Micromechanics of piezoelectric composites with improved effective piezoelectric constant

This paper is concerned with the derivation of a micromechanics model of a new type of piezoelectric fiber reinforced composite (PFRC) materials. A continuum mechanics approach is employed to determine the effective properties of these composites. The piezoelectric fibers of these composites are considered to be electroded at the fiber–matrix interface such that the electric fields in the fiber and matrix become equal in the direction transverse to the fiber direction. The model has been verified with the existing models. The present model also predicts that the effective piezoelectric coefficient of these PFRC which accounts for the actuating capability in the fiber direction due to the applied field in the direction transverse to the fiber direction improves over the corresponding coefficient of the material of the piezoelectric fibers if the fiber volume fraction exceeds a critical fiber volume fraction.     

Effective properties of composites with embedded piezoelectric fibres

The present work deals with the modelling of 1–3 and 0–3 composites made of piezoceramic fibres embedded in a soft non-piezoelectric matrix. We especially focus on the longitudinal and transversal effective piezoelectric constants as a function of several micromechanical parameters such as the fibre volume fraction or the aspect ratio. Finite-element results, based on the concept of a cell model, are compared with results of analytical approaches. This study is restricted to linear piezoelectricity and quasistatic cases.     

The effective properties of smart composites with linear coupling behaviors

The analytical expressions for effective thermal, mechanical, electrical, and magnetic moduli of biphasic smart composites with the linear coupling behavior are developed by employing Mori–Tanaka theory and Dunn model, combined with the equivalent inclusion method for an ellipsoidal inclusion embedded in a transversely isotropic medium. These expressions reflected directly the contributions of each phase and that of the coupling taken place between any combinations of thermal, mechanical, electric, and magnetic behavior and provide a physical insight into how a composites consisting of inclusions perform. For a fibrous reinforced smart composite, the explicit expressions for the sum and product properties are derived and are helpful in understanding the coupling behaviors. The effective properties and the coupling effects as a function of microstructure are discussed theoretically and numerically for piezocomposite and piezomagnetic composite. The results are compared with that of the rule of mixture.     

黏弹阻尼层共固化复合材料不同温度下的阻尼性能

采用共固化工艺制备了以丁腈橡胶为黏弹性阻尼层的复合材料 , 应用动态机械分析仪(DMA)测定了该材料损耗因子的温度谱 , 并对不同温度环境下该材料的阻尼性能和阻尼机制进行了分析。结果表明 : 当温度处于阻尼层玻璃态和高弹态区时 , 共固化复合材料损耗因子较小且随温度变化不大 ; 当温度处于阻尼层黏流态区时 ,共固化复合材料的损耗因子迅速增加到最大值后变小 , 最大损耗因子为 19. 2 % , 约为未插入黏弹阻尼层复合材料的 13倍; 共固化过程中阻尼层损耗因子的减小 , 使共固化复合材料的阻尼性能降低 , 并在阻尼层的黏流态区其损耗因子明显小于预报结果 ; 界面阻尼的影响提高了共固化复合材料的阻尼性能 , 并在阻尼层的玻璃态区其损耗因子大于预报结果。      

金属芯压电纤维/聚合物复合材料压电-黏弹-塑性行为的细观力学模型

为了表征金属芯压电纤维增强聚合物基（MPF/PM）复合材料非线性、时变的压电-黏弹-塑性行为,基于变分渐近理论建立MPF/PM增量形式的细观力学模型。首先分别导出聚合物和MPF增量型本构方程,基于汉密尔顿扩展原理推导出MPF/PM压电-黏弹-塑性变分原理的能量泛函。考虑材料的时变和非线性特征,建立与求解瞬时有效机-电耦合矩阵有关的增量过程,并通过有限元技术实现模型的数值模拟。利用构建模型研究了不同铝芯体积分数、电场变化率和加载条件对MPF/PM有效全局应力-应变和单轴纵向拉伸性能的影响。结果表明,构建的模型能准确模拟MPF/PM多场耦合作用下的非线性、时变行为,为该新型智能材料的实际工程应用奠定理论基础。     

