The Yield of Steel Wire under Stresses of Very Small Duration

Abstract

A steel wire 53 feet long was suspended vertically from a fixed point. Near its lower end a stop was soldered to the wire; a tup, sliding on the wire, was allowed to fall on to the stop from appropriate heights. Waves of tensile stress were thus sent up the wire and reflected at the fixed top. Extensions were measured on certain gauge lengths at the top of the wire. The form of the wave front was inferred from these measurements and from the corresponding distances travelled by the stop; the stresses were calculated from the extensions. The impacts of the tup on the stop were repeated after heat treatment, at a normalizing temperature, of the middle part of a 4-inch gauge length. The static yield being 16·3 tons per sq. in., a yield was found with a wave rising from 3·4 to 28·7 tons per sq. in. in 1·25 × 10−4second and falling again to 3·4 tons per sq. in. after a further 0·45 × 10−4second. Yields above the static yield but lower than the yield just mentioned were found with waves of less intensity but of longer duration. A limiting “higher” yield stress for indefinitely small duration of the stress is inferred. This limiting stress for the wire as normalized was about 30 tons per sq. in., the maximum stress in static tension being 24·8 tons per sq. in. The results are discussed with reference to the “higher” and “lower” yield stresses.