Tribology Online
Online ISSN : 1881-2198
ISSN-L : 1881-218X
Special issue: Tribology Online
Volume 14 , Issue 5
ITC Sendai 2019 Special Issue (Part 1)
Showing 1-26 articles out of 26 articles from the selected issue
Editorial
  • Kazuo Hokkirigawa
    2019 Volume 14 Issue 5 Pages ii
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The International Tribology Conference (ITC) Sendai 2019 was held on 17–21 September 2019 at Sendai International Center in Sendai City, Japan. About 900 people participated from 40 countries and regions, and about 600 papers were presented, where more than half of the presenters were from overseas. We thank all the people who joined and contributed to ITC.

    Papers submitted to this special issue went through normal peer-review process, and 24 papers were accepted for publication in this Part 1. On behalf of the Organizing Committee, I would like to thank all the authors for their contributions, and also thank the editors, reviewers and the editorial office for their efforts.

    The Paper Award Selection Committee of the Organizing Committee selected excellent papers from those papers submitted before the end of June, and the following three papers were awarded the ITC 2019 Best Paper Award. Award Trophies were presented to the authors at the award ceremony in the Banquet held on 19th September, 2019. Congratulations!

    “Propagation of Large Spalls in Rolling Bearings,” by Guillermo E. Morales-Espejel, Philip Engelen and Gerrit van Njien

    “Intercalation Technology for Preparing a Mica–Organic Hybrid Solid Lubricant and Spectroscopic Evaluation of its Lubrication Mechanism,” by Kenichiro Oshita, Shinobu Komiyama and Shinya Sasaki

    “Effect of lubrication on friction and wear properties of PEEK with steel counterparts,” by Go Tatsumi, Monica Ratoi, Yuji Shitara, Kiyomi Sakamoto and Brian G. Mellor More ITC 2019 papers currently being reviewed will be published in the ITC Special Issue Part 2 before mid 2020.

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Review
  • Fabrice Dassenoy
    2019 Volume 14 Issue 5 Pages 237-253
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    There has been growing interest in nanoparticles for tribological applications over the past 20 years. Studies have shown their remarkable lubricating properties, namely friction-reduction and anti-wear, especially when used as lubricant additives. This makes them potential candidates for replacing the additives currently used in automobile lubricants, known to be pollutants and less efficient in certain specific conditions. Among the nanoparticles with proven tribological performance are carbon nanoparticles (nanotubes, onion, diamond, etc.), BN and TiO2 nanoparticles, and Inorganic Fullerene-like (IF) metal disulfides (IF-MoS2, IF-WS2). At the Laboratory of Tribology and Dynamic of Systems (LTDS) of the Ecole Centrale of Lyon (ECL), these nanoparticles have been the subject of detailed investigation for more than fifteen years. Many key issues have been tackled, such as the conditions leading to these properties, the lubrication mechanisms involved, and the influence of parameters such as the size, the structure, and the morphology of the nanoparticles on both their tribological properties and lubrication mechanisms. In order to answer such questions, state-of-the-art characterization techniques are required, often in situ, and sometimes extremely complex to set up. Some of them can even visualize the behavior of a nanoparticle in real time while it is undergoing tribological testing. Researchers now have good understanding of the way these nanoparticles behave, and are able to identify the key parameters to be adjusted to optimize their lubrication properties. In this article, the performance of nanoparticles when used as additives will be described, with particular attention given to metal disulfide nanoparticles. Furthermore, the influence of key parameters on the performance of oils containing nanoparticles will be discussed and the lubrication mechanisms of the metal disulfide nanoparticles will be presented in detail. The issues remaining to be solved before developing new lubricants containing nanoparticles will be also discussed. Finally, we show how fully formulated lubricants containing nanoparticles behave when tested under conditions close to the final application (automotive engine and gearboxes).

