Development of Structural Health Monitoring System and Damage Assessment Technique with Piezoelectric Sensor/Actuator

本研究的目的是开发一种实用的定量损伤评估技术和结构健康监测系统。由于压电致动器可以在很高的频率下驱动，而压电传感器对应变变化非常敏感，因此，压电贴片既可以作为振荡器，也可以作为接收器。通过驱动一对压电贴片，使简谐纵向弹性波在结构中传播，同时测量贴片的电阻抗。因此，可以通过测量电阻抗的变化来估计由于幼年损伤引起的微小的机械阻抗变化。在本研究的第一步中，对通常用作结构基本单元的简支梁进行了基础研究。提出了基于纵波产生和基于阻抗的测量技术，研究了基于纵向应变模式的损伤评估方法。在此基础上，研制了一套简单的压电片阻抗测量系统。大量的实验结果验证了基于纵向应变模式的阻抗技术对结构损伤状态和位置的评估是有效的。考虑到实际使用，构造了一个嵌入压电片的桁架结构来建立损伤指标。作为实例，对节点处紧固螺栓的评估进行了研究。提出了由阻抗响应计算的三个损伤指标：峰值频移ΔF、峰值幅值比δ和品质因数比γ。通过试验验证，用这三个损伤指标可以准确地判断桁架结构节点螺栓松动的情况。

The objective of this research is to develop a practical and quantitative technique for damage assessment and structural health monitoring system by embedded in a pair of piezoelectric patches. Since the piezoelectric actuator can be driven at very high frequency and the piezoelectric sensor is very sensitive to the rate of strain changes, the piezoceramic patches can be utilized as both oscillators and receivers. A pair of piezoelectric patches is droved in a way so that a harmonic longitudinal elastic wave is propagated in the structure and the patches' electric impedance is measured simultaneously. Therefore the minute mechanical impedance change due to infancy damage can be estimated measuring the change of the electric impedance. At the first step of this research, a simple beam, which is usually used as a basic element of a structure, is dealt with for fundamental study. The longitudinal wave generation and impedance-based measurement techniques were proposed and the damage assessment based on the longitudinal strain mode was investigated. Further, a simple impedance measuring system for piezoelectric patches were developed. A plenty of experimental results were validated that impedance-based technique with longitudinal strain mode is efficient for assessment of damaged condition and position in the structure.Considering for practice use, a truss structure embedded with piezoelectric patches was constructed to establish the damage indices. As an example, the evaluation of the fastening bolts at the joint was investigated. Three damage indices, Peak Frequency Shift ΔF, Peak Amplitude Ratio δ and Quality Factor Ratio γ, which are calculated from the electric impedance response, are proposed. It is validated experimentally that the condition of a loosening bolts at the joint in a truss structure can be estimated accurately by using the three damage indices.