Study On SAFT Ultrasonic Imaging Method For Concealed Defect Of Ballastless Track

Ballastless track structure is the main structural form of high-speed railways in China,and its hidden defects seriously threaten traffic safety.Aiming at the problem of fast and accurate imaging of hidden defects in ballastless tracks,this paper proposes an ultrasonic SAFT imaging method for high-speed ballastless track multilayer structures.Accurate and fast imaging of hidden defects.The specific research content is as follows:(1)The imaging method based on RMS-SAFT is studied,and the imaging of multilayer structure without ballastless orbit is realized.The theoretical basis of the traditional timedomain SAFT imaging method is studied,and the limitations of the traditional time-domain SAFT imaging method are analyzed.A root-mean-square velocity acoustic time calculation model suitable for ballastless orbital multi-layer structures is proposed,and the difference between the calculation results of this model and the theoretical analysis calculation results is compared.Based on this,a RMS-SAFT imaging detection method is constructed.Through three-dimensional finite element simulation and foot size model experiments,it is proved that RMS-SAFT has higher imaging accuracy in ballastless track structure detection than traditional time-domain SAFT.(2)The imaging method based on RR-SAFT is researched,and the accurate imaging of the ballastless orbital multilayer structure is realized.A ray-tracing inverse acoustic time calculation model was established.The iterative calculation of the refraction points was used to find the ultrasonic wave propagation time corresponding to the pixel points.The calculation results were consistent with the theoretical analysis calculation results.This acoustic time calculation model is fused with time-domain SAFT to form the RR-SAFT imaging detection method.Through 3D finite element simulation and full-size model experiments,it is proved that RR-SAFT has higher detection accuracy than RMS-SAFT,but the RR-SAFT algorithm has high complexity and time-consuming.(3)The imaging method based on RF-SAFT is studied,and fast and accurate imaging of ballastless orbital multilayer structures is realized.A forward acoustic time calculation model based on ray tracing was established.Ultrasonic travel time was calculated quickly using the linear equation of the propagation path of ultrasound in the ballastless orbital structure and the acoustic time matching algorithm based on Bresenham’s algorithm.Formed RF-SAFT imaging detection method.Through three-dimensional finite element simulation and foot size model experiments,it is proved that RF-SAFT and RR-SAFT have the same high-precision detection performance and faster imaging speed.The calculation accuracy of the SAFT imaging method depends on the accurate calculation of the acoustic travel time.However,the traditional SAFT imaging method of concrete does not consider the complex propagation path of ultrasonic waves in the ballastless orbital multilayer structure,and it is difficult to accurately calculate the travel time of acoustic waves.In order to solve this problem,this paper proposes RMS-SAFT,RRSAFT and RF-SAFT imaging methods,and verifies the feasibility of the three methods through finite element and experimental analysis.Fast and accurate imaging detection of void defects inside the Ballastless track structure.The research work in this paper provides a theoretical basis and practical guidance for the imaging detection of ballastless orbital structures and multilayer dielectric structures.