SPクリープ試験を用いたフェライト系ステンレス鋼の延性消耗則による累積クリープ損傷評価

抄録

In order to ensure the integrity of high temperature components, it is important to evaluate the creep damage of them. Destructive tests are more reliable methods for evaluation than non-destructive and/or numerical ones. However, in some circumstances, conventional uniaxial specimen is too large to sample from some limited areas, e.g. , Heat Affected Zone. Small Punch (SP) creep test has been recognized as a small sample testing method and to solve problems mentioned above. SP creep test employs a small and thin disk, and its volume is smaller than that of conventional uniaxial specimen. In this study, applicability of cumulative damage evaluation by ductility exhaustion rule was examined employing pre-crept ferritic stainless steel. SP creep specimens were prepared from conventional uniaxial creep specimens that were interrupted at life time ratio of 0.27 - 0.98. A series of SP creep test were conducted at three load levels. The thickness strain in SP creep specimen at rupture was calculated by measuring the thickness of fracture edge of ruptured specimen, and the circumference strain in the SP creep specimen was calculated by Finite Element Analysis. Combining the thickness and the circumference strains, equivalent creep strain at rupture was introduced, and ductility exhaustion rule was applied. Test results show that the ductility exhaustion rule can be applied to estimate residual creep life except just before rupture, but that it would underestimate damage of severely pre-crept specimen.