Development of Small Bulge Fatigue Testing Technique

-Application of SBF Test to Fatigue Life Assessment of Type 316 Steel-

Abstract

The small bulge fatigue (SBF) test equipment using a small disk-type specimen with flat and concave surfaces has been developed by the author’s group. In this study, the crack initiation/growth behavior during the SBF test and its strain range dependence were investigated for establishing this method as a fatigue test. The experimental results revealed that the crack growth behavior in the SBF test was strongly dependent on the strain range, and its rate was faster than that in uniaxial fatigue test due to the effect of biaxial stress/strain. However, the crack growth behavior was well correlated with the normalized number of cycles, which was normalized by the fatigue life, and it was found that the number of cycles to the crack penetration corresponded to 35% of fatigue life irrespective of strain range.