Research Of Rail Crack Detection Based On Infrared Thermal Wake Nondestructive Testing Technology

Rail as the extremely fatal upper member in the wheel-rail contact system of railway line,and play an important role to guide train and endure complex vehicle load directly,whether the rail is in good health or not,will be directly related to smooth railway transportation and traffic safety.Therefore,a timely detection of rail base cracks and a quantitative measurement of these base cracks have some practical significance for the engineering department of railway to timely and reasonably repair damage that can prolong the service life of rail,debase the extent of damage accumulation and reduce economic losses.Since coupling must be used when detecting,and cracks cannot be quantitatively measured out by the traditional detection method based on piezoelectric ultrasonic detection,at the same time,base cracks are still the blind area of ultrasonic detection method and the detection accuracy is imprecision.An active infrared thermal nondestructive detecting technique is adopted in thesis for a quantitative measurement of base cracks,the infrared thermal wave detection experiment,infrared image processing method and ANSYS finite element simulation are intensive studied.The main research content is as follows:Firstly,a three-dimensional model of finite element of the rail and base cracks was constructed by the ANSYS software,and the process of infrared thermal wave detecting was simulated using the method of loading heat flux,according to the simulation results,and the quantitative measurement of the reference point of base crack depth were completed by using peak of second-order derivative temperature-time(PSDT)method;through the simulation of cracks under the condition of different sizes,the influence of crack size parameters for infrared thermal wave detection process were qualitatively analyzed.Secondly,on analyzing infrared thermal wave nondestructive testing technology,including basic law and the theory of infrared radiation,detection system and its basic principle were analyzed,and an experimental platform of infrared thermal base crack of detection was set up,and infrared images with cracks damage were acquired by using a thermal imager.Thirdly,aiming at the characteristics that the infrared image of base crack with low contrast,poor definition of overall image and fuzzy texture detail,contrast and fuzzy texture details of the image were enhanced using top-hat transform and bottom-hat transform algorithm based on multi-scale;the minutia areas of enhanced crack image were segmented using the improved Otsu algorithm;information of the characteristics of minutia pixels were extracted from the segmentation-processed images by threshold matrix method,based on these information,quantitative measurement of the depth and size of the cracks were realized using specific calculation method of defect parameters.Finally,it is confirmed the proposed method of this research is feasible and effective for quantitative detection of rail base crack damage under the results of model experiment and simulation.