Digital holographic study on the dynamic response of plates with geometric and material discontinuities simulating potted-insert metallic honeycomb sandwich structures

The inspection of face sheet bonding, through optical interferometry techniques like holography and shearography, in potted-insert honeycomb-cored sandwich panels is different from the inspection of panels without inserts due to their complex response toward thermal and vibration stressing. In this paper, the dynamic responses of metallic honeycomb-cored sandwich structures with bonded and debonded inserts are studied using time-averaged digital holography and illustrated. At high frequencies, the face sheet regions at perfectly bonded inserts act as hard points, and regions across a debonded insert locally resonate in the sensitivity range of interferometry. Since the discontinuities created by such inserts are very complex to simulate numerically, we simulate potted-insert sandwich structures through plates with multiple holes and with multiple fully and partially bonded local stiffeners to validate this fast inspection procedure. The simulated dynamic response of the plates is compared with the time-averaged digital holography results. The operational deflection shapes near stiffeners are similar to those of fully potted inserts in a sandwich panel. Thus, the extent of debond can be evaluated at high frequencies as simulated through partially bonded stiffeners.