COMBINED DAMAGE FRACTURE CRITERIA FOR PIEZOELECTRIC CERAMICS

Mechanical and electrical damages are introduced to study the fracture mechanics of piezoelectric ceramics in this paper. Two kinds of piezoelectric fracture criteria are established using the method of least squares combined with a damage analysis of the well-known piezoelectric fracture experiments of Park and Sun’s. One is based on a linear combination of the mechanical and electrical damages and the other on their nonlinear combination. When the combined damage D is up to its critical value Dc, piezoelectric fracture occurs. It is found from the qualitative comparison of the numerical results with the experimental data that the nonlinearly combined damage fracture criterion can give a better prediction of piezoelectric fracture. And it is concluded from the nonlinearly combined damage fracture criterion that a negative electric feld impedes fracture whereas the efect of a positive electric feld on fracture depends on its magnitude.

STUDY ON STRUCTURE AND PROPERTIES OF PMMN PIEZOELECTRIC CERAMICS

Piezoelectric ceramics based on PZT ceramics were prepared in solid state reaction with mixture of PbO, TiO2 and ZrO2, etc. XRD and SEM were used to confirm that the main phase in the material is tetragonal P4mm symmetry. Samples sintered are of high density. Measurement on polarized products indicate that dielectric constant, piezoelectric constant, electromechanic coupling factor and mechanical quality factor are epsilon(r)=2015, d33=578.06X10(12)C/N, K-33=0.81 and Q(m)=543.8,,respectively.

Control of electromechanical performance in 3D printing latticestructured BaTiO_(3) piezoelectric ceramics

Barium titanate(BaTiO_(3))piezoelectric ceramics with triply periodic minimal surface(TPMS)structures have been frequently used in filters,engines,artificial bones,and other fields due to their high specific surface area,high thermal stability,and good heat dissipation.However,only a limited number of studies have analyzed the effect of various parameters,such as different wall thicknesses and porosities of TPMS structures,on ceramic electromechanical performance.In this study,we first employed vat photopolymerization(VPP)three-dimensional(3D)printing technology to fabricate high-performance BaTiO_(3) ceramics.We investigated the slurry composition design and forming process and designed a stepwise sintering postprocessing technique to achieve a density of 96.3%and a compressive strength of 250±25 MPa,with the piezoelectric coefficient(d_(33))reaching 263 pC/N.Subsequently,we explored the influence of three TPMS structures,namely,diamond,gyroid,and Schwarz P,on the piezoelectric and mechanical properties of BaTiO_(3) ceramics,with the gyroid structure identified as exhibiting optimal performance.Finally,we examined the piezoelectric and mechanical properties of BaTiO_(3) ceramics with the gyroid structure of varying wall thicknesses and porosities,thus enabling the modulation of ceramic electromechanical performance.

Oxygen octahedron tilting,electrical properties and mechanical behaviors in alkali niobate-based lead-free piezoelectric ceramics

In this work,we present a new piezoelectric solid solution consisting of two typical alkali niobate-based materials,K_(0.5)Na_(0.5)NbO_(3)(KNN)and Li_(0.15)Na_(0.85)NbO_(3)(LNN).Although KNN and LNN have the same perovskite structure,they exhibit extremely different electrical properties and mechanical behaviors.The phase structures,electrical and mechanical evolutions of the new lead-free piezoelectric materials with different ratios of KNN and LNN are comprehensively and theoretically investigated.According to the Xray diffraction patterns and curves of permittivity versus temperature,a series of complicated phase transitions can be found with varied LNN content.Rietveld refinement results based on XRD patterns reveal an oxygen octahedron tilting in the LNN-rich crystal structure,and simultaneously the reasons for octahedron tilting are discussed.The distorted crystal structure is accompanied by extremely decreased electric properties but increased mechanical properties,which reveals electrical and mechanical properties of alkali niobate-based piezoelectric ceramics strongly depend on their inner structures,and the enhancement of intrinsic hardness results in the deterioration of piezoelectric properties.Our work exhibits the detailed evolutions of structure,electrical and mechanical properties from KNN to LNN,which provides experimental and theoretical basis for development of new alkali niobate-based piezoelectric materials.

