PSI - Issue 41

R. Nobile et al. / Procedia Structural Integrity 41 (2022) 421–429 Riccardo Nobile et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. ERC vs. average temperature in the cooling phase for evaluation of the resistance temperature coefficient A.

Figure 6 shows the trends of raw data of experimental resistance at approximately 20-40% of the fatigue life for all tested specimens. The application of the load cycles is clearly visible in the oscillation of the electric resistance values and require to be averaged in order to capture the general evolution of the resistance against the number of cycles.

Fig. 6. Variation of unmediated resistance ΔR/R 0 at around 20-40% of fatigue life [%] during tension-tension fatigue tests for all specimens.

The change in electrical resistance measured during the tests, including the thermal term and the one due to damage, is shown in Fig. 7a. The acquired resistance data were averaged over a time interval of 20.2 s, corresponding approximatively to 202 load cycles. As described in the previous work by the authors (Nobile et al. (2020)), the real-time evolution of the electrical resistance clearly follows the loading and unloading of the sample in an approximate way. From the trend of the curves shown in Fig. 7a, it is observed that the specimen P 1 , stressed with a higher load, has an increase in resistance up to about 25% of the fatigue life. From 25 to 42% the resistance increases rapidly.