| Many machine elements are designed to work in the mixed-film lubrication regime in which the lubricant film can only partially separate the contact surfaces. Due to the difficulties in the deterministic modeling of the transient contact process, available mixed-film models basically take the stochastic approach that, however, leaves many fundamental mechanisms to be explored. The objective of this thesis is to develop a deterministic mixed-film model with balanced modeling accuracy, numerical robustness and calculation efficiency, and to conduct analyses with the model to achieve a better understanding of the problem.; In this thesis, the nonlinear mixed-film contact problem is modeled in two steps. A base model is first developed to calculate the nominal film thickness, asperity pressures for the global contact. By simulating the contact at the asperity level and using other modeling techniques, the base model significantly reduces the numerical efforts and improves the numerical stability. It provides a robust platform upon which the mixed-film thermal model is added to calculate the contact temperature. Both the asperity frictional heating and lubricant viscous dissipation are taken into account in the thermal model. To account for the time-varying contact surface profiles, the energy equations are solved in an unevenly and dynamically discretized calculation domain transformed from the original thermal domain. The complete mixed-film model is extensively evaluated in the thesis.; The thesis further conducts some fundamental studies on mixed-film contacts based on transient deterministic simulation results. The effects of the asperity/lubricant thermal interaction and the thermal side-leakage on the asperity temperature are studied. Results show that the lubricant cooling effect could be so significant that it may not be neglected especially for the contacts with high entraining velocities. On the other hand, thermal side-leakage effect is found to be weak under high-velocity conditions. In addition to the fundamental mechanism studies, the thesis also performs parametric studies to analyze the effects of major contact parameters on the global thermal performance of the mixed-film lubrication to provide meaningful guidance for the engineering contact design and analysis. |
