Twisters: An analogy of bilayers for twisting

Benders, such as bilayers, are well-known shape-changing structures which bend upon activation by a stimulus, such as temperature. The objective of this contribution is to propose new shape-changing rod-like structures, referred to as twisters, which twist upon activation. A simple biomimetic design principle based on symmetry considerations is proposed. FEM simulations show that the proposed design does feature a twisting instability in reaction to an increasing stimulus. A simpler generic mechanical model with two state variables, whose kinematics is inspired from the FEM simulations, is then proposed and its governing equations are derived analytically. As in the FEM simulations, such twisters are shown to first stretch as the stimulus increases until a bifurcation is reached, then, they undergo a mixed stretching–twisting regime. An accurate approximation of the bifurcation point is derived and serves as a guideline for the design of twisters in accordance with chosen specifications. Results are illustrated using twisters with three different behaviours.