An investigation of fretting behaviour of several synthetic base oils

The chemical and physical properties are quite different for mineral oil and synthetic oil. Compared to the investigation of mineral oil, less work on fretting behaviour of synthetic oils was reported. In this paper, a study of typical synthetic base oils such as polyalkylene glycol (PAG), polyalphaolefin (PAO) and silicone oil has been conducted. The contact consisted of a fixed flat specimen (GCr15 steel and 45 steel) opposite to a moving ball specimen (GCr15 steel) with a diameter of 12.3 mm. Other main parameters were as follows: the slip amplitude was ranged from 5 to 80 μm, the frequency was varied from 2 to 5 Hz; the normal load, temperature and relative humidity were respectively 100 N, 23 °C and 60%. Variations in the tangential force versus the displacement as a function of the fretting cycles were recorded. For comparison, fretting tests under dry condition have also been performed. The fretting scars were examined after tests. The evolution of coefficient of friction and wear volume were analyzed and compared at different fretting regimes for different synthetic base oils. The competitions between oil penetration into the interface and self-cleaning by fretting in different fretting regimes, the effect of physical properties such as surface tension, pressure–viscosity coefficient and compressibility on fretting behaviour have been particularly discussed.