Tribology Online
Online ISSN : 1881-2198
ISSN-L : 1881-218X
16 巻, 1 号
選択された号の論文の8件中1~8を表示しています
Article
  • Maria Sarno, Claudia Cirillo, Adolfo Senatore, Davide Scarpa, Waleed A ...
    2021 年 16 巻 1 号 p. 1-15
    発行日: 2021/01/31
    公開日: 2021/01/31
    ジャーナル オープンアクセス

    Herein, with the aim of enhancing tribological properties of lubricating oils, by adopting stable nano-additives and without substantially modifying oil rheological properties, carbon nanotubes and graphene-based nano-carbons were synthesized through simple and scalable processes. Afterward, a systematic study of their stability in Group I and III base oils, with and without low amounts of dispersant/surfactants, was performed, revealing the effectiveness of the synergistic combination of SDBS and Tween 80. Tribological tests showed a significative reduction of coefficient of friction and wear scar diameter up to 22% and 19%. Moreover, a significant reduction of the surface roughness was also recorded both at ambient temperature and 80°C due to the addition of the 0.1 mass% FLG sample.

  • Naoki Yashiro, Kouya Oohira, Natsuko Sugimura, Hitoshi Washizu
    2021 年 16 巻 1 号 p. 16-23
    発行日: 2021/01/31
    公開日: 2021/01/31
    ジャーナル オープンアクセス

    The filling behavior of Fe-Ni-Mo steel powder for sintered machine parts is simulated using our original DEM (Discrete Element Method) code based on FDPS (Framework for Developing Particle Simulator). The difference between the simulated and experimental apparent densities after self-weight filling is only -6.7%, which is a significantly higher prediction accuracy than the prior study. This result is obtained by only calculating the repulsive force, viscous damping, friction force and gravity using the actual Young's modulus. This is due to using the experimental friction coefficients and the upper limit setting of the distance between the particle surfaces based on the experimental study. This method can be used to simulate the porosity, especially the low density region, in the actual filling process.

  • Koji Takiwatari, Shinya Sato, Yasushi Hoshi, Hidetaka Nanao, Shigeyuki ...
    2021 年 16 巻 1 号 p. 24-30
    発行日: 2021/02/28
    公開日: 2021/02/28
    ジャーナル オープンアクセス

    The effect of molecular structure on the traction properties of polyglycol oils was investigated using a traction tester, and in-situ observation of the oil film was performed with a micro-Fourier transform infrared spectrometer under elastohydrodynamic lubrication conditions. The sample oils used were polypropylene glycol (PPG) diol, PPG triol, PPG dimethyl ether, PPG diester, PPG diamine, PPG triamine, and poly-α-olefin. The traction coefficient and oil film thickness of the sample oils were sensitive to the functional group at the terminal of the molecule. The sample oil containing polar functional group is larger in oil film thickness and traction coefficient than non-polar hydrocarbon oil, poly-α-olefin. These results suggest that the hydrogen bonding of functional groups was strengthened by high pressure in the Hertzian contact region. Moreover, the effect of water in the sample oils on the traction behavior was discussed. Water was dissolved into the sample oils from the atmosphere during the lubrication test, and it is implied that water in PPG diamine affect the traction coefficient.

  • Zbigniew Stępień
    2021 年 16 巻 1 号 p. 31-37
    発行日: 2021/03/15
    公開日: 2021/03/15
    ジャーナル オープンアクセス

    The main purpose of this article is to draw attention to the possibility of uncontrolled degradation of lubricating oil during its routine operation. Such degradation can pose a serious threat to engine operation and can even cause its permanent damage. The research of the work was aimed at determining the rate, size and directions of degradation processes of lubricating engine oil used in a turbocharged positive-ignition engine. After the on-road use in the vehicle, the used oil was subjected to multidirectional tests, and the results obtained were compared with those of equivalent tests of the unused oil. Furthermore, photographic documentation of selected internal engine components covered with deposits was made, and then the sludge collected from them was tested. The results showed that in the case of real (non-optimal from the vehicle manufacturer's point of view) operating conditions, significant acceleration of multidirectional lubricating oil degradation processes in the engine can occur. This necessitates its more frequent replacement. It was also found that systems used by engine manufacturers to monitor oil level and also its quality during operation do not always early enough detect the degradation of lubricating oil to the degree threatening the proper and safe functioning of the engine.

