Experiments to Detect Damage Progression in Axially Compressed CFRP Panels under Cyclic Loading

The aircraft industry strives for significantly reduced development and operating costs. Reduction of structural weight at safe design is one possibility to reach this objective which is aimed by the running EU project COCOMAT. The main objective of COCOMAT is a future design scenario for composite curved stiffened panels which are understood as parts of real aircraft structures. This design scenario exploits considerable reserve carrying capacities in fibre composite fuselage structures by accurate simulation of collapse. The project results will comprise an experimental data base, improved slow and fast computational tools as well as design guidelines. A reliable simulation of the collapse load requires also taking degradation into account. For the validation of the tools a sound database of experiments are needed which give information about the progress of damage during the loading process. This paper focuses on experimental results of four nominally identical CFRP panels tested within the COCOMAT project at the buckling test facility of the Institute of Composite Structures and Adaptive Systems (DLR). In a first step, three of the four panels were loaded several thousand times. Each time the panel was loaded beyond global buckling and was unloaded to zero. Finally, all panels were tested until collapse. During the tests, advanced measurement systems such as High-Speed-ARAMIS, thermography and Lamb-waves were applied. The test results given in this paper may be used as benchmarks.