具有线性介电常数的Ogden型介电弹性体的本构关系和机电稳定性

应用多材料常数的Ogden弹性应变能函数分析了介电弹性体的力学行为,研究了介电弹性体的机电稳定性.数值结果表明,通过对材料系数(如材料常数比和电致伸缩系数等)的恰当调节可以使得介电弹性体材料或介电弹性体结构更趋稳定.这些有益于深入理解介电弹性体的机电稳定性行为,进而设计恰当的介电弹性体器件.     

温度对介电弹性体材料力电耦合变形的影响

介电弹性体(Dielectric Elastomer,简称DE)材料是一类在电场激励下可以产生大幅度尺寸或形状变化的新型柔性功能材料.DE材料具有非常宽的温度应用范围,这种宽的温度工作范围和快速大变形性能为各种柔性致动器结构提供了良好的基础,但作为一种粘弹性高分子材料,温度对其性能的影响也是非常明显的.然而到目前为止,所有关于DE材料驱动性能的研究仅局限于室温条件下,温度变化对DE材料力电耦合稳定性的影响几乎没有相关报道.基于此,通过实验研究了温度对最常用的DE材料(VHB 4910,3M)力电耦合变形的影响,结果表明:升高温度可以提高DE材料的力电耦合变形;温度越高,DE材料越容易发生力电耦合失稳.然后,从热力学和粘弹性力学出发,建立了考虑温度影响后的DE材料的粘弹性力电耦合模型,数值模拟理论结果和实验结果定性地吻合.     

压电材料椭圆夹杂界面开裂问题的电弹性耦合解

本文研究了在反平面剪切和面内电场的共同作用下，压电材料椭圆夹杂的界面开裂问题，假定夹杂是刚性的导体，采用复变函数保角变换和级数展开方法，可确定压电材料基体的复势表达式，进而求得夹杂界面开裂的电弹性耦合的能量释放率。     

多晶铁电材料的有效电弹性能预报

本文利用细观力学方法———Ｅｓｈｅｌｂｙ等效夹杂法和Ｍｏｒｉ Ｔａｎａｋａ的平均场理论,根据铁电材料的微结构特点,建立了一个细观统计模型对多晶铁电材料的有效电弹性能和模量进行分析预报．在本细观统计模型中,不仅考虑到单晶粒的形状影响,而且考虑铁电畴在外场作用下发生极化转动的影响．本文针对ＢａＴｉＯ３铁电陶瓷的有效电弹性能与系数的预报结果与实验观测结果相符     

介电弹性作动器主动隔振模糊控制试验研究

采用模糊控制策略,开展介电弹性作动器的主动隔振性能试验研究。基于介电弹性材料的Maxwell应力模型建立了作动器的力电耦合模型,分析了作动器的非线性特性;针对隔振系统设计了Mamdani型模糊控制器,建立了控制电压信号与振动响应之间的关系;在此基础上,开展了介电弹性作动器主动隔振试验研究,并与加速度反馈控制进行了对比。试验结果表明,在相同驱动电压的情况下,基于模糊控制策略的主动隔振性能要优于加速度反馈控制,且能够显著降低由于非线性驱动力导致的倍频响应幅值,有助于提高隔振系统的稳定性。     

弹性涂层材料的冲蚀损伤特性研究

文章设计了材料冲蚀疲劳特性试验及通过曲线拟合确定弹性接触条件下材料冲蚀特性参数的方法，并用力学分析与冲蚀试验相结合得出弹性涂层材料的粒子冲蚀疲劳特性曲线(lgσ-lgN^*曲线)。进一步分析了弹性接触状态下冲蚀磨损率与材料特性及工况主要参数之间的定量关系。结果表明，这种材料的冲蚀疲劳极限应力σ0在MPa左右，冲蚀磨损率大约与冲击速度及冲击角的正弦成2．6次方关系。     

极性材料的热弹性力学

本文在文献[1]、[2]、[3]、[5]、[7]的基础上,讨论了线性耦合下,极性材料三维热弹性力学的能量方程、熵生成定律、耗散函数、Fourier热传导方程和它的变分原理。     

