Tubular channel growth in piezoelectric ceramics under electric fields

Tubular channel growth in a piezoelectric material with a conductive channel is investigated. Breakdown tests are performed on PZT807 samples with cylindrical bar shapes under purely electrical loading. It is experimentally observed that dielectric breakdown occurs via the formation of tubular channels, and the new tubular channel propagates in a straight direction through the specimen. The three-dimensional J integral for a tubular channel is used as a criterion for dielectric breakdown failure. The J integral at the onset of breakdown is calculated numerically through finite element analysis. The critical J integrals at the onset of breakdown are obtained.     

Electrical failure of piezoelectric ceramics with a conductive crack under electric fields

The failure behavior of piezoelectric ceramics with a conductive crack under purely electric loading is investigated. Electrical fracture tests are conducted to study the influence of the directions of poling and electric loading. Two failure modes of piezoelectric materials are observed: fracture that is accompanied with dielectric discharging and the formation of tubular channels without fracture. The critical J integrals at the onset of both fracture and breakdown are calculated numerically via finite element analysis. The effects of both the direction of the electric field and the poling direction on both fracture and breakdown resistance are discussed.     

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.     

Piezoelectric and pyroelectric properties of PZT/P(VDF-TrFE) composites with constituent phases poled in parallel or antiparallel directions

Composites of lead zirconate titanate (PZT) powder dispersed in a vinylidene fluoride-trifluoroethylene copolymer [P(VDF-TrFE)] matrix have been prepared by compression molding. Three groups of polarized samples have been prepared by poling: only the ceramic phase, the ceramic and polymer phases in parallel directions, and the two phases in antiparallel directions. The measured permittivities of the unpoled composites are consistent with the predictions of the Bruggeman model. The changes in the pyroelectric and piezoelectric coefficients of the poled composites with increasing ceramic volume fraction can be described by modified linear mixture rules. When the ceramic and copolymer phases are poled in the same direction, their pyroelectric activities reinforce while their piezoelectric activities partially cancel. However, when the ceramic and copolymer phases are poled in opposite directions, their piezoelectric activities reinforce while their pyroelectric activities partially cancel.     

PZSN系压电陶瓷X射线衍射分析

用Ｘ射线衍射法研究了ｐｂ「Ｚｎ１／３Ｎｂ２／３）（Ｓｎ１／３Ｎｂ２／３）」（ＺｒＴｉ）Ｏ３体系压电陶瓷的结构，探讨了微量元素掺杂对材料晶胞参数的影响，以及电极化前后的状况。结果表明：样品均为四方相钙钛矿型结构；掺杂微量元素后晶胞参数略有变化；极化使畴区发生９０°旋转，微应变增加，表现为晶胞中晶面的峰强反转。     

The charge-free zone model for electrically conductive cracks in dielectric and piezoelectric ceramics

The charge-free zone model for electrically conductive cracks in dielectric and piezoelectric ceramics is reviewed with the simplified constitutive equations and the regular constitutive equations and then applied to interpret the experimental results on window ceramic glass and poled lead zirconate titanate PIC 151 ceramics. A good agreement is found between the experimental results and the theoretical predictions from the charge-free zone model, which indicates that the concepts of fracture mechanics can be applied to the failure of conductive cracks in dielectric and piezoelectric ceramics.     

A Note on Tensile Testing of Poled and Unpoled Piezoelectric Ceramics

Abstract:  Tensile tests were carried out on unpoled and poled soft lead zirconate titanate (PZT) ceramic materials: APC #855 (APC International) and PZT-5H (Morgan Electro Ceramics). The tests were performed on a dog-bone specimen with holes at its edges. A methodology is presented for carrying out these tests. A tensile stress was applied by means of Kevlar strings through the specimen holes. The poling direction was perpendicular to the longitudinal specimen axis. For the poled specimens, two electrical boundary conditions were applied, namely, E  =   0 and D  =   0. Strains were measured at four points on the sample. For each specimen, the bending percentage was calculated. For all specimens, stress–strain curves were found to be initially linear; at a strain of approximately 0.0001, the curves became nonlinear. Young's modulus was measured in the linear region of the stress–strain curve. Young's modulus values were highest for the poled material with an open circuit boundary condition ( D  =   0) and lowest for the unpoled material.     

