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Publisher Summary This chapter describes the utilization of conventional and advanced nondestructive inspection (NDI) techniques to detect flaws in bonded composite doublers and metallic aircraft substrates. It focuses mainly on the extensive nondestructive evaluation (NDE) capability that has been developed by research at both the Defense Science Technology Organization (DSTO) in Australia and the U.S. FAA/AANC in developing crack reinforcement/repair technology for military and civil aircraft. Although composite doublers have long been used by DSTO on military aircraft, their application in commercial aviation in particular has been suppressed by uncertainties surrounding their application, subsequent inspection, and long-term endurance. Before the use of composite doublers could be accepted for widespread use in the civil aviation industry, the FAA/AANC program was necessary to ensure that methods were available to quickly, easily, and reliably assess the integrity of a doubler. A major inspection requirement for doublers is the identification of disbonds between the composite laminate and metallic substrate, and delaminations between adjacent composite laminate plies. Detection of voids, or porosity, is also critical since these defects can reduce the strength of the doubler. The absence of disbonds, delaminations, and porosity in an installation quality assurance check indicates that the doubler is able to perform its duty. However, due to the relative newness of the technology and lack of performance data under actual flight conditions, the current approach is to continue inspections of the substrate material. Thus, in the case of doubler reinforcements, inspection for new cracks in the substrate beneath the composite doubler is necessary. For doubler repairs, accurate monitoring of existing cracks is essential. |
