An Advanced Creep Model Allowing for Hardening and Damage Effects

:  In this work an original creep prediction model is presented with a unified comprehensive formulation with primary, secondary and tertiary stages for variable stresses and temperature fields. The creep model is implemented in the ANSYS FEM code, using the Fortran subroutine usercreep, specifically suited for the cases examined, in order to assess the material behaviour more accurately than that provided by the mono-dimensional approach. Furthermore, the residual stresses that arise from thermo-mechanical loading and unloading cycles, under the temperature-dependent bilinear elastic–plastic hypothesis, are considered. In order to validate the model proposed, an investigation into the final stages of turbine blade is presented and discussed. The nonlinear properties of the material are taken from an industrial context and the literature. In addition to the temperature dependence of the properties of the material, geometric nonlinearities are also considered. The material adopted for model calibration is a polycrystalline Ni-based superalloy. Load conditions used in the simulations are obtained using a computational fluid dynamics (CFD) analysis under working conditions provided by industrial research and the constraints modelled are representative of the real joining condition of the blade. Finally, the simulation results are compared with those obtained by the Norton–Bailey prediction model.

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