Study Of Pulsed Eddy Current Testing System For Weld Of Stainless Steel Passenger Train Body

With the rapid development of China’s railway,the number of running trains is large and the maintenance task is heavy.In order to eliminate and find the various defects and damages of vehicle in time,the detection technology is particularly important.Train body is the main structure of the rail vehicle,the welding technology accounts for a large proportion in the manufacturing process.The quality of the weld directly affects the final quality of the train body.Five nondestructive testing methods including ultrasonic testing,ray testing,magnetic testing powder testing,penetration testing and eddy current testing provide a good means for maintenance work,in which eddy current testing is widely used in the field of non-destructive testing because of its non-contact,no coupling agent,flexible probe and high sensitivity to surface and subsurface defects.The current research in the field of eddy current testing mainly focuses on the proposal of new eddy current testing methods,the development of highperformance probes and the development of high-efficiency eddy current testing system.Based on the new pulsed eddy current testing technology,this thesis made the related detection research,including the probe design,hardware test system design and the test detection of weld crack defects simulated by stainless steel test block.The main tasks are as follows:1.The importance of weld quality of passenger train body and the key role of NDT in weld defect detection are highlighted.Finally,the pulsed eddy current testing technology is selected to carry out the related research.2.The basic theory of electromagnetic field,the mechanism of eddy current generation and the principle of traditional eddy current testing are introduced;On the basis of introducing the principle of skin effect,the calculation of skin depth of pulsed eddy current testing is completed,and the principle and characteristics of pulsed eddy current testing technology are analyzed.3.The optimization design of the pulsed eddy current probe is completed.As an important part of the probe,the geometric size of the excitation coil is closely related to the sensitivity of the probe.COMSOL software is used to model the probe,and the influence of the geometric size of the excitation coil on the sensitivity of the probe is studied,so as to determine the optimal geometric size of the excitation coil.4.The hardware test system of pulsed eddy current(PEC)for weld defects of stainless steel train body is designed.The overall scheme of the system is designed.The functions and implementation methods of each module are introduced in detail.5.The preprocessing method of pulsed eddy current testing signal is introduced.The laser welding method of stainless steel train body and the detection of weld seam are briefly analyzed;At the same time,the stainless steel test block was prepared to simulate the weld surface and subsurface crack defects.Through the test,the corresponding relationship between the characteristic quantity and the weld crack defect parameters was determined.