A concept for airfoil-like active bistable twisting structures

A novel type of morphing structure capable of a large change in shape with a small energy input is discussed. The considered structures consist of two curved shells that are joined in a specific manner to form an airfoil-like structure with two stable configurations. These configurations have a difference in axial twist, and the structure can be transformed between the stable shapes by a simple snap-through action. The benefit of a bistable structure of this type is that, if the stable shapes are operational ones, power is needed only to transform the structure from one shape to another. Several composites and one steel device are considered as proof-of-concept models and active control using piezocomposite actuators is demonstrated. Finite-element analysis is used to compare the predicted shapes with the experimental shapes, and to study how changes to the geometric input values affect the shape and operational characteristics of the structures. An interesting method for combining both continuous shape change with the bistable behavior is discussed.