EXPERIMENTAL DETECTION OF DISBONDS AND DELAMINATION IN HONEYCOMB STRUCTURES

The effects of disbond (delamination) sizes and skin thicknesses on th e dynamic response of honeycomb structures were investigated. A mechan ical impedance instrument (MIA 3000) was used to test the specimens wh ich were made of two layers of thin aluminium skins with Nomex honeyco mb cores. Firstly, this study concentrated on the influence of disbond size on its resonance frequency and the amplitude and phase of impeda nce in honeycomb structures. Secondly, the influences of skin and hone ycomb core thicknesses on these parameters were also investigated. It was found that, having the same skin thicknesses and materials, the re sonance frequency of a large disbond was lower than that of a small di sbond, and also lower than that of a good area. With a thicker skin, t he resonance frequency was higher than that of a thinner skin. It was also observed that, with a thicker honeycomb core, the resonance frequ ency in a good area was larger than in that of a thinner one. The reso nance frequency in a constant disbond, however, was invariant when the skin thicknesses and materials were kept the same. It was further evi dent that, with a swept frequency ranging from 1 to 8 kHz, most disbon ds could be detected if the thicknesses of aluminium skin were between 0.5 and 2.0 mm.