The transient response of a functionally graded piezoelectric rod subjected to a moving heat source under fractional order theory of thermoelasticity

The transient thermo-piezoelectric response of a functionally graded piezoelectric rod subjected to a moving heat source is investigated in the context of fractional order theory of thermoelasticity proposed by Sherief. The material properties of the functionally graded piezoelectric rod are assumed to vary exponentially along the length, except for the thermal relaxation time and the specific heat, which are taken to be constant. To solve the governing equations of the problem, Laplace transform is applied, eliminating the time effect; the analytical solutions of the displacement, stress, temperature, and electric field in Laplace domain are obtained. Subsequently, the solutions of the considered variables in time domain are obtained by numerical Laplace inversion and illustrated graphically. In calculation, the effect of the fractional order parameter on the variations of the considered variables is presented.     

压电与导体双材料界面端的奇异性研究

提出了一种求解平面应变条件下横观各向同性压电与导体双材料界面端的应力及电位移奇异性的特征值法。基于横观各向同性压电材料的基本方程和一阶近似假设,利用分离变量形式的位移函数和电势函数,导出了关于应力和电位移奇异性指数的奇异性特征方程。求解由无网格法离散的特征方程,即可得到应力和电位移的各阶奇异性指数,同时还可得到相应的应力和电位移角函数。数值计算结果与文献中给出的结果非常吻合,表明该方法具有很高的精度和效率。     

基于分数阶热弹性理论的含有球型空腔无限大体的热冲击动态响应

基于新近提出的分数阶广义热弹性理论,研究了含有球型空腔的无限大体受热冲击作用时的动态响应。该文给出分数阶广义热弹性理论下的控制方程,通过拉普拉斯积分变换及其数值反变换对控制方程进行了求解,得到了带有球型空腔无限大体中的无量纲温度、位移、径向应力和环向应力等物理量的分布规律。计算中重点研究了分数阶参数对各物理量的影响效应。结果表明:含有球腔的无限大体内由于热冲击而出现了热弹耦合效应;分数阶参数显著地影响各物理量的分布规律。     

压电陶瓷场致疲劳特性与机理研究进展

压电陶瓷的场致疲劳是材料性能在外加循环载荷作用下逐步退化的现象, 是导致其失效的主要因素, 近年来一直是国内外的研究热点. 本文综合分析了压电陶瓷在电场, 多场耦合(力-电-温度)作用下的疲劳机理和影响因素, 并对压电陶瓷场致疲劳的未来研究方向进行了展望.     

Electric response to pulse thermal impact from layered magnetoelectric composites of PZT-NiZn-ferrite ceramics

Electric responses of magnetoelectric composite structures with 2–2 coherence to thermal impact are presented. The detected electric response consists of two components having different dependences on the modulation frequency of heat flow. It is shown that in the piezoelectric ceramics PZT-NiZn-ferrite two-layered composite system electric signal forms as a result of the pyroelectric effect and mechanical interaction of ferrite and PZT plate that have expanded from heating.     

BiAlO3掺杂PZT陶瓷的高压电性能和低电场应变滞后

铅基压电陶瓷因其优异的压电性能, 被广泛应用于压电器件。其中, 压电驱动器要求压电陶瓷具有较高压电性能并且在电场下具有较高的电致应变和较小的应变滞后。本研究通过施主-受主共掺, 得到高压电性能和低电场应变滞后的PZT陶瓷。采用传统固相反应法制备了(1-x)(Pb_0.95Sr_0.05)(Zr₅₃Ti₄₇)O₃-xBiAlO₃+0.2%MnO₂陶瓷(掺杂量为质量百分数), 并对其微观结构和压电性能进行了研究。结果表明：BiAlO₃掺杂量较少时, 陶瓷中缺陷偶极子的“钉扎”效应使得陶瓷畴壁转动困难, 陶瓷压电性能较弱, 应变滞后也较小。随BiAlO₃掺杂量增加, 缺陷偶极子“钉扎”效应减弱, 陶瓷的压电性能和应变滞后随之提高。本实验得到的性能最优组分为x=1.75%, 该组份陶瓷的压电系数d₃₃=504 pC/N, 机电耦合系数k_p=0.71, 机械品质因数Q_m=281, 居里温度T_C=312 ℃, 在10 kV/cm电场下的应变滞后仅为15%, 并且还具有较好的温度稳定性, 是一种具有应用价值的压电驱动器用压电陶瓷材料。     

Effect of gravity field and moving internal heat source on a 2-D problem of thermoelastic fiber-reinforced medium: Comparison of different theories

A new fiber-reinforced model has been constructed by taking into account the deformation of a generalized thermoelastic medium with internal heat source. A general model of the equations of the formulation in the context of the Lord–Shulman theory that includes one relaxation time and Green–Lindsay theory with two relaxation times, as well as the classical dynamical coupled theory, is applied to study the influence of gravity and reinforcement on the total deformation of a thermoelastic medium. The normal mode analysis is used to obtain the exact expressions for the physical quantities. The variations of the considered variables with the horizontal distance are illustrated graphically. Comparisons are made with the results in the three theories in the presence and absence of reinforcement, gravity, and moving internal heat source.     

