EXPERIMENTAL DETECTION OF DISBONDS AND DELAMINATION IN HONEYCOMB STRUCTURES

The effects of disbond (delamination) sizes and skin thicknesses on the dynamic response of honeycomb structures were investigated. A mechanical impedance instrument (MIA 3000) was used to test the specimens which were made of two layers of thin aluminium skins with Nomex honeycomb cores. Firstly, this study concentrated on the influence of disbond size on its resonance frequency and the amplitude and phase of impedance in honeycomb structures. Secondly, the influences of skin and honeycomb core thicknesses on these parameters were also investigated. It was found that, having the same skin thicknesses and materials, the resonance frequency of a large disbond was lower than that of a small disbond, and also lower than that of a good area. With a thicker skin, the resonance frequency was higher than that of a thinner skin. It was also observed that, with a thicker honeycomb core, the resonance frequency in a good area was larger than in that of a thinner one. The resonance frequency in a constant disbond, however, was invariant when the skin thicknesses and materials were kept the same. It was further evident that, with a swept frequency ranging from 1 to 8 kHz, most disbonds could be detected if the thicknesses of aluminium skin were between 0.5 and 2.0 mm.