PSI - Issue 69

Diego Scaccabarozzi et al. / Procedia Structural Integrity 69 (2025) 80–88

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Fig. 5. (Top) Time domain signal acquired from the LDV – sample #3 (bottom) FRF amplitude, phase, and coherence.

Table 3 summarises the measured natural frequencies, loss factors, and their variations across the samples, which reflect the reproducibility of measurements. The measured repeatability from a single test replication, i.e. comprising 10 sweeps, showed 1σ worst-case variability of 2%, whereas averaging on the three test repetitions aiming to assess the reproducibility of the measured data, as shown in Table 3, the repeatability of the measured loss factors was found to vary between 1% and 10%. The measurements were performed at 25.8°C ± 0.6°C. Fig. 6 highlights the changes in loss factor before and after heat treatments. All samples in heat-treated condition exhibited loss factors, which are higher than the ones obtained in as-built condition by a factor of 2 or 3.5, a result that reflects a considerably improved damping capacity. This is consistent with the material microstructure before ageing, where the absence of optimised phase distribution limits energy dissipation, depending on the phase exactly present at room temperature (see DSC scans in Figure 3). Moreover, it can also be mentioned that the residual stresses in the as-built condition may reduce the damping capacity of the Nitinol samples.

Table 3. Measured natural frequency and loss factor for the three samples before and after heat treatments.

As built

After (T500-5)

After (T500-10’)

!

!

!

η

η

η

Average [Hz]

1σ [%]

Average [10 -3 ]

1σ [%]

Average [Hz]

Average [10 -3 ]

Average [Hz]

1σ [%]

Average [10 -3 ]

1σ [%]

1σ [%]

1σ [%]