Abstract
When metal structures are subjected to long-term cyclic loading at high temperature, simultaneous creep and fatigue damage may occur. In this paper probabilistic life models, described by hold times in tension and total strain range at elevated temperature have been derived based on the creeprupture behavior of 316FR austenitic stainless steel, which is one of the candidate structural materials for fast reactors and future Generation IV nuclear power plants operating at high temperatures. The parameters of the proposed creepfatigue model were estimated using a standard Bayesian regression approach. This approach has been performed using the WinBUGS software tool, which is an open source Bayesian analysis software tool that uses the Markov Chain Monte Carlo sampling method. The results have shown a reasonable fit between the experimental data and the proposed probabilistic creep-fatigue life assessment models. The models are useful for predicting expended life of the critical structures in advanced high temperature reactors when performing structural health management.
Highlights
Interest in future reactor designs focuses on Generation IV nuclear power plants
Wave form and frequency: Tensile hold periods appear to be more damaging at high temperatures (e.g., 650°C) than the corresponding compressive hold periods at high strain ranges (e.g., 1%), but the reverse is true at lower strain ranges (e.g., 0.4%)
This study proposed modifications to some of the existing creep models to arrive at new CF life assessment models
Summary
Interest in future reactor designs focuses on Generation IV nuclear power plants. In the design of fast reactor structural materials, the most important failure mode to be prevented is creep–fatigue (CF) damage at elevated temperatures. The 316FR stainless steel has been subjected to low loading rates, cyclic frequencies and temperatures at 550-600 C to develop probabilistic models for CF degradation and expended life assessment of reactor structures. A number of standard methods and guidelines exist for design and life assessment of structures subject to cyclic high temperature (Riou, 2008; Asayama & Tachibana, 2007; Asayama, 2009) Most of these are methods where creep and fatigue life fractions of the loading history are evaluated separately, combined as additive quantities, and compared to case- or material-specific limits. These methods fail to explicitly account for the synergy that exists between these two failure mechanisms.
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