Evolution of Serrated Flow Behavior Due to Dynamic Strain Aging in High‐Temperature Structural Materials Under Various Cyclic Loading Waveforms

Structural materials exposed to service conditions undergo complex cyclic loadings at elevated temperatures, where combined fatigue and creep loadings can cause severe damage due to creep–fatigue interaction (CFI) and thermo‐mechanical fatigue (TMF). As dynamic strain aging (DSA) is often manifested by jerky flow behavior and incidentally service temperatures of components encompass the operating window of DSA, a comprehensive understanding of the DSA behavior is of paramount importance. Due to the complexity in the analysis of the evolving serrated hysteresis loops, visualization of the DSA phenomenon under cyclic loading is not much attempted. Mapping of stress drops at each moment under various cyclic loading waveforms can aid in visualizing the entire DSA event throughout a material's lifetime. To the best of the authors’ knowledge, the synergistic effects of fatigue, creep, and DSA have not been reported earlier and hence the intent of this paper is to comprehend the waveform synergy in the DSA operative range under isothermal low cycle fatigue, TMF, and CFI loading waveforms, on structural materials as face centered cubic alloys (nickel based alloy: Alloy 617M and iron based alloy including type 321 stainless steel) and body centered cubic alloys (soft iron and a reduced activation ferritic martensitic steel).