Ultrasonic Imaging Methods Of Spindle Based On Frequency Domain Synthetic Aperture Focusing Technique

The spindle components were the key parts of wind power,amusement facilities and engines,which bear heavy loads and easily produce fatigue cracks.At present,small angle longitudinal wave detection technology was mainly used in the testing of spindle parts,it was often difficult to identify the reflection echo of fatigue crack at the step of the spindle and reflection echo of the step structure,which leads to missing or misjudgment of the spindle defect.In addition,it was often difficult to evaluate the defect quantitatively by the pulse echo method of single probe mode.In this paper,an array longitudinal wave method was used to detect the spindle workpiece based on the frequency domain synthetic aperture focusing imaging(F-SAFT),it overcomes the limitation of traditional ultrasonic imaging method,gives the imaging results of the internal structure of the spindle workpiece and improves the image quality.This thesis mainly covers the following aspects:First,the theory and method of synthetic aperture focused ultrasound imaging were introduced,and focuses on the analysis of the frequency domain synthetic aperture imaging method based on phase shift migration,and discusses the parameters of evaluating the quality of defect imaging.In order to verify the influence of imaging algorithm and imaging quality parameters,numerical simulation and experimental verification were carried out.Based on finite difference method,a numerical model of square steel workpiece with transverse pass was established.Simulation of excitation longitudinal wave frequency domain synthetic aperture focusing imaging technique for cross-hole in the model,the simulation results show that,compared with the original B-scan imaging,the ?2 cross-hole defect with different depths in the model was reduced from 4mm to 2mm,and the resolution was increased by 50%,and the cross-hole was positioned accurately.The experimental verification of the imaging algorithm was carried out on an aluminum specimen with the cross-hole and a steel specimen with the flat bottom hole,and the resolution of the imaging was estimated by-6d B method.It was shown from the experimental results that the half lateral width of ?2 cross-hole in different depths was reduced from 10mm~16mm to 1mm,and the range of imaging resolution can be increased 90%~94%.The half lateral width of ?3 flat-bottom hole in different heights was reduced from 4mm~6mm to 2mm,then the lateral resolution can be increased to 67%,and the location of the defect in the imaging results was basically in agreement with the actual position of the specimen.On the basis of the above simulation and experiment verification work,the imaging test of the spindle of amusement facilities was carried out.The spindle imaging results show that for surface groove with 0.5mm width and 1mm depth,the half lateral width of defect were reduced from 23mm~29mm to 19mm~22mm,and the range of resolution can be increased 17%~24%.Compared with the tradition delay-and-sum synthetic aperture focusing imaging method,the frequency domain synthetic aperture focusing algorithm has higher computational efficiency and was suitable for real-time imaging detection requirements.