Mode Shape Experimental Holographic Technique for Spacecraft Sandwich Panels

Mode shapes acquired using holographic interferometry with both stroboscopic real time and time average techniques and mode shapes retrieved with a broad band approach are compared. The test structure is a sandwich panel made with an aluminum honeycomb core and two CFRP skins. Such materials are used for light spacecraft structures subjected to dynamic loads especially during the launch. In the first approach excitation will be obtained driving a transducer by a single frequency sine-wave, while in the second one the structure will be excited by an impact hammer. In general the holographic interferometry is conducted on clamped structures while impact testing, whenever possible, on free-free configurations. In this work we have succeeded in comparing the holographic interferometry experimental data with the experimental ones from the broad band approach, both obtained in free-free condition. The problem how to correctly realize the constraints and to approach the free-free configuration, maintaining the rigid motion of the whole structure small enough not to confuse the interferometric pattern, has been successfully overcome.