PSI - Issue 28

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Costanzo Bellini et al. / Procedia Structural Integrity 28 (2020) 2283–2290 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3. Ingots and dog bone mini specimen dimensions.

3. Results The stress-strain curve of the analyzed SMA shows a hysteretic behavior at each investigated cycle. For instance, in Fig. 4 the different behaviour in loading and in unloading conditions is shown, due to the different transformations that take place in loading condition (austenite in martensite) and unloading condition (martensite in austenite).

Fig. 4. Loading and unloading stress-strain curves.

These differences can be justified precisely by these microstructural variations. In order to highlight them, the spectra of austenite and martensite have been analyzed, and through Bragg's law the cell parameters have been calculated. In Fig. 5 the analysis of the undeformed material (austenite phases) shows a cubic cell, whereas in Fig. 6 the structure of martensite (deformed at 10%) is characterized by a monoclinic elementary cell.