Bandpass high frequency blisk vibration measurements by down-sampled stereo-DIC acquisitions

In this paper the stereo digital image correlation (stereo-DIC) was combined with the down-sampling technique to observe the three-dimensional vibration shapes of an open bladed disk (blisk) in a chosen frequency range. Since, this type of structure features many natural modes in small frequency ranges, the analysis of just a single frequency at a time may be cumbersome and not effective. For this reason, an innovative down-sampling frequency-band acquisition was proposed in this work. A sampling frequency twice the band width is proven to be enough to avoid any aliasing phenomena, provided that the load applied to the structure is band-limited. The method was applied at approximately 2500 Hz and 6300 Hz, with a band of 20 Hz for both. A validation with an independent laser doppler vibrometer measure, not implementing any down-sampling technique, was performed at the same frequency ranges, observing very similar trends of the amplitudes at the blade tip.