Using the optical interferometry technique the film profile in circular elastohydrodynamic contacts is examined with several kinds of fluid under wide ranges of loads and speeds. It is found that under a sliding condition a deep conical depression (dimple) occurs in the contact surface in place of the flat plateau predicted by the EHL theory. This dimple phenomena can be explained by the squeeze film effect acting parallel to the contact plane attributable to the difference in surface deflections of the contact bodies. That is, if the contacting bodies are different in their elastic moduli, EHL film shape is markedly influenced by the slide/roll ratio even if the rolling or entrainment velocity is kept constant. This result suggests that the establishment of a new EHL theory, which takes into consideration the effects of the difference in elastic moduli of the contacting surfaces and surface pressure components parallel to the contact tangent plane, is necessary for deeper understanding of the EHL regime.

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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.

The steady-state elastohydrodynamic lubrication (EHL) is now quite well understood both computationally and experimentally. However, many practical machine elements such as rolling element bearings and traction continuously variable transmission (CVT) operate often under the halting of machine, the suspension of long time and start of machine. It is often in such operating condition that breakdown of lubrication films occurs, which eventually gives rise to fail of the lubricated surfaces. This paper describes an experimental study of EHL film thickness at halting of operation and a change by the time of an entrapped film thickness. The film thickness is investigated with some different type of lubricating oil, which a phase diagram is known by high-pressure density measurements. The results demonstrate an entrapped oil film thickness at EHL halting is dependant on αηa, where α is the pressure-viscosity coefficient, η is the dynamic viscosity, a is the deceleration, and squeeze out time of entrapped oil film is dependant on a phase diagram parameter TVE - T, where TVE is the viscoelastic solid transition temperature at Hertzian pressure, and T is the oil temperature.

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