| Ultrasonic C-scan imaging technology can be used to detect internal defects of metal workpieces.It has the advantages of non-contact and high sensitivity,and is widely used in the field of industrial non-destructive testing.However,when the defect size is small,the signalto-noise ratio of the echo signal received by the ultrasonic C-scan experiment is low,which makes the defect imaging more difficult.In addition,when the ultrasonic beam scans the edge of the defect,there will be significant edge scattering phenomenon,which affects the accuracy of ultrasonic C-scan imaging.Aiming at the above problems,this paper studies a deconvolution reconstruction method of ultrasonic C-scan image based on time-delayed cumulative averaging,and researches the noise reduction and deconvolution restoration method of ultrasonic C-scan image.The main research contents and innovations are as follows:(1)The principle of ultrasonic C-scan imaging technology is analyzed,and a linear timeinvariant theoretical model of ultrasonic C-scan imaging process is established on this basis.The ultrasonic C-scan images of flat-bottom hole defects of different sizes were simulated by the imaging model,and the images obtained from the ultrasonic C-scan experiments were compared to verify the effectiveness of the ultrasonic C-scan imaging model.It provides theoretical support for the follow-up research on the optimal iterative algorithm for deconvolution image restoration.(2)A time-delayed cumulative average noise reduction technique is studied,which is used to process the echo signal of the ultrasonic C-scan experiment,and improves the ultrasonic signal-to-noise ratio and imaging effect.The reasons for the difficulty in imaging of small flatbottomed holes were analyzed,and the ultrasonic response signal of the internal defects of the test block was obtained through the ultrasonic C-scan experiment of water immersion.ratio and imaging effects.The results show that this method can significantly improve the ultrasonic signal-to-noise ratio and C-scan imaging effect,which provides a basis for the deconvolution restoration of the subsequent ultrasonic C-scan experimental images.(3)A method of reconstructing ultrasonic C-scan images using Richardson-Lucy deconvolution iterative algorithm and defect measurement model is studied,which improves the accuracy of ultrasonic C-scan imaging.Firstly,the functional relationship between the optimal number of iterations required to reconstruct the ultrasonic C-scan simulated image and the defect size is deduced.Then a defect measurement model is established,the equivalent size of the defect is obtained,and the optimal number of iterations is obtained by substituting it into the above functional relationship.Finally,according to the optimal number of iterations,the Richardson-lucy iterative algorithm was used to reconstruct the ultrasonic C-scan image of the flat-bottom hole obtained in the experiment.The results show that the size error of ultrasonic C-scan imaging of defects before reconstruction is relatively large,and the maximum size error of imaging after reconstruction is 20%and the lowest is 3.3%.This method effectively improves the ultrasonic C-scan imaging accuracy of defects. |