Fatigue crack growth driven by electric fields in piezoelectric ceramics and its governing fracture parameters

Fatigue crack growth test for piezoelectric ceramics was performed under cyclic electric loading. Double cantilever beam specimen, which was made of two different piezoelectric ceramics, with a through notch was used. The specimens were, varying the amplitude and the mean value, subjected to various cyclic electric fields. It was found that crack growth behavior is greatly dependent on the amplitude and mean value of cyclic electric field and materials. Crack growth rate decreased as electric field increased and finally stopped. Crack growths under the positive, the negative and the shifted electric field were very slow compared to that under fully reversed electric field. However, threshold for the crack propagation did not depend greatly on materials. Then, as possible governing fracture parameters, CED and electric displacement intensity factor were chosen based on the results of electromechanical finite element analysis within linear framework and their closed form equations were also obtained considering the influences of electric boundary conditions inside the notch. Finally, the parameters were correlated with crack growth rate measured experimentally by employing Paris law type equation.     

压电梯度薄壳的高阶理论解

压电功能梯度执行器能产生较大的位移、降低应力峰值并避免了粘结层带来的问题,压电梯度超声换能器能拓展频带宽度。本文作者提出了一个简单而有效的求解压电梯度薄壳力、电行为特性的高阶理论。设定位移分量为壳厚的线性函数,而电势沿厚度方向为二次分布。考虑了压电作动元的驱动信号不同时所具有的不同形式的电荷平衡方程。应用Fourier级数法得到压电系数沿厚度坐标变化的梯度壳的力电耦合的解析解。所得结果可退化至梁、板等多种特殊情况。利用所得方程分析了一非均匀简支压电层合板,并与三维精确结果作了对比,两者吻合得很好,表明该理论的正确性。最后具体求解了压电梯度圆柱壳的力、电特性,给出了位移、应力、电势沿厚度方向的变化规律。     

PZN-PZT压电陶瓷及其PVDF压电复合材料的制备和性能

采用固相烧结法合成了PZN-PZT(铌锌锆钛酸铅)三元系压电陶瓷烧结块材和粉末,并采用XRD、SEM等测试方法对其结构和性能进行了分析。PZN-PZT常压烧结陶瓷具有优良的压电性能,PZN-PZT颗粒粒径在0.5~4 μm之间,颗粒形态不太规整。采用溶液共混法将PZN-PZT粒子均匀分散于PVDF基体中,制备了PZN-PZT/PVDF 0-3型压电复合材料。研究了PZN-PZT质量分数、极化电场等因素对该压电复合材料压电和介电性能的影响。实验结果表明,选用压电活性更高的压电陶瓷粉末进行复合,可有效提高压电复合材料的压电性能。增加PZN-PZT质量分数、提高极化电压均有利于复合材料压电性能的提高。     

(Na1/2Bi1/2)TiO3(NBT)无铅压电陶瓷的研究进展

对(Na1/2Bi1/2)TiO3基无铅压电陶瓷的研究现状进行了综述.着重概括了通过元素替代/掺杂手段对NBT陶瓷性能的影响规律.该系统陶瓷具有的强铁电性质与Bi3 密切相关;材料压电性能可通过改性技术进行调节:如通过加入第二组元化合物降低其矫顽场而提高NBT基陶瓷压电性能.总结了(Na1/2Bi1/2)TiO3基无铅压电陶瓷组成的研究思路和方向.     

Quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics under both DC and AC bias

The basic quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) transparent ceramics have been studied under both DC and AC electric field bias. The contribution of piezoelectric resonance to electro-optic effect for this quadratic electro-optic ceramics material has been experimentally demonstrated and theoretically analyzed. It is found that, at the piezoelectric resonance frequencies, the piezoelectric induced electro-optic effect dominates and leads to a dramatically high sensitivity for weak electric signal detection. About 20 dB signal-to-noise ratio is attained when detecting AC electric field strength of 1 V/m with optimized DC bias. Besides, the effects of AC frequency and amplitude on halfwave voltage V(π) of PMN-PT are investigated.     

A study on influence of poling direction on piezoelectric plate weakened by two collinear semi-permeable cracks

A study on the influence of change in poling direction is carried out for mechanical and electric strip-yield model for a transversely isotropic piezoelectric plate cut along two equal collinear semi-permeable straight hairline cracks. Two cases are considered, when the developed saturation zone is bigger or smaller than mechanical yield zone. The Stroh formalism and complex variable technique are employed to obtain the solution. The effect of change in poling direction is studied on crack opening displacement, crack opening potential drop and energy release rate. Also, a study is carried out on the suitability of crack closure for different piezoelectric ceramics. The obtained results are presented graphically and discussed.     

