Design of variable stiffness composites for maximum fundamental frequency considering manufacturing constraints of tow steering

In this study, an in-house finite element approach is developed to optimize fundamental frequency of variable stiffness composites considering manufacturing constraints of tow steering process. The method uses the lamination parameters as the design variables. Tow angles or fiber angles and their stacking sequence are computed from the optimum lamination parameters by direct search method. The Least-Squares and Continuity (LSC) method is applied to maintain the fiber or tow continuity within a prescribed curvature limit for manufacturability. Finally the discrete fiber angles or tow directions were converted into paths by using stream functions to have continuous manufacturable paths. The results of the method were compared to various literature findings for constant, balanced variable, and general variable stiffness designs for different boundary conditions, aspect ratios, and material properties. The optimum lamination parameter distributions were in good agreement with literature findings. The fundamental frequency improvements up to 11.9% and 10.2% were computed by the LSC method with respect to the optimum constant stiffness results for fully simply-supported and fully clamped cases, respectively.