Non-Newtonian Film Thickness Formation in Ultra-thin Film

Abstract

This paper aims to show the characteristics of ultra-thin films for non-Newtonian fluid using Ree-Eyring model where intermolecular forces of solvation and Van der Waal's are considered in addition to the hydrodynamic action to fulfill an identified need for such a conjunction. In this case, the film thickness and pressure distribution are obtained by simultaneous solution of the modified Reynolds’ equation incorporating the effect of non-Newtonian fluid, film thickness equation including elastic deformation caused by all contributing pressures and the load balance equation using Newton-Raphson method with Gauss-Seidel iterations. Effect of changing the operating conditions of speed, load, Eyring shear stress and slide-roll ratio on the characteristic of the contact has been studied. The results show that, for the case where the hydrodynamic action is the only pressure acting to support the applied load capacity, the film thickness and the pressure gradient at the exit of the contact obtained using non-Newtonian model is different than that formed using the Newtonian model especially for the increased value of slide-roll ratio. The main results of this study are that for ultra-thin film, the film thickness formed using non-Newtonian model is smaller compared to that obtained using Newtonian case and the discretization of the film thickness as the gap is reduced occurs similar to the results obtained using Newtonian model. The pressure shape shows no difference compared to that formed using the Newtonian case in which an oscillation around the Hertizan contact pressure shape due to the solvation effect appears. The results also show that for ultra-thin film, changing the Eyring shear stress does not affect the film thickness formation.

Elastohydrodynamic ultrathin film formation at the start-up of motion under the combined effect of surface force and hydrodynamic action

“…The period of inactive motion was chosen to be 0.3 s. Obviously, during the inactive period of motion, the film thickness remains constant throughout the contact region at about 3.6 nm, regardless of the value of the acceleration rate, indicating that the film thickness has a unique value in this region. The physical explanation for this behavior is due to the effects of intermolecular solvation and Van der Waals’ forces, as previously reported by Matsuoka and Kato(1997), Al-Samieh and Rahnejat (2001) and Al-Samieh (2019a, 2019b). At the start-up of the entraining motion, the thickness of the central film was rapidly increased to a value greater than its steady-state value, and hence, the thickness of the central film rapidly decreased to its steady-state value of 3.6 nm at the end of the motion.…”

“…The equation for the film thickness can be given as follows (Al-Samieh, 2019a, 2019b): where m is the entrance length, l is the lateral limit distance, H 0 is the central film thickness and δ is the total elastic deformation: …”

“…As in recent years, there has been an increasing trend toward the miniaturization of components in production; therefore, the separation of the loading area has been significantly reduced. Many researchers, including Matsuoka and Kato (1997), Al-Samieh and Rahnejat (2001), Chu et al (2012) and Al-Samieh (2019a, 2019b), have reported that the effects of intermolecular forces on the formation of ultra-thin films cannot be ignored at smaller distances. Therefore, current research focuses on studying the behavior of ultra-thin film formation of elastohydrodynamic lubrication at the start-up of motion at different rates of acceleration and final entrainment speeds.…”