Research On Key Technologies Of Submersible Ultrasonic Imaging Inspection For Hollow Shafts Of High-speed Rails

The high-speed railway has got rapid development in recent years,which brought more and more security challenges.In order to meet the high speed requirements of high-speed rail,high-speed trains must be lightweight designed,wherein using the hollow shafts is a very important part of it.However,the shafts are the most important bearing and guiding parts of railway trains,and their qualities directly affect the safety operating efficiency of railway trains,and the hollow design in structure will inevitably bring about the weakening of mechanical strength of shaft.And in the course of processing and assembling,damage and internal defects are generated inevitably.At the same time,when high-speed trains are in the operation,the hollow shafts will inevitably suffer high-frequency shock and huge vibration,coupled with the driving environment corrosion and alternating temperature and alternating heat stress,fatigue damage is very serious.Therefore,the hollow shafts are not only the most critical components of the high-speed trains,but also the weakest parts of the high-speed trains,using non-destructive testing technology to monitor the quality of its implementation is very necessary.Unfortunately,the relevant technology and high-performance testing equipments are monopolized by industrialized countries.Based on the above background,funded by the National Natural Science Fund Project "cylindrical components of high-performance automated phased array ultrasound imaging detection theory and technology research"(No.51675480),the research on the key technologies of submerged ultrasonic imaging inspection for the hollow shafts of high-speed rails was put forward.Based on the understanding of the system's structure for high-speed hollow shafts testing,its ultrasonic imaging detection mechanism and related technology research status and development trend,the ultrasonic imaging theory foundation is established,the overall scheme of the ultrasonic imaging detection system is determined,A prototype of a submerged ultrasonic imaging inspection system for hollow shafts of high-speed rails was developed.The preliminary operation showed that the targets were achieved.The prototype of the ultrasonic imaging system was designed and fabricated on the basis of the research of the technology of ultrasonic scanning and the results.The detailed contents and innovative points of the paper are presented as below:In chapter one,expatiated the significance of high-speed rails' development and the influence of hollow shafts on the safe operation of high-speed trains.Analyzed the current research status and development trend of ultrasonic non-destructive testing technology for hollow shafts of high-speed rails.Clarified the current situation and existed problems of on-line ultrasonic imaging inspection for hollow shafts high-speed trains.Also,pointed out the direction of this paper.In chapter two,analyzed the principle of ultrasonic imaging and the factors influencing the imaging performance,which lays a theoretical foundation for the follow-up study.At the same time,on the basis of introducing the structure of the hollow shafts of high-speed rails and the detection targets,the design of the whole scheme of the submerged ultrasonic imaging detection system of high-speed railway hollow shaft was completed.In chapter three,completed the design and development of automatic scanning device for hollow shafts of high-speed rails.The device consists of a scanning transducer equipped with ultrasonic transducer,a chain-based telescopic folding linear push-pull mechanism,and an adapter and a storage device.By combining the local rotary motion of the scanning head with the global linear motion of the push-pull mechanism,enable the ability of automated helical scanning and the ability to have a wide range of inspection and compact storage devices.At the same time,the multi-axis motion control card based on PXI bus is used to control the scanning device,and the spiral scanning with different motion parameters was realized.In chapter four,a hollow-shaft frequency-domain synthetic aperture ultrasound imaging technique was implemented in liquid immersion environment and internal scanning mode.Based on the wave equation in cylindrical coordinate system,the ultrasonic signal was modeled for cylinder scanning.According to Fourier transform,the sound field reconstruction formula of uniform cylinder was obtained.Based on the principle of phase shift in frequency domain and considering the influence of cylinder interface acoustic effect on the resolution of ultrasonic imaging,a recursive reconstruction technique of sound field of laminated cylindrical structure for hollow shafts was developed,and the hollow shafts Frequency domain synthetic aperture imaging,which effectively improved the lateral resolution of submerged ultrasound imaging.At the same time,the simulation experiment was carried out,which proved the feasibility and validity of this technology.In chapter five,based on the distributed architecture and the modular design strategy,a prototype of online ultrasonic imaging inspection system for submerged hollow shafts of high-speed rails was developed by using inner scanning mode of ultrasonic transducer and high-speed iron hollow shaft relative to spiral movement.Preliminary operation showed that the R&D targets had been achieved.In chapter six,summarized the research achievements as well as the innovative points of this paper,and forecasted the future works.