DOT/FAA/AR-03/74, BONDED REPAIR OF AIRCRAFT COMPOSITE SANDWICH STRUCTURES (FEB-2004) (FINAL REPORT)

DOT/FAA/AR-03/74, BONDED REPAIR OF AIRCRAFT COMPOSITE SANDWICH STRUCTURES (FEB-2004) (FINAL REPORT)., With the increasing use of fiber-reinforced composite sandwich structures in aircraft components, it has become necessary to develop repair methods that will restore the component’s original design strength without compromising its structural integrity. One of the main concerns is whether large repairs are always necessary to restore strength or whether smaller, less intrusive repairs can be implemented instead. Cure temperature can also become an issue if the repair patch requires curing at 350°F. Residual thermal stresses due to the bonding of the patch to the parent structure may induce further damage to the component. With these concerns in mind, the main objective of this study was to evaluate the effectiveness of scarf repairs applied to sandwich structures, given several bonding repair variables. The overall program was divided into three tasks. The first task investigated the performance of different airline depots in repairing picture frame shear elements using two different repair methods: SAE’s Commercial Aircraft Composite Repair Committee-developed wet lay-up procedure and a Boeing, i.e., original equipment manufacturer, prepreg procedure. Each method had different cure temperatures and used different materials. The second task performed in this investigation examined the effect of different repair variables on repair performance. The variables considered included three different scarf overlaps and two different core cell sizes (1/8 and 3/8 inch) and impact damage inflicted on the repair. The third task provided a comparison between several existing analytical models and available experimental results. This report summarizes the experimental and analytical results of the investigation, addresses the limitations of the experimental and analytical efforts, and provides recommendations for future research.