Static and fatigue testing thin riveted, bonded and hybrid carbon fiber double lap joints used in aircraft structures

The static strength and fatigue resistance of mechanically fastened, bonded and hybrid double lap joints using relatively thin carbon fiber adherends have been experimentally investigated. The aim was to compare the static strength and fatigue resistance of a hybrid joint configuration consisting of both bonding and riveting, a purely riveted joint and a purely bonded joint. The effect of changing various parameters such as the mechanical fastener array configuration, rivet clamping pressure, bond strength, initial defects and curing conditions were also investigated.No significant difference in the static strength of the bonded joints and hybrid joints was observed. However, the investigation showed that the fatigue resistance of a hybrid joint is superior to that of a bonded joint, particularly in the case where defects are present in the adhesive bondline; such defects may include cracking or an improperly cured bondline that would significantly reduce joint static strength and fatigue life.The damage mechanism and failure mode in these three different joint configurations varied, ranging from bearing failure of the riveted joints through to tension failure in the hybrid joints. These were found to be controlled by the various parameters such as adhesive bond strength, clamping pressure and adherend bearing strength.