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Stability of thin-walled composite structures

Experiment Calculation Figure 1: Out-of-plane deformation of a tested CFK-panel

Light weight structures in the aerospace, mechanical engineering or civil engineering are on the one hand under compression or shear loading susceptible for buckling but on the other hand they have large reserve capacities in the postbuckling region. In order to save weight in these fields the use of materials made of Carbon-Fibre-Reinforced-Plastics (CFRP) is increasing. However, the design and computation of composite structures is more challenging than using classic materials. Stability, non-linear computations and degradation have therefore here an essential relevance. The structural behaviour of stability and deformations is simulated by nonlinear numerical simulations and experiments. Figure 1 illustrates the comparison of an experiment and simulation of a buckled, stringer-stiffened (on the reverse side) CFRP panel. The institute has in the field of stability of thin-walled composite structures competence in the following 4 main topics: Postbuckling behaviour, Imperfection tolerance, Buckling due to dynamic loading, Thermo-mechanical buckling. The objective is to develop fast and reliable software tools in order to simulate the buckling and postbuckling behaviour up to collapse. These software tools can then be incorporated into a design process as well as to deduce simple design rules. To fulfil these tasks numerical and experimental work is essential. The experimental examination is employed to provide a better understanding of the physical behaviour of the structure and to validate the developed software tools.

Our competence:

• Postbuckling 
• Imperfection tolerance
• Dynamic buckling
• Thermal buckling

Running projects:

• COCOMAT (Co-ordinator, Improved Material Exploitation of Safe Design of Composite Structures by Accurate Simulation of Collapse, EC 6th FP)
• ALCAS (Advanced low cost Airframe Structures, EC 6th FP)
• MUSCA (Nonlinear static MUltiSCAle analysis of large aero-structures, EC 6th FP)
• Design of optimal CFRP panels for fuselage structures (DLR - China)
• Advanced Aerospace Structures (Fortschrittliche Flugzeugstrukturen, DLR - EADS)
• Composite Fuselage Demonstrator (DLR-Airbus)
• Probabilistic aspects of buckling knock down factors, Tests and analysis (ESA)
• Buckling Handbook (ESA, ECSS-E-30-24)

Some finished projects:

• IBUCK - a fast semi-analytical design tool for stiffened panels (DLR - Airbus Deutschland)
• POSICOSS (Coordinator, Improved Post-buckling Simulation for Design of Fibre Composite Stiffened Fuselage Structures, EC 5th FP)
• Robust Design (DLR - Airbus Germany)
• GARTEUR SM AG 25 (WP-leader, Postbuckling and Collapse Analysis, established recommendations for buckling, postbuckling and collapse analysis of CFRP shells)
• Globales Tragverhalten (Virtual testing of stringer and frame stiffened shells, Airbus Germany)
• Multiobjective optimisation of fibre composite structures endangered by buckling (DLR - China)
• Identification of the Stiffnesses of Stringer Stiffened Laminated Materials (DLR - China)
• Schwarzer Rumpf (Black fuselage, DLR - Airbus Deutschland)
• Buckling under dynamic loading(German - Israeli foundation)
• FESTIP (Refinement of Buckling Prediction Techniques for Large Thin Shells Under Mechanical and Thermal Load Conditions, ESA)
• Fracture Mechanics of Composites (Damage tolerance of CFRP panels and cylinders prone to buckling, ESA)
• EDAVCOS (Efficient Design and Verification of Composite Structures, EC 5th FP)
• DEVILS (Design and Validation of Imperfection-Tolerant Laminated Shell Structures, EC 4th FP)
• GARTEUR SM AG05 (Chairman, Buckling and Postbuckling Behaviour of Composite Panels)
• Composite Bulkhead (Stability investigation of an Airbus CFRP bulkhead, A340-500 and A340-600)