Behaviors of Fatigue Crack Initiation and Propagation for Type 316NG Stainless Steel under Multiaxial States of Stress

摘要

A lot of actual components are subjected to multiaxial stress. The rotating shafts or pipes are subjected to bending and torsion loads. In order to investigate the behaivor of fatigue crack initiation and propagation under multiaxial stress, bending-torsion fatigue test was performed in air using cylindrical specimen with a small hale. The test material was type 316 stainless steel. When the specimen was subjected in torsion and bending loads, which were same amount of stress, the direction of crack initiation was 57 deg against the specimen axis. This direction was found to be corresponding to a vertical direction of maximum principal stress estimated based on combined stress field. The fatigue crack initiation life could be estimated by the principal stress multiplied with stress concentration factor. The fatigue crack propagation rate was very large compared with ASEM Sec. XI reference curve.