超声激励-相移光纤光栅分布全方位传感的机械损伤识别与成像技术

Phase shifted fiber Bragg grating is a special fiber grating which is introduced a certain phase shift in the gate region of a uniform fiber Bragg grating. In addition to having the detection advantages of fiber Bragg gratings such as electromagnetic interference immunity, distributed multi-parameter measurement, high reliability characteristics, it also has the special spectral characteristics of high wavelength selection and very narrow line width. In this project, the phase shifted fiber Bragg grating sensing technology is combined with ultrasonic detection technology to create a new damage identification and imaging theory of the large mechanical equipments by using ultrasonic wave to excite the mechanical structure and the distributed phase shifted fiber Bragg gratings to measure the mechanical damage field signals such as ultrasonic waves, structure stress. It focuses on the following scientific problems: the structure and sensing characteristics of the phase shifted fiber Bragg grating sensor which is sensitive to ultrasonic wave in all directions; the high-speed demodulation and information fusion technology of distributed phase shifted fiber Bragg grating signals; mechanical damage identification and imaging algorithm based on distributed test data. The innovation of this project is that it breaks through the traditional mechanical damage detection technology limitation and connects the phase shift fiber grating sensing technology with ultrasonic detection technology to study the basic problems of mechanical structure damage online dynamic detection, identification and imaging. The launching of this project can improve the safe and stable operation level of the large mechanical equipments as well as enrich and develop the theory of the state detection and fault diagnosis of mechanical equipments.

相移光纤光栅是在均匀光栅栅区引入一定相移而形成的特殊光栅，除具有光纤光栅的抗电磁干扰、分布式多参数测量、可靠性高等特点外，还具有极高波长选择度和极窄线宽的特殊光谱特性。本项目将相移光纤光栅传感技术与超声波检测技术相结合，通过超声波激励机械装置，利用分布式布置的相移光纤光栅测量超声应变波、结构应力等机械损伤的场信号，创建大型机械装备结构损伤识别与成像的新理论和新技术。项目主要研究全方位超声敏感的相移光纤光栅传感体结构及传感特性、相移光纤光栅分布式测量的结构损伤场信号高速解调与信息融合、基于分布式测试数据的机械损伤的识别与成像算法等科学问题。本项目的创新点在于突破传统机械损伤的检测局限，将相移光纤光栅分布传感技术和超声波检测技术相结合，研究机械结构损伤在线动态检测、识别与成像的基础问题。本项目的开展对提高大型机械装备安全稳定运行水平，丰富和发展机械设备状态检测与故障诊断理论，具有重要的意义。

对大型机械装备结构损伤进行有效的检测，是其可靠运行的重要保证。超声激励-相移光纤光栅（Phase shifted Fiber Bragg gratings--PS-FBG）检测技术将PS-FBG 极窄线宽的光谱特征，抗电磁干扰、分布式多参数测量的检测优势与超声检测的强穿透能力的特点相结合，在机械损伤检测领域有很好的发展潜力。本项目就该技术的一些基础问题展开研究，主要工作如下：.1. 构建了不同角度超声波作用下的PS-FBG传感模型，利用耦合模原理和传输矩阵理论，研究了超声激励下PS-FBG光谱特征和光谱的影响因素。考虑双折射效应，提出了PS-FBG对超声波的空间响应规律呈中间带尖峰的类余弦曲线。.2.设计了一种便携式PS-FBG超声传感器，仿真分析了超声激励下待测结构的应力场及应变波传播过程；提出了一种随机-精英型差分进化算法实现PS-FBG对空间应力波的全方位解耦。.3.构建了一种分布式传感的光栅布点结构，成功实现声发射和超声波的同步检测，实验证明了传感网络中声轴附近纵向布置的光栅较横向布置的光栅具有良好超声响应特性。 .4.搭建了基于可调激光光源的PS-FBG高速解调系统，推导了输出电压与所测超声应变的关系式，利用解调系统测量到高达12MHz的超声信号，证明了PS-FBG相比于FBG在超声波检测中具有信号强、信噪比好、响应频率高的检测优势。.5.将分布式光栅传感用于超声波、钢球冲击声发射、混凝土早期凝固、铝合金板焊接过程等多物理场的检测，利用快速傅里叶变换和小波波包分解对多物理场信号进行综合处理。.6.提出一种超声激励-分布式PS-FBG传感损伤检测识别方法，利用损伤前后连续小波时频图像差异识别损伤的有无，探索时频参数与损伤位置和程度的映射关系。.上述理论与试验研究的开展，对丰富和发展测试理论和检测技术，提高机械装备运行的可靠性和安全性，具有重要的意义。