【作者】 黄红梅；

【导师】 袁慎芳；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2011， 博士

【摘要】 目前,国内外FBG传感技术在结构监测方面的研究已取得较多的研究成果,这种利用FBG传感器反射谱中心波长的漂移进行损伤识别的方法是一种有效的结构损伤监测方法。然而,对于有些结构的部分区域,比如金属修补结构的修补区域以及复合材料接头结构的接头区域等等,所受的应变并非均匀应变,若再通过FBG反射谱中心波长的漂移进行损伤识别势必会产生误差,甚至发生错误。本文研究了FBG传感器在非均匀应变作用下的光谱特性,并将这一原理应用于航空结构的典型损伤监测中。主要研究工作包括以下几个方面:首先,介绍了结构健康监测技术和光纤布拉格光栅传感技术的研究背景、研究现状以及研究意义,给出了本文的研究内容。第二,从光纤布拉格光栅的传输原理出发,对其应变传感进行严格的理论推证;在此基础上,研究了重构非均匀应变作用下光纤布拉格光栅反射谱的数值模拟的实现过程及其优缺点;最后,对现有的方法进行改进,并设计了实验来验证改进后方法的可行性与准确性。第三,提出了基于FBG传感器光谱特性来监测铝合金试件疲劳裂纹的扩展情况。通过有限元分析确定FBG传感器的布置位置;基于结构应变分布从理论上重构了裂纹扩展过程中FBG的非均匀反射光谱,最后将实验所得的光谱与理论结果进行了对比,两者具有较好的一致性。第四,提出了利用FBG传感器对修补结构中裂纹再次扩展的监测方法。通过有限元分析方法获得修补结构中的应变场分布,建立了裂纹扩展长度与FBG传感器的非均匀反射光谱特征之间的关系,并通过实验进行了对比验证。第五,整体化复合材料结构可大幅降低制造装配成本和减轻结构重量,复合材料胶接接头是实现整体化复合材料结构的有效连接形式。以碳纤维π形胶接接头结构为研究对象,提出了利用FBG传感器的光谱特性监测其结构失效的方法。通过有限元方法分析了π形胶接接头结构各铺层的失效次序及其对应载荷的大小,并提取了对应情况下的应变分布,据此重构了FBG传感器的非均匀反射光谱;最后,与实验结果相比较,对应失效载荷大小和FBG反射谱变化趋势基本吻合。第六,提出了一种基于FBG传感器的冲击载荷实时监测系统,结合支持向量机算法对碳纤维飞行器壁板进行了冲击载荷位置及程度的识别研究,并与传统的BP神经网络识别结果进行了对比。最后,总结了本文的主要研究内容和创新点,并给出了今后进一步研究工作的方向。更多还原

【Abstract】 Much progress has been made in strucrural heath mornitoring using FBG sensor technology. It is one of effective structural health mornitoring techniques by measuring the shift of central wavelength. However, for subregion of some structure, such as repaired region of repaired structure, joint region of composite joint structure and so on, is subjected non-uniform strain. In such circumstances, the spectrum shape of FBG will be not the same as before, and we cannot identify damages directly by examine the shift of central wavelength. In this paper, spectral characteristics of fiber Bragg grating under non-uniform strain is researched, which is applied to typical damages monitoring for aerospace materials.The main works done in this dissertation include:Firstly, it was summarized on research background, present situation, significance of SHM and fiber Bragg grating sensing technology. Then, the researching contents were proposed.Secondly, starting form the transimission theory of FBG, strain sensing mechanism is derived strictly. On this basis, using Runge-Kutta method and transfer matrix method, the numerical simulation of reflection spectrum is studied when a non-uniform strain is subjected to FBG, then the advantages and disadvantages were analyzed. At last, Methods that have existed are optimized and experiment is designed to validate the veracity and feasibility.Thirdly, fiber Bragg grating sensor is used to monitor the fatigue crack propagation of aluminum alloy specimen with pre-crack under cyclic loading. The reflection spectra of FBG for different crack lengths have been calculated with the aid of a finite-element model of the strain field resulting from a crack, and compared with the results of the experiment.Fourthly, fiber Bragg grating sensor is used to monitor the propagation of crack beneath the repaired patch under cyclic loading condition. The reflection spectra of FBG for different crack lengths have been calculated with the aid of a finite-element model of the strain field resulting from a crack. Then, comparison between the theoretical result and the experimental result was done.Fifthly, taking carbon fiberπ-joint structure for research subject, a kind real-time online monitoring system using fiber Bragg grating sensor was studied. Firstly, based on the general FEM software, the 3-D finite element model of compositeπ-joint is established, the failure process and every layer failure load of compositeπ-joint were investigated by maximum stress criteria. Then, strain distributions belong the length of fiber Bragg grating were extracted, the reflection spectrum of fiber Bragg grating have been calculated according the strain distribution. Finally, to verify the numerical results, a test scheme was performed and the experimental spectrums of fiber Bragg grating were recorded. The experimental results indicate that the failure sequence and the corresponding loads were consistent with numerical predictions.Sixthly, a real-time monitoring system based on the fiber Bragg grating sensors is set up in this paper. Support vector machine is applied to detect the impact damage for the carbon fiber composite laminated plates, and compared with the results from traditional BP neural network.Lastly, summarize the contents and the achievements of this paper, then pointed out the further research direction.更多还原