A Piezoelectric Friction-Inertial Linear Motor Based on Piezoelectric Single-Crystal Cymbal Displacement Amplification Mechanism

Piezoelectric friction-inertial motor is known for its promise for a long-range and high-resolution motion.The movement of the slider/rotor of the motor is achieved by stick-slip effect.We report a relaxor-based-ferroelectric-single-crystal cymbal actuator and a miniature piezoelectric friction-inertial linear motor(abbreviated as PFILM)fabricated with the cymbal actuator.The cymbal actuator is fabricated with a 10 mm diameter disk of 0.70Pb(Mg_(1/3)Nb_(2/3))O_3-0.30PbTiO_3 single crystal.The displacement of the cymbal actuator increases almost proportionally from 0to 23μm with driving voltage up to 500 V,and the minimal hysteresis is observed.The cymbalPFILM with 20 mm motion range works under driving voltage frequency of ca.100 Hz to ca.5kHz,the fastest speed is obtained with 3.5kHz and the no-load speed is 14mm/s and the maximum thrust force is 98 mN.Compared with a PFILM based on multilayer piezoelectric ceramic,the proposed motor has a larger stroke under DC/quasistatic input voltage in fine motion mode,but a smaller driving force in long-travel mode due to lower resonance frequency.

Outstanding electromechanical performance in piezoelectric ceramics via synergistic effects of defect engineering and domain miniaturization

Piezoelectric ceramics with high mechanical quality factor Q_(m) and large piezoelectric coefficient d_(33) are urgently required for advanced piezoelectric applications.However,obtaining both of these prop-erties simultaneously remains a difficult challenge due to their mutually restrictive relationship.Here 0.5Pb(Ni_(1/3)Nb_(2/3))O_(3)-0.5Pb(Zr_(0.3)Ti_(0.7))O_(3) piezoceramic with tetragonal(T)-rich MPB is designed as a matrix to construct the defect engineering by doping low-valent Mn ions.The strong coupling of defect dipole and T-rich phase can effectively hinder the rotation of P_(s),restrict domain wall motion and improve Q_(m).At the same time,the substituted Mn ions will introduce local random field,destroying the long-range or-dering of ferroelectric domain and reducing domain size.The miniaturized domain structure can increase poling efficiency and inhibit the reduction of d_(33).Guided by this strategy,Q_(m) has increased by more than 10 times and d_(33) has only decreased by about 25%.The optimized electromechanical performance with Q_(m)=822,d_(33)=502 pC/N,k_(p)=0.55 and tanδ=0.0069 can be obtained in the present study.

Characterization and Microstructure of PLZT RAINBOW Ceramics

A new type of large-displacement actuating materials called RAINBOW (Reduced and Internally Biased Oxide Wafer) ceramics is fabricated by a chemical reduction of PLZT piezoelectric ceramics. It is found that PLZT is easily reduced and the thickness of reduced layer has a linear relationship with the reduction time. The optimal conditions for producing RAINBOW samples from PLZT are determined to be 950℃ for 1-1.5 hours. SEM micrograph shows that the RAINBOW ceramics are composed of reduced and unreduced layer obviously. And the reduced layer is transgranularly fractured while the unreduced ceramic is intergranularly fractured. Metallic lead and refractor oxides (PbO, ZrO_2, ZrTiO_4, etc.) are found in the reduced layer by XRD analyses, however, the crystal structure of PLZT is not found. The analysis of the reduction mechanism is in good accordance with experimental data.

ANALYSIS OF DAMAGE NEAR A CONDUCTING CRACK IN A PIEZOELECTRIC CERAMIC

The finite element formulation for analyzing static damage near a conducting crack in a thin piezoelectric plate is established from the virtual work principle of piezoelectricity.The damage fields under various mechanical and electrical loads are calculated carefully by using an effective iterative procedure.The numerical results show that all the damage fields around a crack tip are fan-shaped and the electric field applied has great influence on the mechanical damage, which is related to the piezoelectric properties.

Effect of NaCl on synthesis of ZrB2 by a borothermal reduction reaction of ZrO2

ZrB2 powders were synthesized via a borothermal reduction reaction of ZrO2 with the assistance of NaCl under a flowing Ar atmosphere. The optimal temperature and reaction time were 1223 K and 3 h, respectively. Compared with the reactions conducted without the addition of NaCl, those performed with the addition of an appropriate amount of NaCl finished at substantially lower temperatures. However, the addition of too much NaCl suppressed this effect. With the assistance of NaCl, a special morphology of polyhedral ZrB2 particles covered with ZrB2 nanosheets was obtained. Moreover, the experimental results revealed that the special morphology was the result of the combined effects of B2O3 and NaCl. The formation of the special microstructure is explained on the basis of the “dissolution–recrystallization” mechanism.