Material properties of piezoelectric composites by BEM and homogenization method

Applications of boundary element method (BEM) to piezoelectric composites in conjunction with homogenization approach for determining their effective material properties are discussed in this paper. The composites considered here consist of inclusion and matrix phases. The homogenization model for composites with inhomogeneities is developed and introduced into a BE formulation to provide an effective means for estimating overall material constants of two-phase composites. In this model, a representative volume element (RVE) is used whose volume average stress and strain are calculated by the boundary tractions and displacements of the RVE. Thus BEM is suitable for performing calculations on average stress and strain fields of the composites. Numerical results for a piezoelectric plate with circular inclusions are presented to illustrate the application of the proposed micromechanics––BE formulation.     

1-3型水泥基压电复合材料的制备及性能

采用切割-浇注法, 以硫铝酸盐水泥为基体, 制备了1-3型水泥基压电复合材料。详细阐述了1-3型水泥基压电复合材料的制备过程; 研究了0.375Pb(Mg_1/3Nb_2/3)O₃-0.375PbTiO₃-0.25PbZrO₃压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料的压电性能、 介电性能和声阻抗的影响。结果表明: 压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料性能有很大影响, 随着w/t的增加, 其压电应变常数d₃₃、 机电耦合系数K_p与K_t、 机械品质因数Q_m、 介电常数ε_r和介电损耗tanδ均随着w/t的增加而减小, 而压电电压常数g₃₃值几乎不受w/t的影响。在压电陶瓷体积分数仅为22.72%的条件下, 调节压电陶瓷柱的宽厚比w/t至0.130, 可使复合材料的声阻抗与混凝土的声阻抗十分接近, 从而有效地解决了智能材料在土木工程中的声阻抗相容性问题。      

PVDF/PZNZT压电复合材料的结构与性能

为了扩展压电复合材料的应用领域,首先,通过固相合成法制备了0-3型聚偏氟乙烯(PVDF)/Pb(Zn_1/3Nb_2/3)_0.05Zr_0.47Ti_0.48O₃ (PZNZT)压电复合材料;然后,研究了PVDF含量对PVDF/PZNZT复合材料物相、显微结构及性能的影响。结果表明:PZNZT陶瓷粉料与PVDF粉料混合后,其平均粒度接近于纯PVDF粉料的。于220℃下烧结后, PVDF/PZNZT复合材料在XRD谱图中主要显现出PZNZT钙钛矿结构的衍射峰。当PVDF含量较低时, PZNZT陶瓷晶粒间的结合较松散;随着PVDF含量的增加,陶瓷晶粒几乎都被PVDF相包围。因显微结构不同,不同PVDF含量的PVDF/PZNZT复合材料在极化电场中呈现出不同的串、并联电路。极化后, 5wt% PVDF/PZNZT复合材料的电性能最佳,其介电常数为116、介电损耗tan δ为0.04、压电常数为48 pC/N且机电耦合系数为0.28。随PVDF含量的增加, PVDF/PZNZT复合材料的居里温度降低,维氏硬度有所增加,但仍小于纯PZNZT压电陶瓷的硬度。所得结论显示PVDF/PZNZT压电复合材料的性能可以满足水声、电声及超声换能器等的要求。      

1-3型聚合物改性水泥基压电复合材料的制备及其性能

采用切割-浇注法,以聚合物改性硫铝酸盐水泥为基体,铌锂锆钛酸铅(简称P(LN)ZT)为功能体制备了1-3型聚合物改性水泥基压电复合材料。研究了P(LN)ZT陶瓷体积分数对复合材料的压电和介电性能的影响。结果表明：随着P(LN)ZT陶瓷体积分数的增加,压电应变常数d₃₃、相对介电常数εr和声阻抗率Z呈现明显的增大趋势;而压电电压常数g₃₃和介电损耗tanδ则呈现下降趋势。与P(LN)ZT陶瓷相比较,1-3型压电复合材料厚度方向振动增强,机械品质因素明显降低,当P(LN)ZT陶瓷体积分数为30.86%时,其声阻抗率为8.24×106 N·s/m3,接近于混凝土的声阻抗率9.0×106 N·s/m3,适用于制作混凝土超声无损检/监测换能器。     