温度对介电弹性体材料力电耦合变形的影响（固体力学大会文章）

介电弹性体（Dielectric elastomer,简称DE）材料是一类在电场激励下可以产生大幅度尺寸或形状变化的新型柔性功能材料。DE材料具有非常宽的温度应用范围,这种宽的温度工作范围和快速大变形性能为各种柔性致动器结构提供了良好的基础,但作为一种粘弹性高分子材料,温度对其性能的影响也是非常明显的。然而到目前为止,所有关于DE材料驱动性能的研究仅局限于室温条件下,温度变化对DE材料力电耦合稳定性的影响几乎没有相关报道。基于此,通过实验研究了温度对最常用的DE材料（VHB 4910,3M）力电耦合变形的影响,结果表明：升高温度可以提高DE材料的力电耦合变形;温度越高,DE材料越容易发生力电耦合失效。然后,从热力学和粘弹性力学出发,建立了考虑温度影响后的DE材料的粘弹性力电耦合模型,数值模拟理论结果和实验结果非常吻合。     

介电弹性球膜的动力稳定性分析

介电弹性体结构具有卓越的力电性能,然而由于其大变形特性,在动态工作模式下极易出现各类失效问题,这极大阻碍了其工程应用.论文研究与力电失稳行为直接相关的理想介电弹性球膜动力稳定性问题.首先据虚功原理建立电压及压力共同作用下关于伸长比的动力学方程,系统自由能由弹性应变能与静电能组成,而前者基于Mooney-Rivlin模型表出.通过系统首次积分解析给出稳态响应峰值与阶跃电压/阶跃压力的关系曲线,其与静态平衡曲线的交点决定了临界电压/临界压力.研究表明:给定任意电压,材料参数存在某阈值,当超过该值后系统始终保持稳定;对于任意非零压力值,存在类似材料参数阈值;而当压力恰为零时,则始终存在临界电压值,超过该值则系统动力不稳定.     

压电材料V型切口端部电弹性场研究

通过广义Hellinger-Reissner变分原理导出了一个环绕V型切口端部邻域的超级奇异单元,并将其与全域压电杂交元结合,建立了一种新型数值求解压电材料切口端部奇异电弹性场的杂交元模型.为了验证该模型的有效性,以含V型切口的三点弯曲试件为例,首先用杂交元数值模型计算了切口端部的广义应力强度因子及其延长向上的应变分布,然后与用云纹干涉实验法测定的相应实验结果相比较,比较结果表明:两者吻合良好.     

Large conversion of energy in dielectric elastomers by electromechanical phase transition

When air is pumped in, a tubular balloon initially inflates slightly and homogeneously. A short section of the balloon then forms a bulge, which coexists with the unbulged section of the balloon. As more air is pumped in, the bulged section elongates at the expense of the unbulged section, until the entire balloon is bulged. The phenomenon is analogous to the liquid-to-vapor phase transition. Here we study the bulging transition in a dielectric elastomer tube as air is pumped into the balloon and a voltage is applied through the thickness of the membrane. We formulate the condition for coexistent budged and unbulged sections, and identify allowable states set by electrical breakdown and mechanical rupture. We find that the bulging transition dramatically amplifies electromechanical energy conversion. Energy converted in an electromechanical cycle consisting of unbulged and bulged states is thousands of times that in an electrome-chanical cycle consisting of only unbulged states.     

RATE DEPENDENT STRESS-STRETCH RELATION OF DIELECTRIC ELASTOMERS SUBJECTED TO PURE SHEAR LIKE LOADING AND ELECTRIC FIELD

The performance of dielectric elastomer(DE) transducers is significantly affected by viscoelastic relaxation-induced electromechanical dissipations.This paper presents an experimental study to obtain the rate dependent stress-stretch relation of DE membranes(VHB TM 9473) subjected to pure shear like loading and electric loading simultaneously.Stretching rate dependent behavior is observed.The results also show that the tensile force decreases as the voltage increases.The observations are compared with predictions by a viscoelastic model of DE.This experiment may be used for further studies of dynamic electromechanical coupling properties of DEs.     

