Study Of The Lubricant Film Formation Characteristic And Temperature Distribution In Nanogap Under High Pressure

With the rapid development of nanotechnology, especially in such areas as spaceflight and aviation, ultra-precision mechanics and huge operating machines, etc, the moving and manufacturing precisions become the sub-micron and even nano scale in some critical components accompanied by very complex cases, e.g., high pressure and high shear rate. High shear rate can result in the rupture of the lubricant molecular chains, and high pressure can result in the collapse of the lubricant film. Both cases will induce the lubrication failure between tribo-pairs, and even lead to the non-function of the whole mechanical system. Thus, it is of great theoretical implication and of significant value to application to investigate the behavior and scale effect of lubricants under high pressure and high shear rate for ensuring the stability, reliability, and economical benefits of systems. The main works and conclusions in this paper are summarized as follows:Firstly, a measuring instrument for lubricating films confined in nanogap under high pressure has been developed, which can be used to in-situ measure the lubricant film thickness, friction force and temperature distribution under the rigorous conditions (high pressure, high shear rate and nanogap). The relative optical interference intensity technique has been used in the measuring system in this paper, and the film thickness resolution in the vertical direction is 0.5 nm, and 1.0μm in the horizontal direction. The automation of the load system and the velocity set is realized with the computer. This system can be laid a base for the investigation of the film forming characteristics for point contact case in nanogap under high pressure,Next, the sapphire disk and GCr15 ball were used as the tribopairs in the experiments under high pressure. The viscosity and molecular weight of the lubricants have been taken into consideration under various pressures and entrainment velocities. The results show that the higher the velocity, the thicker the lubricant film thickness, and the curve measured film thickness is nearly in accord with the theoretical curve predicted with Hamrock-Dowson equation suggesting that the lubrication state falls into the hydrodynamic lubrication region. For the low velocity, the film thickness is relatively small, and the accuracy of the predication with Hamrock-Dowson equation decreases evidently in that the experimental data deviates from the theoretical value. The experimental curve is higher than the theoretical curve calculated by Hamrock-Dowson equation for the lubricant with high viscosity and high molecular weight. In contrast, the experimental curve is lower than the theoretical curve calculated by Hamrock-Dowson equation for the lubricant with low viscosity and low molecular weight.Finally, the infrared thermal camera was used to measure the temperature distribution in the contact region by the thermal radiation theory, and the friction force was measured for comparison. The results show that the temperature rise increases with the load under a same rolling velocity. There is a lag between the temperature in the contact region and the friction force. Initially, the temperature increases, while the fictional force decreases though its value is relative large resulting in the continuous increase of the temperature. When the frictional force tends to be stable, there is a slight decrease in the temperature in the contact region, followed by a small temperature increase. When the velocity is great, the film thickness becomes large, and then the heat dissipation taken away increases, resulting in a slight temperature decrease.