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On the Loss of Ellipticity in Electroactive Polymer Composites
Stephan Rudykh
Ben-Gurion University
P.O.B. 653, Department of Mechanical Engineering, Beer Sheva, 84105, IL
Phone: 97286477046, Email: rudykh@bgu.ac.il
Gal deBotton
Ben Gurion University, Beer Sheva, Israel
Kaushik Bhattacharya
California Institute of Technology, Pasadena, CA
Abstract:
Electroactive polymers (EAP) are soft dielectrics that change their shape and size in response to electric
excitation. Various applications of EAP actuators have been considered in recent years [1, 2]. In this
study, the behavior of homogeneous and periodic composite EAPs under coupled electromechanical
boundary conditions in finite deformations is investigated with emphasis on the important aspect of
instabilities phenomena.
First, we examine pure mechanical instabilities that may develop in fiber composites and detect
the associated critical stretch ratios. In particular, we focus on macroscopic instabilities that are
associated with long waves and considered as loss of ellipticity of the homogenized governing
equations. Analytical estimations of the onset of ellipticity loss are given by making use of a new
effective energy-density function for Gent fiber composites [3]. This model enables to capture the wellknown
"lock-up" effect of polymer molecular extensibility limit. The analytical estimations are
compared with both 2D and 3D finite element simulations. For the 2D case the representative unit cell
is a laminated structure. In the spatial case, we examine the responses of composites with periodic
hexagonal unit cell [3]. It is demonstrated that the analytical estimations for the onset of failure are in
fine agreement with the corresponding numerical results.
In the coupled electromechanical problems, instabilities may arise from geometry of a particular
application, from material properties, or from a composite microstructure. These instabilities may be
utilized as triggers for shifting actuators from one configuration to another. In other words, a relatively
small value of electric excitation may lead to a significant actuation. Theoretical and numerical
examples are considered.
REFERENCES:
[1] K.Bhattacharya, J. Y. Li, and Y. Xiao, in Electroactive Polymer(EAP) Actuators as Artificial
Muscles, edited by Y. Bar-Cohen (SPIE press, 2001) Chap. 12, pp. 309-330.
[2] S.M. Ha, W. Yuan, Q.B. Pei, R. Pelrine, S. Stanford, Interpenetrating polymer networks for highperformance
electroelastomer artificial muscles, Advanced Materials 18, pp. 887-891, 2006.
[3] S. Rudykh and G. deBotton, Instabilities of hyperelastic fiber composites: micromechanical versus
numerical analyses, 2010 (Submitted).
Society of Engineering Science ▪ 47 th Annual Technical Meeting 406