Micromechanical modeling of load transfer in fibrous composites

A unified analytical treatment is presented for the study of micromechanical stress distribution in unidirectional fibrous composites loaded with various thermal and mechanical loads. Two models are considered to represent the composite. Both use a concentric cylindrical system with the difference that one requires laterally free while the other requires laterally constrained outer boundaries, broadly describing situations of plane stress and plane strain, respectively. The present work has been motivated by the recent work of McCartney (McCartney, Proc. Roy. Soc. London, Ser. A 425 (1989) 215–244) who analyzed the laterally free system, and by our previous work (Nayfeh, Fibre Sci. Technol. 10 (1977)) in which we analyzed the laterally constrained one. For axisymmetric loading, and upon adopting some appropriate restrictions on the radial behavior of some field quantities, an elasticity-based procedure reduces the two-dimensional field equations, which hold in both the fiber and matrix components, together with the appropriate interface and boundary conditions, to a quasi-one-dimensional system. The resulting system is capable of identifying the stress distribution in each component as influenced by the other component via the readily identifiable interaction (transfer) terms. The model is general and applicable to a large variety of situations. These include situations of matrix cracking, fiber break and even regions of slip at the fiber–matrix interface. As a by-product, the model was capable of obtaining the classical Lamé solutions (the iso-strain case) as a degenerate case. Confidence in the modeling was gained when it identically reproduced all of the numerical examples presented by McCartney. Numerical results that parallel some of the ones presented by McCartney are included in the form of comparisons between results obtained based upon the laterally constrained and the laterally free systems.     

Micromechanics based analysis of randomly distributed fiber reinforced composites using simplified unit cell model

The geometry of the simplified unit cell (SUC) model [Aghdam MM, Smith DJ, Pavier MJ. Finite element micromechanical modeling of yield and collapse behavior of metal matrix composites. J Mech Phys Solids 48 (2000) 499–528] is extended to study effects of random fiber arrangement on the mechanical and thermal characterizations of unidirectional composites. The representative volume element (RVE) considered in the model consists of an r × c unit cells in which fibers are surrounded randomly by matrix cells. The presented model is general and can be used to predict the behavior of a fibrous composite subjected to thermal and mechanical, normal and shear, loading. The model also is capable of analyzing various combinations of these loading conditions such as off-axis test of unidirectional coupons. Both random and repeating fiber arrays can be considered in the model. Results for the overall thermal and elastic properties of a SiC/Ti metal matrix composite (MMC) show good agreement with both the finite element and other analytical models with repeating fiber arrays. Results of transverse properties also revealed that hexagonal array assumption for fiber arrangement is more realistic than square array assumption.     

Micromechanics modeling of fatigue failure mechanisms in a hybrid polymer matrix composite

Initiation of fatigue damage for a hybrid polymer matrix composite material was studied via 3-Dimensional viscoelastic representative volume element modeling in order to gain further understanding. It was found that carbon fiber reinforced composites perform better in fatigue loading, in comparison to glass fiber reinforced composites, due to the fact that the state of stress within the matrix material was considerably lower for carbon fiber reinforced composites eliminating (or at least prolonging) fatigue damage initiation. The effect of polymer aging was also evaluated through thermal aging of neat resin specimens. Short-term viscoelastic material properties of unaged and aged neat resin specimens were measured using Dynamic Mechanical Analysis. With increasing aging time a corresponding increase in storage modulus was found. Increases in the storage modulus of the epoxy matrix subsequently resulted in a higher state of predicted stress within the matrix material from representative volume element analyses. Various parameters common to unidirectional composites were numerically investigated and found to have varying levels of impact on the prediction of the initiation of fatigue damage.     

