Research On Mechanical Structure Crack Propagation Identification Based On Strain Field And Optical Fiber Bragg Grating Sensor

With the development of modern industrial equipment large-scale, the mechanical structure bearing is more and more heavier, the working time is more and more longer. Fracture failure of mechanical structure has become the biggest threat of equipment structure of safety, reliability and service life. According to statistics, in all kinds of mechanical structure of the fracture accident,80%of them are ascribed to fatigue fracture, the fatigue fracture of great danger[2]. Monitoring the mechanical structure fatigue crack and the formation of the extension of structure security is very important. To solve this problem, a kind of effective mechanical structure crack propagation identification method is researched in this paper, which is used to identify and monitor the fatigue crack propagation. It has reference value on crack damage mechanical structure health monitoring and safety analysis.+This paper first reviews, and analysis of crack identification technology at home and abroad, and the research status, emphasis on the introduction of the parameters based on strain crack identification technology and FBG sensing technology in crack identification and monitoring application, the analysis of various technical advantages and disadvantages. Then it is studied on the crack identification theory based on strain parameters, deduces strain mode through three methods, modal test method research strain and modal parameter identification method. Then it introduces four kinds of parameters of the damage identification based on strain method, expounds formulas, principle and features. By analysing four damage detecting methods based on strain parameters, figures out that strain frequency response function parameters is the most advantage in crack damage identification. The author establishes finite element model of the penetrated crack sheet by using finite element software ANSYS. The stress intensity factor at the crack tip is calculated. Finite element analysis on strain field of a four corners fixed sheet with crack is carried out. The distribution of strain field around and change in crack propagation process is analysed. The crack damage identification index based on change amplitude of strain frequency response function parameters(SFRF) is presented. Finally, the fiber Bragg grating strain sensor strain principle is studied. The sheet crack propagation identification test bench based on optical fiber grating sensors is established. Experiments and analysis are carried out. Experiments show that:the technique in this paper can identify and monitor crack damage occurs and propagation effectively.The innovative point of this paper is presenting crack damage identification index based on change amplitude of SFRF. The basic principle is structure bearing capacity reduces after crack damage occurred, stress concentrates near the crack tip, strain near the crack tip mutates, strain frequency response function parameters change a lot after damage occurred. And with the crack propagation, the change amplitude increase, while it is not obvious in other region far from the crack. We can identify and monitor crack damage occurs and propagation by using the index.The achievement of this paper is a new kind of effective mechanical structure crack identification method, it has reference value for mechanical structure health monitoring and safety analysis based on crack damage.