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Article
  • Guillermo E. Morales-Espejel, Philip Engelen, Gerrit van Nijen
    2019 Volume 14 Issue 5 Pages 254-266
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The paper focuses on studying the propagation of large spalls on the raceways of rolling bearings. This is done by means of experiments and modelling. It is shown that the application of a relatively simple model to describe a spall evolution in time in rolling bearings is feasible. The proposed model is validated using experiments, where rolling bearings with initial pre-damage have been tested and the surface spall progression has been monitored in time. Surprisingly, spall progression in rolling bearings appears to be correctly described by a model of damage initiation. Without the need of a more sophisticated crack propagation model, at least this seems to be the case for a relatively large spall (larger than the Hertzian contact). Where the effects of the pressure build up from lubrication can be ignored. However, dynamic effects cannot be disregarded, since they seem to be the driving force for the propagation direction in some cases. The effect of the shape, size of the initiation point and load sequence is studied as well as the shape of the contact (line or elliptical), giving interesting insights of the propagation mechanisms.

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  • Kyosuke Ono
    2019 Volume 14 Issue 5 Pages 267-278
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The development of thin film lubrication theory is vital for future micro-textured lubrication technologies. Therefore, a modified Reynolds equation was derived in this research by incorporating the variable viscosity effect in a tribochemical adsorbed layer. The modified factors of the Reynolds equation were expressed as closed form functions for a one-sided viscosity function determined from the measured effective viscosity. Using the one-dimensional modified Reynolds equation, the load capacity and friction coefficients of micro-tapered/tapered land bearings as texture models were numerically investigated. By performing a parametric study with different viscosity ratios (10 and 100), taper lengths (10, 50, and 250 µm), taper angles, and land length ratios and a surface layer thickness of 10-nm, it was found that a high load capacity and an extremely low friction coefficient of less than 10–4 on the stationary surface could be achieved with a bearing gap of a few tens of nanometers. Since the surface height irregularities between the textures can be compensated for by the elastic deformation caused by high pressures, the lubrication regime in a parallel textured slider can be realized if the roughness heights on the mating surfaces are reduced to less than the bearing gap, using the running-in process.

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  • Yusliza Yusuf, Mariyam Jameelah Ghazali, Yuichi Otsuka, Sarita Morakul ...
    2019 Volume 14 Issue 5 Pages 279-284
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Surface wettability behaviour is generally categorised as hydrophobic and hydrophilic depending on the contact angle value. Surface wettability has been attracting considerable attention in research due to its unique behaviour in the field of self-cleaning, anti-fouling and anti-corrosion. Surfaces with high and low wettabilities can be fabricated using various methods, including chemical etching, anodisation and laser surface texturing. The present study investigated the effects of textured surfaces via laser surface texturing on the wettability properties of TiO2/ZnO coatings. TiO2/ZnO coating was selected due to its high photocatalytic activity, non-toxicity and low cost, which are essential properties for self-cleaning and anti-fouling applications. Picosecond laser ablation was used to produce micro- dimple textures on the coating surfaces. The wettability of the laser-textured surfaces was greatly reduced, achieving superhydrophilic properties with contact angle of 1.4° ± 2.42° for laser-textured TiO2 coating. On the other hand, coatings with ZnO compositions exhibited increased contact angles for both textured and non-textured surfaces. Moreover, no clear cut correlations between the surface roughness properties of non-textured and laser-textured TiO2/ZnO coatings and the surface wettability properties was observed. This finding provides new approaches in designing textured surface materials that can effectively increase the wettability properties for self-cleaning and anti-fouling applications.

