation; however, only two analysts performed the tests in a significantly similar way and they had engineering backgrounds.
      PubDate: 2016-02-04
      DOI: 10.3390/lubricants4010003
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 4: A Review of Transfer Films and Their Role in
           Ultra-Low-Wear Sliding of Polymers

    • Authors: Jiaxin Ye, David Burris, Ting Xie
      First page: 4
      Abstract: In dry sliding conditions, polytetrafluoroethylene (PTFE) composites can form thin, uniform, and protective transfer films on hard, metallic counterfaces that may play a significant role in friction and wear control. Qualitative characterizations of transfer film morphology, composition, and adhesion to the counterface suggest they are all good predictors of friction and, particularly, wear performance. However, a lack of quantitative transfer film characterization methods and uncertainty regarding specific mechanisms of friction and wear control make definitive conclusions about causal relationships between transfer film and tribological properties difficult. This paper reviews the state of the art in the solid lubricant transfer film literature and highlights recent advances in quantitative characterization thereof.
      PubDate: 2016-02-26
      DOI: 10.3390/lubricants4010004
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 5: The Role of Solid Lubricants for Brake
           Friction Materials

    • Authors: Werner Österle, Andrey Dmitriev
      First page: 5
      Abstract: This review article comprises of three parts. Firstly, reports of brake manufacturers on the beneficial impact of solid lubricants for pad formulations are surveyed. Secondly, since tribofilms were identified to play a crucial role in friction stabilization and wear reduction, the knowledge about tribofilm structures formed during automotive braking was reviewed comprehensively. Finally, a model for simulating the sliding behavior of tribofilms is suggested and a review on modelling efforts with different model structures related to real tribofilms will be presented. Although the variety of friction composites involved in commercial brake systems is very broad, striking similarities were observed in respect to tribofilm nanostructures. Thus, a generalization of the tribofilm nanostructure is suggested and prerequisites for smooth sliding performance and minimal wear rates have been identified. A minimum of 13 vol % of soft inclusions embedded in an iron oxide based tribofilm is crucial for obtaining the desired properties. As long as the solid lubricants or their reaction products are softer than magnetite, the main constituent of the tribofilm, the model predicts smooth sliding and minimum wear.
      PubDate: 2016-02-29
      DOI: 10.3390/lubricants4010005
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 6: Friction of Human Skin against Different
           Fabrics for Medical Use

    • Authors: Luís Vilhena, Amílcar Ramalho
      First page: 6
      Abstract: Knowledge of the tribology of human skin is essential to improve and optimize surfaces and materials in contact with the skin. Besides that, friction between the human skin and textiles is a critical factor in the formation of skin injuries, which are caused if the loads and shear forces are high enough and/or over long periods of time. This factor is of particular importance in bedridden patients, since they are not moving about or are confined to wheelchairs. Decubitus ulcers are one of the most frequently-reported iatrogenic injuries in developed countries. The risk of developing decubitus ulcers can be predicted by using the “Braden Scale for Predicting Pressure Ulcer Risk” that was developed in 1987 and contains six areas of risk (cognitive-perceptual, immobility, inactivity, moisture, nutrition, friction/shear), although there are limitations to the use of such tools. The coefficient of friction of textiles against skin is mainly influenced by: the nature of the textile, skin moisture content and ambient humidity. This study will investigate how skin friction (different anatomical regions) varies, rubbing against different types of contacting materials (i.e., fabrics for medical use) under different contact conditions and their relationship in the formation and prevention of decubitus ulcers.
      PubDate: 2016-03-01
      DOI: 10.3390/lubricants4010006
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 7: Kinetic Friction of Sport Fabrics on Snow

    • Authors: Werner Nachbauer, Martin Mössner, Sebastian Rohm, Kurt Schindelwig, Michael Hasler
      First page: 7
      Abstract: After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier’s friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction of different fabrics of ski garments with respect to roughness, speed, and contact pressure. Three types of fabrics were investigated: a commercially available ski overall, a smooth downhill racing suit, and a dimpled downhill racing suit. Friction was measured for fabrics taped on a short ski using a linear tribometer. The fabrics’ roughness was determined by focus variation microscopy. Friction coefficients were between 0.19 and 0.48. Roughness, friction coefficient, and friction force were highest for the dimpled race suit. The friction force of the fabrics was higher for the higher contact pressure than for the lower one at all speeds. It was concluded that the main friction mechanism for the fabrics was dry friction. Only the fabric with the roughest surface showed friction coefficients, which were high enough to sufficiently decelerate a sliding skier on beginner and intermediate slopes.
      PubDate: 2016-03-14
      DOI: 10.3390/lubricants4010007
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 8: Tribological Behaviour of PVD Coatings
           Lubricated with a FAP− Anion-Based Ionic Liquid Used as an Additive

    • Authors: José-Luis Viesca, Mayank Anand, David Blanco, Alfonso Fernández-González, Alberto García, Mark Hadfield
      First page: 8
      Abstract: This paper studies 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ionic liquid ([BMP][FAP]) as a 1 wt% additive to a polyalphaolefin (PAO 6) in the lubrication of CrN and TiN PVD coatings. Friction and wear behaviour were determined by using a ball-on-plate reciprocating tribometer at two loads (20 and 40 N) and a reciprocating frequency of 10 Hz. The tribological behaviour of this mixture has also been compared to a traditional oil additive, like zinc dialkyldithiophosphate (ZDDP). As an additive, ionic liquid exhibited an important friction and wear reduction compared to the base oil. However, tests conducted with ZDDP show slightly better results. XPS was used to analyse wear surfaces. The interactions of each additive with the surface contributed to improving the tribological behaviour of the lubricants.
      PubDate: 2016-03-17
      DOI: 10.3390/lubricants4010008
      Issue No: Vol. 4, No. 1 (2016)
  • Lubricants, Vol. 4, Pages 9: Investigation of Couple Stress Fluid and
           Surface Roughness Effects in the Elastohydrodynamic Lubrication Problems
           using Wavelet-Based Decoupled Method

    • Authors: Siddu Shiralashetti, Mounesha Kantli
      First page: 9
      Abstract: The standard decoupled method with Newton-generalized minimum residual procedure performs poorly or may break down when used to solve certain elastohydrodynamic lubrication problems. The authors Zargari et al., 2007 presented decoupled and coupled methods in which the limitations of the decoupled method for some set of physical parameters and slight variation in these values (physical parameters) give a non-convergence solution. To overcome this aspect the wavelet-based preconditioners technique is used in this paper to solve the elastohydrodynamic lubrication problem. The effect of coupled stress fluids on elastohydrodynamic lubrication behavior in smooth, as well as rough, contact is investigated using the proposed method, numerically, in a low-speed-high load condition. The elastohydrodynamic lubrication characteristics computed for couple stress fluids are found to have strong dependence on the couple stress parameter, which shows the versatility and applicability of the proposed method.
      PubDate: 2016-03-21
      DOI: 10.3390/lubricants4010009
      Issue No: Vol. 4, No. 1 (2016)
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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