CEA and JNC approaches for creep-fatigue evaluation of weldments and inter-comparison through benchmark analyses

摘要

Creep-fatigue is an important failure mode in elevated temperature components especially for weldments. To establish rational design-by-analysis methods for weldments, the CEA and JNC have developed creep-fatigue evaluation methods. Both organizations have compared data and ideas through two kinds of benchmark analyses. The CEA benchmark is fatigue and creep-fatigue evaluation of welded plates under reverse bending at 550 癈. The JNC benchmark is creep-fatigue evaluation of a welded vessel under cyclic thermal transients. The main differences in the methods are the strain concentration factors for base metal fatigue strength reduction factors of weldments. To evaluate inferior performance of weldments to base metal, the CEA pays attention to material strength reduction in the weld metal, while the JNC examines strain redistribution between the base and weld metals. Both the CEA and JNC calculations gave good results for welded plates. Both methods obtained conservative results for a welded vessel because evaluation methods for base metal are conservative.