Damage Evolution of High Chromium Steels Utilised for High Temperature Components

Several cumulative methods were developed to define and evaluate fatigue and creep damage with dependence on state variables. A phenomenological damage definition is selected under the scope of continuum damage mechanics, which fulfills various requirements of independency of critical damage on state variables. In this thesis, experimental data of strain-controlled LCF experiments performed with and without hold-time on high-chromium steels were received. A method to determine the true and critical damage is shown, where the critical damage is independent of the temperature and the strain range. Also, damage threshold based on accumulated plastic strain is determined showing explicit dependence on strain range. Moreover, the material parameter of the damage evolution equation is calculated by minimizing the equation using function minimizing algorithms, where it is approximately same for experiments without and with hold-time at the same temperature. Multiaxial fatigue damage model (Sermage et al., 2001) is employed to compute damage showing reasonable results with an error as high as 9.17%. Furthermore, lifetime prediction is performed using constants from experiments without hold-time for experiments with hold-time showing acceptable results with an error as high as 16.66%. Also, the error for prediction of experiment with a service-type cycle is 15.9%