Research On Rail Weld Defect Detection Capability Based On Ultrasonic TOFD Technology

This paper takes the rail aluminothermic welded joints with many defects as the starting point.In view of the fact that the flaw detection of the in-service rail weld seam is heavy and the flaw detection cycle is long,through the analysis of the detection principle and detection ability of the current non-destructive testing methods,it is found that the ultrasonic TOFD detection technology has greater automatic detection capability than other detection technologies.In order to explore the feasibility of ultrasonic TOFD detection technology for automatic detection of rail welds,the ability of ultrasonic TOFD detection technology to detect defects in rail welds is verified through experiments.In order to verify the ability of ultrasonic TOFD inspection technology to detect defects and the resolution of defect depth,the possible problems of using ultrasonic TOFD inspection technology to detect rail weld defects were explored,and manual test verification was carried out.In the test,the test block with the same material as the rail was used to simulate the change of the defect depth by wire cutting.Three sets of probes with different sound paths were arranged on the test block to detect the expansion of the defect.The test results show that ultrasonic TOFD detection has high sensitivity and resolution to the change of defects.In addition,the ultrasonic TOFD probe has a large sound beam angle and a wide sound field coverage,so it has a large detection area and detection latitude.However,the test results also revealed that the existence of throughwave and back-surface echoes in ultrasonic TOFD testing also resulted in the existence of blind spots within a certain area on the upper and lower surfaces of the workpiece to be inspected.Combined with the results of preliminary experiments and actual working condition of the rail in service,design a set of ultrasonic TOFD probe module,test equipment,data transmission module,terminal analysis module,power supply module not overrun of rail defects such as monitoring system solutions,encountered in the pilot experiment of direct wave and bottom reflection wave blind area problem,through the optimization of TOFD ultrasound probe,The direct and reflected waves were successfully reduced to within4 mm from the upper and lower surfaces.According to the form size of rail(60 rail)in service,according to the characteristics of rail top,rail waist and rail bottom three parts of the design of the probe layout scheme.In order to solve the coupling effect between ultrasonic TOFD probe and rail surface in monitoring process,a coupling scheme using epoxy resin adhesive as coupling agent was proposed,and a probe fixing scheme using epoxy resin adhesive and probe fixing device was designed.The monitoring system scheme,probe arrangement scheme,probe coupling and fixing scheme together constitute the monitoring scheme of the rail welding seam not exceeding the limit.In order to verify the feasibility of the monitoring scheme for nonexceeded defects in rail welds,it is decided to select a test rail with a weld and process slotted artificial defects on the bottom surface of the rail at the test rail welds comprehensively considering the types of common defects in rail welds in actual working conditions.The pulse fatigue testing machine is used to conduct fatigue test on the test track so as to simulate the initiation and propagation process of fatigue defects under real working conditions.The partial probe arrangement scheme at the bottom of the rail was selected to monitor the defect expansion,and eight groups of ultrasonic reflection channels were added to compare the effect of ultrasonic reflection method and ultrasonic TOFD detection technology to monitor the defect development.The fatigue test lasted 17.7 hours and the test rail broke.Through the analysis of ultrasonic TOFD channel monitoring data,the development process of the crack was restored,and the analysis results were highly consistent with the macroscopic morphology analysis results of the test rail fracture,which confirmed the feasibility of the monitoring scheme for rail welds not exceeding the limit defect.Compared with the monitoring results of ultrasonic channels by reflection method,the advantages of ultrasonic TOFD detection in defect expansion monitoring are confirmed...