Observation of uncommon elastic wave group velocity in common honeycomb structure and its potential for debonding detection

Abstract

We report wave propagation with an uncommon negative group velocity (NGV) feature in the common honeycomb structure. Theoretical analysis indicates that the NGV feature arises from the repulsion between skin's localized resonance modes in the same family, influenced by the relative parameters between the core and skin, such as skin thickness. Experimental results show that the NGV feature in honeycomb structure is unlike in isotropic plates, and it only appears in the front half of the hexagon hollow unit, which is surrounded by the honeycomb core. More notably, the NGV feature disappears in the skin–core debonding area and reappears in the intact area, suggesting potential applicability for detecting debonding defects.