A study of the damage tolerance of composite-metal hybrid joints reinforced by multiple and penetrative thin pins

The application of adhesive bonding technology in aircraft structures can reduce the total wight greatly, but the bonded joints are very sensitive to the possible manufacturing defects and damages during service operations, which makes them difficult to meet the damage tolerance requirements of the current transport airplane structures. In this study, the damage tolerance of composite-metal hybrid joints reinforced by multiple and penetrative thin pins was studied. The damage tolerance performance of the composite-metal joint is supposed to be enhanced by multiple through-the-thickness penetrative thin reinforcements in the bonding region, and the thin reinforcements were bonded together with both the composite and metallic joint plates. Both experimental tests and finite element simulations were conducted to investigate the effects of the through-the-thickness reinforcements on the damage tolerance performance of the joints with and without pre-fabricated disbond defects. Through the comparative analyses, it was found that the penetrative thin pins in the bonding region significantly improved the static load carrying capacity, the failure strain, the fracture energy, and the fatigue lives of the composite-metal bonded joints. Moreover, the reinforcements decreased the sensitivity of the bonded joints to the disbond defects in the bonding region. The damage tolerance performance of the composite-metal adhesively bonded joints was significantly increased by the through-the-thickness penetrative reinforcements and the enhancement mechanism was revealed by the combined analysis of test results and simulation results.