Self-stress analysis and design of the Core-Expander tensegrity family

V-Expander tensegrity structures are lightweight and easily assembled modular structures originally put forward by Raducanu and Motro that, owing to their versatility, have been investigated regarding their morphology, load-carrying properties, and static and dynamic actuation. This study presents a novel tensegrity family, named Core-Expander, obtained as a morphological variation of the V-Expander family. Core-Expanders are Class-3 tensegrities that enable a large internal space of the tensegrity cell to be utilized while preserving the features of modularity, achirality, and absence of internal mechanisms that are typical of V-Expanders. After detailing the topology and connectivity of Core-Expander cells, a procedure to design the self-stress state of the structure, accounting for the unilateral behavior of the elements and the symmetry properties of the cell, is described. Such a procedure was employed to perform a parametric analysis in terms of the axial and radial aspect ratios and the complexity parameter. The results of the analysis were verified by finite element simulations carried out in a regime of small elongations and large displacements, by considering cells with different complexities. The feasibility of the Core-Expander was verified by assembling a physical model with additively manufactured elements. The findings of this work can be applied to the design of single cells and modular assemblies.