Research On A Hybrid System Combining Fiber Bragg Grating And Ultrasonic Nondestructive Testing

Sheet structure components are widely used in industry.In the process of production and use,the internal structural defects often damage the strength,stiffness and other characteristics of parts,which affects the service life of structure,and cause great risks.In this paper,a hybrid method combining fiber Bragg grating and ultrasonic nondestructive testing is proposed,which the ultrasonic signal is detect by the fiber Bragg grating(FBG).Combined with the advantages of traditional ultrasonic nondestructive testing,such as high resolution,high detection efficiency,free from electromagnetic interference and wide application.The function generator is used to introduce the Lamb wave signals into the plate.The response data is recorded using the optical fiber sensing and demodulation system.The defect can be identified through signal analyzing.It has important scientific significance and application value for nondestructive testing of plate-like structures.Aiming at the hybrid method combining fiber Bragg grating and ultrasonic nondestructive testing,the generation of ultrasonic Lamb wave,the wave equation and dispersion effect of ultrasonic Lamb wave are studied.According to the above theory,the dispersion characteristic curve of ultrasonic Lamb wave in aluminum plate is drawn.The sound pressure distribution of ultrasonic Lamb wave in aluminum plate at different times is simulated by finite element method.The propagation law of ultrasonic Lamb wave in aluminum plate is obtained.The basic theory of fiber sensing and the sensing characteristics of fiber Bragg grating under the action of ultrasonic wave are studied.The reflection spectrum curves of different grating lengths under the action of specific wavelength ultrasonic wave are simulated and analyzed,which provides a theoretical basis for the subsequent parameter selection and position arrangement of FBG.Aiming at the hybrid method combining fiber Bragg grating and ultrasonic nondestructive testing,the demodulation principles and advantages and disadvantages of several commonly used fiber demodulation methods are analyzed,and the transmission matched grating demodulation system based on matched grating method is designed.The selection criteria of the main components of the demodulation system are determined,and the components are selected to build the demodulation system based on the matched grating method.The data acquisition and storage program is written,and the demodulation accuracy of the fiber Bragg grating demodulation system is verified by ultrasonic testing experiment.Based on the hybrid method combining fiber Bragg grating and ultrasonic nondestructive testing proposed in this paper,an experimental platform of the hybrid system combining fiber Bragg grating and ultrasonic nondestructive testing is built,aluminum plate samples with defects are designed and testing experiments are carried out.The accurate identification of different defects in the aluminum plate verifies the feasibility of the fiber grating and ultrasonic combined nondestructive testing method and the reliability of the system.