Research On Ultrasonic Feature Extraction Method Of Metal Micro-defect Structure

Ultrasonic testing and metal materials are widely used in the industrial field.The rapid development of industrial technology has also created new technical requirements.It is necessary to understand the different sizes and shape distributions of metal material defects,and the size of detected defects is becoming more and more subtle.How to use the ultrasonic characteristics of the reflection and scattering of defective metal materials and extract the parameters with measurement significance to infer the size and shape of defects is the core research problem of metal ultrasonic testing technology.In this thesis,the finite difference time domain(FDTD)method is used to simulate the aluminum-water structure of different defect conditions.The ultrasonic echo characteristics are extracted and analyzed,and the quantitative relationship between these features and defects is studied.In this paper,the aluminum-water structure composed of two sub-wavelength scatterers is mainly studied.The paper simulates the propagation of ultrasonic waves in the defect structure of different scatterers in diameter,spacing and angle.It is found that the ultrasonic echo wave forms of different defect structures are also different.The paper defines amplitude of trough(AOT)and amplitude of crest(AOC)to quantify the ultrasound characteristics of different micro-defective structures.The results show that the normalized amplitude is positively correlated with the diameter of the scatterer.The increase of the spacing between the two scatterers will cause different changes in the two normalized amplitudes.The paper finds the relationship between the reflected echo AOT value and the AOC value and the scatterer spacing and scatterer diameter which can be used to determine the scatterer diameter and position distribution in ultrasonic testing.The change of the angle of the two scatterers will also cause a significant change in the reflected echo.The paper finds that the reflected echoes exhibit different waveform characteristics when the two scatterers are at different angles.It has been found that accurate detection of micro defects within the material can be achieved by changing the angle of the ultrasonic inspection.This paper also explores the ultrasonic characteristics of defects in different frequency sound sources,and finds that different frequency sound sources are suitable for different scatterer spacing.The high frequency sound source is more sensitive to the case where the scatterer spacing is small,and the low frequency sound source should be used when the scatterer spacing is large.This paper also studies the influence of sound sources with different signal-to-noise ratios on the detection ability,and analyzes the characteristics of transmitted acoustic waves of different defects.The study found that the reflected echoes of different defects have rich temporal characteristics.The paper systematically studies the relationship between the reflected echo characteristics and the defect parameters,which is of guiding significance for the widely used ultrasound A-scan.