Research On Rail Stress Concentration Detection Technology Based On Magnetic Memory

In recent years, Chinese high-speed railway has made great progress. The safe transportation of rail is related to the people's livelihood. The steel rail is the foundation of rail transport. Using electromagnetic nondestructive testing method to detect the steel rail is of great significance.In this paper, the principle, development and advantages of metal magnetic memory testing technology are introduced by comparing several conventional nondestructive testing methods.Based on the force magnetic coupling model, a method for measuring the stress concentration of the metal magnetic memory which is based on the measurement of the magnetic field gradient is proposed. According to the model of leakage magnetic field, the relationship between the normal magnetic field gradient of the surface of the ferromagnetic component and the position is established. It is also determined that the local maximum value of the gradient of the magnetic field in the stress concentration area is the criterion of the magnetic memory detection. A metal magnetic memory testing instrument based on probe scanning method is developed in this paper.The hardware part of the instrument include: vibration scanning probe with the shielded enclosure,sine wave reference signal generating circuit, a pressure electric bimorph driver circuit, power supply circuit, detection signal preprocessing circuit, the orthogonal vector lock-in-amplifying circuit, microprocessor interface conversion circuit and the hardware circuit based on ARM microprocessor as the core. And the corresponding software system is designed, including the human-computer interaction software in lower computer of metal magnetic memory testing instrument based on STM32F107VCT6 and the magnetic memory analysis software in the host computer.Tensile tests were performed on a set of standard tensile specimens of Q235 steel with annular grooves using the self-made metal magnetic memory testing instrument, the purpose of is researching on the relationship between the gradient of the magnetic field and the stress concentration. Steel Rail with artificial crack defect was detected by magnetic memory method.the purpose of which is comparing different characteristics of the magnetic memory signals with different depth, width and angle.