Ultrasonic Imaging Methods Of Wheels Detection Based On Synthetic Aperture Focusing Technique

With the development of public safety awareness in China, security of the high-speed train is increasingly concerned in today’s society, and nondestructive testing standards for wheels are also improved rapidly. As a key component of the train, wheel is one of the most important positions to detect, and it is the core development direction to optimize the detection effect and improve precision for the wheel ultrasonic detection imaging system. As a technique that effectively enhance the lateral resolution in imaging process under the premise of not increasing system cost, synthetic aperture focusing technique has developed rapidly in the field of ultrasonic imaging and nondestructive testing.Based on the research of traditional synthetic aperture confocal imaging algorithm, the thesis modeled the imaging system in the platform of Field Ⅱ, and achieve the simulation imaging process using the algorithm. A new weighted imaging method of an ultrasonic synthetic aperture focusing technique (SAFT) based on the correlation of signals is presented for the purpose of promoting the performance of traditional imaging of SAFT with low Signal to noise ratio (SNR) and low lateral resolution. Based on the synthetic aperture focusing algorithm, the correlation between the ultrasonic echo signals within synthetic aperture range is analyzed. And the distribution of the correlativity coefficient between the signals is confirmed to parabolic equation in the region of defect echo waves. Theoretical and experimental results show that weighted imaging method is optimized than traditional one both in the improvement of the SNR and the lateral resolution.Now in the nondestructive testing field, more and more practical industrial applications choose multi-element array probe in the detection system. Compared with the normal single array element probe, array probe has obvious superiority and has become the mainstream to be researched. The thesis expounded the principle of beam forming by delay superposition for the array probe, then created an array probe model based on the synthetic aperture, and analyzed the ultrasonic beam directivities for single array element and multi array elements probe. The thesis compared the imaging performances of a variety of models through simulations and experiments. The work provide theoretical foundation for the follow-round research to the wheel ultrasonic nondestructive testing system based on array probes.At last, combining with the CRH EMU wheel ultrasonic nondestructive testing system using in the depots, the thesis proposed a mobile synthesis focus model for the rotary scanning mode, and finished the modeling, analyzed the ultrasonic beam directivities, and finally validated the model by simulation and experiments.