层状柱壳磁电复合材料的非线性磁电效应研究

本文基于超磁致伸缩材料非线性本构,从基本的控制方程出发,对层状柱壳磁电复合材料的非线性磁电响应进行理论研究,讨论了不同边界下磁场频率以及压电材料厚度比对磁电系数的影响,并得到了不同预压力下磁场大小对于磁电系数的影响。数值计算结果显示,对于Tefernol-D/PZT-5层状磁电复合材料,随着预压力值增大,磁电系数最大值减小,取得最大值时对应的磁场值逐渐增大;不同边界条件、磁场频率和磁场大小下,材料厚度比对磁电系数的也有着不同的影响。特别地当外加磁场频率较大时,相应于压电层厚度比,磁电系数呈现多极值现象。     

磁电复合材料的力学实验与理论研究进展

磁电复合材料同时具备铁磁、铁电性,并且具有磁电耦合效应,在新型磁电器件、自旋电子器件、高性能信息存储等领域有着广泛的应用前景,已成为目前功能材料领域新的研究热点。本文对磁电复合材料在力电磁多场耦合下的力学行为研究的最新进展进行总结和回顾。着重介绍磁电复合材料的磁电耦合效应实验以及多场耦合微纳米力学实验仪器的研制和表征方法。同时,也阐述了磁电复合材料在多场耦合本构理论、失效断裂理论以及多尺度计算方面的研究进展。最后,总结已有研究存在的不足,就目前有待解决科学问题的进一步研究提出建议。     

不均匀磁电弹板中的厚度扭曲波的传播

压电-压磁复合材料或结构的许多应用是与弹性波的传播密切相关的,这要求人们首先从理论的角度弄清楚弹性波的传播规律。本文研究由多个不均匀磁电弹介质组成的薄板厚度扭曲波的传播性质,从磁电弹全耦合场三维方程出发得到了其精确解,根据所得到的解分析了波的传播特征,这些结果对于理解和设计谐振器、滤波器以及声波元件提供了有价值的理论基础。     

压电压磁复合材料中正六边形孔边裂纹的反平面断裂问题

基于线性磁电弹性理论,利用Schwarz-Christoffel(CS)变换技术和Stroth公式,首次系统研究了压电压磁复合材料中含带两个不对称裂纹的正六边形孔口问题在部分渗透磁电边界条件下的解析解.当忽略磁场时,磁电非渗透裂纹和磁电渗透裂纹两种极端情况下的解析解答可退化为文献已有研究结果.数值结果揭示了正六边形孔口尺寸、裂纹长度以及力电载荷和磁载荷对能量释放率的影响规律.研究结果表明：减小孔口边长和裂纹长度可以提高材料的可靠性;机械载荷总是促进裂纹扩展;在磁电非渗透和磁电部分渗透边界条件下,负电场和负磁场会延缓裂纹的扩展,而正电场可以增强或阻碍裂纹的扩展,这取决于所施加的电场和磁场的强度以及机械载荷的水平;在磁电渗透边界条件下,电场和磁场对裂纹的扩展没有影响.     

空气耦合层状复合材料的声传播研究

本文研究了空气耦合层状复合材料的声传播。从基本波动方程出发,由气固边界条件,利用势函数法求解声波任意角入射层状复合材料的声传播,并通过数值计算得到其透声系数幅度和相位随频率变化的规律。基于MATLAB建立了测量任一入射角透声系数的实验平台,并对复合材料试样进行了实验,得到的透声系数幅度与理论计算结果吻合,说明了所建立的声传播理论和实验检测方法的有效性。     

磁电弹性复合材料热接触特性研究

磁电弹性(Magneto-electro-elastic, MEE)复合材料在接触热载荷作用下将产生复杂热应力、热电和热磁多物理场响应.基于半解析法建立MEE复合材料热接触模型,其中,推导了单位集中法向力、切向力、电荷、磁荷和温升载荷下各物理量的频率响应函数,引入热流-温升影响系数计算摩擦热产生的温升,并采用离散卷积快速傅里叶变换和共轭梯度法加速其计算过程.将模型计算结果与有限元仿真进行对比,验证模型有效性.进一步利用所提模型分析热接触过程中摩擦热对各物理场的影响规律,结果表明：滑动速度、摩擦系数和表面形貌改变将影响摩擦热分布,进而显著影响应力、电势和磁势的大小和分布;弹性场和电场与摩擦温升呈负相关,而磁场与其为正相关,并且耦合场对温升的敏感程度由高至低为弹性场、电场和磁场.     

