1 Using Laser Vibrometry for Precise FRF Measurements in Experimental Substructuring 11 The following observations are made: • Both experimental coupling results match very well numerical data in magnitude and phase up to a high frequency range (Fig. 1.5a,b). Note that the laser seems to be more accurate at very low (0−−30 Hz) and very high (above 2000 Hz) frequencies. In particular, the capability of the laser to measure static or quasi-static responses is highlighted in Fig. 1.6a,b. • The validation of the coupled FRF with the assembled FRF is highly affected by the rigid IDMs left uncoupled (two translations and three rotations) and the residual flexibility. This result is expected as the uncoupled horizontal DoF is highly correlated with the vertical one and plays an important role in most modes of the assembled structure. • The discrepancies in the shape of the coupled FRF (in the position of antiresonances) between piezo and laser measurements depend mainly on the different impact location in the observed FRF (Fig. 1.5a,b). In addition, the different dynamics acquired at the interface for the VPT in the two cases may slightly affect the coupling results. The added mass effect in piezo measurements is minimal due to the small number of lightweight sensors used. 1.5 Conclusions In this paper, the use of laser vibrometry in the context of experimental LM-FBS coupling via VPT is investigated. The noncontact measurement technique allows to minimize the disturbances in the overall system dynamics related to the presence of a physical device mounted on the measured component. In this sense, the use of a non-intrusive approach in sensing motion is strongly suggested when dealing with small-sized, lightweight structures. A further advantage of laser technology over standard accelerometers is the capability to reach inaccessible areas and measure a large number of points. A comparison between the coupling results of the two different measurement approaches is provided. Although the experimental data acquired with both accelerometers and LDV fit very well with the simulated data, the laser reveals great accuracy over a broader frequency range. Additional analysis can be conducted on more complex applications (e.g. 3D interface coupling) to explore the potential of laser vibrometry in FBS. References 1. De Klerk, D., Rixen, D.J., Voormeeren, S.: General framework for dynamic substructuring: history, review and classification of techniques. AIAAJ. 46.5, 1169–1181 (2008) 2. 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