Thermoelastic analysis of contacts defined by straight or curved boundaries under dry or elastohydrodynamic lubrication conditions

Abstract

Improvement of the characteristics of bearings and contacts in general is a constant need of the industry. This study proposes a precise, reliable and time efficient method that, while taking into account thermoelasticity, it can also handle contact surfaces with different negative or positive asperity geometries. This goal is achieved by adding thermoelastic consideration and curved edge treatment capability to the well-known half-space semi-analytical method (SAM) developed by Hartnett (Hartnett, 1980). To prepare a comprehensive contact simulation model, the study identifies the weaknesses of the available half-space method, which has already been proven more effective and less time consuming than FEA approaches, and targets those weaknesses. One of the weaknesses of the half-space based methods is the inability to reliably simulate the curved edges. In order to handle curved edges, first, the study defines the position of the counterbalance pressure for each position inside the contact area to eliminate the remaining shear stress at the curved freesurface. Second, it introduces a correction factor for the counterbalance pressure to eliminate the remaining normal stress on the curved free-surface. Another important weakness of SAM is the consideration of thermoelastic effects, specifically in the presence of free-edges. To rectify this weakness, the study introduces thermoelastic influence factors to be calculated only once at the beginning of the simulation process. Similar to elastic errors imposed by free-edges, because of the half-space assumption, free-edges impose some errors for thermoelastic considerations as well. These errors come from the generated heat flux and thermoelastic normal stress at the free-surface. This study first treats straight free-edges by taking advantage of the generated heat flux at the free-surface in order to define the corresponding thermal boundary condition by applying counterbalance heat patches and introducing a thermal boundary modification factor. At the second step, the process calculates a correction factor for the applied counterbalance heat patch to account for the generated thermoelastic normal stress at the straight free-surface. At the next step, the study considers the curved free-edges while taking into account the thermoelastic effects. Since the initial steps of the study have already treated the elastic aspects of the curved free-edges, this step focuses only on the thermoelastic aspects. To do so, first, the study calculates the position of the counterbalance heat patches and then applies the thermal boundary modification factor introduced in the previous steps to define the thermal boundary condition at the curved free-edge. Then, the study calculates a correction factor for the counterbalance heat patch to eliminate the thermoelastic normal stress generated at the curved free-surface for a specific thermal boundary condition (adiabatic boundary condition). In the final step, the study introduces a final modification for the correction factor introduced in the previous step to account for other thermal boundary conditions. Since the proposed model is flexible enough to handle any contact with arbitrary and variable pressure profile, the study used the developed model for modeling a thermoelastic thermal elastohydrodynamic rolling contact with free-edges. Then, the study performed a comprehensive factorial analysis on the effects of the three main contact variables (Load, average velocity and viscosity grade of the employed lubricant) on the characteristic parameters of the lubricated contact (Maximum pressure, maximum temperature and minimum film thickness).

Date	27 Sept 2021
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Raynald Guilbault (Supervisor)