Launch vehicle structures are commonly composed of cylindrical and conical shells, which are inherently sensitive to buckling. The axial compression experienced during launch can consequently be a sizing load case, so it is important to understand the axial buckling behavior of these shells. Experimental testing is an essential part of studying this phenomenon because manufacturing imperfections can cause large discrepancies between theory and reality. In addition, conical shells have been researched less frequently than cylindrical shells, such that their behavior is less well understood. Experimental testing of launch vehicle structures is difficult and expensive due to their large size, hence it is preferred to test reduced-scale shells, representative of the full-scale ones. In this thesis, a scaling methodology is developed which allows designing representative reduced-scale conical shells for full-scale composite conical shells buckling in axial compression. The conical shells are assumed to have a symmetric, balanced layup with negligible flexural anisotropy. The scaling methodology is developed using the nondimensional governing equations, obtained through Nemeth's procedure, which allows to directly use the coefficients of the equations as scaling parameters. It also provides a framework to not only compare the buckling load of the shells of different sizes, but also the displacement upon buckling, the deformation shape, and the radial displacement. The methodology is set up such that the reduced-scale design parameters are determined sequentially. The buckling behavior of the two shells is compared using a semi-analytical approach, linear eigenvalue, and implicit dynamic finite element analyses. The eigenmode imperfection sensitivity is also evaluated. The methodology is successfully applied to isotropic, cross-ply, quasi-isotropic, and sandwich conical shells. The prediction accuracy is mainly affected by not being able to simultaneously satisfy all scaling parameters, by non-negligible flexural anisotropy and transverse shear, and by differences in imperfection sensitivity between the full-scale and reduced-scale shells. In any case, accurate results are obtained for the considered shells. The radial displacement is most difficult to predict, which is attributed to the membrane prebuckling assumption and neglecting the presence of imperfections. Finally, it is observed that larger eigenmode imperfections affect the accuracy, but they do not cause the methodology to fail. For future work, it is recommended to validate the methodology through experimental testing.

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...