Multiaxial deformations of ionic polymer metal composites
Multiaxial deformations of ionic polymer metal composites
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DOI：
10.1016/j.ijengsci.2020.103227
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发表时间：
2020-04-01
影响因子：
6.6
通讯作者：
Porfiri, Maurizio
中科院分区：
文献类型：
--
作者：
Boldini, Alain;Porfiri, Maurizio
离子聚合物金属复合材料(IPMCs)是一类很有前途的软活性材料。它们的高顺应性、低驱动电压和在潮湿环境中工作的能力促使人们对IPMC执行器进行了20年的深入研究。虽然我们已经见证了IPMC技术的几项突破，从加法制造到基于IPMC的机器人，但我们对其驱动的物理基础的理解仍然难以捉摸。研究IPMC驱动的连续介质物理模型很少，文献依赖于结构模型，这些模型假设了经典的梁或板理论中允许的机械变形。在这个意义上，我们对反离子通过离聚体的扩散和电迁移所引起的多轴变形知之甚少。在这里，我们证明了IPMCs的宏观驱动伴随着电极附近的局部机械变形，这是由渗透压力和麦克斯韦应力引起的。为此，我们提出了在ABAQUS(TM)中通过新开发的用户元素进行全面的非线性有限元分析，该用户元素允许测试关于IPMC致动器内部工作原理的假设并探索复杂的配置。结合计算的进展，我们基于线弹性和非线性电化学建立了IPMC平面应变驱动的二维圣维南问题的精确解。与有限元结果对比，精确解提供了一种数学上易于处理的处理电极附近局部现象的方法。我们的结果揭示了电极附近形成的电双电层对贯穿厚度变形的丰富依赖性。由于阴极和阳极附近边界层的不对称性，离聚体相对于其中轴不对称变形，该中轴也经历了轴向拉伸。研究发现，离聚体的泊松比在IPMC从启动到松弛的整个过程中起着至关重要的作用。这项研究是阐明IPMC复杂的多轴变形的第一步，理解这些变形对于设计和制造高性能的IPMC致动器至关重要。(C)2020爱思唯尔有限公司。保留所有权利。
Ionic polymer metal composites (IPMCs) are a promising class of soft active materials. Their high compliance, low actuation voltage, and ability to operate in wet environments have motivated two decades of intensive research on IPMC actuators. While we have witnessed several breakthroughs in the technology of IPMCs, from additive manufacturing to IPMC-based robots, our understanding of the physical underpinnings of their actuation remains elusive. There is a paucity of continuum physically-based models to investigate IPMC actuation, where the literature relies on structural models that postulate admissible mechanical deformations from classical beam or plate theories. In this sense, we know little about multiaxial deformations elicited by counterions diffusion and electromigration through the ionomer. Here, we demonstrate that macroscopic actuation of IPMCs is accompanied by localized mechanical deformations in the vicinity of the electrodes, caused by osmotic pressure and Maxwell stress. Toward this aim, we put forward a comprehensive nonlinear finite element analysis, conducted in Abaqus (TM) through a newly developed user element that allows for testing hypotheses on the inner workings of IPMC actuation and exploring complex configurations. Alongside with computational advances, we establish an exact solution for the two-dimensional Saint-Venant problem of plane-strain actuation of an IPMC, based on linear elasticity and nonlinear electrochemistry. Verified against finite element results, the exact solution offers a mathematically-tractable treatment of localized phenomena in the vicinity of the electrodes. Our results unveil a rich dependence of through-the-thickness deformation on the electric double layers that are formed in the vicinity of the electrodes. Due to the asymmetry of the boundary layers in the vicinity of the cathode and the anode, the ionomer deforms asymmetrically with respect to its mid-axis that also experiences an axial stretch. The Poisson ratio of the ionomer is found to have a critical role in shaping the response of the IPMC, from the onset of actuation to its back-relaxation. This study constitutes a first modeling step toward illuminating complex, multiaxial deformations of IPMCs, whose understanding is critical toward the design and manufacturing of high performance IPMC actuators. (C) 2020 Elsevier Ltd. All rights reserved.