The influence of bearing elasticity and micropolar parameters of micropolar lubricant on the performance and stability margin of a smooth hole-entry hybrid journal bearing system compensated with capillary restrictor has been presented in this paper. Isothermal conditions are assumed for the operation of journal bearing system. Finite element method is used to obtain the coupled solution of modified Reynold’s equation and three dimensional elasticity equations. Performance characteristics are calculated in terms of minimum fluid film thickness, maximum fluid film pressure, attitude angle, critical journal mass, threshold speed and frequency of whirl for various values of design parameters like external load, restrictor design parameter, coefficient of deformation and micropolar parameters of the micropolar lubricant. The results presented in this study may be quite useful in the selection of the appropriate combination of the restrictor design parameter and elasticity of bearing so as to ensure the design of a stable bearing operating with micropolar lubricant. There exist an optimum value of restrictor design parameter (C_S2) where the performance characteristics and stability margin are maximum for rigid as well as flexible bearing operating with Newtonian and micropolar lubricants.

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The erosion behavior of three high velocity oxy-fuel/air-fuel (HVOF/HVAF) sprayed WC-Co-Cr coatings has been investigated using Al₂O₃ as erodent at impingement angles of 15° and 90° and impact velocity of 30 m/s. The results indicated that the mixed removal of Co-Cr binder and WC cuboids, plastic deformation, fracture of lips and coatings spallation were main erosion mechanisms. The erosion resistance of coatings at different erosion conditions was very much dependent on the microstructure of coatings. To sum up, the coatings with denser and more homogeneous microstructure exhibited better erosion resistance.

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Unidirectional friction experiments on uniaxially compressed pure Cu powder were performed to clarify how the solid-phase interparticle bonding proceeds during a powder molding method by applying biaxial force, termed as a compression shearing method at room temperature. Relations among the applied normal load, number of sliding cycles, and microstructural changes of the powder particles were investigated by morphological and cross-sectional observations of the samples after the friction experiments. The structural observations revealed some layered regions with different microstructures within the sample cross-section. All regions increased in size at a higher applied normal load, but their size did not change as the number of the sliding cycles increased. This phenomenon was quantitatively explained by Hamilton and Goodman’s model, which showed that the applied normal load correlated with the stress distribution applied to the sample. Tensile stress applied to the powder particles along the sliding direction appeared to be most effective for interparticle bonding. In addition, it was suggested that the bonding process of the powder particles proceeded through the steps: (1) plastic deformation; (2) initially crystal grain refinement to micrometer size; (3) bonding by local sliding between powder particles; and (4) crystal grain refinement to sub-micrometer size.

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The demand for renewable and biodegradable cutting fluids is increasing day by day. Owing to the desirable properties of vegetable oils as cutting fluids, an attempt is made to explore the potentiality of plentifully available vegetable oils as a cutting fluid for drilling of AISI 304L stainless steel using Minimum Quantity Lubrication (MQL) method. Taguchi’s orthogonal array (L27) is used for obtaining the experimental design. The performances of two Vegetable oil based cutting fluids (VBCFs) Neem (Azadirachta indica) and Mahua (Madhuca indica) and commercial Mineral oil based cutting fluid (Servocut 945) are compared in terms of thrust force, surface roughness, temperature and tool wear during drilling of AISI 304L stainless steel with carbide tool. Experimental observations and statistical analysis show that Neem and Mahua oils have a considerable potential to be used as an alternative to conventional cutting fluids. Confirmation tests verified that the selected optimal combination through Taguchi design was able to achieve desired performance.

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Sliding tests with a polyethylene (PE) pin against aluminum (Al) and titanium (Ti) disks were conducted under dry conditions, in n-undecane and in ethanol using a unidirectional pin-on-disk machine to evaluate lubrication compatibility. Compared to the dry condition, n-undecane lubrication reduced friction of both the PE pin/Al disk pair and PE pin/Ti disk pair and increased the wear of the tested materials other than PE pin slid against Ti disk. Ethanol lubrication reduced friction and wear of the PE pin/Ti disk pair but increased those of the PE pin/Al disk pair. In all environments tested, the wear of the PE pin/Ti disk pair was lower than that of PE pin/Al disk pair. Profile measurements of the wear tracks on the disks, microstructural observation and chemical analysis of the worn surfaces were performed. The results suggest that the tribological behavior was influenced by the abrasive wear resistance of the metal, the permeability of the solvent into PE, chemical reactivity of the solvent and the thermal conductivity of the metal.

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Effect of polytetrafluoroethylene (PTFE) and some additives of engine oil on tribological properties between polyamide (PA) and carbon steel was studied with a pin-on-disk type tribometer. Friction and wear properties of PA were improved by blending PTFE of 10 mass% into PA matrix, in which chemically blended material f-PTFE/PA was superior to physically blended material PTFE/PA. This is because f-PTFE/PA has a characteristic surface with fine PTFE particles dispersed in PA matrix, while the surface of PTFE/PA has agglomerated PTFE particles easily removed when rubbing. Then, the effect of lubricating oils on tribological properties of PA was studied using the additive free hydrocarbon oil and the fuel-saving type engine oil. The friction-sliding speed characteristics were evaluated taking practical use in automobiles into consideration. The coefficient of friction under the low sliding speed region was much lower for the engine oil than for the hydrocarbon oil. In addition, the engine oil showed a flat friction-sliding speed curve while the hydrocarbon oil showed a curve with large negative gradient. By surface analysis on the rubbed surface and by conducting additional experiments, it became clear that Ca-detergent containing CaCO₃ in the engine oil was effective for improvement of the friction and wear properties between PA and carbon steel.

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The Japanese Society of Tribologists is very pleased to announce that the Paper Award of Tribology Online 2017 was awarded to:

◊ “Development of a New Tapping Tool Covered with Nickel/Abrasive Particles Composite Film for Preventing Chip Snarling and Tool Service Life Extension,”  by Yasuyoshi Saito, Takeshi Yamaguchi, Kei Shibata, Yuki Kadota, Takeshi Kubo, Wataru Watanabe, and Kazuo Hokkirigawa, Tribology Online, Vol. 11, No. 2 (2016) 81-87.

◊ “Role of Water and Oxygen Molecules in the Lubricity of Carbon Nitride Coatings under a Nitrogen Atmosphere,”  by Naohiro Yamada, Tomomi Watari, Takanori Takeno, and Koshi Adachi, Tribology Online, Vol. 11, No. 2 (2016) 308-319.

and

◊ “Prediction of Shallow Indentation Effects in a Rolling-Sliding EHL Contact Based on Amplitude Attenuation Theory,”  by Petr Šperka, Ivan Křupka, and Martin Hartl, Tribology Online, Vol. 12, No. 1 (2017) 1-7.

The Award Medals were presented to the attended authors at the award ceremony by Prof. Takashi Nakamura, the President of the Japanese Society of Tribologists, at the JAST Annual Meeting on 22nd May, 2018. The medals were mailed to all the authors who were unable to attend the ceremony.

The Paper Award of Tribology Online is given annually to the author(s), either the JAST members or non-members, of the paper(s) judged as the best paper(s) published in Tribology Online (TROL) for the previous three years. All papers that appeared in TROL for the three years are reviewed by the JAST Awards Committee.

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