  • ―Prediction of High-Pressure Viscosity of Polymer VII-Blended Oil, and Viscosity-Temperature Properties under Pressure―
    Hitoshi Hata, Yoshitaka Tamoto
    2021 年 16 巻 1 号 p. 38-48
    発行日: 2021/03/31
    公開日: 2021/03/31
    ジャーナル オープンアクセス

    Using high-pressure viscosity measurements of 23 kinds of VII-blended oil reported in Part 1, a high-pressure viscosity prediction formula for VII-blended oil was derived. This equation is expressed in a so-called Barus formula, and the pressure-viscosity coefficient is the secant pressure-viscosity coefficient αB(p)-Bl (= ln(ηpt / ηot) /P) in each ln(ηpt) ‒ P relation curve. The calculation formula of αB(p)-Bl is composed of the corresponding base oil value αB(p)-Bf, the polymer coil itself pressure-viscosity coefficient αPm and the polymer concentration wPm (wt%). In relation to mentioned above, the volume fraction of one polymer molecule in hydrodynamically equivalent sphere, and the volume fraction of the hydrodynamic volume occupied in 100 cm3 of VII-blended oil at critical concentration c* of polymer coil were investigated. It was also found that the viscosity index VIo-Bl in the atmospheric pressure of the VII-blended oil drops with pressure. For this reason, the effect of temperature on the ln(ηpt) ‒ P relation curve, the influence of polymer type and base oil in ηiPt relationship, and the influence of polymer type on atmospheric pressure viscosity ηott relationship were discussed.

  • Tatsuya Okamoto, Noritsugu Umehara, Motoyuki Murashima, Koji Saito, Ka ...
    2021 年 16 巻 1 号 p. 49-58
    発行日: 2021/03/31
    公開日: 2021/03/31
    ジャーナル オープンアクセス

    To clarify the low friction mechanism of CNx coating in PAO oil lubrication, we measured reflectance spectrum at friction area in-situ by reflectance spectroscopy during friction test against a sapphire hemisphere pin in PAO oil. We observed and estimated the thickness of PAO oil film, the surface roughness of CNx coating, thicknesses, and polarizability of the transformed layer formed on bulk CNx coating during friction test by analyzing reflectance spectrum. We proposed that the decreasing of load ratio of boundary lubrication mode to total load is the one of governing factor to reduce friction on the basis of the increasing of Λ value. Also we proposed the increasing of adsorption of PAO oil to the CNx transformed layer is the second governing factor on the basis of the increasing of polarizability of PAO oil and transformed layer, that leads to the increasing of van der Waals force between transformed layer and PAO oil as low friction mechanism of CNx in PAO oil lubrication.

  • Kiichi Nakagome, Kaisei Sato, Hikaru Okubo, Seiya Watanabe, Shinya Sas ...
    2021 年 16 巻 1 号 p. 59-69
    発行日: 2021/03/31
    公開日: 2021/03/31
    ジャーナル オープンアクセス

    When various sliding components of combustion engines protected with hard coatings are slid with automotive lubricants, unexpected interfacial phenomena may occur because typical automotive lubricants have been formulated with additives suitable for steel/steel sliding components. Therefore, understanding the effects of hard coatings on the performance of lubricant additives is crucial for further improving the lubrication properties of fully formulated oils through the optimization of additive formulations for hard coatings. In this study, friction tests were performed with a steel surface against steel surfaces coated with two ceramic materials and two diamond-like carbon materials under lubrication with a fully formulated oil. Atomic force microscopy and X-ray photoelectron spectroscopic (XPS) investigation of the steel surfaces after the friction tests revealed that the tribofilms comprised a bottom layer composed of calcium compounds and a top layer composed of phosphorous, zinc, and sulfur compounds. The thickness of each layer, which is closely related to the wear property, depends on the hard coating material. Moreover, XPS analysis focusing on the molybdenum element suggested that rate of chemical kinetics to form MoS2 differs among the hard coating materials, and dominantly affects the frictional property.

  • Mohd Danial Ibrahim, Susan Philip, Su Shiung Lam, Yuta Sunami
    2021 年 16 巻 1 号 p. 70-80
    発行日: 2021/03/31
    公開日: 2021/03/31
    ジャーナル オープンアクセス

    Our research aims to study the properties of real shark skin in accordance with its topographical features and the biomimicry for friction reduction. In this paper, we are focusing on antifouling surface modification based on the surface roughness and frictional resistance inspired from the shark’s denticule arrangements. Biomimetic shark skins were prepared using the silicone laminated transfer molding method to investigate the antifouling effects. Anti-algae formations were investigated to examine and assess the antifouling properties of the biomimetic shark skin surface microstructure. The results indicated that the effect of microreplication with shark skin on the surface had reduced 13% - 40% of algae formation. The characteristics of the hydrophobic properties for shark skin had also been investigated through the analysis of the contact angle (CA). Scanning electron microscopy (SEM) is used to observe the surfaces morphologies of the shark skin as well as the biomimetic shark skin. In addition to that, the frictional resistance experiment was carried out to evaluate the friction of coefficient (COF) of different surface modifications. The frictional resistance experiment for real shark skin and replicated shark skin demonstrated lowered COF value ranging from μ = 0 to 1, compared to the COF for controlled surface whereby the value ranges from μ = 0 to 5.

feedback
Top