Design, analysis, manufacture, and experimental performance of hat-stiffened composite panel

In this study, design considerations, structural analysis and manufacturing techniques for hat-stiffened composite panels were investigated. The material used in this study was unidirectional carbon fibres preimpregnated with bismaleimide resin, Cytec's Rigidite 5250-4 and the carbon fibres were Hercules Corp. Magnamite continuous type IM7. A stiffened panel configuration consisting of a flat 12-ply skin and three equally spaced longitudinal hat-shaped stiffeners, having a web of 12 plies, a flange of 5 plies and a cap of 24 plies, was designed. The co-curing manufacturing technique was used to produce the stiffened composite panel and simple techniques were developed to efficiently lay up plies for stiffener elements and built-up composite structure. The panel was designed to carry loads after the initiation of skin buckling. Both the buckling and post-buckling behavior were predicted using the finite element method (NISA Code). The 3-D laminated composite general shell element was used in the modeling. A quarter of the whole panel was modeled, due to the symmetry, using a total of 864 8-node quadrilateral elements with 2566 active nodes. The panel was tested in compression to verify its structural performance. Strain and load outputs were gathered by a data acquisition system (Sciemetric System 200) and recorded by a computer. The shadow Moire technique was used to monitor buckling patterns during the test. The finite element predictions were compared with the test data and good agreement was obtained.