Buckling analysis of sandwich composite cylindrical-conical shells

Abstract

Cylindrical shells and conical shells have been analysed and tested separately for the last decade. However, due to new manufacturing techniques and the use of composite material systems more complex structures can be made. By combining a cylindrical shell and a conical shell one structural component can be created: a cylindrical-conical shell. This is a potential design solution for launch vehicle structures, but there is limited research available about it. Not much is known about the buckling behavior or imperfection sensitivity of these structures, especially not for sandwich composite shells. The objective of this research is to understand these two phenomena in cylindrical-conical structures, considering a sandwich composite. The buckling behavior is studied by using finite element analysis and the behavior of the individual shells are compared to the combined structure. Different shell geometries such as height of the cone, angle of the cone, and radius of curvature at the transition are considered. The imperfection sensitivity of the different shells is investigated by adding axisymmetric and eigenmode imperfections using different amplitudes. The results indicate that the buckling behavior of the individual components without initial imperfections can be captured by the linear eigenvalue analysis as well as by a postbuckling analysis using a dynamic implicit solver with non-linear geometry enabled. In case of the cylindrical-conical shell, the linear eigenvalue analysis is not able to capture the buckling shape and results in an overpredicted buckling load. This can be explained by the non-linear behavior at the transition area before buckling that can be observed in the dynamic implicit analysis. This non-linear behavior before buckling is mitigated when a reinforcement or radius of curvature is added to the cylinder to cone transition region. A similar sensitivity to geometrical imperfections is observed for the cylindrical shell and conical shell. The cylindrical-conical shell has a much lower sensitivity, because the non-linear behavior at the transition region is dominating the buckling behavior of the whole structure. The results obtained from the thesis show the importance of the non-linear behavior at the transition for the sandwich composite cylindrical-conical shell. This means that for further research it is important that the non-linear effects are included when analysing such a structure.