A unified material model for multiaxial ductile fracture and extremely low cycle fatigue of Inconel 718

This paper summarizes an extensive work of experimental and numerical studies of extremely low cycle fatigue (ELCF) on IN718 under room temperature. The ELCF is focused on low numbers of cyclic loading (fewer than 100 cycles) of fatigue failure. The IN718 cyclic plasticity behavior and the Bauschinger effect are studied and simulated using the well-known nonlinear kinematic hardening law by J.L. Chaboche and his co-workers under different strain amplitudes and different stress states. Moreover, the Vocé isotropic hardening law was used in combination with the Bai-Wierzbicki plasticity model. The Bai-Wierzbicki plasticity model was used to capture the effect of different stress states on ELCF based on the stress triaxiality and Lode angle parameters. On the other hand, the modified Mohr-Coulomb (MMC) ductile fracture model for monotonic loading was extended by a new damage evolution rule to cover the ELCF regime. A new parameter was introduced to represent the effect of the cyclic loading at ELCF. The new parameter is responsible to capture the change of non-proportional loading direction between the current stress and the backstress tensors. A comparison between the experimental data and the finite element simulation results (by Abaqus/Explicit) shows excellent correlations. Lastly, a fractographic examinations and fracture modes simulations are presented.