Elastic hysteresis in steel

Abstract

The rate of dissipation of energy by internal molecular friction, when steel undergoes variations of stress within what is ordinarily regarded as the elastic limit, was the subject of a recent paper by Hopkinson and Trevor-Williams. A bar of steel having an elastic range of about 25 tons per square inch was subjected to direct (axial) push and pull, the limits of tension and compression being equal, and the frequency of the cycles about 120 per second. The dissipation of energy by elastic hysteresis was determined by the fall of temperature between the middle point of the bar and the ends. It could be measured accurately in this way when the range of stress was near the elastic limit (25 tons per square inch) and could be detected when the range was 10 tons per square inch. One object of the research just referred to was to ascertain whether the dissipation of energy per cycle of stress increased with the speed of reversal, in other words whether the internal friction to which this dissipation is due is of the nature of solid friction, or is more analogous to the viscosity of fluids. For this purpose the bar was alternately compressed and extended, statically, in a testing machine, between the same limits of stress as in the high-speed tests, and the stress-strain curve was obtained by means of a specially designed extensometer.