| Research Abstract |
When there is a difference in thermal conductivity of the contact materials in concentrated rolling/sliding contacts, the surface temperature of the material having a low thermal conductivity is higher than that of the material having a high thermal conductivity. Consequently, the temperature and viscosity of the lubricating oil vary across the oil film. In particular, when the surface velocity of the material having a low thermal conductivity is larger than that of the material having a high thermal conductivity, an extra pressure peak is generated, and thus a thick film or a dimple is formed by the temperature-viscosity wedge action. The film pressure peaks play an important role in the formation of dimple, and multi-dimples are caused by the cooperated interaction of the main pressure peak and pressure spike. The experimental results can be explained in more detail by considering three dimensional energy balance and non-Newtonian oil flow behavior. The other important results obtain
… More
ed are summarized as follows :
1.In elliptical contacts, when the oil entrainment vector is directed along the minor principal axis of the contact ellipse, the dimples formed are stable, but when the entrainment vector is directed along the major principal axis, the dimples formed are unstable. The change of the entrainment angle plays an important role in the temperature distribution but does not influence the maximum temperature. The traction coefficient hardly depends on the entrainment angle.
2.When the slide-roll ratio is small enough, the traction coefficient is controls by the compressive heating and non-Newtonian flow behavior. The effect of the viscous heating on the traction coefficient increases with increasing in the slide-roll ratio.
3.In cases where the contacting materials have the same thermal conductivity, a larger thermal conductivity leads to a larger traction coefficient and overall film thickness. When the thermal properties of the contacting materials differ each other, the velocity of the surface having a high thermal conductivity should be larger than that having a low thermal conductivity, in order to prevent the rolling contact, fatigue. Less
|