Penny shaped crack in a three-dimensional piezoelectric strip under in-plane normal loadings

Summary The singular mechanical and electric fields in a three-dimensional piezoelectric ceramic strip containing a penny shaped crack under in-plane normal mechanical and electrical loadings based on the continuous electric boundary conditions on the crack surface are considered here. The potential theory and Hankel transforms are used to obtain a system of dual integral equations, which is then expressed as a Fredholm integral equation. All sorts of field intensity factors of Mode I are given, and numerical values for PZT-6B piezoelectric ceramic are graphically shown.     

锆钛酸铅/聚苯胺/聚氨酯三元阻尼复合材料

为减少压电陶瓷/导电填料/聚合物阻尼复合材料中填料的含量,制备了锆钛酸铅(PZT)/聚苯胺/聚氨酯三元复合材料,其中,聚苯胺(PANI)通过原位聚合的方法包覆于压电陶瓷粒子的表面.采用FTIR,TGA,SEM、EDS研究了PANI包覆PZT的组成和形态.用DMA评价了复合材料的阻尼性能.结果表明,通过原位聚合的方法能够制备PANI包覆的PZT粉末;三元复合材料的阻尼性能与PANI的导电率有关,在一定的PANI导电率时达到最大,并且在任意导电率下均高于单一聚氨酯.用PANI包覆的压电陶瓷与聚合物复合,能够提高聚合物的阻尼性能.通过调整PANI的导电率,可以使材料的阻尼性能达到相应振动频率下的最大值.     

Boundary integral equation method for conductive cracks in two and three-dimensional transversely isotropic piezoelectric media

Using the fundamental solutions and the Somigliana identity of piezoelectric medium, the boundary integral equations are obtained for a conductive planar crack of arbitrary shape in three-dimensional transversely isotropic piezoelectric medium. The singular behaviors near the crack edge are studied by boundary integral equation approach, and the intensity factors are derived in terms of the displacement discontinuity and the electric displacement boundary value sum near the crack edge on crack faces. The boundary integral equations for two dimensional crack problems are deduced as a special case of infinite strip planar crack. Based on the analogy of the obtained boundary integral equations and those for cracks in conventional isotropic elastic material and for contact problem of half-space under the action of a rigid punch, an analysis method is proposed. As an example, the solution to conductive Griffith crack is derived.     

Triple-resonant transducers

A detailed analysis is presented of two novel multiple-resonant transducers which produce a wider transmit response than that of a conventional Tonpilz-type transducer. These multi-resonant transducers are Tonpilz-type longitudinal vibrators that produce three coupled resonances and are referred to as triple-resonant transducers (TRTs). One of these designs is a mechanical series arrangement of a tail mass, piezoelectric ceramic stack, central mass, compliant spring, second central mass, second compliant spring, and a piston-radiating head mass. The other TRT design is a mechanical series arrangement of a tail mass, piezoelectric ceramic stack, central mass, compliant spring, and head mass with a quarter-wave matching layer of poly(methyl methacrylate) on the head mass. Several prototype transducer element designs were fabricated that demonstrated proof-of-concept.     

On fracture testing of piezoelectric ceramics

Fracture tests carried out on unpoled and poled PZT-5H four-point bend specimens are presented in this paper. The crack faces were parallel to the poling direction. Both mechanical loads and electric fields were applied to the poled specimens. The experimental results were analyzed by means of the finite element method and a conservative M-integral including the crack face boundary conditions. Fracture tests on four-point bend PIC-151 specimens with the crack faces perpendicular to the poling directions were also analyzed here; the experimental results were taken from the literature. A mixed mode fracture criterion is proposed for piezoelectric ceramics. This criterion is based upon the energy release rate and two phase angles. This criterion was implemented with experimental results from the literature and from this investigation. Excellent agrement was found between the fracture curve and the experimental results of the specimens with the crack faces perpendicular to the poling direction. With some scatter, reasonable agreement was observed between the fracture curve and the experimental results of the specimens with crack faces parallel to the poling direction.     

