Thickness effect on electrostrictive polyurethane strain performances: A three-layer model

The electrical field requirements of Electro Active Polymer (EAP) actuators have to be lowered in order for them to be used with other electro devices. The research field on EAP expands day by day. As determined by many studies on polymeric samples, the electrostrictive strain becomes saturated when increasing the input electrical field. It was also found that the maximum strain value depends strongly on the sample thickness. A combination of the polarization saturation effect and heterogeneities in the polymer thickness led to a three-layer model that could correctly describe the strain behavior versus the electrical field as well as versus the polymer thickness. The model assumes that the polymer is not homogeneous along the thickness but presents some skin effects formed during its curing. It is considered that the characteristics of the skin layer, such as relative permittivity and Young's modulus, differ from those of the inner layer. When the electrical field is applied parallel to the polymer thickness, the outer and inner layers present varying strains. Since the layers are attached together and since only an in-plane motion is considered, the strain must be the same in each layer. Consequently, stresses appear in the layers. The obtained simulation results fit the experimental data well. Moreover, the results from the model displayed the electrical distribution in the material.