【作者】 刘荣梅；

【导师】 梁大开；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2010， 博士

【摘要】 由于具有抗电磁干扰、灵敏度高、便于成网、尺寸小、易于埋放以及能够在高温等恶劣环境下工作等特点,光纤传感系统可以埋放于复合材料中构成智能结构。光纤智能结构可以实时探测结构内部的损伤情况,从而能够对结构进行监测和寿命预测。然而埋入的光纤不仅起感知内外部环境变化的作用,同时还要受载荷作用,此外,光纤的埋入会在一定程度上损坏基体结构材料的完整性和连续性,因此很有必要将光纤当作内置材料,研究光纤与基体材料之间力学性能的相互影响问题。论文研究光纤与纤维增强材料及基体之间形成的界面,研究了界面对光纤智能复合材料结构力学性能的影响。提出了提高界面强度和改善界面结构的方法,其中措施之一就是采用小直径光纤构建智能结构,因此论文还研究了小直径光纤的制作和其传感性能,并将其应用到复合材料监测中。文中主要研究工作有以下几个方面:(1)研究了光纤智能复合材料结构的宏观力学性能。实验研究了光纤智能复合材料结构的拉伸性能和弯曲性能,分析光纤对材料力学性能产生影响的因素,提出光纤埋入时,应尽可能避免光纤方向和增强纤维铺设方向正交,以达到优化结构提高性能的目的,为光纤智能复合材料结构制作提供了实验数据参考。(2)从细观角度出发,设计了实验方案,研究了光纤和基体材料间界面剪切强度,并从界面处理角度,提出采用偶联处理方法来提高光纤智能复合材料结构力学性能的方法。界面实验研究结果表明,无机材料光纤和聚合物材料间界面剪切强度低,结构承载时易发生界面破坏,从而降低整体力学性能。压缩性能实验对比结果表明,通过偶联剂的媒介作用,使光纤和有机材料(即光纤涂覆层和树脂材料)间的界面形成化学键,可以大大提高黏结强度,从而有效提高光纤智能复合材料的力学性能。(3)研究了光纤与复合材料之间界面结构,分析了界面结构尺寸与智能复合材料结构力学性能之间的关系。提出可通过减小埋入光纤尺寸,从而减小其和基体间界面尺寸,降低界面尖端应力奇异值,达到提高整体性能的目的。(4)研制了小直径光纤Bragg光栅,并对其应变传感和温度特性进行了实验研究。根据耦合模理论,对光纤Bragg光栅的光谱进行了仿真。研究了光栅长度与折射率调制周期改变情况下,FBG的反射、透射光谱,为光栅传感特性的研究提供了理论基础。设计了小直径单模光纤加工布拉格光栅的技术参数以及小直径光纤光栅和设备间连接方式。由于光纤Bragg光栅中心波长的变化量与应变变化或温度变化成线性关系,所以可以通过监测光纤Bragg光栅中心波长的变化来监测结构的应变和温度。为了克服温度和应变对光纤Bragg光栅测量的交叉敏感性,设计了基于悬臂梁的双光栅传感系统。(5)研究并证明了小直径光纤Bragg光栅的动态信号监测功能。设计实验,利用小直径光纤光栅检测铝板振动信号和碳纤维层合板冲击信号,实现了动态信号的频率识别,并利用支持向量机方法对层合板上作用载荷位置进行判别。更多还原

【Abstract】 Optical fiber sensors have the advantages of their insensitivity to electromagnetic interference, high sensitivity, and convenience for network. They have the predominance of small physical size, capability of sensing at high temperature and in environmentally unfavorable conditions. Therefore, individual fibers or fiber networks are often embedded in the composites as sensors for real time structural health monitoring. Optical smart composites have extensive potential applications in monitoring fatigue and damage inside the structures. Accordingly, the life of the structure can be prognosticated. However, despite of the small physical size of the optical fiber compared with the host composite structure, the diameter of the optical fiber was much larger than that of reinforcing fibers. This mismatch in dimensions would inevitably lead to incontinuity of the composites. On the other hand, the embedded optical fibers not only apperceive surrounding changes, but also are subjected to load. The interrelationship of the embedded optical fibers and the composite were deserved study.The interface between the embedded optical fibers and the resin and the reinforced fibers were studied. So did the mechanical influence of interface on the smart composite. The methods to improve the interface structure were proposed. Small diameter optical fiber was accordingly used to compose a smart structure. Therefore, new optical fiber sensing systems were developed and applied in load signal monitoring of composite.The main achievements are described as follows:(1) The mechiancal performance of smart composite with embedded optical fibers was studied. Experimental tests on tensile and bending performance of the composite were carried out. It was proposed that angle difference between the optical fiber and the reinforced fiber should be as small as possible. Thus the structure property was optimized.(2) Experimental program and set-up were designed to study the interfacial shear strength between the embedded optical fiber and the matrix.Coupling was proposed to enhance the optical smart composite from the point of interfacial treatment. Interfacial strength study showed that the shear strength was very low. The interface between the optical fiber and the polymer could be easily destroyed. Thus the mechanical performance of the structure would be weakened. With the help of coupling agent, the optical fiber was chemically bonded with organic material. Therefore, the two materials were glued well and the mechanical character of the smart composite could be enhanced. Experiment on compressive strength showed that the composite with coupled optical fiber embedded inside had better mechanical facility.(3) The interfacial structure was studied experimentally. The relation between the mechanical characteristic of smart composite and the size of interface was studied. Another way to improve the mechanical performance was to decrease the size of the used optical fiber. Hence, the size of the interface between the optical fiber and the composite was reduced. The stress singularity at the pointed end would be depressed.(4)Fiber Bragg grating sensors in small diameter were developed. The strain and temperature sensitivities of the fabricated fiber Bragg grating were studied experimentally. Based on coupled-mode theory, optical properties of the designed FBG were studied. The reflection and transmission spectrums of the designed FBG with small diameter were studied as the grating length and the refractive index were changed. The parameters for manufactiong FBG from a single mode fiber were studied. The connector of the optical fiber sensor in small diameter and the demodulator was designed. The central wavelength of the FBG in small size changed linearly with strain. The relation between the wavelength shift and temperature change is linear too. Therefore, the deformation of the structures can be captured by monitoring the central wavelength changes of FBG. In order to overcome the disadvantage of cross sensitivity, and to measure both parameters at the same time and location, a novel scheme for simultaneous strain and temperature sensing system was presented with the help of a uniform strength cantilever.(5)Dynamic monitor capacity of a small size optical fiber sensor system was studied. The sensor system was experimentally applied in aluminum plate frequency detection. It was applied in monitoring impact signal of a carbon fiber reinforced plastic too. Support vector machine was applied in discrimination load locations on composite.更多还原