Achievements in the buckling of thin-walled composite launcher structures

For most structural parts of real launcher structures buckling is the critical design criterion. Due to the high imperfection sensitivity of these structures and to the unknown geometric imperfections during the design phase, it is still today a challenge to predict a reliable design buckling load and to experimentally and non-destructively evaluate the load carrying capacity of real structures. The space industry is looking for new and alternative less-conservative design methods, and non-destructive experimental strategies. This paper presents a summary of different examples to numerically and experimentally predict the buckling load of imperfection sensitive structures. The numerical strategies herein covered are based on the fast Ritz-method, developed for conical and cylindrical structures applicable for linear and non-linear buckling, and static calculations. The experimental examples are all based on the non-destructive buckling estimation enabled by means of the Vibration Correlation Technique (VCT). An overview of experiments on different types of cylindrical shells (unstiffened, stringer-stiffened and grid) with different materials (composite and metallic) and for different load cases and their combination (axial compression, internal pressure and bending) is presented. The examples are on academic laboratory level and on qualification tests of real full-scale space structures.