Summary of the POSICOSS project

In order to substantially reduce weight of aircraft without prejudice to costs and safety, increased use of advanced fibre composites for primary structures and exploitation of all structural reserves are indispensable. An actual demand emphasized by industry in this respect is to design fibre composite fuselage structures for postbuckling under ultimate load. For realizing this economically, improved simulation tools and new design procedures for stiffened panels are needed; as yet the calculations were extremely time consuming. The POSICOSS project developed fast and reliable procedures ready for industrial application, which reduce design and analysis time by an order of magnitude and thus constitute an indispensable contribution to concurrent engineering. This substantially reduces weight, increases life, reduces response-to-market time and creates jobs in industry. Fuel consumption and air pollution decrease, raw material and fossil energy resources are conserved. The work was divided into six technical packages:

• Benchmarking for postbuckling and collapse analysis. Knowledge of the partners was assembled and compared, and the actual deficiencies of existing software and benchmarks were identified.
  
• Design of stiffened fibre composite verification structures. Material properties were characterized, test structures were designed as to the requirements of research in order to overcome the deficiencies.
  
• Manufacture, characterization and testing of verification structures. The data base for evaluation of improved simulation procedures was extended by testing the verification structures.
  
• Development of improved simulation procedures and preliminary design guidelines. Improved simulation procedures were developed and their validation was based on exploitation of the extended data base. Preliminary design guidelines were derived by parametric studies.
  
• Design, manufacture and testing of fibre composite industrial panels. They were made according to the requirements of industrial application.
  
• Development of final design guidelines for stiffened fibre composite curved panels. Improved simulation procedures and preliminary design guidelines were reconsidered as to test results of the industrial panels. Based on this, final design guidelines were derived.
  

Industrial partners contributed experience with design and manufacture of real shells, research partners complementarily brought in mainly knowledge on testing and on development of simulation tools. Results were checked by industry, final design guidelines were defined in common. Practical and theoretical disciplines were closely combined, and experience from four states was exchanged and exploited together. The European cohesion benefits through inclusion of three partners from associated states (Israel, Latvia).

The results comprise substantially increased experimental data bases on material properties and postbuckling as well as fast, reliable software and design guidelines. Close interaction between industry and research, a Users Group with SMEs, and a multitude of publications based on POSICOSS work make sure their dissemination and exploitation.

It is well-known that thin-walled structures made of carbon fibre reinforced plastics are able to tolerate repeated buckling without any change in their buckling behavior. However, it has to be found out, how far loading can go into the postbuckling regime, because structural degradation might happen, and consequently not only the geometrical nonlinearity as dealt with in POSICOSS has to be considered, but also the onset of degradation and its effect on collapse. Prediction on this by fast and precise simulation procedures will be the main topic of the POSICOSS follower project COCOMAT.