Dynamic fatigue behavior of cracked piezoelectric ceramics in three-point bending under AC electric fields

This paper describes an experimental and analytical study on the dynamic fatigue behavior of cracked piezoelectric ceramics under AC electric fields. Constant load-rate testing was conducted in three-point bending with the single-edge precracked-beam specimens. The crack was created normal to the poling direction. The effects of AC electric fields and loading-rate on the fracture load were examined. A phenomenological model of domain wall motion was also used in finite element computation, and the energy release rate for the permeable crack model was calculated. The effect of AC electric fields on the critical energy release rate was then examined. The results suggest that (1) the fracture load of PZT ceramics decreases as the load-rate decreases; (2) an overall decrease in the fracture load occurs when testing under AC electric fields; and (3) the critical energy release rate is not very affected by the AC electric fields.     

Fracture Mechanisms in Ferroelectric-Ferroelastic Lead Zirconate Titanate (Zr: Ti=0.54:0.46) Ceramics

Fracture toughness, K _IC, of a single-phase commercial lead zirconate titanate (PZT) ceramic (Zr/Ti=0.54/0.46) of tetragonal structure ( c/a =1.019) was measured using the single edge notched beam method above and below the Curie temperature. Domain switching (poling) under electrical and mechanical loading was examined using X-ray diffraction. Surface grinding, electrical poling, and mechanical poling caused crystallographic texture. Similar texture, indicative of domain switching, was also observed on fracture surfaces of some saples fractured at room temperature. At room temperature, the highest K _IC measured was 1.85 MPa·m^1/2, while above the Curie temperature it was about 1.0 MPa·m^1/2. Cracks emanating from Vickers indents in poled samples were different in the poling and the transverse directions. The difference in crack sizes is explained on the basis of domain switching during crack growth. These results indicate that ferroelastic domain switching (twinning) is a viable toughening mechanism in the PZT materials tested.     

Ferroelastic Properties of Lead Zirconate Titanate Ceramics

To increase the reliability of multilayer actuators, calculation of the mechanical stress inside the device during operation is important. This paper shows that the small-signal value of the elastic constant s is not sufficient to describe the complicated behavior of lead zirconate titanate (PZT) ceramics. Therefore, compressive strain and depolarization have been measured as a function of large-signal stress applied parallel to the poling direction. The nonlinear dependence of the strain and depolarization can clearly be explained by domain processes. Soft and hard PZT ceramics have been investigated. In hard PZT, domain switching appears at higher stresses than in soft PZT. Moreover, in hard PZT, the domains partly switch back during unloading. The critical stress (coercive stress) necessary for a domain-switching process shows a dependence on the Zr:Ti ratio that is quite similar to the dependence of the electric coercive field. The influence of an electric field applied parallel to the poling direction and superimposed on the compression experiment also has been examined. The coercive stress depends linearly on the electric field. The linear coefficient of this relation is given by the ratio of depolarization to compressive strain caused by domain switching.     

Voltage effect of corona poling on characteristics of PbZrxTi1−xO3 (PZT) film

The paper investigates the voltage effect of corona poling on the characteristics of PbZr_xTi_1−xO₃ (PZT) thin film. Purchased PZT powder and lab-made PZT solution were mixed together as sol-gel that was spin-coated on titanium (Ti) substrate. X-ray diffractometer (XRD), scanning electron microscopy (SEM), impedance analyzer were utilized to measure the orientation and dielectric characteristics of films for comparison. The experimental results indicated that the poling voltage would not affect the orientation of crystallization, microstructure and grain size of PZT film surface. However, the higher applied poling voltage would result in better charge storage capacity and energy transfer efficiency of the film.     

Delectric properties of single grain in PLZT ferroelectric ceramics

The hot pressed and grain-grown transparent ceramics with maximum grain size 80∼100 μm provides the possibility of investigating the dielectric properties of single grain from ceramic specimens. The ion milling technique was employed to separate the grains. The dielectric permittivities of single grain of PLZT have been measured. It is found that the range of dielectric constant of single grains in unpoled state is larger than that of the bulk ceramic. Poling in both single grains and bulk ceramics reduces the dielectric constant in the poling direction, and increases it in the direction perpendicular to the poling field. The anisotropy of dielectric permittivity for PLZT 8/65/35 is calculated from the single grain data.     

