Thermoplastic composite three-stringer panels with omega stiffeners and conduction welded joints are designed, analysed and tested until final failure to investigate the performance of the welded joint in post-buckling. The three-stringer panels are designed to be structurally representative of the fuselage demonstrator of the Clean Sky 2 project STUNNING. A simplified model of the fuselage keel section is analysed by finite element analysis, using the virtual crack closure technique to model skin-stringer separation of the welded joint. The post-buckling and skin-stringer separation behaviour of the fuselage section is then adopted as the reference for the design of the three-stringer panels. Two panels are then tested. The test setup utilises digital image correlation to measure the deformation of the panels, and a high-speed camera to capture the final failure mode. The panels failed in post-buckling due to the separation of the middle stringer, with unstable separation growth followed by separation of the outer stringers and then stringer fracture. The numerical analysis of the panels, with geometrical imperfections included, is able to predict the structural behaviour accurately, with only minor differences in buckling shape and separation behaviour.@en

A buckling analysis and imperfection sensitivity study of scaled launch-vehicle cylindrical shells have been executed. The emphasis is on scaled cylindrical shells due to the expensive nature of full scale launch-vehicle cylindrical shells and the size constraints of experimental testing equipment. The work as presented in this thesis is part of a framework of a collaboration with NASA Langley. The main objective was to investigate if a scaling method, which is developed as part of this afore mentioned collaboration, results in representative scaled cylindrical composite shells. These scaled cylindrical composite shells will be validated by experimental tests at NASA Langley. The scaling of structures can be a challenging process, as a scaled model which shows full scale representative behaviour is difficult to design due to constraints such as manufacturability. The buckling of cylindrical shells is considered to be a structural problem which is yet to be fully understood. The cylindrical shells show a high imperfection sensitivity, but the exact influence of imperfections caused by different manufacturing processes is a source of uncertainty. The thesis will focus on two scaled cylindrical shells which resulted from the scaling method, next to the full scale CTA 8.1 cylindrical shell they are based on. The CTA 8.1 is a sandwich cylindrical shell with a honeycomb core which is designed to be representative for a launch-vehicle structure. The first scaled cylindrical shell consists of a solid laminate and the second scaled cylindrical shell consists of a sandwich with foam core. A scaled solid laminate cylindrical shell is of interest, as the core thickness of a scaled sandwich cylindrical shell can become too thin to manufacture...