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  • Shouhei Kawada, Shinya Sasaki, Masaaki Miyatake
    2019 Volume 14 Issue 5 Pages 285-292
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The properties of ionic liquids make them an appealing choice for use as lubricant oil. However, the effect of moisture on the friction properties of ionic liquids needs to be elucidated. Moisture affects the disappearance and growth of the lubricating layer of these liquids. To express the high friction reduction effect, the lubricating layer formed by the ionic liquids at the friction interface plays a very important role. Thus, it is necessary to evaluate the relationship between these liquid structures and moisture, for the development of design guidelines for new ionic liquid structures that can achieve very low friction. This investigation evaluated the friction properties and the friction mechanisms of hydrophobic ionic liquids (1-butyl-3-methylimidazolium dicyanamide [BMIM][DCN] and 1-butyl-3- methylimidazolium tetrafluoroborate [BMIM][BF4]), and a hydrophilic ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6]) under various atmospheres (vacuum, dry air, and air) to better understand the effect of moisture on the friction properties. The hydrophilic ionic liquid exhibited differences in the friction properties depending on the atmosphere, while the hydrophobic ionic liquid remained unaffected by the atmosphere. The adsorption layer formed by [BMIM][DCN] was anion-rich, both ion-rich, and cation-rich in vacuum, dry air, and air respectively. In air, [BMIM][BF4] developed corrosive wear and the reaction layer formed by [BMIM][PF6] increased with moisture.

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  • Izatul Hamimi Abdul Razak, Mohamad Ali Ahmad, Siti Wahidah Puasa
    2019 Volume 14 Issue 5 Pages 293-300
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Rail lubrication is vital in determines the friction, wear and noise level in the wheel and rail contacts. In general, the primary function of a rail curve grease is to minimize friction between the contact as well as to protect side wear of rails on a curved track. In this study, three commercially applied railway greases were identified and the wear and friction behavior, as well as the load-carrying ability, were investigated. Before that, the grease's physiochemical properties in terms of the consistency and drop point, as well as the element content, were also examined. The tribological investigation of the greases was also carried out using four-ball wear tester. In this test, the wear preventive (WP) and extreme pressure (EP) properties of the grease were measured under sliding actions between the balls, and the wear surface analysis was also carried out. The tests results explained that the rail curve greases are very soft in texture yet have stable structure over a high-temperature range. The greases also presenting low friction coefficient; ranges between 0.070 to 0.090, and acceptable wear scar diameter indicating the good anti-friction and anti-wear properties. High load-carrying ability up to 400 kg is also the significant properties for a rail curve grease to perform as the desired functions.

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  • Hongyang Hu, Ming Feng
    2019 Volume 14 Issue 5 Pages 301-311
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The performance of air foil journal bearings is closely related to the stiffness of the bump foil. In this paper, the stiffness characteristics of bump foil having a rounding in the structure are investigated and compared with previous models. The dynamic coefficients of bearings and the stability threshold speed (STS) of a rotor supported by the bearings are numerically calculated using FEM and are compared to models with various rounding radius and friction coefficients. The results show that the presence of rounding indicates a significant effect on the total dynamic and the stability performance of foil bearings and there is an optimum rounding radius to maximize the structural stiffness and stability. The validity of the theoretical analysis was verified by the structural stiffness and stability experiments. The results are expected to be helpful to bearing designers, researchers, and academicians concerned.

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  • Kenichiro Oshita, Shinobu Komiyama, Shinya Sasaki
    2019 Volume 14 Issue 5 Pages 312-320
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The lubrication behavior of mica–alkyl ammonium cation hybrid solid lubricants fabricated via an intercalation reaction was evaluated by reciprocating sliding tests, and the lubrication mechanism was investigated from the viewpoint of interlayer adhesion strength by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Evaluation of hybrid micas with three alkyl ammonium cations, which have different lengths and numbers of alkyl chains, indicated that the friction coefficient decreased from 0.4–0.5 to a minimum of 0.12 with increase in the length and the number of alkyl chains of the organic cations. The results of X-ray diffraction revealed that the intercalated organic cations increase the d-spacing of mica, and the effect became prominent with increase in the length and the number of alkyl chains. The results of FTIR and XPS analyses indicated that the interlayer adhesion strength of mica is weakened with increase in the d-spacing, which correlated well with the results of friction coefficient.

