Robust knockdown factors for the design of cylindrical shells under axial compression: potentials, practical application and reliability analysis

This paper overviews the efforts that led to new improved knockdown factors for the design of cylindrical metal shells under axial compression. The corresponding design methods were derived by means of three step procedure involving deterministic methods for the buckling load prediction, high-fidelity experimental results and an extensive probabilistic analysis. The new design procedure is demonstrated by means of a full-scale primary launch-vehicle shell and the results show an estimated weight reduction of about 20 %. The potentials of the new design guidelines are shown and open questions regarding the influence of manufacturing specific imperfection signatures on the buckling load are addressed and design implications are derived and discussed. Dynamic load-controlled simulations with imperfection signatures for different manufacturing qualities and processes are performed and the influence of load introduction and mechanical boundary conditions on the buckling loadise studied. From the results it is concluded that the commonly used practice of displacement-controlled shell buckling experiments and numerical simulations is sufficient for conservative design of real shell applications.