Study On Several Key Problems Of Ultrasonic Inspection Based On Ultrasonic Beam Analysis

Nowadays ultrasonic non-destructive inspection technology is the most frequently used and fastest growing means for product quality control. With the drastic growth in the application of new materials, new structures and new processes, new demands on the current ultrasonic non-destructive inspection method have been raised in modern industry. Especially for the complex surfaces and composite components are widely used in the aerospace field, how to improve precision, efficiency and the level of automation in ultrasonic inspection is the front subject in recent years. Combined with the actual requirements and its realization scheme in the ultrasonic inspection for these components, some key problems in relation to acoustic modeling in ultrasonic testing system, registration of complex surface parts, ultrasonic probe position and orientation planning method and sensitivity compensation method for complex curved components, ultrasonic inspection on porosity in carbon fibre composites with variable thickness are systematically studied in this dissertation.In chapter1, the background of the research work and significance of the dissertation were discussed. The research status of some related technologies involved with the research, such as ultrasonic inspection technologies for curved components, acoustic modeling in ultrasonic inspection, registration of surface parts, ultrasonic probe position and orientation planning method and sensitivity compensation method, ultrasonic inspection of porosity in carbon fibre composites, were overviewed. Finally, main research contents and chapters arrangement were introduced.In chapter2, the acoustic model in the ultrasonic testing system was established. Firstly, a Multi-Gaussian beam model was described and the reason for choosing the model to simulate the probe beam was given. Then propagation of probe beam in multilayered medium was discussed. Finally, the relationship between the received signal and sound field distribution was set up. The realization of quantitative and digital calculation and analysis for ultrasonic beams was the foundation of the follow study.In chapter3, the registration method for curved components was studied. Firstly, the kinematics equations for the11DOF ultrasonic mechanic arm were established, and the relationship between the received signal and probe orientation had been got based on ultrasonic beams analysis to guide the arm for automatic measurement. After processes such as surface reconstruction and profiling measurement, a template would be generated. Then a registration method was proposed using the template and a few measurement points on the component to be inspected. The component CAD model in the inspection coordinate would be got rapidly. Finally, the simulation and experimental studies had been carried out.In chapter4, probe position and orientation planning method and sensitivity compensation method for complex curved components in automatic ultrasonic inspection were studied. Firstly, the shortage of present method was analyzed. Then how the probe position and orientation affects the received signal were analyzed based on simulations and experiments, and the best probe position and orientation was pointed out. At last, a new probe position and orientation planning method was proposed. About the problem of sensitivity compensation, a probe beam attenuation model was established and the model parameters determined method was given to realize the probe beam attenuation prediction and sensitivity compensation. Finally, contrast experiments were designed to validate performance of the parameters optimized method.In chapter5, ultrasonic inspection method on porosity in carbon fibre composites with variable thickness was studied. Firstly, the variable relationship models about porosity and attenuation were analyzed, and the model in frequency domain was chosen to be the inspection model according the characteristic of composites to be inspected. Then the attenuation measurement method for composites with variable thickness was given. After the parameter in the inspection model was calibrated by destructive method, the porosity in the composites could be measured by ultrasonic attenuation. Finally, experiments showed the availability of the proposed method.At last, the main results and conclusions of this dissertation were summarized, and the prospects of the future research work were discussed.