| Experimentally validated constitutive models are an integral part of design-by-analysis procedures that allow high temperature components in the aerospace, nuclear power, chemical and automobile industry to be exposed to higher temperatures to maximize performance efficiency. Faithful fatigue life estimation techniques call for accurate description of stress-stress redistribution during service and hence demand accurate constitutive models. This dissertation is concerned with the development of a macroscopic constitutive model for a nickel-base superalloy, Haynes 230, used as combustor liner material in airplane turbine engines, where the temperatures can be as high as 982°C (1800°F).;The material response of Haynes 230 was characterized by performing a broad set of experiments, both isothermal and anisothermal, under loading conditions that replicated operating conditions as closely as possible. Such a broad set of experiments did not previously exist in literature for Haynes 230. Under isothermal fatigue conditions the material exhibited rate-independence at temperatures including and below 760°C (1400°F) and rate-dependence at higher temperatures. The material exhibited stress relaxation even at temperatures of 649 and 760°C (1200 and 1400°F) where the material was otherwise rate-independent. The thermo-mechanical fatigue experiments revealed mean stress evolution which was positive for out-of-phase experiments and negative for in-phase experiments. Experimental results suggested a strong influence of the maximum temperature in the loading cycle on the overall material response.;A constitutive model was developed in an integrated manner and the features of the model were driven by experimental evidence. The constitutive model was validated against the broad set of isothermal fatigue & creep-fatigue, and thermo-mechanical creep-fatigue responses. The developed Chaboche-based constitutive model includes features of rate-dependence, static recovery, kinematic hardening evolution, strain range dependence, mean stress evolution and novel features of maximum temperature influence. Implementations of the constitutive model, both as a stand-alone code and as a custom material model in commercial finite element analysis software, are developed and discussed in detail. The derivation of the consistent tangent modulus is presented for implementation of the constitutive model as a custom model in any commercial finite element software. Overall, the proposed constitutive model is adequately able to simulate the isothermal fatigue & creep-fatigue responses, as well as the thermo-mechanical creep-fatigue out-of-phase and in-phase hysteresis loops, stress amplitude & mean stress, and stress relaxation responses. |
