【作者】 徐东宇；

【导师】 蒋民华； 程新；

【作者基本信息】 山东大学 ， 材料学， 2010， 博士

【摘要】 水泥基压电复合材料是近几年发展起来的一种新型功能材料,它具有压电性能好、机电耦合性能突出、与混凝土材料力学、声学性能相匹配等特点,在土木工程结构健康监测中具有潜在的应用前景。针对土木工程结构的特点,本文分别以压电陶瓷、水泥基及水泥／聚合物基(水泥、环氧树脂及固化剂的混合物)压电复合材料作为传感元件制备压电传感器,并在以下几个方面进行了实验研究和理论分析工作：以PZT压电陶瓷为功能组分,普通硅酸盐水泥及水泥／聚合物作为基体材料,采用切割-浇注法制备2-2型、1-3型水泥基和水泥／聚合物基压电复合材料,并对其性能进行测试与分析。研究结果表明：与压电陶瓷相比,压电复合材料的压电电压常数及厚度机电耦合系数均明显增大,且声阻抗率及机械品质因数也显著的降低,从而能够用于制备高接收灵敏度、宽频及与混凝土材料声阻抗相匹配的压电传感器。分别以压电陶瓷及压电复合材料为传感元件,水泥／聚合物作为封装材料制备水泥基压电传感器,并对其性能进行测试及分析。研究结果表明：采用该封装材料制备出的压电传感器具有机械强度高、耐久性能好、动态输出能力强,可靠性高等优异性能。其中,以压电复合材料为元件制备的压电传感器兼有声阻抗低、宽频等特性,能够适用于水泥的水化反应进程监测及土木工程结构的动态监测；以压电陶瓷为元件制备的压电传感器则更适用于基于机电阻抗技术的土木工程结构监测,对耦合于结构的压电传感器机电阻抗变化进行分析,能够获得结构的机械阻抗变化信息,从而实现对结构的无损检测；此外,以压电陶瓷为元件制备的压电交通传感器兼有线性度高、输出响应良好、可重复性好、抗压强度高等优点,能够满足其用于道路交通状况监测的要求。以埋入式压电陶瓷及压电复合材料传感器作为发射-接收单元,分别基于压电传感器的超声波传播法及机电阻抗技术对水泥的水化反应进程进行监测。研究结果表明：压电复合材料传感器所接收的超声波信号普遍具有首次波比大、首波明显、主频单一等特点,尤其是以水泥／聚合物为基体材料制备的压电复合材料传感器的接收性能最佳；由压电传感器的接收波波形及频谱随水泥水化反应进程的变化规律可知,水泥水化反应开始后的8 h内,接收波的波形曲线微弱、接收波的幅值较小、主频谱变化较大,在接近水泥的终凝时刻,波形及主频率均发生了明显的变化；当水化进行到约8 h之后,水化反应仍较为剧烈、接收波的首波起始点明显前移,首波幅值也显著增大,但主频谱的变化则较为稳定；当水化进行到约24 h之后,接收波参数随着水化反应的进行逐渐趋于稳定。根据压电传感器接收的超声波参数(主频率、主频幅值、波速、首波波幅等)随水泥水化反应进程的变化特点,可将水泥水化反应开始后的24 h分为三个阶段,即诱导期(约0 h-5 h)、加速期(约5 h-10 h)、衰减期(约10 h-24 h),其中在加速期阶段,超声波参数会出现明显的转变点,该点基本为水泥的终凝时间点。根据埋入水泥浆体中压电传感器的机电阻抗随水泥水化反应进程的变化特点,能够获得与超声波传播法相一致的水泥水化反应规律,从实验的角度进一步证明了基于压电传感器的机电阻抗技术监测水泥水化反应是完全可行的。分别采用外贴式及埋入式压电传感器,基于机电阻抗技术对小型的混凝土结构进行温度、荷载及裂缝损伤研究。研究结果表明：温度变化对外贴及埋入式PZT压电传感器的机电阻抗均具有明显的影响,能够引起压电传感器的谐振频率漂移及谐振峰值的相应变化,基于压电传感器的这一特性,我们可以通过测量其机电阻抗参数的变化来实现对温度的监测；荷载作用对埋入式PZT压电传感器的机电阻抗也具有明显的影响,无论结构受到来自哪个方向的载荷作用,其机械阻抗的变化都可以通过PZT压电传感器的机电阻抗谱图反映出来,尤其是当结构由于受到强烈的载荷作用而发生损伤时,PZT压电传感器的机电阻抗会发生显著的突变；外贴式及埋入式PZT压电传感器的机电阻抗均能良好的反映出砂浆试块产生裂缝损伤的情况,尤其是对试块的初始裂缝损伤更加敏感；采用数学统计的方法对PZT压电传感器的机电阻抗谱图进行处理,建立了一种损伤量化指数,通过该指数能够更加直观、有效的获得耦合于结构的PZT压电传感器机电阻抗随各种因素的变化规律,从而间接获得结构的损伤及发展状况。将制备的压电交通传感器埋于实际路面,建立一套包括水泥基压电智能传感器、小型电荷放大器、多通道数据采集仪和监测软件的压电传感器系统。利用该系统对行人流量、车辆速度及载重进行测试,研究结果表明：通过统计压电传感器的输出脉冲响应个数能够获知通过该传感路段的行人数量及人员密集程度,从而为相关部门提供有效的统计数据；采集车辆通过传感路段时压电传感器所产生的脉冲响应时间间隔,通过简单的数学计算能够精确的获得车辆通过该传感路段时的即时速度,从而实现超速判断,为交通部门提供可靠的数据；依据车辆通过传感路段时梁式压电传感器的输出脉冲电压峰值及或输出脉冲峰包围的面积,通过线性拟合计算能够准确的获得车辆通过该传感路段时的动态载重信息,当路面平整且车辆以匀速通过梁式压电传感器时,理论计算的车辆载重误差均小于5%,能够有效的对行驶中的车辆进行动态称重,从而实现超载预警；此外,由于水泥基压电复合材料传感器与混凝土结构之间具有良好的相容特性,因此利用水泥基传感器也可以对桥梁结构的局部振动状态进行在线监测。更多还原

【Abstract】 Cement based piezoelectric composite is a kind of newly developed piezoelectric material with superior piezoelectric properties, high electromechanical coupling coefficient and good compatibility with concrete materials in mechanical and acoustic etc aspects, which has potential application prospect in health monitoring of civil engineering structure. According to the characteristics of civil engineering structure, piezoelectric ceramic, cement based and cement/polymer based (mixtures of cement, epoxy and solidified agent) piezoelectric composites were used as sensing elements to fabricate cement based piezoelectric sensors, respectively. In this research, the fabricated piezoelectric sensors were used to conduct the experiment tests and theoretical analysis as follows.PZT piezoelectric ceramic was used as functional component, Portland cement and cement/polymer were used as matrix materials to fabricate 2-2 type and 1-3 type cement based, cement/polymer based piezoelectric composite using cutting-and-filling technique. The researches indicate that comparing with piezoelectric ceramic, the piezoelectric voltage constant g33 and the thickness electromechanical coupling coefficient Kt of the piezoelectric composites increase greatly, while the acoustic impedance Z and mechanical quality factor Qm decrease