A practical method for repairing disbonded skin in aircraft panels

Abstract

The aim of this study was to evaluate a practical method of repairing a typical defect of aircraft sandwich panels that were bonded with stepped metal skins and consisted of an open rectangular edge core. This structure caused delamination or disbond between the honeycomb core and the outer skin, and it was typically due to ‘residual stresses’. A ‘positive mark-off’ was also found at the top of the inner skin at the bagging side along the stepped metal area. After a period of service time, the upper skin of the sandwich panel tended to totally delaminate, unlike the inner skin. The principle of the microcomposite concept is to use an additional thin microfabric of ‘Cerec’ embedded into the film adhesive, and this can be adopted practically to overcome permanent gap of the deformed structure. This applied method successfully eliminated possible ‘mark-off’ and ‘print-off’, and also reduced possible residual stresses that may initiate the delamination propagation, which will be stimulated by vibration during the service time. The success of the repair process was initiated by a sufficient metal surface preparation, a proper operational condition during the manufacturing process, and also an appropriate material selection of the surface layer to fill the gap distance over the repair area.