PSI - Issue 68

Danilo D’Andrea et al. / Procedia Structural Integrity 68 (2025) 746–755 D’Andrea et al./ Structural Integrity Procedia 00 (2025) 000–000

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a)

b)

Figure 4. Stress and temperature trends over time during static tensile test: a) specimen 002, b) specimen 004

To confirm the results obtained using the STM, stepwise test was performed according to the method proposed by Curti et al. (Curti et al. 1986) In fact, when a material is cyclically stressed beyond its fatigue limit, three different phases can be observed in the temperature signal: an initial temperature increase, a plateau region corresponding to a stabilization of the temperature signal and a further increase until the material failure. If multiple stress levels are gradually applied, as shown in the Figure 6a, it is possible to obtain the different stabilization temperatures for each stress level. As explained by Curà et al. (Curà, Curti, and Sesana 2005) the fatigue limit can be obtained in iterative way as the value of the knee of the curve obtained as the intersection between the two straight lines interpolating negligible and significant stabilization temperatures measured for each stress level. In Figure 5a it can be observed how the higher is the stress applied, the higher is the temperature increment. As shown in Figure 5b, the value obtained