obviously. Therefore, it can be concluded that the piezoelectric sensors with superior receving sensitivity, broad band and good acoustic impedance compatibility with concrete can be tailored to meet the requirements of civil engineering.Piezoelectric ceramic and piezoelectric composite were used as sensing elements, cement/polymer was used as packaging materials to fabricate kinds of piezoelectric sensors, respectively. The researches indicate that the piezoelectric sensors that fabricated using cement/polymer as packing materials have the common properties such as high mechanical strength, good durability, strong dynamic output ability and high reliability. Furthermore, the piezoelectric sensors using piezoelectric composites as sensing elements also have the properties of low acoustic impedance and broad band, which can be used effectively to monitor the cement hydration reaction process and dynamic vibrations of civil structures. The piezoelectric sensors using piezoelectric ceramic as sensing elements are more suitable for civil engineering structure monitoring based on electromechanical impedance technique. The mechanical impedance variation of the structures can be reflected by the electromechanical impedance variation of piezoelectric sensors that coupled with the structures. Therefore, the structure damage state can be detected using this method. Besides, the piezoelectric traffic sensors using piezoelectric ceramic as sensing elements also have the good linearity, good output response and repeatability, and high strength etc, which make it more suitable for traffic monitoring.The embedded piezoelectric ceramic and piezoelectric composite were used as emitter and receiver to monitor the cement hydration reaction process. Two kinds of different methods, that is, ultrasonic wave transmitting method and electromechanical impedance technique, were adopted in the research, respectively. The researchs indicate that the ultrasonic waves received by the piezoelectric composite sensors have the characteristics of large head/secondary wave ratio, obvious head wave and single dominant frequency etc. Among all the piezoelectric sensors, the piezoelectric composite sensors using cement/polymer as matrix materials have the best receiving ability. The cement hydration reaction variation in different stages can be obtained by analyzing the wave shape and frequency spectra of the receiving waves. In the initial 8 h of hydration reaction, the wave shape curves of the receiving wave are very weak and the amplitudes are not obvious, while the dominant frequency is clear. At approximately the final setting time, both the wave shape curve and dominant frequency show the obvious mutation phenomenon. After 8 h of hydration reaction, the starting point of head wave moves forward obviously and the amplitudes of the head wave also increase significantly, while the dominant frequency is independent of the hydration reaction time. After cement hydration reaction for 24 h, the wave shapes and parameters of the receiving wave tend gradually to be steady with increasing the hydration time.According to the variation of ultrasonic wave parameters received by the piezoelectric sensors, such as dominant frequency, amplitude of dominant frequency, wave speed and amplitude of head wave, the cement hydration reaction in 24 h can be defined to three periods, that is, induction period (about 0 h-5 h), acceleration period (about 5 h-10 h) and attenuation period (about 10 h-24 h). In the acceleration period, there will be an obvious transition point in the chart of wave