Viscoelastic strain response of dielectric elastomer materials for artificial muscles

Abstract Dielectric elastomer actuators (DEAs) are promising candidates for artificial muscle systems due to their lightweight structure, large deformation capabilities, and rapid response to electrical stimulation. This work investigates the electro-mechanical performance of cross-linked synthetic polychloroprene (CR), polyurethane (PUR), and hydrogenated acrylonitrile-butadiene rubbers (HNBR) as alternative dielectric elastomers (DEs) for DEAs. These elastomers demonstrated enhanced dielectric constants of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> = 8.5 (CR), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> = 6.4 (PUR), and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> = 10 (HNBR) compared to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> values of conventional DEs <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> = 2.3 (Elastosil 2030) and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> = 4.7 (VHB 4910). Circular DEAs were manufactured to investigate the time-dependent actuation strain at a low excitation field strength of 16 V μm −1 . CR showed a response time of 1.2 s, indicating potential for fast-response applications. In contrast, the response time of PUR and HNBR is significantly higher (ca. 5 s) caused by a viscoelastic creep deformation. At a field strength of 16 V μm −1 the electro-active strain of all alternative DEs exceeds that of commercially Elastosil 2030. Among the alternative materials, HNBR exhibits the highest electro-active radial strain (2.2%) at the highest tested field strength of 26 V μm −1 . A linear-elastic model and a viscoelastic model were implemented in LTspice using electro-mechanical analogies to simulate the actuator behavior. While the linear model effectively estimated the strain magnitude, the viscoelastic model allowed a more accurate representation of the time-dependent actuation dynamics. The results highlight the potential of CR, PUR, and HNBR as viable alternatives for tailored DEA applications across varying actuation speed and strain requirements.