Modeling and analysis of hybrid bonded-bolted joining in large-scale aircraft assembly

Hybrid bonded-bolted (HBB) joining is common method used in aircraft assembly, particularly for critical junctions such as the wing-to-fuselage joint, to ensure both quality and durability. Accurate simulation of HBB joining presents a significant challenge, as it requires a proper description of the contact interaction of the assembled parts, the flow of adhesive used for bonding, and their mutual influence. In this paper, the process of HBB joining of the upper wing panel and fuselage of a commercial aircraft is simulated. The utilized mathematical model is comprehensive in several ways. Firstly, it covers all the most important physical phenomena determining the intermediate and final result of the assembly process, notably including the two-way fluid-structure interaction and the presence of a free surface in the fluid part. Secondly, the finite element model of the joint has dimensions and level of detail comparable to models used in industrial applications. Finally, the complete sequence of assembly stages is reproduced during the simulation, including the installation of temporary fasteners and their replacement by permanent ones. The paper focuses on investigating the problem of permanent fasteners loosening, a critical issue in aircraft assembly. The state-of-the-art aircraft assembly technologies typically include requirements intended to prevent significant loosening of permanent fasteners by the end of the assembly process. The validity of these requirements is studied using a series of numerical tests with a specially developed simulation tool. Three distinct fastening installation scenarios during the multistage wing-to-fuselage assembly process were considered. The simulation results were analyzed and compared in terms of permanent fastener loosening.