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Title: Novel Experiments to Characterize Creep-Fatigue Degradation in VHTR Alloys

It is well known in energy systems that the creep lifetime of high temperature alloys is significantly degraded when a cyclic load is superimposed on components operating in the creep regime. A test method has been developed in an attempt to characterize creep-fatigue behavior of alloys at high temperature. The test imposes a hold time during the tensile phase of a fully reversed strain-controlled low cycle fatigue test. Stress relaxation occurs during the strain-controlled hold period. This type of fatigue stress relaxation test tends to emphasize the fatigue portion of the total damage and does not necessarily represent the behavior of a component in-service well. Several different approaches to laboratory testing of creep-fatigue at 950°C have been investigated for Alloy 617, the primary candidate for application in VHTR heat exchangers. The potential for mode switching in a cyclic test from strain control to load control, to allow specimen extension by creep, has been investigated to further emphasize the creep damage. In addition, tests with a lower strain rate during loading have been conducted to examine the influence of creep damage occurring during loading. Very short constant strain hold time tests have also been conducted to examine the influence of themore » rapid stress relaxation that occurs at the beginning of strain holds.« less
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Conference: SMINS-3,Idaho Falls,10/07/2013,10/10/2013
Research Org:
Idaho National Laboratory (INL)
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Country of Publication:
United States
36 MATERIALS SCIENCE; Alloy 617; creep fatigue; Creep-fatigue testing; VHTR