Domain Structure of Potassium‐Sodium Niobate Ceramics Before and After Poling

Domain structure and domain wall motion play important roles on the piezoelectric properties of ferroelectric ceramics. In this work, the domain structure of hot‐pressed (K_0.50Na_0.50)NbO₃ (KNN) ceramics before and after poling were studied by observing the domain patterns with an acid‐etching technique, and the extrinsic contribution to the piezoelectric properties were evaluated. It was found that the domain structure of the unpoled KNN ceramic was relatively complicated with many watermark, herringbone and zigzag patterns, while only a single set or few sets of parallel domain stripes were observed in the poled KNN ceramic, due to the domain reorientation and domain wall motion during the poling process. The average domain width changes from 200 (±10) nm before poling to 250 (±10) nm after poling. Domain configurations of “Herringbone‐Zigzag‐Watermark” and “Herringbone‐ Herringbone‐Zigzag” types observed in the unpoled KNN ceramic were then further analyzed. The extrinsic contribution to the piezoelectric properties from the domain reorientation and irreversible domain wall motion in the hot‐pressed KNN ceramic was found to be 71%, slightly higher than that of conventional sintered KNN ceramics ~68%.     

Influence of Microcracking and Slow Crack Growth on the Planar Coupling Coefficient in PZT

The difference in the planar coupling coefficient, k_p, of two PZT specimens with different grain sizes under the same poling treatment was attributed to a greater tendency for microcracking in the large grain-size specimens. In the absence of microcracking, as shown in small grain-size specimens, the decrease in k_p and failure of the poled specimens is attributed to slow crack growth. The optimum poling conditions for small grain-size specimens were evaluated in terms of reducing the slow crack-growth effect.     

Effect of polarization treatment on bending strength of barium titanate/zirconia composite

The change in strength of barium titanate/zirconia composite on polarization treatment is evaluated, and the mechanism of this phenomenon is discussed. We have already reported that the bending strength of this composite has increased on longitudinal poling. In this paper, poling time and applied electric field intensity are varied in order to elucidate the strengthening mechanism. Moreover, it is found out that the polarization strengthened specimen can be weakened to the almost original state by heating above T_c of barium titanate. Then, the crack propagation after polarization treatment is observed by SEM, and the detour of cracks around barium titanate grains is found in the cracks going along the poling direction. The detour of crack probably has close connection with the increase in strength in the poling direction.     

A study of the electric power generation properties of a lead zirconate titanate piezoelectric ceramic

Electric power generation characteristics of lead zirconate titanate (PZT) piezoelectric ceramic have been investigated experimentally and numerically. A thin PZT ceramic plate attached to a thin brass plate was used to examine the electric voltage generated during cyclic loading. On increasing the number of PZT ceramic plates combined together in the longitudinal direction, the electric voltage increases with the highest electric voltage being obtained for four PZT ceramic plates; and the maximum electric voltage becomes almost constant even if the number of PZT ceramic plates combined together increases more than four. This is attributed to the low strain level and the mixed strain (compressive and tensile strain). The effect of strain characteristic on the electric voltage value was analyzed numerically using our strain definition, and a clear correlation between the extent of compressive strain and generated electric voltage is clarified. A different electric generation characteristic was further observed depending on the stress conditions: generation of positive and negative electric voltage occurs when the PZT ceramic is subjected to mainly compressive and tensile stress, respectively.     

多孔PZT压电陶瓷膜的制备及其抗污染性能

以 PbZr_xTi_1-xO₃（PZT）压电陶瓷粉体为原料,通过干压成型的方法制备多孔PZT陶瓷膜,考察了煅烧温度对多孔PZT陶瓷膜的机械强度、孔隙率以及纯水渗透性能的影响。当煅烧温度为950℃时,可制备出纯水渗透率为850 L·m^-2·h^-1·MPa^-1,孔径为300 nm,机械强度为47.8 MPa,孔隙率为34%的多孔PZT陶瓷膜。在此基础上,考察了极化温度与极化电压对多孔PZT陶瓷膜压电性能的影响,并对极化后的PZT压电陶瓷膜进行萃取和表面等离子刻蚀处理。结果表明：极化温度为120℃、极化电压强度为4 kV·mm^-1,极化后经热乙醇萃取及表面等离子刻蚀4 min后,多孔PZT压电陶瓷膜在外加交流电为20 V时,产生的共振振幅信号值达34.8 mV。将制备的多孔PZT压电陶瓷膜在粒径为600 nm的含油乳化液中进行过滤实验,发现陶瓷膜两端未加交流电时,其通量在2 h内衰减至4%。而加交流电后,其稳定通量可维持在20%左右,表明制备的多孔PZT压电陶瓷膜具有良好的抗污染效果。     