Coefficients of thermal expansion for single crystal piezoelectric fiber composites

Piezoelectric fiber composites were developed to overcome drawbacks of typical monolithic piezoceramic (PZT) actuators. Although piezoelectric fiber composites had many improvements over the monolithic PZT, there are still improvements. Thus, the single crystal piezoelectric fiber composite actuator is proposed. Single crystal piezoelectric materials such as PMN-PT have larger piezoelectric strain constants, higher bandwidth and higher energy density than polycrystalline counterparts. Piezoelectric fiber composites can improve the performance of various structures, and can be subject to wide temperature range where the thermoelastic behavior is important. Therefore, this paper studies the coefficients of thermal expansion (CTE) for single crystal piezoelectric fiber composites. The Macro Fiber Composite (MFC) as the piezoelectric fiber composite is considered. To calculate the effective properties of two orthotropic layers of the MFC, PMN-PT(or PZT)/epoxy and copper/epoxy layers, the rule of mixture is adopted. With the effective properties known for each layers, the two CTE of the MFC actuator are obtained from the classical lamination theory considering thermal effects. The difference of the CTE between the single crystal MFC and the standard MFC is studied.     

Homogenization of fibrous piezoelectric composites with general imperfect interfaces under anti-plane mechanical and in-plane electrical loadings

The present paper aims mainly to estimate the size-dependent effective properties of fibrous piezoelectric composites with general imperfect interfaces. The interface model used states that the displacement, traction, electric potential, and normal electric displacement all suffer jumps across an interface. In addition, it can degenerate into the well-known special ones by employing appropriate high-contrast interfacial parameters. To achieve our objective, an auxiliary inhomogeneity problem of a circular fiber embedded in an infinite cylindrical reference phase via general imperfect interface under anti-plane mechanical and in-plane electrical boundary conditions is analytically solved. This solution allows us to apply the well-known micromechanical schemes such as the dilute, Mori–Tanaka to obtain the closed-form expressions for the size-dependent overall properties of composites under consideration. Some numerical examples are provided for illustrating the features of the obtained general results.     

镧掺杂PZN-PZT陶瓷及其PVDF压电复合材料的制备与性能

采用固相烧结法合成了不同镧掺杂量的PZN-PZT压电陶瓷和粉体．并用XRD分析了陶瓷的晶相，扫描电镜观察到PZN-PZT陶瓷粉体形态不太规整，颗粒粒径主要分布在1～4μm之间．将PZN-PZT粒子均匀分散于PVDF基体中，制备了PZN-PZT/PVDF压电复合材料．研究了镧掺杂量对PZN-PZT陶瓷及复合材料压电性能的影响．结果表明，适量的镧掺杂可有效提高复合材料的压电性能，当镧掺杂量为4％（摩尔分数）时，复合材料的压电性能最好，压电常数d33值为36pC/N。     

Dielectric modeling of multiphase composites

In this paper effective medium theory based on Clausius–Mossoti relation was used to predict dielectric properties of multiphase composite system. The composite consisted of E-glass fibers (plain weave S-glass, J.B. Martin) embedded in bisphenol A diglycidylether epoxy matrix (D.E.R. 324, D.O.W. chemicals) with hollow ceramic spherical inclusions (SF 14, P.Q. Corp.) at different volume fractions. In many engineering applications, materials with designed dielectric properties are often sought. An important question in engineering design of a composite material is how the overall properties of the composite depend on those of the individual constituents. Mixing the epoxy resin with hollow ceramic inclusions can effectively reduce dielectric constant of the resin, which is often desirable, rendering composites as good candidates for many applications, especially in telecommunications. Compensation for degradation of mechanical properties of matrix (due to inclusion insertion) is obtained by embedding fibers into the mixture. Measurements of dielectric constant and loss tangent for this multiphase composite system were conducted in the region between 0.1 and 100 kHz range using DEA 290 (T.A. Instruments) dielectric analyzer and experimental results are presented. Good correlation between analytical model and experimental results was observed throughout all frequency range of investigation.     

