Stacking-sequence optimization of composite delta wing to improve flutter limit using fractal branch and bound method

Abstract

The authors developed a fractal branch and bound method for optimization of stacking sequences of laminated composites to maximize buckling load of composite structures. The method demands an approximation of a design space with a response surface comprising quadratic polynomials for pruning branches of stacking sequences. Approximation of the objective function with quadratic polynomials has been confirmed for buckling load maximizations and panel-flutter-speed-limit maximizations using lamination parameters as predictors. Flutter speed maximization of composite delta wing is employed in this study as an example of stacking-sequence optimization using the fractal branch and bound method. This paper describes the theoretical background of the fractal branch and bound method. Then approximations are performed using quadratic polynomials with lamination parameters as predictors. Subsequently, we investigated effectiveness of this method for supersonic flutter of a composite delta wing. Results indicate that the method was applied successfully; a practical optimal stacking-sequence was obtained using modified response surfaces.