Dielectric and Mechanical Nonlinear Behavior of Mn Doped PMN-35PT Ceramics

This paper presents an investigation on dielectric and mechanical nonlinear properties in Mn-doped PMN-35PT ceramics. The structural study of the ceramics verifies that the 1% mol Mn doped PMN-35PT is a pure perovskite phase with a tetragonal symmetry. SEM micrograph shows the same microstructural mor- phology of an undoped ceramic. From the EPR spectra, it has been concluded that the major part of Mn is present in Mn2+ rather than in Mn4+ form. The addition of Mn2+ ions acts on the dielectric, piezoelectric and mechanical properties by decreasing the relative dielectric permittivity (3800 to 2074), the dielectric losses (0.60 to 0.53), the piezoelectric coefficient d33 (650 to 403 pC/N), and increasing the mechanical quality fac- tor Qm (78 to 317). It was found that in Mn2+ doped ceramics the dielectric response can not be described by Rayleigh law. This result can be understood taking into account that reversible motion of the domain wall is a relevant contribution to response of this material.

高频动态压电式压力传感器结构设计与实验研究

针对激波压力信号快速测量需求的提升,提出了一种基于压电效应的高频动态激波压力传感器结构形式及测量原理。通过分析激波信号的时频特性,确定高频动态压电式压力传感器的性能需求;采用高频动态压电式压力传感器的测量原理,对提出的激波压力测量进行了分析;基于变形协调一致原则,建立了静力学和动力学模型,分析传感器结构参数对灵敏度和固有频率的影响规律;将优化后的传感器三维模型导入ANSYS中进行静力学、动力学和压电耦合分析,验证了传感器结构及其测量原理的可行性。通过准静态标定和动态标定实验,得到传感器的电压灵敏度、非线性度和固有频率等测量性能指标,实验结果表明:研制的高频动态压电式激波压力传感器样机具有高灵敏度3.19 mV/kPa、高固有频率特性95.625 Hz和短上升时间10.45μs特性,能够满足实际测试需求。

基于EMI-CNN的建筑施工模板支撑体系节点健康监测

为预防模板坍塌引发建筑施工安全事故风险,提出一种基于压电阻抗法(EMI)和卷积神经网络(CNN)的模板支撑体系节点智能监测方法。首先,利用压电陶瓷传感器(PZT)的机电耦合特性及其集驱动-传感于一体的特点,建立PZT-节点耦合系统的机电阻抗传感机制模型;其次,基于EMI法,以与待测结构耦合的PZT片电导信号为监测指标,确定模板支撑体系节点松动的发生;然后,以敏感频段内PZT片的801个原始电导信号为模型输入,9个节点松动程度为模型输出,构建162组学习样本和27组测试样本,建立EMI-CNN模型,确定节点松动程度;最后,以一个实际工程中的建筑施工模板体系节点为例,验证EMI-CNN模型的有效性,并对比分析EMI-BP模型。研究结果表明:EMI-CNN模型经过85次迭代达到收敛,预测准确率达到100%,相较于EMI-BP模型提高29.63%。该监测方法可实现对建筑施工模板支撑体系节点健康状态实时、准确、无损监测。

硬性BSPT基高温压电陶瓷温度稳定性研究

采用固相合成法在1125~1175℃烧结范围内制备了0.15BiScO_(3)-0.85(Pb_(0.88)Bi_(0.08))(Ti^(0.97)Mn_(0.03))O_(3)(BSPT-Mn)高温压电陶瓷。所有样品均为纯相,晶粒尺寸分布符合正态规律,掺杂元素均匀,未发现明显的富集现象。研究表明,在1150℃烧结制备的BSPT-Mn高温压电陶瓷的最大机械品质因数为1500.3,在484.4℃温度下压电常数为289.8 pC/N,压电性能良好。

