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Improved Material Exploitation at Safe Design of Composite Airframe Structures by Accurate Simulation of Collapse

Final Report Summary - COCOMAT (Improved material exploitation at safe design of composite airframe structures by accurate simulation of collapse)

The EU project COCOMAT was a Specific Targeted Research Project (STREP) funded under the Sixth Framework Programme (FP6). COCOMAT aimed to exploit considerable reserves in the capacities of composite aircraft panels by accurate simulation of collapse. The main objective of COCOMAT was a future design scenario for composite curved stiffened panels which are understood as parts of real aircraft structures. The project results comprised of an experimental data base, improved slow certification tools, fast design tools as well as design guidelines.

European aircraft industry demands for reduced development and operating costs, by 20 % and 50 % in the short and long term, respectively. The COCOMAT project contributed to this aim by reducing structural weight at safe design; it exploits considerable reserves in primary fibre composite fuselage structures by accurate and reliable simulation of collapse. Collapse is specified by that point of the load-shortening curve where a sharp decrease occurs thus limiting the load carrying capacity.

COCOMAT was fully based upon the results of the finished Fifth Framework Programme (FP5) project 'Improved postbuckling simulation for design of fibre composite stiffened fuselage structures' (POSICOSS) which developed improved, fast and reliable procedures for buckling and post-buckling analysis of fibre composite stiffened panels of future fuselage structures, created experimental data bases and derived design guidelines.

The COCOMAT project extended the POSICOSS results and goes beyond by accounting for degradation. That requires knowing about degradation due to static as well as low cycle loading in the post-buckling range. 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 behaviour. However, it has to be found out, how deep into the post-buckling regime one can go without severely damaging the structure, and how this can be predicted by fast and precise simulation procedures. This issue was dealt with by COCOMAT.

The partners cooperated in the following six technical work packages (WPs):
- Benchmarking on collapse analysis of undamaged and damaged panels with existing tools: Knowledge of the partners is compared and the deficiencies of existing software are identified.
- Material characterisation, degradation investigation and design of panels for static and cyclic tests: Material properties are characterised, degradation models are developed and test panels are designed as to the requirements of research in order to overcome the deficiencies.
- Development of improved simulation procedures for collapse: Slow certification and fast design tools are developed and validated by the tests.
- Manufacture, inspection and testing by static and cyclic loading of undamaged panels: The experimental data base is extended by testing of undamaged panels.
- Manufacture, inspection and testing by static and cyclic loading of pre-damaged panels: The experimental data base is extended by testing of pre-damaged panels.
- Design guidelines and industrial validation: All project results are assembled and final design guidelines are derived. The tools are validated by the industrial partners.

Industrial partners bring in their experience with design and manufacture of real shells; research partners contribute knowledge on testing and on development of simulation tools. Design guidelines are defined in common, and the developed tools are validated by the industrial partners.

The conference and the COCOMAT workshop (3-5 September 2008) were primarily organised as the final events of the project COCOMAT demonstrating its results to that date.

Behaviour of composite laminated shell structures was presented in terms of:
- experimental methods and results;
- degradation models;
- failure criteria;
- advanced finite element tools for certification;
- fast design tools;
- influence of imperfections;
- structural optimisation;
- design guidelines

The scientific community and industry in general were invited to attend. Both events aimed to promote discussion and an exchange of information between scientists and engineers in the field of buckling, post-buckling and collapse behaviour of composite structures. The conference aimed at presenting scientific achievements from the COCOMAT project. In addition, papers with recent results on the same topic but from outside the project were as well presented. Within the workshop new fast design tools and improved commercial tools, developed by COCOMAT, were demonstrated.

More information on the project can be found at the project's website, at:

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