A FINITE ELEMENT METHOD FOR DIELECTRIC ELASTOMER TRANSDUCERS

We present a finite element method for dielectric elastomer(DE) transducers based on the nonlinear field theory of DE.The method is implemented in the commercial finite element software ABAQUS,which provides a large library functions to describe finite elasticity.This method can be used to solve electromechanical coupling problems of DE transducers with complex configurations and under inhomogeneous deformation.     

Temperature effects on the dynamic response of viscoelastic dielectric elastomer

Viscoelasticity and temperature can significantly affect the performance of a dielectric elastomer. In the current study, we use a thermodynamic model to describe the effect of temperature and viscoelasticity on the electromechanical response undergoing a cyclic electric load by taking into account of the temperature dependent dielectric constant. Because of the significant viscoelasticity in the dielectric elastomer, the deformation and the nominal electric displacement can not keep in phase with the electric field at low frequencies. The results show that the magnitude of the cyclic electromechanical actuation strain increases with the decrease of the temperature and decreases with the increasing frequency, and viscoelasticity can result in significant hysteresis for dielectric elastomers under a relative low temperature and a low frequency.     

Thermomechanical modeling of the thermo-order-mechanical coupling behaviors in liquid crystal elastomers

Liquid crystal elastomer is a kind of anisotropic polymeric material, with complicated micro-structures and thermo-order-mechanical coupling behaviors. In this paper, we propose a method to systematically model these coupling behaviors. We derive the constitutive model in full tensor structure according to the Clausius-Duhem inequality. Two of the constitutive equations represent the mechanical equilibrium and the other two represent the phase equilibrium. Choosing the total free energy as the combination of the neo-classical free energy and the Landau-de Gennes nematic free energy, we obtain the Cauchy stress-deformation gradient relation and the order-mechanical coupling equations. We find the analytical homogeneous solutions of the deformation for the typical mechanical loadings, such as uniaxial stretch, and simple shear in any directions. We also compare the compression behavior of prolate liquid crystal elastomers with the stretch behavior of oblate liquid crystal elastomers. As a result, the stress, strain, temperature, order parameter, biaxiality and the direction of the director of liquid crystal elastomers couple with each other. When the prolate liquid crystal elastomer sample is stretched in the direction parallel to its director, the deviatoric stress makes the mesogens more order and increase the transition temperature. When the sample is sheared or stretched in the direction non-parallel to the director, the director of the liquid crystal elastomer will rotate, and the biaxiality will be induced. Because of the order-mechanical coupling, under infinitesimal deformation, liquid crystal elastomer has anisotropic Young’s modulus and zero shear modulus in the direction parallel or perpendicular to the director. While for the oblate liquid crystal elastomers, the stretch parallel to the director will cause the rotation of the director and induce the biaxiality.     

Characteristics of strength control of adaptive structure with electromechanical coupling

Based on the programming method, an electromechanical coupling adaptive statically indeterminate truss structure is controlled for increasing its load capacity. Several main parameters during the process of design of the adaptive structure are selected for a study of its characteristic during the control stage. The curves of each parameter for the effect of control results are plotted and corresponding conclusions are drawn. Thus, the theoretical basis is presented for optimal design, manufacture and control of the adaptive structure. Project supported by the National Natural Science Foundation of China (10072005), Beijing Educational Committee (99LG-11) and Beijing Natural Science (3002002) Foundation.     

Strain tunability of dielectric and ferroelectric properties in epitaxial lead titanate thin films

Many distinguished properties of epitaxial ferroelectric thin films can be tunable through the misfit strain. The strain tunability of ferroelectric and dielectric properties in epitaxial lead titanate ultrathin films is numerically investigated by using a phase field model, in which the surface effect of polarization is taken into account. The response of polarization to the applied electric field in the thickness direction is examined with different misfit strains at room temperature. It is found that a compressive misfit strain increases the coercive field and the remanent polarization while a tensile misfit strain decreases both of them. The nonlinear dielectric constants of the thin films with tensile misfit strains are much larger than those of the thin films without misfit strains, which are attributed to the existence of the a/c/a/c multiple domains in the thin films under tensile misfit strains.