Fatigue properties of steel wire

Abstract

Because of surface imperfections the fatigue limit of a structural member may be appreciably lower than the fatigue limit determined on machined and polished specimens of the material. This was shown by fatigue tests made by the rotating-beam method on galvanized heat-treated steel wire, Swedish valve-spring wire and cold-rolled mild steel wire: the fatigue limits of specimens with the original surfaces as produced by the manufacturers were 40, 60, and 82 percent, respectively , of the fatigue limits of machined and polished specimens of the same materials. The development of a suitable gripping device made possible the determination of the limiting range of pulsating tensile stresses on unmachined (in the test length) specimens of wire in the Haigh alternating-stress testing machine. The effect of variation of the mean stress between 50,000 and 200,000 Ib/in.2 on the limiting ranges of pulsating tensile stresses was determined on cold-drawn and galvanized, and heat-treated and galvanized, steel suspension-bridge wires, and on a high-strength steel wire electroplated with zinc. The results showed that the limiting ranges of pulsating tensile stresses were practically independent of the mean stress within the range investigated.