Manufacture and Buckling Test of a Variable-Stiffness, Variable-Thickness Composite Cylinder Under Axial Compression

Variable-angle tow (VAT) manufacturing methods significantly increase the design space for elastic tailoring of composite structures by smoothly changing fiber angle and ply thickness across a component. Rapid tow shearing (RTS) is a VAT manufacturing technique that uses in-plane shearing (rather than in-plane bending) to steer tows of dry or pre-impregnated fibers. RTS offers a number of benefits over conventional bending-driven steering processes, including tessellation of adjacent tow courses; no overlaps or gaps between tows; and no fiber wrinkling or bridging. Further to this, RTS offers an additional design variable: fiber orientation to tow thickness coupling due to the volumetric relation between tow shearing and the tow's thickness and width. Previous computational work has shown that through a judicious choice of curvilinear fiber trajectories along a cylinder's length and across its circumference, the imperfection sensitivity of cylindrical shells under axial compression can be reduced and load-carrying capacity increased. The present work aims to verify these predictions by manufacturing and testing two cylinders: an RTS cylinder and a straight-fiber, quasi-isotropic cylinder as a benchmark. The tow-steered manufacturing process, imperfection measurements, instrumentation, and buckling tests of both cylinders are discussed herein. The experimental tests results are compared against high-fidelity geometrically nonlinear finite element models that include measured geometric and loading imperfections before and during the tests. Finally, a discussion is provided on the outstanding challenges in designing and manufacturing RTS cylinders for primary aerostructures.

Automated summary

Variable-angle tow (VAT) manufacturing methods, such as rapid tow shearing (RTS), greatly enhance the design possibilities for composite structures by smoothly changing fiber angle and ply thickness. RTS offers numerous advantages over conventional bending-driven steering processes, including improved tessellation, elimination of overlaps or gaps between tows, and prevention of fiber wrinkling or bridging. This study aims to validate previous predictions on the imperfection sensitivity reduction and increased load-carrying capacity of cylindrical shells through the manufacturing and testing of RTS cylinders. The experimental results are compared with high-fidelity finite element models, taking into consideration the geometric and loading imperfections.