Development Of Quantitative Detection Instrument For Rail Tread Oblique Crack Based On ACFM Technology

Oblique cracks on the rail treads originate at the gauge corners.After reaching a certain depth,the cracks will rapidly extend and cause the rail head to fracture laterally,which threatens train operation safety seriously.Aiming at the quantitative detection requirements of oblique cracks on rail treads,the alternating current field measurement(ACFM)technology is introduced in this paper.The ACFM detection theory and simulation model for oblique cracks on rail treads are established.The electromagnetic field distortion laws near different vertical angles and different sizes of oblique cracks are studied.The oblique crack quantitative identification algorithm is developed based on BP neural network.The rail detection single probe and the rail profiling array detection probe are designed and developed.The ACFM detector is developed.Finally the rail tread oblique crack ACFM detection instrument system is developed,which provides a new method for effective quantitative evaluation of rail tread oblique cracks.The main research contents of the paper are as follows:(1)Theoretical research and simulation analysis of rail tread oblique cracks ACFM detectionBased on the principle of ACFM detection technology,the theory of rail tread oblique crack detection is researched.A simulation model for oblique crack ACFM detection is established,comparing the characteristic signals of oblique cracks under different scanning methods.The model analyzes The induced current distribution and electromagnetic field distortion law is analyzed by the model with different angles and sizes oblique cracks,which lays a theoretical foundation for the judgment and quantitative evaluation of oblique cracks.(2)Design and development of rail detection single probe and rail profiling array probeAccording to the distribution of oblique cracks on the rail tread,the rail detection single probe is designed.The magnetic core structure is designed.The excitation module parameters are optimized through simulation.The signal processing circuit is designed.Then according to the structural characteristics of the rail gauge corner,the profiling array probe is developed.The array magnetic core structure is determined by further simulation.The array sensor model is selected.The optimal sensor spacing is determined.(3)Development of ACFM instrument system for rail tread oblique cracksIn response to the detection requirements of oblique cracks on the rail tread,the rail flaw detection scanning frame is designed.The ACFM detector is designed,the rms-to-dc converter is designed and integrated according to the high-speed detection requirements.The quantitative identification algorithm is developed for oblique cracks based on BP neural network.The oblique cracks detection software system is developed.Finally the ACFM instrument system for rail tread oblique cracks is set up.(4)Tests of rail tread oblique crack ACFM detection instrumentBased on the rail tread oblique crack ACFM detection instrument,the tests are carried out to detect oblique cracks with different lengths,depths and angles.The high-speed tests are carried out.The results show that the detection instrument and the quantitative identification algorithm can realize the effective detection and quantitative evaluation of the oblique cracks.The instrument can detect the oblique cracks at the top detection speed of 120km/h.