The Influence of the Defects in Welded Metal on Bending Fatigue Strength of Large Shafts

Abstract

The authors have carried out rotary bending fatigue tests on large cylindrical specimens (0.2% carbon steel) having a circumferential groove welded by manual electric welding and also on small specimens taken from the welded part of the large ones. Two series of specimens, stress-relieved and not stress-relieved, have been tested in order to investigate the influence of residual stress at the same time. The results are summarized as follows : (1) The fatigue strengths of the large and small stress-relieved welded specimens have decreased to 43% and 58% of that of the solid specimens having respective sizes. Such decrease of fatigue strength may be caused by the defects such as blow holes in welded metal, which may result in the sharp notch effect. (2) The fatigue strengths of the large specimens which were not stress-relieved have decreased more remarkably, and are 38% of that of the solid specimens. However, for small specimens, the fatigue strength has not practically shown any effect of stress-relieving.