Modeling the influence of surface pitting on contact pressure and friction coefficient under elastohydrodynamic lubrication conditions

Abstract

Mechanical components used in machinery are lubricated to prevent wear and enhance their efficiency. Fluid film lubrication reduces heat generation, attenuates surface pressure, and eventually, results in improvements in equipment operation. Depending on external loads and speed, different lubrication regimes may take place. Specifically, the elastohydrodynamic regime describes the lubrication response produced between two mating surfaces sustaining an external load concentrated on a small contact area and causing elastic deformations comparable to the fluid film thickness. This regime of lubricationmainly appears between non-conformal surfaces. Classical numerical models for elastohydrodynamic lubrication were developed to predict the pressure distributions and the lubricant film thickness profiles generated between smooth or rough surfaces. In addition, in real-world applications, different failure types deteriorate the surface quality and cause micro and even macro changes in the contact conditions. Pitting is one of the most common surface failures. This damage results from cyclic contact loadings. Surface pits significantly affect pressure distributions, lubricant film thickness, and friction coefficients. In this thesis, we examine the consequences of surface pitting on the line contact problem. The thesis first tackles the modeling of the dry contact between two cylinders. The considered approach is based on the Hartnet algorithm. This algorithm is enhanced by the mirroring of the pressure patches associated with the Guilbault’s overcorrection factor to eliminate the shear and normal stress distributions generated onto the free surfaces. Afterward, the model preparation introduces the Reynolds equation to the solution and form the elastohydrodynamic model for smooth surfaces. The model validation compares the predicted pressure distributions and film thicknesses to reference values. This process considers different loading and speed conditions. Then, the developments integrate the time-variant term of the Reynolds equation into the model. This element allows for modeling surface pits. The study examines different pit depths and arrangements to investigate the influence of surface damages on the lubrication of cylindrical rollers. The analysis compares the response established for smooth and pitted surfaces. The numerical predictions confirm that the introduction of pits significantly affects the surface pressures, the film thicknesses, and the coefficients of friction.

Date	22 Jul 2020
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Raynald Guilbault (Supervisor)