Creep-Fatigue Evaluation by Hysteresis Energy in Modified 9Cr-1Mo Steel

Abstract

Researchers proposed the methods of creep-fatigue evaluation, such as time fraction rules or ductility exhaustion rules. However, the microstructure change during creep-fatigue should not be directly considered in these methods. The hysteresis energy contributes to the microstructure change before the crack initiation and the crack initiation and propagation. The creep-fatigue has evaluated by the hysteresis energy in modified 9Cr-1Mo steel which is a candidate for structural material in Fast Breeder Reactor (FBR) plant. Creep-fatigue and fatigue tests were carried out at 723-873K in air. The hysteresis energy per hour at the middle of life (N f / 2, N f is the number of cycles to failure) has been evaluated. It is clear that the relationship between this parameter and the time to failure can be expressed by the power-law function. The creep-fatigue life can be evaluated based on the hysteresis energy an hour at N f / 2 using this relation.

Evaluation of creep–fatigue life based on fracture energy for modified 9Cr–1Mo steel

“…As mentioned in the introduction, change in hysteresis energy density with increasing number of cycles is small, but hysteresis density energy is increased around the fracture cycle [5]. In addition, the effect of test temperature, hold time, and strain rate on energy density is limited and hysteresis energy density is dependent on the total strain range [5].…”

“…In addition, the effect of test temperature, hold time, and strain rate on energy density is limited and hysteresis energy density is dependent on the total strain range [5]. As shown in Fig.…”

“…Our work proposes a new method to evaluate creep-fatigue life on the basis of fracture energy [5,6]. Change in fracture energy was considered to be time dependent.…”

An efficient fatigue and creep‐fatigue life prediction method by using the hysteresis energy density rate concept

“…In order to account for the frequency and hold time effects, Ostergren 3 proposed a tensile hysteresis energy‐based method in which a frequency factor is introduced to account for the loading waveform effect. In addition to Ostergren damage model, many other energy‐based models are also established, which can also account for the loading waveform effect, such as the inelastic strain energy density exhaustion criteria, 27–30 strain energy‐partition methods, 31,32 frequency modified energy criteria 33 and the HEDR model 34,35 . However, though the methods reviewed above can give good prediction performance, some limitations are also existed.…”