Influences of small defects on torsional fatigue limit of 17-4PH stainless steel

The sensitivity of 17-4PH stainless steel to small defects under torsional fatigue loading condition at a stress ratio of R = −1 is examined in the high-cycle fatigue regime. Fatigue crack initiation and growth behaviors are observed, and fractographic investigations are performed. As a key geometric parameter, area is used to investigate the influence of small defects on torsional fatigue limit. Further, the results are compared to the data obtained in the uniaxial fatigue tests, which allows the effect of biaxial stresses on the surface of the material to be discussed.