【作者】 付涛；

【导师】 冷劲松；

【作者基本信息】 哈尔滨工业大学 ， 工程力学， 2014， 博士

【摘要】 随着纤维增强复合材料在航空航天、交通运输、能源、航海与军事等领域的广泛应用，复合材料的结构健康监测也引起科研人员的广泛重视。传统的无损检测技术已无法实时监测复合材料结构服役期间因受静、动载荷，疲劳而产生的损伤和破坏，亟待开发新技术实现先进复合材料结构的在线健康监测。声发射技术作为一种现代新兴的无损检测技术，与传感器技术、测量技术、信号采集与分析处理等多种技术相融合，在无损检测领域中具有广阔的应用前景。传统的声发射传感器通常为压电陶瓷材料，不仅易受电磁干扰，而且因为体积大而不适合埋藏于纤维复合材料结构中。本文研制了一种可埋藏在纤维复合材料结构内的新型光纤声发射传感器，将其应用于各向异性复合材料平板结构的声发射源定位研究，主要内容如下：首先，基于熔锥型光纤耦合器提出并研制了一种新型光纤声发射传感器。该传感器采用细小的毛细玻璃管封装，易埋藏于纤维复合材料结构中。从振动力学角度分析了传感器的振动特性，指出封装管对传感器内耦合光纤的预拉伸力是影响传感器对应力波响应的主要因素。利用光波导理论分析了光纤声发射传感器的传感原理，得出传感器耦合区的光纤纤芯间距与传感器对应力波的敏感特性之间的关系。根据电子显微镜测量传感器内部光纤的细观结构尺寸，使用有限差分光束传输法模拟光纤传感器中光波导的传输特性，仿真结果为提高传感器的灵敏度提供参考。针对新型光纤声发射传感器，开发了声发射源定位监测系统。在监测系统程序中嵌入声发射源定位算法，能够及时准确判断声发射源位置，提高测试效率。其次，将光纤声发射传感器埋藏在纤维复合材料层合板中，形成具有感知应力波、识别声发射源位置功能的智能纤维层合板，突破了传统压电声发射传感器体积大、不易埋藏在复合材料结构中的限制。结合商用压电声发射传感器，对比测试了光纤声发射传感器对应力波的幅频响应特性，证明新研制的光纤声发射传感器适用于低频声发射源监测。该传感器可以识别出具有波形特征的扩展波(S0波)与弯曲波(A0波)，通过实验测量出它们在不同材料平板中不同方向的传播速度，为识别声发射源位置提供信息。再次，研究了各向同性与各向异性材料平板的声发射源定位方法，使用光纤声发射传感器及其源定位监测系统进行了测试与验证，包括声发射源的线性定位和平面定位两种方式。在研究声发射源的线性定位方法中，将三个光纤声发射传感器以等间距线性阵列布局在纤维复合材料平板内任意方向上，在无需应力波传播速度的前提下识别出声发射源位置。将该方法应用于长为1.2m的玻璃纤维风机叶片模型，通过等间距的逐点测试，相对误差不超过1.3%，验证了该线性定位方法较高的准确性。在研究声发射源的平面定位方法中，使用代数算法对传感器正方形布局测量的声发射源坐标进行计算。实验结果显示三个参量的代数算法在迭代运算中易产生非线性误差和非实数解。为解决以上缺点，建立了时间差为输入的BP神经网络算法。该算法适用于传感器任意布局的源定位方法，具有较强的通用性。为削弱应力波在各向异性的纤维复合材料中不同方向的传播速度不一致对代数算法的影响，提出了传感器菱形布局的源定位算法。该方法利用菱形两个对角线方向的速度计算声发射源位置，实现了声发射源在各向异性材料平板内的高精度快速定位功能。最后，使用落锤低速冲击方法模拟冰雹和沙石等自然灾害和恶劣环境对碳纤维复合材料进行冲击测试，应用本文建立的光纤声发射源定位系统对碳纤维复合材料的落锤冲击源进行定位研究。通过光纤声发射传感器的表面粘贴和埋藏两种方式，准确地识别出碳纤维复合材料层合板的冲击源位置。分析预埋缺陷与冲击损伤对声发射源定位的影响程度，证明光纤声发射传感器阵列的测量结果与嵌入在源定位系统内的代数算方法均具有较高的精度。在一定的冲击能量范围内，传感器对应力波的幅值响应线性地反映出落锤冲击能量，具有操作方便、数据处理简单、可靠性强等优点。综上，本文研制的新型光纤声发射传感器开拓了无损检测技术的研究方向。传感器阵列埋藏在纤维复合材料结构中的研究成果，为自感知智能复合材料结构的发展提供重要的参考价值。声发射源定位监测系统的开发与应用在先进复合材料结构健康监测的研究中具有重要意义。更多还原

