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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