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  • Hiroaki Yoshida, Kei Shibata, Takeshi Yamaguchi, Kazuo Hokkirigawa
    2019 Volume 14 Issue 5 Pages 321-326
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    This study focused on the effects of combinations of fillers comprising particulate and fibrous carbon materials on the tribological behaviors of a polyacetal (POM) composite under water lubrication. The filler materials were rice bran ceramics (RBC) particles and carbon fibers (CFs). Friction tests were conducted using a ring-on-disk-type friction tester under water lubrication and the ring specimen was an austenitic-stainless-steel ring. The RBC/CF composite exhibited the lowest friction coefficients (0.10–0.14) compared with the other composites, including pure POM, irrespective of the number of friction cycles. The CF composite produced a low friction coefficient during the initial stage of friction but then increased to 0.25. The wear volume of the RBC/CF composite was the smallest, irrespective of the number of friction cycles. The specific wear rate of the RBC/CF composite decreased over the wear periods, indicating a low value of 10−6 mm3/N·m at the end of the long-term friction cycles. Scanning electron microscopy observations and measurements of the surface geometries indicated that the combination of RBC particles and CFs produced the low friction and low wear because the RBC particles complemented the poor wear resistance of the CFs.

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  • Taisuke Maruyama, Masayuki Maeda, Ken Nakano
    2019 Volume 14 Issue 5 Pages 327-338
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    In this study, the electrical impedance method was developed to monitor the thickness and breakdown ratio of oil films in elliptical elastohydrodynamic (EHD) contacts of practical ball bearings. First, it is theoretically shown that the oil film thickness and breakdown ratio can be simultaneously measured from the complex impedance generated when a sinusoidal voltage is applied to elliptical contacts. Subsequently, lubrication conditions of practical ball bearings were monitored at an ambient temperature to verify the measurement accuracy of the developed method. The oil film thickness in the low-speed range was consistent with the theoretical value calculated by Hamrock–Dowson equation. However, in the high-speed range, the oil film was thinner than the theoretical value considered an ambient temperature. In this high-speed range, the results of both the outer ring temperature and bearing torque revealed that the viscous shear heating and starvation were occurring simultaneously, thus supporting that the measured thickness would be thinner than the theoretical value. Besides, the developed method can also measure the breakdown ratio, confirming that it increases in the low-speed range where the bearing torque increases. That is, it indicates that not only the oil film thickness but also the breakdown ratio can be evaluated quantitatively.

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  • Hyuga Kikuchi, Mohd Danial Ibrahim, Masayuki Ochiai
    2019 Volume 14 Issue 5 Pages 339-344
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Foil bearings have excellent characteristics such as a high damping performance and acceptable dimensional changes caused by installation errors and thermal expansion. However, the problem of large friction losses also occurs at the top foil under the high rotational speed required to support a shaft without any contact. In this paper, a new type of foil bearing with a surface texture on the top foil is proposed. The effects of the texture were verified by the rotational motion experimental analysis under a high circumferential speed and dry lubrication. For a bearing with dimples on the contact area, the effect of friction reduction could be observed under boundary lubrication. Moreover, it was also confirmed that the dimples adversely affected the air film formation with the sliding speed increase. For a newly designed F-grooved model, the phenomenon of an early transition from boundary lubrication to fluid lubrication can be seen. However, the friction coefficient increases at the boundary lubrication. In this study, it was also the highest friction reduction effect was confirmed at the maximum sliding speed. Furthermore, an additional friction reduction effect and a small temperature rise were obtained by combining the above textures.

