Experimental and Numerical Investigation of High-Temperature Low-Cycle Fatigue and Creep-Fatigue Life of Bellows

SS316Ti is one of the widely used materials for bellows in sodium cooled fast reactor systems. Conventional design codes for bellows do not address the high-temperature failure modes. In this investigation, a methodology has been proposed for the high-temperature design of the bellows. The bellows were preliminarily designed by standards of EJMA for room temperature application. Subsequently, the detailed visco-plastic finite element analysis of the bellows has been carried out to estimate the high-temperature low-cycle fatigue (LCF) and creep-fatigue (CFI) life. The material parameters required for the visco-plastic constitutive model were generated and validated for fatigue specimens. The LCF and CFI life of the bellows based on analysis were 83 and 74 cycles, respectively. The proposed methodology has been validated by high-temperature testing of the bellows. The LCF and CFI lives of the bellows obtained experimentally were found to be 281 and 237 cycles, respectively. The life arrived based on analysis was found to be conservative compared to corresponding life by testing. The safety margin available over failure based on testing of the bellows is 3.4 under LCF and 3.2 for CFI loading.