Improved Exploitation of Composite Airframe Structures by Accurate Simulation of Collapse – The COCOMAT project

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Supported by the European Commission the project COCOMAT, which started in January 2004 and was finished October 2008, contributes to this aim. COCOMAT stands for Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures by Accurate Simulation of Collapse. The project was co-ordinated by DLR, Institute of Composite Structures and Adaptive Systems. It aims at allowing for a structural weight reduction by exploiting considerable reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse (cf. Figure 1). The paper presents the main objectives of the project COCOMAT and gives an overview about major results. The COCOMAT project developed improved, fast and reliable procedures for buckling and postbuckling and collapse analysis of fibre composite stiffened panels of future fuselage structures. That requires knowing about degradation due to static as well as low cycle loading in the postbuckling 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 postbuckling regime the loading can be extended without severely damaging the structure, and how the behaviour can be predicted by fast and precise simulation procedures. This issue is dealt with by COCOMAT. COCOMAT improved existing slow and fast simulation tools and set up design guidelines for stiffened panels taking skin stringer separation and material degradation into account. Reliable fast tools allow for an economic design process, whereas very accurate but necessarily slow tools are required for the final certification. The project results comprise a substantially extended data base on material properties and on collapse of undamaged and predamaged structures subjected to static and low cycle loading, degradation models, improved slow and fast computation tools as well as design guidelines. More details can be found at www.cocomat.de