Differentiating Test Frequency and Self‐Heating Effects on the Fatigue Behavior of Normalized SAE 1045 Steel by In Situ Multisensor Monitoring

In this research, the fatigue behavior of a normalized SAE 1045 (C45E, 1.1191) steel was investigated at test frequencies between 5 and 260 Hz. The focus was on differentiating between frequency‐induced lifetime extension and lifetime‐reducing self‐heating phenomena. Load increase tests and constant amplitude tests were performed to characterize the cyclic deformation behavior, whereas the material response was continuously monitored using Internal Energy Tracing Sensors, which use nondestructively measured signals to assess material degradation processes. In addition, a phase‐specific temperature‐correction of the electrical resistance is proposed to distinguish between microstructural and thermal contributions during cyclic loading. The results show no discernible frequency effect on fatigue life within the range of 80–150 Hz, whereas a pronounced influence is observed between 5 and 260 Hz. These findings contribute to the understanding of frequency‐temperature interactions in fatigue and improve the understanding of thermally activated degradation mechanisms at higher test frequencies.