Extension of low cycle fatigue life model to thermal aging for 20000 h of a low alloy steel

Axial low cycle fatigue tests were performed on the thermal aged low alloy steels (LASs). The fatigue life declined after thermal aging for 20000 h, characterized by diminished plastic strain amplitude, enhanced cyclic hardening, and reduced ductility. Post-fatigue fractography of the material after thermal aging revealed elevated dislocation density, dense dislocation pile-ups and tangles, which compromised carbide’s ability to block cracks and degraded the bainite phase, and further accelerated crack initiation and propagation. A previously established fatigue model based on the thermal aging parameter was extended to 20000 h and demonstrated sound applicability. Moreover, this model was embedded in a Physics-Informed Neural Network (PINN) framework to enhance the accuracy of fatigue life prediction. This study provides both data and guidance for LAS fatigue design in extended service applications.