Effect of bound water on piezoelectric,dielectric, and elastic properties of wood

The interaction of water with wood, such as bamboo and cedar, is investigated by measuring their complex piezoelectric, dielectric, and elastic constants between -150 and 150°C at 10 Hz. Bamboo and cedar are found to have two hydration-dependent elastic loss peaks; one is observed at about -100°C and the other at about -40°C. The former loss peak is due to the adsorbed water in the hydration range between 0 and 4% moisture content (MC) and the latter to the adsorbed water above 4% MC. These two types of water are considered bound on different sites in the regions around crystalline cellulose, where molecules of one type associate with each other and molecules of the other are unassociated. We consider that the piezoelectric polarization of wood is attributed to the rotation of hydroxyl groups in the crystal lattice of cellulose. The piezoelectric constants are observed to decrease but the elastic and dielectric constants to increase with increasing hydration. The effect of adsorbed water on elastic losses in bamboo and cedar are found to be similar to that in collagenous substances.     

三维编织压电陶瓷基复合材料有效电弹性性能有限元分析

基于三维编织预制件的细观结构,建立了三维编织压电陶瓷基复合材料位移-电耦合场有限元模型,利用电弹性场体积平均思想和有限元方法研究了周期分布三维编织压电陶瓷基复合材料的有效电弹性性能。通过对代表性体积单元施加位移载荷和电载荷边界条件,预测了不同纤维体积分数下三维编织压电陶瓷基复合材料的有效弹性常数、压电常数和介电常数。计算结果表明,三维编织压电陶瓷基复合材料可显著改善压电陶瓷的整体力学性能,且保持了较好的电学性能。     

Method for Obtaining the Full Set of Linear Electric, Mechanical, and Electromechanical Coefficients and All Related Losses of a Piezoelectric Ceramic

A method based on the use of four piezoelectric resonances for three sample geometries is presented that allows one to obtain all the dielectric permittivities, compliances, and piezoelectric coefficients of a piezoelectric ceramic in complex form and, therefore, all related losses. Piezoelectric losses are responsible for heat generation and hysteresis in actuators. The method is applied to a Navy type II PZT-based piezoelectric ceramic (PZT = lead zirconate titanate), for which the full set of linear electric, mechanical, and electromechanical coefficients is given in complex form. Full sets of coefficients for the available piezoceramics are required for exploiting all the possibilities of finite element analysis, both in fundamental research (mechanisms of degradation) and in development (element design). This numerical technique is necessary to explore arbitrary shapes provided by solid free-form-fabrication technologies.     

Intrinsic Elastic, Dielectric, and Piezoelectric Losses in Lead Zirconate Titanate Ceramics Determined by an Immittance-Fitting Method

The material coefficients of "soft" and "hard" lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least-squares-fitting of immittance data measured for length-extensional bar resonators. The piezoelectric d -constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not "intrinsic" losses, a calculation process to evaluate the "intrinsic" losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ∼50% of the loss of piezoelectric d -constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses.     

Noniterative method for evaluation of the complex material constants of piezoelectric ceramics in the radial vibration mode

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the radial mode, was proposed.This method uses the standard procedure to determine the elastic compliance and Poisson factor and the measurement of admittance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations.The accuracy of the new method was determined for materials with different planar coupling coefficients (k_p = 2.5-57%) and mechanical quality factors (Q_m = 20-3000). This method proved to be very accurate for all materials especially for those with large coupling factors. The accuracy of standard method was also evaluated for the same materials.     

Algorithm for solving problems related to the natural vibrations of electro-viscoelastic structures with shunt circuits using ANSYS data

ABSTRACT

An algorithm for numerical realisation of a mathematical statement of the natural vibrations problem for electro-viscoelastic bodies with passive external electric circuits (i.e. shunting circuits) with an arbitrary configuration using the finite element method is proposed in the present paper. The proposed algorithm allows considering the viscoelastic properties of materials using the model of linear hereditary viscoelasticity with complex dynamic moduli and is used to solve 3D solid structure problems that are compatible for ANSYS package element types. This technique implies the usage of the global assembled matrices of stiffness and mass, formed in the ANSYS package. The basis of the algorithm is a novel approach that allows performing decomposition of the global assembled stiffness matrix formed in the ANSYS software package into constituents that are needed for calculation of the natural vibration frequencies of the objects under study. These matrix components are used in the program that was written in FORTRAN (Formula Translation) language. This problem could be efficiently applied for analysis of the dynamic processes in smart systems based on piezoelectric materials and could also form a basis for the development of numerical finite element algorithms for optimization of the dissipative characteristics of electromechanical systems with shunted piezoelectric elements.     

Evaluation of the complex material constants of piezoelectric ceramics in the thickness vibration mode

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the thickness extensional mode, was proposed.This method is very flexible, as it is based on the standard approach to determine the elastic stiffness, followed by the measurement of the impedance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations.The new method was tested on materials with various thickness coupling factors (k_t = 4.5–60%) and mechanical quality factors (Q_mt = 20–1600), proving very good accuracy for all of them.The accuracy of standard method was also evaluated for the same materials.     

