Research On Rail Defect Detection Based On Arrayed Ultrasonic Guided Wave Technology

At present,China's high-speed rail mileage and operating speed ranks first in the world,of which about 80% of the track service time has been more than two years,by the environment and train operating conditions,track cracks are inevitable,especially in the tip rail part.For the detection of track defects are mostly used non-destructive testing,including eddy current detection,electromagnetic detection,ultrasonic detection,visual detection,etc.,these methods have their differences and similarities.Compared to other inspection methods,ultrasonic inspection has the advantages of high-cost performance and simple operation.Ultrasonic inspection equipment of steel rails has hand-pushed digital rail flaw detection vehicle,etc.,by moving monitoring equipment to experiment with different locations of defect monitoring,time-consuming,limited monitoring range,unable to achieve long-distance flaw detection;monitoring frequency is low,able to detect the smallest defects are limited.Based on the above existing problems,the use of efficient and sensitive detection methods will be the future development trend.Therefore,this thesis proposes a detection method based on ultrasonic guided wave,which has the characteristics of fast propagation speed and wide coverage,and is divided into two parts according to the detection content as follows.1)Due to the irregular shape of the straight rail cross-section and its complex dispersion characteristics,the existing research and application of ultrasonic guided wave technology in steel rails mainly focus on the relatively low frequency range of 0-90 k Hz,which leads to its insufficient discriminatory power for tiny defects.In order to improve the defect detection capability of ultrasonic guided waves in rails,this thesis proposes to stimulate single-mode ultrasonic guided waves in the high frequency range based on array sensing technology.Firstly,based on the semi-analytical finite element method,the propagation characteristics of ultrasonic guided waves in steel rails are studied,and the dispersion curves and mode vibration patterns of CHN60 straight rails are obtained,and the guided wave modes that are sensitive to specific locations are selected and their excitation locations are determined according to the mode vibration information.By means of 3D finite element simulation,the parameters of the excitation transducer such as array element spacing,total array length,excitation period and window function are learnt and optimized to realize the excitation of a 100 k Hz single-mode ultrasonic guided wave at the bottom of the rail.This mode has a high sensitivity to both internal and surface defects(down to 3 mm)on the rail bottom.Experimental tests also show that the optimized excitation conditions can be used to excite a high signal-to-noise ratio unimodal ultrasonic waveguide in rails.2)Point rail as a typical irregular cross-section waveguide,due to the variation of the cross-section,there are a large number of dispersive ultrasonic waveguide mode,it is difficult to excite an effective single-mode ultrasonic waveguide.However,due to the critical parts of the rail turnout and other critical parts of the detection of small defects have high requirements,this thesis proposes a defect detection method based on the frequency domain energy of the array of high frequency guided waves.Based on the following two main points: 1.the semianalytical finite element method can analyze the sensitivity of each mode to rail bottom defects;2.based on the variable cross-sectional characteristics of the sharp rail,it can be predicted that the dispersion changes of the selected mode encountering defects will be more different compared to other modes,which will affect the energy change in the frequency domain.A specific high-frequency mode is first selected based on a semi-analytical method,and then an array sensing technique is used to excite the high-frequency ultrasonic guide wave.Next a principal component analysis method based on the energy in the frequency domain of the high frequency guide wave is used to create a composite score metric for evaluating the length of defects.To validate the feasibility of the technique,tip rail defect simulations and field tests were carried out.The results surface the defect signal of the pointed rail obtained by 3D simulation: the composite score of the defective guide wave signal decreases with increasing defects and has a good linear relationship;for variable section waveguides,the composite score method based on guide wave frequency energy outperforms the traditional amplitude method;and in straight rails,the amplitude method outperforms the composite score method.Finally,a field test on a pointed rail was carried out to further validate that the integrated scoring method based on guided wave frequency energy can predict the size of defects with a maximum error of 3mm detected.