An analytical model for shape morphing through combined bending and twisting in piezo composites

Bilayer piezo macro fiber composites (MFCs) with specific fiber orientations are experimentally known to undergo bending as well as twisting, under the action of an externally applied electric field. An analytical model is developed for this shape-morphing phenomenon using continuum mechanics and energy minimization considering material anisotropy. A detailed parametric study is carried out using a coupled electro-mechanical finite element model and the results are used to validate the analytical model. The analytical model quantitatively predicts the variation of curvatures with the system parameters (bilayer geometry and electric field magnitude) with good accuracy. The tendency of a bilayer to undergo pure bending, pure twisting or a helical deformation is predicted using stress-free strain mismatch between anisotropic layers. Both bending and twisting deformations are found to be strongly dependent on the fiber orientation, vary linearly with the applied electric field magnitude, independent of length and decrease with an increase in width or thickness of MFC.