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  • Go Tatsumi, Monica Ratoi, Yuji Shitara, Kiyomi Sakamoto, Brian G. Mell ...
    2019 Volume 14 Issue 5 Pages 345-352
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Poly-Ether-Ether-Ketone (PEEK) has been widely used for tribological applications with steel counterparts because of its superior mechanical and self-lubricating properties. Fluid lubrication has the potential to further improve the performance of PEEK/steel contacts but its effect has been shown to depend on the operating conditions. To elucidate these aspects and establish the mechanism of fluid lubrication, the friction and wear properties of the PEEK/steel contacts in both dry and poly-α-olefin (PAO) lubricated conditions were investigated by tribological tests and surface analytical techniques. The nanoindentation measurements showed that lubrication with PAO had a softening effect on the wear track of PEEK, but no correlation was established with the wear of PEEK. The tribological behavior, for both dry and lubricated contacts, was correlated with the thickness of PEEK transfer films on the steel counterparts. The thickness of these films, as determined by Electron Probe Micro Analysis (EPMA) and X-ray Photoelectron Spectroscopy (XPS), was controlled by the rates of their formation and removal and depended on the operating conditions. Moreover, lubrication with PAO inhibited not only the formation but also the removal of PEEK transfer films. This study thus sheds light on the mechanism of fluid lubrication of the PEEK/steel contacts.

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  • Kanao Fukuda, Sie Leeh Sheng, Zaid Ali Subhi
    2019 Volume 14 Issue 5 Pages 353-358
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The significant influences of atmospheric humidity on tribological phenomena are widely recognized. Although the influencing mechanisms of the humidity have been studied for a long time, many of the previous explanations remain in the qualitative estimation of mechanisms particularly from chemical effects viewpoint. In order to elucidate how the adsorbed water on a surface influences tribological phenomena, the current authors conducted ball to ball scratch tests for austenitic stainless steel (JIS SUS304) and proposed the mechanisms from a physical/mechanical viewpoint. A singular phenomenon was found; a lateral force, which can be regarded as a friction resistance, at a downhill motion showed significantly higher value than that at an uphill motion. The phenomenon was hypothesized to be influenced by Laplace pressure effect at a meniscus formed due to adsorbed water on the surface. In this study, polytetrafluoroethylene (PTFE) as the hydrophobic material was tested in comparison with SUS304 to show that the adsorbed water layer causes the singular phenomenon. PTFE successfully prevented the singular phenomenon while SUS304 reproduced it. The equilibrium analysis of the ball showed that adsorbed water contributed to the increase of the coefficient of kinetic friction but not of negative normal force at the contact point of SUS304.

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  • Nino Dakov, Simon Feldmeth, Mario Stoll, Frank Bauer
    2019 Volume 14 Issue 5 Pages 359-366
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Lip seals made of PTFE compound are used due to their high thermal and chemical stability for the sealing of shaft interfaces in housings. For a better dynamic leak-tightness hydrodynamic sealing aids are manufactured on the sealing lip. Thus a PTFE lip seal is capable of back-pumping fluid from the air to the fluid side. The pumping rate serves as an important parameter for the dynamic leaktightness of seals with a unidirectional sealing aid design. The correlation of pumping rate and dynamic leak-tightness for bi-directional sealing aid designs is deficient. A new hydrodynamic parameter is introduced to assess the dynamic leak-tightness of a sealing aid design. The so called pressure drag is the force resulting from the integral of the hydrodynamic pressure over the surface of the sealing aid. A hypothesis is proposed, stating that in order to guarantee a dynamically leak-tight shaft seal, two conditions should be satisfied. First, the pumping rate should be greater than zero. Second, the axial pressure drag should be directed entirely towards the fluid side. The hypothesis is verified on different types of unidirectional and bi-directional sealing aid design. In conclusion the axial pressure drag is shown to be a suitable performance parameter for the sealing aid design.

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  • Alessandra Ciniero, Giulio Fatti, Maria Clelia Righi, Daniele Dini, To ...
    2019 Volume 14 Issue 5 Pages 367-374
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    This work describes recent research into the mechanisms behind tribocharging and the influence of triboemission. The term tribocharging is a type of contact-induced electrification and refers to the transfer of charge between rubbing components. The term triboemission, on the other hand, refers to emission of electrons, ions and photons generated when surfaces are rubbed together. The understanding of tribocharging is of wide interest for several industrial applications and in particular the combination of tribocharging and triboemission may be important in lubricated contacts in the formation of boundary lubricant films. We report the use of a unique vacuum measurement system that enables to measure surface charge variations while simultaneously recording triboemission events during the sliding of a diamond tip on silica specimens. Results show for the first time that tribocharging and triboemission behavior are linked and depend on the surface wear. The contribution of contact-induced electrification to the charging of the surface is then described by means of density functional theory (DFT). Results give insight into the transfer of charge from the SiO2 amorphous surface (silica) to the C(111) surface (diamond ) and into the variation of charging during simulated sliding contact.

