CYCLIC BUCKLING UNDER COMBINED LOADS OF COMPOSITE PANELS H. Abramovich Technion, Faculty of Aerospace Engineering, Technion City, 32000, Haifa, Israel E-mail: haim@aerodyne.technion.ac.il C. Bisagni and P. Cordisco Politecnico di Milano, Dipartimento di Ingegneria Aerospaziale, Via La Masa 34, 20156, Milan, Italy E-mail: chiara.bisagni@polimi.it , potito.cordisco@polimi.it SUMMARY Experimental results obtained on CFRP panels subjected to static and cyclic combined loadings in compression and shear are presented. Some of the panels present pre- damaged areas in correspondence of the stringers. Results show that this kind of structures, even with pre-damages, can well work under cyclic post-buckling loads. Keywords: Cyclic buckling, post-buckling field, CFRP panels INTRODUCTION Fibre reinforced composites are an important class of engineering materials due to their high specific mechanical properties. Unlike isotropic materials, they offer a not well- known behaviour in the post-buckling field, 1,2 especially when the buckling load is reached thousands of times during the operative life. Indeed, in literature, very few results 3 are available on how cyclic buckling under combined loading influences the non-linear behaviour of CFRP aeronautical panels and their collapse. This leads to the necessity to conduct an intensive investigation of the damage onset in composite structures subjected to different load conditions. Some results obtained during the COCOMAT European project 4 on stringer stiffened composite panels subjected to static and cyclic buckling under combined compression and shear loading are here presented. In particular, the first part of present paper summarizes the results obtained on two undamaged panels, assembled in close box configuration and loaded under several combination of axial compression and shear. The second part of the paper resumes the results obtained on two pre-damaged panels individually loaded under axial compression. The idea behind the closed box configuration is that in this way it is possible to load each panel under shear by applying a torque on the whole box 5 . Besides, both static and cyclic loads are investigated.