Application of SPD to enhance the structural integrity of fuseage skins and centre barells

The chapter summarises a building block approach that has been used to demonstrate the potential of SPD for repairing and enhancing the airworthiness and integrity of fuselage skins, fuselage lap joints and centre barrel structures. The initial focus is on the application of SPD doublers to fuselage lap joints representative of civil transport aircraft. These successful tests are then supported by an application to an F/A-18 Hornet wing attachment centre barrel laboratory test article that was subsequently tested for more than three design life times without detectable evidence of degradation to the SPD doublers, including those over fastener holes, or the surrounding structure. We also show that even though, during fastener removal to install a Canadian modification, the SPD was damaged there was no cracking or disbonding induced and the SPD, and the surrounding structure, remained intact even after cycling a further 13,000 flight hours, which corresponds to in excess of two lifetimes. This finding highlights the damage-tolerant nature of SPD. As such this test programme revealed SPD to be very durable and that it can be used to restore structural integrity of full-scale aircraft components under a representative fighter aircraft spectrum. As a result it is found that SPD doublers can withstand cyclic stress amplitudes of approximately 200. MPa without disbonding or failure. This is an important finding since it represents a realistic upper bound on the stresses seen on the exterior wetted surface of operation aircraft.