Design, modeling, optimization, manufacturing and testing of variable-angle filament-wound cylinders

This work demonstrates the potential of manufacturing variable-angle composite cylinders via filament winding (FW), called VAFW. The proposed design strategy allows different filament angles along the axial direction by dividing the cylinder into regions of constant angle called frames. Designs using two, four, or eight frames are herein investigated. A genetic algorithm is applied to optimize each design for maximum axial buckling load. A design with minimum manufacturable filament angle is included in the study. All structures are manufactured and tested under axial compression, with displacements and strains measured by digital image correlation (DIC). The thickness and mid-surface imperfections of the different designs are measured through DIC and used to explain the observed buckling mechanisms. These imperfections are incorporated into a nonlinear numerical model along with a progressive damage analysis. Additionally, a scaling factor is applied on the measured imperfections to enable an imperfection sensitivity study on the proposed designs. The VAFW design shows buckling strength, stiffness, and absorbed energy substantially higher than the constant-angle configuration, attributed to tailored thickness buildup and optimized tow steered angles at particular regions of the cylinder. The experimental and numerical results indicate that VAFW designs can be tailored to postpone buckling so that the material strength can be better exploited.