The formation of wedges of displaced metal between sliding metal surfaces

Abstract

In order to obtain more detailed information about the mechanism of sliding, the regions of interaction between sliding metal surfaces were observed through a low power microscope. In experiments with a hemispherical copper rider sliding against a large slowly-rotating copper drum, it was found that most of the time during sliding the drum and rider were held apart by a wedge of displaced metal which was formed between them. Whenever this wedge broke away from the rider, a new wedge was quickly formed to replace it. The formation of similar wedges has subsequently been observed to occur in experiments with a variety of other metals and with pairs of flat metal surfaces. When pairs of flat metal surfaces slide, several wedges are formed at different places between each pair of surfaces. Further investigation using metallographic techniques has shown that the adhesive junctions which are formed when the metal surfaces are first placed in contact do not break when the surfaces begin to slide. The relative motion of sliding is accommodated by plastic shearing of the metal near the junctions. The shearing takes place in a direction slightly inclined to the surfaces, and this causes the formation of the wedges.