PSI - Issue 77

L.M. Sauer et al. / Procedia Structural Integrity 77 (2026) 34–40

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Author name / Structural Integrity Procedia 00 (2026) 000–000

Therefore, the electrical resistance change through temperature were minimal. The minor thermal variations can be attributed to the low measurement frequency. Since higher measurement frequencies will be investigated in future experiments, the influence of temperature was also examined. = · = · · 2 / 4 0 · � 1 + , � (1) = 0 · (1+ α · ( 0 )) (2) By the determination of the temperature-independent electrical resistivity ρ D the influence of length, diameter and temperature on the electrical resistance were considered. Therefore, the evolution of damage during fatigue was evaluated. During the first 75% of the lifetime, the temperature-independent electrical resistivity ρ D remains within the same range, indicating only minor changes in the microstructure. Following a period of 75% of the lifetime, an increase becomes observable, indicating changes in the microstructure, such as an increase in dislocation density or the void volume fraction. A higher increase is observed in the final 1% of the lifetime, indicating the growth of the fracture-inducing crack. 3.2. Comparison of the individual influence on the electrical resistance The combined in-situ measurement of the electrical resistance, strain, diameter and temperature allows the calculation and comparison of the individual electrical resistance change due to the geometry ΔR Geometry and temperature ΔR Temperature changes with the measured electrical resistance change ΔR S , thereby unveiling the impact of the microstructure, see Fig. 6 .

Fig. 6 . Individual electrical resistance changes through geometry ΔR Geometry and temperature ΔR Temperature in comparison with the measured electrical resistance change ΔR S versus the number of cycles N .

Due to the low temperature changes during fatigue, the individual change due to temperature is comparably low. For the first 75% of the lifetime the measured electrical resistance change follows the individual electrical resistance change due to geometry. This indicates, that for the first 75% of the lifetime, most of the electrical resistance changes can be explained through the geometry. As with temperature independent electrical resistivity, an increase can be observed here after 75% of the lifetime. This increase cannot be explained by thermal or geometric influences and therefore also indicates a significant change in the microstructure. 4. Summary and outlook In this study a method for the evaluation of damage evolution of full-forward rod extruded 16MnCrS5 during fatigue through the electrical resistance measurement was evaluated. Therefore, the change of length, diameter, electrical resistance and temperature were measured with a complex in-situ experimental setup. By using the