Variations of an EHL film under boundary slippage

The typical film shape in the classical EHL theory, featuring a parallel flat contact region and a constriction at the outlet, has been readily demonstrated by both numerical analyses and laboratory tests. Recently, the lubricant limiting-shear-stress property and boundary slippage have been incorporated into EHL numerical computations. Instead of the parallel flat part in the conventional EHL film, a dimple (film thickness increasing) occurs at the inlet, and a bump (film thickness decreasing) appears in the downstream contact region. In a previous paper by the authors, some purposely devised tests were carried out and a film shape with an inlet dimple, qualitatively the same as the numerical results, was obtained. More recently, tests have been carried out over an extensive range of slide-roll ratios and interesting variations of film shape are found. The present paper reports some of the results. A viscosity wedge, referred to as the drastic drop of the effective viscosity of lubricant adjacent to the bounding surfaces, is proposed tentatively to explain the film deviation.