Fatigue Modeling of 508 LAS Under Variable Amplitude Loading: A Mechanistic Based Analytical Approach

A Chaboche-based evolutionary cyclic plasticity model is proposed to model the elastic-plastic behavior of 508 Low Alloy Steel (LAS), a commonly used material for Light Water Reactor (LWR), under variable amplitude loading. A novel parameter estimation technique is developed to incorporate the amplitude dependency of the material behavior into the earlier developed time-dependent material models based on constant amplitude fatigue test data. The resulting new material model can be referred as time-dependent-amplitude-independent material models. Variable amplitude fatigue tests under different environmental conditions (in air and pressurized water reactor (PWR) coolant water at 300°C) are analytically/mechanistically modeled. The analytical modeling results show that the time-dependent-amplitude-independent material parameters are able to capture the stress-strain state under variable amplitude fatigue loading. The developed model and reported material parameters can be utilized for more accurate stress analysis of safety-critical reactor components under real-life loading scenarios with variable/random loading transients. Recently a report on related 508 LAS material characterization work has been published by Argonne National Laboratory [1]. In this work a summary of the related work is presented.