Anisotropic Bistable Electroactive Polymers: Large Strain Actuation of Shape Memory Polymers

Abstract

In this paper, constitutive equations to model the electromechanical behavior of shape memory polymers (SMPs) are introduced for the first time. SMPs are unique material that can be transformed into complicated shapes and recover their original shapes even under large deformations [1]. Above their transition temperature, elastic modulus decreases and they can be easily deformed by mechanical or electrical input. Advantage of this behavior is returning to the deformed shape utilizing a triggering temperature without any applied forces. This can be used to actuate the electroactive polymer to restore the deformed shape without applying an electric field [2]. Therefore in this paper, the equibiaxial extension of two different SMPs (PTBA (poly(tert-butylacrylate)) [2] and Sylgard (Sylgard 184)/PCL (poly(ε-caprolactone)) composite [3]) is simulated numerically to demonstrate the electromechanical behavior with respect to mechanical and electromechanical inputs. For simplification, the response of the SMP above the transition temperature is considered, so that material properties are constant and not a function of temperature. The SMPs are considered a fiber-reinforced membrane with two families of fibers, which enable to tune the material properties of SMPs [3]. To describe the constitutive relation of the SMPs, Mooney-Rivlin and Ogden model for isotropic SMPs, as well as Gasser et al model [4] for anisotropic SMPs, are applied. In the numerical computations, the isotropic and anisotropic electromechanical response of PTBA and Sylgard/PCL composite are presented. PTBA shows larger electromechanical effect in the range of stretch 1.5–2.5. Additionally, the effects of the fiber stiffness, angle, and dispersion on the deformation of the SMPs are observed. According to the result, the fiber stiffness can significantly affect on the electromechanical response and fiber angle and dispersion can influence the anisotropic deformation.