【作者】 黄润；

【导师】 陈雨；

【作者基本信息】 重庆大学 ， 仪器科学与技术， 2011， 硕士

【摘要】 随着社会的发展,大型化、复杂化的土木工程结构特别是混凝土结构越来越多,人们也越来越关注这些结构在服役期间的健康状态,逐渐将新材料技术、计算机技术和通信技术等高新技术应用到结构的健康监测中,以保证生命财产安全。传统的混凝土结构检测方法往往只是对在服役期间的混凝土结构健康状态进行定时和关键部位的抽查。智能材料结构在混凝土结构健康检测中的应用为结构健康监测开辟了一个广阔的空间,它兼具传统复合材料和功能材料的双重特性,可实现混凝土结构的实时在线检测。在课题前期提出了一种基于压电埋入式混凝土敏感模块的超声检测方法,在该方法中超声波信号作为混凝土结构内部信息的载体,需要有良好的特性,因此本文开展了埋入混凝土中压电陶瓷换能器声辐射特性研究。(1)讨论了声波在介质中声场指向性形成原理;将压电陶瓷换能器声辐射面等效成具有相同振幅的单一点声源的叠加,对其进行了声场指向性理论推导,得到了随着对压电陶瓷换能器激励频率的增加,其辐射超声波声场指向性越集中的结论;分析了超声检测中影响超声波声能的原因。(2)推导了埋入混凝土中压电陶瓷换能器机械振动数学模型,并根据等效原理,得到了其机械振动等效电路图,等效模型直接反应了压电陶瓷换能器在振动过程中电能-机械能间相互转换的动态过程;分析了埋入状态下混凝土夹持力对压电陶瓷换能器声辐射的影响。(3)通过Ansys有限元模态分析,得到了埋入混凝土中压电陶瓷换能器一阶到四阶振动模态及其固有频率;并进行了在预应力下压电陶瓷换能器Ansys模态分析,分析表明可将埋入混凝土中压电陶瓷换能器振动模态看成是在自由状态下的振动模态;进行了基于压电埋入式混凝土敏感模块的声场指向性和声能实验,结合Ansys仿真和实验,分析得到了如下结论:在声场指向性理论推导中,忽略不同频率下埋入混凝土中压电陶瓷换能器声辐射面振动模态不同,会使得压电陶瓷换能器辐射超声波声场指向性随频率变化规律偏离实际较大,而在相同频率下声场指向性理论结果比实验结果发散;在各阶固有频率下,压电陶瓷换能器的声场指向性集中,但在一阶固有频率下声能最高,因此更适用于超声检测。(4)系统总结了传统的混凝土结构超声检测中利用接收波信号时域和频域特性进行超声检测的手段和原理,为基于压电埋入式混凝土敏感模块的超声检测提供了理论依据和技术支持。(5)进行了埋入混凝土中压电陶瓷换能器辐射超声波在通过混凝土不同测试距离下接收波信号分析实验,将获取到的接收波信号从时域(声速、波幅、首波相位、波形和包络线)和频域(幅度谱、功率谱)两方面分析了测试距离对其信号特性的影响。更多还原

【Abstract】 With the rapid pace of society, large-scale and complex civil engineering structure, especially concrete structures are more and more. People are also growing concerns about the structure health status during service, and applying the new materials technology, computer technology, communication technology and other high technology to the structural health monitoring, which can ensure the safety of life and property. The concrete structure of traditional detection methods are only concentrate on the key parts concrete structures or sampling. The applications of smart materials and structures provide a wide space for the concrete structure health monitoring. It features double features of traditional materials and composite materials. It can achieve Real-time online detection of concrete structure.In the previous study, a ultrasonic detection method was proposed which bases on the PZT smart concrete module. In this method, ultrasonic wave need excellent features, as being the vector of concrete internal information. So in this paper the acoustic characteristics of PZT transducer embedded in concrete is researched.(1) The formation principle of acoustic field directivity is analyzed. The acoustic field directivity theory of PZT transducer is derived, when it’s acoustic radiating surface is seen as the superposition of equal amplitude single point source. The result displays that the acoustic field directivity is more and more concentrate with the frequency increasing. The reasons are analyzed that influences acoustic energy in ultrasonic detection.(2) The equivalent vibration mode is derived, and according to the equivalence principle, obtain the equivalent circuit of mechanical vibration. The equivalent vibration mode reflects the dynamic converting process of the electric energy– mechanical energy. The influence is analyzed of the concrete clamping force to PZT transducer radiating acoustic energy in buried state.(3) By the Ansys modal analysis of PZT transducer embedded concrete, the first to fourth order modal and their nature frequencies are obtained. The modal analysis and acoustic field directivity and acoustic energy experiment basing on smart concrete module shows vibration mode stimulated by frequency affecting acoustic directivity and energy; the acoustic source seen as superposition of equal multitude single point source the acoustic directivity deviate from the actual in each mode frequency and becomes divergent at a frequency; and the first natural frequency is more suitable for ultrasonic testing considering the acoustic directivity and energy.(4) By the time domain and frequency domain of signal, the traditional methods of concrete ultrasonic detection are analyzed, including acoustic speed, amplitude, the first wave phase, waveform and envelope in domain, Amplitude spectrum, phase spectrum and power spectrum in frequency domain. The internal defects and performances parameters of concrete can be detected with those signal feathers. The detection methods are theoretical basis and technical supports for the ultrasonic detection of basing on smart PZT concrete module.(5) The experimental is developed that PZT transducer embedded concrete radiating ultrasonic signal after ultrasonic propagating the concrete different testing distance. Analyze the signal feathers after ultrasonic propagating the different testing distance in concrete from time domain (acoustic speed, amplitude, the first wave phase, waveform and envelope) and frequency domain(Amplitude spectrum and power spectrum).更多还原