parameters, which basically corresponds to the final setting time of cement.Besides, the cement hydration reaction process can also be reflected by the electromechanical impedance spectra of piezoelectric sensors embedded in the cement paste, and the similar variation regularity can also be obtained. Therefore, it is feasible to monitor the cement hydration reaction based on the electromechanical impedance technique of piezoelectric sensors.Based on electromechanical impedance technology, nondestructive detection on the little concrete structures was performed. The influences of temperature variation, loading and crack damage on electromechanical impedance spectra of affixed and embedded piezoelectric sensors were studied. The results indicate that temperature variation has great influence on the electromechanical impedance of the PZT piezoelectric sensor that coupled with structures, which can result in the drift of resonant frequency and the variation of resonant peak value. Therefore, the PZT piezoelectric sensors can be used as a kind of temperature sensor to monitor the environmental temperature variation. External loading also has great influence on the electromechanical impedance of the embedded PZT piezoelectric sensors. The variation of structural mechanical impedance can be reflected by the electromechanical impedance spectra of PZT piezoelectric sensors when the mechanical loading is applied to the structure. Especially when the structure generates damage due to the strong loading effect, the electromechanical impedance spectra of PZT piezoelectric sensors will appear obvious mutation.The structure damage induced by cracks, especially for the structural initial damage, can also be well reflected by both the affixed and embedded PZT piezoelectric sensors. The electromechanical impedance spectra were analyzed employing the mathematics statistical method. The variation regularity of electromechanical impedance of PZT piezoelectric sensors with kinds of influencing factors can be visualized and effectively observed by a kind of damage quantitative index. Therefore, the the apperance and development of the structure damage can be obtained using this method.The fabricated piezoelectric traffic sensors were embedded in the road. A set of piezoelectric sensor system, including cement based piezoelectric sensor, small charge amplifier, multichannel data collecting device and monitoring software was established to monitor the people flow, vehicle speed and loading. The results indicate that the amounts of people who passed through the sensing section as well as the population density can be calculated by the pulse response amounts of the piezoelectric sensors. The instantaneous vehicle speed can also be accurately calculated by the sensors distance and the time interval between two pulse responses, so the over-speed phenomena can be identified using this method. Besides, the dynamic loading information of vehicles can be calculatedd in terms of the output pulse voltage peak value or areas enclosed by the output pulse peaks, respectively. When the road was level and the vehicles passed through it at uniform speed, the vehicle loading error calculated by the linear fitting formulation is less than 5%. Therefore, the wight in motion of the vehicles can be realized and the overweight phenomenon can also be controlled effectively using this kind of traffic sensors. Besides, the cement based piezoelectric composite sensor can also be used to monitor the critical regions of bridges due to its superior compatibility with concrete structures.更多还原