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、定量的、嵌入一对压电片的损伤评估和结构健康监测系统技术。由于压电驱动器可以在非常高的频率下驱动，并且压电传感器对应变变化率非常敏感，因此压电陶瓷片既可以用作振荡器，也可以用作接收器。对一对压电片进行了验证，使谐波纵波在结构中传播，同时测量了压电片的电阻抗。因此，可以通过测量电阻抗的变化来估计由于婴儿损伤引起的微小机械阻抗变化。在本研究的第一步，简单的梁，通常作为一个结构的基本元素，处理基础研究。提出了基于纵波产生和阻抗的测量技术，并研究了基于纵向应变模态的损伤评估方法。此外，还开发了一种简单的压电片阻抗测量系统。大量实验结果表明，基于阻抗的纵向应变模态技术是评估结构损伤状态和位置的有效方法。考虑到实际应用，构造了嵌入压电片的桁架结构，建立了损伤指标。以节点处紧固螺栓的评价为例进行了研究。提出了由电阻抗响应计算得出的三个损伤指标：峰值频移ΔF、峰值幅值比δ和品质因子比γ。试验结果表明，利用这三种损伤指标可以准确地预测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.