The pressure-viscosity coeffi cient is an important parameter in tribology. Experimentally, it is calculated using the high-pressure viscosity measurement. Also, the adiabatic bulk modulus is calculated using the sound velocity in the lubricating oil. Several lubricating oils are considered on the group basis such as traction oil, mineral oil, polyalphaolefi n oil, perfl uoropolyether oil and glycerol, depending on their molecular structure. Experimental pressure-viscosity coeffi cient is compared with the adiabatic bulk modulus. It is found that the pressure-viscosity coeffi cient increases exponentially with the adiabatic bulk modulus, and the relationship depends on the molecular structure of the lubricating oils. This study proposes two equations to predict the pressure-viscosity coeffi cient from the adiabatic bulk modulus based on sound velocity, one for the traction oil, and another for the paraffi nic mineral oil and the polyalphaolefi n oil.

Two synthetic base oils (815Z and 2001A) and two greases (601EF and R2000) used for space applications have been studied at ground level. Rheological tests were performed in order to characterize the behavior of each of the base oils versus the pressure and the temperature. Next, the effect of base oils and greases on ball bearing fatigue life was carried out using thrust ball bearings. The results of L 10 life tests showed a bearing life order from the highest to the lowest of grease 601EF (blended with base oil 815Z), base oil 2001A, grease R2000 (blended with the base oil 2001A) and, the lowest, the base oil 815Z. The general tendency of the base oils and the greases shows that the bearing life increases with the EHL film parameter. However, the anticipated beneficial effect of an apparently high film parameter for the base oil 815Z was not seen due to permanent viscosity loss in the EHL contact. The results showed that the viscosity of the base oil 815Z, which contains the acetal group , was decreased by mechanical shear at the high shear rate in the EHL conjunction and the EHL oil film was thinner than expected. Hydrogen fluoride is released with the decomposition of the acetal group. As a result, the permanent viscosity loss at high Hertzian pressure and the hydrogen fluoride generation shortened bearing life with the 815Z base oil. In the case of grease 601EF with base oil 815Z, the permanent viscosity loss did not occur in ball bearings and the bearing life is extended.

This study investigates about the characteristic of the thermo-reversible gel-lubricant (TR Gel-Lube) under elastohydrodynamic lubrication (EHL) conditions. TR Gel-Lube is the lubricant, which consists of base fluid and a gel agent. TR Gel-Lube is repeatedly able to change gel-state to liquid-state at the melting point of its gel agent. Moreover, TR Gel-Lube has good tribological properties, anti-evaporability and so on. This paper describes about investigation of the EHL oil film thickness characteristic, the oil starvation at EHL inlet region and the EHL traction characteristic. It was observed that TR Gel-Lube had low EHL traction, thick EHL film thickness and good stability of EHL oil film formation compared with conventional greases.

The pressure-viscosity coefficient α is one of the most important property for EHL condition, however its measurement has difficulty. Therefore authors attempt to predict α for blend oils by using the relationship between pressure-viscosity coefficient and logarithm of kinematic viscosity at atmospheric pressure, which is used for single oil as ever. The pressure-viscosity coefficient of mixtures enables to predict with base oils properties and viscosity of mixture at atmospheric pressure. Test fluids are SN-HV, PBSN, DOS, BBPH and mixtures of these oils. High-pressure viscosity measurement was done at pressure up to 0.4 GPa and temperature range at 20ºC to 100ºC. The authors proposed the prediction method of α for mixtures.

Different types of synthetic polyalphaolefin (PAO) oils and a mineral oil are considered in this study. High-pressure viscosity test was done and pressure-viscosity coefficient was measured for all sample oils. Results showed the better performance of PAO oils than the mineral oil. Authors also tested some other tribological properties such as low-temperature behavior, bulk property, frictional coefficient, and wear behavior, which are important for wind turbine gear oil. Low-temperature behavior and frictional property of PAO oils exhibited the better results. Study also showed that the prediction of low-temperature fluidity is possible using the sound velocity in the oil. Finally, the presence of polymethakrylate (PMA) absorbent in PAO oil exposed comparatively better results among all PAO oils.