The flexible disc of Ti-6Al-4V alloy is one of the most significant member in the structural design of superconducting generator rotor. It is necessary to establish the multiaxial fatigue criterion considering the effect of mean stress in order to estimate the fatigue life of flexible disc under the combined load conditions using the operation. In this study, multiaxial fatigue tests of tension-compression and torsional load were carried out by use of thin walled tubular specimens of Ti-6Al-4V alloy to investigate the effect of the amplitude and mean components of axial and torsional stresses on the fatigue strength. Moreover, multiaxial fatigue tests of the flexible disc model specimens under the operating load conditions are performed by use of the exclusive testing machine and the stress conditions are calculated by FEM. The test results are analyzed by means of the equivalent stress involving the effect of mean stress introduced from the Kawata's criterion based on the concept of internal friction theory. The validity of fatigue life prediction by this approach is confirmed for the structural design of superconducting generator rotor.
