Buckling analysis of an imperfection-insensitive hybrid composite cylinder under axial compression - numerical simulation, destructive and non-destructive experimental testing

Thin-walled shells like cylinders are primary structures in launch-vehicle systems. When subjected to axial loading these shells are prone to buckling. The corresponding critical load heavily depends on deviations from the ideal shell shape. In general, these deviations are defined as geometric imperfections and although imperfections exhibit comparatively low amplitudes, they can significantly reduce the critical load. Considering the influence of geometric imperfections adequately into the design process of thin-walled shells poses major challenges for structural design. An alternative to robust design of thin-walled shell by accurate consideration of geometric imperfections is the development of a robust or imperfection-insensitive shell architecture. In this article a special hybrid cylinder is presented and analyzed. The composite shell design is based on an interstage structure of the Ariane 6 by MT Aerospace and has special CFRP belts which are intended to reduce the imperfection sensitivity of the shell. The shell was tested at the German Aerospace Center in Braunschweig and the corresponding results are presented and described. The hybrid cylinder was analyzed with the Southwell-method and geometrically nonlinear finite element analyzes. The results show that the Southwell-method delivers conservative buckling load estimations and that the CFRP belts reduce the imperfection sensitivity significantly.