Long-term aging characteristics of high coupling factor PMS piezoelectric ceramics

The aging characteristics of high coupling factor piezoelectric ceramics (K_p = 63%) in the PMS system [x Pb(Mn_1/3Sb_2/3)O₃-y PbTiO₃-z PbZrO₃, where x + y + z = 11 have been measured for the duration of 14 years. The results indicate that the aging properties of the ceramic are very good. The piezoelectric and dielectric constants of the material stabilized and remained at constant levels one month after the time of poling. In a comparison of the parameters measured after 14 years against those measured one month after poling, the resonance frequency f_r increased by 0.1%, the antiresonance frequency f_a decreased by 0.2%, the planar coupling factor K_p decreased by 0.5%, and the dielectric constant, mechanical and dielectric quality factors showed no noticeable change. It is anticipated that this piezoelectric ceramic may be used more widely in different devices.     

Complex piezoelectric, elastic, and dielectric coefficients of La-DOPED 0.93 Pb(Mg1/3Nb2/3)O3:0.07 PbTiO3 under DC bias

Complex material parameters (piezoelectric coefficient d₃₁, elastic s₁₁^E, and the dielectric constant K₃₃) of the relaxor ferroelectric ceramic (1-x) Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃(x =.07) with 1% La (lanthanum) were measured as a function of bias field using a bar resonator. The values of the dielectric and piezoelectric phase angles are found to be comparable (i.e., around 0.04 for a d.c. bias field of 2.5 kV/cm), while the elastic phase angle is an order of magnitude smaller (0.001 for the same d.c. bias). For comparison of complex material parameters found from bar resonators, a sample in the form of a small disk is used to measure Poisson's ratio as well as the real components of the piezoelectric and elastic coefficients as a function of bias field.     

0-3型压电陶瓷/硫铝酸盐水泥复合材料的介电性能和压电性能

用压制成型法，以水泥为基体，铌镁锆钛酸铅(lead magnesium niobate-lead zireonate-lead titanate，PMN)陶瓷颗粒为功能体制备了水泥基压电复合材料。分析讨论了复合材料的压电性能和介电性能。研究了水泥水化龄期对复合材料压电性能的影响，并对其机理进行了初探。结果表明：随着PMN含量的增加，压电复合材料的压电应变常数d33和介电常数均增大；不像压电陶瓷或压电复合材料的压电性能随时问的延长而减弱，水泥基压电复合材料的压电性则是随着水泥水化龄期的延长而增加，当到达一定龄期后，压电性能趋于稳定。     

The role of 90° domain wall displacements in forming physical properties of perovskite ferroelectric ceramics

A proposed model which takes into account an elastic interaction between a polydomain grain and a surrounding ceramic matrix under weak external mechanical stresses has been used for evaluating a contribution from 90° domain wall displacements to piezoelectric and elastic constants of the perovskite ferroelectric ceramics. A difference between experimental and averaged constants of BaTiO₃ ceramics can be explained by the estimated contribution.     

INFLUENCE OF THE DRYING MEDIUM PARAMETERS ON DRYING INDUCED STRESSES

ABSTRACT

A thermomechanical model of drying of capillary-porous materials whose material constants depend on moisture content and temperature is presented in the paper. The finite element method is used for the solution of two-dimensional problem of convective drying of a prismatic bar. The moisture distributions, temperature distributions, drying induced strains and stresses for various drying medium parameters are determined. The effect of these parameters on moisture distribution and in particular on drying induced stresses is discussed.     

Fabrication and evaluation of PZT/Pt piezoelectric composites and functionally graded actuators

The PZT/Pt composites with various compositions were fabricated by using powder processing, and their mechanical, dielectric, piezoelectric and elastic properties were evaluated with the purpose to develop piezoelectric actuators with functionally graded microstructure (FGM). The piezoelectric and dielectric constants of the PZT/Pt composites decreased monotonously with increasing Pt content, whereas the addition of the Pt particles greatly improved the mechanical properties, particularly the fracture toughness in the composites. Miniature bimorph-type FGM actuators that consist of a composite internal-electrode (70 vol.%PZT/30 vol.%Pt) and three piezoelectric layers (100 vol.%PZT to 80 vol.%PZT/20 vol.%Pt) were fabricated by powder stacking and normal sintering techniques. The electrically-induced deflection characteristics of such an FGM actuator were measured with electric strain gages mounted on the top and bottom surfaces of the actuators, and the measured data were consistent with the analytical results given by the modified classical lamination theory model (CLT).     