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  • Shinpei Kotani, Masayuki Ochiai
    2019 Volume 14 Issue 5 Pages 375-381
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    A floating bush bearing has a double oil film, which is difficult to observe using traditional methods. In this study, the oil film of a floating bush bearing is observed using X-ray computer tomography. By appropriately processing the acquired CT images, double oil films can be observed efficiently. The CT images show that the oil film area decreases in the inner clearance and does not change in the outer clearance when the increase of the bush rotation speed is suppressed despite the increase in the shaft rotation speed. This phenomenon can be explained by the oil film area of the inner clearance decreasing under the influence of the centrifugal force acting on the oil film. When there is enough oil in the inner clearance, it is observed that the bush rotation speed increases linearly. These results indicate that the bush rotation speed is closely related to the oil film area of the inner clearance.

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  • Hiroshi Kinoshita, Naohiro Matsumoto
    2019 Volume 14 Issue 5 Pages 382-387
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    In this study, a novel method was developed for in situ scanning electron microscopy (SEM) observations of friction interfaces, from a top view, using a Si3N4 thin film (SiN film), which has high electron transmission ability, and a microtribometer. Nanodiamond (ND) aggregates were adsorbed on the back surface of the SiN film. A JIS-SUS304 ball, on which surface ND aggregates were adsorbed and tribofilms were already formed, contacted and slid with the back surface of the SiN film. An SEM electron beam went through the SiN film, and generated secondary electrons from the ball surface contacting the back surface of the SiN film and the adsorbed ND aggregates. Thereafter, the generated secondary electrons from the ball surface penetrated again through the SiN film and reached the SEM electron detector. In other words, the contacting ball surface and the adsorbed ND aggregates were successfully imaged through the SiN film. Energy dispersive X-ray spectroscopy analyses of the friction interfaces were also accomplished. Moreover, in situ SEM observations of friction interfaces under boundary lubrication, using poly-alpha olefin (PAO) oil with graphene oxide aggregates and lithium grease with MoS2 particles, were successfully accomplished. The PAO oil and lithium grease had electron transmission ability, and the friction interfaces were imaged by SEM as seen with an optical microscope.

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  • Mohd Muhyiddin Bin Mustafa, Noritsugu Umehara, Takayuki Tokoroyama, Mo ...
    2019 Volume 14 Issue 5 Pages 388-397
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Wear by fracture is among the factors associated with the DLC coating failures in the tribological application. The current study investigated the link between the wear and the fracture-toughness on the novel Pillar and Mesh structure ta-C coatings, in addition to conventional ta-C coatings. The tribological properties of these coatings were examined under base-oil lubrication via ball-on-disk tribo-tester and micro indentation technique was used to characterize the fracture toughness. The wear track and the indentation mark were analyzed using the optical microscope, 3D laser microscope and FE-SEM. The friction coefficient for ta-C, Pillar ta-C and Mesh ta-C are within the range of 0.071 to 0.106. Mesh ta-C indicated the highest wear resistance, followed by the Pillar ta-C and conventional ta-C. Also, Mesh ta-C demonstrated the highest fracture-toughness value with 16.6 MPa·m1/2, followed by Pillar ta-C with 13.4 MPa·m1/2 in contrast to ta-C. Greater resistance to wear for ta-C with Pillar and Mesh structure was detected with an increased fracture-toughness and improvement in crack propagation inhibition. Moreover, the Pillar and Mesh ta-C provides superior rate of crack-energy dissipation as compared to the ta-C.

