On The Transient Response Of Ehl Films Subjected To Entrainment Speed Variation

The project mainly aims to study the transient response of EHL films subjected to entrainment speed variations experimentally and theoratically.To measure EHL film thickness under transient conditions, the related interferograms at different time instants was captured by OK image card and the images were processed off-line using a non-linear editing and acquisition system—"Canopus EDIUS".A mathematical model was established to describe the impact entrapment of lubricants and its lateral movement after impact in an elastohydrodynamic contact, and numerical simulations have been carried out to trace the movement of the dimple core. The results showed that there existed a critical value for the displacement of the entrapped lubricant core. When the displacement was lower than the critical value, it moved at the entrainment speed and the dimple depth kept unchanged. But the speed of the core became lower than the entrainment speed and the core film thickness decreased as soon as it moved beyond the critical position. It was found that with the entrainment speed increasing and the initial gap reducing, the critical displacement increased. The above numerical results were correlated to the experiment measurements.In the second part, in order to simulate the response of EHL films during the processes of start-up and shut-down a mathematical model was developed. Numerical results showed that film thickness experienced damped oscillations before reaching stable state. The damped oscillation time depended on some parameters, such as entrainment velocities, masses of lubrication couple, pressure-viscosity indices and reduced elastic modulus. During the start-up, the film thickness increased gradually and a wedge film profile was formed. Some lubricant was entrapped in the contact region and a dimple was formed during the shut-down. The dimple shape depended on the entrainment speed and the acceleration speed. The present numerical solutions were compared qualitatively with experiments by the author and previous researchers and...