PSI - Issue 5

H. Lopes et al. / Procedia Structural Integrity 5 (2017) 1205–1212

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H. Lopes et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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order of the modal rotation field. We also observe that the RMS is always higher in the first modal rotation. The lowest RMS for any the modal rotation field is obtained with the shearing amount of 10 mm.

Fig. 4. RMS of noise in the first four modal rotation fields as a function of the shearing amount.

The SNR of the first four modal rotation fields as function of the shearing amounts are shown in Fig. 5. This figure reveals an almost linear increase of the SNR with the shearing amount, being this linearity more clear in the first and fourth modal rotations. We can also observe that the SNR is much higher in the first modal rotation field than in the others, thus indicating a better relative accuracy in the measurement of the first modal rotation.

Fig. 5. SNR of the first four modal rotation fields as a function of the shearing amount.

4.2. Vibration amplitude

The second set of measurements consists in a total of 48 measurements, divided in 16 groups of three determinations of each modal rotation field. These groups result from the combination of the first four modal rotations with four different vibration amplitudes. The different vibration amplitudes in the rotations are achieved by progressively increasing the amplitude of the signal applied to the loudspeaker. The RMS of noise and the SNR