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Abstract
The phase diagrams corresponding to transition from liquid to viscoelastic solid and that from viscoelastic solid to elastic-plastic solid of Santotrac100 (SN100), mineral oil, synthetic naphthenic oil, polybutene, and tetradecane were first made up by high-pressure density measurements and others. The bulk modulus of lubricating oils under a quasi-static condition was evaluated using a phase diagram. The results indicated that the bulk modulus of lubricating oils is closely related to the oil molecular packing parameter T VE −T (where T VE is the viscoelastic solid transition temperature at pressure p, and T is the oil temperature). The constant values of the bulk modulus in the elastic-plastic range are different depending on the molecular structures of the oils. It has also been shown that SN100, mineral oil, synthetic naphthenic oil, and polybutene converted to amorphous solids at high pressures and tetradecane converted to molecular crystal. Next, the elastohydrodynamic lubrication tractions were measured by a ball-on-disk machine. The results indicated that the maximum traction coefficient is closely related to T VE −T. As a result, the importance of the bulk modulus as a predominant factor for traction characteristics of lubricating oil was pointed out.
ACKNOWLEDGMENTS
This work was partly funded by the Grant-in-Aid for Scientific Research (no. 14550127) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. The authors wish to express their thanks to K. Horikami and S. Yamada for their cooperation. The oils were supplied by Idemitsu Kosan Co., Ltd.
Presented at the 58th STLE Annual Meeting in New York City, New York April 28-May 1, 2003 Manuscript approved September 11, 2004 Review led by Steve Danyluk