“Creep Rupture Materials Design Manual”
William J. O’Donnell, Carl Spaeder, Jeremy Himes, Bill O’Donnell, B. Kasraie, October, 2008
Keywords: creep rupture; sterling cycle; creep rupture damage; elevated temperature; cyclic loading; triaxiality effects; thermal stresses
This Creep Rupture Design Manual was developed as a guide to maximize the efficiency of a sterling cycle engine for power generation. This Design Manual focuses on creep rupture damage that occurs as a result of high stresses acting over long times at elevated temperature. Such damage for cyclic loading conditions is obtained by integrating the ratio of the operating time at a particular temperature and stress level, divided by the time to rupture at that temperature and stress level. Of course, factors on the average creep rupture time are needed to account for heat-to-heat variations, scatter in the data, load sequence effects, surface finish, size effects, fabrication straining and local triaxiality effects.
Residual fabrication stresses produce creep rupture damage during their relaxation. Thermal stresses must be taken into account since the material is only aware of the magnitude of stress, temperature and time to which it is subjected. This Design Manual provides curves for design life based on 2/3 of the average creep rupture strength. As more data is obtained for these materials, particularly long-term data, metallurgical aging changes can be more accurately quantified.
Company President, Bill, Sr. is active on the ASME Subcommittee on Design, and serves as a Contributing Member of the ASME (BPV III) Working Group on Fatigue Strength. He has co-authored numerous papers on various engineering topics, including Elevated Temperature Design & Analysis.