Single-lap shear joints made from fabric T300/polyphenylene sulfide (T300/PPS) and unidirectional T700/low-melt polyaryletherketone (T700/LM-PAEK) laminates are joined via induction and conduction welding at different processing temperatures. The joints are tested experimentally to investigate the influence of the processing temperature on the damage evolution in the specimens which is tracked using digital image correlation. Cracks grow rapidly in the unwelded parts of the joint interface but assume a stable steady-state propagation rate when reaching the fully welded overlap region. It is found that higher welding temperatures lead to longer weld lengths, which improve the strength and stiffness of the specimens and delay damage initiation. An accelerated crack growth rate indicates that the structure is close to its ultimate load after which the joint fails abruptly as the crack growth becomes unstable. Induction welding temperatures at the upper end of the recommended processing window (330 C for T300/PPS and 385 C for T700/LM-PAEK) result in the joints with the highest load-carrying capacity and slowest crack propagation, but also the least damage tolerance.

An analytical model for predicting the displacement field in composite single-lap shear joints with zero-thickness interfaces is developed and verified with numerical simulations. This two-dimensional model imposes no restrictions on the composite layup or the dimensions of the adherends. It closely aligns with the displacement field predicted by numerical simulations, provided that the assumptions of small deformations and plane strain are satisfied. Small discrepancies are observed near the overlap region because the stress-free boundary condition at the overlap ends is not satisfied exactly. Consequently, the joint stiffness is slightly overestimated compared to the numerical simulations. Nonetheless, the analytical model can serve as a useful tool for providing input for more detailed analyses of single-lap shear joints, for example for determining the interlaminar stress field at the interface between the two adherends.

Modern aircraft structures consist of a multi-material mix, dominated by high-performance composites, but also including metal alloys, e.g., for load introduction parts. This experimental research investigates the static and fatigue strength of pinned hybrid titanium-composite single-lap-shear joints. The Ti6Al4V adherend is manufactured by laser powder bed fusion. The joining is done by co-curing with the carbon fiber reinforced polymer adherend. The static tests focus on damage initiation and ultimate load, and are benchmarked by identical joints without pins. The fatigue tests focus on damage initiation and propagation. Digital image correlation is used for damage monitoring. Results show, (i) a high ratio of static ultimate failure to damage initiation load, (ii) early low-cycle damage initiation but then long high-cycle fatigue life until failure, and (iii) the crack stopping effect of the interlocking pins. Furthermore, visual joint failure analysis reveals a variety of damage modes, suggesting comprehensive testing and proper pin design.

Composite single-lap shear joints made from virgin plies and recycled core material are manufactured via induction and conduction welding using T300/polyphenylene sulfide (T300/PPS) as well as T700/low-melt polyaryletherketone (T700/LM-PAEK). The specimens are tested in quasi-static conditions to evaluate their mechanical performance and damage growth. Digital image correlation and high-speed cameras are used to capture the specimen behavior until after failure. While joints with recycled core material show a lower load-transferring capacity than their virgin counterparts (reduction of 13.8% for T300/PPS and 41.2% for T700/LM-PAEK), they are nonetheless an appealing option for applications where sustainability is a priority. Damage in virgin thermoplastic welded single-lap shear joints grows along the weld line. Conversely, specimens containing recycled core material may also experience delaminations between the core and the virgin outer plies. This suggests that thermoplastic welding can create interfaces with higher fracture toughness properties than those achieved during the consolidation of the base laminates.

Cylindrical shells are common structural elements in the aerospace sector due to their high load-carrying capacity per unit weight. Cutouts may, however, significantly reduce this load-carrying capacity, especially when cylindrical shells buckle under axial compression. Since the buckling load is often a crucial design parameter, it is important to predict this value efficiently. Hence, a procedure to rapidly calculate the linear buckling load of axially compressed quasi-isotropic composite cylindrical shells with circular cutouts was derived. After minimizing the total potential energy of the structure with the Ritz method, the buckling loads were obtained as the solutions to an eigenvalue problem. Comparing these predictions with the results from linear and nonlinear finite element analyses shows that the analytical buckling loads follow the general trends of the numerical solutions and are calculated orders of magnitude faster. This makes the approach suitable for preliminary design where many design permutations must be evaluated in a short period of time.