Study On Rapid Retection Of Internal Defects Of Slab Ballastless Track Based On Air-coupled Impact-echo

China has the largest high-speed rail system in the world,of which the most widely used high-speed rail slab ballastless track is prone to void defects of elastic bearing layer due to the repeated action of train load during service.At present,there is little research on the internal defect detection of slab ballastless track,and rapid and accurate identification of its internal defects is still a major challenge for high-speed railway repair and maintenance.This thesis first introduces the propagation law of stress wave in the slab structure and the propagation theory at the structure air interface.Based on this,the response characteristics of air-coupled impact-echo under different defect sizes,different defect depths,different defect locations and different knock positions are studied.A multi-channel rapid detection system based on air-coupled impact-echo is developed,and a test model of high-speed slab ballastless track is established,The aircoupled impact-echo rapid detection of internal defects of slab ballastless track was carried out.The main research results of this thesis are as follows:(1)The numerical model of slab ballastless track was established,and the law of air-coupled impact-echo method to detect the internal defects of slab ballastless track was analyzed.The working conditions such as different defect sizes,different defect depths,defects under sleepers and different striking positions were set respectively to explore the response characteristics of impact-echo under different working conditions.The collected signal is subjected to FFT transformation to obtain its frequency domain diagram,and the spectral components are analyzed to achieve defect recognition and localization.(2)The full-size physical model of P5600 slab ballastless track slab was made,and the defects corresponding to the numerical simulation setting conditions were embedded to verify the response characteristics of the impact-echo under the preset conditions during the actual measurement.The response characteristics of impact-echo obtained in the actual measurement process are basically consistent with the numerical simulation results.The identification and location of internal defects of slab ballastless track can be achieved by analyzing the frequency domain diagram of the signal.(3)A rapid detection system based on air-coupled impact-echo was developed,and the P5600 type slab ballastless track model with embedded defects was measured using the developed detection vehicle,and the peak frequency of each point was recorded and replaced with the coordinate point for imaging.In the detection cloud map,there is a difference in color between the defect area and the defect free area,but there are misjudgment points in the sleeper area.Due to the different theoretical frequencies corresponding to each area,the color composition of the cloud map is more complex,which affects the judgment of the defect area.(4)An improved imaging method based on thickness frequency filtering is proposed.After processing the echo signal collected by the rapid detection system based on air-coupled impact-echo,an improved detection cloud image is obtained.The improved imaging method reduces the misjudgment point position at the sleeper,eliminates the color difference between the defect free area at the sleeper and the flat plate,and strengthens the contrast of the color of the cloud image between the defect area and the defect free area,with better identification.