Repair of Aircraft Structures Using Composite Patches Bonded Through Induction Heating

Abstract

With the increasing aging aircraft, many unanticipated structural defects have been occurred in aircraft. Accordingly, many aircraft structural repair methods have been developed, but we need efficient method except for conventional repair method as mechanical riveting. This paper presents research on composite patch repair to damaged aluminum aircraft structure. Composite patches, bonded on cracked or corroded metallic aircraft structures, have shown to be a highly cost effective method for extending the service life and maintaining high structural efficiency. An aluminum double lap joint plate was considered as a damaged aircraft structural element in this paper. We repaired the plate with carbon fiber epoxy composite patch by induction curing, and by oven curing method. We also repaired it by precured composite patch bonding method, and by cocured composite patch bonding method. Then, the bond strengths were compared among different processing methods. The technique of electromagnetic induction is able to locally and rapidly heat the area close to the adhesive bond line. This allows for the efficient repair of the metallic substrate of aircraft, and may hence be regarded as a more efficient process. Induction heating constitutes an ideal candidate for supplying the heat needed for curing adhesives and resins, which are used for the fabrication of reinforcing patches, either on the flat, or over geometrically complex surfaces. We had conducted the experiment and numerical simulation to show that the induction curing was efficient repair heat sources in repairing metallic substrate of aircraft. We also investigated whether the incorporation of carbon nanotubes (CNTs) in the adhesive bondline affected bond strength. We found that the induction-cured samples exhibited bond strengths similar to those of the corresponding oven-cured samples

this was true for both the baseline and the CNT-reinforced samples. Further, the samples processed using cocured patches exhibited higher bond strengths than did the corresponding samples processed using precured patches. In the case of both the precured and the cocured patch samples, the dispersion of 0.5 wt% CNTs in the adhesive bondline increased bond strength slightly. The effect of the two different types of patches placed on top of the aluminum substrate on the rate of temperature increase by induction curing was shown experimentally. And, numerical simulations were performed in case of the precured patch and un-cured patch on top of the aluminum substrate. The results from this study show that the induction curing and cocuring method may be regarded as a sound and efficient method for composite patch bonding repair.