The Research Of Heavy Rail Faliure Mechanism And Nondestructive Testing Methods

Rail is an important part of railway transportation. With the high-speeding andoverloaded process of railway in our country, the rail failure modes caused by variousfactors is becoming more and more. This will cause serious threat to the safety ofrailway transportation. Carrying out failure analysis on the defect rail, finding out thefailure reasons and then taking measures to prevent such kind of failure modes. Byexploring new methods of non-destructive flaw testing,different forms of the railinternal defects can be detected and the rail potential safety hazard can be eradicated.All these have become a meaningful research issue.Through the failure analysis and nondestructive testing methods research to aenterprise’s push-coke machine which uses U71Mn rail, this article finds out the rail’sdamage model and analyzes its failure mechanism.By carrying out the finite elementstimulation and calculation of fracture mechanics on the steel rail containing this kindof defect, This article provides theory basis for the safety assessment of defected rail.At the same time, the ultrasonic imaging technology is applied to the defected raildetection, which explore new ways of ultrasonic testing of the rail.There are many macroscopic defects on the surface of the rail through themacroscopic detection to U71Mn rail, mainly the tread extrusion deformation andlongitudinal cracks. The magnetic particle inspection result shows that there are a largenumber of micro cracks in the rail’s longitudinal profile center, which is the cracksource of the longitudinal crack. The mechanics performance test to the rail steelindicates that the rail steel’s tensile strength and hardness conform to the requirementsof the standard, then the residual stress testing results further illustrate the non-uniformstress on the tread of rail.Through the microstructure and chemical composition analysis to the rail steel,this article finds that the root reason of rail failure is flakes behavior, furthermore thisarticle analyzes the microscopic morphology of the flakes’s fracture, and expounds theforming mechanism of the flakes. In addition, the article confirms that the normalmetallographic structure of U71Mn rail steel is lamellar pearlite, its inclusions are mainly manganese sulfide. Furthermore, this article analyzes the influence of traceelements, especially manganese element, to the rail’s physical property.Through the finite element simulation and calculation of fracture mechanics,finding out the stress factors of rail failure, working out rail’s maximum stress andcritical flaw size aims to the crack defects of the flakes, and establishing a safetyassessment method to the containing defects.By using CIVA software, the rail ultrasonic imaging simulation results suggestthat we can utilize ultrasonic phased array to detect transverse crack and ultrasonicTOFD to detect longitudinal crack. Then this article manages the simulation testingresults and realizes the defect location and quantitative analysis.