C2.1 "Paolo Santini Memorial Lecture" - Buckling of Composite Structures
Symposium: C2. IAF MATERIALS AND STRUCTURES SYMPOSIUM
Session: 1. Space Structures I Design, Development and Verification (Launch Vehicles and Space Vehicles, including their Mechanical/Thermal/ Fluidic Systems)
Day: Monday 5 October 2026
Time: 16:30 GMT+3
Room: E7
For thin-walled structures buckling is often the design criterion. Stringer-dominant structures as typically used in aerospace show significant post-buckling behaviour. For metallic structures this area is already fully exploited in the design. For composites materials industry is allowing this in the design not to the full extent yet due to the more complex damage behaviour. Unstiffened or skin-dominant structures as used more in space applications do not have relevant post-buckling area and show a very high imperfection sensitivity. The NASA-SP 8007 allows safe design; however, the knock-down factors are very conservative. Using composite materials with appropriate lay-ups allows not only lighter structures but promises less conservative know-down factors. This paper summarizes recent achievements in the field of buckling of composite thin-walled structures and gives 2 more detailed examples. The first is a fast Ritz-method and the second is a non-destructive buckling estimation in the experiment by the vibration-correlation-technique.
Fast simulation of unstiffened cylindrical and conical composite structures
New designs require - especially for composite materials - very high computational effort. Fast tools which are significant faster than FEM-tools are needed. A semi-analytical method based on the Ritz-approach capable to predict the static and the instability response of the non-linear buckling of unstiffened laminated composite cones and cylinders under various loads and boundary conditions is presented. The tool considers geometric and load imperfections. The Ritz method is selected to solve the non-linear set of equations and a new set of appropriate approximation functions for the displacement field is proposed, in order to simulate axial compression, torsion, pressure, load asymmetry, any arbitrary surface or concentrated loads, and any load case combining these loads.
Non-destructive prediction of the buckling load by vibrations
The Vibration Correlation Technique (VCT) allows a non-destructive prediction of the buckling load in the experiment. It is based on the relation that the eigenfrequency becomes smaller under the increase of the axial compression and in the case of the bucking the eigenfrequency is zero. For beams the analytical relationship is linear. For shells the relation is due to the imperfection sensitivity nonlinear, however, an empirical relation was developed and later also analytically proved. During the experiment eigenfrequencies are measured during loading. The relation between them allows a prediction of the real buckling load in the experiment. VCT was demonstrated on academic and also industrial level. Recent developments focused on combined loading, loading imperfections, sensitivities and also consideration of damaged structures. The paper summarizes the benefits and limitations of VCT.