Optical Flow-Based Eddy Current Pulsed Thermography For Oblique Cracks Detection In Rail Tracks

Nondestructive Testing(NDT)is of great significance in the protection of material quality and the service inspection of important equipment and facilities because it does not impair the advantages of the materials to be inspected.The existence of cracks will affect the safety of key equipment,causing significant economic losses and casualties,so it is necessary to carry out non-destructive testing of cracks.In the actual situation,due to the complex structure of various components and the variety of crack shapes,there are certain difficulties and challenges in completely detecting crack defects.Eddy Current Pulsed Thermography(ECPT)is applied to the detection of defects on the surface and near surface of conductor materials due to its large single-shot area,fast and non-contact detection,but related crack quantification.The research of detection is not deep enough,which affects the popularization and application of eddy current thermal imaging.Therefore,this thesis introduces the optical flow method into eddy current pulse thermal imaging technology,and establishes the surface oblique crack model to study the motion of heat flow on the surface and near surface.The sparse and dense optical flow method is used to detect and quantitatively evaluate the detection results,and the objective judgment basis is obtained.It can provide a new solution for the crack detection and promotion of eddy current pulse thermal imaging.The main research contents of this thesis are as follows:The analysis and simulation modeling of the rail oblique crack detection process is carried out.The Maxwell’s equations are used to study the eddy current induction heating,heat conduction and heat radiation processes,and the interaction between the excitation parameters and the fields is selected to build the model,and then the simulation software is used to complete the simulation.The establishment of eddy current pulse thermal imaging oblique crack heat conduction model.Since the heat map sequence can be regarded as the slow motion of the heat flow with time,and the heat flow at the defect is significantly different from the heat flow at the non-defective,the optical flow method for motion detection is introduced into the heat map sequence to realize The combination of optical flow method and eddy current thermal imaging detection.The simulation results were processed by the dense optical flow method HS(Horn-Schunck)and the sparse optical flow method LK(Lucas-Kanade).The comparison of the dense optical flow has a good effect.Finally,the optical flow method is used to deal with the actual experimental results,and the feasibility of the optical flow method for oblique crack detection is determined.