Review on electro-mechanically coupled cyclic deformation and fatigue failure behavior of dielectric elastomers
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摘要: 介电高弹体的力−电耦合循环变形和疲劳失效行为目前在相关功能器件的设计和寿命评估中得到了越来越多的关注. 因此, 为了促进软体机器人等领域的发展, 文章对介电高弹体的力−电耦合循环变形和疲劳失效行为的实验和理论研究现状进行了较为全面地综述: 首先, 对介电高弹体VHBTM材料在单一力场和力−电耦合作用下的循环变形行为及其演化特征进行了评述, 重点总结了该材料在循环载荷作用下表现出的循环软化、棘轮行为和疲劳失效行为及其力−电耦合效应; 然后, 对已有的、描述介电高弹体单一力场和力−电耦合变形行为的本构模型进行综述, 评述了已有的超弹性、黏−超弹性和黏−超弹性−塑性本构模型对介电高弹体循环变形行为及其力−电耦合效应的描述能力; 最后, 对介电高弹体的力−电耦合失效行为研究现状进行了评述, 特别关注了介电高弹体在力−电耦合大变形作用下的低周疲劳失效行为. 基于已有研究现状的评述, 文章还对相关领域的未来研究方向进行了展望, 力求促进相关研究领域的发展.Abstract: The electro-mechanically coupled cyclic deformation and fatigue failure of dielectric elastomers (DEs) has attracted more and more attention in the design and life-assessment of related functional devices. Thus, to prompt the developments of soft robots and other related fields, the progress in the experimental and theoretical researches on the electro-mechanically coupled cyclic deformation and fatigue failure of DEs is reviewed in this work as follows: At first, the cyclic deformation and its evolution feature of DEs presented under the mechanical and electro-mechanically coupled loading conditions are summarized by specifically addressing the cyclic softening, ratchetting, fatigue failure and their electro-mechanical coupling effect; then, the existing constitutive models describing the mechanical and electro-mechanically coupled deformations of DEs are reviewed by discussing the capability of proposed hyperelastic, visco-hyperelastic and visco-hyperelastic-plastic constitutive models to reproduce the cyclic deformation of DEs and its electro-mechanical coupling effect; finally, the progress in the researches on the electro-mechanically coupled failure of DEs is outlined by addressing the low-cycle fatigue failure of DEs subjected to a kind of electro-mechanically coupled large deformation. Based on the comprehensive review on the existing literature, some topics are also recommended in this work for the future research, which are helpful to prompt the development of related fields concerning the DEs.
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图 2 VHBTM4910的滞回环现象及其率相关性 (Hossain et al. 2012)
图 3 VHBTM4905从−30℃至80℃的单次拉伸−卸载应力−伸长比曲线 (Liao et al. 2020)
图 4 介电高弹体VHBTM4910在应变控制 (最大伸长比分别为1.5和3) 循环载荷下的伸长比−应力曲线 (Thylander et al. 2017)
图 5 应力控制循环变形实验结果 (Chen et al. 2019). (a) 应力−应变曲线 (25 kPa ± 25 kPa), (b) 循环变形后零应力保持60 min时残余应变的回复曲线, (c) 不同应力水平下棘轮应变的演化曲线, (d) 不同应力速率下棘轮应变的演化曲线
图 6 介电高弹体在预拉伸后的电致大变形实验 (Pelrine et al. 2000)
图 7 介电高弹体VHBTM4910的介电常数随等双轴拉伸变形的增大而减小 (Wissler & Mazza 2007a)
图 8 介电高弹体应变随循环电压的变化曲线 (Bai et al. 2014)
图 9 力−电耦合循环加载下的应力−应变曲线 (Chen et al. 2020b). (a) 无电压−循环应力 (参照实验), (b) 循环电压−循环应力同相加载, (c) 循环电压−循环应力反相加载
图 10 VHBTM材料在大变形拉伸下的应变刚化效应 (Lu et al. 2020)
图 12 应变−时间曲线的实验结果和模拟结果的对比 (Wissler & Mazza 2007b). (a) 第1圈, (b) 全部75圈
图 13 VHBTM拉伸−卸载和多步松弛实验和模拟结果的对比 (Hossain et al. 2012). (a) 拉伸−卸载, (b) 多步松弛
图 14 改进Kelvin-Voigt模型的一维流变学示意图 (Chang et al. 2017), 其中,
$\mu _{\rm{s}}$ 代表串联弹簧的模量;$\mu _{\rm{p}}$ 代表并联弹簧的模量;$\eta $ 代表并联阻尼的黏度图 15 VHBTM材料实验和模拟应力−应变曲线的对比 (Xiang et al. 2019). (a) 准静态拉伸, (b) 不同速率的拉伸
图 16 耦合Mullins损伤的黏−超弹性流变学模型 (Lu T et al. 2017)
图 17 黏−超弹性−塑性本构模型的流变学示意图, 其中,
$\mu _{}^{\text{e}}$ ,$\mu _{}^{\text{v}}$ 和$\mu _{}^{\text{p}}$ 分别表示超弹性分支A、黏弹性分支B和塑性分支C的剪切模量;$\tau _{}^{\text{v}}$ 和$c_{}^{\text{p}}$ 分别表示与黏弹性和塑性内变量演化相关的材料参数; P表示外加载荷 (Chen et al. 2020a)图 18 黏−超弹−塑性本构模型对VHBTM介电高弹体循环应力−应变曲线的模拟 (Chen et al. 2020a). (a) 应变控制循环加载, (b) 应力控制循环加载, (c) 不同平均应力的棘轮应变, (d) 不同应力速率的棘轮应变
图 19 VHBTM介电高弹体在不同电压和拉伸速率下的变形−应力曲线 (Qu et al. 2012). (a) 理论模拟结果, (b) 实验结果
图 20 力−电耦合的黏−超弹性−塑性本构模型对VHBTM介电高弹体循环应力−应变曲线的模拟 (Chen et al. 2020b). (a) 6 kV下的应力循环的应力−应变曲线, (b) 6 kV下的应力循环的棘轮应变和峰谷应变, (c) 不同电压下应变循环的峰值应力, (d) 不同电压下应力循环的棘轮应变
图 21 介电高弹体的输出电流和能量密度在第9个循环周次出现显著的下降, 说明漏电的发生 (Huang et al. 2013). (a) 输出电流, (b) 能量密度
图 22 介电高弹体材料的力−电耦合低周疲劳实验结果 (Chen et al. 2021). (a) 常电压−循环应力加载下的应力−应变曲线和疲劳寿命, (b) 疲劳寿命−应力幅值关系曲线
图 23 基于构型应力的力−电耦合低周疲劳模型对VHBTM材料疲劳寿命的预测结果 (Chen et al. 2021)
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