Evaluation of high temperature multiaxial fatigue behavior or 304 steel (3rd report)

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A series or multiaxial creep-fatigue tests (uniaxial fatigue, pure torsional fatigue, pure torsional creep-fatigue, proportional fatigue, proportional creep-fatigue) was conducted by Toshiba Corporation as a part of a joint study with PNC. The results of the tests were evaluated by the multi-axial creep-fatigue evaluation method which was developed by the authors in the previous report. The following observation were obtained. (1)Results of multiaxial creep-fatigue tests obtained by Toshiba Corporation coincide well with those obtained by PNC, except those of pure torsional fatigue/creep-fatigue tests. In the case of pure torsional fatigue/creep-fatigue, Toshiba data showed slightly longer lives, (2)Pure torsional creep-fatigue lives reduced as the peak strain hold time increased from 3 minites to 60 minites. A longer hold time would have redeced the creep-fatigue lives even more. (3)In pure torsional creep-fatigue tests with a peak strain hold of 15 minuites, recovery of life was not observed with an additional strain hold time (from 3 minites to 15 minuites) at the other strain peak. (4)It was shown that the multiaxial creep-fatigue evaluation method proposed by the authors could cvaluate the Toshiba data conservatively. Life predictionswere conservative for a factor of 5 and nonconservative for a factor of 2.