Research On Stress Concentration And Defect Detection Of The Rail Based On Moving/vibration Magnetic Memory Technology

As one of ferromagnetic materials,rail is the foundation of railway transportation.In the process of long-term service,under the action of external loads,elastoplastic deformation will occur to form stress concentration areas or macroscopic cracks,and then cause safety accidents.Therefore,it is of great significance to the nondestructive evaluation of rail.Aiming at the different detection conditions in practical engineering application,this paper studied magnetic memory detection technology under the condition of moving and vibration measurement,and applied it to rail stress concentration and crack detection.The research was mainly carried out from the following aspects:(1)Aiming at the problem that the theoretical model of the quantitative relationship between magnetic memory signal and stress concentration is not perfect,the magneto-mechanical coupling relationship of magnetic memory effect was studied from a microscopic perspective,and relevant modeling and simulation were carried out.Based on the theory of magnetic dipole,a magnetic leakage field model of stress concentration and crack defects was established,and the relationship between the defect parameters and the magnetic leakage field was numerically simulated,which provided theoretical basis for subsequent experiments.(2)The normal magnetic memory signal characteristics of the component surface when the probe moves parallel to the component surface were studied,and the influence of the moving speed of the probe on the magnetic memory signal was analyzed.In addition,the magnetic memory method of the normal magnetic field gradient on the surface of the vibration scanning component was adopted to improve the SNR in the non-moving state.The relationship between the sensor output and the normal magnetic field gradient was derived.A moving/vibrating magnetic memory dual-mode detection system was built and the design principle of each module was introduced in detail.(3)Magnetic memory method was used to test the stress concentration of Q235 steel bar during stretching,and the relationship between the normal magnetic field gradient and the stress concentration coefficient was studied.The rail samples with artificial cracks and those with natural damage cracks were tested and the magnetic memory signal characteristics of different crack defects were analyzed.Finally simulated magnetic memory high-speed inspection test,the different types of crack defects in the NDT test turntable,the lift-off effect and speed effect and the relationship between the magnetic memory signal,the experimental results showed that as the speed of inspection,defect signal amplitude is reduced,but the magnetic memory method can identify minimum 0.2 mm width,depth,minimum 2 mm crack defects.It can be seen from the above experimental results that magnetic memory detection technology can not only identify crack defects,but also have a good recognition effect on micro defects such as stress concentration.