磁电弹性体中纳米孔边任意位置贯穿裂纹的解析解

本文研究了反平面机械载荷、面内电载荷和面内磁载荷作用下磁电弹材料中含有纳米尺度孔边任意位置贯穿裂纹的Ⅲ型断裂力学性能.基于Gurtin-Murdoch表面弹性理论考虑纳米缺陷(孔洞和裂纹)的表面效应,利用磁电弹理论和复变弹性理论获得了纳米缺陷表面为磁电不可通条件下磁电弹场的精确解,给出了贯穿裂纹两端裂尖的磁电弹场强因子的解析表达.所得结果与已有研究比较说明了本文方法的有效性.讨论了裂纹位置、裂纹相互作用与施加多物理场载荷对无量纲磁电弹场强因子的影响.结果表明：贯穿裂纹裂尖的无量纲磁电弹场强因子尺寸效应显著;缺陷表面效应对裂纹耦合尖端场的影响受裂纹位置的制约;无量纲磁电弹场强因子受贯穿裂纹两端的裂纹长度比与施加力电磁载荷的显著影响.     

SMA短纤维复合材料的热胀系数和相变应变系数

基于Eshelby的等效夹杂模型、Mori和Tanaka的场平均法,考虑到形状记忆合金（SMA）的强物理非线性,发展了增量型的等效夹杂模型（Incremental Equivalent Inclusion Model)。讨论了SMA短纤维增强的铝基复合材料的热胀系数和相变应变系数。特别研究了SMA短纤维复合材料纤维几何尺寸和体积分数等参数对SMA复合材料的热胀系数和相变应变系数的影响。这些工作对于指导材料设计和了解SMA复合材料热机械特性是非常有意义的。     

短纤维复合材料的压缩强度

细观力学理论得到的复合材料内应力是均值应力,在进行破坏和强度预报前,必须转化到真实值.对于短纤维复合材料,除了轴向压缩真实应力外,基体其它方向真实应力计算已得到解决,等于其均值应力乘以基体应力集中系数.论文基于弹性力学方法得到了短纤维复合材料轴向压缩下基体的应力场,并据此定义基体的轴向压缩应力集中系数.与基体其它方向应...     

三维机织复合材料的弹性性能预报模型

建立了基于等效响应比拟技术的三维机织复合材料弹性性能预报模型．首先将三维机织物的结构单元分解为4个子元(经纱、纬纱、填充纱和接结纱),用几何模型去估算这些子元的体积分数．然后依据不同的外载形式,将复合材料的应力-应变关系等效地表达为3组诸子元所组成的三维弹簧网络．根据刚度系数的物理意义,采用不同的弹簧网络连接形式,并按体积平均化方法获得材料总体刚度矩阵中相应的刚度系数,进而计算得到三维机织复合材料的9个弹性系数．该模型考虑了层内交织经纱、层间交织接结纱的弯曲以及材料内部纯树脂区对三维机织复合材料弹性性能的影响．试验结果与模型的理论预测值进行比较,表明这个模型是有效的。     

An analytical and numerical approach for calculating effective material coefficients of piezoelectric fiber composites

The present work deals with the modeling of 1–3 periodic composites made of piezoceramic (PZT) fibers embedded in a soft non-piezoelectric matrix (polymer). We especially focus on predicting the effective coefficients of periodic transversely isotropic piezoelectric fiber composites using representative volume element method (unit cell method). In this paper the focus is on square arrangements of cylindrical fibers in the composite. Two ways for calculating the effective coefficients are presented, an analytical and a numerical approach. The analytical solution is based on the asymptotic homogenization method (AHM) and for the numerical approach the finite element method (FEM) is used. Special attention is given on definition of appropriate boundary conditions for the unit cell to ensure periodicity. With the two introduced methods the effective coefficients were calculated for different fiber volume fractions. Finally the results are compared and discussed.     

