Research On Response Characteristics Of FBG Sensing Subject To Ultrasonic Stimulation

The effective detection and prevention to the crack damage in mechanical structure is the foundation of the healthy operation of the equipment, and it's provides security to the economic development and life safety. It is difficult to implement real-time dynamic monitoring with multiple points for the traditional method of mechanical structure damage identification. Meanwhile the electric sensors are vulnerable to environmental noise in the actual working condition, so the detective effect is not good enough. Therefore, a new method, using fiber Bragg grating (FBG) sensor to test the ultrasonic which is propagating in the structure, has been provided to achieve structure health monitoring. This paper makes a study of the response characteristics of the FBG to ultrasonic in non-defects structures as this is the foundation of damage identification.This paper studied the working performance of the testing system firstly, and the response characteristics of FBG to the ultrasonic, which was stimulated by different irradiation modes, had been studied. Then the position for FBGs distributed measuring was determined, so that the distributed measuring for FBGs to ultrasound had been realized. The main content of this paper includes:1. The study of the working performance of the testing system. The performance parameters of the system were obtained. The influence on the working performance, which was changed by variation of parameters in light source, had been examined. A method of setting up reasonable parameters and the notes had been proposed.2. The ultrasound signal was successfully extracted from different metal materials. The response characteristic of FBG to ultrasonic, which is stimulated in different frequency and incident angle, was studied.3. The one-dimensional and two-dimensional response characteristics of FBG to ultrasonic had been studied. One-dimensional response reveals the influence law of the response characteristics of FBG to ultrasonic when the straight-line distance between sound sources and FBG is changing. Two-dimensional response researches the characteristics of FBG to ultrasonic when sound axis and the optical fiber axis in different angle position. 4. According to the research conclusion, the locations of the FBGs for multi-points measurements had been determined. Proved by the experiment, FBG sensors working as distributed measurement were well sensitive to the ultrasonic, which was stimulated by one PZT. It indicates that the decoration and the locations of FBGs are applicable.The study of this dissertation can provide some useful experiences to the research on FBG-ultrasonic damage detection technology, which will achieve great application prospects and realistic significance in maintenance of large equipments and instruments.