Study On Ultrasonic Guided Wave Quantitative Monitoring Method For Damage And Propagation In The Critical Zones Of Structure

Considering that the hotspot regions of railway traffic bogie structure and CR929 aircraft composite structure are complex and prominent,they are easy to produce high stress concentration or damage when they are subjected to various loading forces.Simultaneously,they are the research hotspots and have been extensively concerned.Although many studies have been researched by the nondestructive testing and structural health monitoring(SHM)methods,they merely determine the existence of damages.It is still a certain challenge to accurately identify and quantitatively characterize the damage propagation process.Ultrasonic guided wave SHM technology based on intelligent piezoelectric sensor network can be integrated in the hotspot regions of railway traffic bogie structure and CR929 aircraft composite structure.It can be used to identify damage types,damage location,the size of the damage,and the extension degree of damage by monitoring the structure state parameters of hotspot regions timely.It is also used to rapidly assess and judge the the overall health condition of structure and predict the residual service life of structure,thereby it can ensure the security and stability of the trains and aircraft operation.Ultrasonic guided wave SHM technology has a good application prospect in the hotspot region,it can quickly,comprehensively,and accurately detect the damage distribution and damage propagation in the the hotspot regions of the train and aircraft.Hence,ultrasonic guided wave SHM method is selected for monitoring the structural damage in this distertation.In this distertation,the fusion damage indices(DIs)characterization method and the modified probabilistic diagnostic imaging(MPDI)algorithm are used to deeply study the damage propagation process,the location,size,number and other damage feature information of different types of multi-defects in the hotspot regions of the aircraft composite structure and railway traffic bogie structure.The main research contents are diaplayed as follow:(1)The intelligent sensor network layer is designed and optimized in the hotspot regions of the train and aircraft,and the appropriate excitation frequency,excitation mode and signal acquisition parameters of ultrasonic guided wave are selected to improve the signal performance parameters.(2)Ultrasonic guided wave signal characteristic parameters of all actuator-sensor paths are extracted by the advanced software analysis and signal processing method to construct the time or frequency amplitude,energy and signal difference coefficient(SDC)DIs in the whole monitoring area.The DIs characterization methods with different acoustic characteristics can effectively identify the initiation and propagation process of damage.(3)According to the weight value of the initial DIs at each actuator-sensor path,the linear and the first-order differential fusion methods are used to fuse the all available DIs at each path,the proposed fusion DIs characterization method can directly and quantitatively characterize the propagation progress of different damage sizes or depths in the hotspot regions of the bogie frame and the airplane composites structure,the fusion DIs characterization method can quickly reflect the the overall health status of the inspected structure.(4)Ultrasonic guided wave SHM method is applied to construct the fitting regression mathematical model relationship between the SDC Dls of different damage sizes expansion and the relative distance RD and damage area DA in the hotspot regions of composite structure R specimen by the experiment.Then the unknown damage size information can be deduced by the fitting regression function relation.(5)The damage shape factor from the damage-impaired paths can be optimized according to the relationship between the damage existence region and the elliptical affected zone controlled by the damage shape factor,the MPDI algorithm related with the damage shape factor of each damage-impaired path is proposed in this distertation.The MPDI algorithm is used to study the expansion of different damage sizes and the damage characteristic information of various types of multi-defects in the hotspot regions of the curved and arched composite structure.The experimental results show that the MPDI algorithm can accurately identify the damage distribution condition,the number,location,size and other damage feature information of different types of multidefects and quantitatively represent the extension process of different damage sizes in the hotspot regions of composite structure.It is also demonstrated that MPDI algorithm can improve the resolution and accuracy of damage identification,and the optimization of the damage shape factor is feasible in the MPDI algorithm.