CV. The mechanism of rolling friction

Summary An investigation has been made of the friction and surface damage produced when a hard steel ball rolls between flat parallel surfaces of a softer metal. The behaviour may be divided into two parts. When rolling first commences, even at small loads, there is marked plastic flow and the resistance to rolling is due primarily to the plastic displacement of metal ahead of the ball. With successive traversals of the same track there is an increase in track width and a diminution in rolling resistance. An equilibrium state is ultimately reached where no further increase in track width occurs so that the deformations are essentially elastic. The rolling resistance is now constant and is unaffected by boundary lubricants. From a detailed study of the rolling of spheres and cylinders on rubber it is shown that there is no interfacial slip, the whole of the rolling resistance being due to elastic hysteresis losses. It is suggested that in the rolling experiments on metals within the elastic range the resistance to rolling is also due primarily to elastic hysteresis losses. Thus in rolling, there is no ‘ friction ’ in the conventional sense of the word.