Unflat-foldable Square-Twist origami composite structure with bistable load-bearing capability

Origami structures have attracted much attention owing to their ability to transform from flat structures to three-dimensional structures by folding, and their rich mechanical properties are of critical importance in engineering applications. Square-Twist (S-T) origami structures have typical torsional bistability mechanical characteristics, which have special applications in fields such as mechanical metamaterials and deployable antennas. However, the current research on S-T origami structures is limited to flat-foldable geometry conditions, resulting in a restricted space for their mechanical design. This work is orientated towards high load-bearing origami structures to generate modified S-T (M-S-T) origami designs and unlock their unflat-foldable geometric conditions. Bistable M-S-T origami composite structures consisting of Al₂O₃ sheet as the rigid facet, PET sheet as the facet to provide additional bending degree of freedom, and glass-fibre reinforced PET-based tape as the elastic crease are fabricated, where the corresponding structures with unflat-foldable properties are found to possess high out-of-plane load carrying capacity in the folded stable state through experiments and finite element analyses. A non-rigid origami theoretical model for the M-S-T origami structure discretised with rigid facets and torsion springs is established. Combined with the theoretical model, the key geometrical parameters' influence on the mechanical properties of the M-S-T origami structure is revealed, and a method is established to determine the real folded stable state of unflat-foldable M-S-T origami structures by combining total energy and contact distance. The design phase diagram for the composite origami structure with bistable unflat-foldable property is described. The bistable high load-bearing M-S-T origami composite structure proposed in this work features consistent load-bearing direction and deformation direction, easy transport and stable load-bearing state, which paves the way for the load-bearing origami structure to better serve the engineering.