CdSe-Based Quantum Dots as In Situ Pressure and Temperature Non-intrusive Sensors in Elastohydrodynamic Contacts

We present a new technique designed for in situ measurement of pressure and temperature in lubricating films. An innovative methodology has been developed, based on the photoluminescence properties of non-intrusive CdSe-based nanosize sensors (quantum dots). The sensitivity to pressure and temperature of these sensors dispersed in a carrier fluid was established through calibrations performed in diamond anvil cells. Elastohydrodynamic (EHD) contacts of different combinations of contacting solids (glass-steel, glass-Si 3 N 4 , sapphire-steel and sapphire-Si 3 N 4 ) and submitted to various operating conditions were studied through in situ experiments and numerical simulations. Isothermal experiments were performed first: both experimental central pressures and pressure profiles were obtained, with a very good agreement with the values predicted by the numerical model. A series of non-isothermal experiments were then carried out to perform temperature measurements. Temperature rises in the central zone of EHD contacts involving various material pairs were measured and compared to predictions, leading to a very satisfying agreement. Overall, the deviation between measurements and predictions remained smaller than the uncertainty of the measurement method. Therefore, these findings proved the potential of the methodology to probe in situ pressure and temperature in EHD contacts. Comparative performance with competing techniques was examined in terms of intrusiveness, level of reliability, spatial resolution, accuracy and complexity. As this work is a pioneering development, the technique may be improved in the near future, opening an avenue for even more accurate or faster measurements for example, and eventually offering a better understanding of the mechanisms at work in this type of lubricated interface.