Effective multi-field properties of electro-magneto-thermoelastic composites estimated by finite element method approach

A finite element approach based on the micromechanics was performed to estimate the multi-field properties of electro-magneto-thermoelastic composites. The thermal field and the involved pyroelectric and pyromagnetic effect of the multi-phase composite materials were taken into account in the investigation and implemented in the finite element modeling. The multifields related to the electric field, magnetic field, deformation and temperature field, as well as their coupling effects of the smart composites under periodic boundary conditions were obtained numerically. Especially, by means of the homogenization approximation, the effective thermal expansion coefficients, pyroelectric coefficients, pyromagnetic coefficients and other elastic, electric,and magnetic properties for the piezoelectric material, piezomagnetic material and magnetoelectric material were calculated, respectively. Some results are compared to the theoretical predictions by the well-known Mori-Tanaka method to show good agreements.     

Variational bounds for anisotropic elastic multiphase composites with different shapes of inclusions

In the present work, unified formulae for the overall elastic bounds for multiphase transversely isotropic composites with different geometrical types of inclusions embedded in a matrix are calculated, including the spherical and long or short continuous cylindrical fiber cases. The influence of the different geometrical configurations of the inclusions on the composites is studied. The transversely isotropic effective bounds are obtained by applying the variational formulation for anisotropic composites developed by Willis, which relies on expressions for the static transversely isotropic Green’s function. Some numerical calculations and comparisons with the effective coefficients derived from the self-consistent approach, asymptotic homogenization method, and finite element method (FEM) are shown for different aspect ratio values, exhibiting good agreement.     

Antiplane magneto-electro-elastic effective properties of three-phase fiber composites

In the present work, applying the asymptotic homogenization method (AHM), the derivation of the antiplane effective properties for three-phase magneto-electro-elastic fiber unidirectional reinforced composite with parallelogram cell symmetry is reported. Closed analytical expressions for the antiplane local problems on the periodic cell and the corresponding effective coefficients are provided. Matrix and inclusions materials belong to symmetry class 6mm. Numerical results are reported and compared with the eigenfunction expansion-variational method (EEVM) and other theoretical models. Good agreements are found for these comparisons. In addition, with the herein implemented solution, it is possible to reproduce the effective properties of the reduced cases such as piezoelectric or elastic composites obtaining good agreements with previous reports.     

粘弹性树脂基三维编织复合材料的热膨胀性能研究

首先利用均匀化理论并结合有限元法研究了三维编织复合材料的粘弹性效应,根据松弛模量的计算结果研究了材料热膨胀系数随时间的变化关系,在此基础上,给出了编织结构和工艺参数(编织角、纤维体积比)对材料初始热膨胀系数的影响规律,计算结果与实验值吻合较好。本文工作为深入研究三维编织复合材料的热粘弹性能提供了基础。     

Thermoelastic determination of individual stress components in loaded composites

An experimental-numerical hybrid method is developed for determining the individual stresses in orthotropic composites from measured thermoelastic information. This includes evaluating the thermoelastic calibration coefficients, effective processing of the noisy measured data, and separating the stress components at nonboundary locations. The method is illustrated experimentally by application to a uniaxially loaded fiber-reinforced composite plate containing a central circular hole.     

Micromechanics of ferroelectric polymer-based electrostrictive composites

Electrostriction refers to the strain induced in a dielectric by electric polarization, which is usually very small for practical application. In this paper, we present a micromechanical analysis on the effective electrostriction of a ferroelectric polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] polymer-based composite, where the exact connections between the effective electrostrictive coefficients and effective elastic moduli are established, and numerical algorithm for the prediction of the effective electrostrictive coefficients of the composite in terms of its microstructural information is developed. From our calculations, enhanced electrostriction in the composite has been demonstrated, and optimal microstructure for electrostriction enhancement has been identified. Our analysis provides a mechanism for the electrostriction enhancement, where the electrostrictive strain several times higher than that of polymer matrix can be obtained, if the microstructure of the composites can be carefully tailored.     

