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Introduction to Design of Composite Structures
Published in Robert M. Jones, Mechanics of Composite Materials, 2018
Certain terms are commonly used to describe stiffened aerospace structures. The relatively common eccentrically stiffened circular cylindrical shell configuration is used as an example for discussion purposes. A panel is the unstiffened flat or curved sheet between stiffeners. For example, a panel occupies the space a by b in the shell in Figure 7-24. Stiffeners have different names depending on their direction and often on the type of structure (e.g., aircraft versus ships). Rings are circumferential stiffeners as shown on the inside of the shell in Figure 7-24. The ring stiffeners could be on the outside of the shell, unless not permitted for aerodynamic or hydrodynamic reasons. Rings are sometimes called frames or ribs. Stringers are axial stiffeners as shown on the outside of the shell in Figure 7-24. Of course, the stringers could be placed on the inside of the shell. Stringers are also known as longerons or spars in the aircraft industry. Often, both rings and stringers are placed on the same side of the shell, resulting in intersecting stiffeners. For example, in aircraft, submarine, and missile fuselage applications, all stiffeners must be placed on the inside to maintain an aerodynamically or hydrodynamically clean exterior. Then, quite often the rings are continuous, and the stringers are only long enough to fit between rings.
Gap measurement for thermoplastic adhesive joining of aircraft frames
Published in The Journal of Adhesion, 2022
Aircraft fuselage shells are constructed with stringer and frames to stiffen the structure. In the A350 series, the fuselages are made of carbon fiber reinforced plastics (CFRP) to use their advantages of lightweight materials, higher strength, and stiffness. While the stringers are directly integrated into the fuselage structure during bagging, the frames are assembled later to adjust form and stiffness. Up to now, frames are made of thermoset CFRP with separate stiffness elements adjusting any form deviations. Before riveting the frames for assembly, the occurring gaps between the parts are filled with a shimming and sealing to also avoid corrosion. Compared with thermosetting, thermoplastics have shorter cycle times, they can be further processed through welding processes or overmolding, and they have unlimited storage time for the semi-finished products, along with a higher impact strength and elongation at break.[1] Thermoplastic matrix systems are ideally suited for a faster and more complex production due to their reversible solidification, as they can be re-shaped, welded (i.e. joining technology) with the appropriate temperature application (with amorphous thermoplastics above the softening or with partially crystalline thermoplastics above the melting temperature) or subsequent better recycling possibilities. This is a significantly different to thermoset materials used for aircrafts, which cannot be re-melted after chemical cross-linking, which, depending on the material system and the required mechanical and thermophysical performances, requires correspondingly longer curing times.[1]
Testing mechanical performance of adhesively bonded composite joints in engineering applications: an overview
Published in The Journal of Adhesion, 2022
Michal K. Budzik, Markus Wolfahrt, Paulo Reis, Marcin Kozłowski, José Sena-Cruz, Loucas Papadakis, Mohamed Nasr Saleh, Klara V. Machalicka, Sofia Teixeira de Freitas, Anastasios P. Vassilopoulos
As far as the compression testing is concerned, [252,253,262,268,277,278] these tests are used to evaluate the effectiveness of the adhesively-bonded joints, in maintaining the structural integrity, in the case of buckling and post-buckling. This serves one of the main objectives of attaching stringers/stiffeners to the skin of fuselage or wing structures, aiming to provide the required strength against buckling loads in service.[16] These tests can include a single-stiffener or multiple stiffeners in parallel, as shown in Figure 15.