含金属芯压电压磁纤维/聚合物基复合材料时变、非线性和多物理场响应的细观力学模型

为有效模拟新型多功能智能材料——金属芯压电压磁纤维/聚合物基复合材料(MPPF/PMCs)的有效时变、非线性和多物理场响应,基于变分渐近法建立增量形式的细观力学模型。首先分别导出聚合物、压电压磁材料和金属芯的增量本构关系,建立统一的本构方程;以此为基础,推导出能量变化泛函的变分表达式。考虑材料的时变和非线性特征,建立与求解瞬时切线电-磁-力耦合矩阵有关的增量过程;通过最小化近似泛函求解场变量的波动函数,并通过有限元数值实现,从而建立逼近物理和工程真实性的细观力学模型。通过含铝芯压电(BaTiO_3)压磁(CoFe_2O_4)聚合物基复合材料算例表明:构建的模型可用于模拟不同多物理场下MPPF/PMCs的有效响应,可准确捕捉纤维与基体间的应力突变现象。     

The influences of soft and stiff inclusions on the mechanical properties of cementitious composites

The embedment of microencapsulated phase change materials (PCMs) is a promising means for improving the thermal inertia of concrete. However the addition of such soft microcapsules degrades the mechanical properties, i.e., the elastic moduli and compressive strength, of cement-based composites. This study experimentally quantifies the effects of stiff quartz inclusions and soft PCM microcapsules, individually, and when added together, on the mechanical properties of cementitious composites. In addition, a variety of effective medium approximations (EMAs) were evaluated for their ability to predict the experimentally measured composite effective moduli. The EMAs proposed by Hobbs and Garboczi and Berryman (G-B) reliably estimate experimental data. The experimental data and the EMAs were applied to develop a design rule for performance equivalence, such that the composite modulus of elasticity can be maintained equivalent to that of the cementitious paste matrix, in spite of the addition of soft PCM microcapsules.     

基于压电堆和粘弹性材料的新型整星混合隔振系统

摘　要：为了降低振动载荷对卫星的影响,采用压电堆和粘弹性材料作为主被动隔振元件,设计一种新型的整星混合隔振系统,并对其隔振原理进行理论分析。通过有限元方法建立该隔振系统的有限元模型并分析其频率响应特性,根据分析结果,运用特征系统实现算法获取系统的最小阶状态空间模型来设计控制器,完成离线仿真。在此基础上,对低柔性模拟卫星进行整星混合隔振试验。仿真和试验结果表明,整星混合隔振系统能够有效地降低运载火箭传递到卫星的振动载荷。与整星被动隔振系统相比,整星混合隔振系统对低频振动分量具有显著的抑制作用,证明了该隔振系统的可行性和有效性,大大提高了卫星的安全性和可靠性。     

粘弹阻尼层共固化复合材料的阻尼特征分析

利用动态力学热分析技术(DMTA)测试了粘弹性阻尼材料在与复合材料共固化前后的动态力学性能,并利用有限元分析方法考察了复合材料共固化、粘弹性阻尼层的厚度以及复合材料柔性层对共固化复合材料的阻尼特征的影响.结果表明,复合材料共固化过程中由于树脂渗透等原因,共固化复合材料的阻尼峰值仅为理想状态的54%左右且阻尼峰值所对应的温度向高温方向移动;增加粘弹性阻尼层的厚度以及在阻尼层附近插入柔性层不仅可以提高粘弹阻尼层共固化复合材料的阻尼峰值,而且可拓宽共固化复合材料的阻尼温域.