On the criticality of bondline flaw in scarf joints under impact loading

The main problem with adhesively bonded repair technology is the weak or 'kissing' bonds which cannot be detected using current NDT techniques. To overcome this problem, a damage tolerance assessment methodology for bonded structures has to be developed to demonstrate their compliance with airworthiness requirements. The main objective of this study was to investigate the structural behaviour of a scarf joint with an initial flaw present in the bondline and subjected to impact loading. Adhesively bonded scarf joints with defects of various sizes and locations along the bondline were impacted under three different impact scenarios. The effects of the bondline flaw on the post-impact compression strength of the scarf joints were also examined. As it is expected, the higher impact energy case was found to have the greatest influence on the residual strength of the scarf joints. Large reductions in compression after impact strength (up to 84%) were recorded in the case of a large flaw located at the edge of the bondline. In addition, it was also found that the bondline flaw size and its location are more critical under low-impact energy levels in comparison to the high-energy scenarios. This fact can be used in developing a damage tolerance assessment methodology for scarf repairs.