Damage Imaging And Localization Of Metro Vehicle Bogie Frame Using Lamb Wave

Metro vehicles have the characteristics of strong carrying capacity,resource utilization and fast running speed,and are important means of transportation for urban traveling.The train bogie frame is subjected to carrying stress loads from complex frequencies in multiple directions.Its irregular geometry and welded joints are prone to local dynamic stress concentration,causing damage or even fragitue.Normally,the detection of fatigue of bogie frame is mainly based on the long-term accumulated running mileage,and it is difficult to find the damage in time between the inspection and repair period.The Lamb wave is sensitive to minor damage in the initial stage The monitoring process does not require structural disassembly and is an effective way to monitor the damage.Therefore,the Lamb wave is introduced into the metro vehicle bogie frame fatigue monitoring.The contents of this thesis mainly includes:(1)The characteristics of Lamb wave propagation and selection of excitation parameters are studied.The effects of different material parameters and boundary conditions on the propagation of Lamb wave signals are also studied.The MATLAB is used to solve the Lamb wave dispersion curve in a steel plate,and the excitation parameters such as the lamb wave excitation mode,the sensor type,the sensor network layout,the signal main frequency and the signal gain are determined.(2)Improved damage imaging algorithm based on signal correlation coefficient.According to the distance between the sensors,the distance between the sensor and the structure boundary,and the wave velocity of the Lamb wave modes in the material,the effective signal segment received by the receiving sensor is automatically extracted,and the extracted effective signal segment is used to reduce the interference of the unrelated data.In the thesis a new correlation coefficient calculation methods is also proposed,and put forward a concept of image enhancement factors and damage thresholds to improve damage contrast and reduce positioning range by using the dependence of energy spectrum correlation on external environmental conditions(3)A non-benchmark damage imaging method based on signal correlation coefficient is proposed.The method determines the healthy path in the structure based on the signal correlation coefficient between the equidistant excitation-received path,without benchmark signals.The benchmark signal path is screened by solving the correlation degree of the equidistant response signals with each other,and the signal transmission path that is not generated or far away from the damage is used as the benchmark signal on the transmission distance,and the damage imaged by caculating the probability of the signal from the path with the damage and without damage.(4)A hybrid positioning algorithm based on signal's time of flight is proposed.According to the time delay phenomenon caused by the damage in the structure,a hybrid positioning algorithm is designed based on the elliptical localization algorithm and hyperbolic localization algorithm.The method can make full use of the arrival time of each propagation path signal,thereby improving the utilization of data.At the same time,the calculation method of scattered wave signal without reference is addressed,which acheived the hybrid localization with benchmark and without benchmark,which reduces the dependence on the condition and expands the application range.Finally,the Lamb wave-based damage imaging and localization algorithm of the designed bogie frame is verified by the practical experiment on the damage of the bogie frame,which provides a reference for the monitoring of the damage of the metro bogie frame.