Nonlinear elastic modeling of differential expansion in trilayer conjugated polymer actuators

Conjugated polymers are promising actuation materials for biomimetic robots and biomedical devices. Large bending is involved in some of these applications. This poses significant challenges in electromechanical modeling, because the linear elasticity theory is only valid when the strain is small. In this paper an effective strategy based on the nonlinear elasticity theory is proposed to model the mechanical output of a trilayer conjugated polymer beam under actuation. Instead of using the elastic modulus as in the linear elasticity theory, we use a nonlinear strain energy function to capture the stored elastic energy under actuation-induced swelling, which further allows us to compute the induced stress. The deformation variables are obtained by numerically solving the force and bending moment balance equations simultaneously. Experimental results have demonstrated that the proposed model shows superiority over the linear model, and is able to capture the actuation behavior well under large actuation voltages. The proposed framework can also be applied to the analysis of large deformations in some other electroactive polymers.