Geometric curvature effects-induced twisting mechanics of a double helical structure

The rapid development of aerospace technology has continuously promoted the demand for lightweight and systematic design of twisting structures, where advanced composites have drawn great expectations. A double helical structure has been developed to introduce large axial twistable capability, where thin-walled cured composite strips with a longitudinal curvature were prestressed or flattened to be employed as shape-changing units, and then assembled by using rigid spokes, pins, or webs; however, its twisting performance would be susceptible to thermal effects, and affected by the curvature variations induced by flattening and assembling of the precured curved strips. Here, we proposed a novel double helical structural design, where thin-walled curved tapes with transverse curvature were applied as the shape-changing units without prestressing. The double helical structures were produced and investigated with isotropic transverse curved tapes, orthotropic flat strips, as well as orthotropic transverse curved tapes, in order to reveal its geometric curvature effects-induced twisting mechanics. An inextensible shell model was formulated to analyse the shape-changing process, and expose the regulating mechanisms on structural stability. Experiments and finite element analysis were carried out to investigate the material and geometric curvature dependencies. It is found that the material orthotropy contributes to the bistability of the helical structure; geometric curvature promotes the stiffness and shape-changing stability of the double helix. The twisting mechanisms were then concluded in detail. These findings are expected to facilitate torsional structural design and application of deployable composite structures for aerospace engineering.