The Ultrasonic Inspection Technology Research About Metallic Materials Micro-defects Under A Noisy Background

With the development of science and technology, the applications of metallic materials have gradually increased especially in the field of National defense, aerospace, nuclear industry, etc. And all companies in these areas formulated a series of highly strict standards to control the quality of these metal materials.In chapter 1, main defect types and defect wave characteristics of metallic materials were described. Metallic defects testing technology and digital signal processing technology were analyzed. Moreover, the background of the research and significance of the dissertation were discussed. Finally, main research contents were introduced. The importance of ultrasonic testing of small metallic material micro defects was pointed.In chapter 2, the detection principle of ultrasonic nondestructive testing and some important experimental prerequisite for ultrasonic nondestructive testing liquid immersion method were introduced. Meanwhile, the theoretical foundation of ultrasonic attenuation theory in non-destructive testing and theoretical foundation of defects quantitative ultrasonic testing were described.In chapter 3, this dissertation theoretically analyzed the micro defect of the metallic materials based on sound field theory. It also analyzed the structure noises within the backscattered signal. To the micro defect of the metallic materials, this dissertation build some models to describe the defect as hollow cylinder and spheroid. And to the structure noises, we considered it caused by the numbers of grains. Therefore, this dissertation also build a model to describe the structure noises. At the end of this chapter, this dissertation described the influence of the non-acoustic noise to the backscattered signal.In chapter 4, to the micro defects of metallic materials, this dissertation established an improved model of ultrasonic echo with the theory mentioned in chapter 3. On the basis of wavelet packet denoising method, this dissertation put forward an adaptive denoise method based on the theory of wavelet energy spectrum entropy and Shannon information spectrum. And this new denoise method is applied for the improved model of ultrasonic echo in this chapter.In chapter 5, to a test metallic material block which exists some man-made defects, this dissertation has built a real ultrasonic test bench. This test bench has an excellent function of collecting test data and calculating data. On the basis of the denoised signal, this dissertation put forward a defect identification method of micro defect with the theory of correlation coefficient. This dissertation applied this new identification method to the improved model of ultrasonic echo and the real signals. It is proved that this new identification method is suitable for the metallic materials defect identification. In dealing with the real test data, this dissertation accurately calculated the size of the man-made defects in the block with the theory of defect quantification. All this calculation has proved that the collected data in the test bench was extremely correct with the mentioned method in this chapter.In chapter 6, main results and conclusions of this dissertation were systematically summarized; the prospects and the future research work were discussed and forecast.