Basic Application Study On Fiber Optical Sensing In The Monitoring Of Composites Enduring Impact

Composite materials have lots of excellent characteristics, such as high strength, high hardness, light weight, good thermal stability, good flexibility and chemical resistance, facility to process and mold, and et al. In the military, aerospace, transportation, electrical and electronic, construction and some other fields, composite materials have been widely used. However, due to low sensitivity of crack damage and weak shear strength of composite materials, the real-time monitoring for the damages of composite materials is required in some applications. In the past few years, fiber Bragg grating sensor, with its inherent safety, light weight and small diameter, high sensitivity, free from magnetic interference and other outstanding performance has been fully affirmed in the sensing field, and is suitable for the monitoring of physical quantities, such as strain and temperature in engineering. By combining theoretical and experimental methods, as well as optical fiber sensing technology, this thesis attempts to study the feasibility of real-time monitoring for the strain and damage of composite materials under external force or impact, to lay the foundation of using fiber optical sensing in the monitoring of composites enduring impact.The main work in this thesis includes:The development history of monitoring composite structures, the application status, and the advantages of using optical fiber sensing technology to monitor composite structures are described. The mechanism of fiber grating sensor, the dependence of fiber Bragg grating wavelength shifting on strain or temperature change, and the characteristics of SM130 fiber grating sensor demodulator are introduced.The dependences of deflection and strain of the composite strip under elasticity constraint upon external force, and how the central wavelength of FBG changes with the azimuth angle of FBG, the measuring point and external force are investigated.The glass fiber reinforced resin composite laminates are produced. By using SM130 fiber grating demodulator, the dependences of strain of the composite strip under fixed constraint upon external force, and how the central wavelength of FBG changes with the azimuth angle of FBG and external force are studied experimentally.Using SM130 fiber grating demodulator, the dynamic strains of the composite strip under fixed constraint and the wavelength shift of FBG under different impact energy are measured; moreover the change curves of center wavelengths of FBGs with time are given and discussed.For two-dimensional composite plate enduring the impact, the dynamic changes of the central wavelengths of four FBGs pasted rigidly on the plate, and the influence of different paste angles on the central wavelength are researched experimentally.To compare with the experimental results and increase the understanding for the strain situation of the composite plate enduring impact, some impact experiments of a two-dimensional composite plate have been simulated by using ANSYS finite element software.