片状正交异性压电复合材料的研究

研究了具有压电正交异性特征的片状压电复合材料及其正交异性压电传感元件、驱动元件的构造机理、性能。正交异性压电复合材料在相互垂直的两主方向上呈现出明显的压电特性差异,作为传感元件它能够有效地分解构件中的应力、应变分量,对特定方向上的应力波反应灵敏。作为驱动片,片状正交异性压电复合材料在相互垂直的两主方向表现出相反的变形,该特性符合一般工程材料的变形规律。片状正交异性压电复合材料所具有的上述优越性可使得它们在自诊断、自适应智能结构中发挥更加重要和广泛的作用。     

基于FEM的正交异性压电复合材料传感研究

通过建立被测构件与压电正交异性复合材料(Orthotropic Piezoelectric Composite Materials，OPCM)传感元件的三维有限元(Finite Eleinelit Model，FEM)模型研究OPCM的动态传感特性．采用对被测构件施加冲击载荷的方法获得传感元件输出的电压时域信号，并进行傅立叶变换分析，计算和实验结果都表明OPCM传感元件对同平面内相互正交的应力波具有不同的频响特性，且两者之间有较好的吻合性．     

水泥基压电复合材料的研究进展

综述了水泥基压电复合材料的研究进展.对于0-3型水泥基压电复合材料,压电陶瓷相的性能、复合材料的制备工艺以及微观结构等对其压电及介电性能有重要影响.压电陶瓷相含量越高、粒度越大,复合材料的压电响应就越大.提高极化电压有助于增强复合材料的压电响应.增加成型压力可提高复合材料微观结构的致密性,从而提高压电性能.总结了压电陶瓷的体积分数、形貌以及环境湿度与1-3型水泥基压电复合材料的性能关系,介绍了2-2型水泥基压电复合材料的传感效应及驱动效应的相关研究成果,最后展望了该领域的发展前景.     

PVDF压电薄膜的应变传感特性研究

PVDF压电薄膜是一种重要的智能材料。本文理论分析了智能材料——PVDF压电薄膜的应变传感机理；研究了PVDF应变传感器的制作与布设工艺；试验研究了PVDF传感元件在准静态和动态响应下的传感特性．得到了PVDF传感元件的电压灵敏度，并分析了PVDF压电薄膜的尺寸对灵敏度的影响。研究结果表明：PVDF传感器具有灵敏度高、线性度好、制作与布置工艺简单、面监测等优点．适用于土木工程结构的健康监测。     

不同聚合物基压电纤维复合材料应变性能的温度稳定性

压电纤维复合材料驱动器应用于航天器件中时要经历严酷的环境载荷,其中温度对压电纤维复合材料驱动性能的影响至关重要.本研究制备了三种不同聚合物基压电纤维复合材料,并在-15～60℃的环境温度下测试了压电纤维复合材料的自由应变性能.结果表明,不同聚合物基压电纤维复合材料的自由应变性能均强烈依赖于环境温度,其自由应变性能均呈现...     

应用ANSYS分析聚合物和压电相对1-3型PCM传感性能的影响

1-3型压电复合材料(PCM)是一维连通的压电相平行排列于三维连通的基体相中而形成的具有压电效应的两相压电复合材料.本文首先比较了分析压电复合材料性能的两种不同方法--解析法和有限元法的优缺点,接着应用ANSYS软件分析了基体相性能和压电相性能对压电复合材料传感性能的影响.研究结果表明:选择低值泊松比、低弹性模量、高剪切模量的基体相和低泊松比、高弹性模量、低介电常数的压电相能有效提高1-3型压电复合材料的传感性能.     

