5 Modal Testing of a Nose Cone Using Three-Dimensional Scanning Laser Doppler Vibrometry 55 Fig. 5.18 Drive point FRF showing the three tests compared to a hammer impact near the suspicious modes Fig. 5.19 Automatic hammers for impact testing with SLDV 5.5 Conclusions A series of modal tests were performed on a conical test article with two surface finishes to identify the capabilities of a newly purchased 3D SLDV system. The new SLDV system performed significantly better than the previous generation system and was able to produce clean FRFs at high angle of incidences and on dark surfaces. During modal analysis, it was found that the shaker hardware that was used to excite the test article produced false modes and imparted mass loading effects. These were identified by performing a quick hammer tap test and comparing drive point frequency response functions. This investigation allowed test personnel to gain experience with using the new 3D SLDV system and identify gaps in the capability that could be improved for production tests. Alignment procedures and excitation methods have since been improved, and a number of production articles have been tested successfully. References 1. Castellini, P., Martarelli, M., Tomasini, E.P.: Laser Doppler Vibrometry: development of advanced solutions answering to technology’s needs. Mech. Syst. Signal Process. 20(6), 1265–1285 (2006) 2. Hensley, D.P., Mayes, R.L.: Extending SMAC to multiple references. In: Proceedings of the 24th International Modal Analysis Conference, pp. 220–230, February 2006 3. Avitabile, P.: Back to basics. Exp. Tech. 29(6), 23–24 (2006)
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