| At present,we almost use hand-push ultrasonic equipment which has low efficiency for rail flaw detection in our country.Besides,it is difficult to detect cracks quantitatively,prone to misstatements and omissions of defects,so as to create hidden dangers for serious safety accidents.This thesis aims to study techniques for accurately quantifying cracks in rails,improving imaging performance and detection efficiency.A numerical model based on full-matrix acquisition(FMC)for ultrasonic transmission and reception of phased-array units in double-layer media was established.It was used to optimize the detection image to reduce the interference and improve the peak signal-to-noise ratio and resolution.In combination with UT technology,ultrasound layout was established through CIVA simulation,and an ultrasonic combined channel detection system was built.The detection speed was significantly improved,which effectively solves the problems of difficult detection of rail squats and realizes quantitative location and detection for all kinds of typical defects of rails.The specific research content is as follows:In order to obtain better definition and higher resolution of the defect imaging,this thesis based on the ultrasonic phased array technology,using the full matrix capture technology as the collection of the original defect data,the total focusing method(TFM)was deduced.And the evaluation index of ultrasonic imaging quality is given.Study the propagation theory of sound field in double-layer media here.According to Snell’s law and the principle of acoustic propagation along the shortest time path,the univariate quartic equation of the ultrasonic beam at the boundary of the double-layer media is obtained.Based on the Ferrari,we can get the method for calculating the position of the incident point of the ultrasonic beam at the interface of the medium.And then a total focus model based on a double-layer media(WTFM)is derived.Through experimental verification,the improved wedge-based TFM has the characteristics of accurate positioning and strong ability to quantify defects in the rails,which shows that imaging effect of the algorithm is obviously better than the TFM.For the problem that the cracks in the rail head are difficult to detect,the CIVA simulation was performed in conjunction with the UT technology,the ultrasonic layout simulation model was established.In combination with WTFM algorithm,an ultrasonic combined channel detection system was established for different types of defects in different locations.The experiment proves that the system can not only detect the surface and interior cracks of rails quantitatively,but also has the ability of rapid automatic inspection,which greatly improves the detection efficiency.The research in this dissertation provides a solid foundation for realizing high-quality rapid imaging of WTFM quantitative detection algorithm,and it has a good promotion significance for the development of real-time defect imaging based on WTFM algorithm. |