1-3型水泥基压电复合材料传感器的性能

以 123型水泥基压电复合材料作为传感元件制备了水泥基压电复合材料传感器。研究了水泥基压电复合材料传感器的频率响应、 线性性能以及应用于混凝土后的传感性能。结果表明: 当加载频率小于 5 Hz时 , 所有载荷下传感器输出电压的幅值均增大 , 但当加载频率大于 5 Hz时 , 所有载荷下传感器输出电压的幅值几乎与输入载荷频率无关 ; 传感器的输出电压幅值和输入载荷幅值之间存在明显的线性关系。水泥基压电传感器在实际混凝土结构中具有良好的传感特性 , 其输出电压与复杂载荷、 随机载荷和脉冲载荷均呈现明显的一一对应关系 ,且与输入载荷基本同步 , 不存在滞后现象 , 试验输出电压值与理论输出电压值也非常吻合。该传感器非常适合于土木工程结构的健康监测。      

复合材料无损检测中Lamb波的优化

如何解决Lamb波检测机理的复杂性并将之运用于复合材料损伤检测是个重要课题.以玻璃纤维增强的复合材料层合板为研究对象,搭建试验平台,利用集成在复合材料层合板上的PZT压电陶瓷片作为驱动元件和传感元件,对接收的Lamb波信号进行分析与研究,从信号频率范围、信号中心频率、波振幅值、波形个数和信号激励形式等五个方面完成Lam...     

用压电元件实现复合材料层合板振动控制的数值分析

采用板的一阶剪切变形理论，对含有压电材料层的复合材料层合板，从机电耦合的变分方程及Ｈａｍｉｌｔｏｎ原理出发，建立起求解其动态响应 的有限元方程。同时也给出了压电材料层作为传感元件时的传感方程及作为作动元件时的作动方程。并采用速度反馈控制实现了层合板的主动振动。最后给出了计算实例。     

压电传感技术在轮轨力实时监测中的应用探讨

目前轮轨力测试传感元件大多采用应变片,但应变片存在零漂、抗干扰能力差、测试系统稳定性差的问题,不满足高速重载铁路轮轨力实时监测对传感元件的要求,针对这一情形,提出了基于压电传感技术的轮轨力实时监测方法。首先,根据轮轨相互作用的特点和轨道系统约束条件,以及压电应变传感特性,提出了轮轨垂向力和横向力测试原理。然后,实验研究了PVDF压电传感器的动态特性、抗电磁干扰、抗零漂、可重复性等性能,并与普通电阻应变片进行了对比,论证了应用压电传感技术进行轮轨力实时监测的可行性。最后通过有限元仿真计算验证了所提出的轮轨力监测原理的正确性。     

The potential of active fiber composites made from piezoelectric fibers for actuating and sensing applications in structural health monitoring

Active Fiber Composites made from piezoelectric fibers were originally developed as actuators for adaptive materials systems. Their properties, however, also allow their use as sensor or emitter-receiver in variours applications. After presenting selected characteristics, the potential of Active Fiber Composites for structural health monitoring is discussed in comparison with that of conventional piezoelectric elements.     

基于含金属芯压电纤维与Lamb波的结构损伤定位研究

摘要：含金属芯压电纤维（Metal-core Piezoelectric Ceramic Fiber,MPF）是一种新型压电功能器件。介绍了MPF的结构及其对圆形压电片激励Lamb波的传感响应模型。利用Gabor小波变换计算损伤反射信号到达时间延迟的原理,把MPF传感单一模式Lamb波在一维结构中进行了损伤定位研究。研究结果表明：MPF可以进行Lamb波的单一模式传感,采用Gabor小波变换计算损伤反射信号到达时间延迟效果较好,损伤定位精度较高。     

Design and optimization of an OPFC ultrasonic linear phased array transducer

In contrast to piezoceramics, orthotropic piezoelectric fibre composites (OPFC) which can be used as actuator/sensor elements in damage detection show clear advantages because of their high sensitivity along the fibre direction and directivity. The focusing acoustic field distribution of the OPFC phased array transducer is analyzed by the finite element method together with directivity analysis in metallic materials. The optimal array parameters such as spacing, width and number of elements are obtained by studying the total displacement changes as various parameters change at the focus point. The feasibility of an OPFC ultrasonic phased array transducer for damage detection is validated.     

