Low cycle fatigue lifetime of HIP bonded Bi-metallic first wall structuresof fusion reactors

A HIP bonded bi-metallic panel composed of a dispersion strengthened copper (DSCu) layer and type 316L stainless steel (SS316L) cooling pipes is the r eference design of the ITER first wall. To examine the fatigue lifetime of the first wall panel under cyclic mechanical loads, low cycle fatigue tests of HIP bonded bi-metallic specimens made of SS316L and DSCu were conducted with the stress ratio of -1.0 and five nominal strain range conditions ran ging from 0.2 to 1.0 %. Elasto-plastic analysis has also been conducted to evaluate local strain ranges under the nominal strains applied. Initial cra cks were observed at the inner surface of the SS316L cooling pipes for all of the specimens tested, which was confirmed by the elasto-plastic analysis that the maximum strains of the test specimens were developed at the same locations. It was found that the HIP bonded bi-metallic test specimens had a fatigue Lifetime longer than that of the SS316L raw material obtained by round bar specimens. Similarly, the fatigue lifetime of the DSCu/SS316L HIP interface was also longer than the round bar test results for the HIP join ts. From these results, it has been confirmed that the bi-metallic first wa ll panel with built-in cooling pipes made by HIP bonding has a sufficient f atigue lifetime in comparison with the raw fatigue data of the materials, w hich also suggests that the fatigue lifetime evaluation has an adequate mar gin against fracture if it follows the design fatigue curve based on the ma terial fatigue data.