Design, Optimization, and Evaluation of Integrally Stiffened Al-7050 Panel with Curved Stiffeners

A curvilinear stiffened panel was designed, manufactured, and tested at the NASA Langley Research Center in the Combined Load Test Fixture. The panel was optimized for minimum mass subjected to constraints on buckling load, yielding, and crippling or local stiffener failure using a new analysis tool named EBF3PanelOpt. The panel was designed for a combined compression-shear loading configuration that is a realistic load case for a typical aircraft wing panel. The panel was loaded beyond buckling and strains and out-of-plane displacements were extracted from a total of 32 strain gages and 5 linear variable displacement transducers. The VIC-3D system was utilized to obtain full field displacements/strains in the lower half of the stiffened side of the panel. The experimental data were compared with the strains and out-of-plane deflections from a high fidelity nonlinear finite element analysis. The experimental data were also compared with linear elastic finite element results of the panel/test-fixture assembly. The numerical results indicated that the panel buckles at the linearly elastic buckling eigenvalue predicted for the panel/test-fixture assembly. The out-of-plane displacement measured by the VIC-3D system compared well both qualitatively and quantitatively with the nonlinear finite element solution in the post-buckling regime. Furthermore, the experimental strains prior to buckling compared well with both the linear and nonlinear finite element model. For the post-buckling regime, the nonlinear model compared well at some locations and poorly at others.