Dielectric breakdown model for a conductive crack and electrode in piezoelectric materials

The strip dielectric breakdown (DB) model introduced by Zhang and Gao [T.Y. Zhang, C.F. Gao, Fracture behavior of piezoelectric materials, Thero. Appl. Fract. Mech. 41 (2004) 339–379] is used to study the generalized 2D problem of a conductive crack and an electrode in an infinite piezoelectric material. The energy release rate and stress intensity factors are derived based on the Stroh formalism, and then they are applied as failure criteria to predict the critical fracture loads. It is found that the DB strip may take the shielding effect on a conductive crack or electrode. For the case of an electrode, the local energy release rate and stress intensity factor become zero when DB happens ahead of the electrode tip. For the case of a mode-I conductive crack in a transversely isotropic piezoelectric solid, the results based on the DB model show that the critical stress intensity factor linearly increases as the applied electric field parallel to the poling direction increases, while it linearly decreases as the applied electric field anti-parallel to the poling direction increases. Finally, the upper and lower bounds of the actual critical fracture loads are proposed for a conductive crack in a piezoelectric material under combined mechanical–electrical loads.     

Punch problem for piezoelectric ceramic half-plane

Based on the theory of linear piezoelectricity, this study presents an exact solution for a two dimensional indentation on a piezoelectric ceramic half-plane with different contact conditions. The flat-ended indenters are assumed to be rigid. Besides, they can either be insulating or conducting. In addition, different contact conditions, including frictionless, frictional, and adhesive punches are investigated. Lekhnitskii's formulism and Fourier transforms are used to obtain the Green's function of a piezoelectric ceramic half-plane subjected to a point loading. Utilizing Green's half-plane function, we obtain the three integral equations by connecting generalized displacement gradients at the surface and surface loading. Both uncoupled and coupled integral equations can be transformed into a Fredholm integral equation. The analytical closed form solutions of the contact forces and the electric charges under the indenter can be derived by solving the Fredholm integral equations. Once the distributions of the contact forces and the electric charges on the surface are known, the electroelastic response in the half-plane can also be obtained.     

Microstructural effects on the phase transitions and the thermal evolution of elastic and piezoelectric properties in highly dense,submicron-structured NaNbO<Subscript>3</Subscript> ceramics

The dielectric, piezoelectric and elastic coefficients, as well as the electromechanical coupling factors, of NaNbO₃ submicron-structured ceramics have been obtained by an automatic iterative method from impedance measurements at resonance. Poled thin discs were measured from room temperature up to the depoling one, close to 300 °C. Dielectric thermal behaviour was determined also for unpoled ceramics up to the highest phase transition temperature. Ceramics were processed by hot-pressing from mechanically activated precursors. Microstructural effects on the properties are discussed. The suppression of the classical maximum in dielectric permittivity in unpoled ceramics at the phase transition at 370 °C was found when a bimodal distribution of grain sizes, with a population of average grain size of 110 nm in between much coarser grains, is observed. The appearance of a phase transition at 150 °C took place when Na vacancies are minimised. The occurrence of a non-centrosymmetric, ferroelectric phase, in the unpoled ceramic from room temperature to ~300 °C, highly polarisable resulting in high ferro–piezoelectric properties was also observed in the ceramic which presents grain size below 160 nm. Maximum values of k _p = 14%, d ₃₁ = −8.7 × 10⁻¹² C N⁻¹ and N _p = 3772 Hz m at room temperature, and k _p = 18%, d ₃₁ = −25.4 × 10⁻¹² C N⁻¹ and N _p = 3722 Hz m at 295 °C were achieved in the best processing conditions of the ceramics.     