B位前躯体法制备PZT/ZrO2纳米复相压电陶瓷的力学性能研究

采用改进的聚合物法制备B位前驱体PZT/ZrO2纳米复相陶瓷.采用TEM观察到马氏体相变和热失配产生的应力条纹和应力斑,发现ZrO2粒子截断电畴和使电畴弯曲的现象.应力场有效吸收裂纹扩展能量,加之ZrO2粒子强化基体晶界,PZT/ZrO2纳米复相陶瓷得到了强韧化.SEM分析显示陶瓷断裂模式随ZrO2加入向穿晶断裂模式转变.抗弯强度和断裂韧性随Zr2加入量增加明显提高,可达141.6 MPa和2.3 MPa·m1/2.     

Direct observation of domain switching and crack nucleation in a piezoelectric material

The effect of an electric field on domain switching and fatigue induced crack nucleation and growth in a piezoelectric material of nominal composition Pb(Zr_0.5, Ti_0.5)O₃ has been investigated. The ceramic was subjected to localised static and cyclic electric fields, which were applied via pairs of closely spaced surface-mounted electrodes, while simultaneously imaging the microstructure in the SEM. Electric field–polarisation hysteresis loops were also collected from the local region using the same electrodes.Domain wall mobility was observed above a threshold electric field strength, as was microcracking. Cracks were seen to nucleate at grain boundaries, and were sometimes associated with microstructural features, such as pores. Crack propagation was mainly intergranular, and occurred preferentially in a direction parallel to the local field direction. Transgranular fracture was also observed, with the crack path being influenced by interaction with domain boundaries. Factors affecting domain switching and crack propagation are discussed in the context of the locally applied electric field.     

Cyclic fatigue of silica refractories – effect of test method on failure process

Silica refractories serving in high temperature industrial installations fail due to thermo-mechanical cyclic loads. The failure process was investigated by performing cyclic fatigue tests of several methods. In uni-axial compression the samples were tested either with constant force or displacement amplitude or with fixed upper displacement limit. In bending constant displacement amplitude tests were done. The investigation was supported by monotonic loading tests and microstructural analysis. It was determined that the fatigue failure occurs due to the degradation of interlocking in the crack wake. Cracking of larger grains is important for the crack initiation. The test set-up and the loading procedures significantly influence the potential to resist the crack propagation. Cyclic loading produces less brittle failure than monotonic loading. The displacement controlled method allows more gradual, less brittle, failure than the force controlled method. The potential of the crack arrest is less developed in bending than in compression.     

Poling of soft piezoceramic PZT

The properties of piezoelectric ceramic materials are strongly dependent on the degree of polarization as set by the poling process. In the present work a soft piezoceramic PZT material was polarized at different poling conditions. The hysteresis loop, the polarization current and pyroelectric current measurements were used to evaluate the polarization state of the material. The hysteresis loop was monitored using a home-made computer controlled Sawyer–Tower circuit. The polarization current was recorded during the poling process at different applied electric fields, poling time and temperature. The pyroelectric coefficient and the polarization were calculated from the pyroelectric current. The polarization calculated from these data was in excellent agreement with the polarization as calculated from the poling current. The relative permittivity and loss factor were measured as a function of temperature after different poling conditions. The effects of the various poling conditions on the dielectric and ferroelectric properties of the soft PZT are discussed. It is shown that, contrary to common practice, poling at a field slightly larger than the coercive field is adequate to reach full polarization at room temperature.     

Cracking energy density calculation of hyperelastic constitutive model and its application in rubber fatigue life estimations

The finite deformation of rubber under multiaxial stress will finally result in its fatigue failure. The ability to predict the effects of complex strain histories on fatigue life is a critical need. The cracking energy density (CED) distribution characteristics in the finite deformation and rubber fatigue life estimated by the CED criterion are investigated. Then the influences of the crack orientation angle θ and the principal stretch ratio λ on the relationship between CED and strain energy density (SED) are obtained. Finally, the results are used for predicting the fatigue life of rubber material and are compared to experimental values. The results indicate that the ratios of the predicted lives based on the CED damage parameter and measured lives are within two times scatter factor and that of the predicted lives based on the SED damage parameter and measured lives are greatly influenced by the crack orientation angle θ. The rubber fatigue life has great relationship with the angle of the crack plane normal vector and the first principal stretch direction. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44195.     

