Friction is investigated in a rolling–sliding, lubricated, steel ball on elastomer flat contact. Two different types of friction are identified: rolling friction, which results from the movement of the surfaces relative to the contact, and sliding or interfacial friction, which arises from relative motion of the two contacting surfaces. A novel experimental technique is
described to measure these two types of friction simultaneously in a single test. This enables separate rolling and interfacial ‘Stribeck-type’ friction curves to be produced for Newtonian lubricants. These curves are compared with theoretical predictions of friction. The results show that rolling friction originates primarily from two sources: Poiseuille flow of lubricant in the contact and elastic hysteresis. There are also two main types of interfacial friction; due to Couette flow and solid surface adhesion. For compliant elastomer-on-steel contacts, rolling friction forms a significant proportion of the total friction even at quite high slide–roll ratios.
Keywords: Soft-elastohydrodynamic, Isoviscous-elastic, Friction, Rolling friction, Sliding friction, Interfacial friction, Couette friction, Poiseuille friction, Hysteresis