16th U.S. National Congress on Computational Mechanics (Alain Boldini’s talk)

#21722255 – Modeling Mechanics and Electrochemistry of Ionic Polymer Metal Composites: From Continuum Theories to Finite Element Analysis and Structural Modeling

Minisymposium #103: Symposium Honoring J. Tinsley Oden’s Monumental Contributions to Computational Mechanics

Authors: Alain Boldini (presenting), Lorenzo Bardella, Maurizio Porfiri

Location: Room #14 – B-14

Abstract:

Ionic polymer metal composites (IPMCs) are electroactive polymers composed by an ionic polymer between two plated noble metal electrodes. The ionic polymer is a negatively charged porous membrane. A solution with cations saturates the membrane, neutralizing its negative charges and ensuring electroneutrality. A voltage applied across the electrodes disrupts such equilibrium, causing cations’ migration within the membrane along with the formation of boundary layers at the interface between the membrane and electrodes. This phenomenon is accompanied by water migration associated with osmotic pressure and by Maxwell stress due to material polarization. These two stresses contribute to the overall eigenstress in the membrane, thereby eliciting macroscopic bending of the IPMC. Despite the vast literature on IPMC modeling, several questions about their mechanics and electrochemistry remain untapped. Finite element (FE) simulations of chemoelectromechanics of IPMCs are scarce, due to the challenges in resolving nanometer-thick boundary layers of charge. Further, whether classical structural models can be utilized to describe IPMC deformations is still unclear. Here, we seek to address these technical gaps through advancements in computational mechanics and structural theories. Building on our group’s continuum model of IPMCs [1], we investigate the plane-strain response of a simply supported membrane. We implement a FE model of nonlinear IPMC chemoelectromechanics through a user-defined continuum element in Abaqus, and compare its results against an analytical solution based on matched asymptotic expansions for the electrochemistry and a Saint-Venant solution for the mechanics [2]. We discover a dramatic effect of localized through-the-thickness deformations near the electrodes on membrane’s macroscopic bending, thereby challenging the use of low-order structural models. Motivated by this discovery, we establish a new structural model for IPMCs, which extends Euler-Bernoulli beam theory to account for through-the-thickness deformations, computed a-priori from the analytical solution for uniform bending. We demonstrate the accuracy of our model against FE, in the presence of non-uniform bending and metal electrodes. Our work finds application in reduced-order modeling of IPMCs, a critical component of inverse design and optimization. References [1] Cha, Y., & Porfiri, M. (2014). Mechanics and electrochemistry of ionic polymer metal composites. Journal of the Mechanics and Physics of Solids, 71, 156-178. [2] Boldini, A., & Porfiri, M. (2020). Multiaxial deformations of ionic polymer metal composites. International Journal of Engineering Science, 149, 103227. [3] Boldini, A., Bardella, L., & Porfiri, M. (2020). On Structural Theories for Ionic Polymer Metal Composites: Balancing Between Accuracy and Simplicity. Journal of Elasticity, 141(2), 227-272.