Saddle-shaped, bistable morphing panel with shape memory alloy spring actuator

Bistable structures are attractive morphing components because they can transform from one stable state to another simply through the application of an external force or moment. Each stable state is preserved despite the absence of a continuous energy supply. However, its competency is quite limited because most bistable composites (unsymmetric laminated bistable composites) have limited equilibrium shape configurations after curing. Most of them are cylindrical in shape. In this paper, for the first time, we present a saddle-shaped bistable panel that can be used for various soft-morphing applications. The mechanics of the saddle-shaped, bistable panel are investigated using the Rayleigh-Ritz approximation. A simple analytical model is proposed to obtain saddle bistability and deformations. Finite element (FE) numerical analysis is also performed to validate the analytical model approach. The numerical FE analysis shows good correlation with simple analytical solutions. Furthermore, for practical, smart-structure applications of the saddle-shaped bistable panel, the FE method simulated a snap-through action induced by a shape memory alloy (SMA) spring actuator. A simple design criterion for the snap-through action of a saddle composite panel actuated by an SMA spring component is suggested, based on the FE analysis.