This paper presents a modular, assemblable mortice-and-tenon load-bearing structure with variable stiffness, driven by embedded electrically controlled shape memory alloy (SMA) wires functioning as tendons within a tensegrity system. The study addresses three key aspects: modular design, topology optimisation of tree-like configurations, and active stiffness control through voltage-regulated contraction of the SMA wires. A variable stiffness component utilising the shape memory effect of SMA is proposed. In each unit, electrically controlled SMA wires serve as tendons and are connected via universal joints, enabling two-degree-of-freedom rotation. By coordinating the contraction of multiple SMA wires, both the stiffness and spatial orientation of the module can be adjusted, facilitating stiffness-tunable control across various spatial configurations. Geometric and mechanical theoretical models are established for the variable stiffness components and topological configurations. Experimental results validate the geometric models and confirm the effectiveness of the stiffness modulation. This work presents a design methodology for assemblable mortice-and-tenon variable stiffness structures actuated by embedded SMA wires. The proposed approach offers an efficient means for active stiffness–flexibility transformation and holds promise for applications such as flexible robotic joints and intelligent suspension systems.
Yuan et al. (Sun,) studied this question.