Grant: Discovery Grants Program - Individual

Lubrication is the introduction of a substance (fluid or solid) between the contact surfaces of moving parts to reduce friction and wear, and to dissipate heat. In a Hydrodynamic regime, ideal conditions can be created through design to develop a convergent wedge of lubricant able to fully support the bearing load while separating completely the mating surfaces. On the other hand, elasto-hydrodynamic (EHL) regime is generated when the load is carried by very small contact area, causing significant surface elastic deformation. Although the pressure distribution along the conjunction and film thickness can be predicted with accuracy, anticipating the traction is problematic, as the rheological properties of the film are difficult to predict, keeping in mind that the pressure may induce a large variation of the viscosity. Grease acts as a sealant to prevent leakage and impede the entrance of corrosive contaminants, and it is a good damping and noise-suppressor medium; it is therefore a very common lubricant. Although grease is used to lubricate more than 80% of at least 20 billion bearings mounted on a large number of mechanical systems, limited knowledge of its behavior, previously thought to be similar to oil, is causing problems of premature failures in applications related to cutting-edge technology. Lubrication using grease is believed to generate starved mixed-EHL, meaning that the film is thinner and thus contact between at least some asperities takes place. Therefore the prediction of the friction in these systems becomes an even more challenging task due to the requirement to combine the traction in a discontinuous film and the component arising from the interaction of the asperities, which are deformed due to the loading and pressure as well as subjected to wear. The aim of this research is to develop and experimentally validate mathematical models for the prediction of friction and lubrication-failure applicable to grease-lubricated starved sliding contact. A successful outcome will definitely constitute a great achievement toward the development of cutting-edge technology and for the production of higher performance bearing-mechanisms, which will generate substantial energy savings and environmental benefits.