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  • Koji Takiwatari, Hidetaka Nanao, Yasushi Hoshi, Michimasa Uchidate, Sh ...
    2019 Volume 14 Issue 5 Pages 398-403
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    This study investigates the effects of both, molecular structure and surface roughness, on the tribochemical decomposition of synthetic base oils under high-vacuum conditions. Nascent steel surfaces exhibit high activity to catalyze the decomposition of synthetic oil under lubricating conditions. Decomposition was performed on multiply alkylated cyclopentane (MAC) and alkyl diphenyl ether (ADE) at the nascent surface of bearing steel 52100 and was monitored by a ball-on-disk friction tester in a vacuum chamber attached to a quadrupole mass spectrometer. Although MAC decomposed, ADE did not decompose on the flat steel surface. Steel surfaces used within this experiment underwent procedural abrasion, providing the requisite roughness to generate the nascent steel surface for the friction test. Decomposition of ADE and desorption of benzene were observed in the presence of the nascent steel surface under friction. As the surface morphology of the pretreated roughened surfaces changed during friction, the contact pressure and plasticity of the surface decreased. We concluded that the tribochemical decomposition of ADE was accelerated on rough steel surfaces by the generation of a nascent surface at the point of metal-metal contact. From these results, the critical role of a nascent steel surface on the tribochemical decomposition of syntheticoils is discussed.

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  • Yasuaki Inoue, Kien-Wee Tan, Philip A. Hutchinson, Boris Eisenberg, Fr ...
    2019 Volume 14 Issue 5 Pages 404-410
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The demands on the automotive Industry to deliver improved fuel economy are long standing and continuing. A common and cost effective way to improve the fuel economy is to optimize the viscosity-temperature profile of a lubricating oil by employing a Viscosity Index Improver (VII). In this paper, we investigated the impact of the viscosity of engine lubricating oils on fuel economy and the influence of the VII in tuning the viscosity-temperature profile of the oil to maximize the fuel economy effect without compromising the protection under conditions of high temperature and high shear. We introduced novel comb type VIIs which have been specifically developed to provide the optimized viscosity-temperature profile required to give this balance. The way how these novel comb type VIIs were compared to more conventional VIIs in terms of the lubricating oil viscosity-temperature performance and also the resulting benefit in fuel economy are illustrated. We highlighted a recent study on a SAE 0W-16 oil, which is already of low viscosity, and further viscosity modification of what is already a quite efficient lubricating oil are less pronounced in terms of measurable influence on fuel economy.

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Short Communication
  • Hilmi Amiruddin, Mohd Fadzli Bin Abdollah, Maziah Ibrahim
    2019 Volume 14 Issue 5 Pages 411-416
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    The purpose of this research is to propose a technique for friction reduction of palm kernel activated carbon (PKAC) polymer composite by palm oil, paraffin oil and water impregnations. A biocomposite sample formed by mixing epoxy and PKAC was made using the method of powder metallurgy. Before test of dry sliding, the sample was impregnated with palm oil, paraffin oil, and water for about 1–8 days. The test of dry sliding was then conducted at room temperature and by applying constant load, sliding distance and sliding speed. The test of sustainability for checking the biocomposite’s ability of maintaining the lubricant was also carried out without any more impregnation. A considerable amount of friction of lubricant-impregnated PKAC composite is reduced although there is increases in residual depth due to plastic deformation in comparison to the sample devoid of any impregnation. Water impregnation caused an unexpected rise in the coefficient of friction within the initial few hours following which it became comparatively steady. The sample impregnated with palm and paraffin oils can soak up the lubricant and sustain it for some time prior to the subsequent inflow. More decrease on the coefficient of friction and residual depth were noticed when the soaking time was raised. Besides, no wear is observed on the surface of all samples impregnated with palm oil. Thus, the application of bio-based lubricant to obtain an improved performance in comparison to the synthetic oil is more worthwhile.

