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1

Effective shear modulus of an oil film under elastohydrodynamic conditions

Muraki M., Kawabata R.

International Journal of Applied Mechanics and Engineering

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2005

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Vol. 10, no spec

263-268

EN

Traction in transverse direction based on spin and side-slip was determined with a disk-on-roller machine. The measurements for di-octyl phthalate showed that the traction based on only spin was due to the elasticity of an EHL oil film from the viewpoint of rheological behaviour. Then, the influence of some parameters on the traction was examined for the synthetic naphthenes. The traction increased with increasing contact pressure and decreasing temperature. On the other hand, decrease in the radius of curvature of transverse direction increased traction because of increase in the elastic strain through decrease in the film thickness. Effective shear modulus derived from the traction measurements was an order of 0.1GPa at 30oC for the synthetic naphthenes, which slightly decreased as the contact pressure was increased.

2

Influence of biodegradable lubricants on tribological characteristcs of aluminum alloy

Muraki M., Washino K., Suzuki A.

International Journal of Applied Mechanics and Engineering

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2004

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Vol. 9, no spec.

117-122

EN

The influence of biodegradable lubricants such as rape seed oil and some synthetic esters on tribological properties of aluminium-silicon alloy were studied at a mild operating condition with a pin-on-disk tribometer. It was found that the rape seed oil was inferior to the hydrocarbon oils and the synthetic esters in the friction and anti-wear properties. In addition, presence of double bond in acyl group of synthetic ester was detrimental to the friction and anti-wear properties. XPS analysis showed the boundary lubrication film containing aluminium soap on the surfaces with rape seed oil and the synthetic esters. The difference in tribological properties between rape seed oil and the synthetic ester may be due to the difference of mechanical properties of aluminium soap.

3

Rheological properties of mineral base oils and polymer solutions for engine lubricants

Muraki M., Kurihara I., Igarashi J.

International Journal of Applied Mechanics and Engineering

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2003

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Vol. 8, no spec.

87-92

EN

Viscosity-pressure-temperature relations of paraffinic mineral base oils at a pressure up to 0.7GPa were determined with a falling ball type viscometer. The viscosity at a higher pressure condition than that of the viscometer was derived from traction curves determined with a disk-on-ball type EHD tester. When the viscosity were plotted against pressure, for the oils with higher viscosity index than 120, the viscosity derived from traction measurements followed the extrapolated curve to the high pressure region by the Yasutomi formula using the parameters obtained with the viscometer. Then, traction characteristics and oil film formability were determined for polymer solutions compared to their base oils. The addition of polymer had little effect on traction but shows a slight increase in film thickness compared to the results for its base oil. This is because the viscosity-pressure coefficient governing traction is little affected by the addition of polymer. Moreover, it was shown that the EHD inlet viscosity of polymer solutions derived by applying the Hamrock-Dowson formula to the film thickness measurements revealed a much lower value than its atmospheric viscosity at low shear rates.

4

Friction and wear properties of polyol ester, polyalphaolefin and their blended oils containing MoDTC and ZnDTP

Muraki M., Aoyanagi M., Sakaguchi K.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, Spec. is

397-402

EN

The effect of MoDTC with and without ZnDTP on reduction in friction and wear was determined under partial EHL conditions with a two roller machine, where the experiments were conducted using polyalphaolefin (PAO), polyol ester (POE), and their blended oils as the base fluids. When using PAO as a base fluid, a significant friction and wear reducing effect appeared at a low Mo concentration. On the contrary, the coefficient of friction and the wear amount in POE containing MoDTC with and without ZnDTP increased with increasing Mo concentration. In the blended oils containing MoDTC with a constant Mo concentration, the additive effect decreased as the ratio of POE was increased. This indicates that the co-adsorption between POE and MoDTC onto the rubbing surface prevented the formation of an effective boundary lubrication film. The experimental results also showed that a friction and wear-reducing effect depends on the ratio of concentration of ZnDTP to that of POE.