A fast thermoelastic model based on the half-space theory applied to elastohydrodynamic lubrication of line contacts involving free boundaries

This study allows contact models based on semi-analytical methods including the impacts of thermoelastic deformations in contacts of finite dimension bodies. The proposed method controls heat flows crossing free boundaries. A comparison with FEA reveals that the proposed method can reduce the calculation times by more than 98%. The paper introduces the thermoelasticity effects into thermal-elastohydrodynamic lubrication (TEHL) modeling of line contact problems. The analysis reveals that including thermoelastic deformations changes the pressure profile and tends to localize the pressure close to the distribution center. Compared to TEHL simulations, the examined configurations caused an overall increase in the maximum pressure by about 9%, an overall film thickness reduction of about 7%, and an overall temperature increase of about 2 K.

Thermal Elastohydrodynamic Lubrication of Axially Crowned Rollers

This work presents a comprehensive numerical study of thermal elastohydrodynamic lubrication performance in axially crowned rollers, based on a full-system finite element approach. Axial crowning has always been introduced to finite line contacts, as a mean for improving film thickness. Its influence on friction has often been overlooked though. The current work reveals that axial crowning has a negative influence on friction, increasing it significantly with respect to the reference case of straight rollers. It is shown that, with increased crowning height (or reduced crowning radius), minimum film thickness is increased, but so is friction. Therefore, film thickness enhancement comes at the expense of a deterioration in friction. Besides, achieving sufficient enhancements in minimum film thickness would require using relatively low crowning radii, which would lead to a substantial increase in friction. The frictional increase is traced back to an overall increase in contact pressures and effective contact area within the lubricating conjunction. It is also shown that, when film thickness is the most critical design parameter, the best compromise between enhanced film thickness and deteriorated friction would be to combine axial crowning with roller-end profiling. However, when friction is the most critical design parameter, a simple roller-end profiling would offer the best compromise.

A Three-Dimensional Finite Element Damage Mechanics Model to Simulate Fretting Wear of Hertzian Line and Circular Contacts in Partial Slip Regime

In this investigation, a 3D finite element model (FEM) was developed to study fretting wear of Hertzian circular and line contacts. The wear law incorporated in this model is based on the accumulated dissipated energy (ADE). A stress-based damage mechanics finite element model using the ADE was developed to determine wear of non-conformal bodies in contact. Voronoi tessellation was used to simulate the microstructure of the materials during the fretting process. To simulate the wear area, a material removal approach was implemented in the model. The FEM was used to investigate partial slip regimes under various operating conditions. The normal and shear surface tractions for the circular and line contacts were applied to the domain in order to improve the computational efficiency. The influence of modulus of elasticity, hardness and coefficient of friction on the partial slip fretting phenomenon were studied. In order to verify the model, several fretting wear tests were conducted using AISI 8620 steel and AISI 1566 steel in partial slip regime of circular contact configuration. The properties for each material such as the modulus of elasticity, hardness, and the grain size were measured experimentally and compared with the model. For the defined load and displacement amplitude of the experimental fretting tests, both materials have shown a partial slip behavior in the initial cycles and then transition to a gross slip regime. The numerical model predicted the worn surface and wear rate in partial slip regime which corroborated well with these experimental test results.

An Investigation on Starvation Onset of Rough Surface Line Contacts

Utilizing a computational approach, this study quantifies the onset of lubrication starvation for line contacts of rough surfaces operating under typical ranges of automotive gearing applications. The response parameter is selected as the critical film thickness supply, at which starvation initiates. The potential influential parameters (predictors) considered include normal force density, rolling velocity, sliding, lubricant viscosity, and surface roughness amplitude. A non-Newtonian thermal mixed lubrication model is employed to determine the critical lubricant supply under various operating and surface roughness conditions. General linear regression is implemented to reach an easy-to-use equation (R-squared value higher than 97%), facilitating the quantification of starvation dependence on the predictors that are statistically significant.

Influence of Roller-End Axial Profiling Type on Lubrication Performance in Thermal Elastohydrodynamic Finite Line Contacts

This study presents a finite-element-based numerical investigation of the influence of roller-end axial profiling type on the lubrication performance of thermal elastohydrodynamic finite line contacts. Performance is evaluated with respect to the reference case of straight rollers. The two most commonly used profiling types (i.e., dub-off and logarithmic) are compared under similar profiling length and height. It is found that a logarithmic profile outperforms a dub-off one by all accounts (i.e., frictional dissipation, lubricant film thickness, pressure buildup, and temperature rise), unless an extremely steep logarithmic shape is adopted. In the latter case, lubricant film thickness and pressure buildup may end up being negatively affected.

Influences of Iteration Details on Flow Continuities of Numerical solutions to Isothermal Elastohydrodynamic Lubrication with Micro-Cavitations

Studying elastohydrodynamic lubrication (EHL) of line contacts involving micro-cavitations, this paper exams various numerical solutions with a focus of their explicit flow continuities from inlet to exit. For the first time, influences of relaxation details, error controls, differential schemes, and mesh densities on flow continuity in EHL are revealed in a systemic fashion. Furthermore, hybrid relaxation-factors are introduced, the line relaxation is enabled with earlier boundary condition enforcement, and a typical iteration process is updated with a three-in-one iteration control. Such a process is further integrated with two different starvation/cavitation treatments: one explicitly adjusts reformation locations, and the other uses a fractional film content parameter to adjust the Couette term originated by Bayada et al.. The mass conservation results for problems with multiple micro-cavitations occurring inside the lubrication region are compared and flow curves clearly demonstrate satisfactory continuities. These insights are beneficial for EHL simulations.