Riveted Lap Joints in a Pressurized Aircraft Fuselage

Abstract

The contemporary transport aircraft fuselage is a skin structure supported by frames and stringers, Fig. 1.1. The skin and the stiffening elements carry the flight loads including those due to cabin pressurization. The stringers are joined by riveting, bonding or spot welding directly to the skin, as exemplified in Fig. 1.2. In order to connect the skin with the frames, two different solutions can be applied. One of these, addressed as the shear-tied frame, involves attaching the frame directly to the skin and tear straps, Fig. 1.2. Another possibility, illustrated in Fig. 1.3, is to connect the frames only to the stringers by means of stringer clips. This solution is referred to as the floating frames. The internal tear straps, Fig. 1.4, located at and sometimes also between the frame stations, force longitudinal skin cracks (parallel to the fuselage axis) to turn circumferentially. If this situation takes place between the tear straps, a segment of the skin bends back creating an opening. This phenomenon, described as “flapping”, is a safe failure mode that limits the failure to the affected bay only (Kosai et al. 1992). A thin skin will flap more easily than a thick one (Maclin 1991). More information on flapping one can find in Swift (Swift 1987). Some aspects are also considered further on in this book. The straps can carry the load of the cracked skin. These crack stopper bands, although undesirable from the production point of view, are applied in several types of aircraft. Sometimes, instead of the fail-safe straps, waffle pattern doublers bonded to the skin are used, Fig. 1.5. Different types of crack stopper bands (integral, riveted and bonded made of the 2024-T3 and 7075-T6 Al alloys, a Ti alloy and ARALL) and their capability to cause crack growth retardation are reported by Schijve (1990).