Leveraging viscoelasticity for load enhancement in rotating contacts

Tribological components such as bearings and gears sustain a tremendous external load and operate at high relative speeds. For hydrodynamically lubricated contacts, subject to these extreme conditions, the lubricating fluid film exhibits non-Newtonian characteristics. In particular, when the ratio of fluid relaxation time to the flow residence time, i.e., the Deborah number (De), becomes appreciable, viscoelastic effects emerge. In this work, we model the effect of viscoelasticity using the viscoelastic Reynolds equation (VR) in cylindrical coordinates under the ultra-dilute limit in which the solvent concentration in terms of viscosity is larger than the polymeric contribution. As such, the velocity field remains Newtonian and the polymer stress constitutive relation is further simplified. We examine the effect of fluid viscoelasticity on the load carrying capacity for two geometries; (i) a conical configuration (that could be aligned or misaligned) and (ii) a flat surface embedded with different kind of textures. Our results show that viscoelasticity can enhance the load carrying capacity in both cases. Small errors in alignment strongly affect the trend in the load versus De and a strong nonlinear trend emerges exhibiting load both saturation and diminishment. Introducing pockets in the surface further improves the load bearing capability beyond the Newtonian values. However, numerical simulation of such textured configurations is challenging and, unlike the inclined asymmetric cone, large values of the Deborah number could not be reached.