Influence of tensile vs. compressive stress on fatigue of lead zirconate titanate thin films

Novel applications of ferroelectric films require a variety of different substrates, which exert different mechanical stress on the film. This raises the question of reliability of differently stressed films. This work compares the cycling-induced fatigue of the polarization hysteresis of PZT films in different stress states. A tensile stress of +270 MPa, for PZT on fused silica glass, causes gradual degradation, while degradation sets in abruptly under compressive stress of −100 MPa, for PZT on sapphire. The main fatigue mechanism is domain wall pinning on charged defects. Reversible and irreversible domain wall processes in the small- and large-signal permittivity reveal that the fatigue behavior results from a variation of the ferroelectric domain structure. Films under tensile stress contain more 90° domain walls, which get pinned continuously on isolated defects. Compressive stress creates more 180° domain walls, which require formation of defect agglomerates during a certain threshold cycle number for pinning.     

Static fatigue behavior of cracked piezoelectric ceramics in three-point bending under electric fields

This paper describes an experimental and analytical study on the static fatigue behavior of piezoelectric ceramics under electromechanical loading. Static fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens. The crack was created perpendicular to the poling direction. Time-to-failure under different mechanical loads and dc electric fields were obtained from the experiment. Microscopic examination of the fracture surface of the piezoelectric ceramics was performed as well. A finite element analysis was also made, and the applied energy release rate for the permeable crack model was calculated. The effect of applied dc electric fields on the energy release rate versus lifetime curve is examined. The most important conclusion we reach is that the lifetimes for the piezoelectric specimens under a positive electric field are much shorter than the failure times of specimens under a negative electric field for the same mechanical load level.     

Effects of an Electric Field on the Fracture Toughness of Poled Lead Zirconate Titanate Ceramics

Compact tension tests and indentation-fracture tests have been conducted to study the effects of an applied electric field on the fracture toughness ( K _{I C} ) of poled commercial lead zirconate titanate (PZT) ceramics. The experimental results show that an applied electric field, either parallel or antiparallel to the poling direction, considerably reduces the K _{I C} value of the PZT ceramics. The reduction in K _{I C} for a negative field is larger than that for a positive field of the same strength. The failure mode in the PZT ceramics is basically transgranular, insensitive to the applied electric field.     

Adhesion of Electrolessly Deposited Nickel on Lead Zirconate Titanate Ceramic

The adhesion of electrolessly deposited Ni onto lead zirconate titanate (PZT) ceramic has been measured as a function of both the ceramics surface preparation prior to metalization and the plated Ni thickness. A maximum in NI/PZT interfacial adhesion of approximately 27 kg/cm², as measured by a pull test, occurs when the ceramic grain boundaries are chemically etched, thereby providing points to mechanically anchor the Ni deposit. The adhesion decreases with overetching as the ceramic grains are undercut and drops off dramatically with increasing plated Ni thickness.     

Detection and Analysis of Crack Propagation in PZT Multilayer Ceramics

The flaw propagation in Lead zirconate titanate (PZT) multilayer ceramics under mechanical load was examined using impedance spectroscopy and three‐point bending studies. Initial flaws were generated by applying a positive sinusoidal electric field to the specimens. The cracks were sequentially propagated and after the release of the external mechanical load, impedance spectroscopy was conducted. The shift in the resonance frequencies and the subresonance height of the impedance spectroscopy were used as a measure of flaw extension. A functional dependence of the resonance frequency and the phase shift on the crack length was found. The crack propagation was studied on flaws starting at the positive and negative electrode, respectively. The maximum fracture strength, as well as the crack path, depends on the electrode potential. The variation in the fracture strength was caused by different observed fracture mode: interface cracking, matrix‐cracking, or a combination of both. The morphology of the fracture surfaces was ascribed to a textured microstructure, which is created by the sample processing, for example, by the poling process. A modified poling procedure with a lower poling temperature was analyzed, which yielded a reduction of the anisotropy of the electrode strength. Impedance spectroscopy was found to be a reliable measurement tool for automated flaw detection in PZT multilayer ceramics.