基于细胞打印的压电式喷墨头研究进展

目的综述细胞打印用压电式喷墨头的研究进展。方法从压电式喷墨头的角度出发,总结压电式喷墨头中影响细胞打印的关键因素,主要包括喷墨腔内部的压力波形态、压电陶瓷驱动器、喷墨头内部流体动力学特征以及喷嘴几何形状设计等对压电式喷墨头喷射行为的影响,同时针对各因素对细胞打印的具体影响进行分析讨论。结论研究成果对当前普通桌面打印机如何改进应用于细胞打印,优化细胞打印用压电式喷墨头的设计方案以及促进细胞打印的应用发展具有重要的指导意义。     

Yoffe-type moving edge crack in a piezoelectric block

Summary We consider an anti-plane edge moving crack problem with the constant velocity in a piezoelectric ceramic block. The far-field anti-plane shear mechanical and in-plane electrical loads are applied to the piezoelectric block. It is expressed to a Fredholm integral equation of the second kind. Expressions for the dynamic field intensity factors and the dynamic energy release rate are obtained. The dynamic stress intensity factor and the dynamic energy release rate depend on the crack propagation speed. Numerical results for several piezoelectric materials are also presented.     

Fabrication of piezoelectric ceramic micro-actuator and its reliability for hard disk drives

A new U-type micro-actuator for precisely positioning a magnetic head in high-density hard disk drives was proposed and developed. The micro-actuator is composed of a U-type stainless steel substrate and two piezoelectric ceramic elements. Using a high-d31 piezoelectric coefficient PMN-PZT ceramic plate and adopting reactive ion etching process fabricate the piezoelectric elements. Reliability against temperature was investigated to ensure the practical application to the drive products. The U-type substrate attached to each side via piezoelectric elements also was simulated by the finite-element method and practically measured by a laser Doppler vibrometer in order to testify the driving mechanics of it. The micro-actuator coupled with two piezoelectric elements featured large displacement of 0.875 microm and high-resonance frequency over 22 kHz. The novel piezoelectric micro-actuators then possess a useful compromise performance to displacement, resonance frequency, and generative force. The results reveal that the new design concept provides a valuable alternative for multilayer piezoelectric micro-actuators.     

Electroelastic analysis of an interface anti-plane shear crack in a layered piezoelectric plate

The problem of an anti-plane interface crack in a layered piezoelectric plate composed of two bonded dissimilar piezoelectric ceramic layers subjected to applied voltage is considered. It is assumed that the crack is either impermeable or permeable. An integral transform technique is employed to reduce the problem considered to dual integral equations, then to a Fredholm integral equation by introducing an auxiliary function. Field intensity factors and energy release rate are obtained in explicit form in terms of the auxiliary function. In particular, by solving analytically a resulting singular integral equation, they are determined explicitly in terms of given electromechanical loadings for the case of two bonded layers of equal thickness. Some numerical results are presented graphically to show the influence of the geometric parameters on the field intensity factors and the energy release rate.     

Verformungsverhalten und rechnerische Abschätzung der Ermüdungslebensdauer metallischer Werkstoffe unter mehrachsig nichtproportionaler Beanspruchung

Deformation behaviour and numerical fatigue lifetime prediction of metallic materials under multiaxial nonproportional loading The development and evaluation of a model for lifetime prediction under multiaxial nonproportional loading is the aim of the current research project. It is assumed that the technical crack initiation life is consumed by short crack growth. This phenomenon is described using a fracture mechanics based approach. Herein, the effective cyclic J‐integral is used as crack tip parameter. Crack opening levels and J‐integral values are calculated applying approximation formulas. A plasticity model that is based on the Jiang model [Jia93] and extended to describe nonproportional hardening is used to predict the deformation behaviour. Experimental investigations on tubular and notched specimens with a wide range of different loading spectra serve for the verification of the model and for the identification of damage mechanisms.