Development Of Rail's Top Surface Crack Inspection System

Nowadays,rail travel is preferred way of people's long-haul travel,thousands of life and properties are related to the security of rail travel.The safety of rail which bore load stress when train running at a high speed is very important to ensure the security of rail travel.The study found that rail's top surface crack is mainly caused by rolling contact fatigue,detection of rail's top surface tiny crack as soon as possible has been a problem to be solved by the railway department.As the rail is a kind of ferromagnetic material with high permeability,it is impossible that magnetic flux leakage testing,belonged to electromagnetic nondestructive testing technology,can apply to the steel rail defect detection.Magnetic flux leakage testing technique is a kind of non-contact?applicable to the nondestructive testing of surface defect detection technology,it is very suitable for railway rail top surface crack inspection at a high speed.This paper studies the rail's top surface tiny crack which the width of crack is less than 1mm and the depth of crack is less than 2.7mm.First of all,this paper analysis a variety of physical laws about magnetic flux leakage testing in theory,especially the magnetic circuit of magnetic flux leakage testing model based on U-shaped magnet yoke.Then,constructed 2D magnetic flux leakage testing model using Ansoft Maxwell,the influence of the depth of crack and the lift-off distance on the test results from the perspective of finite element method.On design of inspect system,considering the actual rail's crack size and distribution,designed the multiple-trolley probe is easier to realize shorter lift-off distance and the position of single trolley can adjust independently.Also this paper design RC filter and differential amplification signal processing circuit so as to eliminate DC output of sensors and the inconsistencies versus ground in transmission.Finally,the experiment of trigger acquisition on high speed rotary platform and hand-push experiment on rail which have small crack had been conducted taking advantage of DC-MFL?AC-MFL and permanent magnetization.The results shows that the system can effectively detect rail's top surface tiny crack if the probe is closer to rail and improve practicability to the real vehicle experiment.