Gas turbines and aircraft engines are required to operate with fundamentally changed operating regime and dominated by cyclic operating modes with fatigue related loads. This results in acceleration of damage development on the components. Critical components of turbine blades, discs are exposed to multiaxial cyclic thermal and mechanical fatigue stresses. In order to meet the requirements, the components have to be investigated in detail under biaxial loading condition to predict the lifetime and to create a failsafe design.&nbsp;In the current work, the cruciform specimens are considered to describe the effects of strain biaxiality at different test temperatures namely 400°C and 630°C. The conventional cast and wrought nickel base alloy IN718 has been chosen for investigations. Two different batches of IN718 has been used because of difference in industrial applications. Experiments are carried out for two batches under a range of loading conditions at isothermal conditions.Unlike uniaxial specimen, the stress calculation for the cruciform cannot be obtained, due to its complexity. Therefore, there is a need of Finite Element simulation to calculate the stress distribution especially in the gauge area and along the arms of the specimen. A viscoplastic material model is considered to simulate the material behaviour subjected to uniaxial and different biaxial loading conditions. The material parameters for the deformation model are adapted from Complex Low Cycle Fatigue tests (CLCF).At first, uniaxial simulation results are compared with the uniaxial experiment results for both batches. Then, the same material parameters are used for simulating the biaxial loading cases. Since the experiments are strain controlled, an iterative algorithm is used to control the strains in the gauge section. The results of the biaxial simulation are compared with the uniaxial results. Furthermore, the lifetime is calculated based on the stabilized cycle from the simulation and by using different multiaxial stress- and strain- based approaches and finally it compared with the experimental lifetime

Experimental and Numerical Investigation of High-Temperature Multiaxial Fatigue

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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