A 2D problem of time-fractional heat order for two-temperature thermoelasticity under hydrostatic initial stress

The present study solves the problem of thermoelastic interactions in a half-space medium under hydrostatic initial stress in the context of a fractional order heat conduction model with two-temperature theory. The analytical solutions of the field variables are obtained by using the normal mode analysis. The obtained solutions are then applied to a specific problem for a thermally insulated surface which is acted upon by a load. The distributions of the two temperatures, displacements, and the stress components inside the half-space are studied. The graphical results depict that the fractional parameter has significant effects on all the studied field variables. Comparisons are made within the theory in the presence and absence of the hydrostatic initial stress. Thus, we can conclude that the fractional order generalized thermoelasticity model may be an improvement on studying elastic materials.     

Analysis of nonlinear transient responses of piezoelectric resonators

The electric transient response method is an effective technique to evaluate material constants of piezoelectric ceramics under high-power driving. In this study, we tried to incorporate nonlinear piezoelectric behaviors in the analysis of transient responses. As a base for handling the nonlinear piezoelectric responses, we proposed an assumption that the electric displacement is proportional to the strain without phase lag, which could be described by a real and constant piezoelectric e-coefficient. Piezoelectric constitutive equations including nonlinear responses were proposed to calculate transient responses of a piezoelectric resonator. The envelopes and waveforms of current and vibration velocity in transient responses observed in some piezoelectric ceramics could be fitted with the calculation including nonlinear responses. The procedure for calculation of mechanical quality factor Q(m) for piezoelectric resonators with nonlinear behaviors was also proposed.     

Fractional Order Thermoelasticity Theory for a Half-Space Subjected to an Axisymmetric Heat Distribution

The present work is concerned with a traction-free thermoelastic half-space subjected to a known axisymmetric temperature distribution. The thermoelastic interactions inside the medium are investigated by employing the fractional order theory of thermoelasticity. The problem is solved by using Laplace's and Hankel's transforms. The inverse transforms are computed numerically. The variations of temperature, displacements, and stresses inside the half-space are investigated. The field variables for a particular material are graphically presented. Comparisons are made within the theory in the presence and absence of fractional order parameter.     

Nonlinear thermal bending response of FGM plates due to heat conduction

Nonlinear thermal bending analysis is presented for a simply supported, shear deformable functionally graded plate without or with piezoelectric actuators subjected to the combined action of thermal and electrical loads. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction and the electric field considered only has non-zero-valued component E_Z. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM and piezoelectric layers are assumed to be temperature-dependent. The governing equations of an FGM plate are based on a higher order shear deformation plate theory that includes thermo-piezoelectric effects. A two step perturbation technique is employed to determine the thermal load–deflection and thermal load–bending moment curves. The numerical illustrations concern nonlinear bending response of FGM plates without or with surface bonded piezoelectric actuators due to heat conduction and under different sets of electric loading conditions. The results reveal that for the case of heat conduction the nonlinear thermal bending responses are quite different to those of FGM plates subjected to transverse mechanical loads, and the temperature-dependency of FGMs could not be neglected in the thermal bending analysis.     

基于压电效应的人工耳蜗的实验研究

为了提高聋耳的听力, 将压电材料植入到耳蜗内, 利用压电效应直接将声波转化为电信号刺激听神经, 以提高听力. 本研究通过未极化与极化的高灵敏性压电陶瓷的对比, 从体外模拟实验中的声电响应曲线和动物体内植入实验的结果中得到: 未极化的压电陶瓷没有压电响应, 而极化后的压电陶瓷能够将声音信号转化为电信号, 证实了压电陶瓷的压电特性的确可以刺激动物的听神经, 从而降低听阈阈值. 比较了压电陶瓷与压电高分子之间的差异, 结果表明压电高分子也可以刺激听神经来提高听力.     

Assessment of coupled 1D models for hybrid piezoelectric layered functionally graded beams

A unified formulation is presented for coupled efficient zigzag, third order, consistent third order and first order models for hybrid piezoelectric layered FGM beams under thermoelectromechanical load. The transverse as well as inplane electric fields are considered. The potential and thermal fields are discretised sublayerwise as piecewise linear which can adequately approximate the actual distributions of these fields across the thickness. The zigzag theory accounts for the non-uniform deflection across the thickness due to the potential and thermal fields and satisfies exactly the conditions on transverse shear stress at the top, bottom and layer interfaces. The governing equilibrium equations have been derived from a variational principle. For the first time, the accuracy of the 1D models is assessed in direct comparison with the exact 2D solutions for elastic as well as piezoelectric hybrid layered FGM beams for mechanical, potential and thermal loads. The effects of the inhomogeneity parameter, span-to-thickness ratio and electric boundary conditions are investigated. It is established that the zigzag theory results are superior to those of other 1D models, even though they have the same number of displacement variables.