压电陶瓷可控机械密封多场耦合模型与调控性能分析

提出一种基于压电陶瓷的可控机械密封结构,基于有限元软件分析施加电压和压电陶瓷数量对密封静环端面的变形规律;考虑密封动静环与润滑液膜间的热力耦合作用,建立可控机械密封的流固热耦合模型,研究施加电压和压电陶瓷数量对密封调控性能的影响。结果表明:施加电压的压电陶瓷使静环端面产生了径向锥度和周向波度变形,变形量随电压的增大而增加;静环端面变形在增大液膜承载力的同时减小了端面接触力;压电陶瓷数量的增多减小了周向波度变形,增大了径向锥度变形,使静环端面变形趋于周向均匀化;增大压电陶瓷电压可实现密封端面润滑状态的转变,使密封端面摩擦温升降低,使泄漏率控制在允许范围之内。

空间四自由度柔顺并联机构设计与仿真

设计了一种由压电陶瓷驱动的整体式空间四自由度柔顺并联定位平台,使用柔性铰链代替传统的运动副,消除了传统机构铰链配合的摩擦与间隙。建立了空间四自由度定位平台的运动学模型,使用三维建模软件建立几何模型。通过计算得到解析结果,并对空间四自由度柔顺并联定位平台进行有限元分析,得到其位移特性。比较理论计算和有限元仿真结果,得出误差在允许范围内,验证了设计的定位平台的可行性。

军用便携式机械能发电技术

鉴于便携式机械能发供电技术可从多维度丰富战场电能源保障方式,聚焦机械外骨骼发电、摩擦发电、压电发电和手摇发电机(微型电机)等便携式机械能发电技术,分析比较各发电技术的原理及其衍生的前沿技术或装备成品在军事上的应用效能和发展前景。机械外骨骼可为士兵系统提供稳定电源,延长作战续航时间;摩擦发电可为通信和导航设备充电,增强士兵战场感知能力;压电技术嵌入军服可为泛在传感器和医疗监测设备供电,提升士兵生存能力;手摇发电机可用于紧急情况中关键设备的应急供电。由此,提出后续应从泛在能量收集、能量高效存储和电源管理系统的集成设计方面提升便携式机械能发电装置的性能,也可将其与物理或化学电源进行灵活组装以获得供电能力更高、适应性更强、可靠性和安全性更好的供电体系。总体而言,这些技术应结合装备和设施供电能力需求等来考虑技术可行性、可靠性和安全性,以确保在实战中发挥最大效益。

压电陶瓷发电能力测试系统的研制

为了进行压电陶瓷材料发电性能测试与研究,设计并制作了一套压电陶瓷发电能力的测试系统。根据压电陶瓷发电性能指标以及影响因素,设计了采用霍尔位移传感器和电荷放大器对压电陶瓷振幅和电荷量进行测量的系统。设计制作了数据采集软件,可以对测试数据进行处理和显示。该测试系统为研究压电陶瓷尺寸参数、外界激励的频率和振幅对压电陶瓷发电能力的影响提供了测试分析平台。

高Q_m、低损耗压电陶瓷材料的研究

本文对Pb[(Mn_(1/3)Sb_(2/3))_x(Co_(1/3)Sb_(2/3))_yTi_zZr_w]O_3四元素和以CeO_2掺杂的Pb_aSr_(1-a)[(Mn_(1/3)Sb_(2/3))_xTi_yZr_z]O_3三元系压电陶瓷进行了研究.该材料具有高机械品质因数、低介电损耗、高居里点、高机械强度、烧结范围宽、工艺重复性好等特点.这两种材料在驻波超声马达中得到了应用.

压电直线精密驱动器研究

提出一种新型的压电直线精密步进驱动器。该驱动器采用仿生运动的原理,以定子主动箝位的方式和双侧薄壁铰链微变形结构,解决了以往压电精密驱动器箝位不牢固、步进频率较低、行程小、分辨率低、速度低、驱动力不稳定等问题。研制的精密直线驱动器能够实现高频率 100 Hz,高速度30 mm/min,大行程>10 mm,高分辨率0.05μm,大驱动力100 N等特点,大幅度提高了压电型步进驱动器的驱动性能。

具有大驱动位移的复合结构型PZT压电陶瓷

采用PZT作为基体材料,通过化学还原的方法制备了具有大位移驱动能力的复合结构型压电陶瓷。研究了其预制应力的分布,探索了还原制备工艺,测试了驱动性能。结果表明,复合结构的优化设计方案是,还原层厚度比率为0.3;与普通压电陶瓷驱动器相比,复合结构型PZT压电陶瓷具有较低的谐振频率,驱动位移量提高3倍多;还原层相结构中存在二次氧化的基体相,表明其还原工艺仍需改进。