An experimentally validated model of a dielectric elastomer bending actuator

Abstract

This paper presents an experimentally validated, nonlinear finite element model capable of predicting the blocked force produced by Dielectric Elastomer Minimum Energy Structure (DEMES) bending actuators. DEMES consist of pre-stretched dielectric elastomer (DE) films bonded to thin frames, the complex collapse of which can produce useful bending actuation. Key advantages of DEMES include the ability to be fabricated in-plane, and the elimination of bulky pre-stretch supports which are often found in other DE devices. Triangular DEMES with 3 different pre-stretch ratios were fabricated. Six DEMES at each stretch ratio combination were built to quantify experimental scatter which was significant due to the highly sensitive nature of the erect DEMES equilibrium point. The best actuators produced approximately 10mN blocked force at 2500V. We integrate an Arruda-Boyce model incorporating viscoelastic effects with the Proney series to describe the stress-strain response of the elastomer, and a Neo-Hookean model to describe the frame. Maxwell pressure was simulated using a constant thickness approximation and an isotropic membrane permittivity was calculated for the stress state of the DEMES membrane. Experimental data was compared with the model and gave reasonable correlation. The model tended to underestimate the blocked force due to a constant thickness assumption during the application of Maxwell stress. The spread due to dielectric constant variance is also presented and compared with the spread of experimental scatter in the results.