Composite Detection Research On Multi-source Excitation-fiber Grating Sensing For The Mechanical Plate Structural Damage

In recent years,the machinery equipment is gradually to develop towards the direction of large scale,intelligent.In view of the running environment of multivariate random,the structure response is often characterized by multiple source common effect.It is difficult to meet the actual response features for traditional test methods using single incentive because of its limitations.Therefore,the research and development of new detection technology is one of the most important trends of aircraft structure damage detection.Multiple source excitation-fiber Bragg grating detection technique(MSE-FBG)is a new kind of detection method,whose basic principle is to apply multiple incentive source to the specimen material at the same time in order to simulate the actual working condition,and use distributed optical fiber grating sensing technology to obtain the measured strain information for the analysis of structure state.This technology adopts multi-source excitation technology,combined with the advantages of fiber grating,such as light quality,easy to distributed sensing,anti-electromagnetic interference ability,has a wide development prospect in the field of the mechanical structure structural damage detection.However,this detection technology is rarely reported.This paper proposes a new principle and method of dynamic detection based on multi-source excitation-fiber grating sensing for mechanical damage,taking the aircraft plates as the object.The researches of multi-source excitation detection focus on the coupling mechanism of multi-source excitation signal,signal modulation mechanism by mechanical damage,excitation signal characteristics and mapping relationship between mechanical damage and fiber grating sensing signal and other scientific problems.FBG strain sensor characteristics under multi-source excitation according to the distributed FBG measurement is revealed,and the technical problem of online is solved.The main characteristics and innovations of the new mechanical structure crack damage detection and localization is to combine the advantage of ultrasonic detection and vibration testing technology,and create a new distribution dynamic detection method for the aircraft structure damage through the fiber Bragg grating distributed dynamic detection.Paper's main work is as follows:Three multi-source excitation models are set up,double vibration mode,vibration-ultrasonic mode and double-ultrasonic mode are discussed.The frequency response function in double vibration mode,the nonlinear ultrasonic wave equation in vibration-ultrasonic mode and the strain response function in double-ultrasonic mode are derived respectively,which provide theoretical basis for multiple source excitation detection.The FBG sensing characteristic and characteristic parameters are researched under three multi-source excitation models,focusing on frequency,phase and amplitude,location of two excitation signals and other factors.It can provide parameters for subsequent damage location.At the same time,the signal extraction analysis are studied: modulation properties for vibration-ultrasonic modulation is analyzed through the simulation of frequency modulation,amplitude modulation.And the signal denoising,filtering and other processing are implemented by wavelet transform tools,which can provide data for the analysis of damage location assurance.Multi-source excitation-FBG test system is built.Signal is provided by the signal generator,and wave signal is obtained in board structure by the converse piezoelectric effect of piezoelectric element,whose demodulation for FBG center wavelength shift is used adjustable laser light source.This system is used in the isotropic plate to research sensing properties of FBG under multi-source excitation,whose experimental results verify the feasibility of the system that multi-source excitation signal can be measured to detect damage on the plate.On this basis,multi-source excitation-FBG test system for plate structure damage location is built.And two kinds of localization algorithm are proposed respectively: two step method and the elliptic imaging method.Experiment results show that the two step method can reduce damage determination range,and the elliptical image positioning method is effective for hole damage and crack damage of the isotropic plate.