Electroelastic behavior modeling of piezoelectric composite materials containing spatially oriented reinforcements

In this work, a modeling of electroelastic composite materials is proposed. The extension of the heterogeneous inclusion problem of Eshelby for elastic to electroelastic behavior is formulated in terms of four interaction tensors related to Eshelby’s electroelastic tensors. Analytical formulations of interaction tensors are presented for ellipsoidal inclusions. These tensors are basically used to derive the self-consistent model, Mori–Tanaka and dilute approaches. Numerical solutions are based on numerical computations of these tensors for various types of inclusions. Using the obtained results, effective electroelastic moduli of piezoelectric multiphase composites are investigated by an iterative procedure in the context of self-consistent scheme. Generalised Mori–Tanaka’s model and dilute approach are re-formulated and the three models are deeply analysed. Concentration tensors corresponding to each model are presented and relationships of effective coefficients are given. Numerical results of effective electroelastic moduli are presented for various types of piezoelectric inclusions and for various orientations and compared to existing experimental and theoretical ones.     

Effect of pore shape on effective porothermoelastic properties of isotropic rocks

The present work is devoted to the determination of the macroscopic poroelastic and porothermoelastic properties of geomaterials or rock-like composites constituted by an isotropic matrix with embedded ellipsoidal inhomogeneities and/or pores randomly oriented. By considering the solution of a single ellipsoidal inhomogeneity in the homogenization problem it is possible to observe the significant influence of the shape of inhomogeneities on the effective porothermoelastic properties. In the particular case of microscopic and macroscopic isotropic behaviors, a closed form solution based on analytical integrate of the Eshelby solution for the single ellipsoidal inhomogeneity can be obtained for the randomly oriented distribution. This result completes the well known solutions in the limiting cases of spherical and penny shape inhomogeneities. Based on recent works on porous rock-like composites such as shales or argillites, an application of the developed solution to a two-level microporomechanics model is presented. The microporosity in homogenized at the first level, and multiple solid mineral phase inclusions are added at the second level. The overall porothermoelastic coefficients are estimated in the particular context of heterogeneous solid matrix. Numerical results are presented for data representative of isotropic rock-like composites.     

The analysis of thermoplastic characteristics of special polymer sulfur composite

Specific chemical environments step out in the industry objects. Portland cement composites (concrete and mortar) were impregnated by using the special polymerized sulfur and technical soot as a filler (polymer sulfur composite). Sulfur and technical soot was applied as the industrial waste. Portland cement composites were made of the same aggregate, cement and water. The process of special polymer sulfur composite applied as the industrial waste is a thermal treatment process in the temperature of about 150–155 \(^{\circ }\hbox {C}\). The result of such treatment is special polymer sulfur composite in a liquid state. This paper presents the plastic constants and coefficients of thermal expansion of special polymer sulfur composites, with isotropic porous matrix, reinforced by disoriented ellipsoidal inclusions with orthotropic symmetry of the thermoplastic properties. The investigations are based on the stochastic differential equations of solid mechanics. A model and algorithm for calculating the effective characteristics of special polymer sulfur composites are suggested. The effective thermoplastic characteristics of special polymer sulfur composites, with disoriented ellipsoidal inclusions, are calculated in two stages: First, the properties of materials with oriented inclusions are determined, and then effective constants of a composite with disoriented inclusions are determined on the basis of the Voigt or Rice scheme. A brief summary of new products related to special polymer sulfur composites is given as follows: Impregnation, repair, overlays and precast polymer concrete will be presented. Special polymer sulfur as polymer coating impregnation, which has received little attention in recent years, currently has some very interesting applications.