In-situ Pressure Measurements Using Raman Microspectroscopy in a Rolling Elastohydrodynamic Contact

The physical conditions (pressure, shear stress, temperature) generated in an elastohydrodynamic (EHD) contact are the main parameters governing the evolution of the physico-chemical properties of the lubricant within the contact. This paper presents in-situ measurements of pressure in an EHD point contact using Raman microspectroscopy. Two model lubricants are studied: a pure polyphenyl ether (5P4E) oil and a mixture of this oil with a liquid crystal. The influence of load and speed on the pressure distributions is investigated. The Petrusevich pressure spike is measured and its evolution with the operating parameters is in good agreement with the theoretical predictions. The addition of the liquid crystal to the base oil leads to an important diminution of the mixture viscosity, and consequently of the film thickness in the contact. The different rheological properties of the lubricants induce significant variations of the pressure profiles.