Monitoring of Crack Propagation in Repaired Structures Based on Characteristics of FBG Sensors Reflecting Spectra
YUAN Shen-fang1, JIN Xin1, QIU Lei1, HUANG Hong-mei2
1. State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China 2. School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China
Abstract：In order to improve the security of aircraft repaired structures, a method of crack propagation monitoring in repaired structures is put forward basing on characteristics of Fiber Bragg Grating(FBG) reflecting spectra in this article. With the cyclic loading effecting on repaired structure, cracks propagate, whilenon-uniform strain field appears nearby the tip of crack which leads to the FBG sensors’ reflecting spectra deformations. The crack propagating can be monitored by extracting the characteristics of FBG sensors’ reflecting spectral deformations. A finite element model (FEM) of the specimen is established. Meanwhile, the distributions of strains which are under the action of cracks of different angles and lengths are obtained. The characteristics, such as main peak wavelength shift, area of reflecting spectra, second and third peak valueand so on, are extracted from the FBGs’ reflecting spectral which are calculated by transfer matrix algorithm. An artificial neural network is built to act as the model between the characteristics of the reflecting spectral and the propagation of crack. As a result, the crack propagation of repaired structures is monitored accurately and the error of crack length is less than 0.5 mm, the error of crack angle is less than 5 degree. The accurately monitoring problem of crack propagation of repaired structures is solved by taking use of this method. It has important significance in aircrafts safety improvement and maintenance cost reducing.
Key words：FBG;Monitoring of crack propagation;Repairedstructure;Characteristics of reflecting spectra;Artificial neural network
