| The railway traffic in our country is gradually moving to the period of safe operation from the period of large-scale construction.How to ensure the railway safety,stable and reliable long-term operation will become a major problem facing the railway transportation in China.In the detection of railway rail damage,the traditional ultrasonic detection methods are limited by the detection speed and efficiency,and a large number of researchers are trying to find new methods to make up for the shortcomings of ultrasonic detection.Compared with other nondestructive testing methods,acoustic emission technology can detect the dynamic crack,crack initiation and crack growth of the object,that is,the information it detects is the information sent by the defect itself,without the need for external input signal to scan the defect.Therefore,acoustic emission technology can be used to realize the detection of rail crack damage.However,the practical application of acoustic emission technology in rail damage detection is still in the preliminary research stage.The feasibility of this technology in rail damage detection is only verified theoretically and experimentally,and further research is needed.In view of the above situation,this paper takes the switch sharp rail as the research object,through the technical means of Abaqus simulation,acoustic emission experiment and field acoustic emission signal measurement,to study the acoustic emission source characteristics of the switch sharp rail,AE wave propagation characteristics inside the rail in the switch area,and because in the actual detection operation,Acoustic emission detection technology is often used together with ultrasonic guided wave detection technology in the damage detection of the measured object.This paper also simulates the propagation process of ultrasonic guided wave in the turnout spike rail,and does a step study on the difference between ultrasonic guided wave signal and acoustic emission signal in the turnout spike rail.The main research contents of this paper are as follows:Through the research of semi-analytical finite element method,the dynamic characteristics of switch rail and ordinary 60 rail are analyzed,and it is concluded that there are similar modes in the dispersion curves of switch rail and ordinary 60 rail.However,due to the differences in section characteristics,the wave number at the same frequency will vary.The cutoff frequency of some wave modes continuously increases from the AT rail section to the switch rail tip section,and the wave mode gradually decreases.Through field measurement of acoustic emission signals,the characteristics of acoustic emission signals when trains pass through are studied.For abnormal data that produces baseline drift,TVD filtering can be used for filtering.Due to different fixation methods,the effective value voltage of the acoustic emission signal of the stock rail is generally smaller than that of the switch rail,and the damage inside the rail will cause the amplitude of its acoustic emission signal to increase,and generate abnormal peaks in the high-frequency part.However,for different types of trains passing through the same switch rail,the modal characteristics of the acoustic emission signal will not be changed,but the amplitude of the acoustic emission signal will become larger as the mass increases.The conditions for acoustic emission simulation modeling of switch rails are analyzed.A pair of electrodes are used to simulate the acoustic emission signals generated by cracks,and finite element simulation is conducted.The acoustic emission signals when rail cracks occur are studied.The correctness of the acoustic emission finite element simulation method in this paper is verified through lead breaking experiments.By simulating the propagation process of ultrasonic guided wave signals in switch rails,it is concluded that the mode of ultrasonic guided wave signals is single through analysis and comparison;The mode of acoustic emission signals is more complex.Through acoustic emission simulation of lead breakage on switch rails,it is found that the rail sections of the four characteristic sections of the switch rails have similar acoustic emission modal characteristics,but the energy intensity gradually decreases with the increase of the characteristic section.As the conduction distance increases,on the wavelet time-frequency map,its energy will disperse to other frequency bands as the conduction distance increases.In acoustic emission simulation under train load,the amplitude of the acoustic emission signal increases as the section of the switch rail decreases.The addition of the damage model does not change the position of the main frequency,but it increases the response of each frequency band to varying degrees,and produces abnormal peaks in the high-frequency part. |