【Abstract】 With the fiber reinforced plastic (FRP) composite laminates are widely used in the field of aerospace, transportation, energy, navigation and military, more and more researchers have drawn attention to the structural health monitoring (SHM) of composites. In order to effectively detect damages and failures of composites due to the static or dynamic load and fatigue, a novel technology instead of traditional nondestructive testing technology is necessary to be developed for achieving the on-line health monitoring of advanced composites materials and structures. Acoustic emission (AE) technique as a kind of modern new non-destructive testing technology, integrating multiple techniques such as sensor technique, measurement technique, signal acquisition and analysis technique, has a broad potential application in the field of nondestructive testing. Traditional AE sensors are usually made of piezoelectric (PZT) ceramic materials, not only susceptible to electromagnetic interference, but also unsuitable for being embedded into FRP composites structure as its bulky structure. In this thesis, a new type of fiber optic acoustic emission sensor (FOAES) is developed, which is able to be embedded in FRP composite laminates. The sensors are applied for the research of AE source localization in anisotropic plate-like composites structures. The main contents in this thesis include:Firstly, a novel FOAES is proposed and developed on the fused-tapered optical fiber coupler. It is packed with a short and thin capillary tube, and easy to be embedded into composite structures. The vibration characteristic of the sensor is established on the perspective of vibration mechanics, which points out that the main influence factor is the pre-tension from the packed tube to the coupled fibers of the sensor. The sensing principle of the FOAES is analyzed with the optical waveguide theory, obtaining the relationship between the fiber core spacing at the sensor coupling part and the sensor sensitivity to the stress wave. According to the mesoscopic structure size of optical fibers in the sensor measured by the electron microscope, optical waveguide transmission properties in the optical fiber sensor are simulated with the method of finite difference beam propagation, and their optical waveguide simulation results provide reference for improving the sensitivity of the sensor during its fabrication. At the same time, a AE source localization monitoring system is built and developed for the novel FOAES. An algebra algorithm of AE source localization is embedded in the system program, which is able to accurately and quickly estimate the AE source location improving the testing efficiency.Secondly, FOAESs are embedded into a FRP plate, constituting of a smart composites plate that has the function of sensing stress waves and identifying the position of the AE source. This technique breaks through the limit of bulky and difficult to be embedded into the composite structures of traditional PZT AE sensor. Through a series of comparison experiments, amplitude frequency response characteristics of the FOAES to stress waves are measured compared with a PZT AE sensor. Their experiment results prove that the new-designed FOAES is completely suitable for the AE source of low-frequency. The sensor can distinguish waveforms feature of the expansion wave (S0wave) and flexural wave (A0wave). Their propagation velocities in different directions are measured in different materials plate by experiments, which support the information for identifying the AE source location.Thirdly, the AE source localization method is researched on the plate of isotropic and anisotropic materials. The FOAES and its monitoring system are used for experimental measurement and validation, including linear and planar localization of AE source. In the study of linear localization method for acoustic emission source, three FOAESs with equally spaced linear array are distributed on the fiber composite plate in any direction. The AE source location is identified using the linear array without the information of propagation velocities of stress waves. A composite wind turbine blade with1.2m length is tested in the method of evenly spaced points. The measurement relative error less than1.3%verifies the linear positioning method has a high accuracy. In the study of planar localization method of AE source, the algebra algorithm is used to calculate the AE source location measured by a square sensor array. Experiment results prove that nonlinear errors and unreal solutions are easy to be obtained using the algebra algorithm with three parameters. An algorithm based on artificial neural network with time differences as inputs is established to solve the above shortcomings, which is suitable for any source localization method of distribution of sensors. The algorithm of source localization using sensors as a diamond array is also proposed for weakening the influence of which is introduced stress wave propagation velocities are different in directions of anisotropic composites materials. Two velocities in the diagonal directions of the diamond are selected for calculating the location of acoustic emission source in the algorithm, which achieve the function of acoustic emission source localization in anisotropic materials plate accurately and fastly.Finally, CFRP composite materials are tested by using drop-weight impact method, which are simulate to natural disasters and harsh environment, such as hails and sands. The drop-weight impact source localization method for CFRP laminates are also researched by using the optical fiber AE source localization system of this article. The impact source location of CFRP laminates is accurately identified by the surface-mounted and embedded sensors. The incidences of AE source localization from impact damage are analyzed, which prove that the measurement results of the FOAES array and the algebra calculate method embedded in the source localization system both have higher precision. In a range of impact energy, the amplitude response of the sensor to stress wave will linearly increase along with the augment of the drop-weight impact energy, which is easy to operate, simple to process data, reliable and so on.Above all, the development of the new FOAES in this thesis expands the research area of nondestructive testing technology. The research results of the FRP composite structures embedded with sensor array provide important reference value for the development of self-sensing smart composite structures. The development of monitoring system for acoustic emission source localization and its application have important research significance for the structural health monitoring (SMH) of advanced composites.更多还原