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  • Suvin Parayantayyathu Somarajan, Jeng-Haur Horng, Satish Vasu Kailas
    2019 Volume 14 Issue 5 Pages 417-421
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Lubricity of cutting fluids is assessed by (i) Rubbing tests and (ii) Chip generation tests. In a rubbing test, there is very little possibility of exploring the behavior of the fluid on a nascent surface. Any method which aims to assess the lubricity of cutting fluids should be such that it tests the tribological properties on the nascent surface generated by cutting. Conventional tribological equipments like a scratch tester, pin-on-disk apparatus or a four-ball tester may not be successful in satisfying this criterion. A unique tribometer which can perform friction testing on freshly cut surfaces has been developed for experimental investigation. The lathe tribometer is set up that constitutes a cutting tool and a pin setup. The pin is independent of the tool and it is placed just below the cutting tool to ensure proper contact required to measure the component of the forces during the machining operation. The major advantage of the lathe tribometer is that it is portable and it can be used in the real-time machining operation. When the lathe tribometer is fixed on the lathe the spring in the tribometer is compressed against which the normal force is measured. The friction force comes into play when the workpiece is rotated against the tool in contact which is measured by the load cell in position. A cutting fluid (Green cutting fluid) developed in our lab and commercially available cutting fluids (CCF) were used for the experiments. Green cutting fluid (GCF) gave better machining performance in terms of COF and Roughness measurement at the 400 rpm speed (COF and Ra of GCF and CCF1 were 2.5/1.07 and 2.7/1.24 respectively). The performance of GCF was reliable and competent with cutting speed change. Thus the observations from the study provide an upshot for analysis, further study, and improvement of tribometer and green cutting fluid.

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  • Yuichi Nakamura, Yuta Yamamura, Masahito Matsui
    2019 Volume 14 Issue 5 Pages 422-427
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    Expecting to obtain a temperature-independent curve, pressure temperature superposition graph of lubricant high-pressure viscosity was tentatively constructed by adapting P/(T-Ts) as the horizontal axis, where P, T and Ts are pressure, temperature and the solidification temperature at atmospheric pressure, respectively. Published high-pressure viscosity data of mainly synthetic oils compiled in ASME pressure-viscosity report at different temperature could be plotted only on one curve named "master curve" depending on the kinds of oils with few data scattering up to 3 GPa or up to 220°C. The master curves were almost linear, but showed slightly nonlinear tendencies and convex in semi-logarithmic scale. Slope δ of the graph at the ambient point on the master curve is equivalent to α/(T-Ts), where α is the pressure-viscosity coefficient, so that α at the ambient temperature T can be easily obtained from δ determined by published or measured data (temperature). Employing this graph and its slope, high-pressure viscosity and α at 0°C and -18°C were estimated and they roughly agreed with the published data.

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Article
  • Monica Beyer, Gareth Brown, Michael Gahagan, Tomoya Higuchi, Gregory H ...
    2019 Volume 14 Issue 5 Pages 428-437
    Published: December 15, 2019
    Released: December 15, 2019
    JOURNALS FREE ACCESS

    It is anticipated that many future electrified vehicle transmissions and axles will incorporate the electric motor within the unit housing. In such an arrangement, the lubricant will be in direct contact with powered motor windings, which raises new concerns regarding its electrical conductivity and its propensity to corrode copper. The heat produced at the motor windings will challenge the lubricant’s heat transfer ability and its thermal stability. Expected high temperature excursions warrant the use of new plastics, which may give rise to new compatibility concerns. In this paper we share our learnings regarding the electrical properties of lubricants and discuss new methods to characterize copper corrosion. We review the factors that affect the heat transfer characteristics of lubricants and illustrate how improving heat transfer will favor the use of lower viscosity lubricants. We also share our early efforts to quantify lubricant compatibility with higher temperature plastics using tensile strength measurements. Finally, we discuss how these new concerns will shift the perception of what is required for lubricants used in different types of electrified transmission hardware.

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