Exploiting imaging techniques to overcome the limits of vibration testing in high excitation level conditions

Traditional vibration testing procedures fail when extremely high excitation levels are reached. On the other hands, large displacements are well suitable to be analysed by imaging techniques based on high-speed cameras. This work aims at identifying the exploitability of imaging techniques for output-only experimental modal analysis, the so-called Operational Modal Analysis (OMA).Mode shapes evaluated from image-extracted Frequency Response Functions (FRFs) have been compared with mode shapes extracted from mobility FRFs measured by Laser Doppler Vibrometry. The test has been performed on a simple structure showing large displacements but using excitation levels that made it possible to still consider Laser Doppler Vibrometry the reference technique. Once assessed that, even at limited excitation levels, results from the two approaches are similar, the validity of the image-based approach in high excitation level tests can be derived accordingly. Sensitivity to image processing parameters, as spatial resolution and averaging, has been evaluated quantitatively exploiting the Modal Assurance Criterion (MAC) to correlate the mode shapes from the image-based approach with those extracted exploiting Laser Doppler Vibrometry.