Studies on ratcheting fatigue life prediction of 1Cr18Ni10Ti pressure pipe considering in-service loadings

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Ratcheting behavior of aero-engine pressure pipe subjected to in-service loadings, including bolts preload, cyclic bending force, and internal fluid pressure, has been rarely incorporated in open experimental research. An optimized fatigue testing system was constructed to overcome the challenge caused by the non-standardized shape of the pipe. The objective of this paper is to investigate the ratcheting behavior of 1Cr18Ni10Ti pressure pipe subjected to in-service loadings and establish the ratcheting fatigue life prediction model based on the strain approach. Firstly, the effects of cyclic bending force amplitude and internal fluid pressure on the ratcheting behavior of the pressure pipe subjected to in-service loadings were analyzed. The results highlight that increasing force amplitude and internal fluid pressure lead to a remarkable ratcheting effect and shortened fatigue life. Then, the strain-based ratcheting fatigue life prediction model of the pressure pipe considering in-service loadings was developed based on finite element analysis (FEM). The main novelty of this method is that the model parameters were innovatively determined by incorporating the effects of cyclic bending force amplitude and internal fluid pressure. Lastly, the application boundary of the ratcheting fatigue life prediction method was compared by employing the KTA/ASME code, RCC-MR code, and C-TDF rule, confirming the effectiveness and feasibility of the proposed C-TDF rule. These findings advance our comprehensive understanding of the fatigue properties of the aero-engine pressure pipe considering in-service loadings.