Polypropylene composites with natural fibers and wood – General mechanical property profiles

Natural Fiber Composites (NFCs) and Wood Polymer Composites (WPCs) based on polypropylene (PP) have gained increasing interest over the past two decades, both in the scientific community and in industry. Meanwhile, a large number of publications is available, but yet the actual market penetration of such materials is rather limited. To close the existing gap between scientific and technical knowledge, on the one hand, and actual market applications, on the other, it is the purpose of this paper to analyze the current state of knowledge on mechanical performance profiles of injection molded NFCs and WPCs. As the composite properties are a result of the constituent properties and their interactions, special attention is also given to mechanical fiber/filler properties. Moreover, considering that NFCs and WPCs for a variety of potential applications compete with mineral reinforced (mr; represented in this study by talc), short glass fiber (sgf), long glass fiber (lgf) and short carbon fiber (scf) reinforced PP, property profiles of the latter materials are included in the analysis. To visualize the performance characteristics of the various materials in a comparative manner, the data were compiled and illustrated in so-called Ashby plots. Based on these comparisons, an assessment of the substitution potential of NFCs and WPCs is finally performed, along with a discussion of still open issues, which may help in guiding future material development and market application efforts.     

A Parametric Study on Admittance Signatures of a PZT Transducer Under Free Vibration

Piezoelectric material is proven to be a versatile collocated sensor and actuator. Its specific application includes electromechanical impedance (EMI)-based structural health monitoring (SHM). To date, several EMI models are available in the literature but parametric studies are scarcely available. This study aims at providing a parametric study on selected models, considering a freely vibrating piezoelectric transducer. The effect of varying mechanical and electrical parameters of the transducer on the admittance signatures was investigated. The theoretical results were compared against the experiments. Accuracy of the model was successfully refined upon model updating.     

Morphological changes of carbon nanotubes in polyethylene matrices under oscillatory tests as determined by dielectrical measurements

By combining a high sensitive dielectric sensor into a parallel plate rheometer, the time evolution of the dielectric properties of polyethylene/carbon nanotube composites was measured in the molten state under oscillatory shear. Composites with single- (SWCNT) or multiwall (MWCNT) carbon nanotubes initially decrease its conductivity proportional to the oscillatory shear-strain applied. After this initial drop, some composites increase the conductivity under these non-quiescent conditions reflecting a possible shear-induced agglomeration process. The latter based on the complex permittivity spectrum showing a shortening in the CNT-CNT distances in these composites after shear. At concentrations below the electrical percolation threshold, the presence of both SWCNTs and MWCNTs reduces the DC conductivity of the molten matrices. This result shows that carbon nanotubes can act as a scavenger for impurities or additives present in commercial polyethylenes.     

Polyazomethine/carbon nanotube composites

Composites were synthesized by “in-situ” polymerization of polyazomethine, a liquid crystal polymer (LCP), in presence of multi-walled carbon nanotubes (MWNTs) previously dispersed in one of the employed monomers. Fiber processing was carried out by extrusion from the composites containing 1 and 10 wt.% of MWNTs at the mesophase temperature. We have observed that the typical highly oriented internal fibrillar structure can be significantly disrupted by increasing the nanotube content in the composite fibers. Evidences of MWNT alignment were found in the studied LCP/MWNT composites.     

PZT-epoxy piezoelectric transducers: A simplified fabrication procedure

Composite piezoelectric transducers have been constructed by partially dicing PZT ceramics and back-filling with epoxy. Composites containing 10 to 70 volume percent PZT were prepared with several different rod diameters. Measured dielectric constants ranged from 200 to 1000, longitudinal piezoelectric coefficients d₃₃ from 200 to 350 pC/N, and hydrostatic piezoelectric coefficients d_h from 40 to 80 pC/N. Piezoelectric properties are compared with solid PZT and with 3-1 composites made by extrusion.     

Estimation of fatigue damage in holed composite laminates using an embedded FBG sensor

This study investigated damage identification in holed CFRP laminates under cyclic loading by using an embedded Fiber Bragg Grating (FBG) sensor. Ply cracks and delamination extended near the hole with an increasing number of cycles, and the reflection spectrum from the FBG sensor was distorted. Moreover, debonding growth of the FBG sensor was observed. This study then estimated laminate damage pattern from reflection spectra and investigated the influence of the sensor debonding on damage identification. The debonding length was estimated from the spectrum simulated with a given debonding length and was successfully identified only when an appropriate damage pattern was assumed. Moreover, greater debonding induced invalid damage-pattern estimates, even if the debonding length was given in the estimation. The damage identification for simulations and for experiments required half of the intact gage section. These estimates indicated that information on the damage pattern disappeared from the spectrum shape because of debonding.