DESIGN OF A BLADE-STIFFENED COMPOSITE PANEL WITH A HOLE

The results of a structural design and optimization study for a minimum weight design of a compression-loaded blade-stiffened composite panel with a centrally located hole are presented. The design variables are ply thicknesses in the skin and stiffener laminates and the stiffener height. Constraints are imposed on the buckling load on the maximum strain near the hole. The optimization procedure is based on simultaneous use of the PASCO panel buckling analysis and sizing code together with the Engineering Analysis Language finite-element analysis code EAL. PASCO performs the buckling analysis using linked plate elements to model stiffened panels. EAL is used to calculate the maximum strains around the hole boundary and their derivatives with respect to the design variables. These derivatives are used to construct a linear approximation to the maximum strain constraint, and this constraint approximation is enforced in PASCO as a side constraint in addition to the buckling constraint. The PASCO optimum design is then used to update the skin and stiffener ply thicknesses and the stiffener height of the EAL model, and to construct a new linear approximation to the maximum strain. This procedure is repeated until convergence to the optimum design is obtained. The thicknesses of the final design are rounded up to an integral number of plies. The procedure is used to evaluate the relative efficiencies of soft-skin and stiff-skin designs. Results of experiments conducted to validate some of the analytical predictions are also presented.