Abstract
Using double-V-notched specimens of austenitic steel SUS310S with high ductility, creep rupture tests are conducted in tension, torsion and combined tension-torsion stress states at 700°C. Creep fracture surfaces of the ruptured notches as well as longitudinal sections of the un-ruptured notches are observed in detail with scanning electron micrographs. The creep fracture modes and the initiation and growth behaviors of creep voids in the notched specimens under the stress conditions stated above are investigated and discussed, based on the stress distributions in notch cross-sections calculated by finite element method. It is confirmed that the mean stress in a specimen at a multi-axial stress state promotes the brittle creep fracture. It is also suggested that the von Mises effective stress and the mean stress promote the initiation of creep voids and their growth, respectively.
