Comparison of the performance of aircraft repair patches consisting of riveted lap joints on aluminium and composite substrates

Abstract

One of the major contributions to aircraft operational costs corresponds to maintenance. This is a time consuming and expensive process, but necessary, for instance, to detect early formation of cracks, monitoring crack growth, and for removing or fixing parts with repairs to regain their original strength. Thus, repair technologies play an important role in minimizing the aircraft operational costs, and airlines pay careful attention to these technologies to improve their efficiency and revenue. Aircraft repair patches are usually made of aluminium or composites. Composites have very high strength to weight ratio compared to aluminium but, when riveted, they may lose nearly 60% of their total strength and carrying capacity. In spite of these drawbacks, the aviation industry still uses nowadays riveting of composites as common practice. This work analyses and compares the performance of several configurations of aircraft repair patches; particularly, riveted lap joints consisting of aluminium or composite substrates repaired with aluminium or composite doublers. Each of the studied joints consists of two substrate plates separated by a gap of 12.7 mm (simulating and induced crack or hole), repaired with two doublers riveted to the substrate plates, with a total of eight rivets. The performance is computed numerically using commercial Finite Element Analysis (FEA) code ABAQUS for the riveted joints with substrate-doubler configurations as follows: aluminium alloy (AA)-AA, AA-Carbon fibre reinforced polymer (CFRP), CFRP-CFRP and CFRP-AA. For the different configurations, the joints are loaded with their limit load (7.5 kN) and ultimate load (11.3 kN), as derived from experimental results, and the stresses at various locations on the substrates are compared. The experiments and simulations presented in this work are compliant with FAR 25.571 requirements.