Fatigue Properties of Electro-Active Papers for Biomimetic Actuators

Abstract

Cellulose-based Electro-Active Papers (EAPap) have been studied as potential actuators as a result of their low voltage operation, light weight, and low power consumption. In addition, they are bio-degradable and potentially inexpensive.1 The construction of many EAPap electromechanical actuators has been based on cellulose paper film coated with thin electrode layers. This EAPap actuator has shown a reversible and reproducible bending movement as well as longitudinal displacement under low voltage alternating current. However, the EAPap is a complex anisotropic material, which has not been extensively characterized and additional basic and design testing is required before developing EAPap application and devices. It is important to know the extended fatigue and elastic properties of EAPap materials, and this requires testing and evaluation. It has been known that the cellulose based EAPap has two distinct elastic constants connected by a bifurcation point along the stress strain diagram.2 The initial Young’s modulus of EAPap is in the range of 5-8GPa, - quite high compared to other polymer materials.3 Since these materials are anisotropic, elastic properties also differ as a function of orientation. These materials are sensitive to humidity and temperature. Fatigue tests conducted and described in this paper identify critical properties of this under-analyzed class of materials to provide a measure of its fatigue capabilities. Mechanical strain of EAPap materials has been evaluated, and it appears to follow closely a linear creep model as confirmed by low frequency cyclic (fatigue) loading. The creep parameter has also been determined to be a function of temperature and load level for all the EAPap materials tested.