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This study aims to determine the life time of turbo-machines combustion chambers manufactured in superalloy or turbine blades made of single crystal material. The determination of crack initiation spots in fatigue is based on an incremental damage law applied on finite element calculations. Incremental damage laws present many advantages: it avoids any concept of cycle counting and it is more suitable for calculation with complex cycles. This numerical damage model is implemented as a post processor. First, the stored energy is computed via the accumulation of plastic strain. Then, the stored energy eventually reaches a threshold from which damage starts to grow. Finally, the cumulated damage reaches a critical value corresponding to crack initiation. Various forms of energy accumulation and energy threshold are presented. In particular, a decoupled calculation of stored energy using internal variables of the Chaboche behavior is detailed. Two plastic potentials allow taking into account low and fast strain rate viscosities. In this scheme, different methods of energy accumulation are used for creep and fatigue contributions. The reliability is then tested on high temperature experimental results, representative of classic chamber or turbine blade loads. Finally, the robustness is evaluated on low temperature test results. The good correlation between numerical and experimental Wöhler curves validates the incremental lifetime prediction with a decoupled method. Further numerical simulations will validate its industrial use. |
