Experimental and numerical investigation of torsion fatigue of a nickel-based alloy at elevated temperature

The objectives of this investigation were to measure high cycle torsional fatigue properties of Inconel 617 at elevated temperature of 850 degrees C in atmospheric conditions. An MTS torsional fatigue test rig was modified with customized mechanical grips and cooling fms and used to obtain the stress-cycle results of Inconel 617 at the elevated temperature. Post inspection and evaluation of the cracks on the specimens in high cycle regime demonstrated that initiation occurred due to shear followed by normal stress for the propagation. In order to achieve the objectives of analytical aspects of this investigation, a 3D elastic-plastic finite element model was developed to examine the torsional fatigue damage in Inconel 617 material at high temperatures. Continuum damage mechanics was utilized to model material degradation during the torsional fatigue process. Voronoi tessellation was used to represent the material grains and intergranular failure was coupled with the continuum damage mechanics criterion to model the material degradation during the fatigue process. The effects of material plasticity were included by incorporating Mises based plasticity with kinematic hardening approach. The stress and accumulated plastic strain-based damage law were incorporated in the model for the fatigue initiation and propagation. The numerical model predicts fatigue lives and crack growth which corroborate well with the high-temperature torsional fatigue experiments.