An Experimental and Analytical Study on the Development of Extrapolation Method for the Creep-Fatigue Life of Alloy 617 to Low Strain Ranges and Long Hold Times at 950°C

Abstract

Abstract Creep-fatigue is the most severe damage mode for high temperate components under cyclic loading. Experimentally, standard creep-fatigue testing is mostly performed at strain ranges of 0.3% and above. There is a major data gap in creep-fatigue failure information for strain ranges at 0.3%, or lower, which are more prototypical for advanced reactor plant operations. To develop design curves for creep-fatigue evaluations, it will require a method for extrapolating the creep-fatigue cyclic lives to lower strain ranges and longer hold times. In this study, methods for creep-fatigue life prediction of Alloy 617 at lower strain ranges and longer hold times at 950°C were assessed. Two types of experimental data were generated to support the development of the creep-fatigue design curves at low strain ranges and long hold times. First, standard strain-controlled creep-fatigue testing using the concept of block-strain range was conducted to generate the information needed for extrapolating the creep-fatigue design curves to lower strain ranges and longer hold times. Second, creep-fatigue experiments with elastic follow-up were performed to failure to verify the proposed design curves. Based on this new testing approach and analysis method, a preliminary creep-fatigue design curve was developed for Alloy 617 at 950°C. This study shows the potential of generating a set of creep-fatigue design curves with different hold times within a reasonable amount of test times and testing effort at the low strain range region.