On the Role of Contact Stresses in Frictional Damping of Mechanical Oscillation

Abstract

Damping of spinning oscillations of a steel ball on an elastic base has been investigated. These oscillations are excited by the elastic force of a spring and damped by spinning friction. Oscillograms show the decrease of the amplitude to zero and of the period to a constant value, which can be calculated from the “elastic compliance of contact” and the compliance of the spring. Three different phases of oscillations, corresponding to three different kinds of damping can be distinguished. These are caused by: (a) Sliding over the entire contact area; (b) slips over the annular areas, while the internal stuck circle increases with decreasing amplitude; (c) oscillations of the ball, already stuck to the base by adhesion forces over the entire contact circle. The damping arises now from internal damping of base material. The periods of oscillations in two cases have been calculated theoretically.