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 the fiber angle and 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-thickness coupling due to the volumetric relation between tow shearing and the tow 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 realize 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 imperfections before and during the tests. Finally, we discuss outstanding challenges in designing and manufacturing RTS cylinders for primary aerostructures.