Towards the realization of composite metastructures: A failure analysis of connections

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Metastructures hold significant potential for applications such as adaptive structures and soft robotics. Architectures of fiber-reinforced polymer metastructures may relate to modular arrangement of straight and curved laminates, with their connections to resemble perfect cracks, thus susceptible to delamination. This study investigated geometrical effects on the load-carrying capabilities of these connections upon a global tensile deformation, as well as lean modeling tools to facilitate the development of architected composite metastructures. Numerical fracture mechanics approach on different connection geometries and thicknesses showed that connection delamination is a critical failure mode, but crack-driving-force has low dependence on connection shape for given ligament thickness (and stiffness). Adopted analytical models could capture either moment or force-driven delamination failure, while the intermediate regime necessitates numerical tools. First-ply failure may precede depending on shape and ligament stiffness. These trends were also verified on an exemplary rotating chiral composite geometry. Furthermore, interface load-carrying capability improvements were studied via design considerations including connection filler material and element variable thickness. Indicatively, the latter showed a 157 % increase in bending deflection (and global deformations), while reducing crack driving force by 38 % for a given load case. The conducted analysis offers valuable insights into the design of lightweight, load-carrying composite metastructures.