Calibration of nanosensors for pressure and temperature mapping within lubricated contacts

Elastohydrodynamic lubrication (EHL) regime is a frequently occurring situation in highly stressed machine elements such as rolling bearings, gears, cams and followers. The elastic deformation of the rubbing materials, the important increase of lubricant viscosity and the extremely reduced dimensions of the separating lubricant film are the main characteristics of this regime. As a consequence of the above-mentioned features, in situ measurements in EHL regime are not trivial.On the other hand, the key parameter that has to be controlled and optimized in EHL contact is film thickness. It should be the smallest possible to minimize the viscous friction and thus improve lubrication performance, but it still has to be sufficiently thick to ensure a full separation between the surfaces in contact in order to prevent wear and consequently extend the lifetime of mechanical components.Film thickness is directly related to the viscosity of the solution used as lubricant. The viscosity is, in turn, and in any point of the lubricant, a function of the local temperature and pressure that are imposed or generated in the contact. These dependencies show the importance of measuring and mapping temperature and pressure across the contact in order to predict more precisely the film thickness, and to fully understand and analyze the complexity of the physical mechanisms involved in EHL.In this context, the present work focuses on the development of a new experimental method allowing in situ measurement of temperature and pressure in EHL contact. This method is based on the temperature and pressure-dependent fluorescence emission of semiconductor nanoparticles (NPs) dispersed within the lubricant in an appropriate EHL experimental arrangement.