Electromechanical Response of Piezoelectric Honeycomb Foam Structures

A finite element model is developed to characterize the complete electromechanical properties of the most general form of elastically anisotropic and piezoelectrically active foams with honeycomb structures. Four classes of piezoelectric honeycomb structures are identified depending on the relative orientation of the poling direction with the porosity direction (longitudinal and transverse) and the geometry of the honeycombs (isotropic and anisotropic). It is observed that: (i) Most of the elastic, dielectric, and piezoelectric constants of the longitudinally porous honeycomb foams exhibit linear dependence on the volume fraction (or relative density) of the material; (ii) The electromechanical properties of transversely porous foam structures (with the exception of C₂₂ and κ₂₂) exhibit significant dependence on the shape of the porosity; (iii) The piezoelectric figures of merit of the longitudinally porous foams do not exhibit significant dependence on the shape of the porosity; (iv) The piezoelectric figures of merit of the transversely porous foams exhibit a strong dependence on the shape of the porosity with the hexagonal foams exhibiting enhanced hydrostatic strain coefficient and lower acoustic impedance while the square foams exhibiting enhanced piezoelectric coupling constant and hydrostatic figure of merit; (v) In transversely porous anisotropic honeycomb structures, the shear elastic constants such as C₁₂ and C₆₆ and some figures of merit are enhanced significantly when compared to their isotropic counterparts. For example, in the PZT–7A transversely porous anisotropic honeycomb structures with 10% relative density, the hydrostatic figure of merit is expected to be 2485% greater than that predicted for the transversely porous isotropic honeycomb structures.     

A model for 0‐3 piezoelectric composites with an interlayer

Based on the model for 0‐3 piezoelectric composites without an interlayer, a modified model for 0‐3 piezoelectric composites with an interlayer has been proposed and the expressions for this model consequently have been derived. The interlayer is supposed to act as a bridge between the ceramic and polymer matrix during the poling process. The calculated results show that the electric field strength on ceramic phase is influenced by the volume fraction of interlayer and ceramic in the composite, and dielectric constants of interlayer, ceramic, and polymer matrix. The electric field strength on ceramic phase increases with the interlayer volume fraction and dielectric constant ratio of interlayer and polymer matrix. This indicates that the ceramic polarization and piezoelectric performance of 0‐3 piezoelectric composites can be improved by design of the interlayer with appropriate dielectric constants and volume fractions into the 0‐3 piezoelectric composites. POLYM. COMPOS., 31:1922–1927, 2010. © 2010 Society of Plastics Engineers.     

Finite Element Simulation of Magnetostrictive and Piezoelectric Coupling in a Layered Structure

A magnetostrictive and piezoelectric coupling model that estimates the electric/magnetic transfer efficiency (dE/dH) is presented. The simulation is based on finite element method with partial differential equations correlating electrical, elastic, and magnetic properties, within certain volume at different boundary conditions. A mathematical formula is appended to the original piezoelectric and magnetostrictive equations to simulate the saturated elastic responses in the coupled systems. A sandwich magnetostrictive/piezoelectric/magnetostrictive structure is modeled that permits simulated evaluation of coupling properties e.g., magnetostrictive coefficient and strain vs. magnetic field response. The electromagnetic transfer efficiency of the modeled results is in good agreement with experimental value in literature.     

Multi-parameter models of the viscoelastic/plastic mechanical properties of coatings via combined nanoindentation and non-linear finite element modeling

Coatings deteriorate from a variety of failure mechanisms. To improve coating durability and/or enable structure-performance correlations, it is necessary to develop more advanced methods of mechanical characterization. For complex multifunctional coatings, multi-parametric constitutive models that simultaneously account for elastic, viscoelastic, and plastic mechanical properties should be used, especially when mechanical properties in the (macro-scale) bulk state differ from properties that occur as a result of thin-film application, post-treatment processes, or aging effects. The nanoindentation creep experiment combined with non-linear finite element modeling of nanoindentation is an effective tool for characterizing the properties of such coatings. Three- and four-parameter viscoelastic/plastic finite element models, implemented using the ABAQUS™ commercial finite element software, have been developed to simulate the isotropic indentation response of coatings. Unified constitutive models where both plastic and viscoelastic deformation are considered simultaneously have not been published previously within the indentation modeling literature. The parameters are determined by an optimization program that automatically matches the load vs. indentation deformation plot from the nanoindentation experiment, with the load vs. indentation deformation plot obtained by the finite element simulation. The computed parameters become a unique “thumbprint” for a particular coating. These parameters may then be used as input data for more complex simulations, for example, capable of computing stress and strain fields, strain energy dissipation, residual stress, and residual strain during particulate scratching; or various other forms of mechanical loading.     

Electromechanical Properties of Porous Piezoelectric Ceramics

A theoretical approach is forwarded to predict the electromechanical properties of porous piezoelectric ceramics. The analysis is able to account for the effects of porosity shape and concentration and is applicable to piezoelectric ceramics of arbitrary material symmetry. By coupling the exact solution for a single ellipsoidal pore embedded in an infinite piezoelectric matrix with an effective medium approximation, the theory considers, in an approximate manner, interaction effects at finite porosity concentrations. The theoretical estimates are developed using a matrix formulation which enables all elastic, dielectric, and piezoelectric moduli of the porous solid to be readily computed. Numerical results are presented to illustrate the effects of the shape and concentration of the porosity on the effective electroelastic moduli and transducer parameters of practical importance. Particular attention is devoted to assessing the sensitivity of the effective electromechanical properties to the accuracy of the input data. Finally, theoretical estimates are shown to be in good agreement with existing experimental results for porous piezoelectric ceramics with various microstructural geometries.