Voltage-driven torsion of electroactive thick tubes reinforced with helical fibers

Abstract

This work studies the voltage-driven torsional deformation of a thick-walled circular cylindrical tube composed of a dielectric elastomer (DE) reinforced with a family of helical fibers. The Helmholtz free energy of the DE composite tube involves separate DE matrix and fiber contributions. Upon the application of an electrical voltage difference on its inner and outer surfaces, the DE matrix contracts through the thickness and expands in cylindrical surfaces due to the Maxwell stress. Since the composite is stiffened along the fiber direction, it preferentially expands in the direction orthogonal to the fiber within the cylindrical surfaces. As a result, voltage-driven torsional deformation will occur in the helical fiber-reinforced DE tube. Although membrane theory was usually adopted to model fiber-reinforced thin DE membranes, the finite deformation theory is utilized in the present work to model relatively thick DE composite tubes. It is found that the bending effect plays an important role in the voltage-driven torsional deformation. The reorientation of the fibers and the distribution of the stress carried by the fibers in the tubes are discussed in detail so as to provide an interpretation to some new voltage-driven torsional behaviors. The theoretical model and physical insights provided in this work will aid the design and optimization of soft electroactive actuators and soft robotics.