In situ pressure measurements in dimpled elastohydrodynamic sliding contacts by Raman microspectroscopy

In situ pressure measurements within dimples formed in glass–steel point contacts under various sliding conditions were performed using Raman microspectroscopy. Experiments were conducted using a ball-on-disc type apparatus in which a circular contact is formed between a rotating glass disc and a rotating steel ball. Film thickness distributions were measured by duochromatic optical interferometry. Polyphenyl ether oil (5P4E) which has a high pressure–viscosity coefficient was used to produce a dimple in the contact area. Experimental results show that the pressure increases locally in the dimple zone and the pressure profile changes, accompanying the changes of the dimple location as a function of the slide-to-roll ratio. The maximum pressure is located downstream the maximum height of the dimple. The rheological response of the oil film under dimple occurrence conditions is discussed.