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.Aerospace Structures & Computational Mechanic

Sensitivity analysis for buckling characterisation using the vibration correlation technique

The Vibration Correlation Technique (VCT) is a non-destructive method to predict buckling loads for imperfection-sensitive structures. While successfully used to validate numerical models and predict experimental buckling loads, recommendations for defining the VCT experiment are scarce. Here, its sensitivity towards the number of load steps and the maximum load level measured is studied, and an uncertainty quantification of the measured frequency affecting the VCT prediction is performed First, a series of finite element (FE) models representing nominally identical cylinders, and validated by buckling experiments, are used to perform a sensitivity study. When no frequency deviations are introduced in the FE results, a positive correlation between the VCT predictions and the maximum load used for measurements is found, the number of load steps used being only relevant in reducing the errors. Introducing frequency deviations deterred the predictions correlation with the maximum load, while using more load steps reduced this influence. Second, a sensitivity study based on experimental data confirmed most of the trends previously observed using the FE results, the exception being a poor prediction sensitivity as a function of the maximum load, owing to several cylinders for which the VCT method gave predictions that progressively decreased with increasing the load.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerospace Structures & Computational Mechanic